Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/145—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue
  • A61B5/1455—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters
  • A61B5/14551—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters for measuring blood gases
  • A61B5/14552—Details of sensors specially adapted therefor
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
  • A61B5/024—Detecting, measuring or recording pulse rate or heart rate
  • A61B5/02416—Detecting, measuring or recording pulse rate or heart rate using photoplethysmograph signals, e.g. generated by infrared radiation
  • A61B5/02427—Details of sensor
  • A61B5/02433—Details of sensor for infrared radiation
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/145—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue
  • A61B5/1455—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters
  • A61B5/14551—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters for measuring blood gases
  • A61B5/14553—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters for measuring blood gases specially adapted for cerebral tissue
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/40—Detecting, measuring or recording for evaluating the nervous system
  • A61B5/4058—Detecting, measuring or recording for evaluating the nervous system for evaluating the central nervous system
  • A61B5/4064—Evaluating the brain

Definitions

• This invention relates generally to in vivo
• spectrophotometric methods and apparatus for examining and/or monitoring biological tissue, substances and/or conditions in living subjects, in particular humans.
• the invention relates to the novel application of such in vivo methods and apparatus to provide a new form of biomedical device for
• mammalian e.g. human subjects on an in vivo basis
• a specific and preferred embodiment of which comprises means for so-monitoring regional oxygen saturation in the brain, and for providing a quantitative readout thereof in terms familiar to medical practitioners, i.e., percent oxygen saturation.
• Spectrophotometry has, of course, long been used as a valuable investigative tool in various scientific fields, particularly biological and medical research, and various applications of the underlying principles
• N.I.R. selected wavelengths of light in the near infrared range
• spectrophotometry have for quite some time been utilized for certain in vivo procedures and/or investigation on human beings.
• a frequently-encountered such device is the pulse oximeter conventionally used in hospitals and other medical facilities to provide a direct indication of arterial oxygen saturation by means of a clip or the like which fastens to an appendage such as the ear or finger of the patient.
• Brain damage through injury or cerebral vascular disease is responsible for numerous deaths and serious illnesses each year, involving on the order of at least 100,000 surgical procedures annually in recent years. Brain vitality is primarily a function of oxidative metabolism, and the predominant cause of neurological dysfunction and
• malfunction relates to the lack of sufficient brain oxidation, typically as a result of obstruction or otherwise insufficient arterial blood flow to the brain.
• this can occur even during surgery, and it has been estimated that at least 2,000 patients die each year in the United States alone due to anesthetic accidents, while numerous other such incidents result in brain damage of some degree;
• certain major and complex surgical procedures particularly of a neurological, cardiac or vascular nature, may require induced low blood flow or pressure conditions, which inevitably involves the potential of insufficient oxygen delivery to the brain.
• the brain is the human organ which is most intolerant of oxygen deprivation, and brain cells will die within a few minutes if not sufficiently oxygenated. Moreover, such cells are not replaced, and thus involve irreversible brain damage which may potentially result in paralysis, disability, or even death.
• EEG electroencephalograph
• arterial pulse oximeter and blood pressure monitors etc.
• invasive catheter monitoring of blood oxygen content, acidity, etc. by penetration of the jugular bulb (jugular vein) do not provide accurate, ongoing, timely (instantaneous) information as to cerebral (brain) blood oxygenation state, particularly since the brain blood supply is extensive, diffuse, pervasive, and largely venous in nature rather then arterial.
• EEG electroencephalograph
• such devices are not appropriate for cerebral usage, and of course they are typically made to be applied only to peripheral tissue or appendages in any event, i.e., a finger or an ear lobe, and are not
• jugular bulb catheters are highly invasive and relatively traumatic; at the same time, they merely provide blood samples which are removed and analyzed in another
• the present invention provides a spectrophotometric cerebral
• oximeter which non-invasively and harmlessly provides accurate and continuous real-time information as to the oxygenation state of the human brain, on an in vivo basis, without attendant patient stress or discomfort of any nature. More broadly considered, the present
• the invention provides an in vivo, spectrophotometric cerebral oximeter which will non-invasively provide continuous monitoring of cerebral oxidation, and will do so in a form and format of a nature immediately understandable and familiar to physicians, i.e., percent oxygen saturation.
• the cerebral oximeter so provided operates by examining (sampling) the cerebral blood supply throughout the complete vascularization (arterial, venous, and capillary systems) within the area of investigation, and the particular region investigated is or may be selectively accessed in accordance with the invention, i.e., the tissue volume examined is regional in nature and of a generally predetermined extent and location, constituting less than the entire brain or other area.
• the apparatus and methodology in accordance with the invention includes the provision of a convenient and readily-usable sensor which may for example be used in a number of different locations, and/or moved from one location to another, for comparative consideration of the regions selectively accessed and examined, whether cranial or otherwise.
• the cerebral oximeter in accordance with the invention examines, and measures, blood oxygen saturation (and thus, oxidative metabolism) in the entire array of blood vessels present in the cranial region being monitored, which in the brain may generally be considered as comprising (by volume) approximately 75 percent venous, 20 percent arterial, and 5 percent capillary.
• the cerebral oximeter provided in accordance with the invention addresses not only oxygen delivery via hemoglobin molecules moved arterially, but in addition addresses the general, overall state of cerebral oxygen consumption, which is of course directly related to brain vitality and state, and indicative of continued viability.
• the invention provides such information on an instantaneous real-time basis, and as a result provides critical immediate information capable of clearly and quantitatively
• cerebral oximeter or other such apparatus provided in accordance with the invention is convenient to use, non-invasive and non-traumatic, produces no attendant side effects, and provides
• Such apparatus is compact and relatively portable in nature, may provide direct visible monitoring via CRT or other visual display, and provides digitally storable data which may readily be maintained for future review or comparison or printed out in hard copy, plotted, etc., and/or periodically accessed to provide ongoing trend data, for displaying or
• the apparatus may be used in such diverse circumstances as emergency or trauma conditions, whether in the field (at the scene of accidents, etc. for example) or in emergency medical centers, intensive care units, surgical operating rooms, hospital trauma centers, or at bedside, etc.
• emergency medical centers for example
• emergency medical centers for example
• emergency medical centers for example
• major blood vessels for example, carotid endarterectomy; or other bypass surgery, etc.
• blood flow is maintained through heart-lung machines and there is no arterial pulse present at all in the brain or body.
• Fig. 1 is a pictorial schematic representation simplistically showing the basic application and utilization of apparatus in accordance with the invention
• Fig. 2 is a further pictorial schematic representation somewhat similar to Fig. 1 showing additional aspects of the subject matter disclosed;
• Fig. 3 is an end view of a first optical sensor assembly for use in conjunction with the invention
• Fig. 4 is a pictorial side view representation of a different form of optical sensor, of a more preferred nature;
• Fig. 5 is a schematic representation depicting the regional examination of the head and brain in accordance with the invention;
• Fig. 6 is a graphical representation illustrating the spectral absorption characteristics of hemoglobin
• Fig. 7 is a graphical representation showing
• Fig. 8 is a graphical representation showing
• Fig. 9 is a graphical representation showing
• Fig. 10 is a further graphical representation showing cerebral oximetry measurements in accordance with the invention.
• Oxygen is supplied to the brain by hemoglobin molecules contained in the blood supply, to which the oxygen molecules become bonded during the oxygenation process which occurs in the lungs as the blood is pumped by the heart through arteries and capillaries to the brain.
• the brain extracts oxygen from the hemoglobin by oxidative metabolism, and
• spectrophotometry utilized by the invention is based upon the selective attenuation of particular light spectra in the near infrared range which is exhibited by oxygenated hemoglobin as compared to reduced (deoxygenated)
• FIGs. 1 and 2 show a human subject 10 upon whom apparatus in accordance with the invention is being utilized, such apparatus comprising a sensor means 12 for applying and receiving selected light spectra to a particular region 14 of the brain through or via conductors 16 (which, as
• spectrophotometry unit 18 which includes in part a small digital computer 20 having a monitor 22 on which various forms of readout information may be presented.
• the sensor assembly 12 applies selected light wavelengths which may emanate from a broadband source 24 (e.g., an incandescent lamp) and be selectively
• L.E.D.s dedicated light-emitting diodes
• computer 20 generally includes an A/D converter section 28, control circuitry 30 (depicted as a circuit board configured to mount in the expansion slots of computer 20), together with requisite computer memory 32 and an operator control in the form of a keyboard 34.
• the sensor assembly 12 may as a general matter be in accordance with copending United States application
• such a sensor assembly 12' generally comprises a housing or other support 36 which carries a light-emitting element 38, a first light-detector or receiver 40 (i.e., the "near” receiver) and a second such detector or receiver 42 (the “far” receiver) which is disposed a predetermined and particular distance away from the source 38 and the "near" receiver 40.
• a first light-detector or receiver 40 i.e., the "near” receiver
• the second such detector or receiver 42 the “far” receiver
• the sensor assembly 12 is more elongated in overall shape and preferably has a somewhat flexible support 136 which carries the light source 138 and the near and far receivers 140, 142, respectively, all arranged in a longitudinal array, disposed along a common linear axis.
• the source 138 comprises a pair of separate (but
• the entire sensor assembly 12" is relatively small and compact, lightweight, and thin, as well as being at least modestly flexible; of course in this form the conductor array 16' comprises electrical conductors, since the operative elements are electro-optical emitters and detectors. Of course, such components operate with very low levels of electrical excitation, and the actual conductors 16' are each insulated from one another and carried within an insulating outer sheath 116.
• the near receiver (40, 140) is close to but spaced a particular distance from the source (38, 138) so that the photons (light energy) which it detects in response to the emission of selected light spectra by the source will traverse primarily only the skin (scalp) and bone (skull) of the subject 10, whereas the "far" receiver (42, 142) is disposed a particular further distance from the source whereby the light energy
• This selected brain tissue volume which is sampled constitutes the selected region 14 noted previously (Fig. 1), and it will be observed that such region constitutes a particular internal volume within the overall brain content whose location is determined by the relative disposition and separation of the source 38, 138, near receiver 40, 140, and far receiver 42, 142, together with the relative placement and location of the sensor assembly 12 upon the head of the subject 10.
• transmission mode as those terms are conventionally used (i.e., they are disposed along mean optical paths which are curved, and are relatively close to the source).
• this is directly consistent with monitoring regional brain function, which represents the preferred embodiment of the invention.
• the distance between the source and near receiver is approximately 0.3 inches, while the distance between the source and far receiver is approximately 1.0 inches; once again, however, reference is made to copending U.S. applications Serial Nos. 329,945, and
• the spectral absorption characteristics of oxygenated hemoglobin describe a family of curves which intersect, and reverse, at a wavelength of approximately 800 nanometers ("nm"), which constitutes the isobestic point (typically considered to be at 815 nm).
• nm nanometers
• the oxygen content of sampled hemoglobin may be determined.
• such sampling is preferably carried out at wavelengths
• a first sampling wavelength may be in the range of about 735 nm, and another may be at approximately 760 nm. Since the specific point at which isobestic conditions exist may vary somewhat as a result of a number of factors, the reference wavelength is preferably selected to be at approximately 805 nm.
• the methodology of the invention utilizes diffused near-infrared spectroscopic procedures of a generally transmission-mode character for quantitative evaluation of tissue which is highly scattering and partially absorptive in nature, utilizing spatial
• the quantity I(w) represents intensity of transmitted light at wavelength w
• the term l(w)O represents the intensity of the incident light at wavelength w
• the term a represents the molar extinction coefficient of the light-absorbing molecule (chromophore)
• the term C represents the content of such chromophore in the tissue under examination
• the term s represents the photon pathlength in the tissue of interest.
• the measurements made at the selected examination wavelengths may be usefully referenced by subtracting them from referenced measurements made at second selected wavelength i.e., the isobestic point of hemoglobin noted above in connection with Fig. 6. Since the above
• chromophore concentration may be quantified for
• oxyhemoglobin and deoxyhemoglobin if such expression is solved by making (N+1) measurements of M to solve for C(j)s (oxyhemogolbin) and C(j)s (deoxyhemogolbin)
• chromophore content The value s is a constant, and by calculating the ratio of deoxy- to oxy- hemoglobin, this constant cancels out of the expression. If this is assumed to be constant, the number of unknowns does not increase subsequent measurements, and this assumption appears to be well-supported.
• oxyhemoglobin which may then be used to solve for the regional saturation of hemoglobin designated rSHgbo2 below: / ,
• this region constitutes the ratio of oxygenated hemoglobin to total hemoglobin in the sampled field (defined region) of the brain under investigation.
• this region will contain both arterial and venous blood, as well as a small capillary content, but the venous blood will heavily outweigh the arterial blood because the great majority (on the order of 70-80 percent) of the cerebral blood is in the venous compartment.
• the transmitted light of wavelengths w, w', etc. is preferably sequentially applied in short bursts (pulses) by use of a suitable number of repetitions which alternate application of the selected wavelengths. Detection of resulting light for each such burst thus occurs at both the near and far locations essentially simultaneously, and is preferably obtained on a time-gated basis corresponding to the occurrence of the pulsed incident light wavelengths, providing synchronous detection/demodulation techniques.
• wavelengths constitute an analog quantity as detected, and these are preferably converted to digital form for subsequent processing.
• connection with Figs. 1 and 2 is preferably utilized to control all time-based functions, as well as for the processing of digitized data in accordance with the aforementioned algorithm.
• differential processing in essence, subtraction of the near-far detection measurements is considered to be of the essence in order to define the selected internal region which is to be examined, and in particular to exclude the effects of the sampled near field from the measurements of the desired far field, thereby eliminating not only boundary (initial impingement and peripheral penetration) effects but also those attributable to transmission through the skin, bone and dura by the selected examination spectra.
• This processing may be carried out incrementally, prior to each iterative spectrophotometric transmission and detection sequence, since the digitized data may readily be stored on an increment-by-increment basis and used for further processing (or storage) as desired.
• Fig. 7 presents a graphical-form chart showing measured regional cerebral hemoglobin saturation with respect to time, obtained by actual clinical measurement of a human subject undergoing progressive cerebral hypoxia.
• a rapid shift from baseline to abnormal values is clearly indicated, commencing at about the four minute point, as a result of the progressive hypoxia, as is the very rapid return to baseline (and in fact slightly elevated initial level exceeding baseline) following corrective patient respiration on one-hundred percent oxygen.
• the clear indications of serious abnormality provided in accordance with the invention occurred well over a full minute before the earliest such EEG indication, and of course this occurs through
• Fig. 8 comprises a chart somewhat analogous to that presented in Fig. 7 and described above, but showing a longer-duration procedure during which the monitored patient underwent elective hypothermic cardiac
• brain oxygen saturation is shown to rapidly return toward baseline, and may clearly be monitored during the highly important ensuing period.
• Fig. 9 comprises a different form of chart
• optical density i.e., attenuative effect
• This chart thus shows transit of the tracer through the cerebral vasculature; that is, selective introduction of the tracer in the internal carotid artery results in initial presence thereof only in the deep tissue; thus, ipsilateral spectroscopic measurements made in accordance with the invention show (bottom trace) relatively immediate detection of the tracer at the "far" receiver monitoring the deeper brain tissue, without any attendant indication at the "near” receiver (upper trace) which monitors superficial tissue, etc., until substantially later, after the tracer has recirculated through the heart and entered the external carotid system, at approximately fifty seconds after the initial introduction of the tracer.
• the far receiver also shows recirculation of the bolus at this second point in time, as well as graphically displaying the declining persistence of the tracer within the deep tissue over this interval.
• Fig. 10 constitutes a further graphical showing illustrative of the versatility, usefulness and value of information provided in accordance with the invention, by way of a pair of comparative traces showing (lower trace) continuous regional cerebral oxygen saturation
• cerebral oxygen extraction causes rapid changes in cerebral venous oxygen saturation when cerebral oxygen delivery decreases for any reason, as for example the presence of systemic hypoxia, cerebral oligemia, systemic anemia, etc., even though cerebral oxygen consumption may remain normal.
• cerebral oxygen extraction causes rapid changes in cerebral venous oxygen saturation when cerebral oxygen delivery decreases for any reason, as for example the presence of systemic hypoxia, cerebral oligemia, systemic anemia, etc., even though cerebral oxygen consumption may remain normal.
• saturation provided in accordance with the invention constitute field values, i.e., represent hemoglobin contained in three separate vascular compartments
• intraparenchymal tissue compartments could or may potentially interfere with the strict accuracy of the quantifications provided, even though relative or trend data based thereon would seemingly still be of
• the spatial resolution capabilities of the invention may in fact provide a way to comparatively assess such anomalies, particularly if they are reasonably well defined.
• the paradigms set forth above being primarily designed to measure and account for extraparenchymal conditions, have the potential to overcome such problems.

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Cited By (16)

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• 1992
  • 1992-06-04 JP JP5500635A patent/JPH07500259A/ja active Pending
  • 1992-06-04 CA CA002110716A patent/CA2110716C/en not_active Expired - Lifetime
  • 1992-06-04 WO PCT/US1992/004654 patent/WO1992021283A1/en not_active Application Discontinuation
  • 1992-06-04 EP EP92913850A patent/EP0597875A4/en not_active Withdrawn

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