All animal cells require oxygen (O2) for the conversion of carbohydrates, fats and proteins into carbon dioxide (CO2), water and energy in a process known as aerobic respiration. The circulatory system functions to transport the blood to deliver O2, nutrients and chemicals to the cells of the body to ensure their health and proper function, and to remove the cellular waste products.
The circulatory system is a connected series of tubes, which includes the heart, the arteries, the microcirculation, and the veins.
Hemodynamics is an important part of cardiovascular physiology dealing with the forces the pump (the heart) has to develop to circulate blood through the cardiovascular system. Adequate blood circulation (blood flow) is a necessary condition for adequate supply of oxygen to all tissues, which, in return, is synonymous with cardiovascular health, survival of surgical patients, longevity and quality of life. To an outside observer (a physician or a nurse) these hemodynamic forces demonstrate themselves as blood pressure and blood flow paired values at different nodes of the cardiovascular system. We will concentrate on systemic hemodynamics - the blood pressure and blood flow at the output of the left heart. The interest in systemic hemodynamics is obvious: A significant majority of all cardiovascular diseases and disorders is related to systemic hemodynamic dysfunction. Hypertension and congestive heart failure are two best known systemic hemodynamic disorders.
Current State of the Art of Systemic HemodynamicsUnderstanding and teaching of hemodynamics at medical and nursing schools has not significantly changed over the last forty years. Measurement of arterial blood pressure is considered to be a "hemodynamic measurement." Measurement of Cardiac Output, CO [liter/min], or measurement of the wedge pressure by the flow-directed pulmonary artery catheter (sometimes called the Swan-Ganz or the thermodilution catheter) are considered to be "hemodynamic measurements." Hemodynamics is taught at the level made available in the '70s by introduction of this catheter. Since this measurement is very expensive, risky, require a sterile environment and a highly skilled physician for catheter insertion, it is only used in about 2% of patient population. In addition, it propagated myths about its "ability" to assess intravascular volume, which have subsequently been disputed [Calvin JE et al: Does the pulmonary capillary wedge pressure predict left ventricular performance in critically ill patients? Crit Care Med, Vol 9, No 6:437]. It propagated a myth that in a stable patient the hemodynamics do not change and, therefore, it is adequate to measure hemodynamics only intermittently, several times a day. The use of the catheter almost become a cult [Robin ED: The Cult of Swan-Ganz Catheter. Intens & Crit Care Digest, Vol 5, No 1, June 1986:18]. However, its most negative impact has been the way it affected hemodynamic thinking of several generations of medical professionals: Though everybody understands that an adequate oxygen delivery to all organs is an essential condition for the organs' health, and that oxygen delivery is a blood flow and not blood pressure-related phenomenon (blood is the vehicle, oxygen is the cargo), the blood flow is measured today only in very small percentage of patient population. Most of hemodynamic management decisions are made just upon the arterial blood pressure measurement (such as in management of hypertension,....). There is no intellectual need to simultaneously measure both blood pressure and blood flow in every patient. Equally, there is no clear understanding that both normotension and normodynamic state (blood flow within normal range) must be part of the therapeutic goal.
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PDF: Appendix 1: Useful Hemodynamics Formulas- Cardiovascular Hemodynamics for the Clinician- Wiley Online Library : http://onlinelibrary.wiley.com/doi/10.1002/9780470692608.app1/pdf