[Effect of respiration on variations of central venous blood temperature]

We examined the course of right ventricular blood temperature before, during and after treadmill exercise in three patients with implanted cardiac pacemakers, and in two healthy volunteers. Temperature measurements were performed with a specially developed 5F electrode with an incorporated thermistor (measurement accuracy: 1/100 degrees C). After electronic amplification, the temperature signals were recorded on a three-channel strip chart recorder, together with ECG and respiration (measured by impedance plethysmography). In one of the volunteers, blood flow in the jugular and femoral veins was recorded by Doppler sonography, before and after exercise. We observed a decrease in central venous blood temperature with inspiration and an increase with expiration before, during and after exercise. The amplitudes of the variations became smaller during exercise, reached a maximum immediately after exercise and returned to their resting values within a few minutes after the end of exercise. We suppose different distributions of venous blood flow in different phases of the respiratory cycle to be the reason for the respiration-induced variations in central venous blood temperature. Under exercise conditions, the influence of respiration on the blood flow in the larger veins is small compared to the influence of an increased cardiac output; at rest, respiration has a more pronounced effect on venous blood flow. The analysis of our blood flow measurements in the femoral and jugular veins supported this assumption.