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[Respiratory function tests during artificial ventilation. Application in the choice of apparatus settings (author's transl)].

Twenty seven patients on artificial ventilation were studied in terms of gas exchange, respiratory mechanics and haemodynamics. The characteristics of acute respiratory failure (dead space effect, shunt effect, disturbances in respiratory mechanics) may be identified and their severity determined. The effects of adjusting artificial ventilation settings (tidal volume, frequency, inspiration/expiration ratio, inspiratory flow, end expiratory pressure, inspired oxygen fraction) may be studied and better adapted to the individual functional requirements of each patient. An organigram of settings based upon the experience gained in this series is suggested.

Asthma↗

[The value of respiratory function tests in the surveillance of asthmatic children].

The purpose of pulmonary function testing in children with asthma is to search for obstructive airway disease. We examined the charts of 169 asthmatic children during intervals between acute exacerbations. The severity of asthma was determined according to VIALATTE classification, with the Tiffeneau ration FEV1/VC (1) and the MMFR/VC ratio serving as obstructive indices. According to these data, children were classified into three groups: normal children (normal FEV1/VC and MMFR/VC), children with probable obstruction of the distal airways (normal FEV1/VC and decreased MMFR/VC), and children with both proximal and distal airway obstruction (decreased FEV1/VC and MMFR/VC). Since suggested normal values vary in the literature, we compared FEV1 and MMFR to determine as accurately as possible the number of children with obstructive disease. The relationship between the degree of clinical involvement and pulmonary function testing results was studied. Clinically, asymptomatic children with suspected normal respiratory function had evidence of obstructive disease in two out of three cases, and would benefit from drug therapy.

Adolescent↗

Novel technique to average breathing loops for infant respiratory function testing.

Breathing loops can be obtained by plotting two respiratory signals on an x-y diagram: the resulting loops represent a non-parametric description of the respiratory system. In infancy, loops are commonly measured during tidal breathing and their interpretation is hampered by high within-subject variability. Therefore a two-dimensional averaging technique for loops has been developed. The algorithm is based on segmentation of the loops and required two steps. First, the total length of the loop of every breathing cycle was divided into a specified number of equidistant intervals and the co-ordinates calculated by stepwise linear approximation of the curve. Second, averaged loops were calculated using the arithmetical mean (or the median if there were artifacts) of the x and y co-ordinates of the loops for all calculated points. To compare the new technique with averaging in the time domain a simulation study was performed using respiratory signals with a coefficient of variation (CV) of 5%, 10%, 15% and 20%. In contrast to the new technique, with increasing CV, averaging in the time domain led to increasing contortions in the averaged flow-volume loops. Mean errors of peak tidal expiratory flow were -3.3%, -13.9%, -21.3% and -34.2%, whereas errors with the new technique were considerably lower (0.5%, 0.4%, 0.5% and -0.1%) and independent of the level of CV.

Algorithms↗