Methods and devices for sensing respiration and providing ventilation therapy

This application claims priority to U.S. Provisional Patent Application Ser. No. 60/924,514, filed May 18, 2007, the disclosure of which is hereby incorporated by reference in its entirety. This application further incorporates by reference in their entireties: U.S. Non-Provisional patent application Ser. No. 10/771,803 (U.S. Printed Publication 2005/0034721), filed Feb. 4, 2004, U.S. Non-Provisional patent application Ser. No. 10/870,849 (U.S. Printed Publication 2005/0005936), filed Jun. 17, 2004, U.S. Non-Provisional patent application Ser. No. 11/523,519, filed Sep. 20, 2006 and U.S. Non-Provisional patent application Ser. No. 11/523,518, filed Sep. 20, 2006.

The present invention relates to ventilation therapy for persons suffering from respiratory impairment and breathing disorders, such as chronic obstructive pulmonary disease (COPD), pulmonary fibrosis, acute respiratory distress syndrome (ARDS), neuromuscular impairment, sleep apnea and/or other related conditions. More specifically, the present invention relates to accurately and reliably measuring a patient\'s respiratory pattern using breath sensing, including providing methods, systems and apparatus to protect breath sensors.

There are two general types of control systems for conventional ventilators. A first type is delivery of gas to a patient based on a frequency selected by the clinician. The frequency selected delivery is independent of patient activity. This control system is used when the patient is non-alert, sedated, unresponsive or paralyzed. In this type of system the ventilator is breathing for the patient. A second type of control system is delivery of gas to the patient in response to an inspiratory effort created by the patient. This type of ventilation helps the patient breathe. There are also ventilators and modes of ventilation that combine the two types of control systems.

In the case of a control system that responds to patient breathing effort, breath effort sensors are required to detect inspiration. In basic conventional systems, the breath sensors detect the start of inspiration using a pressure or flow sensor. The inspiratory effort sensor is located somewhere in the path of ventilation gas delivered by a ventilation gas delivery circuit. A ventilation gas delivery circuit is generally defined as the path of respiration gas delivered by a ventilator. The inspiratory effort sensor may be either inside the ventilator, or in the tubing between the ventilator and the patient, including at the patient end of the tubing. Various attempts have been made to place the inspiratory effort sensor(s) inside the patient, or externally attached to the patient to improve breath effort detection and/or improve response time of the ventilator gas delivery.

Pressure or flow sensors within the ventilation gas delivery circuit have successfully been used to detect the start of inspiration to trigger the ventilator to deliver gas to the patient. However, when there is a need or desire to measure the entire respiratory curve in addition to start of inspiration, sensors within the ventilation gas delivery circuit produce inadequate results because the gas being delivered by the ventilator also moves past the sensor. Thus, the sensor no longer measures the patient\'s respiration, but rather the gas delivered through the ventilation gas circuit. In a closed ventilation system, the ventilator activity approximates the overall lung activity, hence this positioning of sensors may be adequate. In an open ventilation system, or in ventilation systems that augment a patient\'s spontaneous breathing, sensors within the ventilation gas delivery circuit are inadequate in measuring the entire respiratory curve.

Sensors not within the ventilator gas delivery circuit have the ability to measure the entire respiration activity. For example, chest impedance sensors can be used to measure the entire respiratory curve of a patient and to use that signal to control the ventilator and synchronize the ventilator to the patient\'s breathing. Although an improvement, this approach has the disadvantage that the chest impedance signal is prone to drift, noise and artifacts caused by patient motion and abdominal movement. In another technology, neural activity related to the respiratory drive is used to measure the respiration of a patient. However, this has the disadvantage that it is invasive and requires electrodes typically placed in the esophagus to detect the neural activity.

U.S. Non-Provisional patent application Ser. No. 10/870,849 (U.S. Printed Publication 2005/0034721), which is incorporated by reference in its entirety above, describes a new form of breath sensing with sensors not within a ventilation gas delivery circuit. The sensors may be located in the airway of a patient, for example, in the patient\'s trachea, but not within the ventilation gas delivery circuit. In this manner, the gas delivery from the ventilator may not dominate the sensor measurements. This intra-airway sensor may measure naturally inspired gas flow of the patient, naturally exhaled gas flow of the patient, and the effect of the ventilator gas delivery on lung volumes. The sensor may not measure gas flowing in the ventilator delivery circuit as in conventional systems. This breath sensing method may then measure, not just the start of inspiration, but the entire respiratory pattern of the patient. This may be advantageous to optimize the synchrony of the ventilator to the patient\'s natural breath pattern, so that the patient is comfortable. Also, if the goal is to provide therapy during different portions of the respiratory curve, such as during the middle of inspiration, or during a particular part of the expiratory phase, then this method may be used to accurately measure the entire respiratory curve. This new breath sensing technology, however, may not be simple or obvious to reduce to practice. Sensors within the airway of the patient are prone to problems stemming from tissue interaction, patient-to-patient variability, variability within a given patient over time, and a variable physiological environment that can not be controlled. For example, debris in the airway may collect on the sensors and may cause signal artifacts and disrupt the sensors\' ability to accurately and reliably measure the entire breath curve. Or, the sensor could come into contact with the tracheal wall, which may disrupt the sensors\' signal. Alternatively, tracheal movement during breathing can affect the signal.

Need exists for improved breath sensing systems and methods for ensuring reliable and accurate breath measurements.

The present invention may be directed to methods and systems for intra-airway breath sensors, especially those sensors not within a ventilation gas delivery circuit, but exposed to a patient\'s spontaneous respiration airflow. The present invention is an improvement over existing breath sensing techniques. Further, apparatus and methods for shielding and protecting the intra-airway sensors from disruptions such as contacting tissue or accumulating debris are provided.

One aspect of the invention is directed to a breath sensing and ventilation delivery apparatus comprising: a catheter, one or more intra-airway breath sensors coupled to an outer surface of the catheter, and an airflow permeable protector with a proximal end adapted to be positioned outside a patient and a distal end adapted to be placed in an airway of the patient, wherein the airflow permeable protector at least partially surrounds the catheter such that the airflow permeable protector prevents the one or more intra-airway breath sensors from contacting a tissue and reduces accumulation of debris on the one or more intra-airway breath sensors. The airflow permeable protector may be a tracheostomy tube cannula. The cannula may have one or more fenestrations. The cannula may at least partially surround the catheter forming an annular space between the cannula and the catheter. The airflow permeable protector may be a protective shield. The protective shield may be selected from the group consisting of a shield tapered on at least one end, a shield collapsible against an outer surface of the ventilation catheter, stoma sleeve, and combinations thereof. The one or more intra-airway breath sensors may be selected from the group consisting of thermal sensors, pressure sensors, pressure sensing lumen, gas composition sensors, flow sensors, ultrasonic sensors, resistivity sensors, piezoelectric sensors, light emittance/reflectance sensors, and combinations thereof.

Another aspect of the invention is directed to a breath sensing and ventilation delivery apparatus comprising: a ventilation catheter, a tracheostomy tube cannula with one or more fenestrations, wherein the cannula at least partially surrounds the ventilation catheter to create an annular space between an inner diameter of the cannula and an outer diameter of the ventilation catheter, and one or more intra-airway breath sensors within the annular space between an inner diameter of the cannula and an outer diameter of the ventilation catheter. The ventilation catheter may extend beyond a distal portion of the cannula and into an airway. A positioner may be provided for positioning the ventilation catheter at a predetermined position within the cannula. The positioner may be a basket-type device. The positioner may be a deflector in a wall of the cannula. An anchor may be provided for preventing movement of a distal tip of the ventilation catheter. The one or more fenestrations may be located in a position selected from the group consisting of a superior side of the cannula, an inferior side of the cannula, a lateral side of the outer cannula, and combinations thereof. The one or more intra-airway breath sensors may be selected from the group consisting of thermal sensors, pressure sensors, pressure sensing lumen, tubes with sensing lumen, sensing subassemblies, gas composition sensors, flow sensors, ultrasonic sensors, resistivity sensors, piezoelectric sensors, light emittance/reflectance sensors, and combinations thereof. The one or more intra-airway breath sensors may be multiple elements placed in an array, wherein one element is used as a reference signal. The one or more intra-airway breath sensors may be coupled to the ventilation catheter. The one or more intra-airway breath sensors may be coupled to the cannula. The one or more intra-airway breath sensors may be de-coupled from the ventilation catheter and the cannula. The one or more intra-airway breath sensors may be a sensing lumen not in communication with a ventilation catheter gas delivery circuit, wherein the sensing lumen comprises a sensing element and a port positioned in the annular space and wherein the sensing element is located external to a body and communicating with the sensing lumen. The ventilation catheter may be removable from the cannula. A seal may be provided between the cannula and the ventilation catheter at a location proximal to the one or more intra-airway breath sensors. The ventilation catheter may comprise a moveable connection with the cannula.

Another aspect of the invention includes breath sensing and ventilation delivery apparatus comprising: (a) a tubular member with a proximal end and a distal end, wherein the proximal end is adapted to be positioned outside a patient and the distal end is adapted to be positioned in an airway of the patient, wherein the tubular member includes one or more fenestrations, wherein spontaneous respiration by a patient passes through the one or more fenestrations, (b) one or more intra-airway breath sensors within a lumen of the tubular member, wherein a distal end portion of the tubular member is positioned in the airway such that the one or more intra-airway breath sensors are located within the airway, and wherein the one or more intra-airway breath sensors are exposed to the spontaneous respiration by the patient while within the airway. The one or more fenestrations may be located in a position selected from the group consisting of a superior side of the tubular member, an inferior side of the tubular member, a lateral side of the tubular member, and combinations thereof. The one or more intra-airway breath sensors may be selected from the group consisting of thermal sensors, pressure sensors, pressure sensing lumen, tubes with sensing lumen, sensing subassemblies, gas composition sensors, flow sensors, ultrasonic sensors, resistivity sensors, piezoelectric sensors, light emittance/reflectance sensors, and combinations thereof.

Another aspect of the invention includes a breath sensing and ventilation delivery apparatus comprising: (a) a ventilation catheter for ventilation gas delivery including at least one breath sensing lumen including a breath sensing lumen port, (b) an airflow permeable protector at least partially surrounding a portion of the catheter to protect the at least one breath sensing lumen port, (c) a connection to connect the at least one breath sensing lumen to an external sensor, and further wherein the catheter is configured to be placed into an airway of the patient to position the at least one breath sensing lumen port and permeable protector in the airway, and wherein the at least on breath sensing lumen port is protected by the airflow permable protector but is exposed to spontaneous airflow in the airway. The airflow permeable protector may comprises one or more fenestrations, which are located in a position selected from the group consisting of a superior side of the airflow permeable protector, an inferior side of the airflow permeable protector, a lateral side of the airflow permeable protector, and combinations thereof. The external sensor is selected from the group consisting of thermal sensors, gas composition sensors, flow sensors, ultrasonic sensors, resistivity sensors, piezoelectric sensors, light emittance/reflectance sensors, and combinations thereof.

Another aspect of the invention includes a breath sensing and ventilation catheter apparatus comprising: a ventilation catheter for ventilation gas delivery, at least one breath sensing lumen port positioned on an outside surface of the ventilation catheter, an airflow permeable shield at least partially surrounding the at least one breath sensing lumen port, and wherein the airflow permeable shield prevents contact of the at least one breath sensing lumen port with tissue and reduces accumulation of debris on the at least one breath sensing lumen port. The airflow permeable shield may be a collapsible basket. The airflow permeable shield may be a cone tapering from a proximal end to a distal end, and wherein the cone further comprises one or more fenestrations. The airflow permeable shield may be a cuff. The airflow permeable shield may be a stoma sleeve. The airflow permeable shield may be collapsible against an outer surface of the ventilation catheter. The at least one breath sensing lumen port may be connected to a sensor external to a patient, the sensor selected from the group consisting of thermal sensors, pressure sensors, gas composition sensors, flow sensors, ultrasonic sensors, resistivity sensors, piezoelectric sensors, light emittance/reflectance sensors, and combinations thereof.

Another aspect of the invention includes a method for breath sensing and ventilation comprising: inserting at least one intra-airway breath sensor into a tubular guide positioned with a proximal end adapted to be outside of the patient and a distal end adapted to be inside an airway of a patient, wherein the at least one intra-airway breath sensor is not located within a ventilator gas flow, and wherein the at least one intra-airway breath sensor is shielded from contacting tissue and from accumulating debris by the tubular guide. The tubular guide may be a tracheostomy tube cannula. The cannula may at least partially surround a ventilation catheter for providing the ventilator gas flow, wherein the cannula forms an annular space between the cannula and the ventilation catheter. The at least one intra-airway breath sensor may be within the annular space. The cannula may have one or more fenestrations. The tubular guide may be a protective shield. The protective shield may be selected from the group consisting of a shield tapered on at least one end, a shield collapsible against an outer surface of the ventilation catheter, stoma sleeve, and combinations thereof. The at least one intra-airway breath sensor may be selected from the group consisting of thermal sensors, pressure sensors, pressure sensing lumen, gas composition sensors, flow sensors, ultrasonic sensors, resistivity sensors, piezoelectric sensors, light emittance/reflectance sensors, and combinations thereof.

Another aspect of the invention relates to a method for breath sensing and ventilation comprising: inserting at least one intra-airway breath sensor in a path of a patient\'s airway airflow, but not within a ventilation gas delivery circuit, monitoring the patient\'s airway airflow with the at least one intra-airway breath sensor, operating at least one ventilation gas sensor within a ventilation gas delivery circuit, and monitoring the ventilator gas delivery with the at least one ventilation gas sensor simultaneous with monitoring the patient\'s airway airflow with the at least one intra-airway breath sensor. The at least one intra-airway breath sensor may be coupled to a ventilation catheter. The at least one intra-airway breath sensor can be at least partially surrounded by a protector. The protector may be a tracheostomy tube cannula. The cannula may comprise one or more fenestrations. The protector may be an airflow permeable shield. The airflow permeable shield may be selected from the group consisting of a basket, a cone, a cuff, a grouping of wires or filaments, a shield tapered on at least one end, a shield collapsible against an outer surface of the ventilation catheter, stoma sleeve, and combinations thereof. The at least one intra-airway breath sensor may be selected from the group consisting of thermal sensors, pressure sensors, pressure sensing lumen, gas composition sensors, flow sensors, ultrasonic sensors, resistivity sensors, piezoelectric sensors, light emittance/reflectance sensors, and combinations thereof.

Another aspect of the invention relates to an apparatus for breath sensing and ventilation comprising: a ventilation catheter for supplying ventilation gas to a patient via a ventilation gas delivery channel in the catheter, a sensing conduit not in communication with the ventilation catheter gas delivery circuit, an opening in the sensing conduit for sensing respiration of the patient through the sensing conduit when the opening is positioned within an airway, and a sensing element communicating with the sensing conduit for sensing respiration of the patient, wherein the sensing element is located external to the patient, and a protector at least partially surrounding the ventilation catheter and sensing conduit opening. The protector may be a tracheostomy tube cannula. The cannula may comprise one or more fenestrations. The sensing element may be selected from the group consisting of: a pressure sensor, a flow sensor, a thermal sensor, or an ultrasonic sensor. The protector may be selected from the group consisting of a basket, a cone, a cuff, a grouping of wires or filaments, a shield tapered on at least one end, a shield collapsible against an outer surface of the ventilation catheter, stoma sleeve, and combinations thereof.