Cardiopulmonary Function in Exercise 2023 PDF

Cardiopulmonary Function in Exercise MEDI221/EXSC221 Lecture Objectives: Review the structure of the cardiovascular system and its components Review the function and control of the cardiovascular system and its components Describe changes in function of the cardiovascular system in...

Cardiopulmonary Function in Exercise MEDI221/EXSC221 Lecture Objectives: Review the structure of the cardiovascular system and its components Review the function and control of the cardiovascular system and its components Describe changes in function of the cardiovascular system in response to exercise acutely Compare athletes and a non-athlete in terms of their cardiovascular structure and function  Lecture Objectives: Briefly review cardiovascular system (CVS) structure and function Overview CVS responses to exercise Generally, have ~ linear relation with VO2 & workload VO2max depends on heart rate (HR), stroke volume (SV), O2 carried, O2 extracted Focus on heart: Cardiac output (Q) = HR x SV Effects of time, intensity, age, fitness level and sex Important application for exercise prescription What determines or controls SV and HR Reading Chapter 15 & 16. The Cardiovascular System / Regulation and Integration McArdle, W.D., Katch, F.I. and Katch, V.L. Exercise Physiology: Nutrition, Energy and Human Performance. Lippingcott, Williams and Wilkins, Sydney, NSW, 2014. ISBN/ISSN: 9781451191554. Review CVS Functions Primarily Transport Work: Pump/ control blood flow Supply cells with O2 Remove products of cellular metabolism Mediated by perfusion of 10-40 billion capillaries Heat regulation (organ and whole body) Transport endocrine hormones Immune functions Review CVS Structure Two systems in Series: Pulmonary: low pressure, reoxygenation Systemic: high pressure, deoxygenation Each has arteriesarteriolescapillariesvenulesveins Systemic is far more complex! How does the body accommodate the increased Oxygen demand of active muscles during exercise: 1. Local vessels dilate to increased metabolites 2. Cardiac output  (linear with work rate) 3. Blood flow redistributed in favour of active muscle 4.  oxygen extraction from each unit of blood (mainly intrinsic)  proportion going to active muscle  PO2 gradient blood to muscle- faster rate of gas exchange  offloading from Hb (Bohr effect) (Figure 17.3 In Text) CVS control Net flow to each tissue is a balance of intrinsic & extrinsic control: Intrinsic control - is inherent in an organ; the organ can maintain homeostasis within itself Example: the heart can control its own HR Extrinsic control exists outside of the organ (i.e., nervous and endocrine systems) and importantly these systems can override intrinsic systems. Example: HR during exercise is increased because or extrinsic control (Adrenaline) Extrinsic control mediated mainly by SNS (via Nad & Ad) Arterioles in each tissue respond differently To Extrinsic factors (Nad & Ad, Arterial Pressure) To Local factors (Metabolites) Key concepts in CV response to exercise Four ways active muscle gets more blood in exercise: 1. Local vessels dilate to increased metabolites (intrinsic control) 2. Cardiac output  (linear with work rate) (mostly by extrinsic control) 3. Blood flow redistributed in favour of active muscle (intrinsic & extrinsic) 4.  oxygen extraction from each unit of blood (mainly intrinsic) Net flow to each tissue is a balance of intrinsic & extrinsic control External control mediated mainly by SNS (via Nad & Ad) Review Heart & Cardiac Cycle Review Chapter 16 Text book Anatomy & direction of flow Electrical properties (mediated by SNS and PNS) Autorhytmicity Long AP (separate contractions) Electrical conduction system Myocardial structure Oxidative fibre type  Mitochondrial “density” Mainly FFAs at rest Lactate under hard exercise Review Heart & Cardiac Cycle Systole Diastole Isovolumetric phases Duty cycle: REST: 0.3 : 0.5 s HEAVY EXERCISE: 0.2 : 0.13 s Cardiovascular Adjustments to Exercise VO2 rises linearly with Power Output, and Qc rises linearly with VO2 So aerobic power & fitness depends on ability to: 1.Increase Qc (SV and HR) 2. Carry arterial oxygen 3. Redistribute blood flow to active muscle 4. Extract oxygen from blood in those muscles  Sex and fitness differences in Cardiac Output Sedentary Males have a higher CO than females. During Submax Exercise (same absolute workload) CO is 5-10% higher in females Less O2 per unit blood because 10-15% less Hb During Max Exercise: Max cardiac output ~20% higher in males Can  4-5 times in untrained, vs 6-8 times in trained Stroke Volume Time Exercise intensity Fitness level Hydration/temperature Stroke Volume response with exercise TIME Across exercise time: Rapid to large  to plateau  rise in athletes Less rise if arm exercise Higher BP (afterload)  later with dehydration and heat stress  central blood volume Stroke Volume response to exercise INTENSITY Athletes: have higher SV at rest than sedentary people even reach during exercise!! maintain  SV over much bigger range of intensity till ~50% VO2max in untrained till ~100% VO2max in athletes have  SV at rest and any exercise intensity so HR is proportionately  Determinants of Stroke Volume in exercise 1. End Diastolic Volume (Preload) 2. Contractility (Frank Starling Mechanism) 3. Mean Arterial Pressure (MAP) Determinants of Stroke Volume in exercise EDV -> Venous Return ‘how much blood is returning back to the heart’ Blood volume is an important determinant Hydration Determinants of Stroke Volume in exercise EDV -> Venous Return ‘how much blood is returning back to the heart’ Blood volume is an important determinant Training: LV wall thickness Heart Rate Time, Exercise intensity Fitness level Sex Heart rate response with exercise TIME Rapid to large  to plateau  PNS activity on SA node  SNS activity on SA node Much less rise in athletes! Higher SV More rise if arm exercise More SNS activity  later with dehydration with and heat stress  central blood volume Heart rate response to exercise INTENSITY Rises linearly, till 100% VO2max Untrained have a higher HR at rest and throughout exercise. Untrained higher and steeper rise to maximal HR. Reach a similar HRmax but athletes will do so at a much higher work rate. What determines Heart rate in exercise? Brake Accelerator Remember: VO2 = SV x HR x a-vO2 difference  Control of HR Initially due to withdrawal of PNS Proportion of input PNS SNS Exercise Intensity Max HR drops with age ~ linear effect HRmax = 220 – age (± 10bpm) Due to  adrenoreceptor sensitivity Major component of  in max Qc with age Also  muscle quality? (disuse vs aging?) Also valve stiffness Implications of Heart Rate Responses Resting heart function important Determines HR range (i.e. Cardiac Reserve) Potentially valuable indicator of health status Low HR indicates less cardiac O2 demand & high potential for power Fast recovery from (standardised) exercise provides basic indicator of higher aerobic fitness Slower rate of rise in HR generally good Note: Can also reflect anti-hypertensive therapy (alpha blocker) Summary of the Control of Cardiac Output: Cardiac Output (Qc) = SV x HR Stroke volume: Intrinsic (Autoregulation): Frank- Starling Law of Heart = contractility if  EDV because heart operates below optimal length Extrinsic: Direct neural from SNS Ad & Nad from Adrenal Medulla SNS & other effects on blood vessels HR: Direct neural drive (balance of SNS & PNS) Hormonal from SNS on Adrenal Medulla