METHOD FOR CONTINUOUS AND NON-INVASIVE DETERMINATION OF EFFECTIVE LUNG VOLUME AND CARDIAC OUTPUT

• US 20130253359A1
• Filed: 03/21/2013
• Published: 09/26/2013
• Est. Priority Date: 03/21/2012
• Status: Active Grant

• Current Assignee: Maquet Critical Care AB (Getinge AB)
• Original Assignee: Maquet Critical Care AB (Getinge AB)
• Inventors: Emtell, Par, Hallback, Magnus
• Granted Patent: US 10,085,673 B2
• Time in Patent Office: Days
• US Class Current: 600/532
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: A61B 5/082 Evaluation by breath analysis, e.g. determination of the chemical composition of exhaled breath A61B5/083, A61B5/091 take precedence
• CPC Class Codes: A61B 5/0836 Measuring rate of CO2 production
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: A61B 5/72 Signal processing specially adapted for physiological signals or for diagnostic purposes character recognition, recognising digital ink, document-oriented image-based pattern recognition G06V30/00; recognition or understanding of postal images G06V30/424
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/026 specially adapted for predicting, e.g. for determining an information representative of a flow limitation during a ventilation cycle by using a root square technique or a regression analysis
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase
• CPC Class Codes: A61M 2230/432 partial CO2 pressure (P-CO2)
• CPC Class Codes: G16H 50/50 for simulation or modelling of medical disorders

Abstract

In a method for continuous and non-invasive determination of the effective lung volume, the cardiac output, and/or the carbon dioxide content of venous blood of a subject during a sequence of respiratory cycles, the inspiratory and expiratory flow, and the carbon dioxide content of at least the expiration gas are measured. In each respiratory cycle, a first parameter related to the subject'"'"'s fraction of alveolar carbon dioxide, a second parameter related to the carbon dioxide content of the subject'"'"'s arterial blood, and a third parameter related to the subject'"'"'s carbon dioxide elimination are determined based on the measured inspiratory flow, expiratory flow and carbon dioxide content. The effective lung volume, the cardiac output, and/or the carbon dioxide content of venous blood of the subject is determined based on the correlation of the first, second and third parameters.

Claims

1. A non-invasive method for determining at least one physiological parameter related to the effective lung volume, the cardiac output, and/or the carbon dioxide content of venous blood of a subject, the method comprising the steps of, during a sequence of respiratory cycles:

measuring an inspiratory flow of inspiration gas inhaled by the subject and an expiratory flow of expiration gas exhaled by the subject, and

measuring the carbon dioxide content of at least the expiration gas,

determining, for each respiratory cycle in the sequence of respiratory cycles, a first parameter related to the fraction of alveolar carbon dioxide of the subject, a second parameter related to the carbon dioxide content of the arterial blood of the subject, and a third parameter related to carbon dioxide elimination of the subject, based on the measured inspiratory flow, expiratory flow and carbon dioxide content; and

determining said at least one physiological parameter based on the correlation of the first, second and third parameters in the sequence of respiratory cycles.

2. The method according to claim 1, wherein the step of determining said at least one physiological parameter comprises simultaneous determination of a physiological parameter related to the effective lung volume of the subject and a physiological parameter related to the cardiac output of the subject, based on said correlation.

3. The method according to claim 1, wherein the step of determining said at least one physiological parameter comprises simultaneous determination of a physiological parameter related to the effective lung volume of the subject, a physiological parameter related to the cardiac output of the subject, and a physiological parameter related the carbon dioxide content of venous blood of the subject, based on said correlation.

4. The method according to claim 1, further comprising the steps of:

for each respiratory cycle in the sequence of respiratory cycles, inserting the determined values of the first, second and third parameters into a capnodynamic equation describing a relationship between parameters relating to effective lung volume, cardiac output, carbon dioxide content of venous blood, fraction of alveolar carbon dioxide, carbon dioxide content of arterial blood and carbon dioxide elimination of a subject, so as to form an overdetermined system of equations; and

determining the at least one physiological parameter by finding an approximate solution to said overdetermined system of equations.

5. The method according to claim 4, wherein said capnodynamic equation is:

V·

Δ

F_ACO₂=Δ

t·

Q(CvCO₂—

CaCO₂)—

VTCO₂,

where V is the effective lung volume during the respiratory cycle, Δ

FACO₂ is the change in volume fraction of alveolar carbon dioxide during the respiratory cycle, At is the duration in time of the respiratory cycle, Q is the effective pulmonary capillary blood flow during the respiratory cycle, CvCO₂ is the carbon dioxide content of venous blood during the respiratory cycle, CaCO₂ is the carbon dioxide content of arterial blood during the respiratory cycle, and VTCO₂ is the tidal volume elimination of carbon dioxide during the respiratory cycle.

6. The method according to claim 1, wherein the at least one physiological parameter is determined on a breath-by-breath basis by, for each respiratory cycle, replacing the values of the first, second and third parameters obtained during the oldest respiratory cycle in the sequence of respiratory cycles with the values obtained during the most recent respiratory cycle.

7. The method according to claim 1, wherein at least a physiological parameter related to the effective lung volume of the subject is determined, further comprising the steps of:

calculating the difference in volume of inspired and expired gas in each respiratory cycle from the measured inspiratory and expiratory flows; and

determining an updated value of a current effective lung volume of the subject based on the determined physiological parameter and said differences.

8. The method according to claim 1, further comprising the steps of obtaining, prior to determination of the at least one physiological parameter, a priori information comprising at least one value of at least one of said physiological parameters using another method for determination of at least one of said physiological parameters, and using said a priori information in the determination of the at least one physiological parameter.

9. The method according to claim 1, further comprising the steps of determining an error in the determination of the at least one physiological parameter based on the correlation of the first, second and third parameters in the sequence of respiratory cycles, and generating an alarm signal if the error indicates that the correlation is weak.

10. A non-transitory, computer-readable data storage medium encoded with programming instructions for non-invasive determination of at least one physiological parameter related to the effective lung volume, the cardiac output, and/or the carbon dioxide content of venous blood of a subject, said storage medium being loaded into a processor of a device that also comprises at least one flow sensor for measuring an inspiratory flow of inspiration gas inhaled by the subject and an expiratory flow of expiration gas exhaled by the subject, at least one gas analyzer for measuring the carbon dioxide content of at least the expiration gas exhaled by the subject, said programming instructions causing said processor to:

measure an inspiratory flow of inspiration gas inhaled by the subject and an expiratory flow of expiration gas exhaled by the subject, and

measure the carbon dioxide content of at least the expiration gas,

determine, for each respiratory cycle in the sequence of respiratory cycles, a first parameter related to the fraction of alveolar carbon dioxide of the subject, a second parameter related to the carbon dioxide content of the arterial blood of the subject, and a third parameter related to carbon dioxide elimination of the subject, based on the measured inspiratory flow, expiratory flow and carbon dioxide content; and

determine said at least one physiological parameter based on the correlation of the first, second and third parameters in the sequence of respiratory cycles.

11. A device for non-invasive determination of at least one physiological parameter related to the effective lung volume, the cardiac output, and/or the carbon dioxide content of venous blood of a subject, comprising:

at least one flow sensor that measures an inspiratory flow of inspiration gas inhaled by the subject and an expiratory flow of expiration gas exhaled by the subject, during a sequence of respiratory cycles;

at least one gas analyzer that measures the carbon dioxide content of at least the expiration gas; and

a control unit configured to determine, for each respiratory cycle in the sequence of respiratory cycles, a first parameter related to the fraction of alveolar carbon dioxide of the subject, a second parameter related to the carbon dioxide content of the arterial blood of the subject, and a third parameter related to carbon dioxide elimination of the subject, based on the measured inspiratory flow, expiratory flow and carbon dioxide content, and to determine said at least one physiological parameter based on the correlation of the first, second and third parameters in the sequence of respiratory cycles. The device according to claim 11, comprising components forming a breathing-assist apparatus, and wherein said control unit is configured to operate said breathing-assist apparatus to provide a ventilatory treatment to the subject.

13. The device according to claim 12 wherein the control unit is configured to cause a change in the effective ventilation of the subject to cause the carbon dioxide content of the expiration gas exhaled by the subject to vary in a range of 0.5%-1% during said sequence of respiratory cycles.

14. The device according to claim 13, wherein the control unit is configured to change the effective ventilation of the subject to deliver a ventilation pattern with alternating sequences of breaths of increased ventilation and breaths of decreased ventilation to the subject.