Unit Four: The Circulation

Chapter 22: Cardiac Failure

Guyton and Hall, Textbook of Medical Physiology, 12 edition

Circulatory Dynamics in Cardiac Failure

• Acute Effects of Moderate Cardiac Failure

a. Reduced cardiac output

b. Damming of blood in the veins, resulting inincreased venous pressure

Circulatory Dynamics in Cardiac Failure

• Compensation for Acute Cardiac Failure bySympathetic Nervous Reflexes

a. Baroreceptor reflexb. Chemoreceptor reflex

Fig. 22.1

Circulatory Dynamics in Cardiac Failure

• Chronic Stage of Failure

a. Retention of fluid by the kidneys-normal urineoutput does not occur until the CO and arterialpressure are back to normal

b. Various degrees of recovery by the heart (Fig. 22.1; light green line

Circulatory Dynamics in Cardiac Failure

• Moderate Fluid Retention Can Be Beneficial

a. Increases the mean systemic filling pressure whichincreases the pressure gradient for causing venous flowtoward the heart

b. Distends the veins which reduces the venous resistance

Circulatory Dynamics in Cardiac Failure

• Detrimental Effects of Excess Fluid Retention

a. Increases the workload on the damaged heart

b. Overstretching of the heart causing further damage

c. Filtration of fluid into the lungs, causing edema and deoxygenation of the blood

d. Development of extensive edema in other parts ofthe body

Circulatory Dynamics in Cardiac Failure

• Recovery of the Myocardium after Myocardial Infarction

a. New collateral blood supply penetrates the periphery ofthe infarcted area

b. Undamaged musculature hypertrophies

c. Degree of recovery depends on the amount of damage

Circulatory Dynamics in Cardiac Failure

• Decompensated Heart Failure

a. If severely damaged, no amount of compensation can make the heart pump a normal output

Fig. 22.2

Circulatory Dynamics in Cardiac Failure

• Treatment of Decompensation

a. Strengthening the heart by cardiotonic drugs, such asdigitalis

b. Administering diuretic drugs to increase kidney excretion

Unilateral Left Heart Failure

• Blood continues to be pumped by the right side withusual vigor

• Therefore, the mean pulmonary filling pressure rises• Volume of blood in the lung increases and results in:

a. Pulmonary vascular congestonb. Pulmonary edema

Low-Output Cardiac Failure—Cardiogenic Shock

• Circle of Cardiac Deterioration Leading to Shockand Death

• Treatment

a. Surgically removing the clot in the coronary artery

b. Catheterizing the blocked coronary and infusion with chemicals to dissolve the clot

Edema in Patients with Cardiac Failure

• Inability of Acute Cardiac Failure to Cause PeripheralEdema

a. Decreased glomerular filtration rateb. Activation of the renin-angiotensin system and increased

reabsorption of water and salt by the renal tubulesc. Increased aldosterone secretiond. Activation of the sympathetic nervous system

• Role of ANP to Delay Onset of Cardiac Decompensation

a. Direct effect on kidneys to increase excretion of salt and water

Cardiac Reserve

• Maximum percentage that the CO can increase above normal

Fig. 22.4 Cardiac reserve in different conditions, showing less than zero reserve for two of the conditions