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At least 1,207 records · Page 67Linked to original sources
PubMed2000

Effects of controlled breathing, mental activity and mental stress with or without verbalization on heart rate variability.

OBJECTIVES: To assess whether talking or reading (silently or aloud) could affect heart rate variability (HRV) and to what extent these changes require a simultaneous recording of respiratory activity to be correctly interpreted. BACKGROUND: Sympathetic predominance in the power spectrum obtained from short- and long-term HRV recordings predicts a poor prognosis in a number of cardiac diseases. Heart rate variability is often recorded without measuring respiration; slow breaths might artefactually increase low frequency power in RR interval (RR) and falsely mimic sympathetic activation. METHODS: In 12 healthy volunteers we evaluated the effect of free talking and reading, silently and aloud, on respiration, RR and blood pressure (BP). We also compared spontaneous breathing to controlled breathing and mental arithmetic, silent or aloud. The power in the so called low- (LF) and high-frequency (HF) bands in RR and BP was obtained from autoregressive power spectrum analysis. RESULTS: Compared with spontaneous breathing, reading silently increased the speed of breathing (p < 0.05), decreased mean RR and RR variability and increased BP. Reading aloud, free talking and mental arithmetic aloud shifted the respiratory frequency into the LF band, thus increasing LF% and decreasing HF% to a similar degree in both RR and respiration, with decrease in mean RR but with minor differences in crude RR variability. CONCLUSIONS: Simple mental and verbal activities markedly affect HRV through changes in respiratory frequency. This possibility should be taken into account when analyzing HRV without simultaneous acquisition and analysis of respiration.

Arousal↗
PubMed2002

Changes in circadian rhythm in heart rate and parasympathetic nerve activity after an eastward transmeridian flight.

Distortions of the circadian rhythm structure of the heart rate and parasympathetic nerve activity after an eastward transmeridian flight were studied. We recorded the ambulatory electrocardiograms of 12 healthy young men for 11 days: 3 days in Tokyo before the flight and 8 days in San Francisco following it. Heart rate variability was determined by power spectrum analysis, and high frequency power (0.15-0.4 Hz) was used as the index of parasympathetic tone. The structural characteristics of the circadian rhythm were analyzed by dividing consecutive RR data into four parts: the preflight days, the second and third days, the fourth and fifth days (Days 5-6) and the sixth and seventh days. Eight of the 12 cases were analyzed completely. The circadian period of the heart rate decreased after the flight. The peak time of parasympathetic nerve activity shifted from the small hours to the daytime, the maximum shift being during days 5-6 after the flight. We concluded that a structural disturbance of the circadian rhythm of the heart rate and parasympathetic nerve activity were observed.

Adult↗
PubMed2002

Progressive opacification of hydrophilic acrylic intraocular lenses in diabetic patients.

Four patients with diabetes mellitus had cataract extraction with implantation of a hydrophilic acrylic intraocular lens (IOL) (ACRL-C160, Ophthalmed). The IOLs showed progressive and generalized opacification 10 to 20 months after implantation, decreasing visual acuity. All 4 IOLs were removed. By light microscopic examination, the IOL surfaces were wrinkled and encrusted with microspheres. Electron microscopy revealed the material to be crystalline in nature. Energy dispersive x-ray spectrum analysis showed that the deposits were mainly composed of calcium and phosphate.

Acrylic Resins↗
PubMed1997

Evaluation and characterization of carotid plaque.

Doppler sonography, combining high-resolution imaging and Doppler spectrum analysis, has proven to be the best choice for safe, noninvasive, low-cost screening for the etiology of stroke. With high-resolution imaging, plaque can be characterized relative to the risk for intraplaque hemorrhage, thought by many to be the precursor of plaque ulceration. Using high-resolution ultrasound, heterogeneous plaque has been shown to be associated with intraplaque hemorrhage. Criteria for distinguishing heterogeneous from homogeneous plaque are discussed, as are techniques for characterizing plaque. Several published articles strongly suggest that, when heterogeneous plaques are identified, the incidence of neurological symptoms and stroke on follow-up increases, relative to patients with homogeneous plaques. Additional long-term follow-up studies of heterogeneous plaque are needed. Most recently, carotid wall thickness has been evaluated as a physiological marker for atherosclerotic disease and as a gauge of the effectiveness of medical therapies. It is likely that carotid wall thickness will become important in the diagnosis and management of atherosclerosis. Radiologist are encouraged to learn this new form of ultrasound examination, which is reviewed briefly in this article.

Arteriosclerosis↗
PubMed2001

Level and center frequency of the singer's formant.

The "singer's formant" is a prominent spectrum envelope peak near 3 kHz, typically found in voiced sounds produced by classical operatic singers. According to previous research, it is mainly a resonatory phenomenon produced by a clustering of formants 3, 4, and 5. Its level relative to the first formant peak varies depending on vowel, vocal loudness, and other factors. Its dependence on vowel formant frequencies is examined. Applying the acoustic theory of voice production, the level difference between the first and third formant is calulated for some standard vowels. The difference between observed and calculated levels is determined for various voices. It is found to vary considerably more between vowels sung by professional singers than by untrained voices. The center frequency of the singer's formant as determined from long-term spectrum analysis of commercial recordings is found to increase slightly with the pitch range of the voice classification.

Female↗
PubMed2001

Comparison of singer's formant, speaker's ring, and LTA spectrum among classical singers and untrained normal speakers.

Many studies have described and analyzed the singer's formant. A similar phenomenon produced by trained speakers led some authors to examine the speaker's ring. If we consider these phenomena as resonance effects associated with vocal tract adjustments and training, can we hypothesize that trained singers can carry over their singing formant ability into speech, also obtaining a speaker's ring? Can we find similar differences for energy distribution in continuous speech? Forty classically trained singers and forty untrained normal speakers performed an all-voiced reading task and produced a sample of a sustained spoken vowel /a/. The singers were also requested to perform a sustained sung vowel /a/ at a comfortable pitch. The reading was analyzed by the long-term average spectrum (LTAS) method. The sustained vowels were analyzed through power spectrum analysis. The data suggest that singers show more energy concentration in the singer's formant/speaker's ring region in both sung and spoken vowels. The singers' spoken vowel energy in the speaker's ring area was found to be significantly larger than that of the untrained speakers. The LTAS showed similar findings suggesting that those differences also occur in continuous speech. This finding supports the value of further research on the effect of singing training on the resonance of the speaking voice.

Adult↗
PubMed1998

Vagal cardiac activity in essential hypertension: the effects of metoprolol and ramipril.

Cardiovascular parasympathetic activity is attenuated in essential hypertension. Both beta-adrenoceptor antagonists and angiotensin converting enzyme inhibitors have been reported to increase vagal modulation of heart rate and baroreflex sensitivity, but the relations between the antihypertensive and vagal cardiac effects of these drugs have remained unclear in essential hypertension. In the present study we evaluated the effects of a 4-week crossover monotherapy with metoprolol and ramipril on spectrum analysis indices of heart rate variability in the supine rest and head-up tilted positions, baroreflex sensitivity (phenylephrine method), and 24-h ambulatory blood pressure (BP) in 12 formerly untreated stage 1-2 essential hypertensive patients. Compared to the pretreatment values, both drugs decreased BP similarly and significantly. However, the drugs showed different effects on cardiac vagal activity: metoprolol increased significantly mean R-R interval, R-R interval total, and high-frequency variability at supine rest and baroreflex sensitivity, but ramipril did not significantly affect these variables. The metoprolol-induced decrease in ambulatory BP correlated with the prolongation of the R-R interval and the increase of high-frequency variability at supine rest. The present data show that 4-week treatment with metoprolol increases tonic and reflex vagal cardiac activity, whereas ramipril does not affect vagal cardiac control in essential hypertension. Increase in vagal activity may contribute to the BP-lowering effect of metoprolol in hypertensive patients.

Adult↗
PubMed1989

Outcome of TIAs of unknown aetiology following non-invasive evaluation.

A proportion of patients with apparently classical transient ischaemic attacks (TIA), will have no cause for their symptoms discovered when investigated. We have reviewed 74 patients with TIA and a further 28 with amaurosis fugax whose symptoms remained unexplained following non-invasive carotid evaluation using pulsed Doppler imaging with spectrum analysis. After a mean follow-up of 31.7 months, 48.6% of TIA patients were symptom free, 36.5% had experienced recurrent symptoms and 8.1% had suffered a stroke. Among the patients with amaurosis fugax the equivalent figures were 32.1% symptom free, 42.7% recurrent symptoms, and 10.7% stroke. These figures suggest that unexplained TIAs do not necessarily have a benign prognosis and more extensive or repeated investigation of these patients is warranted.

Adult↗
PubMed2003

Reliability of burst superimposed technique to assess central activation failure during fatiguing contraction.

Recording a superimposed electrically-induced contraction at the limit of endurance during voluntary contraction is used as an indicator of failure of muscle activation by the central nervous system and discards the existence of peripheral muscle fatigue. We questioned on the reliability of this method by using other means to explore peripheral muscle failure. Fifteen normal subjects sustained handgrip at 60% of maximal voluntary contraction (MVC) until exhaustion. During sustained contraction, the power spectrum analysis of the flexor digitorum surface electromyogram allowed us to calculate the leftward shift of median frequency (MF). A superimposed 60 Hz 3 s pulse train (burst superimposition) was delivered to the muscle when force levelled off close to the preset value. Immediately after the fatigue trial had ended, the subject was asked to perform a 5 s 60% MVC and we measured the peak contractile response to a 60 Hz 3 s burst stimulation. Recordings of the compound evoked muscle action potential (M-wave) allowed us to explore an impairment of neuromuscular propagation. A superimposed contraction was measured in 7 subjects in their two forearms, whereas it was absent in the 8 others. Despite these discrepancies, all subjects were able to reproduce a 3 s 60% MVC immediately after the fatigue trial ended and there was no post-fatigue decrease of contraction elicited by the 60 Hz 3 s burst stimulation, as well as no M-wave decrease in amplitude and conduction time. Thus, there was no indication of peripheral muscle fatigue. MF decrease was present in all individuals throughout the fatiguing contraction and it was not correlated with the magnitude of superimposed force. These observations indicate that an absence of superimposed electrically-induced muscle contraction does not allow us to conclude the existence of a sole peripheral muscle fatigue in these circumstances.

Adult↗
PubMed2003

Changes in contractile properties and neuromuscular propagation evaluated by simultaneous mechanomyogram and electromyogram during experimentally induced hypothermia.

The present study examined, whether or not mechanomyogram (MMG) amplitude and frequency component could reflect the contractile properties of the triceps surae muscles, composed of relatively slow soleus (SOL) and fast medial gastrocnemius (MG), during experimentally induced hypothermia condition. In eight male subjects, lying in prone position, supramaximal single twitch and repetitive electrical stimulations at 10 Hz were applied at the intramuscular temperatures of control (34 degrees C), 15, 20, and 25 degrees C, respectively. The hypothermia induced substantial reduction in muscle contractile properties, e.g. prolonged twitch contraction and half relaxation times, resulted in a highly significant reduction in the fluctuation of force signal during the repetitive stimulations. These changes were almost mirrored by the similar and significant reductions in the MMG amplitude in both SOL and MG. Power spectrum analysis revealed that peak frequency components of MMG and fluctuation of force were almost matched with the applied stimulation frequencies, independent of the temperature condition. These results strongly suggest that MMG analysis could be employed to study muscle contractile properties varying across different physiological conditions.

Adult↗
PubMed2003

Quantitative electroencephalographic findings in beagles anaesthetized with propofol.

The purpose of this study was to assess quantitative electroencephalography (q-EEG) in 10 healthy beagle dogs under propofol anaesthesia in order to determine objective guidelines for diagnostic electroencephalographic (EEG) recordings and interpretation. The basic pattern after preliminary visual examination of EEG recordings was characterized by spindles, k-complexes, vertex sharp transients, and positive occipital transients that were superimposed on the slow background activity. The results of the q-EEG were characterized by the prevalence of slow rhythms delta and theta, both in absolute and relative power spectrum analysis, while fast rhythms (alpha and beta) were poorly represented. The distribution of single frequency bands was widespread for delta, focal for frontal and central for theta, as well as for most alpha and beta patterns. The present study has shown that the use of quantitative EEG gives information on the frequency content of the bio-electrical activity and defines the distribution of the single frequency bands under a standardized anaesthetic protocol.

Anesthesia, General↗
PubMed2002

Cardiac rhythms in prenatal and perinatal emu embryos.

Emu eggs weigh approximately 600 g and have an incubation duration (ID) of approximately 50 days. The egg mass is approximately 10-fold heavier than the chicken egg and the ID is approximately 2.5-fold longer. Daily changes in mean heart rate (MHR) of emu embryos were previously determined, but further measurement was needed to investigate the species-specific behavior of cardiac rhythm for comparison with other species. In the present study, we continuously measured the electrocardiogram of emu embryos while maintaining adequate gas exchange through the eggshell and determined instantaneous heart rate (IHR) during the last 2-7 days of incubation until hatching or death. The MHR over 1-min intervals was calculated from IHR data in order to present continuous developmental patterns of heart rate (HR) in a single graph and 24-h recordings of HR in a single panel, showing the HR trend over a prolonged period. However, neither circadian nor ultradian rhythms of HR were shown in these figures or by power spectrum analysis. The IHR distinctively fluctuated and the fluctuations were mainly comprised of three patterns of irregular HR accelerations in embryos that hatched. Respiratory sinus arrhythmia also occurred in perinatal embryos. During the final stages of the perinatal period, short-term, repeated, large accelerations of IHR appeared, which signaled imminent hatching and has been reported for chick embryos. IHR fluctuations in embryos that failed to hatch tended to become inactive towards death.

Animals↗
PubMed2002

Cardiac rhythms in developing emu hatchlings.

Six emu hatchlings were non-invasively measured for electrocardiogram (ECG) from their chest wall using flexible electrodes, and the instantaneous heart rate (IHR) was determined from ECG throughout the first week of post-hatching life. Although the baseline heart rate (HR) was low, approximately 100-200 beats per min (bpm), compared with chick hatchlings, the IHR fluctuated markedly. The fluctuation of IHR comprised HR variability and irregularities that were designated as types I, II and III in chick hatchlings and additional large accelerations distinctive of emu hatchlings. Type I was HR oscillation with a mean frequency of 0.37 Hz (range 0.2-0.7 Hz), i.e. respiratory sinus arrhythmia (RSA). From RSA, breathing frequency in emu hatchlings was estimated to be approximately half of that in chickens. Type II HR oscillation was also found in the emu; the frequency ranged from approximately 0.04 to 0.1 with a mean of 0.06 Hz, and the magnitude tended to be large compared with that of chickens. In addition to type III HRI, which was designated in chickens, large, irregular HR accelerations were characteristic of emu hatchlings. From IHR data, developmental patterns of mean heart rate (MHR) were constructed and plotted on a single graph to inspect the diurnal rhythm of MHR by visual inspection and power spectrum analysis. A circadian rhythm was not clear in the emu hatchlings, in contrast to chick hatchlings, which showed a dominant diurnal rhythm.

Animals↗
PubMed2000

The impact of cyclic alternating pattern on heart rate variability during sleep in healthy young adults.

OBJECTIVE: Cyclic alternating pattern (CAP) consists of arousal-related phasic events while the complementary condition, non-CAP (NCAP), is characterized by a rhythmic background activity, reflecting a condition of stable arousal, during non-REM sleep. The arousal swings that accompany the appearance of CAP on the EEG are associated with transient variations of muscle tone and autonomic activities, including heart rate (HR). The aim of our study was to evaluate HR variability in relation to CAP during non-REM sleep in healthy adults. METHODS: Ten healthy subjects (mean age = 28.1 years) underwent 8 h polysomnography. HR variations were measured by power spectrum analysis. The ECG signals were segmented in correspondence of the different sleep stages and different CAP conditions. RESULTS: A significant difference between CAP and NCAP conditions was found in low frequency (LF) component (increased in CAP) and high frequency (HF) component (decreased in CAP). LF/HF ratio was increased in CAP. CONCLUSION: Physiological fluctuations of the EEG arousal level influence cardiac autonomic activity in normal subjects. The studies on nocturnal variation in sympathetic and vagal tone should take in account the microstructural sleep changes, other than the conventional polysomnographic parameters.

Activity Cycles↗
PubMed2000

QT interval lengthening in cardiac disease relates more to left ventricular systolic dysfunction than to autonomic function.

BACKGROUND: There are multiple influences on the QTc interval, including the autonomic nervous system. Which influence is the principal determinant of the variation in QTc interval between different cardiac diseases is not yet clear, though some studies have suggested that the QTc interval primarily reflects sympatho-vagal balance. This study investigated this claim further. AIM: To determine if autonomic tone was the prime determinant of variation in the QTc interval between subjects with different cardiac diseases. METHODS: Subjects with different cardiac diseases were studied, QTc interval determined and correlated with three different measures of the autonomic nervous system, that of baroreflex sensitivity, catecholamine levels (epinephrine and norepinephrine) and sympatho-vagal balance as determined by power spectrum analysis. RESULTS: 47 subjects were studied, comprising 17 subjects with heart failure, 14 subjects with left ventricular hypertrophy and 16 control subjects. For the group as a whole there was no relationship between QTc interval and any measure of the autonomic nervous system function, but there was a reasonable relationship between fractional shortening and QTc interval (r=0.47, P<0.003). For subjects with an echocardiographic fractional shortenings less than 0.35 (which correlates with an ejection fraction of <50%), a strong relationship between fractional shortening and QTc interval remained (r=0.57, P<0.002), but in addition a relationship between QTc interval and catecholamine levels developed (for epinephrine: r=0.67, P<0.002; and for norepinephrine: r=0.62, P<0.005). Multiple regression analysis showed that fractional shortening and epinephrine levels were independently related to QTc interval. CONCLUSION: In subjects with a variety of cardiac diseases, the prime determinant of QTc interval is left ventricular systolic performance rather than the autonomic nervous system, though in subjects with low normal and less fractional shortenings catecholamine levels are independently related to QTc interval.

Autonomic Nervous System↗
PubMed2002

Sleep and EEG power spectrum in post encephalitis hypersomnia: a case report.

The nocturnal recordings of breathing, and sleep and daytime multiple sleep latency tests over the 5 year follow-up of a patient with post encephalitis hypersomnia are presented. EEG power spectrum analysis was performed on the last polysomnographic recording, and the results were compared with those obtained for a matched control subject. The patient presented initially a hypoventilation syndrome controlled by nasal bilevel positive pressure at night. The syndrome progressively improved, but daytime sleepiness stayed unchanged with limited help from stimulants. Fast Fourier transformation analysis of the last nocturnal recording demonstrates a decrease in absolute power for all frequency bands in all sleep stages, but a cyclical presence of the NREM/REM.

Journal Article↗
PubMed2003

Automated analysis of SEM X-ray spectral images: a powerful new microanalysis tool.

Spectral imaging in the scanning electron microscope (SEM) equipped with an energy-dispersive X-ray (EDX) analyzer has the potential to be a powerful tool for chemical phase identification, but the large data sets have, in the past, proved too large to efficiently analyze. In the present work, we describe the application of a new automated, unbiased, multivariate statistical analysis technique to very large X-ray spectral image data sets. The method, based in part on principal components analysis, returns physically accurate (all positive) component spectra and images in a few minutes on a standard personal computer. The efficacy of the technique for microanalysis is illustrated by the analysis of complex multi-phase materials, particulates, a diffusion couple, and a single-pixel-detection problem.

Ceramics↗