In the early 1970's it was found that certain medicines could be administered in dry-powder form directly to the lungs by inhalation through the mouth or inspiration through the nose. This process allows the medicine to bypass the digestive system, and may, in certain cases, allow smaller dosages to be used to achieve the same results as orally ingested or injected medicines. In some cases, it provides a delivery technique that reduces side effects for medicines and interactions with other prescribed medicines, as well as providing a more rapid drug medication uptake.
Inhaler devices typically deliver medicine in a liquid droplet mist or as a dry powder aerosol. Deposition of particulate matter within the human lungs is a very complex and not fully understood phenomenon. People breathe over a relatively broad tidal volume. It is known that lower transport velocities of gas-entrained particles entering the mouth avoid impaction better within the oropharyngeal cavity. This is particularly true of particles greater than one to two microns in diameter.
In order for particles to remain suspended in a gas stream, their superficial transport velocity must be greater than their gravity settling velocity. For example, a 100 micron particle must have a transport gas velocity of approximately 7 ft/sec or greater for the 100 micron particle to remain in a particle/gas entrainment state. The required transport velocity for smaller particles is much less High speed particles have a greater propensity to impact and deposit on the tissue lining of the oropharyngeal cavity, as noted above. Thus, a significant number of particles are lost and will not enter the lungs, if those particles are not transported at the correct velocity.
Another common problem with inhalers is that the particles agglomerate, causing clumping of particles that then adhere to the inhaler or the oral cavity, rather than entering the lungs. Most approaches to this problem have been to include a surfactant in, on or with the particles to decrease the adhesion between particles.
Importantly, it should not be difficult for a patient to load the inhaler with medicine, and to easily and properly use the inhaler so that the correct dosage is actually administered. Many current dry particle inhalers fail in one or more of these important criteria.
It is therefore an object of the present invention to provide inhalers which are easy to properly use, and which deliver drug powders so that the powder enters the lungs instead of adhering to the back of the throat.
It is an object of the invention to provide an inhaler which will operate effectively with dry powder medicaments having particles ranging in size from about 0.5 to about 10 microns, and preferably from about 1 to about 5 microns in size.
It is a further object of the present invention to provide an inhaler that can operate effectively over a broad inhalation tidal volume range of human breath.
It is a still further object of the present invention to provide an inhaler which controls the volume and velocity of air flow so as to provide effective and desirable colimation, de-agglomeration and entrainment of the inhaled drug.
A related object is to provide an inhaler which creates a high-shear air flow field and controlled circulating gas action to break up particle agglomeration during proper inhaler usage.
A more specific object is to provide an inhaler mouthpiece which is sized and shaped to develop an air flow which will air stream entrained medicament particles through the oropharyngeal cavity.
Another specific object is to provide a medicament-containing inhaler cartridge which will supply medicament for complete air entrainment and proper dispersion into the air stream.
Yet another object is to provide an inhaler air-flow-controlling check valve which will straighten the air flow and limit the air flow volume and velocity to values between pre-determined maxima and minima so as to properly entrain, de-agglomerate and deliver medicament particles to the inhaler user.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings. Throughout the drawings, like reference numerals refer to like parts.