Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
2000-08-07
2002-12-24
Winakur, Eric F. (Department: 3736)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
C600S322000, C600S323000
Reexamination Certificate
active
06498942
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for non-invasive, real-time, continuous and/or discretely monitoring of cerebral venous oxygenation and a method for continuously and/or discretely monitoring tissue oxygenation including venous oxygenation.
More particularly, the present invention relates to an optoacoustic apparatus including one or more nanosecond pulsed laser, a probe including a sensitive acoustic transducer located in a head of the probe, a fiber-optic delivery system connected to each laser and terminating in the head of the probe, and hardware and software for converting a received acoustic signal into a measure of tissue oxygenation including cerebral venous oxygenation. The present invention also relates to methods for monitoring tissue oxygenation and for making the apparatus of this invention. The present invention is especially well suited for non-invasive monitoring of tissue sites that otherwise would be hard to monitor even with invasive monitoring apparatuses and methods.
2. Description of the Related Art
Clinical Cerebral Oxygenation Monitoring
Over the past fifteen years, compelling clinical evidence has accumulated to suggest that monitoring cerebral oxygenation can detect otherwise unrecognized cerebral ischemia and be used to guide therapeutic interventions. Although randomized clinical trials do not yet demonstrate that interventions based on cerebral oxygenation monitoring can influence outcome, abundant evidence illustrates the association between cerebral hypoxia and worse outcome in such diverse situations as traumatic brain injury and cardiac surgery using cardiopulmonary bypass. In such situations, unlike circumstances in healthy humans, the adequacy of cerebral oxygen delivery (the product of cerebral blood flow and arterial oxygen content) cannot be inferred from measurements of systemic blood pressure and arterial oxygenation because cerebral blood flow is inadequate to satisfy cerebral metabolic demand. To date, the two primary methods used to monitor brain oxygenation are invasive—one requires percutaneous insertion of a catheter into the jugular bulb to continuously measure cerebral venous oxygenation and the other requires insertion of a probe through the skull into the brain parenchyma to measure tissue PO
2
. Jugular venous bulb monitoring is based on the following equation:
CjvO
2
=CaO
2
−CMRO
2
/CBF (1)
where CjvO
2
represents jugular venous bulb oxygenation content; CaO
2
represents arterial oxygen content; CMRO
2
represents the cerebral metabolic rate for oxygen; and CBF represents cerebral blood flow [1]. Because oxygen content is linearly related to hemoglobin oxygen saturation at a constant hemoglobin concentration, SjvO
2
can be measured or monitored as a surrogate for jugular venous oxygen content.
Jugular venous monitoring provides a global assessment of brain oxygenation, but requires frequent recalibration and is invasive, thereby both introducing the complications of catheter insertion and also delaying the initiation of brain oxygenation monitoring until a patient has been acutely stabilized. Nevertheless, jugular venous bulb measurements have been used in extensive clinical investigations in head-injured patients [2-9] and during cardiac surgery [10-16] and have proven clinically useful in patients who have traumatic brain injury [4, 6] and in patients undergoing cardiopulmonary bypass [10, 17].
Most importantly, single episodes ofjugular venous desaturation have been associated with worse outcome after traumatic brain injury [6] and jugular venous desaturation during rewarming after hypothermic cardiopulmonary bypass has been associated with worse cognitive performance after cardiopulmonary bypass [18]. Clinical protocols have been developed that initiate interventions such as changing blood pressure or PaCO2 in response to decreasing SjvO
2
[4, 6].
More recently, brain tissue PO
2
monitoring has been introduced for the management of patients with traumatic brain injury [19]. In patients with traumatic brain injury, brain tissue PO
2
correlates highly with outcome [19]. However, although brain tissue PO
2
monitoring provides a precise regional measurement of tissue oxygenation, it provides no information about inadequate tissue oxygenation in remote sites.
Optical Monitoring of Cerebral Blood Oxygenation
Near-infrared spectroscopy, a third, noninvasive method of monitoring cerebral blood oxygenation, utilizes differences in optical absorption coefficients of oxy- and deoxyhemoglobin [20, 21]. Two wavelengths of the NIR spectral range are usually used in the optical oximeters. One wavelength is shorter and the other is longer than 805 nm (isosbestic point). The technique is promising, but has yet to be satisfactorily calibrated to provide quantitative measurement of cerebral venous oxygenation [22, 23] at least in part because techniques have not been devised to distinguish venous from arterial blood [24].
Moreover, unlike the remarkable success of pulse oximetry for monitoring of systemic arterial hemoglobin saturation, the development of near-infrared monitoring of brain oxygenation has been slowed by the difficulty posed by measuring or estimating the pathlength of scattered light through biologic media [25]. Strong light scattering in tissues presents a great obstacle to quantitative measurement of cerebral blood oxygenation.
Encouraging reports of the use of near-infrared spectroscopy during carotid endarterectomy [26] and cardiac surgery [27] must be balanced against the fact that current technology is qualitative and can be used only as a trend monitor rather than as accurate measurement technique. As a consequence, the technique has yet to be incorporated into routine clinical practice. However, the technology continues to improve as investigators continue to develop more accurate methods of quantifying the signal [28, 29A].
Recently, the method of near-infra-red spectroscopy at two wavelengths coinciding with maxima of oxy and deoxy hemoglobin in microcirculation network of tumors, angiogenesis, was shown useful in differentiating malignant and benign tumors [29B]. However, resolution of pure optical imaging method is insufficient to determine exact dimensions, shape and location of tumors.
Therefore, despite major advances in understanding the physiology of the blood circulation in patients, including patients at high risk for neurologic injury, clinical monitoring of tissue oxygenation including brain oxygenation remains invasive and relatively expensive. Moreover, these procedures generally cannot easily be initiated until a patient is stabilized or until diagnostic tests such as computed tomography or magnetic resonance imaging are completed. Furthermore, these procedures often cannot be initiated until the patient is transferred to the operating suite or intensive care unit. Thus, there is a need in the art for a non-invasive, real-time, continuous and/or discrete monitoring of tissue oxygenation including cerebral venous oxygenation.
SUMMARY OF THE INVENTION
The present invention provides an optoacoustic apparatus including one or more short duration pulsed lasers (preferably the duration is in the nanosecond or shorter duration) and a fiber-optic delivery system including a plurality of optical fibers, where the fibers, at their proximal ends, are optically connected to an output of the laser(s) and terminate in a distal face of an irradiation probe. The apparatus also includes an acoustic probe having a pressure sensing device such as a piezoelectric transducer mounted in a distal face of the acoustic probe. The transducer is connected via a cable which exits from a proximal end of the acoustic probe to a processing unit that converts a transducer output signal into a measure of blood oxygenation of a target tissue. The output signal c
Esenaliev Rinat O.
Motamedi Massoud
Oraevsky Alexander A.
Prough Donald S.
Kremer Matthew
Strozier Robert W.
The University of Texas System
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