IMPEDANCE PNEUMOGRAPH

• US 3,677,261 A
• Filed: 04/03/1970
• Issued: 07/18/1972
• Est. Priority Date: 04/03/1970
• Status: Expired due to Term

• Current Assignee: Warner-Lambert Company (Pfizer Inc.)
• Original Assignee: Christopher C. Day
• Inventors: Day, Christopher C.
• Primary Examiner(s): Howell, Kyle L.
• Application Number:
  US05/025,353
• Time in Patent Office: 837 Days
• Field of Search: 128/2.5R,2.1R,2.1Z 307/231,263 330/145,138
• US Class Current: 600/536
• CPC Class Codes: A61B 5/0809 by impedance pneumography
• CPC Class Codes: H03G 3/3015 using diodes or transistors

Abstract

An impedance pneumograph, utilizing the change in thoracic impedance due to respiration to amplitude modulate a fixed amplitude electrical carrier signal applied to the thorax of a mammalian subject, wherein the modulation provides breathing rate information for monitoring purposes. A gain stabilizer circuit is provided to automatically adjust the gain when the carrier component deviates from a predetermined voltage range, to be insensitive to fluctuations of the carrier component when it does not deviate from that predetermined range, and to be unresponsive to the modulation signal.

Claims

1. An impedance pneumograph comprising electrode means adopted for attachment to a breathing subject, means for generating a fixed-amplitude carrier signal, means connected to said electrode means and to said carrier signal generating means for deriving a modulated carrier signal in accordance with the impedance between said electrode means when attached to a breathing subject, AC amplifying means for amplifying said modulated carrier signal and demodulating it to produce a DC signal representative of the impedance between said electrode means when attached to a breathing subject, rate indicator means connected to receive said DC signal and indicate mean breathing rate, and feedback means responsive to said DC signal for varying the gain of said AC amplifying means in a direction to counteract changes in said DC signal, said feedback means including threshold detecting means for preventing a change in the gain of said AC amplifying means whenever the amplitude of said DC signal is within predetermined upper and lower limits.

2. An impedance pneumograph in accordance with claim 1 wherein said carrier signal generating means includes means for genErating a constant-current carrier signal, said modulated carrier signal deriving means includes means for deriving a signal at the frequency of said carrier signal and whose amplitude is proportional to the impedance between said electrode means when attached to a breathing subject, and said AC amplifying means includes variable divider means at the input thereof for attenuating the modulated carrier signal by a factor determined by said feedback means.

3. An impedance pneumograph in accordance with claim 2 wherein said variable divider means includes capacitor means, resistor means, transistor means, said resistor means and said transistor means being connected in series with said modulated carrier signal being applied to one end of the series circuit and the junction of said resistor means and said transistor means representing thereon the attenuated modulated carrier signal, said capacitor means being connected to said transistor means for controlling the impedance thereof, and said feedback means includes means for charging and discharging said capacitor means in accordance with the amplitude of said DC signal when it is outside the bounds of said upper and lower limits.

4. An impedance pneumograph in accordance with claim 3 wherein said threshold detecting means includes first and second diode means connected to said capacitor means in oppositely poled directions for respectively controlling the charging and discharging of said capacitor means when the amplitude of said DC signal is outside the bounds of said upper and lower limits.

5. An impedance pneumograph in accordance with claim 1 wherein said AC amplifying means includes a stage having capacitor means, resistor means, transistor means, said resistor means and said transistor means being connected in series with said modulated carrier signal being applied to the input of the stage at one end of the series circuit and the output of the stage being taken at the junction of said resistor means and said transistor means, said capacitor means being connected to said transistor means for controlling the impedance thereof, and said feedback means includes means for charging and discharging said capacitor means in accordance with the amplitude of said DC signal when it is outside the bounds of said upper and lower limits.

6. An impedance pneumograph in accordance with claim 5 wherein said threshold detecting means includes first and second diode means connected to said capacitor means in oppositely poled directions for respectively controlling the charging and discharging of said capacitor means when the amplitude of said DC signal is outside the bounds of said upper and lower limits.

7. An impedance pneumograph in accordance with claim 6 wherein said capacitor means is connected to said transistor means such that the voltage thereacross remains substantially constant in the absence of the conduction of said first and second diode means.

8. An impedance pneumograph in accordance with claim 1 wherein said carrier signal generating means includes means for generating a constant-current carrier signal, and said modulated carrier signal deriving means includes means for deriving a signal at the frequency of said carrier signal and whose amplitude is proportional to the impedance between said electrode means when attached to a breathing subject.

9. An impedance pneumograph in accordance with claim 1 wherein said feedback means includes capacitor means for varying the gain of said AC amplifying means in accordance with the voltage thereacross, and oppositely poled first and second diode means connected to said capacitor means for respectively charging and discharging said capacitor means when the amplitude of said DC signal is outside the bounds of said upper and lower limits.

10. An impedance pneumograph in accordance with claim 9 wherein said capacitor means is connected to said AC amplifying means such that the voltage thereacross remains substantially constant in the absence of the conduction of said fIrst and second diode means.

11. An impedance pneumograph in accordance with claim 10 further including biasing means connected to each of said first and second diode means for inhibiting the conduction thereof until the difference between the voltage across said capacitor means and the amplitude of said DC signal exceeds a respective predetermined threshold value.