1 2
Rather, the typical optical blood saturation probe is OPTICAL BLOOD OXYGEN SATURATION mounted to the surface skin, such as on the chest, finger,
PROBE FOR INSERTION INTO THE ESOPHAGUS or earlobe. Unwanted motion artifacts may appear in
the measured oxygen saturation level due to alteration BACKGROUND OF THE INVENTION 5 in the optical path and/or peripheral perfusion to the
1. Field of the Invention tissue block. Such an externally-mounted sensor or The present invention generally relates to blood oxy- monitor is also susceptible to being accidentally dis
gen saturation probes or sensors and, in particular, to placed by physicians or other medical personnel workblood oxygen saturation probes or sensors which em- ing in the vicinity of the patient. Moreover, the tissue ploy an optical technique for sensing the level of blood 10 near the skin may not be adequately perfused with oxygen saturation. blood, particularly during physiological stress such as
2. Description of Related Art hypothermia or shock.
The amount of saturation of blood by oxygen is a Other conventional blood oxygen saturation techuseful physiologic index of oxygen transport. A variety ... include an intravascular sensor or probe. An of techniques have been provided for measuring the 15 intravascular probe is inserted into an artery, particulevel by which arterial blood is saturated by oxygen. larly the umbiiicai artery. Although an artery is a more The majority of oxygen earned in healthy blood is stable site than the skin> the ess of insertm an bound to hemoglobin the remainder being dissolved m intravascular obe is invasive and is neither convenient the plasma. Hemoglobin the oxygen-carrying protein for ^ h idan nQr lete, safe for the tient in blood, chemically binds to oxygen atoms and m 20 p to intravj£cu]ar insertion; thePblood
doing so, undergoes a change in physical structure ... , -'
,.? L . .J~ ,- , _.. r .. c oxygen saturation sensor must be of extremely small
which affects the light absorption properties of the . Jb - , ,
hemoelobin . size, a constraint which increases the cost, and de
One technique for measuring oxygen saturation in creases th,e reliability, of the sensor, blood exploits the change in the light absorption prop- 25 Examples of previous oximeters and blood oxygen erties of hemoglobin to detect the oxygen saturation saturation sensors are provided m U.S. Pat. No. level optically. With the optical technique, blood, or a 4,830,014 to Goodman et al., U.S. Pat. No. 5,061,632 to portion of tissue carrying blood, is optically illuminated Shepherd et al., and U.S. Pat. No. 4,805,623 to Jobis. by a sensor or probe connected to an instrument, com- Tne patent to Shepherd et al. discloses an oximeter with monly referred to as an oximeter. The optical blood 30 a capillary tube sensor. The patent to Goodman et al. oxygen saturation measurement is dependent on the includes a description of the deficiencies of prior art relative absorption of infrared light by saturated versus skin-mounted oximeters.
desaturated hemoglobin. Heretofore, no optical blood oxygen saturation sen
Thus, optical methods of blood oxygen saturation sors or probes have been developed which have the measurement rely on the measurement of transmitted or 35 safety, ease of use, and low cost of an external probe, reflected light through or from a perfused tissue block while also being mountable or insertable to a physiologwith the magnitude of the transmitted or reflected light ically stable monitoring site having adequate blood indicating the amount of oxygen bound to hemoglobin. perfusion. However, the amount of reflected or transmitted light is
affected by the total optical path, which is related to the 40 SUMMARY OF THE INVENTION
size and absorption of the tissue block and the distance From tne foregoing, it can be appreciated that there is of emitters and sensors from the block. These factors a need t0 provide an improved optical blood oxygen are not controlled at a given anatomical site. Hence, a satUration probe. This object, and other general objects reference light source of wavelength not absorbed by of the inventioil; are achieved by the provision of a saturated hemoglobin is used to obtain a baseline signal. 45 probe sized for insertion int0 the eSophagus of a patient Thus, transmitted or reflected light intensity measure- which indudes a Wood saturation sensing
ments are made using two alternating light sources, one me£ms for ... ^ saturation level o{hloo%
source to establish baseline and a second source to rfusj ^ {issue Qf ^ h determine the oxygen saturation. D, ,„ ... ,, , *
When the sampling rate of saturation measurement is 50 By ProvldlnS .a blood oxygen saturation sensing high enough, real time variation in saturation of blood meanf for msertln§ mt0 Oesophagus of a patient, as it flows through the tissue block is obtainable. The blood oxyS?n Ration is detected in tissue which saturation varies as the oxygen is unloaded to the tissue Purovld" * ... f*ble monitoring site. When and as fresh oxygenated blood flows into the tissue with the Probe_18 mss^ preferably into an anesthetized each heartbeat. Therefore, pulse rate can be measured 55 Patlent' the esophagus of the patient tends to collapse from the saturation signal. In addition, correlation of onto the Probe> thereby stabilizing the probe. Furtherthe saturation signal with the pulse signal aids in the more> the tlssue of the esophagus is highly perfused determination of the saturation level that is most repre- wlth blood Vla sma11 branches of the thoracic aorta and sentative of the arterial blood oxygen saturation. bronchial arteries. Moreover, unlike externally
If saturation waveforms are measured at two sites in 60 mounted optical blood oxygen saturation sensors which the body at different distances from the heart, the time can be affected by ambient light, the probe of the invenrelationship between distinguishing points on the wave- tion is completely isolated from ambient light, allowing forms can be correlated to blood pressure. This mea- for accurate and precise detection of blood oxygen surement requires a physiologically stable monitoring saturation levels. Hence, the esophagus provides a desite with ample perfusion. 65 sirable anatomical site for blood oxygen saturation mea
Heretofore, conventional optical oxygen saturation surement because of its depth in the body, proximity to probes and sensors have not been designed for use in the heart, high level of blood perfusion, and physiologadequately physiologically stable monitoring sites. ical stability.
