Chapter 22 - Guyton Flashcards
Define heart failure.
failure of the heart to pump enough blood to satisfy the needs of the body
What two main effects occur immediately as a result of myocardial infarction?
reduced cardiac output and damming of blood in the veins resulting in increased venous pressure
What occurs after acute cardiac failure to compensate for reduced cardiac output?
strong sympathetic stimulation with parasympathetic inhibition (heart becomes stronger pump and mean systemic filling pressure increases–>increased venous return)
How long does it take for the sympathetic reflex to kick in after a myocardial infarction?
The sympathetic reflexes become maximally developed in about 30 seconds.
After the first few minutes of an acute heart attack, a prolonged semi-chronic state begins, characterized mainly by two events:
retention of fluid by the kidneys and (2) varying degrees of recovery of the heart itself over a period of weeks to months
In what two ways can fluid retention be helpful in a patient with cardiac failure?
it increases the mean systemic filling pressure, which increases the pressure gradient for causing venous flow of blood toward the heart; second, it distends the veins, which reduces the venous resistance and allows even more ease of flow of blood to the heart
What are some of the detrimental effects of excessive fluid retention in severe cardiac failure?
overstretching of the heart, thus weakening the heart still more; filtration of fluid into the lungs, causing pulmonary edema and consequent deoxygenation of the blood; and development of extensive edema in most parts of the body
What is compensated heart failure?
chronic compensations resulting from partial heart recovery and renal retention of fluid (several days to several weeks later)
Many people, especially older people, have ______ resting cardiac outputs but mildly to moderately ________ right atrial pressures because of various degrees of “compensated heart failure.”
normal; elevated (increase in right atrial pressure can maintain normal cardiac output despite continued weakness of the heart - these individuals have a diminished cardiac reserve)
The main cause of decompensated heart failure is:
failure of the heart to pump sufficient blood to make the kidneys excrete daily the necessary amounts of fluid.
What are some treatment options for decompensated heart failure (otherwise the patient will die from fluid retention)?
strengthening the heart in any one of several ways, especially by administration of a cardiotonic drug, (digitalis); administering diuretic drugs to increase kidney excretion while at the same time reducing water and salt intake
What is the mechanism of action for digitalis?
strengthen heart contraction by increasing the quantity of calcium ions in muscle fibers (depresses the calcium pump that normally pumps calcium out)
In unilateral left heart failure, why could pulmonary edema result?
mean pulmonary filling pressure rises because of shift of large volumes of blood from the systemic circulation into the pulmonary circulation–>pulmonary edema
Why does acute cardiac failure typically NOT result in immediate peripheral edema?
severe acute cardiac failure often causes a fall in peripheral capillary pressure rather than a rise
Once a person develops _________ shock, the survival rate is often less than 15 per cent.
cardiogenic or cardiac