Factors influencing orthostatic blood pressure regulation in healthy humans

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The normal beat-to-beat regulation of arterial blood pressure is vital, and exquisitely controlled by numerous integrated mechanisms. The arterial baroreflex (a blood pressure regulating reflex), volume of blood, ability to regulate blood vessel tone in the brain and body, postural sway (rhythmic muscle contraction when standing), osmopressor reflex (blood vessel constriction triggered by drinking water) and emotional responses all contribute to normal blood pressure control. However, their regulation and interrelationships in this critical biological system are poorly understood. One of the greatest challenges to blood pressure regulation is the standing posture (orthostasis). When upright gravity causes blood and fluid to pool in the lower parts of the body, reducing the return of blood to the heart, and this must be compensated to prevent blood pressure falling and impairing physiological function. This is of particular importance in military personnel where orthostatic stress, coupled with exacerbating physiological stressors such as thermal stress or dehydration, places particular strain on the cardiovascular system. The long-term goal of my research is to elucidate the physiological factors that influence normal orthostatic blood pressure control in healthy humans. The proposed Discovery program will examine the effects of three key physiological conditions that influence orthostatic cardiovascular control via three short-term objectives: 1) Elucidate the relationships between lower extremity muscle activity and orthostatic cardiovascular control; 2) Examine the role of the osmopressor reflex in cardiovascular regulation; and 3) Determine how emotional reactions (blood/needle phobia) influence orthostatic responses. We will determine the relationships between postural sway and blood pressure control, identify whether certain sway profiles have a greater effect on blood pressure control, and examine whether there is a sway "signature" that heralds the onset of cardiovascular instability. We will test whether water temperature influences the interrelationships between the osmopressor reflex, and the impact of increased stomach distension from drinking carbonated water on the osmopressor response. We will also study the mechanisms underlying hypotensive responses with blood-injection-injury phobia. We propose a novel, combined experimental approach from a multidisciplinary team with expertise in physiology, cardiology, biomechanics and postural control, wearable technology, statistics, as well as military applications. We will perform assessments using cutting-edge approaches, both in a controlled laboratory environment, as well as in real-world conditions in the field using wearable sensors. These studies will provide fundamental data on the mechanisms underlying blood pressure regulation in healthy humans. These data are critical to understanding of normal human physiology, and have key relevance to the military community and beyond.