Cardiopulmonary stress testing Flashcards
Definitions of VO2, MVO2, RQ, RER, Lactic Acid
VO2 – Oxygen consumption: Amount of oxygen utilized by the body’s metabolic processes
MVO2 – Maximum oxygen consumption: Measured at peak exercise
RQ – Respiratory quotient: Ratio of the rate of carbon dioxide production to oxygen consumption at the tissue level
RER – Respiratory exchange ratio: Measurement of RQ at the atmospheric level
Lactic Acid – One of the end products of glucose oxidation and is a marker of anaerobic metabolism
What are the physiologic goals during exercise?
Supply oxygen
Eliminate carbon dioxide
Maintain acid/base balance
What changes occur to lungs, heart, circulation?
Lungs: Increase alveolar ventilation 20 fold
Heart: Increase cardiac contractility and heart rate
Circulation:
Pulmonary artery vasodilation – Decrease PVR
Systemic vasodilation – Reduces afterload
More oxygen extraction – Reducing venous oxygen
What is the pKa of lactic acid?
What is the pH of muscle?
How is it buffered?
pKa = 3.9
pH of exercising muscle is 7.00
Biacarbonate is primary buffer, decreases equal number of mMol as lactate increases
What is the anaerobic threshold?
What is the critical PaO2 of exercising muscle?
Why is it important?
What is the threshold with respect to maximal metabolic rate?
Describes the level of VO2 at which the critical capillary PaO2 has been reached for a given work load
Critical PaO2 of exercising muscle approaches 15-20 mm Hg: Aerobic metabolism ceases, anaerobic metabolism ends
Important physiologic marker when homeostasis is no longer maintained
Anaerobic threshold occurs at approximately 60% of maximal metabolic rate
What are the phases of exercuse and the transitions?
Phase I – Very light exercise
First LactateTransition I to II: “Aerobic threshold” (40-60% of MVO2)
Phase II – Light to moderate exercise
Second Lactate Transition II to III: “Anaerobic threshold” (60-90% of MVO2)
Phase III – Heavy exercise
What is the invasive measurement of lactate?
What is the non-invasive method of measurement?
Drawing blood lactate levels
Non-invasive: Plotting VCO2 as a function of VO2
Determining two different regimes of CO2 increase and slopes of each
Intersection of the two regimes: Anaerobic threshold
What is CPET?
Procedure of CPET?
What does CPET assess?
CPET – Cardiopulmonary Exercise Testing
CPET is a progressive workload test
Patient exercises to exhaustion and/or until symptoms are reproduced
CPET assess the integrated physiology of the cardiac and respiratory system to determine which is limiting the patient: lung or heart
What are the measuremetns involved in a CPET?
Pre/post spirometry
Lactate and blood gas at rest/exercise
O2 consumption
CO2 production
Tidal volume
Respiratory rate
Minute ventilation
What is CPET indicated for?
Most commonly for evaluation of unexplained dyspnea
Undiagnosed exercise intolerance
Suitability for heart and/or lung transplant
Pre-operative evaluation (will patient survive surgery)
Disability determination
Prognostication
Do not do on patient who become unstable on exercise
What are potential limiting factors for exericse?
Cardiac (most often for healthy individuals), pulmonary (most often for healthy horses), muscular, deconditioning, obesity, poor effort/motivation
What are the values for METS?
1 – Sitting
4 – Light housework
6 - Heavy housework (mopping vacuuming)
How much of a change of lactate indicats anaerobic metabolism?
Change of 6 or 7 indicates anaerobic metabolsim
