Sympathetic function during whole-body cooling is altered in hypertensive adults

During moderate cold exposure, cardiovascular-related morbidity and mortality increase disproportionately in hypertensive adults (HTN); however, the mechanisms underlying this association are not well defined. We hypothesized that whole-body cold stress would evoke exaggerated increases in blood pressure (BP) and muscle sympathetic nerve activity (MSNA) in HTN compared to normotensive adults (NTN) and that sympathetic baroreflex function would be altered during cooling in HTN. MSNA (peroneal microneurography) and beat-to-beat BP (Finometer) were measured continuously in 10 NTN (6M/4W; age 53±3 yrs; resting BP 125±3/79±1 mmHg) and 13 HTN (7M/6W; age 58±2 yrs; resting BP 146±5/88±2 mmHg) during whole-body cooling-induced reductions in mean skin temperature (T_sk; water-perfused suit) from 34.0 to 30.5°C. During cooling, the increase in mean arterial pressure was greater in HTN (NTN: 6±2 vs. HTN: 11±1 mmHg; P=0.02) and accompanied by exaggerated increases in MSNA (NTN: 8±3 vs. HTN: 20±3 bursts•(100 heartbeats)^-1; P<0.01). The slope of the relation between MSNA and diastolic BP did not change during cooling in NTN (T_sk 34.0°C: -4.4±0.8 vs. T_sk 30.5°C: -5.0±0.3 bursts•(100 heartbeats)^-1•mmHg^-1; P=0.47) but increased in HTN (T_sk 34.0°C: -3.6±0.4 vs. T_sk 30.5°C: -5.4±0.4 bursts•(100 heartbeats)^-1•mmHg^-1; P=0.02). These findings demonstrate that the cooling-induced increases in BP and MSNA are exaggerated in HTN. Further, during cooling, sympathetic baroreflex sensitivity increases in HTN, but not NTN, presumably to allow for baroreflex-mediated buffering of excessive cooling-induced increases in BP. Collectively, these findings suggest that sympathetic function is altered during whole-body cooling in hypertension.

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