Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1998-09-11
2001-09-18
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S475000, C600S549000, C374S100000, C374S104000, C374S112000, C374S121000, C374S123000, C374S124000, C374S126000, C374S129000, C374S132000, C374S133000
Reexamination Certificate
active
06292685
ABSTRACT:
BACKGROUND OF THE INVENTION
In recent years, infrared thermometers have come into wide use for detection of temperature of adults. For core temperature readings, infrared thermometers which are adapted to be inserted into the patient's ear have been very successful. Early infrared thermometers were adapted to extend into the ear canal in order to view the tympanic membrane and provide an uncorrected, direct reading of tympanic temperature which correlates with pulmonary artery temperature. More recently, however, to provide for greater comfort and ease of use, ear thermometers have been designed to provide corrected readings of the generally cooler distal ear canal. Such thermometers measure temperature of distal ear canal tissue and calculate arterial core temperature via heat balance.
Core temperature is a term used to describe deep body temperature and is approximated by oral, rectal, ear, pulmonary artery, esophageal and bladder temperatures and the like. Of those temperatures, pulmonary artery temperature is the most precise definition of core temperature since it is closest to the heart and its blood is supplied to all tissues. Calculations of arterial core temperature via heat balance provide approximations of the pulmonary artery temperature, and unless otherwise indicated, core temperature refers to the pulmonary artery temperature.
The arterial heat balance approach is based on a model of heat flow through series thermal resistances from the arterial core temperature to the ear skin temperature and from the ear skin temperature to ambient temperature. Accordingly, after sensing both the skin temperature and ambient temperature, the arterial core temperature can be calculated. The thermal resistance model also allows for computation of equivalent oral and rectal temperatures with the mere adjustment of a weighting factor in the computation. Infrared ear thermometers using the arterial heat balance are disclosed in U.S. Pat. Nos. 4,993,419; 5,012,813; 5,199,436; 5,381,796; 5,445,158; 5,653,238 and 5,271,407, the entire teachings of which are incorporated herein by reference.
To avoid clinical difficulties in using ear thermometers, particularly with neonates, axillary (underarm) infrared thermometers have been introduced. Infrared thermometers designed for axillary temperature measurements are presented in U.S. patent applications Ser. Nos. 08/469,484, 08/738,300 and 08/881,891, the entire teachings of which are incorporated herein by reference. In each of those devices, an infrared detector probe extends from a temperature display housing and may easily slide into the axilla to lightly touch the apex of the axilla and provide an accurate infrared temperature reading in as little as one-half second. The axillary thermometer also relies on the arterial heat balance approach to provide arterial, oral or rectal temperature.
The axillary infrared thermometer has found great utility not only with neonates but as a screening tool in general, and especially for small children where conventional temperature measurements such as a thermometer under the tongue or a rectal thermometer are difficult.
In ear and neonate axillary thermometry, the difference between skin temperature and ambient temperature has been weighted by a coefficient approximating h/pc, where h is an empirically determined coefficient which includes a radiation view factor between the skin tissue and ambient, p is perfusion rate and c is blood specific heat. In ear and neonate axillary thermometry, that coefficient was found empirically to be about 0.09 and 0.05, respectively, with only minor variations. However, with greater exposure for heat transfer and higher vasomotor functions, that coefficient has been determined empirically for the adult axillary region to be about 0.13 with much more significant variations according to the patient's temperature.
SUMMARY OF THE INVENTION
The present invention provides for particularly convenient temperature readings of neonate, child and adult temperatures by detecting the temperature of the forehead directly over the superficial temporal artery.
Because arteries receive blood directly from the heart, they are a good choice for detecting core temperature, but an artery at the extremities of the body, such as those felt as pulse points at the wrist or ankle, are highly subject to vasoconstriction. This means, for example, that when an individual is extremely sick, in shock, or even just cold or nervous, the arteries constrict to reduce the flow of blood to that area as a means of retaining heat, or as in the case of shock, in an effort to redirect the blood to more critical areas of the body. This can result in a large temperature change at the artery which is a local artifact only and not representative of core temperature.
Ruling out those arteries located in the extremities, in attempting to replicate the temperature at the source (the heart), we find, in the temporal artery, an artery as short a distance from the heart as possible, with a high and relatively constant blood flow, and that is readily accessible on all individuals. The heart, the lungs and the brain are vital to our very existence, so the supply of blood is high to these organs and continues as high as possible even through, in the face of grave illness, other areas may shut down to accommodate.
Originating in the heart is the aorta, the main trunk of the arterial system. A direct extension of the aorta is the common carotid artery, a robust artery which runs upward in the neck and divides into the internal and external carotids. But, the carotids, even the external carotid, are at best partially embedded, and at worst completely embedded in the skull, and therefore are not accessible at the skin. Extending directly from the carotid is the temporal artery, again an artery dividing internally and externally. We look to the external branch which travels in front of the ear and up into the soft temple area, terminating in a fork directly between the skin and the skull adjoining the eyebrow.
Demonstrably, the temporal artery is very easily accessible; in fact in most individuals, it is usually quite visible. Terminating in a two-prong fork, it easily doubles the assurance of measuring the correct area. Touching it does not present a risk of injury. There are no mucous membranes present, thus eliminating the risk of contaminates such as those found in the mouth and rectum. And, despite lying so close to the skin surface, the temporal artery perfusion, which is the flow of blood per unit volume of tissue, remains relatively constant and so ensures the stability of blood flow required for our measurement.
In accordance with one aspect of the invention, a temperature sensor is scanned across the forehead, preferably in the vicinity of the temporal artery, and a peak temperature reading is provided from the scan. At least three readings per second should be made during the scan, preferably about ten readings per second. The method can be extended to other arteries near the skin such as in the axilla. The preferred radiation sensor is a radiation sensor which views a target surface of the forehead through a reflective cup. The cup has a large open diameter close to the target surface and a window at the base of the cup through which the radiation sensor views the target, the cup being out of the field of view of the sensor. The reflective cup is spaced from the target surface by a smooth lip of low thermal conductivity material.
As in prior ear and axillary thermometers, internal core temperature can be computed from the function
T
c
=(1+(
h/pc
))(
T
s
−T
a
)+
T
a
(1)
where T
s
and T
a
are the skin and ambient temperatures. The function can be seen to include a weighted difference of surface temperature and ambient temperature with a weighting coefficient h/pc.
In accordance with another aspect of the invention, electronics in the detector compute an internal temperature of the body as a function of ambient temperature and sensed surface temperature. The function i
Exergen Corporation
Hamilton Brook Smith & Reynolds P.C.
Lateef Marvin M.
Lin Jeoyuh
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