# US 5,350,405 A · Method and apparatus for capacitor tolerance compensation in a cardiac stimulating device

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- Number: US 5,350,405 A
- Document ID: US5350405A
- Status: Granted
- Kind: A
- Application number: 07/946,276
- Filed: 1992-09-16
- Granted: 1994-09-27
- Earliest claimed: 1992-09-16
- Assignees: Siemens-Pacesetter, Inc.
- Inventors: Sergiu Silvian
- Web page: https://patentgrep.com/patent/US5350405A

## CPC

- A61N 1/3937: {Monitoring output parameters}
- A61N 1/37: Monitoring; Protecting
- A61N: ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY (measurement of bioelectric currents A61B; surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body A61B18/00; anaesthetic apparatus in general A61M; incandescent lamps H01K; infrared radiators for heating H05B)

## Abstract

A method and apparatus for determining the actual capacitance of a capacitor in a cardiac stimulating device in order to determine the potential necessary to store a desired amount of energy on the capacitor, are provided. The discharge curve of the capacitor is measured during re-forming to determine the time constant of the capacitor and the dumping resistor, and hence the actual capacitance.

## Claims

### Claim 1

A method for determining a target potential to which a capacitor in a cardiac stimulating device must be charged to allow said cardiac stimulating device to deliver a desired energy output, wherein said capacitor has a nominal capacitance and an actual capacitance that may differ from said nominal capacitance and is in series with a resistor having a known resistance, said method comprising:
charging the capacitor to develop a potential thereon;
discharging the capacitor for thereby changing the potential on the capacitor as a function of time;
measuring the potential on one of (a) the capacitor, and (b) the resistor, while said potential on the capacitor is changing;
measuring the time interval required for said potential on said one of (a) the capacitor, and (b) the resistor, to fall from a first predetermined potential to a second predetermined potential; and
calculating said target potential from said first and second predetermined potentials, said time interval, said known resistance and said desired energy output.

### Claim 2 (depends on 1)

The method of claim 1, wherein said step of calculating said target potential comprises determining said actual capacitance from said first and second predetermined potentials, said time interval and said known resistance.

### Claim 3 (depends on 2)

The method of claim 2, wherein said step of determining said actual capacitance comprises determining a time constant for a series circuit of said capacitor and said resistor from said first and second predetermined potentials and said time interval.

### Claim 4 (depends on 1)

The method of claim 1, wherein said step of calculating said target potential comprises calculating said target potential from said first and second predetermined potentials, said time interval and said known resistance.

### Claim 5 (depends on 1)

The method of claim 1, wherein:
said step of changing potential on said capacitor comprises discharging said capacitor from said first predetermined potential to said second predetermined potential; and
said step of measuring potential comprises measuring potential on said capacitor.

### Claim 6 (depends on 5)

The method of claim 5, wherein said second predetermined potential is one-half of said first predetermined potential.

### Claim 7 (depends on 6)

The method of claim 6, wherein said step calculating said target potential comprises calculating said target potential in accordance with the formula:
V.sub.c =.sqroot.(1.386RE/t),
where V.sub.c is said target potential, R is said known resistance, E is said desired energy output, and t is said time interval.

### Claim 8 (depends on 5)

The method of claim 5, wherein said step of calculating said target potential comprises calculating said target potential in accordance with the formula:
V.sub.c =.sqroot.[2REln(x)/t],
where V.sub.c is said target potential, R is said known resistance, E is said desired energy output, t is said time interval, and x is the ratio of said first predetermined potential to said second predetermined potential.

### Claim 9

In a cardiac stimulating device, said cardiac stimulating device including:
a capacitor having a nominal capacitance and an actual capacitance that may differ from said nominal capacitance,
a power source for charging said capacitor to a target potential for delivering a desired energy output,
a potential measuring circuit for measuring potential on said capacitor,
a microprocessor for controlling functions of said cardiac stimulating device, and
a resistor having a known resistance for re-forming said capacitor;
a method for determining said target potential to which said capacitor must be charged to allow said cardiac stimulating device to deliver said desired energy output, accounting for variation between said nominal capacitance and said actual capacitance, without increasing power consumption in said cardiac stimulating device, said method comprising:
initiating re-forming of said capacitor including:
charging said capacitor from said power source to a first predetermined potential, and
discharging said capacitor through said resistor;
measuring, with said potential measuring circuit, potential on said capacitor while said capacitor is discharging through said resistor;
measuring with said microprocessor the time interval required for said capacitor to discharge from said first predetermined potential to a second predetermined potential; and
calculating with said microprocessor said target potential from said first and second predetermined potentials, said time interval, said known resistance and said desired energy output.

### Claim 10 (depends on 9)

The method of claim 9, wherein said step of calculating said target potential comprises determining said actual capacitance from said first and second predetermined potentials, said time interval and said known resistance.

### Claim 11 (depends on 10)

The method of claim 10, wherein said step of determining said actual capacitance comprises determining a time constant for a series circuit of said capacitor and said resistor from said first and second predetermined potentials and said time interval.

### Claim 12 (depends on 9)

The method of claim 9, wherein said step of calculating said target potential comprises calculating said target potential from said first and second predetermined potentials, said time interval and said known resistance.

### Claim 13 (depends on 9)

The method of claim 9, wherein said second predetermined potential is one-half of said first predetermined potential.

### Claim 14 (depends on 13)

The method of claim 13, wherein said step of calculating said target potential comprises calculating said target potential in accordance with the formula:
V.sub.c =.sqroot.(1.386RE/t),
where V.sub.c is said target potential, R is said known resistance, E is said desired energy output, and t is said time interval.

### Claim 15 (depends on 9)

The method of claim 9, wherein said step of calculating said target potential comprises calculating said target potential in accordance with the formula:
V.sub.c =.sqroot.[2REln(x)/t],
where V.sub.c is said target potential, R is said known resistance, E is said desired energy output, t is said time interval, and x is the ratio of said first predetermined potential to said second predetermined potential.

### Claim 16

A cardiac stimulating device comprising:
a capacitor having a nominal capacitance and an actual capacitance that may differ from said nominal capacitance,
a power source coupled to said capacitor for charging said capacitor to a target potential for delivering a desired energy output,
a resistor having a known resistance switchably coupled to said capacitor for discharging said capacitor for re-forming said capacitor;
a potential measuring circuit coupled to said capacitor for measuring the potential on said capacitor;
a microprocessor for controlling operation of said cardiac stimulating device; and wherein:
said microprocessor initiates re-forming of said capacitor, by initiating charging of said capacitor from said power source to a first predetermined potential and discharging said capacitor through said resistor; and further wherein:
said microprocessor measures the time interval required for said capacitor to discharge from said first predetermined potential to a second predetermined potential; and still further wherein:
said microprocessor calculates said target potential from said first and second predetermined potentials, said time interval, said known resistance and said desire energy output.

### Claim 17 (depends on 16)

The cardiac stimulating device of claim 16, wherein said microprocessor calculates said target potential by determining said actual capacitance from said first and second predetermined potentials, said time interval and said known resistance.

### Claim 18 (depends on 17)

The cardiac stimulating device of claim 17, wherein said microprocessor determines said actual capacitance by determining a time constant for a series circuit of said capacitor and said resistor from said first and second predetermined potentials and said time interval.

### Claim 19 (depends on 16)

The cardiac stimulating device of claim 16, wherein said microprocessor calculates said target potential from said first and second predetermined potentials, said time interval and said known resistance.

### Claim 20 (depends on 16)

The cardiac stimulating device of claim 16, wherein said second predetermined potential is one-half of said first predetermined potential.

### Claim 21 (depends on 20)

The cardiac stimulating device of claim 20, wherein said microprocessor calculates said target potential in accordance with the formula:
V.sub.c =.sqroot.(1.386RE/t),
where V.sub.c is said target potential, R is said known resistance, E is said desired energy output, and t is said time interval.

### Claim 22 (depends on 21)

The cardiac stimulating device of claim 21, further comprising a lookup table loaded in accordance with said formula, said microprocessor calculating said target potential with reference to said lookup table.

### Claim 23 (depends on 22)

The cardiac stimulating device of claim 22, wherein said microprocessor interpolates between values in said lookup table.

### Claim 24 (depends on 16)

The cardiac stimulating device of claim 16, wherein said microprocessor calculates said target potential in accordance with the formula:
V.sub.c =.sqroot.[2REln(x)/t],
where V.sub.c is said target potential, R is said known resistance, E is said desired energy output, t is said time interval, and x is the ratio of said first predetermined potential to said second predetermined potential.

### Claim 25 (depends on 24)

The cardiac stimulating device of claim 24, further comprising a lookup table loaded in accordance with said formula, said microprocessor calculating said target potential with reference to said lookup table.

### Claim 26 (depends on 25)

The cardiac stimulating device of claim 25, wherein said microprocessor interpolates between values in said lookup table.