Sound intensity and respiratory responses in the neonate. Comparison with cardiac rate responses.

This report is concerned primarily with the effect of sound intensity on the respiratory response in newborn infants. Each of 9 infants between the ages of 2 and 5 days was presented repeatedly with a 5-sec. duration white noise stimulus varying in intensity from 55 to 100 db., while cardiac and respiratory activities were continuously recorded. In general, the response to a sound stimulus consisted of a progressive decrease in respiratory cycle length, reaching a minimum, then a subsequent return toward the prestimulus cycle length. Increasing sound intensity resulted in a decrease in the time to peak and a greater magnitude change in the peak and return portions of the response. In addition, increased stimulus intensity produced an increase in the slope of the regression line between response magnitude and the prestimulus respiratory cycle, as well as an increase in the variability around this line. There was a tendency for the respiratory response measures at 85 db. to allow prediction of those at 100 db. The first respiratory cycle following the onset of stimulation was generally longer than the prestimulus cycle for low intensity sounds and shorter for the more intense sounds. Respiratory response measures were generally not predictive of the comparable cardiac rate measures.