Method for Determining Compliance of a Cavity in Minimally Invasive Surgery

Abstract

The invention relates to a method for determining compliance of a cavity in minimally invasive surgery and to devices for carrying out said method.

Claims

1. A method for determining compliance of a cavity C.sub.c using a medical-technical device by a) controlled introduction of a fluid, b) single or multiple measurements of the volume introduced into the cavity and of the cavity pressure resulting therefrom, c) calculation of the compliance C.sub.c using the equation C.sub.c=V.sub.c/p.sub.c.

2. The method for determining compliance of a cavity according to claim 1, characterized by a temporally offset introduction of at least two defined fluid volumes into the cavity and consequent calculation of the partial pressure increase (dp.sub.c/dV.sub.c).

3. The method for determining compliance of a cavity according to claim 1, characterized by the determination of the leakage volumetric flow q.sub.l before the single or multiple measurements of the volume introduced into the cavity and of the cavity pressure resulting therefrom and by taking into account the leakage volumetric flow q.sub.l when calculating C.sub.c using the equation (ΔC.sub.c=(ΔV.sub.c−q.sub.l)/Δp.sub.c)I.

4. A medical-technical device for determining compliance of a cavity C.sub.c, comprising the components at least one fluid reservoir (1), from which the fluid is taken and supplied to the supply unit (4) through the connecting element (2), at least one regulated pump (actuator or supply unit) (4) for supplying the fluid in a regulated manner, at least one measuring device (5) for the volumetric flow of the fluid, at least one pressure sensor (6) for determining the dynamic and static pressure of the fluid, at least one connecting element (7) (e.g., tube) for supplying the fluid from the device to the body cavity (8), at least one electronic storage element, which serves for detecting measurement data, at least one electronic computing unit (e.g., microcontroller}, for supplying necessary control commands to the actuators, to carry out the determination method according to claim 1 and to load parameter data sets from the storage element or to write them on the storage element.

Description

METHOD I.A

[0026] First, the device is connected to the body cavity through the connecting element. Then, the device is turned on. Before initially applying a volumetric flow, the device determines the pressure in the cavity. Then, a predefined temporal volumetric flow q is generated using the actuator (e.g., a pulsed volumetric flow, with a defined length in time). The volumetric flow generates a pressure increase q.sub.c in the cavity.

[0027] The volume V can be determined by the integration of the volumetric flow by the measurement unit. After the defined volumetric flow, the device stops the supply and identifies the static pressure in the cavity. Thus, the elasticity can be determined using the partial pressure increase (dp.sub.c/dV.sub.c). This procedure can be repeated until a desired reference pressure in the cavity is achieved. From the partial pressure increases, then the so-called p-V diagram can be derived. This diagram, thus, provides information about the size of the cavity or the location of the indication. Then, by comparison to system parameters, the parameterization and selection of optimum system parameters (e.g., maximum flow rate, control, and regulation parameters) can be performed. By an optional confirmation by the user, the automatic cavity detection can be confirmed.

[0028] In FIG. 4, an example of this method is shown. Two volumes V.sub.1 and V.sub.2 are supplied temporally offset into the hollow space. Then, the pressure in the cavity p.sub.c increases, and the pressure of the cavity can be determined using the pressure sensor p.sub.d. This results in the working points V.sub.c1=V.sub.1, p.sub.c1=p.sub.d1 and V.sub.c2=V.sub.2+V.sub.1, p.sub.c2=p.sub.d2. By, e.g., linear approximation, then an approximation of the p-V diagram can be calculated (see FIG. 4). The “transient response” of the pressure measurement signal at the starting point and at the stopping point of the volumetric flow can clearly be seen in the measurement diagram (FIGS. 5 to 7 bottom).

METHOD I.B

[0029] In the reality of minimally invasive interventions, often leakages in the cavities occur. Such leakages falsify the procedure in Method I.a due to this fluid outflow of an unknown quantity. In order to compensate for the influence of the leakage in the measurement data, Method I.a is extended as follows:

[0030] By a pressure regulation device, a pressure is generated in the cavity. In this case, the volumetric flow necessary for achieving the desired pressure is predefined. In a closed cavity—without leakage—, the pressure regulation device would regulate the volumetric flow to zero when the desired pressure is achieved (see FIG. 6).

[0031] With an existing leakage in the body cavity, the pressure regulation system would permanently adjust a volumetric flow, in order to compensate for the leakage. This volumetric flow, which is necessary to maintain the pressure, is the leakage volumetric flow q.sub.l for the present cavity pressure. This is exemplarily shown in FIG. 7. Therefrom, the volumes V.sub.2 and V.sub.3, which leave the body cavity through the leakage, can be determined. Then, the introduced volume can be cleared from the leakage.

[0032] The pressure in the cavity p.sub.c1 at the time when the volumetric flow is stopped can be determined or approximated through prior knowledge of the pressure drop across the connecting element and the measured pressure p.sub.d1. At this time is p.sub.d≈p.sub.c1.

[0033] Herein, the evaluation can be applied as in Method I.a. In order to allow for several working points for the calculation of the p-V diagram, the reference pressure can be increased (temporarily).

[0034] By repetition for other reference pressure values, different working points of the p-V diagram and thus the cavity size can be determined.

METHOD II

[0035] During the operation of the device, the actual working point in the p-V diagram of the body cavity can be determined. A low partial capacity value (ΔC.sub.c=ΔV.sub.c/Δp.sub.c) suggests a large body cavity, or a large value suggests a small body cavity. In order to obtain this information, a measurement pause is generated during the operation of the device. Herein, the volumetric flow rate is briefly interrupted, and the stationary cavity pressure p.sub.c1 is identified. Then, a predefined temporal volumetric flow is generated using the actuator (e.g., a pulsed volumetric flow with a defined length in time). The volumetric flow generates a pressure increase in the cavity. The volume V.sub.2 supplied in this period can be determined by the integration of the volumetric flow by the measurement unit. After the defined volumetric flow, the device stops the supply and identifies the static pressure in the cavity p.sub.c2. Then, the device resumes its normal functionality (see FIG. 7). From the measurements results ΔC.sub.c=V.sub.2/(p.sub.c2−p.sub.c1). Different from Method I is that no complete information about the cavity size or the p-V diagram is known. Thus, this information only applies to the actual working point of the volumetric flow, which is necessary for maintaining the cavity pressure. However, in this working point, the plausibility for the selected default setting by the user and actually determined characteristic values can be adjusted (see FIG. 8). In the case of a discrepancy, thus, the device can automatically adjust the parameter set of the device, in order to allow the user an optimum system setup for carrying out the intervention.

METHOD III

[0036] During the operation of the device, the pressure is temporarily increased. To this end, an active pressure control/regulation is used. The necessary additional volume for obtaining the desired pressure in the cavity is determined in the phase of the pressure increase. Therefrom, the partial capacity value (ΔC=ΔV/Δp) can be determined. This is identical to the procedure in Method II. However, Method III can also be used in the initial filling phase of the cavity. To this end, the desired reference pressure of the pressure regulation is increased quasi-stationarily (very slowly in time or step-by-step). A measurement pause is not necessary with the present system parameters for the device and the connecting unit between the device and the body cavity. The data of the volume and the generated pressure can thus be transferred into a p-V diagram. This provides, same as in Method I, the basis for deriving the cavity size or indication. Thus, the possibility to perform a parameterization and selection of optimum system parameters (e.g., maximum flow rate, control, and regulation parameters) will result. By an optional confirmation by the user, the automatic cavity detection can be confirmed.

METHOD IV

[0037] In a variation of Method II, the volumetric flow is increased after the determination of the actual cavity pressure p.sub.c1. The rising pressure at the sensor correlates with the pressure rise in the cavity (see FIG. 9). Therefrom results that a measurement of the cavity pressure p.sub.c2 is not necessary (comp. Method II). Instead (see FIG. 10), the increase Δp.sub.c relative to the volume V.sub.2 is identified. After the determination of the values, the device resumes the previous operation.

[0038] In contrast to Method II, thus, it lacks the exact knowledge of the value of the cavity pressure p.sub.c2, however, the same partial increases will result, and thus, the value can be used by the user for comparison of the parameter set of the device to the determined cavity values (FIG. 11) and be modified if necessary, in order to guarantee an optimum parameterization of the device.

LIST OF REFERENCES

[0039] (1) fluid reservoir [0040] (2) fluid connection (supply tube of the fluid between reservoir and medical-technical device for supplying a fluid (3) [0041] (3) medical-technical device for supplying fluids [0042] (4) supply device [0043] (S) measuring device for the volumetric flow of the fluid [0044] (6) pressure sensor [0045] (7) fluid connection [0046] (8) body cavity