Cardiovascular Regulation Exercise Physiology Mc Ardle Katch and

Cardiovascular Regulation Exercise Physiology Mc. Ardle, Katch, and Katch, 4 th ed.

Regulation of the Cardiovascular System Heart Rate Regulation Blood Flow Regulation

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.

Intrinsic Regulation of HR • Sino atrial node: pacemaker

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

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

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

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.

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

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

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

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

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

Vagus Nerve Parasympathetic Nerve • Innervates SA node & AV node • Releases acetylcholine • Slows heart rate • Lowers pressure

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

Peripheral Influences on HR Peripheral receptors monitor state of active muscle; modify vagal or sympathetic • Chemoreceptors – Monitor p. CO 2, H+, p. O 2 • Mechanoreceptors – Heart and skeletal muscle mechanical receptors • Baroreceptors

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

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.

Blood Flow Regulation • Flow = pressure gradient x vessel radius 4 vessel length x viscosity • Blood flow Resistance Factors 1. Viscosity or blood thickness 2. Length of conducting tube 3. Radius of blood vessel

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

Local Factors Resulting in Dilation • ↓ tissue O 2 produces potent vasodilation in skeletal and cardiac muscle • • Increased temperature Elevated CO 2 Lowered p. H Increased ADP Nitric Oxide (NO) Ions of Mg+2 and K+ Acetylcholine

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

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

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

Neural Factors of Flow Control

Integrated Response

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

Integrated Response in Exercise