Control of respiratory oxygen delivery

Abstract

Methods and systems for supplying respiratory oxygen to users when the users are inhaling are disclosed. The methods and systems may rely on delivery devices that are selectively placed in fluid communication with either a respiration sensor or a source of oxygen. The methods and systems may actively monitor for exhalations, as well as monitor for oxygen in the oxygen source. The respiration sensor may preferably be a flow sensor.

Description

RELATED APPLICATIONS [0001] This is a continuation of U.S. patent application Ser. No. 10 / 695,436, filed 28 Oct. 2003, which is a continuation of U.S. patent application Ser. No. 10 / 370,799, filed 20 Feb. 2003, which is a continuation of U.S. patent application Ser. No. 10 / 076,001, filed 14 Feb. 2002, (issued as U.S. Pat. No. 6,561,187), which is a continuation of U.S. patent application Ser. No. 09 / 463,614, filed 25 Jan. 2000 (with a 35 U.S.C. §371 date of May 8, 2000, now issued as U.S. Pat. No. 6,371,114), which is a U.S. National Stage Application of PCT / US98 / 15490, filed 24 Jul. 1998, which claims priority to U.S. Provisional Patent Application Ser. No. 60 / 064,578, filed 4 Nov. 1997 and which also claims priority to (and is a continuation-in-part of) U.S. patent application Ser. No. 08 / 900,686 filed 25 Jul. 1997, (issued as U.S. Pat. No. 6,532,958). All of the above-identified patent applications are incorporated herein by reference in their respective entiretiesFIELD OF THE IN...

AI Technical Summary

Benefits of technology

[0014] The present invention provides respiratory oxygen supply methods and systems. In some aspects, the systems / methods rely on respiration sensors sensing variations in patient respiration to determine when a patient is inhaling and allow for the determination of an inhalation event after exhalation has been determined. In other aspects, the respiration sensors may be advantageously used to detect the presence of oxygen from the oxygen supply. In still other aspects, when the present invention uses a flow sensor as a respiration sensor, the system may automatically correct for variations in the signals provided by the flow sensor using a zero-flow offset signal, thereby improving the accuracy of the system.

[0019] In another aspect, the present invention provides a system for delivering respiratory oxygen to a patient including a delivery line adapted for connection to an oxygen delivery device located on a patient; a source line adapted for connection to an oxygen source; a respiration sensor; at least one valve in fluid communication with the delivery line, the source line and the respiration sensor; wherein the at least one valve places the delivery line in fluid communication with only one of the source line and the respiration sensor at any given time; means for monitoring the respiration sensor for variations in respiration of a patient; means for determining when the patient is inhaling and exhaling based on the monitoring of the respiration sensor; and means for preventing a determination that the patient is inhaling until after a determination that the patient has exhaled has been made.

Problems solved by technology

Continuous oxygen delivery in sub-critical and critical care is, however, wasteful because oxygen is only needed by patients when they are inhaling and the oxygen delivered at other times is wasted.

In supplemental oxygen delivery, the most significant financial cost associated with this waste is found in the increased service visits required by the oxygen provider to replenish the patient's oxygen supply, because the actual cost of the oxygen is only a small fraction of the total cost of the therapy.

It is, however, difficult (if not impossible) to accomplish both of those functions with a single flow sensor because the flow rates that need to be sensed differ by orders of magnitude.

One significant problem is in sensing inhalation or exhalation simultaneously with the delivery of oxygen in these situations.

In addition to the above-listed problems, even if the flow sensor has a dynamic range capable of sensing respiration and delivery oxygen, the systems do not allow for correction in the “drift” often associated with such sensors.

In other words, over time the accuracy of the sensor may be impaired because of dynamic changes in the flow sensor during use.

Because the flow sensors are always in use, monitoring either oxygen flow or respiration, adjustments are difficult if not impossible to make to correct for voltage drift.

One disadvantage to this approach is that if one side of the patient's nasal cavity is blocked due to an upper respiratory infection or cold, the system will either be unable to effectively deliver oxygen or sense respiration (depending on which port of the cannula is located on the blocked side).

Even if the patient is not experiencing blockage, it may be difficult for the sensor to detect exhalation if the patient is breathing through his or her mouth.

The nasal respiratory flow rate is significantly reduced in such patients, and if flow sensing is occurring only through one port in the cannula, it may be too low to be accurately detected.

Another disadvantage is that the system requires a more expensive and obscure dual-line cannula.

Regardless of whether pressure or flow sensors are used to detect respiration, shallow respiration can make respiration sensing in systems relying on pressure / flow sensors difficult or impossible because the flow volume and / or flow rate of gases associated with respiration deteriorate as the gases from inhalation or exhalation travel through the lines connecting the patient's respiratory system to the sensor.

The flow volume / rate deterioration caused by the lines further reduces the flow volume / rate produced by a patient engaging in shallow respiration.

As a result, the respiration sensor may be unable to detect respiration or may detect only a portion of the actual inhalation / exhalation events.

Another problem associated with patients experiencing rapid respiration rates is that some demand delivery systems include a time delay period to prevent sensing of the same inhalation period more than once.

Because the patient is, however, experiencing rapid respiration, the patient may actually inhale two or more times during the delay period.

In addition, if the respirations are rapid and the system delivers oxygen too slowly, the patient may already be exhaling by the time the system begins to deliver oxygen.

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