The ratio of the first derivative (dP/dt) of a carotid artery pulse to the developed pressure (P), (dP/dt)/P, is an easily measurable, noninvasive index of cardiac contractility even in moderate exercise. We examined the effects of transient cold exposure on cardiac contractility in normal reactors (n = 12) and hyperreactors (an increase in systolic or diastolic pressure >15 mm Hg; n = 6) by using this index. Eighteen healthy participants were subjected to the cold pressor test, which required them to immerse the right hand in chilly water (4 degrees C) for 2 min. Although cold stress maximally increased mean blood pressure during the second minute, it maximally increased heart rate and cardiac contractility after 60 s of immersion in both groups of subjects. Comparing normal reactors and hyperreactors by two-way ANOVA revealed a group x time interaction for heart rate but not for cardiac contractility. These findings suggest that the increase in cardiac contractility during cold-water immersion dose not reflect the levels of heart rate and muscle sympathetic nerve activity, and that the specific responses of cardiac function to a cold pressor test in hyperreactors depends on heart rate rather than cardiac contractility.

Individuals who respond with a rise of 15 mmHg or more in their systolic and/or diastolic blood pressure to a cold pressor test are called blood pressure hyperreactors. We examined whether hyperreactors (n = 8) showed greater reactivity of arterial stiffness, i.e., pulse wave velocity (PWV) and augmentation index normalized to a heart rate of 75 bpm (AIx@75), to the cold pressor test than normal reactors (n = 15), and whether the former showed larger cardiovascular responses to isometric handgrip exercise. The cold pressor test was performed following Hines-Brown's method, with subjects immersing their right hand in 4 degrees C water for 2 min. Isometric handgrip exercise was performed at 30% maximal voluntary contraction for 2 min. Comparison between hyperreactors and normal reactors by two-way ANOVA during cold pressor test revealed a group x time interaction for PWV and AIx@75 with a greater increase in hyperreactors. During isometric handgrip exercise, no group x time interactions were detected for all measurements. Blood pressure hyperreactors show larger cardiovascular responses to the cold pressor test, but not to isometric handgrip exercise in comparison to normal blood pressure reactors.

By using (dP/dt)/P of carotid artery pulse, a non-invasive index of cardiac contractility, we examined the regulatory mechanism of cardiac function during a cold pressor test in athletes and untrained subjects. Twenty-four healthy subjects (9 athletes, 8 untrained subjects, and 7 hyperreactors of 4 athletes and 3 untrained subjects with a rise of 15 mmHg or greater in systolic and/or diastolic blood pressure) underwent the cold pressor test according to Hines and Brown (Am Heart J 11:1-9, 1936): immersion of the right hand in 4 degrees C water for 1 min. Although mean blood pressure increased during the cold stress in all the groups, cardiac function differed. In athletes, heart rate and cardiac contractility caused cardiac output to increase while total peripheral resistance (TPR) did not change. In untrained subjects, however, heart rate and cardiac contractility tended to decrease cardiac output and thus TPR increased. In hyperreactors, heart rate and cardiac contractility increased during cold stress, and also TPR increased. After the end of the test, heart rate and cardiac contractility decreased only in untrained group. The findings that during a cold pressor test heart rate and cardiac contractility are enhanced in athletes but depressed in untrained subjects indicate that the state of physical training influences cardiac sympathetic neural reactivity to cold stress, except for hyperreactors.