Seasonal variation in sympathetic autonomic activity in undergraduate health science students of Karnali province

Abstract

Background: Seasonal variations in autonomic function have been linked to cardiovascular morbidity and mortality. The cold pressor test (CPT) and handgrip test (HGT) have been used in various studies to determine blood pressure (BP) regulation during stress, but their differential effects in various seasons are less explored. Thus, the study aimed to investigate seasonal differences in cardiovascular sympathetic activity in healthy young adults of Nepal. Methodology: This pre-test post-test study recruited 45 healthy students (55.6% female) aged 21.62±2.93 years, who underwent CPT and HGT interventions during summer and winter seasons. Blood pressure was measured before and after each intervention, and maximum voluntary contraction (MVC) was recorded during the handgrip test. The baseline systolic and diastolic blood pressure (SBP and DBP) and their rise during interventions were compared between summer and winter season. Result: Baseline BP were lower in summer than in winter season (SBP: 107.71±12.17 vs 120.78±11.31, p=0.001; DBP: 71.49±8.74 vs 77.60±8.83, p=0.001; paired t-test); but the mean maximum SBP and DBP during CPT and HGT was not significantly different between seasons. In CPT, there was a statistically significant rise in BP during summer compared to winter (SBP: 25.27±11.56 vs 13.84±11.17, p<0.001; DBP: 25.53±10.14 vs 13.51±7.15, p<0.001; paired t-test). Similarly, HGT also raised the BP higher in summer than winter (SBP: 35.07±17.11 vs 25.47±14.81, p=0.008; DBP: 30.96±12.12 vs 24.16±11.64, p=0.009; paired t-test); and was confirmed in linear regression analysis (p<0.01). Hyper responders (those with >21 mmHg rise in SBP) during CPT were higher in summer (22) than winter (10). Conclusion: This study demonstrates that while resting blood pressure is lower in summer, the sympathetic response to stress is heightened, indicating seasonal modulation of autonomic function, which may have implications for cardiovascular risk and adaptability to environmental changes. Keywords: Autonomic, Cardiovascular health, Cold pressor test (CPT), Handgrip test (HGT), Seasonal variation, Sympathetic activity.