Quantitative calibration of breathing monitors with transducers placed on both rib cage and abdomen

• US 6,413,225 B1
• Filed: 06/16/2000
• Issued: 07/02/2002
• Est. Priority Date: 06/18/1999
• Status: Expired due to Term

• Current Assignee: Adidas AG
• Original Assignee: VivoMetrics, Inc.
• Inventors: Inman, D. Michael, Sackner, Marvin A.
• Primary Examiner(s): Nasser, Robert L.
• Application Number:
  US09/595,317
• Time in Patent Office: 746 Days
• Field of Search: 600/529-538, 128/897-898
• US Class Current: 600/529
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• CPC Class Codes: A61B 5/0803 Recording apparatus specially adapted therefor
• CPC Class Codes: A61B 5/1135 by monitoring thoracic expansion

Abstract

A method for calibrating non-invasive breathing monitors with sensors placed on the rib-cage and abdomen of a subject includes determining an initial scaling factor and an optimal multiplicative factor for the readings of the rib-cage and abdomen sensors using one of a least squares, linear regression, or multi-linear regression techniques. A current scaling factor is determined on a periodic basis using qualitative device calibration techniques. The current scaling factor is used to monitor breathing and diagnose obstructive apneas. Furthermore, the optimal multiplicative and the current scaling factor are used to determine the current tidal volume.

Claims

1. A method for calibrating a non-invasive breathing monitor having a rib-cage sensor and an abdomen sensor for diagnosing obstructive apneas and providing an estimation of tidal volume, comprising the steps of:

(a) determining a multiplicative factor (M) for use with readings from the rib cage sensor and the abdominal sensor for estimating tidal volume by a method including the steps of;

(i) recording a first set of readings from the rib cage sensor (RC) and the abdomen sensor (AB), and a tidal flow volume (V) as measured by an airway monitoring device while recording the first set of readings;

(ii) determining a first scaling factor (K_I) for relative contributions of said rib cage sensor and said abdomen sensor to said tidal volume using one of the least squares, linear regression, and multi-linear regression techniques applied to the first set of readings;

(iii) applying the first scaling factor to said first set of readings to obtain, K_I(RC)+(AB), the first scaled set of readings; and

(iv) calculating the multiplicative factor (M) by dividing the tidal volume reading (V) by the first scaled set of readings using the equation;

2. The method of claim 1, wherein said recording a current set of readings comprises recording for a baseline period at a substantially steady state tidal volume, wherein said determining a standard deviation comprises calculating one of a standard deviation and an average variability of each of said rib-cage and abdomen readings during the baseline period, and wherein said setting comprises calculating the current scaling factor in accordance with the equation:

3. A method for calibrating a non-invasive breathing monitor having a rib-cage sensor and an abdomen sensor for diagnosing obstructive apneas and providing an estimation of tidal volume, comprising the steps of:

(a) determining a multiplicative factor (M) for use with readings from the rib cage sensor and the abdominal sensor for estimating tidal volume by a method including the steps of;

(i) recording a first set of readings from the rib cage sensor and the abdomen sensor;

recording a second set of readings from the rib cage sensor and the abdomen sensor having a different scaling factor than said first set of readings; and

recording the tidal volume (V) as measured by an airway monitoring device while recording the first and second sets of readings;

(ii) determining a first scaling factor (K_I) for relative contributions of said rib cage sensor and said abdomen sensor to said tidal volume using one of the least squares, linear regression, and multi-linear regression techniques applied to the first and second sets of readings;

(iii) applying the first scaling factor to said first and second set of readings to obtain, K_I(RC)+(AB), the first scaled set of readings, wherein;

AB=the average of unweighted abdomen sensor readings in the first and second sets; and

RC=the average of the unweighted rib-cage sensor readings in the first and second sets; and

(iv) calculating the multiplicative factor (M) by dividing the tidal volume reading (V) by the first scaled set of readings using the equation;

4. The method of claim 3, wherein said recording a current set of readings comprises recording rib-cage and abdomen readings from the abdomen and rib cage sensors for a baseline period at a substantially steady state tidal volume, wherein said determining a standard deviation comprises calculating one of a standard deviation and an average variability of each of said rib-cage and abdomen readings during the baseline period;

and wherein said setting comprises calculating the current scaling factor in accordance with the equation;

5. A method for calibrating a non-invasive breathing monitor having a rib-cage sensor and an abdomen sensor for diagnosing obstructive apneas and providing an estimation of tidal volume, comprising the steps of:

(a) determining a multiplicative value for use with readings from the rib cage sensor and abdomen sensor for estimating tidal volume by simultaneously recording a first set of readings from the rib cage sensor and the abdomen sensor and a tidal volume reading using an airway monitoring device, determining an average scaling factor for relative contributions of said rib cage sensor and said abdomen sensor to said tidal volume via one of at least square, linear regression, and multi-linear regression techniques, applying the average scaling factor to said first set of readings to obtain a first scaled set of readings, and calculating the multiplicative value by dividing the tidal volume reading by the first scaled set of readings; and

(b) determining a current scaling factor (K_C) for the current posture and breathing pattern of the subject for use with readings from the rib-cage sensor and abdomen sensor for diagnosing apneas by;

(i) recording rib-cage and abdomen readings from the abdomen and rib cage sensors for a baseline period at a substantially steady state tidal volume;

(ii) calculating one of a standard deviation and an average variability of each of said rib-cage abdomen readings during the baseline period; and

(iii) calculating the current scaling factor in accordance with the equation;