Cardiovascular hemodynamics
Dr Pramod Kumar Asstt. Professor
Department of Veterinary Physiology Bihar Veterinary College, Patna
Dynamics of Circulation
1.Functional organization and structure of Vascular System
2. Pressure and Blood Flow in different segments of circulatory system
3.Hemodynamic 4. Blood pressure
Windkessel vessels: large arteries Resistance vessels: small arteries
Exchange vessels: formed by a single layer of endothelial cells
Capacitance vessels: veins
Shunt vessels: Meta-arterioles
Characteristics of various types of
blood vessels
SYSTEMIC CIRCULATION: Structure Pressure in mmHg
Left Atrium 7-8/0
Left Ventricle 120/0
Aorta & large arteries 120/80
Arterioles 60
Capillaries 25
Venules & large veins 10
Vena cava (SVC&IVC) 2
PULMONARY CIRCULATION: Structure Pressure in mmHg
Right Atrium 4-6/0
Right Ventricle 25/0
Pulmonary arteries 25/8
Arterioles 10
Capillaries 6-8
Venules & larger branches 5
Pulmonary veins 2
Pressures in Vascular System
Vessel % of blood volume Systemic 84 % Arteries 13 %
Arteriole 1-2 % Capillary 5 % Veins 64 %
Pulmonary/Heart 16 % Lungs 9 %
Heart 7 %
The word hemodynamics means blood circulation in an animals body. Cardiovascular hemodynamics comprises of blood circulation to the heart and in turn the blood circulation regulated by the heart.
Main coronary arteries lie on the surface of the heart and small arteries penetrate into the cardiac muscle mass. Heart receives nutrition supply through these arteries. Left coronary artery supplies mainly anterior and lateral portion of left ventricle. Right coronary artery supplies most of right ventricle as well as posterior part of left ventricle.
Venous blood flow from left ventricle leaves by way of coronary sinus. Most of venous blood from right ventricle flows through small anterior cardiac vein directly into the right atrium and not connected with coronary sinus. Small amount of coronary blood flows back into the heart through Thebesian vein.
During cardiac contraction – Intra myocardial pressure in the inner layer of the heart muscle is so much greater than the outer layer. It compresses the sub endocardial blood vessels far more than it compresses the outer vessel.
Oxygen demand is major factor in local blood flow regulation.
Determinants of oxygen consumption.
Importance of increase in coronary blood flow in response to myocardial oxygen usage.
Reactive hyperemia in coronary system.
Local metabolism acts as primary control of coronary flow. Blood flow through coronary system is regulated almost entirely by vascular response to the local needs.
Blood flow in coronary arteries is proportion to the need of cardiac musculature for oxygen. Decrease in oxygen concentration in the heart causes vasodilator substance to be released from the muscle cells .
There are different factors that can alter myocardial oxygen consumption. Cardiac oxygen consumption is related to work performed by the heart. Greater the work, greater the oxygen consumption.
Important principle of heart function is myocardial energy consumption, and oxygen usage are very nearly proportional to tension time. The time that the tension is maintained during cardiac cycle .
Consumption or stimulation of heart by epinephrine, norepinephrine, thyroxine and calcium ions.
During resting heart, most of the oxygen extract from the coronary blood as it flows through the heart muscles. when coronary blood flow fails to increase when demand of the strength of muscle diminishes rapidly and it causes acute heart
failure.
When coronary flow to heart is occluded for a few seconds to few minutes and then
disoccluded the blood flow increases to as high as 3 to 4 times normal. It may remains high for a few second to few minutes.
Stimulation of autonomic nerves to the heart can affect coronary blood flow in 2 ways:
1. Directly 2. Indirectly
Action of nerve transmitter substance on the blood vessels will reduce the coronary blood flow through the release of acetylcholine & nor- epinephrine.
Sympathetic stimulation of nerve to the heart can affect the coronary blood flow by the release of nor- epinephrine.
