Annotated Bibliography

High-Frequency Chest Wall Oscillation

This annotated bibliography describes studies of High Frequency Chest Wall Oscillation (HFCWO), the technology used by The Vest® Airway Clearance System to administer Airway Clearance Therapy. In some studies, HFCWO is referred to as: external chest wall oscillation (ECWO), high- frequency chest compression (HFCC), high frequency chest wall compression (HFCWC) or high-frequency transthoracic ventilation (HFTV). The Vest® Airway Clearance System received FDA clearance to market for bronchial secretion clearance in 1988 and for sputum induction in 2000.

Studies are arranged alphabetically by subject, then by author.

In addition to studies of HFCWO, the final section includes a number of "Airway Clearance Overviews." These articles are not reports on formal studies, but are a compilation of information on a number of therapeutic options currently available for airway clearance.

For additional information on The Vest® System, please contact Hill-Rom Inc., 1020 County Road F, St. Paul, Minnesota 55126, or phone 800-426-4224.

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Acute Care/ICU/Post Surgical

Allan JS, Garrity JM, Donahue DM. The utility of High Frequency Chest Wall Oscillation therapy in the post-operative management of thoracic surgical patients. Chest 2003;124(suppl 4):235S.
Twenty-five patients undergoing a wide variety of elective thoracic surgical procedures were evaluated after randomization to receive High Frequency Chest Wall Oscillation (HFCWO). No major adverse events were encountered, demonstrating that HFCWO can be used safely with a high degree of patient acceptance in an acute care population. HFCWO was preferred to conventional chest physiotherapy by a 2:1 margin.
Brierley S, Adams C, Suelter J, Gooch T, Becker B. Safety and tolerance of High Frequency Chest Wall Oscillation (HFCWO) in hospitalized critical care patients. Respir Care 2003;48(11):1112.
This study assessed safety and tolerance of HFCWO in acutely ill hospitalized patients in the presence of multiple therapeutic interventions. Seventy-three subjects were evaluated. The study concluded that HFCWO was safe and well-tolerated for many post surgical and other critical care patients.
Ganz SS, Levi DM, Nishida S, Raines JK, Anton M, Osorio M, Hollingsworth K, Bellinger EL, Pham SM. Improving pulmonary function and lung recovery for transplantation using the LinkTM during organ donor management. Poster presentation at Association of Organ Procurement Organizations (AOPO), Chicago, IL, June 14-18, 2004.
HFCWO-treated donors demonstrated a statistically significant improvement in lung procurement (p=0.015), maintained P/F ratios > 300 mm Hg, and trended toward improvement in chest x-ray densities and reduction in white blood cells on Gram staining.

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Aerosol Deposition, Effects on

Chambers C, Klous D, Nantel N, King M, Newhouse M. Does high-frequency chest compression (HFCC) during aerosol therapy affect lung deposition? Am J Respir Crit Care Med 1998; 157(Suppl 3): A131.
The effects of high-frequency chest compression (HFCC) on aerosol delivery to the lung was studied in ten normal subjects who inhaled Technetium-labeled Human Serum Albumin (HSA) aerosol alternately with and without HFCC. The study suggests that HFCC does not impair aerosol delivery in normal subjects and that it improves delivery to the lower respiratory tract to a degree just short of significance.
Perry GV, Stites SW, Peddicord T, Cox G, McMillian C. Effect of High Frequency Chest Wall Oscillation on the central and peripheral distribution of aerosolized DTPA as compared to standard chest physiotherapy in cystic fibrosis. Am J Respir Care Med 1999; 159(Suppl 3): A686.
This crossover evaluation compares deposition of aerosolized DTPA administered simultaneously with HFCWO versus DTPA aerosolized after standard chest physiotherapy in patients with cystic fibrosis. Combined HFCWO and aerosol therapies displayed a non-significant trend toward more central deposition of aerosolized medications.

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Asthma, Use in

This study of normal and asthmatic subjects reveals that breathing Heliox (30% O2-70% He mixture) during high frequency chest wall compression (HFCWC) increased oscillatory airway flow (Vosc) measured at the mouth over that achieved when the subjects breathed room air during HFCWC. Arm raising (to increase chest wall muscle tone) has a variable effect on Vosc. Researchers hypothesize that breathing Heliox during HFCWC could further improve mucus clearance in selected patients.
Wen AS, Woo MS, Keens TG. Safety of chest physiotherapy in asthma. Am J Respir Crit Care Med 1996; 153(4 pt. 2): A77.
A study of the effects of conventional chest physiotherapy as delivered by HFCC on 13 subjects with mild to moderate asthma reveals no significant differences in the amount of bronchospasm observed between control (no HFCC) and treatment with HFCC. Researchers speculate that CPT as delivered by HFCC with a nebulized bronchodilator treatment is a safe adjunct therapy for patients with asthma.

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Chronic Obstructive Pulmonary Disease, Use in

Diette GB, Rand CS, Wise RA, Thompson K, Merriman B. Feasibility of using a sham control device in clinical trials of High Frequency Chest Wall Oscillation (HFCWO) in COPD. Am J Respir Critical Care Med 2004;167:A613
This study demonstrates the feasibility of a sham device for use in controlled clinical trials.
Piquet J, Brochard L, Isabey D, De Cremoux H, Chang HK, Bignon J, Harf A. High Frequency Chest Wall Oscillation in patients with chronic airflow obstruction. Am Rev Respir Dis 1987; 136: 1355-1359.
A study of 12 patients with severe chronic obstructive pulmonary disease (COPD) reveals that HFCWO during expiration resulted in decreased breathing frequency, increased tidal volume, increased arterial PO2, decreased arterial PCO2, and decreased duty cycle (time of inspiration/total breath period or Ti/Ttot). These results imply that HFCWO facilitates inspiratory muscle work and that it might enhance both gas exchange and inspiratory muscle function in patients with severe COPD.
Perry RJ, Man GCW, Jones RL. Effects of positive end-expiratory pressure on oscillated flow rate during high frequency chest compression. Chest 1998; 113(4): 1028-1033.
A comparative study of six normal subjects and six subjects with stable chronic obstructive pulmonary disease (COPD) demonstrated that a modest amount of positive end-expiratory pressure (PEEP) during HFCC prevented the decrease in end-expiratory lung volume (EELV) and increased mean oscillated flow rate (Vosc) during both phases of spontaneous breathing in COPD patients. Researchers suggest that the higher Vosc associated with PEEP + HFCC may improve the effectiveness of HFCC in clearing secretions from the lungs of these patients.

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Cost Analysis

Klous DR, Boyle M, Hazelwood A, McComb RC. Chest Vest & CF: better care for patients. Adv Mgrs Respir Care 1993; 2(3): 45-50.
This article summarizes the early research into the efficacy and mechanism of action of High Frequency Chest Wall Oscillation (HFCWO), provides an assessment tool to follow the patient throughout the training process, and discusses labor and consequent cost savings that follow from disease self-management with HFCWO as a replacement for the more labor-intensive conventional CPT in the hospital setting.
Ohnsorg F. A cost analysis of High Frequency Chest Wall Oscillation in cystic fibrosis. Am J Respir Crit Care Med 1994; 149(4 pt. 2): A669.
In a retrospective record-bases analysis of the impact of the ABI Vest® Airway Clearance System (aka ThAIRapy® Vest) on total health care expenditures, BlueCross and BlueShield of Minnesota (BCBS/MN) found a 49% reduction in total direct expenditures for 23 cystic fibrosis patients insured by BCBS/MN after the initiation of The Vest® System. The analysis compares expenditures for the year preceding initiation of therapy with The Vest® System with expenditures during the first year of usage with The Vest® System. The cost of The Vest® System is included as a health care expenditure during the post-Vest year.

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Cystic Fibrosis, Use in

Anbar RD, Powell KN, Iannuzzi DM. Short-term effect of ThAIRapy® Vest on pulmonary function of cystic fibrosis patients. Am J Respir Crit Care Med 1998; 157(Suppl 3): A130.
This retrospective study of 54 cystic fibrosis patients who had received the ABI Vest® (aka ThAIRapy® Vest) shows that FEV1 improved an average of 8% when comparing the best pulmonary function test (PFT) results from the time interval 0–6 months prior to The Vest® System initiation to the best PFT results from the time interval 0–6 months following it. Improvement for those patients who had received CPT prior to receiving The Vest® System averaged 7%; for those who did not receive CPT prior to The Vest® System initiation, improvement averaged 11%.
Anbar RD. Compliance with use of ThAIRapy® Vest by patients with cystic fibrosis. Pediatr Pulmonol 1998; Suppl 17: 346, A497.
This retrospective study evaluated therapy with The Vest® System compliance for 82 patients who used the ABI Vest® for more than six months. Compliance tracked by a meter on the device is reported to be higher than ranges previously reported for patients receiving conventional CPT.
Anbar RD. Use of ThAIRapy® Vest does not affect liver function of patients with cystic fibrosis. Am J Respir Crit Care Med 1999; 159(3), A687.
This retrospective study indicates that short-term use of the HFCWO does not affect liver function as measured by liver enzyme levels.
Arens R, Gozal D, Omlin KJ, Vega J, Boyd KP, Keens TG, Woo MS. Comparison of high frequency chest compression and conventional chest physiotherapy in hospitalized patients with cystic fibrosis. Am J Respir Crit Care Med 1994; 150: 1154-7.
A study of 50 cystic fibrosis (CF) patients hospitalized for acute pulmonary exacerbation who were randomized to receive either conventional chest physiotherapy or HFCC reveals significant improvements in pulmonary function and clinical status in both groups and no significant differences between the two. The authors speculate that HFCC may provide an adequate alternative in management of patients with CF in a hospital setting.
Braggion C, Cappelletti LM, Cornacchia M, Zanolla L, Mastella G. Short-term effects of three chest physiotherapy regimens in patients hospitalized for pulmonary exacerbations of cystic fibrosis: a cross- over randomized study. Pediatr Pulmonol 1995; 19: 16-22.
A study of three different chest physiotherapy regimens—postural drainage, positive expiratory pressure, and HFCC—administered to 16 cystic fibrosis patients hospitalized for acute pulmonary exacerbation of their disease shows no significant differences in short-term efficacy among the three regimens.
Burnett M, Takis C, Hoffmeyer B, Patil S, Pichurko B. Comparative efficacy of manual chest physiotherapy and a high frequency chest compression vest in inpatient treatment of cystic fibrosis. Am Rev Respir Dis 1993; Suppl 147: A30.
A controlled comparison of conventional CPT and ABI Vest® (aka ThAIRapy® Vest) treatments in ten adult cystic fibrosis patients hospitalized for infectious exacerbations resulted in comparable spirometry measurement results and oxygen saturation effects, but expectorated secretions were greater following treatments with The Vest® System. The authors speculate that the advantage of The Vest® System may be due to its simultaneous treatment of numerous affected sites and/or to a beneficial effect of HFCC on peripheral mucus clearance.
Butler S, O'Neill B. High frequency chest compression therapy: a case study. Pediatr Pulmonol 1995; 19: 56-59.
This article presents a case study of one cystic fibrosis patient who used the ABI Vest® (aka ThAIRapy® Vest Bronchial Drainage System) with positive results, including enhanced mucociliary clearance and stabilized pulmonary function.
Clayton Sr RG, Donahue M. ThAIRapy use in 6 to 12 year old children with cystic fibrosis. Pediatr Pulmonol 1998; Suppl 17: 345, A496.
This retrospective study evaluates the change in lung function before and after initiation of therapy with The Vest® System in 40 children with cystic fibrosis. Adherence to therapy with The Vest® System is reported at 68.1% over a 22-month period. Although there was no significant change in FEV1 after initiation of therapy with The Vest® System, there was an increasing trend in FEV1 after one year.
D'Angelo S, Craigmyle L, Kanga J. How are patients using alternating pressure vests for chest physiotherapy? Pediatr Pulmonol 1994; Suppl 10: 266, A314.
This abstract reports on ABI Vest® (aka ThAIRapy® Vest) use by 27 patients in one CF clinic who were prescribed The Vest® System, Model 102. Fifty-eight percent of those patients were using their devices one hour or less per week. During the first three months, the majority of patients' average use per day was very stable, suggesting that early use habits are a strong predictor of future compliance.
D'Angelo S, McClendon T, Kanga J. Using objective data to monitor and increase use of chest physiotherapy (CPT) in patient education. Pediatr Pulmonol 1997; Suppl 14: 327-328, A448.
This is a preliminary report on a project designed to use objective data gathered from the usage monitor on the ABI Vest® (aka ThAIRapy® Vest) to monitor adherence and improve patient education. Patients also completed subjective ratings of health status and satisfaction with method of chest therapy. Researchers are using the data to work with patients to overcome barriers to therapy and find ways of increasing therapy adherence.
Grece, CA. Effectiveness of high frequency chest compression: a 3-year retrospective study. Pediatr Pulmonol 2000;(suppl 20):452.
In the study of 41 cystic fibrosis (CF) patients using either manual chest physiotherapy (CPT) or High Frequency Chest Wall Oscillation (HFCWO), changes in weight and number of hospital days were measured retrospectively over a 3-year period. The study demonstrated no appreciable differences in pulmonary function or number of hospital days between the two groups, but a significant (p=0.0001) improvement in weight gain in the group using HFCWO.
Hull KK, Warren RH. ThAIRapy® Vest vs. conventional chest physical therapy (CPT): case report. Respir Care 1991; 36(11): 1266-1267.
A 32-year old male hospitalized with end-stage cystic fibrosis was placed on the ABI Vest® (aka ThAIRapy® Vest) after showing no improvement in sputum mobilization after receiving manual CPT for 26 days. Results of initiation with The Vest® System included copious sputum production, improved PFTs, and a subjective sense of feeling better. The patient was able to be discharged on day 30.
Kluft J, Beker L, Castagnino M, Gaiser J, Chaney H, Fink R. A comparison of bronchial drainage treatments in cystic fibrosis. Pediatr Pulmonol 1996; 22: 271-274.
A comparative study of standard chest physiotherapy and HFCWO in a group of stable cystic fibrosis (CF) patients resulted in significantly more sputum expectorated, determined by both wet and dry weights, as a result of HFCWO. This study suggests that HFCWO is at least as effective as manual CPT in clearing secretions from the airways in patients with CF.
McColley SA, Schulz C, Qualter N, Boas SR, Jain M, Goodman DM. Participation in an observational study of airway clearance in cystic fibrosis does not influence patient adherence. Pediatr Pulmonol 1999; Suppl 19: 331, A581.
This prospective study evaluates The Vest® System adherence and QOL in patients (ages 7-23) with mild to moderate cystic fibrosis. All subjects were enrolled in the standard Outcomes Monitoring Program offered by American Biosystems. Adherence to therapy with The Vest® System was 48±28% for study participants. No significant difference in percent adherence was seen between the study group and a group of age-comparable patients who received the standard Outcomes Monitoring provided by the company but were not enrolled in the study, suggesting that study participation does not affect therapy adherence behavior.
McColley SA, Harris CV, Qualter N, O'Malley C, Boas SR, Jain M. Predictors of adherence to an airway clearance technique in cystic fibrosis. Pediatr Pulmonol 1999; Suppl 19: 332, A582.
This prospective study evaluates adherence to therapy with The Vest® System and adherence predictors in 28 subjects (ages 7-23) with cystic fibrosis. Adherence was measured using the hour meter on the device. Six- month adherence in this population was 43±27%. Increased age as well as poorer nutrition, pulmonary function status, and perceived quality of life were associated with poor adherence to Airway Clearance Therapy.
Oermann CM, Accurso F, Castile R, Sockrider MM. Evaluation of the safety, efficacy and impact on quality of life of the ThAIRapy® Vest and Flutter® compared to conventional chest physical therapy (CPT) in patients with cystic fibrosis. Am J Respir Crit Care Med 1997; 155(Suppl 4): A638.
This multicenter, randomized, cross-over study of 24 cystic fibrosis patients was designed to compare the efficacy, safety and patient acceptance of manual CPT, the ABI Vest® (aka ThAIRapy® Vest), and the Flutter® valve. Results indicate that the three therapy modalities are comparably efficacious with no significant differences emerging in PFT scores. NIH scores, which evaluate disease severity and predict prognosis, improved from baseline with the use of The Vest® System. Given a choice among modalities, 50% of patients chose the ABI Vest®, 37% chose the Flutter®, and 13% chose manual CPT.
Oermann CM, Swank PR, Sockrider MM. Validation of an instrument measuring patient satisfaction with Chest Physiotherapy (CPT) techniques in cystic fibrosis. Chest 2000; 118(1):92-97.
This large, cross-sectional study evaluates results of a chest physiotherapy satisfaction questionnaire distributed among patients using manual CPT, Flutter® system, and The Vest® System. The results indicate that therapy with The Vest® System provides more overall satisfaction than manual CPT. While the Flutter® system ranked higher in terms of convenience, The Vest® System ranked higher in efficacy and compliance. Results suggest greater adherence to therapy in the HFCWO group, as 64 % of subjects using HFCWO reported never missing therapy compared with only 30 % of those using manual CPT and 21% of subjects using the Flutter® system. Flutter® is a registered trademark of Varioraw Percutive SARL.
Oermann CM, Sockrider MM, Giles D, Sontag MK, Accurso FJ, Castile RG. Comparison of High Frequency Chest Wall Oscillation and oscilating positive expiratory pressure in the home management of cystic fibrosis: A pilot study. Pediatr Pulmonol 2001;32:372-377.
This study suggests that High Frequency Chest Wall Oscillation (HFCWO) and oscillating positive expiratory pressure (OPEP) are safe and as effective as postural drainage, percussion, and vibration (PDPV). Compliance between methods was similar, though significant differences were seen in patient satisfaction. HFCWO was preferred by 50% of subjects if given a choice of therapies, while 37% preferred OPEP and 13% preferred PDPV.
Robinson C, Hernried L. Evaluation of a high frequency chest compression device in cystic fibrosis. Pediatr Pulmonol 1992; Suppl 8: 304, A255.
A study of the effects on pulmonary function of HFCWO delivered by the ABI Vest® (aka ThAIRapy® Vest) during a three-month period shows no significant improvement or deterioration of lung function while using The Vest® System, but that the device did increase feelings of independence, enhanced breathing techniques and allowed patients to increase therapy by themselves.
Scherer TA, Barandun J, Martinez E, Wanner A, Rubin EM. Effect of high frequency oral airway and chest wall oscillation and conventional chest physical therapy on expectoration in patients with stable cystic fibrosis. Chest 1998; 113(4): 1019-1027.
A study comparing the effects of high frequency oral airway oscillation, HFCWO, and conventional chest physical therapy finds no significant differences among the modalities with respect to weight of expectorated sputum, effect on pulmonary function, or effect on oxygen saturation. All therapies were tolerated well. Researchers suggest that the two self-administered modalities (high frequency oscillation of the oral airway and of the chest wall) have cost advantages.
Tecklin JS, Clayton RG, Scanlin TF. High Frequency Chest Wall Oscillation vs. traditional chest physical therapy in CF – a large, one year, controlled study. Pediatr Pulmonol 2000;(suppl 20):459.
A retrospective year-long study of the efffecacy of High Frequency Chest Wall Oscillation (HFCWO) vs. manual chest physical therapy (CPT) in a large group of cyctic fibrosis (CF) patients yielded no statistically significant difference between the groups in terms of measured pulmonary function values (FVC, FEV1, PEF, FEF, sGAW, and RV/TLC). There was a statistically significant improvement (p=0.0049) in the Brasfield chest x-ray score in the group using HFCWO. Investigators concluded the HFCWO is an acceptable long=term alternative to CPT for airway clearance in individuals with CF.
Varekojis SM, Dounce FH, Flucke RL, Filburn DA, Tice JS, McCoy KS, Castile RG. A comparison of the therapeutic effectiveness and preference for postural drainage and percussion, intrapulmonary percussive ventilation, and high frequency chest wall compression in hospitalized cystic fibrosis patients. Respir Care 2003; 48(1): 24-28.
In an effort to evauate the efficacy of and overall patient satisfaction with three airway clearance modalities, investigators designed a randomized, cross-over study of 24 cystic fibrosis (CF) patients hospitalized with acute exacerbations. The modalities evaluated were postural drainage and percussion (PD&P), intrapulmonary percussive ventilation (IPV), and high frequency chest compression (HFCC). Efficacy of the modalities was determined by wet and dry sputum weights. Patient satisfaction was determined by the results of questionnaire. Investigators concluded that HFCC and IPV were at least as effective as PD&P for mucus clearance in hospitalized CF patients and that there was no significant difference in patient preference between the three modalities. Based on their findings, the investigators suggest that patients be allowed to experience each modality and choose based on individual preference.
Warwick WJ, Hansen LG. The long-term effect of high frequency chest compression therapy on pulmonary complications of cystic fibrosis. Pediatr Pulmonol 1991; 11: 265-271.
In this retrospective analysis of the pulmonary function of 16 CF patients, the authors evaluate the regression line slopes for percent predicted forced vital capacity (FVC) and forced expiratory volume in one second (FEV1). Ninety-four percent of the patients' regression line slopes became more positive during self- administered HFCC therapy as compared to slopes before HFCC therapy, when manual chest physical therapy was used.
Wielinski CL, Warwick WJ. Change in pulmonary function over a 30-month period for high frequency vest users vs. non-users in a cystic fibrosis population. Am J Respir Crit Care Med 1996; 153: A71.
A study of the long-term effects of HFCC on cystic fibrosis patients over a thirty-month period shows that, in those exposed to HFCC, as a group there was less decline in FEF25-75%, and, in males, there was an improvement in FEV1 and FEF25-75%.

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Mechanically Ventilation – Use Among People Requiring Long-Term Ventilatory Support

Ndukwu IM, Shapiro S, Nam AJ, Schumm PL. Comparison of High Frequency Chest Wall Oscillation (HFCWO) and manual chest therapy (MCPT) in long-term acute care hospital (LTAC) ventilator- dependent patients. Chest 1999; 116(4 Suppl 2): 311S.
This prospective, randomized, controlled study of long-term mechanically-ventilated patients shows HFCWO to be more effective than manual CPT in promoting early airway clearance, improving negative inspiratory force over time, and liberating patients from ventilator support.
Whitman J, Van Beusekom R, Olson S, Worm M, Indihar F. Preliminary evaluation of high frequency chest compression for secretion clearance in mechanically ventilated patients. Respir Care 1993; 38(10): 1081-1087.
An evaluation of HFCC in comparison to percussion and postural drainage in long-term mechanically- ventilated patients shows no significant differences between the two methods with respect to wet weight of collected sputum, pulse-oximetry saturation, or changes in blood pressure, heart rate or patient comfort. Seventy percent of respiratory therapists involved in the study believe The Vest® System is an acceptable alternative to conventional chest physiotherapy, and 80% believe using the HFCC device results in time savings.

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Mechanism of Action for Mucus Clearance

App EM, Lohse P, Matthys H, King M. Physiotherapy and mechanical breakdown of the excessive DNA load in CF sputum – an anti-inflammatory therapeutic strategy. Pediatr Pulmonol;(suppl 17):349, A507.
This study evaluates the effects of high frequency oscillations on the breakdown of high-molecular weight DNA in cystic fibrosis (CF) sputum samples. Results suggest that high frequency oscillations are capable of breaking down DNA to levels comparable to those obtained through rhDNAse treatment. Authors estimate reduction in intact DNA to be approximately 15% after 30 minutes of treatment.
App EM, Wunderlich MO, Lohse P, King M, Matthys H. Oscillatory physiotherapy for bronchial diseases: rheological and anti-inflammatory effects. Pneumologie 1999;53:348-359.
Oscillatory physiotherapy has been shown to have a mucolytic impact on bronchial secretions. This article briefly reviews the rheologic and inflammatory sequela of chronic lung disease and describes the physical changes to pulmonary mucus during oscillation. The mode of action for oscillatory physiotherapy is discussed, and an overview of various devices including the Flutter® valve, RC-Cornet®, The Vest® System, and the Hyaek Oscillator 1000® is presented. Flutter® is a registered trademark of Varioraw Percutive SARL.
Hayek™ is a trademark of Dranez Anstalt.
RC-Cornet®, distributed by Bonicur.
Chang HK, Weber ME, King M. E. Mucus transport by high frequency nonsymmetrical oscillatory airflow. J Appl Physiol 1988; 65(3): 1203-1209.
This in vitro study of the effects of oscillatory airflow on simulated mucus suggests that shearing at the air mucus interface could be a significant factor in the enhanced tracheal mucus clearance during HFCWO.
Dasgupta B, Tomkiewicz RP, Boyd WP, Brown NE, King M. Effects of combined treatment with rhDNase and airflow oscillations on spinnability of cystic fibrosis sputum in vitro. Pediatr Pulmonol 1995; 20: 78-82.
An in vitro study of sputum samples from eight cystic fibrosis (CF) patients demonstrates an optimal effect on sputum spinnability when Dnase and oscillation are used concomitantly. This suggests that combining biochemical (rhDNase) and physical (HFCC) treatments in CF patients may provide greater benefits than treatment with one modality at a time.
Hansen LG, Warwick WW, Hansen KL. Mucus transport mechanisms in relation to the effect of high frequency chest compression (HFCC) on mucus clearance. Pediatr Pulmonol 1994; 17: 113-118.
The authors suggest that HFCC enhances mucus transport in three essential ways: by altering the crosslinkage density of mucus glycoproteins, by creating a cough-like expiratory airflow bias, and by increasing the strength of ciliary beat through resonance.
King M, Zidulka A, Phillips D, Wight D, Gross D, Chang HK. Tracheal mucus clearance in high- frequency oscillation: effect of peak flow rate bias. Eur Respir J 1990; 3: 6-13.
A study of tracheal mucus clearance in eight anesthetized, spontaneously breathing dogs suggests that mucus clearance is enhanced by HFCWO but not by high frequency oscillation via the airway opening. Moreover, this study indicates that the effectiveness of airflow oscillation in clearing secretions may be due in part to an expiratory airflow bias.
Majaesic CM, Montgomery M, Jones R, King M. Reduction in sputum viscosity using high frequency chest compression compared to conventional chest physiotherapy. Pediatr Pulmonol 1996; Suppl 13: A358.
A study of the sputum cleared by HFCC vs. conventional chest physiotherapy suggests that HFCC reduces the viscosity of mucus secretions, potentially contributing to improvement in lung function over the long term.
Tomkiewicz RP, Biviji AA, King M. Effects of oscillating air flow on the rheological properties and clearability of mucous gel simulants. Biorheology 1994; 31(5): 511-20.
An in vitro study of the spinnability and viscoelasticity of mucous gel simulants subjected to oscillating airflow suggests that oscillating airflow acts as a physical "mucolytic," reducing both the spinnability and viscoelasticity of the simulants and enhancing cough-clearability.
Warwick W. High-frequency chest compression moves mucus by means of sustained staccato coughs. Pediatr Pulmonol 1991; Suppl 6: 283, A219.
This study reports that the volume of air expelled from the lungs was, with rare exception, much greater with the passive staccato coughs resulting from HFCC than it was with forced expiration. Warwick argues that the efficacy of HFCC relies in part on the 300 to 1500 staccato coughs produced by the vest each minute.

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Mucus Clearance, General

Chiappetta A, Mendendez A, Gozal D, Kiernan M. High Frequency Chest Wall Oscillation in hospitalized non-cystic fibrosis patients. Am J Respir Crit Care Med 1996; 153: A566.
A retrospective chart review suggests that HFCWO could be a cost-effective Airway Clearance Therapy for hospitalized non-cystic fibrosis patients and supports the need for a prospective evaluation of efficacy and safety of this technique for a variety of patients.
Gomez A, Elisan I, hardy K. Utilization of High Frequency Chest Wall Oscillation (Vest therapy) during therapeutic pediatric flexible fiberoptic bronchoscopy. Poster presentation at the 46th International Respiratory Congress of the American Association for Respiratory Care, October 7, 2000, Cincinnati, Ohio, USA.
There is evidence to support the use of therapeutic bronchoscopy to remove tenacious airway secretions and mucus plugs from the airways of pediatric patients. In this case series of three pediatric patients, investigators used High Frequency Chest Wall Oscillation (HFCWO) in conjunction with therapeutic bronchoscopy to determine if combined therapy would enhance the mobilization of mucus from the distal airways. In two of the three patients, improved secretion clearance during therapeutic bronchoscopy with HFCWO therapy was noted. Investigators concluded that HFCWO during therapeutic bronchoscopy appeared to promote enhance secretion clearance and was safe in the inpatient setting. Further investigation is recommended.
Gross D, Zidulka A, O'Brien C, Wight D, Fraser R, Rosenthal L, King M. Peripheral mucociliary clearance with high frequency chest wall compression. J Appl Physiol 1985; 58(4): 1157-1163.
This study of the effects of HFCC on peripheral and tracheal mucus clearance in five anesthetized, spontaneously breathing dogs demonstrates that HFCC at moderate pressure is both a safe and an effective means of enhancing peripheral and central mucus clearance in dogs.
Hansen L, Warwick W. High frequency chest compression system to aid in clearance of mucus from the lung. Biomed Instrum Technol 1990; 24: 289-294.
This article introduces an HFCC device that, in preliminary clinical trials, yielded a mean volume of 3.3 cc of cleared mucus per session as compared to a mean volume of 1.8 cc cleared during conventional chest physiotherapy.
King M, Phillips D, Gross D, Vartian V, Chang HK, Zidulka A. Enhanced tracheal mucus clearance with high frequency chest wall compression. Am Rev Respir Dis 1983; 128: 511-515.
A study of the effects of HFCC on tracheal mucus clearance in nine anesthetized dogs reveals that enhancement of clearance was most pronounced in the range of 11-15 Hz and peaked at 13 Hz and suggests that HFCC might be of considerable benefit as a mode of chest physiotherapy.
King M, Phillips D, Zidulka A, Chang HK. Tracheal mucus clearance in high frequency oscillation: chest wall versus mouth oscillation. Am Rev Respir Dis 1984; 130: 703-706.
A study comparing the rate of tracheal mucus clearance during spontaneous breathing, HFCWO and high frequency oscillation at the airway opening suggests that HFCWO enhances tracheal mucus clearance whereas high frequency oscillation at the mouth does not.
Rubin E, Scantlen G, Chapman A, Eldridge M, Menendez R, Wanner A. Effect of chest wall oscillation on mucus clearance: comparison of two vibrators. Pediatr Pulmonol 1989; 6: 122-126.
This comparative study of the effects of a mechanical percussor and a chest-wall oscillator on central airway mucociliary clearance in anesthetized dogs reveals that moderate oscillatory power applied to the chest wall can enhance mucus clearance in central airways, but that currently available commercial percussors may not meet the mechanical requirements for this effect.

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Neuromuscular Weakness, Use in

Castagnino M, Vojtova J, Kaminski S, Fink R. Safety of High Frequency Chest Wall Oscillation in patients with respiratory muscle weakness. Chest 1996; 110: S65.
This study of eight patients with neuromuscular weakness suggests that HFCC might be a tolerable and safe mode of airway clearance for people in this patient population.
Chiappetta A, Beckerman R. High Frequency Chest Wall Oscillation in spinal muscular atrophy (SMA). RT J Respir Care Pract 1995; 8(4): 112-114.
A ten-year-old female with spinal muscular atrophy showed significant improvement in pulmonary function after receiving HFCWO via the ABI Vest® (aka ThAIRapy® Vest) for six weeks. This improvement could be a result of a stronger cough and better secretion clearance associated with the use of HFCWO.
Gomez A, Elisan I, Hardy K. High Frequency Chest Wall Oscillation: video documentation of effect on a patient with duchenne's muscular dystrophy and severe scoliosis. Poster presentation at the 46th International Respiratory Congress of the American Association for Respiratory Care, October 7, 2000, Cincinnati, Ohio, USA.
Duchenne's muscular dystrophy (DMD) is frequently complicated by scoliosis/kyphoscoliosis, an ineffective cough response, and consequent respiratory compromise. This poster presents the case of a 16 year-old severely kyphoscoliotic DMD patient whose respiratory status was rapidly deteriorating due to thick bronchial secretions, mucus plugging, and persistent atelectasis. Manual chest physiotherapy and multiple bronchoscopies failed to reverse the patient's respiratory decline. The decision was made to facilitate airway clearance using High Frequency Chest Wall Oscillation (HFCWO). After several days, videotaped bronchoscopy during HFCWO revealed healing bronchial mucosa, minimal secretions, and significant movement of secretions from the peripheral airways. The investigators concluded that HFCWO therapy was effective at mobilizing secretions from the distal airways in a patient with severe skeletal deformities and recommended that this airway clearance method be considered for patients with similar pathophysiology.
Piloplys AV, Lewis S, Kasnicka I. Pulmonary vest therapy in pediatric long-term care. J Am Med Dir Assoc 2002;3:318-321.
A retrospective-prospective study of seven individuals with cerebral palsy indicates that initiation of Airway Clearance Therapy using High Frequency Chest Wall Oscillation (HFCWO) administered by The Vest® System resulted in decreased pneumonias requiring antibiotic treatment, decreased hospitalizations, and improved efficacy of pulmonary secretion suctioning. Researchers noted no increase in emetic episodes or seizure activity during therapy with The Vest® System.

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Respiratory System Mechanics, Effects on

Fink JB, Fahey PJ. A comparison of common bronchial hygiene devices and their effects on esophageal pressure. Chest 1998; 114(4): 293S.
This study evaluates the effect of various bronchial hygiene techniques (Flutter® Valve, The Vest® System, Hayek, EPAP, PEP) on airway and esophageal pressures in normal subjects. Each device generated considerably different flow and pressure fluctuations in both frequency and magnitude at the airway. Significant differences in esophageal patterns were also demonstrated. These differences in the mechanical effects were evident inside and outside the same general functional category of the device.
Flutter® is a registered trademark of Varioraw Percutive SARL.
Jones RL, Lester RT, Brown NE. Effects of high frequency chest compression on respiratory system mechanics in normal subjects and cystic fibrosis patients. Can Respir J 1995; 2(1): 40-46.
A comparative, blinded and randomized physiological study of ten normal volunteers and 11 clinically stable cystic fibrosis (CF) patients, designed to measure the short-term effects of HFCC in both populations, shows that CF patients with moderate or severe airway obstruction may gain maximal benefit from HFCC therapy when low vest pressure is used at an oscillation frequency of 10-15 Hz. The lowest pressure with The Vest® System minimized the decrease in end-expiratory lung volume and a frequency of 10-15 Hz maximized oscillating flow.

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Sputum Induction, Use in

Agostinis R, Man SFP, Mourad WA, Nguyen A, Thurber DL, Lien DC, Jones RL. High frequency chest compression in combination with hypertonic saline improves induced sputum cytologic yield. Am J Respir Crit Care Med 1995; 151: A844.
This study of nine patients reveals that the combination of HFCC and hypertonic saline solution results in more coughed-up sputum in thirty minutes than either saline solution or HFCC alone. Results also indicate that sputum samples derived in such a fashion may contain more cells from the peripheral airways than those derived from saline solution alone.
Jones RL, Man SFP, Lien DC. Use of high frequency chest compression plus hypertonic saline aerosol to provide sputum samples for diagnosis of lung cancer. Abstract presented at the Alberta Respiratory Diseases Symposium, Jasper, Alberta, 1995.
Having previously shown that HFCC in combination with saline solution aerosol results in a larger sputum sample than saline aerosol alone, researchers attempted to determine the usefulness of the HFCC-saline combination in obtaining a sputum sample for lung cancer diagnosis. This method of sputum induction proved to have a sensitivity of 71%, specificity of 80%, positive predictive value of 63%, negative predictive value of 86% and an accuracy of 77%.
Lam S. Key issues in lung cancer chemoprevention trials of new agents. Cancer Res 2003;163:182-195.
High Frequency Chest Wall Oscillation is discussed as a means of sputum induction, for the purpose of analyzing sputum biomarkers and cells for the detection of aberrant methylation. These techniques offer the potential to identify individuals at highest risk for chemopreventitive interventions. Novel imaging methods are also discussed.
McKinnon M, Payne P, MacAulay C, LeRiche JC, Lee A, Astrop C, Palcic B, Lam S. Evaluation of sputum cytology collection methods. Abstract presented at 8th World Conference on Lung Cancer, Dublin, Ireland, August 10-15, 1997.
In a study of sputum samples collected from 108 current/former smokers, 82% of those induced via inhalation of nebulized water during delivery of HFCWO were adequate (yielded cells of diagnostic importance), compared to 67% of those induced via nebulized water alone. In addition, Automated Image Cytometry was found to be several fold more sensitive than conventional microscopy in detecting small numbers of atypical cells in sputum cytology specimens.
McWilliams A, Mayo J, Muller N, Palcic B, English J, Lam S. Combination of computer-assisted sputum analysis and low-dose spiral CT scan for lung cancer screening. Chest 2001;120(4):166S.
This study used High Frequency Chest Wall Oscillation (HFCWO) for sputum induction. The sputum was then analyzed and classified as normal or atypical. Atypical sputum may improve lung cancer risk assessment in high-risk subjects, in whom lung cancer may be missed by low-dose spiral CT scan.
Rhame F, Armstrong J, Beneke J, Klous D, Sadowski P. Comparison of high frequency chest compression with hypertonic saline for the induction of sputum. Abstract presented at VIII International Conference on AIDS/III STD World Congress, Amsterdam, the Netherlands, November 1992.
In a study designed to measure alveolar macrophage recovery in sputum samples induced in HIV positive specimens using hypertonic saline vs. HFCC, both methods produced similar samples as measured by the fraction of cells which were pulmonary and the fraction of pulmonary cells which were alveolar macrophages.

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Ventilatory Considerations in Prescribing HFCWO

al-Saady NM, Fernando SS, Petros AJ, Cummin AR, Sidhu VS, Bennett ED. External high frequency oscillation in normal subjects and in patients with acute respiratory failure. Anaesthesia 1995;50(12):1031-1035.
In 20 normal subjects, the Hayek Oscillator proved capable of providing adequate ventilation by means of external chest wall oscillation (ECWO). In five patients with respiratory failure, ECWO via the Hayek Oscillator improved oxygenation by 16% and reduced arterial carbon dioxide by 6% over intermittent positive pressure ventilation.
Calverley PMA, Chang HK, Vartian V, Zidulka A. High Frequency Chest Wall Oscillation: assistance to ventilation in spontaneously breathing subjects. Chest 1986; 89(6): 218-223.
The effects of High Frequency Chest Wall Oscillation (HFCWO) on five supine normal subjects breathing spontaneously were studied using oscillations of 3.5 and 8 Hz for fifteen minutes each at both maximal and half-maximal peak tolerable cuff pressures. Researchers conclude that HFCWO may potentially assist ventilation in spontaneously breathing subjects without requiring an endotracheal tube.
Dolmage TE, Eisenberg HA, Davis LL, Goldstein RS. Chest wall oscillation at 1 Hz reduces spontaneous ventilation in healthy subjects during sleep. Chest 1996;110(1):128-135.
A study designed to determine the ventilatory effects of ECWO delivered by the Hayek Oscillator on seven normal subjects during sleep demonstrated that ECWO provided adequate gas exchange despite a reduction in spontaneous ventilation over several hours and therefore can be considered among the options for noninvasive ventilatory support. However, it was also associated with a reduction in the total sleep time and an increase in the number of apneas and hypoapneas when compared with control measures.
Harf A, Zidulka A, Chang HK. Nitrogen washout during tidal breathing with superimposed High Frequency Chest Wall Oscillation. Am Rev Respir Dis 1985; 132: 350-353.
A study of the effects of HFCWO superimposed on tidal ventilation on seven normal, seated subjects leads researchers to postulate that, during inspiration, HFCWO enhances gas mixing in the lung periphery and that during expiration, it improves gas mixing in the airways. Both of these actions tend to increase the effectiveness of alveolar ventilation.
Isabey D, Piquet J. The ventilatory effect of external oscillation. Acta Anaesthesiol Scand 1989; 33 (Suppl 90): 87-92.
External oscillation of the chest wall produced a beneficial effect on the ventilation of bronchoconstricted rabbits whereas internal high frequency ventilation via the trachea did not. In human subjects, the oscillations achieved were smaller but still produced a clear change in breathing pattern associated with a slight improvement in gas exchange and a potentially positive effect on inspiratory muscle fatigue.
Khoo M, Gelmont D, Howell S, Johnson R, Yang F, Chang HK. Effects of High Frequency Chest Wall Oscillation on respiratory control in humans. Am Rev Respir Dis 1989; 139: 1223-1230.
A study of the spontaneous breathing patterns of ten normal adult volunteers during HFCWO reveals that HFCWO increased breath-to-breath variability of spontaneous respiration in all subjects, prolonging expiration pauses and producing short apneas in some cases. PaCO2 decreased significantly.
Piquet J, Isabey D, Chang HK, Harf A. High frequency transthoracic ventilation improves gas exchange during experimental bronchoconstriction in rabbits. Am Rev Respir Dis 1986; 133: 605-608.
Ten anesthetized rabbits received high frequency transthoracic ventilation (HFTV) through a body box connected to a piston pump during induced bronchoconstriction and during a control period. Results indicate that HFTV at 5 Hz facilitates CO2 removal and improves arterial oxygenation in rabbits without noticeable adverse effects. Researchers suggest that the improvements were a result of a decrease in maldistribution of ventilation in the obstructed lung.
Zidulka A, Gross D, Minami H, Vartian V, Chang HK. Ventilation by high frequency chest wall compression in dogs with normal lungs. Am Rev Respir Dis 1983; 127: 709-713.
HFCWO applied to six anesthetized and paralyzed supine dogs suggested that HFCWO may assist spontaneous ventilation in dogs with normal lungs, but that in paralyzed dogs, it may cause hyperventilation.

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Airway Clearance Overviews

Chiappetta A, Davis S. Airway clearance practices of respiratory care practitioners, physical therapists and physiotherapists from CF centers. Pediatr Pulmonol 1996; Suppl 13: A353.
This abstract summarizes the results of a questionnaire designed to assess airway clearance techniques used in various cystic fibrosis centers, the team member recommending airway clearance techniques, the monitoring of efficacy, and the use of guidelines for prescribing different types of airway clearance techniques. The questionnaire was completed by 64 out of 75 participants at the initial session for respiratory care practitioners, physical therapists, and physiotherapists of the Ninth Annual North American CF Conference in 1995.
Hardy KA, Anderson BD. Noninvasive clearance of airway secretions. Respir Care Clin N Am 1996; 2(2): 323-45.
This article provides an overview of the need for airway clearance and the types, advantages and disadvantages of airway clearance modalities available for use in a variety of patient populations.
Hess DR. The evidence for secretion clearance techniques. Respir Care 2001;46(11):1276-1292.
An evidence-based medicine approach to reviewing the available airway clearance modalities. The author concludes that the majority of studies performed to date were small and limited to short term outcomes. Very few studies used sham therapy, and most were cross-over designs.
Langenderfer B. Alternatives to percussion and postural drainage. J Cardipulmonary Rehabil 1998;18:283-289.
This article provides a review of the literature pertaining to mucus clearance therapies. A discussion of percussion and postural drainage (P&PD), autogenic drainage (AD), positive expiratory pressure (PEP), the Flutter® valve, intrapulmonary percussive ventilation (IPV), and High Frequency Chest Wall Oscillation (HFCWO) is included.
Flutter® is a registered trademark of Varioraw Percutive SARL.
Prasad A, Esta-Lee T, Mikelsons C. Physiotherapy in cystic fibrosis. J R Soc Med 2000;(suppl 38):93;27-36.
This article presents a comprehensive overview of current clinical opinion on the efficacy of Airway Clearance Therapy via chest physiotherapy (CPT) in the treatment of chronic lung disease. Concise descriptions of current available modalities including active cycle breathing techniques (ACBT), exercise, High Frequency Chest Wall Oscillation (HFCWO), intrapulmonary percussive ventilation (IPV), and the Flutter® valve, are presented. The authors suggest that despite these modalities, there is yet to be a scientifically proven "gold standard" airway clearance technique for patients with cystic fibrosis.
Flutter® is a registered trademark of Varioraw Percutive SARL.
Pryor JA. Physiotherpay for airway clearance in adults. Eur Respir J 1999;14:1418-1424.
The difficulty in accurately assessing the efficacy of various mucociliary clearance techniques is addressed in this review. A brief discussion of the historical background and development of airway clearance therapies is followed by concise overviews of current and emerging modalities. Postural drainage, percussion and vibration, High Frequency Chest Wall Oscillation (HFCWO), glossopharyngeal breathing, Flutter VRPI®, RC- Cornet®, and others are presented.
Flutter® is a registered trademark of Varioraw Percutive SARL.
Rubin BK. Physiology of airway mucus clearance. Respir Care 2002;47(7):761-768.
A concise review of mucus composition and the cellular mechanisms for mucus clearance. This review details the role of mucus in mucociliary clearance, mucus properties, sputum, cilia, airway surfactant, cough, and the role of inflammation in producing hypersecretion.
Toder DS. Respiratory problems in the adolescent with developmental delay. Adolescent Medicine: State of the Art Reviews 2000;11(3):617-631.
This article is an overview of the pulmonary complications that may arise in the subset of developmentally delayed patients who suffer from neuromuscular dysfunction. Respiratory risk factors such as drooling, aspiration, gastroesophageal reflux, and scoliosis are considered. The elements of a good pulmonary hygiene program for this patient population, including prophylactic Airway Clearance Therapy, are discussed. A review of current airway clearance treatment options, including High Frequency Chest Wall Oscillation (HFCWO), is presented.

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