SKELETAL-MUSCLE DEOXYGENATION DURING EXERCISE ASSESSED BY NEAR-INFRARED SPECTROSCOPY AND ITS RELATION TO EXPIRED GAS-ANALYSIS PARAMETERS

The present study was performed to determine the relation between oxyg enated hemoglobin (oxy-Kb) changes in working muscles and ventilatory parameters. Six active normal subjects, 21 sedentary normal subjects a nd 16 patients with heart failure performed an incremental exercise wi th expired gas analysis. Deoxygenation of the vastus lateralis muscle was monitored for oxy-Hb changes using near-infrared spectroscopy. Nea r the anaerobic threshold (AT), oxy-Hb started to decrease, forming th e first inflection point (PI). Near the respiratory compensation point (RCP), the second inflection point (P2) was observed. Oxygen uptake a t the AT, RCP, PI and P2 decreased in magnitude first in the active no rmal subjects, then in sedentary normal subjects and finally in the he art failure patients. High correlation was demonstrated between AT and P1 (r=0.8, p<0.0005) and between RCP and P2 (r=0.9, p<0.0005). In 12 sedentary normal subjects who underwent repeat exercise, reproducibili ty was confirmed for both Pi and P2. Constant work rate exercises were performed in 5 sedentary normal subjects, and in all of them the oxy- Hb remained unchanged below the AT work rate, whereas oxy-Hb decreased above the AT work rate. Exercise capacity, with respect to both worki ng muscle deoxygenation and ventilation, could be evaluated in detail by the concomitant use of near-infrared spectroscopy and expired gas a nalysis.