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PubMed2004

Sympathovagal balance fluctuates during colonoscopy.

BACKGROUND AND STUDY AIM: Colonoscopy is a common gastroenterological procedure for investigation of the bowel. The main side effects of colonoscopy are pain during investigation, cardiovascular complications and very rarely even death. The aim of this study was to compare the continuous fluctuation of heart rate variability (HRV) components during colonoscopy under normal conditions, analgesia/sedation, and total intravenous anesthesia. PATIENTS AND METHODS: 37 consecutive patients (aged 35 - 65), were randomly allocated to three groups: no sedation (control group 1); analgesia/sedation (group 2); and total intravenous anesthesia (group 3). Holter electrocardiography and subsequent frequency domain analysis were undertaken. The low-frequency (LF, 0.04 - 0.15 Hz) and the high-frequency (HF, 0.15 - 0.40 Hz) components were estimated using spectral analysis in the usual way. Normalized units (nu) were calculated from the following equations: LFnu = LF/(LF + HF), and HFnu = HF/(LF + HF). RESULTS: Groups 2 and 3 were found to have a significantly lower HFnu and higher LFnu than group 1 essentially throughout the procedure. A one-way analysis of variance and t-test confirmed that the differences were significant when the colonoscope reached the splenic flexure as were the LF/HF balances at the splenic and hepatic flexures and the cecum. The percentage change in LF/HF was also analyzed, and it was found that in group 3 the mean change was over 136 % when the colonoscope reached the sigmoid flexure, which was significantly higher than in the other two groups. CONCLUSION: Most changes in HRV components occurred during colonoscopy of the left side of the bowel. Analgesia/sedation and total intravenous anesthesia increased HRV by increasing the LF component.

Adult↗
PubMed1993

Periodic hemodynamics (flow motion) in peripheral arterial occlusive disease.

PURPOSE: The occurrence of periodic blood flow variations (flow motion) in health and disease is controversially discussed. This is partly due to not reporting the incidence and to performing the analysis solely visually. We have therefore studied flow motion with computerized methods. METHODS: We used a computerized Prony spectral line estimator program to analyze the frequencies of resting skin blood flow variations, as determined by laser Doppler flowmetry on the thumb and great toe, in 50 male control subjects (group a), in 50 patients with mild peripheral arterial occlusive disease (PAOD stages I and II; group b), and in 25 patients with severe PAOD (stages III and IV; group c). RESULTS: The median ankle/arm pressure ratio was 1.10 in the control group, 0.72 in the mild PAOD group, and 0.66 in the severe PAOD group. Slow wave flow motion was detected in 19% of all thumbs from groups a and b (systolic arm pressures > 100 mm Hg) and in 12% of the toes in the control group. Patients with mild PAOD exhibited slow wave flow motion in 46% of the toes. Patients with severe PAOD showed slow waves in 77% of the toes. The median flow motion frequencies were about 1.6 cycles/min for groups a and b, when present. The median frequency in group c was significantly higher at 4.0 cycles/min, though still in the range of slow waves. The median peak-to-through amplitude was between 17% and 20% of mean flow for all groups. CONCLUSIONS: We conclude that evaluation of flow motion requires computerized frequency analysis and that slow wave flow motion is a perfusion pattern characteristic of PAOD rather than of normal perfusion states. This finding has potential implications for diagnostic and therapeutic approaches in arterial occlusive disease.

Arterial Occlusive Diseases↗
PubMed2007

Cerebral lateralisation for facial processing: gender-related cognitive styles determined using Fourier analysis of mean cerebral blood flow velocity in the middle cerebral arteries.

Facial processing was studied in 16 (eight men and eight women) right-handed healthy participants using a new functional transcranial Doppler technique called functional transcranial Doppler spectroscopy (fTCDS). MFV was recorded simultaneously in both right and left middle cerebral arteries in dark condition and during visual processing of object and facial tasks. fTCDS used Fourier analysis of mean flow velocity (MFV) time series to derive spectral density estimates that correlate with expected mental activity. Men were right lateralised for object and facial perception, while women were left lateralised for facial tasks but showed a right tendency or no lateralisation for object perception. For facial perception, men used a category-specific process-mapping system for right cognitive style, but women used same for the left.

Adult↗
PubMed2005

Objective analysis of the singing voice as a training aid.

A new tool for robust tracking of fundamental frequency is proposed, along with an objective measure of main singing voice parameters, such as vibrato rate, vibrato extent, and vocal intonation. High-resolution Power Spectral Density estimation is implemented, based on AutoRegressive models of suitable order, allowing reliable formant tracking also in vocalizations characterized by highly varying values. The proposed techniques are applied to about 1000 vocalizations, coming from both professional and non-professional singers, and show better performance as compared to classical Fourier-based approaches. If properly implemented, and with a user-friendly interface, the new tool would allow real-time analysis of singing voice. Hence, it could be of help in giving non-professional singers and singing teachers reliable measures of possible improvements during and after training.

Acoustics↗
PubMed2006

The effect of 2 sympatholytic medications--propranolol and clonidine--on sleep bruxism: experimental randomized controlled studies.

STUDY OBJECTIVE: To examine whether 2 sympatholytic medications decrease sleep bruxism and prevent the rise in sympathetic activity preceding the onset of sleep bruxism: propranolol, a nonselective adrenergic beta-blocker, and clonidine, a selective alpha2-agonist. DESIGN: Experimental randomized controlled crossover studies with placebo and active treatments (propranolol 120 mg; clonidine 0.3 mg). SETTING: Hospital-based sleep research laboratory. PATIENTS: Twenty-five subjects with a history and diagnosis of SLEEP BRUXISM (11 men, 14 women; age range, 21 to 31 years). INTERVENTION: Polygraphic study. MEASUREMENTS AND RESULTS: Polygraphic sleep laboratory recordings were done for 4 nights: the first night was habituation, the second, sleep bruxism diagnosis; and 3 and 4 were study nights. The sleep bruxism index was estimated using masseter muscle activity. Heart rate variability was estimated with spectral analysis of RR intervals. Sleep and sleep bruxism variables were not significantly influenced by propranolol. A reduction of the mean RR intervals and of the sympathetic dominance (p < .05) was seen. Under clonidine, duration of sleep stage 2 was prolonged, whereas REM sleep was suppressed in 14 of 16 subjects with sleep bruxism. The sleep bruxism index was reduced by 61% (p < .05). Under clonidine, a reduction in heart rate and sympathetic dominance was observed in stable sleep and in the minute preceding the onset of sleep bruxism (p < .05). CONCLUSION: Although propranolol did not affect sleep bruxism, clonidine decreased sympathetic tone in the minute preceding the onset of sleep bruxism, thus reducing sleep bruxism by preventing the sequence of autonomic to motor activation of sleep bruxism. This further supports the role of sympathetic activity in the pathophysiology of sleep bruxism. Because morning hypotension was seen in 19% of patients, further dose-dependant research is required to assess the safety of clonidine for the management of sleep bruxism.

Adrenergic alpha-Agonists↗
PubMed2000

Could heart rate variability analysis become an early predictor of imminent brain death? A pilot study.

UNLABELLED: Physiology of brain death is characterized by major disturbances of autonomic nervous system (ANS) activity which can lead to graft dysfunction. These findings exhibit the importance of early diagnosis of brain death to improve transplantation outcome. The aim of this prospective study was to assess whether heart rate variability (HRV) analysis, a noninvasive method to investigate ANS activity in comatose patients, could achieve this goal. A total of 14 brain-injured patients were included in the study as soon as they exhibited the clinical signs of imminent brain death. The electrocardiogram was then recorded from two leads with a Holter digital monitor. The clinical diagnosis of brain death was considered after an autonomic storm had occurred. HRV was assessed from 6 h before to 6 h after brain death in both time domain and spectral analysis, estimating either global ANS activity (index of variability, total power), parasympathetic activity (percentage of delta of R-R interval >50 ms, root mean square for successive interval differences, LnHF) or sympathetic activity (LnLF). Hourly averages of these variables were compared by using one-way analysis of variance. To assess whether HRV could per se diagnose brain death, receiver operating characteristic curves were generated for total power, root mean square for successive interval differences, and LnHF. We observed, for 6 h before brain death, a progressive extinction of the influence of the ANS on cardiovascular regulation. There was no activity in the two components of the ANS as soon as brain death occurred. HRV analysis appeared to be a very sensitive but a less specific method of diagnosing brain death. IMPLICATIONS: A total of 14 brain-injured patients with the clinical criteria of imminent brain death were enrolled for electrocardiogram recording and heart rate variability analysis (a noninvasive method to investigate autonomic nervous system activity). For 6 h before brain death, we observed a progressive extinction of autonomic nervous system activity which was not present as soon as brain death was clinically evoked.

Adult↗
PubMed1981

In vivo phytochrome difference spectrum from dark grown gametophytes of anemia phyllitidis L. Sw. Treated with norflurazon.

An in vivo phytochrome difference spectrum of dark grown Anemia phyllitidis L. Sw. gametophytes has been measured. The spectral characteristics estimated from the difference spectrum were as follows: red maximum at 662 nanometers, far red maximum at 737 nanometers, isosbestic point at 695 nanometers, and a shoulder from 620 to 630 nanometers. To diminish the influence of chlorophyll on phytochrome measurements in dark grown gametophytes, total chlorophyll content could be reduced by about 65% by treatment with 1 micromolar Norflurazon. In gametophytes grown in red light, the inhibition caused by 1 micromolar Norflurazon was 97.5%, based on g spores. Total carotenoid content of dark grown gametophytes was not appreciably different from that already present in dry spores. Herbicide treatment reduced this level to about 60%. Gametophytes grown in red light showed a nearly 7-fold increase in total carotenoids compared with that of the dark control. In treated light grown protonemata, no carotenoid accumulation took place, and the level remaining corresponded with that found in treated dark grown protonemata.

Journal Article↗
PubMed1992

Assessment of input-output properties and control of neuroprosthetic hand grasp.

Three tests have been developed to evaluate rapidly and quantitatively the input-output properties and patient control of neuroprosthetic hand grasp. Each test utilizes a visual pursuit tracking task during which the subject controls the grasp force and grasp opening (position) of the hand. The first test characterizes the static input-output properties of the hand grasp, where the input is a slowly changing patient generated command signal and the outputs are grasp force and grasp opening. Nonlinearities and inappropriate slopes have been documented in these relationships, and in some instances the need for system returning has been indicated. For each subject larger grasp forces were produced when grasping larger objects, and for some subjects the shapes of the relationships also varied with object size. The second test quantifies the ability of the subject to control the hand grasp outputs while tracking steps and ramps. Neuroprosthesis users had rms errors two to three times larger when tracking steps versus ramps, and had rms errors four to five times larger than normals when tracking ramps. The third test provides an estimate of the frequency response of the hand grasp system dynamics, from input and output data collected during a random tracking task. Transfer functions were estimated by spectral analysis after removal of the static input-output nonlinearities measured in the first test. The dynamics had low-pass filter characteristics with 3 dB cutoff frequencies from 1.0 to 1.4 Hz. The tests developed in this study provide a rapid evaluation of both the system and the user. They provide information to 1) help interpret subject performance of functional tasks, 2) evaluate the efficacy of system features such as closed-loop control, and 3) screen the neuroprosthesis to indicate the need for retuning.

Cervical Vertebrae↗
PubMed2005

Effect of remifentanil with and without atropine on heart rate variability and RR interval in children.

Remifentanil can cause bradycardia either by parasympathetic activation or by other negative chronotropic effects. The high frequency (HF) component of heart rate variability (HRV) is a marker of parasympathetic activity. This study aimed to evaluate the effect of remifentanil on RR interval and on HRV in children. Forty children ASA I or II were studied after approval by the human studies committee and informed parental consent was obtained. After stabilisation at sevoflurane 1 MAC, they were randomly divided into two groups: one received a 20 microg.kg(-1) atropine injection (AT + REMI) and the other ringer lactate solution (REMI). Three minutes later, a 1 microg.kg(-1) bolus of remifentanil was administered over 1 min, followed by a continual infusion at 0.25 microg.kg(-1).min(-1) for 10 min increased to 0.5 microg.kg(-1).min(-1) for a further 10 min. A time varying, autoregressive analysis of RR sequences was used to estimate classical spectral parameters: low (0.04-0.15 Hz; LF) and high (0.15-0.45 Hz; HF) frequency, whereas the root mean square of successive differences of RR intervals (rmssd) was derived directly from the temporal sequence. Statistical analyses were conducted by means of the multiple correspondence analysis and with non parametrical tests. Remifentanil induced an RR interval lengthening, i.e. bradycardia, in both groups compared to pretreatment values and was associated with an increase of HF and rmssd only for the REMI group. The parasympathetic inhibition by atropine did not totally prevent remifentanil's negative chronotropic effect. A direct negative chronotropic effect of remifentanil is proposed.

Adolescent↗
PubMed2001

Agents that increase tyrosine phosphorylation activate a non-selective cation current in single rabbit portal vein smooth muscle cells.

The effects of agents that increase tyrosine phosphorylation were studied with whole-cell recording of membrane currents in single smooth muscle cells from the rabbit portal vein. In K+-free conditions with the chloride equilibrium potential at about -50 mV, intracellular application via the patch pipette of 200 microM sodium orthovanadate (Na3VO4), which inhibits tyrosine phosphatases, activated a "noisy" inward current at a holding potential of -50 mV. Intracellular dialysis with 100 microM (pY)EEI, a peptide activator of the cytosolic tyrosine kinase pp60c-src, and bath application of 5 microM insulin, which activates receptor-coupled tyrosine kinases, also evoked a "noisy" inward current. The current-voltage relationships and the reversal potential (about +10 mV) of the Na3VO4-, pp60c-src- and insulin-induced currents were similar to those of the noradrenaline-evoked non-selective cation current (Icat). The inward currents evoked by noradrenaline, Na3VO4, (pY)EEI and insulin were all greatly potentiated when the bathing calcium concentration was reduced from 1.5 mM to 50 microM. The single channel conductance estimated from spectral density analysis of the whole-cell current was about 20 pS for noradrenaline, Na3VO4, (pY)EEI and insulin. Moreover for all agents the spectra were described by the sum of two Lorentzians with similar corner frequencies. Noradrenaline-evoked Icat was inhibited to a similar degree by the tyrosine kinase inhibitors genistein and tyrphostin 23 and their inactive analogues daidzein and tyrphostin A1, respectively. In the presence of Na3VO4, application of noradrenaline evoked a cation current of similar peak amplitude to control Icat although the rate of decay of Icat was enhanced in the presence of Na3VO4. This study shows that stimulation of both cytosolic and receptor-coupled tyrosine kinases evokes a non-selective cation current and the conductance is similar to that activated by noradrenaline.

Animals↗
PubMed1979

Tremor in the tension developed isometrically by soleus during the tonic vibration reflex in the decerebrate cat.

1. Irregularities in the development of tension during the tonic vibration reflex of the soleus muscle of the decerebrate cat have been analysed into their frequency components. The reflex was recorded isometrically and elicited by longitudinal vibration, normally at 150 Hz. The amplitude of vibration was set so as to elicit a maximal reflex response, suggesting 1:1 driving of the majority of the Ia afferents at the frequency of vibration. 2. The resulting power spectrum regularly showed a well marked tremor peak separated by a trough from any slow irregularities. The predominant frequency of this tremor varied from 4 to 11 Hz in different preparations, with a mean of 7.4 Hz; on average, frequencies within 1.7 Hz on either side contained over half the power of the predominant frequency. Altering the frequency of vibration did not alter the distribution of tremor frequencies. 3. The root mean square value of the tension irregularities, over the range 4-14 Hz, varied from 12 to 110 mN in different preparations (median value, 23 mN); this was superimposed on mean active reflex tensions varying from 2 to 10 N. 4. The 'tremor' due to a single motor unit was estimated from spectral analysis of tetanic contractions of the whole muscle and decreased with increasing frequency of activation. Comparison of the single unit values with the tremor seen during vibration in the same preparations showed that equivalent amounts of tremor to the latter could typically have been produced by the continued synchronous contraction of about five 'average' motor units firing at the predominant tremor frequency. 5. When a tonic stretch reflex was present its tremor frequencies did not differ consistently from those of the tonic vibration reflex. On average, the tremor was smaller for the stretch reflex than for the tonic vibration reflex; the difference was usually slight and might have been related to the stretch refex tension being smaller. 6. Evidence was obtained that the tremor was not due to any insecurity of 1:1 driving of the Ia afferents by the vibration. First, the tremor did not increase when the amplitude of vibration was decreased sufficiently to ensure that the degree of 1:1 driving must have been reduced. Secondly, the introduction of a comparable 'artificial tremor' by sinusoidally oscillating the muscle at low frequency did not produce the e.m.g. response that would have been expected if the applied 'tremor' had been modulating the firing of the Ia or any other group of afferents. 7. It is concluded that the observed tremor cannot be attributed to 'oscillation in the stretch reflex arc', though without prejudice to the role of this mechanism under other conditions and especially when the recording is not isometric. However, the genesis of the tremor has not been established and much of it might result simply from the chance synchronization of motor units that are firing below their tetanic fusion frequency.

Action Potentials↗
PubMed1997

Can abnormalities of ventricular repolarisation identify insulin dependent diabetic patients at risk of sudden cardiac death?

OBJECTIVE: To study the possible association or QT dispersion and mean QTc intervals, as measured from standard 12 lead electrocardiograms, with baroreceptor-cardiac reflex sensitivity (BRS) in insulin dependent diabetic patients. DESIGN: Comparative study of non-invasive assessment of BRS, QT interval, and QT dispersion. SETTING: Large teaching hospital. SUBJECTS: 31 young asymptomatic, normotensive, insulin dependent diabetic patients, aged 20-55 years with normal clinical autonomic function. METHODS: QT intervals and QT dispersion were measured by a single observer blinded to other data about the patients. BRS was measured after activating the baroreflex with a Valsalva manoeuvre, and the rate in change of R-R interval to increasing systolic pressure during phase 4 was measured; in addition sequence analysis of resting systolic blood pressure and heart rate was performed during standing. The alpha coefficient--an index of the overall gain of the baroreflex mechanisms--was estimated from spectral analysis data of systolic blood pressure and pulse interval variability. RESULTS: Mean (SD) QTc interval was 406 (23) ms, QT dispersion was 44 (13) ms. There was no association between QT dispersion and any measurement of BRS. There was a negative correlation between mean QTc intervals and sequence analysis BRS (r = -0.355, P = 0.049), but no association with Valsalva BRS. The alpha coefficient, showed a significant negative correlation with mean QTc (r = -0.42, P = 0.008). CONCLUSIONS: Abnormal BRS may be reflected in the heart by global prolongation of ventricular repolarisation, but not by dispersion of ventricular repolarisation. This may, in part, explain the increase in sudden cardiac death seen in IDDM patients.

Adult↗
PubMed1990

Effect of naloxone on spectral shifts of the diaphragm EMG during inspiratory loading.

Shifts in the power spectrum of the diaphragm EMG to lower frequencies may occur in the presence of fatiguing inspiratory flow-resistive loads (IRL). However, such a shift of the centroid frequency (fc) could follow a reduction in central output through a differential reduction in end-inspiratory high-frequency power (HFP). In unanesthetized goats, we tested the hypothesis that activation of the endogenous opioid system by IRL would differentially reduce central respiratory output, causing a reduction in fc. IRL was imposed for 180 min after which naloxone (0.1 mg/kg, NLX) was given. fc was computed from the power spectral density estimated by the Welch method. IRL reduced fc from 148.0 +/- 9.8 (SE) Hz at base line to 141.1 +/- 8.9 Hz or to 95.5 +/- 1.3% of base line by 180 min (both P less than 0.05). NLX increased fc to 148.9 +/- 9.9 Hz or to 100.6 +/- 1.1% of base line (both P less than 0.05). The decline in fc during IRL was found to be the result of a reduction in HFP, predominantly toward the end of inspiration. The reversibility of this fc shift with NLX suggests a central mechanism consequent to elaboration of endogenous opioids and not a peripheral (muscular) event consequent to muscle fatigue.

Animals↗
PubMed1985

Specular reflector noise: effect and correction for in vivo attenuation estimation.

After reviewing the usual models proposed for the echographic response of soft tissues, we discuss the interaction between the ultrasonic wave and large size obstacles. Structures of this size, specular reflectors, can be found in tissues. The influence of such reflectors on in vivo attenuation measurements is detailed. We point out the importance of the specular echo noise originating from two kinds of reflectors: plane-like and vessel-like reflectors. We present a complete study of their influence on two different algorithms for attenuation estimates: the spectral centroid shift and the narrow band methods. Results are presented on stimulated data, a tissue-mimicking phantom and in vivo muscle data. Different procedures for minimizing the specular echo noise are also discussed.

Humans↗
PubMed2003

Specific interactions study in complexes of poly(mono-n-alkyl itaconates) with tertiary polyamides.

This paper reports an FT-IR study of blends of poly(mono-n-alkyl itaconates) with poly(N,N-dimethylacrylamide) (PDMA) and poly(ethyloxazoline) (PEOX). Strong hydrogen bonding has been found, and both polybases have shown similar acceptor strengths. Derivative techniques show asymmetric profiles for the free carbonyl band of the polybases, resulting in shifted band locations. The extent of the interassociation has been estimated by spectral curve fitting of the polybase carbonyl band. The results show that the interaction degree in blends with PEOX does not depend on the length of the poly(monoalkyl itaconate) side group, while an inter-associating ability loss is observed in blends with PDMA as the side-group size of the polyacid increases. This different behavior is attributed to the greater interspacing between vicinal carbonyl groups in PEOX. This band shows conformational sensitivity and reflects the conformational changes that occur as the steric hindrances present in the medium (due to the bulky side groups of the polyacids) increase.

Acrylamides↗
PubMed2006

Fast and robust method for the determination of microstructure and composition in butadiene, styrene-butadiene, and isoprene rubber by near-infrared spectroscopy.

In the tire industry, synthetic styrene-butadiene rubber (SBR), butadiene rubber (BR), and isoprene rubber (IR) elastomers are essential for conferring to the product its properties of grip and rolling resistance. Their physical properties depend on their chemical composition, i. e., their microstructure and styrene content, which must be accurately controlled. This paper describes a fast, robust, and highly reproducible near-infrared analytical method for the quantitative determination of the microstructure and styrene content. The quantitative models are calculated with the help of pure spectral profiles estimated from a partial least squares (PLS) regression, using (13)C nuclear magnetic resonance (NMR) as the reference method. This versatile approach allows the models to be applied over a large range of compositions, from a single BR to an SBR-IR blend. The resulting quantitative predictions are independent of the sample path length. As a consequence, the sample preparation is solvent free and simplified with a very fast (five minutes) hot filming step of a bulk polymer piece. No precise thickness control is required. Thus, the operator effect becomes negligible and the method is easily transferable. The root mean square error of prediction, depending on the rubber composition, is between 0.7% and 1.3%. The reproducibility standard error is less than 0.2% in every case.

Journal Article↗
PubMed2005

Spectral unmixing of flavin autofluorescence components in cardiac myocytes.

We applied linear unmixing approach to reveal individual components of intrinsic flavin fluorescence signal recorded in living cardiac cells by spectrally resolved confocal microscopy. Responses of whole-cell autofluorescence to modulators of cell metabolism and respiration were used as a tool of separation of its components; their spectral profiles, estimated by principal component analysis, correspond to free FAD and FAD bound to different enzymes of electron transport chain.

Algorithms↗