2 Cardiovascular Physiology: Function

Cardiovascular Physiology Objectives Describe the sequence of blood flow through the heart Describe the cardiac cycle, including Definition Systole Diastole

Cardiovascular Physiology Objectives (continued) Discuss the term stroke volume Discuss cardiac output, preload, Starling’s law, and afterload Describe the autonomic nervous system

Blood Flow Through The Heart First component: blood flow through right heart: Unoxygenated blood flows from inferior and superior vena cava, into the right atrium, through the tricuspid valve, into the right ventricle, and through the pulmonic valve

Blood Flow Through The Heart Second component: blood flow through the pulmonary circulation continues when The blood travels from pulmonary arteries, into the lungs, through the pulmonary alveolar-capillary network, and into the pulmonary veins

Blood Flow Through The Heart The third and final component: blood flow through the pulmonary circulation continues when: Blood travels from the pulmonary veins into the left atrium, through the mitral valve, into the left ventricle, through the aortic valve, and out to the rest of the body (coronary arteries first)

Cardiac Cycle Cardiac cycle Systole Represents the actual time sequence between ventricular contraction and ventricular relaxation Systole Simultaneous contraction of the ventricles

Cardiac Cycle Diastole Synonymous with ventricular relaxation Ventricles fill with 70% of blood passively from atria Atriums add the last 30% upon contraction Atrial kick

Cardiac Cycle During periods of ventricular relaxation, cardiac filling and coronary perfusion occur passively One cardiac cycle = every 0.8 seconds Systole lasts = about 0.2 seconds Diastole lasts = about 0.52 seconds

Cardiac Cycle

Relation of Blood Flow to Cardiac Contraction

Stroke Volume Stroke volume Heart rate Volume of blood pumped out of one ventricle of the heart in single beat or contraction Estimated at approximately 70 ml per beat Heart rate Number of contractions/beats per minute Normal heart rate 60-100 bpm

Stroke volume (SV) X heart rate (HR) Cardiac Output Cardiac output Amount of blood pumped by left ventricle in 1 min FORMULA to determine cardiac output Cardiac output (CO) = Stroke volume (SV) X heart rate (HR)

Cardiac Output Cardiac output Varies from person to person What effects Cardiac Output Stoke Volume, PVR, Heart Rate Inadequate cardiac output may be caused by CHF, MI, or shock

Cardiac Output Decreased Cardiac output May see combinations of symptoms: Shortness of breath Dizziness Chest pain Decreased blood pressure Cool and clammy skin

End-Diastolic Pressure Preload Pressure in the ventricles at the end of diastole Directly affected by volume of blood that returns to right atrium May be decreased or increased based on returning volume What can effect preload? At the end of relaxation (just before contraction) is the diastole pressure of blood pressure which is the pressure in the vena cava…or the pressure of blood entering the heart……..and if pressure is too there will be no blood entering the atrium and thus none in left ventricle for contraction… After load is the pressure in the arteries just before contraction, the amount of pressure the aortic valve has to over come for blood flow..

Affects stroke volume and cardiac output Afterload Resistance against which the heart must pump Affects stroke volume and cardiac output

Starling’s Law of the Heart This concept is a law of physiology which states that the more the myocardial fibers are stretched, up to a certain point, the more forceful the subsequent contraction will be “Rubber band theory” The farther you stretch a rubber band, the harder it snaps back to original size

Peripheral Vascular Resistance (PVR) Amount of opposition to blood flow offered by arterioles Determined by vasoconstriction and vasodilation Blood pressure (BP) = Cardiac output (CO) x peripheral vascular resistance (PVR)

Autonomic Nervous System Regulates functions of the body that are involuntary or are not under conscious control HEART RATE and BLOOD PRESSURE are regulated by this component of nervous system Where is this center located?

Two Major Divisions of Autonomic Nervous System Sympathetic nervous system Preparation of body for physical activity (“fight or flight”) Parasympathetic nervous system Regulates the calmer (“rest and digest”) functions of our existence Feed or breed

Nervous Control of the Heart

Receptors and Neurotransmitters Sympathetic nervous system Receptors are alpha- and beta-receptors Chemical neurotransmitter is norepinephrine These nerve endings are called adrenergic Increases the heart rate and contractile forces of cardiac muscle and vasoconstriction

Receptors and Neurotransmitters Parasympathetic nervous system Chemical neurotransmitter is acetylcholine Nerve endings are known as Cholinergic With a neurotransmitter of Acetylcholine Which causes what to happen? The heart rate slows, as do atrioventricular conduction rates

Adrenergic Receptors and Their Effect on Heart Rate Sympathetic nerve fibers that use epinephrine or epinephrine-like substances as neurotransmitters Receptor A reactive site or cell surface or within that combines with molecule to produce physiological effect

Adrenergic Receptors and Their Effect on Heart Rate Cholinergic Parasympathetic nerve fibers that use acetylcholine as neurotransmitter

Effects of Alpha/Beta Receptors

Effects of Alpha/Beta Receptors

How drugs effect the heart Inotropic Strength of contractions Chronotropic Heart Rate Dromotropic Velocity of conduction

Summary What did you learn? You direct the summary….everyone tell me something DIFFERENT!!