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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 non-steady-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.

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First Claim