INSPIRATORY RESISTANCE EFFECTS ON EXERCISE BREATHING PATTERN RELATIONSHIPS TO CHEMORESPONSIVENESS

This study examined the effects of added inspiratory resistance (R(5) cm H2O . L(-1). s(-1)) on the relationsip between exercise breathing p attern and resting hypercapnic ventilatory responsiveness (HCVR). Twel ve men completed an HCVR test and two progressive intensity exercise t asks with minimal (R(0)) and elevated (R(5)) resistance. Peak oxygen u ptake, and peak power output were not different, but peak VE was decre ased with the R(5) load. Exercise ventilation (VE was tightly coupled to VCO2 (r = 0.97) as was mean inspiratory flow rate (V-T/T-I, r = 0.9 5), but not duty cycle (T-I/TTOT, r = 0.39). With imposition of R(5), V-T/T-I was depressed (p < 0.05) at mild (similar to 40 % VO(2)peak) t o peak exercise intensities, whereas T-I/T-TOT was relatively unaffect ed. At both moderate (similar to 60 % peak VO2) and peak exercise inte nsities, VE was positively correlated (r = 0.62, p < 0.05 and r = 0.82 , p < 0.01, respectively) to subjects' HCVR, However, when normalized, VE . VCO2-1 was significantly correlated to HCVR only at peak exercis e ventilation during the R(0) load. Analysis of the exercise breathing pattern revealed that at both moderate and peak exercise intensities, V-T/T-I was positively correlated to HCVR, but T-I/T-TOT was not. The imposition of R(5) decreased the slope of the relationship between ex ercise V-T/T-I and HCVR at both moderate and peak exercise intensities , and weakened the positive correlation at the moderate exercise inten sity. Our analysis indicates that: 1) the positive correlation between exercise hyperpnea and HCVR is mediated by the mean inspiratory flow rate rather than the duty cycle component of the breathing pattern and , 2) at moderate exercise the relationship between mean inspiratory fl ow rate and resting HCVR is more sensitive to added inspiratory resist ance than minute ventilation per se. These findings suggest that the d egree of influence resting HCVR has on exercise hyperpnea is dependent upon the magnitudes of both the ventilatory hyperpnea and mechanical loading placed on the ventilatory system.