Aserosol dispensers have been provided heretofore in a wide variety of configurations for distributing or concentrating a fine mist of a liquid, such as a medicament which can be used in the treatment of illnesses responding to inhalation administration of medicaments.
In the treatment of asthma, for example, there are many liquid medicaments which are administered by inhalation techniques and are intended to be taken in by mouth or nasal inhalation to penetrate the lugs and bronchial system of the patient.
In very early technology of this type, the aerosol dispenser was usually a glass flask to which a bulb was affixed to drive a stream of air through an outlet, the medicament being drawn by, for example, venturi action into this stream, for atomization and distribution in finely divided form to produce the aerosol or mist. In more modern inhalation therapy, spray packages have been provided of small size so that they can readily be held in the hand of the user, the liquid medicament being combined in the package with a propellant usually a freon, which is retained under pressure until a button-operated valve is depressed to discharge a predetermined quantity of the aerosol or a continuous stream thereof.
While these systems have proved to be effective in carrying the medicament to the far reaches of the respiratory system, they have certain disadvantages which limited their applicability.
The inhaled propellant tends to remain as a residual gas in the lungs. It has been found, for example, that during the inhalation phase, this propellant mixes with ambient air and is drawn through the respiratory tract to the alveolae and, because of the greater density of the propellant, a portion of the propellant tends to remain when the air is exhaled during the next phase of the respiration cycle. The accumulation of the heavier propellant in the lungs of the patient has been found to be disadvantageous because it can cause damage to the lungs which, in many cases, is a defective organ in the patients who require treatment by inhalation threapy, such as asthmatics.
Modern inhalators and aerosol medicament dispensers have also been provided with spraying pumps which are actuated by the hand of the user and generally are of the plunger type. In such systems, when the patient depresses the actuating knob or button, he operates the pump to drive a portion of the liquid through an atomizing passage.
A disadvantage of the latter system is that the actuation of the device no longer is as simple as those using a readily operated valve. Furthermore, the operation of the device requires not only significant skill but also considerable effort which frequently cannot be exerted by a seriously ill patient or one in the throes of a significant asthma attack. When the device is improperly operated or operated with insufficient pressure, and frequently when the device is properly operated, the particle size of the liquid in the mist or aerosol is insufficiently fine to permit entrainment to the far reaches of the respiratory tract.
Attempts have been made to improve upon both types of systems, as described in U.S. Pat. No. 3,221,950, by connecting the aerosol valve with a guide tube or mouthpiece intended to carry the aerosol into the mouth of the user. However, when the aerosol utilizes a propellant, the disadvantages noted above result and when the aerosol generator is of the pump type, the problems of these systems are multiplied by the provision of the additional tube since the larger aerosol particles in part collect on the wall of the tube.