A hierarchy of oscillators? Interaction between temperature regulation, respiratory sinus arrhythmia and blood pressure variability

The project investigated two important parts of the cardiovascular control mechanisms; 1) Cerebral blood flow in interaction with circulation and respiration, and 2) The role of temperature regulation in human cardiovascular control. 1) Could the optimal interplay between breathing and heart beats promote cerebral perfusion? Cerebral perfusion is important to maintain vital functions. In this part of the study, we performed three separate experimental protocols. In the first experimental series, we challenged the cerebral perfusion by the combination of positive pressure ventilation and mild simulated hypovolemia. We found that this combination reduced cerebral blood flow by 15 %. In addition, we showed that heart rate variability during respiration is of importance for a stable cerebral perfusion. The second experimental series showed that cerebral perfusion did not change during increase in blood pressure due to static hand grip. The third experimental series, we measured the cerebral blood flow in patients undergoing laparoscopic gall bladder removal. We showed that in patients there was a decrease in cerebral blood flow coinciding with decrease in cardiac output. 2) The temperature control is vital also for the cardiovascular control in humans. We are analyzing which role the temperature regulation plays when combined with the cardiorespiratory control mechanisms. We have a new analytical method provided a better tool for investigation of changes in the fluctuation pattern of skin blood flow. The temperature control mechanisms induce large fluctuations in skin blood flow, but affect the cardiovascular variables to a minor extent.

Vi har hittil hatt 17 fulltekst-publikasjoner i internasjonale tidsskrift og vi har lagt fram resultater på et titalls internasjonale konferanser. Fortsatt er det to-tre artikler som kommer på et senere tidspunkt. Av funn har vi utvidet kunnskapen om kontroll av blodstrøm til hjernen. Vi har undersøkt både friske frivillige og pasienter, og fått klare holdepunkter for at hjertets minuttvolum er en viktig regulator av hjernens blodtilførsel. Dette jobber vi videre med i kommende studier hos friske mennesker, og det vil formidles til relevante kliniske miljøer. Vi har videre fått utvidet kunnskap om temperaturregulering ved endret blodstrøm til hender og føtter. Hos friske mennesker er det store endringer i blodtilførsel til huden i hender og føtter, mens vi fortsatt undersøker hvordan kontrollmekanismene påvirkes av temperaturendringer.

The homeostasis of an organism is maintained by several regulatory mechanisms, controlling blood pressure, respiration and temperature, to mention only a few. A proposed underlying cause of sudden unexplained deaths, is a conflict between regulatory mecha nisms. In the current project we will study interactions between thermoregulatory, respiratory and cardiovascular control systems in healthy humans. All these control systems show oscillatory activity that is evident in the response of skin circulation, respiratory pattern, arterial blood pressure and heart rate. The oscillations have different frequency ranges, but we believe they interact to stabilise the circulation. We hypothesise that the oscillatory regulatory systems for thermoregulation, respir ation, and the cardiovascular system form a hierarchical structure in healthy humans. We will study: A) the thermoregulatory effect on the respiratory and cardiovascular system, B) the interaction between respiratory-related heart rate variations and cere bral perfusion challenged by hypovolemia and postive pressure ventilation, and C) the skin blood flow fluctuations in newborns during reduced core temperature. We record and analyse variables in healthy humans. We hypothesise that thermoregulation is the most important regulatory system, and that respiratory and cardiovascular control are subordinate even within the thermoneutral zone. Maintaining homeostasis is vital to optimise the body for daily activities like breathing, standing and exercise. In pati ents, one or several mechanisms may be malfunctioning. The project will provide deeper understanding of brain-heart interactions, and may shed light on sudden unexplained deaths, which may result in conflict, rather than adaptation, between regulatory mec hanisms. Knowledge of regulatory control mechanisms in healthy humans is applicable to most patient groups, and advances in our understanding of such mechanisms will improve clinical practice.