Apparatus and method for the estimation of flow -independent parameters which characterize the relevant features of nitric oxide production and exchange in the human lungs
First Claim
1. A method for determining flow independent parameters characteristic of nitrogen monoxide exchange and of lung function in a subject during one or more exhalations during which flow rate of exhalation varies in time comprising:
- exhaling into a mouthpiece in which the resistance to airflow can vary in time and;
measuring exhaled nitrogen monoxide concentration, Cexh, from said subject as a function of time; and
simultaneously measuring volumetric exhalation flow rate, E, as a function of time with measurement of exhaled nitrogen monoxide concentration;
backwards integrating said volumetric exhalation flow rate, J, over time to convert exhalation time to residence time of each exhaled bolus of gas in said airway compartment of said subject; and
selecting said flow independent parameters to fit said measured nitrogen monoxide concentration as a function of time given residence time obtained by backwards integration.
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Abstract
The invention provides an estimation of key flow-independent parameters characteristic of NO exchange in the lungs, namely: 1) the steady state alveolar concentration, Calv,ss; 2) the maximum flux of NO from the airways, JNO,max; and 3) the diffusing capacity of NO in the airways, DNO,air. The parameters were estimated from a single exhalation maneuver comprised of a pre-expiratory breathhold, followed by an exhalation in which the flow rate progressively decreased. The mean values for JNO,max, DNO,air, and Calv,ss do not depend on breathhold time for breathhold times greater than approximately 10 seconds. A priori estimates of the parameter confidence intervals demonstrates that a breathhold no longer than 20 seconds may be adequate, and that JNO,max be can estimated with the smallest uncertainty, and DNO,air the largest.
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Citations
34 Claims
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1. A method for determining flow independent parameters characteristic of nitrogen monoxide exchange and of lung function in a subject during one or more exhalations during which flow rate of exhalation varies in time comprising:
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exhaling into a mouthpiece in which the resistance to airflow can vary in time and;
measuring exhaled nitrogen monoxide concentration, Cexh, from said subject as a function of time; and
simultaneously measuring volumetric exhalation flow rate, E, as a function of time with measurement of exhaled nitrogen monoxide concentration;
backwards integrating said volumetric exhalation flow rate, J, over time to convert exhalation time to residence time of each exhaled bolus of gas in said airway compartment of said subject; and
selecting said flow independent parameters to fit said measured nitrogen monoxide concentration as a function of time given residence time obtained by backwards integration. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. An apparatus for determining flow independent parameters of lung function in a subject during one exhalation during which flow rate of exhalation varies in time comprising:
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a sampling line into which said subject exhales;
a nitrogen monoxide analyzer coupled to said sampling line to measure exhaled nitrogen monoxide concentration, Cexh, from said subject as a function of time;
a flow meter coupled to said sampling line to measure to measure volumetric exhalation flow rate, E, as a function of time; and
a computer coupled to said nitrogen monoxide analyzer and to said flow meter to backwards integrate said volumetric exhalation flow rate, E, over time to convert exhalation time to residence time of each exhaled bolus of gas in said airway compartment of said subject; and
to select said flow independent parameters to fit said measured nitrogen monoxide concentration as a function of time given residence time obtained by backwards integration. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
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Specification