GB2285134A

GB2285134A - Monitoring body temperature

Info

Publication number: GB2285134A
Application number: GB9423720A
Authority: GB
Inventors: Noel Edward Evans; William New; John Mccune Anderson
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-11-26
Filing date: 1994-11-24
Publication date: 1995-06-28
Also published as: JPH07234161A; DE4441720A1; GB9423720D0; IE930912A1

Description

2285134 APPARATUS FOR MONITORING TEMPERATURE This invention relates to an

apparatus for monitoring temperature, especially but not limited to temperature monitoring in female humans.

Temperature monitoring in females is an established method of indicating ovulation, and hence the likelihood of the subject to conceive. The information obtained is valuable for both in-vitro fertilisation and contraceptive advice. The temperature measurements are made by the subject at home, usually with an oral thermometer or, for greater accuracy, a rectal or vaginal sensor.

Temperature records of this type are often difficult for an untrained observer to take accurately. Research has shown that women do not make measurements at the same time every day and the manual logging of a single reading is prone to error. Also, the data obtained is more reliable if semi-continuous readings are taken, for example overnight, but this is not practical using conventional thermometers.

2 - It is an object of the invention to provide an apparatus for monitoring a physiological parameter, such as temperature, which can be nworn" for long periods to permit multiple readings to be taken and logged.

is According to the present invention there is provided an apparatus for monitoring temperature, comprising a transmitter unit including a housing for insertion into a body cavity, the housing containing a component having an electrical characteristic which varies in dependence upon the value of the temperature to be measured and a radio transmitter for transmitting a radio signal in which variations in the electrical characteristic are encoded as a modulation of the signal, and a physically separate receiver unit for detecting and demodulating the radio signal.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows the transmitter unit of the embodiment; Figure 2 is a diagram of the electrical circuit within the transmitter unit; Figure 3 illustrates the nature of the signals at various points in the transmitter unit electrical circuit; and Figure 4 is a block circuit diagram of the receiver unit of the embodiment.

The apparatus shown in the drawings is for monitoring the temperature of a female human, and in essence comprises a transmitter unit (figures 1, 2 and 3) which monitors the temperature and transmits it as an amplitude modulated radio signal, and a physically separate receiver unit (figure 4) which detects and demodulates such signal.

is The transmitter unit comprises a tampon-like housing 10, figure 1, in the form of a hollow, sealed, non-metallic cylinder with approximate dimensions 10 mm diameter by 30 mm long. In use the housing 10 is inserted in the subject's vagina, for which purpose it is made of, or coated with, a suitably inert medically approved barrier coating. A draw cord 11 facilitates removal of the housing.

The subject's temperature is detected by a thermistor THI, and this is located in the wall of the housing 10, just below the exterior surface, to ensure good thermal transfer from the body tissues. As is well known, the resistance of the thermistor varies as a function of its temperature.

Within the housing 10 there is a printed circuit board 12 carrying the circuit shown in figure 2. This circuit comprises a baseband generator 13 which converts the temperature as measured by the thermistor TH1 into a pulse train whose interpulse period is dependent upon the measured temperature, and a keyed RF oscillator circuit 14 in which the pulse train amplitude modulation a UHF radio signal which is transmitted, by the tank inductor Ll serving as an antenna, to the receiver unit.

4 is The baseband generator 13 is essentially a relaxation oscillator built around a low power CMOS operational amplifier Al. The circuit produces a baseband signal 15 (figure 3) in the form of an output pulse train whose interpulse period T is directly proportional to the resistance of the curve-matched thermistor TH1. T may therefore be easily related to the thermistor's temperature, using published manufacturer's tables.

The oscillator has two operational time constants, set by the capacitor Cl and either the resistor R2 (for charge up via the steering diode D1) or the series combination of RI and THI (for capacitor discharge). Resistors R3, R4 and RB form the positive feedback path in the circuit and determine the comparator switching thresholds during the oscillatory cycle. Suitable component values result in an output 15 with a low duty cycle, suitable for keying an active RF source in a low power consumption mode.

The RF oscillator circuit 14 is built around the transistor Ql as the active gain element in a common-base, Colpitts configuration. Resistors R6 and R7 set the bias currents in the oscillator, with R6 also providing ON/OFF control. Capacitors C3 and C4 provide feedback and resonate (in combination with the transistor's parasitic capacitances) with inductor Li at the desired UHF operating frequency of 418 MHz as determined by a surface acoustic wave resonator SAWR. Such resonators are available which allow circuits to be built over the frequency range 200 - 2000 MHz. The capacitor C2 decouples the power supply rail +Vcc, - nominally set at between 3 and 6 V DC by an internal battery source 16 (figure 1).

The radiated output from the inductor L1, which is radiating inductor or printed loop antenna, consists therefore of a pulse amplitude modulated (PAM) waveform, 17 (figure 3) with a duty cycle set by the baseband generator 13. This is the signal detected by the receiver unit.

is The receiver unit (figure 4) is contained within a housing 18 to provide a compact, portable unit which may be carried unobtrusively on the body of the subject, similar for example to a radio pager.

In the receiver unit, the transmitted PAM waveform is recovered by a suitable low power receiver 19 with integral antenna 20. The receiver 19 is preferably a superregenerative detector using a SAWR for centrefrequency control. The output form this mimics the original baseband waveform 15 generated at the transmitter unit and so contains the temperature information.

A microprocessor 21 processes the baseband signal to extract the temperature data (using a look-up table, for example) and stores it for trend indication as and when required. The microprocessor has a control input 22 to enable the receiver unit to be programmed to carry out specific functions, for example, to set the timing of temperature sampling operations and the number of samples stored per session. Thus, although the transmitter unit is continuously monitoring the temperature and transmitting a corresponding PAM signal, a - 6 the receiver unit only samples and processes this signal at times determined by the program. The control input data may be provided from a plug-in keyboard or from another computer. A data output 23 is also provided, to enable the microprocessor's memory to be interrogated as appropriate, for example, at the end of a 10-day measurement period.

is Finally, an LCD display 24 provides a status indicator, having outputs such as "ACTIVW, "LAST TEMPERATURE REAW, "BATTERY LOW, etc.

The receiver unit is powered by a rechargeable battery pack (not shown) and the microprocessor preferably incorporates a realtime clock and the ability to enter a "sleep" mode to conserve battery power.

Although the receiver unit is normally worn on the body, the range of the signal transmitted by the transmitter unit is about 1 - 2 meters to permit the receiver unit to be removed during sleep periods.

The apparatus can be used in animals or humans. Naturally, the housing 10 of the transmitter unit will be adapted in size and shape to the appropriate cavity into which it is to be inserted.

Claims

CLAIMS -

7 - 1. An apparatus for monitoring temperature, comprising a transmitter unit including a housing for insertion into a body cavity, the housing containing a component having an electrical characteristic which varies in dependence upon the value of the temperature to be measured and a radio transmitter for transmitting a radio signal in which variations in the electrical characteristic are encoded as a modulation of the signal, and a physically separate receiver unit for detecting and demodulating the radio signal.
2. An apparatus as claimed in claim 1, wherein thp housing contains an electrical circuit for providing a pulse train whose interpulse period is dependent upon the value of the electrical characteristic, the radio signal being amplitude modulated by the pulse train.
3.

An apparatus as claimed in claim 2, wherein the electrical circuit comprises a relaxation oscillator having the component as a timing element.
4. An apparatus as claimed in claim 2 or 3, wherein the radio transmitter comprises a SAWR-controlled oscillator operating in the UHF band.
5. An apparatus as claimed in claim 2, 3 or 4, wherein the receiver unit comprises a radio receiver for recovering the pulse train and means for determining the value of the temperature therefrom.
6. An apparatus as claimed in claim 5, wherein the radio receiver comprises a superregenerative detector using a SAWR for centre frequency control.
7. An apparatus as claimed in claim 5 or 6, wherein the means for determining the value of the parameter comprises a microprocessor.
is An apparatus as claimed in any of claims 1-8, wherein the component is a thermistor.
An apparatus as claimed in any preceding claim, wherein the housing is of cylindrical form for insertion into a vagina.
10. An apparatus for monitoring body temperature, substantially as described herein with reference to the accompanying drawings.