EP0555652B1 - Coupled control of operating parameters of an incubator - Google Patents

Description

The invention relates to a method for controlling the operating parameters determining the heat balance of a premature or newborn in an incubator, which include at least the incubator temperature and the humidity to be set in the interior of the incubator, of which the actual values are compared with their associated target values and new setpoints are set for the parameters in the event of a deviation.

The purpose of controlling the operating parameters of an incubator is always to determine the ambient conditions for a premature or newborn in the interior of the incubator in such a way that the body loses as little heat as possible from the environment. Maintaining a heat balance necessary for the well-being of the patient means an increased effort for the patient, which is to be reduced by the ambient conditions in the incubator. Essential parameters for maintaining the desired ambient conditions are: Incubator air temperature to avoid convection heat losses, surface temperatures of the incubator hood or the lying surface to avoid temperature losses via heat conduction or heat radiation, and very significantly the moisture content of the incubator air temperature. It is also important to provide the patient with sufficient oxygen to support the heat-producing metabolic balance.

It has been proposed to link those parameters which define the required cheap incubator environment to one another via a process computer in such a way that default values for the parameters are input and stored therein which are based on patient-related selection variables (DE-A1 39 30 363). The selection sizes are e.g. by body weight, age, gestational age. Depending on these selection variables, empirical values for the associated incubator parameters are known. The preset values stored in this way are compared with the actual values from the incubator, and if the specified tolerance values are exceeded or undershot, certain combinations of actual values lead to a statement about the patient's thermal condition. If it is no longer possible to maintain the required heat, the setpoint of suitable parameters is changed. E.g. the comparison of the actual values with the stored default values to the result that the patient is hypothermic, the setpoint of the incubator air temperature is increased.

With this type of control of operating parameters of an incubator as a function of the measured actual values, however, it is not taken into account that the change in one parameter also affects the influence of another parameter on the thermal balance of the premature or newborn. For example, the increase in the incubator air temperature means a reduction in the relative humidity in the incubator air, which increases the possibility of evaporation of the patient's body to the environment and thus to it Evaporation heat is removed. On the other hand, a lowering of the incubator air temperature means an increase in the relative air humidity, so that, despite the low incubator air temperature, the body temperature of the patient may even be increased, since the possibility of giving off heat of evaporation is reduced. In addition, it may be necessary that the necessary oxygen supply is reduced with an increased incubator air temperature and corresponding heating of the body core temperature.

Therefore, if one of the operating parameters of its setpoint has to be changed, it is necessary in the sense of an optimal setting of the environmental conditions of the premature or newborn in the incubator to also adapt a second parameter to the changed conditions. For the user of an incubator, this would mean the additional setting of a company size, which would also have to be constantly monitored by him. However, since the care of the patient in the incubator must always have priority, the observation of the setting of the operating parameters must be kept to a minimum; this means that the user is generally willing to have to set at most one operating parameter.

The present invention is therefore based on the object of improving a method of the type mentioned in such a way that when the parameters determining the climate in the room of the premature and newborns are taken into account, their functional relationships which optimize the heat balance are also taken into account without complex multiple settings for the Individual parameters are necessary.

The problem is solved in that a mother control loop for controlling a first parameter gives the associated actual value or setpoint as a guide value to a link generator, by means of which a link value is determined by means of a link circuit which is forwarded to a daughter circuit for setting the setpoint of a second parameter becomes.

If you use the method according to the invention to select the control circuit for regulating the incubator air temperature to a predefined setpoint value and the circuit for setting the incubator air humidity, the user only needs to set the desired incubator temperature, as a result of which the associated setpoint value for the Setting the incubator humidity is set. The logic circuit in the logic generator determines the functional relationship between the setpoint or actual value of one parameter and the setpoint of the second parameter. The setting of only one parameter (for example incubator air temperature) thus has a favorable influence on another, for the heat balance of the early and Newborn in the incubator relevant second parameter (eg humidity). The indirect setting of several parameters by coupling a link generator enables the parameters to be adapted to the physiological conditions of the patient in the incubator.

In addition to the incubator air temperature, the incubator inner wall temperature or the bed surface temperature and the flow rate of the incubator air temperature can also be used as the first parameter for the mother control loop.

Both the actual value and the setpoint of the first parameter can be used as a reference value. If the actual value is selected as the reference value for the linkage generator, it is possible to quickly adapt the second parameter to the current status values of the incubator control. This is particularly favorable for the control of parameters whose associated control or switching circuits have a short time constant. On the other hand, it is favorable to select the setpoint of the first parameter as a guide value for the logic generator if parameters are controlled, the associated control or switching circuits of which have a long time constant.

It has been found that in addition to the incubator air temperature, a change in the air humidity has a significant influence on the heat balance of the patient in the incubator. Via a targeted, finely adjustable moisture dosage in the incubator air Incubator temperature fine-tuned and adjustable uniformly distributed over the lounge. The air temperature remains as usual as the parameter to be set by the operator. It is therefore expedient to store stored values in the link generator, which define the functional relationship between the setting of the incubator temperature as the first parameter and the air humidity as the second parameter, and that the reference value specifies an operating point on the link function thus formed, by means of which a pair of values Leading value / subsequent value is determined, and which is changed depending on the size of the leading value along this linking function. The corresponding air humidity is selected via the link function by appropriate specification or setting of the incubator temperature and passed on to the circuit for setting the incubator air humidity. Each time the actual value or setpoint of the incubator air temperature changes, a new assigned setpoint for the incubator air humidity is determined via the linking function and passed on to the circuit.

The mode of operation of the control loop, logic generator and circuit can just as well lead to success if, for example, the incubator humidity parameter is used as an adjustable control variable, according to which an associated incubator air temperature can be set using the linking function.

Since the coupled adjustable operating parameters reflect the physiological conditions with regard to the Should take into account the heat balance of premature and newborns, it is advisable to adapt the functional relationship between the operating parameters to be linked to personal selection parameters based on experience. For example, an older newborn or one with a higher birth weight needs less humidity at a given incubator air temperature than a patient with a lower weight and younger age, because the skin surface evaporates less body fluid due to its more mature formation and thus loses less heat of evaporation. It can therefore be in a drier atmosphere. For this purpose, the stored values are stored in a multidimensional table form in which a dimension level is determined by the parameter assignment of temperature and humidity, over which a third and possibly a further dimension is laid, which is determined by one or another personal selection variable, and that by defining the third and further dimensions by entering the selection variables, a multidimensional linking function corresponding to this dimension is selected. Thus, the simplest form of the table is that a two-dimensional assignment of temperature and air humidity is established for the standard values of personal selection variables, such as age, birth weight, gestational age, are fixed in the link generator. However, depending on the circumstances, the user can leave this standard level defined by entering other personal selection parameters and select a link function that is adapted to the changed selection parameters. He receives thus the possibility of selection from a large number of curve groups, each of which defines a linking function which is assigned to the predetermined selection variables. So z. B. for a small premature baby the increase in the incubator humidity with increasing incubator air temperature is steeper than in a premature baby who has been in the incubator for a long time and has assumed a correspondingly larger body weight.

In a further development of the invention, it is advantageous to design the daughter circuit as a second control circuit by connecting an actual value transmitter for the second parameter to the circuit and comparing the actual value with the setpoint value supplied by the logic generator. If the two values differ, the setting is changed. In this way, two coupled control loops are obtained for different operating parameters, which operate as master-slave control loops, so to speak: The first control loop determines the setpoint of the second control loop via a link generator.

In order to limit the control or regulation of the coupled operating parameters to the values that are favorable for the warmth balance of the premature and newborn babies, it is appropriate to provide upper and / or lower limit values for the linking function. If the operating point exceeds the respective upper or lower limits, only the leading value of the first parameter can be changed without the subsequent value being changed. As an example, select the incubator air temperature as a guide value and the humidity as a follow-up value in a Cartesian Coordinate system, where the incubator temperature is the independent variable and the incubator humidity is the dependent variable, the linking function extends beyond the upper and lower limit values in a horizontal direction. A shift in the operating point as a result of a change in the actual value or setpoint of the incubator air temperature then means no change in the associated incubator air humidity.

Under certain circumstances, it may be necessary to interrupt the coupling of the operating parameters in order to set each parameter individually, for example when the upper and lower limit values of the logic function are exceeded or undershot and nevertheless a change in the setpoints is to be effected for both control loops , or if the treatment therapy makes it necessary to provide individual combinations of the setting parameters regardless of the personal selection variables that can be entered. In these cases, the forwarding of the command value to the logic generator is prevented by an interrupter switch. The circuit breaker can be located at a point in the power train which is expedient due to the circuit between the control circuit for the first parameter and the circuit or control circuit for the second parameter. When the circuit breaker is open, ie when the line connection between the two circuits or control loops is open, the setpoint for each parameter can be given to the control loop or circuit individually via an associated input unit.

An incubator for carrying out the method for the coupled control of operating parameters has an enclosed lounge for the premature or newborn, in which a lying surface is provided, and an aggregate room in which a fan for circulating the lounge air heated by a heater and moistened by a humidification device is arranged is. The incubator air temperature is set and maintained using a temperature control loop. The humidification device is connected to a circuit for setting the moisture to be released through it into the lounge air. The control circuit for the incubator air temperature is connected to a link generator, which receives the actual value or setpoint relevant for the control loop as a guide value and is connected to the circuit to deliver a subsequent value determined from the guide value via a link function to the circuit. The subsequent value influences the control of the humidification device as a setpoint.

The circuit for setting the incubator humidity can be easily completed to form a control circuit by connecting a humidity sensor to the circuit and forwarding the actual value to it. The setting of the humidification device to achieve the desired value is influenced by comparison between the desired value and the actual value and, if there is a corresponding deviation.

Under certain circumstances, a separate, individual input of setpoints to the control or To enable circuits, an interrupter switch is arranged in the cable between the control circuit, logic generator, and circuit.

The invention is illustrated using a schematic drawing and explained in more detail below.

Fig. 1

das Blockschema eines Inkubators mit zugehöriger gekoppelter Steuerung zweier Betriebsparameter

Fig. 2

den funktionalen Zusammenhang zwischen zwei Betriebsparametern über eine Verknüpfungsfunktion

In Fig. 1 ist ein Inkubator (1) dargestellt, dessen Innenraum (2) der Aufenthaltsraum für ein Frühgeborenes (3) auf einer Liegefläche (4) bildet. Die Innenraumluft des Inkubators wird über einen Lüfter (5) im Aggregatraum (6) umgewälzt und dabei sowohl über eine Heizung (7) als auch über eine Befeuchtungsvorrichtung (8) geleitet. Die Heizung (7) wärmt die Inkubatorluft auf einen vorgewählten, von einem Lufttemperaturfühler (81) erfaßten Temperaturwert an. Während der Umwälzung der Inkubatorluft streicht diese über eine Befeuchtungsöffnung (9) der Befeuchtungsvorrichtung (8), über welche eine mehr oder weniger große Menge an Wasserdampf an die Inkubatorluft abgegeben wird. Der Feuchtigkeitsgehalt der Inkubatorluft wird über einen Luftfeuchtigkeitsfühler (10) erfaßt. Der von dem Lufttemperaturfühler (81) gemessene Meßwert wird als Istwert an einen Mutterregelkreis (11) abgegeben, der ihn mit einem Sollwert vergleicht, der über eine Sollwerteingabe (12) an den Mutterregelkreis eingegeben wird. Der Mutterregelkreis (11) ist ein Leistungsregelkreis, welcher die Heizleistung der Heizung (7) derart beeinflußt, daß der geforderte Sollwert am Lufttemperaturfühler (81) erfaßt wird. Von dem Mutterregelkreis (11) wird entweder der Sollwert oder der Istwert als Führungswert über einen geschlossenen Unterbrecherschalter (13) an einen Verknüpfungsgenerator (14) weitergeleitet. In dem Verknüpfungsgenerator (14) ist der Führungswert, im Beispiel der Istwert der Inkubator-Lufttemperatur, wie sie vom Lüfttemperaturfühler (81) gemessen wird, in funktionalem Zusammenhang mit der über den Luftfeuchtigkeitsfühler (10) gemessenen relativen Luftfeuchtigkeit gebracht. Diesen funktionalen Zusammenhang stellt eine Verknüpfungsfunktion (15) dar (Fig. 2). Je nach gemessener Lufttemperatur T wird auf der Verknüpfungsfunktion (15) ein Arbeitspunkt A festgelegt, zu welchem ein Wert für die Luftfeuchtigkeit H gehört. Dieser Feuchtigkeitswert wird über eine Signalleitung (16) an einen Tochterschaltkreis (17) als Folgewert abgegeben, der für diesen Schaltkreis (17) die Sollwertvorgabe für die Luftfeuchtigkeit im Inkubator (1) darstellt. Dieser Sollwert wird mit dem Istwert der Luftfeuchtigkeit, wie sie vom Luftfeuchtigkeitsfühler (10) ermittelt wurde, verglichen. Bei entsprechender Abweichung zwischen Istwert und Sollwert (Folgewert) wird über eine Heizungssteuerleitung (18) eine Befeuchterheizung (19) der Befeuchtungsvorrichtung (8) angesteuert. Je nach Heizleistung der Befeuchterheizung (19) wird ein darüber befindliches Wasserreservoir (20) erwärmt, wodurch aus der Befeuchtungsöffnung (9) des Wasserreservoirs (20) eine vorgegebene Menge an verdampfter Flüssigkeit an die durch den Lüfter (5) umgewälzte Innenraumluft abgegeben wird. Der Verknüpfungsgenerator (14) ist an eine Eingabeeinheit (21) angeschlossen, über deren Tastenfeld (22) personenbezogene Auswahldaten eingegeben werden können, wodurch im Verknüpfungsgenerator (14) unterschiedliche Verknüpfungsfunktionen (15) festgelegt werden. Die über die Eingabeeinheit (21) eingegebenen personenbezogenen Auswahldaten beziehen sich auf den im Aufenthaltsraum (2) befindlichen Patienten (3), so daß im Verknüpfungsgenerator (14) eine auf diesen speziellen Patienten bezogene Verknüpfungsfunktion (15) die Verbindung zwischen eingestellter Inkubator-Lufttemperatur und erforderlicher Inkubator-Luftfeuchtigkeit hergestellt wird. Sollen die Sollwerte von dem Mutterregelkreis (11) und dem Tochterschaltkreis (17) unabhängig voneinander eingegeben werden können, wird der Unterbrecherschalter (13) in seine gestrichelt dargestellte geöffnete Schaltposition versetzt. Dadurch ist die Verbindungsleitung (23) zwischen Mutterregelkreis (11) und Verknüpfungsgenerator (14) unterbrochen. Die erforderliche Eingabe der Sollwerte für die Inkubator-Lufttemperatur wird über die Sollwerteingabe (12), und der Sollwert der Inkubator-Luftfeuchte wird über die Eingabeeinheit (21) eingegeben.Show it:

Fig. 1

the block diagram of an incubator with associated coupled control of two operating parameters

Fig. 2

the functional relationship between two operating parameters via a link function

In Fig. 1, an incubator (1) is shown, the interior (2) of which is the lounge for a premature baby (3) on a lying surface (4). The interior air of the incubator is circulated via a fan (5) in the unit space (6) and is passed both via a heater (7) and a humidification device (8). The heater (7) heats the incubator air to a preselected temperature value detected by an air temperature sensor (81). During the circulation of the incubator air, it sweeps over a humidification opening (9) of the humidification device (8), through which a more or less large amount of water vapor is released to the incubator air. The moisture content of the incubator air is measured using a humidity sensor (10). The measured value measured by the air temperature sensor (81) is output as an actual value to a mother control circuit (11) which compares it with a setpoint that is entered into the mother control loop via a setpoint input (12). The mother control loop (11) is a power control loop which influences the heating power of the heater (7) in such a way that the required setpoint is detected at the air temperature sensor (81). The mother control loop (11) either forwards the setpoint or the actual value as a guide value via a closed circuit breaker (13) to a link generator (14). In the linkage generator (14), the reference value, in the example the actual value of the incubator air temperature, as measured by the ventilation temperature sensor (81), is brought into a functional connection with the relative air humidity measured via the air humidity sensor (10). A linkage function (15) represents this functional relationship (FIG. 2). Depending on the measured air temperature T, an operating point A is defined on the linking function (15), to which a value for the air humidity H belongs. This moisture value is output via a signal line (16) to a daughter circuit (17) as a follow-up value, which represents the setpoint value for the air humidity in the incubator (1) for this circuit (17). This setpoint is compared with the actual value of the air humidity as determined by the air humidity sensor (10). If there is a corresponding deviation between the actual value and the target value (subsequent value), a humidifier heater (19) of the humidification device (8) is controlled via a heating control line (18). Depending on the heating output of the humidifier heater (19), a water reservoir (20) located above it is heated, so that one from the humidification opening (9) of the water reservoir (20) predetermined amount of evaporated liquid to which indoor air circulated by the fan (5) is released. The link generator (14) is connected to an input unit (21), via the keypad (22) of which personal selection data can be entered, as a result of which different link functions (15) are defined in the link generator (14). The personal selection data entered via the input unit (21) relate to the patient (3) located in the common room (2), so that in the link generator (14) a link function (15) related to this special patient, the connection between the set incubator air temperature and required incubator humidity is produced. If the setpoints should be able to be entered independently of one another by the mother control circuit (11) and the daughter circuit (17), the circuit breaker (13) is set to its open switching position, shown in dashed lines. As a result, the connecting line (23) between the mother control loop (11) and the link generator (14) is interrupted. The required entry of the setpoints for the incubator air temperature is made via the setpoint input (12) and the setpoint of the incubator air humidity is entered via the input unit (21).

In order to simplify the control circuit (10, 17, 8) shown, the humidity sensor (10) can be removed, and the circuit, depending on the preselected temperature, sets the humidification heater (19) to predetermined heating levels, which are divided into ten equal parts from minimum to maximum, the one correspond relative humidity of, for example, 35 to 85%. In the link generator (14), only the association between air temperature and heating levels is then related.

2 shows a functional relationship between the incubator air temperature T and the incubator air humidity H. In the hatched area B there are such parameter values that should not be selected for regulating the climatic conditions in the lounge (2) of the incubator (1). The parameter range of temperature T ranges from 28 ° C to 39 ° C, and the parameter range of humidity H ranges from 25% relative humidity to 85% relative humidity. The linking function (15) is defined for a patient (3) located in the incubator (1) in accordance with the personal selection data entered via the input unit (21). Accordingly, the working point A is set at a selected incubator air temperature of 36 ° C, to which a relative air humidity of 78% belongs. This moisture value is given by the link generator (14) as a follow-up value via the line (16) to the daughter circuit (17) and processed there as a setpoint for the setting of the humidification device (8). An upper limit (HI) for the incubator air temperature is 37 ° C, above which an unchanged relative humidity of 85% remains set. If the temperature falls below a lower limit (LO) at 30.5 ° C, the set relative humidity remains constant at 35%. If other personal selection data are entered in the input unit (21), for example for a very small premature baby, a linking function (115) is selected, which is defined along the dashed line. The relative humidity to be set rises more steeply with increasing incubator air temperature and already reaches the upper limit (G) at around 34.7 ° C.

Claims (9)

1. A method for controlling the operating parameters determining the temperature balance of a premature or newborn baby located in an incubator (1), the parameters at least including the incubator temperature and the air humidity which is to be adjusted in the incubator interior (2), the actual values of these parameters being compared with their associated nominal values and in the event of a deviation new nominal values being determined for the parameters, characterised in that a master control circuit (11) for controlling a first parameter transmitting the associated actual value or nominal value as a reference value to a combination generator (14), which determines a follow-on value by means of a combination circuit, the follow-on value being transmitted to an auxiliary circuit (17) for the adjustment of the nominal value of a second parameter.
2. A method according to claim 1, characterised in that storage values which determine the functional relationship between the incubator temperature as the first parameter and the air humidity as the second parameter are stored in the combination generator (14), and the reference value determines a working point A on the combination function (15) formed in this manner, by means of which working point a reference value/follow-on value pair is formed, and the working point being variable along this combination function (15) as a function of the size of the reference value.
3. A method according to claim 1 or 2, characterised in that the storage values are stored in the combination generator (14) in multi-dimensional tabular form, in which a dimensional plane is determined by the parameter relationship of temperature and humidity, to which a third and optionally a further dimension is added which is determined by one or possibly more selection values related to the individual baby, and by determining the third and optionally further dimensions by means of inputting the selection values a combination function (15) is selected as a function of these dimensions.
4. A method according to one of claims 2 or 3, characterised in that the combination function (15) has upper (HI) and/or lower (LO) threshold values, and when the value exceeds or falls below these threshold values the working point A is only displaced along the combination function (15) parallel to the variation in the reference value of the first parameter.
5. A method according to one of claims 1 to 4, characterised in that the auxiliary circuit (17) is connected to an actual value transmitter (10) of the second parameter, and the adjustment of the second parameter is monitored with the aid of the actual value transmitter (10) and in the event of a deviation of the actual value from the nominal value the actual value is adjusted to the nominal value.
6. A method according to one of claims 1 to 5, characterised in that the transmission of the reference value to the combination generator (14) is prevented by a interrupter switch (13).
7. An incubator for carrying out the method according to one of claims 1 to 6, in which a bed (4) is provided in an enclosed accommodation space (2) for the premature or newborn baby, and a fan (5) is arranged in an aggregate chamber (6) for circulating the internal incubator air which is heated by a heating element (7) and moistened by a humidifier (8), the incubator air temperature being adjusted and maintained by means of a temperature control circuit (11) and the humidifier (8) being connected to a circuit for adjusting the moisture which is to be released to the incubator air, characterised in that the control circuit is connected as a master control circuit (11) to a combination generator (14), which receives the actual value or nominal value of the control circuit (11) as a reference value and is connected to the circuit (17) as an auxiliary circuit for transmitting to the said circuit a follow-on value determined from the reference value via a combination function (15), and the follow-on value is provided as a nominal value for controlling the humidifier (8).
8. An incubator according to claim 7, characterised in that a humidity sensor (10) is connected to the auxiliary circuit (17), which compares the actual value of the humidity sensor (10) with the nominal value and in the event of a deviation of the two values influences the adjustment of the humidifier (8) in order to obtain the nominal value.
9. An incubator according to one of claims 7 or 8, characterised in that an interrupter switch (13) is arranged in the electrical path between the master control circuit (11), the combination generator (14) and the auxiliary circuit (17).

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