Valved holding chamber

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. 

Coppolo, D. P, Mitchell, J. P., and Nagel, M. W. (2006), Levalbuterol aerosol delivery with a nonelectrostatic versus a nonconducting valved holding chamber, Respir. Care, 51,511-514. 

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... 

Finlay WH, Zuberbuhler P. In vitro comparison of beclomethasone and salbutamol metered-dose inhaler aerosols inhaled during pediatric tidal breathing from four valved holding chambers. Chest 1998 114 1676-1680. 

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. 

Fig. 7.2. Diagram of the PDS-1000/He, a stationary particle bombardment machine that is connected to a helium gas container. Controlled by adjustable valves, the gas stream (He) terminates in an acceleration tube, which is mounted on the top of a target chamber. This chamber is closed by a door and set under vacuum shortly before bombardment. When gas flows into the acceleration tube, the rupture disc bursts releasing the shock wave into the lower part of the tube. The gas pressure then accelerates the macrocarrier sheet containing the microprojectiles on its lower surface. The net-like stopping screen holds the macrocarrier sheet back and serves to block the shock wave, while the microprojectiles slip through the pores of the grid and continue on towards their final target.

The first step in the wetted path in the HPLC is the solvent reservoir holding freshly filtered (and possibly degassed or deoxygenated) solvent. Most systems use a porous fritted stone (5-30-/an filter) as a solvent line sinker. The tubing to the solvent inlet is wide-diameter Teflon . In the solvent inlet line we may have another frit and a sapphire ball/stainless steel check valve. The wetted surfaces in the pumping chamber are all stainless steel except for the plunger... 

Disc holder Has a dual function First, it holds the disc, and second, its skirt or hood shape determines the opening characteristics of the valve as it forms the huddling chamber. It also determines the flow path and hence can have an influence on the flow coefficient. The design of disc holders is very different from manufacturer to manufacturer. 

Spring Returns and holds the stem of the valve in the rest position after actuation. May be located inside or outside of the metering chamber. 

The basic components of the system are a liquid driver with only one carrier stream, a multi-port selection valve and a detector (Fig. 2.9). The valve is the heart of the sequential injection system and normally comprises 6—10 peripheral ports and a central port in a multi-position valve configuration. The central port is linked to a holding coil and the peripheral ports are connected to different solution aspiration tubes and transmission lines that are linked to different manifold components, e.g., detector and mixing chamber. Only one peripheral port is connected to the central port at any one time. Stream management inside the holding coil is accomplished by a bi-directional piston (or peristaltic) pump. The analyser is fully computer controlled and the injection volumes, residence times, delivery of solutions and analytical path lengths are selected based on a valve timing sequence and related flow rates. 

Fig. 7. DuPont gradient elution accessory, a, b = proportioning valves, c = holding coil, d, e, T, g, k = valves, h = solvent reservoirs, 1 = source of gas under constant pressure 25 psi), j - vacuum, 1 = pump, m = drain, n = mixing chamber, p = chrofnatograph (injection port, column, detector(s)), q = measuring container.

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