High-Frequency Chest Compression: A Summary of the Literature

Dosman.qxd 2/4/2005 1:34 PM Page 37 REVIEW High-frequency chest compression: A summary of the literature Cara F Dosman MD FRCPC FAAP1, Richard L Jones PhD FCCP2 CF Dosman, RL Jones. High-frequency chest compression: A summary of the literature. Can Respir J 2005;12(1):37-41. Vibrations mécaniques de haute fréquence : Sommaire de la littérature The purpose of the present literature summary is to describe highfrequency chest compression (HFCC), summarize its history and outline study results on its effect on mucolysis, mucus transport, pulmonary function and quality of life. HFCC is a mechanical method of self-administered chest physiotherapy, which induces rapid air movement in and out of the lungs. This mean oscillated volume is an effective method of mucolysis and mucus clearance. HFCC can increase independence. Some studies have shown that HFCC leads to more mucus clearance and better lung function compared with conventional chest physiotherapy. However, HFCC also decreases end-expiratory lung volume, which can lead to increased airway resistance and a decreased oscillated volume. Adding positive endexpiratory pressure to HFCC has been shown to prevent this decrease in end-expiratory lung volume and to increase the oscillated volume. It is possible that the HFCC-induced decrease in endexpiratory lung volume may result in more mucus clearance in airways that remain open by reducing airway size. Adjunctive methods, such as positive end-expiratory pressure, may not always be needed to make HFCC more effective. Le but du présente résumé de la littérature est de décrire la technique de vibrations mécaniques de haute fréquence, d’en résumer l’historique et de donner un aperçu des résultats d’une étude ayant mesuré ses effets sur la mucolyse, le dégagement du mucus, la fonction pulmonaire et la qualité de vie. Les vibrations mécaniques de haute fréquence sont une technique de physiothérapie pulmonaire auto-administrée qui accélèrent l’entrée et la sortie de l’air durant la respiration. Cette technique stimule efficacement la mucolyse et l’élimination du mucus et peut de ce fait favoriser l’autonomie. Certaines études ont montré qu’elle favorise l’expectoration et améliore la fonction pulmonaire comparativement à la physiothérapie pulmonaire classique. Par contre, elle réduit également le volume pulmonaire télé-expiratoire et peut entraîner une résistance respiratoire accrue et une baisse du volume oscillatoire. L’ajout d’une pression téléexpiratoire s’est révélée susceptible d’atténuer la baisse du volume pulmonaire télé-expiratoire et d’accroître le volume oscillatoire. Il est possible que la diminution du volume télé-expiratoire induite par les vibrations mécaniques de haute pression favorise une plus grande élimination du mucus dans les voies aériennes qui restent ainsi dégagées, en réduisant le calibre des voies respiratoires. Des méthodes d’appoint, comme la pression positive télé-expiratoire ne seraient pas toujours nécessaires pour rendre cette technique plus efficace. Key Words: Chest physiotherapy; End-expiratory lung volume; High-frequency chest compression; Mucus clearance; Positive end-expiratory pressure atients with cystic fibrosis have excessively thick lung mucus, which tends to plug the small peripheral airways. The cycle of hypersecretion, infection (1), inflammation and impaired mucus clearance (2,3) leads to progressive airway obstruction and destruction, especially in the lung periphery where cough and conventional chest physiotherapy are less effective at clearing mucus (3,4). High-frequency chest compression (HFCC) is a patientdelivered form of chest physiotherapy, which causes mucolysis (5,6), as well as increased mucus clearance (7-10) and improvement in pulmonary function (1,10,11) compared with that achieved by conventional chest percussion and postural drainage. Also called high-frequency oscillation, HFCC was initially administered only to patients with cystic fibrosis, but is now starting to be used for a wide range of pulmonary, neurological and neuromuscular disorders (12). P DESCRIPTION AND HISTORY OF HFCC HFCC is a portable mechanical method of self-administered chest physiotherapy (13), and is analogous to frequent repetitive coughing (7). Cough generates a shear stress at the air-mucus interface (14), which increases mucus flow rate (15). Repetitive cough induces significantly more mucus clearance than a single cough, and even more clearance with an increased frequency of repetitive cough or air flow oscillations (14,16). Therefore, it follows that rapid air movement may also enhance mucus clearance. HFCC is delivered by a pneumatic vest that surrounds the thorax. The vest is inflated to a nearly constant (11) positive background pressure with a superimposed frequency of air pressure oscillations (17). These oscillations induce rapid air movement in and out of the lungs, which is measured at the mouth as mean oscillated volume. Mean oscillated volume increases mucus clearance (11), particularly from the periphery of the lung (18). The volume of mucus moved has been thought to be greatest at frequencies between 10 Hz and 20 Hz, which can be alternated to maximize the volume of air and rate of air flow (19). HFCC may be advantageous in patients with cystic fibrosis in which plugging of the peripheral airways is a major problem and in patients with other obstructive lung disease where peripheral mucociliary clearance is impaired and cough is less effective (18). Departments of 1Pediatrics and 2Medicine, University of Alberta, Edmonton, Alberta Correspondence and reprints: Dr Cara F Dosman, Glenrose Rehabilitation Hospital, 10230-111 Avenue, Edmonton, Alberta T5G 0B7. Telephone 780-471-8235, fax 780-471-7907, e-mail Can Respir J Vol 12 No 1 January/February 2005 ©2005 Pulsus Group Inc. All rights reserved 37 Dosman.qxd 2/4/2005 1:34 PM Page 38 Dosman and Jones In 1966, high-frequency vibration of the chest was first used to effectively relieve respiratory airway obstruction due to retained secretions, thereby increasing vital capacity (20). A cycled external vibrocompressor applied pressure to the upper abdomen and lower thorax during expiration (20). The ThAIRapy Vest for high-frequency chest wall compression was developed in the 1980s by Hansen and Warwick, and was approved for use and met all the criteria for airway clearance therapy published by the American Association for Respiratory Care (21). This modality is now called The Vest (Advanced Respiratory, USA) (12). The pressure pulse frequency is adjustable from 5 Hz to 25 Hz. In 1983, King et al (7,8) found that, in anesthetized dogs, a modified blood pressure cuff placed around the lower thorax, providing high-frequency chest wall oscillations at 5 Hz to 17 Hz and of the same magnitude as used for ventilation, led to the enhancement of the tracheal mucus clearance rate (8). The tracheal mucus clearance rate was frequency-dependent, with a maximal effect at 13 (...truncated)