Reproducibility of the short-latency reflex inhibition to loading of human inspiratory muscles

Loading of inspiratory muscles produces a profound short-latency inhibitory response (IR) of the electromyogram (EMG), followed by an excitatory response (ER). Duration of IR correlates positively with the apnoea hypopnoea index in obstructive sleep apnoea (OSA) patients, for whom measurement of this reflex may allow the assessment of a physiological response to therapy. To test the reliability of reflex measurement, we studied 11 human subjects on 4 separate days. Inspiration was transiently occluded during 2 sets of 30 trials on each day. Scalene muscle EMG was rectified and averaged. Ten parameters (4 latencies and 6 EMG sizes) were measured. Reproducibility was analysed by ANOVA, intraclass correlation coefficient (ICC) and coefficient of variation (CV). The mean ICC was 0.56 (range 0.30-0.76) and the mean CV was 25% (range 6.7-48%). These results show good measurement reliability. The abnormalities seen in disease are significantly larger than these CVs. The reflex response to airway occlusion may be assessed reliably using our method.