Breath test apparatus and methods
First Claim
1. A method of performing a breath test, comprising the steps of:
- using a predetermined criterion for determining when a change in a measurement of an isotopic ratio of at least one breath sample of a subject is clinically significant; and
allowing said criterion to change during said breath test.
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Accused Products
Abstract
Breath test methods and apparatus for increasing accuracy and reducing the time taken to achieve diagnostically useful results. In order to determine when an increase in isotopic ratio of the exhaled breath is clinically significant, methods are described for the use of a variable and multiple threshold level; for reducing the time taken to determine an accurate baseline level; and for avoiding the effects of oral activity when making measurements. To increase measurement accuracy, methods are described, using the results of the breath tests themselves, of continuous and automatic self-calibration to correct for drifts in the gas spectrometer absorption curves. A method for increasing the spectral stability of cold cathode discharge infra-red light sources for use in breath test instrumentation is described. Calibration checking devices and methods of mandating their use at regular time intervals are described, to ensure maintenance of the accuracy of breath tests.
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Citations
47 Claims
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1. A method of performing a breath test, comprising the steps of:
using a predetermined criterion for determining when a change in a measurement of an isotopic ratio of at least one breath sample of a subject is clinically significant; and
allowing said criterion to change during said breath test.- View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A breath test method, comprising the steps of:
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performing a first measurement of the isotopic ratio of at least a first breath sample of a subject;
performing a second measurement of the isotopic ratio of at least a second breath sample of said subject; and
determining when said second measurement shows sufficient deviation from said first measurement that a clinically significant result of the breath test may be concluded;
wherein the level of said sufficient deviation is allowed to undergo variation during said breath test. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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27. A breath test method for determining the presence of a clinically significant state in a subject, comprising the steps of:
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performing measurements of the changes from a baseline of an isotopic ratio in a plurality of samples of exhaled breath of said subject, following the effective cessation of oral activity;
determining a polynomial which approximates the functional plot of said measurements with time;
calculating a weighted standard deviation of said measurements from said polynomial, wherein for measurements over said baseline by more than a predetermined amount, a predefined fractional part of the measurement is taken, while for measurements not over said baseline by more than said predetermined amount, the measurement is taken in its entirety; and
determining whether said weighted standard deviation exceeds a predetermined level.
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28. A breath test method comprising the steps of:
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performing a measurement of the isotopic ratio of at least a first breath sample of a subject; and
determining when said measurement shows sufficient deviation from a baseline measurement that a clinically significant result of the breath test may be concluded;
wherein said deviation comprises an upper and a lower threshold band of uncertainty, and wherein the extent of this band is dependent on at least one of the parameters selected from the group consisting of the elapsed time of said breath test, the standard deviation of the physiological spread of results, the dynamics of the physiological change in isotopic ratio, the number of points measured in the breath test, the environmental conditions present during the breath test, and the noise and/or drift levels of the instrument executing the breath test.
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29. A method for determining the reliability of a breath test, comprising the steps of:
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obtaining results from said breath test;
defining a reliability parameter by combining at least one of the criteria selected from the group consisting of the instrument noise and/or drift level, the standard deviation of the physiological spread of results, the dynamics of the physiological change in isotopic ratio, and the time elapsed since ingestion of a labeled substrate; and
using said reliability parameter to assess the results of said breath test according to a predetermined reliability criterion. - View Dependent Claims (30, 31)
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32. A breath test instrument comprising:
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tubing for collecting breath from a subject; and
a gas analyzer for determining isotopic ratio in said gas;
wherein said gas analyzer monitors changes in an isotopic ratio of a gas in exhaled breath samples of said subject virtually continuously, and determines that said test has a clinically significant outcome in accordance with the ongoing results of said test. - View Dependent Claims (33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47)
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Specification