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Biomedical subjects

J P Butler

Publications and source records attributed to J P Butler.

4 recordsLinked to original sources
PubMed1979

Estimating a distribution's central moments: a specific tidal ventilation application.

A method is presented for extracting central moments of a distribution from data generated by the distribution over a known kernel. It is applied to the problem of the specific tidal ventilation in the lung in the multiple-breath N2-washout setting, and we found that in estimating the mean and variance, the method accurately recovers from test data those values characteristic of a test distribution. Some preliminary results on normal subjects are shown.

Humans↗
PubMed1978

Indirect estimation of physiological distribution functions.

Multicompartment models, such as sums of exponential decays and sums of effects of different ventilation-perfusion ratios, are cast in the form of integrals. Difficulties in obtaining the density function in such an integral from measured values of the integral are attributed to amplification of error in the inversion solution and to the limited number of measurement points. The present approach to control the effect of the error is regularization with the use of a non-negativity constraint on the density function. The answers are sums of the influence or kernel functions of the integral wherever the sum is positive, and zero elsewhere. Such non-negative answers not only ensure that true density functions are obtained but also permit the answer to fall abruptly to zero. For example, a delta function can be much more closely approximated with the non-negativity constraint than without. A rule is developed to choose the value of smoothing parameter so as to minimize an approximate upper bound on the integral of the squared error of the answer. This typically tends to result in some oversmoothing. Functions tested without error and with 2% relative error are as follows: one of the kernel functions (best results); rectangular boxes and delta functions (fair results); and wide boxes (poor results).

Models, Biological↗
PubMed1977

Airway geometry by analysis of acoustic pulse response measurements.

Serial distribution of airway properties determines in part the response of the lung to high frequency oscillations. We measured the response of excised dog lungs and lobes between 156 and 10,000 Hz and determined the area-distance function of the acoustically equivalent structure having rigid walls, regular branching, and negligible internal losses. The utility of this techique was tested by determining the effects of air trapping, removal of pleura from a dried lung, central airway smooth muscle tone. A strong correlation was found between relative changes in equivalent acoustic area and relative area changes measured radiographically in individual airways at corresponding distances. We conclude that despite departures of the properties of the real lung from the characteristics of the acoustically equivalent structure, changes in the area-distance function computed by this technique provide reasonable estimates of the magnitude and serial distribution of actual changes in airway cross-sectional area.

Acoustic Impedance Tests↗