Device for determining the transition between systole and diastole
Determining the transition between systole and diastole is important for pulse contour-analytical determination of hemodynamic, first of all cardiac output. During the temporal progression of arterial pressure P(t) on which pulse contour analysis is based, the transition between systole and diastole appears as a local minimum. This local slump of the pressure curve downward is very short and is often little recognizable in the actually measured curves due to inaccuracies conditioned by measuring techniques. It was also found that the transition between systole and diastole can be more reliably and accurately determined as the site of maximum curvature of function P(t). Consequently, the invention relates to a device having a calculation unit that comprises evaluation means for detecting the site of maximum curvature of function P(t) in a detection area between the maximum and minimum functional value of the pulse cycle as the site of transition between systole and diastole.
1. Device for determining the transition between systole and diastole within a pulse cycle, having an input channel for reading in a pressure signal that can change over time and at least approximately corresponds to the aorta pressure of a patient, as a function of the time P(t), and a calculation unit that has differentiation means for forming the second derivation y″ from the function P(t), as well as evaluation means for determining a location of maximal curvature of the function P(t) in a determination range between the maximal and the minimal function value of the pulse cycle as the location of the transition between systole and diastole, and furthermore having differentiation means for forming the first derivation y′ from the function P(t),
wherein the location of maximal curvature is defined for the evaluation means as the location of the smallest radius of curvature
(1+ y′ 2 ) 3/2 /y″.
2. Device according to claim 1 , which has memory means for temporary storage of the pressure signal read in, at least over the pulse cycle, as a function of the time P(t).
3. Device according to claim 1 , which has filtering means for carrying out function smoothing.
4. Device according to claim 1 , wherein the determination range extends within 90% to 10% of the maximal function value of the pulse cycle.
5. Device according to claim 4 , wherein the determination range extends within 75% to 10% of the maximal function value of the pulse cycle.
6. Device according to claim 1 , wherein the evaluation means furthermore have adaptation means for axis adjustment of the function P(t), and the axis adjustment is provided in such a manner that a typical progression of an arterial pressure function, obtained from empirically collected data, possesses approximately the shape of an arc at the transition between systole and diastole.
7. Device according to claim 1 , wherein the evaluation means furthermore comprise correction means for correcting the position of the location determined for the transition between systole and diastole, in order to take delay elements into consideration.
8. Device according to claim 1 , wherein the differentiation means, filter means, and evaluation means are implemented, at least in part, in terms of program technology, in the form of software.
9. Device according to claim 1 , wherein the calculation unit has means for determining at least one additional hemodynamic parameter from the function P(t).
10. Device according to claim 9 , having output means for outputting the hemodynamic parameters.
11. Device according to claim 1 , furthermore having connection means for connecting an arterial catheter that is suitable for the pressure measurement.