Insufflation apparatus

Claim 1

The control of the average flow, that is to say averaged over a complete cycle, compensates the interruption or reduction of the flow during the 2 measuring phases, which is required for measuring the pressure. The average flow automatically set therefore corresponds to an uninterrupted filling with this set f low, as a result of which a very f ast f illing operation is ensured. In this case, the observation of the prescribed flow is so precisely controlled that there is no risk to the patient in normal operation. Exercising control to achieve the desired average flow automatically compensates all the factors influencing the flow, such as, in particular, the falling pressure gradient between the body cavity and supply line. The representation and processing of the signals according to the features of Claim 2 is clear and effective. HInitial filling" which takes place with a manually prescribable maximum flow is carried out by means of the features of Claim 3, the maximum value being prescribed by the doctor from a medical point of view. As soon as the pressure in the body cavity reaches a range about the DESIRED pressure, there is an automatic switchover to "final filling", in which the filling phases become shorter until finally there is no longer any filling once the DESIRED pressure is reached. In accordance with Claim 4, it is possible to use pressure sensors which according to the present technology detect finer pressure differences and thus permit a more exact flow calculation than is possible using direct flow-measuring instruments. In accordance with the preferred configuration according to Claim 5, the valve which is present in 3 is any case and necessarily has a restricting effect, is used simultaneously as measuring restrictor. This reduces the complexity and avoids an additional resistance acting to reduce the flow. Thus, a higher peak flow can be realized for a given inlet pressure. The embodiment according to Claim 6 highlights a type of pressure determination as described in Patent specification GB 2 246 442. In this case the characteristic curve of the pressure drop is identified during a measuring phase by three successive pressure measurements, and from this the body cavity pressure later produced in the static state is calculated in advance without having to wait for the static pressure equalization. As a result, the measuring phase can be substantially shortened by comparison with the principle known from DE 3,000,218 C2 mentioned at the beginning, in accordance with which the pressure equalization has to be awaited for the current pressure measurement. The accumulator required for this "dynamic pressure measurement" need maintain an (exponentially) falling flow only for as long as the three pressure measurements can be carried out. The more precise the pressure-measuring element available, and the better its measuring resolution, the more shortly the pressure measurements can succeed one another. Consequently, in the case of a selfcompressible medium (gas) a length of tube or hose only 10cm long can serve as an adequate accumulator volume. The invention is explained in more detail below with the aid of an exemplary embodiment illustrated in the drawing, in which 4 Fig 1 shows a block diagram of a device in accordance with the invention Fig 2 shows timing diagrams to functioning of the device. illustrate the In the following description, it is assumed for the sake of simplicity that the medium to be insufflated is gas (in particular C02). In accordance with Fig. 1, a gas cartridge 10 supplies a feed line 12 via a reducing valve 11 with gas which is available here with the set pressure Pmax = 50 mm Hg. Located in the following conduit path 13 is a restrictor 14 and an electromagnetically operable valve 15 which can open and close the conduit path to a following accumulator 16. The output of the accumulator 16 leads to a discharge line 17 to which an insufflation needle 19 is connected via a hose 18. The conduit path for the gas is - by contrast with electrical lines emphasized by thick lines. Thus, a differential pressure sensor 20 is in each case pressurized from both sides of the restrictor 14 by gas, which sensor delivers an electrical signal, corresponding to the pressure drop at the restrictor 14, to a computing module 21 which calculates therefrom, while taking account of the flow resistance of the restrictor 14, the flow through the restrictor, which it outputs as the FACT signal. The differential pressure sensor 20 and the computing module 21 form a flow-measuring device. The pressure P in the accumulator 16 is converted by a pressure transducer 22 into an electric signal which is evaluated by a pressure- measuring device 23 in the manner described in more detail in Patent Specification GB 2 246 442 in order to generate therefrom an electric PACT signal which represents the pressure, extrapolated from the previous curve, in the abdominal cavity after the pressure equalization between the accumulator and the abdominal cavity. The P sianal ACT is is input together with a PDES signal tapped by a manually settable desired heightvalue transmitter 24 into a subtractor 25 which forms a AP signal therefrom. A generator device 26 consists of a first and second function generator 27, 28 and a selector module 29. The first function generator 27 generates an fmax signal which rises linearly in value with time, and does so starting repeatedly with zero, as will be further explained with the aid of Fig. 2. In this case, the rise per unit time can be varied via a manually settable adjustor 30. The second function generator 28 generates an F-signal, which likewise rises linearly in value with time, and does so starting repeatedly from zero, something which will likewise be explained in more detail with the aid of Fig. 2. In this case, the rise per unit time is variable as a function of the AP signal, specifically in such a way that when AP = zero, the F signal likewise remains zero (= no rise), and with an increasing value of AP an increasingly steeper rise is produced. The selector module 29 now outputs the respectively smallest of these two signals F and:Fmax as FDES signal. 6 A valve controller 31 contains a switching amplifier 32 which drives the magnet coil of the valve 15, as well as a coincidence module 33 which is f ed the FACT signal and DES signal. In the event of equality of these signals, the coincidence module 33 trips a control signal S which effects the start of a new cycle in a manner yet to be described. Since various functions proceed as a function of time, a timing clock generator 34 is represented which acts both on the generator device 26 and on the valve controller 31. When analogue signals are being processed, correspondingly high voltage values are involved, depending on the signal value. In the case of digitally coded signals, the value is hidden in the bit pattern. The signal values are represented in analogue f orm in the following diagram of Fig. 2 in order to enhance the clarity. It goes without saying that in the case of digital signal processing most of the previously mentioned modules and devices run as "organization programs", in the sense that a unit of hardware executes various timedisplaced operations under programmed control. Fig 2a represents the variation in the pressure P in the accumulator 16 as a function of time over a plurality of cycles. The f low F, in particular FACT is illustrated in Fig. 2b. The gas volume V is shown as a function of time t in Fig. 2c. When the valve 15 is open, the pressure P in the j 1 7 accumulator 16 can reach at most the limiting value Pmax prescribed by the reducing valve 11. This state obtains at the moment when the timescale starts. At the instant tol, a new cycle starts with the start of a measuring phase, with which the valve 15 closes. In consequence, the accumulator is emptied exponentially, the asymptote of the curve representing the pressure last set in the body cavity in the static state in the case of pressure equalization. However, it is not necessary to wait for this state. it suffices to identify the characteristic curve with the aid of three pressure measurements symbolized by points on the curve. A family of curves is stored in a model memory which belongs to the pressure-measuring device 23. once one of the curves has been identified, the pressure-measuring device outputs the associated value of PACTO, It may be seen in Fig. 2 that PACTO is at first far removed from PDES. The measuring phase lasts approximately 0.2-1 sec and ends at the instant til. At the instant t1l, a filling phase begins with the opening of the valve 15. The pressure P in the accumulator 16 rises rapidly again to Pmax (Fig. 2a). Since the pressure gradient to the still very low pressure in the body cavity PACTO is large, a high flow FACTO (Fig. 2b) can form during the filling phase. The aim of the control during the "initial filling" now consists in setting up a uniform average flow Fmax over the duration of a cycle. When the duration of the measuring phase has been fixed and the magnitude of the flow FACT depends essentially on the pressure difference and the flow resistances, the control is exercised by automatically varying the duration of the filling phase. For this purpose, in accordance with 8 Fig. 2c the generation of the Fmax signal starting with zero is started at the instant tOl. The FACTOI which rises as time progresses, is produced at the instant t1I with the opening of the valve 15. Since the flow is equal to the gas volume V per unit time T, the diagrams for fmax and FACTO are represented in the V-t diagram as straight lines with the origin at tOl and til, respectively, and with different gradients. The condition FACTO = Fmax is fulfilled at the point of interception of the two straight lines. This state is recorded by the coincidence module 33, which thereupon indicates the end of the filling phase and thus the end of the previous cycle. This state corresponds simultaneously to the start of a new measuring phase of a new cycle at the instant t02. After expiry of the measuring phase at the instant t12, a reduced flow FACT1 is set since the pressure gradient to the body cavity has become smaller due to the previous filling. Consequently, the straight line of FACT1 in the diagram of Fig. 2c is inclined slightly less steeply than previously. The point of intersection with the fmax straight lines started at t02 therefore occurs later this time, so that the filling phase for equalizing the smaller flow FACT1 lasts longer. This sequence is repeated analogously in the following cycles, FACT becoming continuously smaller with the increasing degree of filling the body cavity and the filling phase thus becoming longer. The averaging is illustrated once more using the 9 example of the 4th cycle. The magnitude of the area FACT4 X tF4 is equal to the area of Pmax tZ4 The operation is illustrated only in principle in the diagram of Fig. 2. In f act the absolute magnitudes and timing conditions are different. Thus, the measuring phase is usually shorter than the f illing phase. However, if the real relationships are shown, it is not possible to reproduce a plurality of clearly differentiated cycles on the format of the drawing. This becomes clear when it is considered that one cycle can actually last up to a plurality of seconds in relation to a maximum of 1 sec of a measuring phase. So far, the normal sequence during the "initial filling" has been described, in which the aim is to fill the body cavity as quickly as possible. The limiting criteria from the medical point of view are prescribed in this case as Pmax and Fmax, which value has previously been relayed by the selector module 29 as reference variable FDES. Assuming that the doctor leaves the setting at the adjustor 30 unchanged, the rise in the straight line Fmax remains the same in each cycle. As soon, however, as the pressure in the body cavity reaches the vicinity of the set desired value PDESO a different operating module or 11 final filling" is carried out, in which the reference variable FDES become smaller. the smaller the difference AP. The criterion for this is the 9 signal in accordance with Fig. 1. As long as its signal value is greater than the Fmax signal, the latter is used as ref erence variable FDES However as soon as the F signal, whose rise with time is a function of AP, is equal to and less than the Pmax signal, F takes over the control. is The straight line Flo in Fig. 2c has a distinctly smaller gradient than the straight line Fmax. Consequently, the point of intersection of the straight lines Flo and FACT10 is closer in time to the instant t110, although the gradient of the straight line FACT10 is still flatter than in the previous cycles. As a result, the filling phase is now distinctly shortened, as a result of which, with the smaller FACTIO, a correspondingly smaller average flow Flo is produced for this cycle. In the following 11th cycle, PACT11 is even closer to PDES1 with the consequence that the filling phase from t111 to t012 is even shorter. In this way, the equalization of PACT and PDES is now produced very gently, without the risk of overshooting the target. As soon as PACT: PDES obtains, the rise in the F signal is zero, that is to say its value remains zero, so that one measuring phase is immediately followed by a new measuring phase. Here, it is expedient to activate a monitoring module which has the effect of interposing a pause interval of possibly 500 ms. If a pressure loss occurs in the body cavity, this is recorded in the following measuring phase and, depending on the magnitude of the AP determined, this once again trips a filling phase of matching duration, with the automatic effect that the DESIRED pressure is maintained. 11 In the described embodiment, an apparatus for the insuf f lation of a medium into a body cavity has a valve (15) and a restrictor (14) in the conduit path (13). The valve (15) is used to block the conduit path (13) during a measuring phase at the start of a cycle, so that the pressure PACT in the body cavity can be determined on the apparatus side. During the following filling phase of a cycle, the flow, FACT is determined via the restrictor (14). A generator device generates a DES signal which represents the prescribed average flow during a cycle. A coincidence module (33) trips the end of the filling phase and the start of a new cycle in the event of the equality of FACT and FDES As a result, the length of the filling phases varies in the manner of a pulse width control. Initially,:9 max is output as i;DES via a selector module (29), resulting in quick filling. At the end, an F which becomes smaller with smaller AP is output as FDES11 SO that the DESIRED pressure of the body cavity is reached gently. In the example of Fig. 1, the restrictor 14 was represented as a separate element. However, the valve 15 also represents a restrictor, even if as low a flow resistance as possible is aimed at in its design. Given sufficiently sensitive pressure sensors as are currently already available, even this slight restricting effect can, however, be used to determine the flow. Thus, use is made not of a valve converted to function as a restrictor, but of a normal valve, and a further limitation of the maximum flow, which is already limited anyway by the insufflation needle, is thus eliminated. The control illustrated above depends on the 12 1 princple used to d6tgiblifig thg DrAg9UY9 jA thg ta&y cavity - whether in the state of static pressure equalization in accordance with DE 3,000,218 C2 or of the dynamic interpolation in accordance with DE 4,019,239 Al. The valve named above is a representative of elements by means of which the f low can be inf luenced in a comparable manner, such as by means of a controlled pressure regulator, for example. V' 13 PATENT CLAIMS: is 1. Apparatus for the insuf f lation of a medium into a body cavity, having a restrictor and an electromagnetically operable valve in a conduit path situated between a feed line and a discharge line, having a valve controller which respectively closes the valve during a measuring phase that starts at the start of a cycle, and respectively opens the valve during the subsequent filling phase, which lasts till the end of the cycle, a timing clock generator respectively determining the duration of the measuring phase, as well as having a pressure-measuring device which generates an electric PACT signal which determines the pressure in the body cavity and is respectively determined during measuring phase, characterized in that there is provided in the conduit path (13) a flowmeasuring device (20, 21) which generates an FACT signal representing the flow during a cycle, in that a generator device (26) is provided which generates an:FDES signal representing the average flow to be set during a cycle, and in that a coincidence module (33) is provided which in the event of the agreement of the FACT signal and FDES signal respectively trips the end of a filling phase of a cycle, and thus the start of a measuring phase of the following cycle.