ELECTRONIC SPIROMETER

• US 3,645,133 A
• Filed: 04/15/1970
• Issued: 02/29/1972
• Est. Priority Date: 04/15/1970
• Status: Expired due to Term

• Current Assignee: Peter G. Simeth, Richard C. Seeley
• Original Assignee: Peter G. Simeth, Richard C. Seeley
• Inventors: Simeth, Peter G., Seeley, Richard C.
• Primary Examiner(s): Ruehl, Charles A.
• Assistant Examiner(s): Goldstein, Herbert
• Application Number:
  US05/028,862
• Time in Patent Office: 685 Days
• Field of Search: 73/204
• US Class Current: 73/204.15
• CPC Class Codes: A61B 5/0878 using temperature sensing means
• CPC Class Codes: G01F 1/68 by using thermal effects

Abstract

An electronic spirometer having an accurate indication of exhaled tidal or minute volume. In the preferred embodiment, an adapter fits on the exhalation port of the breathing circle and monitors a patient'"'"''"'"'s exhaled volume when being ventilated. A heated thermistor mounted in the adapter senses the gas flow as an approximate fourth power function of the current necessary to maintain the thermistor at a constant temperature. A signal conditioner provides the current required to keep the thermistor at a constant temperature and converts the nonlinear heater current into a signal which is proportional to flow. A second thermistor in the probe corrects for temperature variations. The output of the signal conditioner is fed into the integrator circuit which converts the flow signal to a volume signal. In the minute volume mode, a clock generates a command signal every 30 seconds. This transfers the integrator output into a readout unit and resets the integrator to zero. In the tidal volume mode, the flow is integrated on a breath by breath basis and the volume signal is read out when the exhaled flow reaches zero. Outputs are provided for recording the flow rate and the minute integrated volume. An alarm system is provided for indicating when minute volume limits are too low or too high.

Claims

1. A flow-meter for measuring the flow rate of gases and other fluid masses comprising:

a sensing bridge;

a heated thermistor;

means for mounting said thermistor in the path of a moving fluid mass and connecting said heated thermistor into one leg of said sensing bridge;

a branch circuit connected to the input of said sensing bridge and varying the bias to said bridge;

a second thermistor to correct for temperature variations in the fluid mass;

means for mounting said second thermistor in the path of the moving fluid mass and connecting said second thermistor into said branch circuit;

means including an electrical power supply connected to said sensing bridge and a variable resistance for altering the power supplied to said sensing bridge and maintaining said heated thermistor at a substantially constant temperature;

a constant current source connected to said branch circuit;

a differential amplifier connected to said sensing bridge;

a feedback amplifier connected to the output of said differential amplifier, and electrical means responsive to the signal of said feedback amplifier for changing the resistance in said means for maintaining the thermistor at a substantially constant temperature which linearizes the voltage output of the differential amplifier and provides a signal which is linearly proportional to flow rate.

2. The flow-meter of claim 1, and further comprising an integrating amplifier connected to the linearized output signal of said differential amplifier, means for recording the integrated volume flow of a patient'"'"''"'"'s breath on a tidal basis, and means for displaying the total volume of air expelled by each breath of the patient.