Nonchemical influence of inspiratory pressure support on inspiratory activity in humans

To determinewhether nonchemical inhibition of respiratory activity occurs duringinspiratory pressure support (IPS) ventilation (IPSV), respiratorymotor output (in 9 subjects), obtained by calculatingtransdiaphragmatic pressure-time products, and central respiratoryoutput (in 5 subjects), obtained by integrating the electromyographicactivity of the diaphragm (EMGdi) during mechanical inspiratory time,EMGdi per minute, and electrical inspiratory time, asdetermined from onset to peak EMGdi, were compared during spontaneous ventilation (control) and IPSV with(IPS+CO₂) and without (IPS)correction of hypocapnia. Both IPS andIPS+CO₂ induced significantdecreases in transdiaphragmatic pressure-time products (46 ± 31 and53 ± 23%, respectively), EMGdi during mechanical inspiratory time(49 ± 12 and 57 ± 14%, respectively), EMGdi per minute (65 ± 22 and 69 ± 15%, respectively), andelectrical inspiratory time (73 ± 8 and 65 ± 6%,respectively). Because correction of hypocapnia failed to eliminate themarked inhibition of both respiratory and central motor output seenwith IPS, we conclude that nonchemical inhibition of respiratoryactivity occurs during IPSV.