Nebulizers mass output

There are many commercially available nebulizers with differing mass output rates and aerosol size distributions which will be a function of operating conditions, such as compressed air flow rate. As described above, for maximum efficacy, the drug-loaded droplets need to be less than 5 pm. In the treatment or prophylaxis of P.carinii pneumonia with nebulized pentamidine where the target is the alveolar space it is preferable to use nebulizers capable of generating droplets of less than 2 pm. 

Output is often assessed by weighing the device before and after the nebulization period. Output is usually expressed as volume/unit time (mL min-1) or volume per unit airflow (mL L 1 air) although density of solutions is not always considered. Such measurements of mass output do not, however, provide information on dmg delivery rates. 

The delivery efficiency, or the nebulizer output, can be expressed in many different ways, as widely documented in the literature. Sometimes it is represented as the volume output, or solution mass output. However, it is more practical to use the drug mass emitted from the nebulizer at or near the mouthpiece to estimate the nebulizer output, because the amount of aerosolized drug mass at this point in the system is the best measure of how much drug the patient has available to inhale. 

Table 1 Design features of ultrasonic nebulizers determining particle size distribution and mass output...

The FisoNeb and Pulmosonic nebulizers both operate at a frequency of 1.3 MHz that generates a mass median aerodynamic diameter (MMDA) of 4-6 pm [9,10]. The Pulmosonic nebulizer has been reported not to deliver many particles smaller than 2 pm and, therefore, is unsuitable for pentamidine administration [10]. The Portosonic (DeVilbiss) device is a 2.3-MHz ultrasonic nebulizer and may offer the combination of less than 2-pm MMAD and a high output. In any study using ultrasonic nebulizers, the output and particle size of each device need to be periodically sampled, because the frequency of the piezoelectric crystal may alter with age [10]. Any MMADs between 0.5 and 2 pm are available. The Respirgard nebulizer II has one-way valves that control a drug reservoir, allow entrainment of room air in patients whose minute ventilation is... 

Nebulizers also vary in terms of their mass output. Smith and coworkers measured the size distribution and the mass output of 23 nebulizer/compressor combinations. Like Matthys et al. (92), they found a wide range in MMADs 2.6-16.2 jm. They also reported a broad range in mass output minimum output was 47% of a 2.5-mL fill maximum output was 81%. Figure 12 shows that there was a weak correlation between the percentage of particles <5 pm and the volume output over a fixed amount of time (94). 

Nebulizers vary significantly in terms of their particle size and mass output. However, it is not clear how these differences effect the deposition pattern and the clinical response to various inhaled drugs, because, until recently, nebulizers... 

The airflow (and the variability thereof) and its effect on nebulizer output (mass) and the respirable dose... 

The ICP source subsystem incorporates its own internal microcomputer and memory in order to execute the controller s commands. The RF power supply Is under computer control. Likewise, all of the argon flows, the ignitor, peristaltic pump and safety interlocks are directly controlled by the system computer. The RF power output Is stable to less than 0.01 over 1 h of operation. The nebulizer argon flow is controlled through a thermostated mass flow controller to ensure long-term stability. The uptake rate of the two-channel peristaltic pump Incorporated within the source subsystem Is variable by the system controller. 

Figure 4 Cartoon depicting technique for quantification of nebulizer output and measurement of deposition. On the left, a patient inhales nebulized particles via a Y piece. The exhalation filter captures exhaled particles. On the right, the same patient performs a similar maneuver. The inhaled mass filter captures particles that would have been inhaled. Differences between filters measure deposition. Breathing pattern can be monitored using a pneumotachograph represents the sum of minute ventilation plus nebulizer flow leaving the expiratory arm of the Y piece). (From Ref. 9.)...

Figure 21 Influence of ventilator choice on aerosol output expressed as inhaled mass (%) versus time for four ventilators utilizing the Misty-Neb nebulizer. (Baxter Healthcare Corp., Valencia CA from Ref. 32.)...

Mass detector. The liquid chromatographer s demand for a universal detector which overcomes some of the problems encountered with the RI detector, (such as poor sensitivity and temperature instability) led to the development about ten years ago of the mass detector described here. The transport detectors of the 1960s detected the solute by means of a flame ionization detector after removal of the solvent from the eluent stream. They were abandoned, owing to lack of sensitivity and mechanical problems associated with the moving belt or wire. The new mass detector is similar in principle, but here the eluent leaves the column and is pumped into a nebulizer, assisted by an air supply. The atomized liquid is passed into a heated evaporation column where all the solutes less volatile than the solvent are carried down the column as a cloud of fine particles. A light source and photomultiplier arranged at the bottom of the column, perpendicular to the flow, detect the cloud of particles. The output from the photomultiplier, which is proportional to the concentration, can be amplified and directed to a recorder or data system. 

D), the output of which is positioned orthogonal to the ESI nebulizer of the mass spectrometer... 

---