Respiratory nitric oxide meter

Details Respiratory nitric oxide meter Respiratory nitric oxide meter

2000-10-11

2003-09-02

Lewis, Aaron J. (Department: 3761)

Surgery

Respiratory method or device

Means for supplying respiratory gas under positive pressure

C128S200240, C128S200220, C128S204230, C128S205230

Reexamination Certificate

active

06612306

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to the detection of nitric oxide in a gaseous mixture and, more specifically, to the detection of nitric oxide in a flow pathway.
BACKGROUND OF THE INVENTION
Definition of Nitric Oxide
Nitric oxide, NO, is a colorless gas useful in the detection and treatment of a variety of medical conditions such as asthma. Nitric oxide, NO, should not be confused with nitrous oxide, N
2
O, or nitrogen dioxide, NO
2
. Nitrogen and oxygen also form other compounds, especially during combustion processes. These typically take the form of NO
x
where x represents an integer. These forms are generally referred to as NOX. Detection of nitric oxide, NO, is the primary focus of the present application. Nitric oxide has a variety of beneficial uses and detection of nitric oxide, especially in small concentrations, is necessary for the proper administration of nitric oxide and diagnosis of disease.
Use of Nitric Oxide in Treatment of Physiological Conditions
Nitric oxide is beneficial in both the treatment and diagnosis of asthma and other forms of lung disorders. Asthma is a chronic disease characterized by intermittent, reversible, widespread constriction of the airways of the lungs in response to any of a variety of stimuli that do not affect the normal lung. A variety of drugs are commonly used to treat asthma. It is known that inhalation of nitric oxide (NO) is therapeutically beneficial in the prevention and treatment of asthma attacks and other forms of bronchoconstriction, of acute respiratory failure, or of reversible pulmonary vasoconstriction as discussed in U.S. Pat. No. 5,873,359 to Zapol et al, incorporated herein by reference. U.S. Pat. Nos. 5,904,938 and 6,063,407, both to Zapol et al. and incorporated herein by reference, disclose the use of inhaled nitric oxide in the treatment of vascular thrombosis and retinosis. Typically, treatment utilizing nitric oxide includes the introduction of nitric oxide as a portion of the respiratory gases being inhaled by the patient. The nitric oxide concentration is usually in the range of 1 to 180 parts per million (ppm). The difficulty presented in the administration of controlled amounts of nitric oxide is the determination of the concentration being introduced. It has traditionally been very difficult to quickly and accurately determine the concentration of nitric oxide in the gas mixture, especially where the concentration of nitric oxide is very low.
U.S. Pat. No. 5,839,433 to Higenbottam, incorporated herein by reference, describes the use of nitric oxide in the treatment of certain lung diseases and conditions. As discussed in the specification, a drawback to the administration of gaseous nitric oxide is that it rapidly converts to nitrogen dioxide, a potentially harmful substance. Consequently, it is often preferable to intubate the patient so that nitric oxide is administered directly to the lungs. Whether or not intubated, it is very important to accurately monitor the amount of nitric oxide being introduced to the lungs. The Higenbottam reference proposes an improvement wherein the nitric oxide is introduced as a short pulse of known volume, rather than continuously during inhalation.
U.S. Pat. No. 5,531,218 to Krebs, incorporated herein by reference, discusses the benefits of nitric oxide inhalation in the treatment of various disorders, including adult respiratory distress syndrome, (ARDS). The specification discloses a system for administering nitric oxide that includes a source of nitric oxide, an analyzer for analyzing nitric oxide concentration, and a control unit, with the analyzer and the control unit cooperating to maintain the appropriate nitric oxide concentration. However, this system relies on the use of nitric oxide sensors utilizing infrared absorption measurement, electrochemical sensors, or chemiluminescence detectors. Each of these analyzers have drawbacks and cannot provide instantaneous nitric oxide concentration measurements.
Use of Nitric Oxide in Diagnosis
Nitric oxide may also be used in the diagnosis of various physiological conditions. For example, the reversibility of chronic pulmonary vasorestriction may be diagnosed by administering known quantities of nitric oxide and monitoring changes in pulmonary arterial pressure (PAP) and cardiac output as described in U.S. Pat. No. 5,873,359 to Zapol et al.
Endogenous production of nitric oxide in the human airway has been shown to be increased in patients with asthma and other inflammatory lung diseases. Expired nitric oxide concentrations are also elevated in patients with reactive airways disease. Therefore, detection of nitric oxide is beneficial in diagnosing these conditions. However, proper diagnosis requires accurate measurement of nitric oxide in parts per billion (ppb) of gas-phase nitric oxide.
Determination of the level of nitric oxide is useful in the diagnosis of inflammatory conditions of the airways, such as allergic asthma and rhinitis, in respiratory tract infections in humans and Kartagener's syndrome. It also has been noted that the level of nitric oxide in the exhalation of smokers is decreased. U.S. Pat. No. 5,922,610 to Alving et al., incorporated herein by reference, discusses the detection of nitric oxide in diagnosing these conditions, as well as gastric disturbances.
In addition to the above, nitric oxide may be used in the determination of lung function. For example, U.S. Pat. No. 5,447,165 to Gustafsson, incorporated herein by reference, explains that nitric oxide in exhalation air is indicative of lung condition. As one test of lung function, a subject may inhale a trace gas, such as nitric oxide. Then the concentration and time-dispersment of the gas in the exhalation air is measured. The shape of the curve representing the time dependent gas concentration in the exhalation air is indicative of lung function or condition. Obviously, it is necessary to have an accurate determination of both the concentration and the time-dependence of the concentration to allow for the most accurate diagnosis.
During exhalation, gas mixture changes during the breath. The initial portion of the exhalation is “dead space” air that has not entered the lungs. This includes the respiratory gases in the mouth and respiratory passages above the lungs. Also, some portion of the exhalation measured by an analytical instrument may be attributed to dead air in the mask and flow passages of the apparatus. As a breath continues, respiratory gases from within the lungs are exhaled. The last portion of respiratory gases exhaled is considered alveolar air. Often it is beneficial to measure gas concentrations in alveolar air to determine various pulmonary parameters. For example, nitric oxide, as an indicator of various disease states, may be concentrated in the alveolar air. However, nitric oxide is also produced by various mucus membranes and therefore nitric oxide may be present in both the dead air space and in the alveolar air. During an exhalation, the dead air space may be overly contaminated with nitric oxide due to residence in the mouth and nasal cavities where nitric oxide is absorbed from the mucus membranes. Therefore, it is necessary to distinguish the various portions of exhalation for proper diagnosis. U.S. Pat. No. 6,038,913 to Gustafsson et al., incorporated herein by reference, discusses having an exhalation occur with very little resistance during an initial “dead space” phase of exhalation and then creating resistance against the remaining portion of the exhalation.
Nitric Oxide Measurement Methods
Numerous approaches have been used and proposed for monitoring the concentration of nitric oxide in a gas mixture. These include mass spectroscopy, electrochemical analysis, calorimetric analysis, chemiluminescence analysis, and piezoelectric resonance techniques. Each of these approaches have shortcomings that make them poorly suited to widespread use in the diagnosis and treatment of disease.
Mass spectroscopy utilizes a mass spectrometer to identify particles present in a substance. The

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