During ventilation, phasic diaphragmatic EMG amplitude decreased to below 10 percent of control measurements in each group. These reductions in inspiratory muscle activity were associated with positive intrathoracic pressure swings on inspiration in all subjects. Therefore, Carrey et al reasoned that nocturnal ventilation should improve daytime inspiratory muscle performance. However, few studies have measured inspiratory muscle function. Marino and Braun used negative or positive pressure ventilation in 35 patients, some of whom had parenchymal disease, and observed an improvement in their respiratory muscle strength (RMS) and their maximal voluntary ventilation. Ellis et al reported an improvement in RMS in four of their subjects receiving positive pressure ventilation. We therefore explored the influence of IPPV on RMS and inspiratory muscle endurance. birth control yasmin
The RMS did not change among our subjects (Table 2) despite repeated measurements at regular intervals, nor did we observe changes in lung volumes except in one patient (idiopathic neuromuscular disease) in whom the inspiratory capacity increased from 0.6 to 1 L. These findings are consistent with our previous work in which neither standard measurements of lung function nor RMS changed following two months of nocturnal negative pressure ventilation.