S. Lino

Role of echocardiography in acute chest pain syndrome.

Fewer than one third of patients presenting to the emergency department with complaints of chest pain have an acute coronary syndrome. The electrocardiogram provides a specific diagnosis only in 40% of patients with acute myocardial infarction. The presence of regional wall-motion abnormalities at echocardiography in patients without known coronary artery disease is a moderate indicator of an increased likelihood of acute myocardial ischemia or myocardial infarction with a positive predictive accuracy of about 50%. More important, the absence of regional wall-motion abnormalities identifies a subset of patients unlikely to have a myocardial infarction with a negative predictive accuracy of about 95%. Echocardiography can provide incremental prognostic information to identify patients at risk of early or late cardiac events, even after consideration of clinical, historical, and electrocardiographic variables. The application of new contrast agents to echocardiography will probably allow an early and more accurate evaluation of patients with chest pain of uncertain significance.

ECG fiducial points detection through wavelet transform

The wavelet transform is introduced as a novel method to analyze signals in both time and frequency domains, and therefore it is suitable for analysis of time-varying signals such as ECG. Detection of ECG signal characteristic patterns has been achieved using an algorithm based on the wavelet transform decomposition. ECG signals are represented by a pyramidal algorithm at successive scales into fine and coarse components used for the successive fiducial points detection. The presented time-scale diagrams illustrate the detection capability of fiducial points on ECG signal (QRS complexes, P and T waves).

Sympathetic-Parasympathetic Activation During Spontaneous Attacks of Cluster Headache: Evaluation by Spectral Analysis of Heart-Rate Fluctuations

Twenty-four hour ECG Holter and blood-pressure monitorings were performed in eight patients suffering from cluster headache. Spectral analysis of heart-rate fluctuation was used to assess the autonomic balance under basal conditions, after head-up tilt, and during a spontaneous attack. Normal autonomic balance was found at rest and during sympathetic activation obtained with head-up tilt in the interparoxysmal period. Before the onset of headache, an increase in the low-frequency (LF) component of the power spectrum was apparent in all patients. This sign of sympathetic activation was followed by an increase in the high-frequency (HF) component that developed about 2000 beats after the onset of headache and rapidly overcame the LF component until the end of pain. Significant differences were found when comparing the spectral parameters [total spectral values (TP), power of the LF and HF components and LF/HF ratio] obtained before, during and after headache. During the attack, blood pressure increased and heart rate decreased in all subjects. There appears to be a primary activation of both sympathetic and parasympathetic functions in cluster headache attacks. The sympathetic component seems to be involved mostly in the development of the attack, whereas the parasympathetic activation seems to occur, following the onset of the attack, independently of the pain.

Autonomic nervous activity during sleep in middle cerebral artery infarction.

No data are available on the autonomic system during sleep in patients with stroke. The purpose of this study was to determine the influence of acute ischemic stroke on the autonomic cardiovascular system during sleep, and to correlate autonomic activity with the clinical status of patients. Ten patients with ischemic stroke in the middle cerebral artery were studied by means of an all-night polysomnographic recording within the 1st week of the onset of symptoms and at the 3-week follow-up examination. Power spectrum analysis of the heart rate variability was performed using an autoregressive algorithm in 180 consecutive electrocardiographic RR intervals. Spectral power was calculated in 3 main frequency bands: high frequency (HF), 0.15–0.4 Hz; low frequency (LF), 0.04–0.15 Hz; very low frequency (VLF), <0.04 Hz. The data were compared with those of 10 age-matched controls. A significant increase in VLF (p < 0.0005) and a decrease in HF (p < 0.0002) components were found in ischemic stroke patients. The sympathetic-parasympathetic balance (VLF + LF/HF) was higher in patients than controls (p < 0.005). However, these components changed significantly during sleep, revealing a physiological pattern. These power spectral data were still present at the 3-week follow-up. The 4 patients who developed cardiac arrhythmias showed higher sympathetic-parasympathetic balance than patients without arrhythmias (p < 0.05). These data suggest a sympathetic predominance in patients with acute ischemic stroke during sleep. However, the flexible and dynamic properties of the autonomic nervous system are preserved. Cardiac arrhythmias following stroke may be related to the degree of sympathetic predominance.

Pupil diameter variability in humans

The aim of this study was to investigate the origin of the pupil fluctuations in humans. The authors assess whether and to which extent LF and HF cardiovascular rhythms contribute to spontaneous pupil diameter fluctuations at rest, during sympathetic activation by Head-Up Tilt Test 70/spl deg/ and during a non-invasive modulation of carotid baroreceptors by Neck Suction (NS). The responses of the pupil to the NS was studied at stimulation frequencies of 0.10 and 0.20 Hz. The effect of tilting on PD fluctuations spectra and the physiological background of the pupil control are consistent with the hypothesis that pupil fluctuations reflect a generalized increase of the sympathetic tone. The findings obtained with the NS stimulation suggest that blood pressure fluctuations propagate to the pupil via carotid baroreceptor afferent pathways. However a central contribution can not be excluded.

1/f spectrum slope of 24 hour heart rate variability signal in normal and hypertensive subjects

The power spectrum density of the heart rate beat to beat variability signal shows, in a frequency range of less than 0.01 Hz, a behaviour inversely proportional to frequency. This finding has been related to the chaotical component of the signal and the expression of the complexity of the heart rate control mechanisms. The authors tested the 1/f mathematical model on the 24 hour heart rate in 40 subjects, half normal and half young essential hypertensive. The authors found that 1/f slope is 1.12/spl plusmn/0.14 in the normal subjects and 1.24/spl plusmn/0.15 in the hypertensive ones (p<0.02). The data suggest a loss of complexity in cardiovascular control in essential hypertension.<<ETX>>

Effects of Carvedilol Therapy on Autonomic Function and Baroreflex Sensitivity in Individuals with Newly-Diagnosed Essential Hypertension

AbstractObjective: To investigate the effects of carvedilol therapy on autonomic cardiovascular regulation and baroreflex sensitivity, by short-term spectral analysis of heart rate (R-R) and systolic blood pressure (S-S) variability. Patients and Methods: The trial was conducted in 12 adults (seven men and five women, mean age 37 ±7 years) with newly diagnosed hypertension. Patients were classified as having mild or moderate hypertension (stages I to II). R-R, S-S and respiratory signals were recorded during rest and after sympathetic activation by head-up tilt, before and after receiving a 15-day course of carvedilol (25mg once daily). Cross-spectral analysis of R-R and S-S signals was used to determine the baroreflex sensitivity index (α index). Results: At rest after carvedilol therapy, the R-R and S-S LF (low frequency) normalised units (nu) significantly decreased (p = 0.0002 and p = 0.003, respectively), while the HF (high frequency) component reciprocally increased. The R-R LF/HF ratio decreased significantly (1.28 ±1.58 vs 0.41 ±0.29, p = 0.008). The α index also increased significantly (12.04 ±6.25 vs 16.05 ±7.45, p = 0.002). During tilt, carvedilol therapy reduced the R-R and S-S LF (p = 0.0003 and 0.002, respectively), but preserved the LF increase normally induced by passive ortho-statism, and significantly increased the α index (6.18 ±1.97 vs 8.89 + 3.29, p = 0.014). Conclusion: Our findings suggested that carvedilol attenuates cardiovascular sympathetic responsiveness and improves baroreflex sensitivity.

Interference and phase locking patterns between low and high frequency rhythms of cardiovascular variability signals in normal subjects

Analysis of interference and phase locking phenomena between respiration and short-term Heart Rate and Blood Pressure variability signals have been performed by using nonlinear signal processing techniques, such as Poincare Maps, Recurrence Maps, Time-Space Separation Plots and Bispectrum Estimation. Data obtained from normal subjects confirm the hypothesis of non-linear interaction of Low and High frequency rhythms with respiration.