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Results for “Repeatability and Reproducibility”

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PubMed2003

Simultaneous non-invasive assessment of arterial stiffness and haemodynamics - a validation study.

The purpose of the study was to estimate the reliability of whole-body impedance cardiography (ICGWB)-derived pulse wave velocity (PWV) and stroke volume index to pulse pressure (SI/PP) measurements. The repeatability and reproducibility of ICGWB parameters were also determined. Agreement between the impedance and Doppler ultrasound-based PWV measurements was estimated in 25 healthy subjects in two consecutive measurements. Impedance-derived SI/PP (SIICG/PP) estimates were compared with simultaneously measured SI/PP based on thermodilution (SITD/PP) and direct Fick (SIFICK/PP) methods in 30 surgical patients. PWV measured between the aortic arch and popliteal artery using the impedance technique with selective electrode configuration (PWVIS) agreed well with the Doppler ultrasound method (PWVDOPP), the bias (PWVDOPP - PWVIS) and precision (+/- SD of differences) being 0.00 and 0.79 m s-1, respectively. PWV derived from the whole-body and popliteal impedance plethysmograms (PWVICG) overestimated slightly PWVDOPP values. The repeatability value for PWVIS was excellent, being 0.54 m s-1. The reproducibility values for PWVDOPP and PWVIS were very similar (2.17 and 2.42 m s-1, respectively). Changes in PWVIS correlated strongly with changes in PWVDOPP (r=0.74; P<0.0001), indicating that both methods reflected the true physiological variation in PWV. The agreement between SIICG/PP and SITD/PP or SIFICK was almost identical to the agreement between the SITD/PP and SIFICK/PP. In conclusion,whole-body impedance cardiography provides handy and reliable means of evaluating arterial stiffness on the basis of PWV and SI/PP simultaneously with conventional haemodynamic parameters. The method is highly repeatable and reproducible.

Adolescent↗

PubMed1999

Reproducibility of head-up tilt testing potentiated with sublingual nitroglycerin in patients with unexplained syncope.

Head-up tilt testing (HUTT) potentiated with sublingual nitroglycerin has gained acceptance as means of diagnosing neurally mediated syncope. To evaluate the reproducibility of HUTT potentiated with sublingual nitroglycerin, 48 patients with unexplained syncope prospectively underwent 2 consecutive tests 1 to 28 days apart. The initial test ended in syncope in 34 patients (71%). In 9 patients (19%) the test was positive during the drug-free phase, whereas 25 patients (52%) had syncope after nitroglycerin administration. Of these 34 patients with an initial positive test result, 27 (79%) had a reproducible outcome on repeat testing. Of 12 patients (25%) with an initial negative test result, 10 (83%) had a reproducible outcome on repeat testing. Of 2 patients (4%) with a first test ending in exaggerated response, both had a negative repeat test response. The overall reproducibility of sublingual nitroglycerin tilt-table testing was 77%. In a group of 23 patients with both positive tests, 19 (83%) had the same response modality (2 vasodepressor, 4 cardioinhibitory, 13 mixed response). In the same group of patients, individual trough heart rates correlated well with each other between tests. Finally, in the 27 patients with both positive tests, intrapatient time of onset of symptoms did not significantly correlate between tests. Thus, in patients with syncope of unknown origin, HUTT potentiated with sublingual nitroglycerin provides an adequate reproducibility when repeated on different days.

Administration, Sublingual↗

PubMed2006

Inherent variability of CT lung nodule measurements in vivo using semiautomated volumetric measurements.

OBJECTIVE: The objective of our study was to evaluate repeatability and reproducibility of lung nodule volume measurements using volumetric nodule-sizing software. MATERIALS AND METHODS: Fifty nodules, less than 20 mm in diameter, in 29 patients were scanned with 1.25-mm collimation using MDCT (time 1 = T1). During the same session, two additional scans, using identical technique, were obtained through each nodule (T2, T3). Three observers working independently then obtained volumetric measurements using a semiautomated volumetric nodule-sizing software package. Qualitative nodule characterization was also performed. The Bland-Altman method for assessing measurement agreement was used to calculate the 95% limits for agreement for nodule volumes at T1, T2, and T3. RESULTS: Automated nodule segmentation was successful in 438 (97%) of 450 measurements. Forty-three nodules were available for final evaluation. Twenty-six nodules had well-defined edges, and 17 had irregular or spiculated margins. Seventeen were freestanding, 16 were juxtapleural, and 10 were juxtavascular in location. Average nodule volume was 345.5 mm(3) (range, 49.3-1,434 mm(3)). The mean interobserver variability (repeatability) was 0.018% (SD = 0.73%), and the SD of the mean for the three contemporaneous scans (reproducibility) was 13.1% (confidence limits, +/- 25.6%). SD and confidence limits narrowed as volumes increased. CONCLUSION: Volumetric measurements show minimal interobserver variability (0.018%) but an interscan SEM of 13.1% (confidence limits, +/- 25.6%). Repeatability and reproducibility of volumetric measurements are better than those of linear measurements reported in the literature.

Adult↗

PubMed1998

Comparison between mixed venous oxygen saturation and thermodilution cardiac output in monitoring patients with severe heart failure treated with milrinone and dobutamine.

PURPOSE: Although thermodilution cardiac output (COtd) is the accepted method for monitoring patients with heart failure in the intensive care unit, it is particularly inaccurate in low-flow states and in the presence of tricuspid regurgitation; in addition, it does not adequately reflect the interaction between oxygen delivery and tissue oxygen extraction. We were concerned about the underuse of mixed venous oxygen saturation (SvO2) in this setting and hypothesized that it might be a more useful parameter than COtd for evaluating hemodynamic status and monitoring therapy in patients with severe congestive heart failure. PATIENTS AND METHODS: We determined the correlation coefficients between increasing dose of inotrope and each of the parameters COtd and SvO2 in 18 patients with congestive heart failure who received a 3-day trial of either milrinone or dobutamine during admission to the Veterans Affairs Medical Center in San Diego. In addition, we analyzed reproducibility of repeated COtd and SvO2 measurements taken at a single dose of inotrope. RESULTS: In patients receiving milrinone the increase in dose correlated much better with SvO2 (average correlation coefficient 0.79) than with COtd; this stronger correlation with SvO2 was seen in 82% of the trials reviewed (p < 0.05). In addition, we found that repeated SvO2 measurements taken at a single dose of milrinone were more reproducible than COtd as indicated by smaller relative 95% confidence intervals. In patients receiving dobutamine no significant trend in correlation coefficients or reproducibility was observed. CONCLUSION: The knowledge that there is a significant relation between SvO2 and increasing dose of milrinone therapy in patients with severe heart failure and tricuspid regurgitation has practical value for physicians monitoring these patients in the intensive care unit. We believe this study demonstrates the worth of SvO2 in detecting hemodynamic change during trials of milrinone therapy and that this parameter may in fact be more reproducible than traditional thermodilution methods.

Aged↗

PubMed1994

Characterization of mechanosensitive pelvic nerve afferent fibers innervating the colon of the rat.

1. Single-unit activity was recorded from S1 sacral dorsal root afferent fibers in the anesthetized rat. A total of 364 afferent fibers were identified by electrical stimulation of the pelvic nerve and subsequently tested for response to colorectal distension (CRD) and urinary bladder distension (UBD). Sixty-seven percent (n = 244) of the fibers were unmyelinated C-fibers and 33% (n = 120) were thinly myelinated A delta-fibers. 2. In three initial experiments, 35 fibers were identified by pelvic nerve stimulation and tested for response only to CRD; none of these fibers responded to CRD. In 20 subsequent experiments, 329 pelvic nerve afferent fibers were tested for response to CRD and UBD. Thirty-four percent (n = 112) of the 329 fibers were unresponsive to noxious CRD (80 mmHg) or to UBD (slow filling < or = 100 mmHg), 44% (n = 146) responded to UBD, 16% (n = 53) responded to CRD, and 6% (n = 18) responded to mechanical stimulation of the anal mucosa. 3. Of the total of 53 pelvic nerve afferent fibers that responded to CRD, 43 (81%) were C-fibers (mean: 1.5 m/s) and 10 (19%) were A delta-fibers (mean: 4.7 m/s). Fifteen of the CRD-sensitive fibers had no resting activity, whereas 38 fibers exhibited some resting activity (mean: 2.6 imp/s). 4. Reproducibility of responses to repeated CRD (80 mmHg, 30s, 10 trials at 4-min intervals) was tested in 17 fibers. In 16, responses to repeated distension were reproducible without evidence of facilitation or inhibition of subsequent responses. One fiber gave greater responses during the 9th and 10th trials. 5. Responses to graded CRD were studied in 44 fibers. All fibers exhibited monotonic, increasing stimulus-response functions < or = 80 mmHg of distension. Thresholds for response of the 44 fibers were determined after extrapolation of the least-squares linear-regression line to the ordinate and varied between 0 and 40 mmHg. Two populations of pelvic nerve afferent fibers in the colon were apparent: low threshold (LT) afferent fibers had a mean threshold of 2.9 mmHg (range: 0-10 mmHg; n = 34) and high threshold (HT) afferent fibers had a mean threshold of 32.6 mmHg (range: 28.0-40.0 mmHg; n = 10). 6. Chemosensitivity to bradykinin (BK) was tested in nine LT fibers. Seven fibers responded to BK (0.1 to 100 micrograms/kg ia) and two fibers did not respond up to 100 micrograms/kg of BK. Responses to BK tested in three fibers were dose dependent.(ABSTRACT TRUNCATED AT 400 WORDS)

Anal Canal↗

PubMed1999

Ultrasonic extraction and portable anodic stripping voltammetric measurement of lead in paint, dust wipes, soil, and air: an interlaboratory evaluation.

Recent studies have demonstrated the utility of ultrasonic extraction (UE), followed by portable anodic stripping voltammetry (ASV), for the on-site determination of lead in environmental and industrial hygiene samples. The aim of this work was to conduct an interlaboratory evaluation of the UE-ASV procedure, with a goal of establishing estimates of method performance based on results from collaborative interlaboratory analysis. In this investigation, performance evaluation materials (PEMs) with characterized lead concentrations were used for interlaboratory testing of the UE-ASV procedure. The UE-ASV protocol examined has been promulgated in the form of two separate national voluntary consensus standards (one for UE and another for electroanalysis, which includes ASV). The PEMs consisted of characterized and homogenized paints, soils, and dusts (the last of which were spiked onto wipes meeting national voluntary consensus standard specifications), and air filter samples (mixed cellulose ester membrane) generated using characterized paints within an aerosol chamber. The lead concentrations within the PEMs were chosen so as to bracket pertinent action levels for lead in the various sample matrices. The interlaboratory evaluation was conducted so as to comply with an applicable national voluntary consensus standard that can be used to estimate the interlaboratory precision of a given analytical test method. Based on the analytical results reported by the participating laboratories, relative standard deviations (RSDs) for repeatability and reproducibility were computed for three different lead contents of the four PEMs. RSDs for repeatability were 0.019-0.100 for paints; 0.030-0.151 for soils; 0.085-0.134 for dust wipes; and 0.095-0.137 for air filters. RSDs for reproducibility were 0.127-0.213 for paints; 0.062-0.162 for soils; 0.085-0.134 for dust wipes; and 0.114-0.220 for air filters. With the exception of one of the air filter samples and one of the paint samples, the precision estimates were within the +/- 20% precision requirement specified in the US Environmental Protection Agency National Lead Laboratory Accreditation Program (NLLAP). The results of this investigation illustrate that the UE-ASV procedure is an effective method for the quantitative measurement of lead in the matrices evaluated in this study.

Air Pollution, Indoor↗

PubMed2005

Intra and interobserver variability of renal allograft ultrasound volume and resistive index measurements.

PURPOSE: Aim of the present study was to evaluate the repeatability and reproducibility of the Doppler Resistive Index (R.I.) and the Ultrasound renal volume measurement in renal transplants. MATERIALS AND METHODS: Twenty-six consecutive patients (18 men, 8 women) mean age of 42,8+/-12,4 years (M+/-SD) (range 22-65 years) were studied twice by each of two trained sonographers using a color Doppler ultrasound scanner. Twelve of them had a normal allograft function (defined as stable serum creatinine levels = or <123,76 micromol/L), whilst the remaining 14 had decreased allograft function (serum creatinine 132.6-265.2 micromol/L). Results were given as mean of 6 measurements performed at upper, middle and lower pole of the kidney. Intra- and interobserver variability was assessed by the repeatability coefficient and coefficient of variation (CV). RESULTS: Regarding Resistive Index measurement, repeatability coefficient was between 0.04 and 0.06 and the coefficient of variation was <5%. The analysis of the Student's t test did not show any significant difference between the measurements (t=0.15; p=0.87 n.s.). A good reproducibility was also detected in US measurements of renal length and volume. CONCLUSIONS: These results suggest that Color Doppler Resistive Index measurements of renal allograft and Ultrasound renal volume measurements are repeatable and reproducible.

Adult↗

PubMed1988

Collaborative evaluation in seven laboratories of a standardized micromethod for yeast susceptibility testing.

The new micromethod for yeast susceptibility testing, MYCOTOTAL, was evaluated with 10 reference strains in seven laboratories. Ready-to-use microtitration plates and the same synthetic medium were used with two dilutions of imidazoles, flucytosine, and amphotericin B, permitting the categorization of each strain as susceptible, intermediate, or resistant. The results were compared with the MIC for each reference strain, and the repeatability and reproducibility were evaluated. The yeasts tested presenting different patterns of susceptibilities in reference MICs included six strains of Candida albicans, two strains of Candida tropicalis, one strain of Candida parapsilosis, and one strain of Torulopsis glabrata. For 4,200 antifungal agent-yeast results, the repeatability was 99.3% and the reproducibility was 96.3%. The correlation between the reference MICs and the category results was 91.5% for seven laboratories (and 92.7% for six laboratories excluding the laboratory which did not follow exactly the same protocol). We observed only 7.9% minor discrepancies, 0.5% (0.29% for six laboratories) major discrepancies, and 0.1% uninterpretable results. The percentages of concording results were similar for each strain and each antifungal agent tested. The overall results indicated that MYCOTOTAL was a reliable and reproducible method, well correlated with reference MICs. This ready-to-use micromethod with the same medium for all antifungal agents would be an important step in the necessary standardization of yeast susceptibility testing.

Antifungal Agents↗

PubMed2001

Comparison of frequency doubling perimetry and standard achromatic computerized perimetry in patients with glaucoma.

PURPOSE: To evaluate the reproducibility and efficacy of frequency-doubling perimetry (FDP), a new perimetric method for the detection of functional glaucomatous damage. METHODS: Thirty-four glaucomatous eyes of 34 patients were examined by FDP (using the complete N30 threshold test of the Humphrey Frequency Perimeter) and by standard achromatic computerized perimetry (SAC; using the full threshold program 30-2 of the Humphrey Field Analyzer). Twenty-six of these eyes were examined twice by FDP. Reproducibility of repeated FDP was tested by the difference and the average of mean deviations (MD). Efficacy was studied by comparison of FDP and SAC using MD, as well as threshold results of FDP and corresponding SAC-tested areas. Spearman's rank correlation was calculated. RESULTS: A significant correlation of repeated FDP examinations was found regarding MD [r=0.94, P<0.00001 (n=26)]. The reproducibility of FDP was independent of the glaucomatous damage [r=0.04, P=0.85 (n=26)], based on the correlation of the difference, and the average of MD. The MD of FDP and that of SAC showed a significant correlation [r=0.87, P<0.00001 (n=34)]. In advanced glaucoma, FDP tended to yield lower measurement values than SAC. Regarding corresponding areas, there was a significant correlation between threshold results of FDP-tested areas and the corresponding SAC testpoints [r=0.92, P<0.00001 (n=34)]. The conformity decreased from the peripheral to the central tested visual field. CONCLUSIONS: Sufficient reproducibility of FDP could be demonstrated in early and advanced glaucomatous visual field defects. Conformity between FDP and SAC was shown in terms of MD and threshold results of FDP-tested areas and corresponding SAC testpoints.

Aged↗

PubMed2002

A prospective study of serum bile acid concentrations and colorectal cancer risk in post-menopausal women on the island of Guernsey.

Secondary bile acids produced by the action of the colonic microflora may increase risk of colorectal cancer. Serum bile acid concentrations reflect the faecal bile acid profile and may be of value as biomarkers of risk of colorectal cancer. In a pilot investigation we examined: (i) the reproducibility of measurements of serum bile acids in two blood samples collected several years apart; and (ii) the hypothesis that relatively high levels of secondary bile acids, particularly deoxycholic acid, would be positively associated with an increased risk of colorectal cancer in a prospective study of 3680 women in Guernsey. There was poor reproducibility between repeat measurements of absolute serum concentrations of bile acids, but there was moderately good reproducibility for the ratios of serum concentrations of deoxycholic/cholic acid, lithocholic/chenodeoxycholic and secondary/primary bile acid concentrations (duplicate blood samples were available for 30 women). There were no significant differences in ratios of serum secondary to primary bile acids or in absolute concentrations of bile acids between the 46 women who developed colorectal cancer and their matched controls, although there was a suggestion that an increased risk was associated with a high ratio of deoxycholic/cholic acid (relative risk in top third compared to lower third=3.92 (95% CI 0.91-17.0, P for trend=0.096). These findings suggest that the ratios of serum bile acid concentrations are sufficiently reproducible for epidemiological studies, but that a larger study than our own is needed to adequately test the hypothesis of their relation to cancer risk.

Adult↗

PubMed2004

Local round robin test for determination of aromatics in diesel fuels by HPLC.

Determination of aromatics in diesel fuels by HPLC is covered by European Standard EN 12916 (April 2000). The Standard is based on former standards IP 391/90 and IP 391/95. The method used for measurements is NP HPLC and separation is performed on silica or modified silica columns with RI detection. The precision of the method was checked by determining the repeatability and reproducibility. The content of aromatics was measured in a number of commercial samples. The measurements have been performed in three different laboratories and under different working and instrumental conditions. Satisfactory agreement was established for repeatability and was slightly poorer for reproducibility. The content of polyaromatics is within the tolerance range (IP 590/99) and the content of tricyclic and higher aromatics (tri+) is close to the limit of quantitition in some samples. Clear differences in the content of polycyclic aromatics in domestic diesel and eurodiesel fuels were observed. The results have confirmed the ruggedness and robustness of the measuring method.

Journal Article↗

PubMed1992

Non-modulation as an intermediate phenotype in essential hypertension.

Non-modulation is a trait characterized by abnormal angiotensin-mediated control of aldosterone release and the renal blood supply. To determine whether non-modulation defines a specific subgroup of the hypertensive population and its utility as an intermediate phenotype, we have studied the distribution of this quantitative trait, whether its features are reproducible on repeated testing, and whether there is concordance of its multiple features. Essential hypertensive patients (224) and normotensive subjects (119) received an infusion of angiotensin II (Ang II) at 3 ng.kg-1.min-1 for 30-45 minutes. p-Aminohippurate (PAH) clearance was assessed as an index of renal plasma flow while the subjects were on a 200 meq sodium diet; plasma aldosterone levels were measured while the subjects were on a 10 meq sodium diet. In 54 subjects, diuretic-induced volume depletion superimposed on a low salt diet was substituted for the Ang II infusion. The results of each study were submitted to maximum likelihood analysis to assess bimodality. In response to both diuretic-induced volume depletion (p < 0.000023) and Ang II infusion (p < 0.0009), aldosterone responses were bimodally distributed in the essential hypertensive but not in the normotensive subjects, suggesting that this trait identifies a discrete subgroup. In the 59 subjects who had both an adrenal and renal study, 50 (85%) were concordant. Finally, in 27 subjects studied two to six times over a span of 1-60 months, the intraclass correlations of the adrenal, PAH, or both responses were highly significant (p values between 0.001 and 0.00007), indicating high reproducibility of results on repeated testing.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗

PubMed2001

Evaluation of the oxidative stress in growing pigs by microplate assays.

The ability of pigs to neutralize the reactive oxygen species (ROS) plays a key role in their welfare. Two micromethods were developed to evaluate the oxidative stress and the anti-oxidative response in sera. We tested these methods for linearity, repeatability and reproducibility. A hydroxyl radicals (HR) test, based on the Fenton reaction, showed a linearity between 0.26 and 4.5 mM H2O2 (r = 0.997), with a coefficient of repeatability (CVr) of 1.9 and a coefficient of reproducibility (CVR) of 2.9. An anti-oxidant power (AOP) test, based on the capability of sera to neutralize a titred hypochlorous acid solution (HClO), showed a linearity between 55 and 880 microM HClO neutralized (r = 0.984), with CVr = 3.1 and CVR = 4.9. We assessed the applicability of such tests in field conditions on three different farms. Farm A recorded a positive anamnesis of Mulberry heart disease. Dietary Vitamin E supplementation was given at 50 p.p.m. in farms A and B and at 150 p.p.m. in farm C, respectively. The group from farm A showed HR sera levels higher than those of farm B and farm C (farm A, mean = 31.61 +/- 2.87 mM H2O2, n = 10; farm B, 28.53 +/- 2.30, n = 10; and farm C, 25.63 +/- 1.03, n = 10; P < 0.01). The AOP test was not able to discriminate between farms. The AOP levels found (mean = 472.50 microM HClO neutralized: n = 30) probably represent the maximum response of the organism to compensate the oxidative stress. HR and AOP are stable in sera stored at +4 degrees C. We discuss the application of such methods for the assessment of farmed animals' welfare.

Animals↗

PubMed1996

Arterial baroreflex sensitivity assessed from phase IV of the Valsalva maneuver.

To assess the feasibility of 2 noninvasive methods for arterial baroreflex sensitivity testing based on phase IV of the Valsalva maneuver, the performance of a simple arterial baroreflex sensitivity index compared with a slope method and reproducibility of repeated measurements of either parameter were evaluated in 36 subjects without structural heart disease. The study showed feasibility and reproducibility of both these methods for arterial baroreflex sensitivity assessment and demonstrated the importance of an appropriate rest period between repeated Valsalva maneuvers, giving a basis for prospective testing of noninvasive determination of arterial baroreflex sensitivity together with phenylephrine method in survivors of myocardial infarction.

Adolescent↗

PubMed2004

Intra- and interlaboratory calibration of the DR CALUX bioassay for the analysis of dioxins and dioxin-like chemicals in sediments.

In the Fourth National Policy Document on Water Management in The Netherlands, it is defined that in 2003, in addition to the assessment of chemical substances, special guidelines for the assessment of dredged material should be recorded. The assessment of dredged material is based on integrated chemical and biological effect measurements. Among others, the DR CALUX (dioxin responsive-chemically activated luciferase expression) bioassay has tentatively been recommended for inclusion in the dredged material assessment. To ensure the reliability of this bioassay, an intra- and interlaboratory validation study, or ring test, was performed, organized by the Dutch National Institute for Coastal and Marine Management (RIKZ) in cooperation with BioDetection Systems BV (BDS). The intralaboratory repeatability and reproducibility and the limit of detection (LOD) and quantification (LOQ) of the DR CALUX bioassay were determined by analyzing sediment extracts and dimethyl sulfoxide (DMSO) blanks. The highest observed repeatability was found to be 24.1%, whereas the highest observed reproducibility was calculated to be 19.9%. Based on the obtained results, the LOD and LOQ to be applied for the bioassay are 0.3 and 1.0 pM, respectively. The interlaboratory calibration study was divided into three phases, starting with analyzing pure chemicals. During the second phase, sediment extracts were analyzed, whereas in the third phase, whole sediments had to be extracted, cleaned, and analyzed. The average interlaboratory repeatability increased from 14.6% for the analysis of pure compound to 26.1% for the analysis of whole matrix. A similar increase in reproducibility with increasing complexity of handlings was observed with the interlaboratory reproducibility of 6.5% for pure compound and 27.9% for whole matrix. The results of this study are intended as a starting point for implementing the integrated chemical-biological assessment strategy and for systematic monitoring of dredged materials and related materials in the coming years.

Animals↗

PubMed1994

Method validation in relation to accuracy and precision for the gas chromatography-mass spectrometric analysis of 19-nortestosterone in urine with heptafluorobutyric anhydride and N-methyl-N-(trimethylsilyl)trifluoroacetamide.

Method validation for all the analytical methods used in food control is of the highest priority. For this control there is a lack of reference materials, thus, it is necessary to validate the methods each time they are used for new applications. Among the many aspects of validation, this report pays particular attention to repeatability and reproducibility. The within-assay variability gives a good indication of the precision of the method shown by the repeatability. The between-assay variability gives no indication on the accuracy (or trueness) because no certified reference material is available. The reproducibility however, also gives an indication of the precision of the method. In this work the limit of detection, also an aspect of validation, was found to be below 0.375 micrograms 1-1 for both derivatization methods; however, the precision of the heptafluorobutyric anhydride method was found to be better than that of the N-methyl-N-(trimethylsilyl)trifluoroacetamide method.

Acetamides↗

PubMedDate not supplied

Mechanism of thrombin-induced endothelium-dependent coronary vasodilation in dogs: role of its proteolytic enzymatic activity.

We have recently reported that exogenous thrombin produced a dose- and endothelium-dependent coronary vasodilation in both intact open-chested dogs and in isolated dog coronary artery preparations. To determine whether the observed vasodilatory effect may be related to thrombin proteolytic enzymatic activity, effects of other proteases, such as trypsin, chymotrypsin, and pepsin, on the mechanical responses of isolated dog coronary arteries were studied. Among the four proteases evaluated, only thrombin (0.01-0.1 U/ml) and trypsin (0.03-0.67 U/ml) consistently produced a potent dose- and endothelium-dependent relaxation, that was reproducible with repeated testings. Addition of chymotrypsin (0.01-1.0 U/ml) produced only a minimal effect and was not reproducible, while addition of pepsin, as much as 10 U/ml, did not produce any effect. The specific soybean trypsin inhibitor and aprotinin, but not heparin and hirudin, competitively shifted the trypsin dose-response to the right, whereas heparin, hirudin, and antithrombin III proved to be more effective than trypsin inhibitors in inhibiting the thrombin-induced vasodilation. In all cases, the thrombin- and trypsin-induced vasodilation were equally sensitive to inhibition by the specific synthetic thrombin inhibitor, PPACK (D-phenylalanyl-L-propyl-L-arginine chloromethyl ketone, 1-30 nM). PPACK, however, had no effect on the other endothelium-dependent coronary vasodilators, such as acetylcholine and adenosine triphosphate, in our isolated dog coronary artery preparations. Biochemical determinations of the amidolytic activity of thrombin, using Tosylglycyl-L-prolyl-L-arginine-p-nitroanilide as a chromogen, also indicated a similar PPACK and heparin-antithrombin III dose-dependent inhibition of the thrombin enzymatic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Chloromethyl Ketones↗

PubMed1997

Incremental threshold loading: a standard protocol and establishment of a reference range in naive normal subjects.

Incremental threshold loading (ITL) has been proposed as a test of inspiratory muscle strength and endurance. To date, however, there has been no standardized protocol for an ITL test, and no reference range, with different investigators using a variety of different pressure increments in small numbers of subjects. We developed an ITL test using the weighted plunger (WP) principle, which uses standard increments of pressure. In our protocol subjects inspire through the WP generating an initial threshold opening pressure of 10 cmH2O. This pressure is raised at 2 min intervals in increments of 5 cmH2O until they fail to lift the plunger on two consecutive attempted breaths. Sixty healthy volunteers (30 males and 30 females) aged 20-80 yrs performed the ITL test. Twelve subjects (six females and six males) performed the test twice to assess reproducibility and repeatability. Using stepwise multiple linear regression, we regressed the maximum threshold pressure sustained for a full 2 min (Pmax) against age, height, weight and static maximum inspiratory mouth pressure (MIP). Pmax was significantly related to age but not to either height or weight, the regression equation for males was Pmax (cmH2O)=103.8 - (1.0 x age in years), and for females was Pmax (cmH2O)=93.7 - (1.0 x age in years). The within-subject standard deviation for those repeating the ITL test was 5.4 cmH2O. Incremental threshold loading is a simple technique with good reproducibility, which most naive subjects can use without difficulty. By using standard pressure increments and performing the test in a large number of naive subjects, we have established a reference range that should be applicable wherever similar pressure increments are used.

Adult↗