Surgery – Respiratory method or device – Means for mixing treating agent with respiratory gas
Reexamination Certificate
2000-06-30
2003-07-01
Dawson, Glenn K. (Department: 3761)
Surgery
Respiratory method or device
Means for mixing treating agent with respiratory gas
C128S203120, C128S203230, C128S203240
Reexamination Certificate
active
06584971
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to drug delivery apparatus, particularly, but not exclusively, nebulizers and dosimetric spacers.
(2) Description of the Related Art
Many different types of nebulizers are known for delivering medication directly into the lungs of a patient, usually for treatment of respiratory diseases. Nebulizers normally deliver medication in the form of droplets or a dry powder. In most nebulizers, atomization of the medicament into a stream of air occurs continuously, regardless of whether the patient is inspiring or expiring. However, the effect of continuous atomization is that a significant proportion of the medication is lost during expiration.
Commonly known nebulizers are either pneumatically operated from a compressed air source connected to the nebulizer which atomizes the liquid, or are ultrasonic nebulizers which use a piezoelectric crystal to atomize the liquid. More recently, a mesh-type nebulizer has been developed in which the medication is forced through a fine mesh in order to create droplets of the medication. A further type of nebulizer, or inhaler, is one which uses a piezoelectric vibrator together with an electro-static charge plate to fluidize and disperse a dry powder aerosol into an airstream. Such a nebulizer is disclosed in U.S. Pat. No. 5,694,920.
The optimum diameter of medication particles or droplets is about 1-5 microns. If the particles or droplets are bigger than this, they are likely to be impacted in the airway before they reach the lungs, but if they are smaller than one micron, they tend to be carried out of the lungs again on exhalation without sedimenting in the lungs.
Nebulizers and inhalers disperse the small particles of medication into an air stream, or stream of other gas, leading to a patient. References to the air which carries the medication entrained in it include other gases suitable for carrying the medication.
One known nebulizer analyses the pressure changes within the device during the first three breaths to determine an average shape of the breathing pattern. A timed pulse of atomization is commenced when starting subsequent inspirations such that atomization occurs for the first 50% of the inspiration. This is illustrated in
FIG. 1
where the breathing pattern and pulse are superimposed. This is effective in reducing the loss of medication during exhalation to about 3%.
FIG. 1
shows the breaths in a graph of flow rate against time. When the treatment is commenced, a patient breathes in and out three times through the nebulizer before treatment commences. The first three breaths are measured so that the timed pulse of atomization occurs for 50% of the average time of inhalation. The duration of inhalation is indicated as T
1
, T
2
and T
3
. These timed periods are averaged, and divided by two in order to determine the pulse length for the next fourth breath where treatment starts. For each subsequent breath, the duration of the pulse of atomization is determined by summing the time period of inhalation of the previous three breaths, dividing by three to obtain an average and dividing by two. The dose administered to the patient is directly proportional to the duration of the pulse of atomization, and so the period of atomization is summed, and the atomizer is switched off, or indicates that the patient should stop once the dose administered to the patient reaches the amount of medication prescribed for that treatment.
Other nebulizers are known in which the timed pulse of atomization is fixed to be other than 50% of the duration of inspiration. However, in these other nebulizers, the pulse length must be set for each patient by the clinician. Many of the nebulizers are, therefore, suitable only for use in a controlled environment, such as a hospital. The setting of the pulse length for each patient means that most nebulizers are not suitable for a patient to use at home.
Reference is made to our co-pending International Patent Publication No. WO 97/48431, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length.
FIGS. 2 and 3
of this application show the nebulizer which is disclosed in the above co-pending Patent application. Referring to
FIG. 2
, a mouthpiece
1
is shown through which a patient inhales in the direction of arrow
2
. Below the mouthpiece
1
is a removable atomizing section
3
which, in turn, rests on a base
4
.
The base
4
is shown in more detail in FIG.
3
. Referring to
FIG. 3
, the base
4
includes an inlet
5
through which air is supplied under pressure from a compressor (not shown). The pressurized air is led via a tube
6
to a manifold
7
which controls the flow of pressurized air to an air outlet
8
which directs air into the atomizing section
3
shown in FIG.
2
. The base
4
also includes a pressure sensor
9
which detects the pressure within the atomizing section
3
via a port
10
.
Referring again to
FIG. 2
, air under pressure passes through the air outlet
8
of the base
4
and is conducted through a tubular post
11
to an atomizer nozzle
12
out of which the air issues under pressure. A deflector
13
is located in the path of the pressurised air issuing from the nozzle
12
so that the pressurized air is deflected laterally so as to pass beneath a baffle
14
. The passage of the pressurized air across the top of the tubular post
11
causes medication
15
to be drawn up between the outer surface of the tubular post
11
and the inner surface of a sleeve
16
which surrounds the tubular post
11
. The medication
15
is atomized in the stream of air, and carried away in the stream of air below the rim of the baffle
14
and up through the mouthpiece
1
to a patient.
The pressure sensor
9
in the base
4
monitors the breathing pattern of a patient, and on the basis of the breathing pattern, the manifold
7
is controlled to supply pressurized air to the atomizing section
3
only during the first 50% of an inhalation phase.
While a particular type of nebulizer is described above, the present application is suitable for application to any type of nebulizer.
The invention also relates to other drug delivery apparatus, such as spacers in which a dose of a drug in droplet or powder form is released into a spacer chamber or holding chamber from which the patient inhales. These are most appropriate for elderly patients or children who have difficulty in using a multi-dose inhaler or dry powder inhaler, for example, because they have trouble coordinating the release of the drug with the beginning of inhalation, or because their inhalation flow rates are too small. For example, spacers are disclosed in International patent publication number WO 96/13294, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length.
BRIEF SUMMARY OF THE INVENTION
According to a first aspect of the present invention, a drug delivery apparatus comprises a drug delivery device for selectively delivering medication-laden air or air not carrying any medication to a patient for inspiration, wherein medication-laden air is selected to be delivered in pulses; a sensor for monitoring a patient's breathing pattern; and a controller for controlling the said delivery device to deliver the medication in pulses, wherein the length of the pulses, and their proportion of the inspiratory phase of the breathing pattern are varied by the controller depending on the breathing pattern monitored by the sensor.
Preferably, the drug delivery apparatus is a nebulizer in which atomization occurs in pulses. It could, alternatively be a dosimetric spacer in which drug-laden air or gas is released from a holding chamber in pulses.
According to a second aspect of the invention, a method for determining the duration of a pulse during which medication-laden air is delivered to a patient during inspiration comprises:
(i) measuring the tidal volume of a patient;
(ii) measuring the duration of inspiration of a patient;
(iii) storing an estimate of the volume of a patien
Denyer Jonathan Stanley Harold
Dyche Anthony
Prince Ivan Richard
Dawson Glenn K.
Medic-Aid Limited
Simons William A.
Wiggin & Dana
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