Noninvasive assessment of the tension-time index of inspiratory muscles at rest in obese male subjects

OBJECTIVE: The aim of this study was to investigate the effect of excessive mechanical load caused by obesity on the inspiratory muscle performance in obese men at rest. METHODS: We therefore measure at rest spirometric flows and the noninvasive tension time index of inspiratory muscle (T-Tmus P-I/P-Imax x T-I/T-TOT) in eight obese male subjects (body mass index (BMI) > 30) and 10 controls. RESULTS: Spirometric flow (FEV1% pred, FVC% pred) and maximal inspiratory pressure (P-Imax) were significantly lower in obese subjects compared to controls (P<0.001). The mean T-Tmus was significantly higher in obese subjects than in controls (0.136+/-0.003 vs 0.045+/-0.01). The increase in T-Tmus was primarily due to an increase in the ratio of mean inspiratory pressure to maximal inspiratory pressure (P-I/P-Imax) and the duty cycle (T-I/T-TOT). We found a significant negative relationship between P-Imax and BMI (r = -0.74, P<0.001), a positive correlation between T-Tmus and BMI (r = 0.80, P<0.001) and a negative correlation between T-Tmus and forced expiratory volume in 1 s (r = 0.85, P < 0.001). CONCLUSION: Excessive mechanical load caused by obesity imposes a great burden on the inspiratory muscle, which may predispose such subjects to respiratory muscle weakness at rest.