Clinical cardiac and pulmonary physiology Flashcards
equation: MAP
MAP = SVR x CO
equation: SVR
80 x (MAP-CVP)/CO *80 converts mmHg and L/min into dyne/s/cm^5
relationship between resistance and radius
resistance inversely proportional to r^4
Where is most resistance to blood flow?
arterioles (not capillaries bc large combined area)
equation: CO
HR x SV
normal EF and causes of change
60-70%
increased in hyperdynamic states (sepsis, liver failure)
decreased in poor cardiac function
measures of preload
EDV, LA pressure, PCWP (~LA), PA diastolic pressure
causes of low preload
hypovolemia, venodilation, tension ptx, pericardial tamponade
systolic pressure variation
changes in SBP with tidal breathing or ventilation that may be observed on arterial blood pressure tracing; extreme form is pulsus paradoxus
pulse pressure variation
analagous to SPV, calculated by computer
= (PPpeak-PPnadir)/PPavg
What shifts LV filling pressure vs. CO/SV curve down and to the right?
lower contractility or higher SVR
conditions associated with decreased myocardial contractility as a cause of hypotension
myocardial ischemia, anesthetic drugs, cardiomyopathy, previous MI, valvular heart disease (dec SV independent of preload)
What shifts cardiac cycle loop down and to left on systolic pressure-volume relationship curve?
decreasing SVR
Sympathetics effect on heart
stimulation: activates B1 receptors, increasing HR via AV node conduction; increases contractility
Parasympathetics effect on heart
stimulation: profoundly slowed heart rate via muscarinic ACh receptors in SA and AV nodes
suppression: increased HR, minor effect on contractility
location and activation of baroreceptors
carotid sinus and aortic arch
-increased systemic BP -> stretch receptors signal via vagus and glossopharyngeal to CNS -> parasympathetic-mediated dec in HR and decreased sympathetics = dec contractility and reflex vasodilatation
sensitivity of baroreceptors
varies; altered by longstanding HTN
Bainbridge reflex
atrial stretch -> increased HR, helps match CO to venous return
location and activation of chemoreceptors
carotid sinus
arterial hypoxemia -> sympathetic stimulation
prolonged hypoxemia -> bradycardia, possibly via central mechanisms
oculocardiac reflex
increased ocular pressure -> bradycardia
what reflex occurs with abdominal visceral stretch?
bradycardia