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Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
Chapter 43
Review of Hemodynamics
2Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.
Review of Hemodynamics Overview of the circulatory system
Delivery of oxygen, nutrients, hormones, electrolytes, and other essentials to the cells
Removal of carbon dioxide, metabolic wastes, and other detritus from cells
Two major divisions• Pulmonary circulation and systemic circulation
Regulation of cardiac output Regulation of arterial pressure (AP)
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Overview of the Circulatory System
Components of the circulatory system Arteries Arterioles Capillaries Venules Veins
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Overview of the Circulatory System
Distribution of blood 9% in the pulmonary circulation 7% in the heart 84% in the systemic circulation
What makes blood flow? Force that drives flow is greater than resistance
How does blood get back to the heart?
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Fig. 43–1. Distribution of blood in the circulatory system.
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Fig. 43–2. Forces that promote and impede flow of blood.
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Fig. 43–3. Distribution of pressure within the systemic circulation.
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Regulation of Cardiac Output Determinants of cardiac output
Average adult, 5 L/min Cardiac output = Heart rate × Stroke volume Heart rate
• Controlled by the autonomic nervous system Stroke volume
• Myocardial contractility• Cardiac afterload• Cardiac preload
Preload• End-diastolic volume or end-diastolic pressure
Afterload• Arterial pressure the left ventricle must overcome to eject blood
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Regulation of Cardiac Output Control of stroke volume by venous return
Starling’s law of the heart Factors that determine venous return
• Systemic filling pressure• Auxiliary muscle pumps• Resistance to flow between peripheral vessels and the
right atrium• Right atrial pressure
Starling’s law and maintenance of systemic-pulmonary balance
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Fig. 43–4. Venous valves and the auxiliary venous “pump.”
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Fig. 43–5. The Starling relationship between myocardial fiber lengthand contractile force.
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Fig. 43–6. Systemic-pulmonary imbalance that develops when the output of the left and right ventricles is not identical.
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Regulation of Arterial Pressure Overview of control system
AP = Peripheral resistance × Cardiac output Arterial pressure is regulated by:
• Autonomic nervous system (ANS)• Renin-angiotensin system• Kidneys
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Regulation of Arterial Pressure Steady-state control by the ANS
Regulates AP by adjusting cardiac output (CO) and peripheral resistance
Rapid control by the ANS: the baroreceptor reflex Constriction of nearly all arterioles Constriction of veins Acceleration of heart rate
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Regulation of Arterial Pressure Renin-angiotensin-aldosterone system
Constriction of arterioles and veins (angiotensin II) Retention of water by the kidney (aldosterone)
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Regulation of Arterial Pressure Renal retention of water Postural hypotension (orthostatic
hypotension) Natriuretic peptides
Protect the cardiovascular system in the event of volume overload
Three principal members• Atrial natriuretic peptide (ANP)• B (brain)-natriuretic peptide (BNP)• C-natriuretic peptide (CNP)