Biomedical subjects

G D Pinna

Publications and source records attributed to G D Pinna.

47 records · Page 3Linked to original sources

PubMed1997

Depressed arterial baroreflex sensitivity and not reduced heart rate variability identifies patients with chronic heart failure and nonsustained ventricular tachycardia: the effect of high ventricular filling pressure.

In chronic heart failure (CHF) the contributing role of increased sympathetic activity and hemodynamic dysfunction in the genesis of ventricular arrhythmias has not been well established. To assess the relation between severe ventricular arrhythmias, hemodynamic impairment, and autonomic nervous system derangement, 142 patients with CHF in sinus rhythm underwent 24-hour electrocardiographic recording, right-sided heart catheterization, and evaluation of sympathovagal balance by heart rate variability (HRV) and baroreflex sensitivity (BRS). Patients were grouped according to the absence (without nonsustained ventricular tachycardia [NSVT]; n = 87) or presence (with NSVT; n = 55) of NSVT. Patients with NSVT had higher pulmonary artery and capillary pressures and more pronounced signs of sympathetic activation and parasympathetic withdrawal compared with those without NSVT. However, logistic regression analysis revealed that depressed BRS but not reduced HRV was significantly associated with the presence of NSVT, at both univariate analysis and after adjustment for clinical and hemodynamic variables. Moreover, it was found that when depressed BRS was associated with high pulmonary capillary pressure, the odds ratio for having NSVT rose markedly from 3.8 to 6.5. In conclusion, this study indicates that in stable CHF the assessment of arterial baroreflex function, but not HRV analysis, allows identification of patients at high risk of NSVT. It is suggested that the effect of depressed BRS is strengthened by the simultaneous presence of increased myocardial wall stress. These data support the hypothesis of a contributory role of autonomic nervous system dysfunction as expressed by the inability to activate effective vagal reflexes and an indirect index of ventricular stretch in the genesis of life-threatening arrhythmias.

Autonomic Nervous System↗

PubMed1997

POLYAN: a package for a polyparametric approach to cardio-respiratory variability signals analysis.

POLYAN, a computer program based on a point-and-click graphical user interface for easy and efficient polyparametric analysis of cardio-respiratory variability signals is described. The main tasks performed by the package are: univariate and bivariate spectral analysis on selected portions of the signals with the computation of some clinically relevant indices and baroreflex sensitivity assessment by the analysis of the relationship between systolic pressure and heart period signals. Some tools which help the analyst in the solution of common practical problems have been implemented to make analysis easier and more rigorous. Using Matlab language, POLYAN has the flexibility and expandability necessary for a research tool, which often requires implementation of new algorithms and computation of new parameters.

Computer Graphics↗

PubMed1997

From clinical data records to research: a database system for the study of clinical and functional indicators of chronic heart failure.

The identification of reliable clinical and functional indicators of Chronic Heart Failure (CHF) is currently a major research challenge for physicians dealing with this pathology. With the aim of providing an adequate infrastructure for this research, we have developed a Database System where all relevant information concerning CHF patients during follow-up can be efficiently recorded, monitored, extracted and easily transferred to commercial packages for data processing and statistical analysis. Patient clinical status is recorded every 6 months, whereas data from several laboratory investigations are recorded every 12 months. All complications or events between two successive controls are recorded too. Patients needing cardiac transplantation are entered in a transplantation waiting list. The Database is fully integrated into the Hospital Information System and meets the standards of the national database of CHF patients. It grows with the concurrent activity of several independent teams, all of which have access to complete and structured information for research purposes. A user-friendly procedure allows the export in a standard format (Microsoft Excel) of all patients' data pertaining to a selected set of controls and variables of interest. These data are used directly for analysis or sub-selections are performed by the investigator through a simple query language. Depending on the objectives and complexity of the research, different commercial statistical analysis packages are available, which are used by clinical investigators autonomously or with the aid of a statistician. This overall approach allows great autonomy of each user in extracting, manipulating and statistically analyzing data. The Database has been in use at the Heart Failure Unit of our Rehabilitation Center since October 1992 and 595 patients have been enrolled since then. Several studies based on these data have been performed and more than 120 scientific communications and 30 articles in national and international journals have been produced. Hence, this experience represents a successful example of how clinical data records can be efficiently and effectively linked to valuable clinical research.

Aged↗

PubMed1996

Application of time series spectral analysis theory: analysis of cardiovascular variability signals.

The paper focuses on the most important application problems commonly encountered in spectral analysis of short-term (less than 10 min) recordings of cardiovascular variability signals (CVSs), critically analysing the different approaches to these problems presented in the literature and suggesting practical solutions based on sound theoretical and empirical considerations. The Blackman-Tukey (BT) and Burg methods have been selected as the most representative of classical and AR spectral estimators, respectively. For realistic simulations, 'synthetic' CVSs are generated as AR processes whose parameters are estimated on corresponding time series of normal, post-myocardial infarction and congestive heart failure subjects. The problem of resolution of spectral estimates is addressed, and an empirical method is proposed for model order selection in AR estimation. The issue of the understandability and interpretability of spectral shapes is discussed. The problem of non-stationarity and removing trends is dealt with. The important issue of identification and estimation of spectral components is discussed, and the main advantages and drawbacks of spectral decomposition algorithms are critically evaluated.

Heart Diseases↗

PubMed1996

Accuracy of telemetry signals in the post-implantation monitoring of electrograms sensed by pacemakers.

Monitoring of electrograms (EGMs) sensed by pacemakers (PMs) during their lifetime is the utmost importance, since changes of these signals, due to modifications of the electrode-myocardial interface may occur compromising the proper functioning of the PM. Since after implantation these intracardiac signals are accessible only by means of a telemetry system, it is necessary to ascertain how faithfully the telemetric signals reproduce the direct ones. To this aim we devised an accurate method, based on linear system theory, which allows the estimation of the transfer function of the PM-telemetry system and the comparison of a set of time and frequency domain parameters (wave amplitude, slew rate, frequency at the spectrum peak and bandwidth) computed on both direct and telemetric signals. To overcome the problem that these two signals cannot be recorded simultaneously, an appropriate model of the input and output signals of the PM-telemetry system and of their interrelationship was identified. This model relies on a set of reasonable assumptions about the nature of the direct signal (supposed to have a fixed morphology within a predefined analysis window) and of noise sources corrupting both the direct and telemetric signals. Owing to the involvement of deterministic and stochastic signals, the theory of quasi-stationary signals was employed to obtain the system transfer function. To test our method, direct and telemetric recordings were performed on 12 patients with atrial sensing carrying Medtronic Pacemakers (Mod Elite 7077/7086, programmer Mod 9760) with unipolar steroid eluting leads (Medtronic Capsure 4523). The results we obtained demonstrate that the specific system considered acts as a low-pass filter with a -3 dB frequency at about 90 Hz this ensures that the telemetric signal contains almost all the information of the direct one and can be used to monitor the changes of the signals sensed by the PM.

Aged↗

PubMed1996

Alterations of breathing in chronic heart failure: clinical relevance of arterial oxygen saturation instability.

1. In patients with chronic heart failure (CHF) alterations of breathing such as Cheyne-Stokes respiration (CSR) or periodic breathing, (PB) have been frequently described during both day- and night-time. These respiratory rhythm disorders are associated with marked oscillations of arterial oxygen saturation (SaO2) which may expose the patients to prolonged hypoxia. 2. In 40 stable CHF patients and 8 controls during awake day-time, we studied the relationship between alterations of breathing and SaO2, to verify the effect of voluntary control of respiration or oxygen therapy on the instability of SaO2 (analyzed as standard deviation (SD) of the mean value). Simultaneous recordings of ECG, lung volumes and SaO2 were made during 10 min. resting and 4 min. controlled breathing In a subgroup of 5 CHF the effect of oxygen therapy was compared to that of controlled breathing. 3. It was found that 62% of CHF had CSR or PB. Mean SaO2 and SD of SaO2 were significantly different in CHF as compared to controls (respectively 92.4 +/- 2.5 vs 95.4 +/- 0.5%, p < 0.002 and (1.27 +/- 0.9 vs 0.28 +/- 0.13%, p < 0.01), but among CHF pts those with CSR and PB had a lower SaO2 and a more pronounced instability of SaO2. Controlled breathing eliminated apneas and reduced or abolished the variation of tidal volume. In both control and CHF it resulted in an increase of mean SaO2 while a significant reduction of SaO2 instability was observed only in CHF, particularly if CSR or PB were present. Voluntary control of respiration was similar to oxygen therapy in increasing SaO2, but more effective on SaO2 SD. 4. It is concluded that in stable CHF, resting SaO2 is reduced and showed a marked instability particularly when periodic alterations of breathing were present. Continuous beat-to-beat recording of SaO2 may detect patients who have PB or CSR. Training to produce more regular breathing, regardless of the amount of ventilation, may represent a useful intervention.

Adult↗

PubMed1996

An oscillation of the respiratory control system accounts for most of the heart period variability of chronic heart failure patients.

A periodic breathing (PB) pattern is often observed in chronic heart failure (CHF) patients (pts). In order to clarify the role of this abnormal respiratory activity upon heart period variability we investigated, in a group of 20 stable CHF pts (NYHA class II to III, median EF 24%) showing a PB pattern, 1) whether observed data were consistent with the instability hypothesis of PB and 2) the relationship between oscillations of heart period and the contemporary fluctuations of ventilatory and chemoreceptor activity. Univariate and bivariate spectral analysis were performed on short-term resting recordings of instantaneous lung volume (ILV), instantaneous minute ventilation (IMV), heart period (HP) and arterial O2 saturation at the ear (SpO2). A very low frequency (VLF) oscillation around 0.02 Hz, associated with PB, was observed in all signals and contributed to 75% (23 divided by .99) (median (range)) of the HP variability. The coherence between ILV and HP was 0.77 (0.3 divided by 0.95) and between SpO2 and HP 0.8 (0.4 divided by 0.98. A high coherence was also found between IMV and SpO2: 0.9 (0.6 divided by 0.98). The median phase lag between IMB and SpO2 was -211 degrees (-240 divided by -156), between ILV and HP -205 degrees (-260 divided by -180) and between SpO2 and HP 0 degree (-26 divided by 30). The estimated lung-to-ear circulation time was 24.5 s (12.5 divided by 36.5). This study definitely confirms that during PB a common rhythm is shared between the respiratory and cardiovascular regulatory system Taking into account the error introduced by the measuring process, our results, are consistent with the hypothesis that periodic breathing of CHF pts originates from an instability of the feedback control system of ventilation. Hence most of the HP variability of these pts simply reflects abnormal pattern of respiratory activity.

Adult↗

PubMed1996

Estimation of arterial blood pressure variability by spectral analysis: comparison between Finapres and invasive measurements.

In order to assess the accuracy of spectral analysis of beat-by-beat arterial blood pressure fluctuations recorded by the finger technique we analysed simultaneous ipsilateral resting sequences (180 s) of systolic blood pressure (SP) and diastolic blood pressure (DP) obtained by brachial artery cannulation and by the Finapres device in 26 post-myocardial infarction (post-MI) and 24 chronic heart failure (CHF) patients. We estimated: (i) the total variability and the power in the bands 0.01-0.04 Hz (band 1), 0.04-0.07 Hz (band I), 0.07-0.15 Hz (band III) and 0.15-0.45 Hz (band IV); and (ii) the group-average transfer function between the invasive and non-invasive channel. The total variability of intra-arterial SP was greatly enhanced by the Finapres device in both populations (p < 0.01) mainly due to the increase of power in bands I and II (mean percentage errors 157 and 111% in post-MI and 368 and 245% in CHF patients respectively). The power in band IV was significantly reduced in post-MI (p < 0.001) but not in CHF patients. The total DP variability increased in post-MI patients (p < 0.001) due to the increase in bands I and II (mean percentage errors 62 and 43% respectively). No significant difference was found in bands III and IV of the same group and in the overall variability of CHF. Linear system analysis showed that intra-arterial SP oscillations in both groups are amplified by the Finapres device in bands I and II, with a higher gain in CHF patients, whereas they are attenuated in band IV. Band III acts as a transition band. DP oscillations recorded non-invasively are slightly amplified in bands I and II of post-MI patients only and are attenuated in band IV of both groups. A substantial fraction (approximately 30%) of the non-invasive SP variability in band I cannot be explained as a pure linear transformation (amplification) of the invasive signal. A phase delay in the range 7 degrees-10 degrees relates the non-invasive signal to the invasive one in the region 0.025-0.17 Hz and approaches zero elsewhere. Several mechanisms were examined as potential causes of the invasive-non-invasive differences. We argue that these differences are mainly due to the complex rhythmic behaviour of peripheral resistance vessels.

Adult↗

PubMed1996

Effects of record length selection on the accuracy of spectral estimates of heart rate variability: a simulation study.

To evaluate the effects of record length selection on the accuracy of spectral estimates of heart rate variability (HRV), a simulation study was carried out using a set of 58 signals obtained by autoregressive (AR) fitting a representative sample of real HRV signals. Four record lengths of 180, 300, 420, and 540 s were considered. Spectral estimation was performed by both the Blackman-Tukey (B-T) and AR methods. Accuracy was assessed for: 1) point spectral estimates, by computing the normalized averaged bias (NAB) and variance (NAV); and 2) the most commonly used spectral parameters [total power (TP) and the powers in the bands: very low frequency (VLF) (0 divided by 0.04 Hz), low frequency (LF) (0.04 divided by 0.15 Hz), and high frequency (HF) (0.15 divided by 0.45 Hz)], by computing the normalized bias (NB) and variance (NV). The results are: whatever the record length considered, the 90th percentiles (90P) of the NAB were < 10%, whereas those of the NB were < 9% for TP, LF, and HF powers, and < 14% for the VLF power, in both methods. The NAV was proportional to the reciprocal of record length, showing high 90P values for the shortest record length (26.4% for B-T and 44.2% for AR). The NV showed the same trend but 90P values were much lower (< 8% for TP, LF, and HF powers and < 19% for VLF power, in both methods). In the final part of the paper a procedure for the computation of approximate upper bounds of the relative absolute error of spectral measures at each record length, based on the knowledge of the NB and NV, is presented.

Algorithms↗

PubMed1995

Heart rate variability during specific sleep stages. A comparison of healthy subjects with patients after myocardial infarction.

BACKGROUND: Heart 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. METHODS AND RESULTS: HRV 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). CONCLUSIONS: Myocardial 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.

Electrocardiography↗

PubMed1994

The accuracy of power-spectrum analysis of heart-rate variability from annotated RR lists generated by Holter systems.

The accuracy of spectral analysis of heart-rate variability performed on annotated RR interval lists obtained from several commercial Holter systems was appraised. Five tape-recorder-based systems (Del Mar 750, Marquette 8000, Oxford Medilog Excel, Remco Cardioline AD 35 and Reynolds Pathfinder PA3) and four solid-state systems (Hewlett Packard 43420B, Marquette Seer, Oxford 6000FD2, Reynolds E-Ram) were considered. Two ECG signals with fixed real morphology but characterized by a different degree of modulation of the RR interval (reduced and normal variability) were fed into the recorders evaluated. The total power and the power in the very low-, low- and high-frequency bands were then estimated on all Holter-generated RR sequences. Spectral analysis was performed by both the autoregressive and fast-Fourier-transform methods. The estimation error of each parameter was statistically characterized and, for tape-recorder-based systems, inferential analysis was used to test for differences between recorders, tapes and times of recording. The centre and dispersion of the estimation error changed markedly from system to system. Some tape-recording systems showed large inter-recorder differences. The degree of spectral distortion was never uniform among selected bands. Solid-state systems performed better than tape-recording ones but both were limited in the accuracy by the quantization of RR interval measurement. The fast Fourier method yielded spectral estimates more stable than the autoregressive method. Our data clearly show that spectral analysis of very low-variability signals may be seriously affected by Holter recording and preprocessing of ECG signals.

Electrocardiography↗