Correlation of blood temperature fluctuations with blood pressure waves

Constant blood temperature in the pulmonary artery is assumed when the thermal dilution method is used for cardiac output determination. In some cases, however, slow temperature fluctuations (2-6 cycles per min.) occur in arterial and venous blood and interfere in the measurement. Those thermal fluctuations were investigated in the pulmonary artery and venae cavae of dogs. The temperature variations were found to be correlated with blood pressure waves: an increase of blood pressure was accompanied by an increase in the blood temperature in the pulmonary artery and a decrease in the blood temperature in the venae cavae. Therefore, measurement of the temperature of the pulmonary artery relative to that of the venae cavae does not rule out those fluctuations, and will not improve the thermal dilution method.