Circulatory Responses to Exercise PDF

Circulatory responses to exercise Fundamentals of Sport and Exercise Science PSA762 Dr Laura A. Barrett By the end of this lecture you should be able to: appreciate the functions of the C.V system describe the characteristics of the components of the C.V system Outline the ca...

Circulatory responses to exercise Fundamentals of Sport and Exercise Science PSA762 Dr Laura A. Barrett By the end of this lecture you should be able to: appreciate the functions of the C.V system describe the characteristics of the components of the C.V system Outline the cardiac and circulatory responses to exercise  Delivery Removal Functions of the C.V system Transport Protection Maintenance The components of the circulatory (cardiovascular) system A fluid medium - BLOOD A system of channels - BLOOD VESSELS (the vascular system) A pump - THE HEART Structure of the Heart Figure 9.1 Composition of total blood volume Plasma volume and endurance training 3.4 2.8 Plasma volume 56% 59% The Vascular System The Vascular System Branching system Vessel Lumen Wall Total % Blood diameter thickness x-sectional volume area (cm2) contained Aorta 2.5 cm 2 mm 4.5 3 Artery 0.4 cm 1 mm 20 10 Arteriole 30 m 20 m 400 2 Capillary 5 m 1 m 4500 5 Venule 20 m 2 m 4000 Vein 0.5 cm 0.5 mm 40 64 Vena Cava 3 cm 1.5 mm 18 Arterioles - ‘resistance vessels’ Determine blood flow to individual organs – important in the redistribution of blood flow with exercise intrinsic control extrinsic control (autoregulation) (vasomotor tone - SNS) Vasodilation Vasodilation Vasoconstriction  O2,  CO2,  H+,  K+  adrenaline  noradrenaline (-receptors) (-receptors)  SNS discharge Redistribution of blood flow with exercise Venous System - ‘capacitance vessels’ Low pressure, easily distended Blood = ~ 50% H2O hydrostatic pressure ‘venous pooling’ ‘postural hypotension’ Critical thinking challenge What are the physiological mechanisms to overcome this?? Venous valves and muscle pump Summary - components of the cardiovascular system The heart consists of 2 pumps that pump together 2 circuits: ‘pulmonary’ (right side), ‘systemic’ (left side) Arteries and arterioles ‘resistance vessels’ carry blood away from the heart determine redistribution of blood flow during exercise Capillaries Exchange of O2, CO2, and nutrients with tissues Veins and venules Carry blood toward the heart Skeletal muscle pump (and deeper breathing?) increases the amount of venous blood returning to the heart during exercise. Cardiac Output (Q) - definitions Q = total volume pumped out by each ventricle per minute (l/min) Q = heart rate (HR) x stroke volume (SV) SV = the blood volume ejected by each ventricle with each beat (ml) SV = End Diastolic Volume (EDV) - End Systolic Volume (ESV) Regulation of heart rate Parasympathetic nervous system Via vagus nerve Slows HR by inhibiting SA and AV node Sympathetic nervous system Via cardiac accelerator nerves Increases HR by stimulating SA and AV node Low resting HR due to parasympathetic tone Increase in HR at onset of exercise Initial increase due to parasympathetic withdrawal Up to ~100 beats/min Later increase due to increased SNS stimulation Factors affecting Stroke Volume  force of contraction  SV Two main ways: 1.  sympathetic nervous system activation effects of circulating adrenaline and noradrenaline direct stimulation of the heart muscle 2.  EDV length-tension relationship  EDV  stretch of ventricular sarcomeres  stretch  force of contraction also training : may  LV compliance?  EDV - The Frank -Starling Mechanism “Force of contraction is proportional to fibre length” sympathetic 200 stimulation SV (ml) 100 Normal resting value 100 200 300 400 EDV (ml) Major factors affecting EDV  activity of  blood  skeletal  inspiration sympathetic volume muscle pump movements nerves to veins Peripheral veins  venous pressure  venous return  atrial pressure  ventricular EDV Cardiac Muscle  SV Changes in Cardiac Output During Exercise Cardiac output increases due to: Increased HR Linear increase to max [Max HR = 220 – age (years)] Increased SV Increase, then plateau at ~40% VO2 max No plateau in highly trained subjects Cardiac output can  to ~35 l/min in highly trained endurance athletes  to 20-25 l/min in untrained individuals Higher in males males have higher SV and lower HR Transition from rest to submaximal exercise to recovery Cardiovascular changes during prolonged exercise ↓ venous return ‘cardiac drift’ Summary: circulatory adjustments with exercise Oxygen delivery to exercising skeletal muscle increases due to: increased cardiac output redistribution of blood flow from inactive organs to the contracting skeletal muscle. Cardiac output increases as a linear function of oxygen uptake during exercise. stroke volume reaches a plateau at approximately 40% of VO2 max; at work rates above 40% VO2 max, the rise in cardiac output is due to increases in heart rate alone. Summary of Cardiovascular Responses to Exercise Figure 9.28 Reading Powers and Howley, Exercise Physiology: Theory and Application to Fitness and Performance. Chapter 9  Example Exam Questions 1. What are the major purposes of the cardiovascular system? 2. Briefly, outline the design of the heart. Why is the heart often called “two pumps in one”? 3. Graph the heart rate, stroke volume, and cardiac output response to incremental exercise. 4. What factors regulate heart rate during exercise? Stroke volume? 5. How does exercise influence venous return?