Devices and methods for monitoring chest compressions
A method for monitoring chest compressions using a compression member includes measuring a force exerted by the compression member, measuring a displacement of the compression member, providing a chest stiffness function representing the relationship between force and displacement based on values derived from the measured force and the measured displacement, and analyzing linearity of the chest stiffness function. Embodiments of the invention also include devices for performing the method.
1. A method for monitoring chest compressions performed using a compression member, the method comprising:
measuring a force exerted by the compression member;
measuring a displacement of the compression member;
providing a chest stiffness function representing a relationship between force and displacement based in part on the measured force and the measured displacement;
analyzing linearity of the chest stiffness function; and
providing an indication of efficient chest compressions when operating in a non-linear part of the chest stiffness function.
2. The method according to claim 1 , wherein the act of analyzing linearity comprises calculating a second derivative of the chest stiffness function.
3. The method according to claim 2 , further comprising comparing the second derivative of the chest stiffness function to a threshold to assess linearity or non-linearity.
4. The method according to claim 1 , wherein the act of analyzing linearity is based on an average or median of a predetermined number of compressions.
5. The method according to claim 1 , wherein the chest stiffness function is determined by calculating and subtracting a damping force component from the measured force, the damping force being dependent in part on a velocity of the chest compression member.
6. The method according to claim 1 , wherein the act of analyzing linearity includes fitting the measured chest stiffness function to a polynomial, exponential or spline function.
7. The method according to claim 1 , further comprising providing an indication of patient category based on results of said linearity analysis, where a degree of non-linearity at least in part determines the patient category.
8. The method according to claim 7 , wherein the indication of patient category distinguishes between patients of different age.
9. The method according to claim 7 , wherein the indication of patient category distinguishes between patients of different chest size.
10. The method according to claim 7 , wherein the indication of patient category distinguishes between patients lying on surfaces of different stiffness.
11. The method according to claim 1 , further comprising providing an indication of a non-efficient compression when the non-liner part of the chest stiffness function does not exceed a predetermined value.
12. The method according to claim 1 , wherein the chest stiffness function comprises a force-displaCement curve having a non-linear part and a linear part.
13. A device for monitoring chest compressions performed using a compression member, the device comprising:
a first sensor configured to measure force exerted by the compression member;
a second sensor configured to measure displacement of the compression member;
a processor programmed to provide a chest stiffness funtion representing a relationship between force and displacement based on values derived from the measured force and the measured displacement, programed to analyze linearity of the chest stiffness function, and programmed to provide an indication of efficient chest compressions when operating in a non-linear part of the chest stiffness function.
14. The device according to claim 13 , wherein the chest stiffness function comprises a force-displacement curve having a non-linear part and a linear part.