Medical sensor with amplitude independent output

• US 6,370,408 B1
• Filed: 07/26/1999
• Issued: 04/09/2002
• Est. Priority Date: 12/17/1993
• Status: Expired due to Fees

• Current Assignee: Mallinckrodt Incorporated (Mallinckrodt plc), Nellcor Incorporated (Medtronic Plc)
• Original Assignee: Mallinckrodt Incorporated (Mallinckrodt plc)
• Inventors: Merchant, Adnan I., Bernstein, Michael
• Primary Examiner(s): Nasser, Robert L.
• Application Number:
  US09/360,777
• Time in Patent Office: 988 Days
• Field of Search: 600/310, 600/322-324, 356/41
• US Class Current: 600/322
• CPC Class Codes: A61B 5/0017 transmitting optical signals transmission by light H04B10/00
• CPC Class Codes: A61B 5/14551 for measuring blood gases

Abstract

The present invention provides a medical sensor for detecting a blood characteristic. The sensor includes a transducer for producing an analog signal related to the blood characteristic. The analog signal is converted into a transmission signal which is in amplitude-independent form for transmission to a remote analyzer. In one embodiment, a current-to-frequency converter converts a signal from a pulse oximeter sensor into a frequency signal which can be transmitted over a transmission line to a remote pulse oximeter.

Claims

1. A medical diagnostic apparatus for detecting a blood characteristic, comprising:

a radiation emitter for directing radiation into a patient, the radiation having an intensity, the intensity of at least one wavelength component of said radiation being modified by interaction with blood having said blood characteristic to produce a modified intensity radiation signal;

a photodetector mounted to receive said modified intensity radiation signal;

a converter connected to said photodetector, said converter generating a converted signal in response to the detected intensity of said modified intensity radiation signal, said converted signal having said detected intensity encoded in one of a frequency and a digital component of said converted signal, eliminating the encoding of said intensity signal as an electrical signal level; and

an output, coupled to said converter, for transmitting said converted signal to a remote signal processing unit.

2. The apparatus of claim 1 wherein said photodetector and said converter comprise a light-to-frequency converter integrated on a single chip.

3. The apparatus of claim 1 wherein said radiation emitter and said photodetector are mounted in a sensor, and said converter is mounted in a module connected to said sensor.

4. The apparatus of claim 1 further comprising at least one automatic gain control circuit coupled to said converter for controlling the nominal output of said converter.

5. The apparatus of claim 4 further comprising:

said radiation emitter comprising first and second light emitters;

a control line for alternately pulsing said first and second light emitters; and

a controller, included in said automatic gain control circuit and connected to said control line, for switching a nominal output of said converter, with said automatic gain control circuit, as said light emitters are alternately pulsed.

6. A method for detecting a blood characteristic, comprising:

directing radiation into a patient, the radiation having an intensity, the intensity of at least one wavelength component of said radiation being modified by interaction with blood having said blood characteristic to produce a modified intensity radiation signal;

receiving said modified intensity radiation signal;

generating a converted signal in response to the detected intensity of said modified intensity radiation signal, said converted signal having said detected intensity encoded in one of a frequency and a digital component of said converted signal, eliminating the encoding of said intensity signal as an electrical signal level; and

transmitting said converted signal to a remote signal processing unit.

7. A medical diagnostic system for detecting a blood characteristic, comprising:

a radiation emitter for directing radiation into a patient, the radiation having an intensity, the intensity of at least one wavelength component of said radiation being modified by interaction with blood having said blood characteristic to produce a modified intensity radiation signal;

a photodetector mounted to receive said modified intensity radiation signal;

a converter connected to said photodetector, said converter generating a converted signal in response to the detected intensity of said modified intensity radiation signal, said converted signal having said detected intensity encoded in one of a frequency and a digital component of said converted signal, and eliminating the encoding of said intensity signal as an electrical signal level; and

an analyzer system electromagnetically coupled to said converter for receiving and processing said converted signal to determine said blood characteristic.