CN104740735A

CN104740735A - Expiratory tidal volume (VTE) calculating method

Info

Publication number: CN104740735A
Application number: CN201310733971.2A
Authority: CN
Inventors: 成杰
Original assignee: Beijing Aeonmed Co Ltd
Current assignee: Beijing Aeonmed Co Ltd
Priority date: 2013-12-26
Filing date: 2013-12-26
Publication date: 2015-07-01
Anticipated expiration: 2033-12-26
Also published as: CN104740735B

Abstract

The invention discloses an expiratory tidal volume (VTE) calculating method. The VTE calculating method comprises the following steps of acquiring expiratory flow data X at time interval delta t in a timing mode; calculating the variance D of the expiratory flow data X acquired at the recent nth time, determining that the current moment is an expiratory termination moment if the variance D is changed from the value greater than a preset variance threshold value to the value smaller than the preset variance threshold value, wherein n is a positive integer; performing integration of the expiratory flow data X from the preset expiration start moment to the expiration termination moment obtained through judgment so as to obtain the VTE. The VTE calculating method has the advantages of being simple, convenient and easy to perform, accurate and reliable in VTE.

Description

Expiration tidal volume VTE computational methods

Technical field

The present invention relates to respirator technical field, be specifically related to a kind of expiration tidal volume VTE computational methods.

Background technology

In the monitor value of respirator, expiration tidal volume VTE(Expiratory Tidal Volume, is also designated as VTe) monitoring be the most complicated.Under particularly respirator is operated in flow velocity trigger mode, expiration phase respirator can continue to provide certain flow to trigger for patient, this will cause the sampled value of expiratory flow sensor to comprise two parts, and a part is the tidal volume of the actual exhalation of patient, and a part is the elementary streams that respirator provides.In the ideal case, the elementary streams that respirator provides is from inspiratory flow sensor out, then goes out from expiratory flow sensor, if patient does not trigger, these two values should be equal, is exactly that exhalation flow rate deducts inspiratory flow rate and just equals 0.But in real process, because exhalation flow rate sensor and inspiratory flow rate sensor are not the sensors of same model, this flow speed value that same flow velocity will be caused to sample out is different, and this will cause VTE to have error.

Summary of the invention

The present invention is intended at least to solve the larger technical problem of the error that exists in prior art.

For this reason, the object of the invention is to propose one expiration tidal volume accurately and reliably VTE computational methods.

To achieve these goals, according to the expiration tidal volume VTE computational methods of the embodiment of the present invention, comprise the following steps: interval of delta t interval time ground timing acquiring expiratory gas flow data X; Calculate the variance D of the nearest expiratory gas flow data X collected for n time, if variance D becomes be less than default variance threshold values from being greater than default variance threshold values, then think that current time is finish time of exhaling, wherein n is positive integer; Do the integration of expiratory gas flow data X in time between the expiration finish time that the expiration start time of presetting and judgement are obtained, obtain expiration tidal volume VTE.

According to the expiration tidal volume VTE computational methods of the embodiment of the present invention, have simple and easy to do, accurately and reliably advantage.

In addition, according to the expiration tidal volume VTE computational methods of the embodiment of the present invention, also there is following additional technical feature:

In one embodiment of the invention, described interval Δ t is 2-10ms, and the unit of expiratory gas flow data X is ml/s.

In one embodiment of the invention, described n value is 5-25.

In one embodiment of the invention, described variance threshold values is 30-60.

In one embodiment of the invention, described expiration tidal volume VTE computational methods are applied to turbine respirator.

Additional aspect of the present invention and advantage will part provide in the following description, and part will become obvious from the following description, or be recognized by practice of the present invention.

Accompanying drawing explanation

Above-mentioned and/or additional aspect of the present invention and advantage will become obvious and easy understand from accompanying drawing below combining to the description of embodiment, wherein:

Fig. 1 is the schematic flow sheet of the expiration tidal volume VTE computational methods according to the embodiment of the present invention.

Detailed description of the invention

Be described below in detail embodiments of the invention, the example of described embodiment is shown in the drawings, and wherein same or similar label represents same or similar element or has element that is identical or similar functions from start to finish.Be exemplary below by the embodiment be described with reference to the drawings, be intended to for explaining the present invention, and can not limitation of the present invention be interpreted as.

In order to make those skilled in the art, methods of this invention will be better understood, first briefly introduces the relevant knowledge of respirator:

One, the computing formula of VTE on respirator

In expiration phase, the integration of exhalation flow rate to the time just equals tidal volume VTE.During integration, also different to the segmentation of time according to the difference of system.Such as, in certain respirator, every 5ms gets a sampled point, and then the tidal volume that all-pair is answered being added up mutually just equals VTE.Such as certain is exhaled the moment, and exhalation flow rate equals 1000ml/s, and the flow that so this 5ms flows through equals 1000*0.005=5ml.Such as expiratory duration 1s, is divided into 200 intervals 1s, each interval 5ms, the flow in each interval is added the value just equaling VTE.

Two, the error of calculation of VTE

In expiration phase, if flow velocity triggers, respirator can provide certain minimum flow, so-called flow velocity triggers, be exactly that respirator is according to the flow velocity trigger sensitivity arranged, certain minimum flow is provided, this minimum flow is greater than trigger sensitivity, such as trigger sensitivity Vsens=2LPM (rising per minute), turbine respirator mentioned in this article can provide the minimum flow of 5LPM, this flow enters from suction line, go out from expiration pipeline, if expiration phase sometime, patient thinks air-breathing, certain minimum flow will be siphoned away, will cause from air entry flow out that some enters Patients with Lung like this, such inspiratory flow deducts expiratory gas flow and just equals the flow that patient siphons away, if the difference after subtracting each other is greater than trigger sensitivity, both inspiratory flow rate-exhalation flow rate >2LPM, respirator is just according to the logical once gas of given parameter, represent that patient triggers.

According to the computing formula of VTE and the concept of triggering, be not difficult to find out that the sampling of exhalation flow rate sensor comprises two parts: a part is the expiratory gas flow of patient, a part is the minimum flow that respirator provides.Say that VTE produces the reason of deviation for volume control pattern below.Under volume control pattern, tidal volume setting value VT=500ml, Vsens=2LPM.At the end of air-breathing, respirator provides the tidal volume of 500ml to patient, namely sucks tidal volume VTI=500ml.If expiratory duration is 30s, within this 30s time, respirator provides the minimum flow of 5LPM, and the flow of the air entry that 30s flows through equals 0.5*5=2.5L, adds the 500ml in Patients with Lung, comes to 3L.If the sampling flow VTE=3.2L of expiratory flow sensor within this 30s time, which results in the error of 3.2-3=0.2L.That is: air-breathing tidal volume VTI=500, expiration tidal volume VTE=700, the two is unequal.The reason of expiration tidal volume VTE> air-breathing tidal volume VTI is caused to be because the sampling of minimum flow causes.If patient has exhaled, at this time the flow velocity of exhalation vents should equal the flow velocity of air entry, but due to the error of two sensor samples, such as inspiratory flow rate sensor V_in=5LPM, the error of V_out=5.2LPM, this 0.2LPM, respirator will think it is the flow velocity that patient breathes out by mistake.

Three, the core concept of method of the present invention

Solve VTE deviation, respirator is just needed to judge the moment that patient expiration terminates, such as respirator arranges frequency f=10bpm (secondary per minute), inspiratory duration T=1s, that expiratory duration just equals 60/10-1=5s, but patient likely just exhales after 2s and is over, remaining 3s just waits for ventilation next time, so we need a Rule of judgment, see when patient has exhaled, just no longer to VTE integration after having exhaled, so just can reduce error, can judge whether patient expiration terminates according to the variance of exhalation flow rate.

Variance is the degree that description stochastic variable departs from pre-estimation, and the little explanation of variance is more close estimates evaluation, in discrete variable, usually describe variance with formula the following

D = \frac{1}{n} Σ_{i = 1}^{n} {(X_{i} - \overset{&OverBar;}{X})}^{2}

D represents variance, x _irepresent the value of stochastic variable i-th point, represent the average of n point.

In the calculating of VTE, variance can be utilized to find finish time of exhaling.If patient expiration terminates, the sampled value of exhalation flow rate sensor is the part of elementary streams, and the flow of elementary streams is more stable, and variance is smaller.If patient expiration does not terminate, the sampled value of that exhalation flow rate sensor can be data of slowly successively decreasing from big to small, if get several sampled datas to do variance, variance is larger.Therefore, can variance size be passed through, judge whether patient completes exhalation process.

In one embodiment of the invention, interval Δ t is 2-10ms, and the unit of expiratory gas flow data X is ml/s.T is too small for interval Δ, means that sampling is too frequent, adds the workload of sensor.T is excessive for interval Δ, likely misses data message, makes result of calculation inaccurate.

In one embodiment of the invention, n value is 5-25.N is too small, and likely cause result of calculation inaccurate, n is excessive, causes amount of calculation significantly to increase.

In one embodiment of the invention, variance threshold values is 30-60.When variance threshold values is in this span, result of calculation is the most reasonable.

In one embodiment of the invention, expiration tidal volume VTE computational methods are applied to turbine respirator.

For making those skilled in the art understand the present invention better, below applicant be further elaborated in conjunction with specific embodiments.

The expiratory flow sensor of turbine type respirator is utilized to detect exhalation flow rate.Expiratory gas flow data are gathered every 10ms.Then and calculate two groups of nearest 10 sampled datas are obtained, two moment.

First group: when exhalation process does not complete, sampled data is as shown in table 1.

Table 1 first group of sampled data points

Sampled point sequence number	1	2	3	4	56	7	8	9	10
										Expiratory gas flow ml/s	503	478	452	433	400354	300	298	296	300

Can find out according to data, the data of the first seven point are successively decreased, and rear four data have tended towards stability, and illustrate close to exhaling finally.In table, data substitute into variance technique formula

D = \frac{1}{n} Σ_{i = 1}^{n} {(X_{i} - \overset{&OverBar;}{X})}^{2}

N=10, calculate D=6038.Variance is comparatively large, judges that now exhalation process does not complete.

Second group: when exhalation process completes, sampled data is as shown in table 1.

Table 1 first group of sampled data points

Sampled point sequence number	1	2	3	4	5	6	7	8	9	10
											Expiratory gas flow ml/s	300	296	296	304	302	300	292	298	296	300

Can find out according to data, although exhalation flow rate sensor has numerical value (non-vanishing) always, be not the flow velocity that patient expiration produces, but the flow velocity that elementary streams produces.In table, data substitute into variance computing formula

D = \frac{1}{n} Σ_{i = 1}^{n} {(X_{i} - \overset{&OverBar;}{X})}^{2}

N=10, calculate D=14.Variance is very little, exhalation flow rate is described close to meansigma methods, if the variance setting continuous ten numbers is less than default variance threshold values 50, that just thinks that patient expiration terminates, and the integration of expiration tidal volume VTE just leaves it at that, no longer cumulative.Respirator is ventilated and then calculates the tidal volume in next cycle in this manner next time.

In the description of this description, specific features, structure, material or feature that the description of reference term " embodiment ", " some embodiments ", " example ", " concrete example " or " some examples " etc. means to describe in conjunction with this embodiment or example are contained at least one embodiment of the present invention or example.In this manual, to the schematic representation of above-mentioned term not must for be identical embodiment or example.And the specific features of description, structure, material or feature can combine in one or more embodiment in office or example in an appropriate manner.In addition, the different embodiment described in this description or example can carry out combining and combining by those skilled in the art.

Although illustrate and describe embodiments of the invention above, be understandable that, above-described embodiment is exemplary, can not be interpreted as limitation of the present invention, and those of ordinary skill in the art can change above-described embodiment within the scope of the invention, revises, replace and modification.

Claims

1. expiration tidal volume VTE computational methods, is characterized in that, comprise the following steps:

Interval of delta t interval time ground timing acquiring expiratory gas flow data X;

Calculate the variance D of the nearest described expiratory gas flow data X collected for n time, if described variance D becomes be less than described default variance threshold values from being greater than default variance threshold values, then think that current time is finish time of exhaling, wherein n is positive integer;

Do the integration of described expiratory gas flow data X in time between the described expiration finish time that the expiration start time of presetting and judgement are obtained, obtain expiration tidal volume VTE.

2. expiration tidal volume VTE computational methods according to claim 1, is characterized in that, described interval Δ t is 2-10ms, and the unit of expiratory gas flow data X is ml/s.

3. the expiration tidal volume VTE computational methods according to claim 1 and 2, is characterized in that, described n value is 5-25.

4. the expiration tidal volume VTE computational methods according to claim 1-3, is characterized in that, described variance threshold values is 30-60.

5. the expiration tidal volume VTE computational methods according to claim 1-4, is characterized in that, described expiration tidal volume VTE computational methods are applied to turbine respirator.