Physiology of heart Flashcards
Facts
- heart beats 115,000x/day
- 2000 gallons of blood/day
- aorta is almost the diameter of a garden hose
- capillaries are so small that it takes ten of them to equal the thickness of a human hair
Hemodynamics
Used to describe a collection of mechanisms that influence the active and changing (dynamic) circulation of blood
- circulation of different volumes of blood per minute at different times is essential for survival
- circulation control mechanisms must accomplish 2 functions: maintain a circulation and vary volume and distribution of the blood circulated
Cardiac cycle
Complete heartbeat or pumping cycle consisting of contraction (systole) and relaxation (diastole) of both atria and both ventricles
Systole
Contraction of both ventricles of the heart forcing blood out of these chambers
- atria are in a relaxed state
Diastole
Ventricular muscles relax, allowing for blood to fill these chambers
- at the end, the atria start contracting to fill the ventricles
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Autorhythmic cardiac muscle fibers
These repeatedly generate action potentials that trigger contraction
- they continue to stimulate a heart beat even after the heart has been removed from the body (for several minutes)
- ensures that the cardiac chambers are stimulated to contract in a coordinated manner
- hormones, chemicals, and nerve impulses can alter the heartbeat strength and heart rate but do not change the coordinated contractions of the heart
Conduction system has four structures
- Sinoatrail node
- Atrioventricular node
- AV bundle (bundle of His)
- Subendocardial branches (purkinje fibers)
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SA node
Natural pacemaker of the heart
- initiates each heartbeat and sets its pace
- located high in the R atrial wall
- impulses spread from the SA node to the muscle fibers of both atria causing atrial contraction
- fires between 60-100 BPM
AV node
Acts as the only gateway for electrical impulses from the atria to the ventricles
- located at the base of the R atrium
- electrical activity travels very slowly thought the AV node
AV bundle (bundle of His)
- AV node stimulation sends impulses to the AV bundle of His
- the bundle of His carries electrical impulses (action potentials) into the ventricles
- bundle of His impulses travel though the R and L bundle branches to the purkinje fibers
Subendocardial branches
Purkinje fibers
- fibers that further spread electrical activity to all parts of the ventricles so that there is a coordinated contraction of each ventricle
electrocardiogram
ECG or graphic record of the heart’s electrical activity, specifically the conduction of impulses
- it is not a record of the heart’s contractions, but of the electrical events/current that precede them
- a composite record of action potentials produced by the heart muscle fibers during each heartbeat
- changes in voltage are seen as deflections of a line drawn on a paper or traced on a video monitor
- the normal ECG is composed of defection waves called P wave, QRS wave, and T wave
- 12lead ECG obtains 12 electrical tracings of the heart from different angles or orientations
- patterns of abnormalities can indicate areas of abnormal conduction
- these abnormalities can correlate to areas of decreased blood flow
ECG pic
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P wave
Represent depolarization of the atria
- deflection related to passage of an electrical impulse from the SA node thought the muscle of both atria
QRS complex
Represents depolarization of the ventricles and repolarization of the atria
T wave
Represents ventricular repolarization
P-R interval
The length of time for atrial depolarization and conduction from the SA node to the AV node
ST interval/segment
The time period from the end of ventricular depolarization through ventricular repolarization
- clinically, unhealthy myocardium can affect the height of this interval (either upward or downward)
Cardiac cycle
- complete heartbeat consisting of systole and diastole of both atria and ventricles
- two atria contract simultaneously filling the ventricles more efficiently
- as the atria relax, the two ventricles contract, instead of the entire heart contracting as one unit. Allows for a pumping action o the heart
Cardiac cycle events
- atrial systole
- isovolumetric ventricular contraction
- ejection
- isovolumetric ventricular relaxation
- passive ventricular filling
Atrial systole
- begins with the P wave of the ECG: electricity precedes contraction
- the atria contract simultaneously completing emptying blood out of the atria into the ventricles
- AV valves are open
- SL valves are closed
- ventricles are relaxed and filling with blood
Chart
Chart
Isovolumetric ventricular contraction
- onset of ventricular systole coincides with R wave and appearance of the first heart sound (S1), as the AV valves close
- between the start of ventricular systole and the opening of the SL valves
- volume in the ventricles remains constant as the pressure increases rapidly = isovolumetric contraction
Ejection
- pressure increases enough to open the aortic and pulmonary SL valves and blood is ejected from the heart
- blood enters the systemic and pulmonary circulations via the aorta and pulmonary artery
- this period coincides with ST interval
- residual volume: the blood that remains in the ventricles at the end of the ejection period (roughly half)
Isovolumetric ventricular relaxation
- ventricular diastole/relaxation begins with an isovolumetric period
- occurs between closure of the SL valves and opening of the AV valves
- closure of the SL valves produce the second heart sound (S2)
- this corresponds to the T wave and continues until the next P wave
- there is a dramatic fall in intraventricular pressure
Passive ventricular filling
- returning venous blood increases intraatrail pressure until the AV valves are forced open and blood rushes into the relaxing ventricle
- results in a dramatize increase in ventricular volume before the atria contract
- lasts about 0.1 sec
Cardiac output
Amount of blood that flows out of a ventricles of the heart per unit of time
- (mL/min) = stroke volume (mL/beat) x HR (beats/min)
Stroke volume
Measured by the mL of blood pumped out of the L ventricles in one stoke (beat)
At rest vs during exercise
CO = SV (70mL/beat) x HR (75bpm) = 5250 mL/min
CO = SV (140 mL/beat) x HR (150 bpm) = 21000mL/min
Heart sounds
- the heart makes certain typical sounds during each cardiac cycle
- sounds like lub dup
- sounds are created by blood turbulence and vibration as valves close
- **
- S1, lub: comes with the closure of the mitral and tricuspid valves as ventricular systole begins
- S2, dup: comes with the closure of the aortic and pulmonary SL valves as systole ends and diastole begins
- any variation from normal in these sounds indicates imperfect functioning of the valves
- surgery can repair damaged valves
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Stethoscope
- using the bell is most useful for low sounds nand may work best with pediatric patients
- using the diaphragm is most useful for higher pitch sounds
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Using a stethoscope
- with men, the stethoscope can be placed under the shirt or removal of the shirt if necessary
- with women, it may be necessary to remove bra, and/or use a gown
- with women, it may be necessary for the pt to move the left breast, so that the stethoscope can be applied to the chest wall in the correct positions
- clean stethoscope bell/diaphragm with alcohol between pts
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Preload:
Degree of stretch on the heart prior to contraction
Contractility
Forcefulness of contraction of individual ventricular mm fibers
Afterload
Pressure that must be exceeded before the ejection of blood from the ventricles can occur
CAD
Reduction of blood flow to the myocardium
- leading cause of death for men and women
- arteriosclerosis/atherosclerosis
cardiomegaly
- physiological: hypertrophy related to fitness training
- pathological: related to heart disease
CHF
- loss of pumping efficiency by the heart
- caused by CAD, congenital defects, long term high blood pressure, valve disorders
Tachycardia
Heart rate higher than the normal SA node range 60-100
- med related
- hyperthyroidism
- increase in interstitial Ca+
Bradycardia
A resting heart rate under 50 BPM
- can be normal depending on fitness level
- med related
- bradycardia
- tachycardia
- fibrillation
