Patent ID: 6254546
Filing Date: 2001-07-03
Classification: A61B

Abstract:
A method for determining the distribution of the tidal volume (V.sub.t) of gases inspired by a subject into his/her lungs, the distribution being among a plurality of compartments (i), each compartment having an assigned ratio value of a compartmental tidal volume (V.sub.ti) to a compartmental perfusion (Q.sub.i) and an assigned ratio value of the compartmental tidal volume (V.sub.ti) to a compartmental volume (V.sub.ai) so that the compartments, collectively, cover at least one of a range of ventilation/perfusion ratio (V.sub.t /Q) values and a range of ventilation/volume (V.sub.t /V.sub.a) ratio values, said method comprising the steps of:(a) causing the subject to inspire a bolus of analytical gases in a tidal volume of breathing gases, the analytical gases of the bolus having differing solubilities in the blood of the subject and being inspired in known amounts;(b) measuring the concentrations of the analytical gases in the breathing gases expired by the subject for at least one breath of the subject;(c) expressing the expired concentrations of analytical gases in a formF.sub.exp (.lambda.,n)=(V.sub.bolus /V.sub.t.sup.2).SIGMA..sub.i V.sub.ti g(x.sub.i,y.sub.i,.lambda.,n) (8)whereg(x.sub.i,y.sub.i,.lambda.,n)=x.sub.i /(x.sub.i +1).sup.n exp(-.lambda.x.sub.i n.DELTA.t/(y.sub.i (x.sub.i +1))) (9)wherein:F.sub.exp =expired analytical gas concentrationV.sub.bolus =volume of analytical gas bolusV.sub.t =tidal volumeV.sub.ti =compartmental tidal volumeV.sub.ai =compartmental alveolar volumeX.sub.i =compartmental ventilation/volume ratio, V.sub.ti /V.sub.aiy.sub.i =compartmental ventilation/perfusion ratio, V.sub.ti /Q.sub.i.lambda.=solubilityn=breath number.DELTA.t=duration of breath(d) solving the expressions of step (c) to obtain a compartmental tidal volume (V.sub.ti) distribution among the compartments that represents a solution to the expressions of step (c).