Beat-to-beat variability of microvascular peripheral resistances assessed with a non-invasive approach

The pressure-flow relationship at peripheral level is non-invasively studied in human subjects: the impedance function and the beat-to-beat variability series of microvascular peripheral resistance are estimated. The frequency content of this variability signal is compared to those of more classical variability series at rest and during mild supine physical exercise

EFFICACY AND TOLERABILITY OF LERCANIDIPINE IN ELDERLY PATIENTS WITH MILD TO MODERATE HYPERTENSION IN A PLACEBO-CONTROLLED, DOUBLE-BLIND STUDY

Цель. Оценить эффективность лерканидипина (антагониста кальция из группы дигидропиридинов) у пожилых больных артериальной гипертонией (АГ). Материал и методы. В многоцентровое рандомизированное двойное слепое плацебо-контролируемое исследование включены 144 больных в возрасте 60-85 лет, разделенных на группы, получавших лерканидипин в дозе 10 мг или плацебо в течение 4 нед. При недостаточной антигипертензивной эффективности исходную дозу лерканидипина увеличивали (вплоть до 30 мг один раз/день в течение 12 нед).  Результаты. Диастолическое артериальное давление (АД) под действием лерканидипина в дозе 10 мг снижалось в большей степени (-10,3 мм рт.ст.), чем под действием плацебо (-6,1 мм рт.ст.; p<0,05). Доля больных, положительно ответивших на прием лерканидипина, также была выше, чем при приеме плацебо (59,1% и 37,8 %, соответственно; p<0,05). При увеличении дозы препарата до 20 мг доля больных, положительно ответивших на лечение, возросла до 69,4%; увеличение дозы до 30 мг потребовалось лишь небольшому числу пациентов. Частота сердечных сокращений и лабораторные показатели на фоне лечения не менялись. Процент больных с побочными эффектами был одинаковым в обеих группах. Заключение. Прием лерканидипина один раз в день значительно снижает АД у пожилых пациентов с легкой и умеренной АГ . Эффект сохраняется в течение 24 ч и не сопровождается рефлекторной тахикардией. Препарат хорошо переносится и, учитывая его фармакологические и фармакодинамические особенности, может быть рекомендован, особенно пожилым пациентам

Phase shifts of synchronized oscillators and the systolic/diastolic blood pressure relation

We study the phase-synchronization properties of systolic and diastolic arterial pressure in healthy subjects. We find that delays in the oscillatory components of the time series depend on the frequency bands that are considered, in particular we find a change of sign in the phase shift going from the Very Low Frequency band to the High Frequency band. This behavior should reflect a collective behavior of a system of nonlinear interacting elementary oscillators. We prove that some models describing such systems, e.g. the Winfree and the Kuramoto models offer a clue to this phenomenon. For these theoretical models there is a linear relationship between phase shifts and the difference of natural frequencies of oscillators and a change of sign in the phase shift naturally emerges.Comment: 8 figures, 9 page

Clinical and haemodynamic correlates of heart rate turbulence as a non-invasive index of baroreflex sensitivity in chronic heart failure

HRT (heart rate turbulence), describing the heart rate changes following a premature ventricular contraction, has been regarded as an indirect index of baroreflex function. However, limited data are available on its relationship with invasive assessment by phenylephrine injection (Phe-slope). In the present study, we therefore compared these methodologies in a series of patients with HF (heart failure) in which both measures together with clinical and haemodynamic data were available. HRT parameters [TO (turbulence onset) and TS (turbulence slope)] were measured from 24-h Holter recordings obtained within 1 week of baroreflex sensitivity assessment and right heart haemodynamic evaluation (Swan-Ganz catheter). HRT was computable in 135 out of 157 (86%) patients who had both a phenylephrine test and haemodynamic evaluation. TO and TS significantly correlated with Phe-slope (r=−0.39, P<0.0001 and r=0.66, P<0.0001 respectively). Age, baseline heart rate, LVEF (left ventricular ejection fraction), PCP (pulmonary capillary pressure), CI (cardiac index) and sodium were significant and independent predictors of Phe-slope, accounting for 51% of its variability. Similarly, age, baseline heart rate and PCP, and NYHA (New York Heart Association) classes III–IV were independent predictors for TS and explained 48% of its variability, whereas only CI and LVEF were found to be significantly related to TO and explained a very limited proportion (20%) of the variability. In conclusion, these results suggest that HRT may be regarded as a surrogate measure of baroreflex sensitivity in clinical and prognostic evaluation in patients with HF

Sequential Modulation of Cardiac Autonomic Control Induced by Cardiopulmonary and Arterial Baroreflex Mechanisms

Background—Nonhypotensive lower body negative pressure (LBNP) induces a reflex increase in forearm vascular resistance and muscle sympathetic neural discharge without affecting mean heart rate. We tested the hypothesis that a reflex change of the autonomic modulation of heartbeat might arise during low intensity LBNP without changes of mean heart rate.Methods and Results—Ten healthy volunteers underwent plasma catecholamine evaluation and a continuous recording of ECG, finger blood pressure, respiratory activity, and central venous pressure (CVP) during increasing levels of LBNP up to −40 mm Hg. Spectrum and cross-spectrum analyses assessed the changes in the spontaneous variability of R-R interval, respiration, systolic arterial pressure (SAP), and CVP and in the gain (αLF) of arterial baroreflex control of heart rate. Baroreceptor sensitivity was also evaluated by the SAP/R-R spontaneous sequences technique. LBNP began decreasing significantly: CVP at −10, R-R interval at −20, SAP at −40, and the indexes αLFand baroreceptor sensitivity at −30 and −20 mm Hg, compared with baseline conditions. Plasma norepinephrine increased significantly at −20 mm Hg. The normalized low-frequency component of R-R variability (LFR-R) progressively increased and was significantly higher than in the control condition at −15 mm Hg.Conclusions—Nonhypotensive LBNP elicits a reflex increase of cardiac sympathetic modulation, as evaluated by LFR-R, which precedes the changes in the hemodynamics and in the indexes of arterial baroreflex control

Abnormalities in autonomic function in obese boys at-risk for insulin resistance and obstructive sleep apnea.

Study objectivesCurrent evidence in adults suggests that, independent of obesity, obstructive sleep apnea (OSA) can lead to autonomic dysfunction and impaired glucose metabolism, but these relationships are less clear in children. The purpose of this study was to investigate the associations among OSA, glucose metabolism, and daytime autonomic function in obese pediatric subjects.MethodsTwenty-three obese boys participated in: overnight polysomnography; a frequently sampled intravenous glucose tolerance test; and recordings of spontaneous cardiorespiratory data in both the supine (baseline) and standing (sympathetic stimulus) postures.ResultsBaseline systolic blood pressure and reactivity of low-frequency heart rate variability to postural stress correlated with insulin resistance, increased fasting glucose, and reduced beta-cell function, but not OSA severity. Baroreflex sensitivity reactivity was reduced with sleep fragmentation, but only for subjects with low insulin sensitivity and/or low first-phase insulin response to glucose.ConclusionsThese findings suggest that vascular sympathetic activity impairment is more strongly affected by metabolic dysfunction than by OSA severity, while blunted vagal autonomic function associated with sleep fragmentation in OSA is enhanced when metabolic dysfunction is also present

Algorithm for the classification of multi-modulating signals on the electrocardiogram

This article discusses the algorithm to measure electrocardiogram (ECG) and respiration simultaneously and to have the diagnostic potentiality for sleep apnoea from ECG recordings. The algorithm is composed by the combination with the three particular scale transform of a(j)(t), u(j)(t), o(j)(a(j)) and the statistical Fourier transform (SFT). Time and magnitude scale transforms of a(j)(t), u(j)(t) change the source into the periodic signal and τ(j) = o(j)(a(j)) confines its harmonics into a few instantaneous components at τ(j) being a common instant on two scales between t and τ(j). As a result, the multi-modulating source is decomposed by the SFT and is reconstructed into ECG, respiration and the other signals by inverse transform. The algorithm is expected to get the partial ventilation and the heart rate variability from scale transforms among a(j)(t), a(j+1)(t) and u(j+1)(t) joining with each modulation. The algorithm has a high potentiality of the clinical checkup for the diagnosis of sleep apnoea from ECG recordings

Impact of gonadectomy on blood pressure regulation in ageing male and female rats

Sexual dimorphism in blood pressure has been associated with differential expression of the angiotensin II (AII) receptors and with activity of the nervous system. It is generally accepted that aging affects kidney function as well as autonomic nervous system and hormonal balance. Given that hypertension is more prevalent in men than women until women reach their seventh decade we hypothesised that females would be relatively protected from adverse effects of ageing compared to males, and that this would be mediated by the protective effect of ovarian steroids. Intact and gonadectomised male and female normotensive Wistar rats aged 6, 12 and 18 months were used to study renal function, blood pressure, heart rate and blood pressure variability. We observed that intact females had lower levels of proteinuria and higher (12.5%) creatinine clearance compared to intact males, and that this difference was abolished by castration but not by ovariectomy. Ovariectomy resulted in a change by 9% in heart rate, resulting in similar cardiovascular parameters to those observed in males or gonadectomised males. Spectral analysis of systolic blood pressure revealed that high frequency power spectra were significantly elevated in the females vs. males and were reduced by ovariectomy. Taken altogether the results show that females are protected from age-related declining renal function and to a lesser extent from rising blood pressure in comparison to males. Whilst ovariectomy had some deleterious effects in females, the strongest effects were associated with gonadectomy in males, suggesting a damaging effect of male hormones