Ever since High Frequency Chest Wall Oscillation (HFCWO) devices were developed to help patients with cystic fibrosis breathe easier, clinical researchers required appropriate parameters to assess the efficacy of HFCWO-based therapies. It is common practice to look at three main indicators of pulmonary and overall health: mucus clearance, clinical measurements, and pulmonary function tests.
Mucus clearance, which is especially important for cystic fibrosis patients, determines how much mucus (by volume, wet weight, or dry weight) is coughed up by a patient in a span of time. Clinical measurements include weight, blood oxygen saturation, and blood cell counts. These give a picture of the patient’s general health. However, pulmonary function tests are especially telling of how well the lungs of a cystic fibrosis patient work.
According to the National Library of Medicine, pulmonary function tests evaluate how well the lungs operate while breathing. The series of tests are conducted by breathing in and out normally and/or forcibly through a spirometer (spirometry), breathing normally inside an enclosed box (plethysmography), and breathing a tracer gas. From these tests, clinicians are able to determine a variety of parameters related to lung function, including: tidal volume (VT), diffusion capacity to carbon monoxide (DLCO), expiratory reserve volume (ERV), forced vital capacity (FVC), forced expiratory volume (FEV), forced expiratory flow 25% to 75%, functional residual capacity (FRC), maximum voluntary ventilation (MVV), residual volume (RV), peak expiratory flow (PEF), slow vital capacity (SVC), and total lung capacity (TLC).
Interestingly, two of these seemingly distinct measures — mucus clearance and pulmonary function — are related. When mucus is cleared from the lungs, the lungs seem to be more effective in normal function, as demonstrated by a handful of studies investigating HFCWO-mediated or High Frequency Chest Compression (HFCC)-mediated mucus clearance in patients with cystic fibrosis. These devices apply cyclical pressure to the chest to help move, break up, and clear mucus from the lungs.
Stable CF Patients Show Benefits in Pulmonary Function with HFCC
An early study from 1991 identified the benefits of self-administered HFCC on FVC and FEV in one second (FEV1) in a small group of 16 cystic fibrosis patients who were previously receiving conventional chest physiotherapy (CPT). The patients underwent approximately 22 months of HFCC therapy using “a variable air pulse delivery system and a non-stretch inflatable vest,” according to the journal article published in Pediatric Pulmonology entitled “The Long-term Effect of High-frequency Chest Compression Therapy on Pulmonary Complications of Cystic Fibrosis.” While the patients were on different HFCC therapy regimens involving between 30 and 240 minutes of HFCC a day, each patient underwent at least one 30-minute session per day split into five-minute periods of HFCC. The six total periods were each conducted at a different frequency ranging from 5 and 22 Hz. Following the therapy period, patients experienced a positive change in both FVC and FEV1 compared to conventional CPT.
Another study with 14 stable cystic fibrosis patients in a pediatric pulmonary division of a tertiary care center compared self-administered HFCWO to high-frequency oral airway oscillation and conventional CPT. As described in the study, two modes of HFCWO, two modes of oral airway oscillation, or CPT were applied to a patient once a day in the afternoon, with two days between treatments. The two different HFCWO regimens — 3 Hz or oscillations alternating between 3 and 16 Hz — performed similarly to the other three CPT regimens and allowed patients to expectorate more sputum than they were able to when entering the study. However, there was no change from baseline in pulmonary function tests (FVC, FEV1, or oxygen saturation), possibly because the patients were already in a stable condition and did not have deficient pulmonary function.
HFCC Improves Pulmonary Function Following an Exacerbation
When observing cystic fibrosis patients in a hospital setting, HFCC is just as safe and effective as conventional CPT and may serve as an alternative to help patients enhance their pulmonary function following an acute exacerbation. The study, “Comparison of High Frequency Chest Compression and Conventional Chest Physiotherapy in Hospitalized Patients with Cystic Fibrosis,” which was published in American Journal of Respiratory and Critical Care Medicine, analyzed pulmonary function in 50 cystic fibrosis patients who were admitted to the hospital for an acute exacerbation. Similar to the previous study, patients were treated in six, five-minute periods of HFCC at 6 to 19 Hz. When compared to patients receiving conventional CPT, patients receiving HFCC demonstrated equally significant improvements in pulmonary function tests. All patients were required to receive treatment for at least 14 days, and the hospital discharge rates were similar between the two groups.
These results were replicated in a more short-term setting from a research group at the Cystic Fibrosis Center in Italy. The team conducted a two-day study with 16 cystic fibrosis patients receiving three different CPT regimens, and one form was HFCC. As described in “Short-term Effects of Three Chest Physiotherapy Regimens in Patients Hospitalized for Pulmonary Exacerbations of Cystic Fibrosis: A Cross-over Randomized Study,” which was published in Pediatric Pulmonology, the patients were treated twice a day with each type of CPT for a total of 50 minutes in each session. Following treatment, patients were monitored for wet and dry weight of mucus clearance and lung function. Throughout the two treatment days, the patients experienced no difference in effects as a result of the three different CPT treatment programs, but there was a significant difference in the amount of mucus cleared when looking at any of the three CPT treatments versus a control treatment.
Importance of Pulmonary Function in Cystic Fibrosis Patients
Researchers and clinicians have continued to design and develop HFCWO therapy vests with the goal of breaking up mucus secretions and allowing cystic fibrosis patient to improve pulmonary function. From a clinician’s point of view, each patient is born with normal lungs and airways but defective chloride channels. Early inflammation, infection, and scarring contribute to loss of lung function, especially following exacerbations. Therefore, it is important to frequently and regularly measure pulmonary function to ensure patients have adequate function relative to reference values. With abundant evidence establishing the ability of HFCWO-based vests to improve pulmonary and overall health, clinicians have begun to incorporate these vests into normal treatment plans for cystic fibrosis.