Cardiac response to local cooling in man.

Abstract

1. Changer in cardiac rate and blood pressure when the hand or foot was immersed in cold water was investigated in human subjects. 2. When the water temperature was above 12°C no change in cardiac rate was observed in spite of the subjects' distinct feeling of cold. At temperatures below 12°C the heart became accelerated, along with a rise of blood pressure and respiratory rate. The cardiac rate, after it had attained its peak value in 60 to 90 seconds of immersion, showed a tendency to return gradually to its original rate notwithstanding that the hand was remaining in cold water (adaptation). 3. In cases when the water temperature was below 12°C, the increase in cardiac rate changed in a linear function with the logarithm of water temperature. It is also proportional to the area of the skin exposed to cold, or to the sum of areas when several parts of hands or feet were cooled simultaneously (spatial summation). 4. With the temperature of water sufficiently low, an aching sensation (so-called “cold pain”) was aroused shortly after immersion beside the sensation of cold. This pain also tended to subside spontaneously after a few minutes. Almost at the same time and in the same pace there took place the subsidence of increase in heart rate, of rise in blood pressure as described above, concomitantly with a slight rise of skin temperature which had fallen to its minimum value. 5. When the blood circulation to the immersed part was arrested neither adaptation of cold pain nor that of cardiovascular reactions were observed. 6. These facts indicate that the cardiac rate and blood pressure changes are reflexes brought about by local cooling, for which predominantly the sensation of pain rather than cold is responsible, and suggest that the phenomena of adaptation in cardiovascular response are probably based on a common factor, the adaptation of cold pain. The cause of the latter may be sought in a possible increase of peripheral blood flow as a reaction to local cooling.