heart function

Question 1

Heart contractions

Answer 1

Determinants of heart contractile function: preload, afterload, contractility, pressure volume loops

Heart failure: categories of heart failure, compensatory mechnisms

Determinants of myocardial oxygen supply and demand

Question 2

determinants of contractile function

Answer 2

normally cardiac output is matched to metabolic needs (CO=HRxSV)

3 major determinants of stroke volume: contractility, preload, afterload

Preload (the more the ventricle is stretched, during diastole the more blood thats ejected during the next contraction (cardiac function increases as a funciton of preload)

Preload measured as end diastolic volume or pressure

Afterload: resistance the ventricle must overcome to empty its contents (rises in response to higher pressure or increased chamber size, increases in wall thickness

Contractility: accounts for the changes in myocardial force for a given set of preload and afterload condiotion s

Question 3

changing preload after load

Answer 3

increase in preload augments Stroke volume via the frank starling mechanism

Question 4

Heart failure

Answer 4

heart cant pump blood at a rate sufficient to meet the requirements of metabolizing tissues,

Produces a complex of symptoms related to inadequate perfusion of tissues and retention of fluid

Final and most severe form of nearly every form of cardiac disease
Prevalant

Result of a wide variety of CV diseases, (impair ventricular contractility, increase afterload, impair relaxation and filing

Heart failure due to abnormal emptying or filling (systolic vs diastolic dysfunction)
Patients categorized according to ejection fracture (reduced EF, preserved EF)

Question 5

heart failure with ejection fraction reduced

Answer 5

Ventricle has diminished capacity to eject blood because of impaired contractility or pressure overload, loss of contractility may result from (destruction of myocytes, abnormal myocyte function, fibrosis), with pressure overload, ejection is impaired by increased resistance to outflow

Question 6

Heart failure with preserved ejection fraction

Answer 6

usually demonstrate abnormalities in diastolic function, impaired early relaxation and wall stiffness

Acute ischemia, hypertrophy, fibrosis, restrictive cardiomyopathy, pericardial disease

Question 7

Compensatory mechanisms of heart failure

Answer 7

increasing filling pressure may result in pulmonary edema

Neurohormonal activation- increases vascular resistance (maintains perfusion of vital organs (reduced CO), promotes sodium and water and sodium retention which increases intravascular volume (initial benefit but harmful)

Hypertrophy and remodeling

Question 8

Determinants of myocardial oxygen supply

Answer 8

Depends on O2 content of blood (75% extracted from blood in one pass), coronary blood flow (dynamic, increased demand met by increased coronary flow)

Question 9

Coronary blood flow

Answer 9

Resting coronary flow (225 mlMin), 4-5% of CO can increase 4-7 fold, flow is phasic

Question 10

Myocardial distribution of blood flow

Answer 10

blood supplied by epicardial coronary arteries, smaller arteries that branch from epicardial arteries supply the inner layers of muscle and feed the subendocardium

Flow to the endocardium is limited to a greater extent during systole bc compressive forces

Question 11

myocardial oxygen demand

Answer 11

wall stress, heart rate, contractile state