Medium-frequency Oscillations Research Articles

Tree-ring minimum density chronologies of Picea schrenkiana along an elevation gradient in the Tien Shan Mountains, China

ABSTRACT We selected four sampling areas to collect tree-ring samples along an elevation gradient on north-facing slopes in three regions of the Tien Shan Mountains. Samples were collected at sites located at intervals of about 100 m.a.s.l. in each sampling area. For all sampling sites, the mean tree age, mean sensitivity, and standard deviation of the minimum density chronologies were associated with elevation. Within the same region and between different areas, the consistency of the minimum density of tree rings was highest in the high-elevation sites, followed by the low-elevation sites, and lowest in the mid-elevation forest. Marked changes in slope aspect and inclination affected the consistency of the minimum density in the same area. Significant differences were observed in tree-ring density at 2000–2200 m.a.s.l. Several environmental factors influenced the variation in minimum density of tree rings at different elevations; the factors that were significantly affected by high elevation were observed in the western and central regions of the Tien Shan. High-frequency oscillation was the main reason affecting the change in minimum density and significant differences were observed in medium-frequency oscillations before and after the 1980s.

Role of response time of a Babcock-Leighton solar dynamo model in meridional flow-speed reconstruction by EnKF data assimilation

Ensemble Kalman Filter in the framework of Data Assimilation Research Testbed (DART) has been successfully implemented into a 2D kinematic flux-transport dynamo model by Dikpati and colleagues in order to do a parameter estimation, the parameter being the meridional flow-speed as function of time. They performed several ‘Observing System Simulation Experiments’ (OSSEs), and showed that an optimal reconstruction of time-series of meridional flow-speed can be obtained by using 16 ensemble members and only one surface magnetic observation with 30% observational error. Error in reconstruction can be reduced by increasing the ensemble size and number of observations. However, this parameter reconstruction has been found to be sensitive to locations from where observational data are taken. While assimilation of low-latitudes’ surface poloidal magnetic field data can produce good reconstruction, medium-frequency oscillations appear in time-series of reconstructed flow-speed if tachocline toroidal field data are assimilated. These oscillations occur primarily because tachocline toroidal fields change very little during an assimilation interval taken to be 15days, due to changes in meridional flow. A Babcock-Leighton dynamo model’s response time to changes in meridional flow-speed is a few months. We show here that rms error in reconstruction can be significantly reduced if model’s response time is taken into consideration in assimilation of tachocline toroidal field data.

ОСОБЕННОСТИ РЕАКЦИИ ДЫХАТЕЛЬНОГО ЦЕНТРА НОВОРОЖДЕННЫХ КРЫС, ПЕРЕНЕСШИХ ПРЕНАТАЛЬНОЕ ПАССИВНОЕ КУРЕНИЕ, НА ГИПОКСИЧЕСКОЕ ВОЗДЕЙСТВИЕ (IN VITRO)

It is expected that in neonates that underwent prenatal chronic effect of nicotine the identification of the reduction of intensiveness of respiratory response to hypoxic exposure may be the cause of sudden infant death. The effect of cigarette smoke may differ from the effect of nicotine. The study was performed on brain stem spinal cord preparations (BSS) in the brain of newborn rats (n=38) in vitro. In the experimental group (EG) the modeling of passive smoking was carried out by fumigation of cigarette smoke of rat females from the 1st to 20th day of gestation. Hypoxia was simulated by an artificial cerebrospinal fluid saturated with a gas mixture of 5% CO2 and 95% N2. Hypoxic depression of BSS respiratory rhythm of the control group (CG) occurred at the 5th minute; the restoration took place in 10 minutes at normoxia, at the same time there was an increase of the amplitude of the inspiratory discharges which did not return to baseline values (15 minutes). In preparations of CG at the 10th minute of hypoxia the duration of inspiratory discharges decreased and restored after 10 minutes at normoxia. The increase of the ratio of the power of low-frequency and medium-frequency oscillations was observed in the CG at the 15th minute of hypoxia with the restoration during 10 minutes. In the experimental group (EG) the increase of the duration of the respiratory cycle occurred at the 10th minute of hypoxia with the dynamics of recovery similar to that of CG. The increase of the amplitude of inspiratory discharges occurred at the 10th minute of hypoxia; a recovery period took 10 minutes. In the BSS of EG the reduction in the duration of the inspiratory discharges and the increase of the ratio of the power oscillations of low- and mid-range occurred at the 5th and 10th minutes of hypoxia and these parameters never returned to baseline values. Our data suggest that prenatal exposure to secondhand smoke has an effect on the mechanisms of central chemosensitivity in the offspring in the early postnatal period.

Dominant and Non-Dominant Structure of Ventricular Fibrillation in Canine Heart.

Organized activity of the myocardium manifested in dominant frequency structure of EСG was typical of the first 10 min of ventricular fibrillation in canine heart. The first minute of fibrillation was characterized by the most pronounced changes in the structure of oscillation frequency and transition from domination of high frequency oscillations (13-17 Hz) to domination of medium (8-12 Hz) and then low frequency (4-7 Hz) oscillations. The second minute was characterized by transition from domination of low frequency oscillations to domination of low and medium frequency oscillations; minutes 3-10 were characterized by domination of low and medium frequency oscillations; after 10 min, non-dominant ventricular oscillations were recorded.

Medium-Term Business Cycles

Over the postwar period, many industrialized countries have experienced significant medium-frequency oscillations between periods of robust growth versus relative stagnation. Conventional business cycle filters, however, tend to sweep these oscillations into the trend. In this paper we explore whether they may, instead, reflect a persistent response of economic activity to the high-frequency fluctuations normally associated with the cycle. We define as the medium-term cycle the sum of the high- and medium-frequency variation in the data, and then show that these kinds of fluctuations are substantially more volatile and persistent than are the conventional measures. These fluctuations, further, feature significant procyclical movements in both embodied and disembodied technological change, and research and development (R&D), as well as the efficiency and intensity of resource utilization. We then develop a model of medium-term business cycles. A virtue of the framework is that, in addition to offering a unified approach to explaining the high- and medium-frequency variation in the data, it fully endogenizes the movements in productivity that appear central to the persistence of these fluctuations. For comparison, we also explore how well an exogenous productivity model can explain the facts.

Burst‐To‐Burst Variability In Spectral Activity Underlying Diaphragm Electromyogram (EMG) Bursts In Anesthetized C57BL/6 Mice In Vivo

Previous work from our laboratory using time-frequency spectral analysis has suggested that the spectral characteristics of inspiratory motor output in mice are highly dynamic. In that work, burst-to-burst variability analysis was performed on 10-s segments of diaphragm EMG activity recorded from urethane-anesthetized adult C57BL/6 mice. Although short-term burst-to-burst variability was reported, the extent of long-term burst-to-burst variability in this model requires clarification. Here, we characterize the burst-to-burst variability of temporal and spectral features for basal diaphragm EMG bursts recorded from 6 mice using Poincaré plot analysis of breath n vs. n+1 on 5-min time segments, which contain ~750-1245 bursts. Analyses on temporal parameters (i.e., TI, TE, burst frequency, area) show a high degree of correlation between adjacent bursts, suggesting a small degree of both short- and long-term burst-to-burst variability. For spectral characteristics, power of medium frequency oscillations (MFO) appeared to be more deterministic than that seen in the high (HFO) or upper-high (UHFO) ranges, with low power MFO peaks being followed primarily by other low power MFO peaks. In contrast, power for the HFO and UHFO peaks were widely dispersed, indicating aperiodic behavior. Interestingly, however, there were some HFO peaks exhibiting low power that seemed to predict subsequent low power HFO peaks. These data are among the first to quantify short-term and long-term burst-to-burst variability of spectral features using mathematical fits to Poincaré plots, and demonstrate new insight into dynamic variability in the fast oscillatory rhythms inherent in inspiratory motor discharges. Supported by NS045321

Medium-frequency oscillations dominate the inspiratory nerve discharge of anesthetized newborn rats

In this study we examined the synchronization of the discharge of phrenic and recurrent laryngeal motoneurons in anesthetized rat pups 14 to 36 days of age and kittens, 14–15 days old. We found that the inspiratory nerve activity consisted of synchronized bursts separated by 20–35 ms, corresponding to medium-frequency oscillations (MFO). Accordingly, the autospectra of the neurograms had two peaks, one at the respiratory rate and the other between 22.8–43.0 Hz. No significant coherence was found between MFOs in the discharges of different nerves. High-frequency oscillations (HFO) characteristic for the adult inspiratory nerve activity were not present in the newborn rats. These findings demonstrate that phrenic nerve discharge of rat pups, like that of kittens and piglets, is in the MFO range, and suggest that MFO activity is an index of an early developmental stage of the respiratory system.

Power spectral analysis of inspiratory nerve activity in the anesthetized rat: uncorrelated fast oscillations in different inspiratory nerves

The spectral composition of the inspiratory nerve discharge was studied in spontaneously breathing Sprague–Dawley rats under urethane ( n=7) or barbiturate ( n=10) anesthesia. Left phrenic nerve activity was recorded simultaneously with right phrenic or left recurrent laryngeal nerves. We found that all neurograms showed prominent fast oscillations at common frequencies in the high frequency (HFO) range. Concurrent medium frequency oscillations (MFO) were present in inspiratory nerve discharges of four rats anesthetized with Nembutal. Significant coherences between different nerves were uncommon ( n=2) and were only found between HFOs. Thus although nerve autospectra were dominated by HFO, weak correlations indicated a relatively weak system HFO in the central pattern generator, in the anesthetized rat.

Analysis of recurrent laryngeal inspiratory discharges in relation to fast rhythms.

1. Inspiratory (I) activities of recurrent laryngeal (RL) motoneurons and efferent nerves were studied by autospectral, interval, and coherence analyses, with emphasis on fast rhythms of two types: medium-frequency oscillations (MFO, usual range 20-50 Hz for nerve autospectral peaks) and high-frequency oscillations (HFO, usual range 50-100 Hz). 2. In decerebrate, paralyzed, and artificially ventilated cats, recordings were taken from 27 isolated single RL fibers (14 cats) and 8 identified RL motoneurons in the medulla (6 cats), together with recordings of phrenic (PHR) and RL whole-nerve activities. In another 50 cats, RL and PHR nerve discharges were recorded simultaneously. 3. The autospectra of RL units showed prominent MFO peaks with frequencies close to that of the RL nerve MFO spectral peak, indicating presence of this type of fast rhythm in the units' discharges. Spectral analysis of RL unit activity in different segments of the I phase showed that the frequency of a unit's MFO was very close to the peak (maintained) firing rate of the unit during the portion of I analyzed. Thus a motoneuron's MFO spectral peak reflected its rhythmic discharge arising from the cell's refractoriness (and possibly with the rate changing in the course of I). 4. The coherences of motoneurons' MFOs to nerve MFOs were very low or 0, indicating that correlations between unitary MFOs of the RL population were rare and/or weak. 5. In those cats (19/20) that had discernible PHR nerve HFO autospectral peaks, about half of the recorded RL motoneurons (16/34) had HFO. For these motoneurons, the unit-nerve HFO coherences were substantial, indicating widespread correlations between unitary HFOs. 6. In a fraction of cats, coherence peaks in the MFO frequency range were observed between bilateral RL nerves, and between RL and PHR nerves, at frequencies that were subharmonics of the HFO frequency. 7. In light of theoretical considerations on the generation of aggregate rhythms from superposition of unitary rhythms, these observations indicate that, similarly, to the case of PHR motoneurons and nerves. 1) RL nerve MFO arises from superposition of uncorrelated, or at most partially correlated, MFOs of RL units, representing the rhythmic discharges of the cells. It is manifested therefore as a spectral deflection with a maximum in the band of peak firing rates of the units. 2) RL nerve HFO arises from correlated, common-frequency HFOs in a subpopulation of RL units, caused by HFO inputs from antecedent medullary I neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Spectral analysis of blood pressure and heart rate variability in response to stress from air‐jet in the Lyon rat

1. Power spectral analysis of the frequency of wave-forms of blood pressure and heart rate was used to characterize short-term fluctuations of these parameters in three strains of conscious Lyon rat, normotensive (LL and LN) and hypertensive LH. 2. A mild stress produced by means of a jet of air elicited blood pressure rises, associated with tachycardia. This response was of similar magnitude in the three strains. The stressor amplified the medium frequency (195-605 mHz) Mayer waves of blood pressure and heart rate which are under autonomic control. 3. Clonidine (10 micrograms kg-1 i.v.) lowered blood pressure and heart rate and dramatically reduced the amplitude of blood pressure and heart rate oscillations in the frequency region of 195-605 mHz. 4. A jet of air applied after clonidine administration led to blood pressure rise associated with tachycardia and enhanced oscillations in the 195-605 mHz region. 5. These results indicate that in Lyon normotensive and hypertensive rats, a mild emotional stressor elicits blood pressure and heart rate rises associated with spectral modifications reflecting sympathetic hyperactivity. Clonidine lowers blood pressure and heart rate and reduces their related variabilities. This effect is more pronounced in LH rats than in their normotensive controls. Clonidine appears to reduce the autonomic response to stress as indicated by the medium frequency oscillations.

Phrenic and recurrent laryngeal motoneuron activities during hyperoxia and hypoxia in piglets

We hypothesized that synchronization of inspiratory motoneurons may involve inputs from two central pattern generators (CPG): one characterized by medium-frequency (< 50 Hz) and the other by high-frequency oscillations (≧ 50 Hz). We studied phrenic and recurrent laryngeal nerve activities recorded during hyperoxia and hypoxia in Saffan anesthetized, paralyzed, and artificially ventilated piglets. Spectral analyses, derived from the full as well as partitioned halves of inspiration, showed that phrenic and recurrent laryngeal discharges contained peaks in the medium-frequency band, which were indicative of common inputs. The phrenic spectra of many animals had peaks in the high-frequency band; such peaks were uncommon in recurrent laryngeal spectra; consequently, correlated activities corresponding to high-frequency oscillations were not usually observed. Thus, it is likely that acquisition of modulating inputs from a high-frequency CPG may emerge in an age-dependent manner in different motoneuron pools. During hypoxia, both phrenic and recurrent laryngeal discharges were facilitated as shown by increases in both the amplitudes of signal-averaged histograms and the magnitudes of their respective power spectral activities. Also, there was a significant increase in the values of phrenic-recurrent laryngeal coherence estimates in the medium-frequency region. Hence, medium-frequency oscillations are more apparent in early development, perhaps to facilitate synchronization of inspiratory motoneuron activities, especially under conditions of increased chemical drive.

Fast rhythms in phrenic motoneuron and nerve discharges

1. Fast rhythms in discharges of individual phrenic (PHR) motoneurons were studied by spectral and interval analyses; and they were compared, using coherence analysis, with similar rhythms in whole-PHR nerve discharge. The purpose of this study was to ascertain the origin of the two rhythms, manifested as distinct spectral peaks, in PHR motoneuron and nerve discharge: medium-frequency oscillations (MFO, usual range 20-50 Hz); and high-frequency oscillations (HFO, usual range 50-100 Hz). 2. In paralyzed artificially ventilated cats, unit recordings were taken from 1) 26 isolated single PHR fibers (in 8 sodium pentobarbital-anesthetized cats) and 2) 27 identified PHR motoneuron somata in the spinal cord (in 5 decerebrate cats). Simultaneous whole-PHR activity was monophasically recorded from the contralateral PHR nerve for 1 and from both PHR nerves for 2. 3. The signals were subjected to time- and frequency-domain analyses. The latter included a novel application of coherence analysis to the study of population synchrony. 4. The autospectra of all PHR units showed prominent MFO peaks in the frequency range of the nerve MFO spectral peaks, as well as harmonic peaks, indicating the presence of this type of fast rhythm in the units' discharges. Spectral analysis of the augmenting PHR activities in different segments of the inspiratory (I) phase showed that the frequency of unit MFO and of nerve MFO rose during the course of I. Further, cycle-triggered histogram and interval analysis indicated that the frequencies of unit MFO autospectral peaks were very close to the peak firing rates of the units during the portion of I analyzed. Thus unit MFO spectral peaks reflected the rhythmic and augmenting discharges of the motoneurons, and similar nerve MFO peaks reflected the superposition of individual motoneuron discharges. 5. The coherences of motoneurons' MFOs to nerve MFOs were low or zero, indicating that only partial and weak MFO correlations occurred within the PHR motoneuron population. 6. In those cats (n = 11) that had clear PHR nerve HFO spectral peaks, about one-half of the recorded PHR motoneurons had HFO, as indicated by HFO peaks in the unit autospectra and/or the unit-nerve coherences. 7. For motoneurons having HFO, the coherence between unit and nerve HFOs was substantial, particularly when the latter were strong, indicating HFO correlations among a number of PHR motoneurons. 8. In the light of theoretical considerations on the generation of aggregate rhythms from superposition of unitary rhythms, these observations indicate the following.(ABSTRACT TRUNCATED AT 400 WORDS)

Concurrent fast and slow synchronized efferent phrenic activities in time and frequency domain

In urethane-anesthetized or decerebrated vagotomized rabbits efferent multifiber activity of the phrenic nerve was investigated for synchronized activities both in time and frequency domains. When respiratory drive was steadily increased by either an elevation of end-tidal CO 2 concentration or i.v. administration of 4-aminopyridine, medium-frequency oscillations (MFO) first increased, then decreased and finally became absent. The power of high-frequency oscillations (HFO) steadily rose with increasing respiratory drive. In contrast to HFO which revealed a unimodal spectral peak of mostly small bandwidth, the MFO spectrum in most cases consisted of a broad complex. This complex in some cases was composed of two distinct peaks, i.e. MFO were heterogenous. The low- and high-frequency fractions of the MFO complex were related predominantly to the first and last third of inspiration, respectively. Examination of the on-going multifiber activity of the phrenic nerve with an expanded time scale revealed that lower frequency MFO probably result from synchronized ramp-like wave activity during early and mid-inspiration. The duration of the observed ramps well matched the corresponding MFO frequency. We suggest that these ramps might result from propagated synchronized waves of high-threshold phrenic motoneurons. During the last part of inspiration, however, MFO, like HFO, resulted from burst-like synchronized discharge of phenic motoneurons. Thus HFO are superimposed on ramp-like and burst-like activity of the MFO. It is assumed that the decline of MFO at high respiratory drive may be due to the increasing strength of HFO bursts which interrupt ramp activity in the MFO range and thus let MFO appear ‘invisible’ to the recording electrode. Both MFO and HFO were visually detectable in postinspiration.

Changes in frequency content of inspiratory neuron and nerve activities in the course of inspiration

In decerebrate paralyzed cats, the spectra and coherences of inspiratory (I) nerve activities and of medullary I neuron discharges were compared between different stages of I. The correlated high-frequency oscillations (HFOs) in the activities had common time courses of frequency and strength, which were influenced by lung afferent input; whereas the time courses for the uncorrelated medium-frequency oscillations (MFOs) depended on individual activity patterns. These results indicate that HFOs are characteristic of the common I pattern generator, whereas MFOs are specific to individual activities.

Fast rhythms in the discharges of medullary inspiratory neurons

The discharges of 44 medullary inspiratory (I) neurons in decerebrate paralyzed cats were studied using interval and spectral analysis. Most neurons had a rhythm in their discharge. In 31 the rhythm was at the frequency of, and coherent to, the high-frequency oscillations (HFOs) of I nerves, and in 7 the rhythm was in the range of medium-frequency oscillations (MFOs), with no coherence to nerve MFOs. Thus, correlated HFOs are characteristic of the I system at all levels, whereas MFOs are uncommon in medullary neurons and seem to be unrelated to general mechanisms.

The effects of systemic glucose administration on brain metabolism and intracellular pH (pH) during cerebral ischaemia studied by in vivo31P and1H magnetic resonance spectroscopy in the lamb

The spectral composition of the inspiratory nerve discharge was studied in spontaneously breathing Sprague–Dawley rats under urethane (n=7) or barbiturate (n=10) anesthesia. Left phrenic nerve activity was recorded simultaneously with right phrenic or left recurrent laryngeal nerves. We found that all neurograms showed prominent fast oscillations at common frequencies in the high frequency (HFO) range. Concurrent medium frequency oscillations (MFO) were present in inspiratory nerve discharges of four rats anesthetized with Nembutal. Significant coherences between different nerves were uncommon (n=2) and were only found between HFOs. Thus although nerve autospectra were dominated by HFO, weak correlations indicated a relatively weak system HFO in the central pattern generator, in the anesthetized rat.

The neuroelectrophysiological follow up of pre-term infants

The spectral composition of the inspiratory nerve discharge was studied in spontaneously breathing Sprague–Dawley rats under urethane (n=7) or barbiturate (n=10) anesthesia. Left phrenic nerve activity was recorded simultaneously with right phrenic or left recurrent laryngeal nerves. We found that all neurograms showed prominent fast oscillations at common frequencies in the high frequency (HFO) range. Concurrent medium frequency oscillations (MFO) were present in inspiratory nerve discharges of four rats anesthetized with Nembutal. Significant coherences between different nerves were uncommon (n=2) and were only found between HFOs. Thus although nerve autospectra were dominated by HFO, weak correlations indicated a relatively weak system HFO in the central pattern generator, in the anesthetized rat.

Age-related changes in power spectra of efferent phrenic activity in the piglet

Power spectral analysis of phrenic nerve discharge in neonatal swine revealed the presence of both high-frequency oscillations (HFO) (95-150 Hz) and medium-frequency oscillations (MFO) (15-35 Hz). The HFO was shown to be age-related; the MFO was not. The data indicated that at least one manifestation of maturation of the respiratory rhythm generator is the increase with age of the frequency of the HFO.

Climatic impacts on the vegetation of eastern North America during the past 2000 years

Pollen diagrams from seven lakes with annually laminated sediments sampled at 40-year intervals are analyzed to isolate the climatic effects from other effects on the long-term dynamics of vegetation during the past 1000–2000 years along a transect from Maine to Minnesota. Principal components analysis is used to reduce the dimensionality of the pollen data. The pollen records from all lakes show long-term trends, medium frequency oscillations, and higher frequency fluctuations. The long-term trend is associated with the neoglacial expansion of the boreal forest. The mechanism causing this replacement is a change in frequency of air masses in the area. The medium-frequency oscillations are also associated with climate changes, the most recent of which is the ‘Little Ice Age’. The climate-related mechanism causing the medium-frequency changes may be changes in disturbance frequency. The higher frequency fluctuations may also be related to disturbance.

High frequency de Haas-van Alphen oscillations and the Fermi surface in indium

De Haas-van Alphen oscillations from the second zone and the third zone Fermi surface in indium have been studied. Emphasis is placed on the high frequency oscillations attributed to the second zone, which show a strong mixing with the medium frequency oscillations from the third zone. The results combined with the low frequency oscillations from the third zone surface measured by Hughes and Shepherd (1969) have been used to obtain the parameters on an empirical pseudopotential calculation. The parameters in eV are: V111=-0.601, V002=-0.435, V200=0.167 and EF=8.702.