Gian Domenico Pinna

Heart Rate Variability During Specific Sleep Stages A Comparison of Healthy Subjects With Patients After Myocardial Infarction

BACKGROUNDnHeart rate variability (HRV) is typically higher during nighttime. This evidence supports the concept that overall, sleep is a condition during which vagal activity is dominant. Myocardial infarction (MI) results in a loss in the overall nocturnal HRV increase. However, the characteristics of HRV during specific sleep stages in normal subjects and, more importantly, after MI, are unknown. This study describes HRV during sleep stages in normal subjects and in patients with a recent MI.nnnMETHODS AND RESULTSnHRV was measured from 5 minutes of continuous ECG recording in 8 subjects with no clinical evidence of coronary artery disease (age, 47 +/- 4 years) and in 8 patients with a recent MI (age, 51 +/- 2 years; NS versus control subjects) in the awake state, non-rapid eye movement (REM), and REM sleep. In normal subjects, the low- to high-frequency ratio (LF/HF) derived from power spectral analysis of HRV decreased significantly from the awake state to non-REM sleep (from 4 +/- 1.4 to 1.22 +/- 0.33, P < .01). During REM sleep, the LF/HF increased to 3 +/- 0.74 (P < .01 versus non-REM, NS versus awake). In post-MI patients, the LF/HF showed an opposite trend toward an increase from 2.4 +/- 0.7 to 5.11 +/- 1.4 (NS, P < .01 versus the control subjects). REM sleep produced a further increase in the LF/HF up to 8.9 +/- 1.6 (P < .01 versus awake and versus REM in control subjects).nnnCONCLUSIONSnMyocardial infarction causes a loss in the capability of the vagus to physiologically activate during sleep. This results in a condition of relative sympathetic dominance even in a situation such as sleep, normally described as a condition of vagal dominance and, consequently, low risk for lethal events. The evidence that the sleep-related vagal activation is lost after MI may provide new insights to understanding the nocturnal occurrence of sudden death.

Abnormal Awake Respiratory Patterns Are Common in Chronic Heart Failure and May Prevent Evaluation of Autonomic Tone by Measures of Heart Rate Variability

BACKGROUNDnReduced heart rate variability, particularly in the Very-low-frequency (VLF) spectral band, has been found to be a marker for poor prognosis in patients after myocardial infarction, but the origin of the VLF oscillations is unclear. In this study, we demonstrate that the power of cardiovascular oscillations in the VLF band in awake patients with mild to severe chronic heart failure is greatly increased by the common occurrence of unrecognized irregularity of breathing, which may confound the use of heart rate variability measures as indexes of autonomic tone or prognosis.nnnMETHODS AND RESULTSnAmong 110 consecutive patients referred for consideration of transplantation, 90 were in sinus rhythm, of whom 10 were excluded as unstable. The remaining 80 patients underwent recordings of ECG, beat-to-beat arterial oxygen saturation (SaO2), and respiration during both spontaneous and controlled breathing. During spontaneous awake breathing, 64% showed periodic breathing or Cheyne-Stokes respiration (CSR), which was associated with dominant power in the VLF band of all signals. This VLF power accounted for 55%, 77%, and 87% of heart rate variability, respectively, in patients with normal breathing, periodic breathing, and CSR. It was reduced by 48% and 62%, respectively, during controlled breathing in patients with periodic breathing or CSR. Controlled ventilation also improved oxygen saturation and markedly reduced its variability.nnnCONCLUSIONSnBreathing disorders are surprisingly common in awake patients with poor left ventricular function and produce large VLF oscillations in heart rate variability. If measures of heart rate variability are used for prognostic purposes during both short-term and long-term recordings, the confounding effects of variable respiratory patterns should be excluded. Respiratory rehabilitation might help control potentially hazardous surges in sympathetic tone.

Assessment of Baroreflex Sensitivity

By governing autonomic outflow to the heart and circulation, arterial baroreceptors play a central role in controlling short-term blood pressure responses to the continuous perturbations produced by various stimuli occurring in daily life. Although in a physiological setting baroreflex mediated changes in autonomic outflow affect heart rate, myocardial contractility and peripheral resistance, the baroreflex control of heart rate in pathological conditions is of particular interest, since it has been associated with an increased propensity for cardiac mortality and sudden cardiac death.1

Not Only Sleep Apnea: The “Awake” Apneas of the Failing Heart

In its original descriptions, an abnormal breathing pattern characterized by episodes of hyperpnea alternating with periods of apnea and subsequently defined as Cheyne–Stokes respiration was actually observed in the awake state, although in the preterminal condition, of patients with advanced heart failure. It was more than one century later that it appeared that a periodic breathing pattern characterized by a cyclic waxing and waning of tidal volume alternating with central apneas or hypopneas can be observed during daytime in a remarkably high proportion of patients with poor left ventricular function and compensated heart failure.

Whispering During Sleep: Autonomic Signaling During Sleep, Sleep Apnea, and Sudden Death

Sleep is an orchestrated neurochemical process involving different biological systems. Many theories have attempted to explain the biological meaning of sleep including a primary restorative function, a central role in reinforcement, and consolidation of memory, an important place for thermoregulatory processes. Despite the lack of a general consensus on its purposes, the brain mechanisms controlling sleep and wakefulness as well as the associated changes in cardiovascular and respiratory function are largely known. The autonomic nervous system is of paramount importance in the regulation of the cardiovascular function during sleep, and it can also mediate cardiovascular events occurring during sleep as a result of cardiovascular diseases or primary sleep disorders such as sleep-disordered breathing.

A computer application for the investigation of cardiac autonomic effects of sleep-disordered breathing in heart failure patients

Sleep-disordered breathing (SDB) in the form of periodic breathing is common in heart failure patients and is thought to increase sympathetic activity. Since heart rate (HR) cyclically increases during SDB in synchrony with the oscillation in ventilation, these increases have been interpreted as indirect evidence of an augmented adrenergic activity brought about by SDB. To support this hypothesis, however, the distribution of HR fluctuations during SDB has to be compared with the distribution of spontaneous HR variation during normal breathing within the same night. The aim of this work was to develop a computer application to carry out this task efficiently, analyzing HR across different sleep stages, breathing conditions and abnormal breathing type (obstructive and central). The system automatically selects homogeneous segments of HR from standard polysomnographic recordings and computes a set of relevant distribution descriptors of HR. A pilot testing of the system has been performed in five stable heart failure patients.