Chronic stage of heart failure: compensated fluid retention and cardiac output

2021-04-29 02:46 PM

Adverse effects of fluid retention on severe heart failure. Contrary to the positive effects of moderate fluid retention in heart failure, too much fluid build-up has serious physiological consequences.

A few minutes after an acute heart attack, a prolonged subacute phase begins, characterized by two problems: (1) renal fluid retention and (2) degrees of cardiac self-healing over the next few weeks. months, shown by the blue curve in the figure.

Figure. Progressive change in cardiac output after acute myocardial infarction. Both cardiac output and right atrial pressure gradually change from point A to point D (illustrated by the black line) over a period of seconds, minutes, days and weeks.

The kidneys retain fluid and increase blood volume for a few hours to a few days

The decrease in circulating volume has a significant effect on renal function, sometimes causing oliguria when the circulating volume is reduced to 50-60% of normal. Overall, decreased urine output was accompanied by circulating volume and arterial blood pressure remained lower than normal; Urine output usually does not return to normal after an acute heart attack until circulating volume and arterial blood pressure rise to normal levels.

Moderate fluid retention in heart failure can be beneficial

Many cardiologists consider fluid retention has a multidimensional effect on heart failure. However, a moderate increase in body fluids and circulating volume is an important factor in helping to compensate for the heart's ability to pump by increasing venous return. Increasing blood volume increases the amount of venous blood to the heart in two ways: first, it increases the pressure to fill the system, increases the difference in pressure to help venous blood return to the heart. Second, it dilates veins, reduces venous resistance and allows blood to return to the heart more easily. If the heart is not too damaged, increasing venous blood flow can compensate for the heart's ability to pump blood - even if the heart's ejection capacity is reduced to only 40-50% compared to normal, increasing blood volume. Return vein can return the circulating volume to normal while the patient is at rest. As the heart's ability to pump blood decreases, The blood to the kidneys drop too low for the kidneys to remove salt and water to balance the salt and water intake. Therefore, prolonged water retention if there is no treatment to prevent consequences. Moreover, because the heart has pumped to its full capacity, too much fluid no longer has a positive effect on circulation. Instead, fluid retention increases the burden on the damaged heart and progresses throughout the body, which can be harmful and lead to death.

Adverse effects of fluid retention on severe heart failure. Contrary to the positive effects of moderate fluid retention in heart failure, too much fluid build-up has serious physiological consequences. The consequences include: (1) increased cardiac burden, (2) excessive cardiac relaxation, weakening of the heart muscle, (3) pulmonary fluid retention leading to pulmonary oedema and hypoxia, (4) progressive oedema in many parts of the body.

Cardiac recovery after an infarction

After the heart is suddenly damaged by a heart attack, the body's natural repair process begins to restore the heart's function. For example, a new circulation is provided to the peripheral infarction area, usually the peripheral myocardium, to restore function. Areas of the heart muscle that are not damaged will overproduce, compensating for the damaged heart muscle. The degree of recovery depends on the type of injury, ranging from non-healing to full recovery. After an acute myocardial infarction, the myocardium recovers rapidly in the first few days and complete final recovery is achieved in 5-7 weeks, albeit mild, but recovery lasts for several months.

Cardiac output curve after partial recovery

Cardiac function when partially recovering from an acute infarction 1 week. Up to this point, the fluid is retained significantly and the tendency to increase venous blood is evident; Therefore, left atrial pressure increases. As a result, the circulatory state changed from point C to point D, indicating a normal cardiac output of 5 L / min but right atrial pressure increased by 6 mmHg. Since cardiac output returns to normal, urine is normal and there is no fluid retention, except that fluid retention occurs constantly to maintain fluid levels. Therefore, with the exception of the high left atrial pressure at point D in the figure, the present patient has normal resting hemodynamic. If the heart recovers to its peak and if sufficient fluid volume is maintained, sympathetic stimulation will gradually decrease to normal levels. Only with sympathetic stimulation, Partial restoration of the heart can increase the cardiac output curve. Therefore, due to slow recovery of the heart, fast heart rate, cold and pale skin, the consequences of sympathetic stimulation in the acute stage of heart failure gradually disappear.

 

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