Method and apparatus for determining cardiac performance in a patient with a conductance catheter
An apparatus for determining cardiac performance in the patient. The apparatus includes a conductance catheter for measuring conductance and blood volume in a heart chamber of the patient. The apparatus includes a processor for determining instantaneous volume of the ventricle by applying a non-linear relationship between the measured conductance and the volume of blood in the heart chamber to identify mechanical strength of the chamber. The processor is in communication with the conductance catheter. Methods for determining cardiac performance in a patient. Apparatuses for determining cardiac performance in a patient.
1. An apparatus for determining cardiac performance in a patient from a plurality of desired wave forms received from electrodes placed in the patient and in communication with a heart chamber of the patient comprising:
a data acquisition mechanism for receiving and separating the plurality of desired wave forms at desired frequencies from the electrodes; and
a computer for determining instantaneous volume of a ventricle of the heart chamber by applying a non-linear relationship between measured conductance and volume of blood in the heart chamber to identify mechanical strength of the chamber from the desired wave forms at desired frequencies, the processor in communication with the data acquisition mechanism.
2. The apparatus of claim 1 including a signal synthesizer which produces the plurality of desired wave forms at desired frequencies for the electrodes.
3. An apparatus as described in claim 2 wherein the signal synthesizer produces the plurality of desired wave forms at desired frequencies simultaneously, and the data acquisition mechanism separates the plurality of desired wave forms at desired frequencies the data acquisition mechanism receives from the electrodes.
4. An apparatus as described in claim 3 wherein the non-linear relationship depends on a number of the electrodes, dimensions and spacing of the electrodes, and an electrical conductivity of a medium in which the electrodes of the catheter are disposed.
5. An apparatus as described in claim 4 wherein the non-linear relationship is
β( G )(σ=0.928 S/m)=1+1.774(10 7.481×10 −4 (G−2057) )
where: G is the measured conductance (S), the calculations have been corrected to the Conductivity of whole blood at body temperature (0.928 S/m), and 2057 is the asymptotic conductance in μS when the cuvette is filled with a large volume of whole blood.
6. An apparatus as described in claim 5 wherein the nonlinear relationship further includes:
Vol
(
t
)
=
[
β
(
G
)
]
[
L
2
σ
b
]
[
Y
(
t
)
-
Y
p
]
where: β(G)=the field geometry calibration function (dimensionless), Y(t)=the measured combined admittance, σ b is blood conductivity, L is distance between measuring electrodes, and Y p =the parallel leakage admittance, dominated by cardiac muscle.
7. An apparatus as described in claim 6 including a pressure sensor for measuring instantaneous pressure of the heart chamber in communication with the computer.
8. An apparatus as described in claim 7 wherein the pressure sensor is in contact with the conductance catheter to measure ventricular pressure in the chamber.
9. An apparatus as described in claim 8 wherein the computer converts conductance into a volume.
10. An apparatus as described in claim 9 wherein the computer produces a drive signal having a plurality of desired wave forms at desired frequencies to drive the electrodes.
11. An apparatus as described in claim 4 wherein
Vol( t )=ρ L 2 g b ( t )exp[γ·( g b ( t )) 2 ]
where Vol(t) is the instantaneous volume, ρ is the blood resistivity, L is the distance between the sensing electrodes, g b (t) is the instantaneous blood conductance, and γ is an empirical calibration factor.
12. An apparatus for determining cardiac performance in a patient from a plurality of desired wave forms received from electrodes placed in the patient and in communication with a heart chamber of the patient comprising:
a data acquisition mechanism for receiving and separating the plurality of desired wave forms at desired frequencies from the electrodes; and
a computer for determining instantaneous volume of the heart chamber by removing a muscle contribution from conductance that includes contributions from blood and muscle with respect to the heart chamber, the processor in communication with the data acquisition mechanism.
13. The apparatus of claim 12 including a signal synthesizer which produces the plurality of desired wave forms at desired frequencies for the electrodes.
14. An apparatus as described in claim 13 wherein the signal synthesizer produces the plurality of desired wave forms at desired frequencies simultaneously, and the data acquisition mechanism separates the plurality of desired wave forms at desired frequencies the data acquisition mechanism receives from the electrodes.
15. An apparatus as described in claim 14 wherein the computer measures complex admittance with the electrodes to identify the muscle contribution.
16. An apparatus as described in claim 15 wherein the complex admittance is defined as
Yp=Gm+jωCm ( Y subscript p )
where
Cm=capacitance component of muscle (F=Farads) (C subscript m)
ω=angular frequency (radians/second) (greek “omega”=2 pi f)
Gm=conductance of muscle (S=Siemens) (G subscript m).
17. An apparatus as described in claim 16 wherein the conductance is defined as
Y ( t )= Gb+Gm+jωCm
where Gb=conductance of blood (S) (G subscript b).