CN112754465B - Method for estimating quasi-static compliance of lung under pressure-controlled mechanical ventilation - Google Patents

Method for estimating quasi-static compliance of lung under pressure-controlled mechanical ventilation Download PDF

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CN112754465B
CN112754465B CN202110049428.5A CN202110049428A CN112754465B CN 112754465 B CN112754465 B CN 112754465B CN 202110049428 A CN202110049428 A CN 202110049428A CN 112754465 B CN112754465 B CN 112754465B
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潘�清
潘杰
葛慧青
张浩源
冯伟达
顾立锋
章灵伟
方路平
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Zhejiang University of Technology ZJUT
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/08—Detecting, measuring or recording devices for evaluating the respiratory organs
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
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    • A61M16/00—Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes
    • A61M16/0003—Accessories therefor, e.g. sensors, vibrators, negative pressure

Abstract

The invention provides a method for estimating lung quasi-static compliance under pressure control mechanical ventilation, which is characterized in that least square fitting is carried out on inspiratory phase data of flow velocity waveform of each respiration in acquired sampling data by using an exponential function to obtain a flow velocity waveform curve, and then the flow velocity waveform curve is integrated to obtain tidal volume, so that the quasi-static compliance can be calculated by utilizing a mechanical ventilation waveform. The change trend of the measurement value based on the quasi-static compliance provides possibility for a clinician to dynamically evaluate the pathological state of the lung of the patient, and can better guide the implementation of mechanical ventilation.

Description

Method for estimating quasi-static compliance of lung under pressure-controlled mechanical ventilation
Technical Field
The invention relates to a method for estimating quasi-static compliance of a lung under pressure control mechanical ventilation, and belongs to the field of medical signal processing.
Background
During invasive mechanical ventilation of critically ill patients using a ventilator, pulmonary compliance is an important indicator for assessing respiratory mechanics. Reduced compliance has been associated with several pulmonary pathologies, including (1) restrictive diseases such as pulmonary fibrosis; (2) pulmonary alveolar filling diseases such as pulmonary edema, pulmonary congestion, and alveolar hemorrhage; (3) acute respiratory distress syndrome. Emphysema or chronic obstructive pulmonary disease may occur due to loss of alveoli and lung elastic tissue, leading to increased compliance.
In clinical application, compliance is measured in a static method and a dynamic method. Static compliance refers to the measurement of intrathoracic pressure during the respiratory cycle after a set volume of gas has been inhaled by the patient holding his breath to temporarily block airflow. Then using more moistureThe relationship between pressure and volume is traced out several times, and the slope is compliance. Since this curve is measured without airflow, it is called static compliance (C) because breath holding causes the intra-pulmonary pressure to be zerostat). The calculation formula is
Figure BDA0002898687700000011
Wherein, VTi-meaRepresenting the actual measured inspired tidal volume. PplatRepresentative of plateau pressure, measured by the operation of breath-hold to interrupt the flow of gas (about greater than 0.5s) after the end of inspiration and before the beginning of expiration. During this operation, the effect of airway resistance is eliminated. PEEP stands for positive end expiratory pressure.
Dynamic method: refers to the compliance of the lungs and thorax measured during the respiratory cycle when airflow is not blocked. By using two zero flow rate points of the respiratory cycle, and by measuring the two pressure values when the tidal volume of the patient is gradually increased, a curve of the change of the volume relative to the intrathoracic pressure is traced, and the slope of the curve is the dynamic compliance (C)dyn). Is calculated by the formula
Figure BDA0002898687700000012
Wherein, PpeakRepresenting the maximum value of the inspiratory phase pressure.
Static compliance reflects the elasticity of the lung tissue, and dynamic compliance reflects the compliance of the entire respiratory system since it is also calculated to overcome airway resistance.
Although the dynamic compliance can be automatically and continuously measured by a dynamic measuring method, the result is easily influenced by factors such as the change of tidal volume and the possible existence of spontaneous respiratory ability of a patient, and the measuring result can only be used as a reference and cannot provide more accurate dynamic lung compliance assessment for clinical medical staff. And (3) calculating the plateau pressure by using a least square fitting method through a respirator of part of manufacturers so as to obtain the compliance. Static compliance more accurately reflects the elasticity of lung tissue, and in certain pathologies, continuous monitoring of lung compliance is instructive in understanding disease progression and in administering mechanical ventilation therapy, but requires the operation of a ventilator by medical personnel and patient coordination, which increases physician workload. The invention aims to provide a lung quasi-static compliance calculation method based on a breathing machine waveform, which is used for obtaining the quasi-static compliance by analyzing the morphological characteristics of the waveform and providing reference for more conveniently evaluating lung lesions.
Disclosure of Invention
In order to solve the problems that the static compliance index needs the medical care personnel to carry out breath holding operation, the measurement is inconvenient, the workload of the medical care personnel is increased and the like, the invention provides the method for estimating the quasi-static compliance of the lung under the pressure control mechanical ventilation.
The technical scheme adopted by the invention for solving the technical problem is as follows:
(1) acquiring continuous airway pressure and flow rate waveform sampling data under pressure control mechanical ventilation;
(2) calculating the quasi-static compliance of each breath in the sampled data, taking the first N compliance values in the sampled data in a descending order, and taking the average value of the first N compliance values as the approximate static compliance of the sampled data; wherein, the quasi-static compliance of each breath is calculated by the following formula:
Figure BDA0002898687700000021
wherein, PiendRepresenting end of inspiration pressure, VT-estIs the inhaled tidal volume when the end-inspiratory flow rate is 0L/min under pressure control ventilation, and PEEP represents the end-expiratory positive pressure. The above formula is derived from the following approximate formula:
Figure BDA0002898687700000022
wherein, PiendRepresenting end of inspiration pressure, VT-estThe flow rate of the last inspiration under the pressure control ventilation is 0L/miTidal volume inspired at n. The precondition that the above formula is satisfied is that the flow rate at the end of gas suction is 0L/min. When the flow rate at the end of inspiration is 0L/min, Piend≈Pplat、VT-est≈VTi-mea(ii) a When the flow rate at the end of inspiration is not 0L/min, fitting the waveform of the inspiration phase after the maximum flow rate according to an inspiration phase flow rate equation, and prolonging the waveform of the inspiration phase to the expiration phase until the flow rate approaches 0L/min. Calculating tidal volume by integrating the original flow velocity before the maximum flow velocity and the theoretical flow velocity obtained by fitting after the maximum flow velocity to obtain V required by the calculation of the formulaT-estAt this time, corresponding PiendIs approximately equal to Pplat。
The theoretical equation of inspiratory phase flow rate is derived from the equation of motion of the respiratory system:
f＝ae-bt
wherein a ═ C/Rrs(C is a constant), b-Ers/Rrs。
The approximate formula condition is that the end-inspiratory flow rate is 0L/min. When the flow rate at the end of inspiration is not 0L/min, fitting the waveform of the inspiration phase after the maximum flow rate according to the inspiration phase flow rate equation, and prolonging the waveform of the inspiration phase to the expiration phase until the flow rate approaches 0L/min. Data for inspiratory phase after the maximum value of the flow waveform for each breath under pressure-controlled ventilation is obtained by using an exponential function: ae ═ e-btPerforming least square fitting, extending the fitted line to the expiratory phase until f is less than 0.001L/min (i.e. the flow rate is close to zero), and then fitting the flow rate waveform curve f before the maximum flow rate1And integrating the fitted flow velocity waveform curve f with respect to time to obtain the tidal volume:
Figure BDA0002898687700000031
wherein, t0At the start of inspiration, t1To fit the starting time, t2The flow rate reaches a point of approximately 0L/min for the end of inspiration and for the extension to expiration.
Further, in the step (1), continuous airway pressure and flow waveform sampling data are acquired by using a respirator, and the sampling frequency is above 50 Hz.
Further, the quasi-static compliance C per breath for M minutes was calculated separatelyqsTaking the minimum N compliances of the waveform in the M minutes, and taking the average value of the N compliances as the quasi-static compliance of the mechanical ventilation in the M minutes; the reason for the minimum N compliances is that autonomous inspiration results in higher tidal volumes and thus larger quasi-static compliance estimates. The minimum N compliances most likely represent true static compliances.
Further, in the step (2), the fitted flow velocity waveform curve f is integrated, and the time of integration is calculated by the product of the sampling point and the sampling frequency in the fitted flow velocity waveform curve f.
Further, in the step (2), the condition of approaching zero is that f is less than 0.001L/min.
Further, in the step (2), the end-inspiratory pressure PiendThe calculation is based on expiratory point detection, as follows: and (3) carrying out difference on the pressure waveform, wherein the minimum point is an expiration point, and the average value of the last 5 sampling points of the inspiration phase pressure waveform is taken as the inspiration end pressure value of the current breath.
Further, in the step (2), the calculation of the end-expiratory pressure is based on the expiratory point detection, which is specifically as follows: and (3) carrying out difference on the pressure waveform, wherein the minimum point is an expiration point, and the average value of the last five sampling points of the expiration phase is taken as the end expiration pressure value of the current breath.
The invention has the following beneficial effects: based on the mechanical ventilation waveform, under the pressure control ventilation mode, a quasi-static compliance value can be obtained, and the process that medical personnel need to frequently operate a breathing machine to measure the static compliance is omitted. By acquiring quasi-static compliance in combination with other clinically measured parameters, a basis is provided for clinicians to dynamically assess the pathological state of the patient's lung, thereby better performing mechanical ventilation.
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FIG. 1 is a schematic flow chart of the present invention.
FIG. 2 is a schematic diagram of the end inspiratory pressure point, PEEP point, expiratory point, tidal volume point in the pressure, flow rate, tidal volume waveform of the present invention.
FIG. 3 is a schematic diagram of an exponential fit to the inspiratory phase of a flow waveform according to the present invention.
Fig. 4 is a graph illustrating the consistency of compliance between the pressure-controlled ventilation mode and the volume-controlled ventilation mode according to the present invention.
Detailed Description
For the purpose of better explaining the present invention and to facilitate understanding, the present invention will be described in detail by way of specific embodiments with reference to the accompanying drawings.
Referring to fig. 1, the method for estimating the quasi-static compliance of the lung under mechanical ventilation under pressure control according to the present invention comprises the following steps:
(1) acquiring continuous airway pressure and flow waveform sampling data under pressure control ventilation;
(2) calculating the quasi-static compliance of each breath in the sampled data, taking the first N compliance values in the sampled data in a descending order, and taking the average value of the first N compliance values as the approximate static compliance of the sampled data;
in the pressure-controlled ventilation mode, the quasi-static compliance per breath can be calculated by the following approximate formula:
Figure BDA0002898687700000041
wherein, PiendRepresenting end of inspiration pressure, VT-estIs the inhaled tidal volume when the end-inspiratory flow rate is 0L/min under pressure control ventilation, and PEEP represents the end-expiratory positive pressure.
The precondition that the above formula is satisfied is that the flow rate at the end of gas suction is 0L/min. When the flow rate at the end of inspiration is 0L/min, Piend≈Pplat、VT-est≈VTi-mea(ii) a When the flow rate at the end of inspiration is not 0L/min, fitting the waveform of the inspiration phase after the maximum flow rate according to the inspiration phase flow rate equation, and prolonging the waveform of the inspiration phase to the expiration phase until the flow rate approaches 0L/min.
The invention adopts the theoretical flow velocity obtained by fitting the original flow velocity before the maximum value of the flow velocity and the maximum value of the flow velocityThe tidal volume is calculated by integration, so as to obtain the required V for satisfying the above formulaT-est。
Specifically, the theoretical equation for inspiratory phase flow rate is derived from the equation of motion of the respiratory system. The respiratory system equation of motion is:
Paw(t)＝Rrsf+ErsVT(t)+PEEP
wherein, PawIs representative of airway pressure, RrsRepresenting airway resistance, ErsRepresenting elasticity and f representing flow rate.
The pressure P at which the driving air flow is obtained by moving the PEEP to the leftd：
Pd(t)＝Rrsf+ErsVT(t)
In the pressure-controlled ventilation mode, if there is no spontaneous respiration disturbance, P can be considered in one breathd，Rrs，ErsIs a constant number, VTIs the integral of f over time t. Based on this condition, the above formula can be solved to obtain:
Figure BDA0002898687700000051
the inspiratory phase flow rate can be derived based on the derivation of the formula:
f＝ae-bt
wherein a ═ C/Rrs(C is a constant), b ═ Ers/Rrs。
The approximate formula condition is that the end-inspiratory flow rate is 0L/min. When the flow rate at the end of inspiration is not 0L/min, fitting the waveform of the inspiration phase after the maximum flow rate according to the inspiration phase flow rate equation, and prolonging the waveform of the inspiration phase to the expiration phase until the flow rate approaches 0L/min. Data for inspiratory phase after the maximum value of the flow waveform for each breath under pressure-controlled ventilation is obtained by using an exponential function: ae ═ e-btPerforming least square fitting, extending the fitted line to the expiratory phase until f is less than 0.001L/min (i.e. the flow rate is close to zero), and then fitting the flow rate waveform curve f before the maximum flow rate1Integrating the fitted flow velocity waveform curve f with respect to time to obtain the tidal volume
Figure BDA0002898687700000052
Wherein, t0At the start of inspiration, t1To fit the starting time, t2The flow rate reaches a point of approximately 0L/min for the end of inspiration and for the extension to expiration.
Based on the first zero-crossing expiratory point detection, the last sampling point of the inspiratory tidal volume waveform of each breath is taken as the inspiratory tidal volume value of the current breath (the maximum point of the V-t diagram in FIG. 2).
The end inspiratory pressure is calculated as follows: based on the expiratory point detection: and (3) carrying out difference on the pressure waveform, wherein the minimum point is an expiration point, and the average value of the last 5 sampling points of the inspiration phase pressure waveform is taken as the inspiration end pressure value of the current breath.
The positive end-expiratory pressure is calculated as follows: based on the expiratory point detection: and (4) carrying out difference on the pressure waveform, wherein the minimum point is an expiration point, and the average value of the last five sampling points of the expiration phase is taken as the positive end expiratory pressure value of the current breath. The results are shown in FIG. 2.
And respectively calculating the compliance of each breath in continuous sampling data, then taking the N compliances with the minimum waveform in the sampling data, and taking the average value of the compliances as the quasi-static compliance of the mechanical ventilation of the sampling data.
According to the invention, the quasi-static compliance is calculated by utilizing the mechanical ventilation waveform under a specific condition, so that the process of frequently operating a breathing machine manually to measure the static compliance is avoided, and the workload of medical staff is reduced. The change trend of the measurement value based on the quasi-static compliance provides possibility for a clinician to dynamically evaluate the pathological state of the lung of the patient, and can better guide the implementation of mechanical ventilation.
One specific example is provided below:
in the embodiment, a pressure control ventilation mode is adopted, the acquired airway pressure and flow rate waveforms within 1 hour are divided according to 5 minutes, the compliance of each waveform is calculated, the minimum 30 compliances are taken, and the average value of the compliances is taken as the physiological index of mechanical ventilation within 5 minutes. The number of selected compliance N and the sampling time M are set to 30 and 5min based on experience in the example, but in the application, the number can be properly adjusted after analysis according to the actual situation.
To verify the effectiveness of the method, 20 static compliance measurements were taken as gold standards for the last inspiratory breath operation, and the quasi-static compliance was calculated from the waveform 5 minutes prior to each gold standard, the results of the consistency analysis of both are shown in fig. 4. It can be seen that the two have a higher consistency, R2＝0.89。
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. This need not be, nor should all embodiments be exhaustive. And obvious variations or modifications of the invention may be made without departing from the scope of the invention.

Claims (7)

1. A method for estimating the quasi-static compliance of the lung under pressure-controlled mechanical ventilation is characterized by comprising the following steps:
(1) acquiring continuous airway pressure and flow rate waveform sampling data under pressure control mechanical ventilation;
(2) calculating the quasi-static compliance of each breath in the sampled data, taking the first N compliance values in the sampled data which are sorted from small to large, and taking the average value of the first N compliance values as the approximate static compliance of the sampled data; wherein, the quasi-static compliance of each breath is calculated by the following formula:
Figure FDA0003585891330000011
wherein, PiendRepresenting end of inspiration pressure, VT-estThe tidal volume of the inhaled air is the inhaled tidal volume when the flow rate of the end of the inhaled air under pressure control ventilation is 0L/min, and PEEP represents the positive end expiratory pressure;
VT-estthe method comprises the following steps: based on the flow maximum detection, the data of the inspiration phase after the flow maximum of each breath is processed by an exponential function: ae ═ e-btPerforming least square fitting, and prolonging the fitted line to the expiratory phase to make the fitted line tend to zero;
flow velocity waveform curve f before maximum value of flow velocity1Integrating the fitted flow velocity waveform curve f to obtain an integral sum, namely the inhaled tidal volume VT-est。
2. The method for estimating the quasi-static pulmonary compliance under mechanical ventilation under pressure control according to claim 1, wherein in the step (1), the sampling frequency of the sampled data is above 50 Hz.
3. The method for estimating the quasi-static pulmonary compliance under mechanical ventilation under pressure control according to claim 1, wherein in the step (1), the sampling time of the sampled data is 5 minutes.
4. The method according to claim 1, wherein in the step (2), the fitted flow velocity waveform curve f is integrated, and the integration time is calculated by multiplying the sampling point and the sampling frequency in the fitted flow velocity waveform curve f.
5. The method for estimating the quasi-static pulmonary compliance under mechanical ventilation under pressure control according to claim 1, wherein in the step (2), the condition of approaching zero is f < 0.001L/min.
6. The method according to claim 1, wherein in the step (2), the end-inspiratory pressure P is determined as the end-inspiratory pressure PiendThe calculation is based on expiratory point detection, as follows: the pressure waveform is differentiated, the minimum point is the expiration point, and the average value of the last 5 sampling points of the inspiration phase pressure waveform is taken as the inspiration of the current breathPressure at end of gas.
7. The method for estimating the quasi-static pulmonary compliance under mechanical pressure ventilation according to claim 1, wherein in the step (2), the calculation of the positive end-expiratory pressure is based on the expiratory point detection, and specifically comprises the following steps: and (3) carrying out difference on the pressure waveform, wherein the minimum point is an expiration point, and the average value of the last five sampling points of the expiration phase is taken as the end expiration pressure value of the current breath.
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