High-frequency chest wall oscillation (HFCWO) is an airway clearance technique in which external chest wall oscillations are applied to the chest using an inflatable vest that wraps around the chest. These machines produce vibrations at variable frequencies and intensities, helping to loosen and thin mucus and separate it from airway walls.

How does HFCWO work?

HFCWO devices use positive and negative pressure changes to increase peripheral and tracheal mucus movement toward the airway opening. High-frequency air pulses to the vest make oscillatory chest wall compressions, increasing the pressure during inflation and leading to a short burst of expiratory flow of up to 1.6L/second. Typically, a user pauses during the 20- to 30-minute HFCWO treatment every 5 minutes to cough out loosened mucus that has moved into the large airways.

Different lines of thought exist as to why airway clearance vests are effective at mobilizing secretions to clear the airways. The first is that the HFCWO device increases the air-liquid sheer forces during expiration (breathing out) to improve mucus removal. The second is the oscillation of the airway walls loosens secretions to improve air-liquid flow. Finally, the device is believed to boost ciliary beating to change the nature of bronchial secretions, making them less thick and sticky and, hence, easier to expel.

HFCWO in clinical trials

A number of studies have tested the various HFCWO devices available, often used as a treatment for cystic fibrosis.  A study in bronchiectasis patients, published in BMC Pulmonary Medicine in 2013, found that high-frequency oscillation of the chest wall (HFCWO) improved both “pulmonary function and quality of life” in patients needing daily airway clearance.

Several ongoing clinical trials are currently recruiting patients. The first trial (NCT04017312) is investigating Oscillating Positive Expiratory Pressure (OPEP) therapy compared to HFCWO in 70 patients with bronchiectasis. The study is recruiting patients in New York and Tennessee and aims to collect data from participants for 12 months. The study has a target completion date of November 2020.

Another study (NCT04271969) is comparing patients’ quality of life before and after a year of using HFCWO. The study has a targeted recruitment of 100 patients with bronchiectasis from locations in Alabama, Georgia, Ohio, Texas. The study is estimated to conclude in June 2021.

Most of these devices use air bladder technology, requiring connection to an external generator that delivers the air pulses that squeeze and release the chest. A newer device, called the AffloVest, uses individual oscillators built into the vest, and is battery powered so a generator is not required, making it a more portable device.

A clinical trial (NCT04266873) is testing the efficacy of the AffloVest in 30 bronchiectasis patients. Participants will use the AffloVest for 30 minutes, twice a day for six months. The study is recruiting patients from the United Kingdom and has a targeted completion date of December 2020.

Another device, called the SmartVest Connect, can connect to its own app to deliver real-time performance tracking and give reminders of when to use the device. The performance tracking can allow healthcare teams to make more informed care decisions according to Electromed, the manufacturer of SmartVest.

HFCWO devices are doctor prescribed to improve bronchial drainage (clear mucus) in a number of diseases or conditions, from bronchiectasis to cystic fibrosis, acute asthma, and immotile cilia syndrome.


Last updated: Mar. 18, 2020


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