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Effects of water temperature on hemodynamic responses to cold pressor test.

We have used the cold pressor test in Sprague Dawley rats to elicit behavioral stress. In this paradigm, ice‐cold water (1 cm deep) is rapidly added to a watertight cage while recording hemodynamic responses. The initial startle response (5 ‐ 10 sec) is characterized by a profound pressor response due to an increase in systemic vascular resistance (SVR). The sustained modest pressor response (15‐60 sec) is characterized by tachycardia. We hypothesized that the sustained response but not the initial startle response is dependent on water temperature. Rats instrumented for cardiac output, mean arterial pressure (MAP) and heart rate determination were acclimated then tested with each temperature in the following order: room temperature (22‐24 °C), warm (33‐36 °C), then cold (2‐4 °C) water. After acclimation, we rapidly added water and recorded the response for one minute. The initial startle response was independent of temperature since all rats responded by increasing MAP and SVR. The sustained responses were highly dependent on water temperature since the modest pressor response and tachycardia observed with cold water were smaller with room temperature water and not observed with warm water. Our results suggest the initial startle response is independent of water temperature whereas the sustained modest pressor response is dependent on cold water. This work was supported by USPHS DA0017371 and HL091440.