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PubMed1999

Contributions of temporal encodings of voicing, voicelessness, fundamental frequency, and amplitude variation to audio-visual and auditory speech perception.

Auditory and audio-visual speech perception was investigated using auditory signals of invariant spectral envelope that temporally encoded the presence of voiced and voiceless excitation, variations in amplitude envelope and F0. In experiment 1, the contribution of the timing of voicing was compared in consonant identification to the additional effects of variations in F0 and the amplitude of voiced speech. In audio-visual conditions only, amplitude variation slightly increased accuracy globally and for manner features. F0 variation slightly increased overall accuracy and manner perception in auditory and audio-visual conditions. Experiment 2 examined consonant information derived from the presence and amplitude variation of voiceless speech in addition to that from voicing, F0, and voiced speech amplitude. Binary indication of voiceless excitation improved accuracy overall and for voicing and manner. The amplitude variation of voiceless speech produced only a small increment in place of articulation scores. A final experiment examined audio-visual sentence perception using encodings of voiceless excitation and amplitude variation added to a signal representing voicing and F0. There was a contribution of amplitude variation to sentence perception, but not of voiceless excitation. The timing of voiced and voiceless excitation appears to be the major temporal cues to consonant identity.

Acoustic Stimulation↗

PubMed1985

Genetic analysis of the phase variation control of expression of type 1 fimbriae in Escherichia coli.

Expression of type 1 fimbriae in Escherichia coli exhibits phase variation, whereby individual cells can alternate between states of organelle expression (Fim+) and nonexpression (Fim-). Strains with a fimD-lac operon fusion, in which lac, rather than fimD, expression is under the control of the fimD promoter, undergo Lac+ in equilibrium Lac- phase variation, instead. After positioning a lambda prophage adjacent to the operon fusion, we were able to isolate specialized lambda phage carrying both the fimD-lac fusion and the phase variation control region. Introduction of such phage into an Fim+ strain resulted in construction of a strain with a double, independently switching phenotype (Fim+ in equilibrium Fim- and Lac+ in equilibrium Lac-), demonstrating that the region controlling phase variation is contiguous with the fimD-lac operon fusion and is cis acting. When the specialized lambda phage was propagated on a delta lac delta fim strain, phase variation occurred within the plaques, confirming that the phase variation control region is carried on the specialized transducing phage. All lysogens acquired the Lac+ in equilibrium Lac- phenotype, except for two nonswitching Lac+ recombinants, which acquired Lac+ in equilibrium Lac- phase variation only by trans complementation with fim. Phase variation of type 1 fimbriae, therefore, appears to involve both a cis-active element, which is cloned on a specialized lambda phage, and a trans-active permissive factor, which is not present on the phage, but rather must be supplied by the recipient strain in the transduction.

Escherichia coli↗

PubMed1994

Comparison of circadian variations using FEV1 and peak expiratory flow rates among normal and asthmatic subjects.

BACKGROUND: Most studies that describe circadian variations in asthma have used maximum rate of peak expiratory flow (PEF) rather than forced expiratory volume in one second (FEV1) to assess airway calibre. This study was designed to assess circadian variations in PEF and FEV1 measured simultaneously and to compare variations in these measurements in normal and asthmatic subjects in a stable clinical state. METHODS: Twenty nine subjects (nine asthmatic subjects on bronchodilators, 10 on inhaled steroids, and 10 normal controls) were asked to record their PEF and FEV1 with a new portable instrument every two hours during the day and once on waking at night for two weeks. Circadian variations were examined in different ways using arithmetical indices and cosinor analysis. RESULTS: 78% of PEF values and 75% of FEV1 values were considered to be reproducible and were included in the analysis. Variations obtained using PEF did not differ from those obtained using FEV1. Significant cosinor variations were found in at least 50% of recording days for most of the subjects and showed the same features as for arithmetical indices. Daily variations in PEF and FEV1 were significantly correlated with airway calibre and PC20 methacholine (r approximately 0.5 to approximately 0.6). CONCLUSIONS: PEF is as satisfactory as FEV1 for describing circadian variations among normal subjects and stable asthmatic subjects.

Adolescent↗

PubMed1999

Peak flow variation in childhood asthma: correlation with symptoms, airways obstruction, and hyperresponsiveness during long-term treatment with inhaled corticosteroids. Dutch CNSLD Study Group.

BACKGROUND: Guidelines for asthma management focus on treatment with inhaled corticosteroids and on home recording of peak expiratory flow (PEF). The effect of maintenance treatment with inhaled corticosteroids on PEF variation and its relation to other parameters of disease activity were examined in 102 asthmatic children aged 7-14 years. METHODS: During 20 months of treatment with inhaled salbutamol, with or without inhaled budesonide (600 micrograms daily), forced expiratory volume in one second (FEV1), the dose of histamine required to provoke a fall in FEV1 of more than 20% (PD20), the percentage of symptom free days, and PEF variation were assessed bimonthly. PEF variation was computed as the lowest PEF as a percentage of the highest PEF occurring over 14 days, the usual way of expressing PEF variation in asthma self-management plans. For each patient using inhaled corticosteroids within subject correlation coefficients (rho) were computed of PEF variation to the percentage of symptom free days, FEV1, and PD20. RESULTS: PEF variation decreased significantly during the first two months of treatment with inhaled corticosteroids and then remained stable. The same pattern was observed for symptoms and FEV1. In contrast, PD20 histamine continued to improve throughout the whole follow up period. In individual patients predominantly positive associations of PEF variation with symptoms, FEV1, and PD20 were found, but the ranges of these associations were wide. CONCLUSIONS: During treatment with inhaled corticosteroids the changes in PEF variation over time show poor concordance with changes in other parameters of asthma severity. When only PEF is monitored, clinically relevant deteriorations in symptoms, FEV1, or PD20 may be missed. This suggests that home recording of PEF alone may not be sufficient to monitor asthma severity reliably in children.

Administration, Inhalation↗

PubMed2005

Geographic patterns of prostate cancer mortality and variations in access to medical care in the United States.

BACKGROUND: Striking geographic variation in prostate cancer death rates have been observed in the United States since at least the 1950s; reasons for these variations are unknown. Here we examine the association between geographic variations in prostate cancer mortality and regional variations in access to medical care, as reflected by the incidence of late-stage disease, prostate-specific antigen (PSA) utilization, and residence in rural counties. METHODS: We analyzed mortality data from the National Center for Health Statistics, 1996 to 2000, and incidence data from 30 population-based central cancer registries from the North American Association of Central Cancer Registries, 1995 to 2000. Ecological data on the rate of PSA screening by registry area were obtained from the 2001 Behavioral Risk Factor Surveillance System. Counties were grouped into metro and nonmetro areas according to Beale codes from the Department of Agriculture. Pearson correlation analyses were used to examine associations. RESULTS: Significant correlations were observed between the incidence of late-stage prostate cancer and death rates for Whites (r = 0.38, P = 0.04) and Blacks (r = 0.53, P = 0.03). The variation in late-stage disease corresponded to about 14% of the variation in prostate cancer death rates in White men and 28% in Black men. PSA screening rate was positively associated with total prostate cancer incidence (r = 0.42, P = 0.02) but inversely associated with the incidence of late-stage disease (r = -0.58, P = 0.009) among White men. Nonmetro counties generally had higher death rates and incidence of late-stage disease and lower prevalence of PSA screening (53%) than metro areas (58%), despite lower overall incidence rates. CONCLUSION: These ecological data suggest that 10% to 30% of the geographic variation in mortality rates may relate to variations in access to medical care.

Adult↗

PubMed1996

Diurnal mood variation in melancholic patients and healthy controls.

In 30 melancholic patients and 21 healthy controls, diurnal mood variation was investigated on 3 successive days at 7.30 a.m., 11.30 a.m., 3.30 p.m. and 7.30 p.m. Daily courses with no variation or with a so-called typical variation (morning low, afternoon/evening high) occurred with the same frequency in both samples. Circadian mood variations vary substantially inter- and intraindividually in both depressive patients and healthy controls. However, the controls reported short (ultradian) mood variations more frequently than the patients. Using a semistructured interview, the subjective experience of diurnal mood variations was compared: In melancholic patients, mood variations occur spontaneously in more than half of all cases, whereas healthy controls attribute them almost exclusively to their own activities and/or external circumstances. It is discussed whether "typical' diurnal variations in melancholic patients may have been emphasized in earlier psychopathological literature not because of their frequency but because patients experience the circadian mood rhythm as uninfluenceable.

Adult↗

PubMed2000

Diurnal blood pressure variation in progressive autonomic failure.

To investigate the role of the autonomic nervous system (ANS) in the generation of the circadian blood pressure (BP) variation, the degree of impairment of the ANS was related to the results of ambulatory BP recordings in 212 patients with progressive autonomic failure due to familial amyloid polyneuropathy. On the basis of BP and/or heart rate (HR) responses to the Valsalva maneuver, 60 degrees head-up tilting, deep-breathing tests, and plasma norepinephrine levels, 4 groups of patients were distinguished. In all patients and in 38 age-matched control subjects, ambulatory BP was monitored. Patients of group I (n=40, aged 32+/-3 y), with no evidence yet of impairment of their ANS, had circadian BP and HR variations indistinguishable from controls. Patients of group II (n=41, aged 34+/-5 y) had a variable degree of impairment of their parasympathetic ANS, but their sympathetic ANS was still intact. Twenty-four-hour HR was higher in these patients than in controls (88+/-11 versus 78+/-7 bpm, P<0.01). Their circadian HR variation was maintained, but their circadian BP variation was diminished (10+/-6/11+/-4 versus 17+/-6/16+/-4 mm Hg in controls, P<0.01) because of an attenuation of the nocturnal BP decline. Patients of group III (n=69, aged 36+/-6 y), with parasympathetic failure and intermediate sympathetic dysfunction, had a blunted diurnal BP variation, whereas patients of group IV (n=62, aged 38+/-6 y), with parasympathetic failure and severe sympathetic dysfunction, had an absent diurnal BP variation. In patients of groups III and IV, a decrease in daytime BP accounted for the blunted circadian BP variation. This extensive study in progressive autonomic failure confirms the important role of the ANS in the generation of circadian BP variation. For the maintenance of a normal circadian BP pattern, not only an intact sympathetic but also an intact afferent parasympathetic ANS is a prerequisite.

Adult↗

PubMed1998

Effect of resistive loading on variational activity of breathing.

To examine the effect of resistive loading on variational activity of breathing, we studied 18 healthy subjects breathing at rest and with inspiratory resistive loads of 3 and 6 cm H2O/L/s, applied randomly for 1 h each. Compared with resting breathing, a resistive load of 3 cm H2O/L/s decreased the total variational activity of expiratory time (TE) and minute ventilation (V I), whereas a load of 6 cm H2O/L/s increased the total variational activity of inspiratory time (TI). Compared with the load of 3 cm H2O/L/s, the load of 6 cm H2O/L/s increased total variational activity of tidal volume (VT), TI, TE, and V I. Partitioning of the total variational activity revealed that these alterations were due to changes in the random uncorrelated fraction. Compared with rest, both the resistive loads of 3 and 6 cm H2O/L/s increased the number of breath lags displaying significant serial correlations ("short-term memory") of TI. Compared with rest, the load of 3 cm H2O/L/s increased the autocorrelation coefficient at a lag of one breath for VT and the load of 6 cm H2O/L/s increased the correlated fraction of variational activity of VT. Thus, three measures of correlated behavior-autocorrelation coefficient at a lag of 1 breath, "short-term memory," and the correlated fraction of total variational activity- increased with loading. In conclusion, resistive loading changed total variational activity according to the size of the load: the random fraction decreased with the smaller load but increased with the larger load; in contrast, correlated behavior increased with both loads. The different behaviors of random and correlated variability with loading may reflect different physiologic influences on respiratory control.

Adult↗

PubMed1997

Peak flow variation in childhood asthma: relationship to symptoms, atopy, airways obstruction and hyperresponsiveness. Dutch CNSLD Study Group.

Although home recording of peak expiratory flow (PEF) is considered useful in managing asthma, little is known about the relationship of PEF variation to other indicators of disease activity. We examined the relationship of PEF variation, expressed in various ways, to symptoms, atopy, level of lung function, and airways hyperresponsiveness in schoolchildren with asthma. One hundred and two asthmatic children (aged 7-14 yrs) recorded symptoms and PEF (twice daily) in a diary for 2 weeks after withdrawal of all anti-inflammatory maintenance medication. PEF variation was expressed as amplitude % mean, as standard deviation and coefficient of variation of all recordings, and as low % best (lowest PEF as percentage of the highest of all values). Atopy and level of forced expiratory volume in one second (FEV1) % predicted were not significantly related to PEF variation. The provocative dose of histamine causing a 20% fall in FEV1 (PD20) and symptom scores were significantly, but weakly, related to PEF variation. The index, low % best, proved easy to calculate and effective in identifying a short-term episode of reduced PEF. We conclude that peak expiratory flow variation in children with stable, moderately severe asthma is significantly, but weakly, related to symptoms and airways hyperresponsiveness. These three phenomena, therefore, all provide different information on the actual disease state. Expressing peak expiratory flow variation as low % best is easy to perform and appears to be clinically relevant.

Adolescent↗

PubMed2005

Sources of variation in Affymetrix microarray experiments.

BACKGROUND: A typical microarray experiment has many sources of variation which can be attributed to biological and technical causes. Identifying sources of variation and assessing their magnitude, among other factors, are important for optimal experimental design. The objectives of this study were: (1) to estimate relative magnitudes of different sources of variation and (2) to evaluate agreement between biological and technical replicates. RESULTS: We performed a microarray experiment using a total of 24 Affymetrix GeneChip arrays. The study included 4th mammary gland samples from eight 21-day-old Sprague Dawley CD female rats exposed to genistein (soy isoflavone). RNA samples from each rat were split to assess variation arising at labeling and hybridization steps. A general linear model was used to estimate variance components. Pearson correlations were computed to evaluate agreement between technical and biological replicates. CONCLUSION: The greatest source of variation was biological variation, followed by residual error, and finally variation due to labeling when *.cel files were processed with dChip and RMA image processing algorithms. When MAS 5.0 or GCRMA-EB were used, the greatest source of variation was residual error, followed by biology and labeling. Correlations between technical replicates were consistently higher than between biological replicates.

Animals↗

PubMed1982

Diurnal variations of plasma thyrotropin, thyroxine, and triiodothyronine in female rats are phase shifted after inversion of the photoperiod.

The present study examined plasma TSH, T4, and T3 concentrations in rats throughout the day to determine if diurnal variations of these hormones occurred. Female rats on a 12-h light, 12-h dark cycle (onset of light, 0730 h) were sampled by cardiac puncture at 2-h intervals throughout the day on 2 days, 1 week apart. Significant diurnal variations of plasma TSH, T4, and T3 were detected (P less than 0.01), Peak TSH concentrations occurred soon after the onset of light, whereas T4 and T3 concentrations peaked 3-4 h later. After these variations were detected, the effect of inverting the photoperiod was examined. Female rats were placed on 12-h light,, 12-h dark cycles, with the onset of light at 0730 h (LD) or 1930 h (DL). After 3 weeks, rats from each group were killed by decapitation at 4-h intervals throughout the day, and trunk blood was collected. Diurnal variations in plasma TSH, T4, and T3 (P less than 0.01) were similar to those found with 2-h sampling intervals in the previous experiment, and plasma corticosterone and PRL rhythms peaked near the onset of darkness (P less than 0.05). Inversion of the photoperiod phase shifted all diurnal variations, such that they maintained a similar phase relationship to the light-dark cycle on both LD and DL photoperiods. These results indicated that diurnal variations of plasma TSH, T4, and T3 concentrations could be repeatedly detected with different sampling protocols. These variations were phase shifted by inverting the photoperiod, which indicated that some aspect of the light-dark cycle can act to set the phase of these diurnal variations in the pituitary-thyroid axis.

Animals↗

PubMed2003

Brachial plexus variations in human fetuses.

OBJECTIVE: We examined the anatomic variations of the brachial plexus (BP) in human fetuses. METHODS: This study was performed with 200 BPs from spontaneously aborted fetuses without detectable malformations. The plexuses were dissected, and the normal position and/or morphological variations of the BP were determined and photographed. RESULTS: There were no variations in 93 plexuses, and 107 plexuses were observed to have different variations. Morphological variations were observed more frequently among female fetuses and right sides. The BPs were composed mostly of the C5, C6, C7, and C8 nerves and the T1 nerve (71.5%). A prefixed plexus was observed in 25.5% of cases, and a postfixed plexus was observed in 2.5% of cases. In one case (0.5%), the C4 and T2 nerves joined the formation. The inferior trunk was not formed in 9% of cases. The superior trunk was not formed in 1% of cases. In one plexus, the superior trunk was formed by the ventral rami of the C4 and C5 nerves. In one case, the inferior trunk was formed by the ventral rami of the T1 and T2 nerves. Division variations were observed most frequently. There were also variations in the terminal branches, such as the roots of the median nerve joining in the distal part of the arm (8.5%), the axillary nerve being separate from the posterior division of the superior trunk (2.5%), and a connection existing between the median and musculocutaneous nerves (1%). CONCLUSION: Knowledge of BP variations is important for surgeons who perform surgical procedures in the cervical and axillary regions.

Axilla↗

PubMed2005

Giant wood spider Nephila pilipes alters silk protein in response to prey variation.

Recent studies have demonstrated that orb-weaving spiders may alter web structures, foraging localities or silk output in response to prey variations. In this study we conducted field surveys and food manipulations to examine whether orb-weaving spiders may also adjust the protein of silk to prey variations. A comparison of dragline silks collected from nine giant wood spider Nephila pilipes populations in Taiwan showed a spatial variation. The percentage of all amino acids (except alanine and glycine) exhibited significant differences among populations. A survey of prey composition also revealed a significant spatial variation among N. pilipes populations. To determine whether prey variation was responsible for silk protein variation, we fed N. pilipes with different types of prey (dipteran vs orthopteran) then compared the percentage of five major dragline amino acids and secondary structures. The results showed that dragline of N. pilipes fed with orthopteran prey contained significantly higher proline and glutamine but lower alanine. Congruent with this result were those from FTIR spectroscopy, which showed that dragline of N. pilipes fed with crickets exhibited significantly higher percentage of proline- and glutamine-containing beta turns, and lower percentage of alanine-containing beta sheet structures. Since the results of feeding manipulations showed that diet significantly affected the compositions of dragline silks, the observed spatial variation seemed to reflect the different types of prey these spiders had consumed. Results of this study thus indicated that orb-weaving spiders can alter dragline protein in response to prey variations.

Amino Acids↗

PubMed2004

Contribution of the LRP5 gene to normal variation in peak BMD in women.

UNLABELLED: The role of the LRP5 gene in rare BMD-related traits has recently been shown. We tested whether variation in this gene might play a role in normal variation in peak BMD. Association between SNPs in LRP5 and hip and spine BMD was measured in 1301 premenopausal women. Only a small proportion of the BMD variation was attributable to LRP5 in our sample. INTRODUCTION: Mutations in the low-density lipoprotein receptor-related protein 5 (LRP5) gene have been implicated as the cause of multiple distinct BMD-related rare Mendelian phenotypes. We sought to examine whether the LRP5 gene contributes to the observed variation in peak BMD in the normal population. MATERIALS AND METHODS: We genotyped 12 single nucleotide polymorphisms (SNPs) in LRP5 using allele-specific PCR and mass spectrometry methods. Linkage disequilibrium between the genotyped LRP5 SNPs was measured. We tested for association between these SNPs and both hip and spine BMD (adjusted for age and body weight) in 1301 healthy premenopausal women who took part in a sibling pair study aimed at identifying the genes underlying peak bone mass. Our study used both population-based (ANOVA) and family-based (quantitative transmission disequilibrium test) association methodology. RESULTS AND CONCLUSIONS: The linkage disequilibrium pattern and haplotype block structure within the LRP5 gene were consistent with that observed in other studies. Although significant evidence of association was found between LRP5 SNPs and both hip and spine BMD, only a small proportion of the total variation in these phenotypes was accounted for. The genotyped SNPs accounted for approximately 0.8% of the variation in femoral neck BMD and 1.1% of the variation in spine BMD. Results from our sample suggest that natural variation in and around LRP5 is not a major contributor to the observed variability in peak BMD at either the femoral neck or lumbar spine in white women.

Adult↗

PubMed2000

Seasonal variation of livebirths, stillbirths, extramarital births and twin maternities in Switzerland.

A study was made of the seasonal variation in all births, and births according to marital status, multiplicity and birth status (live and still) in Switzerland recorded between 1876 and 1990. To obtain seasonal variation in as pure as possible form, our analyses are based on rates. When comparing the seasonality in data sets showing markedly different levels, standardised indices were used. Assuming the length of pregnancies with twins to be about one month shorter than for pregnancies with singletons, lagged twinning rates were calculated but, in comparison with actual twinning rates, the general seasonal variation remained. Therefore, this study was based on actual twinning rates. A monotonic increase in the amplitude of the seasonal variation in general births was noted for the period 1876-1930, with strong seasonal variation holding for 1921-1980. After that, a marked decline in the amplitude can be observed. Seasonality of both all births and twin maternities showed very similar pattern for the periods 1876-1930 and 1969-1990, with maxima in the spring (March-May) and troughs in late autumn (October-December). Twin maternities showed a strong seasonality for the period 1876-1930, being about 20% higher in March than in October. The twinning rate in the period 1876-1930 was about 2.6 per thousand units higher than in the period 1969-90. For twin maternities there was also a stronger seasonal variation during the earlier period than during the later one. The pattern of the seasonal variation for extramarital births, showing a maximum in February (conceptions in May-June) and a minimum in August (conceptions in November-December) with a difference of no less than 24% was more marked than for the marital births. It seems likely that this seasonality of extra-marital maternities was due mainly to seasonal variation of coital rates and multiple ovulation in the early summer months coinciding with optima of light, temperature and food supply. A strong reduction in the rate of stillbirths (gestational age more than 29 weeks) was observed during the twentieth century. The stillbirth rate declined from about 40 per 1000 in the 1870s to fewer than 5 per 1000 in the 1980s. Irrespective of this strong decline in the stillbirth rate, the same seasonal rhythm was noticed throughout the period with high stillbirth rates among births around March and low rates during the summer and autumn.

Abortion, Spontaneous↗

PubMed1992

The amplitude of circadian FEV1 variation suitable for phase determination by cosinor analysis in stable asthmatic children.

To elucidate the criterion for amplitude of circadian FEV1 variation suitable for phase analysis, six FEV1 measurements within a day were made on 346 days in 125 stable asthmatic children aged 8 to 12 years. Since coefficient of variation (CV) of FEV1 within a day in nonasthmatic children in our laboratory is less than 5 percent, circadian FEV1 variations were divided into CV greater than or equal to 5 percent and CV less than 5 percent groups. Forty-two (12 percent) variations with significant fit of cosinor rhythm were CV greater than or equal to 5 percent. Troughs in 32 (76 percent) variations of the 42 were distributed between 12 PM and 6 AM, and the deviation was highly significant against a uniform distribution (p less than 0.001). This was consistent with nocturnal asthma. Thirty-five (10 percent) variations with significant fit of cosinor rhythm were CV less than 5 percent. Troughs in 12 (34 percent) variations of the 35 were distributed between 12 PM and 6 AM, and the deviation from a uniform distribution was nonsignificant. These suggest that 5 percent or more of CV of FEV1 may be clinically suitable for analysis of circadian FEV1 variation.

Asthma↗

PubMed2000

Variation in performance on cry1Ab-transformed and nontransgenic rice varieties among populations of Scirpophaga incertulas (Lepidoptera: Pyralidae) from Luzon Island, Philippines.

We quantified variation in performance under greenhouse conditions among seven populations of Scirpophaga incertulas (Walker) from Luzon Island, Philippines, on three rice varieties: 'IR58' transformed with the cry1Ab gene from Bacillus thuringiensis Berliner, and nontransgenic IR58 and IR62. On IR62, S. incertutas performance did not differ among provinces for any of the 10 parameters measured, but there was a significant effect of town within province for one parameter, 20-d-old larval weight. Larval survival after 48 h on cy1Ab-transformed IR58 did not differ significantly among provinces, but did differ significantly among towns within a province. There was no geographic variation in larval survival after 48 h on control plants of IR58. Surviving insects from the cry1Ab-transformed IR58 were transferred to IR62 to complete development. There was no geographic variation in the percentage of insects completing development to adult emergence and the time required by the transferred female insects to complete development. However, there was variation among provinces in male developmental time. The absence of geographic variation on nontransgenic IR58 and the very limited variation on IR62 indicated that there was little variation in general vigor among the S. incertulas populations and thus that the variation in performance oil cry1Ab-transformed IR58 was probably attributable to differences in susceptibility to Cry1Ab.

Animals↗

PubMedDate not supplied

Normal adult values, diurnal variation, and repeatability of nasal nitric oxide measurement.

Reports of elevated nasal nitric oxide (NO) levels in allergic rhinitis suggest that nasal NO levels could be a valuable marker of upper airway inflammation, provided that the reproducibility of nasal NO measurement is acceptable. The aims of this study were to evaluate the precision with which nasal NO levels can be measured at single point in time, and to quantify within-day and between-day variation. Nasal NO was measured using a modified chemiluminescence analyzer. Population data were normally distributed, as judged by testing for skewness and kurtosis. NO levels were not related to age or gender, and there was no evidence of diurnal variation. Sampling rates of 250 mL/minute and 500 mL/minute at a single point in time had acceptable reproducibility (coefficients of variation 10.2% and 6.6%, respectively). However, within-day variation (coefficient of variation 13.4%) and between-day variation (coefficient of variation 11.8%), at a sampling rate of 500 L/minute, were substantially higher. These findings highlight the importance of taking measurement variation into account, in the interpretation of NO levels, in clinical research and, potentially, in routine practice. In individual patients, an alteration of 20-25% in NO levels is required, to ensure that change is genuine and not ascribable to the noise of measurement.

Adolescent↗