INTRODUCTION TO SPORT SCIENCE SESSION 4 BLOOD FLOW

INTRODUCTION TO SPORT SCIENCE SESSION 4: BLOOD FLOW

Contents 1) Theory (20 min) 2) Practical (20 min)

BLOOD • Blood represent approx 8% of the body weight. • Approx. 5. 5 L in men and 5. 0 L in women • Formed of: – Water (90%) – Proteins – Cells: Red blood cells (carry oxygen) White blood cells (help fight against disease) Platelets (aid in clotting the blood after a cut)

Systemic Circulation q Oxygen rich blood is pumped from the L atrium L ventricle aorta to the organs and tissues of the body (except the lungs) and then to the R atrium q Transfer of gases, nutrients and waste products occurs in the capillary beds

Blood Flow = Pressure/Resistance

Blood Flow q Volume of blood flowing through a vessel, an organ or the entire circulation in a given time (ml/min)

Blood Flow: Rest vs. Exercise

Flow P Pressure difference is the driving force that pushes the flow of liquid through a pipe or blood vessel Resistance Measure of the various factors that hinder the flow of liquid through a pipe

Direction of Flow q What happens to the air inside a balloon if you move your fingers from the nozzle? q Rushes out q Why? q Difference in pressure between the inside the outside of the balloon q Air will flow from area of high pressure to area of low pressure

Bulk Flow q Driving force for flow is always a pressure gradient q Direction of flow is always down a gradient from a region of higher pressure to a region of lower pressure

Pressure Gradients q Single blood vessel represented by a tube connecting two reservoirs containing liquid q Pressure at either end of the blood vessel is determined by the vertical distance from the vessel to the surface of the liquid (hydrostatic pressure) q Difference in pressure in the 2 reservoirs produces a pressure gradient q Is there a pressure gradient in the example?

Role of the Heart in Generating Pressure Gradient 1. Primary function of the heart is to generate the pressure that drives the flow of blood through the body’s blood vessels 2. By pumping blood into the arteries the heart raises pressure in the arteries 3. Creates a difference in pressure between the arteries and veins that drives the flow of blood

Pressure Gradients q Pressure gradually as blood flows from arteries to veins q Blood enters the systemic circulation at an average pressure of ~ 90 mm Hg q The pressure in the large veins entering the right side of the heart is approx 0 mm. Hg q The pressure difference is 90 -0 = 90 mm. Hg

Resistance 1. Measure of the friction that blood encounters as it passes through the blood vessels 2. Measures how difficult it is for blood to flow between 2 points at a given pressure difference 3. Since most friction is encountered in the peripheral (systemic) circulation it is termed peripheral resistance (PR)

Resistance q For a given pressure gradient a vessel with a higher resistance yields a lower flow q For a given pressure difference blood flow is greater when resistance is lower because it is easier for blood to flow

Sources of Resistance 1. Length of the tube 2. Diameter of the tube 3. Fluids viscosity - “thickness” or “syrupiness”

Resistance: Blood Vessel Length q The longer the total vessel length the greater the resistance encountered q For the most part constant (except during growth) blood vessels do not change in length

Resistance: Blood Vessel Diameter q Changes in blood vessel diameter significantly alters resistance q Changes in resistance to blood flow in the CV system almost always result from changes in the diameter of blood vessels q The diameter of blood vessels can change because they contain smooth muscle that can relax and contract q Relaxation of smooth muscle causes an in vessel radius (vasodilation) and a in resistance q Contraction of smooth muscle causes an in vessel radius (vasoconstriction) and a in resistance

Resistance: Blood Viscosity q Related to the thickness of a fluid q Blood is much more viscous than water because it contains formed elements and plasma proteins - flow more slowly under the same conditions q The greater the viscosity the less easily molecules slide past one another - more difficult to get and keep fluid moving q Blood viscosity is fairly constant q May be altered –polycythemia , anemia or dehydration

PRACTICAL Effect of vessel diameter and fluid viscosity on flow

1. EFFECT OF VESSEL DIAMETER AND FLUID VISCOSITY ON FLOW Equipment • Straws of different length and diamter (long and narrow straw, short and wide straw) • Cocoa powder (or similar) • Full fat milk • Water • Container Protocol Fill a container with water, and another with milk with different amounts of cocoa powder added. Drink from the 2 glasses using the different straws.

1. EFFECT OF VESSEL DIAMETER AND FLUID VISCOSITY ON FLOW - Results What was the easiest combination? q Long and narrow straw with milkshake? q Short and wide straw with milkshake? q Long and narrow straw with water? q Short and wide straw with water?

1. Discussion q Why do you think it was easier to drink with one straw than with another? q What were the factors affecting the flow of milk through the straw?

Teachers Resource – Sources of Resistance Length of the Tube: The longer the total vessel length the greater the resistance encountered. For the most part constant (except during growth) blood vessels do not change in length.

Teachers Resource – Diameter Changes in blood vessel diameter significantly alters resistance Changes in resistance to blood flow in the CV system almost always result from changes in the radii of blood vessels. Relaxation causes an in vessel radius (vasodilation) and a in resistance Contraction causes an in vessel radius (vasoconstriction) and a in resistance. Resistance varies inversely with the fourth power of the vessel radius (½ the diameter) If the radius of a vessel is doubled the resistance is 1/16 as much. The radius of blood vessel 2 fold increases its resistance 16 (if the pressure is held constant)

Teachers Resource - Viscosity Related to the thickness of a fluid Blood is much more viscous than water because it contains formed elements and plasma proteins – flow more slowly under the same conditions. Milkshake is similar to blood in this respect The greater the viscosity the less easily molecules slide past one another - more difficult to get and keep fluid moving Blood viscosity is fairly constant. May be altered -polycythemia, anemia or dehydration Polycythemia is related to blood doping and in particular erythropoietin. Ask the class to find out about erythropoietin. They should now it beneficial and harmful effects. Ask the class to find out about hematocrit, and explain why high hematocrit levels can result in death Ask the class to research blood doping, particularly in relation to cycling and distance running Question to pose to the class: What is the maximal hematocrit level allowed in the Tour de France? Why was the value set at that level? Ask the class to determine how dehydration could increase blood viscosity