Ebook Cardiovascular physiology (10th edition): Part 2
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Ebook Cardiovascular physiology (10th edition): Part 2
OBJECTIVES1Explain how the pulsatile blood (low in the large arteries is converted into a steady flow in the capillaries.2Discuss arterial compliance Ebook Cardiovascular physiology (10th edition): Part 2 and its relation to stroke volume and pulse pressure.Vz I w3Explain the (actors that determine the mean, systolic, and diastolic arterial pressures and the arterial pulse pressure.4Describe the common procedure for measuring the arterial blood pressure in humans.THE HYDRAULIC FILTERCONVERTS PULSATI Ebook Cardiovascular physiology (10th edition): Part 2LE FLOWTO STEADY FLOWThe principal functions of the systemic and piilmo nary arterial systems are to distribute blood to the cap illary beds throughouEbook Cardiovascular physiology (10th edition): Part 2
t the body. The arterioles, which are the terminal components of the arterial system, regulate the distribution of flow to the various capil lary bedsOBJECTIVES1Explain how the pulsatile blood (low in the large arteries is converted into a steady flow in the capillaries.2Discuss arterial compliance Ebook Cardiovascular physiology (10th edition): Part 2sider able volume and distensibility. This system of clastic conduits and high-resistance terminals constitutes a hydraulic filter that is analogous to the resistancecapacitance filters of electrical circuits.I lydraulic filtering converts the intermittent output of the heart to a steady flow throug Ebook Cardiovascular physiology (10th edition): Part 2h the capillaries. This important function of the large elastic arteries has been likened to the Windkessels of antique fire engines. The Windkessel iEbook Cardiovascular physiology (10th edition): Part 2
n such a fire engine containsa large volume of trapped air. The compressibility of the air trapped in the Windkessel converts the inter mittent inflowOBJECTIVES1Explain how the pulsatile blood (low in the large arteries is converted into a steady flow in the capillaries.2Discuss arterial compliance Ebook Cardiovascular physiology (10th edition): Part 21. The heart is an intermittent pump. The cardiac stroke volume is discharged into the arterial system during systole. The duration of the discharge usually occupies about one third of the car diac cycle. In fact, as shown in Figure 4 13, most of the stroke volume is pumped during the rapid ejection Ebook Cardiovascular physiology (10th edition): Part 2 phase. This phase constitutes about half of systole. Part of the energy of cardiac contraction is dissipated as forward capillary flow during systoleEbook Cardiovascular physiology (10th edition): Part 2
. The remaining energy in the distensible arteries is stored as potential energy (Figure 7-1A and B). During diastole, the elastic recoil of the arterOBJECTIVES1Explain how the pulsatile blood (low in the large arteries is converted into a steady flow in the capillaries.2Discuss arterial compliance Ebook Cardiovascular physiology (10th edition): Part 2tole.135136CARDIOVASCULAR PHYSIOLOGYCompliant arteriesA When the arteries arc normally compliant, a substantial fraction of the stroke volume is stored in the arteries during ventricular systole. The arterial walls arc stretched.B During ventricular diastole the previously stretched arteries recoil. Ebook Cardiovascular physiology (10th edition): Part 2 The volume of blood that is displaced by the recoil furnishes continuous capillary flow diastole.c When the arteries are rigid, virtually none of theEbook Cardiovascular physiology (10th edition): Part 2
D Rigid arteries cannot recoil appreciably during stroke volume can be stored in the arteries.diastole.FIGURE 7-1 A to D, when the arteries are normaOBJECTIVES1Explain how the pulsatile blood (low in the large arteries is converted into a steady flow in the capillaries.2Discuss arterial compliance Ebook Cardiovascular physiology (10th edition): Part 2g systole, but flow ceases during diastole.THt AKI CKIML if 3 I ClVI13/Hydraulic filtering minimizes the cardiac workload. More work is required to pump a given flow intermittently than steadily; the steadier the flow, the less is the excess work. A simple example illustrates this point.Consider fir Ebook Cardiovascular physiology (10th edition): Part 2st that a fluid flows at the steady rate of 100 mL per second (s) through a hydraulic system that has a resistance of 1 mm Hg/mL/s. This combination oEbook Cardiovascular physiology (10th edition): Part 2
f flow and resistance would result in a constant pressure of 100 mm Hg, as shown in Figure 7-2A. Neglecting any inertial effect, hydraulic work, IV, mOBJECTIVES1Explain how the pulsatile blood (low in the large arteries is converted into a steady flow in the capillaries.2Discuss arterial compliance Ebook Cardiovascular physiology (10th edition): Part 2ts are integrated over the lime interval, G — lj, to yield the total work, when flow is steady,w = pv-2In the example in figure 7-2A, the work done in pumping the fluid for I s would be 10,000 mm I Ig ml. (or 1.33 X 10" dyne-cm). Next, consider an inlennil-tenl pump that generates a constant flow of Ebook Cardiovascular physiology (10th edition): Part 2 fluid for 0.5 s, and then pumps nothing during the next 0.5 s. Hence, flow is generated at the rate of 200 mL/s for 0.5 s, as shown in Figure 7 2B anEbook Cardiovascular physiology (10th edition): Part 2
d c. In panel B, the conduit is rigid, and the fluid is incompressible. However, the system has the same resistance to flow as in panel A. During the OBJECTIVES1Explain how the pulsatile blood (low in the large arteries is converted into a steady flow in the capillaries.2Discuss arterial compliance Ebook Cardiovascular physiology (10th edition): Part 2ling phase (diastole) of the pump, the pressure in this rigid system would be 0 mm Hg. The work done during systole would be 20,000 mm Hg ffiL This value is twice that required in the exam pie shown in Figure 7 2A.If the system were very distensible, hydraulic filtering would be very effective and t Ebook Cardiovascular physiology (10th edition): Part 2he pressure would remain virtually constant throughout the entire cycle (Figure 7-2(1). of the 100 ml, of fluid pumped during the 0.5 s of systole, onEbook Cardiovascular physiology (10th edition): Part 2
ly 50 ml, would be emitted through the high-resistance outflow end of the system during systole. The remaining 50 mb would be stored by the distensiblOBJECTIVES1Explain how the pulsatile blood (low in the large arteries is converted into a steady flow in the capillaries.2Discuss arterial compliance Ebook Cardiovascular physiology (10th edition): Part 2fluid pumped during systole would be ejected at only half the pressure that prevailed in Figure 7-2B. Therefore, the work would be only half as great. If filtering were nearly perfect, as in Figure 7-2C, the work would be identical to that for steady flow (Figure 7-2A).Naturally, the filtering accom Ebook Cardiovascular physiology (10th edition): Part 2plished by the systemic and pulmonic arterial systems is intermediate between the examples in Figures 7-2B and c. The additional work imposed by the iEbook Cardiovascular physiology (10th edition): Part 2
ntermittent pumping, in excess of that for steady flow, is about 35% for the right ventricle and about 10% for the left ventricle. These fractions chaOBJECTIVES1Explain how the pulsatile blood (low in the large arteries is converted into a steady flow in the capillaries.2Discuss arterial compliance Ebook Cardiovascular physiology (10th edition): Part 2gid arterial system is illustrated in Figure 7-3. In a group ol anesthetized dogs, the cardiac output pumped by the left ventricle was allowed to flow either through the natural route (the aorta) or through a stiff plastic lube to the peripheral arteries, rhe total peripheral resistance (TPR) values Ebook Cardiovascular physiology (10th edition): Part 2 were virtually identical, regardless ol which pathway was selected. The data (see Figure 7-3) from a representative animal show that, for any given sEbook Cardiovascular physiology (10th edition): Part 2
troke volume, the myocardial oxygen consumption (MVqj) was substantially greater when the blood was diverted through the plas tic tubing than when it OBJECTIVES1Explain how the pulsatile blood (low in the large arteries is converted into a steady flow in the capillaries.2Discuss arterial compliance Ebook Cardiovascular physiology (10th edition): Part 2nduit than through a more compliant conduit.ARTERIAL ELASTICITYCOMPENSATES FOR THE INTERMITTENT FLOW DELIVEREDBY THE HEART_______________________________The clastic properties of the arterial wall are determined by the composition and mechanical properties of the vessel. Two important constituents o Ebook Cardiovascular physiology (10th edition): Part 2f the arterial wall are clastic fibers, composed of elastin and microfibrils, and collagen. Elastin is elaborated by endothelial cells and is found inEbook Cardiovascular physiology (10th edition): Part 2
the tunica intima, whereas collagen is derived from myofibroblasts and located in the tunica adventitia.OBJECTIVES1Explain how the pulsatile blood (low in the large arteries is converted into a steady flow in the capillaries.2Discuss arterial compliance OBJECTIVES1Explain how the pulsatile blood (low in the large arteries is converted into a steady flow in the capillaries.2Discuss arterial complianceGọi ngay
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