METABOREFLEX CHANGES RELATIONSHIP BETWEEN END-TIDAL CO2 PARTIAL PRESSURE AND VENTILATION

Abstract

PURPOSE We investigated the effect of metaboreflex induced by post-exercise occlusion on ventilation (VE) against an equivalent arterial CO2 concentration. METHODS Five subjects performed 2-min of sustained leg extension exercise at 30% of maximal voluntary contraction, followed by 6-min of recovery period where upper thigh was occluded by a cuff inflated at 220 mmHg in occlusion trials. The occlusion limits blood flow into and from the active muscle, so the by-products during exercise are secured in the muscle to activate metaboreflex. In normal trials, the occlusion was not applied. During whole recovery period, a subject inhaled variable gases, that is, 0% (air), 3.5% or 5% of CO2 concentration. The CO2 and VE were determined at the last minute of the recovery period. To estimate the increase in VE against the increase in PETCO2, VE was plotted against the PETCO2. RESULTS The VE and PETCO2 at air inhalation, showed no significant difference between control and occlusion trials (VE 11± 1 vs 12± 1 L/min, PETCO2 39±1 vs. 38±1 mmHg; mean±SE). The change of PETCO2-VE slope showed large individual variation, i.e., it did not changed in a subject, and it had gentler (n=3) or steeper (n=1) slope in the occlusion trial than in the control trial. But, in all subjects, the line of occlusion trials was above the control line over 38–42mmHg of PETCO2. CONCLUSION This result suggests that the metaboreflex changes the relationship between PETCO2 and VE.