Cardiovascular System

Transcription

1 Cardiovascular System Major Jobs of the CV system? Transport O 2 & nutrients to tissues Removal of waste Helps regulate body temperature 1

2 A Coupled Unit Circulatory & Respiratory systems work TOGETHER Respiratory: Adds O 2 & Removes CO 2 Circulation: delivery Pulmonary circuit right side Pumps deoxygenated blood from RV to the lungs via pulmonary arteries (aorta) Pulmonary vein Returns oxygenated blood to the LA via pulmonary veins Systemic circuit left side Pumps oxygenated blood from LV to the whole body via aorta Returns deoxygenated blood to the RA via vena cavae 2

3 Arteries, Capillaries & Veins What s unique to veins? 3

4 What s the job of the heart? To create P to pump the bld 4

5 What cell types exist in the myocardium? Contractile & Electrical 5

6 What are the 2 phases of a cardiac cycle? Think mechanical phases 6

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9 Volumes of the Heart Stroke Volume (SV) 80mL End-diastolic volume (EDV) 125 ml End-systolic volume (ESV) 40 ml Ejection Fraction % of EDV pumped by ventricles Normal.67 (LV) &.54 for right = EDV-ESV/EDV Cardiac output Electrical Activity Resting heart tissue is polarized. Cells are on the inside, and + on surface Heart muscle must DEPOLARIZE for it to contract 9

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12 Cardiac cycle Determinants of cardiac performance (i.e. Q)?? 6 items Preload Afterload Contractility HR Synergy of Ventricular contraction Distensibility of the Ventricles 12

13 Preload End-diastolic pressure extent to which the heart chambers are STRETCHED when they fill with bld. Frank-Starling mechanism: relationship b/w myocardial stretch & SV Rubber band principle: Stretch, d pressure, d SV, usually s stroke work. How does EDV impact SV? Frank-Starling Mechanism: The more the ventricles are stretched (i.e. greater EDV) the more forceful the contraction. High Contractility control SV (ml) Low Contractility EDV (ml) 13

14 Factors Affecting Preload w/ EXERCISE Q (i.e. venous return) Bld volume Muscle/Thoracic pump Posture Heart size Venous tone Bld shunting 14

15 Geometric Heart Size Any in internal radius of chambers of heart are going to increase the energy needed for contraction. Law of Laplace: Tension = Pressure * Radius 2 15

16 A word on SV & Posture What is the standard response to SV with acute exercise? Does SV really w/ ex? Supine resting SVI = 57 Upright maximal SVI = 58 16

17 Body Position & SV during ex Cardiac Index Stroke Index Supine Sitting Rowland et al, Int J Sports Med, 2003 Body Position & SV during ex HR LVED LVES Rowland et al, Int J Sports Med,

18 Take Home Message Body Position SV only s during upright ex SV does not beyond supine rest Thus, the conventional thought that SV s during ex is probably wrong s in SV w/ upright ex is probably mobilization of bld volume and refilling of the heart i.e. improved venous return Determinants of cardiac performance (i.e. Q)?? Preload Afterload Contractility HR Synergy of Ventricular contraction Distensibility of ventricles 18

19 Afterload - tension before shortening Aortic pressure (BP) Valvular resistance Distensibility of the vascular system Peripheral resistance Physiological responses of d afterload??? s shortening velocity Heart then tries to contractility why?? Example: Weight lifting d afterload in SV (acutely) EDV in next cycle: WHY??? 19

20 Why is resistance ex associated w/ d afterload?? Valsalva s intrathoracic pressure, partially responsible for d afterload. Upper body exercises smaller muscle mass, bld flow is slower. RE places a pressure load whereas endurance ex places a flow load (i.e. volume). Determinants of cardiac performance (i.e. Q)?? Preload Afterload Contractility HR Synergy of Ventricular contraction Distensibility of ventricles 20

21 Contractility quality of ventricular performance at constant conditions of loading & HR Higher contractility = d SV High Contractility control SV (ml) Low Contractility EDV (ml) Fig

22 With regards to muscle force how are cardiac & skeletal muscle different? Determinants of cardiac performance (i.e. Q)?? Preload Afterload Contractility HR Synergy of Ventricular contraction Distensibility of ventricles 22

23 HR Probably considered the most important determinant of Q, especially during exercise. Why? 23