AM/FM multi-channel implantable/ingestible biomedical monitoring telemetry system

• US 5,415,181 A
• Filed: 12/01/1993
• Issued: 05/16/1995
• Est. Priority Date: 12/01/1993
• Status: Expired due to Term

• Current Assignee: Johns Hopkins University
• Original Assignee: Johns Hopkins University
• Inventors: Lesho, Jeffery C., Hogrefe, Arthur F., Eaton, Harry A. C.
• Primary Examiner(s): Sykes, Angela D.
• Application Number:
  US08/160,716
• Time in Patent Office: 531 Days
• Field of Search: 128/903, 128/736, 128/630-631, 607/60
• US Class Current: 600/549
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: G01K 1/045 temperature indication combined with the indication of another variable indicating of human comfort G01W1/17
• CPC Class Codes: H03C 5/00 Amplitude modulation and angle modulation produced simultaneously or at will by the same modulating signal H03C7/00 takes precedence
• CPC Class Codes: Y10S 128/903 Radio telemetry

Abstract

A multi-channel circuit for telemetering signals representing physiological values from a point in a human body to a receiver (24) outside of the body. The two signals (S₁, S₂) other than the temperature signal (27'"'"') are used to provide two frequency modulated signals (14, 16) summed by an amplifier (18) with the summed FM signal then being applied to amplitude modulate (21) a carrier (8) whose frequency varies as a function of temperature. The resulting FM/AM signal (22) is telemetered inductively outside of the body to an external receiver (24). Appropriate demodulation, filter, and shaping circuits within the external circuit detect the FM signals (14, 16) and thus produce three independent frequencies two of which are the original physiological variables and the third a function of local temperature. Real time plot of the two physiological variables can be obtained using FM discriminators while the temperature dependent frequency is best monitored by a counter.

Claims

1. A system for propagating a plurality of signals indicative of physiological stimuli from a point inside a human body to a point external to the body comprising:

a. first sensor means responsive to a first physiological stimulus for producing a first signal;

b. second sensor means responsive to a second physiological stimulus for producing a second signal;

c. a first oscillator modulated by said first signal and having a frequency depending on the instantaneous amplitude of said first signal;

d. a second oscillator modulated by said second signal and having a frequency dependent on the instantaneous amplitude of said second signal;

e. said first and second oscillators having two different subcarrier frequencies;

f. means for summing the output signals of said oscillators thereby producing a third signal;

g. temperature responsive means for independently of said first and second oscillators producing a fourth signal which varies in frequency as a function of body temperature;

h. modulator means coupled to the outputs of said summing means and said temperature responsive means for modulating said fourth signal by said third signal thereby producing a fifth signal which contains information of said first, second, and fourth signals;

i. means for propagating said fifth signal to a point external of said human body; and

j. receiver means intercepting said fifth signal for separating said first, second, and fourth signals from each other thereby providing means for indicating said physiological stimuli and said body temperature.

2. A system defined by claim 1, wherein said first and second signals lie within a bandwidth of approximately 0-150 Hz and 0-1500 Hz, respectively.

3. A system defined by claim 1, wherein said first and second oscillators have subcarrier frequencies of approximately 2 kHz and 20 kHz, respectively.

4. A system defined by claim 1, wherein said summing means is an amplifier.

5. A system defined by claim 1, wherein said temperature responsive means includes an oscillator whose center frequency is approximately 262 kHz.

6. A system defined by claim 1, wherein said modulator means comprises an amplitude modulator.

7. A system defined by claim 5, wherein said temperature responsive means has a transfer function of approximately 9 Hz shift per °

C. change in temperature.

8. A system defined by claim 1, wherein said receiver means comprises first and second demodulating circuits to produce replicas of said first and second signals and said fourth signal.

9. A system for propagating a plurality of signals indicative of physiological stimuli from a point inside a human body to a point external to the body comprising:

a. first sensor means responsive to a first physiological stimulus for producing a first signal;

b. second sensor means responsive to a second physiological stimulus for producing a second signal;

c. a first oscillator modulated by said first signal and having a frequency depending on the instantaneous amplitude of said first signal;

d. a second oscillator modulated by said second signal and having a frequency dependent on the instantaneous amplitude of said second signal;

e. said first and second oscillators having two different subcarrier frequencies;

f. means for summing the output signals of said oscillators thereby producing a third signal;

g. temperature responsive means for independently of said first and second oscillators producing a fourth signal which varies in frequency as a function of body temperature;

h. modulator means coupled to the outputs of said summing means and said temperature responsive means for modulating said fourth signal by said third signal thereby producing a fifth signal which contains information of said first, second, and fourth signals;

i. means for propagating said fifth signal to a point external of said human body; and

j. a receiver means intercepting said fifth signal and including;

A. means for producing a replica of said fourth signal;

B. first demodulator means for detecting the FM signals produced by said first and second oscillators;

D. second demodulator means coupled to said first demodulator means for demodulating said FM signals; and

D. filter means coupled to said second demodulator means for receiving said first and second signals.

10. A system defined by claim 9, wherein said first and second signals lie within a bandwidth of approximately 0-150 Hz and 0-1500 Hz, respectively.

11. A system defined by claim 9, wherein said first and second oscillators have subcarrier frequencies of 2 kHz and 20 kHz, respectively.

12. A system defined by claim 9, wherein said summing means is an amplifier.

13. A system defined by claim 9, wherein said temperature responsive means includes an oscillator whose center frequency is approximately 262 kHz.

14. A system defined by claim 13, wherein said temperature responsive means has a transfer function of approximately 9 Hz shift per °

C. change in temperature.

15. A system defined by claim 9, wherein said modulator means comprises an amplitude modulator.

16. A system for propagating a plurality of signals indicative of physiological signals from a point inside a human body to a point external to the body comprising:

a. first op-amp means responsive to a first physiological stimulus for producing a first signal;

b. second op-amp means responsive to a second physiological stimulus for producing a second signal;

c. a first oscillator modulated by said first signal and having a frequency dependent on the instantaneous amplitude of said first signal;

d. a second oscillator modulated by said second signal and having a frequency dependent on the instantaneous amplitude of said second signal;

e. said first and second oscillators having two different subcarrier frequencies;

f. shaping means coupled to each of said oscillators for attenuating the odd harmonics present in the frequency modulated (FM) outputs of said first and second oscillators;

g. means for summing the output signals of said shaping means thereby producing a third signal;

h. temperature responsive means for independently of said first and second oscillators producing a fourth signal which varies as a function of temperature;

i. modulator means coupled to the outputs of said summing means and said temperature responsive means for modulating said fourth signal as a function of said third signal thereby producing a fifth signal which contains information of said first, second, and fourth signals;

j. means for propagating said fifth signal to a point external of said human body; and

k. receiver means intercepting said fifth signal for separating said first, second, and fourth signals from each other thereby providing means for indicating said physiological stimuli and said body temperature.

17. A system defined by claim 16, wherein said first and second signals lie within a bandwidth of approximately 0-250 and 0-1300 Hz, respectively.

18. A system defined by claim 16, wherein said temperature responsive means includes an oscillator whose center frequency is approximately 262 kHz.

19. A system defined by claim 18, wherein said temperature responsive means has a transfer function of approximately 9 Hz shift per °

C. change in temperature.

20. A system defined by claim 16, wherein said modulator means comprises an amplitude modulator.

21. A system for propagating a plurality of signals indicative of measurable variables from an enclosure:

a. first sensor means responsive to a first measurable variable for producing a first signal;

b. second detector means responsive to a second measurable variable for producing a second signal;

c. a first oscillator modulated by said first signal and having a frequency dependent on the instantaneous amplitude of said first signal;

d. a second oscillator modulated by said second signal and having a frequency dependent on the instantaneous amplitude of said second signal;

e. said first and second oscillators having two different subcarrier frequencies;

f. means for summing the output signals of said oscillators thereby producing a third signal;

g. temperature responsive means for independently of said first and second oscillators producing a fourth signal which varies in frequency as a function of temperature;

h. modulator means coupled to the outputs of said summing means and said temperature responsive means for modulating said second signal as a function of said third signal thereby producing a fifth signal which contains information of said first, second, and fourth signals.

i. means for propagating said fifth signal to a point external of said human body; and

j. receiver means intercepting said fifth signal for separating said first, second, and fourth signals from each other thereby providing means for indicating said first and second measured variables and said temperature.