INCREASED HYPOXIC VENTILATORY SENSITIVITY DURING EXERCISE IN MAN - ARE NEURAL AFFERENTS NECESSARY

1. The acute ventilatory response to 3 min periods of hypoxia (AKR) wa s examined in nine patients with clinically complete spinal cord trans ection (T4-T7) during (a) rest and (b) electrically induced leg exerci se (EEL). 2. EEL was produced by surface electrode stimulation of the quadriceps muscles so as to cause the legs to extend at the knee again st gravity. End-tidal P-CO2 was held constant 1-2 mmHg above resting v alues throughout both protocols. 3. On exercise, the average increase in metabolic CO2 production (V-CO2+/-S.E.M.) was 41 +/- 5 ml min(-1). Venous lactate levels did not rise with exercise.4. Baseline euoxic ve ntilation did not increase significantly with EEL, but there was a con sistent and highly significant increase in the ventilatory response to hypoxia during EEL (mean Delta AHR +/- S.E.M. Of 1.6 +/- 0.2 l min(-1 )).5. We conclude that an increase in hypoxic sensitivity during exerc ise can occur in the absence of volitional control of exercise and in the absence of afferent neural input from the limbs.