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The Circulatory Responses to Exercise. Chapter 9 Powers & Howley 7 th Edition. The Circulatory System. Cardiopulmonary system: works to maintain oxygen and carbon dioxide homeostasis in body tissues The cardiovascular system includes the heart, vessels, and blood

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The Circulatory Responses to Exercise

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the circulatory responses to exercise

The Circulatory Responses to Exercise

Chapter 9

Powers & Howley

7th Edition

the circulatory system
The Circulatory System
  • Cardiopulmonary system: works to maintain oxygen and carbon dioxide homeostasis in body tissues
  • The cardiovascular system includes the heart, vessels, and blood
  • The purposes of the CV system are:
    • Transport of O2 to tissues and removal of wastes
    • Transport of nutrients to tissues
    • Regulation of body temperature
organization of the circulatory system
Organization of the circulatory system

The heart is divided into four chambers (two pumps in one)

  • Right side: pumps “deoxygenated” blood to the lungs via the pulmonary circuit
  • Left side: pumps “oxygenated” blood to the various tissues via the systemic circulation
  • Heart wall composed of 3 tissues:
    • Epicardium: Outer layer
    • Myocardium: Middle layer (muscle responsible for contracting and forcing blood out of the heart)
    • Endocardium: Inner layer
electrical activity of the heart
Electrical Activity of the Heart


Sinoatrial (SA) Node: Pacemaker of the heart

Atrioventricular (AV) Node: Located in floor of right atrium

Bundle of HIS, Bundle Branches, Purkinje Fibers

Electrocardiogram (ECG): A recording of the electrical changes that occur in the myocardium during the cardiac cycle

Contraction of chambers represented by P-wave, QRS complex, T-wave


Cardiac Cycle

Cardiac Cycle - one complete sequence of contraction and relaxation of the heart

the heart terminology
The Heart - Terminology
  • Stroke Volume - amount of blood ejected from the ventricles with each beat of the heart
  • Heart rate = beats per minute
  • Cardiac Output - the amount of blood pumped per unit of time, in liters per minute
    • Q = SV  HR
  • Arterio-venous O2 difference (a-VO2 diff) - The amount of O2 that is taken up from 100 ml of blood by the tissue during one trip around the systemic circuit
  • Fick Equation: VO2 = Q x (a-VO2 diff)
the heart terminology11
The Heart - Terminology
  • Blood Pressure: The force exerted by blood against the arterial walls, determined by the product of:
      • how much blood is pumped (Q)
      • resistance to blood flow (TPR)
  • SBP: the arterial pressure generated during ventricular systole (contraction phase)
  • DBP: the arterial pressure during ventricular diastole (relaxation phase)
regulation of cardiac function
Regulation of Cardiac Function

Parasympathetic Nervous System

  • Causes HR to decrease
  • Parasympathetic tone:
    • Initial increase in HR during exercise is due to withdrawal of parasympathetic tone

Sympathetic Nervous System

  • Causes HR to increase
  • Sympathetic Tone:
    • Increase tone => increased heart rate and increased force of contraction
principles of blood flow
Principles of Blood Flow
  • Pressure: Rate of blood flow is proportional to the pressure difference between the two ends of the vessel
    • Blood will flow from region of high pressure to a region of low pressure
  • Resistance: Blood flow is inversely proportional to resistance

Length x viscosity


  • Major Factor determining resistance is the vascular diameter/radius *
    • Resistance is inversely proportional to the 4th power of the radius

Resistance =

cardiovascular responses to exercise
Cardiovascular Responses to Exercise

Q, SV, HR, BP, a-VO2 diff

  • Relationship betweenVO2 and Q, HR, and SBP is essentially linear
  • Relationship between VO2 and SV (plateaus @ 40-50%), a-VO2 diff. (plateaus @ 40-50%), and DBP is nonlinear

Arterio-venous O2 difference (a-VO2 diff)

  • Increases during exercise due to an increase in the amount of O2 taken up and used for oxidative production of ATP by skeletal muscle

Redistribution of Blood Flow

  • Shifting of blood from inactive to active tissue
integrated response in exercise
Integrated Response in Exercise

Activation of motor cortex and higher areas of brain (central command)

  • Reciprocal inhibition of parasympathetic activity =>
    • Acceleration of heart rate (up to ~100 bpm)
  • Increase in sympathetic outflow =>
    • General visceral vasoconstriction
    • Increased myocardial contractility, hence increase in BP, SV & HR (Q )

Regulation of local blood flow during muscle contraction & relaxation

  • Alterations in local / intrinsic metabolic conditions
    • due to increased production of local vasodilatory factors (i.e. hypoxia; decreased pH; increased PCO2, ADP, Mg++, Ca++, and temperature)
    • results in redistribution of blood flow
integrated response in exercise26
Integrated Response in Exercise

Central command, cont.

  • Continued sympathetic outflow in conjunction with increases in epinephrine and norepinephrine
    • Continued constriction of vasculature in inactive tissues to maintain adequate perfusion pressure
  • Venous vessels stiffen to reduce their capacity
      • Facilitates venous return and maintains central blood volume

Local regulation, cont.

  • Augmented local metabolic conditions
    • Further dilation of active muscle vasculature
factors influencing venous return
Factors influencing Venous Return
  • Venoconstriction - Reducing the volume capacity of the veins to store blood
  • Muscle Pump - Mechanical action of rhythmic skeletal muscle contractions
  • One-way valves located in large veins
arm versus leg exercise
Arm versus Leg Exercise
  • HR and BP response to arm exercise is greater than during leg exercise
    • HR & BP during arm exercise exceeds expected values based on relative oxygen consumption
    • Greater sympathetic outflow to heart during arm work
    • Less arterioles dilated, therefore greater vascular resistance