TABLE 1
Definitions of terms and equations used
| Abbreviation | Physiological parameter | Significance |
| PaCO2 | Arterial carbon dioxide tension (kPa) | Reflective of the concentration of CO2 in the arterial blood |
| d | Dead space volume (L) | Volume of air that is inhaled that does not take part in gas exchange |
| VT | Tidal volume (L) | Volume of air moved into and out of the lungs during each ventilation cycle |
| V′E | Minute ventilation (L·min−1) | Volume of gas exhaled/inhaled in 1 min, equal to the VT multiplied by the RR |
| V′CO2 | Carbon dioxide production (L·min−1) | |
| d/VT | Ratio of dead space volume to tidal volume | A higher value indicates a larger proportion of air not engaging in gas exchange within the lungs |
| V′E/V′CO2 | Gradient of the V′E/V′CO2 slope | The minute ventilation required to exhale 1 L of CO2 |
Equation A: 
| ||
| RR | Respiratory rate (min−1) | Number of breaths taken per minute |
| dsyst | Dead 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 |
| VeqCO2 | Ventilatory equivalent for carbon dioxide | Measures the efficiency of ventilation |
Equation B:  | ||
Equation A describes the relationship of the V′E/V′CO2 slope to the physiological variables of PaCO2, d and VT. Equation B describes the relationship of VeqCO2 to the V′E, dsyst, RR and V′CO2. Definitions and significance of the relevant parameters are also described for the understanding of the presented equations CPET: cardiopulmonary exercise testing.