RESPONSE TO EXERCISE

• mp and respiratory pump

  Help with venous return during exercise
• Blood return


  1. Blood is returned through the veins to the heart and enters the atria

  2. Blood then moves from the atria to the ventricles causing the myocardium (cardiac muscle) in the ventricles to stretch

  3. The greater the venous return the more blood that enters the ventricles, the greater the myocardium is stretched. The further it is stretched the stronger and more forceful the contract will be
• Stroke Volume Trained Vs Untrained

  • Trained individuals have a larger SV then untrained
• Q


  The amount of blood pumped from the heart every minute (litres/minute)
• As HR and SV ↑

  Q ↑ during exercise, to a maximum!

  
• Resting Q is about 5.0 L/min, but varies with size of person
• As intensity increases


  Q increases
• When exercise intensity above 40-60% Hrmax, Q is a result of increase HR rather than SV

  
• Cardiovascular Drift


  Upward drift of heart rate over time, coupled with a progressive decline in stroke volume and the continued maintenance of cardiac output
• Cardiovascular drift occurs while exercise intensity remains constant

  
• Causes of Cardiovascular Drift

  • Increase in core temperature and body water losses
• How Cardiovascular Drift occurs

  1. With prolonged exercise or exercise in heat, BV is reduced by loss of water via sweating and shifting of fluid out of the blood into the tissue (edema)

  2. With the total BV decreasing, with a redistribution of more blood to the periphery for cooling, cardiac filling pressure is reduced

  3. This causes decreased venous return to the right side of the heart. In turn this reduce in SV (EDV is decreased; SV = EDV – ESV)

  4. HR compensates for the decreased SV by increasing, in an effort to maintain Q
• HR and exercise intensity

  Linear relationship

  
• SV changes


  Due to changes in venous return, ventricular contractility and peripheral resistance
• Q and exercise intensity


  Linear relationship

  
• SBP increase as intensity increases


  DBP rarely change
• DBP reflects the pressure in the arteries when the heart is at rest. None of the changes alter this pressure significantly
• With steady state exercise, SBP rise rapidly in first few minutes, and then plateu @ 140-160 bpm
• Systolic Blood Pressure (SBP)


  Maximum pressure
• Diastolic Blood Pressure (DBP)

  Minimum pressure
• Endurance Exercise - SBP

  1. Increases in proportion to increase in exercise intensity

  2. As exercise begins, the baroreceptors found in the aortic and carotid arteries detect a decrease in blood pressure specifically SBP

  3. CNS responds by constricting (vasoconstriction – narrowing of the blood vessel lumen) blood vessels and increasing SBP and further increases HR

  4. CNS detects that SBP needs to be reduced and is reduced via the vasodilation of the vessels

  5. The CNS will continue to regulate BP throughout exercise until maximal levels are reached

  
• Endurance Exercise - DBP

  1. Does not change significantly (may even decrease)

  2. DBP reflects the pressure in the arteries when the heart is at rest. None of the changes alter this pressure significantly

  3. Increased in DBP of 15mmHg or more are considered abnormal responses to exercise and are one of several indicators for immediately stopping a diagnostic exercise test

  
• Resistance Exercise


  1. Can exaggerate BP as high as 480/350 bpm

  2. Lower body exercise – BP higher due to smaller muscle mass in the UB compared to LB

  3. Static resistance training (isometric) increased BP compare to dynamic exercise (isotonic)

  
• As exercise intensity increases

  SBP in both arms and legs increases in a linear fashion

  
• Small or little changes in DBP
• Acute changes in Q and BP during exercise

  Causing for increased total blood flow
• Blood flow patterns change in transition from rest to exercise

  Blood must be redistributed to other areas such as muscle this is often called a vascular shunt
• Sympathetic Nervous System (SNS)

  Initiates blood to be redirected to active areas during exercise
• SNS activity


  1. Causes the vasoconstriction and vasodilatation of blood vessels

  2. Also pre capillary sphincters open and close to allow for blood to either travel in or away from a certain area of the body

  3. This causes blood to be redirected to other areas of the body during exercise
• Vasodilation


  • Dilation of arterioles and opening of precapillary sphincters increases blood flow to active muscle
• Vasoconstriction


  • Constriction of arterioles and closure of precapillary sphincters reduces blood flow to inactive organs
• Exercise + other demands for blood flow = competition for limited Q
• During exercise, blood is redistributed to active muscles - 88% to active muscles, Decrease flow to inactive muscles, non-essential organs, Same volume to brain
• Arterial-Venous Oxygen Difference


  The extent to which oxygen is extracted from the blood as it passes through the body
• Arterial-Venous Oxygen Difference


  Increases with increasing exercise intensity, with more oxygen being extracted from the blood
• Plasma volume changes with exercise

  1. With the onset of exercise, there is an almost immediate increase in the loss of plasma volume, going to interstitial fluid space

  2. Increase intensity and environment causing sweating, causing hemoconcentration which can impede blood flow and thus limit O2 transport

  3. A 10 to 20% or greater reduction in plasma volume can occur in prolonged work

  4. Resistance training – 7.7-13.9% loses

  5. Reduction of plasma volume will impair performance
• Blood pH


  Changes significantly during exercise, becoming more acidic - moves from the slightly alkaline resting value of 7.4 to 7.0 or lower
• Muscle pH decreases even further (< 6.5) due to increased blood lactate accumulations during increased exercise intensity
• Respiratory responses before exercise

  Increase in ventilation due to anticipation, anticipatory response from central command
• Respiratory responses during exercise

  Increase in ventilation due to mechanoreceptor in muscles and joints, driven by chemical changes in arterial blood - ↑CO2, H+ sensed by chemoreceptors, right atrial stretch receptors