Portable pulse oximeter

• US 5,575,284 A
• Filed: 04/01/1994
• Issued: 11/19/1996
• Est. Priority Date: 04/01/1994
• Status: Expired due to Term

• Current Assignee: University of South Florida (State University System of Florida)
• Original Assignee: University of South Florida (State University System of Florida)
• Inventors: Scharf, John E., Athan, Stephan P.
• Primary Examiner(s): Sykes, Angela D.
• Assistant Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US08/221,958
• Time in Patent Office: 963 Days
• Field of Search: 128/633, 128/903, 356/41, 250/214 A, 250/214 L, 607/60
• US Class Current: 600/323
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A61B 5/726 using Wavelet transforms

Abstract

A diagnostic instrument for determining a cardiovascular system parameter. In one embodiment, the instrument takes the form of a portable pulse oximeter comprising a light to frequency converter (LFC) as a sensor. Also provided is a light to frequency converter comprising a photoresistor and capacitor in circuit communication with an inverting Schmitt trigger and configured such that the inverter generates a periodic electrical signal corresponding to the amount of electromagnetic radiation illuminating the photoresistor.

Claims

1. A diagnostic instrument for determining a parameter of a cardiovascular system comprising:

a. an electromagnetic radiation source for illumination of a volume of intravascular blood with electromagnetic radiation, the electromagnetic radiation having at least one frequency component having an intensity, the intensity of the at least one frequency component of the electromagnetic radiation being altered by interaction with the volume of intravascular blood thereby generating an optical signal from the interaction of the at least one frequency component of the electromagnetic radiation with the volume of intravascular blood, the optical signal having an intensity;

b. a light-to-frequency converter having an electromagnetic radiation sensor electrically connected to an electronic signal generator, said electromagnetic radiation sensor being optically coupled to said electromagnetic radiation source for reception of the optical signal and said electronic signal generator generating a periodic electrical signal responsive to said electromagnetic radiation sensor, the periodic electrical signal comprising a digital pulse train having pulses, the timing of the pulses of the electrical signal corresponding to the intensity of the optical signal; and

c. a signal analyzer electrically connected to said light-to-frequency converter for determining from the pulses of the periodic electrical signal the cardiovascular system parameter.

2. A diagnostic instrument according to claim 1 further comprising a display circuit electrically connected to said signal analyzer for presenting a display corresponding to the determined cardiovascular system parameter, for determining from the pulses of the periodic electrical signal the oxygen saturation of the hemoglobin within the volume of blood.

3. A diagnostic instrument according to any of claims 1 or 2 further comprising an inflatable cuff associated with said electromagnetic radiation source and wherein said electromagnetic radiation source is placed in optical communication with a patient'"'"'s skin associated with the volume of intravascular blood.

4. A diagnostic instrument according to claim 1 wherein said signal analyzer comprises means for determining from the pulses of the periodic electrical signal the cardiovascular system parameter.

5. A pulse oximeter comprising:

a. an electromagnetic radiation source for illumination of a volume of intravascular blood with electromagnetic radiation, the volume of intravascular blood having an oxygen saturation level of hemoglobin within the volume of blood, the electromagnetic radiation having at least one frequency component having an intensity, the intensity of the at least one frequency component of the electromagnetic radiation being altered by interaction with oxyhemoglobin in the volume of intravascular blood thereby generating an optical signal from the interaction of the at least one frequency component of the electromagnetic radiation with the oxyhemoglobin in the volume of intravascular blood, the optical signal having an intensity;

b. a light-to-frequency converter having an electromagnetic radiation sensor electrically connected to an electronic signal generator, said electromagnetic radiation sensor being optically coupled to said electromagnetic radiation source for reception of the optical signal and said electronic signal generator generating a periodic electrical signal responsive to said electromagnetic radiation sensor, the periodic electrical signal comprising a digital pulse train having pulses, the timing of the pulses of the electrical signal corresponding to the intensity of the optical signal; and

c. a signal analyzer electrically connected to said light-to-frequency converter for determining from the pulses of the periodic electrical signal the oxygen saturation level of the hemoglobin within the volume of blood.

6. A pulse oximeter according to claim 5 further comprising a display circuit electrically connected to said signal analyzer for presenting a display corresponding to the determined oxygen saturation level of the hemoglobin within the volume of blood.

7. A pulse oximeter according to claim 5 wherein a value associated with the intensity of the optical signal received by said electromagnetic radiation sensor has a logarithm, the periodic electrical signal generated by said electronic signal generator of said light-to-frequency converter has a frequency, a value associated with the frequency has a logarithm, and the logarithm of the value associated with the frequency is in linear relationship to the logarithm of the value associated with the intensity of the optical signal received by said electromagnetic radiation sensor of said light-to-frequency converter.

8. A pulse oximeter according to claim 5 wherein said electromagnetic radiation source comprises a first emitter of electromagnetic radiation for selectively illuminating the intravascular blood with electromagnetic radiation of a first frequency and a second emitter of electromagnetic radiation for selectively illuminating the intravascular blood with electromagnetic radiation of a second frequency;

wherein electromagnetic radiation at said second frequency has an absorption coefficient with respect to oxyhemoglobin; and

wherein electromagnetic radiation at said first frequency has an absorption coefficient with respect to oxyhemoglobin that is substantially different than the absorption coefficient with respect to hemoglobin of electromagnetic radiation at said second frequency.

9. A pulse oximeter according to any of claims 5, 6, or 8 further comprising an inflatable cuff associated with said electromagnetic radiation source and wherein said electromagnetic radiation source is placed in optical communication with a patient'"'"'s skin associated with the volume of intravascular blood.

10. A pulse oximeter according to claim 5 wherein said signal analyzer comprises means for determining from the pulses of the periodic electrical signal the oxygen saturation level of the hemoglobin within the volume of blood.

11. A diagnostic instrument for determining a parameter of a cardiovascular system comprising:

(1) an electromagnetic radiation source for illumination of a volume of intravascular blood with electromagnetic radiation, the electromagnetic radiation having at least one frequency component having an intensity, the intensity of the at least one frequency component of the electromagnetic radiation being altered by interaction with the volume of intravascular blood thereby generating an optical signal from the interaction of the at least one frequency component of the electromagnetic radiation with the volume of intravascular blood, the optical signal having an intensity;

(2) a light-to-frequency converter having an electromagnetic radiation sensor electrically connected to an electronic signal generator, said electromagnetic radiation sensor being optically coupled to said electromagnetic radiation source for reception of the optical signal and said electronic signal generator generating a periodic electrical signal responsive to said electromagnetic radiation sensor, the periodic electrical signal comprising a digital pulse train having pulses, the timing of the pulses of the electrical signal corresponding to the intensity of the optical signal; and

(3) a signal analyzer electrically connected to said light-to-frequency converter for determining from the pulses of the periodic electrical signal the cardiovascular system parameter;

(a) wherein said electromagnetic radiation sensor comprises a photoresistor having a resistance, the resistance being variable and corresponding to an amount of electromagnetic radiation illuminating said photoresistor;

(b) wherein said electronic signal generator comprises an inverting circuit electrically connected to a capacitor;

(c) wherein said capacitor charges and discharges over a period of time responsive to said inverting circuit and said photoresistor; and

(d) wherein the period of time in which said capacitor charges and discharges corresponds to the resistance of said photoresistor.

12. A diagnostic instrument according to claim 11 wherein said inverting circuit has an input and an output and wherein said photoresistor is electrically connected in a feedback path between said output and said input of said inverting circuit.

13. A diagnostic instrument according to claim 11 further comprising an additional resistive device, wherein said inverting circuit has an input and an output, and wherein said photoresistor is electrically connected in series relation with the additional resistive device in a feedback path between said output and said input of said inverting circuit.

14. A diagnostic instrument according to claim 11 wherein said inverting circuit has an input and an output and wherein the digital pulse train of the periodic electrical signal is generated at said output of said inverting circuit.

15. A diagnostic instrument according to claim 11 further comprising an inflatable cuff associated with said electromagnetic radiation source and wherein said electromagnetic radiation source is placed in optical communication with a patient'"'"'s skin associated with the volume of intravascular blood.

16. A pulse oximeter comprising:

a. an electromagnetic radiation source for illumination of a volume of intravascular blood with electromagnetic radiation, the volume of intravascular blood having an oxygen saturation level of hemoglobin within the volume of blood, the electromagnetic radiation having at least one frequency component having an intensity, the intensity of the at least one frequency component of the electromagnetic radiation being altered by interaction with oxyhemoglobin in the volume of intravascular blood thereby generating an optical signal from the interaction of the at least one frequency component of the electromagnetic radiation with the oxyhemoglobin in the volume of intravascular blood, the optical signal having an intensity;

b. a light-to-frequency converter having an electromagnetic radiation sensor electrically connected to an electronic signal generator, said electromagnetic radiation sensor being optically coupled to said electromagnetic radiation source for reception of the optical signal and said electronic signal generator generating a periodic electrical signal responsive to said electromagnetic radiation sensor, the periodic electrical signal comprising a digital pulse train having pulses, the timing of the pulses of the electrical signal corresponding to the intensity of the optical signal; and

c. a signal analyzer electrically connected to said light-to-frequency converter for determining from the pulses of the periodic electrical signal the oxygen saturation level of the hemoglobin within the volume of blood;

(a) wherein said electromagnetic radiation sensor comprises a photoresistor having a resistance, the resistance being variable and corresponding to an amount of electromagnetic radiation illuminating said photoresistor;

(b) wherein said electronic signal generator comprises an inverting circuit electrically connected to a capacitor;

(c) wherein said capacitor charges and discharges over a period of time responsive to said inverting circuit and said photoresistor; and

(d) wherein the period of time in which said capacitor charges and discharges corresponds to the resistance of said photoresistor.

17. A pulse oximeter according to claim 16 wherein said inverting circuit has an input and an output and wherein said photoresistor is electrically connected in a feedback path between said output and said input of said inverting circuit.

18. A pulse oximeter according to claim 16 further comprising an additional resistive device, wherein said inverting circuit has an input and an output, and wherein said photoresistor is electrically connected in series relation with the additional resistive device in a feedback path between said output and said input of said inverting circuit.

19. A pulse oximeter according to claim 16 wherein said inverting circuit has an input and an output and wherein the digital pulse train of the periodic electrical signal is generated at said output of said inverting circuit.

20. A pulse oximeter according to claim 16 further comprising an inflatable cuff associated with said electromagnetic radiation source and wherein said electromagnetic radiation source is placed in optical communication with a patient'"'"'s skin associated with the volume of intravascular blood.

21. A diagnostic instrument for determining a parameter of a cardiovascular system comprising:

a. an electromagnetic radiation source for illumination of a volume of intravascular blood with electromagnetic radiation, the electromagnetic radiation having at least one frequency component having an intensity, the intensity of the at least one frequency component of the electromagnetic radiation being altered by interaction with the volume of intravascular blood thereby generating an optical signal from the interaction of the at least one frequency component of the electromagnetic radiation with the volume of intravascular blood, the optical signal having an intensity;

b. a light-to-frequency converter having an electromagnetic radiation sensor electrically connected to an electronic signal generator, said electromagnetic radiation sensor being optically coupled to said electromagnetic radiation source for reception of the optical signal and said electronic signal generator generating a periodic electrical signal responsive to said electromagnetic radiation sensor, the periodic electrical signal comprising a digital pulse train having pulses, the timing of the pulses of the electrical signal corresponding to the intensity of the optical signal;

c. a signal analyzer electrically connected to said light-to-frequency converter for determining from the pulses of the periodic electrical signal the cardiovascular system parameter; and

d. a transmitter electrically connected to said signal analyzer for wirelessly transmitting to a remote receiver a signal corresponding to the determined cardiovascular system parameter.

22. A pulse oximeter comprising:

a. an electromagnetic radiation source for illumination of a volume of intravascular blood with electromagnetic radiation, the volume of intravascular blood having an oxygen saturation level of hemoglobin within the volume of blood, the electromagnetic radiation having at least one frequency component having an intensity, the intensity of the at least one frequency component of the electromagnetic radiation being altered by interaction with oxyhemoglobin in the volume of intravascular blood thereby generating an optical signal from the interaction of the at least one frequency component of the electromagnetic radiation with the oxyhemoglobin in the volume of intravascular blood, the optical signal having an intensity;

b. a light-to-frequency converter having an electromagnetic radiation sensor electrically connected to an electronic signal generator, said electromagnetic radiation sensor being optically coupled to said electromagnetic radiation source for reception of the optical signal and said electronic signal generator generating a periodic electrical signal responsive to said electromagnetic radiation sensor, the periodic electrical signal comprising a digital pulse train having pulses, the timing of the pulses of the electrical signal corresponding to the intensity of the optical signal;

c. a signal analyzer electrically connected to said light-to-frequency converter for determining from the pulses of the periodic electrical signal the oxygen saturation level of the hemoglobin within the volume of blood; and

d. a transmitter electrically connected to said signal analyzer for wirelessly transmitting to a remote receiver a signal corresponding to the determined oxygen saturation level of the hemoglobin within the volume of blood.