1. Cardiovascular Regulation
Exercise Physiology
McArdle, Katch, and Katch, 4th ed.

2. Regulation of the Cardiovascular System
Heart Rate Regulation
Blood Flow Regulation

3. Heart Rate Regulation
The heart has both intrinsic (situated within the heart) and extrinsic (originating outside the heart) regulation.
Many myocardial cells have unique potential for spontaneous electrical activity (intrinsic rhythm).
In normal heart, spontaneous electrical activity is limited to special region.
Sinoatrial node serves as pacemaker.

4. Intrinsic Regulation of HR
Sino atrial node: pacemaker

5. Intrinsic Regulation
Depolarization muscle membrane creates an action potential or electrical impulse
Impulse travels through the heart in an established pathway
SA node →across atria →AV node →AV bundle →left & right bundle branches → Purkinjie fibers → Ventricles

6. Normal Route of Depolarization
S-A Node 
Atria
A-V Node
Bundle of His
Purkinje Fibers
Ventricles

7. Intrinsic Heart Rate SA node rate approximately 90 bpm
Parasympathetic innervation slows rate
referred to as parasympathetic tone
training increases parasympathetic tone

8. Electrocardiogram
The ECG is recorded by placing electrodes on the surface of the body that are connected to an amplifier and recorder.
Each wave in the shape of the ECG is related to specific electrical change in heart.
Purposes of ECG to monitor heart rate and diagnose rhythm.

9. Electrocardiogram
Each wave of ECG related to specific electrical change in the heart
P wave - atrial depolarization
QRS complex - ventricular depolarization
masks atrial repolarization
T wave - ventricular repolarization

10. ECG Arrhythmias PACs- premature atrial contraction
PVCs- premature ventricular contraction
Ventricular fibrillation- cardiovert

11. Extrinsic Regulation of HR
Neural Influences override intrinsic rhythm
Sympathetic: catecholamines
Epinephrine
Norepinephrine
Parasympathetic
Acetylcholine
Cortical Input
Peripheral Input

12. Neural Regulation of HR
Sympathetic influence
Epinephrine  ↑HR (tachycardia) and ↑ contractility
Norepinephrine  general vasoconstrictor
Parasympathetic influence
Acetylcholine→↓HR (bradycardia)
Endurance (aerobic) trg. increases vagal dominance

13. Cardiac Accelerator Nerves
Sympathetic Fibers
Innervate SA node & ventricles
Increase heart rate
Increase contractility
Increase pressure

14. Vagus Nerve Parasympathetic Nerve Innervates SA node & AV node
Releases acetylcholine
Slows heart rate
Lowers pressure
Strong vagal stimulation of the heart can actually stop the heart for a few seconds, but then the heart escapes.
In addition, strong vagal stimulation can decrease strength of contraction by as much as 20 to 30%.
Not a great decrease because vagal fibers are distributed mainly to atria and not much to ventricles.

15. Cortical Influences on Heart Rate
Cerebral cortex impulses pass through cardiovascular control center in medulla oblongata.
Emotional state affects cardiovascular response
Cause heart rate to increase in anticipation of exercise

16. Peripheral Influences on HR
Peripheral receptors monitor state of active muscle; modify vagal or sympathetic
Chemoreceptors
Monitor pCO2, H+, pO2
Mechanoreceptors
Heart and skeletal muscle mechanical receptors
Baroreceptors

17. Peripheral Influence on HR
Baroreceptors in carotid sinus and aortic arch.
↑ pressure → ? HR & contractility
↓ pressure → ? HR & contractility

18. Blood Flow Regulation
During exercise, local arterioles dilate and venous capacitance vessels constrict.
Blood flow is regulated according to Poiseuille’s Law: Flow = pressure  resistance.
Pwah-swe’ law

19. Blood Flow Regulation Flow = pressure gradient x vessel radius4
vessel length x viscosity
Blood flow Resistance Factors
Viscosity or blood thickness
Length of conducting tube
Radius of blood vessel

20. Blood Flow Regulation
1 of every 30 or 40 capillaries is open in muscle at rest
Opening “dormant” capillaries during exercise
Increases blood flow to muscle
Reduces speed of blood flow
Increases surface area for gas exchange

21. Local Factors Resulting in Dilation
↓ tissue O2 produces potent vasodilation in skeletal and cardiac muscle
Increased temperature
Elevated CO2
Lowered pH
Increased ADP
Nitric Oxide (NO)
Ions of Mg+2 and K+
Acetylcholine

22. Blood Flow Neural Factors
Sympathetic nerves (adrenergic): norepinephrine general vasoconstrictor
Sympathetic nerves (cholingergic): acetylcholine vasodilation in skeletal and cardiac muscle.

23. Blood Flow Humoral Factors
Sympathetic nerves to adrenal medulla causes release of epinephrine & norepinephrine into blood (humor).

24. Blood Flow Humoral Factors
Sympathetic Nerves to
Adrenal Medulla 
epi & norepi in blood
vasoconstriction
except in skeletal muscle

25. Neural Factors of Flow Control

26. Integrated Response

27. Regulation from Rest to Exercise
Rapid increase in heart rate, SV, cardiac output
due to withdrawal of parasympathetic stimuli
increased input from sympathetic nerves
Continued increase in heart rate
temperature increases
feedback from proprioceptors
accumulation of metabolites

28. Integrated Response in Exercise