[New technology and methods for analysis of representation of signal variability in ventricular repolarization].
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Animals↗
Biomedical subjects
A Porta
Publications and source records attributed to A Porta.
Relationship between spectral components of cardiovascular variabilities and direct measures of muscle sympathetic nerve activity in humans.
BACKGROUND: Spectral analysis of RR interval and systolic arterial pressure variabilities may provide indirect markers of the balance between sympathetic and vagal cardiovascular control. METHODS AND RESULTS: We examined the relationship between power spectral measurements of variabilities in RR interval, systolic arterial pressure, and muscle sympathetic nerve activity (MSNA) obtained by microneurography over a range of blood pressures. In eight healthy human volunteers, MSNA, RR interval, intra-arterial pressure, and respiration were measured during blood pressure reductions induced by nitroprusside and during blood pressure increases induced by phenylephrine. Both low-frequency (LF; 0.10 +/- 0.01 Hz) and high-frequency (HF; 0.23 +/- 0.01 Hz) components were detected in MSNA variability. Increasing levels of MSNA were associated with a shift of the spectral power toward its LF component. Decreasing levels of MSNA were associated with a shift of MSNA spectral power toward the HF component. Over the range of pressure changes, the LF component of MSNA variability was positively and tightly correlated with LF components of RR interval (in normalized units; P < 10(-6)) and of systolic arterial pressure variability (both in millimeters of mercury squared and normalized units; P < 5 x 10(-5) and P < 5 x 10(-6), respectively). The HF component of MSNA variability was positively and tightly correlated with the HF component (in normalized units) of RR-interval variability (P < 3 x 10(-4)) and of systolic arterial pressure variability (P < .01). CONCLUSIONS: During sympathetic activation in normal humans, there is a predominance in the LF oscillation of blood pressure, RR interval, and sympathetic nerve activity. During sympathetic inhibition, the HF component of cardiovascular variability predominates. This relationship is best seen when power spectral components are normalized for total power. Synchronous changes in the LF and HF rhythms of both RR interval and MSNA during different levels of sympathetic drive are suggestive of common central mechanisms governing both parasympathetic and sympathetic cardiovascular modulation.
Blood Pressure↗
[Commonplace use of "H"].
OBJECTIVES: Describe characteristic use of cannabis and tobacco. CASE REPORT: A young couple were nicotine-dependent smokers who also regularly used cannabis. After treatment for nicotine withdrawal they no longer had a craving for cigarettes but use of hashish increased. DISCUSSION: Although illegal in France, consumption of cannabis has become commonplace. Short-term risk may be low but the liposolubility of hallucinogenic tetrahydrocannabinol retards elimination leading to the risk of neuropsychiatric disorders after chronic, or even episodic use.
Adult↗
Non-invasive assessment of the changes in static and oscillatory components of peripheral pressure/flow relationships produced by moderate exercise in humans.
OBJECTIVE: The generalized sympathetic activation induced by exercise is accompanied by an increase in heart rate, blood pressure and vascular resistance in non-exercising vascular beds. The aim of the present study was to test the feasibility of assessing, non-invasively, the static and oscillatory pressure/flow relationships of peripheral arteries and their continuous changes during dynamic exercise. DESIGN: We studied 44 healthy humans at rest, during moderate exercise (recumbent bicycle exercise) and recovery using a totally non-invasive approach. METHODS: Arterial pressure was measured using a plethysmographic device, and ipsilateral brachial artery flow and palmar skin microcirculation flow were assessed with continuous wave Doppler and laser Doppler, respectively. Continuous, long data segments (> 90 s) were acquired with a personal computer and used to determine the changes of pressure/flow relationships of peripheral arteries during dynamic exercise. A new simplified method utilizing a transfer function analysis extracted automatically unequivocal indexes of static and oscillatory properties of vascular system. RESULTS: Moderate exercise induced significant increases of the static (Zo) and oscillatory (Zc) components of peripheral pressure/flow relationships in both brachial artery and skin microcirculation beds. Both indexes returned to control values during early recovery. CONCLUSIONS: This simple, non-invasive approach was capable of assessing the changes of static and oscillatory vascular properties induced by dynamic exercise. This method could be applied for a better understanding of the vascular modifications that occur in other physiological or pathophysiological conditions also characterized by increases in sympathetic drive.
Adult↗
Spectral decomposition in multichannel recordings based on multivariate parametric identification.
A method of spectral decomposition in multichannel recordings is proposed, which represents the results of multivariate (MV) parametric identification in terms of classification and quantification of different oscillating mechanisms. For this purpose, a class of MV dynamic adjustment (MDA) models in which a MV autoregressive (MAR) network of causal interactions is fed by uncorrelated autoregressive (AR) processes is defined. Poles relevant to the MAR network closed-loop interactions (cl-poles) and poles relevant to each AR input are disentangled and accordingly classified. The autospectrum of each channel can be divided into partial spectra each relevant to an input. Each partial spectrum is affected by the cl-poles and by the poles of the corresponding input; consequently, it is decomposed into the relevant components by means of the residual method. Therefore, different oscillating mechanisms, even at similar frequencies, are classified by different poles and quantified by the corresponding components. The structure of MDA models is quite flexible and can be adapted to various sets of available signals and a priori hypotheses about the existing interactions; a graphical layout is proposed that emphasizes the oscillation sources and the corresponding closed-loop interactions. Application examples relevant to cardiovascular variability are briefly illustrated.
Algorithms↗
Low and high frequency components of blood pressure variability.
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Animals↗
Presence of vasomotor and respiratory rhythms in the discharge of single medullary neurons involved in the regulation of cardiovascular system.
We analyzed the discharges of 77 single neurons located in the rostral ventrolateral medulla (RVLM, n = 25), caudal ventrolateral medulla (CVLM, n = 18), lateral tegmental field (LTF, n = 19) and caudal raphe nuclei (n = 15). These recordings were made from 36 vagotomized and sinoaortic denervated cats that were either decerebrate (n = 27) or anesthetized with urethane (n = 9) and from 3 decerebrate cats with intact sinoartic and vagal nerves. These neurons were classified as sympathetic-related (n = 61) if spike triggered averaging showed that their naturally occurring discharges were correlated to either the cardiac related (2-6 Hz) or a faster (10 Hz) oscillation in inferior cardiac sympathetic nerve discharge. Neurons were classified as sympathetic-unrelated (n = 16) if they lacked these characteristics. We used autoregressive spectral techniques to detect additional slower oscillations hidden in the variability of neuronal discharge and possibly correlated to the oscillations of systolic arterial pressure (SAP). This analysis revealed the existence of a low frequency (LF) oscillation (0.12 +/- 0.02 Hz) in the discharges of 36 sympathetic-related and 9 sympathetic-unrelated neurons. In relation to 35 neurons in 21 animals there was also an LF component in SAP variability. In 29 instances the LF neuronal discharges and SAP variabilities were significantly correlated. In addition, there was a high frequency (HF) oscillation (0.34 +/- 0.06 Hz) in the discharges of 59 medullary neurons. In 56 cases the HF in neuronal discharge variability cohered to that in SAP variability. These data are the first to demonstrate the existence of an LF component in the discharges of individual medullary neurons, at least some of which were likely to be involved in the regulation of the cardiovascular system. Since these oscillations were evident in cats with section of sinoaortic and vagal nerves, they likely reflect central rhythmogenic properties.
Animals↗
Classification of coupling patterns among spontaneous rhythms and ventilation in the sympathetic discharge of decerebrate cats.
The spontaneous low- and high-frequency rhythms in the sympathetic discharge of decerebrate artificially ventilated cats are affected by external ventilation. Two graphical methods (i.e. the space-time separation plot and the frequency tracking locus) are used to classify the non-linear interactions. The observed behaviours in the sympathetic discharge consist of phase-locked periodic dynamics (at various frequency ratios with ventilation), quasiperiodic and aperiodic patterns. They depend on the experimental condition. In control condition the sympathetic discharge appears more frequently locked to each ventilatory cycle (1:1 dynamics). However, some cases of quasiperiodic dynamics are found. A sympathetic activation stimulus, such as inferior vena cava occlusion, is able to synchronize slow rhythms in the sympathetic discharge to a subharmonic of ventilation. During a sympathetic inhibition stimulus, such as aortic constriction, 1:1 dynamics is detected but the amplitude of the sympathetic responses can be modulated by unlocked slow rhythms. Moreover some cases of aperiodic dynamics are observed. Vagotomy reduces the 1:1 coupling between sympathetic outflow and ventilation. Vagotomy plus spinalisation disrupts periodic dynamics in the sympathetic discharge so that irregular and complex patterns are found.
Animals↗
Spectral analysis of short term R-Tapex interval variability during sinus rhythm and fixed atrial rate.
Analysis of heart rate variability has been proven useful in stratifying post myocardial patients at risk and in evaluating autonomic dysfunction. Recently augmented inter-lead variability of the QT interval has been associated with increased mortality as a result of arrhythmia and proposed as a marker of dispersion of ventricular repolarization. As the duration of the QT interval is largely dependent upon the length of the preceding cardiac cycle it is tempting to analyse whether neural mechanisms might also directly exert additional modulation. Using autoregressive algorithms we therefore analysed RR and R-Tapex interval variabilities in 15 normal subjects during sinus rhythm and in six patients with a fixed atrial rate. In controls mean R-Tapex interval and variance measured on the vector magnitude were, respectively, 245 +/- 6 ms and 5.1 +/- 0.7 ms2. Spectral analysis of R-Tapex indicated the presence of two spectral components which corresponded to the low and high frequency components of heart rate variability. In R-Tapex variability, high frequency (44 +/- 4 nu) was predominant over low frequency (29 +/- 4 nu). During controlled respiration, a manoeuvre associated with enhanced vagal modulation of sinus node, there was a further increase in high frequency (58 +/- 4 nu) whereas during tilt the low frequency component of R-Tapex variability became predominant (57 +/- 6 nu). In patients with a fixed atrial rate, variance was extremely low (3 +/- 0.9 ms2) and only a respiration-related high frequency component was recognizable in spectral analysis of RR and R-Tapex variabilities. This component was likely to depend upon mechanically induced changes in cardiac vector orientation. These data indicate that during sinus rhythm short-term R-Tapex interval variability is characterized by the same rhythmical components present in RR variability. However, the presence of a very low variance and of only a high frequency component in patients in whom the physiological variability of sinus node is abolished by atrial pacing. suggests that neural modulatory mechanisms do not exert a direct effect on the length of the R-Tapex interval.
Adult↗
Non-linear dynamics and chaotic indices in heart rate variability of normal subjects and heart-transplanted patients.
OBJECTIVES: Heart rate variability (HRV) is characterised by a variety of linear, non-linear, periodical and non-periodical oscillations. The aim of the present study was mainly to investigate the role played by neural mechanisms in determining non-linear and non-periodical components. METHODS: Analysis was performed in 7 recently heart transplanted patients and in 7 controls of similar age whose HRV signal was collected during 24 h. Parameters that quantify non-linear dynamic behaviour, in a time series, were calculated. We first assessed the specific non-linear nature of the time series by a test on surrogate data after Fourier phase randomization. Furthermore, the D2 correlation dimension, K2 Kolmogorov entropy, and H self-similarity exponent of the signal were estimated. From this last parameter, the dimension D = 1/H can be obtained. In order to assess whether the dynamics of the system are compatible with chaotic characteristics, the entire spectrum of Lyapunov exponents was calculated. We used return maps to graphically represent the non-linear and non-periodical behaviours in patients and controls. RESULTS: Surrogate data suggest that the HRV time courses have unique non-linear characteristics. D2, K2 and 1/H parameters were significantly lower in transplanted subjects than in controls. Positivity of the first Lyapunov exponent indicates divergence of trajectories in state-space. Furthermore, the display of return maps on projections obtained after Singular Value Decomposition, especially in low-complexity data (as in transplanted patients), shows a structure which is suggestive of a strange attractor. These findings support the hypothesis that chaotic dynamics underlie HRV. CONCLUSION: These results indicate that non-linear dynamics are likely to be present in HRV control mechanisms, giving rise to complex and qualitatively different behaviours. System complexity decreases in transplanted patients and this may be related to loss of the neural modulation of heart rate.
Adult↗
Sympathovagal effects of spinal anesthesia assessed by heart rate variability analysis.
Heart rate variations (HRV) result from moment-to-moment changes in sympathetic and parasympathetic activity in response to many conditions. These two neural inputs to the heart can be identified by analyzing power spectra of HRV for frequency components at the vasomotor (low-frequency [LF]) and the respiratory (high-frequency [HF]) rhythms. HRV analysis has been used successfully in humans to noninvasively evaluate the autonomic responses to specific maneuvers and drugs, as well as responses to more chronic preexisting pathologic conditions. The effects of an isolated "acute" withdrawal of sympathetic activity in humans, however, have not as yet been evaluated using an autoregressive (AR) technique. We examined HRV using this technique in a group of patients receiving subarachnoid block for abdominal surgery. The sensory levels achieved were within the range of those reported to interrupt sympathetic outflow to the heart. Electrocardiograms were recorded and subjected to AR analysis. AR analysis of HRV after spinal anesthesia revealed significant decreases in both dominant frequency components (LF and HF) that occur between 0.03 Hz and 0.5 Hz. These reductions coincided with blockade of cardiac sympathetic outflow after cephalad spread of the spinal block. The power spectra were almost abolished in patients with sensory blocks reaching T1-2. The decreases in amplitude of the LF and HF components, therefore, act as markers of diminished sympathetic and parasympathetic activity to the heart, while the ratio of LF:HF indicated that sympathovagal balance was predominantly maintained during most of the block.(ABSTRACT TRUNCATED AT 250 WORDS)
Anesthesia, Spinal↗
[Role of low-frequency neuronal activity in the medulla in the regulation of the cardiovascular system].
We recorded discharge activity of 45 single neurons located in the rostral ventrolateral medulla (n = 21), lateral tegmental field (n = 10) and caudal raphe (n = 14) nuclei in baroreceptor-denervated decerebrate cats (n = 27). Autoregressive spectral analysis was performed on neuronal activity and systolic arterial pressure (SAP). The discharges of the recorded neurons were correlated to 2- to 6 Hz oscillations or 10 Hz rhythm present in sympathetic neural discharge. A low frequency (LF) oscillation (0.12 +/- 0.02 Hz) was observed in 25 (55%) units. The same rhythmicity was found in SAP variability in 25 of 45 (55%) recordings. In 21 of these cases the LF in SAP variability was highly correlated to LF in neural activity. Moreover, 32 out of 45 (71%) neurons showed a higher rhythm (HF; 0.34 +/- 0.06 Hz) related to the ventilation rate. These data demonstrate the presence of an LF oscillation in the discharge of single medullary neurons, involved in the regulation of cardiovascular system. This LF component was similar to that detectable in the spectral analysis of SAP variability, thus supporting the hypothesis of a central origin of this rhythm, largely independent of baroreceptor input.
Analysis of Variance↗
Mechanical effects of respiration and stepping on systolic arterial pressure variability during treadmill exercise.
AIM: To evaluate the changes produced by maximal dynamic exercise in the rhythmic components of systolic arterial pressure variability. PATIENTS AND METHODS: We studied seven normotensive subjects during different levels of a modified treadmill test (Bruce protocol, up to stage 4). Arterial pressure was measured directly by a high-fidelity microtip pressure transducer. Spectral analysis provided two main oscillatory components of systolic arterial pressure variability, a low-frequency component related to the sympathetic-mediated neural control of vasomotion and a high-frequency component reflecting the mechanical effects of respiration on blood pressure. RESULTS: The low-frequency component increased at the beginning of exercise and remained stable thereafter, while the high-frequency component increased progressively. A third rhythmic component (very high frequency) with a frequency higher than respiration and synchronous with the rate of the subjects' footsteps, which was undetectable on a visual inspection of analog tracings, became progressively more apparent, reaching its maximum at exercise stage 4. CONCLUSIONS: These findings emphasize the importance of high-fidelity techniques and computer analysis for the evaluation of arterial pressure variability in dynamic conditions.
Adult↗
Model for the assessment of heart period and arterial pressure variability interactions and of respiration influences.
A model which assesses the closed-loop interaction between heart period (HP) and arterial pressure (AP) variabilities and the influence of respiration on both is applied to evaluate the sources of low frequency (LF approximately 0.1 Hz) and high frequency (HF, respiratory rate approximately 0.25 Hz) in conscious dogs (n = 18) and humans (n = 5). A resonance of AP closed-loop regulation is found to amplify LF oscillations. In dogs, the resonance gain increases slightly during baroreceptor unloading (mild hypotension obtained with nitroglycerine (NTG) i.v. infusion, n = 8) and coronary artery occlusion ((CAO), n = 6), and it is abolished by ganglionic transmission blockade ((ARF), Arfonad i.v. infusion, n = 3). In humans, this gain is considerably increased by passive tilt. Different, possibly central, sources of LF oscillations are also evaluated, finding a strong rhythmic modulation of HP during CAO. At HF, a direct respiratory arrhythmia is dominant in dogs at control, while it is considerably reduced during CAO. On the contrary, in humans, a strong influence of respiration on AP is shown which induces a reflex respiratory arrhythmia. An index of the gain of baroreceptive response, alpha cl, was decreased by NTG and CAO, and virtually abolished by chronic arterial baroreceptive denervation (TABD, n = 4) and ARF.
Animals↗
Power spectrum analysis of heart rate variability to assess the changes in sympathovagal balance during graded orthostatic tilt.
BACKGROUND: The powers of the low-frequency (LF) and high-frequency (HF) oscillations characterizing heart rate variability (HRV) appear to reflect, in their reciprocal relationship, changes in the state of the sympathovagal balance occurring during numerous physiological and pathophysiological conditions. However, no adequate information is available on the quantitative resolution of this methodology. METHODS AND RESULTS: We studied 22 healthy volunteers (median age, 46.5 years) who were subjected after a rest period to a series of passive head-up tilt steps randomly chosen from the following angles: 15 degrees, 30 degrees, 45 degrees, 60 degrees, and 90 degrees. From the continuous ECG, after appropriate analog-to-digital conversion, a personal computer was used to compute, with an autoregressive methodology, time and frequency domain indexes of RR interval variability. Spectral and cross-spectral analysis with the simultaneously recorded respiratory signal excluded its contribution to LF. Age was significantly correlated to variance and to the absolute values in milliseconds squared of very-low-frequency (VLF), LF, and HF components. The tilt angle was correlated to both LF and HF (expressed in normalized units [nu]) and to the LF-to-HF ratio (r = .78, -.72, and .68; respectively). Lower levels of correlation were found with HF (in ms2) and RR interval. No correlation was present between tilt angle and variance, VLF, or LF (in ms2). Individual analysis confirmed that the use of nu provided the greatest consistency of results. CONCLUSIONS: Spectral analysis of HRV, using nu or LF-to-HF ratio, appears to be capable of providing a noninvasive quantitative evaluation of graded changes in the state of the sympathovagal balance.
Adult↗
Non-linear dynamics in the beat-to-beat variability of sympathetic activity in decerebrate cats.
Non-linear interactions between low-frequency rhythms (0.1 Hz) of beat-to-beat variability series of sympathetic discharge and respiratory rhythm (0.3 Hz) are observed in decerebrate artificially ventilated cats. Simple graphical tools as Poincaré and recurrence maps are used to detect, in a qualitative way, phase-locking phenomena. Non-parametric bispectral analysis is also carried out to quantify the degree of second-order coupling between oscillations at different frequencies.
Animals↗
Long-term treatment of retinitis pigmentosa with acetazolamide. A pilot study.
The therapeutic effect of long-term treatment with acetazolamide (from 3 weeks to 16 months) of seven patients with retinitis pigmentosa was studied. Improvement in visual acuity was found in almost all the eyes, accompanied by an improvement in the macular threshold in two patients. The therapeutic effect was independent of reduction of macular edema, as judged by fluorescein angiography.
Acetazolamide↗
Power spectrum analysis of cardiovascular variability monitored by telemetry in conscious unrestrained rats.
Beat-to-beat variability of arterial pressure and heart period (R-R) was studied in eight conscious freely-moving adult male rats in which telemetric recordings of arterial pressure, ECG and respiratory movements were obtained under unrestrained and unstressed conditions. The beat-to-beat time series of these signals (systolic arterial pressure, diastolic arterial pressure and R-R) were analyzed, in the frequency domain, using autoregressive spectral analysis in order to detect and quantify the rhythmic components. In basal conditions, the systolic arterial pressure variability spectrum was characterized by three major spectral components which had central frequencies respectively of 0.08 +/- 0.03 Hz (very low frequency), 0.43 +/- 0.02 Hz (low frequency) and 1.36 +/- 0.19 Hz (high frequency). Similar rhythmic components were found in R-R signal variability. The very low frequency component included a higher percentage of total power in R-R variability spectrum (75.3%) than in systolic arterial pressure variability spectrum (58.4%). The low frequency component was more pronounced in both systolic and diastolic arterial pressure variability spectra. The high frequency component of R-R, systolic and diastolic arterial pressure was synchronous with respiration. Cross-spectral analysis revealed a high statistical coherence between R-R and arterial pressure variabilities in all the three frequency bands. An alpha-adrenergic blocker (phentolamine) specifically abolished the low frequency components of systolic and diastolic arterial pressure variability spectra, thus suggesting that low frequency is a marker of sympathetic modulation of vasomotor activity. The low frequency component of R-R variability spectrum was also markedly blunted. We suggest that cardiovascular variability signals, (R-R, systolic and diastolic arterial pressure) are composed almost of two main rhythms linked to respiration and vasomotor activity. These rhythms can be quantified in conscious unrestrained rats by using telemetry and spectral analysis. This approach seems to offer a new powerful tool for pharmacological studies in conscious small animals.
Animals↗