Cold-induced pulmonary hypertension in cattle

Area of Science:

• Veterinary Medicine
• Environmental Physiology
• Cardiovascular Research

Background:

• Right-heart failure in cattle during winter at high altitudes suggests a link between cold and pulmonary hypertension.
• Preliminary studies indicated cold exposure can elevate pulmonary arterial pressures in calves with hyperreactive pulmonary vessels.

Purpose of the Study:

• To investigate the effects of cold exposure on pulmonary arterial pressure and vascular resistance in cattle.
• To determine if cold contributes to hypoxic pulmonary hypertension in cattle at moderate altitudes.

Main Methods:

• Calves were exposed to cold temperatures (0 to -5 degrees C) for 48 hours in a climatic chamber.
• Pulmonary arterial pressure, blood flow, and vascular resistance were monitored.
• Arterial blood gases (PO2 and PCO2) were measured to assess ventilation.

Main Results:

• Cold exposure significantly increased mean pulmonary arterial pressure (up to +60%) and vascular resistance (up to +38%) in calves.
• Hyperreactive calves showed greater increases in pulmonary arterial pressure compared to less reactive ones.
• Cold exposure led to decreased arterial PO2 and increased PCO2, indicating hypoventilation.

Conclusions:

• Cold exposure induces pulmonary hypertension in cattle at moderate altitudes (1,524 m) via hypoxic pulmonary vasoconstriction.
• The pressor response to cold is more pronounced in cattle with inherently reactive pulmonary vessels.
• Oxygen administration reversed the cold-induced pulmonary hypertension, supporting the role of hypoxia.