Nonchemical influence of inspiratory pressure support on inspiratory activity in humans

To determine whether nonchemical inhibition of respiratory activity occurs during inspiratory pressure support (IPS) ventilation (IPSV), respiratory m otor output (in 9 subjects), obtained by calculating transdiaphragmatic pre ssure-time products, and central respiratory output (in 5 subjects), obtain ed by integrating the electromyographic activity of the diaphragm (EMGdi) d uring mechanical inspiratory time, EMGdi per minute, and electrical inspira tory time, as determined from onset to peak EMGdi, were compared during spo ntaneous ventilation (control) and IPSV with (IPS+CO2) and without (IPS) co rrection of hypocapnia. Both IFS and IPS+CO2 induced significant decreases in transdiaphragmatic pressure-time products (46 +/- 31 and 53 +/- 23%, res pectively), EMGdi during mechanical inspiratory time (49 +/-. 12 and 57 +/- 14%, respectively), EMGdi per minute (65 +/- 22 and 69 +/- 15%, respective ly), and electrical inspiratory time (73 +/- 8 and 65 +/- 6%, respectively) . Because correction of hypocapnia failed to eliminate the marked inhibitio n of both respiratory and central motor output seen with IFS, we conclude t hat nonchemical inhibition of respiratory activity occurs during IPSV.