Cardiovascular responses to thermal stress in conscious goats

Impaired cardiovascular responsiveness to an acute cold wind stress in streptozotocin-diabetic rats

In vivo cardiovascular responses were measured using modified impedance cardiographic techniques in urethane-anesthetized (1.5 g/kg) streptozotocin-diabetic (STZ; 65 mg/kg) rats during acute (30 min) cold wind (0 degree C, 1 m/s) exposure. Both control (CON) and diabetic (STZ) groups experienced significant decreases (P < 0.05) in colonic temperature (Tcol) over time with the STZ rats exhibiting greater decrements (P < 0.05) throughout the later stages of cooling. Similar increases (P < 0.05) in cardiac output (Q) and mean arterial pressure (MAP) were observed in both groups during the initial 10 min of cold exposure. Heart rate (HR) accounted for the major portion of the rise in Q since stroke volume remained relatively constant throughout the experimental period. During the later stages of cold wind exposure, Q and MAP were significantly lower (P < 0.05) in STZ compared to CON. In fact, Q and MAP continued to rise during the entire cold period in CON whereas the STZ group failed to respond to the continued decline in Tcol. The results indicate that STZ rats are more vulnerable to cold wind stress as evidenced by the impaired responsiveness of the cardiovascular system to hypothermia. The pattern of responses for both the thermoregulatory and cardiovascular systems could be partially explained by beta-receptor insensitivity to catecholamine stimulation.

Cardiovascular and blood gas responses to shivering produced by external and central cooling in the pigeon

Cardiovascular and blood gas responses of pigeons to spinal cord cooling (35-36 degrees C) were measured at thermoneutral (28 degrees C) and low (5 degrees C) ambient temperatures. Spinal cord cooling at thermoneutral temperatures caused immediate shivering and increases in heat production (223%), heart rate (152%) and cardiac output (169%), but blood pressure and stroke volume did not change. PaCO2 and PvCO2 increased slightly during the cooling; PaO2 and CaO2 decreased slightly while PvO2 and CvO2 decreased considerably (10 Torr and 1.7 mmol . l-1, respectively), resulting in a greater a-v difference in O2 content. Ambient cooling produced responses comparable to spinal cord cooling. Simultaneous spinal cord and ambient cooling produced similar responses that were generally greater in magnitude than either kind of cooling alone. Consequently, heart rate, cardiac output and O2 extraction from the blood were all significantly, linearly related to heat production over the wide range studied. Comparisons are made between cardiovascular responses of birds to shivering and exercise in regards to the relative importance of increases in heart rate, stroke volume and blood pressure. It is suggested that exercise and shivering may effect cardiovascular responses through similar receptor mechanisms.