AN APPLICATION OF AUTOCORRELATION METHODS TO THE INTERPRETATION OF INTESTINAL MOTILITY RECORDS* Bx' MELVIN D. SMALL,

Many physiologic functions fluctuate with time and the wave forms vary in complexity. Simple waves, such as the peripheral pulse, present no serious problem in analysis. When, however, the wave form is complex in appearance, existing analytic methods do not yield precise information. The general similarity between complex physiologic wave patterns and communication signals, such as sound waves, suggested that a method of statistical analysis recently developed in the field of communications might be applied to these complex waves. In the application of this method a complex wave is reduced mathematically to a simpler form from which the periodic and random components can be isolated and statistically evaluated. The periodic component is sinusoidal; the random component is irregular in form, and has no definite frequency. Any random function is known to consist of the sum of many sine waves with no particular relationship, while the periodic component usually consists of a few (sometimes only one) sine waves of harmonically related frequencies. Although the random component is sometimes considered to be useless "noise," at other times it may contain valuable information. An intestinal motility record is an example of a complex physiologic wave pattern which has been d~cul t to interpret. In this paper, the communications method has been applied to the analysis of records of intestinal motility in rabbits. Four motility records were analyzed in this study and for each record we have derived quantitative expressions for total intestinal activity and for frequency, amplitude, and variations of amplitude of the periodic components. In addition, a measure of the total random activity was obtained as well as the range of frequencies and relative amplitudes of the sine waves making up