First Pass Miss Flashcards
What is the formula for wall stress? What increases / decreases it?
Wall stress = (Pressure x Radius) / 2(wall thickness)
-> force with cardiomyocytes must push against
Increased by greater radius from center to wall of ventricle, and systolic pressure (afterload)
Stress is normalized via increasing wall thickness
Why is afterload approximated by mean arterial pressure?
Afterload can basically be thought of as the force per unit area the heart must push against
However, we assume that ventricular radius and wall thickness are pretty much constant, so pressure (in the numerator of wall stress equation) is a pretty good proxy.
Pressure = Force per area
Radius = length (i.e. cm)
Wall thickness = length (i.e. cm)
(F/A * cm) / cm = F/A, Laplace’s law
How does wall stress change during ejection?
It decreases because
- The size of the LV cavity decreases -> Radius decreases
- LV wall thickness increases -> more sarcomeres pushed together
Give a few conditions causing concentric hypertrophy?
Uncontrolled HTN
Aortic valve stenosis
Pulmonic valve stenosis (thickening of RV)
-> laying down of fibers in parallel to reduce wall stress by increasing thickness and reducing radius of ventricles
What does eccentric hypertrophy happen in response to, and what is its pathogenesis?
In response to chronically increased preload
- > Lay down more sarcomeres in series to accommodate increased volume
- > Increased volume increases wall stress (radius is larger)
- > Lay down sarcomeres in parallel to increase wall thickness and decrease cavity size
Why is LV hypertrophy bad?
- Volume of myocytes increases disproportionately to capillary growth -> decreased coronary reserve in situations of high demand (i.e. tachycardia)
- Sarcomeres increase more than mitochondria -> inefficient energy use
- Decreased contraction efficiency in myosin ATPase
- Increased collagen deposition -> increased LV stiffness
What is the Fick equation and how is it used to measure cardiac output?
Cardiac output = VO2 (measured via inspiration / expiration, in mL/min) / AV oxygen difference (mL O2 / liter of blood)
Measure the patients arterial and venous O2 concentrations for the AV oxygen difference.
How is vascular resistance measured? Units?
Mean pressure difference across a vascular bed / mean blood flow (Delta P / CO = TPR)
Mean blood flow is measured in volume / time (cm^3/sec)
Thus, units are (Dynes/cm^2) / (cm^3 / sec) = dynesseccm^-5
Dyne is a force per unit area
What does pulmonary capillary wedge pressure (PCWP) approximate?
Left atrial pressure (diastolic pressure from a balloon catheter inserted into the pulmonary artery) -> LVEDP -> implies LVEDV -> preload
How is vascular resistance measured? Units?
Mean pressure difference across a vascular bed / mean blood flow (Delta P / CO = TPR)
Mean blood flow is measured in volume / time (cm^3/sec)
Thus, units are (Dynes/cm^2) / (cm^3 / sec) = dynesseccm^-5
Dyne is a force per unit area
What does pulmonary capillary wedge pressure (PCWP) approximate?
Left atrial pressure (diastolic pressure from a balloon catheter inserted into the pulmonary artery) -> LVEDP -> preload
How is the systemic vascular resistance calculated and what is the normal range?
SVR = (MAP - Mean RAP) / CO
RAP = right atrial pressure
Normal = 900-1300 dynesseccm^-5
What is the definition of hypertensive crisis?
SBP > 180
or
DBP > 110
Urgency = without end-organ damage Emergency = with evidence of end-organ damage
How is the pulmonary vascular resistance calculated and what is the normal range?
PVR = (Mean PAP - Mean LAP) / CO
LAP = Left atrial pressure = PCWP
Normal = 40 to 90 dynesseccm^-5
Who is most likely to get fibromuscular dysplasia and renal artery stenosis?
Fibromuscular dysplasia -> especially young women, developmental defective in large and medium muscular arteries, especially affecting renal artery
Renal artery stenosis -> especially older men, due to atherosclerosis of renal arteries
Other than adrenal disorders, give four endocrine disorders or conditions which can cause hypertension?
- Acromegaly - GH excess
- Hypothyroidism -> Increases sodium, also increases lipid levels for hardening of arteries
- Hyperparathyroidism -> increases renin / kidney dysfunction
- Exogenous hormones -> steroids / oral contraceptives
What are the best antihypertensives to use post-MI and in heart failure / CAD?
Beta blocker and ACE inhibitor
Use diuretics in heart failure and CAD
What is the definition of resistant HTN? Causes?
Persistently elevated BP despite 3+ medications
Causes:
Noncompliance or medications at not max dose, use of other drugs which elevate BP, volume overload, or undiagnosed OSA
When are ACE inhibitors contraindicated?
- C1 esterase inhibitor deficiency (C1 esterase inhibitor also cleaves kallikrein, responsible for converting HMW kininogen to bradykinin. Only other enzyme which breaks down bradykinin is ACE)
- Bilateral renal artery stenosis -> angiotensin II is the only thing maintaining GFR by constricting efferent arteriole
- Pregnancy
What areas of the brain are most susceptible to microaneurysm rupture in systemic hypertension?
Putamen (BG), thalamus, and pons
Rupture.PPT
What can be seen pathologically in hyerplastic arteriolosclerosis? Grossly in kidney?
Concentric proliferation of myofibroblastic cells into intima - “onion-skin” appearance
Accompanied by fibrinoid necrosis and petechial hemorrhages.
Grossly: Kidney will have a flea-bitten appearance due to hemorrhages on cortical surface
How does benign nephrosclerosis appear microscopically in larger arteries? What is benign nephrosclerosis?
Larger arteries include interlobular and arcuate
Fibroelastic hyperplasia -> myofibroblast hyperplasia, reduplication of elastic lamina, medial smooth muscle hypertrophy, and luminal narrowing (large arteries respond somewhat like hyperplastic arteriolosclerosis)
Benign nephrosclerosis occurs in longstanding essential hypertension and diabetes mellitus
How does benign nephrosclerosis appear microscopically in small arteries / arterioles and renal parenchyma?
Small arteries / arterioles - hyaline arteriolosclerosis
Renal parenchyma - ischemic changes - interstitial / glomerular fibrosis and accompanying tubular atrophy
What are the microscopic features of malignant nephrosclerosis? (Grossly = flea-bitten appearance)
Small arteries / arterioles -> hyperplastic arteriolosclerosis with fibrinoid necrosis
Renal parenchyma -> infarction and/or ischemic atrophy (if you had prior benign hypertension) -> infarction due to rapid death of arterioles