Author(s): FUJITA, M., HORIUCHI, M., FUKUOKA, Y., Institution: DOSHISHA UNIVERSITY, Country: JAPAN, Abstract-ID: 1734

INTRODUCTION:
Cold exposure elevates arterial blood pressure; however, the relative contributions of central circulatory response and vascular resistance to blood pressure regulation during exercise remain unclear. Sinusoidal workload allows the assessment of dynamic cardiovascular responses through amplitude and phase shift analyses (Fujita et al., 2022, 2023). Therefore, this study aimed to distinguish the control characteristics of central and peripheral cardiovascular responses during sinusoidal walking under thermoneutral and mild cold conditions in the absence of shivering.
METHODS:
Fifteen healthy young adults (14 men and 1 female) performed sinusoidal walking on a treadmill under two ambient temperature conditions: mild cold condition (19℃; T19) and thermoneutral condition (28℃; T28). The treadmill speed varied sinusoidally between 3 and 6 km•h-1. Beat-by-beat heart rate (HR) and mean arterial pressure (MAP) were continuously measured. Stroke volume (SV) was estimated by model-flow method, and cardiac output (CO) was calculated by multiplying HR and SV. Forearm skin blood flow (SkBf) was continuously measured using a laser tissue blood flowmeter. Total peripheral resistance (TPR) and cutaneous vascular conductance (CVC) were calculated. Core temperature (tympanic) and mean skin temperature (chest, upper arm, thigh, and lower leg) were recorded throughout the protocol. Each variable was fitted to a sinusoidal model to determine amplitude (Amp) and phase shift (PS).
RESULTS:
Mean skin and core temperature were significantly lower under the T19 condition compared to the T28 condition (both p<0.05). MAP was significantly higher under the T19 condition (p<0.01), whereas HR, SV, CO and SkBf did not significantly change between conditions (all p>0.05). CVC was significantly decreased and TPR was significantly increased under the T19 condition compared to the T28 condition (both p<0.05). Moreover, SkBf exhibited larger PS values than cardiovascular variables (HR, SV, and CO), and this delay was more pronounced in the T19 condition. In contrast, Amp did not significantly differ between conditions for any cardiovascular variables.
CONCLUSION:
The elevation in MAP under mild cold condition with unchanged CO and increased TPR indicates that blood pressure regulation was primarily mediated by vascular resistance rather than central circulatory control. Furthermore, the slower dynamics of SkBf with larger PS values, particularly in the T19 condition, suggest that cutaneous blood flow contributes minimally to blood pressure regulation under mild cold conditions. These findings demonstrate distinct control characteristics between central hemodynamics and peripheral vascular resistance during sinusoidal walking in mild cold environments.