Effect of hypothermia on responses to imposed trachea obstruction

¹ Department of Physiology and Pharmacology, Duke University Medical Center, Durham, North Carolina

Respiratory and circulatory responses to three levels of imposed tracheal obstruction were measured in normothermic dogs; the same measurements were repeated after the blood temperature of the animals had been reduced to 28 C by immersion in ice water. Respiratory rate increased, tidal volume decreased, and arterial oxygen saturation progressively declined as a result of tracheal impedance at 37 C. The induction of the hypothermic condition caused a fall in respiratory rate, an increase in tidal volume, and no change in arterial oxygen saturation in response to the same obstruction to air flow. Cardiac output and systemic pressure increased as the magnitude of obstruction was increased in the normothermic animals but were not altered by the same degree of obstruction in the hypothermic animals. The differences in responses observed at the two temperatures studied seem to be related to the degree to which hypoxia develops in the normothermic animals as a result of tracheal air flow impedance.