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THE RELATIONSHIP BETWEEN URINE HYDRATION INDICES AND CARDIOVASCULAR REACTIVITY TO COLD PRESSOR TEST

Abstract

BACKGROUND: The cold pressor test (CPT) is commonly used in physiological research to elicit a robust autonomic response, particularly to provoke increases in mean arterial pressure (MAP) and heart rate (HR). However, research investigating the influence of hydration status on cardiovascular reactivity to a CPT is lacking. Therefore, the purpose of this study was to examine the relationships between urine specific gravity (USG) and urine color (Ucol) with changes in HR and MAP following a CPT. METHODS: A total of 17 (aged 18-23) women completed this protocol which required three laboratory visits. During the first visit, participants completed a familiarization trial to experience the 60-s CPT (≈1.0 °C) and cardiovascular monitoring. During visits 2 and 3, after an overnight fast, the participants reported to the laboratory and provided a urine sample for USG - measured on a digital refractometer - and Ucol according to a chart ranging from 1 (lightest) to 8 (darkest). A CPT was then used to elicit a cardiovascular response for the experimental trials. HR and MAP (MAP = 1/3 systolic blood pressure + 2/3 diastolic blood pressure) were measured prior (pre) to the CPT and immediately after (post) using an automated blood pressure device used in stress testing. Changes in HR (∆HR) and MAP (∆MAP) were calculated by subtracting the pre- from post- measures. Pearson’s correlations were used to explore the direction and strength of the relationship between urine and cardiovascular-reactivity indices. Since all participants completed two visits, there were a total of 34 observations (n = 34). RESULTS: Pearson’s correlations revealed USG (1.0189 ± 0.0075) was positively correlated with ∆HR (6 ± 8 bpm, r = 0.30) and ∆MAP (25 ± 13 mmHG, r = 0.30). Additionally, Ucol (4 ± 2 au) was positively correlated with ∆HR (r = 0.28) and ∆MAP (r = 0.32). CONCLUSIONS: Hydration indices were positively related to measures of cardiovascular reactivity following a CPT, meaning larger changes in HR and MAP were associated indices of increasing hypohydration. Hydration is often not recorded nor reported in CPT protocols. Due to the integrated nature of the cardiovascular system’s response to stressors, hydration status should be accounted for in research protocols.

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