抄録
In preceding studies, we have shown that the ratio of the first derivative (dP/dt) of carotid artery pulse (CAP) to the pressure (P), CAP (dP/dt)/P, is an easily measurable, noninvasive index of cardiac contractility even in moderate exercise (Ifuku et al. 1994). Using this cardiac index, we reported the regulatory mechanism of cardiac function during a cold pressor test in athletes last meeting. In the present study, we compared the time course of changes in this cardiac index with previous studies performed using muscle sympathetic nerve activity (MSNA) (Victor et al. 1987; Yamamoto et al. 1992). Fifteen healthy subjects were subjected to the cold pressor test which required them to immerse the right hand in chilly water (4 °C) for 2 min. Mean blood pressure and heart rate changed by almost following the time course as found with MSNA, whereas changes in the cardiac index showed a different time course from that of the latter. Cold stress maximally increased the mean blood pressure and MSNA during the second minute, however, it maximally increased the heart rate and the cardiac index during the 30-60 s period. The time course of change in the cardiac index also differed from that of the heart rate during the recovery period; the cardiac index returned toward the control value but the heart rate was significantly lower than the control value. The findings suggest that the cardiac contractility did not reflect the level of MSNA during a cold pressor test in terms of time course. [J Physiol Sci. 2006;56 Suppl:S231]
