Central body temperature as a guide to optimal heart rate

Area of Science:

• Cardiovascular Physiology
• Biomedical Engineering

Background:

• Fixed-rate artificial pacemakers do not fully restore normal hemodynamic function during exercise in humans.
• The primary mechanism for increased cardiac output during exercise, elevated heart rate, is not achieved with fixed-rate pacing.
• Specialized pacemakers exist for coordinated atrial and ventricular pacing, but many patients have abnormal atrial function (e.g., atrial fibrillation, sick sinus syndrome).

Purpose of the Study:

• To investigate the physiological effects of exercise on blood temperature returning to the right atrium.
• To determine if exercise-induced temperature changes in right atrial blood correlate with physiological parameters.

Main Methods:

• Conscious dogs were utilized as a model for cardiovascular exercise response.
• Precision thermistors were surgically placed in the right hearts of the animals.
• Blood temperature was continuously monitored during submaximal treadmill exercise.

Main Results:

• Exercise induced a significant increase in blood temperature returning to the right atrium, averaging 1 degree C (range 0.4-1.5 degrees C).
• The observed temperature changes demonstrated a strong positive correlation with the exercise workload.
• Blood temperature variations also correlated well with concurrent changes in heart rate during exercise.

Conclusions:

• Exercise significantly elevates the temperature of blood returning to the right atrium.
• This temperature increase is a measurable physiological response to exercise and is linked to workload and heart rate.
• Findings may inform the development of more responsive artificial pacing systems that better mimic natural cardiovascular regulation during physical activity.