Control of blood pressure in the cold: differentiation of skin and skeletal muscle vascular resistance

Figures

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  FIGURE 1. Whole‐body cooling causes an increase in total and local vascular resistances. (a) Representative time series data of mean weighted skin temperature (T sk, pink line) at baseline and during whole‐body cooling via a fan and the average rectal temperature (T re, white and black circles) at the end of both periods. Whole‐body skin cooling caused an increase in mean arterial pressure (MAP) and no change in cardiac output (Q˙C), and thus total peripheral resistance increased (TPR). (b) Regional vascular resistances (VR) in the forearm and leg highlighting the downstream contribution of combined skeletal muscle and cutaneous circulations. Normally distributed data were analyses using paired t‐tests and non‐normally distributed data (thermal comfort, Q˙C, VR leg, VR forearm) were analysed using the Wilcoxon signed rank test. n = 12

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  FIGURE 2. Whole‐body cooling causes an increase in total vascular resistance due to cutaneous and skeletal muscle vascular resistance. (a) Representative time series data of local forearm skin temperature (T sk) of the right (purple) and left (pink) forearm at baseline, during pre‐cooling of the left forearm and subsequently during whole‐body cooling. The average rectal temperature (T re, white and black circles) is shown at the end of baseline and whole‐body cooling. Whole body cooling increased mean arterial pressure (MAP) with no change in cardiac output (Q˙C), and thus total peripheral resistance increased (TPR). Moreover, there was vasoconstriction in the right forearm and leg. (b) Skin (SR) and forearm (VR) vascular resistance increased in the pre‐cooled arm (iPC) with a further increase in forearm vascular resistance during whole‐body cooling (iWC), despite no further change in skin vascular resistance. Normally distributed data were analyses using paired t‐tests and non‐normally distributed data (thermal comfort, VR leg, VR right forearm) were analysed using Wilcoxon signed rank tests. Data in (b) were analysed with a repeated measures analysis of variance, with Tukey post hoc…

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  FIGURE 3. Face cooling causes an increase in total vascular resistance primarily due to cutaneous vasoconstriction. (a) Representative time series data of local mean face skin temperature (T sk, pink) averaged from the forehead and cheek (pink) and the corrected mean weighted skin temperature (purple) during isolated face cooling (FC). Isolated face cooling caused an increase in mean arterial pressure (MAP) with no change in cardiac output (Q˙C), and thus total peripheral resistance (TPR) increased after removal of an ‘outlier’ highlighted in red. Both data sets for TPR are presented for transparency. (b) Isolated face cooling increased forearm vasoconstriction via a reflex increase in forearm cutaneous vasoconstriction, which also slightly decreased forearm skin temperature. Face cooling also caused a reflex increase in leg cutaneous resistance, but this did not impact leg vascular resistance or leg skin temperature. All analyses were paired t‐tests; if data failed normal distribution (SR leg), the Wilcoxon signed rank test was performed. n = 10, except for cardiac output (n = 9) and total peripheral resistance (n = 8)