Cardiovascular adjustments and pain during repeated cold pressor test.

The cold pressor test is used in the clinical testing of the autonomic nervous system. However, little is known about changes in the autonomic control of the cardiovascular system during repeated challenge with cold. Heart rate (HR), respiratory sinus arrhythmia (RSA), T-wave amplitude of ECG (TWA), blood pressure, body temperature and perceived pain were recorded in 18 male subjects during three CPTs which consisted of four minutes immersion of the left hand into cold water at 1 degree C. Breathing during CPT was either spontaneous or paced at 0.23 Hz or 0.1 Hz. Pain intensity and HR decreased and TWA increased during the cold immersion and in the resting period preceding cold in the second and third trials. Systolic and pulse blood pressure increased in resting periods in the third trial. RSA increased in the second and third cold challenge during paced breathing at 0.1 Hz only. A decrease in body temperature (0.48 degree C) at the end of the experiment correlated marginally with HR changes. Our study shows that sustained cardiovascular changes are induced by the first challenge with cold, and persist or increase with repeated cold pressor tests.