Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS FOR DETERMINING THE LEVEL OF PAIN EXPERIENCED BY
AN ANIMAL AND FOR ADMINISTERING A BENEFICIAL AGENT
Field of the invention
The present invention relates to an apparatus for the delivery of a beneficial
agent to an animal.
Descriation of the urior art
The automated dispensing of liquid medicine, such as analgesia, by
infusion to relieve postoperative pain is increasingly being effected by using
patient controlled or programmable infusion pump units. Typically, a
programmable infusion pump unit includes an electronic infusion unit which can
be
readily activated by a patient. The patient is free to increase the dosage of
medication in response to the pain experienced by repeatedly depressing an
actuator. As the medication administered by such infusion pump units is often
a
narcotic analgesic, the unit is also equipped to limit the maximum dosage thus
avoiding possible negative effects given the onset of an overdose.
The use of patient controlled and programmable infusion pumps has gained
widespread acceptance based on a combination of their reliability in the
timely
administration of medication and the effect of relieving health care workers
of the
routine task of administering dosages of medication.
Animals undergoing surgery in a research or veterinary environment also
invariably experience pain. In such an environment, ethics personnel closely
supervise post-operative pain management in order to minimise any pain and
suffering an animal may have. The current standard of care requires the animal
to
be assessed post operatively by an animal-care giver, and to be medicated
appropriately when there is a subjective impression of the presence of pain.
As animals cannot communicate verbally or cognitively activate an actuator
in response to increased pain, one of the chief modalities used to make the
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assessment of pain is motion and agitation. The more extreme and rapid
the motion, the more intense the pain which is being experienced by the
animal.
While this provides indicia to an animal care-giver of when to deliver
appropriate
analgesic medication, it often means that the animal is medicated only after
the
pain has reached intolerable levels. In addition, there is invariably a delay
between animal experiencing the pain, the physical manifestation of the
animal's
distress, and the interpretation of the manifestation by the animal care-
giver,
who may have a number of animals in her care or may not have the animal
under her surveillance at all times.
It is therefore desirable to provide an apparatus which can automatically
measure the level of pain being experienced by an animal by interpreting the
characteristics of the animal's motion. In addition, the level of pain can be
used
to provide for the infusion of an analgesic agent as an appropriate response
with
a dispensing apparatus operatively connected to the apparatus for measuring
the level of pain; such an apparatus would aid the animal care-giver in the
timely
delivery of an analgesic agent thus reducing the animal's distress and freeing
the animal care-giver to undertake other tasks.
Summary of the invention
It is an object of the present invention to provide an apparatus for the
indication of pain felt by an animal. In accordance with the invention, this
object
is achieved with an apparatus comprising:
(a) at least one motion sensor for sensing motion of the animal, each of said
motion sensors having an output, said motion sensor output being divided into
a
frequency and an amplitude component for separate analysis thereof by a
control unit;
(b) the control unit operatively connected to the output of each motion
sensor, the control unit being capable of generating a trigger signal when the
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2a
output of the motion sensor exceeds a predetermined level, said trigger signal
being representative of the level of pain experienced by the animal;
wherein said apparatus further includes a dispensing means operatively
connected to the trigger signal of the control unit, the dispensing means
causing
a beneficial agent to be discharged from a storage chamber into the animal
upon reception of the trigger signal.
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The trigger signal can be used to trigger a visual or audible alarm, thereby
calling an animal care-giver's attention to the animal in order to provide an
adequate response.
Alternatively, the apparatus according to the invention can also further
include a dispensing means operatively connected to the trigger signal of the
control unit, the dispensing means causing a beneficial agent to be discharged
from a storage chamber into the animal upon reception of the trigger signal.
Consequently, the administration of medication can be automated in response to
the output of the motion sensor, representative of the movement and agitation
of
the animal. In a preferred embodiment, the dispensing means is similar to a
PCA
as used for humans.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention and its advantages will be more easily understood
after reading the following non-restrictive description of preferred
embodiments
thereof, made with reference to the following drawings in which:
FIG. 1 is a block diagram of an apparatus to deliver a beneficial agent to an
animal according to a preferred embodiment of the invention;
FIG. 2 is a detailed perspective view of a platform leg with strain gauge
transducer attached; and
FIG. 3 is a schematic representation of an accelerometer for use in the
apparatus according to the invention.
DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
The invention is an apparatus for automatically measuring the level of pain
experienced by an animal. The apparatus comprises at least one motion sensor
for sensing motion of the animal, each of the motion sensors having an output;
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and a control unit 6 operatively connected to the output of each motion
sensor, the
control unit 6 being capable of generating a trigger signal when the output of
the
motion sensor exceeds a predetermined level.
In a first preferred embodiment of the invention, the motion sensor is
inserted into a typical metabolic cage and consists of a motion platform 12 on
which the animal 16 rests. The metabolic cage is of a size which limits the
movement of the animal such that it may stand up or lie down, but may not turn
around. This type of cage is sometimes required when multiple monitoring
devices
are present in the animal, which it could bite or scratch/rub off if allowed
to roam
free in a cage. As mentioned previously, the motion platform 12 is placed in
the
metabolic cage. The motion platform 12 is preferably made from aluminum with a
grated surface, and is preferably coated with an epoxy-type finish to reduce
the
incidence of injury or blistering to the animal's legs. The grated surface
allows the
animal to defecate or urinate through the motion platform 12 without soiling
itself.
The motion platform 12 rests on four legs 13 that flex when weight is placed
on
them.
Referring to FIG. 2, a detailed perspective view of a platform leg 13 with a
strain gauge transducer 14 attached is shown. As the leg flexes, the strain
gauge
transducer 14 measures the extent of flexion, which is representative of the
change of weight present on the leg. The four strain gauge transducers 14
attached to the four legs 13 of the motion platform are mounted in a
Wheatstone
bridge configuration (not shown) to provide the output 8 of the motion
platform 12.
Referring back to FIG. 1 the output 8 of the motion platform 12 is transferred
to the
control unit 6 via the motion platform output 8.
Accordingly, the motion platform 12 is limited by its requirements of a
metabolic cage for its use. This severely limits the ability of the animal to
move,
and is not desirable when the animal would otherwise have been allowed to roam
free within a larger cage.
In a second preferred embodiment of the invention, the motion sensor is an
accelerometer 11 attached snugly to the neck of the animal by means of a
collar
10. The accelerometer 11 provides a low voltage output that varies directly
with
the motion of the animal. The accelerometer 11 is similar to those used in
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automobiles to sense sudden deceleration and deploy an airbag. The
accelerometer 11 is an electronic circuit that senses acceleration and
converts this
to an electronic signal which can be read by the control unit 6. The
accelerometer
11 senses acceleration on at least two axes, i.e. vertically when the animal
moves
5 up and down and side to side relative to the length of the animal. These
types of
movement are typical of those an animal might make when in distress. However,
as long as both axes are at an angle with respect to the length of the animal,
it will
be sufficient for the invention. Preferably, as shown in FIG. 3, the
accelerometer
11 is an X/Y accelerometer which senses acceleration along axes 62 and 63,
which are preferably orthogonal to axis 64 (length of the animal).
The output of the accelerometer 11 is relayed to the control unit 6 via either
a wire or an RF transmitter 9 and RF receiver 7 pair. If a wire is used, a
swivel is
required that attaches multiple wires and intravenous lines between a
stationary
platform and the animal. This swivel allows the animal to rotate infinitely
without
kinking the intravenous lines or tangling the wires coming off the motion
sensor.
A swivel allows a simple connection between the ACA computer and the
X/Y accelerometer but is expensive (wire + intravenous swivels are much more
expensive than intravenous swivels alone). In addition the swivel length may
be
short, minimizing the size of the area in a cage which the animal can be
allowed to
roam in. An RF transmitter receiver pair 9; 7 allows the accelerometer 11 to
be
attached to it so as to send out the acceleration signals by telemetry to a
receiver
that can be several hundred or more feet away. A lithium-ion battery that is
selected for its lightweight and energy storage powers the transmitter 9.
Under
usual use, the transmitter 9 can send data up to 7 days continuously, without
a
recharge. In its current design, it weighs about 250 gm, but this can be
decreased
by at least half if shorter transmit times between recharges are acceptable.
The
size of the transmitter 7 is about 10x4.2x2.6 cms, it has a connector on one
end
for the X/Y accelerometer 11, and an antenna on the other end. The transmitter
9
contains a microcontroller that allows the coding of the accelerometer data in
a
digital format with embedded error correction and detection codes to allow
error
free transmission of data to the receiver. The X/Y accelerometer 11 on the
neck
collar is connected by a short cable to the transmitter which is tucked in a
pocket
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on the animal's jacket 17 (jackets are used post-operatively to protect
intravenous
lines and incisions from scratching or biting by the animal). The size and
weight of
the jacket 17 used determine the size of the animal that can be monitored.
The X/Y accelerometer 11 when used without an RF transmitter 9, is small
enough to be mounted on an animal the size of a cat. Larger animals can easily
be
monitored by telemetry using the transmitter 9.
The receiver 7 is plugged into the control unit 6, and receives the signal
from the transmitter 9. It too contains a microcontroller, converting the
digital signal
back to the format originally transmitted by the accelerometer 9. It performs
all the
error detection required so as not to pass on invalid data to the control unit
6. Both
devices have a frequency display that allows the user to select a frequency
channel to use to communicate, therefore allowing more than one device to be
used at the same time (as might be present in a busy environment where
multiple
post-operative animals are cared for simultaneously). The receiver 7 also has
a
display that shows the receiving signal and signal strength indicator (in case
noise
is present on that channel that makes communication difficult). A low battery
warning is also present on the receiver (the transmitter sends a low battery
signal
when battery life is low).
Although two types of motion sensors are described herein, it should be
understood that any type of sensor for sensing motion of an animal can be used
for the purpose of the invention and they can be used singly or in
combination.
The control unit 6 acts as an interpreter of the output of the at least one
motion sensor and includes amplifying means, filtering means, and signal
processing means. The control unit 6 amplifies and filters the motion sensor
signal
to remove any DC component such that the resulting signal is representative
only
of the movement of the animal. Signal frequencies greater than those in the
region
of interest are also filtered in order to reduce over all noise and improve
the signal
to noise ratio.
The filtering of the signal also removes DC components of the signal which
could be related to the weight of the animal, or inaccuracies in the
amplifiers. The
resulting signal is then sampled at a frequency at least twice as high as the
3dB
cut off of the high pass filter to prevent aliasing. A fast Fourier transform
is used to
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convert the resulting samples from the time to the frequency domain which are
then analyzed in respect to both signal frequency and signal amplitude. If a
given
signal'is of either an amplitude or a frequency which exceeds a predetermined
level, the control unit generates a trigger signal. A delay circuitry prevents
the
trigger signal from being generated more than once over a period of time,
typically
2 to 5 seconds, to minimize the trigger signals generated by a single
movement.
The predetermined levels of amplitude and frequency are set by means of a
number of control switches 53 located on the control unit. Indicators 52
located on
the control unit 6 provide visual clues as the motion being sensed in order to
aid in
the setting the predetermined levels of amplitude and frequency. All this of
course
could be done through a keyboard and display, and the control unit could be
embodied in a personal computer.
Preferably, the signal amplitude or frequency is also filtered to remove
signals falling below a minimum frequency to remove components related to
slow,
walking-type motion.
Accordingly, the motion sensor continually sends a signal to the control unit
6. The control unit 6 performs the signal processing and will generate a
trigger
signal when the output of the motion sensor falls outside a predetermined
range.
The trigger signal can be applied to a visual or audible alarm, alerting the
animal
care-giver's attention to the animal being monitored. Then, an appropriate
action
can be taken, such as administering a beneficial agent.
Alternatively, the control unit can be operatively connected to a dispensing
means.
The dispensing means 1 is operatively connected to control unit 6 and
responsive to the trigger signal, the dispensing means 1 causing the
beneficial
agent to be discharged from a storage chamber 2 into the animal upon reception
of the trigger signal.
Preferably, the dispensing means determines a rate of delivery of
the beneficial agent, the rate of delivery being determined by the level of
pain
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7a
experienced by the animal and the type of beneficial agent, the level of pain
being related to the number of trigger signals per unit time.
The dispensing means 1 is very similar to a Patient Controlled Analgesia
(PCA) 'pump as widely used for human patients. The dispensing means 1 is
composed of a holder 2 for a storage chamber 15 (here, as will typically be
the
case, a syringe), a pump 4 and a keyboard 50 and display 51. The dispensing
means 1 is a self contained unit preferably encased in its own waterproof
housing.
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The dispensing means 1 has a power source (not shown). An intravenous line 3
delivers the beneficial agent from the storage chamber 15 to the animal 16.
The keyboard 50 and display 51 are used to program variables and
parameters into the dispensing means 1 for delivery of the drug contained in
the
storage chamber 15. The variables that can be programmed include the units of
the drug to be given (for example in grams, milligrams, micrograms, etc..),
the size
of the storage chamber used, the concentration of drug present in the storage
chamber and the volume of the storage chamber. Parameters for delivery include
the number of trigger signals from the control unit 6 via the control unit
output 5
required to give a dose, the dosage to give, the minimum delay which has to
expire before a subsequent dose may be given, and a background infusion rate.
The keyboard 50 and display 51 may also be used to program the dispensing
means 1 to give doses of beneficial agent at predetermined times during the
day,
therefore extending the area of application of the dispensing means 1 to
include
the delivery of, for example, antibiotics or immuno-suppression drugs. The
beneficial agent is driven from the storage chamber 15 by the pump 4 and
introduced into the animal by means of an intravenous/muscular line 3.
Although the present invention has been explained hereinabove by way of a
preferred embodiment thereof, it should be pointed out that any modifications
to
this preferred embodiment within the scope of the appended claims is not
deemed
to alter of change the nature and scope of the present invention.
