Inspiration capacity generated by neural respiratory drive could be further increased by CO2

Abstract

Inspiratory capacity (IC) is widely used to assess dynamic hyperinflation in patients with chronic obstructive pulmonary disease (COPD) based on the assumption that this maneuver maximally activates inspiratory muscle and thus reliably achieves total lung capacity (TLC). However, inspiration during inflation is partially or wholly controlled by involuntary drive from brainstem and whereas the IC is derived from voluntary drive from the motor cortex. We hypothesized that voluntary IC maneuvers initiated from the motor cortex may be increased if there is additional chemical stimulation to the brainstem by hypercapnia. Nineteen healthy subjects (Age 43±15 years, 13 men/6 women) were studied. Diaphragm EMG (EMGdi) from multipair esophageal electrode and ventilation were recorded during inhalation 8%CO 2 (8%CO 2 +92%O 2 ) and room air. The order of inhalation of gases was random and was blind to subjects. Forced inspiratory vital capacity (FIVC) from residual volume and IC were performed. The EMGdi and FIVC elicited by a FIVC maneuver breathing 8%CO 2 were 169±61 µV and 4.92±1.00 l and were significantly greater than those breathing room air (143±47 µV, 4.3±0.89 l, p 2 were 172±55 µV and 3.28±0.66 L and were significantly greater than those during breathing room air (148±42 µV, 2.83±0.72 l, p We concluded that IC and diaphragm EMG generated by IC maneuver is submaximal at normacapnia. Therefore dynamic hyperinflation assessed by IC maneuver could have been underestimated in patients with COPD if they became hypercapnic. This study was supported by NSFC (No.81120108001).