Spacer valves

Drug dehvery from a spacer is critically dependent on the factors outlined above, including the volume and shape of the spacer, valves, and spacer material. The influence of these factors can be illustrated with reference to three of the more commonly used spacers. 

Installing spacer rings between cylinder head and body or under the valves... 

Figure 4-389 gives a series of schematics that show how the spacer and cement slurry displace drilling mud in the well. Two wiper plugs are usually used to separate the spacer and the cement slurry from the drilling mud in the well. The cementing head has two retainer valves that hold the two flexible rubber wiper plugs with two separate plug-release pins (see Figure 4-389a). When the spacer and the cement slurry are to be pumped to the inside of the casing...

Ceramic materials, including sapphire, have been used extensively in HPLC pumps for more than 20 years as pistons and check valve components. These materials have also been used to construct heads because of their good chemical stability. The use of ceramics is limited, however, because of high cost and brittleness. Although many systems have one material as the primary construction material, the wetted surfaces of a pumping system can contain several other materials. Therefore, for material-sensitive applications, all the materials in the HPLC eluent flow path should be considered. Materials that may be encountered are polymeric materials for pump seals such as fluoropolymers, polypropylene, and Teflon sapphire pump pistons and check valve seats ruby check valve balls Kalrez, KelF, or ceramic washers and spacers polymer-based transducer components and in older systems connections and joints made with silver solder. 

Patients who have difficulty in coordination with inhalers can use a spacer device. These remove the need for coordination between actuation of a pressurised metered dose inhaler and inhalation. The spacer device reduces the velocity of the aerosol and subsequent impaction on the oropharynx. In addition, the device allows more time for evaporation of the propellant so that a larger proportion of the particles can be inhaled and deposited in the lungs. The size of the spacer is important, the larger spacers with a one-way valve (Nebuhaler, Volumatic) being most effective. Spacer devices are particularly useful for patients with poor inhalation technique, for children, for patients requiring higher doses, for nocturnal asthma, and for patients who have poor coordination. 

Asmus, M. J., Liang, J., Coowanitwong, I., and Hochhaus, G. (2004), In vitro performance characteristics of valved holding chamber and spacer devices with a fluticasone metered-dose inhaler, Pharmacotherapy, 24,159-166. 

Metered dose inhaler has been the most popular aerosol delivery device for the treatment of respiratory diseases, which is attributable to its portability and simple operation. Although seemingly easy to use, the MDI is a sophisticated device in design. The drug(s) are suspended or dissolved in a liquefied propellant system, which may also contain excipients such as cosolvents or surfactants. The formulation is kept pressurized in a small canister, sealed with a metering valve. Upon actuation through an actuator, the valve opens and the metered dose is dispensed as an aerosol spray from the expansion and vaporization of the propellant under ambient pressure. The inhalers may be used alone or with spacer devices, the electrostatic issues of which are considered in a later section. The present discussion focuses on the inherent charging of particles produced from MDIs. 

The charging of MDI aerosols clearly has a physicochemical basis. It is related to interactions between the contents of the formulation (propellant, actives, and other excipients) and the compositions of the inhaler components (metering valve, valve stem, and actuator). Research in this area is progressing and a clearer understanding on MDI aerosol charging may enhance the design and use of these products, especially when coupled to spacers. 

Spacer devices, also known as holding chambers, are used with MDIs to overcome problems in coordinating inhalation with actuation, especially in children, and minimize oropharyngeal deposition of drug particles.Essentially, a spacer serves as a reservoir to hold the aerosol cloud for the patient to inhale through a one-way valve at a natural pace. 

Figure 2. 12.7-cm diameter electropulse column 1, diaphragm 2, cathode 3, anode 4, spacers 5, cathode bus bar 6, anode bus bar 7, cathode chamber 8, anode chamber 9, organic feed 10, organic effluent 11, aqueous feed 12, aqueous effluent 13, anolyte feed 14, anolyte effluent 15, air purge 16, air purge 17, 18, vent 19, thermocouple 20, pulse leg 21, control valve. 

Different types of spacer device are available for use with metered dose inhalers but all work in basically the same manner. The spacer usually consists of two parts that slot together with a mouthpiece at one end and an opening for an inhaler at the other. There is a one-way valve which ensures that when a dose of the inhaler is expressed into the spacer the drug is stored in what is basically a holding device. This makes it easier to use a metered dose inhaler successfully as the two actions (pressing down on the metered dose inhaler and inhaling the medication) can be separated into two separate events. 

Timing of the aerosol entry at a particular point in the breathing cycle can have a profound effect on deposition. With the metered-dose inhaler without a spacer, poor synchronization of inspiration with the firing of the valve can result in a substantial loss of the aerosol bolus. For this reason, breath-actuated valves have been developed [91-93]. 

Spacer device Volume (>650 mL) One-way valves Holding chamber versus opened-ended Metal versus plastic Mouthpiece versus facemask Inspiratory flow (slow, deep) Time between actuation and inhalation (<5 s) Cleaning with detergent to reduce static Multiple actuations decrease delivery Coordination of actuation and inhalation for the simple open-tube spacers... 

The butterfly valve (A) is shown in the closed position with the spacer collar assembly eliminated for clarity. Continued on next page. 

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