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Arterial PaCO2 during chronic hyperthermia in sheep.
Pflugers Archiv : European Journal of Physiology
|March 1, 1980
Summary
Prolonged hyperthermia in sheep maintains a decrease in arterial carbon dioxide partial pressure (PaCO2). This low PaCO2 level persists regardless of changes in blood pH, indicating a stable respiratory response.
Area of Science:
- Physiology
- Respiratory Regulation
- Thermoregulation
Background:
- Acute hyperthermia typically causes a decrease in PaCO2 and an increase in pHa in mammals.
- The long-term effects of sustained hyperthermia on these parameters are less understood.
Purpose of the Study:
- To investigate if the respiratory response to hyperthermia changes when it is maintained for over 24 hours.
- To determine the relationship between PaCO2 and body temperature during prolonged hyperthermia.
Main Methods:
- Anesthetized ewes underwent surgical placement of arterial catheters.
- Daily arterial blood samples were collected over a 7-day control period and an 8-day hyperthermia period.
Main Results:
- Arterial carbon dioxide partial pressure (PaCO2) decreased and remained low throughout the 8-day hyperthermia period.
- A significant inverse correlation was found between PaCO2 and body temperature (Tr): PaCO2 = -6.08 Tr + 267.8.
- While initial alkalosis was observed, blood pH tended to decrease after day five, and calculated bicarbonate levels declined.
Conclusions:
- Sustained hyperthermia in sheep leads to a consistent reduction in PaCO2.
- This lowered PaCO2 is maintained independently of significant alterations in arterial pH.
- The findings suggest a robust respiratory compensation mechanism during prolonged hyperthermia.