TY - CHAP M1 - Book, Section TI - Distribution of Blood Flow A1 - McDonough, Kathleen H. A1 - Hall, Stanley M. A2 - Levitzky, Michael A2 - McDonough, Kathleen A2 - Kaye, Alan David A2 - Hall, Stanley PY - 2021 T2 - Clinical Physiology in Anesthetic Practice AB - The two variables within the cardiovascular system that are well controlled are the mean arterial blood pressure (MABP) and the cardiac output (CO). As discussed in Chapter 19, MABP is controlled within a fairly limited range by the baroreceptor reflex. CO, however, is not controlled within a limited range but rather is linked to the workload of the body and the metabolism or oxygen consumption of the body (see Figure 13-1). CO can therefore vary from a resting level that is approximately 8% of the body weight (kg) to a level that is four- to sixfold higher. There is no one sensor for CO as there is for MABP. The CO is the result of the interaction between the pump and the vasculature into which it ejects blood. For a normal cardiovascular system, the pump has little control over the magnitude of the CO. The heart’s two properties of contractility (as altered by the sympathetic nervous system [SNS]) and length-tension (as altered by venous return) allow the heart to pump various stroke volumes. The metabolic needs of the peripheral tissues more directly determine the absolute level of CO since CO is simply the sum of the blood flow to all of the systemic organs. The distribution of the CO is independent of pump function but is dependent on the interaction of the central nervous system, via the SNS, with the local control of blood flow by individual organs. The balance between central control and local control of tissue blood flow is tailored to each tissue. For example, blood flow to some tissues, such as the brain and heart, is regulated primarily by local mechanisms. Blood flow to other tissues, such as the gastrointestinal tract, may be more influenced by the central nervous system. Local mechanisms predominate when SNS activity is low; however, SNS activity predominates over local mechanisms in many tissues when SNS activity is high. SN - PB - McGraw Hill CY - New York, NY Y2 - 2024/03/28 UR - accessanesthesiology.mhmedical.com/content.aspx?aid=1175534438 ER -