| General variables | V | Gas volume in general. pressure temp and percentage saturation |
| V̇ | Gas volume per unit of time |
| P | Gas pressure in general |
| F | Fractional concentration in dry gas phase |
| Q̇ | Volume flow of blood |
| C | Content in blood phase |
| f | respiratory frequency |
| R | respiratory echanfe ration in general (volume co / volume 02) |
| D | diffusing capacity in general (volume perunit of time per unit pressure difference) |
| symbols for gas exchange | I | inspired gas |
| E | Expired Gas |
| A | Alveolar gas |
| T | tidal gas |
| D | Dead space gas |
| B | barometric |
| a | arterial |
| v | venous |
| c | capillary |
| special symbols | ẋ | mean value |
| x̄ | time derivitave |
| x’ | end value |
| STPD | standard temperature pressure dry |
| BTPS | Body temperature saturated with water |
| ATPS | Ambient temperature saturated with wather |
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