CPX panel 3 Flashcards
What relationship does panel 3 describe?
HR vs VO2 and VCO2 vs VO2 (AT)
What is the anaerobic threshold?
the level of exercise VO2 above which aerobic energy production is supplemented by anaerobic mechanisms
What is the AT reflected by?
an increase in lactation and lactate to pyruvate ratio in muscle and arterial blood
What is the underlying mechanism for AT measurement?
depends on the onset of anaerobic glycolysis, leading to a net increase in lactic acid production
When does lactic acidosis develop?
at work rates above the AT
How can AT be defined physiologically?
the VO2 above which the critical capillary PO2 has been reached, and production of ATP through anaerobic glycolysis supplements the aerobic ATP production
How does the redox state within the cell change at the AT?
as the VO2 at which lactate
and L/P ratio increase (LT); or in terms of acid–base balance change, as the VO2 at which lactic acidosis develops (lactic acidosis threshold [LAT])
What is the AT measurement influenced by?
the size of the muscle groups involved in the activity
What is the lactate and bicarbonate response during incremental exercise?
both increase
*with training longer buffering time before AT
How does bicarbonate buffer H+ production before the AT?
H+ production increases when lactate accumulates in the cell
bicarbonate is generated from the reaction accompanying hydrolysis of PCr in muscle during early exercise
above this initial increase in lactate, bicarbonate buffers newly produced H+
What is the response of CO2 above the AT?
an increase in CO2 production that is produced above that from aerobic metabolism
How is cellular lactic acidosis detected?
measuring the rate of increase in VCO2 relative to that of VO2 during progressively increasing exercise test
*slope is greater than 1.0
Why is gas exchange an effective measure in detecting cellular metabolic acidosis?
the time delay between the bicarbonate buffering of lactic acid in the cell and its appearance in the lung gas is only a few seconds
What is mechanism one of gas exchange in an exercise test?
gas exchange that results solely from the buffering of newly foreign lactic acid
What is the sequence of events that causes rate changes in VCO2 at the AT?
increase in lactate ->
decrease in bicarbonate ->
VCO2 non-linear increase with WR & VO2 linear increase with WR
decrease in pH
What is the V-slope?
when the net increase in lactate accumulation produces an acidosis, VCO2 accelerates relative to VO2
What is the V-slope method?
when VCO2 and VO2 are plotted against each other, the relationship is composed of two linear components
*where they intersect = AT
At what % peak VO2 does AT occur at?
about 50-60%
- increasing age = small increase where AT occurs relative to peak VO2
Why does HR often increase steeply in an exercise test of someone with heart disease?
HR increases relatively steeply for the VO2 because the SV is reduced
*maintain CO
When does VO2 commonly slow its rate of increase with work rate?
when the myocardium becomes ischemic
Why is pulmonary vascular disease associated with a steep HR response?
venous return to the left side of the heart -> LV output is low
What is HR reserve?
a measure of the difference between the predicted maximal heart rate, based on age, and the measured heart rate at peak VO2
What is HR reserve normally?
relatively small
less than 15bmp
What is HR reserve in patients with silent myocardial ischemia, valvular HD?
usually normal
