DEFENCE OF THE DOCTORAL DISSERTATION BY JASON THOMAS FISHER

Defence of the Doctoral Dissertation by Jason Thomas Fisher

IPS invites you to the Defence of the Doctoral Dissertation by Jason Thomas Fisher titled: Thermal and Non-Thermal Factors Affecting Regional Blood Flow Regulation. The defence will take place on Wednesday, 7 May 2025, at 1:00 p.m. in the conference room of the Čaplja building, Nordic centre Planica. You can also join the defence via the following link: https://us02web.zoom.us/j/86561631353?pwd=gcXwpevasHacT0Qg1aIS6Ba5eHaE9Y.1, Meeting ID: 865 6163 1353, Passcode: 288969.

Short summary:

Whilst the interaction of multiple vascular mechanisms under various stressors is a well-documented topic, how this interaction effects the regional regulation of blood flow is less well known. In order to assess this phenomenon, a series of successive studies were conducted:

1. Assessing the regional blood flow and haemodynamic response to separate and combined effects of an acute orthostatic test during prolonged heat exposure in a simulated 3‑day heatwave.
2. Assessing the regional blood flow and haemodynamic responses to separate and combined effects of two postures and a transient thermoregulatory stressor with ambient temperatures ranging from 15 – 40 °C. Mechanisms of autonomic control were assessed by heart rate variability and wavelet transform analyses.
3. Assessing the regional blood flow and haemodynamic responses to the separate and combined effects of acute artificial gravity (1 and 2 Gz), high and low ambient temperatures, and differing partial pressures of oxygen.
4. Regional blood flow regulation and haemodynamic responses to artificial gravity and differing partial pressures of oxygen between females and males. The implications of similarities or differences between sexes are considered in the context of orthostatic intolerance.

The results of these four studies have led to following conclusions:

1. Skin blood flow of the arm is predominantly controlled via thermoregulatory vascular mechanisms, particularly when no interaction of mechanisms is required (i.e., when temperature is the only stressor). However, the influence of dual stressors (temperature and orthostatic) cause an interaction of multiple mechanisms (thermoregulation and baroreflex) related to the regulation of deep body temperature and blood pressure concurrently.
2. Skin blood flow of the leg, despite substantial levels of heating, appears to be unaffected by thermoregulatory mechanisms and is almost entirely controlled by the baroreflex for maintenance of stable blood pressure.
3. No significant difference in vascular mechanisms exist between females and males, in response to artificial gravity, high ambient temperatures and partial pressure of oxygen.

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