Nonlinear and nonautonomous dynamical properties of the cardiovascular response to a range of ambient temperatures

ALATAWI, Sultan and Stefanovska, Aneta (2024) Nonlinear and nonautonomous dynamical properties of the cardiovascular response to a range of ambient temperatures. PhD thesis, Lancaster University.

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Abstract

There is a significant relationship between temperature and human health. The cardiovascular system undergoes a process of coordinated changes when the external temperature or the amount of heat generated changes. To maintain the internal temperature of the body at a constant level, a variety of physiological and behavioural processes must be controlled. These responses in the cardiovascular system have been shown to manifest themselves in significant changes in cardiac output and regionalblood flow. An increase or decrease in blood flow in the skin is the basic response of the circulatory system to changes in skin surface temperature. In this work, we used the optical technique of laser Doppler flowmetry (LDF) to study the dynamics of blood flow at three different ambient temperatures (20◦C, 26◦C, and 32◦C). We investigated the changes that may be caused by ambient temperature in healthy young subjects on blood flow and cardiovascular dynamics, e.g., heart rate, stroke volume, cardiac output, and blood pressure. Optical methods were used along with a variety of other sensors to assess these changes. In addition, the instantaneous frequencies of heartbeat and respiration were extracted from the measured ECG, blood pressure, and respiration time series. Two additional time series were created from blood pressure, instantaneous systolic and instantaneous diastolic blood pressure. The resulting time series were then analysed using algorithms developed for irregular periodic signals. The wavelet power spectrum was applied to evaluate the contribution of the oscillatory components within the frequency range from 0.0027 to 2 Hz. The physiological characteristics of the six oscillatory components in this range and their changes with temperature are evaluated and discussed. Phase coherence analysis was used to study the interaction between the oscillatory components, and the effects of temperature are evaluated and discussed. We show that while average values are highest at lower temperatures, the coherence is highest at higher temperatures.