RESUMO
Controversy still exists regarding the paper speed necessary for accurate measurements from records of maneuvers for forced vital capacity. Twenty-four spirometric wave forms of known characteristics were plotted by a computer at 1, 2, and 3 cm/sec and were measured in random order by 12 experienced readers. We found that all readers made a surprisingly large number of major errors. The speed of the paper was found to be an important determinant for accurately measuring the forced expiratory volume in one second and the mean forced expiratory flow during the middle half of the forced vital capacity. A minimum paper speed of at least 3 cm/sec is important if spirograms are to be accurately measured by hand. Human errors in measurement may be minimized by obtaining results from at least three acceptable curves, by making duplicate reading of curves, and by making use of validated computerized measurement systems.
Assuntos
Espirometria/métodos , Volume Expiratório Forçado , Humanos , Fluxo Máximo Médio Expiratório , Papel , Capacidade VitalAssuntos
Circulação Coronária , Cardiopatias Congênitas/fisiopatologia , Técnicas de Diluição do Indicador , Modelos Cardiovasculares , Circulação Pulmonar , Cateterismo Cardíaco , Criança , Pré-Escolar , Permeabilidade do Canal Arterial/fisiopatologia , Defeitos dos Septos Cardíacos/fisiopatologia , Humanos , Oxigênio/sangue , Tetralogia de Fallot/fisiopatologia , Fatores de TempoRESUMO
Mathematical models are presented for describing and analyzing indicator dilution curves recorded in patients with intracardiac and great vessel shunts. The models treat individual segments of the circulation as linear system blocks, each having, at its output, a characteristic time response to a rapid injection of indicator at its input. These blocks are combined in feedback and feed-forward configurations to simulate left-to-right, right-to-left, and bidirectional shunts. A shunt analysis algorithm, using discrete analogs of the linear system models, was implemented in a computer program and used to analyze thermodilution curves recorded in patients with congenital heart defects. Results are presented comparing shunt fractions obtained from thermodilution curve analyses with oximetrically determined values in 20 patients. Comparing left-to-right shunts measured by the two methods, the mean systematic difference was 0.7% of pulmonary flow and the standard deviation was 7.6% of pulmonary flow. Statistical validation of the bidirectional shunt method will require acquisition and analysis of more data; however, reasonable shunt fractions were computed in five cases studied and good agreement with oximetric determinations was obtained in two cases where complete oximetric data were available.
