text: the present invention seeks to measure various properties , for example temperature or humidity , at the end of a gas delivery tube or conduit using sensors mounted on a wire , such as a wire used for heating the gases flow through the tube or conduit , where the wire resides within the delivery tube or conduit . a heated tube with a heating wire such as that described in fisher & amp ; paykel healthcare limited u . s . pat . no . 6 , 078 , 730 or any other similar tube and heating wire could be utilised with the present invention . referring to fig1 a ventilation and humidifying system as might be used with the present invention is shown . a patient 13 is receiving humidified and pressurised gases through a nasal cannula 12 connected to a humidified gases transportation pathway or inspiratory conduit 3 that in turn is connected to a humidifier 8 ( including humidification chamber 5 ) supplied with gases from a blower 15 or other appropriate gases supply means . the inspiratory conduit 3 is connected to the outlet 4 of the humidification chamber 5 that contains a volume of water 6 . the humidification chamber 5 is preferably formed from a plastics material and may have a highly heat conductive base ( for example an aluminium base ) that is in direct contact with a heater plate 7 of humidifier 8 . the humidifier 8 is provided with control means or an electronic controller 9 that may comprise a microprocessor based controller executing computer software commands stored in associated memory . gases flowing through the inspiratory conduit 3 are passed to the patient by way of the nasal cannula 12 , but may also be passed to the patient by way of other patient interfaces such as a nasal or full face mask . the controller 9 receives input from sources such as user input means or dial 10 through which a user of the device may , for example , set a predetermined required value ( preset value ) of humidity or temperature of the gases supplied to patient 13 . in response to the user set humidity or temperature value input via dial 10 and other possible inputs such as internal sensors that sense gases flow or temperature , or by parameters calculated in the controller , controller 9 determines when ( or to what level ) to energise heater plate 7 to heat the water 6 within humidification chamber 5 . as the volume of water 6 within humidification chamber 5 is heated , water vapour begins to fill the volume of the chamber above the surface of the water and is passed out of the humidification chamber 5 outlet 4 with the flow of gases ( for example air ) provided from a gases supply means or blower 15 which enters the humidification chamber 5 through inlet 16 . the blower 15 may be provided with a variable speed pump or fan 2 which draws air or other gases through the blower inlet 17 . the speed of the variable speed pump or fan 2 may be controlled by a further control means or electronic controller 18 which responds either to inputs from controller 9 or to user - set predetermined required values ( preset values ) of pressure or fan speed , via dial 19 . alternatively , the function of this controller 18 can be combined with the other controller 9 . a heating element or wire 11 is preferably provided within , around and throughout the conduit or tubing 3 to help prevent condensation of the humidified gases within the conduit . such condensation is due to the temperature of the walls of the conduit being close to the ambient temperature , ( being the temperature of the surrounding atmosphere ) which is usually lower than the temperature of the humidified gases within the conduit . the heater element effectively replaces the energy lost from the gases through conduction and convection during transit through the conduit . thus the conduit heater element ensures the gases delivered are at an optimal temperature and humidity . such a heater wire is commonly driven either with direct current ( dc ) or alternating current ( ac ) and in both cases the heating voltage is usually switched on and off to control the power applied to the heating element . in the present invention the heating element 11 , which is most preferably a wire , is used along with an electronic circuit to determine properties of the gases supplied to the patient . the circuit ( 20 or 40 in fig2 and 3 ) is preferably connected in series with the heater wire 11 . the circuit may be on a printed circuit board , or wired within a housing that may be a plastic moulding in the gases flow , or a circuit board that is at least partially moulded within the wall of the conduit or tubing 3 . the properties that may be measured include temperature , pressure , gas composition and humidity . two embodiments of the present invention are described below , one that operates using only a dc heating voltage and the other that can operate with a dc or ac heating voltage . fig2 shows a circuit 20 that may be utilised for carrying out the method of measuring temperature of the present invention . when a dc heating voltage 25 is applied to the heater wire the diode 22 conducts and current flows through the heater wire 21 , 28 and the heater wire functions as normal and provides heating to the delivery tube 3 . when the heating voltage 25 is switched off using switch 29 , a measurement voltage 26 , which has opposite polarity to the heating voltage 25 is applied to the heater wire . in this case , the current in the heater wire 21 , 28 does not flow through the diode 22 but flows through the thermistor 23 and through a reference resistor 24 . the voltage across the reference resistor 24 can then be measured at the output 27 and the temperature of the gases determined . the voltage measurement 27 across the reference resistor , 24 , is converted to a temperature using a look up table or an equation to calculate a value for temperature . this is similar to a commonly used technique where the thermistor 23 forms a potential divider with the reference resistor 24 . more generally , the thermistor may be replaced by an impedance ( for example , a resistor and a capacitive sensor ) for pressure or humidity measurement . either the impedance can be measured by measuring the voltage across the reference resistor 24 or the rise - time could be determined by looking at the voltage across the reference resistor 24 in time . part of the circuit 20 would be included in the delivery conduit 3 and in particular the diode 22 and thermistor 23 ( in parallel with one another ) are preferably placed in series with the heater wire 21 , 28 at a point in the heater wire at or near the end 30 ( nearest the user 13 , see fig1 , 2 and 4 ) of the delivery tube 3 , for example they may be interconnected on a printed circuit board , overmoulded with plastic for sealing and mounted in the gases stream through the delivery conduit as shown in fig4 . furthermore , the circuit may be formed by interconnected parts in a housing , for example , a plastic housing , that protrudes from the plastic wall of the delivery tube into the gases flow through the conduit , in order to measure that gases properties . all other parts of the circuit 20 including the reference resistor 24 and the switching circuitry 29 would be included in the control circuitry of the humidifier 8 . the thermistor &# 39 ; s value can be chosen to have different resistance curves with known properties at ambient temperature . the choice of a particular thermistor value for use with the circuit allows identification by the control system of the present invention and matching of that thermistor value with a specific conduit or tubing 3 . such that different thermistor values can be matched with a particular and appropriate conduit types and upon connection of the conduit to a humidifier or blower device , the control system can identify that thermistor and apply the appropriate control strategy to the heating of the conduit . the circuit shown in fig2 is intended to be used when a dc heating voltage is used in conjunction with the heater wire , delivery conduit and system as shown in fig1 . an alternative embodiment of a circuit 40 that would provide measurement of the gases properties , such as temperature and is suitable for ac and dc voltages , is shown in fig3 . a number of voltage signals 51 , 52 , 53 , which are at different frequencies , are added together at an adder 50 . these signals include at least one heating signal 51 and at least one measuring signal 53 . the combination of these signals passes down the heater wire 44 , creating currents ( heating and measuring ) in the heater wire 44 . a number of parallel paths are established 41 , 43 , 45 each containing a filter ( for example , as shown in fig3 , one low pass filter 41 and three band pass filters 43 , 45 , 48 ) that each pass a different frequency range . these parallel paths ( that is , filters , thermistors and / or sensors ) are preferably located at the end 30 of the delivery tube 3 , in a similar manner as described in relation to fig2 . the parallel paths allow the heating current to be passed through a different path to the measurement currents . it also allows multiple measurement signals to be passed through the heater wire so that different properties of the gases ( e . g . temperature , pressure , humidity , composition ) may be measured . the heating and measurement currents return through the heater wire 46 and can be filtered through a number of measurement filters 47 , 49 , 57 in parallel that pass frequency bands that correspond to the filters , 41 , 43 , 45 located at the end 30 of the tube 3 . the heating current takes a different path than the measurement currents . the measurement currents each take a different path depending on their frequency and this allows each measurement current to be measured by passing it through a reference resistor 48 , 54 or similar . again a look up table or equation may be used to convert the voltage across the reference resistor 48 , 54 to , for example , a temperature . in the preferred embodiment of the present invention the measurement filters 47 , 49 , 57 would be included in the humidifier 8 control circuitry . in a further embodiment one or more of the sensing elements 55 , 56 at the end 30 of the delivery tube 3 could be replaced by a fixed impedance to allow identification of the tube so that different control algorithms can be used for different conduits or tubes . fig4 shows a cutaway view of a conduit 3 with a printed circuit board 60 housing the parts to one of the circuits of the present invention described above with reference to fig2 or 3 . the circuit board 60 is connected to the heating wires 21 , 28 and as such is positioned within the conduit 3 . in this manner , the thermistor 23 included on the board 60 is exposed to the gases flowing through the conduit 3 and can provide measurements of the properties of the gases . the circuits and method of the present invention can be applied to a number of applications of these technologies for humidification and breathing circuit products . for example , the measurement of the temperature or humidity at the end of the delivery tube ( or in a patient interface , for example , nasal cannula or mask ) can be used to better control the humidifier , such that a more accurate temperature of gases can be supplied to the patient , providing optimal patient comfort and therapy . additionally , other gases properties may be measured , such as the gases pressure or gas composition near the patient . the apparatus of the present invention eliminates the need for external wires for sensing gases properties , as is required by the prior art . furthermore the apparatus of the present invention only uses two pins or contacts ( as opposed to four pins as used in current heated tube implementations ). this means the system of the present invention is likely to be more reliable as the contacts / pins are likely to be less prone to breakage . the utilisation of the heater wire for measuring gases properties may also reduce the cost of the breathing tube 3 and associated parts , especially if the breathing tube is to be disposable .