Respiratory muscle interaction during NREM sleep in patients with occlusive apnea

To study respiratory muscle interaction in patients with occlusive apnea, diaphragmatic electromyogram (EMGdi) and gastric, pleural, and transdiaphragmatic pressures (Pga, Ppl, and Pdi, respectively) were studied in seven patients during non-rapid-eye-movement (NREM) sleep. Diaphragmatic force output, as assessed by Pdi, followed the periodic changes in EMGdi but during the occlusive phase the increase in Pdi was more than the increase in EMGdi. This increase in Pdi was essentially due to an increase in Ppl, since Pga and EMGdi had a linear relationship (r = 0.98, P less than 0.001) that did not change during the occlusive and ventilatory phases. Abdominal muscle recruitment evident in Pga and abdominal motion tracings during the occlusive phase when paradoxical rib cage motion was observed suggested that this increase in diaphragmatic efficiency was likely due to a change in diaphragmatic length-tension characteristics. These results demonstrate that, in patients with occlusive apneas, the diaphragm is the predominant respiratory muscle during NREM sleep and that its function is supported by abdominal muscle recruitment.