CPX panel 2 Flashcards
What does panel two show?
the relationship between heart rate and O2 pulse (VO2/HR) vs time and work rate
What is O2 pulse?
stroke volume x AVO2 diff
*used as a surrogate for SV
What happens to this relationship in patients with CV disease?
HR is high, and VO2/HR is low for a given work rate
What could make the O2 pulse normal or high with CV disease?
with chronotropic incompetence (inability to raise HR) or B-adrenergic blockade (sows HR) without systolic or diastolic dysfunction
What is the immediate increase in O2 pulse at the start of exercise attributable to?
increase in SV
*SV will max out earlier
*AVO2 diff driven later
What is the relationship between work rate and O2 pulse?
as work rate increases the O2 pulse increases
*primarily because of increasing AVO2 diff
What causes the O2 pulse to plateau?
if SV is reduced, the AVO2 diff and, therefore, the O2 pulse reach maximal values t relatively low work rates
What conditions is O2 pulse low in?
anemia
high levels of carboxyhemoglobin
marked arterial hypoxemia
muscle mitochondrial or glycolytic enzyme defects
*because of reduced AVO2 at maximal
What is the equation that estimates SV from O2 pulse?
SV = (O2 pulse/C(AV)O2) x 100
What is the O2 rebound in pulse pressure after exercise?
O2 pulse promptly decreased in a normal subject
it often transiently increases in patients with HF and exercise-induced MI
Why does O2 rebound in HR patients?
the afterload of the LV is abruptly decreased when stopping exercise because of the immediate decrease in systemic arterial blood pressure
*allows improved ventricular ejection and increased SV
What does the increase in SV due to O2 rebound in heart failure patients cause?
allows capillary blood flow to move more rapidly through the lung during the heartbeat -> absorbing more O2
Why Is there not much difference between heart failure and control in AVO2 diff at peak exercise?
because of low CO in HF, the rate of RBC moving is slower, which increases the time for O2 diffusion
What relationship do you expect in panel 2?
linear, straight and fairly steep rise in O2 pulse
should come down immediately after exercise
