Measuring and testing – Gas content of a liquid or a solid – By vibration
Reexamination Certificate
2002-03-26
2002-10-01
Williams, Hezron (Department: 2856)
Measuring and testing
Gas content of a liquid or a solid
By vibration
C073S019100, C073S589000, C422S068100, C128S916000, C128S126100
Reexamination Certificate
active
06457346
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to apparatus and methods for measuring bubbles in fluids and tissues and, more specifically, to apparatus and methods for detecting, sizing, and counting gaseous emboli in a non-invasive manner.
2. Description of Prior Art
In-vivo measurement of the size and number of bubbles in fluids and tissues may be used to prevent, diagnose, and/or treat many potentially serious medical conditions such as, for example only, decompression sickness or stroke following cardiopulmonary bypass procedures. In-vitro or out of the body measurement of bubbles is also useful in connection with medical equipment that involves the flow of fluids into or out of the body. Emboli of various types may occur in the body for many medical reasons. Detecting and/or distinguishing gaseous emboli from other types of emboli is highly desirable so that appropriate medical management decisions can be made. Emboli may consist of formed elements such as blood clots, platelet aggregates, or other particulate Smatter such as pieces of atherosclerotic plaque or fat. Emboli may also consist of gas bubbles introduced to the blood vessels through injection, surgical techniques, cavitation at prosthetic valves, or decompression or compression to lower or higher atmospheric pressures.
In-vivo measurements of bubbles are especially useful with respect to decompression sickness. Decompression sickness poses a risk of serious injury or death to aviators, astronauts, divers, and others who are exposed to varying environmental pressure conditions. NASA, Air Force, Navy, and civilian personnel rely on pressure suits, controlled breathing mixtures, and operating procedures to maintain “acceptable” environmental conditions to prevent decompression sickness. These “acceptable” conditions are determined empirically, based on experimental observations of decompression sickness and its precursors. The symptoms of decompression sickness are attributed to the presence of gas bubbles, comprised mostly of nitrogen, in vascular and extravascular tissue. In vascular tissue, these bubbles can lodge or embolize in vessels in the pulmonary or systemic circulation systems, resulting in a range of pathology which is included in decompression sickness. These bubbles are formed due to local supersaturation of nitrogen upon reduction of ambient pressure or possibly upon warming from a hypothermic condition. The formation of bubbles and the onset of decompression sickness, which do not necessarily coincide, are highly variable and depend on a large range of factors including duration and magnitude of ambient pressure excursions, exercise, hydration, rate of change of pressure, hypoxia, temperature, age, infection, fitness, fatigue, previous injury, sex, and body fat.
In addition to decompression sickness, embolic events associated with the use of cardiopulmonary bypasses have been a serious concern. There are an estimated 700,000 cardiopulmonary bypass procedures performed annually in the U.S. In prospective studies of postoperative neurological dysfunction following cardiopulmonary bypass, the incidence rate is as high as 30% to 60%. The incidence of stroke following cardiopulmonary bypass is 1% to 5%. It is generally accepted that these effects are a consequence of microembolism, and/or compromise of cerebral blood flow. Emboli associated with cardiopulmonary bypass can be comprised of biological material, such as oxygen or nitrogen. The source of blood cell aggregates and thrombi is typically an activation of the thrombogenic cascade by blood interaction with a foreign surface, or they may be introduced with transfused blood. The sources of gaseous emboli include the blood oxygenation system and cavitation in the pumping systems.
Another major source of gaseous emboli is so-called “surgical air”, which can be introduced during cardiotomy for procedures like valvular and septal repair in the heart. These bubbles are of particular concern, because they contain air (primarily nitrogen) and are much less soluble in blood and tissue than oxygen bubbles. “Surgical air” has also been associated with neurological dysfunction in major organ transplant surgeries, such as liver transplants.
Gaseous emboli can also be generated in the body as a result of cavitation associated with artificial heart valves. These devices also potentially create thrombotic emboli, and as a result there is a need for instrumentation which can distinguish between the two types of events to aid device development and to aid diagnosis.
An improved ability to monitor for vascular and extravascular bubbles would have a significant impact on the ability to prevent and minimize decompression sickness and embolic pathology. In particular, better data on the early occurrence of bubbles, their size, and their composition (gaseous
on-gaseous) will permit less restrictive operational and design criteria to be developed for the prevention of decompression sickness in astronauts, aviators, and divers by permitting direct observation of the important variable of bubble size during decompression events. Direct monitoring of operational personnel in high risk decompression sickness circumstances would provide a quantitative indication to provide much more accuracy as to their proximity to the onset of symptomatic decompression sickness.
Improved monitoring would aid in therapy, recovery, and survival of patients being treated for decompression sickness and gaseous embolism by providing the first quantitative information about the size of the bubbles which are giving rise to their pathology. It would be highly desirable to provide for direct monitoring of the presence and size of gaseous bubbles such as gaseous emboli during and after surgical procedures with high likelihood of emboli introduction, such as cardiopulmonary bypass, with the goal being a subsequent decrease in the rate of embolic complications.
More generally, improved monitoring would provide clinicians with early warning of the introduction, size, and composition of emboli, allowing for better informed therapeutic approaches to be used. As well, biomedical researchers would have an improved ability to classify and quantify emboli produced by artificial heart valves and cardiopulmonary bypass machines.
To date, the detection of emboli, both gaseous and non-gaseous, has been largely accomplished through the use of Doppler ultrasound. This technique tells the observer whether there are bubbles or emboli present and provides an indication as to how many are present based on the rate of detection. The Doppler technique is only able to detect emboli flowing with sufficient speed in large vessels, when the direction of motion of the flow and the orientation of the acoustic beam are in a restrictive range. Doppler techniques have virtually no ability to quantify the size of the bubbles, observe bubbles in non-vascular tissue or in slow flowing microvessels, and have limited usefulness in classifying emboli as gaseous or non-gaseous. These are serious limitations with regard to detection and classification of: (1) decompression sickness precursor bubbles, (2) emboli during surgical procedures, and (3) emboli generated by artificial heart valves.
The following patents disclose attempts to solve the above discussed difficult problems and related problems over the last two decades.
U.S. Pat. No. 5,441,051, issued Aug. 15, 1995, to Hileman et al., discloses a method and apparatus for ultrasonically detecting an embolus in blood flow, including an ultrasound transducer for transmitting ultrasound pulses into the blood flow being interrogated and receiving reflections from acoustic impedance changes in the body. The reflected signals are converted to an electronic signal representation which is subsequently processed to detect and classify emboli in the blood flow. A short duration, broad bandwidth ultrasound signal is used to preserve the polarity of the reflected signal. The polarity is then used to classify the emboli based on a positive or negative reflect
Kline-Schoder Robert
Magari Patrick J.
Cate James M.
The United States of America as represented by the Administrator
Wiggins David J.
Williams Hezron
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