Cardiac Physiology Flashcards
What drugs affect Ca release/reuptake by the sarcoplasmic reticulum?
Depress Ca –> depress contractility
- Volatile anesthetics
- Nitrous oxide
- Local anesthetics
- Acidosis
Increase Ca –> increase contractility
- Phosphodiesterase inhibitors (Milrinone)
- Digitalis
Anesthetic-induced cardiac depression is made worse by what? (3)
hypocalcemia
beta blockers
calcium channel blockers
What is the major cardiovascular control center in the brain?
Where is the secondary center?
What center adjusts cardiac reaction to emotional states?
Medulla
Hypothalmus
Cerebral cortex
______ fibers primarily innerate the atria and the conducting tissues.
Parasympathetic
ACh acts on specific cardiac ______ receptors to prduce negative effects.
What are theose muscarinic receptors called?
muscarinic
M2
What are the types of M2 receptors and what are their functions? (3)
chronotropic (HR)
inotropic (contractility)
dromotropic (conduction velocity of AV node)
______ fibers are more widely distributed throughout the heart.
Sympathetic
What are the sympathetic fibers that are widely distributed throughout the heart? (2)
Cardiac sympathetic fibers (T1-T4)
B1-adrenergic receptors from release of norepi
Where are B2-adrenergic receptors found in the heart?
How do these receptors function?
primarily in the atria, but only a few
activation increases HR mainly, some contractility
Neural receptors in the lungs causes HR to _____ during inspiration and _____ during expiration.
increase
decrease
The increase in HR during inspriation is caused by what?
The stretching (activation) of vagal fibers in the lungs cause HR to speed up by inhibiting cardioinhibitory center of the medulla.
Where are the baroreceptors located? (2)
aortic arch
carotid arteries
What changes do the baroreceptor reflex cause? (2)
blood vessels dilate
HR decreases
Baroreceptor reflex returns BP to normal levels. True or false?
False, returns to its previous level which may or may not be normal.
Note: The higher the BP, the greater the reflexive decrease in HR. If BP is decreased, the reflex accelerates HR and causes vessels to constrict.
The baroreceptor reflex is more effective in compensating for a decrease in arterial BP than a rise in pressure. True or false?
true
The myocardium usually extracts____ of the oxygen in arterial blood, compared with____ in most other tissues.
65%
25% (Think of SaO2 - mixed venous)
Thus, the myocardium (unlike other tissues) cannot compensate for reductions in blood flow by extracting more O2 from Hb.
How are increases in myocardial oxygen demand met?
increased coronary blood flow
When does perfusion occur?
during diastole
Note: Increased supply ability with lower heart rates. Fast heart rates diminish the time in diastole (thus decreasing time for coronary filling)
How do you calculate coronary perfusion pressure (CPP)?
Arterial diastolic - LVED (end diastolic)
Note: Decreases in aortic pressure or increases in LVEDP can reduce coronary perfusion pressure.
What is CaO2 equation?
1.36 mLO2/gm Hb x Hb(gm/dL) x SaO2/100 +0.0031 mLO2/(mmHg)dL x PaO2 (mmHg)
What factor significantly alters oxygen supply?
hemoglobin concentration
What factors will worsen blood flow into the coronary arteries? (2)
aortic stenosis
aortic regurgitation
What factors will increase myocardial oxygen demand? (4)
LV hypertrophy
Increased HR
Increased wall tension: increased ventricular volume (preload), increased blood pressure (afterload)
Increased contractility
Ventricular systolic function involves ventricular _______, whereas diastolic function is related to ventricular ______.
ejection
filling
To compensate for variations in body size, CO is often expressed in terms of _______.
cardiac index
CI = CO / BSA
Note: Remember CO = SV * HR
How do you calculate BSA?
BSA (m²) =
( [Height(cm) x Weight(kg)]/ 3600 )½
What is the normal range for CI?
2.5 – 4.2 L/min/m2
A decrease in mixed venous oxygen saturation in response to increased demand (ex. Exercise) usually reflects what?
inadequate tissue perfusion
What is normal mixed venous O2 sat in %?
65-75%
In the absence of what 2 conditions does measurement of mixed venous oxygen tension best determine the adequacy of CO?
hypoxia
severe anemia
How do we determine cardiac performance? (4)
Cardiac output
Cardiac index using BSA
Mixed venous gas
Lactic acid can indirectly assess CO (often used in peds)
How are cardiac muscle cells oriented in the ventricular wall?
circumferentially
The _____ of the ventricle affects the way that the length-tension relationship of cardiac muscle fibers influence the volume and pressure of the ventricular chamber.
shape
What is important to know in understanding cardiac dilation and hypertrophy?
LaPlace’s Law
T ∝ P x r
What does the Frank-Starling state?
The greater the volume of blood entering the heart during diastole (end-diastolic volume), the greater the volume of blood ejected during systolic contraction (stroke volume).
As the heart fills with more blood, the force of the muscular contractions will increase. True or false?
True, but only to a certain point.
The stretching of the muscle fibers increases the affinity of _________ for Ca2+.
troponin C
Stroke volume is regulated by what 3 factors?
Preload
Afterload
Contractility
What is defined as the “muscle length prior to contraction”?
preload
What is “tension against which the muscle must contract”?
afterload
What is the pressure generated in the left ventricle at the end of diastole?
Preload
What is the resistance or impedance to ejection of blood from the ventricle?
Afterload
What is the “intrinsic property of the muscle that is related to the force of contraction but is independent of both preload and afterload”?
contractility
Preload is also known as what?
end-diastolic volume
Ventricular filling is influenced by? (3)
Venous return
HR
Heart rhthym
Note: Important because preload is dependent on ventricular filling.
What is afterload measured?
systemic vascular resistance
In the absence of significant pulmonary or RV dysfunction, venous return is also the major determinant of the LV preload (the heart can only pump out what it receives). True or false?
True
Increases in HR cause greater reductions in diastole than systole. True or false?
True
Ventricular filling therefore progressively becomes impaired at high HR (>120 in adults).
Atrial arrhythmias can also reduce ventricular filling (by 20-30%) due to loss of what?
‘atrial kick’
About 15-20% of vent. filling comes from atria squeeze.
Label Starling’s Preload curve
What is used to measure preload?
CVP
Normal = 2-8 mmHg
Useful to monitor trends in preload and volume.
Changes in patient position can alter CVP without actual changes in volume status. True or false?
True
Side note: CVP is a measure of pressure in the central venous pool, which corresponds to the volume in the right atrium and the great vessels in the thorax.
What pressure is nearly equal to central venous pressure (CVP)?
end diastolic pressure in the RV
How do we control CVP? (6)
Blood volume
Gravity (reduces CVP)
Peripheral venous tone (constriction increase CVP)
Muscle pump (compression increase CVP)
Respiration
Cardiac output (venous to art lowers CVP)
Note: Fall in CVP and rise in art pressure can act as a BRAKE on ouput!
Left atrial pressure should be equal to what other pressure?
Left ventricular pressure with the pulmonary catheter balloon up (wedge pressure)
Note: Exception mitral valve stenosis, values may be different.
Again, how do we estimate LVEDP clinically?
PCWP with PA cath
LVEDP can only be used as a measure of preload only if relationship between ventricular _____ and _____is constant.
volume
pressure (compliance)
What conditions can disrupt early diastolic LV compliance? (3)
Hypertrophy
Ischemia
Asynchrony
What are SVR and PVR equations?
SVR= 80 x (MAP-CVP/ CO)
900-1500 dyn * s cm-5
PVR = 80 x (PAP-LAP/ CO)
50-150 dyn * s cm-5
Left is systemic, right is pulmonary vascular resistance.
Myocardial contractility is depressed by what factors? (4)
Anoxia
Acidosis
Depletion of catecholamine stores within the heart
Loss of functioning muscle mass
- Ischemia
- Infarction
What 2 factors increase stroke volume?
What factor decreases stroke volume?
Cardiac sympathetic nerve activity, Filling pressure
Arterial pressure
What are wall motion abnormalities? (3)
Reduce length-tension relationship
- Hypokinesis (decreased contraction)
- Akinesis (failure of contraction)
- Dyskinesis (paradoxic bulging)
Due to ischemia, scarring, hypertrophy or altered conduction
Emptying is impaired
What are points A, B, C, D?
A: Compensated heart failure
B: Uncompensated heart failure
C: Sympathetic stimulation to help with CO
D. Long-term compensated heart failure
What is EF equation?
(EDV-ESV) / EDV
Normal is 60-70%
How do we measure diastolic function?
doppler echocardiography
