Accuracy of breath-by-breath analysis of flow volume loop in identifying flow-limited breathing cycles in patients

• US 5,456,264 A
• Filed: 03/31/1994
• Issued: 10/10/1995
• Est. Priority Date: 03/31/1994
• Status: Expired due to Fees

• Current Assignee: Universite Laval
• Original Assignee: Universite Laval
• Inventors: Marc, Isabelle, Series, Frederick
• Primary Examiner(s): Cohen, Lee S.
• Assistant Examiner(s): GREEN, BRIAN
• Application Number:
  US08/220,733
• Time in Patent Office: 558 Days
• Field of Search: 128/716, 128/720, 128/725, 128/204.18, 128/204.21, 128/204.23, 128/204.26, 128/207.18
• US Class Current: 600/538
• CPC Class Codes: A61B 5/083 Measuring rate of metabolism by using breath test, e.g. measuring rate of oxygen consumption
• CPC Class Codes: A61B 5/7242 using integration
• CPC Class Codes: A61B 5/7264 Classification of physiological signals or data, e.g. using neural networks, statistical classifiers, expert systems or fuzzy systems neural networks per se G06N3/00; expert systems per se G06N5/00

Abstract

Inspiratory flow limitation (IFL) is involved in the pathophysiology of sleep-related breathing disorders. Since the definition of flow-limited cycle is based on a dissociation between flow and respiratory efforts, identification of IFL requires upper airway or intrathoracic pressure measurements. We examined the feasibility and accuracy of the analysis of the flow-volume loop of a tidal breath in identifying IFL. The tidal volume was obtained by integration of the instantaneous airflow signal, and the flow-volume loop was reconstructed for each breathing cycle by plotting the instantaneous flow and the tidal volume. The instantaneous inspiratory and expiratory flows were measured at a 50% of the respective (inspiratory or expiratory) portion of the tidal volume, and a breath-by-breath analysis of the mid tidal volume flow ratio (I/E ratio) was obtained. There was a positive significant relationship between I/E ratio and V_Imax (maximal inspiratory volume) for flow-limited breathing (correlation coefficient range: 0.25-0.54). With a lower limit of the normal I/E ratio threshold of 0.97, the sensitivity and specificity of the method were both 76%. Patients having a I/E ratio lower than 0.97 to 1 are classified as suffering IFL. Therefore, the prevent invention relates to the above-described non-invasive method which is applicable in the evaluation IFL and to an apparatus measuring I/E ratio and correcting IFL.

Claims

1. A non-invasive method of detecting airflow limitation in a patient, which comprises:

installing a tightly fitting nasal mask on the nose of said patient, said mask having an outlet port connected to one end of a tubing;

connecting another end of said tubing to a pneumotachograph;

obtaining an instantaneous airflow signal from said pneumotachograph when said patient is breathing;

obtaining, by integrating calculation of said instantaneous airflow signal, the following parameters;

a value of a breath-by-breath tidal volume;

a flow-volume loop for each breathing cycle by plotting said instantaneous airflow signal and said breath-by-breath tidal volume;

instantaneous inspiratory and expiratory flow values at 50% of each inspiratory and expiratory portion of said tidal volume, these values being obtained from said flow-volume loop;

a ratio of the value of said instantaneous inspiratory flow at 50% of inspiratory portion of said tidal volume divided by the value of said instantaneous expiratory flow at 50% of expiratory portion of said tidal volume, obtaining this way a mid tidal volume flow ratio (MTVFR);

whereby said patient having a MTVFR lower than 0.97 is diagnosed as suffering of airflow limitation.

2. The method of claim 1 further using a computer to make said integrating calculation.

3. An apparatus for detecting and correcting airflow limitation in a patient, which comprises:

a first tubing;

a second tubing;

a compressor;

a tightly fitting nasal mask adapted to be installed on the nose of said patient, said mask having an outlet port connected to one end of said first tubing;

a pneumotachograph which has a first outlet port connected to another end of said first tubing and which has a second outlet port connected to one end of said second tubing, another end of said second tubing being connected to said compressor;

computer means for reading and integrating an instantaneous airflow signal from said pneumotachograph, which reading and integrating result in the calculation of the following parameters;

a breath-by-breath tidal volume;

an instantaneous inspiratory flow value (I) and an instantaneous expiratory flow value (E) at 50% of the inspiratory and expiratory portion of said tidal volume, respectively; and

a I/E ratio;

said computer means sending a retro-control signal to said compressor;

whereby airflow limitation is detected in said patient when the I/E ratio is lower than 0.97 and said airflow limitation is corrected by activating, said compressor supplying a positive air pressure to said patient through said second tubing, pneumotachograph, first tubing and nasal mask.

4. An apparatus for detecting airflow limitation in a patent, which comprises:

a tubing;

a tightly fitting nasal mask adapted to be installed on the nose of said patient, said mask having an outlet port connected to one end of said tubing;

a pneumotachograph which has an outlet port connected to another end of said tubing;

computer means for reading and integrating an instantaneous airflow signal from said pneumotachograph, which reading and integrating result in the calculation of the following parameters;

breath-by-breath tidal volume;

an instantaneous inspiratory flow value (I) and an expiratory flow value (E) at 50% of the inspiratory and expiratory portion of said tidal volume, respectively; and

a I/E ratio;

whereby airflow limitation is detected in said patient when the I/E ratio is lower than 0.97.

5. A non-invasive method of detecting and correcting airflow limitation in a patient, which comprises:

installing a tightly fitting nasal mask on the nose of said patient, said mask having an outlet port connected to one end of a first tubing, another end of said first tubing being connected to a first outlet port of a pneumotachograph, a second outlet port of said pneumotachograph being connected to one end of a second tubing, another end of said second tubing being connected to a compressor;

obtaining an instantaneous airflow signal from said pneumotachograph when said patient is breathing;

obtaining by integrating calculation of said instantaneous airflow signal, the following parameters;

value of a breath-by-breath tidal volume;

a flow-volume loop for each breathing cycle by plotting said instantaneous airflow signal and said breath-by-breath tidal volume;

instantaneous inspiratory and expiratory flow values at 50% of each inspiratory and expiratory portion of said tidal volume, these values being obtained from said flow-volume loop;

a ratio of the value of said instantaneous inspiratory flow at 50% of inspiratory portion of said tidal volume divided by the value of said instantaneous expiratory flow at 50% of expiratory portion of said tidal volume, obtaining this way a mid tidal volume flow ratio (MTVFR);

whereby said patient having a MTVFR lower than 0.97 is diagnosed as suffering of airflow limitation, and airflow is corrected by activating said compressor supplying positive air pressure to said patient through said second tubing, pneumotachograph, first tubing and nasal mask.

6. The method of claim 5 further using a computer to make said integrating calculation and to activate said compressor.