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 20-40

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 70-76 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 70-80 action potentials per minute

• Connects to AV node• Tells atria to contract

AV Node (atrioventricular)• Located on floor of RA• Generates 40-60 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