TAILIEUCHUNG - Introduction to the Cardiovascular System - Part 9

Ngoài ra, không phải tất cả bệnh nhân suy tim mãn tính hạ huyết áp, do đó, nó không phải là rõ ràng những gì ổ đĩa sự gia tăng đặc trưng trong hoạt động giao cảm trong suy tim. Thay đổi quan trọng dịch dịch thể xảy ra trong suy tim để giúp bù đắp cho việc giảm cung lượng tim. | CARDIOVASCULAR INTEGRATION AND ADAPTATION 209 sure and therefore cannot be responsible for the increased sympathetic drive when hypotension accompanies chronic heart failure. In addition not all patients in chronic heart failure are hypotensive therefore it is not clear what drives the characteristic increase in sympathetic activity in heart failure. Important humoral changes occur during heart failure to help compensate for the reduction in cardiac output. Arterial hypotension along with sympathetic activation stimulates renin release leading to the formation of angiotensin II and aldosterone. Vasopressin antidiuretic hormone release from the posterior pituitary is also stimulated. Increased vasopressin release seems paradoxical because right atrial pressure is often elevated in heart failure which should inhibit the release of vasopressin see Chapter 6 . It may be that vasopressin release is stimulated in heart failure by sympathetic activation and increased angiotensin II. These changes in neurohumoral status constrict resistance vessels which causes an increase in systemic vascular resistance to help maintain arterial pressure. Venous capacitance vessels constrict as well. This increased venous tone further increases venous pressure. Angiotensin II and aldosterone along with vasopressin increase blood volume by increasing renal reabsorption of sodium and water. This contributes to a further increase in venous pressure which increases cardiac pre load and helps to maintain stroke volume through the Frank-Starling mechanism. Increased right atrial pressure stimulates the synthesis and release of atrial natriuretic peptide to counter-regulate the renin-angiotensin-aldosterone system. These neurohumoral responses function as compensatory mechanisms but they can aggravate heart failure by increasing ventricular afterload which depresses stroke volume and increasing preload to the point at which pulmonary or systemic congestion and edema occur. Exercise Limitations .

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