Inhalation detector

Abstract

A detector providing an electrical signal in response to the pressures encountered in sensing breath inhalation in respirators. The detector uses a capacitive pressure sensor formed by a flexible conductive diaphragm separated from fixed electrodes by a layer of dielectric film. Deflection of the diaphragm by pressure introduces a low permittivity space in the sensor resulting in a substantial change in capacitance. The change in capacitance modifies the frequency of an oscillator. A frequency responsive circuit provides balancing electrostatic force feedback voltage to the diaphragm. The force feedback stiffens the diaphragm and maintains it in a high capacitance, high sensitivity state. This feedback reduces sensitivity to changes in the diaphragm mechanical properties. Signal filtering reduces the effects of long term drift and environmental factors.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] Not Applicable FEDERALLY SPONSORED RESEARCH [0002] Not Applicable SEQUENCE LISTING OR PROGRAM [0003] Not Applicable FIELD OF THE INVENTION [0004] This invention relates to sensing the inhalation of breath in respirators and providing an electrical output to control the release of medication or gas in coordination with inhalation. BACKGROUND OF THE INVENTION [0005] The dispensing of medication via the respiratory system is receiving increasing use. Medications are commonly in the form of aerosols or powders obtained from pressurized containers or generated by atomizers. The dispensing methods used include patient operated hand-held respirators. To be effective the medication must be released in coordination with inhalation. Often the patient operates a control or actuator to release medication during inhalation. [0006] In cases where coordinating the release of medication with inhalation is difficult or must be precisely controlled, an i...

AI Technical Summary

Benefits of technology

"The invention is a device that can detect the breath of a patient through a respirator and generate an electrical output in response. This device is particularly useful for giving medication or gas to patients who have difficulty breathing. It uses special sensing methods and feedback techniques to be able to detect the low breath flow rates of children and disabled patients. The feedback technique also helps to tolerate the buildup of sputum and medication residue in the device."

Problems solved by technology

Methods using lasers, ultrasonic sound, rotary vanes, and spark ionization have all been used for this purpose but are too large, complex, or costly for this application and will not receive further discussion.

Such sensors are usually fragile and vulnerable to the required cleaning processes.

In addition, sensing the direction of flow with thermal devices requires significant complexity.

Optical sensing of motion can allow the use of a small light-weight flag; however the vulnerability to cleaning damage and the effects of backflow deposits deter the use of the method in tidal breathing applications.

Limiting the pressure drop through the sensor is a demanding requirement.

Their approach requires the added cost and complexity of a microprocessor and a stored look-up table that is custom tailored to each unit.

Negative (inhalation) pressures draw the diaphragm toward the spaced electrode resulting in an increase in capacitance.

Because of the low capacitance it is vulnerable to noise, drift caused by external capacitance changes, and temperature effects.

The flexibility of the plastic diaphragm can be degraded by deposits of backflow material, resulting in a loss of sensitivity.

The configuration of the Ball embodiment cannot be cleaned without disassembly.

The operation of prior art sensors at such low pressures results in excessive error and drift.

Such an offset provides an erroneous response.

Prior art contains cavities, small tabulations, and ports that create difficult to clean traps for deposits.

Prior art sensors either have sensitive elements that will be damaged by the forces of cleaning or do not provide a path for cleaning fluids to access all elements subject to contamination.

Prior art devices with sufficient sensitivity for use in a respirator require a sensing device size or configuration unsuited for hand-held use.

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