Non-invasive method for measuring lung tissue volume and pulmonary blood flow and a probe to carry out the method

Abstract

This is a non-invasive method for measuring pulmonary blood flow and lung tissue volume, called airway thermal volume consisting of dynamic registration of respiratory heat losses in ventilatory loading and/or humidity and temperature changes of the inspired gas. Pulmonary blood flow and airway tissue volume are calculated by solving the differential equation for nonsteady-state heat and mass exchange between the lungs and the environment. The lungs fraction as natural conditioner of the inspired air, having an inner heat source (pulmonary blood flow) and an outgoing heat stream calculated by measuring the volume ventilation and the temperature and humidity of inspired and expired air. Alterations of the baseline steady-state condition of lung respiratory heat exchange with the environment by changes in ventilation lead to achievement of a new steady-state condition where the heat stream from the lungs into environment is balanced by the heat stream from the circulation into the lung tissue. The maximal temperature of the expired air is taken as an initial relative value of lung tissue temperature, so that the quantity of maximal expired temperature change between two different steady-state conditions of lung heat exchange is proportional to the pulmonary blood flow, while the rate at which the new steady-state is achieved is proportional to the quantity of tissue mass. A probe for carrying out measurements includes a low-inertial device for temperature and humidity measurements of the expired and inspired air located in the middle of the airstream near the entrance to the upper respiratory tract, combined with a device for gas volumetric measurements and valves dividing in- and outflowing air for minimizing errors in air temperature and humidity measurements.

What is claimed is: .[.1. A method for carrying out pulmonary blood flow and airway thermal volume measurements of a body, comprising the steps of: 
     
        (t 0 .5) and said gas volume flow (V G )..]. .[.2.  The method of claim 1 comprising the steps of: providing cool dry gas mixture for said body to breathe such that said inspired gas temperature (T Go ) and said inspired gas absolute humidity (C o ) are cool and dry, respectively..]. .[.3. The method of claim 1 comprising the steps of:   providing a low-inertial humidity probe at the entrance of the respiratory tract of said body, and   measuring simultaneously, an expired gas temperature value (T) and said inspired gas temperature (T Go ) and said inspired gas absolute humidity (C o ), and   measuring a humidity (C) by means of said low-inertial humidity probe of said expired gas, and   calculating said pulmonary blood flow and airway thermal volume iteratively by means of a differential equation of lung heat balance in non-steady-state as a function of said humidity (C) and said expired gas   
     
     
        temperature value (T)..]. .Iadd.4.  A method for making pulmonary blood flow measurements of a body, comprising the steps of: (a) measuring a temperature of expired gas from a body;   (b) changing a rate of breathing of said body to vary its lung heat exchange;   (c) recording a curve of expired gas temperature versus time as the rate of breathing is changed;   (d) determining a time constant from the expired gas temperature versus time curve; and   (e) estimating a pulmonary blood flow rate as a function of said time   
     
     
        constant. .Iaddend. .Iadd.5.  A method for making pulmonary blood flow measurements of a body, comprising the steps of: (a) measuring a temperature of expired gas from a body;   (b) changing a humidity of a gas mixture breathed by said body:   (c) recording a curve of expired gas temperature versus time as the humidity of the gas mixture breathed by said body changes;   (d) determining a time constant from the expired gas temperature versus time curve; and   (e) estimating a pulmonary blood flow rate as a function of said time constant. .Iaddend. .Iadd.6. A method for making continuous pulmonary blood flow measurements of a body, comprising the steps of:   (a) measuring a temperature and a gas volume flow of expired gas from a body;   (b) changing a humidity of a gas mixture breathed by said body;   (c) recording a curve of expired gas temperature versus time as the humidity of the gas mixture breathed by said body changes;   (d) determining a time constant from the expired gas temperature versus time curve; and   (e) periodically estimating a pulmonary blood flow rate as a function of said time constant, expired gas temperature, and said gas volume flow, said pulmonary blood flow rate being thereby estimated on a substantially continuous basis. .Iaddend.