Bio 201 – Human Physiology 1 Cardiovascular Physiology – Systems


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Need answers for exercise questions in the attached file. All three questions. ATTACHMENT PREVIEW Download attachment CVsystemsRecit.pdf Bio 201 – Human Physiology 1 Cardiovascular Physiology – Systems Approach Recitation One of the problems in understanding the response of the cardiovascular system to various control actions and perturbations is that there are a number of vascular and cardiac actions and integrating their actions can be difficult. sh is ar stu ed d vi y re aC s ou ou rc rs e eH w er as o. co m Among the cardiovascular actions that are possible are: 1) increases in cardiac contractility 2) increases in heart rate 3) arteriolar vasoconstriction –> increased peripheral resistance 4) venous vasoconstriction (“venoconstriction”) –> increased venous pressures 5) arterial vasoconstriction –> decresed compliance. Many cardiovascular (CV) reflexes and/or drugs affect several of these CV parameters, and it becomes important to have a way to anticipate the effects of the actions of critical parameters like cardiac output and arterial blood pressure. Considering each of the factors in isolation is unproductive and we need a method to synthesize the various effects, even if the predicted effects are only approximations. The “systems” model described here is one tool for making such approximate estimates. At the heart of the model are five simple relationships: 1) the resistance driven relation between the cardiac output through the arteries and the mean pressure in those arteries, 2) the relation between the volume of blood in the arteries and the pressure in the arteries, 3) the analogous relation between volume and pressure in the veins, 4) the relation between left ventricular filling pressure (venous pressure) and the work and flow output of the heart (the Frank-Starling Law of the Heart), and 5) the relation between central venous pressures and the rate of “venous return”, i.e., the flow from the capillaries to the heart. In this exercise, we consider one model that attempt to synthesize these relations into a single (mostly graphical) model of cardiovascular function First we need to consider each of the relationships above. Resistance, flow, and pressure in the arteries If we think of the flow across the arterioles (the major resistance vessels in the CV system) in terms of an Ohm’s Law analogy, we get ∆P Part − Pven = R R Th Q= where Q Part Pven R (1) = steady state blood flow rates (L/min) = mean arterial pressure (mmHg) = venous pressure (mmHg) = peripheral (mostly arteriolar) resistance (mmHg / (L/min)) Because the venous pressures are very low in comparison to the arterial pressures, we usually assume Pven = 0, which gives us Q≈ Part R https://www.coursehero.com/file/10410415/CVsystemsRecit/ (2) This describes a linear relationship between cardiac output and arterial pressures like that shown in Fig. 1. Pressure ∆Flow = Conductance ∆P ∆P = Resistance ∆Flow ∆P ∆Flow Flow sh is ar stu ed d vi y re aC s ou ou rc rs e eH w er as o. co m Figure 1 Pressure-flow relationship Eqs. 1 & 2 ignore a number of factors (like the pulsatile nature of arterial pressure and flow or, indeed, any transient effects), but do a reasonably good job of describing gross CV function. Compliance, pressure and volume in arteries and veins If we take any sort of distensible tube (an artery, a vein, a water balloon) and start filling it with water, recording the volume of water and the pressure on the water (or on the walls of the tube), we find a relationship rather like that in Fig. 2. Pressure ∆P = stiffness ∆Vol ∆Vol = compliance ∆P ∆Vol Unstressed volume Th ∆P Volume Figure 2 P-V relation in a tube. Initially as we infuse water, the pressure stays very low, because we have not yet “filled” the relaxed tube. As the infused volume reaches the unstressed volume of the tube, further infusion of water increases the pressure as the water stretches the walls of the tube and those walls push back on the water. (Remember that water

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