Abstract:
A non-invasive method of determining a physiological characteristic, comprising providing at least one physiological sensor that is adapted to measure at least one physiological characteristic at a target measurement site on a subject&#39;s body, heating an extended tissue region on the subject&#39;s body, whereby blood perfusion of the tissue region is enhanced, and measuring at least one physiological characteristic with the physiological sensor during or within a predetermined period after heating the extended tissue region.

Description:
FIELD OF THE PRESENT INVENTION 
       [0001]    The present invention relates to the field of pulse oximetry. More specifically, the invention relates to a pulse oximetry method and system that employs heating means to enhance blood perfusion. 
       BACKGROUND OF THE INVENTION 
       [0002]    It is well known in the art that pulse oximetry is based on the principle that the color of blood is related to the oxygen saturation level of hemoglobin. Indeed, as blood deoxygenates, the pinkish skin color (in many individuals) transitions to a bluish hue. This phenomenon allows measurements of the degree of oxygen saturation of blood using, what is commonly referred to as, optical pulse oximetry technology. 
         [0003]    Pulse oximetry devices, i.e. oximeters, typically measure and display various blood constituents and blood flow characteristics including, blood oxygen saturation of hemoglobin in arterial blood, the volume of individual blood pulsations supplying the flesh and the rate of blood pulsations corresponding to each heartbeat of the patient. Illustrative are the devices disclosed in U.S. Pat. Nos. 5,193,543, 5,448,991, 4,407,290 and 3,704,706. 
         [0004]    As is well known in the art, a pulse oximeter passes light through human or animal body tissue where blood perfuses the tissue, such as a finger or ear, and photoelectrically senses the absorption of light in the tissue. Since oxygenated and deoxygenated hemoglobin absorb visible and near infrared light differently, two lights having discrete frequencies in the range of about 650-670 nm in the red range and about 800-1000 nm in the infrared range are typically passed through the tissue. The amount of transmitted light passed through the tissue varies in accordance with the changing amount of blood constituent, i.e. oxygen (or oxygen saturation), in the tissue and the related light absorption. 
         [0005]    Two oxygen saturation parameters can readily be ascertained via oximetry; arterial oxygen saturation and peripheral, arterial oxygen saturation. Arterial oxygen saturation (SaO 2 ) is based on direct measurement of light absorption in tissue and/or blood based on all commonly measured hemoglobin components. Peripheral, arterial oxygen saturation (SpO 2 ), as measured by pulse oximetry, is generally determined by measuring the constant (non-pulsatile) and pulsatile light intensities (discussed below) of the two functional components oxyhemoglobin and deoxyhemoglobin, at each of the two noted wavelengths, and correlating the measured intensities to provide peripheral oxygen saturation. 
         [0006]    As is also well known in the art, variations in tissue temperature proximate the measurement site can, and in many instances will, affect blood perfusion and, hence, oximetry measurements dependant thereon. Indeed, a rise in tissue temperature induces or triggers a homeostatic reflex, which enhances local blood flow in order to increase the transfer of heat away from the skin. The enhanced blood flow or perfusion will enhance the accuracy of the oximetry measurement, since the light transmitted to the tissue will encounter a larger volume of blood. 
         [0007]    Various heating means have thus been incorporated in sensors or pulse oximeters to improve blood perfusion adjacent the sensor. Illustrative are the sensors disclosed in U.S. Pat. Nos. 4,926,867, 5,299,570, 4,890,619 and 5,131,391. 
         [0008]    In U.S. Pat. No. 4,926,867, an oximeter sensor is disclosed that includes a metal plate that functions as a heater. According to the invention, the heater is adapted and positioned to heat the tissue proximate the sensor to enhance blood perfusion. A separate thermistor is also provided to monitor the amount of heat transmitted to the tissue by the heater. 
         [0009]    U.S. Pat. Nos. 5,299,570 and 4,890,619 disclose oximeter sensors that employ ultrasonic energy to enhance blood perfusion. The blood perfusion is similarly enhanced primarily proximate the sensor. 
         [0010]    Various substances have also been applied to the skin (or tissue site) to enhance blood perfusion. Illustrative are the pulse oximeter methods disclosed in U.S. Pat. Nos. 5,392,777, 5,267,563 and 6,285,896. 
         [0011]    In U.S. Pat. Nos. 5,392,777 and 5,267,563, a counterirritant is applied to the skin prior to attachment of the oximeter sensor. In U.S. Pat. No. 6,285,896, a vasodilating substance is applied to the skin prior to attachment of the oximeter sensor to reduce the effects of localized oxygen consumption and to increase blood fraction. 
         [0012]    Although the noted sensor systems and methods provide effective means to enhance blood perfusion, there are a number of disadvantages and drawbacks associated with the systems and methods. A major drawback is that the enhanced blood perfusion realized by the conventional sensor systems and methods is typically localized, i.e. proximate the sensor. As discussed in detail herein, applicants have found that the signal-to-noise ratio of an oximeter sensor (and, hence, the accuracy of any physiological characteristic, e.g., O 2  saturation, determined therefrom) can be significantly enhanced by heating an entire organ or appendage, e.g., ear or hand, prior to or in conjunction with taking an oximeter reading. 
         [0013]    A further drawback is that virtually all of the conventional sensor heating means comprise means for heating the sensor (or housing thereof) or a member that is integral thereto, e.g., heated plate. Such heating means necessitates frequent site changes to avoid thermal injury, which makes the monitoring method (employing the heating means) more labor intensive and costly than other non-invasive monitoring methods. 
         [0014]    Additional drawbacks are that the conventional sensor systems and methods require extensive and complex sub-systems to regulate the amount of heat transmitted to the skin site and avoid burning the patient, and are typically limited to one sensor and, hence, one sensor location on the body. 
         [0015]    It would therefore be desirable to provide a simple physiological sensor method and system that substantially reduces or overcomes the disadvantages and drawbacks associated with conventional sensor methods and systems, such as pulse oximeter sensor methods and systems. 
         [0016]    It is therefore an object of the invention to provide a physiological sensor method and system that substantially reduces or overcomes the disadvantages and drawbacks associated with conventional sensor methods and systems. 
         [0017]    It is another object of the invention to provide a physiological sensor method and system that enhance the accuracy of physiological measurements and determinations made therefrom. 
         [0018]    It is another object of the invention to provide a pulse oximetry method and system that includes heating means to enhance blood perfusion. 
         [0019]    It is another object of the invention to provide a pulse oximetry method and system that includes heating means that is adapted to heat a significantly larger tissue region, such as an entire ear or hand, prior to or in conjunction with obtaining an oximeter reading therein. 
         [0020]    It is another object of the invention to provide a pulse oximetry method and system that includes multiple sensors and associated heating means that are adapted to selectively heat a large tissue region. 
       SUMMARY OF THE INVENTION 
       [0021]    In accordance with the above objects and those that will be mentioned and will become apparent below, in one embodiment of the invention, there is provided a non-invasive method of determining a physiological characteristic, comprising the steps of (i) providing at least one physiological sensor that is adapted to measure at least one physiological characteristic at a target measurement site on a subject&#39;s body, (ii) disposing the physiological sensor proximate the target measurement site, (iii) heating an extended tissue region on the subject&#39;s body, whereby blood perfusion of the tissue region is enhanced, the extended tissue region including the target measurement site and a region extending beyond the target measurement site, and (iv) measuring at least one physiological characteristic with the physiological sensor during or within a predetermined period after heating the extended tissue region. 
         [0022]    Preferably, heating of the extended tissue region is sufficient to induce or trigger an optimal homeostatic reflex, whereby tissue perfusion is enhanced, without burning the subject. 
         [0023]    In one embodiment of the invention, the extended tissue region comprises the entire ear of the subject and the target measurement site comprises the earlobe of the heated ear. 
         [0024]    In another embodiment, the extended tissue region comprises the entire ear and adjoining structure, i.e. tissue of the head adjacent the ear, of the subject and the target measurement site comprises the earlobe of the heated ear and adjoining structure. 
         [0025]    In another embodiment of the invention, the extended tissue region comprises the entire arm of the subject and the target measurement site comprises a finger on the heated arm. 
         [0026]    In yet another embodiment, the tissue region comprises a hand of the subject and the target measurement site comprises a finger on the heated hand. 
         [0027]    In one embodiment of the invention, the physiological characteristic comprises the blood oxygen saturation of the subject. 
         [0028]    In accordance with another embodiment of the invention, there is provided a non-invasive method of determining a physiological characteristic, comprising the steps of (i) providing a plurality of physiological sensors that are adapted to measure at least one physiological characteristic at target measurement sites on a subject&#39;s body, (ii) disposing a first physiological sensor proximate a first target measurement site on the subject&#39;s body and a second physiological sensor proximate a second target measurement site on the subject&#39;s body, (iii) heating a first extended tissue region on the subject&#39;s body, whereby blood perfusion of the first extended tissue region is enhanced, the first extended tissue region including the first target measurement site and a region extending beyond the first target measurement site, and (iv) measuring at least one physiological characteristic with the first and second physiological sensors during or within a predetermined period after heating the first extended tissue region. 
         [0029]    In accordance with another embodiment of the invention, there is provided a non-invasive method of determining a physiological characteristic, comprising the steps of (i) providing a plurality of physiological sensors that are adapted to measure at least one physiological characteristic at target measurement sites on a subject&#39;s body, (ii) disposing a first physiological sensor proximate a first target measurement site on the subject&#39;s body and a second physiological sensor proximate a second target measurement site on the subject&#39;s body, (iii) heating a first extended tissue region on the subject&#39;s body, whereby blood perfusion of the first extended tissue region is enhanced, the first extended tissue region including the first target measurement site and a region extending beyond the first target measurement site, (iv) heating a second extended tissue region on the subject&#39;s body, whereby blood perfusion of the second extended tissue region is enhanced, the second extended tissue region including the second target measurement site and a region extending beyond the second target measurement site, and (v) measuring at least one physiological characteristic with the first and second physiological sensors during or within a predetermined period after heating the first and second extended tissue regions. 
         [0030]    In accordance with another embodiment of the invention, there is provided a physiological sensor system, comprising (i) means for measuring at least one physiological characteristic at a target measurement site on a subject&#39;s body, and (ii) means for heating an extended tissue region on the subject&#39;s body, whereby blood perfusion of the tissue region is enhanced, the extended tissue region including the target measurement site and a tissue region extending beyond the target measurement site. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    Further features and advantages will become apparent from the following and more particular description of the preferred embodiments of the invention, as illustrated in the accompanying drawings, and in which like referenced characters generally refer to the same parts or elements throughout the views, and in which: 
           [0032]      FIG. 1  is a schematic illustration of a conventional pulse oximeter system; 
           [0033]      FIGS. 2A and 2B  are schematic illustrations of one embodiment of a pulse oximeter system with heating means, according to the invention; 
           [0034]      FIG. 3  is a schematic illustration of the pulse oximeter system shown in  FIG. 2B , showing heat applied to an appendage, i.e. arm and/or hand, of a subject and measurement of light absorption (i.e. oximeter reading) of the subject&#39;s heated finger, according to the invention; 
           [0035]      FIG. 4  is a schematic illustration of the pulse oximeter system shown in  FIG. 2B , showing heat applied to an ear of a subject and measurement of light absorption of the subject&#39;s heated ear, according to the invention; 
           [0036]      FIGS. 5A and 5B  are schematic illustrations of another embodiment of a pulse oximeter system having a plurality of sensors and associated heating means, according to the invention; 
           [0037]      FIG. 6  is a schematic illustration of the pulse oximeter system shown in  FIG. 5B , showing heat applied to an ear and arm of a subject and measurement of light absorption of the subject&#39;s heated ear and finger, according to the invention; 
           [0038]      FIGS. 7  is an illustration of an IR portion of an oximetry plethysmogram obtained on an area of a subject&#39;s ear at a baseline temperature in the range of approximately 29-32° C., according to the invention; 
           [0039]      FIGS. 8A and 8B  are illustrations of IR portions of oximetry plethysmograms obtained on an area of the ear of first and second subjects, respectively, at an elevated temperature in the range of approximately 35-37° C., according to the invention; and 
           [0040]      FIGS. 9 and 10  are graphical illustrations showing the effect of different heating method or conditions on pulse amplitude for subjects ranging in age from 71-94 years of age and 25-55 years of age, respectively, according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]    Before describing the present invention in detail, it is to be understood that this invention is not limited to particularly exemplified methods or systems as such may, of course, vary. Thus, although a number of methods and systems similar or equivalent to those described herein can be used in the practice of the present invention, the preferred methods and systems are described herein. 
         [0042]    It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention only and is not intended to be limiting. 
         [0043]    Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one having ordinary skill in the art to which the invention pertains. 
         [0044]    Further, all publications, patents and patent applications cited herein, whether supra or infra, are hereby incorporated by reference in their entirety. 
         [0045]    Finally, as used in this specification and the appended claims, the singular forms “a, “an” and “the” include plural referents unless the content clearly dictates otherwise. 
       Definitions 
       [0046]    The terms “pulse oximeter”, “oximeter sensor” and “oximeter”, as used herein, mean and include any conventional light-reflecting oximeter or sensor that is adapted to sense or measure light absorption in tissue and/or blood. 
         [0047]    The term “oximeter reading”, as used herein, means and includes a measure of light absorption in tissue and/or blood. 
         [0048]    The term “heating means”, as used herein, means and includes any means of increasing the core or tissue temperature of a subject, including, without limitation, one or more (i.e. a combination of) devices that transmit heat energy, such as thermoelectric heating devices (e.g., heating elements of various sizes, shapes, materials, etc. that are adapted to cooperate with various heating apparatus and/or configurations, such as a heated glove), contact heaters, lamps, heating blankets, etc., heated rooms, heated liquids, devices that transmit ultrasonic or photoelectric energy, and mentholated, counterirritant and/or vasodilating substances. The term “heating means” also means and includes passive heating means, i.e. means for limiting heat from escaping a specific tissue region of the body. 
         [0049]    The terms “patient” and “subject”, as used herein, is meant to mean and include humans and animals. 
         [0050]    The present invention substantially reduces or eliminates the disadvantages and drawbacks associated with conventional pulse oximetry methods and systems. In one embodiment of the invention, the pulse oximetry method and system includes an oximeter sensor and associated heating means that is adapted to heat a large tissue region or site, such as an entire organ or appendage, prior to or in conjunction with obtaining an oximeter reading. In another embodiment, the pulse oximetry method and system includes a plurality of oximeter sensors and associated heating means that are similarly adapted to selectively heat large tissue regions or sites prior to or in conjunction with obtaining oximeter readings. 
         [0051]    As discussed in detail below, Applicants have found that the signal-to-noise ratio of a sensor, i.e. oximeter sensor, (and, hence, the accuracy of any physiological characteristic, e.g., O 2  saturation, determined therefrom) can be significantly enhanced by heating a significantly larger tissue region, i.e. a region that extends beyond the target measurement site and/or region in direct communication with the sensor, prior to or in conjunction with obtaining an oximeter reading. 
         [0052]    Although the methods and systems of the invention are described herein in conjunction with pulse oximeter methods, sensors and systems, and measurements (or readings) obtained therewith, it is understood that the methods and systems are not limited to pulse oximetry and determinations made therefrom. Indeed, as will be appreciated by one having ordinary skill in the art, the methods and systems of the invention can readily be employed with other physiological monitoring apparatus and methods, which are adapted to monitor and/or determine a physiological characteristic based on the wave form, or amplitude or shape of a plethysmogram. 
         [0053]    Referring first to  FIG. 1 , there is shown one embodiment of a conventional oximeter sensor and associated system (referred to hereinafter as “sensor” and denoted generally “ 100 ”) that can be employed within the scope of the present invention. As illustrated in  FIG. 1 , the sensor  100  preferably includes two emitters  20 ,  22  and detector  28 , which are positioned adjacent the tissue being analyzed, i.e. finger  10 . 
         [0054]    Two lights are emitted by the emitters  20 ,  22 ; in one embodiment, a first light having a discrete wavelength in the range of approximately 650-670 nanometers in the red range and a second light having a discrete wavelength in the range of approximately 800-950 nanometers. The lights, in the illustrated embodiment, are transmitted through finger  10  via emitters  20 ,  22  and detected by detector  28 . 
         [0055]    The emitters  20 ,  22  are driven by drive circuitry  24 , which is, in turn, governed by control signal circuitry  26 . Detector  28  is in communication with or connected to amplifier  30 . The signal from amplifier  30  is transmitted to demodulator  32 , which is also synchronized to control signal circuitry  24 . The demodulator  32 , which is employed in most pulse oximeter systems, removes any common mode signals present and splits the time multiplexed signal into two (2) channels, one representing the red voltage (or optical) signal and the other representing the infrared voltage (or optical) signal. 
         [0056]    The signal from the demodulator  32  is transmitted to an analog-digital converter  34 . As is well known in the art, the output signal from the demodulator  34  is typically a time multiplexed signal comprising (i) a background signal, (ii) the red light range signal, and (iii) the infrared light range signal. 
         [0057]    The desired computations are performed on the output from the converter  34  by signal processor  36  and the results transmitted to and displayed by display  40 . 
         [0058]    Referring now to  FIG. 2A , there is shown a schematic illustration of one embodiment of a pulse oximeter system of the invention (denoted generally “ 200 ”). As illustrated in  FIG. 2A , the system  200  includes sensor  100  (discussed above), heating means  50  and, optionally, display  40 . 
         [0059]    As will readily be appreciated by one having ordinary skill in the art. Various oximeter sensors (and systems) can be employed within the scope of the invention. Thus, although the pulse oximeter system  200  discussed in detail below employs sensor  100  (shown in  FIG. 1 ), such use and discussion herein should not be deemed limiting. 
         [0060]    Referring back to  FIG. 2A , in some embodiments of the invention, the heating means  50  is connected to or in communication with, e.g., wireless communication, with sensor  100 . Similarly, in some embodiments, heating means  50  is in communication with the display  40 , whereby the heat transmitted by the heating means  50  can be displayed and, hence, monitored. 
         [0061]    In some embodiments of the invention, the heating means  50  includes heat regulating means (shown in phantom and designated “ 51 ”), e.g., heating blanket, or integral control means, that is adapted to monitor and regulate the heat transmitted by the heating means  50 . 
         [0062]    Referring now to  FIG. 2B , in some embodiments, the system  200  includes processor means (or processor)  55  that is in communication with heating means  50 , sensor  100  and display  40 , and is programmed and adapted to regulate heating means  50  and/or sensor  100  and/or the output displayed on display  40 . 
         [0063]    In yet additional embodiments, the system  200  further includes at least one heat sensor (shown in phantom and designated “ 60 ”) that is adapted to be disposed proximate the tissue region being heated by the heating means  50  and monitor the temperature of the heated tissue region. In the noted embodiments, the heat sensor  60  preferably is in communication with the processor  55  and, hence, display  40 , whereby the temperature of the heated tissue region can be displayed. 
         [0064]    As indicated above, in a preferred embodiment of the invention, the heating means  50  of the invention is adapted to transmit heat energy to a large or extended tissue region, i.e. a tissue region that extends beyond the target measurement site and/or the tissue region that is proximate to or in direct communication with the sensor (see, e.g.,  FIGS. 3 and 4 ), prior to or in conjunction with obtaining an oximeter reading. In some embodiments of the invention, the heating means  50  is also adapted to heat a smaller tissue region, preferably, a tissue region proximate the sensor. 
         [0065]    The heating means  50  of the invention can thus comprise any means of increasing the core or tissue (or skin) temperature of a subject, including, without limitation, devices that transmit heat energy, such as thermoelectric heating devices (e.g., heating elements of various sizes, shapes, materials, etc. that are adapted to cooperate with various heating apparatus and/or configurations, such as a heated glove), contact heaters, lamps, heating blankets, etc., heated rooms, heated liquids, devices that transmit ultrasonic or photoelectric energy, and mentholated, counterirritant and/or vasodilating substances, and passive heating means, i.e. means for limiting heat from escaping a specific tissue region of the body. As indicated above, the heating means  50  (and  52 , discussed below) can also comprise two or more of the noted devices and means, e.g. two heat lamps. 
         [0066]    According to the invention, the heat or heat energy provided by the heating means  50  can be substantially steady state (or constant) or varied, e.g. oscillated or any function of time-varied heating. 
         [0067]    According to the invention, the heat or heat energy transmitted by the heating means  50  and applied to the tissue is sufficient to induce or trigger an optimal homeostatic reflex, whereby tissue perfusion of the heated tissue region is enhanced, without burning the patient. As will be appreciated my one having ordinary skill in the art, the amount of heat or heat energy that would be necessary to trigger an optimal homeostatic reflex will vary from patient-to-patient, site to site on the same patient as well as over time depending on physical and/or mental health condition, metabolic status, exertion or fatigue and prior thermal conditioning or exposure. 
         [0068]    Applicants have, however, found that when the skin of a patient is heated up to a generally tolerable temperature range of approximately 40-42° C., arterioles in the blood vessel network that spread in the shallow layer within the dermis respond to the heat stimulus by active expansion of the inner diameters of the arterioles and general vasodialation. The expanded diameter results in a lowered resistance to blood flow and, hence, increased blood flow therethrough. Thus, in one embodiment of the invention, to optimize the increase of perfusion, the skin or tissue of the patient is heated to at least a temperature of approximately 35° C. or, at a minimum, 3° C. above the skin or surface temperature and below a temperature of approximately 42° C. to avoid burning the patient. 
         [0069]    A key feature and advantage of the pulse oximeter methods and systems of the invention is the application of the heat or heat energy over a large tissue region, such as an entire organ or appendage, prior to or in conjunction with taking an oximeter reading. As indicated above, Applicants have found that the signal-to-noise ratio of an oximeter sensor (and, hence, the accuracy of any physiological characteristic, e.g., O 2  saturation, determined therefrom) can be significantly enhanced by heating a large tissue region prior to or in conjunction with obtaining an oximeter region. Indeed, Applicants have realized about one order of magnitude improvement in the signal-to-noise ratio by virtue of the methods and systems of the invention. 
         [0070]    As will readily be appreciated by one having ordinary skill in the art, an order of magnitude increase in blood perfusion is significant in that the resulting signal strength enables measurement at an optimum site, such as a site proximate the central circulation, which is, by design, much less affected by vasoconstriction and, which is more proximal the heart and aorta. Such sites were heretofore deemed inaccessible and there was insufficient sensor signal strength to yield useful and high quality measurements, i.e. a quality that is comparable to conventional sites when non-constricted, such as the finger. 
         [0071]    According to the invention, the large tissue region that is subjected to heating can, of course, comprise the entire body of the patient. The heating means  50 , in this instance, could thus comprise a heated liquid bath or a heated room, such as a sauna. 
         [0072]    More preferably, the larger tissue region comprises an entire organ or appendage and, in some embodiments, the adjoining tissue structure. Referring to  FIG. 3 , there is shown the application of heat to a hand  60  (shown as heat zone “h 1 ”) or alternatively, the entire arm  62  (shown as heat zone “h 2 ”) by heating means  50 . According to the invention, the heat can be applied to the hand  60  and/or arm  62  prior to or in conjunction with obtaining an oximeter reading on a site therein, preferably, finger  10 , with oximeter sensor  100 . 
         [0073]    In the noted illustration, the system  200  includes a heat sensor  60 , which is disposed proximate the heated finger  10 . However, as discussed in detail above, the heat sensor  60  can also be readily disposed proximate any desired location within heat zone “h 1 ” and, hence, hand  60  or heat zone “h 2 ” and, hence, arm  62 . According to the invention, two or more heat sensors  60  can also be employed with system  200 , e.g., one heat sensor  60  disposed proximate a location on the heated arm  62  and one heat sensor  60  disposed proximate the heated hand  60  or finger  10 . 
         [0074]    Referring to  FIG. 4 , there is shown the application of heat to an entire ear  64  by heating means  50  (shown as heat zone “h 3 ”). According to the invention, the heat applied to the ear  64  can be applied in such a manner (e.g., intensity and/or direction) that only a portion of the ear  64  is heated or the entire ear  64  is heated or the entire ear  64  and the adjoining tissue region or tissue and/or bone structure of the head are heated (unless otherwise stated, referred to collectively herein as “heated ear”). Thus, in one embodiment of the invention, a significant portion of the ear  64 , more preferably, the entire ear  64  is heated. In another embodiment, the entire ear  64  and the adjoining tissue region or tissue and/or bone structure of the head (referred to collectively hereinafter as “adjoining tissue region) are heated. 
         [0075]    According to the invention, the heat can similarly be applied to the ear  64  (or the entire ear  64  and the adjoining tissue region) prior to or in conjunction with obtaining an oximeter reading on a site therein, preferably, the earlobe  65 , with oximeter sensor  100 . 
         [0076]    Referring now to  FIG. 5A , there is shown a schematic illustration of another embodiment of a pulse oximeter method and system of the invention (denoted generally “ 300 ”). As illustrated in  FIG. 5A , the system  300  includes a plurality of sensors  100   a,    100   b.  According to the invention, the sensors  100   a,    100   b  can be similar or comprise different sensors, e.g., different physical dimensions, attachment means, tuning, etc. Thus, in one embodiment of the invention, at least one sensor, i.e.  100   a  or  100   b,  is similar to sensor  100 . 
         [0077]    According to the invention, each sensor  100   a,    100   b  is adapted to be positioned proximate to or on a desired position of the body, e.g., earlobe and finger, and obtain oximetry readings therefrom. In a preferred embodiment of the invention (discussed below), at least one sensor, e.g.,  100   a,  is disposed proximate a central circulation site, e.g., neck, ear, nose, etc., and at least one sensor, e.g.,  100   b,  is disposed proximate a peripheral circulation site, e.g., arm, hand, finger, etc. 
         [0078]    The system  300  also includes a plurality of associated heating means  50 ,  52 , which are similarly adapted to transmit heat energy to a large tissue region, i.e. a tissue region that extends beyond the respective sensor position or target measurement site and/or the tissue region that is proximate to or in direct communication with the respective sensor, prior to or in conjunction with obtaining an oximeter readings, and, optionally, display  40 . The heating means  50 ,  52  are similarly adapted to be positioned proximate desired locations on the body and transmit heat or heat energy thereto; the term proximate meaning and including in close proximity to and/or in direct contact therewith. 
         [0079]    As will be readily appreciated by one having ordinary skill in the art, each (or both) heating means  50 ,  52  of the invention can also be adapted to heat a smaller tissue region, e.g., a tissue region proximate a respective sensor, if desired. 
         [0080]    According to the invention, heating means  52  can be similar to heating means  50 , e.g., heat lamp, or, alternatively, heating means  50  and  52  can comprise different heat sources, e.g., heat lamp, heat blanket and passive heating means. As is also illustrated in  FIG. 5A , each heating means  50 ,  52  can similarly be in communication with a respective sensor  100   a,    100   b  and/or the display  40 , whereby the heat transmitted by the heating means  50  and/or  52  can be displayed and, hence, monitored. 
         [0081]    Although system  300  is shown with two sensors, i.e. sensors  100   a,    100   b,  and associated heating means  50 ,  52 , it is to be understood that system  300  can include more than two sensors with associated heating means, e.g. three, four, etc. The illustration of system  300  in  FIGS. 5A  (and  5 B, discussed below) should thus not be deemed limiting in any manner. 
         [0082]    Referring to  FIG. 5B , in some embodiments, the system  300  similarly includes processor means (or processor)  55  that is in communication with heating means  50 ,  52 ,sensors  100   a,    100   b  and display  40 , and is programmed and adapted to regulate heating means  50 ,  52  and/or sensors  100   a,    100   b  and/or the output displayed on display  40 . 
         [0083]    In yet additional embodiments, the system  300  further includes at least two heat sensors  60  that are similarly adapted to be disposed proximate the heated tissue regions and monitor the temperature thereof. In the noted embodiments, the heat sensors  60  are preferably in communication with the processor  55  and, hence, display  40 , whereby the temperature of the heated tissue regions can be displayed. 
         [0084]    Referring now to  FIG. 6 , there is shown one application of system  300 , where one sensor  100   a  is positioned proximate to and in communication with an earlobe  65  and one sensor  100   b  is positioned proximate to and in communication with a finger  10 . As illustrated in  FIG. 6 , heating means  50  is also preferably positioned proximate the ear  64 , where heating of the entire ear  64  (shown as heat zone “h 5 ”) or the ear  64  and adjoining tissue region is possible, if desired. Heating means  52  is preferably positioned proximate the arm  62  and hand  60 , where heating of the arm  62  (shown as heat zone “h 6 ”) and/or hand  60  (shown as heat zone “h 7 ”) is possible, if desired. 
         [0085]    According to the invention, one or both regions, e.g., ear  64  and arm  62 , can be heated while obtaining oximetry readings with sensors  100   a,    100   b.  Thus, in one embodiment of the invention, the entire ear  64  (or the ear  64  and adjoining tissue region) is heated with heating means  50  while oximeter readings are acquired at the heated earlobe  65  and the unheated finger  10  with sensors  100   a  and  100   b,  respectively. In another embodiment, the entire arm  62  is heated with heating means  52  while oximeter reading are acquired at the unheated earlobe  65  and heated finger  10  with sensors  100   a  and  100   b,  respectively. In yet another embodiment, the hand  60  is heated with heating means  52  while oximeter reading are acquired at the unheated earlobe  65  and finger  10  with sensors  100   a  and  100   b,  respectively. In yet another embodiment, the entire ear  64  (or the ear  64  and adjoining tissue region) is heated with heating means  50  and the hand  60  is heated with heating means  52  while oximeter reading are acquired at the heated earlobe  65  and heated finger  10  with sensors  100   a  and  100   b,  respectively. 
         [0086]    According to the invention, oximetry readings can also be obtained with sensors  100   a,    100   b  without the application of heat to an extended tissue region or during (or after a predetermined time after) the application of heat to a smaller tissue region proximate one or both sensors  100   a,    100   b.    
         [0087]    System  300  thus provides an effective means of acquiring multiple oximetry readings with enhanced accuracy from sensors disposed at multiple locations on the body. 
       EXAMPLES 
       [0088]    The following examples are provided to enable those skilled in the art to more clearly understand and practice the present invention. They should not be considered as limiting the scope of the invention, but merely as being illustrated as representative thereof. 
       Example 1 
       [0089]    A series of blood oximetry readings were obtained from thirty-three (33) subjects that ranged in age from 28 to 92 years of age. Baseline temperature and plethysmographic readings were initially recorded. The baseline temperature for each subject was obtained on an area of the ear proximate the sensor using a remote IR skin temperature monitoring device. Baseline plethysmographic recordings were obtained with a non-heatable Nellcor Ear Sensor®, model ES-3212-9. 
         [0090]    Referring now to  FIGS. 7 ,  8 A and  8 B, there are shown the IR portions of oximetry plethysmograms obtained on an area of the ear at a baseline temperature in the range of approximately 29-32° C. ( FIG. 7 ) and at an elevated temperature in the range of approximately 35-37° C. for two subjects ( FIGS. 8A and 8B ). It can be seen that the signal-to-noise ratio of the sensor is substantially improved in  FIGS. 8B and 8B  (i.e. elevated temperature), as evidenced by the absence of the spikes associated with the pulse waves at the baseline temperatures (i.e.  FIG. 7 ). 
         [0091]    It should further be noted that the amplitude of the pulse waves shown in  FIG. 8A  were increased from approximately 400 units (A/D counts) to approximately 3900 units, which reflects a substantial increase of approximately one order of magnitude. 
         [0092]    Referring now to  FIG. 9 , there is shown the effect of different heating methods or conditions for subjects ranging in age from 71-94 years of age on pulse amplitude (or signal). The heating methods or conditions comprised heating the ear to a temperature in the range of approximately 33-35° C. via “friction”, i.e. rubbing the earlobe for approximately 30 seconds, and active (or contact) heating, referred to as “heat” to a temperature of approximately 35-37° C. via a heater blanket. 
         [0093]    As illustrated in  FIG. 9 , heating to a temperature of approximately 33-35° C. via “friction” produced an average 2.7-fold improvement in the amplitude ratio. Contact heating produced an average 6-fold improvement in the amplitude ratio. 
         [0094]    Referring now to  FIG. 10 , there is shown the effect of the same heating methods for subjects ranging in age from 25-26 years of age on the pulse amplitude. As illustrated in  FIG. 10 , “friction” heating produced an average 6.1-fold improvement in the amplitude ratio. Contact heating produced an average 10.7-fold improvement in the amplitude ratio. 
         [0095]    The data reflected in  FIGS. 7 ,  8 A,  8 B,  9  and  10  thus demonstrates that significant improvements in the signal-to-noise ratio of a sensor and, hence, the accuracy of physiological characteristics determined therefrom, can be obtained by virtue of the methods and systems of the invention. 
         [0096]    As will readily be appreciated by one having ordinary skill in the art, the physiological sensor methods and systems of the invention provide numerous advantages. Among the advantages are the following:
       The provision of physiological sensor methods and systems that enhance the accuracy of physiological measurements and determinations made therefrom.   The provision of pulse oximetry methods and systems that enhance the accuracy of blood parameter determinations of oximeter sensors, such as oxygen saturation.   The provision of pulse oximetry methods and systems that can readily be incorporated in or employed in conjunction with conventional oximeter sensors to enhance the accuracy of blood parameter readings and/or determinations made therefrom.   The provision of pulse oximetry methods and systems that facilitate the acquisition of signals reflecting physiological characteristic at a site that is supplied by the central circulation, such as a site on the head, and/or allows for monitoring of patients that are peripherally vasoconstricted to the extent that conventional sites, such as a finger or toe, are neither palpable, nor yield usable plethysmographic signals.   The provision of pulse oximetry methods and systems that facilitate the acquisition of signals reflecting physiological characteristic at a site that is proximate the aorta where the wave shape is much less influenced by transit through vasculature of complex shape, branching and length at a patient-dependent degree of hardening of the arterial wall. Thus, the pressure and flow wave shape is more similar to the original shape as it leaves the aorta, which enables accurate measurements and diagnostic information of hemodynamic parameters, such as blood pressure, cardiac output, structure condition and functioning of the arterial vasculature.   The provision of pulse oximetry methods and systems that provide heating at a constant or variable rate to a set temperature and monitoring of amplitudes or time changes of the arterial pressure induced signals, whereby the pressure or flow waveforms yields information on the degree of physiological control of that patient, as well as indirectly on therapeutic or otherwise interventional effectiveness.   The provision of pulse oximetry methods and systems that include thermal control of the measurement site and sensing system, whereby accurate data is provided that is not affected by temperature variability or fluctuation.       
 
         [0104]    Without departing from the spirit and scope of this invention, one having ordinary skill in the art can make various changes and modifications to the invention to adapt it to various usages and conditions. As such, these changes and modifications are properly, equitably, and intended to be, within the full range of equivalence of the following claims.