Human Function Block 2 Lecture 9 (Cardiac Work and Metabolism)
What are the 4 determinants of myocardial o2 consumption?
HR, wall tension (aortic pressure), SV, and contractility
If you decrease contractility of the heart the O2 consumption
decrease O2 consumption
What do beta blockers do?
decrease intracellular Ca, decrease contractility, decrease HR
What do cardiac glycosides do? What is an example of one?
directly inhibit the Na-K ATPase, which leads to indirect inhibition of Na/Ca exchange--> increased intracellular [Ca++]--> increased cardiac contractility. Digitalis
When would the heart use more carbohydrates as the energy substrate rather than lipids?
exercise, hypoxia, hypertrophy, HF
When would the heart use more lipids as the energy substrate rather than carbohydrates?
fasting, diabetes
An increase in pressure of the ventricle will cause the O2 consumption to ...
greatly increase
Wasted work appears as what?
heat
An increase in HR will cause O2 consumption to
increase linearly
Wall movement is a (major/minor) influence on myocardial O2 consumption
minor
What is propranolol?
non-selective beta blocker
What is timolol?
non-selective beta blocker
What generally causes concentric hypertrophy?
pressure overload (increased after load)
Wasted or Internal work is caused by what?
the heart having to overcome internal resistance
What are the drugs that target calcium channel blockers
verapamil, diltiazem, nifedipine
What are the three ways to increase contractility?
1) Beta adrenergic agonists 2) Cardiac glycosides 3) Phosphodiesterase inhibitors
What type of hypertrophy can you create with exercise?
Eccentric (stretches heart cells length and width)
How much of ATP is use for ion transport?
1/3
Cardiac ATP stores are turned over every ___ seconds?
10
How much of ATP is used for contraction?
2/3
how much fo the total energy is useful?
3-10%
Why do we use the double product more than the tension time index to estimate myocardial metabolism?
Because it is hard to measure ejection duration; Double product=systolic P x HR
Does concentric or eccentric hypertrophy reduce tension per unit cross sectional area?
Concentric because total force is spread out over thicker wall
in what hypertrophy do you see myocyte width larger than myocyte length?
Concentric hypertrophy
What are myocytes preferred energy substrate?
Fatty acids (70% of total ATP)
When would the heart use almost completely carbohydrates as the energy substrate?
Fetal & neonatal
Which is the heart more efficient at preforming: flow work or pressure work?
Flow
What is concentric hypertrophy?
Heart walls thicken greatly, internal radius stays relatively the same
What is eccentric hypertrophy?
Heart walls thicken slightly, internal radius greatly increases
What do beta blockers do to EDV, ESV and stroke volume?
Increase ESV, Increase EDV and decrease SV; Increase MAP, lower contractility
increased aortic pressure results in a disproportionately increase in what?
Internal (wasted) work
What is Tension-Time index a measure of?
It is an index of Myocardial Metabolism; estimate of pressure duration product for venatical per minute
Kinetic work allows the ventricle to do what?
Keep pushing out blood even thought Aorta pressure is higher than LV
Cardiac positive inotropic drugs are given because they do what to EDV, ESV, and the ejection fraction?
Lower EDV and ESV, improve ejection fraction (SV/EDV)
There are two cycles (A and B) in a heart that have the same stroke work. Cycle B uses more pressure to complete the stroke work than cycle A. We know that cycle B must have a (higher/lower) stroke volume and has a (higher/lower) metabolic cost
Lower; Higher
Minute Work =
MAP x CO
Stroke Work =
MAP x SV
What is a phosphodiesterase inhibitor? What is an example of one
Prevents the degradation of cAMP to AMP, Increase [Ca], increase contractility. Amrinone
What is the Tension-Time Index?
TTI= mean systolic pressure x ejection duration x HR
what is the law of LaPlace?
The larger the vessel radius, the larger the wall tension required to withstand a given internal fluid pressure. T=Pr/2h h=(wall thickness)
What generally causes eccentric hypertrophy?
Volume overload
Most of the energy the heart produces appears as what?
Wasted energy, heat
What is carvedilol?
an adrenergic atagonist (alpha and beta blocker)
What is atenolol?
beta 1 antagonist
What is bisoprolol?
beta 1 blocker
What is metoprolol?
beta 1 blocker
What is Dilitiazem?
calcium channel blocker
What is Nifedipine?
calcium channel blocker
What is verapamil?
calcium channel blocker
