Cardiac Flashcards
Developmental Competence: Infants and Children
Fetal heart begins to beat after 3 weeks’ gestation
Right and left ventricles equal in weight and muscle wall thickness and both pumping into systemic circulation
Inflation and aeration of lungs at birth produces circulatory changes
Now blood is oxygenated through lungs rather than through placenta
Now left ventricle has greater workload of pumping into systemic circulation
The heart is more horizontal in the chest thus the apex is higher
Developmental Competence: Pregnant Woman
Blood volume increases by 30% to 50% during pregnancy
Most rapid expansion occurs during second trimester
Creates an increase in stroke volume and cardiac output and an increased pulse rate of 10 to 15 beats per minute
Despite increased cardiac output, arterial blood pressure decreases in pregnancy as a result of peripheral vasodilation
Blood pressure drops to lowest point during second trimester, then rises after that
Blood pressure varies with person’s position
Hemodynamic Changes with Aging
With aging, there is an increase in systolic BP due to thickening and stiffening of the arteries
Left ventricular wall becomes thicker but the overall size of the heart does not change
Ability of heart to adjust cardiac output with exercise is decreased
Cardiac function in adults
Amount of collagen in the heart increases and elastin decreases. These changes affect the contractile and distensible properties of the myocardium
Heart valves become thick and stiff
Dysrythmias increase with age
Frequent need for pacemakers
SA node fails
Less sensitive to β-adrenergic agonist drugs
Risk of orthostatic hypotension
Increase in SBP; decrease or no change in DBP
Hypertension and heart failure also increase with age
Diastole
Ventricles relaxed
Tricuspid and mitral (AV) valves are open
Pressure in atria higher than that in ventricles, so blood pours rapidly into ventricles
Toward end of diastole, atria contract and push last amount of blood into ventricles (about 25% of stroke volume) called atrial kick
Systole
Ventricular pressure becomes higher than that in atria
Mitral and tricuspid valves close
Closure of AV valves contributes to first heart sound (S1) and signals beginning of systole
AV valves close to prevent any regurgitation of blood back up into atria during contraction
For a very brief moment, all four valves are closed and ventricular walls contract
presystole, atrial systole or the atrial kick
The contraction of the atria and the end of diastole
Heart’s Pumping Ability
In resting adult, heart normally pumps between 4 and 6 L of blood per minute throughout body: This is cardiac output
Heart can alter its cardiac output to adapt to metabolic needs of body
Preload and afterload affect heart’s ability to increase cardiac output
Cardiac output
equals volume of blood in each systole (called stroke volume) times number of beats per minute (rate)
Preload
known as chamber volume
Preload is venous return, which builds during diastole
How well ventricular muscle can stretch at end of diastole
According to Frank-Starling law, the greater the stretch, the stronger the heart’s contraction
This increased contractility results in an increased volume of blood ejected, increased stroke volume
Afterload
Afterload is the opposing pressure that the ventricle must generate to open aortic valve
Afterload is the resistance against which ventricle must pump its blood
After aortic valve opens, rapid ejection occurs
Factors Affecting Cardiac Output
Preload
Volume of blood in ventricles at the end of diastole
Contractility
How well ventricles can move blood forward
Afterload
Peripheral resistance against which the left ventricle must pump
S1
Occurs when AV valves close (beginning of systole)
Can hear S1 over all precordium, but loudest at apex
S2
Occurs when semilunar valves close
Signals end of systole
Although heard over all precordium, S2 loudest at base
Split S2
Left ventricular systole is slightly shorter so the aortic valve closes earlier than the pulmonic valve and sometimes you can hear it
Normal if heard on inspiration
Heard best at the base