The cold pressor test: effects on sympathetic nerve activity in human muscle and skin nerve fascicles

Abstract

Micro-electrode multi-unit recordings of muscle nerve sympathetic activity (MSA) involved in cardiovascular homeostasis or skin nerve sympathetic activity (SSA) involved in thermoregulation were made in the right peroneal nerve of 48 healthy volunteers during performance of the cold pressor test, i.e. immersion of one hand in ice water (2 +/- 0.5 degrees C) for 1 min. Eleven subjects underwent the same procedure on a second MSA recording occasion. As a rule, immersion evoked an increase in MSA, with a gradual decrease on emersion. The response showed a wide range of variation between and within subjects; the intra-individual difference between first and second immersion on the same recording occasion was up to sevenfold, and from first to second recording up to fivefold. The increase in MSA correlated with the degree of discomfort from the ice water. In nine subjects with a large increase in MSA on ice water immersion, intracutaneous painful electrical stimulation to a level equalling the discomfort from the ice water was added, but it was not accompanied by any change in MSA. The increase in MSA was accompanied by and correlated quite well with an increase in blood pressure. Intra-arterial blood pressure recordings showed that MSA occurred at pressure levels normally associated with total inhibition of MSA, and that an inverse linear relationship between diastolic blood pressure and MSA at rest was abolished during the ice water immersion. SSA showed no consistent change with ice water immersion. It is concluded that the cold pressor test is a powerful activator of MSA, i.e. baroreceptor-governed vasoconstrictor outflow; that MSA contributes to the blood pressure elevation with this manoeuvre; that MSA operates at another blood pressure level during the manoeuvre and that the baroreflex inhibitory level consequently is changed; and that the response is not a reaction to pain only.

Effect of facial cooling and cold air inhalation on sympathetic nerve activity in men

“…Usually, the cardiovascular response to the CPT includes a slight increase in heart rate (Victor et al, 1987;Fagius et al, 1989), which has not been observed in the present experiment of localized hand cooling. However, it has been suggested that the acceleration of heart rate is related to the pain sensation which is induced by the immersion of the whole hand in ice water (Victor et al, 1987).…”

“…The increase in MSNA and blood pressure during hand cooling is a well known effect and this response has been used as CPT in several studies as a standardized baroreflex-independent stimulatory manoeuvre of the MSNA (Victor et al, 1987;Fagius et al, 1989). The parallel increase in blood pressure and MSNA during the CPT has led to the conclusion that a change of the baroreflex inhibitory level was induced by some extraordinary input operating during the manoeuvre (Fagius et al, 1989).…”

“…Immersing the hand in ice water evokes a marked increase in MSNA and blood pres-sure. These changes are accompanied by a minor, albeit significant increase in heart rate (Victor et al, 1987;Fagius et al, 1989). The response is probably evoked either by afferent impulses of cold receptors alone or by a combination of afferent impulses from pain and cold receptors (Fagius et al, 1989).…”

“…The parallel increase in blood pressure and MSNA during the CPT has led to the conclusion that a change of the baroreflex inhibitory level was induced by some extraordinary input operating during the manoeuvre (Fagius et al, 1989). During the CPT, Fig.…”

“…All values are given as mean ± S.E.M. the increase in MSNA is most likely evoked by a combined pattern of afferent impulses from pain and cold receptors to central nervous autonomic centers (Fagius et al, 1989). Both excitation of low-threshold, cold-sensitive receptors (A␦ and C fibres) and of high-threshold, cold-sensitive nociceptive fibres (primarily C fibres) have been postulated during cooling of the hand (Kregel et al, 1992).…”