HEART PHYSIOLOGY

Physiology of Circulation Indicators of efficiency of a person’s circulatory system can be obtained by taking arterial pulse and blood pressure measurements. These, along with respiratory rate and body temperature, are called vital signs.

Heart Work Heart pumps the body’s 6 L of blood over 1,000 times a day = 6,000 L of blood in a day Atria contract (Luppa), then ventricles contract (Duppa) = Luppa Duppa Atria contracts 60 beats/min Ventricles contract beats/min Heart Rate - the number of beats per minute

Arterial Pulse The alternating expansion and recoil of an artery that occurs with each beat of the left ventricle creates a pressure wave – a pulse – that travels through the entire aterial system Normally, the pulse rate equals the heart rate It averages bpm Affected by activity, posture, and emotions

Heart Rate Palpated at one of several arterial locations close to surface Same spots used to stop hemorrhage, called pressure points Radial Carotid Brachial Popliteal Posterior tibial Dorsalis pedis Facial Temporal Use two fingers to palpate – not thumb Coordinated by electrical pacemaker within heart

The Electricity of the Heart Heart contains two special batteries called nodes Made of specialized cardiac tissue that can generate electricity – mixture of nervous and muscle tissue

Intrinsic Conduction System Nodal System – sets basic rhythm of heart Forces contraction rate of 75 beats/min so heart beats as coordinated unit Two nodes: Sinoatrial node (SA Node) Atrioventridcular node (AV Node) AV Bundle of His – bundle of fibers between atria and ventricles Purkinje fibers – spread within muscle of ventricle walls

SA Node (Sinoatrial) Located in RA near junction of SVC Starts heartbeat and sets pace = pacemaker Generates action potentials per minute Connects to AV node Tells atria to contract

AV Node (atrioventricular) Located on floor of RA Generates beats per minute on own Will usually follow rate of SA node Tells ventricles to contract Delays signal (to let atria finish contracting) Passes signal to bundle of His, then to Purkinje fibers

Control of Heart Rate Cardioinhibitory Center ANS– parasympathetic Normal everyday activity Vagus nerve releases Ach to slow heart Acts like a break Decreases heart rate Cardioacceleratory Center ANS – Sympathetic Fight or Flight response Cardiac nerve releases norepinephrine or adrenaline Increases heart rate

Electrocardiogram Also known as ECG Way to measure SA and AV nodes Attach electrodes to skin (moves thru water) Helps us know rhythm and strength of contractions

Reading the ECG P wave – SA node fires telling atria to contract called atrial depolar. QRS complex – AV node fires telling ventricles to contract called vent. Depolar. T wave – ventricular repolarization (reset)

Bradycardia Slow heart rate Usually below 60 Sign of large ventricle or athletic Also can mean death is near Characteristics on ECG?

Tachycardia Means fast heart rate usually over 100 Can mean small ventricle or exercising Death can result around 220 or higher Characteristics on ECG?

Ventricular fibrillation Bad News! Heart has uncoordinated contractions Cannot effectively move blood ECG characteristics? Will use a defibrillator

Atrial flutter Atrium is contracting quickly Many atrial contractions per ventricle contract. Why would this be Bad? ECG characteristics?

Cardiac Output Cardiac Output (CO) is the amount of blood pumped out by each side of the heart in 1 min It is the product of heart rate (HR) and the stroke volume (SV) Stroke volume is the volume of blood pumped out by a ventricle with each heart beat CO = HR X SV CO = HR (75 beats/min) X SV (70 ml/beat) CO = 5,250 ml/min (average adult human)

Regulation Starling’s law of the heart – critical factor of controlling stroke volume is how much the cardiac cells are stretched before they contract More stretch = more contraction Venous return – amount of blood entering the heart and distending its ventricles Anything that increases volume/speed of venous return also increases stroke volume and strength of contraction Example: a slow heartbeat allows more time for ventricles to fill

Blood Pressure Blood pressure is the pressure the blood exerts against the inner walls of the vessels Force that keeps blood circulating evenly Flows along a pressure gradient (high to low) from large arteries to small arterioles

Factors affecting B.P. BP = CO X PR where PR = Peripheral Resistance Peripheral Resistance – amount of friction the blood encounters in blood vessels Vasoconstriction – narrowing of blood vessels. Effect on BP? Increase in BP. When would this occur? Baroreceptors – e.g. when lying down Vasodilation – dilating of blood vessels. Effect on BP? Decrease BP During fight or flight

Factors affecting B.P. 1.Neural factors: ANS – vasodilation/vasoconstriction 2.Renal factors: kidneys – when BP high, kidneys allow more blood to leave body in urine 3.Temp – cold = vasoconstriction, warm = vasodilating 4.Chemicals – nicotine leads to vasoconstriction, alcohol leads to vasodilation 5.Diet – low salt helps prevent hypertension