Hemodynamics in CVS of physiology- c.pptx

Hemodynamics concised ppt

1. Haemodynamics - I Dr. N. Revanth

2. Specific learning objectives Functional & structural organization of blood vessels. Different laws that help us understand the flow and resistance. Factors affecting flow & resistance of blood flow.

3. Functional organization & structure of vascular system Dynamics concerned with blood flow & lymph flow. Vascular system is organized into systemic and pulmonary circulation. Systemic supplies blood to various systems in parallel connection. Pulmonary and systemic circulation is arranged in series connection ensuring equal flow. Lymph is circulated in parallel to blood circulation.

4. Structure Tunica Intima: innermost  endothelial lining- basal lamina- subendothelial connective tissue- internal elastic lamina. Tunica media: middle thickest coat of smooth muscle and elastic tissue. Tunica Adventitia: outermost coat made up of connective tissue prominent of collagen.

5. Innervations: Smooth muscles innervated by sympathetic fibers - α adrenergic receptors – vasoconstriction. These sympathetic fibers help maintain tonicity at night. Skeletal muscle arterioles contain β2 receptors- vasodilation.

6. Factors affecting blood flow: Poiseuille- Hagen Law: Flow- Pressure – Resistance relationship. pressure gradient (P) , tube length – l, viscosity n, radius r. The Poiseuille’s law is valid for straight rigid tubes with Newtonian fluid flowing through them. Blood is not a Newtonian fluid hence doesn’t apply.

7. Pressure vs flow

8. Critical closing pressure The pressure value at which the vessel collapses and lumen closes is called Critical Closing Pressure. A minimum amount of intramural pressure is required to push the RBCs & also to overcome tissue pressure over vessels.

9. Law of Laplace Relationship between distending pressure and tension in wall. In a cylinder one radius is infinite P = T/r T tension in the wall, r radius

10. Flow vs Resistance Peripheral resistance Unit (PRU): flow is inversely proportional to resistance from Poiseuille’s law. Total peripheral Resistance (TPR): resistance of the entire circulation at rest is called TPR. TPR at rest is 1 PRU. Max vasoconstriction- 4 PRU, max vasodilation 0.2 PRU.

11. Factors that affect resistance to blood flow Viscosity of blood Radius of blood vessel Factors affecting the viscosity of blood- shear Rate or velocity gradient, inversely proportional. Plasma skimming- RBCs travel in midline leaving peripheral fluid/ plasma devoid of cells.

12. 2. Hematocrit – directly proportional to viscosity. 3. Temperature- cooling increases viscosity. Radius – flow directly proportional to 4 times r. 1 mm- 1 ml/min 2 mm- 16 ml/min 3 mm- 256 ml/min Arterioles are the major seat of resistance.