Surgery – Diagnostic testing – Respiratory
Reexamination Certificate
2001-09-10
2004-04-20
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
Respiratory
Reexamination Certificate
active
06723055
ABSTRACT:
BACKGROUND OF THE INVENTION
Information regarding respiratory function of a living organism is important in the field of medicine. Respiratory function provides a measure of how efficiently air is moved through the respiratory system, and thus provides important clinical information for the diagnosis and treatment of many respiratory conditions and diseases. Some examples of these conditions are chronic obstructive pulmonary disease (COPD), asthma, and emphysema. In addition, respiratory function measurements allow medical practitioners to observe effects of a bronchodilator or long-term treatments for COPD, or conversely, the airway responses to a bronchoconstrictor challenge for assessment of airway reactivity.
Respiratory function testing includes mechanical function tests which typically compare the effort or driving pressure put forth by the organisms to some quantifiable outcome, such as the output of flow or minute ventilation. Lung function tests differ based on how these inputs and outputs are assessed. Examples of inputs to the respiratory system that are measured, include diaphragmatic electromyographic activity, changes in thoracic esophageal pressure or pleural pressure, changes in airway pressures in ventilated subjects, or noninvasive measures of drive including respiratory inductance plethysmography or impedance plethysmography, and whole body plethysmography. Examples of output measurements include flow, tidal volume, or ventilation measurements using devices that collect: flow at the airway opening. In general, the mechanical function of the respiratory system is best described by combining some measure of drive with output. Variables such as resistance and compliance can then be derived to assess the level of airway obstruction or loss of lung elasticity, respectively. This is the basis for classical physiologic modeling of the respiratory system: the comparison of transpulmonary pressure changes with flow or tidal volume, carefully assessed in the same time domain with avoidance of phase lag between signals.
Classical physiologic modeling measures total pulmonary resistance, dynamic compliance and related variables. However, the classical physiologic modeling relies on the invasive passage of an esophageal balloon for example, for measuring driving pressure, and flow as a measure of output. An esophageal balloon catheter is positioned in the midthoracic esophagus. Thus, classical physiologic measures are not used because of the invasive nature of the esophageal balloon catheter and the difficulty in calibrating the classical system under field conditions.
Lung function tests have evolved with respect to the sensors, recording devices, and analysis techniques used to evaluate input and output. However, a need still exists for the noninvasive determination of lung mechanical function and monitoring in human and animal subjects for clinical and research purposes. In this respect, a number of technologies to measure drive, mentioned above, are available. Devices such as single and double plethysmographs are used to measure drive. In the double chamber plethysmograph, thoracic and nasal flows are recorded as separate signals, whereas in barometric plethysmography, a single signal is recorded that is the net signal from the thoracic and nasal components. The latter is achieved simply on the basis that animals breathe inside a box where pressure changes are the net effects of both components. The aforementioned plethysmographic techniques, due to their size and complexity, preclude their use as a portable field test. In addition, these techniques enclose the subject, which is objectionable to both humans and animals.
Extending lung function tests to animals has been difficult because technological limitations prevent restraining a conscious animal for prolonged periods of time in devices or chambers such as, without limitations in plethysmograph chambers. As a result, most lung function studies to date have been limited to animals which are typically anesthetized or conscious animals that provide data with artifacts such as motion artifacts.
Significant challenges remain in conducting lung function tests in conscious animals. The respiratory system of conscious animals, such as canines, is evaluated by physical examination, x-rays, endoscopy, cytology, arterial blood gases, capnography and oximetry. Fluoroscopy can also be used for imaging the respiratory system in small animals, but only if they are sufficiently sedated. Simple measurements of spirometry using a facemask have been conducted in small animals that provide measurements of flow, tidal volume, minute ventilation, and respiratory frequency. These measurements are generally not useful beyond clinical impressions. None of these currently used methods address the mechanical function of the lungs. At best, the current methods determine tidal volume, airflow resistance, lung elasticity, and diffusion characteristics. Some of these characteristics can be inferred indirectly such as, for example, lung volume using an x-ray, and diffusion based on arterial blood gases or capnography, but are typically inaccurate measures.
A need still exists for improved systems and methods which provide for measuring respiratory function for health care practitioners, are portable and which are non-invasive to the living organisms. Further, there is still a need for pulmonary function testing devices for conscious animals.
SUMMARY OF THE INVENTION
The present invention relates to a system for measuring respiratory function of living organisms such as measuring airway obstruction, airway reactivity and changes in lung volume. In a preferred embodiment, the system for measuring respiratory function includes measuring gas compression or expansion which is the difference between the effort (defined herein as having active and passive work components and change in lung volume) required to breathe and airflow, by the combination of external sensors and direct measures of true flow. A preferred embodiment of the system of the present invention uses a direct comparison of an external flow signal (EFS) indicative of effort required to breathe which includes both an active work component and a passive work component indicative of the passive recoil of the lung, diaphragm and chest wall during exhalation, and the uncompressed flow, preferably in the same time domain, thereby permitting real time analysis using a plurality of measured variables to assess respiratory function. The apparatus and methods of the present invention provide non-invasive measures of airway obstruction or respiration restriction in the subjects.
The present invention is important for patients/subjects with known clinical obstructions. Response to treatments such as bronchodilators can be monitored and assessed to measure improvements using the present invention.
In addition, it is important to measure respiratory function in subjects who have a subclinical form of an airway obstruction, i.e., the subjects who do not normally display the clinical symptoms associated with airway obstructions. The present invention provides diagnosis of subclinical progressive or episodic conditions by testing the airway reactivity of the subjects. This is accomplished by provoking an obstruction of the airways by challenging the airways with a chemical such as a histamine, for example, and using the present invention to measure changes in the respiratory function of the subject.
According to one aspect of the present invention, the methods for measuring respiratory function of the present invention include the steps of obtaining a signal indicative of the effort required to breathe by the living organism, obtaining a signal indicative of uncompressed airflow through the respiratory system of the subject as measured at the airway opening, processing the signals indicative of effort and flow by comparing the signals dynamically in the same time domain to detect transient periods of gas compression or expansion that signify airway obstruction and to provide a signal indicative of the
Bowditch & Dewey LLP
Nasser Robert L.
Trustees of Tufts College
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