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. 2015 Aug;3(8):e12492.
doi: 10.14814/phy2.12492.

Seasonal variation in muscle sympathetic nerve activity

Jian Cui  1 , Matthew D Muller  1 , Cheryl Blaha  1 , Allen R Kunselman  2 , Lawrence I Sinoway  3
Affiliations

Seasonal variation in muscle sympathetic nerve activity

Jian Cui et al. Physiol Rep. 2015 Aug.

Abstract

Epidemiologic data suggest there are seasonal variations in the incidence of severe cardiac events with peak levels being evident in the winter. Whether autonomic indices including muscle sympathetic nerve activity (MSNA) vary with season remains unclear. In this report, we tested the hypothesis that resting MSNA varies with the seasons of the year with peak levels evident in the winter. We analyzed the supine resting MSNA in 60 healthy subjects. Each subject was studied during two, three, or four seasons (total 237 visits). MSNA burst rate in the winter (21.0 ± 6.8 burst/min, mean ± SD) was significantly greater than in the summer (13.5 ± 5.8 burst/min, P < 0.001), the spring (17.1 ± 9.0 burst/min, P = 0.03), and the fall (17.9 ± 7.7 burst/min, P = 0.002). There was no significant difference in MSNA for other seasonal comparisons. The results suggest that resting sympathetic nerve activity varies along the seasons, with peak levels evident in the winter. We speculate that the seasonal changes in sympathetic activity may be a contribution to the previously observed seasonal variations in cardiovascular morbidity and mortality.

Keywords: Cardiovascular diseases; hemodynamic; nervous system; risk factors; sympathetic.

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Figures

Figure 1
Figure 1
Heart rate (HR), mean arterial blood pressure (MAP), MSNA burst rate (right upper panel), and MSNA burst incidence (right lower panel) in the four seasons. Data are reported as means ± SD. Subject numbers for each season are reported in Table1. Unadjusted P value for the seasons: P = 0.109 for HR, P = 0.656 for MAP, P < 0.001 for MSNA burst rate, and P < 0.001 for MSNA burst incidence. After adjusting for gender, age, and BMI, P = 0.117 for HR, P = 0.652 for MAP, P < 0.001 for MSNA burst rate, and P < 0.001 for MSNA burst incidence. P values in the figure (e.g., P = 0.027/0.009) were the unadjusted value and the adjusted value for gender, age, and BMI, respectively.
Figure 2
Figure 2
Systolic (SBP) and diastolic (DBP) blood pressure in the four seasons. Subject numbers for each season are reported in Table1. Unadjusted P value for the seasons: P = 0.043 for SBP and P = 0.286 for DBP. After adjusting for gender, age, and BMI, P = 0.056 for SBP and P = 0.264 for DBP.
Figure 3
Figure 3
Relationships within MAP, HR, and MSNA between the winter and other three seasons. Each dot in the graphs represents the variable observed in two seasons in an individual subject. The subjects for each comparison of the seasons were the same. The subgroups of the subjects in the upper, middle, and lower panels were not the exact same, but had overlap. N = 19 for winter to spring. N = 25 for winter to summer. N = 28 for winter to fall.
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