| 摘要 |
A method for measuring anatomical dead space in a lung, the method comprising: (a) providing, in a supply of inspired gas, at least one indicator gas for inhalation by a patient during a test, the concentration of the indicator gas being controlled such as to follow a sinewave pattern over successive breaths; (b) measuring, over successive breaths, the flow rate and concentration of the indicator gas during both inspiration and exhalation of the patient; (c) fitting sinewave envelopes to the measured concentration values of the indicator gas over the successive breaths and, from the fitted sinewave envelopes, determining the inspired concentration, the mixed expired concentration, and the end expired concentration in respect of the indicator gas for each breath; and (d) calculating the anatomical dead space for each of a plurality of inspirations based on a conservation-of-mass principle. Also provided is a test apparatus for carrying out such a method, and a computer program or set of instruction code which, when executed, causes a processor to implement such a method. |
| 主权项 |
1. A method for measuring anatomical dead space VD in a lung, the method comprising:
(a) providing, in a supply of inspired gas, at least one indicator gas for inhalation by a patient during a test, the concentration of the indicator gas being controlled such as to follow a sinewave pattern over successive breaths; (b) measuring, over successive breaths, the flow rate and concentration of the indicator gas during both inspiration and exhalation of the patient; (c) fitting sinewave envelopes to the measured concentration values of the indicator gas over the successive breaths and, from the fitted sinewave envelopes, determining the inspired concentration FI, the mixed expired concentration FĒ, and the end expired concentration FE with respect to the indicator gas for each breath; and (d) calculating the anatomical dead space VD for each of a plurality of inspirations, by:
(i) calculating the tidal volume VT for the given inspiration by integrating over time, from the start of that inspiration, the flow rate {dot over (V)}T(t) of the inspired gas for that inspiration;(ii) calculating the volume of inspired indicator gas in the given inspiration by integrating over time, from the start of that inspiration, the product of the inspired concentration FI and the flow rate {dot over (V)}T(t) of inspired gas for that inspiration; and(iii) calculating the dead space VD for the given inspiration, based on:
the tidal volume VT for that inspiration;the inspired concentration FI of indicator gas for that inspiration;the mixed expired concentration FĒ of indicator gas for that inspiration; andthe alveolar gas concentration FA for that inspiration, which is taken as the expired concentration FE of indicator gas at the end of that expiration;the calculating involving a conservation-of-mass principle during expiration, between the amount of indicator gas expired out and the sum of the amount of indicator gas remaining in the dead space and the amount of indicator gas expired from the part of the lung where gas exchange has taken place, whereby, having determined the inspired concentration FI, the flow rate {dot over (V)}T(t), the tidal volume VT, the mixed expired concentration FĒ, and the alveolar gas concentration FA, a mass balance equation is solved to give an estimation of the dead space VD for each breath; and further comprising;
varying the period of the sinewave during the course of the test;determining, at different sinewave periods, values of one or more of the dead space VD alveolar volume VA, functional residual capacity, and pulmonary blood flow {dot over (Q)}P; andproviding a measurement of lung inhomogeneity based on the variation in the determined values with sinewave period. |
