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Biomedical subjects

A Harf

Publications and source records attributed to A Harf.

At least 235 records · Page 13Linked to original sources
PubMed1982

PEEP-induced airspace overdistension complicating paraquat lung.

This report describes a case of paraquat poisoning, treated with continuous positive airway pressure. After an initial phase of acute respiratory failure with diffuse pulmonary edema, we observed radiologically a complete clearing of both lungs, associated with an aspect of overdistension. Surprisingly, FRC was above normal, as was total quasi static compliance. The patient died on the 15th day, with intractable hypoxemia. Pathologic analysis revealed large zones of parenchyma with overdistended airspaces, explaining the emphysematous-like aspect of the lungs. We propose that the attempts to increase lung volume with CPAP, at an early phase of diffuse epithelial disorganization, may have, partially at least, dilated the remaining distal airspaces.

Adult↗
PubMed1981

Correction for nonlinearity of body flow plethysmograph.

A modification of conventional signal processing for the pressure-compensated flow plethysmograph is proposed to correct the nonlinearity of the flow element that appears for high flows as encountered during forced expiration. Woven screens behave as porous media with a viscous and an inertial component in the resistance; this explains the nonlinearity (23% at 15.1.s-1 with a 400-mesh wire screen area = 50 cm2). It was shown that the pressure drop-flow relationship can be described by a second-degree equation, which can be included in the computation of the thoracic signal from the box pressure. The need for such a correction is evidenced by testing the plethysmograph with a flow step input (0-15 l.s-1) equivalent both in amplitude and in frequency to the thoracic flow during a forced expiration. Such correction for nonlinearity avoids an overestimation of the thoracic forced vital capacity of up to 0.5 liter in normal subjects.

Humans↗
PubMed1980

Computer determination of thoracic gas volume using plethysmographic "thoracic flow".

Plotting a line to the variables obtained during a panting maneuver, i.e. thoracic volume and mouth pressure, is the conventional way of computing plethysmographic thoracic gas volume (TGV). This procedure is reliable if the magnitude of the thoracic volume changes is large compared to the drift on the signal; this is one of the major problems in volumetric plethysmography. We propose replacing the thoracic volume signal (Vt) by its time derivative (Vt) and similarly mouth pressure (Pm) with its time derivative (Pm). Drift is thus ruled out, and the magnitude of Vt is preserved when the subject fails to carry out noticeable changes in thoracic volume during the panting, since even then the speed of these changes in thoracic volume remains high. The use of Vt and Pm appeared to be necessary when a minicomputer was connected to a pressure-compensated flow plethysmograph to obtain an automatic calculation of TGV. A regression-line technique applied to signals obtained during the panting was used to find the slope of the relation and thus TGV. However, this slope can only be predicted with less than 5% error if the correlation coefficient is very high (i.e., above 0.99). The analysis of 121 recordings from patients showed that the mean r was only 0.954 when Vt and Pm were used. It increased to 0.993 with Vt and Pm. For the same recordings the comparison of hand-calculated TGV and computer-derived TGV showed a much better agreement for the Vt-Pm method (standard error of the estimate (SEE) = 0.14 liter) than for the Vt-Pm method (SEE = 0.34 liter). These results emphasize that, in contrast to the manual technique, the computer does not adequately handle even a small drift of the thoracic signal. The proposed time-derivative method is therefore useful for a hand calculation, but essential to a reliable computer determination of thoracic gas volume

Diagnosis, Computer-Assisted↗
PubMed1980

Functional tests in thirty-nine asbestos spray workers.

Different lung function tests have been studied in a group of 39 spray workers, with exposure of a few months to 20 years, in order to determine early impairments in ventilatory or gaseous exchange parameters. Lung function was assessed by conventional spirometric tests, plethysmographic measurement of lung volume, determination of arterial oxygen tension at rest and on exercise and measurement of single-breath diffusion of carbon monoxide. Asbestos exposure was assessed using a standardized questionnaire administered by an interviewer to determine length of exposure, and light microscopic examination to ascertain the number of ferruginous bodies in one sputum sample or in lung washing fluid. The results of the functional tests are expressed with respect either to duration of working exposure or to the number of ferruginous bodies. Restrictive ventilatory impairment with decrease in diffusion of carbon monoxide and increase in the oxygen alveolar-arterial difference on exercise was observed both in the group with 1-50 ferruginous bodies and in workers exposed for more than five years. The decrease in lung volume was approximately 10% when the length of asbestos exposure varied from 0-5 to 10-15 years, and 15% between those with no ferruginous bodies and those with more than 50. No obstructive profile was observed, even in heavy smokers. All function tests were altered equally. Plethysmography therefore appears to be a suitable technique for the follow-up of asbestos workers.

Adult↗