Impedance cardiograph apparatus and method
First Claim
1. An impedance cardiograph used to evaluate cardiac output of a human patient having a height and a chest circumference and chest cross-sectional area A comprising:
- means for applying an electrical excitation signal to the chest of a patient;
electrodes, adapted to be positioned on the patient with a separation distance of L thereby being responsive to the excitation signal, for producing a first electrical signal Z which varies with impedance changes in the patient;
an input device for receiving values of the height and circumference and providing corresponding second and third electrical signals H and C indicating those values;
electrical circuit means for receiving the first, second and third electrical signals and providing an indication of the patient'"'"'s cardiac stroke volume SV as a function of Z, A, and L;
where A is deduced by the following approximation;
##EQU35## where K is a predetermined constant.
3 Assignments
0 Petitions
Accused Products
Abstract
An impedance cardiograph which determines cardiac output from a measurement of variations of chest impedance, provides an improved method of calculating the effect of patient volume on the measurement from measurable patient height and chest circumference, and provides a correction process that identifies as a source of error variations in the first derivative of impedance. This latter source of error is minimized by preprocessing the impedance derivative value with a compression function which reduces the range of values of the impedance derivative when that value differs significantly from a norm of the population.
-
Citations
16 Claims
-
1. An impedance cardiograph used to evaluate cardiac output of a human patient having a height and a chest circumference and chest cross-sectional area A comprising:
-
means for applying an electrical excitation signal to the chest of a patient; electrodes, adapted to be positioned on the patient with a separation distance of L thereby being responsive to the excitation signal, for producing a first electrical signal Z which varies with impedance changes in the patient; an input device for receiving values of the height and circumference and providing corresponding second and third electrical signals H and C indicating those values; electrical circuit means for receiving the first, second and third electrical signals and providing an indication of the patient'"'"'s cardiac stroke volume SV as a function of Z, A, and L; where A is deduced by the following approximation;
##EQU35## where K is a predetermined constant. - View Dependent Claims (2, 3, 4, 5)
-
-
6. An impedance cardiograph used to evaluate cardiac output of a human patient comprising:
-
means for applying an electrical excitation signal to the chest of a patient; electrodes, adapted to be positioned on the patient for producing a first electrical signal Z which varies with impedance changes in the patient; an electronic processor for calculating a time derivative of Z, and providing a non-linearly non-linearly compressed derivative, having a value less than the time derivative of Z if the time derivative of Z is greater than a predetermined normal value and having a value greater than the time derivative of Z if the time derivative of Z is less than the predetermined normal value; electrical circuit means for providing an indication of patient'"'"'s cardiac stroke volume SV as a function of the compressed time derivative. - View Dependent Claims (7, 8)
-
-
9. A method of evaluating the cardiac output of a human patient having a height H and a chest circumference C and chest cross-sectional area A comprising the step of:
-
(a) applying an electrical excitation signal to the chest of a patient; (b) positioning electrodes on the patient with a separation distance of L thereby being responsive to the excitation signal to produce a first electrical signal Z which varies with impedance changes in the patient; (c) employing an electronic computer to; (i) receive values of the height and circumference and providing corresponding second and third electrical signals H and C indicating those values; (ii) evaluate the patient'"'"'s cardiac stroke volume SV as a function of Z, A, L and left ventricular ejection interval Lvet ; where A is deduced by the following approximation;
##EQU47## in which K is a predetermined constant. - View Dependent Claims (10, 11, 12, 13)
-
-
14. A method of evaluating cardiac output of a human patient comprising the steps of:
-
(a) applying an electrical excitation signal to the chest of a patient; (b) positioning electrodes on the patient for producing a first electrical signal Z which varies with impedance changes in the patient; (c) determining a compressed derivative of the impedance signal Z, having a value less than the time derivative of Z if the time derivative of Z is greater than a predetermined normal value and having a value greater than the time derivative of Z if the time derivative of Z is less than the predetermined normal value; and (e) evaluating the patient'"'"'s cardiac stroke volume SV as a function of the compressed time derivative. - View Dependent Claims (15, 16)
-
Specification