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Exercise and Cellular Respiration - Columbia University

Kristin M Burkart, MD, MSc Assistant Professor of Clinical Medicine Outline Basics of Exercise Physiology Exercise Physiology Cellular Respiration Oxygen utilization (QO2). Oxygen consumption (VO2). Cardiovascular responses Kristin M Burkart, MD, MSc Ventilatory responses Assistant Professor of Clinical Medicine Division of Pulmonary, Allergy, & Critical Care Medicine Exercise Limitations College of Physicians & Surgeons In normal healthy individuals Columbia University Cardiopulmonary Exercise Testing Gas Transport Mechanisms: coupling of Cellular (internal) Respiration to pulmonary (external) Respiration Exercise and Cellular Respiration Exercise requires the release of energy from the terminal phosphate bond of adenosine triphosphate (ATP). for the muscles to contract. - Wasserman K: Circulation 1988;78:1060.

Kristin M Burkart, MD, MSc Assistant Professor of Clinical Medicine 2 Jones NL and Killian KJ. NEJM 2000;343:632 Major Metabolic Pathways During Exercise Aerobic Oxidation of …

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Transcription of Exercise and Cellular Respiration - Columbia University

1 Kristin M Burkart, MD, MSc Assistant Professor of Clinical Medicine Outline Basics of Exercise Physiology Exercise Physiology Cellular Respiration Oxygen utilization (QO2). Oxygen consumption (VO2). Cardiovascular responses Kristin M Burkart, MD, MSc Ventilatory responses Assistant Professor of Clinical Medicine Division of Pulmonary, Allergy, & Critical Care Medicine Exercise Limitations College of Physicians & Surgeons In normal healthy individuals Columbia University Cardiopulmonary Exercise Testing Gas Transport Mechanisms: coupling of Cellular (internal) Respiration to pulmonary (external) Respiration Exercise and Cellular Respiration Exercise requires the release of energy from the terminal phosphate bond of adenosine triphosphate (ATP). for the muscles to contract. - Wasserman K: Circulation 1988;78:1060.

2 The major function of the cardiovascular as well as the ventilatory system is to support Cellular Respiration . Exercise requires the coordinated function of the heart, the lungs, and the peripheral and pulmonary circulations to match the increased Cellular Respiration . Cellular Respiration : Mechanisms Utilized by Muscle to Generate ATP. Mechanisms for ATP generation in the muscle Cellular Respiration 1. Aerobic oxidation of substrates (carbohydrates and fatty acids). 2. The anaerobic hydrolysis of phosphocreatine (PCr). 3. Anaerobic glycolysis produces lactic acid Each is critically important for normal Exercise response and each has a different role 1. Kristin M Burkart, MD, MSc Assistant Professor of Clinical Medicine Major Metabolic Pathways During Exercise Aerobic Oxidation of CHO and FA to Generate ATP.

3 The major source of ATP production Only source of ATP during sustained Exercise of moderate intensity Jones NL and Killian KJ. NEJM 2000;343:632. Anaerobic Hydrolysis of The Glycolytic Pathway: Phosphocreatine (PCr) to Generate ATP Uses Glycogen to Generate ATP. Provides most of the high energy phosphate Produces ATP from glycogen without the need needed in the early phase of Exercise for O2 results in production of lactic acid This is used to regenerate ATP at the myofibril The energy produced by anaerobic glycolysis during early Exercise is relatively small for the amount of glycogen consumed PCr is an immediate source of ATP regeneration The consequence is lactate accumulation Anaerobic Glycolysis: During Exercise , when Uses Glycogen to Generate ATP does anaerobic glycolysis occur? Glycogen Exercising muscle energy needs cannot be met entirely by O2 and PCr-linked ATP generation NADH + H+.

4 Pyruvate Lactate Exercising muscles cells are critically O2 -poor 3 ATP 6 H2 O + 6 CO2. 6 O2 Exercising muscle fibers have different balances acetyl-CoA. of oxidative versus glycolytic enzymes Low intensity: recruit fibers that are primarily oxidative Krebs cycle NADH + H+ Electron transport chain High intensity: recruit fibers that primarily rely on glycolytic pathway 36 ATP. Mitochondria 2. Kristin M Burkart, MD, MSc Assistant Professor of Clinical Medicine Exercise results in increased oxygen utilization (QO2) by muscles Increased extraction of O2 from the blood Oxygen Utilization (QO2). Exercise results in increased Exercise results in increased oxygen oxygen utilization (QO2) by muscles utilization (QO2) by muscles Increased extraction of O2 from the blood Increased extraction of O2 from the blood During Exercise the muscle has Dilation of peripheral vascular beds - Increase in temperature - Increase in [H+].

5 Increased cardiac output Bohr Effect: - Right shift on dissociation curve Increase in pulmonary blood flow - Decrease Hb-O 2 affinity at muscle - Augments O 2 diffusion into the recruitment and vasodilation of pulmonary bed exercising muscles Increase in ventilation Coupling of Cellular (internal) Respiration to pulmonary (external) Respiration In Steady State Conditions QO2 = VO2. At steady-state: oxygen consumption per unit time (VO2) and carbon dioxide output (VCO2) = oxygen utilization (QO2) and carbon dioxide production (QO2). Thus, external Respiration measured at the mouth represents internal Respiration . Wasserman K: Circulation 1988;78:1060. 3. Kristin M Burkart, MD, MSc Assistant Professor of Clinical Medicine Oxygen Consumption (VO2). VO2 is the difference between the volume of gas inhaled and the volume of gas exhaled per Oxygen Consumption (VO2) unit of time VO2 = [(VI x FI O 2 ) (VE x FEO 2 )]/t VI and VE = volumes of inhaled and exhaled gas t = time period of gas volume measurements FI O2 and FEO2 = O2 concentration in the inhaled and mixed gas VO2 Max Determinants of VO2.

6 Maximum Oxygen Consumption LUNGS VO2 is interrelated to blood flow and O2. ventilation, gas exchange extraction HEART Fick Equation Oxygen Delivery CO, SV, HR. VO2 = CO x (CaO2 CvO2 ). CIRCULATION VO2 = oxygen consumption pulmonary, peripheral, Hgb CO = cardiac output CaO2 = arterial oxygen saturation CvO2 = venous oxygen saturation CaO2 CvO2 = arteriovenous O 2 content difference . is related to O2 extraction by tissues Oxygen Utilization MUSCLES CaO2 = ( x Hb x SaO2) + ( x PaO2). limbs, diaphragm, thoracic CvO2 = ( x Hb x SvO2) + ( x PvO2 ). VO2 Max Maximum Oxygen Consumption VO2 Max Maximum Oxygen Consumption Plateau in VO2 = VO2. Max What is normal? > 84% predicted (L/min). > 30 ml/kg/min Average individual 30-50 ml/kg/min Athletes 60-70 ml/kg/min VO2 increases linearly until SV, HR, or tissue extraction approaches its limitations VO2 plateaus Lance Armstrong VO2 max is the point at which there is no further increase in VO2 despite 85 ml/kg/min further increases in workload.

7 - Laughlin, Am J Physiol 1999; 277: S244. 4. Kristin M Burkart, MD, MSc Assistant Professor of Clinical Medicine A Reduced VO2 Max (less than 84% predicted (L/min) or less than 30 ml/kg/min) Anaerobic Threshold Oxygen transport CO, O2-carrying capacity of the blood Pulmonary limitations The VO2 at which anaerobic metabolism mechanical, gas exchange contributes significantly towards Oxygen extraction at the tissues the production of ATP. tissue perfusion, tissue diffusion Neuromuscular or musculoskeletal limitations Decreased Exercise Capacity Anaerobic Threshold Anaerobic Threshold The VO2 at which anaerobic metabolism The VO2 at which anaerobic metabolism contributes significantly towards the production of ATP contributes significantly towards the production of ATP. A non-invasive estimate of cardiovascular function AT demarcates the upper limit of a range of Exercise intensities that can be accomplished Normal AT: > 40% of predicted max VO2 max almost entirely aerobically Average individual AT: 50-60% predicted VO2 max Work rates below AT can be sustained indefinitely Low AT (< 40% predicted max VO2 max).

8 Work rate above AT is associated with Indicates early hypoxia of exercising muscles progressive decrease in Exercise tolerance Suggests cardiovascular or pulmonary vascular limitation VCO2 Anaerobic Threshold Carbon Dioxide Output The VO2 at which anaerobic metabolism contributes significantly towards the production of ATP. The body uses CO2 regulation to compensate for acute metabolic acidosis CO2 increases due to bicarbonate buffering of increased lactic acid production seen at high work rates (anaerobic metabolism). H+ + HCO3- H 2 CO3 CO2 + H 2O. As tissue lactate production increases [ H +] the reaction is driven to the right 5. Kristin M Burkart, MD, MSc Assistant Professor of Clinical Medicine Cardiovascular Responses to Dynamic Exercise Cardiovascular Responses Increase in cardiac output (CO= HR x SV).

9 To Dynamic Exercise Increase in heart rate (HR). Increase in stroke volume (SV). Increase in SBP. DBP remains stable +/- decreased Cardiac Output Predicted Maximum Heart Rate Increases with Dynamic Exercise Standard equation As work intensity rises, the proportion of CO distributed Max HR = 220 - age skeletal muscle increases Alternative equation viscera decreases Max HR = 210 (age x ). Exercise Hyperemia Both have similar values for < 40 years old Increased blood flow to cardiac and skeletal muscles during Exercise Standard method underestimates peak HR in older people - Laughlin, Am J Physiol 1999; 277: S244. Heart Rate, Stroke Volume and Oxygen Pulse(O2 pulse) Cardiac Output Increase with Dynamic Exercise Oxygen pulse = VO2 max/max HR Increase in cardiac output (CO= HR x SV). Reflects the amount of oxygen extracted Early in Exercise : per heart beat Increase in HR and SV.

10 Estimator of stroke volume (SV)* Late in Exercise : Modified Fick Equation: VO2/HR = SV x C(a-v)O2 Primarily due to HR. SV plateaus *Assumption that at max work rate, C(a-v)O2 is constant, thus change in O2 pulse represents change in SV. - ATS / ACCP Statement of CPET; AJRCCM 2003;167:211-77. 6. Kristin M Burkart, MD, MSc Assistant Professor of Clinical Medicine Effects of Dynamic Abnormal Blood Pressure Exercise on Blood Pressure Responses to Dynamic Exercise Marked Rise in SBP. Abnormal patterns of SBP response to Exercise Linear increase Nml < 200 mmHg Fall, reduced rise, excessive rise Increase to > 200 mmHg Minimal Change in DBP. May decrease a little Most alarming FALL in SBP. Indicates a potential serious cardiac limitation Moderate rise in MAP. CHF, ischemia, aortic stenosis, central venous obstruction - Laughlin, Am J Physiol 1999; 277: S244.


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