14. N R = pDv / η p = Density D = Diameter v = Velocity η = Viscosity laminar = 2000 or less

23. SYSTOLE DIASTOLE COMPLIANTE RIGIDO

114. Q=10ml/s A= 2cm 2 10cm 2 1cm 2 V= 5cm/s 1cm/s 10cm/s V = Q / A abc

116. 0 0 100 200

117. 0 20 40 60 80 100 120 mmHg Presión Sistólica Presión Diatólica Notch Dicrotico } Presión pulsatil MAP=(1/3 PP) + DP ~

128. THE ANATOMY OF BLOOD VESSELS Layers: 1.Tunica interna (intima): 2.Tunica media: 3.Tunica externa (adventitia):

129. Comparison of Veins and Arteries Arteries:Veins:

130. Histological Structure of Blood Vessels Notes

131. Capillary Structure Notes Continuous Capillary Fenestrated Capillary

132. The Distribution of Blood

133. Cardiovascular Physiology Pressure- –Blood pressure –Hydrostatic pressure –Venous pressure

134. Cardiovascular Physiology Resistance (total peripheral resistance) –Vascular resistance –Viscosity –turbulence

135. Blood pressures and the vascular system

136. Blood pressures and the vascular system Arterial Pressure- Venous Pressure-

137. Capillary Exchange Diffusion: Filtration: Reabsorption:

138. Capillary Exchange

139. Regulation of Cardiovascular System Overview-

141. Regulation of Cardiovascular System Autoregulation of Blood Flow

142. Regulation of Cardiovascular System Neural Mechanisms –Vasoconstriction –Vaosdilation –Baroreceptors –Chemoreceptors

145. Control of Cardiovascular Function - Hormones ADH- Angiotensin- Erythropoietin- ANP

146. Control of Cardiovascular Function – Hormones Decreased Blood Pressure

147. Control of Cardiovascular Function – Hormones Increased Blood Pressure

148. The Circulation 1.Hemodynamics 2.Vascular Control 3.Regulation of Blood Flow, Oxygen Exchange 4.Blood Pressure

149. The area of physics that considers the flow of blood through tubes like blood vessels assumes long tubes where the tube length is >> than the diameter assumes rigid tube walls assumes constant flow, not pulsatile flow assumes that the fluids are ‘Newtonian’, or that the fluid viscosity is independent of tube properties Hemodynamics:

150. 2) Fluid pressure expands cardiac chambers and blood vessels, and is used to sense pressure and store blood in sites in the vascular system Fluid pressure in the vascular system 1) Pressure gradient produced by heart pumping moves blood in the system from the arterial to the venous side, 5 l/min

151. Hydrostatic pressure depends on where you measure it in the vascular system P P=h  g P=Pressure h=height  =density g=gravitational constant Hydrostatic Pressure

152. h The pressure at any given depth (h) in the liquid is the same no matter what shape the vessel. This is intuitively confirmed by the surface liquid level is the same in all the chambers.

153. Hydrostatic pressures - Effects of gravity and applied pressure

154. Effect of Hydrostatic Pressure on Venous Pressures Throughout the Body Heart level CVP = 0 mmHg (because heart pumps out any excess of blood that would accumulate at this level) Every 13.6 mm Hg distance away from the heart there is a 1 mmHg pressure change (also affects arterial pressure) Pressure veins arteries difference -1070  P=80 0 0100  P=100 11 22 35 40 90190  P=100

155. Effect of body position on pulmonary capillary blood flow (hydrostatic effect) Zone 1 (no flow) Zone 2 (intermittent flow, only during that part of systole, when Palv<Pcap) Zone 3 (continuous flow) low pressure high pressure intermittent pressure

156. Airspace Capillary- Alveolar Unit Airspace Zone 3 - always flows Zone 2 - flows intermittent Zone 1 - no flow P alv >> P cap P alv = P cap flows during systole and stops during diastole P alv << P cap Zonal flow and gravity Alveoli Capillary-Alveolar Unit Airspace

157. Gravitational Effects and Transmural Pressure Transmural pressure = Pressure inside a vessel - Pressure outside the vessel If transmural pressure is rel. low, little impact on effective blood pooling 10 mm Hg -2 mm Hg if P cap increases transmural pressure is high, transcapillary fluid filtration Increases, moves into ISF, decreases effective blood volume, and produces edema 90 mm Hg Transmural = “across the wall”

158. Orthostatic Hypotension Jump up or stand up suddenly Decreased venous return Decreased cardiac output Decreased central blood flow Collapse Removes hydrostatic effects Increases venous return Increases cardiac output Increases cerebral perfusion Conscious

159. Jump up or stand up suddenly Decreased venous return Decreased cardiac output Decreased central blood flow Collapse Removes hydrostatic effects Increases venous return Increases cardiac output Increases cerebral perfusion 100 756050 100756050 Orthostatic Hypotension Conscious

160. Muscle and respiratory ‘pumps’ help minimize pooling and edema formation in the periphery Muscle pump Respiratory pump

161. Muscle Pump 1. Muscle contracts, segment empties 2. Muscle relaxes, column is interrupted 3. Muscle relaxes, refilling from below

162. Venous pressure and muscle pumping When the venous pressure is measured in a leg vein at rest (in a standing individual) the pressure is relatively high. However, immediately on starting rhythmic contraction of the leg, the valves force out fluid and pressure is decreased.

163. Respiratory (Abdominothoracic) Pump Inspiration decreased intrathoracic pressure increased transmular pressure in thoracic cavity distends vessels decreased resistance and effective ‘suction’ of blood enhanced venous return depress diaphragm increase abdominal pressure decrease transmural pressure pushes blood to the heart Both enhance venous return - valves prevent reflux Expiration - opposite effects occurs but less dramatic - overall effect is to increase venous return Expansion of chest

164. Respiratory Pump Inspiration decreased intrathoracic pressure, increased transmular pressure in thoracic cavity distends vessels, decreased resistance and effective ‘suction’ of blood enhanced venous return depress diaphragm increase abdominal pressure decrease transmural pressure pushes blood to the heart Both enhance venous return valves prevent reflux Expiration - opposite effects occurs but less dramatic overall effect is to increase venous return net vacuum net pressure

165. Varicose Veins Varicose veins - edema formation - by continually maintaining the hydrostatic column creates blood pooling the edema can close off arterioles which causes decreased perfusion leading to ulcerative thrombosis Valves may have been congenitally defective or any condition that impedes venous return, pregnancy, large abdominal tumor (how?) Increased venous pressure venous distension valvular incompetence damage to venous valves

166. Varicose Veins Normal Varicose widening of the vein, or damage to the valves from continuous high pressure

167. Blood flow or ‘‘Q B ‘‘ = volume of blood delivered per unit time Volume flow/Unit time e.g. C.O. = 5l/min Skeletal muscle = 4 ml/min/100g at rest Velocity ‘‘Mean linear flow velocity’’ = V the displacement in time of a particle of blood BLOOD FLOW RATE vs. VELOCITY

168. Mean velocity = flow / cross sectional area V = Q B / CSA, then, V X CSA = Q B, cm/sec = ml/min/cm 2

169. Idealized tube without friction, end pressures (total energy) is same, but pressure goes up in segment 2 and down in 3 End pressure (Total energy) End pressure (Total energy) End pressure (Total energy) Pressure (Potential energy) Pressure (Potential energy) Pressure (Potential energy)

170. Fluid drag on the walls of the tube creates a resistance to flow through the tube. Idealized tube with friction, end pressures (total energy) decrease from 1 to 2 to 3 because of fluid drag. Side pressure is still less than end pressure as determined by flow velocity.

171. Driving force for flow = energy imparted to the blood by the heart Total fluid energy = potential energy (pressure)+ kinetic energy (1/2  v 2 ) + gravitational potential energy (  gh) + thermal energy (u) Total energy = P +1/2  v 2 +  gh +u  density

172. Summary 1.In the cardiovascular system, pressure (potential energy), converts to kinetic energy when tube cross sectional area decreases, and increases fluid velocity 1.As blood moves through the cardiovascular system it loses energy due to friction between the blood and the vessel walls,

173. Clinical relevance of pressure in CV system Aneurysm thinned wall Aneurysms or Post-stenotic dilation Increased vessel radius, creates increased cross sectional area, decreased velocity leads to increased lateral pressure and distends already tense vessels, can burst the vessel under some conditions Post-stenotic dilation stenosis

174. Resistance to Blood Flow 1.Blood flow overcomes the forces of friction between the wall and the blood 2.The main function of the heart is to replace energy lost as fluid drag

175. Vascular Resistance mm Hg/L/min 12 9 6 3 0 Where is there the most resistance in the vascular tree? Flow is always 5 l/min in all segments (art, caps, veins) as a whole. large arteries small arteries arterioles capillaries veins pulmonary vessels = 3 7 57 15 10 18 Pressure mm Hg 100 80 60 40 20 0 R=P/Q B site of highest resistance Pressure Drop large arteries small arteries capillaries Pulmonary vessels

176. Determinants of Vascular Resistance Vessel Diameter Small changes in diameter result in enormous changes in flow Poiseulle’s Law: Flow proportionate to Diameter 4 Thus, large arteries have little resistance while small arterioles have a tremendous resistance. Viscosity Greater viscosity = greater resistance Normal viscosity of blood is 3 x that of water; determined largely by the number of red blood cells (hematocrit), which create a frictional drag between cells and blood vessel wall Normal hematocrit ~ 40 (42 for men, 38 for women)

177. Poiseuille’s Law Relation between Pressure and Flow Assumes: 1.Cylindrical tubes w/ constant diameter where the length >> radius 2.Laminar not turbulent flow 3.Newtonian flow - homogeneous fluid with a constant viscosity 4.Rigid walls 5.Steady, non-pulsatile flow 6.Horizontal flow - no gravitational effects

178. Relationships Among Pressure, Resistance, and Blood Flow  P = Q x R R =  P/Q

179. Effect of Vessel Diameter on Blood Flow

180. Poiseuille’s Law (relates pressure, flow and resistance) P=Q X R Resistance = (8L  )/  R 4 = P/Q B, P = Q B [8L  )/  R 4 ] where, P = pressure gradient, like artery to vein Q B = blood flow L = length  = viscosity R = radius (since this term is to the 4 th power, radius is the principal effector of resistance) note - a 2-fold change in diameter gives a 16 fold change in resistance and flow

181. Resistance to flow and tube diameter The tubes on the right and left are of the same length, but the right tubes radius is twice as great. The resistance to flow in the left system is 16 times greater than that on the right. To keep the filling column on the right at the same level, we have to put in 16 times more fluid. Flow = 16Flow = 1

182. Fluid flow and tube length The tubes on the right and left are of the same diameter, but the right tube is twice as long. The resistance to flow is twice as high in the system on the right so the height of the column flowing into it is exactly twice as high and exerts exactly twice the pressure.

183. Resistance in Series QinQout since R = dP/Q, then Rt = R1 + R2 + R3 Resistances add in series, but in the body most vessels are arranged in parallel

184. Resistances in Parallel 1) Qt = Q1 + Q2 +Q3 2) Qt / Pin - Pout = Q1/(Pin -Pout) + Q2/ (Pin -Pout) + Q3/ (Pin -Pout) 3) 1/Res. total = 1/R 1 + 1/R 2 + 1/R 3 Qt

185. Systemic Peripheral Resistance R =  P/Q Systemic Total Peripheral Resistance (TPR) = P aorta - P right atrium /Cardiac Output = (93 mm Hg - 5 mm Hg)/5 l/min Systemic resistance to blood flow = 18.6 mm Hg/l/min

186. Pulmonary Resistance to Blood Flow Pulmonary TPR = (P pulmonary artery - P left atrium )/cardiac output = (16 mm Hg - 4 mm Hg)/(5l/min) = 2.4 mm Hg/l/min 1.Low compared to the systemic resistance of 18.6 mm Hg/l/min, 2.The lung is a low resistance microvascular bed, 3.The lung must not offer high resistance 4.This can lead to pulmonary edema (pressure mediated filtration)

187. Laminar flow The fluid nearest the vessel wall flows the slowest, and fluid in the center of the tube moves the most rapidly This produces layers (laminae) with uniform speeds at certain distances from the wall If the flow rate is increased then the trend for turbulence will increase

188. Turbulence Flow Pressure Gradient critical velocity Q dPQ dP i.e. it takes a progressively greater force to increase flow

189. Reynold’s Number (A term that describes the tendency for turbulence to occur) Re = V D  where V = mean linear flow velocity D = diameter  = density n = viscosity 1. if the Reynold’s (Re) # < 2000, laminar flow 2. if the Reynold’s (Re) # >3000, turbulent flow n

190. Reynolds Number and Turbulence where V = mean linear flow velocity D = diameter  = density n = viscosity Re = V D  /n 1.if velocity increases, turbulence increases 2.if diameter increases, turbulence increases 3.if density increases, turbulence increases 4.if viscosity increases turbulence decreases Small diameter Large diameter

191. Clinical significance of turbulence Good: Turbulence ensures adequate mixing of blood in ventricles ‘‘Cardiohemic’’ vibrations –a) Heart sounds and murmurs –b) Korotkoff sounds Bad: Thrombus formation 1.Generation of atherosclerotic plaques 2.Plays roles in development of aneurysms 3.Anemia - Decreased viscosity promotes turbulence

192. Viscosity 1.Shear stress is the force of drag applied over a unit area (F/A) 2.Shear rate is the velocity of flow at a some distance from the vessel wall 3.Viscosity = (F/A)/(v/L) = Shear stress/Shear rate F V A

193. Non-Newtonian Fluids Blood Apparent fluid viscosity changes when vessel diameter changes Apparent fluid viscosity also changes with temperature, and chemical and metabolic conditions

194. At low rates of flow there are many interactions between blood cells sticks them to each other and increases the apparent viscosity of the blood. In the dotted line, you increase pressure but flow does not go up linearly. Newtonian Fluids

195. Factors influencing Blood Viscosity 1.Hematocrit 2.Tube dimension 3.Shear rate 4.Temperature

196. Hematocrit The fraction of blood volume which is red cells Blood cells are particles High hematocrit - blood behaves more like a solid than a liquid Low hematocrit - blood behaves like a Newtonian fluid

197. Effect of Hematocrit on Viscosity

198. Hematocrit and Viscosity Hematocrit = % volume of blood which is RBC’s (normal = 40- 45%) Shear Rate Viscosity 20% 40% 60% At lower shear rates, (when flow is low), blood particles tend to aggregate and increase apparent viscosity. The higher the hematocrit, the more pronounced this effect will be.

199. Tube dimension Large tubes - blood particles don’t behave like particles (fewer interactions with the vessel wall) Small tubes – (more interactions with the vessel wall) the orientation of blood cells becomes important, as does the deformability of the red cell and the white cells in the circulation

200. Tube Dimension and Viscosity (Fahreus-Lundqvist Effect)

201. Key Points - Hemodynamics 1.Determinants of viscosity 2.Fluid drag 3.Turbulence 4.Pressure 5.Flow 6.Poiseuille’s Law 7.Kinetic Potential Energy Conversion 8.Reynolds’ Number 9.Gravitational Effects