Lecture 27 10/23/23 Flashcards
(25 cards)
What factors determine cardiac output?
-heart rate
-preload
-afterload
-contractility
What two factors determine the regulation/distribution of cardiac output?
-venous return
-vascular resistance
What is heart rate, in terms of cardiac cycles?
the number of cardiac cycles per minute
How does heart rate relate to cardiac output?
direct relation (one increases, the other increases)
What is afterload related to?
-aortic pressure
-ventricular geometry
Why is afterload considered to be complex?
the factors affecting it vary with each cardiac cycle
How does afterload relate to ventricular emptying/stroke volume?
increased afterload = harder for ventricle to empty (inverse relationship between afterload and stroke vol.)
What are the key points of afterload?
-forces that oppose myocardial shortening
-inversely related to stroke volume
How do contractility and stroke volume relate?
increased contractility = increased stroke vol.
What are the characteristics of the Frank-Starling mechanism?
-describes length-tension relationship of intact heart
-describes relationship between preload and cardiac output
How does preload relate to stroke volume?
increased preload (increased ventricular filling) = increased stroke vol.
How does ventricular filling relate to myocardial contraction?
increased end-diastolic volume/ventricular filling and stretch = increased force of contraction
What are the microscopic characteristics of the Frank-Starling mechanism?
-stretch optimizes myosin-actin interaction
-stretch increases sensitivity of troponin-C to Ca2+
What is the Fick principle?
cardiac output is inversely related to arteriovenous oxygen difference
What is an example of the Fick principle?
-fast-moving blood = less O2 used = smaller arteriovenous difference = greater cardiac output
Why does the Fick principle exist?
the slower blood moves, the more oxygen is extracted, causing a larger arteriovenous difference in oxygen conc.
What are the characteristics of physiologic sinus arrythmia?
-normal p-wave preceding QRS by a consistent interval
-vagal input required, occurs at low heart rates
-gradual changes in RR
-rate increases with inspiration
-abolished by atropine
What determines CO according to Frank-Starling?
venous return
How does vascular resistance impact afterload?
vascular resistance changes in response to pressure and flow, and changes the associated afterload
What is a cardiac output curve?
graph showing the relationship between preload and cardiac performance
What are the determinants of venous return?
-intravascular volume
-muscular venous pump
-venous tone
How does venous return impact preload and stroke volume?
increased venous return = increased preload and increased stroke volume
What local factor impacts distribution of cardiac output?
increase in metabolism results in dilation of arterioles and local decrease in resistance/increase in flow
What autonomic factor impacts distribution of cardiac output?
sympathetic tone causes vasoconstriction and local increase in resistance/decrease in flow
