Day-to-day pneumogram variability.

To determine day-to-day variability in respiratory pattern, we obtained 188 comparisons of pneumograms performed during two successive 24-h intervals. The respiratory pattern values calculated were total duration of brief apnea (apnea density), periodic breathing episodes, longest apnea, number of apneas greater than 11 s, and number of apneas greater than 15 s. For day 1 values for apnea density, periodic breathing, and longest apnea which were within the 90th percentile for normal infants at age 1 month, day 2 values fell outside that range in 4.3, 3.5, and 18% of comparisons, respectively. There was a systematic tendency for the day 2 values to be less than the day 1 values. For each parameter, the day 2 range was lower, the slope of the day 2 versus day 1 regression line was significantly less than 1 (p less than 0.01) and the y-intercept was significantly greater than zero (p less than 0.01). Knowledge of day-to-day pneumogram variability should be helpful in interpreting individual pneumogram results and in assessing the clinical usefulness of pneumogram recordings.