The invention relates to a respiratory monitor operable to detect respiration by monitoring movement of a subject's chest and in particular to such a device operable in conjunction with an alarm signal, said alarm signal being generated in response to a cessation of respiratory movement or some other change in respiratory movement and most particularly to such a device adapted to monitor the respiration of an infant.
Sudden Infant death Syndrome (SIDS) causes the deaths of many apparently healthy infants each year. Whilst some precautions can reduce the risk of the condition occurring, there is no precaution that can entirely prevent its occurrence. As a result, this condition is a source of great anxiety to most parents. Infant monitors were developed to provide reassurance to parents. Simple monitors comprise a microphone connected to a loudspeaker either by wires or more commonly by a wireless link. The microphone is placed near the infant and the loudspeaker is placed near the parent thus allowing the parent to hear the infant breathing. Such monitoring devices require the parent to continuously listen to the loudspeaker to detect the existence of breathing noises.
As a result, a number of improved monitoring devices have been proposed, such devices being operative to generate an electronic output signal indicative or related to respiration, which may be monitored automatically. Typically, the monitoring process automatically detects respiration from analysis of the signal and includes the step of generating an alarm if no respiration is detected or if a change in respiration rate is detected. A number of alternative schemes for detecting respiration electronically have been proposed. A first group of schemes utilises one or more
pressure sensing means provided under or otherwise impinged upon by the movement of a subject's chest whilst breathing. Such systems include: US Patent 5,515,865 and US Patent 5,796,340 which each disclose a fluid filled pad incorporating a pressure sensor, the fluid filled pad being placed under the infant and changes in fluid pressure being monitored to detect respiratory movement; US Patent 5,864,291 which discloses strapping a fluid filled enclosure to an infant and monitoring pressure changes in the fluid filled enclosure to detect respiratory motion; US Patent 6,047,201 which discloses monitoring the infants pulse and blood oxygen levels via a device fitted to the infants foot; US Patent 6,267,730 which discloses a device wherein a plunger cooperates with a projection of the device and a piezoelectric member to detect respiratory movement; US Patent 6,280,392 which discloses the provision of a plurality of pressure sensors beneath an infant to detect respiratory movement; and US Patent 6,375,621 which discloses providing a large piezoelectric film under the infant and performing spectrum periodogram or histiogram analysis on signals output by the piezoelectric film to detect respiratory movement or the absence thereof.
However, pressure sensing means provided under a subject or strapped to a subject are prone to detect room noise and movement of the floor or bed/cot in addition to the subject's respiration. These additional signals can mask the respiration signal. These problems limit the accuracy of such systems.
An alternative respiratory monitor disclosed in US 5,914,660 incorporates an optical monitoring arrangement to monitor respiration and determine whether the
subject has moved into a dangerous position i.e. lying upon their front for an infant. The optical arrangement comprises light sensing means operable to detect light
reflected from a reflector means provided on the subject's chest. Such systems are however unreliable as the reflected light may be blocked by bed covers or a misplaced
As a further alternative US Patent 6,289,238 which discloses a wearable electrode arrangement for measuring EEG or ECG signals, body temperature, or body perspiration; and US Patent 6,363,270 which discloses a device having electronic means for monitoring skin conductance, heart rate and blood oxygen and issuing an alarm if simultaneous changes occur in two of the above. In these systems, respiration is detected indirectly by monitoring other body parameters. Furthermore, the detecting means is intrusive and/or potentially uncomfortable when attached to a subject.
It is therefore an object of the present invention to provide a new form of respiratory monitor that overcomes or alleviates some of the above noted problems.
According to a first aspect of the present invention there is provided a respiratory monitor comprising: a base unit and a detector unit; said detector unit being mounted on or next to a subject's thorax, so as to move in phase with respiratory movement of said subject; said detector unit comprising an accelerometer for sensing movement of the detector unit and thereby outputting a signal indicative of the subject's respiratory movement and signal transmitting means for transmitting the signal output by the accelerometer to said base unit; and said base unit comprising signal receiving means for receiving said signal output by said detector unit and means for outputting an indication in response to the signal received from the detector unit.
- A - The present invention thus provides a respiratory monitor, which directly and accurately measures respiration with minimum intrusion or discomfort for the subject.
A processor may be provided in the detector unit, to process signals output by the accelerometer and thereby determine the respiratory rate and respiratory depth of a subject and additionally, change and rates of change in the respiratory rate and respiratory depth, dependent on the determined values, the processor may output either a 'comfort' signal or an 'alarm' signal. Preferably the processor is operable to output the respiratory rate value. Preferably the processor comprises a microprocessor.
Preferably, the processor compares the determined values with predetermined safe ranges of values, before outputting a 'comfort' signal or an 'alarm' signal. Preferably, if the determined values fall within the safe range, then a 'comfort' signal is output by the processing means and if one or more of the determined values falls without said safe range for a predetermined period of time, then an 'alarm' signal is output by the processing means. This predetermined time delay minimises the number of 'false alarms' that are generated from inaccurate signals, recorded during subject movement.
The signal transmitting means preferably comprises an RF signal generator connected to an RF aerial or an RF signal coupling means. The RF signal generator is operable to output an RF signal corresponding to the signal output by the processor unit. The RF signal generator is preferably operable to incorporate a unique identification code in each signal it generates.
Preferably the accelerometer, the processor and the signal transmitting means are implemented in a single integrated circuit. Preferably the detector unit is provided
in a single package.
Preferably, the package contains said integrated circuit and a power source. The power source may conveniently be a battery. Preferably, the package is adapted such that the battery is non replaceable. In this manner the detector unit is disposed of and replaced once the battery runs flat. By providing the elements of the detector unit on a single integrated circuit and by packaging the integrated circuit along with the battery using techniques well established in the semiconductor industry, the detector unit may be manufactured cheaply enough to be disposable.
In alternative embodiments, the power source may comprise a rechargeable battery and/or a means for extracting power from an RF signal.
In order to reduce power consumption by the detector means, the RF signal generator preferably only generates an RF signal intermittently if the output of the processor remains constant. The time interval between successive generated signals may vary dependent upon whether the signal is a 'comfort' signal or an 'alarm' signal.
If the detector unit is disposable, preferably the processor is operable to monitor the battery and output a 'battery level warning' signal when the battery power level drops below a predetermined level. This 'battery level warning' signal may be
different to the 'alarm' signal to minimise confusion between a true apnea episode and a low battery power level, preventing panic in the parent/carer.
Preferably the detector unit is provided with attachment means for mounting the detector unit in a position wherein it moves in phase with the subject's thorax during respiration. The attachment means may comprise one of the following means: a hook and loop fastener fabric (such as Velcro™) for sticking to a subject's clothing, a non slip coating or surface to retain the unit within a subject's pocket, one or more projecting or recessed formations for straps, tapes, ribbons, cords or similar allowing the unit to be connected either to such straps, tapes, ribbons, cords or similar provided as integral parts of the subject's clothing or provided around the subject independently of the subject's clothing.
Preferably, the detector unit is particularly adapted to be used to monitor respiration of infants. In such embodiments, the packaged detector unit may be sufficiently large as not to present choking hazard.
The base unit preferably comprises an RF aerial, an RF signal receiving means connected to said RF aerial and visual means and audio means. The visual means and audio means are preferably controlled by said RF signal receiving means to output a 'comfort' indication, an 'alarm' indication, a 'battery level warning' indication and/or the subjects respiratory rate in response to the received RF signals. The RF signal means may also control the visual and audio means to output an 'alarm' indication if no signal is received from the detector unit in a predetermined time interval. Preferably, the RF signal receiving means is operable to extract an identification code from received signals and thereby verify that the received signals are from the detector unit before controlling the visual or audio means.
Preferably, the visual means comprises an LED, lamp or similar and the audio means comprises a loudspeaker, buzzer or similar. The visual means and/or the audio means may be adapted to provide a 'comfort' indication, when the base unit receives a 'comfort' signal from the detector unit. The 'comfort' indication may be the constant illumination of the visual means. The visual means and/or the audio means may be activated to provide an 'alarm' indication when the base unit receives an 'alarm' signal. If the visual means is activated to provide an 'alarm' indication, the alarm indication may be the intermittent or interrupted lighting of the visual means. If the audio means is used to provide an 'alarm' indication, the 'alarm' indication may be a continuous tone, an interrupted or intermittent tone, a tone sequence, sampled speech/music or similar. The visual means and/or the audio means may be activated to provide a 'battery level warning' indication when the base receives a 'battery level warning' signal. If the visual means is activated to provide a 'battery level warning' indication, the 'battery level warning' indication may be the intermittent or interrupted lighting of the visual means. If the audio means is used to provide a 'battery level warning' indication, the 'battery level warning' indication may be a continuous tone, an interrupted or intermittent tone, a tone sequence, sampled speech/music or similar.
In alternative embodiments, it is possible that visual and/or audio means may be provided on an independent indicator unit in addition to or in place of the visual and audio means on the base unit. The indicator unit may be located remotely of the base unit and may be in communication with the base unit via any suitable fixed or wireless link. In particularly preferred embodiments, the base unit may be positioned in the vicinity of the subject and the indicator unit may be provided in a separate room
to the subject. This will allow those monitoring a subject to go about their business without having to be next to the subject at all times. It means that the subject will not be disturbed by a 'comfort' indication output by the indicator unit.
In some embodiments, the base unit may be operable to communicate with a plurality of indicator units. In the case of a baby at home, such units could be provided in other rooms of the home. In the case of a patient in a hospital, such indicator units could be carried by medical personnel. In further embodiments a single such indicator unit could be operable to communicate with a plurality of base units, hi such an embodiment, the indicator unit would preferably be operable to identify the base unit and hence the subject associated with any alarms output.
Optionally the base may also contain means for generating or for triggering another device to generate a wake up signal in the event of cessation of respiration to startle the subject into recommencing breathing.
As it may not be desirable or required to monitor a suspects respiration constantly, the base unit may be operable to output a control signal to the detector unit switching it between monitoring mode and standby mode. Preferably, when the detector unit receives such a signal from the base unit, it transmits an acknowledgement signal. Preferably, said control signals and said acknowledgement signals each incorporate the detector units unique identification code. When a new detector unit is used for the first time, the base unit may be operable to transmit an identify signal to the detector unit. The identify signal will command the detector unit to transmit its unique identification code to the base unit.
Preferably, the base unit provides a cradle or similar where the detector unit
may be placed whilst not in use.
Preferably, the base unit is provided with an attachment means enabling the base unit to be attached to the parent/carer and be taken from room to room in a
hi some embodiments, it may be possible for a base unit to be in communication with a plurality of detector units, hi one embodiment multiple detector units may be mounted upon the same subject, hi this embodiment the processor may be operable to only output an 'alarm' signal if the determined values of both detector units fall outside the safe range for a predetermined period of time, hi an alternative embodiment, the plurality of detector units may be each mounted upon different subjects. It is of course also possible that a plurality of different subjects may each have multiple detector units mounted upon them, hi this embodiment, the base unit may be operable to identify the detector unit and hence the subject associated with any alarms output. This may be by providing the base unit with a plurality of separate visual means. Alternatively, the base unit may be provided with an additional visual display operable when an 'alarm' indication is output to indicate which detector unit has transmitted the 'alarm' signal. As a further alternative, the audio means may be operable to output a different audio 'alarm' indication in response to alarms output by different detector units.
hi alternative embodiments, it is of course possible that a processor may be provided in the base unit and the signals output by the accelerometer can be transmitted directly to the base unit for processing.
According to a second aspect of the present invention, there is provided a method for monitoring a subject's respiration comprising the steps of: providing a respiratory monitor comprising a base unit and a detector unit, said detector unit comprising an accelerometer; mounting said detector unit on or next to a subject's thorax, so as to move in phase with respiratory movement of said subject and thus sense the respiratory movement of the subject; transmitting the output of said accelerometer to a base unit; and outputting a visual or audio indication of the subject's respiration.
The second aspect of the invention may be implemented by a respiratory monitor according to the first aspect of the present invention incorporating any or all of the features of the first aspect of the present invention.
In order that the invention is more clearly understood, it will now be described further herein with reference to the accompanying drawings, in which:
Figure 1 shows a schematic block diagram of a detector unit of a respiratory monitor according to the present invention; and
Figure 2 shows a schematic block diagram of a base unit of a respiratory monitor according to the present invention.
Referring now to figures 1 and 2, a respiratory monitor comprises a detector unit 100 and a base unit 110. The detector unit is mounted on a subject's chest or on clothing lying around a subject's chest such that the detector unit moves in phase with the respiratory movement of the subject.
The detector unit 100 comprises an accelerometer 101, a processor 102, an RF signal generator 103, an RF aerial 104 and a power source 105. The accelerometer 101 generates electrical signals in response to movement of the detector unit along any of one or more axes. The output of the accelerometer is fed to processor 102.
The processor 102 processes said signals output by the accelerometer 101 to determine respiratory rate, respiratory depth, and changes or rates of changes in these quantities. The processor may further analyse the signals to determine if the subject is making any additional movement. The processor 102 compares the determined values for these quantities with a predetermined range of safe values. If the determined values fall within the safe range the processor 102 outputs a comfort signal If the determined values fall without the safe range the processor 102 outputs an alarm signal.
The processor 102, in some embodiments, may also be operable to store values for respiratory rate, respiratory depth and additional movement and thereby determine an appropriate safe range.
The RF signal generator 103 is operable to generate an RF signal corresponding to the output of the processor 102 and pass said RF signal to the aerial
104. The aerial 104 then transmits said RF signal to the base unit 110. The RF signal generator 103 is also operable to include in each generated RF signal an identification code, identifying the monitoring unit 100.
The accelerometer 101, processor 102, RF signal generator 103 and RF aerial 104 are each provided as part of a common integrated circuit. The integrated circuit is encapsulated in a protective plastic package along with a suitable power source 105,
such as a battery. On the outside of the package is provided suitable mounting means
(not shown) for mounting the detector unit on a subject's chest or to a subject's clothing adjacent to their chest.
In a preferred embodiment the battery is non-replaceable and non- rechargeable and thus the detector unit is disposable once the battery 105 runs flat. In alternative embodiments the battery may be non-replaceable but may be rechargeable, typically by a non-contact coupling arrangement. In yet further embodiments, the power source 105 may be adapted to extract power from external RF signals.
If the output of the processor 102 is a 'comfort' signal, and remains a comfort signal for an extended period of time, rather than constantly outputting an RF
'comfort' signal the RF signal generator 103 generates an RF 'comfort' signal at regular time intervals. These time intervals may be as long as five minutes. If however the processor output changes to alarm, then an alarm signal is immediately generated the RF signal generator 103. The alarm signal may be generated continually until the processor 102 output changes from alarm to comfort or alternatively may be generated at regular time intervals. The time interval between successive alarm signals is typically relatively short compared to the time interval between successive comfort signals.
Referring now to figure 2, the RF signals output by said detector unit 100 are received by an aerial 109 on said base unit 110. An RF signal receiver 106 connected to said aerial 109 processes said received signals to determine if they are comfort
signals or alarm signals. The signal receiving means 106 also processes the signals to determine the identification code incorporated into the signal. If the identification
code does not match the identification code of the detector unit 100, the signal receiving means 106 disregards the signals.
In response to comfort signals or alarm signals received from the detector unit 100 said receiver unit activates visual means 108 and audio means 107 provided on the base unit 110.
hi a preferred embodiment, the visual means 108 comprises an LED. The LED 108 may be illuminated continuously or intermittently in response to a comfort signal or in an alternative embodiment may be illuminated continuously in response to a comfort signal and intermittently in response to an alarm signal. In further alternatives, more complex visual means 108 may be provided such as a combination of two different coloured LEDs or an LED and a display means operable to display text or symbols indicative of the last recorded output status of processor 102.
hi preferred embodiments, the audio means 107 is only activated in response to an alarm signal. The audio means can output any suitable alarm signal such as a continuous tone, an intermittent tone, a tone sequence or sampled speech.
The base unit 110 is typically mains powered or at least mains rechargeable. A parent may thus mount a detector unit 100 on their child when they lie the child down to sleep and be provided with a comfort indication by the base unit whilst they go about their business in, for instance, another room.
hi an alternative embodiment, the base unit 110 may be located in the vicinity of the subject and be operable to communicate with one or more indicator units (not shown) at remote locations. The indicator units may incorporate visual means 107
and audio means 108 for generating comfort signals and alarm signals. The indicator units can be provided in another room or carried on ones person. This allows a person to monitor a subject remotely. It also reduces the necessary power of RF signals emitted from the detector unit 100 in the vicinity of the subject. This increases the typical battery life of the detector unit 100 and reduces the dose of RF radiation that is absorbed by the subject.
It is of course to be understood that the invention is not to be limited to the details of the above embodiments that are described by way of example only.