Effects on dogs of surface-induced hypothermia and rewarming on the right heart function and pulmonary circulation

Hypothermia is commonly found in accidents on land and at sea, yet its pulmonary circulatory effects have not been studied before. To study the effects of hypothermia on the right heart function and pulmonary circulation, cardiac catheterization was carried out on nine anaesthetized beagle dogs. The dogs were cooled between ice bags until the temperature in the pulmonary artery was 25 degrees C and then rewarmed using a heating box especially constructed for this purpose. Heart rate decreased significantly (P < 0.01) during cooling. Cardiac output also diminished mainly because of decreased heart rate. Total pulmonary resistance increased in the cold (P < 0.05) and returned to the initial level during rewarming. The peak rate of increase in pressure (dP/dtmax) of the right ventricular pressure curve did not show any significant change. Retardation in relaxation in hypothermia was indicated by an increase (P < 0.01) in the peak negative dP/dt of the right ventricular pressure curve. According to our results, the contraction rate did not change, but the relaxation rate decreased significantly during cooling. No signs of heart failure were observed and all parameters returned to normal during rewarming. In conclusion, right ventricular function was not compromised even during deep hypothermia.