MicroRint This unique design has taken a hitherto specialized measurement out of the pulmonary function laboratory and into the clinic or home. It enables airway resistance to be measured with the same ease as peak flow but without requiring co-operation by the patient. The patient simply breathes through a mouthpiece or face mask. A rapidly occluding valve automatically interrupts the airway for a period so brief as to be imperceptible to the patient. Rint is automatically computed and displayed. The whole procedure takes only a few minutes and can be used for all age ranges from neonates to adults. With a transducer weighing only 12 oz., the instrument is palm sized and comes complete with carrying case. The MicroRint now also comes with its own software. This will enable live blows to be displayed and stored on screen and is a useful addition to the MicroRint package.

Features The problem
Wheeziness is a common problem in pre-school children. Objective assessment of this is difficult because such children cannot usually co-operate with conventional tests of pulmonary function such as peak expiratory flow (PEF). This has hindered both the diagnosis of respiratory tract conditions and the assessment of response to therapy.

The solution
Airway resistance is determined by the calibre of the airways, the same factor which determines PEF. Airway resistance may be determined by momentary interruption of the airway. During interruption alveolar pressure equilibrates with airway pressure allowing airway resistance (Rint) to be determined from airway pressure immediately after interruption and flow (Q) immediately before interruption (Rint = pressure/flow).

Design Principle
When the interrupting valve shuts, airway pressure (Pao) equilibrates with alveolar pressure (Pa). A screen flow meter gives airflow (Q) immediately before interruption. Rint is computed from Pao/Q.

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