Thermal measuring and testing – Temperature measurement – By electrical or magnetic heat sensor
Reexamination Certificate
2003-08-15
2004-12-07
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Temperature measurement
By electrical or magnetic heat sensor
C374S030000, C374S163000, C374S178000, C374S179000, C374S183000, C600S549000, C600S528000, C600S323000
Reexamination Certificate
active
06827487
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a temperature measuring device for measuring the temperature within a body from a surface of the body.
BACKGROUND OF THE INVENTION
A need exists for the measurement of the temperature within a body from a surface of the body where an internal temperature measurement is necessary, but the inside of the body is inaccessible, or access to the inside of the body would be inconvenient. Examples of such bodies include human and animal bodies and industrial process tanks, for example fermentation tanks or tanks containing corrosive media.
Body temperature is the parameter most frequently measured in patients who are ill or who feel ill. However, there are disadvantages with all of the currently available methods of measuring body temperature. Temperature measurements aim for readings which reflect the core or deep body temperature, an average of the temperatures of the core portions of the body as reflected by the temperature of blood in the major vessels. However, these parts of the body are not readily accessible and body temperature measurements are normally sublingual, axillary or rectal. For various reasons, these locations do not accurately reflect core temperature. Measurements taken under the tongue are sensitive to changes in temperature caused by eating, drinking, oral medication or mouth-breathing, and to incorrect thermometer position. Measurements taken in the armpit are generally lower than the true deep body temperature. Measurements taken rectally are affected by factors including coliform bacterial activity, haemorrhoids, colitis, depth of measurement or presence of faeces.
There are other disadvantages associated with measuring temperature in these locations. Sublingual measurements require 3-4 minute readings and are unsuitable for young children due to the risk of biting. Axillary measurements require 8-11 minute readings. Rectal measurements carry the risk of rectal perforation, may result in cross-contamination if the thermometer is not properly sterilised, and are invasive. Neither sublingual or rectal measurement is considered suitable for measuring the temperature of neonates or premature babies, and usually skin temperature is measured in these cases, giving results which do not accurately reflect deep body temperature.
Accurate deep body temperatures are currently monitored on critically ill patients in Intensive Care Units or operating theatres by means of pulmonary, oesophageal or bladder thermistor catheters, but these are invasive methods which are unsuitable for routine temperature monitoring.
The traditional glass/mercury thermometer is currently being phased out due to the inherent dangers of these materials, and being replaced with electronic stick fever thermometers. These stick thermometers offer faster digital readouts with an audible signal to indicate that a steady value has been reached, and give more accurate results than glass/mercury thermometers, but are still invasive.
The drive for faster and preferably minimally invasive or non-invasive thermometers has opened a large market for optical ear canal infrared thermometers which measure thermal radiation from the tympanic membrane. However, tympanic measurements quite often give inaccurate results in clinical use. This is mainly due to operator error, for example directing the measurement light beam at cooler parts of the ear canal such as skin or ear wax, and/or physiological variations in brain and ear canal temperature. Fouling of the optics may also be a contributing factor to the inaccuracy of these devices. A difference of 1° C. can often be seen between the ears of the same patient. Tympanic measurements are particularly unpleasant for children under the age of two, because of the small diameter of their ear canals.
Consequently, there is a need for thermometers which record an accurate deep body temperature, whilst avoiding invasive techniques, so as to minimise discomfort to the patient.
A non-invasive deep body temperature measurement technique was developed in the 1970s by Dr. R. H. Fox, and is disclosed in U.S. Pat. No. 3,933,045. This thermometer, the “Fox probe”, consists of a semi-infinite heat shield established over a temperature measuring device which is held in contact with the skin surface. Controlling the temperature of the heat shield such that its temperature is equal to the surface sensor temperature establishes a zero heat flux within the probe structure, and thus also between the surface sensor and the deep body temperature, forcing the surface sensor towards the deep body temperature. The Fox probe was developed into an embodiment with a heat shield in the form of a heat-conducting cup, heated to the same temperature as the skin, wherein the rim of the cup is in contact with the edge of the heat shielded area of skin, as disclosed in U.S. Pat. No. 4,539,994. This helps to prevent lateral heat loss from the part of the body beneath the heat shield through the skin outside the heat shield, which will prevent equilibrium from being reached. This embodiment provides a practical alternative to the use of a very large (effectively infinite) heat shield around the skin temperature sensor. The Fox probe heat-conducting cup is filled with air or a heat-insulating compound to avoid thermal coupling between the heat shield and the skin sensor. Without thermal insulation between the heat shield and the skin sensor, a temperature control overshoot could cause an increase in temperature of the skin sensor, and a thermal runaway situation could occur.
The classical and improved versions of the Fox probe are large (e.g. 45-60 mm diameter) and have a substantial settling time (several minutes), and thus they are best suited to long term deep body temperature trend monitoring in intensive care. They have not been widely adopted for individual, routine patient temperature readings due to the long settling time and non-portable design. Further, they are rarely used for temperature monitoring during surgical procedures, where small, invasive catheter probes are generally preferred.
A Fox probe suitable for measuring deep body temperature from a surface which is hotter or cooler than the deep body temperature is disclosed in GB-A-2266771. This probe is stated to be applicable to measurement of skin temperature.
WO 00/58702 discloses an apparatus for measuring deep body temperature comprising a capsule for application to a body surface, having a heat-conducting interior and thermally insulated surfaces. A heating element is used to heat the inside of the capsule, and two temperature sensors measure the temperature at two points inside the capsule. When the temperature recorded by the sensors is equal, this temperature reading should be equivalent to the deep body temperature. I have appreciated that this apparatus has the disadvantages that when measuring animal body temperature lateral blood flow may cause heat loss so that the temperature reading is below deep body temperature, and that it is possible for the temperature sensors to be heated by the heater to the same temperature without being in equilibrium with the core if they are heated too quickly Particularly serious inaccuracy is likely when fast initial heating is carried out and the equilibrium position is estimated by extrapolation as proposed in the application. The effect will be of most significance when measuring the temperature of obese patients, as subcutaneous fat acts a heat insulator between the body core and measurement apparatus.
DE-A-3527942 discloses an apparatus similar to that of WO 00/58702. It is disclosed that the heater may be preheated.
SUMMARY OF THE INVENTION
In a first aspect, the present invention provides a temperature measuring device for measuring the temperature within a body from a surface of the body which is at a lower temperature, said device comprising:
a heat shield for application to the surface of the body, comprising an outer heat-conducting portion, and an inner heat-insulating portion, both said portions having a surface for contact
Altera Law Group LLC
Gutierrez Diego
Pruchnic Jr. Stanley J.
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