Minimally invasive system for assessment of organ function

Details Minimally invasive system for assessment of organ function Minimally invasive system for assessment of organ function

2000-12-13

2003-02-11

Freay, Charles G. (Department: 3736)

Surgery

Diagnostic testing

Measuring or detecting nonradioactive constituent of body...

C600S323000, C600S342000, C600S549000

Reexamination Certificate

active

06519485

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable.
BACKGROUND OF THE INVENTION
The present invention relates generally to the assessment of organ function and to the determination of critical events such as metabolic changes and pathologic responses that may occur within an organ. It is of particular utility for detecting adverse changes which generally become only slowly manifest in other anatomic systems such as blood chemistry, cardiovascular functioning or other indicators of health commonly monitored in a hospital setting.
For a critical care patient whose medical condition may change rapidly over time, constant monitoring of the body functions in real time is considered essential. Such assessment of patient condition is crucial in alerting a physician to potential problems. One serious and extremely dangerous but common problem is rapid blood loss that can induce shock. The onset of shock in critical care patients is swift, and may lead to death if not detected. Current monitoring techniques focus on vital signs such as heart rate or blood pressure, which may be inadequate to detect shock sufficiently early because these parameters do not change immediately upon onset of the underlying condition or provoking stimulus. A patient can lose ten percent or more of total blood volume before blood pressure is even affected.
Parameter changes within an organ such as the liver may be capable of providing a more immediate indication than is provided by circulating blood enzymes or other indicators, since the liver plays a key role in homeostasis. It is thus situated to provide more immediate indicia of critical changes. One might therefore hope that by monitoring parameter changes during hepatic shock, some parameters may be found to correlate with the onset of shock in a patient. If so, these might provide an early warning to allow appropriate intervention. Presently, however, liver condition is determined remotely and inferentially, primarily through blood analysis. Typically, liver function tests measure the ability of the liver to synthesize enough protein to regulate blood coagulation correctly. Although the results of such tests can be helpful, these assays generally involve a delay of hours between the onset of an adverse or trauma condition in the liver and the detection of its effects through blood analysis. After such a delay, the liver itself may already be damaged beyond repair. Thus, the development of a real-time monitoring system for the liver or other organ would greatly aid in the timely assessment of patient medical condition.
Accordingly, it is desirable to provide a method of assessing physiological organ parameters more directly.
It would also be desirable to provide a versatile and simple assay extendible to the detection of different critical parameters or conditions.
SUMMARY OF THE INVENTION
One or more of these and other desirable ends are achieved in accordance with the present invention by a system for assessing organ function wherein a plurality of light emitters of differing spectral characteristic are coupled into a fiber assembly including a percutaneous insertion and penetration body having at least one optical fiber signal guide. The percutaneous insertion body is adapted for insertion through a human body with at least its tip extending to or penetrating an internal organ so that it positions the fiber to illuminate organ tissue. A second (or the same) fiber catches light scattered, reflected or emitted by the surrounding tissue and returns a light signal to the proximal end of the device, where it is coupled to a detector. The device also senses temperature at the tip, either through an electrically connected sensing element such as a thermistor, or by a light-based technique such as infrared thermography, in which case one or more additional fibers adapted to carry a signal in the appropriate thermographic spectral region may be provided.
In a prototype embodiment, control and processing modules drive each of a plurality of laser diodes in succession to emit light in a plurality of different peak regions and at different times. This light is directed at organ tissue to interact therewith, and a detection fiber picks up and returns an interaction light signal for detection by a photo detector to determine the magnitude of each interaction signal. A beam splitter provides a portion of each of the emitted input signals as a reference signal to normalize the detected return values, which may, for example, correspond to the overall absorption in each band of specific substances selected in advance for their known occurrence during shock, or they may be simply spectral absorption values which are empirically determined to occur during organ failure, even if the specific absorbing substance remains unidentified.
In various embodiments, the instrument may assess general organ function or metabolic activity by detecting changes in light absorption attributable to one or more spectral bands characteristic of particular enzymes, proteins, metabolites or the like. In one prototype embodiment, absorption at a peak of deoxygenated hemoglobin and/or at one or more peaks of oxygenated hemoglobin may be monitored. Alternatively, relative absorption of signals on each side of a peak, or surrounding a specific wavelength, may be monitored as an indicator of organ change. Preferably a target pair of substances—biological molecules, enzymes or metabolites—are selected such that coordinated changes in different spectral regions characteristic of the pair of substances occur during shock. This allows the detection of simultaneous change in two or more distinct but associated spectral bands to be detected and more dependably correlated as an indicator of condition. The detection processing may include a time-varying detection protocol which may, for example enhance detection of a blood-flow related substance. In one embodiment, the device performs a relative discrimination of state by monitoring pulse oxygen saturation of hemoglobin in real time together with one or more other parameters such as temperature. A correlation of changes in the different monitored parameters then serves as a warning indicator of organ failure.
As applied to a prototype monitor embodiment for detecting change correlated to shock in the liver, a prototype for a body-insertable device employed four different laser diodes having peaks at 735, 760, 805 and 890 nm, and connected to a common optical fiber. The diodes were driven at output powers between about 50 to 100 mW to illuminate organ tissue, and a front-end splitter separated a portion of the beam as a reference beam that was directed to a photo detector to develop an input power signal used to normalize the level of the detection output from the return fiber. Suitable coupling for the input light signal may be obtained by collimating and focusing each diode output into a bundle whose output is then directed into the delivery fiber, or may be fabricated by fusing pairs of two hundred micrometer core diameter multimode fibers with an SMA connector as an end coupler. The return fiber for collecting an interaction signal consisting of the light collected from or through the organ tissue and returning it to the photo detector may have a collection face (such as a bevel) or a light-gathering pipe, oriented to avoid catching direct illumination. The photo detector may be a broad band detector useful over a range, for example, of 320 to 1100 nanometers. Preferably high sensitivity detectors with a detection threshold of a milliwatt or less are employed. In various embodiments, the system may be used in an absorbance, reflectance or fluorescence mode and may perform detection after filtering the input and/or return signal with one or more narrow band filters and/or band pass or cut-off filters to allow use of lesser quality light sources, or to tailor the applied or return narrow band probe wavelengths for detection of particular materials.
A physical implementation of the perc

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