Exhalation valve

Figures 9-16 and 9-17 show an example of a FF APR with a different type of eartridges that ean be used. The eireular strueture below the faeepieee window with the eross on it houses the exhalation valve and is not a eartridge holder.

FIGURE 6.6 Dust mask with exhalation valve. 

The open circuit apparatus is essentially similar to the closed circuit compressed gas system, except that the user exhales through an exhalation valve... 

FIGURE 11-1 Schematic diagram of a closed anesthesia system. [/] Vaporizer for volatile liquid anesthetics. [2] Compressed gas source. [3] Inhalation unidirectional valve. [4] Mask. [5] Unidirectional exhalation valve. [6] Rebreathing bag. [73 Carbon dioxide absorption chamber. 

The French developed the M-2 mask , consisting of 20 layers of muslin impregnated with Greasene and another 20 impregnated with Complexene . The mask had twin circular celluloid lenses and a weatherproof flap for rain protection, but no outlet valve or filter canister. The M-2 was followed by the Tissot mask , with a thin, moulded rubber facepiece incorporating eyepieces, a flapper-type rubber exhale valve and a flexible, fabric-covered hose running over the shoulder to a filter canister worn in a harness on the back. The Tissot mask also ducted air over the eyepieces to help demist them a feature still used in most present-day respirators. 

After WWI, respirators followed the general style of elastomeric facepieces, with eyepieces/ visors and exhale valves, and filters connected by tubes or mounted directly on the facepiece. The first all-rubber, full-face respirator was issued to the Royal Navy in 1922 and the Army in 1924. The facepiece was moulded in natural rubber and its outer surface was covered in stockinette to aid the wicking out and surface evaporation of chemical agents. The respirator had two-inch diameter glass eyepieces and an expiratory valve fitted in the region of the nosepiece. The filter canister was mounted on the wearer s body and... 

The primary speech module of the S10 respirator does not have a diaphragm instead, the exhale valve housing is in the shape of a folded acoustic horn, to serve both as a speech module and a deadspace. The S10 also has a secondary speech module, that does incorporate a small diaphragm, to which radio microphones can be attached. 

There are three respiratory effects. First, inhalation resistance is imposed by the filter canister, inhalation valve and, to some extent, the airflow pattern. Secondly, exhalation resistance is imposed by the exhale valve and to some extent the exhale valve deadspace design. Thirdly, the internal volume of the respirator increases the respiratory deadspace, which can cause build-up of carbon dioxide. 

Fig. 6.33 Particle-filtering half masks, (a) Mouth protection against coarse dusts (b) protection level FFPl without exhalation valve (c) protection level FFPl with exhalation valve (d) protection level FFP3 with an exhalation valve (e) FFP3 with an exhalation valve.

In this mode, the ventilator maintains a positive pressure at the airway as the patient attempts to inspire. Figure 18.6 illustrates a typical airway pressure waveform during continuous positive airway pressure (CPAP) breath delivery. The therapist sets the sensitivity level lower than PEEP. The sensitivity is the pressure level that the patient has to attain by making an effort to breathe. This, in turn, triggers the ventilator to deliver a spontaneous breath by supplying air (or a mixture of air and oxygen) to raise the pressure back to the PEEP level. Typically, the PEEP and sensitivity levels are selected such that the patient will be impelled to exert effort to breathe independently. As in the case of the mandatory mode, when the patient exhales, the ventilator shuts off the flow of gas and opens the exhalation valve to allow the patient to exhale into the atmosphere. 

Figure 18.7 shows a typical airway pressure waveform during the delivery of a pressure s pporf breath. In this mode, when the patient s airway pressure drops below the therapist-set sensitivity Une, the breath delivery system raises the airway pressure to the pressure support level (>PEEP), selected by the therapist. The ventilator stops the inspiratory gas flow when the patient starts to exhale and controls the exhalation valve to achieve the set PEEP level. 

In a microprocessor-based ventilator, an electronically actuated valve can be employed that has adequate dynamic response ( 20 ms rise time) to regulate PEEP. For this purpose, the pressure in the patient s breath delivery circuit is measured using a pressure transducer (Figure 18.8). The microprocessor initially opens the exhalation valve completely to minimize resistance to expiratory flow. At the same time, it samples the pressure transducer s output and begins to close the exhalation valve as the pressure begins to approach the desired PEEP level, Because the patient s exhaled flow is the only source of pressure, if the airway pressure drops below PEEP, it cannot be brought back up until the next inspiratory period. Hence, an overrun (i.e., a drop to a level below PEEP) in the closed-loop control of PEEP should be avoided. 

The level of protection that can be provided by a respirator is indicated by the respirator s protection factor (PF). This number, determined experimentally by measuring facepiece seal and exhalation valve leakage, indicates the relative difference in concentration of the concentrations of substances outside and inside the facepiece that can be maintained by the respirator. For example, a PF of 10 for a respirator means that a user could expect to inhale no more than one tenth of the airborne contaminant present. A source of protection factors for various types of atmosphere-supplying and air-purifying respirators can be found in the American National Standards Institute (ANSI) standard ANSI Z-88.2-1980. 

A. Positive pressure check. Close off the exhalation valve and exhale gently into the facepiece. The face fit is considered satisfactory if a slight positive pressure can be built up inside the facepiece without any evidence of ontward leakage of air at the seal. For most respirators this... 

A form of gas respirator, which generally incorporates goggles and a visor, with an exhalation valve connected to a chemical canister filter. It normally provides protection against low concentrations of designated toxic gases and vapors. See also Cartridge Respirator Respirator. 

The portion of a respirator that covers the user s nose and mouth in a half-mask facepiece, or the nose, mouth, and eyes in a full facepiece. It is designed to make a gas-tight or dust-tight fit with the face and includes the headband, exhalation valves, and connections for an air purifying device or respirable gas source or both. See also Eye Protection. 

For protection of the airways to inhalation of substances, respirators can be used. Effective respirators however are not pleasant to wear, as the worker never breathes freely and they may be rather heavy as well. Many mouth masks are provided with an in- or exhalation valve or both which eases breathing, see Fig. 26.3. 

All respirators shall be stored to protect them from damage, contamination, dust, sunlight, extrane tanperatures, excessive moisture, and damaging chemicals. They must be packed or stored to prevent deformation of the face piece and exhalation valve. Emergency respirators shall be kept accessible to the work area, stored in compartments or in covers that are clearly marked as containing emergency respirators, and stored in accordance with any applicable manufacturer instructions. 

Positive Pressure Check Procedure (cartridge-type respirator) After the respirator has been put in place and straps adjusted for firm but comfortable tension, the exhalation valve is blocked by the wearer s palm. The wearer takes a deep breath, gently exhales a little air, and holds his or her breath for ten (10) seconds. If the mask fits properly, it will feel as if it wants to pop away from the face, but no leakage will occur. 

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