Cardiovascular System

• SA Node (Sino Atrial):

  • Found in the right atrium
  • Pacemaker
  • Myogenic (self regulating)
  • Emits a signal that crosses the atria
  • Causes atrial systole / ventricular diastole
• AV Node (Atrio-Ventricular):

  • Between the right atria and ventricle
  • Receives a signal from the SA node
  • Relays signals
• Bundle of His:

  • Positioned in the septum
  • Separates the signal into Left & Right
• Purkinje Fibres:

  • Spreads the signal to every muscle cell
  • Causes the myocardial cells to contract (All of Nothing Law)
  • Cause ventricular systole / diastole
• 1. SA Node
  2. Impulse to Left Atrium (Atrial Systole)
  3. AV Node
  4. Bundle of His
  5. Purkinje Fibres (Ventricular Systole)

  
• What mechanism helps increase venous return during exercise?

  The skeletal muscle pump, respiratory pump, and increased pressure gradient.
• What is the skeletal muscle pump's role in venous return during exercise?

  The skeletal muscle pump aids venous return by compressing veins during muscle contraction and relaxation, pushing blood towards the heart through one-way valves.
• What is cardiovascular drift?

  Progressive increase in heart rate during prolonged exercise, especially in hot and humid conditions, due to dehydration and heat stress.
• Starling's Law

  Stroke Volume = Venous Return
• Stroke Volume will increase in proportion to exercise intensity until a plateau is reached at approx. 40-60% of working capacity. This corresponds to sub-maximal intensity exercise
• SV = Q / HR
• As you exercise harder, your heart ejects more blood with each pump, until it plateaus
• At sub-maximal intensity:

  • Increased VR (due to the skeletal muscle pump)
  • Starling's Law states that the heart pumps more blood when it is filled with more blood (due the increased VR)
• As exercise intensity increases towards maximal levels, HR increases significantly, but there is less time for the ventricles to fill completely during the diastolic phase. This limits further increases in SV, causing the plateau
• Resting:

  HR = Lower

  SV = Lower

  Q = Lower

  Moderate:

  HR = Higher

  SV = Higher

  Q = Higher

  Sub-Max:

  HR = High

  SV = Max. Increase

  Q = High

  Maximal:

  HR = Very High

  SV = Plateaued

  Q = Very High
• Venous Return

  The flow of blood back to the heart through the veins
• During exercise VR increases due to several mechanisms
• Skeletal Muscle Pump:

  • As muscles contract & relax during exercise, they act like pumps, squeezing blood out of the veins and pushing it back towards the heart
  • It is very effective in the lower limbs, where large muscle groups are involved
• Respiratory Pump:

  • During exercise, breathing becomes deeper and more rapid
  • Inhalation creates a negative pressure in the thoracic cavity, which helps to pull blood into the heart
  • Exhalation increases the pressure in the abdominal cavity, also pushing the blood upwards
• Pressure Gradient:

  • As the intensity increases, the pressure gradient between the veins and the heart increases, facilitating more blood flow back to the heart
• Cardiovascular Drift


  The progressive increase in HR due to prolonged exercise, particularly in hot and humid conditions. This occurs when intensity remains constant
• Dehydration is a cause of Cardiovascular Drift:

  • Fluid loss - sweating leads to loss of water and electrolytes, reducing blood volume
  • Reduced VR, leading to a decreased SV (SV = VR)
• Heat Stress is a cause of Cardiovascular Drift:

  • The body's attempt to dissipate heat causes vasodilation, which directs blood flow to the surface of the skin for looking, reducing VR
• Compensatory mechanisms are a cause of Cardiovascular Drift:

  • The heart compensates for reduced SV by increasing HR to maintain cardiac output (Q)
  • SV = Q / HR
• Effects Cardiovascular Drift has on performance:

  • Increased HR = more strain on CV system
  • Increased perceived exhaustion and thermoregulatory strain = reduced performance