Source: https://patents.google.com/patent/EP3187205A1/en
Timestamp: 2019-04-24 02:55:01
Document Index: 438203704

Matched Legal Cases: ['art 3', 'art 3', 'art 3', 'art 4', 'art 4', 'art 4']

EP3187205A1 - Methods and devices for performing a negative pressure wound therapy - Google Patents
Methods and devices for performing a negative pressure wound therapy Download PDF
EP3187205A1
EP3187205A1 EP15203114.2A EP15203114A EP3187205A1 EP 3187205 A1 EP3187205 A1 EP 3187205A1 EP 15203114 A EP15203114 A EP 15203114A EP 3187205 A1 EP3187205 A1 EP 3187205A1
EP15203114.2A
2015-12-30 Priority to EP15203114.2A priority Critical patent/EP3187205A1/en
2017-07-05 Publication of EP3187205A1 publication Critical patent/EP3187205A1/en
The present invention relates to a method of determining a canister full condition in a negative pressure wound therapy system during a negative pressure wound therapy.
Said method includes determining and recording a number of pump turns associated with an electrical pump used for generating a negative pressure in the negative pressure wound therapy system, determining and recording a plurality of negative pressure values by means of a pressure sensor, calculating and recording a negative pressure variation score by means of the recorded negative pressure values, and generating a first or a second canister full detection data set. Moreover, the method includes executing a classification algorithm which allows to discriminate a canister not full condition from a canister full condition of the negative pressure wound therapy system using the generated data sets. The invention further relates to another method of determining a canister full condition in a negative pressure wound therapy system during a negative pressure wound therapy. Said further method includes generating a negative pressure at a wound site by means of an electrical pump, generating a first or a second canister full detection data set, and executing a classification algorithm, which allows to discriminate a canister not full condition from a canister full condition of the negative pressure wound therapy system using the generated data sets, whereby the classification algorithm includes a support vector machine. The invention further relates to a negative pressure wound therapy system adapted to execute said methods of determining a canister full condition a negative pressure wound therapy system.
The invention relates to control methods for a negative pressure wound therapy system. In particular, the invention relates to a method of determining a canister full condition in a negative pressure wound therapy system during a negative pressure wound therapy. Moreover, the invention relates to a negative pressure wound therapy system adapted to execute the canister full detection method according to the invention.
In order to achieve the desired wound healing effect for the patient it is necessary that the negative pressure therapy is performed throughout the planned therapy schedule without any unnecessary interruptions. It is therefore also necessary that the therapy device warns the user as soon as any conditions appears that impair a proper continuation of the negative pressure therapy. The user may then be able to eliminate the problem (if possible) by himself/herself. If a restoration of proper function by the user is not possible, the user will have to contact a service technician. One such condition that interferes with proper negative pressure application is a "canister full condition". A canister full condition appears as soon as the canister (or container) provided for collecting the exudates sucked from the wound is full. In such a situation the full canister, which is usually a disposal item, will have to be replace by a new one. Replacement can be performed by the patient or by the caregiver.
Typically, a filter is disposed between the exudate container and the pump in order to prevent the exudates entering the pump. If such a filter is present, a canister full condition will come along with a blocked filter caused by the exudates being sucked towards the filter membrane. A blocked filter membrane will eliminate airflow through the suction fluid pathway leading to no-flow condition. One specific problem connected with detection of a full canister condition in a negative pressure therapy system is that the canister full condition may be difficult to discriminate from other conditions, which also come along with a zero flow through the suction tube: A zero flow condition is also observed if the target pressure is reached and the wound dressing is completely tight. Another zero flow condition occurs if the suction conduit is blocked.
Signalling a canister full warning to the patient under such a zero flow condition, when the canister is actually no full is irritating and annoying for the patient. It may also lead to an unnecessary interruption of therapy.
Based on a device for providing a negative pressure for medical applications, it is the underlying purpose of the present invention to further optimize the user friendliness, reliability and the operational safety of the device. The medical device should be as reliable and as fail-proof as possible under all typical treatment situations (for example, any alarm mechanisms should function proper independent of the volume of the wound space to be treated). In particular, the device should be able to detect a full canister timely but without generating false alarms. The device should be able to recognise a canister full condition as well as to reliably discriminate a canister full condition from other zero-flow conditions. Ideally, the canister full detection method should function on a device that does not require additional sensors (such as an additional pressure sensor or a flow meter) or components. Ideally, even a technically less skilled user or patient should be given the feeling that she/he can handle the device easily.
A solution for the aforementioned problems is provided by the present invention. According to a first aspect the invention a method of determining a canister full condition in a negative pressure wound therapy system during a negative pressure wound therapy is proposed. Said method, which is designated in the present specification as the "canister full detection method", comprises the following steps:
a second canister full detection data set, said second canister full detection data set being correlated to a canister full condition of the negative pressure wound therapy system.
The second aspect of the invention relates to a further method of determining a canister full condition in a negative pressure wound therapy system during a negative pressure wound therapy, comprising the steps of
ii. generating a first or a second canister full detection data set, said first or said second canister full detection data set comprising
one or more variables corresponding to (or derived from) one or more pump speed measurements, wherein a tachometer of the negative pressure wound therapy system performs the pump speed measurements, and/or
one or more variables corresponding to (or derived from) one or more negative pressure measurements, wherein a pressure sensor of the negative pressure wound therapy system performs the negative pressure measurements,
iii. executing a classification algorithm, which allows to discriminate
a second canister full detection data set, said second canister full detection data set being correlated to a canister full condition of the negative pressure wound therapy system, wherein the classification algorithm includes a support vector machine to generate a hyperplane,
iv. optionally generating a canister full signal in a controller of the negative pressure wound therapy system as soon as a canister full condition of the negative pressure wound therapy system is detected by means of the classification algorithm.
The third aspect of the invention pertains to a negative pressure wound therapy system. The negative pressure wound therapy system according to the third aspect of the invention comprises an electrical pump for generating negative pressure, optionally a tachometer for determining a pump speed associated with the electrical pump, a pressure sensor for determining negative pressure values, a controller for controlling activity of the electrical pump, input means for adjusting settings on the negative pressure wound therapy system, said input means being operable by the user of the negative pressure wound therapy system, and a first fluid path fluidly connectable to a wound site and to the electrical pump such that the wound site can be subjected to a negative pressure. The pressure sensor is located in the first fluid path between the wound site and the electrical pump. The negative pressure wound therapy system according to the third aspect of the invention is characterised in that the controller of the negative pressure wound therapy system is adapted to execute a method according to the first or the second aspect of the invention.
A negative pressure control system which is capable of performing the methods for determining a canister full condition in a negative pressure wound therapy system during a negative pressure therapy is able to detect any canister full condition timely and reliably. False alarms are avoided. The inventors discovered that the proposed methods work well for a wide variety of treatment situations including varying wound sizes or wounds secreting extensive amounts of wound exudate. A negative pressure wound therapy system according to the third aspect of the invention can be designed robustly and simply, because additional components (such as an additional pressure sensor or a flow meter) are not required.
The controller of the negative pressure wound therapy system according to the third aspect of the invention is adapted to execute a method according to the first or to the second aspect of the invention. This means that the controller is not only capable of executing the methods (e.g. by having the required processing power and memory), but also actually applies the methods when the negative pressure wound therapy system is used for wound treatment. This requires that the controller is programmed to perform the algorithm of the method according to the first or second aspect of the invention.
PREFERRED EMBODIMENTS OF THE INVENTION Canister full detection method (first aspect of the invention)
In general, the negative pressure variation score provides an indication of the overall pressure change within the fluid-tight sealed components of the npwt system during the predetermined period of time. According to a preferred embodiment of the canister full detection method, the calculation of the negative pressure variation score comprises the steps of
As indicated by the algebraic signs, pd2 and pd3 represents negative pressure increments, wherein pd1 and pd4 represents negative pressure decrements. Therefore, the sum of the negative pressure increments (pd+) amounts to 15 mmHg (pd2 + pd3) and the sum of the negative pressure decrements (pd-) amounts to -15 mmHg (pd1 + pd4). The product (pdx) of the sum of the negative pressure increments (pd+) and the sum of the negative pressure decrements (pd-) amounts to -225 mmHg2 (pd+ x pd-). Extracting the square root of the absolute value of the product (pdx) yields the negative pressure variation score, which in this example amounts to 15 mmHg pdx .
According to a particularly preferred embodiment of the canister full detection method, the classification algorithm includes a support vector machine to generate a hyperplane. In other words, the classification algorithm preferably includes a hyperplane generated by a support vector machine.
Preferably, the negative pressure drop is determined by determining a difference between the negative pressure of step ii. of the first blockage detection method and the negative pressure present in the negative pressure wound therapy system when the predetermined period of time has elapsed. Preferably, the calculated difference is related to the negative pressure of step ii. of the first blockage detection method to obtain a percentage negative pressure drop. For example, a percentage negative pressure drop of 10 % is obtained, if the negative pressure of step ii. is 100 mmHg and the negative pressure at the end of the predetermined period of time is 90 mmHg. The corresponding formula for this example can be summarized as follows: Percentage negative pressure drop = 100 mmHg - 90 mmHg / 100 mmHg × 100 = 10 %
The general formula is: negative pressure drop in % = negative pressure of step ii . - negative pressure at the end of the predetermined period / negative pressure of step ii . ) × 100
Determining the negative pressure gradient may include comparing a first pressure measurement at the start of the ventilation step (typically the recorded negative pressure of step ii.) and a second pressure measurement at the end of the ventilation step. For example, the first pressure measurement may determine a negative pressure value of 100 mmHg and the second pressure measurement may determine a negative pressure value of 80 mmHg, wherein the measurements have been determined in a time interval of 10 seconds. The negative pressure gradient in this example then amounts to -2 mmHg/s. The negative algebraic sign of the negative pressure gradient can be used to indicate that the gradient is related to a negative pressure drop. The corresponding formula for this example can be formulated as follows: Negative pressure gradient : 80 mmHg - 100 mmHg / 10 seconds = - 2 mmHg / s
According to an even more preferred version of the second blockage detection method, the variable yB is derived from the recorded negative pressure gradient by relating the recorded negative pressure gradient to a negative pressure value obtained by calculating (0.5 x (Ps + PD)). Ps is or corresponds to the negative pressure of step ii. of the second blockage detection method. PD is or corresponds to the negative pressure at the end of the ventilation step. The formula to calculate the variable yB can be described as follows: y B = negative pressure gradient / 0.5 × P S + P D
If, for example, the negative pressure gradient is at -2 mmHg/s, Ps is at 100 mmHg and PD is at 80 mmHg, yB according to this preferred embodiment amounts to -1/45 s-1. y B = - 2 mmHg / s / 0.5 × 100 mmHg + 80 mmHg = - 1 / 45 s - 1
To further improve application of the support vector machine, the variable zB may also be subjected to a mathematical transformation. Therefore, according to a particularly preferred version of the second blockage detection method, the variable zB is derived from the recorded number of pump turns by relating the recorded number of pump turns to the negative pressure drop during the ventilation step (or in other words by relating the recorded number of pump turns to the amount of the negative pressure increase to reestablish the negative pressure prior the ventilation step). The corresponding formula can be summarized as follows: z B = number of pump turns / P S - P D
Again, Ps is or corresponds to the negative pressure of step ii. of the second blockage detection method and PD is or corresponds to the negative pressure at the end of the ventilation step. If, for example, the number of pump turns amounts to 20, Ps amounts to 100 mmHg (which corresponds to the negative pressure to which the system is initially regulated after the ventilation step and up to which the number of pump turns is recorded) and PD amounts to 80 mmHg, zB according to this preferred embodiment possesses a value of 1 mmHg-1. z B = 20 / 100 mmHg - 80 mmHg = 1 mmHg - 1
According to another preferred embodiment of the invention, the method according to the first or the second aspect of the invention further comprises determining a leakage condition of a negative pressure wound therapy system. The method, which is designated in the present specification as the "leakage detection method", comprises the following steps:
ii. generating a leakage signal if a pump speed associated with the electrical pump exceeds a predetermined value.
Preferably, the predetermined value for the pump speed is selected of the range of 1500 RPM to 10000 RPM. Even more preferably, the predetermined value for the pump speed is selected of the range of 3000 RPM to 6000 RPM. In particular, the predetermined value is approximately 3000 RPM or approximately 4900 RPM.
The predetermined value may also advantageously be selected such that the negative pressure wound therapy system is still able to essentially maintain a desired target negative pressure when the leakage signal is generated. This may be achieved by selecting a pump speed threshold (predetermined value) as suggested previously.
Flow rate estimation method
Proceeding to another preferred embodiment of the invention, the method according to the first or second aspect of the invention further comprises estimating a flow rate of a negative pressure wound therapy system. The method, which is designated in the present specification as the "flow rate estimation method", comprises the following steps:
Any mathematical equation for estimating the flow rate rate is a "flow rate function" according to the invention as long as the equation comprises the variable pump speed (or a variable derived from the pump speed) and the variable pump current (or a variable derived from the pump current).
Preferably, the negative pressure wound therapy system comprises a canister for collecting liquid from the wound site. The canister is located in the first fluid path between the wound site and the electrical pump. The pressure sensor is located in the first fluid path between the canister and the electrical pump. A suitable canister is disclosed, for example, in the international patent applications WO 2014/177544 A1 and WO 2014/177545 A1 .
If feasible, any of the aforementioned preferred methods, embodiments or advantageous features may be used in combination with each other. Any of said combinations may be used for a negative pressure wound therapy system capable of performing a method according to the first or the second aspect of the invention. For example, a method according to the first or the second aspect of the invention may further include the first or second pressure control method, the wound pressure estimation method, any one of the disclosed blockage detection methods and the leakage detection method. Such a control algorithm for a negative pressure wound therapy device would be capable of controlling the pump activity in order to achieve the desired negative pressure at the wound and to detect certain alarm situations which may occur during the negative pressure wound therapy.
Any feature of the canister full detection method may also be implemented in the method according to the second aspect of the invention.
It can also be seen from FIG 2 d on the side 10 of the second housing part 3 facing the body, a grip recess 11 is formed in the shape of an opening extending right through the second housing part 3.In this way, the device 1, or only its second housing part 3, can be gripped and handled with one hand.
Also shown is an additional rinsing or aeration tube 24 that(according to an exemplary design) proceeds through the container 3 and just like the suction tube 6 leads to the wound dressing 13. When the container 3 is attached in its intended assembly position on the first housing part 4, this rinsing tube 24 communicates with a tube section 25 provided in the first housing part 4. The first housing part 4 comprises an electromagnetically operated valve 26 that can be actuated by the electronic control unit 18. Said valve 26 connects the tube section 25 with the atmospheric air when it is open, so that an air current toward the wound via the rinsing tube 24 can be generated.
"modification value formula"
modification value (mmHg) [i.e. pressure drop] = constant (mmHg/RPM) x pump speed (RPM)
"pressure estimation formula"
estimated negative pressure at the wound (mmHg) = measured negative pressure (mmHg) - (constant (mmHg/RPM) x pump speed (RPM))
A negative pressure value of 125 mmHg is determined using pressure sensor 17. The pressure sensor is located in the fluid path between pump 5 and filter 7. The pump speed of the electrical pump 5 at the time of the pressure measurement is 1000 RPM. The constant determined for the npwt system used for the experiments is 0.0075 mmHg/RPM. Using the "pressure estimation formula" disclosed herein, the estimated negative pressure at the wound site 2 is 117.5 mmHg:
estimated negative pressure at the wound (mmHg) = 125 mmHg - (0.0075 mmHg/RPM x 1000 RPM) = 117.5 mmHg
FIGS 8 a to c show the separation plane (blockage detection function) from different perspectives. The figures provide an example of a three-dimensional space (coordinate system) and a separation plane, which can be used for the blockage detection classification algorithm. The x-axis of the diagrams represents values derived ("transformed") from the number of pump turns (i.e. the number of pump turns were put in relation to the pressure drop (Ps - PD)). The y-axis of the diagrams represents values derived ("transformed") from the pressure gradient (i.e. the pressure gradient was put in relation to 0.5 x (Ps + PD)). Finally, the z-axis of the diagrams represents the start pressure. In this case the negative pressure values represented by the z-axis are provided with negative algebraic signs. The diagrams in FIGS 8 a to c also show the blockage detection data sets that were generated as a result of a plurality of blockage detection training experiments. Each data point in the coordinate system corresponds to a blockage detection data set. The circles in the diagrams indicate first blockage detection data sets each representing an unblocked condition. The triangles in the diagrams indicate second blockage detection data sets each representing a blocked condition. As can be seen in the diagrams, the first and the second blockage detection data sets are forming classes which do not overlap with each other. It is possible to separate the first from the second class by a 2-dimensional plane. The calculation of the separation plane shown in FIGS 8 a to c was done by using a standard support vector machine. The separation plane provides a measure whether any individual future blockage detection event (represented by a blockage detection data set), which is the result of performing the blockage detection method disclosed herein, corresponds to an unblocked condition (first class) or to a blocked condition (second class). All data points located above (to the right of) the separation plane are classified as an unblocked condition (first class) of the examined negative pressure wound therapy system. In contrast, all data points located underneath (to the left of) the separation plane are classified as a blocked condition (second class) of the examined negative pressure wound therapy system. In FIG 8 a, two arrows indicate the direction of "above/to the right (a/r)" and "underneath/to the left (u/I)" in connection with the separation plane.
The results depicted in FIG 10 were obtained by means of the following experiments: A negative pressure wound therapy system as previously described in connection with FIG 2 and FIG 3 including an artificial wound (size: 240 cm3) is subjected to different leakage conditions. The experiments include the use of the wound simulator device as basically disclosed in the international application WO 2010/072349 A1 of the applicant. This wound simulator device comprises the aforementioned artificial wound. The wound simulator device comprises a valve and a flow meter to create and determine the leakage condition of the tested npwt system. To generate negative pressure, the tested negative pressure wound therapy system used the membrane pump SP622 EC-BL of the company Schwarzer. Furthermore, the tested negative pressure wound therapy system executes the aforementioned pressure control method (first and second pressure control method) to control the pump and to generate the desired target negative pressure value. The amount of air entering the fluid path of the negative pressure wound therapy system is represented by the x-axis of the diagram in FIG 10. The y-axis represents the negative pressure within the fluid path of the system. A higher leak flow rate corresponds to a higher leakage condition of the system. During the experiment, a target negative pressure value of approximately 200 mmHg is chosen (line A) and it is studied how long the negative pressure wound therapy system is able to maintain the desired target negative pressure value. The experiment is repeated with a target negative pressure value of approximately 125 mmHg (line B).
The following formulas provide an example how the flow rate can be mathematically derived from the pump current and the pump speed according to the invention. DF stands for "density factor". The density factor relates to the density of the air being evacuated by the npwt system. PC is the measured pump current. PS is the measured pump speed. Typically, PC and PS are measured at the same time. DFA stands for "density factor adjustment" and provides a mathematically modified density factor (DF) value.
Finally, EFR represents the "estimated flow rate". The units of pump current and pump speed are Ampere (A) and revolutions per minute (RPM), respectively. DF = PC + 0.0666 PS 6000 + 0.826
DFA = 0.5 + 1.5 1 + e DF × 48.5 - 8.62
EFR = PS 2000 × DFA
Method of determining a canister full condition in a negative pressure wound therapy system during a negative pressure wound therapy, comprising the steps of
i. determining and recording a number of pump turns associated with an electrical pump used for generating a negative pressure in the negative pressure wound therapy system, wherein the number of pump turns is determined for a predetermined period of time,
ii. determining and recording a plurality of negative pressure values by means of a pressure sensor, wherein the plurality of negative pressure values is determined for the predetermined period of time,
- the recorded number of pump turns and
- the recorded negative pressure variation score,
v. executing a classification algorithm, which allows to discriminate
- a first canister full detection data set, said first canister full detection data set being correlated to a canister not full condition of the negative pressure wound therapy system, from
- a second canister full detection data set, said second canister full detection data set being correlated to a canister full condition of the negative pressure wound therapy system.
Method according to claim 1, wherein the predetermined period of time is a value selected from the range of 1 second to 15 seconds, wherein the range is preferably 1 second to 6 seconds and wherein the predetermined period of time is preferably 3 seconds.
Method according to claim 1 or 2, wherein the calculation of the negative pressure variation score comprises the steps of
Method according to any one of the preceding claims, wherein the first or the second canister full detection data set comprises
- a variable xc corresponding to or derived from the recorded number of pump turns, and
- a variable yc corresponding to or derived from the recorded negative pressure variation score.
Method according to any one of the preceding claims, wherein the classification algorithm includes a support vector machine.
Method according to claim 5, wherein the classification algorithm includes a support vector machine using a two-dimensional space and a separation line, preferably a linear separation line.
Method according to any one of the preceding claims, wherein the method further comprises a step of generating a canister full signal in a controller of the negative pressure wound therapy system as soon as a canister full condition of the negative pressure wound therapy system is detected by means of the classification algorithm.
- one or more variables corresponding to or derived from one or more pump speed measurements, wherein a tachometer of the negative pressure wound therapy system performs the pump speed measurements, and/or
- one or more variables corresponding to or derived from one or more negative pressure measurements, wherein a pressure sensor of the negative pressure wound therapy system performs the negative pressure measurements,
- a second canister full detection data set, said second canister full detection data set being correlated to a canister full condition of the negative pressure wound therapy system,
wherein the classification algorithm includes a support vector machine,
Method according to any one of the preceding claims, wherein the method further comprises the following steps of generating a negative pressure at a wound site during a negative pressure wound therapy:
Method according to any one of the claims 1 to 8, wherein the method further comprises the following steps of generating a negative pressure at a wound site during a negative pressure wound therapy:
Method according to any one of the preceding claims, wherein the method comprises using a negative pressure wound therapy system comprising
- an electrical pump for generating negative pressure,
- optionally a tachometer for determining a pump speed associated with the electrical pump,
- a pressure sensor for determining negative pressure values,
- a controller for controlling activity of the electrical pump,
- an input means for adjusting settings on the negative pressure wound therapy system, said input means being operable by the user of the negative pressure wound therapy system,
- a first fluid path fluidly connectable to a wound site and to the electrical pump such that the wound site can be subjected to a negative pressure, wherein the pressure sensor is located in the first fluid path between the wound site and the electrical pump.
Method according to claim 11, wherein the negative pressure wound therapy system further comprises a canister for collecting liquid from the wound site, wherein the canister is located in the first fluid path between the wound site and the electrical pump and wherein the pressure sensor is located in the first fluid path between the canister and the electrical pump.
Method according to claim 12, wherein the negative pressure wound therapy system further comprises a means for preventing liquid from entering the electrical pump, preferably a moisture sensitive filter or a liquid impermeable membrane, wherein the means for preventing liquid from entering the electrical pump is located in the first fluid path between the canister and the pressure sensor.
- a first fluid path fluidly connectable to a wound site and to the electrical pump such that the wound site can be subjected to a negative pressure, wherein the pressure sensor is located in the first fluid path between the wound site and the electrical pump,
characterised in that the controller of the negative pressure wound therapy system is adapted to execute a method according to any one of the preceding claims.
A negative pressure wound therapy system according to claim 14, wherein the controller of the negative pressure wound therapy system is adapted to execute the method according to any one of the preceding claims 1 to 13 such that the negative pressure wound therapy system in the active state continuously or intermittently executes the method according to any one of the preceding claims 1 to 13.
EP15203114.2A 2015-12-30 2015-12-30 Methods and devices for performing a negative pressure wound therapy Pending EP3187205A1 (en)
EP15203114.2A EP3187205A1 (en) 2015-12-30 2015-12-30 Methods and devices for performing a negative pressure wound therapy
EP3187205A1 true EP3187205A1 (en) 2017-07-05
ID=55027584
EP15203114.2A Pending EP3187205A1 (en) 2015-12-30 2015-12-30 Methods and devices for performing a negative pressure wound therapy
EP (1) EP3187205A1 (en)
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