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THE EFFECT OF FEMALE AGING ON SYMPATHETIC TRANSDUCTION DURING THE COLD PRESSOR TEST

Abstract

BACKGROUND: Older female adults (OF) have the highest risk for hypertension and cardiovascular disease among any demographic in America. Exaggerated blood pressure (BP) responses during the cold pressor test (CPT) are associated with higher cardiovascular disease risk. However, previous studies report no age-related differences in BP or sympathetic responses during the CPT in females, but data are limited and partly confounded by differences in body mass index (BMI), which can independently influence CPT responses. Therefore, we tested the hypothesis that aging increases BP and sympathetic responses during the CPT in OF (>55 years) compared with YF (18 - 35 years) matched for BMI. METHODS: We studied nine post-menopausal OF and 17 YF (early follicular phase) with brachial BP <140/90 mmHg and BMI <30 kg/m2. We measured mean BP (photoplethysmography) during a 10-min rest period and a 2-min CPT. In a subset (6 OF, 10 YF), we also measured muscle sympathetic nerve activity (MSNA; microneurography). We calculated time-averaged sympathetic transduction of BP during the CPT (CPT-baseline) as sympathetic-pressure ratios (mean BP/MSNA burst frequency & mean BP/MSNA total activity). We compared age groups using unpaired, two-tailed t-tests for normally distributed data and Mann-Whitney U tests for non-normally distributed data (i.e., failed Shapiro-Wilk test). RESULTS: The data are presented as OF vs. YF with mean±SD or median[IQR]. By design, age (66±6 vs. 24±4 years, p<0.0001), but not BMI (22.8±2.8 vs. 22.6±3.5 kg/m2, p=0.85), was higher in OF. Mean BP (97±13 vs. 78±4 mmHg, p<0.0001), MSNA burst frequency (35±6 vs. 11±6 bursts/min, p<0.0001), and MSNA total activity (1096[559] vs. 114[147] AU, p=0.001) were higher in OF at rest. Mean BP responses during the CPT did not differ between groups (∆17±9 vs. 14±8 mmHg, p=0.79). However, MSNA burst frequency (∆7±5 vs. 17±11 bursts/min, p=0.01) and total activity (∆24[93] vs. 514[3648] %, p<0.001) responses during the CPT were higher in YF. Finally, the sympathetic-pressure ratios did not differ between groups (1.6[13.7] vs. 0.7[0.4] mmHg/bursts/min, p=0.09 & 0.25[1.69] vs. 0.02[0.04] mmHg/%, p=0.40). CONCLUSION: In partial support of our hypothesis, these preliminary data suggest that MSNA, but not BP, responses during the CPT are attenuated in OF. A higher baseline MSNA in OF relative to YF may explain these reduced sympathetic responses during the CPT.

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