Abstract
Introduction
Chest wall vibration activates chest wall afferents and reduces breathlessness in healthy subjects (Edo et al 1998) and in COPD (Fujie et al 2002). We hypothesised that high frequency airflow oscillation (HFAO)would reduce breathlessness driven by moderate hypercapnia in healthy subjects.
Methods
Ventilation, diaphragm electromyogram activity (EMGdi%max), oesophageal and diaphragm pressure-time-product were recorded whilst breathing 7%CO2 in air over 8 minutes. HFAO was applied during 5 consecutive breaths each minute at 0Hz, 15Hz, 30Hz and 45Hz in random order. Borg breathlessness was measured at baseline and at the end of each minute. Comparisons between HFAO frequencies were made using 1 way ANOVA with post hoc analysis using Dunn’s multiple comparison test.
Results
11 healthy subjects aged 20-37 years completed the study.
Borg breathlessness at minute 8 was significantly lower using HFAO at 30Hz (median (IQR) Borg 2 (1 to 4)) than without HFAO (0Hz) (Borg 3 (3 to 4)), at 15Hz (Borg 3 (2 to 4)) or 45Hz (Borg 3 (2 to 4)); p = 0.004, 0Hz vs 30Hz p<0.05. No significant differences in physiological parameters recorded were observed.
Conclusions
30Hz HFAO reduces breathlessness in healthy subjects during a moderate hypercapnic challenge. The lack of change in neural respiratory drive, or respiratory muscle work suggests improved efferent-afferent matching as a mechanism.
- © 2013 ERS
