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Exercise physiology 7


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Exercise physiology 7

  1. 1. S Cardiovascular System and Exercise
  2. 2. Cardiovascular System S Functions during physical activity includes: S Oxygen delivery S Blood aeration S Thermoregulation S Nutrient delivery S Hormone Transportation
  3. 3. Components of the Cardiovascular System S Heart S Arteries S Capillaries S Veins
  4. 4. Cardiovascular Dynamics During Exercise S Parameters S Heart Rate S Stroke Volume S Cardiac Output S Blood Pressure S Blood Flow S Blood
  5. 5. Heart Rate S Defined as the number of beat per unit of time, usually expressed in beats per minute. S Ones heart rate can be determined through: S Palpation S Auscultation S Heart Rate Monitor S ECG Recorder
  6. 6. Heart Rate S Resting Heart Rate Values S Averages 60 – 80 beats/min S Averages 28 – 40 beats / min - highly conditioned, endurance trained athletes S Secondary to increase in vagal tone S Affected by environmental factors, it increases with extremes in temperature and altitude S Best taken when totally relaxed, such as early mornings. S Heart Rate During Exercise S HR increases directly in proportion to the increase in exercise intensity
  7. 7. Heart Rate S Moving towards maximal intensity, the HR starts to plateau even with further increase in exercise intensity. S This indicates that HR is reaching a maximum value. S Maximum heart rate (HRmax) is the highest HR value achieved in an all out effort to the point of exhaustion.
  8. 8. Heart Rate S HR max can be estimated based on age because of a slight but steady decrease of about one beat per year beginning at age 10 – 15 years S Equations: S HRmax = 220 – age S HRmax = 208 – (0.7 X age)
  9. 9. Heart Rate S If intensity is held at a submaximal intensity, HR increases fairly rapidly until it reaches a plateau. S This plateau is the steady state HR. S This is an optimal HR for meeting the circulatory demands at that specific rate of work. S Valid predictor of cardiorespiratory fitness S A lower steady state HR reflects a greater cardiorespiratory fitness.
  10. 10. Stroke Volume S Defined as the volume of blood pumped from one ventricle of the heart with each beat. S Determinants of SV: S Preload S Ventricular Distensibility S Ventricular Contractibility S Afterload
  11. 11. Stroke Volume S SV increases above resting values during exercise. S Untrained: 60 – 70 ml/ beat @ rest to 110 – 130 ml/beat during maximal exercise. S Highly trained endurance athletes: 80 – 100ml/beat @ rest to 160 – 200 ml/ beat during maximal exercise. S Percentage increase can be determined by body position.
  12. 12. Stroke Volume S Contributing Factors for increase: S Frank Starling mechanism S States that the stroke volume of the heart increases in response to an increase in the volume of blood filling the heart. The increased volume of blood stretches the ventricular wall, causing cardiac muscle to contract more forcefully. S Increased contractility S Increased neural stimulation S Increased release of circulatory catecholamines S Decreased afterload
  13. 13. Cardiac Output S Defined as the volume of blood pumped by the heart per minute (L/min). S CO is the product of HR and SV S CO = HR x SV S Resting CO is approx. 5 L/min S Maximal CO varies between 20 (sedentary person) and 40 (elite endurance athlete) L/min
  14. 14. Cardiac Output S One of the major purpose for the increase in CO is to meet the muscles’ demand for oxygen. S Ensuring that adequate supply of oxygen and nutrients reach the exercising muscles, and waste products of muscle metabolism are removed quickly.
  15. 15. Blood Pressure S Pressure exerted by circulating blood against the wall of the blood vessels.
  16. 16. Blood Pressure S During dynamic exercise mean arterial blood pressure (MAP – average pressure exerted by the blood as it travels through the arteries) increases substantially. S Rhythmic whole body endurance exercise increases systolic blood pressure in direct proportion to the increase exercise intensity. S Diastolic pressure does not change significantly, and may even decrease.
  17. 17. Blood Pressure S Blood pressure responses to resistance exercise is exaggerative. S High intensity resistance training, blood pressure can reach 480/350 mmHg. S Because of the sustained muscular force which compresses the peripheral arterioles, considerably increasing resistance to blood flow.
  18. 18. Blood Pressure S Blood pressure increases more in rhythmic arm compared with rhythmic leg exercise. S The smaller arm muscle mass and vasculature offers greater resistance to blood flow than the larger and more vascularized lower – body region. S The difference between the systolic blood pressure during upper and lower body exercise has important implications for the heart. S Myocardial oxygen uptake and myocardial blood flow are directly related to the product of HR and systolic blood pressure [rate pressure product/ double product (DP = HR X SBP)]
  19. 19. Blood Pressure S In Recovery S After a bout of sustained light to moderate intensity exercise, systolic blood pressure temporarily decreases below pre exercise levels for up to 12 hours in normal and hypertensive individuals.
  20. 20. Blood Flow Exercise Effects S Acute changes in CO and BP during exercise allows for an increase in total blood flow to the body. S This facilitates getting blood flow to the exercising muscle. S Additionally, sympathetic control of the cardiovascular system can redistribute blood to areas of greatest metabolic need.
  21. 21. Blood Flow Blood Flow Regulation S Pressure differentials and resistances determine fluid movement through the vessel. S Resistance varies directly with the length of the vessel and inversely with its diameter. S Flow = Pressure ÷ Resistance
  22. 22. Blood Flow S Three factors determine resistance to blood flow: S Viscosity or Blood thickness S Length of conducting tube S Radius of blood vessel S Poiseuille’s Law expresses the general relationship between pressure differential (gradient), resistance, and flow in a cylindrical vessel: S Flow = Pressure gradient × Vessel radius4 ÷ Vessel length × Fluid viscosity
  23. 23. Blood Flow S Blood viscosity and transport vessel length remains relatively constant in the body. S Blood vessel radius represents the most important factor affecting blood flow. S Resistance to blood flow changes with vessel radius raised to the fourth power (reducing a vessel’s radius by one half decreases flow by a factor of 16, conversely doubling the radius increases volume 16 fold). S This means that a relatively small degree of vasoconstriction or vasodilation can dramatically alter regional blood flow.
  24. 24. Blood S Blood is the fluid of life, growth and health. S As metabolism increases during exercise, the function of the blood becomes more critical for optimal performance. S At rest the blood’s oxygen content varies from 20 ml of oxygen per 100 ml of arterial blood to 14 ml of oxygen per 100 ml of venous blood.
  25. 25. Blood S The difference between these two values is referred to as the a-v O2 difference. S With increasing exercise intensity, the a-v O2 difference increases progressively and can increase approximately threefold from rest to maximal exercise intensities.
  26. 26. Blood S With the onset of exercise there is almost an immediate loss of plasma from the blood to the interstitial space. S Approx. 10 – 15% reduction in plasma volume can occur in prolonged exercise and with brief bouts of exhaustive exercise.
  27. 27. Blood S If exercise intensity or environmental conditions cause sweating, additional plasma volume is lost. S For prolonged duration activities in which dehydration occurs and heat loss is a problem, a reduction in plasma volume will impair performance. S When plasma volume is reduced, hemoconcentration occurs. S Increases red blood cell concentration substantially (20% – 25%) S Hematocrit increases from about 40% - 50%. S Total volume and number of red blood cells do not change substantially. S Increases the blood’s oxygen carrying capacity during exercise.
  28. 28. S Respiratory System and Exercise
  29. 29. Pulmonary Structure and Function
  30. 30. Lung Volumes and Capacities S Static Lung Volumes S Evaluates the dimensional component for air movement within the pulmonary tract and impose no time limitation on the individual. S Dynamic Lung Volumes S Evaluates the power component of pulmonary performances during different phases of the ventilatory excursion.
  31. 31. Static Lung Volumes Lung Volume/ Capacity Definition Average Values (mL) Male Female Tidal Volume (TV) Volume inspired or expired per breath. 600 500 Inspiratory Reserve Volume (IRV) Maximum inspiration at end of tidal inspiration. 3000 1900 Expiratory Reserve Volume (ERV) Maximum expiration at end of tidal expiration. 1200 800 Inspiratory Capacity (IC) Maximum volume inspired after tidal expiration. 3600 2400 Functional Residual Capacity (FRC) Volume in lungs after tidal expiration 2400 1800 Forced Vital Capacity (FVC) Maximum volume expired after maximum inspiration 4800 3200 Residual Lung Volume (RLV) Volume in lungs after maximum expiration. 1200 1000 Total Lung Capacity (TLC) Volume in lungs after maximum inspiration 6000 4200
  32. 32. Dynamic Lung Volumes S Normal values for vital capacity can exist in severe lung disease if no time limit is present to expel air. S Hence, why a dynamic lung function measure such as percentage of the FVC expelled in 1 second (FEV1.0) serves as a more useful diagnostic purpose than static measures. S Forced Expiratory Volume to Forced Vital Capacity Ratio (FEV1.0 / FVC) S Reflects the expiratory power and overall resistance to air movement in the lungs. S Normally this averages 85% of the vital capacity.
  33. 33. Dynamic Lung Volume S Maximum Voluntary Ventilation S This dynamic assessment of ventilatory capacity requires rapid, deep breathing for 15 seconds. S This 15 second volume is then extrapolated to the volume breathed for 1 minute. S Healthy young men: 140 – 280 L/min S Healthy young women: 80 – 120 L/min
  34. 34. Pulmonary Ventilation S Pulmonary Ventilation – Describes how ambient air moves into and exchanges with air in the lungs. S Minute ventilation – Volume of air breathed per minute. S Minute ventilation = Breathing rate × Tidal Volume S Alveolar ventilation – Refers to the portion of the minute ventilation that mixes with the air in the alveolar chamber. S Anatomic dead space – Portion of the air that does not enter the alveoli and engage in gaseous exchange with the blood. 150 – 200 mL or ~30 % of the resting TV. S Physiologic dead space – Portion of the alveolar volume with poor tissue regional perfusion or inadequate ventilation. This can increase to 50% of the resting TV.
  35. 35. Relationship amongst Tidal Volume, Breathing Rate, and Minute and Alveolar Minute Ventilation Breathing Condition Tidal Volume (mL) × Breathing Rate (breaths/min) = Minute Ventilation (mL/min) - Dead Space Ventilation (mL/min) = Alveolar Ventilation (mL/min) Shallow 150 40 6000 150 × 40 0 Normal 500 12 6000 150 × 12 4200 Deep 1000 6 6000 150 × 6 5100
  36. 36. Partial Pressure of Gases S Partial Pressure – Individual pressures from each gas in a mixture. S The air breathed is a mixture of gases; and each exerts a pressure in proportion to its concentration in the gas mixture. S Dalton’s Law – the total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases in that mixture. S Partial pressure = Percentage concentration × Total pressure of gas mixture (standard atmospheric pressure)
  37. 37. Movement of Gas S According to Henry’s Law S Gases dissolves in liquids in proportion to their partial pressures, depending also on their solubilities in specific fluids and on the temperature. S The amount of gas dissolved in a fluid depends on two factors S Pressure differential between the gas above the fluid and dissolved in it S Solubility of the gas in the fluid.
  38. 38. Gas Exchange S Oxygen Exchange S PO2 = 159 mmHg of ambient air S PO2 = 105 mmHg when inhaled and enters the alveoli. Due to the increased water vapor pressure and increased partial pressure of carbon dioxide in the alveoli. S PO2 = approx. 40 mmHg in the pulmonary capillaries S Fick’s Law S States that the rate of diffusion through a tissue such as the respiratory membrane is proportional to the surface area and the difference in the partial pressure of gas between the two sides of the tissue. The rate of diffusion is also inversely proportional to the thickness of the tissue in which the gas must diffuse.
  39. 39. Gas Exchange S Carbon Dioxide Exchange S Moves along a pressure gradient S PCO2 = 40 mmHg in the alveoli S PCO2 = 46 mmHg in the venous blood
  40. 40. Partial Pressure of Respiratory Gases at Sea Level Partial Pressure (mmHg) Gas % in dry air Dry air Alveolar air Arterial Blood Venous Blood Diffusion Gradient Water 0.00 0.0 47 47 47 0 Oxygen 20.93 159.1 105 100 40 60 Carbon Dioxide 0.03 0.2 40 40 46 6 Nitrogen 79.04 600.7 568 573 573 0 Total 100.00 760 760 760 706 0
  41. 41. S Transport of Oxygen and Carbon Dioxide in the Blood
  42. 42. Oxygen Transport By two means: S Combined with hemoglobin S Dissolved in blood plasma S 3 ml dissolved in every L of plasma S If total blood plasma is 3 – 5 L only 9 – 15 ml can be carried in the dissolved state.
  43. 43. Hemoglobin Saturation S Each molecule of hemoglobin can carry 4 molecules of oxygen. The combine molecule is termed oxyhemoglobin. S Binding depends on: S Partial pressure of oxygen in the blood S Bonding strength, affinity between haemoglobin and oxygen.
  44. 44. Oxygen Dissociation Curve
  45. 45. Blood Oxygen Carrying Capacity S The oxygen carrying capacity of blood is the maximal amount of oxygen the blood can transport. S Dependent on: S The blood hemoglobin content S 100 ml of blood – 14 to 18 g of Hb (men), 12 – 16 g of Hb (women). S Each gram of Hb can combine with about 1.34 ml of oxygen, hence the oxygen carrying capacity of blood is approx. 16 – 24 ml per 100 ml of blood
  46. 46. S At rest: Blood is in contact with the alveolar air for approximately 0.75 secs. S With exercise: the contact time is greatly reduced…
  47. 47. Carbon Dioxide Transport S Carbon dioxide is carried in the blood in three forms: S As a bicarbonate S Dissolved in plasma S Bound to hemoglobin (carbaminohemoglobin)
  48. 48. Bicarbonate Ion S Majority carried in this form, accounting for the transport of 60% to 70% of the carbon dioxide in the blood. S Carbon dioxide and water combines to give carbonic acid; catalyzed by the enzyme carbonic anhydrase. S Carbonic acid is unstable and quickly dissociates, freeing the hydrogen ion and forming a bicarbonate ion. S The free hydrogen can bind to hemoglobin triggering off the Bohr effect. S Bicarbonate diffuses into the plasma. S When blood enters the lungs where the partial pressure of oxygen is lower, the reverse holds true.
  49. 49. Dissolved Carbon Dioxide S Only approximately 7% to 10% of the carbon dioxide released from the tissues dissolves in plasma. S The dissolved form comes out of solution when its partial pressure is low as in the lungs. S Here it diffuses from the pulmonary capillaries into the alveoli to be exhaled.
  50. 50. Carbaminohemoglobin S Binding of the gas to hemoglobin will give carbaminohemoglobin. S So named because it binds to the amino acids in the globin part of the Hb molecule. S No competition with oxygen when binding, however binding varies with the oxygenation of the Hb and the partial pressure of carbon dioxide.
  51. 51. Gas Exchange in Muscle S Arterial venous oxygen difference. S Oxygen transport in muscle. S Myoglobin
  52. 52. Factors Influencing Oxygen Delivery and Uptake S Oxygen Content in blood S Blood Flow S Local Conditions
  53. 53. Pulmonary Ventilation During Dynamic Exercise S Onset of exercise is accompanied by an immediate increase in ventilation, followed by a more gradual increase, then a slow rate steady decrease to resting values. S Respiratory recovery takes several minutes suggesting that: S The rate of breathing does not perfectly match the metabolic demands of the tissue. S Post exercise is regulated primarily by acid base balance, partial pressure of dissolved carbon dioxide, and blood temperature.
  54. 54. Ventilatory Response to Exercise
  55. 55. Breathing Irregularities During Exercise S Dyspnea S Common among individuals in poor physical condition. S Increased levels of carbon dioxide and hydrogen ions concentration triggers the inspiratory center to increase the rate and depth of breathing. S Although sensed as an inability to breathe the underlying cause is the inability to adjust breathing to blood carbon dioxide and hydrogen ion concentration.
  56. 56. S Hyperventilation S Increase in ventilation in excess of that needed for exercise metabolism. S Decreases normal partial pressure of carbon dioxide from 40 mmHg to about 15 mmHg. S Decrease in arterial carbon dioxide concentration, increases blood pH. S Resulting in a reduced ventilatory drive
  57. 57. S Valsalva Maneuver S Closure of glottis  increase intra abdominal pressure  increase intrathoracic pressure. S As a result air is trapped and pressurized in the lungs. S Restricted venous return, reducing volume of blood returning to the heart, decreasing cardiac output, and altering arterial blood pressure.
  58. 58. Ventilation and Energy Metabolism S Ventilatory equivalent for oxygen (VE/ VO2) S The ratio between the volume of air expired or ventilated and the amount of oxygen consumed by the tissues in a given amount of time. S Measured in liters of air breathed per liter of oxygen consumed per minute. S At rest: 23 to 28 L of air per liter of oxygen S Mild exercise: Varies little S Moderate – Near maximal levels: can be > 30 L of air per liter of oxygen consumed. S Generally speaking it remains relatively constant over a wide range of exercise intensities, indicating the control of breathing is properly matched to the body’s demand for oxygen.
  59. 59. S Ventilatory Threshold S Point at which ventilation increases disproportionately to oxygen consumption. S Reflects the respiratory response to increased carbon dioxide levels. S Ventilation increases dramatically beyond this point.
  60. 60. Respiratory Regulation of Acid - Base Balance S The metabolism of carbohydrate, fats, or protein produces inorganic acids that dissociate, increasing the hydrogen ion concentration in the body fluid  lowering the pH. S To minimize this effect the blood and muscles contains base substances that combines with and hence buffer or neutralize the ion. S At rest the body fluids have more bases than acids, resulting in a slightly alkaline tissue (7.1 in muscle to 7.4 in arterial blood).
  61. 61. S Acidosis – occurs with increased levels of H ions. S Alkalosis – occurs with decreased level of H ions. S The pH of intra and extra cellular fluid is kept within a relatively narrow range by: S Chemical Buffers S Pulmonary Ventilation S Kidney Function
  62. 62. Chemical Buffers S Major chemical buffers: S Bicarbonate S Inorganic phosphates S Protein
  63. 63. S Bicarbonate combines with H ion to give carbonic acid, which dissociates to give carbon dioxide and water in the lungs. S In the muscle fibers and kidney tubules H ion is primarily buffered by phosphates. S Blood and chemical buffers are required only to transport metabolic acids from their sites of production to the lungs or kidneys for removal. S Once the H ion is transported and removed the buffer molecule can be re used.
  64. 64. Pulmonary Ventilation S Increased levels of free H ions in the blood stimulates the respiratory center to increase ventilation. S Both the chemical buffers and respiratory system provides short term means of neutralizing the acute effects of exercise acidosis.
  65. 65. 27- 71
  66. 66. 27- 72