EFFECTS OF WILLFUL VENTILATORY CONTROL ON RESPIRATORY SENSATION DURING HYPERCAPNIA

Remarkable augmentation of breathing discomfort has been noted when ve ntilation is constrained to the steady state level during progressive hypercapnia. However, the effect of willful enhancement of ventilation on breathing discomfort remains to be evaluated. The present study ex amined the effects of moderate willful increases or decreases in venti lation during progressive hypercapnia on breathing discomfort in 12 su bjects. There were a total of 5 rebreathing trials. In the first (F1) and the fifth trials the subjects rebreathed freely. In the other tria ls subjects breathed by tracking a target to achieve hypercapnic venti latory responses that were the same (HCVR-S), 25% higher (HCVR-H) and 25% lower (HCVR-L) than in the Fl trial. Breathing discomfort was asse ssed every 30 s by a 150-mm visual analog scale (VAS). The sensational response (dVAS/dPCO(2)) during HCVR-S [3.8 +/- (SE) 0.8 mm/Torr] was significantly smaller (p < 0.01) than that during the Fl (6.3 +/- 0.8 mm/ Torr) trial. HCVR-H resulted in a further decrease in dVAS/dPCO(2) to 3.1 +/- 0.7 mm/Torr as compared to HCVR-S (p < 0.05). HCVR-L signi ficantly increased dVAS/dPCO(2) to 4.9 +/- 0.7 mm/Torr compared to HCV R-S (p < 0.05). The final free rebreathing ventilatory response was si gnificantly larger than the initial free rebreathing response (2.7 +/- 0.5 as compared to 2.1 +/- 0.4 liters/min/Torr, p < 0.01). However, t he sensational response did not change(6.3 +/- 0.8 vs. 5.8 +/- 0.7 mm/ Torr). These rebreathing studies indicate that willful control of resp iration decreases respiratory sensation even at comparable levels of v entilation. In particular, moderate willful increases in ventilation p roduce an ameliorating effect on the sensation of breathing discomfort .