J J Pandit — Page 4 | PubMed Health

PubMed1991

The ventilatory effects of sustained isocapnic hypoxia during exercise in humans.

To investigate how the ventilatory response to isocapnic hypoxia is modified by steady-state exercise, five subjects were studied at rest and performing 70 W bicycle exercise. At rest, isocapnic hypoxia (end-tidal PO2 50 Torr) for 25 min resulted in a biphasic response: an initial increase in ventilation was followed by a subsequent decline (HVD). During exercise, an end-tidal PO2 of 55-60 Torr was used. The magnitude of the initial ventilatory response to isocapnic hypoxia was increased from a mean +/ SE of 1.43 +/- 0.323 L/min per % arterial desaturation at rest to 2.41 +/- 0.424 L/min per % during exercise (P less than 0.05), but the magnitude of the HVD was reduced from 0.851 +/- 0.149 L/min per % at rest to 0.497 +/- 0.082 L/min per % during exercise (P less than 0.05). The ratio of HVD to the acute hypoxia response was reduced from 0.696 +/- 0.124 at rest to 0.202 +/- 0.029 during exercise (P less than 0.01). We conclude that while exercise augments the ventilatory sensitivity to hypoxia, it also has a direct effect on the mechanisms by which sustained hypoxia depresses peripheral chemosensitivity.

Adult↗

PubMedDate not supplied

Ventilation and gas exchange during sustained exercise at normal and raised CO2 in man.

Five subjects underwent each of three protocols for 43 min: (A) at rest; end-tidal PCO2 was held constant at 2-5 Torr above resting values; (B) during 70 Watt bicycle exercise; PETCO2 was uncontrolled; (C) during 70 Watt exercise; PETCO2 was held 2-5 Torr above exercising values. During all protocols, end-tidal PO2 (PETO2) was held at 100 Torr. The first 5 min of each protocol were excluded from data analysis to approach a steady state, and the remaining 38 min analysed to determine whether any trends were present. At rest, ventilation did not change over the 38 min period. However, during hypercapnic exercise (protocol C), ventilation rose significantly by a mean +/- SE of 4.9 +/- 0.8 L/min (P less than 0.01) over the 38 min period. In protocol B, ventilation was lower than in protocol C, but did not change over the 38 min period. However, PETCO2 fell significantly by a mean of 0.65 +/- 0.05 Torr (P less than 0.01). This change in PETCO2 was due to a significant fall in the respiratory quotient (mean = -0.05 +/- 0.01, P less than 0.01) and metabolic CO2 production (mean = -0.06 +/- 0.01 L/min, P less than 0.01). The fall in respiratory quotient implies a change in metabolic substrate during exercise. Furthermore, the results suggest that ventilation is not always matched closely to metabolic CO2 production during exercise.

Adult↗