Threshold temperatures for shivering in acute and chronic hypercapnia

Area of Science:

• Physiology
• Environmental Medicine
• Respiratory Physiology

Background:

• Hypercapnia, elevated carbon dioxide levels, can affect thermoregulation.
• Shivering is a key physiological response to cold exposure.
• Understanding the impact of hypercapnia on thermoregulation is crucial for various medical conditions.

Purpose of the Study:

• To investigate the effect of acute and chronic hypercapnia on shivering thresholds during cold exposure.
• To determine how different concentrations of carbon dioxide influence the body's ability to maintain temperature.

Main Methods:

• Guinea pigs were exposed to cold (15°C).
• Cervical cord temperature, skin temperature, oxygen consumption (Vo2), and muscle electrical activity were monitored.
• Animals were subjected to acute and chronic (3 days) exposure to varying carbon dioxide (CO2) concentrations (5%, 7.5%, 15%).

Main Results:

• Acute exposure to increasing CO2 concentrations progressively lowered shivering thresholds.
• At 15% CO2, shivering thresholds decreased by approximately 40°C.
• Chronic exposure to 15% CO2 for 3 days reversed the lowered shivering threshold, suggesting metabolic adaptation.

Conclusions:

• Hypercapnia significantly alters thermoregulatory responses to cold.
• Metabolic adaptation occurs with chronic hypercapnia, restoring normal shivering thresholds.
• These findings have implications for understanding physiological responses in environments with altered CO2 levels.