Pressure/Volume Overload

Question 1

hemodynamic burden

Answer 1

pressure or volume overload

Question 2

what are the two types of responses that the heart has to hemodynamic burden

Answer 2

1. functional response (short term)
2. proliferative response (long term)

Question 3

functional response

Answer 3

short term response (minutes/hours)

responds to immediate changes in burden to attempt to survive the burden

Question 4

proliferative response

Answer 4

long term response (weeks/months/years)

responds to chronic stressors by hypertrophy

main compensatory mechanism

Question 5

hyperplasia vs hypertrophy

Answer 5

hyperplasia: increase in cell number

hypertrophy: increase cell size

Question 6

does cardiomyocyte hyperplasia occur in adults

Answer 6

no - only in fetal myocardium

Question 7

how do cardiomyocytes hypertrophy

Answer 7

sarcomere hyperplasia –> results in cardiomyocyte hypertrophy

Question 8

primary vs secondary hypertrophy

Answer 8

primary: genetic or idiopathic enlargement (ex. HCM)

secondary: increased workload (pressure vs volume overload)

Question 9

pressure overload

Answer 9

increased systolic pressure resulting in increased afterload

causes concentric hypertrophy

Question 10

concentric hypertrophy

Answer 10

sarcomeres are added in parallel

causes wall thickening and chamber constriction

Question 11

volume overload

Answer 11

increased diastolic pressure resulting in increased preload

causes eccentric hypertrophy

Question 12

eccentric hypertrophy

Answer 12

sarcomeres are added in series

causes wall lengthening and chamber dilation

Question 13

how does athletic training affect cardiomyocytes

Answer 13

physiologic, reversible hypertrophy

can be in series, parallel, or both

Question 14

what does the type of hypertrophy depend on

Answer 14

when the wall stress occurs (systole vs diastole)

Question 15

mechanism of pressure overload causing concentric hypertrophy

Answer 15

increased aortic pressure –> increased afterload (systolic wall stress) –> more difficult to push blood out of ventricle –> stroke volume decreases –> myocytes hypertrophy to compensate

LaPlace’s Law: wall thickness can offset wall stress

Question 16

how does concentric hypertrophy affect chamber size and compliance

Answer 16

decrease chamber size and decreased compliance

Question 17

mechanism of volume overload causing eccentric hypertrophy

Answer 17

increased EDV –> increased preload (diastolic wall stress) –> more volume to push out of ventricle –> stroke volume increases –> chamber dilates by eccentric hypertrophy

Question 18

how does eccentric hypertrophy affect stroke volume and ejection fraction

Answer 18

increases stroke volume
decreases ejection fraction

more net blood leaves during systole, but a lower percentage of blood in the ventricles leaves

Question 19

how is hypertrophy maladaptive

Answer 19

proliferative and compensatory growth in response to wall stress provides temporary compensation
BUT
cardiomyocytes can not handle prolonged stressors –> overloads the heart –> cardiomyocytes degenerate and die –> ischemia –> replaced with interstitial fibrosis –> exacerbates maladaptive response + decreases conduction

Question 20

maladapyive outcomes of concentric hypertrophy

Answer 20

1. subendocardial ischemia: caused by thick wall preventing nutrients to reach all the way through
2. myocardial ischemia & fibrosis: myocardium outgrows blood supply leading to ischemia, myocyte death, and necrosis

Question 21

effect of fibrosis on heart function

Answer 21

fibrosis causes loss of compliance –> ventricle cannot hold as much blood –> decreases stroke volume

pressure between atria and ventricles decrease

Question 22

maladaptive outcomes of eccentric hypertrophy

Answer 22

1. progressive dilation: preload leads to chamber dilation and increased filling which leads to more preload and exacerbates the issue
2. AV valve regurgitation: ventricular wall remodeling causes displacement of papillary muscles, which leads to regurgitation and more preload, and more dilation
3. impaired ejection: chamber dilation decreases systolic wall pressure, leading to decreased contractility and impaired ejection

Question 23

neurohormones and hypertrophy

Answer 23

involved in functional response

neurohormones trigger hypertrophic pathways leading to cell death and fibrosis

Question 24

what is the effect of medication on heart failure

Answer 24

decreases load on the heart

does NOT fix heart damage