Definitions of terms and equations used

AbbreviationPhysiological parameterSignificance
PaCO2Arterial carbon dioxide tension (kPa)Reflective of the concentration of CO2 in the arterial blood
dDead space volume (L)Volume of air that is inhaled that does not take part in gas exchange
VTTidal volume (L)Volume of air moved into and out of the lungs during each ventilation cycle
VEMinute ventilation (L·min−1)Volume of gas exhaled/inhaled in 1 min, equal to the VT multiplied by the RR
VCO2Carbon dioxide production (L·min−1)
d/VTRatio of dead space volume to tidal volumeA higher value indicates a larger proportion of air not engaging in gas exchange within the lungs
VE/VCO2Gradient of the VE/VCO2 slopeThe minute ventilation required to exhale 1 L of CO2
Equation A: Embedded Image
RRRespiratory rate (min−1)Number of breaths taken per minute
dsystDead space volume of the apparatus used (L)Volume of air that remains within the CPET apparatus e.g. breathing valve, connectors and mouth piece exterior to the mouth
VeqCO2Ventilatory equivalent for carbon dioxideMeasures the efficiency of ventilation
Equation B: Embedded Image

Equation A describes the relationship of the VE/VCO2 slope to the physiological variables of PaCO2, d and VT. Equation B describes the relationship of VeqCO2 to the VE, dsyst, RR and VCO2. Definitions and significance of the relevant parameters are also described for the understanding of the presented equations CPET: cardiopulmonary exercise testing.