Importance of RR-interval variability in stress test

Abstract

Cardiac rhythmogram (CRG) variability at the early stage of loading and recovery periods has a number of parameters associated with the functional state of subjects. These parameters can be estimated by measuring the probability of pairs of RR intervals with certain length differences (pNNx). At the same time, each of these parameters has its own diagnostic role, such as the binary marker of adaptation reserves (pNN15), loading tolerance level (pNN5, 10) and a criterion for the training level (pNN10, 15). The pNNx coupling with the endured load power and the dynamics of heart rate (HR) is to a great extent determined by the mixed endurance level. Higher pNNx values correspond with the predominant load and lower heart rate, regardless of the period. Physiological relevance of pNNx is determined by their behavior, diagnostic role, the sensitivity of each argument (x), and the level of aerobic/anaerobic endurance of a subject.