Automatically calibrated respiratory ventilation monitor

• US 3,903,875 A
• Filed: 01/24/1974
• Issued: 09/09/1975
• Est. Priority Date: 01/24/1974
• Status: Expired due to Term

• Current Assignee: Philip A. Hughes
• Original Assignee: Philip A. Hughes
• Inventors: Hughes, Philip A.
• Primary Examiner(s): Howell, Kyle L.
• Application Number:
  US05/436,128
• Time in Patent Office: 593 Days
• Field of Search: 128/2.08,2S,DIG.29,2.6B,2.5F 73/194R 330/85,110,9
• US Class Current: 600/537
• CPC Class Codes: A61B 5/0878 using temperature sensing means

Abstract

A respiratory ventilation monitor having a flow sensing transducer including a thermistor connected in a bridge circuit for providing a signal indicative of air flow across the thermistor. The output of the bridge circuit is connected to a differential amplifier for controlling a current source to maintain the bridge in a balanced condition. Changes in current supplied to the bridge circuit are detected and applied to a second differential amplifier having an exhalation signal output corresponding in time and magnitude with the quantity of air being exhaled by a patient being monitored. An automatic calibration system is provided to control the zero level of the exhalation signal and such system includes a feedback circuit connected between the signal output and input terminals of the differential amplifier so that manual calibration is unecessary for overcoming small variations in ambient conditions.

Claims

1. An improved respiration ventilation monitor comprising transducer means for generating an output signal in response to the exhalation of air by a patient during successive breathing cycles, wherein said transducer means comprises a resistance bridge circuit having a thermistor connected therein for mounting in a passage receiving air exhaled by the patient, controlled current source means having inputs coupled to the output of said bridge circuit, and having a first output coupled to said bridge circuit to balance the current applied to said thermistor, said controlled current source means including a second output for producing a signal proportional to said balancing current, amplifier means for producing an exhalation signal comprising a differential amplifier having first and second inputs, wherein said second output of said controlled current source means is coupled to said first input of said differential amplifier, and wherein said amplifier means further comprises an emitter follower output amplifier connected to the output of said differential amplifier, means for automatically calibrating a zero level of said exhalation signal, said calibrating means including a feedback circuit coupled from the output of said emitter follower amplifier to the second input of said differential amplifier, and further comprising a Schmidt trigger circuit having an output, and having an input connected to the output of said emitter follower amplifier, wherein said feedback circuit includes an inverting amplifier, an input gate circuit coupled between said output of said emitter follower amplifier and an input of said inverting amplifier, sample and hold circuit means having an output coupled to said second input of said differential amplifier, an output gate circuit coupled between the output of said inverting amplifier and an input to said sample and hold circuit means, means connecting said input and output gates to the output of said Schmidt trigger circuit, wherein said input and output gate circuits are energized by said Schmidt trigger output to actuate said feedback circuit of said calibrating means during all portions of said breathing cycles except said exhalation portions.

2. An improved respiration ventilation monitor comprising transducer means for generating an electrical output signal in response to the exhalation of air by a patient during successive breathing cycles, differential amplifier means having first and second inputs and having its said first input coupled to the output of said transducer means for producing a signal which is proportional as a function of time to the quantity of air exhaled by the patient, and means for automatically calibrating a zero level of the exhalation signal from the amplifier means;

said calibrating means including Schmidt trigger circuit means having an output, and having an input coupled to the output of said differential amplifier for producing an output signal during the generation of said electrical output signal from said transducer means, an inverting amplifier, an input gate circuit coupled between said output of said amplifier means and an input of said inverting amplifier, sample and hold circuit means having an input, and having an output coupled to said second input of said differential amplifier means, an output gate circuit coupled between the output of said inverting amplifier and said input to said sample and hold circuit means, means connecting said input and output gates to the output of said Schmidt trigger means, wherein said input and output gate circuits are actuated by said Schmidt trigger means output signal to couple said inverting amplifier and sample and hold circuit means in a feedback path between said output and said sEcond input to said differential amplifier means for maintaining said amplifier means output at a zero level during all portions of said breathing cycles except said exhalation portions.