Method and apparatus for determining instantaneous inspired volume of a subject during ventilatory assistance
First Claim
1. A method for calculating the instantaneous phase in the respiratory cycle comprising at least the step of determining that if the instantaneous airflow is small and increasing fast, then it is close to start of inspiration, if the instantaneous airflow is large and steady, then it is close to mid-inspiration, if the instantaneous airflow is small and decreasing fast, then it is close to mid-expiration, if the instantaneous airflow is zero and steady, then it is during an end-expiratory pause, and airflow conditions intermediate between the above are associated with correspondingly intermediate phases.
1 Assignment
0 Petitions
Accused Products
Abstract
The apparatus provides for the determination of the instantaneous phase in the respiratory cycle, subject'"'"'s average respiration rate and the provision of ventilatory assistance. A microprocessor (16) receives an airflow signal from a pressure transducer (18) coupled to a port (17) at a mask (11). The microprocessor (16) controls a servo (19), that in turn controls the fan motor (20) and thus the pressure of air delivered by the blower (10). The blower (10) is coupled to a subject'"'"'s mask (ii) by a conduit (12). The invention seeks to address the following goals: while the subject is awake and making substantial efforts the delivered assistance should be closely matched in phase with the subject'"'"'s efforts; the machine should automatically adjust the degree of assistance to maintain at least a specified minimum ventilation without relying on the integrity of the subject'"'"'s chemoreflexes; and it should continue to work correctly in the pesence of large leaks.
29 Citations
21 Claims
- 1. A method for calculating the instantaneous phase in the respiratory cycle comprising at least the step of determining that if the instantaneous airflow is small and increasing fast, then it is close to start of inspiration, if the instantaneous airflow is large and steady, then it is close to mid-inspiration, if the instantaneous airflow is small and decreasing fast, then it is close to mid-expiration, if the instantaneous airflow is zero and steady, then it is during an end-expiratory pause, and airflow conditions intermediate between the above are associated with correspondingly intermediate phases.
-
2. A method for determining the instantaneous phase in the respiratory cycle as a continuous variable from 0 to 1 revolution, the method comprising the steps of:
-
selecting at least two identifiable features FN of a prototype flow-vs-time waveform f(t) similar to an expected respiratory flow-vs-time waveform, and for each said feature;
determining by inspection the phase φ
N in the respiratory cycle for said feature, assigning a weight WN to said phase,defining a “
magnitude”
fuzzy set MN whose membership function is a function of respiratory airflow, and a “
rate of change”
fuzzy set CN, whose membership function is a function of the time derivative of respiratory airflow, chosen such that the fuzzy intersection MN AND CN will be larger for points on the generalized prototype respiratory waveform whose phase is closer to the said feature FN than for points closer to all other selected features,setting the fuzzy inference rule RN for the selected feature FN to be;
If flow is MN and rate of change of flow CN then phase=φ
N, with weight WN.measuring leak-corrected respiratory airflow, for each feature FN calculating fuzzy membership in fuzzy sets MN and CN, for each feature FN applying fuzzy inference rule RN to determine the fuzzy extent YN=MN AND CN to which the phase is φ
N, andapplying a defuzzification procedure using YN at phasesφ
N and weights WN to determine the instantaneous phase φ
. - View Dependent Claims (3, 4, 5, 6)
-
-
7. A method for measuring the average respiratory rate, comprising the steps of:
-
determining leak-corrected respiratory airflow, from the respiratory airflow, calculating the instantaneous phase φ
in the respiratory cycle as a continuous variable from 0 to 1 revolution, calculating the instantaneous rate of change of phase dφ
/dt, andcalculating the average respiratory rate by low pass filtering said instantaneous rate of change of phase dφ
/dt.
-
-
9. A method for providing ventilatory assistance in a spontaneously breathing subject, comprising the steps, performed at repeated sampling intervals, of:
-
ascribing a desired waveform template function Π
(φ
), with domain 0 to 1 revolution and range 0 to 1,calculating the instantaneous phase φ
in the respiratory cycle as a continuous variable from 0 to 1 revolution,selecting a desired pressure modulation amplitude A, calculating a desired instantaneous delivery pressure as an end expiratory pressure plus the desired pressure modulation amplitude A multiplied by the value of the waveform template function Π
(φ
) at the said calculated phase φ
, andsetting delivered pressure to subject to the desired delivery pressure. - View Dependent Claims (10, 11)
-
-
12. A method for providing ventilatory assistance in a spontaneously breathing subject as described above, in which the step of selecting a desired pressure modulation amplitude comprises the substeps of:
-
specifying a typical respiratory rate giving a typical cycle time, specifying a preset pressure modulation amplitude to apply at said typical respiratory rate, calculating the observed respiratory rate giving an observed cycle time, and calculating the desired amplitude of pressure modulation as said preset pressure modulation amplitude multiplied by said observed cycle time divided by the said specified cycle time.
-
-
13. A method for providing ventilatory assistance in a spontaneously breathing subject, including at least the step of determining the extent that the subject is adequately ventilated, to said extent the phase in the respiratory cycle is determined from the subject'"'"'s respiratory airflow, but to the extent that the subject'"'"'s ventilation is inadequate, the phase in the respiratory cycle is assumed to increase at a pre-set rate, and setting mask pressure as a function of said phase.
-
14. A method for providing ventilatory assistance in a spontaneously breathing subject, comprising the steps of:
- measuring respiratory airflow, determining the extent to which the instantaneous phase in the respiratory cycle can be determined from said airflow, to said extent determining said phase from said airflow but to the extent that the phase in the respiratory cycle cannot be a adequately determined, the phase is assumed to increase at a preset rate, and delivering pressure as a function of said phase.
-
15. A method for calculating the instantaneous inspired volume of a subject, operable substantially without run-away under conditions of suddenly changing leak, the method comprising the steps of:
-
determining respiratory airflow approximately corrected for leak, calculating an index J varying from 0 to 1 equal to the fuzzy extent to which said corrected respiratory airflow is large positive for longer than expected, or large negative for longer than expected, identifying the start of inspiration, calculating the instantaneous inspired volume as the integral of said corrected respiratory airflow multiplied by the fuzzy negation of said index J with respect to time, from start of inspiration.
-
-
16. A method for providing ventilatory assistance in a spontaneously breathing subject, the method comprising the steps, performed at repeated sampling intervals, of:
-
determining respiratory airflow approximately corrected for leak, calculating an index J varying from 0 to 1 equal to the fuzzy extent to which said inspiratory airflow is large positive for longer than expected, or large negative for longer than expected, calculating a modified airflow equal to said respiratory airflow multiplied by the fuzzy negation of said index J, identifying the phase in the respiratory cycle, calculating the instantaneous inspired volume as the integral of said modified airflow with respect to time, with the integral held at zero during the expiratory portion of the respiratory cycle, calculating a desired instantaneous delivery pressure as a function at least of the said instantaneous inspired volume, and setting delivered pressure to subject to the desired delivery pressure. - View Dependent Claims (21)
-
-
17. A method for providing ventilatory assistance in a spontaneously breathing subject, comprising the steps of:
-
determining a respiratory airflow approximately corrected for leak, calculating an index J varying from 0 to 1 equal to the fuzzy extent to which the respiratory airflow is large positive for longer than expected, or large negative for longer than expected, identifying the phase in the respiratory cycle, calculating a modified respiratory airflow equal to the respiratory airflow multiplied by the fuzzy negation of said index J, calculating the instantaneous inspired volume as the integral of the modified airflow with respect to time, with the integral held at zero during the expiratory portion of the respiratory cycle, calculating the desired instantaneous delivery pressure as an expiratory pressure plus a resistance multiplied by the instantaneous respiratory airflow plus a nonlinear resistance multiplied by the respiratory airflow multiplied by the absolute value of the respiratory airflow plus an elastance multiplied by the said adjusted instantaneous inspired volume, setting delivered pressure to subject to the desired delivery pressure.
-
-
18. A method for providing assisted ventilation to match the subject'"'"'s need, comprising the steps of:
-
describing a desired waveform template function Π
(φ
), with domain 0 to 1 revolution and range 0 to 1,determining respiratory airflow approximately corrected for leak, calculating an index J varying from 0 to 1 equal to the fuzzy extent to which the respiratory airflow is large positive for longer than expected, or large negative for longer than expected, calculating JPEAK equal to the recent peak of the index J, calculating the instantaneous phase in the respiratory cycle, calculating a desired amplitude of pressure modulation, chosen to servo-control the degree of ventilation to at least exceed a specified ventilation, calculating a desired delivery pressure as an end expiratory pressure plus the calculated pressure modulation amplitude A multiplied by the value of the waveform template function Π
(φ
) at the said calculated phase φ
, andsetting delivered pressure to subject to said desired instantaneous delivered pressure. - View Dependent Claims (19, 20)
-
Specification