A practical implementation of acoustic reflectometry for determining airway areas in routine clinical use is described. Advances over previous systems include portability, free breathing during measurements. no need to equilibrate with helium/6xygen, and real-time display of airway areas. Validation of the reflectometer with an airway model gave accuracies and reproducibilities (coefficient of variation (cv)) in the range 5-10%. With human volunteers, the within-mn cv was typically IO%, and the day-today c v was 20%. The eKect of breathing pattem on airway areas is demonstrated.In ten normal volunteers, acoustic and magnetic resonance imaging (MRI) methods of assessing pharyngeal and glottal areas were compared. The results (meaniSD) for the oropharynx were l.0+0.3cm2 acoustically and 0.9+0.5cm1 by MRI (p=O.77]. The corresponding figures for glottal areas were 1.3*0.3 cm'and 1.1+0.4cm2 (p=O.O9).

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For the various pumping rates and for the various heights of the gap were calculated the average value of the small-signal gain and its profile across the gap. For the high power slab C02-lasers, RF-excited at 40.68 MHz, were analyzed the ranges of their geometry parameters variation, providing for the possibility of diffraction limited performance. In theory and in experiment was shown the possibility to select the basic waveguide mode of radiation.

The paper presents the results of measuring of the small-signal gain in the active medium of the high-power pulserepetitive RF-excited slab C02-laser. The measurements were carried out for the pumping pulse durations in the range 20.50 Ls and pulse repetition rates 100.500 Hz. The maximal specific energy, delivered to the active medium, was 430 W/cm3. In the experiment were measured the average output power of radiation, pulse energy and power and the output beam divergence.