Body Fluid Compartments Chapter 9 Circulatory Adaptations to Exercise Part 4 Total body fluids (40 L) Intracellular fluid (ICF) 25 L Fluid of each cell (75 trillion) Constituents inside cell vary Extracellular fluid (ECF) 15 L Interstitial Cerebrospinal Intraocular GI Body Fluid Compartments Blood Volume Blood volume (5 L) Plasma (3 L) Liquid portion of blood Ions, proteins, hormones Cells Red blood cells (2 L) Contain hemoglobin White blood cells Immune system Platelets Clotting Blood Volume Viscosity 1
Hemodynamics The study of the physical principles of blood flow Based on interrelationships between: Pressure Resistance Flow Hemodynamics: : Pressure Blood flows from high to low pressure Flow will be proportional to the difference between pressure in aorta and right atrial pressure Blood Flow Through the Systemic Circuit Hemodynamics: : Blood Flow Directly proportional to the pressure difference between the two ends of the system Flow = Δ Pressure Resistance Hemodynamics: : Flow Q = MAP/TPR Q MAP Q TPR Hemodynamics: : Resistance Inversely proportional to resistance Flow = Δ Pressure Resistance 2
Hemodynamics: : Resistance Resistance depends on: Length of vessel Viscosity of blood Radius of vessel A small change in vessel diameter can have a large impact on resistance. Resistance = Length x viscosity Radius 4 Vascular Anatomy Aorta largest artery Muscular Arteries smaller, thicker Resistance vessels (small arteries) Arterioles smaller, 1-21 2 layers of smooth muscle cells in walls Heavily innervated by SNS Capillaries Thin walled, nutrient and gas exchange Vascular Anatomy Venules small vessels extend from capillaries Some smooth muscle With capillaries comprise microcirculation Veins capacitance vessels Smooth muscle in walls Innervated by SNS Blood reservoir (60%) Affected by posture and activity Pressure Changes Across the Systemic Circulation Distribution of Blood Flow Local blood flow control Metabolic regulation - acute control Tissue needs Oxygen Nutrients, glucose, amino acids, fatty acids CO 2 and H + removal Maintenance of ion concentrations Transport of hormones Fig 9.16 3
Acute Control Tissue needs Changes in local constriction of Arterioles Metarterioles Precapillary sphincters Acute Control Autoregulation Vessel s s ability to self regulate blood flow depending on the tissue needs (VC, VD) Vascular smooth muscle is sensitive to stretch Increased pressure (exercise) Smooth muscle contracts in response to stretch Helps maintain constant blood flow to tissues Low pressure Smooth muscle relaxes in response to lack of stretch Blood Distribution Blood flow redistribution with exercise Autoregulation Extrinsic Control (SNS) Blood Flow Distribution Exercise Autoregulation Maintaining blood flow to meet tissue needs VD in active tissues VC in less active tissues helps maintain local BP Extrinsic neural control SNS Diverting blood volume to areas of increased metabolic need Metabolic Regulation Factors causing VD with exercise Increased metabolites Adenosine, CO 2, lactic acid, histamine, potassium ions, hydrogen ions, temperature of muscle, Decreased oxygen Vasodilatory substances Relaxing factors Nintric oxide, prostacyclin,, endothelium-derived derived hyperpolarizing factor 4
Distribution of Blood Flow Depends on needs of individual tissues Rest Liver (27% Q) Kidneys (22% Q) Skeletal muscle (15%- 20% Q) Exercise Skeletal muscle (80% Q) Renal and splanchnic (5%) After a meal Hot environment Prolonged Exercise Submaximal exercise < 30 min Neutral environment Little need for compensation Submaximal exercise > 30 min Neutral environment Constant workload, metabolic requirement Progressive decrease in venous return decreased SV Prolonged Exercise Compensatory measures Progressive rise in HR Cardiovascular drift Cardiac drift Due to Breakdown in sympathetic blood flow control Increased distribution of blood to skin, cooling Both Cardiac Drift Long term BP control Kidneys Acute BP control with exercise Circulation 5
MAP = Q x TPR MAP best reflects the pressure perfusing the tissues at any moment Exercise Q increases TPR decreases Net result BP maintained BF to critical areas-heart, brain MAP Pmean = diastolic pressure + 1/3 (systolic diastolic) Pulse pressure MAP is not exact average because the heart is in diastole longer than systole So equation is weighted towards diastolic Systolic Mainly influenced by SV LV ejection velocity Aortic/arterial stiffness Diastolic Rises with increase in TPR During LV ejection, pressure energy is absorbed by the walls of the aorta and arteries as these structures expand. During LV diastole, energy is returned to the blood as the walls of the aorta and arteries contract. This helps to sustain diastolic blood pressure peripheral blood flow. 6
Maximum systolic pressure 150 to 250 mmhg Failure of SBP to increase Suggest heart failure Falling SBP at end of exercise test-stop Diastolic blood pressure-exercise exercise Little or no change + 10 mmhg >15 mmhg-coronary artery disease Arm vs Leg Work Greater BP response with upper body work Smaller muscle mass Smaller vasculature More resistance to blood flow Increases blood pressure to overcome resistance Rate Pressure Product Myocardial Oxygen Consumption SBP x HR Arms 190 x 190 = 36,100 Legs 160 x 190 = 30,400 7