Prolonged Relaxation Rate of Inspiratory Muscles in Patients with Sleep Apnea

Abstract

To evaluate whether inspiratory muscle function is impaired in patients with sleep apnea, we measured inspiratory muscle strength and relaxation rate before and after sleep in 13 patients. The sleep apnea group was composed of eight patients with severe obstructive sleep apnea, and the non-apnea group was composed of five patients without significant sleep apnea. We chose the time constant of relaxation (TauR) as an index of impaired inspiratory muscle contractility, and in subsets of each group, we measured the inspiratory pressure-time index as an indicator of a fatiguing breathing pattern. In patients with sleep apnea, presleep TauR was 79 +/- 22 ms (SD), longer than that of normal subjects (normal, 59 +/- 7 ms) (p less than 0.05). TauR increased by 21 +/- 16 ms during sleep (p less than 0.01). In patients without apnea, presleep TauR was 67 +/- 7 ms and it did not change after sleep. Maximal inspiratory and expiratory pressures were unchanged after sleep. We conclude that patients with sleep apnea do not develop overt inspiratory muscle failure but do have impaired contractility. We speculate that hypoxemia as well as increased work load was responsible.

Lack of evidence for diaphragmatic fatigue over the course of the night in obstructive sleep apnoea

“…This finding appears to be at variance with the results of GRIGGS et al [11], who reported an increase in the τR of pleural pressure during voluntary sniff manoeuvres, measured prior to sleep and upon awakening in an apparently similar group of OSA patients. They found no change in maximal mouth pressures from night to morning.…”

“…They found no change in maximal mouth pressures from night to morning. The changes in τR were, therefore, interpreted as evidence of impaired inspiratory muscle contractility without development of overt fatigue [11]. Conceivably, their findings may have related to selective changes in contractility of nondiaphragmatic inspiratory muscles identified by assessment of τR using pleural pressure rather than Pdi [24].…”

“…One previous study found evidence of impaired inspiratory muscle contractility in OSA, in that pleural pressure relaxation rates (τR) during voluntary sniff manoeuvres were prolonged in the morning compared with the preceding night prior to sleep [11]. However, the development of inspiratory muscle fatigue during sleep over the course of the night in OSA has not been specifically investigated.…”

Neural respiratory drive during apnoeic events in obstructive sleep apnoea

“…Indeed, some investigators have hypothesised that respiratory muscle fatigue would occur in patients with severe OSA [22,23]. In keeping with this hypothesis, GRIGGS et al [22] reported a prolonged relaxation rate of inspiratory muscle in patients with sleep apnoea.…”

“…Indeed, some investigators have hypothesised that respiratory muscle fatigue would occur in patients with severe OSA [22,23]. In keeping with this hypothesis, GRIGGS et al [22] reported a prolonged relaxation rate of inspiratory muscle in patients with sleep apnoea. In contrast, MONTSERRAT et al [21] and CIBELLA et al [24], using the technique of diaphragm EMG frequency analysis, were unable arterial oxygen saturation (Sa,O2).…”