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when a patient exhales (Figure 6). They are intended to enable more efficient use of the liquid to be aerosolized and can shorten overall treatment time. There is an additional difference between breath-actuated and breath-enhanced technologies that is recognized 20 and should be noted. If a nebulizer of each type were loaded with the same dose and volume of medication and a patient were to use the breath-actuated nebulizer to the point of dryness, they would likely receive a larger dose of medication than with the breath-enhanced nebulizer run to dryness (because a breath-enhanced nebulizer delivers medication during the exhalation phase when a patient is not inhaling). In some circumstances, with a breath-actu- ated nebulizer, this may result in both longer nebulization times and overdosing. However, this difference in the two technologies can be managed by prescribing physicians and clinicians and explained to patients and caregivers before usage of a breath-actuated nebulizer. Categories of ultrasonic nebulizers Conventional ultrasonic nebulizers Ultrasonic devices, on the other hand, typically comprise a piezo member mounted in a chamber that is liquid-filled (often with water) where a medicinal cup filled with the formulation to be nebulized is immersed (Figure 7). The water is used a coupling media to transfer the ultrasonic vibration of the piezo member to the medicinal cup and thereby induce aerosolization by a capillary wave, causing cavitation of the liquid at the liquid/air interface. 21 The droplet size distribution is affected by factors such as energy input/frequency, viscosity and surface tension. 22 Inhalation OCTOBER2016 11 Breath-enhanced nebulizer Figure 5 Breath-actuated nebulizer Figure 6 Air sucked through vent on inspiration Air sucked through vent on inspiration Vent closed on expiration PATIENT PATIENT Feeding tube Liquid Air from compressor Air from compressor PATIENT Button "ON" Inspiration Expiration Button "OFF" PATIENT Air from compressor Air from compressor On/off button controls air flow