Quick Review: Hemodynamics
T Fujii, B Phillips
Citation
T Fujii, B Phillips. Quick Review: Hemodynamics. The Internet Journal of Academic Physician Assistants. 2002 Volume 3 Number 1.
Abstract
Before discussing basic hemodynamics, we should remind ourselves of the systemic circuit:
1. Cardiac Anatomy
2. Circulatory Pathways
This brief review discusses the basics of hemodynamics.
Cardiac Anatomy
The Heart: 2 Separate Volume Pumps !
The in-series nature of these two systems implies that the output of the Right Heart becomes the input of the Left Heart, and therefore, the output of the Left Heart becomes the input of the Right Heart
Flow via Series: Demonstrated by William Harvey, 1628
Desaturated Blood returns from the Systemic Vessels via
Saturated Blood is then returned to the Left Atrium via the Pulmonary Veins !
Myocardial Perfusion occurs primarily during Diastole
Myocardial Blood Flow:
Myocyte Contraction
At the cellular level, electrical depolarization of the myocardial cell membrane allows ionized calcium flux into the cytoplasm - leading to hydrolysis of ATP by Myosin.
This leads to a conformational change in the
Calcium is then removed from the cell by
Over the physiologic range of sarcomere length (1.6 - 2.0 um), the amount of metabolic energy converted to mechanical work is
Work is
This
Otto Frank, 1885
Cardiac Output
Normal C.O. : 3.5 - 8.5 L/min
Manipulation of the factors can lead to augmentation of CO at the lowest possible energy cost !
Determinants of Cardiac Performance & Output
Preload
But Remember, the relationship between LVEDP & LVEDVis
Elevation of CVP to Equal PAD& PCWP
Afterload
The
MBAP (Mean Arterial Blood Pressure) = DBP + [1/3(SBP - DBP)]
SVR units: dynes-second/cm5
Pressure Work................................................Flow Work
Plus, since pressure work is more costly than flow work in terms of myocardial oxygen consumption, by decreasing afterload - you also decrease the overall energy requirement
PVR = {(MPAP - PWP)/CO} x 80
Remember:
Contractility
By increasing intropic state, you increase both Pressure Work & Flow Work - thus, the cost in myocardial oxygen consumption may be high !!
Compliance & Elasticity
“Compliance”: the tendency of an object to return to it's original shape when it has been deformed or altered
(Compliance = change in Volume / change in Pressure)
Heart Rate
Heart Rate can