AJP - Regulatory, Integrative and Comparative Physiology, Vol 236, Issue 5 268-R281, Copyright © 1979 by American Physiological Society
Analysis of circadian periodicity of plasma cortisol in normal man and in Cushing's syndrome
A. H. Vagnucci
In normal subjects, adjusted to a circadian environment, half-hourly plasma
cortisol levels over a 24-h span (time series, TS) outline a circadian
sinusoidal pattern that may be masked by superimposed short-lived
oscillations. The periodogram objectively defines the features (amplitude,
phase) of this pattern in individual TS and, more efficiently, in the
average and concatenation of homogeneous TS. Concatenation is a procedure
by which homogeneous short TS are attached one after the other. Homogeneity
is inferred by variance analysis and by a new measure, h, with statistical
significance, derived from the spectrum of the concatenated TS. Through
concatenation, autocovariance for periodicity identification becomes
possible. The TS from three groups of volunteers are highly homogeneous and
have a predominant, statistically significant amplitude with peak time near
1100 h. The patterns from patients with Cushing's disease differ markedly
in their means and periodic features; by the above criteria, we identify a
subgroup with significant h measure and 24-h amplitude. This analysis
provides a tool for investigation of the circadian clock in man.
