A clinical study into high-frequency chest wall oscillation vests — assessing their short-term impact on standard measures of lung function before and during use — challenges the view that these devices work through airflow bias in the lungs, the process responsible for mucus movement when breathing.
Findings, using established tests that include forced vital capacity (FVC), forced expiratory volume (FEV1), and forced expiratory flow (FEF25%-75%), suggest “that the concept of HFCWO vest-induced cephalad airflow bias is not supported by standard spirometry measurements,” researchers concluded. “None of the vest groups showed statistically significant increased airflow in the lungs.”
The study, claiming to be the first using such measures during vest therapy, is titled “Effect of High Frequency Chest Wall Oscillation Vests on Spirometry Measurements” and published online in the Journal of Pulmonary Technique.
The narrowing of airways during exhalation increases the speed and forces at work in the airway – creating a cephalad airflow bias. Cephalad airflow bias is responsible for movement of mucus in airways during normal breathing.
High-frequency chest wall oscillation (HFCWO) vests are considered a standard of care to help manage respiratory conditions such as cystic fibrosis, non-cystic fibrosis bronchiectasis, and chronic obstructive pulmonary disease.
Currently, two different technologies are utilized for HFCWO vests – one using a pneumatic compressor connected to an inflatable garment, and the other utilizing mechanical oscillators integrated into a wearable garment.
But the manner by which HFCWO vests improve pulmonary function — as determined by established parameters — is not known. Researchers set out to determine the exact mechanism of action through which HFCWO devices improve airflow. They also wanted to investigate potential differences in the lung function parameters between these two device types.
“Vibratory action through the chest wall helps to loosen secretions, much like manual Chest Physical Therapy (CPT). This study was designed to investigate the effects of the application of mechanical oscillatory and compressor-based HFCWO vests during use on standard spirometry parameters,” Thomas W. O’Brien, MD, a pulmonologist at Pulmonary Disease Specialists in Kissimmee, Florida, and the study’s principal investigator, said in a press release.
“It has been claimed that one of the operating principles of HFCWO vests is creating ‘airflow bias’ in the lungs, but valid clinical evidence supporting that claim is lacking,” he added.
The prospective clinical trial (NCT03534986) in 32 healthy volunteers measured airflow bias during use of HFCWO therapy. Four types of vests were compared: AffloVest by International Biophysics — the company that sponsored this study — and The Vest by Hill-Rom, SmartVest by Electromed, and inCourage by RespirTech. The latter three are compressor-based “air bladder” oscillatory devices, and AffloVest is a mechanical oscillator-based device. Data gathered in people using the compressor-based vests were pooled.
Pulmonary function was assessed according to the American Thoracic Society’s (ATS) guidelines for baseline lung function parameters: peak expiratory flow (PEF) and tidal volume (TV) were measured in addition to FVC, FEV1, and forced expiratory flow (FEF25%-75%) — a measure taken between the start and finish of FVC. Specifically FEF25%-75% measures the average flow from the point at which 25 percent of the FVC has been exhaled until the point at which 75 percent has been exhaled.
Researchers found that use of compressor-based HFCWO vests were associated with a significant decrease in FVC, FEV1 and FEF25-75% compared to baseline or study start, but such drops were significant for AffloVest only when FEF25-75% was measured. For instance, a 6.0% decline in FEV1 was seen in the compressor-based group and 1.4% in the AffloVest group; in FEF25-75%, declines recorded in compressor-based and oscillator-based devises were 14.0% and 4.6%, respectively.
However, standard spirometry measurements showed no change in TV and, especially, in PEF in either of the HFCWO vest groups — the latter suggesting these vests do not work by increasing cephalad airflow bias. “Based on the concept of increased cephalad airflow bias in the lungs during use of HFCWO devices, one might expect that the expiratory peak flow [PEF] should be increased,” the study noted.
Once use of vests stopped, lung function measures returned to baseline for both types of HFCWO devices.
“The mode of action of HFCWO vests is not fully understood at this time,” the researchers concluded.