Question

2. (4) Spirometer volume measurements are made in units of ATPS(ambient temperature and pressure, saturated with water vapor at the ambient temperature). Volume measurements can be used to measure lung volumes or metabolic rate from timed volume change measurements. ATPS values must be converted to BTPS(body temperature(generally 37 deg C), ambient pressure, and saturated with water vapor at body temperature) or STPD(0 deg C, 760 mm Hg barometric pressure, and dry)-used for metabolic rates and diffusion capacity measurements. A volume measurement of 1.7 liters ATPS is made(25 deg C, barometric pressure B=720 mm Hg , saturated with water vapor at 25 deg C, ). a) (1) Calculate this volume in BTPS(body temperature 37 deg C, B-=720mm Hg, saturated with water vapor at 37 deg C). b) (2) Calculate this volume in STPD units. PH20(25)=23.8 mm Hg PH2O(37)=47 mm Hg

Answer 1

(a) Following conversion formula is used to convert volume at ATPS to volume at BTPS

where T_b = Body temperature = 37⁰ C , T_r = Room temperature = 25⁰ C, P_B = Barometric pressure = 720 mm Hg,

P_{H2O at Tr} =  water vapour partial pressure at room temperature = 23.8 mm Hg,

P_{H2O at Tb} =  water vapour partial pressure at body temperature = 47 mm Hg.

(b)Following conversion formula is used to convert volume at ATPS to volume at STPD