SKELETAL-MUSCLE CHEMOREFLEX AND PH(I) IN EXERCISE VENTILATORY CONTROL

To determine whether skeletal muscle hydrogen ion mediates ventilatory drive in humans during exercise, 12 healthy subjects performed three bouts of isotonic submaximal quadriceps exercise on each of 2 days in a 1.5-T magnet for P-31-magnetic resonance spectroscopy (P-31-MRS). Bi lateral lower extremity positive pressure cuffs were inflated to 45 To rr during exercise (BLPPex) or recovery (BLPPrec) in a randomized orde r to accentuate a muscle chemoreflex. Simultaneous measurements were m ade of breath-by-breath expired gases and minute ventilation, arterial ized venous blood, and by P-31-MRS of the vastus medialis, acquired fr om the average of 12 radio-frequency pulses at a repetition time of 2. 5 s. With BLPPex end-exercise minute ventilation was higher (53.3 +/- 3.8 vs. 37.3 +/- 2.2 l/min; P < 0.0001), arterialized PCO2 lower (33 /- 1 vs. 36 +/- 1 Torr; P = 0.0009), and quadriceps intracellular pH ( pH(i)) more acid (6.44 +/- 0.07 vs. 6.62 +/- 0.07; P = 0.004), compare d with BLPPrec. Blood lactate was modestly increased with BLPPex but w ithout a change in arterialized pH. For each subject, pH(i) was linear ly related to minute ventilation during exercise but not to arterializ ed pH. These data suggest that skeletal muscle hydrogen ion contribute s to the exercise ventilatory response.