Applied cardiovascular physiology

Abstract: The cardiovascular responses to exercise, haemorrhage, a Valsalva manoeuvre, postural changes and exposure to microgravity are complex patterns made up of a number of common physiological ‘building blocks’. The main cardiovascular response to isotonic exercise is an increase in cardiac output to elevate oxygen delivery to exercising muscle. This is largely mediated via an increase in heart rate and facilitated by an increase in venous return. By contrast, in haemorrhage a reduced venous return leads to a reduction in cardiac output, a fall in arterial pulse pressure and unloading of the arterial baroreceptors. The baroreceptor reflex response is designed to maintain arterial blood pressure by increasing peripheral vascular resistance and limiting the fall in cardiac output via a positive inotropic effect and tachycardia. But, because venous return falls in haemorrhage, the tachycardia is relatively ineffective in sustaining cardiac output (in contrast to the situation in exercise). As the haemorrhage becomes severe, a second reflex, causing a profound vagally mediated bradycardia and hypotension, becomes apparent. This ‘depressor’ reflex is blocked by the response to musculoskeletal injury, hence the biphasic response to ‘simple’ haemorrhage is often not seen in trauma patients. Changing posture and performing the Valsalva manoeuvre also reduce venous return and lead to a reflex tachycardia, an increase in peripheral resistance, and maintenance of arteri...
Source: Anaesthesia and intensive care medicine - Category: Anesthesiology Authors: Tags: Physiology Source Type: research