Canine blood volume and cardiovascular function during hyperthermia.

Area of Science:

• Physiology
• Cardiovascular Research
• Thermoregulation

Background:

• Acute hyperthermia impacts hemodynamic functions and blood volume regulation.
• Splenectomized dogs were used to study the effects of elevated core body temperature.

Purpose of the Study:

• To examine the effects of acute hyperthermia on hemodynamic functions.
• To investigate blood volume regulation during heat stress.
• To assess transvascular fluid equilibrium under normothermic and hyperthermic conditions.

Main Methods:

• Eight splenectomized dogs were subjected to a 2°C core body temperature increase over 90 minutes.
• Ringer solution was infused under both normothermic and hyperthermic conditions.
• Hemodynamic parameters, blood volume, and fluid shifts were monitored.

Main Results:

• Hyperthermia led to peripheral vasodilation, decreased total peripheral resistance (TPR), and increased cardiac output.
• Blood volume, plasma oncotic pressure, and intravascular protein mass remained unchanged during initial warming.
• Fluid infusion during hyperthermia resulted in greater intravascular fluid retention (33.5%) compared to normothermia (9.4%), with decreased transvascular fluid shift and urinary output.

Conclusions:

• Acute hyperthermia induces peripheral vasodilation and compensatory increases in cardiac output.
• The body preferentially retains fluid intravascularly during heat stress to maintain cardiovascular function and blood volume.
• Mobilization of extravascular fluid does not occur; redistribution of blood to cutaneous circulation is the primary response.