[Changes in heart rate variability under informational loading]

Three-dimensional vector spaces were constructed by the method of principal components from large sets of cardiac rhythm spectra obtained in the state of rest and under informational load. The individual and group spaces of cardiac rhythm revealed three common factors having the maximal factor loads within the domain of action of metabolic (0.02-0.04 Hz), vascular (0.06-0.08 Hz), and respiratory (0.12-0.16 Hz) oscillators. Each particular cardiac spectrum in this universal autonomic space can be represented by a three-dimensional vector. Changes in the functional state are reflected in a specific trajectory of this vector in the space. It was found that coactivation of the metabolic, vascular, and respiratory oscillators in combination with a decrease in the heart rate and index of tension is positively correlated with efficiency of task performance and appears to reflect the orienting reflex. The vector autonomic space, in which the metabolic, vascular, and respiratory oscillators act, may be a useful instrument for distinguishing the mechanisms underlying the orienting and defensive reflexes.