Variability in heart rate was a valuable instrument for analyzing autonomic modulation of the heart in arterial hypertension. The autonomic system undergoes significant losses in cardio-modulatory capacity, more evident in subjects between 40 and 59 years old. In those over 60 years old, reduced variability in heart rate imposed by aging was not significantly influenced by the presence of systemic arterial hypertension.

In healthy individuals, the duration of RR intervals in tha surface electrocardiogram varies cyclically from beat to beat. This variation is more significant in youngsters, is modulated by breathing movements, and is called respiratory sinus arrhythmia.The characteristics of the breathing movements can alter the cyclic variations observed between successive electrocardiographic R waves (RR intervals). These alterations result both from direct influences on the modulation of the parasympathetic nervous system and the indirect influences of chemoreceptor mechanismsIn approximately 50% of the individuals with left ventricular global systolic dysfunction, the presence of abnormal patterns of breathing can be identified. In these individuals, oscillatory patterns of breathing (oscillatory breathing) can be observed both during sleep and during wakefulness, and are characterized by successive periods of tachy/hyperpnea followed by brady/hypopnea, and, eventually, apnea [2][3][4][5][6][7][8][9][10] . Of the types of oscillatory breathing of clinical significance, Cheyne-Stokes respiration and periodic breathing stand out. Cheyne-Stokes respiration is the breathing pattern in which periods of tachy/hyperpnea are followed by regular periods of apnea. In periodic breathing, however, the periods of tachy/hyperpnea are cyclically followed by periods of brady/hypopnea with no apnea.Although some authors have reported that oscillatory breathing, especially when observed during wakefulness, may be associated with more severe clinical findings and a more reserved prognosis 2,6-8 , the subject remains controversial.This study aimed at analyzing the effects of oscillatory breathing on the behavior of the cyclic variations of the normal electrocardiographic RR intervals (V-RR) during wakefulness in individuals with left ventricular global systolic dysfunction and in sinus rhythm, and at assessing the influence of oscillatory breathing on clinical and laboratory findings, and on the mortality rate of the individuals studied. Objective -To assess the effect of the oscillatory breathing on the variability of RR intervals (V-RR) and on prognostic significance after one year follow-up in subjects with left ventricular global systolic dysfunction. Methods -We studied 76 subjects, whose age ranged from 40 to 80 years, paired for age and gender, divided into two groups: group I -34 healthy subjects; group II -42 subjects with left ventricular global systolic dysfunction (ejection fraction ≤ 0.40). The ECG signals were acquired during 600s in supine position, and analyzed the variation of the thoracic amplitude and the V-RR. Clinical and V-RR variables were applied into a logistic multivariate model to foretell survival after one year follow-up. Results -