Abstract
The method for estimating the rate of propagation of temperature waves in the myocardium during hypothermia and hyperthermia of the heart based on noninvasive temperature control on the heart surface in conditions of cardiopulmonary bypass is proposed. The solution of the heat conduction equation for temperature waves in the myocardium is presented, which allows determining at each point of the medium the temperature change function, as well as the amplitude and phasing velocity of the temperature wave upon cooling and warming of the heart in conditions of cardiopulmonary bypass. The velocity distribution for the temperature field on the surface of the myocardium and in the depth of tissues during the hypothermia and hyperthermia of the heart is obtained. The thermographic images of the heart during controlled hypothermia and hyperthermia of the heart under cardiopulmonary bypass are obtained. The study of the conditions for spreading the temperature wave in the myocardium is performed, which allows to improve the means of intraoperative protection of vital organs and tools for controlling its effectiveness. The results of introduction of methods of non-invasive temperature control in cardiac surgery and the process of intraoperative cardiac protection in the temperature range from +10°С to +38°С are presented.
Highlights
The propagation of temperature waves in the heart during the process of hypothermia and hyperthermia is a periodic change in the temperature distribution in a homogeneous medium – the myocardium, which is associated with periodic fluctuations in the density of the heat flows entering the environment from the contour of cardiopulmonary bypass
Thermal conductivity is the main mechanism of transferring heat to tissues that are not directly exposed to heat, and the temperature is the main physical value that characterizes all thermal interactions in the myocardium with hypothermia and hyperthermia under artificial blood circulation
The overall reactivity and course of pathological processes in the myocardium are largely determined by the rate of propagation of temperature waves in the tissue layer
Summary
The propagation of temperature waves in the heart during the process of hypothermia and hyperthermia is a periodic change in the temperature distribution in a homogeneous medium – the myocardium, which is associated with periodic fluctuations in the density of the heat flows entering the environment from the contour of cardiopulmonary bypass. The temperature waves contain information on the properties of the myocardium (heat, temperature, conductivity, density) and the nature of the processes and phenomena that give rise to them (blood flow in the contour of artificial blood circulation, oscillatory processes of the temperature in the operating field, the frequency of rotation of the rollers of the cardiopulmonary bypass). Thermal conductivity is the main mechanism of transferring heat to tissues that are not directly exposed to heat, and the temperature is the main physical value that characterizes all thermal interactions in the myocardium with hypothermia and hyperthermia under artificial blood circulation. The change in the depth of penetration of the temperature wave depends on the frequency of thermal defectoscopy depending on the frequency, which allows them to be used to detect microcavities in the tissues, disturbance of blood supply and zones of ischemia in the myocardium
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