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Results for “Repeatability and Reproducibility”

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PubMed1998

Long-term effects of pharmacological therapy for vasovagal syncope on the basis of reproducibility during head-up tilt testing.

The purpose of this study was to determine the efficacy of long-term pharmacological therapy selected on the basis of a head-up tilt test (HUT) in patients in whom reproducibility of the HUT response was demonstrable in the initial study. The HUT (80 degrees upright) was performed for 15 min with or without an infusion of isoproterenol (0.01-0.03 microgram/kg per min) in 54 patients with recurrent unexplained syncope. When vasovagal syncope was induced (positive response), the HUT was repeated to examine the test reproducibility. Vasovagal syncope was induced in 24 patients during HUT alone, and in 30 patients during the HUT with isoproterenol. Acute reproducibility was observed in 49/54 (91%) patients. In the tilt-positive patients, HUT was repeated after an intravenous administration of propranolol (0.1 mg/kg) or disopyramide (1 mg/kg) (acute test). Propranolol proved effective in 21 (80%) of 26 patients, and disopyramide in 13 (56%) of 23 patients. Thereafter, evaluation was done on the long-term clinical follow-up of the pharmacological intervention selected on the basis of the acute test in the 34 patients in whom the HUT could not induce vasovagal syncope after the oral administration of the pharmacological agent (propranolol 60 mg/day, disopyramide 300 mg/day). Thirty-two of 34 patients (94%) did not develop syncopal attacks during a 44 +/- 12-month period. Thus, in patients with unexplained syncope, HUT appears to have a high degree of acute reproducibility, and the acute drug response guided by HUT may be used to develop an effective long-term pharmacological therapy.

Administration, Oral↗

PubMedDate not supplied

[Induced sputum in asthma: study of validity and repeatability].

To assess the validity and reproducibility of determining total and differential cell (DC) counts and of eosinophilic cationic protein (EPC) levels in induced sputum. Clinical analysis of validity and reliability of a measurement tool. Twenty-one asthmatics [age: 31(14) years; FEV1: 78(21)% of reference value; PC20FEV1: 0.02(1.1)mg/ml] and 10 healthy subjects [age: 30(3) years, FEV1: 99(12)% of reference value, PC20FEV1: > 8(3.7)mg/ml]. A sputum sample was collected from each individual using hypertonic saline. Sputum was separated from saliva and then divided into two portions as uncontaminated as possible by squamous cells. Both portions were treated independently and simultaneously within two hours with a solution of bithiothreitol to disperse the cells, and then centrifuged. The supernatant was poured off and frozen al -70 degrees for later determination of EPC. The sediment was stained with Papanicolaou stain, toluidine blue and eosinhematoxylin. DC count was expressed as a percentage of total inflammatory cells. ECP was determined with a CAP-System and a commercial kit (Pharmacia Diagnostics SA, Uppsala, Sweden). Two subjects in each group were unable to produce valid sputum samples (20% of healthy subjects and 10% of asthmatics). The validity of the method was demonstrated by significant differences between asthmatics and healthy subjects in both eosinophil and EPC levels. The reproducibility of method was verified by comparing the results for the sputum fractions; no significant differences were found in cell counts or EPC levels. The within-group correlation coefficients for the sputum fractions ranges between 48 and 77% for all cell types, except squamous cells, which gave a coefficient of 18%. For EPC the correlation coefficient was 98%. DC and EPC determinations in sputum induced by hypertonic saline are valid and reproducible.

Adult↗

PubMed1990

A validation study on the reproducibility of transcranial Doppler velocimetry.

The transcranial Doppler method for the measurement of intracranial arterial blood flow velocity is a useful noninvasive technique with a number of applications. The present study validated the reproducibility of this method for repeated measurements of flow velocity in the middle cerebral and basilar arteries. Fifteen healthy volunteers were studied. Measurements were made twice by one examiner and once by another in a single day and again by the first examiner on another day. The reproducibility was evaluated by calculating the correlation coefficient (r) and the coefficient of variation (CV) of the difference between the values obtained from each pair of measurements. Although depending on the examiner, the time interval between the examinations and the vessels studied some differences were noted in the reproducibility, both the r (0.69-0.95) and CV (6.7%-19.5%) values in the whole study were good enough to warrant the applicability of this method for the repeated measurements of the intracranial arterial blood flow velocity in future studies.

Cerebral Arteries↗

PubMed1977

Cortical thickness measurements and photon absorptiometry for determination of bone quantity.

Reproducibility of estimates of cortical bone quantity in the appendicular skeleton by two methods was studied in healthy individuals and patients undergoing long-term hemodialysis. Repeated measurements of cortical thickness (CT) at the midpoint of the second metacarpal were taken from single radiographs of both hands by two independent observers. Repeated measurements by the same observer were more reproducible and the degree of reproducibility was far greater in healthy subjects than in dialysis patients. Repeated measurements were made of bone mineral content (BMC) and bone width (W) of the distal radius by photon absorptiometry. Repeated BMC/W determinations were highly reproducible in both healthy subjects and dialysis patients. High correlation was found between BMC and cross-sectional cortical area and between both simple cortical thickness and cortical area/width. Thus the photon absorptiometric technique is superior for the serial monitoring of bone quantity, particularly in patients with uremic osteodystrophy, but results obtained by the two methods in group studies should be comparable.

Adult↗

PubMed2003

Reproducibility of the blood flow index as noninvasive, bedside estimation of cerebral blood flow.

OBJECTIVE: To investigate the feasibility and reproducibility of the blood flow index (BFI) method for measuring cerebral blood flow. DESIGN AND SETTING: Prospective functional study in pediatric intensive care. PATIENTS AND PARTICIPANTS: 14 consecutive patients with median age of 2 months (range 1 days-11 years) requiring artificial ventilation, invasive arterial blood pressure monitoring, and central venous access. INTERVENTIONS: The first passage of an intravenous indocyanine green (ICG) bolus through the cerebral vasculature was monitored by noninvasive near-infrared spectroscopy. BFI was calculated by dividing maximal ICG absorption change by rise time. Reproducibility was evaluated by six ICG injections at 5-min intervals. RESULTS: Of all ICG injections 6% were canceled, and 4% were eliminated due to injection failures. Median BFI of 17 reproducibility determinations was 71 (range 12-213) and median coefficient of variation (CV) of BFI was 10% (4.9-18.5). The quantity of ICG bolus did not affect the CV (0.1 vs. 0.3 mg ICG/kg). Eight reproducibility tests in patients after cardiac surgery had smaller CV than the others, and the eight in newborns had higher CV than in older children. Patient parameters such as arterial blood pressure, endtidal CO(2), and percutaneous oxygen saturation were stable and showed CV below 2% during reproducibility determination. CONCLUSIONS: The BFI method allows rapid and repeated measurements of CBF with good feasibility and reproducibility. As a relative but not absolute measure of CBF, BFI seems to be suited for clinical evaluation of intraindividual CBF changes during determination of cerebrovascular reactivities or during therapeutic interventions.

Blood Circulation Time↗

PubMed2001

Comparison of complex DNA mixtures with generic oligonucleotide microchips.

The reproducibility of melting curves for repeated hybridizations of target DNA with generic oligonucleotide microchips is shown experimentally to depend on the character of matching between fragments of target DNA and immobilized oligonucleotides. The reproducibility of melting curves is higher for the perfect match duplexes and decreases as the number of mismatched pairs within duplexes increases. This effect was applied to the comparative analysis of complex DNA mixtures. We developed a scheme in which we can identify and discriminate between the probe oligonucleotides responsible for the distinctions between target DNA mixtures. A scheme is illustrated by comparing DNA mixtures corresponding to V-D-J genes connected with populations of mRNAs CDR3 TCR Vb (T-cell receptor beta complementarity determining region 3) from the thymus and pancreas of NOD mice. Our results demonstrate that generic microchips can be applied efficiently to the analysis of DNA mixtures.

Animals↗

PubMed2006

Cyclic performance of carbon-coated TiO2 for photocatalytic activity of methylene blue decomposition.

Carbon-coated TiO2 powders were prepared from the mixtures of anatase (ST-01) and carbon precursor poly(vinyl alcohol) in different ratios by carbonization at 900 degrees C in a flow of either Ar or N2. Carbon-coated TiQ2 thus prepared was either fixed on an adhesive tape or formed into a film by using the organic binder poly(tetrafluoroethylene) and used for photodecomposition of methylene blue in water repeatedly. On the samples fixed on adhesive tapes, the rate constant was reproduced with about 10-20% scattering during repeated uses in a fresh methylene blue solution up to 7 times. On the samples formed into films by using the organic binder, the rate constant was reproduced after the 3rd or 4th cycle. The mutual relations in rate constant were almost the same among three different conditions for the determination, suspending the sample particles, fixed on an adhesive tape and formed into a film. The rate constant for the photodecomposition was found to give a maximum on the sample containing about 9 mass% carbon.

Carbon↗

PubMed1995

Reproducibility of a food frequency questionnaire and stability of dietary habits determined from five annually repeated measurements.

OBJECTIVES: In studies on diet and cancer, diet assessment should address long-term intake. Therefore, the authors determined the 5-year reproducibility of a self-administered 150-item food frequency questionnaire (FFQ) used to assess dietary habits in the Netherlands Cohort Study on diet and cancer. Since the FFQ was repeated more than once, the pure test-retest reliability of the FFQ could be distinguished from the intra-individual change in nutrient intake over time. These results were furthermore used to investigate the measurement error structure of the FFQ. DESIGN: After baseline administration in 1986, the FFQ was annually repeated from 1987 to 1991 in independent random samples of the cohort (n = 400). Pearson correlation coefficients (r) between baseline and repeated measurements of nutrient intake, calculated for each time interval, were regressed on time interval to provide separate estimates of the test-retest correlation (intercept of regression line) and of the decline in correlation over time (slope). The proportion of correlated measurement error was derived from combining the test-retest results with those from a validation study, in which the FFQ was validated against three 3-day diet records. RESULTS AND CONCLUSIONS: Response was stable at 82%. The test-retest r ranged from 0.42 for selenium intake to 0.90 for alcohol intake. The slopes of the regression lines were relatively flat, but negative for most nutrients; on average, the decline in r amounted to 0.07 after 5 years, indicating that the potential of a single FFQ measurement to rank subjects according to nutrient intake dropped only slightly over time. This is important for studies on cancer since a long induction period may be involved. It was furthermore shown that the proportion of within-subject (error) variance of the FFQ method that could be attributed to correlated error ranged from 0 to 50%. This finding confirms that a reliability study may underestimate the measurement error of a method. SPONSORSHIP: Dutch Cancer Society (grants CIVO 86-1 and CIVO 90-3).

Aged↗

PubMed2006

Noninvasive and three-dimensional imaging of CMRO(2) in rats at 9.4 T: reproducibility test and normothermia/hypothermia comparison study.

Ability to image cerebral metabolic rate of oxygen (CMRO(2)) is essential for studying the fundamental role of oxidative metabolism in brain function and disease. We have demonstrated recently that three-dimensional (3D) CMRO(2) images can be obtained in the rat brain during a 2-min (17)O(2) inhalation using the (17)O MR spectroscopic imaging (MRSI) approach at high field. The feasibility for establishing a completely noninvasive approach for imaging CMRO(2) has also been demonstrated. In this study, we further explored the feasibility of (17)O MRSI approach for performing repeated CMRO(2) measurements within a short period of time and evaluated the reproducibility of the repeated measurements. Subsequently, we applied the (17)O MRSI approach to measure CMRO(2) and cerebral blood flow (CBF) values at two brain temperatures in the alpha-chloralose anesthetized rat brain at 9.4 T. Finally, we tested the validity of simplified model for noninvasively determining CMRO(2) in normothermic and hypothermic rat brain. The results show (i) an excellent reproducibility among repeated measurements of 3D CMRO(2) images under the same physiologic condition; (ii) a 44% decrease of CMRO(2) across the rat brain at mild hypothermic (32 degrees C) condition as compared with normothermic (37 degrees C) condition; and (iii) a close correlation between CMRO(2) and CBF within a relatively wide physiologic range. This study demonstrates the capability of (17)O MRSI approach for noninvasively imaging CMRO(2) and its changes caused by physiologic perturbation. This approach, thus, should provide a promising neuroimaging modality for studying oxidative metabolism and bioenergetics associated with brain functions and diseases.

Animals↗

PubMed1998

Technical abilities and limitations of acoustic rhinometry optimised for infants.

The objective of this model study was to validate in detail the technical capabilities as well as the limitations of a new rhinometric probe optimised for infants in order to improve reliability of measurements and reduce the risk of misleading conclusions. The repeatability was excellent (CV < 0.6%) and the reproducibility was high (CV% < 4%) provided the ambient conditions were fairly stable. The repeatability declined when external noise levels were above 60 dB SPL, and variation in temperature and pressure reduce reproducibility. The accuracy of the minimum cross-sectional area (MCA) as well as the volume corresponding to the nasal cavity in infants (VOL4), was acceptable (% error < 12%) as long as the MCA was larger than 30-40% of the probe dimensions and the cross-sectional area of the cavity posterior to the MCA did not exceed the MCA by a factor of more than 3-4. Variation in the position of the MCA within the anterior 2 cm has minimal influence on the posterior measurements provided the shape and length of the MCA are unaltered. Rods inserted into the tubular model to simulate the slit-like shape of the nasal passage did not reduce the accuracy, which is essential to the clinical value of acoustic rhinometry. Recommendations and guidelines designed to enhance the reliability of acoustic measurements in infants are presented.

Acoustics↗

PubMed2000

Contrast-reduced imaging of tissue concentration and arterial level (CRITICAL) for assessment of cerebral hemodynamics in acute stroke by magnetic resonance.

RATIONALE AND OBJECTIVES: To compare cerebral perfusion data obtained by using a low-dose, T1-weighted MRI technique with radionuclide (single positron emission computed tomography [SPECT]) brain imaging and to assess the reproducibility of parametric MRI data (cerebral blood flow [CBF], cerebral blood volume [CBV], and time to peak [TTP]) by applying a previously described nuclear medicine technique to derive quantitative perfusion data. METHODS: Single-slice brain and neck images were rapidly acquired during the passage of a small (1/10th of normal dose) bolus of contrast. Parametric images were constructed from the MR data by extracting the bolus transit curve for the brain and the peak arterial input curve from the carotid vessels in the neck. These were compared with SPECT perfusion imaging. Twenty-four patients with acute stroke were studied with both techniques; 13 underwent repeated scanning to assess data reproducibility. RESULTS: Relative CBF data were comparable to SPECT data (r = 0.584, P = 0.01). Results were reproducible for relative CBF, CBV, and TTP. The arterial input function was significantly different on the second injection with an average difference of 73.5, suggesting that the signal-concentration relationship had lost linearity with increased contrast load. Absolute quantitative MRI data produced values in the expected range (CBF = 42.6 mL x 100 g(-1) x min(-1)). CONCLUSIONS: This technique allows estimation of CBF in the setting of acute stroke with quantitative values in the expected range. Repeated measurements in the same patients showed that this technique provides a reproducible measure of relative CBF, CBV, and TTP.

Brain↗

PubMed1996

Comparison and reproducibility of visual echocardiographic and quantitative radionuclide left ventricular ejection fractions.

Left ventricular (LV) ejection fraction (EF) is commonly assessed by equilibrium radionuclide angiography and echocardiography. These methods are presumed to be interchangeable for this purpose. This study (1) compares quantification of LVEF by equilibrium radionuclide angiography with visual estimation of LVEF by echocardiography, (2) determines the reproducibility of both methods, and (3) evaluates whether differences in determinations of LVEF are of clinical relevance. Seventy-three clinically stable patients had both equilibrium radionuclide angiography and echocardiography performed within a 4-day period. LVEF by both techniques was compared after blinded analysis by 3 echocardiographers and 3 nuclear technologists. Reproducibility was assessed by blinded repeat analysis after a 1-week interval. The frequency of differences in repeat assessments of EF that the authors considered to be of potential clinical relevance (i.e., difference > or = 10% EF units) was assessed for both techniques. Correlation of LVEF determined by both methods was good (r = 0.81, SEE = 3.5) but with substantial differences in individual patients (limits of agreement, 23.6%). Intra- and inter-observer reproducibility was good for both methods, but better for radionuclide LVEF than for echocardiographic LVEF. Limits of agreement were substantially better for radionuclide LVEF than for echocardiographic LVEF (1.8% to 3.6% versus 13.4% to 17.4%, respectively). Clinically relevant differences did not occur on repeat processing of equilibrium radionuclide angiography. In contrast, potentially clinically relevant differences occurred in 8% to 26% of studies on repeat analysis of echocardiography. Thus, LVEF determined by equilibrium radionuclide angiography and echocardiography show good agreement. Both methods provide clinically valuable measurements for LV function. However, when a precisely reproducible measurement is required for patient management decisions, equilibrium radionuclide angiography is the method of choice.

Adult↗

PubMed1979

Cine-densitometric measurement of coronary arterial stenoses.

Computer-aided operator-interactive densitometry has been developed and applied to determine the percent stenosis for obstructive lesions in the coronary arterial tree. Phantom experiments performed to assess system linearity, accuracy of densitometric measurements, nonuniformity in image amplified response, and the interference of structure noise in measuring precision have been described. Three observers assessed the reproducibility of the method by repeating analyses on 20 stenoses in man recorded on 35-mm cine angiograms. Calculation of the intra- and interobserver errors found that their values significantly decrease with increasing percent stenosis. The reproducibility of the technique was also tested on stenoses that were exposed at multiple angles. The results agreed with those found for the intra- and interoperator errors. Limitations of the densitometric approach and desirability of further automation of the measurements are also discussed.

Cineangiography↗

PubMed2004

Reproducibility of bone mineral density measurement in daily practice.

BACKGROUND: Bone mineral density (BMD) measurements are frequently performed repeatedly for each patient. Subsequent BMD measurements allow reproducibility to be assessed. OBJECTIVE: To examine the reproducibility of BMD by dual energy x ray absorptiometry (DXA) and to investigate the practical value of different measures of reproducibility in a group of postmenopausal women. METHODS: Ninety five women, mean age 59.9 years, underwent two subsequent BMD measurements of spine and hip. Reproducibility was expressed as smallest detectable difference (SDD), coefficient of variation (CV), and intraclass correlation coefficient (ICC). Sources of variation were investigated by multilevel analysis. RESULTS: The median interval between measurements was 0 days (range 0-45). The mean difference (SD) between the measurements (g/cm(2)) was -0.001 (0.02) and -0.0004 (0.02) at L1-4 and the total hip, respectively. At L1-4 and the total hip, SDD (g/cm(2)) was +/-0.05 and +/-0.04 and CV (%) was 1.92 and 1.59, respectively. The ICC at spine and hip was 0.99. CONCLUSIONS: Reproducibility in the postmenopausal women studied was good. In a repeated DXA scan a BMD change exceeding 2 radical 2CV (%), the least significant change (LSC), or the SDD should be regarded as significant. Use of the SDD is preferable to use of the CV and LSC (%) because of its independence from BMD and its expression in absolute units. Expressed as SDD, a BMD change of at least +/-0.05 g/cm(2) at L1-4 and +/-0.04 g/cm(2) at the total hip should be considered significant.

Absorptiometry, Photon↗

PubMed2007

The repeatability of submaximal endurance exercise testing in cystic fibrosis.

Submaximal endurance cycle ergometer exercise tests are used to measure the efficacy of an exercise intervention, but the repeatability of these tests in patients with cystic fibrosis (CF) has not been established. The purpose of this study was to examine the repeatability of submaximal endurance testing in stable CF. Fifteen adults with CF underwent two submaximal endurance tests carried out over a 7-day period. A subset of six subjects returned 28 days later for a third submaximal endurance test. Workload was set at 80% of maximum workload and exercise was performed to exhaustion. Oxygen consumption, minute ventilation, tidal volume, carbon dioxide output, respiratory rate, heart rate, and oxygen saturation were measured at rest, at end exercise and at four matched times during the submaximal endurance tests (20, 40, 60, and 80% of exercise duration calculated from the first endurance test). Submaximal endurance test time was highly repeatable with no significant learning effect identified on multiple testing. Submaximal endurance exercise time demonstrated a variability of 5.7% which is consistent with high levels of repeatability. Metabolic, ventilatory and cardiac variables were all also highly reproducible between test days. Submaximal endurance testing is repeatable in stable CF, confirming that submaximal endurance tests are a reliable tool for assessment of therapeutic benefit in patients with CF.

Adult↗

PubMed2001

Multicenter biometry study of 1 pair of eyes.

PURPOSE: To assess the accuracy of biometry for intraocular lens (IOL) power calculation. SETTING: Six ophthalmic surgery centers in Europe and 1 in the United States. METHODS: Biometry was done as if in preparation for cataract surgery in 2 eyes of the same person with 10 combinations of operator and instrument. Data analysis followed a standardized procedure to assess repeatability (within-center variability) and reproducibility (between-center variability) of the test methods. RESULTS: The reproducibility of the corneal radius measurement was 0.06 mm. The use of different keratometric indices made conversion to K-values less reliable. The repeatability of the axial length (AL) measurement of 0.30 mm and the reproducibility of 0.66 mm converted to a calculated IOL power of 0.75 diopter (D) and 1.65 D, respectively. Thus, this potential patient runs the risk of a refractive surprise of up to 1.10 D purely as a result of a measurement error within a center and up to 2.30 D if the patient goes to the worst-case center. CONCLUSIONS: The biometry results show that the measured corneal radius can be used with confidence. Reproducibility errors in AL determination require personalization of formula constants or correction at the source by proper calibration.

Biometry↗

PubMed1998

Optimisation of a reagentless laccase electrode for the detection of the inhibitor azide.

Here we report on the optimisation of a reagentless enzyme sensor for the detection of azide based on the mediated reduction of O2 by a laccase enzyme co-immobilised in a redox hydrogel on electrode surfaces. The sensor response is shown to be influenced by the enzyme loading, the electrolyte pH and ionic strength. The response of the sensor is stable, decreasing by only 25% over a sixteen-hour period. Reproducible inhibition curves for the determination of azide levels from cyclic voltammetric scans can be obtained by normalisation of the sensor response. The resulting enzyme inhibition biosensor can detect levels of azide as low as 2.5 microM under these conditions. Constant potential amperometric detection at the laccase enzyme electrode in a flow injection set-up yields a peak current for inhibition of the mediated reduction of O2. Reproducible peak currents and areas (8.0 and 6.3% RSD, respectively, for n = 11) are obtained for repeated injections of 100 microM azide. Reproducible response curves can be obtained by injection of a 25 mM azide sample and assuming that the peak height and peak area obtained represent 100% inhibition of the enzyme.

Biosensing Techniques↗

PubMed2005

Platelet-activating factor acts on cortisol secretion by perfused guinea-pig adrenals via calcium-/phospholipid-dependent mechanisms.

Bilateral adrenals of the guinea pig were perfused in situ with an artificial medium equilibrated with 95% O2/5% CO2. Platelet-activating factor (PAF) induced biphasic cortisol responses, which reached a maximum at 10 nM PAF and declined at 100 nM. The effect of the PAF receptor antagonists CV-3988 and CV-6209 on PAF-stimulated cortisol secretion was examined. Prior exposure of adrenal glands to 10 microM CV-3988 or a simultaneous incubation with 10 microM CV-6209 abolished the cortisol response to 10 nM PAF. Lyso-PAF (a PAF precursor and breakdown product) did not affect cortisol secretion. Concentrations of 5-12.5 microM 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), a protein kinase C (PKC) inhibitor, abolished subsequent cortisol secretion in response to 10 nM PAF. N-[2-(Methylamino)ethyl]-5-isoquinoline sulfonamide dihydrochloride (H-8), a protein kinase A inhibitor, was less effective. A calcium ionophore (A23187) at 3.3 and 10 microM increased cortisol secretion, but the activator of PKC, l-alpha-1-oleoyl-2-acetyl-sn-3-glycerol (OAG), at 50 microM had no effect. When infused simultaneously, OAG (50 microM) and A23187 (3.3 microM) stimulated cortisol secretion synergistically. The secretory response of cortisol to repeated infusions of adrenocorticotrophin (100 pg/ml) or forskolin (10 microM) was essentially reproducible. By contrast, cortisol secretion in response to repeated infusions of PAF (10 nM) or OAG plus A23187 was not reproducible and the second response was diminished compared with the first. Our findings suggest that PAF plays a role in the regulation of steroidogenesis via a mechanism mediated by the PAF receptor and PKC.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗