WO2003017835A1

WO2003017835A1 - Flow measurement in respiratory systems

Info

Publication number: WO2003017835A1
Application number: PCT/DK2002/000564
Authority: WO
Inventors: Ole Tidemann; Jakob Martin Riiser; Robert Mikkelsen; Jens Nørkær SØRENSEN; Jens Dahl Poulsen; Bjarke Skovgaard Dam; Jesper Møller PEDERSEN; Søren LARSEN
Original assignee: Rhinometrics A/S
Priority date: 2001-08-28
Filing date: 2002-08-28
Publication date: 2003-03-06

Abstract

The invention relates to a method for measuring flow in a respiratory canal of a patient during inspiration or expiration, where the patient breathes through measuring unit and where the pressure as well as the flow rate are measured simultaneously and where flow e.g in relation to pressure is used to analyze part of the respiratory system, where the pressure measuring results before the analysis are corrected by adding an error correction, whereby the corrected pressure equals formula (I).

Description

Flow measurement in respiratory systems

AREA OF THE INVENTION

The invention relates to the area of flow measurement in respiratory systems, primarily in humans but also in other mammals. The invention particularly relates to the elimination/reduction of hysteresis present in such measurements, which hysteresis gives rise to measuring results deviating from a desired unambiguous result and hence may give rise to an incorrect diagnosis given by the physician evaluating the result.

BACKGROUND OF THE INVENTION

When referring to hysteresis this should be understood as representing a deviation caused by a phase shift in the flow in the respiratory system or in the measuring system. Although there is not necessarily a loss in this system causing the deviation this deviation is still designated a hysteresis in the following.

A number of measuring methods and corresponding equipment for flow measurement is known today. Among the most commonly used are the rliinomanometry and the rhinoresistometry.

The rhinomanometry is through the recent more than 25 years typically performed in the following manner for each of the patient's nostrils: A so-called rhinomanometer comprising a mask with a flow measuring tube mounted thereon is mounted on the nose and a pressure difference transducer in the tube register the pressure drop over an orifice plate, i.e. between the surrounding atmosphere and the inside of the flow tube. The pressure drop created over the orifice plate is hereby an expression for the actual flow. The one side of a second pressure difference transducer opens into the flow measuring tube and its other side opens into a tube, through which the pressure at the rear edge of the nose separation is to be measured. The rhinoresistometry is a somewhat more recent developed method. This method comprises measuring the nasal resistance in relation to airflow. It is hereby possible to see if the flow is laminar or turbulent depending on the degree of flow. Rhinoresistometry can be used to estimate the hydraulic diameter as a value for the nasal patency in nasal airflow and as a parameter for the degree of turbulence. A description of the method appears in the article "Die Rhinoresistometrie - eine Weiterentwicklung der Rhinomanometrie" by G. Mlynski, J. Low published in "Laryngo-Rhino-Otol. 72, (1993)".

In these measurements there is normally an occurrence of hysteresis that has the effect that the curves indicating the pressure/flow relation will not pass through the zero points of both the x-axis and the y-axis. Hence a flow is registered although there is no pressure difference registered. The flow that is actually registered is a result of a phase shift of the flow as mentioned above and referred to as hysteresis.

Due to the existence of the hysteresis resulting in a measuring result that may be very difficult to interpret there is a significant need for improvement in this field in the direction of eliminating/reducing the source(s) of errors occurring.

From DE 3641585 a method of correcting the measuring results is known. The method involves that a mask is placed over a patient's face. The mask is connected to flow and pressure measuring devices. The method involves a determination of a mean value of a number of curves from which some results have been excluded if certain criteria are not satisfied.

By using this method there may be a risk of manipulating the results in a manner that does not reflect the actual measurement, i.e. forcing the curves towards a predeterrnined average value. This may also give rise to erroneous measuring results in the display of these. The results cannot be displayed in a real-time display due to the need for several runs (inspirations and expirations) before the corrected results can be displayed.

The objective of the present invention is therefore to provide a method and a device that can reduce and possibly eliminate the occurrence of the hysteresis in the flow measuring results that form the basis for the evaluation and diagnosis of a possible physical defect of the patient in question with a reduced risk of erroneous manipulation.

SUMMARY OF THE INVENTION

According to the invention this is achieved by means of the method defined in claim 1 or claim 5.

Due to the correction performed in this manner the result will be as close to the desired unambiguous measuring result as possible and hence the risk of coming up with an incorrect conclusion and an incorrect diagnosis is eliminated or at least reduced significantly. The method takes its starting point in the actual anatomic conditions of the patient as well as the physical conditions of the measuring system. This means that the correction will not involve a forced correction based on expectations of the actual measuring results. The correction will only involve correction based on the deviations occurring due to the flow conditions in the patient and the measuring system. This reduces the risk of an erroneous diagnosis. The analysis can for instance be carried out by visually analysing a display of the measuring results.

Particularly advantageous the correction and display is carried out in a real time relation, or at least only with a very short delay, This allows for display of the corrected result during the actual measurement and hence allows for simultaneous observation of the patient and the displayed measuring results.

The correction will be dependent on the type of patient being subject to measurement. In case the patient is a human the correction constant C-σ-p-L should normally be selected in the range between 10 Pa-s²/m and 50 Pa-s²/m.

For other types of patients the correction constants will be dependent on the size of the patient, i.e. a patient larger than a human will require a another constant and a smaller patient than a human will require yet another constant. According to the invention the objective is furthermore achieved by means of the device as set forth in claim 9.

By such device, which may represent a revised Rhinomanometer or a revised Rhinoresistometer the advantages as mentioned above may be implemented in a functional device.

It is further advantageous when a display is provided for simultaneous or real-time display of the measuring results.

The invention will be explained more detailed in the following description of a preferred embodiment with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a screen print showing both the uncorrected and the corrected relations between pressure and flow.

DESCRIPTION OF A PREFERRED EMBODIMENT

As it appears from FIG. 1 the curves 1 and 2 with the hysteresis error will not go through zero flow for zero pressure difference. Here the curve 1 expresses the inspiration whereas the curve 2 expresses the expiration.

The curves 3 is obtained by plotting the flow through the nose during inspiration and

expiration in relation to the expression AP„_0Se + C ■ σ_probe ■ p -L_nose •— |^ where

ΔPno_se is the pressure difference [Pa];

C and σ_Pro _e are empiric values, specific to the patient type and probe in question. For a human the product of these is preferably in the range between 10 Pa-s²-m/kg and 50 Pa-s²-m/kg. p is the density [kg/m³]; Lnose is a value expressing the equivalent length of the nose [m]; U is the average speed [m/s]; t is the time [s];

The curves 3 hereby comprises both inspiration and expiration components.

In a further preferred embodiment the measuring results are displayed as flow dependent on pressure and where the measuring results before the display are corrected according to the following error correction dXJ , AP_^ +C-σ^ - p -L, Jj I probe .static

as a function of P_pr0be =

-U +f_μ -U , where

P_pmbe *^{s tne} pressure difference [Pa] L is the length [m] ε is a parameter in the flow model α is a constant in the flow model [Pa-s^β/ ^β+1)] β is an exponent in the flow model f_μ is a friction constant [Pa-s/m²]

This allows for display of the measuring result simultaneous with the actual measurement being carried out.

It is obvious from the curves that the curves 3 represent a desired unambiguous representation of the pressure-flow relation during inspiration and expiration. The improvement in obtaining these results is as mentioned in the following claims the main subject of this invention and is achieved by a method for providing an error correction and a device for carrying out the method.

Claims

1. A method for measuring flow in a respiratory canal of a patient during inspiration or expiration, where the patient breathes through a measuring unit and where the pressure as well as the flow rate are measured simultaneously and where flow is used to analyse part of the respiratory system, where the pressure measuring results before the analysis are corrected by adding an error correction, whereby the corrected pressure equals

A method according to claim 1, where flow in relation to pressure forms the basis for the analysis.

3. A method according to claim 1 or 2, where the correction is carried out during the measurement allowing the display of the corrected flow or flow/pressure relation during measurement.

4. A method according to claim 1, 2 or 3, where the correction constant C-σ-p-L is selected between 10 Pa-s²/m and 50 Pa-s²/m.

5. A method for measuring flow in a respiratory canal of a patient during inspiration or expiration, where the patient breathes through a measuring unit and where the pressure as well as the flow rate are measured simultaneously and where the measuring results are used for analysis of part of the respiratory system where the flow measuring results before the analysis are corrected in a manner where the flow is determined from

Λ P ose r T n ^' probe ^' P ' nose ' ^ , I \ probe .static and boundary conditions for U.

6. A method according to claim 5, where the flow is related to the pressure determined from ΔP p.robe = L -(ε - a ^■u^β +f_μ U

7. A method according to claim 5 or 6, where the correction is carried out during the measurement allowing the display of the corrected flow/pressure relation during measurement.

8. A method according to claim 4, 5 or 6, where the correction constant C-σ-p-L is selected between 10 Pa-s²/m and 50 Pa-s²/m.

9. A device for measuring flow and corresponding pressure in respiratory systems, the device comprising a measuring tube through which the patient performs expiration and inspiration, where in connection with the measuring tube means for flow measuring are provided as well as means for pressure measuring, where the device furthermore comprises a signal processing means capable of performing a correction of the result according to the method as set forth in any of the preceding claims.

10. A device according to claim 9 where a display for visual indication of the pressure-flow relationship is provided in connection with the device.