CV Adaptation to Changes in Loading Conditions Flashcards
What is relative wall thickness?
RWT = 2*WT/LVID –> allows you to understand how the geometry of the ventricle is changing
e.g. if the cavity enlarges but the wt is the same, then rwt is lower than normal and vice versa
What is the effect of an acute change in volume load? What can cause this?
increased stroke volume
e.g. exercise, anemia, regurgitant valves
What is the effect of an acute change in pressure load? What can cause this?
increased systolic pressure
e.g. hypertension, valvular stenosis
How do we compensate for acute pressure load?
increased pressure load leads to reduced stroke volume b/c increased systolic ejection pressure increases afterload and reduces stroke volume –> 1. can initiate contraction from higher EDV or 2. can increase inotropic state
What is the metabolic price for the adaptive mechanisms that compensate for volume-pressure overload?
wall stress –> large increase in myocyte metabolic demands
Generally, what is the long term consequence of chronic overload?
hypertrophy
How does increase in myocardial mass decrease myocyte oxygen consumption?
burden is shared by more myocytes so each individual is consuming less
What is the long term consequence of chronic increased pressure overload?
concentric hypertrophy:b/c pressure increase manifests as increased systolic pressure
no significant change in cavity diameter, increased LV wall thickness, increased LV mass, increase RWT
What is the long term consequence of chronic increased volume overload?
eccentric hypertrophy b/c diastolic chamber size increases to increase stroke volume:
increased LV wall thickness and mass and commensurate change in cavity size AKA no change in RWT
What is the long term consequence of chronic htn?
b/c both pressure and volume overload –> concentric remodeling:
normal LV mass with elevated RWT
What makes myocyte enlargement “abnormal” in hypertrophy?
there is less mitochondrial proliferation than myofibrillar increase and there is functionally abnormal SR, capillary proliferation is not always commensurate with myocyte mass (increased intercapillary distance), exuberant increase in fibrous components (reduced efficiency of gas/substrate exchange)
parallel or series sarcomere development? pressure overload
concentric hypertrophy = parallel
parallel or series sarcomere development? volume overload
eccentric hypertrophy = series
