Cardiovascular Physiology - Exercise Testing Flashcards
What is CPET?
IMAGE CPET graph
Cardiopulmonary exercise testing is a non-invasive method of testing cardiac and pulmonary function together, in order to assess the body’s physiological reserve, and thus, ability to meet metabolic demands of an operation.
It is more effective at diagnosing HF/IHD than echo and treadmill stress ECGs.
Usually performed on a stationary cycle ergometer, measuring power output, ECG, Spirometry, inspired and expired O2/CO2 levels, and blood pressure.
There are three key parameters:
VO2 Max (Peak O2 Consumption)
AT (Anaerobic Threshold)
VEq (Ventilatory Equivalents)
What are the three key parameters derived from CPET?
IMAGE of graph with the points highlighted
Key parameters:
Peak O2 Consumption (VO2 max) - measured in ml/min/kg
Measure of the maximum aerobic capacity of the patient’s body - the point where oxygen consumption plateaus and cannot be increased further.
A VO2 Max of <800ml/kg/min suggests a substantially higher cardiovascular risk profile
Anaerobic Threshold (AT) - measured in ml/min/kg
When the patient switches from pure aerobic to mixed anaerobic/aerobic respiration, producing lactate, which is buffered by bicarbonate - resulting in excess CO2 exhalation.
Usually around 60% of VO2 Max.
An AT of <11ml/kg/min suggests cardiovascular morbidity.
Ventilatory Equivalents (VEq) - unit-less ratio
The number of litres of ventilation required for each litre of O2 consumed, or CO2 produced.
Measure of efficiency of the cardiopulmonary system.
The smaller the ratio, the more efficient the system, and a larger ratio is caused by VQ mismatch
What techniques are used to measure AT in CPET?
Anaerobic Threshold
IMAGES
V Slope Method - VCO2 plotted against VO2 on a graph. Anaerobic respiration is followed by a sharp rise in CO2 production
VO2 and VCO2 vs work rate Both are plotted against work (in watts).
VCO2 is initially lower than VO2 (as the respiratory quotient is less than 1)
Anaerobic threshold is the point where VCO2 exceeds VO2.
Minute ventilation vs work rate
Ventilation steadily increases with the oxygen demand of the work done, until the anaerobic threshold, where it quicly increases in order to blow off excess CO2, similar to the V Slope method.
