Apparatus for examining a patient's pulmonary function

Claim 1

Apparatus for examining and measuring the pulmonary function of a patient, comprising (a) a sealed reservoir (1) having an interior of variable volume, (b) an inhalation conduit (3) and an exhalation conduit (2), which are connected with the reservoir (1) and include one-way valve means (5,6) permitting flow of gas through the inhalation conduit only in the direction from the reservoir and permitting flow of gas through the exhalation conduit only in the direction toward the reservoir, (c) first connecting means (4) for connecting the inhalation conduit (3) and the exhalation conduit (2) with the respiratory tract of a patient to be examined, such that the patient can inhale from the reservoir (1) through the inhalation conduit and exhale into the reservoir through the exhalation conduit, (d) carbon dioxide adsorbing means (19) for removing carbon dioxide from a stream of gas flowing through the inhalation conduit (3), (e) monitoring means (17,18) for monitoring volumetric variations of the reservoir (1) resulting from the inhalation and exhalation of the patient and for determining the patient's total ventilatory rate, characterized by means (24) for selectively switching the carbon dioxide absorbing means (19) into the inhalation conduit (3), concentration measuring means (25) for measuring the carbon dioxide concentration of a gas mixture, second connecting means (26) for connecting the concentration measuring means (25) with the interior of the reservoir (1) and with the first connecting means (4), and a computing unit (3) which is connected with the concentration measuring means (25) and with the monitoring means (17,18) and which comprises computing means for computing the pulmonary blood flow Q p of the patient essentially in accordance with the equation ##EQU9## wherein MV is the patient's total ventilatory rate, P aCO2 is the carbon dioxide concentration in the reservoir (1) at equilibrium, when the patient inhales from and exhales into the reservoir (10 with the carbon dioxide absorbing means (19) switched into the inhalation conduit (3), P etCO2 is the carbon dioxide concentration of the gas exhaled by the patient at the end of an exhalation with the carbon dioxide absorbing means (19) switched into the inhalation conduit (3), P AstCO2 is the asymptotic value which the carbon dioxide concentration of the gas exhaled by the patient approaches at the end of each exhalation when the patient inhales from and exhales into the reservoir (1) with the carbon dioxide absorbing means (19) disconnected from the inhalation conduit (3), and S c is a known constant.