Restoring heat stress-associated reduction in middle cerebral artery velocity does not reduce fatigue in the heat

• Heat-induced hyperventilation may reduce PaCO2 and thereby cerebral perfusion and oxygenation and in turn exercise performance. To test this hypothesis, eight volunteers completed three incremental exercise tests to exhaustion: (a) 18 degrees C ambient temperature (CON); (b) 38 degrees C (HEAT); and (c) 38 degrees C with addition of CO2 to inspiration to prevent the hyperventilation-induced reduction in PaCO2 (HEAT+CO2). In HEAT and HEAT+CO2, rectal temperature was elevated prior to the exercise tests by means of hot water submersion and was higher (P<0.05) than in CON. Compared with CON, ventilation was elevated (P<0.01), and hence, PaCO2 reduced in HEAT. This caused a reduction (P<0.05) in mean cerebral artery velocity (MCAv(mean)) from 68.6 +/- 15.5 to 53.9 +/- 10.0cm/s, which was completely restored in HEAT+CO2 (68.8 +/- 5.8cm/s). Cerebral oxygenation followed a similar pattern. was 4.6 +/- 0.1L/min in CON and decreased (P<0.05) to 4.1 +/- 0.2L/min in HEAT and remained reduced in HEAT+CO2 (4.1 +/- 0.2L/min). Despite normalization of MCAv(mean) and cerebral oxygenation in HEAT+CO2, this did not improve exercise performance, and thus, the reduced MCAv(mean) in HEAT does not seem to limit exercise performance.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Hälsovetenskap -- Idrottsvetenskap (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Health Sciences -- Sport and Fitness Sciences (hsv//eng)

Nyckelord

Brain blood flow

PaCO2

exercise performance

cerebral oxygenation

BLOOD-FLOW

PROLONGED EXERCISE

OXYGEN DELIVERY

CARBON-DIOXIDE

VENTILATORY RESPONSE

INCREMENTAL EXERCISE

MUSCLE TEMPERATURE

HYPOXIC

EXERCISE

BODY-TEMPERATURE

MAXIMAL EXERCISE

Sport Sciences

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