Department of physiology AIMST UNIVERSITY Dr.N.SUNITHA

Hemodynamics Hemodynamics concerns the physical factors governing blood flow within the circulatory system. Factors are pressure, flow and resistance.

Laws of Hemodynamics

Relationship between blood flow, vascular resistance and blood pressure

Blood Flow Blood flow is defined as the quantity blood passing a given point in the circulation in a given period and is normally expressed in ml/min Overall blood flow in the total circulation of an adult is about 5000 ml/min….The cardiac output

(This is the usual pattern of flow in the vascular system.) Types of Blood Flow Laminar: When velocity of blood flow is below a critical speed, the flow is orderly and streamlined (This is the usual pattern of flow in the vascular system.) Turbulent: disorderly flow with eddies & vortices

Laminar flow and turbulent flow Laminar flow – blood flows in streamlines with each layer of blood remaining the same distance from the wall Laminar flow

Laminar flow and turbulent flow Turbulent flow – blood flow in all directions in the vessel and continually mixes within the vessel. because of the velocity of blood flow is too great, is passing by an obstruction, making a sharp turn, passing over a rough surface) C, constriction; A, anterograde; R, retrograde

Turbulent flow The tendency for turbulent flow increases in direct proportion to the velocity of blood flow, the diameter of the blood vessel, and the density of the blood, and is inversely proportional to the viscosity of the blood, in accordance with the following equation: Re=(v.d.ρ)/ η where Re is Reynolds' number and is the measure of the tendency for turbulence to occur, ν is the mean velocity of blood flow (in centimeters/second), d is the vessel diameter (in centimeters), ρ is density, and η is the viscosity (in poise) When Reynolds’ number increases above about 200 turbulent flow will result

Blood flow can either be laminar or turbulent

Relationship between blood flow, vascular resistance and blood pressure Blood flow through a blood vessel is determined by two factors: (1) pressure difference of the blood between the two ends of the vessel, also sometimes called "pressure gradient" along the vessel, which is the force that pushes the blood through the vessel, and (2) the impediment to blood flow through the vessel, which is called vascular resistance Q=ΔP/R

ΔP: the pressure difference between the two ends of the vessels; (2) Factors determining blood flow (interrelationships among blood flow, pressure and resistance.) ΔP: the pressure difference between the two ends of the vessels; R: frictional force produced when blood fIows through blood vessels. Q = ΔP / R

Relationship between resistance and vessel radius

Poiseuille’s law Pressure = ŋ 8 l V ╥r4 ŋ = blood viscosity l = tube length V = blood flow r = tube radius Pressure increases with increased tube length and gas viscosity. Pressure increases with decreased radius

Pressure = Flow x Resistance Poiseulle equation: Pressure drop across a length of vessel Radius Flow Length of Vessel

Poiseuille’s law Reducing the radius of a tube by ½ requires an increase in pressure 16 fold to maintain the same speed of gas flow through the tube. Pressure =16cmH2O Pressure = 1 cmH2O

Conductance and vessel diameter Slight changes in the diameter of a vessel cause tremendous changes in the vessel's ability to conduct blood when the blood flow is streamlined Although the diameters of these vessels increase only fourfold, the respective flows are 1, 16, and 256 ml/mm, which is a 256-fold increase in flow. Thus, the conductance of the vessel increases in proportion to the fourth power of the diameter

Resistance Diseases that cause an increase in airway resistance Asthma Emphysema Excessive sputum production Tumors Things that decrease airway resistance Bronchodilators Anti-inflammatory agents

3. Blood pressure Blood pressure means the force exerted by the blood against the vessel wall ( or the force exerted by the blood against any unit area of the vessel wall) Blood Pressure is stored energy (potential energy)

Overall Greater Pressure  Greater Blood Differences Flow Greater Resistance  Lesser Blood Flow

Laplace’s Law Laplace’s Law P= 2T/R Force acting on blood vessel wall is proportional to diameter of the vessel times blood pressure P= 2T/R

Capillary Exchange and Interstitial Fluid Volume Regulation Blood pressure, capillary permeability, and osmosis affect movement of fluid from capillaries A net movement of fluid occurs from blood into tissues. Fluid gained by tissues is removed by lymphatic system.

4. Exchange of nutrients and other substances between the blood and interstitial fluid (2) Transport through the capillary membrane by pinocytosis. Proteins and many much large substance in the plasma (such as lipoprotein) are transported through the capillary membrane by means of pinocytosis. (3) Filtration. When the hydrostatic pressure is different on the two sides of membrane, the greater pressure on one side causes slightly increased diffusion of water and dissolved substances toward the opposite side.

Forces involved in Capillary Exchange

1. Formation of the interstitial fluid Effective Filtration Pressure = (Capillary Pressure + Interstitial Colloid Osmotic Pressure) – (Plasma Colloid Osmotic Pressure + Interstitial Hydrostatic Pressure)

PERIPHERAL RESISTANCE: Total peripheral resistance is the sum of the resistance of all peripheral vasculature in the systemic circulation. Three main sources (factors) of peripheral resistance 1.Blood vessel diameter 2.Blood viscosity 3.Total vessel length PERIPHERAL RESISTANCE:

1. The diameter of tube gets smaller a greater proportion of the fluid is in contact with the wall of the tube. Therefore resistance to flow is increases. Vessel diameter is actively regulated by vasomotor fibers, sympathetic nerve fibers that innervate the vessels of smooth muscle layer.

2. The greater the viscosity, the less easily molecules slide pass one another and the more difficult to get the fluid moving. 3. The longer the total vessel length the greater the resistance. An increase in peripheral resistance due to arteriolar constriction decreases venous return. Venous return always matches with cardiac output in all physiological conditions. The peripheral resistance is decreased, as in case of vasodilation, heart tries to pump more blood to fulfill the requirments, thus increasing cardiac output.

Functions of the lymphatic system Drain excess interstitial fluid LYMPHATIC CIRCULATION Consists of lymph, lymphatic vessels, structures and organs containing lymphatic tissue, red bone marrow Functions of the lymphatic system Drain excess interstitial fluid Transport dietary lipid Carry our immune responses

Lymphatic drainage Lymphatics collect proteins, lipids and other large molecules which leak out of capillaries into the interstitial space, to prevent the osmotic pressure of interstitial space from rising, and thereby prevent abnormal accumulation of fluid in the interstitial space. Reduced lymphatic drainage, e.g. in filariasis, or involvement of lymph nodes in malignancy – local or systemic edema.

Mechanism of Edema Lymphatic drainage Lymphatics are the second circulatory system. Structurally, lymphatics are a network of blind-ended thin endothelial tubes. Although the endothelial lining is not fenestrated, the intercellular junctions are permeable to large molecules.

From the physiology of capillaries and lymphatics, Factors Determining Formation of the Interstitial Fluid (Mechanism of Edema) Edema is an abnormally large collection of fluid in the interstitial space. From the physiology of capillaries and lymphatics, edema may be due to one or more of the following causes:

Mechanism of Edema (1) Capillary pressure Right heart failure –systemic edema Left heart failure – pulmonary edema Late pregnancy – edema in legs and foot (pressure of uterus on inferior vena cava)

(2) Plasma colloid osmotic pressure Protein malnutrition, liver disease (inadequate albumin synthesis ) or renal disease (protein loss in urine) – hypoproteinemia – low plasma colloid osmotic pressure (3) Permeability of capillary wall Inflammation or allergy – leakage of abnormally large quantities of proteins from capillaries

Factors that Affect Capillary Exchange Edema = increased Interstitial Fluid 1. Increased BHP (blood hydrostatic pressure) a. increased CO (cardiac output) b. increased blood volume 2. Increased Permeability of Capillaries a. Increased IFOP (intracellular fluid osmotic pressure b. Bacteria c. Tissue damage

Edema = increased Interstitial Fluid 3. Decreased reabsorption a. Decreased BCOP(blood capillary osmotic pressure: liver disease, burns, kidney disease b. Lymphatic blockage: cancer and parasites

Elephantiasis – blockage by parasitic worms

Thank you,,

Haemodyanamics lecture objectives: the objective of this lecture is to discuss the major laws and principles involved in the dynamics of flow of blood and lymph which include the relationship between pressure,flow and resistance; factors affecting vascular resistance; the relationship between blood flow velocity, cross-sectional area and blood flow; the application of Laplace’slaw in cardiovascular physiology; and review starling s forces affecting fluid movement across capillaries. Learning outcomes At the end of the lecture, students should be able to: 1. Define the terms pressure and resistance. Describe the inter-relationship between velocity, flow and cross sectional are. 2.Compare and explain the relationship between pressure, flow and resistance. 3.Explain the Poiseuille- Hagen formula and its relevance to circulatory system 4.Define total peripheral resistance (TPR). Describe the factors affecting total peripheral resistance. 5.Describe the applications of law of Laplace in cardiovascular physiology. 6.Describe streamline flow, turbulent flow, Reynold’s number and cardiac murmurs. 7.Review the role of various forces affecting fluid movement across the capillaries; 8.Review the function of the lymphatic circulation. 9.Review the basic pathophysiologic mechanisms of oedema.