Role of heating in non-invasive blood pressure measurements in rats

The "tail-cuff" technique for indirect blood pressure measurements was standardized, with respect to heating, in experiments on 47 adult Sprague-Dawley rats. The direct, intra-arterial, and the indirect blood pressures were simultaneously obtained. Pulse volume was recorded from the tail by a non-invasive technique, and was controlled by gradual application of heat. It was found that pulse volume and body temperature were poorly related. A stable relation existed, however, between the error in the indirect blood pressure recordings and the pulse volume. The error was minimized, provided that the heating was adjusted to induce a pulse volume of at least 25% of the maximum obtainable value. It was suggested that the validity of the indirect blood pressure recording could be improved, if heat application was regulated on the basis of observations of pulse volume in the tail instead of ambient temperature or body temperature. Errors due to excessive vasoconstriction, or discomfort due to overheating could thereby be minimized.