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Cyclic Variations (cyclic + variation)

Distribution by Scientific Domains

Medical Sciences	35%
Life Sciences	28%
Earth and Environmental Science	21%

Selected Abstracts

Heart Rate Variability in Obstructive Sleep Apnea: A Prospective Study and Frequency Domain Analysis

ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 2 2003
Lorne J Gula F.R.C.P.C.
Background: Cyclic variation of the heart rate is observed during apneic spells in obstructive sleep apnea (OSA). We hypothesized that autonomic changes would affect frequency-domain measures of heart rate variability (HRV). Methods: We studied 20 patients (15 men, 5 women, mean age 47.2 ± 12.2 years) with suspected OSA undergoing overnight polysomnography, and five patients (4 men, 1 woman, mean age 49.2 ± 8.6 years) with recently diagnosed sleep apnea undergoing polysomnography while wearing continuous positive airway pressure (CPAP). Holter monitors were applied during sleep studies and data were analyzed in 5-minute blocks over the course of the night. Using spectral analysis, low frequency (LF) and high frequency (HF) powers were calculated for each interval. Overall mean and standard deviation (SD) for LF power, HF power, and the LF:HF ratio were recorded for each patient. Comparisons were made between patients with severe OSA (apnea hypopnea index (AHI) > 30, n = 8), moderate OSA (AHI 1,30, n = 5), without OSA (AHI < 10, n = 7), and patients wearing CPAP (n = 5). Results: Assessment of overnight LF or HF power revealed no significant difference between the four groups. The LF:HF ratio, which represents sympathovagal balance, was higher among those with moderate disease compared to normals and those with severe OSA (both P = 0.037). The standard deviation of the LF:HF ratio was higher among those with moderate disease compared to normals (P = 0.0064) and those with severe OSA (P = 0.0006). OSA patients receiving CPAP behaved like patients with moderate OSA, with increased SD of the LF:HF ratio. Conclusions: The observed changes in the LF:HF ratio and its SD suggest an increased sympathetic tone and discordance in sympathovagal activity in moderate OSA, which is blunted in severe OSA. CPAP may restore autonomic defects, characteristic of severe OSA, to moderate levels. [source]

A synoptic program for large solar telescopes: Cyclic variation of turbulent magnetic fields

ASTRONOMISCHE NACHRICHTEN, Issue 6 2010
L. Kleint
Abstract Upcoming large solar telescopes will offer the possibility of unprecedented high resolution observations. However, during periods of non-ideal seeing such measurements are impossible and alternative programs should be considered to best use the available observing time. We present a synoptic program, currently carried out at the Istituto Ricerche Solari Locarno (IRSOL), to monitor turbulent magnetic fields employing the differential Hanle effect in atomic and molecular lines. This program can be easily adapted for the use at large telescopes exploring new science goals, nowadays impossible to achieve with smaller telescopes. The current, interesting scientific results prove that such programs are worthwhile to be continued and expanded in the future. We calculate the approximately achievable spatial resolution at a large telescope like ATST for polarimetric measurements with a noise level below 5 × 10 -5 and a temporal resolution which is sufficient to explore variations on the granular scale. We show that it would be important to optimize the system for maximal photon throughput and to install a high-speed camera system to be able to study turbulent magnetic fields with unprecedented accuracy (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

How does alluvial sedimentation at range fronts modify the erosional dynamics of mountain catchments?

BASIN RESEARCH, Issue 3 2005
S. Carretier
At the geological time scale, the way in which the erosion of drainage catchments responds to tectonic uplift and climate changes depends on boundary conditions. In particular, sediment accumulation and erosion occurring at the edge of mountain ranges should influence the base level of mountain catchments, as well as sediment and water discharges. In this paper, we use a landform evolution model (LEM) to investigate how the presence of alluvial sedimentation at range fronts affects catchment responses to climatic or tectonic changes. This approach is applied to a 25 km × 50 km domain, in which the central part is uplifted progressively to simulate the growth of a small mountain range. The LEM includes different slope and river processes that can compete with each other. This competition leads to ,transport-limited', ,detachment-limited' or ,mixed' transport conditions in mountains at dynamic equilibrium. In addition, two end-member algorithms (the channellized-flow and the sheet-flow regimes) have been included for the alluvial fan-flow regime. The three transport conditions and the two flow algorithms represent six different models for which the responses to increase of rock uplift rate and/or cyclic variation of the precipitation rate are investigated. Our results indicate that addition of an alluvial apron increases the long-term mountain denudation. In response to uplift, mountain rivers adapt their profile in two successive stages; first by propagation of an erosion wave and then by slowly increasing their channel gradients. During the second stage, the erosion rate is almost uniform across the catchment area at any one time, which suggests that dynamic equilibrium has been reached, although the balance between erosion and rock uplift rates has not yet been achieved. This second stage is initiated by the uplift of the mountain river outlets because of sedimentation aggradation at the mountain front. The response time depends on the type of water flow imposed on the alluvial fans domains (× by 1.5 for channelized flow regime and by 10 for the sheet flow one). Cyclic variations of precipitation rate generate cyclic incisions in the alluvial apron. These incision pulses create knick-points in the river profile in the case of ,detachment-limited' and ,mixed' river conditions, which could be mistaken for tectonically induced knick-points. ,Transport-limited' conditions do not create such knick-points, but nevertheless trigger erosion in catchments. The feedbacks linked to sedimentation and erosion at range front can therefore control catchment incision or aggradation. In addition, random river captures in the range front trigger auto-cyclic erosion pulses in the catchment, capable of generating incision,aggradation cycles. [source]

Using geostatistics to elucidate temporal change in the spatial variation of aeolian sediment transport

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 6 2003
Adrian Chappell
Abstract Little is known about the spatial and temporal scales of variation in aeolian processes. Studies that aim to investigate surface erodibility often sample aeolian sediment transport at the nodes of a regular grid of arbitrary size. Few aeolian transport investigations have the resources to obtain sufficient samples to produce reliable models for mapping the spatial variation of transport. This study reports the use of an innovative nested strategy for sampling multiple spatial scales simultaneously using 40 sediment samplers. Reliable models of the spatial variation in aeolian sediment transport were produced and used for ordinary punctual kriging and stochastic simulated annealing to produce maps for several wind erosion events over a 25 km2 playa in western Queensland, Australia. The results support the existence of a highly dynamic wind erosion system that was responding to possibly cyclic variation in the availability of material and fluctuations in wind energy. The spatial scale of transport was considerably larger than the small scale expected of the factors controlling surface erodibility. Thus, it appears that transport cannot be used as a surrogate of erodibility at the scale of this investigation. Simulation maps of transport provided considerably more information than those from kriging about the variability in aeolian sediment transport and its possible controlling factors. The proposed optimal sampling strategy involves a nested approach using ca 50 samplers. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Seasonal variation of the onset of presentations in stage 1 sarcoidosis

INTERNATIONAL JOURNAL OF CLINICAL PRACTICE, Issue 11 2006
S. S. DEMIRKOK
Summary Sarcoidosis is a chronic disease with an unknown aetiology. Our aim was to evaluate the pattern of seasonality of stage 1 sarcoidosis subjects who had symptoms by all cases, by age and by both genders. In this study, we used Roger's test for cyclic variation to prove that this seasonal variation was more than chance. Four hundred ninety-two consecutive patients with sarcoidosis who presented different clinical symptoms were included in this retrospective cohort study. According to the chest X-ray examinations, 185 patients had stage 1, while 307 patients in control group had stage 0, 2, 3 and 4 sarcoidosis. The demographic features, presenting clinical features, course of the disease, initial diagnostic methods and both the month and the age at the initial diagnosis for each patient were analysed on chart reviews. Roger's test for cyclic variation was used to determine the significance of any seasonal variation of incidence. Otherwise, t -test was used. The distribution of cumulative monthly presentations for patients with stage 1 peaked in April (108% above the average) and was lowest in October, November and December (48% below the average) (p < 0.001). Seasonality of the control group peaked in May (84% above the average) and was lowest in August (69% below the average) (p < 0.001). The seasonal pattern of subjects within both groups was influenced by some age groups and by both genders (p < 0.05). Some differences in the amplitude of the seasonal variation by age and by both genders increase the possibility of interactions among age, gender and the disease. Further well-designed and prospective studies are required to better understand the importance of our findings and the pathogenesis of the disease. [source]

Changes in Preoptic and Hypothalamic Levels of Progesterone Receptor mRNA Across the Oestrous Cycle of the Ewe

JOURNAL OF NEUROENDOCRINOLOGY, Issue 5 2001
C. J. Scott
Abstract We measured the levels of progesterone receptor (PR) mRNA in the hypothalamus and preoptic area (POA) of the ewe across the oestrous cycle. Perfusion-fixed hypothalamic tissue was collected from sheep killed during the luteal and follicular phases and during behavioural oestrus. Blood samples taken at the time of tissue collection verified that the oestrous ewes were undergoing a preovulatory luteinizing hormone (LH) surge. Matched sections were taken from the POA, periventricular nucleus (PeVN), ventromedial nucleus (VMN) and arcuate nucleus of each animal. In situ hybridization was performed using a sheep specific, 35S-labelled riboprobe for PR and semiquantitative image analysis was conducted on emulsion-dipped slides. The number of silver grains per cell was greater in the VMN and arcuate nucleus of oestrous ewes than in luteal and follicular phase ewes; there was no cyclic variation in the level of PR mRNA expression in the cells of the POA and PeVN. The number of labelled cells per mm2 in the VMN was higher in the oestrous ewes than in luteal phase and follicular phase ewes. The number of labelled cells in the PeVN was also higher in the oestrous ewes than in follicular phase ewes, but there was no cyclic variation in the POA and arcuate nucleus. In the ewe, the onset of behavioural oestrus corresponds to the onset of the preovulatory LH surge and increased PR mRNA expression at this time is likely to be due to the high concentrations of circulating oestrogen that precede this period. [source]

The organic cation transporters (OCT1, OCT2, EMT) and the plasma membrane monoamine transporter (PMAT) show differential distribution and cyclic expression pattern in human endometrium and early pregnancy decidua

MOLECULAR REPRODUCTION & DEVELOPMENT, Issue 10 2007
Barbara Bottalico
Abstract The non-neuronal monoamine transporters (OCT1, OCT2, EMT, and PMAT) play a key role in the clearance of monoamines from extracellular compartments. In a previous report we described endometrial distribution and cyclic variation of the vesicular monoamine transporter (VMAT2) mRNA and the neuronal norepinephrine transporter (NET) mRNA. In the present study we used in situ hybridization, real-time PCR and immunohistochemistry to reveal tissue distribution and cyclic variation of mRNA for the non-neuronal monoamine transporters in the human endometrium and early pregnancy decidua. We found that non-neuronal monoamine transporters are predominantly expressed in the stroma. The plasma membrane monoamine transporter (PMAT) mRNA expression peaked in the proliferative phase, whereas the extra-neuronal monoamine transporter (EMT) mRNA expression peaked in the secretory phase. The organic cation transporter 2 (OCT2) mRNA expression was exclusively detected in few scattered stromal cells and OCT1 mRNA was not detected at all. Our present results demonstrate that PMAT, EMT, and OCT2 transporters are expressed in the endometrial stroma and can potentially regulate reuptake of monoamines in general and histamine in particular. Taken together with our previous finding of VMAT2 mRNA in epithelial cells, we suggest a paracrine interaction between stromal and epithelial cells, which may modulate certain steps of the reproductive process. Mol. Reprod. Dev. 74: 1303,1311, 2007. © 2007 Wiley-Liss, Inc. [source]

How does alluvial sedimentation at range fronts modify the erosional dynamics of mountain catchments?

Profile of the climate change in the Kingdom of Bahrain

ENVIRONMETRICS, Issue 8 2003
W. E. Alnaser
Abstract Long-term meteorological data from the Kingdom of Bahrain (1902 to 2001), along with other data from the Sultanate of Oman and the Kingdom of Saudi Arabia, were used to study the profile and the characteristics of the climate changes in the Kingdom of Bahrain. This article illustrates the possible effects of several factors, such as greenhouse gases (GHG), sunspot number, cosmic ray flux, planet conjunctions, the Earth's magnetic field, as well as volcanic eruption, on the profile of the climate change. In general, we found that the temperature variations, to a certain extent, are associated with the cyclic variations in sunspot number (the 11-year cycle), which in turn affect the pattern of the cosmic ray flux due to the distortion of the interplanetary magnetic field. The latter is believed to influence cloud formation. In addition, the discrepancy in the climate change pattern in Bahrain was also attributed to the combined effect of the high local level of CO2 emissions as well as that of other cooling gases in the region. Copyright © 2003 John Wiley & Sons, Ltd. [source]

A comparison of cyclic variations in anterior knee laxity, genu recurvatum, and general joint laxity across the menstrual cycle

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 11 2010
Sandra J. Shultz
Abstract Changes in anterior knee laxity (AKL), genu recurvatum (GR) and general joint laxity (GJL) were quantified across days of the early follicular and early luteal phases of the menstrual cycle in 66 females, and the similarity in their pattern of cyclic variations examined. Laxity was measured on each of the first 6 days of menses (M1,M6) and the first 8 days following ovulation (L1,L8) over two cycles. The largest mean differences were observed between L5 and L8 for AKL (0.32,mm), and between L5 and M1 for GR (0.56°) and GJL (0.26) (p,<,0.013). At the individual level, mean absolute cyclic changes in AKL (1.8,±,0.7,mm, 1.6,±,0.7,mm), GR (2.8,±,1.0°, 2.4,±,1.0°), and GJL (1.1,±,1.1, 0.7,±,1.0) were more apparent, with minimum, maximum and delta values being quite consistent from month to month (ICC2,3,=,0.51,0.98). Although the average daily pattern of change in laxity was quite similar between variables (Spearman correlation range 0.61 and 0.90), correlations between laxity measures at the individual level were much lower (range ,0.07 to 0.43). Substantial, similar, and reproducible cyclic changes in AKL, GR, and GJL were observed across the menstrual cycle, with the magnitude and pattern of cyclic changes varying considerably among females. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:1411,1417, 2010 [source]

Effect of oral contraceptives on tear physiology

OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 1 2001
Alan Tomlinson
Summary Variations in sex hormones due to the menstrual cycle (and oral contraceptives) were evaluated for their effect on tear physiology. Subjects were 18 females taking oral contraceptives or their age matched controls (no medication), aged 21,33 years. Symptoms of ocular discomfort (visual analog scale), tear film structure (TearScope), non-invasive tear thinning time (HirCal grid), evaporation rate (ServoMed evaporimeter), osmolality (Nanolitre Osmometer), tear turnover rate, tear volume (Fluorotron Master), and tear protein levels (HPLC) were measured around day 2 (D2), actually day 1,4 and day 19 (D19) actually day 18,21 of the cycle. No significant differences were found for any tear parameters between D2 and D19 for either pill users or controls alone, or in the comparison of pill users with controls. No effect on tear physiology was found for serum hormone changes induced by oral contraceptive use or by normal cyclic variations in healthy young females. [source]

Cell Separator Operation within Temperature Ranges To Minimize Effects on Chinese Hamster Ovary Cell Perfusion Culture

BIOTECHNOLOGY PROGRESS, Issue 6 2007
Hans Drouin
A cell retention device that provides reliable high-separation efficiency with minimal negative effects on the cell culture is essential for robust perfusion culture processes. External separation devices generally expose cells to periodic variations in temperature, most commonly temperatures below 37 °C, while the cells are outside the bioreactor. To examine this phenomenon, aliquots of ,5% of a CHO cell culture were exposed to 60 s cyclic variations of temperature simulating an acoustic separator environment. It was found that, for average exposure temperatures between 31.5 and 38.5 °C, there were no significant impacts on the rates of growth, glucose consumption, or t-PA production, defining an acceptable range of operating temperatures. These results were subsequently confirmed in perfusion culture experiments for average exposure temperatures between 31.6 and 38.1 °C. A 25,1 central composite factorial design experiment was then performed to systematically evaluate the effects of different operating variables on the inlet and outlet temperatures of a 10L acoustic separator. The power input, ambient temperature, as well as the perfusion and recycle flow rates significantly influenced the temperature, while the cell concentration did not. An empirical model was developed that predicted the temperature changes between the inlet and the outlet of the acoustic separator within ±0.5 °C. A series of perfusion experiments determined the ranges of the significant operational settings that maintained the acoustic separator inlet and outlet temperatures within the acceptable range. For example, these objectives were always met by using the manufacturer-recommended operational settings as long as the recirculation flow rate was maintained above 15 L day,1 and the ambient temperature was near 22 °C. [source]

Menstrual cycle influences ocular surface parameters in normal and dry eye patients

ACTA OPHTHALMOLOGICA, Issue 2007
P VERSURA
Purpose: We analyzed the changes of ocular surface parameters and symptoms in healthy and dry eye women over the menstrual cycle. To our knowledge, incomplete reports appear in the literature on this issue in healthy women still in the fertile period, and none on dry eye women of the same age. This to comparatively evaluate what then happens in peri- and post-menopause. Methods: 29 females in the fertile age and a regular 26-29 days menstrual cycle were included in the study. 14 subjects with and 15 without dry eye symptoms. Symptoms were scored by the validate questionnaire OSDI. Degree of dryness was evaluated with the Schirmer test I, Jones test, BUT, Ferning test, Tear Function Index (TFI) and conjunctival imprint cytology. Degree of inflammation was evaluated with conjunctival brush cytology and dosage of exudated serum albumin in tears. Hormonal cytology procedures were applied to exfoliated cells in tears. Patients were analysed during menstruation, in the follicular and in luteal phases over two consecutive cycles and results were statistically evaluated Results: TFI, tear stability, surface dryness and inflammation were significantly related to the hormonal fluctuations in menstrual cycle, in particular to the estrogen peak occurring during the follicular phase, especially in dry eye patients. Subjective symptoms appeared to increase in the luteal phase, suggesting the presence of a pre-menstrual syndrome Conclusions: The ocular surface is confirmed to be dependent from hormonal variations; clinicians would take into account these cyclic variations during the examinations of subjects still in the fertile age, with dryness symptoms [source]