Changes in ventilation and breathing pattern produced by changing body temperature and inspired CO2 concentration in...

Area of Science:

• Comparative Physiology
• Environmental Physiology
• Respiratory Physiology

Background:

• Body temperature significantly influences metabolic rate and respiratory function in ectotherms.
• Understanding how temperature affects gas exchange and acid-base balance is crucial for predicting animal responses to environmental changes.

Purpose of the Study:

• To investigate the effects of varying body temperatures and inspired CO2 concentrations on respiratory parameters in freshwater turtles (Chrysemys picta).
• To determine the relationship between temperature, ventilation, gas exchange, and acid-base status.

Main Methods:

• Measurements of respiratory minute ventilation (VE), breathing pattern, oxygen consumption (VO2), and arterial blood gases (PaCO2, pHa) were taken at 10, 20, and 30°C.
• Turtles were exposed to varying inspired CO2 fractions (FICO2 = 0, 2, 4, 6, 8%).

Main Results:

• Increasing temperature led to disproportionate increases in VE and VO2, decreasing the VE/VO2 ratio and causing hypercapnia (increased PaCO2) and acidosis (decreased pHa).
• Elevated FICO2 increased VE significantly at all temperatures, with a greater response at higher temperatures, paradoxically increasing PaCO2 and CO2 sensitivity.
• Increased VE with temperature was mainly due to shortened breath-holding periods, with respiratory frequency changes contributing twice as much as tidal volume changes.

Conclusions:

• Temperature increases cause relative hypoventilation, leading to hypercapnia and acidosis, explained by a Q10 effect of approximately two on both metabolic rate and ventilatory CO2 sensitivity.
• Despite temperature-induced changes in respiratory variables, the relative CO2 response remained consistent across temperatures.