The combined effects of temperature and posture on regional blood flow and haemodynamics, 2024, Jason T Fisher et al

Highlights

• Exposure to combined thermal and postural stressors requires interaction of thermoregulatory and baroreflex responses.
• Regional variation in control from thermoregulatory and baroreflex mechanisms may exist in the maintenance of blood flow.
• Participants experienced a transient ambient temperature (15.7(0.6) °C - 38.9(0.6)°C), in two seperate postures (upright and supine).
• Microvascular blood flow and haemodynamic responses were recorded continuously throughout the protocol.
• Arm blood flow increased during the rise in ambient temperature; however both limbs decreased blood flow during standing
• Arm vasculature seems to be regulated by thermoregulatory and baroreflex mechanisms, while the legs are regulated by the baroreflex alone.

Abstract
Under simultaneous ambient temperature and postural stressors, integrated regional blood flow responses are required to maintain blood pressure and thermoregulatory homeostasis. The aim of the present study was to assess the effect of ambient temperature and body posture on regional regulation of microvascular blood flow, specifically in the arms and legs.

Participants (N = 11) attended two sessions in which they experienced transient ambient conditions, in a climatic chamber. During each 60-min trial, ambient temperature increased from 15.7 (0.6) °C to 38.9 (0.6) °C followed by a linear decrease, and the participants were either standing or in a supine position throughout the trial; relative humidity in the chamber was maintained at 25.9 (6.6) %. Laser doppler flowmetry of the forearm (SkBFarm) and calf (SkBFcalf), and haemodynamic responses (heart rate, HR; stroke volume, SV; cardiac output, CO; blood pressure, BP), were measured continuously. Analyses of heart rate variability and wavelet transform were also conducted.

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