Advanced Cardiac Care in the Streets Understanding EKGs

Advanced Cardiac Care in the Streets Understanding EKGs Ray Taylor Valencia Community College Cardiovascular Physiology { Function }

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Cardiovascular Physiology ä Objectives äDescribe the sequence of blood flow through the heart äDescribe the cardiac cycle ä Definition ä Systole ä Diastole

Cardiovascular Physiology ä Objectives äDiscuss [ continued ] the term “stroke volume “ äDiscuss cardiac output, preload, Starling’s Law, and afterload äDescribe the autonomic nervous system

BLOOD FLOW THROUGH THE HEART ä First component = blood flow through right heart ä Unoxygenated blood flows from inferior and superior vena cavae into the right atrium, through the tricuspid valve, into the right ventricle and through the pulmonic valve

BLOOD FLOW THROUGH THE HEART ä The second component of blood flow through the pulmonary circulation continues: blood travels from PULMONARY ARTERIES into the LUNGS, through the PULMONARY ALVEOLAR-CAPILLARY NETWORK and into the PULMONARY VEINS ä the

BLOOD FLOW THROUGH THE HEART ä The third and final component of blood flow through the pulmonary circulation continues: ä when the 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

Cardiovascular Anatomy ä Blood Flow ä From the Body ä ä To the Lungs ä ä Right Ventricle From the Lungs ä ä Right Atrium Left Atrium To the Body ä Left Ventricle

Cardiac Physiology ä The Cardiac Cycle ä Diastole ä Systole Ejection Fraction ä Stroke Volume ä ä ä Preload Cardiac Contractility Afterload Cardiac Output

CARDIAC CYCLE ä Cardiac Cycle - represents the actual time sequence between ventricular contraction and ventricular relaxation. ä SYSTOLE = simultaneous contraction of the ventricles ä DIASTOLE = synonymous with ventricular relaxation -ventricles fill with 70% of blood passively from atria

CARDIAC CYCLE ä During periods of ventricular relaxation, cardiac filling and coronary perfusion occur passively. ä One Cardiac Cycle = every 0. 8 seconds ä Systole lasts = about 0. 28 seconds ä Diastole lasts = about 0. 52 seconds

Relation of blood flow to cardiac contraction

STROKE VOLUME ä Stroke Volume - volume of blood ejected out of one ventricle of heart during single beat or contraction ä Estimated at approximately 70 cubic centimeters per beat ä Heart Rate = number of contractions / beats per minute ä Normal Heart Rate = 60 to 100 beats per minute

CARDIAC OUTPUT ä Cardiac Output = amount of blood pumped by left ventricle in 1 minute ä FORMULA to determine cardiac output: Cardiac output [CO] = Stroke Volume [SV] X Heart Rate [HR]

End-Diastolic Pressure ä PRE-LOAD = pressure in the ventricles at the end of diastole ä Volume and pressure available to the ventricles for cardiac contraction ä Venous return AFTERLOAD = resistance against which the heart must pump ä Effects stroke volume and cardiac output ä

Starling’s Law of the Heart ä This concept is a law of physiology which states that up to a limit, the more myocardial fibers are stretched by chamber filling, the greater will be the force of contraction. “RUBBER BAND THEORY”, the farther you stretch a rubber band, the harder it snaps back to original size ä The

Peripheral Vascular Resistance [PVR] Peripheral vascular resistance = amount of opposition to blood flow offered by arterioles ä determined by vasoconstriction and vasodilation ä Measured as diastolic pressure BLOOD PRESSURE [BP] = Cardiac Output [CO] x Peripheral vascular resistance [PVR] ä

Cardiac Physiology ä Nervous Control of the Heart (ANS) Sympathetic ä Parasympathetic ä Autonomic Control of the Heart ä Chronotropy ä Inotropy ä Dromotropy ä

Autonomic Nervous System ä Regulates functions of the body that are involuntary or are not under conscious control ä Heart rate and blood pressure are regulated by this component of nervous system

Two Major Divisions of Autonomic Nervous System ä Sympathetic Nervous System = preparation of body for physical activity [ “fight or flight”] ä Parasympathetic Nervous System = regulates the calmer [ “rest and digest” ] functions of our existence

Nervous Control of the Heart

Receptors and Neurotransmitters ä Sympathetic Nervous System ä Receptors are alpha- and beta-receptors ä Chemical neurotransmitter is norepinephrine ä These nerve endings are called Adrenergic ä increase the heart rate and contractile forces of cardiac muscle and vasoconstriction Chronotrophy ä Inotrophy ä

Receptors and Neurotransmitters ä Parasympathetic System Nervous ä Muscurinic and nicotinic receptors ä Chemical neurotransmitter is acetylcholine ä Nerve endings are known as cholinergic ä The heart rate slows, as do atrioventricular conduction rates.

Adrenergic Receptors and Effect on Heart Rate Adrenergic - sympathetic nerve fibers that use epinephrine or epinephrine-like substances as neurotransmitters ä Receptor - a reactive site or cell surface within that combines with molecule to produce physiological effect ä Cholinergic - parasympathetic nerve fibers that use acetylcholine as neurotransmitter ä

Effects of Alpha / Beta receptors Organs affected by Alpha- and Beta-receptors Organ Affected Alpha Beta-1 Beta-2 Heart Yes No Lungs No No Yes Vessels Yes No Yes

Effects of Alpha and Beta receptors Alpha Beta-1 Beta-2 Vasoconstriction Increase HR Bronchial dilation Increase BP Vasodilation Increase contractility

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