Diurnal change of respiratory muscle strength in patients with sleep-disordered breathing.
BACKGROUND
Obstructive sleep apnea is characterized by repetitive pharyngeal collapse, which increases inspiratory resistive load, and causes intermittent oxygen desaturation and frequent arousals during sleep. This could be damaging to respiratory muscles and result in their weakness. Therefore, we investigated respiratory muscle strength before and after nocturnal sleep in patients with sleep-disordered breathing (SDB).


METHODS
Forty eight male patients with SDB undergoing overnight polysomnography were enrolled. Maximal expiratory pressure (MEP) and maximal inspiratory pressure (MIP) were measured before and after the sleep study. Correlation between polysomnographic data and diurnal changes in maximal respiratory pressures were also assessed.


RESULTS
After nocturnal sleep, MEP increased from 94.6 +/- 20.8 cm H2O to 105.9 +/- 24.1 cm H2O (p < 0.001) and MIP increased from 72.9 +/- 20.2 cm H2O to 78.3 +/- 21.7 cm H2O (p = 0.004). There was no significant correlation between changes in MEP/MIP and apnea-hypopnea index, arousal index, and mean and minimal oxygen saturation.


CONCLUSIONS
The respiratory muscle strength of patients with SDB was greater in the morning than at night, which may be contributed to by the restorative effect of nocturnal sleep. This diurnal difference was not correlated to the severity of SDB, which may suggest that respiratory muscles are less impaired by SDB.
Su
Mao-Chang
MC
Division of Pulmonary and Critical Care Medicine, Chang Gung Memorial Hospital, Kaohsiung Medical Center, Chang Gung University College of Medicine, Kaohsiung, Taiwan, ROC.
Chin
Chien-Hung
CH
Chen
Yung-Che
YC
Hsieh
Yu-Tang
YT
Wang
Chin-Chou
CC
Huang
Yi-Chuan
YC
Lin
Meng-Chih
MC
D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology; D006801:Humans; D008297:Male; D053580:Muscle Strength / Q000502:physiology; D012132:Respiratory Muscles / Q000503:physiopathology*; D012891:Sleep Apnea Syndromes / Q000503:physiopathology*