Derivation of VA/Q distribution from blood-gas tensions.

Gas exchange was modelled by a Fortran program. Arterial blood-gas tensions have higher resolution than inert gas retentions in terms of distinguishing a single VA/Q compartment from a progressively broadening lognormal distribution. The maximum number of compartments determinable by arterial blood-gas tensions is three; VA/Q distributions containing more compartments are non-unique. Without utilizing 100% inspired oxygen, arterial blood-gas tensions cannot resolve the relative perfusion in shunt and low-VA/Q compartments, but the total perfusion in these compartments is determinable. The way in which the arterial blood-gas tensions vary with the variables of two and three-compartment distributions is described. Two- and three-compartment VA/Q distributions are derivable from either arterial blood-gas tensions or inert gas retentions.