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1. (WO2010080033) METHOD FOR DETERMINING THE STROKE VOLUME OF A HEART, METHOD FOR DETERMINING THE ELECTRODE POSITIONS THEREFOR, AND SHEET SHAPED DEVICE THEREFOR
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Claims

1. Method for determining the stroke volume of a heart of a human or animal body, wherein the heart is comprised in the thorax of the body, the method comprising:

attaching electrodes to the front legs or arms or head, and the hind legs of the body;

connecting an alternating current source to the left pair of front legs/ arms or head, and hind legs;

connecting an alternating current source to the right pair of front legs/ arms or head, and hind legs;

attaching a number of electrode pairs to the thoracic skin, such that the electrodes are in contact with the skin of the thorax at predetermined positions, wherein the electrode pairs are each connected to an independent input of a data acquisition/ calculation device;

determining the beginning the cardiac cycle and measuring with the number of electrode pairs on the thorax the voltage at the beginning of the cardiac cycle at the predetermined positions;

measuring during the cardiac cycle with the number of electrode pairs on the thorax the voltages at the predetermined positions and determining the voltage changes vmeas{τ ) compared to the voltage at the beginning of the cardiac cycle;

decomposing the vector of voltage changes vraeas{t) into an atrial component α(τ) and ventricular component ψ(τ), wherein both components are proportional to the vector of measured thorax voltages vmeas{t) by a weight factor wA and wv respectively;

converting the ventricular component ψ(τ) to a ventricular stroke volume, by multiplying the ventricular

component with a constant, the constant being a predetermined volume change Vcalib divided by a ventricular component <p calibof a predeterminged calibration measurement.

2. Method according to claim 1, further comprising:

- determining the respiration cycle;

- ignoring cardiac cycles that occur when the lung volume change exceeds a threshold.

3. Method according to claim 1 or 2, comprising:

attaching in the proximity of at least part of the electrodes a further number of electrodes to the thoracic skin, in order to provide support for xnterpatient variation of the optimal electrode position, wherein the electrodes are connected to a switching member, which switching member is configured to select the optimal electrodes for the specific particular patient under examination, from the redundant larger set of electrodes.

4. Method according to claim 1, 2, or 3, further comprising:

directly or indirectly calculating the first or second order time-derivative of the ventricular stroke volume;

minimising the oscillatory energy using the first order or second order time-derivative by varying the weight factors wv and wa for each electrode pair.

5. Method for determining the electrode positions for a sheet shaped device for use in a method according to any of claims

1-4, comprising:

providing a post-mortem human or animal heart, the valves thereof being sealed;

connecting tubing to the heart compartments to fill and empty the heart compartments;

providing the front side of a post-mortem human or animal thorax;

suspending the heart in a salt solution with a specific conductivity equalling the average thoracic tissues- suspending the thorax over the heart in the salt solution, such that the curved inner side of the thoracic wall is in direct contact with the salt solution and the thoracic skin remains dry

applying a number of electrodes to the thoracic skin; applying a reference measuring electrode to the thoracic skin near the cranial ending of the sternum, in the middle of the incisura jugularis, or any other position on the body of the patient that is sufficiently far away from the heart and the moving parts of the thorax during respiration;

measuring with the number of electrodes the voltages at the thoracic skin before the compartments are filled;

filling the atria with a solution having a specific conductivity equalling the average conductivity of blood while the ventricles remain empty and measuring with the number of

electrodes the voltages on the thoracic skin, calculating the voltage changes due to filling the atria, determining positions of at least one electrode pair that shows a significantly distinct response to the filling of the atria;

filling the ventricles with a solution having a specific conductivity equalling the average conductivity of blood while the atria remain empty and measuring with the number of electrodes the voltages on the thoracic skin and calculating the voltage changes due to filling the ventricles, and determining the positions of at least one electrode pair that shows a significantly distinct response to the filling of the ventricles; and

determining the weight of the contribution of the atrial filling and the ventricular filling to the voltage change observed by the electrode pairs that showed a significantly distinct response to the filling.

6. Sheet shaped device for use in a method according to any of claims 1-4 comprising a number of electrodes, the positions of the electrodes obtainable through the method according to claim 5.

7. Sheet shaped device comprising:

a ventricular electrode (V3), located near the caudal side of the heart in order to be located on or near the region of the thoracic skin having the largest voltage shift due to

ventricular filling of emptylng;

an atrial electrode (A3), at a distance between 80 and 150 mm from the ventricular electrode (V3) ; and

a reference electrode near the incisura jugularis on the cranial end of the sternum.

8. Sheet shaped device according to claim 7, comprising at least one marker to guide an operator during application of the sheet shaped device to a placement of the sheet shaped device on the thorax that results in:

a ventricular electrode (V3) to be positioned approximately 20 mm above the caudal edge of the heart;

a atrial electrode (A3) to be positioned at

approximately 80 to 150 mm in the caudal direction with respect to the ventricular electrode (V3) ; and

the reference electrode to be positioned approximately near the incisura jugularis on the cranial end of the sternum, or any other position on the body of the patient that is sufficiently far away from the heart and the moving parts of the thorax during respiration.

9. Sheet shaped device for use in a method according to any of claims 1-4 for application to a thorax comprising at least one marker to direct in proper placement on the thorax, or,

accompanied by guidelines for proper placement on the thorax, comprising:

a first ventricular electrode (VI) ;

a second and/or a third ventricular electrode (V2, V3) ,- wherein, when the sheet shaped device is properly applied to the thorax

the position of the first ventricular electrode (VI) is located directly on the cranial ending of the sternum, in the middle of the incisura jugularis, or any other position on the body of the patient that is sufficiently far away from the heart and the moving parts of the thorax during respiration,

the position of the ventricular electrode (V3) is near the caudal edge of the heart, and

the position of the second ventricular (V2) is approximately :

30 mm left of and 70 mm below the cranial ending of the sternum, in the middle of the incisura jugularis.

10. Sheet shaped device for use in a method according to any of claims 1-4 for application to a thorax comprising at least one marker to direct in proper placement on the thorax, or, accompanied by guidelines for proper placement on the thorax, comprising:

a first atrial electrode (Al) ,· and

a second and/or a third atrial electrode {A2, A3) ,· wherein, when the sheet shaped device is properly applied to the thorax

the first atrial electrode (Al) is located directly on the cranial ending of the sternum, in the middle of the incisura jugularis, or any other position on the body of the patient that is sufficiently far away from the heart and the moving parts of the thorax during respiration,

the position of the third atrial electrode (A3) is approximately 50 mm right of and 210 mm the cranial ending of the sternum and

the position of the second atrial electrode (A2) is approximately 15 mm right of and 70 mm below the cranial ending of the sternum.

11. System for determining the stroke volume of a heart, comprising:

- two alternate current sources for providing a current to the body;

- two skin electrodes attachable to the fore legs or arms of the body or the head, and connectable to the alternating current source;

- two skin electrodes attachable to the hind legs of the body and connectable to the alternating current source;

- a sheet shaped device according to any of claims 6-10;

- a data acquisition/ calculation device connectable to the electrodes of the sheet shaped device for decomposing the vector of thorax voltages into an atrial and a ventricular component as described in claim 1.