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At least 595 records · Page 33Linked to original sources
PubMed1980

A technique for kinematic modeling of anatomical joints.

This paper describes a general technique for fitting a spatial kinematic model to an in-vivo anatomical joint under typical physiological loading conditions. The method employs a nonlinear least squares algorithm to minimize the aggregate deviation between postulated model motion and experimentally measured anatomical joint motion over multiple joint positions. Estimation of the parameters of a universal joint with skew-oblique revolutes to best reproduce wrist motion was used as an example. Experimental motion data from the right wrists of five subjects were analyzed. The technique performed very well and produced repeatable results consistent with previous biomechanical wrist findings.

Biomechanical Phenomena↗
PubMed1978

Effects of lung inflation on pulmonary arterial pressure in dogs with pulmonary edema.

The effects of lung inflation from positive airway pressure (Paw) on pulmonary arterial pressure (Ppa) and the slope deltaPpa/deltaPaw were studied in normal dogs and dogs with pulmonary edema. Under base-line zone 2 conditions with the lungs perfused at constant flow (100 ml/kg per min) and vascular pressures measured relative to pleural (atmospheric) pressure, the slope deltaPpa/deltaPaw was nearly one (at Paw greater than or equal to 5 cmH2O). Pulmonary edema from high capillary pressure and oleic acid caused deltaPpa/deltaPaw and Ppa to decrease at high lung volumes and Ppa to increase at low lung volumes. These changes were not simulated by vasoactive drugs (adenosine and norepinephrine) but were reproduced by instilling dextran into the lungs and, in part, by occluding the right intermediate bronchus. In pulmonary edema the increased Ppa at low lung volumes is caused by the effects of decreases in the caliber of extra-alveolar vessels, by trapped air or liquid raising alveolar pressure, or by both; the decreased deltaPpa/deltaPaw and Ppa at high volumes is caused mainly by nonuniform distribution of driving pressures and blood flow.

Adenosine↗
PubMed2006

Suppression of extinction with TMS in humans: from healthy controls to patients.

We review a series of studies exemplifying some applications of single-pulse and paired-transcranial magnetic stimulation (TMS) in the study of spatial attention and of its deficits. We will focus primarily on sensory extinction, the failure to consciously perceive a contralesional sensory stimulus only during bilateral stimulation of homologous surfaces. TMS studies in healthy controls show that it is possible either to interfere or modulate the excitability of the parietal cortex during sensory (i.e. tactile and visual) attentional tasks, thus reproducing a condition of virtual extinction. TMS studies in patients with unilateral (mainly right) brain damage show that the modulation of the unbalance in cortical excitability between the two cerebral hemispheres transiently improves contralesional sensory extinction. These studies show the possible application of TMS not only as a research method in healthy subjects, but also as a tool for inducing brain excitability changes in patients with sensory extinction, which could be useful for supporting the rehabilitation of this deficit.

Extinction, Psychological↗
PubMed1986

Atrial natriuretic peptide inhibits the stimulation of aldosterone secretion by ACTH in vitro and in vivo.

Previous studies have shown that atrial natriuretic peptide (ANP) inhibits the secretion of aldosterone by isolated adrenal glomerulosa cells stimulated by angiotensin II, ACTH and potassium in vitro and by angiotensin II in conscious unrestrained rats. In this study we investigated further the effects of synthetic ANP on the dose-response curve of aldosterone secretion stimulated by ACTH in vitro. ANP displaced the dose-response curve of aldosterone to ACTH to the right with a significant change in EC50. A similar effect of ANP was reproduced in vivo in conscious unrestrained rats. There was no significant effect of ANP on the corticosterone response to ACTH in vivo. ANP is a potent regulator of aldosterone secretion which may modulate the effects of ACTH on the adrenal in vitro and in vivo.

Adrenal Cortex↗
PubMed1991

[Precise mucostatic primary impression taking in the edentulous mandible. Hemi-arch method].

The author has shown that any impression material and its support in the mouth must be more malleable than the material used for the object to be reproduced. From a fall mandibular arch the impression of both sides, left and right, are taken successively by hemi-impressions without impression trays. Two individual half impression trays are made, placed in the mouth and are joined together using an auto-polymerizing resin. The resulting individual tray permits to make a perfect mucostatic impression. This method, far from taking more time, is a time saver, since the touch-ups to the individual tray and then to the finished prosthesis are practically non-existent or considerably reduced.

Dental Impression Technique↗
PubMed2000

Pain threshold measurements with cutaneous argon laser, comparing a forced choice and a method of limits.

1. With the argon laser technique cutaneous nociceptors can be activated with high specificity and reproducibility making it a useful tool in psychophysical pain studies. This study was designed to examine and compare two different psychophysical methods combined with the argon laser technique. 2. Pain thresholds on different locations of the body and on different skin types were measured with (i) the method of limits and (ii) the forced choice method. 3. A significant correlation between the pain thresholds measured with the two different methods was detected on feet and hands. The method of limits yielded significantly higher pain thresholds in glabrous skin than hairy skin. Higher pain thresholds were also detected on the right side of the body. No statistically significant difference between sexes was found. A high reproducibility over time as well as in-between investigators was found for the method of limits. 4. Its concluded that the argon laser for pain threshold measurement with the method of limits is useful and preferred to the forced choice, since the method of limits is easier to perform and also less time consuming.

Adolescent↗
PubMed1995

How reliable are ultrasound measurements of renal length in adults?

Ultrasound assessment of patients with renal impairment commonly includes measurement of bipolar renal length. Reduction in length is considered to indicate chronic renal disease and is a factor in deciding whether to proceed to renal biopsy. To date, no published data are available on interobserver and intraobserver variation in sonographic renal length measurement in adults. Bilateral renal lengths were measured in 20 adult subjects, with no history of renal disease, by three experienced operators, on two separate occasions. Limits of agreement for replicate measurements by each ultrasonographer and for replicate measurements by each pair of ultrasonographers were determined. Values of repeatability (a measure of intraobserver variation) and reproducibility (a measure of interobserver variation) were calculated for all renal length measurements, and for right and left renal lengths separately. Results indicate that replicate renal length measurements differ by less than 1.85 cm in 95% of cases, and the magnitude of variations is similar when measurements are made by either single or different ultrasonographers, and are similar for right and left renal length measurements. This suggests that sonographic bipolar renal length measurements in normal adult kidneys are reasonably reliable. In diseased kidneys, however, in which identification of renal poles is difficult, interobserver and intraobserver variation may be much greater.

Adult↗
PubMed1995

Quantification of right ventricular function with magnetic resonance imaging in children with normal hearts and with congenital heart disease.

In clinical treatment of children with congenital heart disease (CHD) assessment of right ventricular (RV) function is important. Available imaging techniques have been of limited value because of technical factors and the complex geometry of the right ventricle. To validate magnetic resonance (MR) imaging measurements of RV function in children, gradient echo MR imaging of both ventricles and MR flow mapping of great vessel and tricuspid flow was performed in 20 children with CHD affecting the right ventricle and in 22 healthy children ranging in age from 5 to 16 years. Close correlation between RV versus LV stroke volumes (r = 0.96) and RV stroke volume versus great artery (r = 0.97) or tricuspid flow (r = 0.97) was observed with small interobserver and intraobserver variability. Results of healthy children were end-diastolic volume: 70 +/- 9 ml/m2, end-systolic volume: 21 +/- 5 ml/m2, and ejection fraction: 70% +/- 4%. In the patient groups clinically important differences were noted. We conclude that MR imaging provides accurate noninvasive measurements of RV function in healthy children and patients with (operated) CHD.

Adolescent↗
PubMed1982

Transcutaneous PO2 measurements in health and peripheral arterial occlusive disease.

Transcutaneous oxygen tensions (tcPO2) of the lower extremity were investigated in 24 control subjects and in 69 patients with various degrees of peripheral arterial occlusive disease. With a modified Clark-type oxygen electrode, tcPO2 was monitored from the right subclavicular region (position 1), upper calf (position 2), and dorsum of the foot (position 3). The tcPO2 was significantly lower in patients when compared to control subjects. The reproducibility of the method was determined from double determinations of the tcPO2 (position 2) in control subjects. The comparison of tcPO2 value between the right and left lower extremity showed no significant differences. The tcPO2 of the foot or leg showed an increase, when positioning the limb below the phlebostatic level. The response of the tcPO2 after transient arterial occlusion (4 minutes) was significantly delayed in patients compared to control subjects. Finally, preliminary results of 35 patients in whom amputations had been performed suggest that tcPO2 measurement may become a useful prognosticator for the determination of the optimal amputation level.

Adult↗
PubMed1997

Fixation of the acetabular component. The case for cement.

The long-term success rate of cemented sockets in total hip arthroplasty has been well documented in patients who are 60 years of age and older and who have had a followup of as many as 16 years. The failures with cemented sockets have been observed in young patients, patients with poor bone stock (rheumatoid and dysplastic hips) with metal backed components, and in revision surgery with loss of acetabular bone. Ranawat et al have shown that most mechanical failures of cemented socket fixation within 10 years of primary operation is attributable to failure to achieve a good fixation initially of the cement and bone. Volumetric wear of the polyethylene of a cemented socket against a 22- or 28-mm femoral head is compared with the metal backed cemented and noncemented cups. The increase in volumetric polyethylene particles with metal backed cemented sockets and noncemented sockets will induce histiocytic response. The mechanism of histiocytic invasion should be similar for cemented all polyethylene sockets and noncemented sockets. It manifests itself in the cemented socket as global radiolucency when the socket is loose and as osteolysis when it is well fixed for noncemented and cemented sockets. If the number of particles coming out in a noncemented and hybrid total hip replacement are greater, osteolysis would be expected to increase with longer followup. The technique of cemented polyethylene sockets requires organization of the surgical team and hypotensive epidural anesthesia. Under these conditions the procedure is very reproducible. As far as cost is concerned, the all polyethylene socket is significantly less expensive. It seems that cemented total hip replacement is most suitable and perhaps is the right kind of operation for treating osteoarthritis of the hip for patients who are 60 years of age and older because the procedure is reproducible, the quality of arthroplasty is excellent, and it is durable, lasting as many as 15 years in 90% to 95% of the cases.

Acetabulum↗
PubMed1993

Rat tail flick reflex: magnitude measurement of stimulus-response function, suppression by morphine and habituation.

1. To quantitatively investigate a nocifensive behavioral response, we developed a method to measure the magnitude of the rat's tail flick reflex and its modulation. A radial array of force transducers measured forces of tail flicks (in rostral, horizontal, and vertical planes) elicited by graded noxious radiant thermal stimulation of the conscious rat's tail, from which the overall movement vector was calculated. 2. The rostrally directed component of tail flicks was always larger than dorsal or horizontal components; the latter was usually in a preferred (left or right) direction regardless of which side of the tail was heated. Tail flick force vectors increased from 40 to 46-52 degrees C and then leveled off. Stimulus-response functions were reproducible within and across rats and were fitted by second-order polynomial functions, whose correlation coefficients were similar when the left or right side of the tail was stimulated in separate sessions (r2 = 0.408 and 0.451, respectively). The inverse latency of tail flicks also increased with temperature in a manner fitted by a second-order polynomial (r2 = 0.707, 0.553 for left and right side, respectively). 3. Systemic administration of morphine (1 or 2 mg/kg ip) usually suppressed tail flicks in an all-or-none manner; i.e., flicks at all stimulus temperatures were either totally abolished (n = 7) or unaffected (n = 5) after morphine. In three rats, 1 mg/kg morphine suppressed tail flick magnitude subtotally, reducing the slope of the linear portion of the stimulus-response function. Morphine effects were reversed by the opiate antagonist naloxone. 4. Tail flick magnitude decreased over repeated trials of 44 degrees C heat stimuli delivered to one tail site, recovered after a 15-min rest period, and decremented more quickly with subsequent stimulus repetition. The decrement was less at long (2 or 4 min) than at short (1 min) interstimulus intervals, and high (50 degrees C) than at low (44 degrees C) stimulus intensities. The reflex decrement transferred to a nearby stimulus site in some rats, and was "dishabituated" after a noxious tail pinch. These observations are consistent with habituation of the tail flick reflex. 5. This method, therefore, provides a quantitative and reproducible measure of tail flick reflex magnitude that is sensitive to morphine. The underlying neural circuitry of the tail flick reflex is discussed in relation to limb withdrawal reflexes.

Afferent Pathways↗
PubMed1987

Variability and reproducibility of morphologic findings in endomyocardial biopsies of patients with hypertrophic obstructive cardiomyopathy.

Morphometric investigations of endomyocardial catheter biopsies (EMCB) promise to give more insight in the morphologic-functional relationship in patients with hypertrophic obstructive cardiomyopathy (HOCM), and may disclose the morphologic course of the disease. Variability and reproducibility of morphologic findings in EMCB of patients with HOCM are still undefined. We investigated 112 right ventricular biopsies of 25 patients with HOCM of a mean age of 38.3 +/- 15.2 years (six women, 19 men). Mean EMCB size was 0.755 +/- 0.567 mm2. 28.6% of EMCB were not suitable for morphometric investigation. Variability of morphologic findings was investigated by analysis of variance and described by the coefficient of variation (CV). Sampling variabilities of muscle fiber diameter (CV = 5%), volume density of interstitium (CV = 9%) and fibrous tissue (CV = 17%) differed. Reproducibility in terms of intra- and interobserver variations for these variables reached a comparable level, diminishing observed differences between biopsies from the same heart, which became non-significant. Sampling variability of endocardial thickness (CV = 79%) and muscle fiber disarray (CV = 100%) were higher than intra- and interobserver variations. For an estimate of muscle fiber size, one EMCB specimen is sufficient, three for volume density of interstitium and nine for fibrous tissue. High sampling variability of endocardial thickness and muscle fiber disarray demand numerous biopsies; here the greatest measured value from a few biopsies may be of more clinical relevance. From our data, five EMBC are desirable, and give the most information at an acceptable strain.

Adult↗
PubMed2002

Expression profiling of Drosophila imaginal discs.

BACKGROUND: In the Drosophila larva, imaginal discs are programmed to produce adult structures at metamorphosis. Although their fate is precisely determined, these organs remain largely undifferentiated in the larva. To identify genes that establish and express the different states of determination in discs and larval tissues, we used DNA microarrays to analyze mRNAs isolated from single imaginal discs. RESULTS: Linear amplification protocols were used to generate hybridization probes for microarray analysis from poly(A)+ RNA from single imaginal discs containing between 10,000 and 60,000 cells. Probe reproducibility and degree of representation were tested using microarrays with approximately 6,000 different cDNAs. Hybridizations with probes that had been prepared separately from the same starting RNA pool had a correlation coefficient of 0.97. Expression-profile comparisons of the left and right wing imaginal discs from the same larva correlated with a coefficient of 0.99, indicating a high degree of reproducibility of independent amplifications. Using this method, we identified genes with preferential expression in the different imaginal discs using pairwise comparisons of discs and larval organs. Whereas disc-to-disc comparisons revealed only moderate differences, profiles differed substantially between imaginal discs and larval tissues, such as larval endodermal midgut and mesodermal fat body. CONCLUSIONS: The combination of linear RNA amplification and DNA microarray hybridization allowed us to determine the expression profiles of individual imaginal discs and larval tissues and to identify genes expressed in tissue-specific patterns. These methods should be widely applicable to comparisons of expression profiles for tissues or parts of tissues that are available only in small amounts.

Animals↗
PubMed2006

A percutaneous swine model of myocardial infarction.

INTRODUCTION: The aim of this study was to develop a percutaneous, low risk, and reproducible technique of MI that simulates human disease. METHODS: MI was induced in 44 swine (32.8+/-7.2 kg) by percutaneous embolization coil deployment in the left anterior descending coronary artery. Hemodynamic measurements, left heart catheterization, and echocardiography were performed pre, post, and 30 days after MI. 3D NOGA viability mapping was performed at baseline and 30 days. Excised hearts were examined histologically. RESULTS: Pre-MI mortality was 6.8% and 24 h mortality was 13.6%. All pigs that survived 24 h after MI remained alive at 30 days. The mean left ventricular ejection fraction decreased from 58.4% to 42.1% (p<0.001) at 30 days. The average thrombolysis in myocardial infarction score was 3, 0, and 1.5 at baseline, post-MI, and 30 days, respectively. At 30 days, the end diastolic diameter, end diastolic volume, end systolic volume, and wall motion index increased from 3.76 to 3.89 cm, 32.5 to 50.0 ml, 14.9 to 27.0 ml, and 1.01 to 1.38, respectively (all p<0.05), while the ejection fraction decreased from 56.5% to 49.4% (p<0.01). Additionally, at 30 days, statistically significant reductions in both unipolar and bipolar voltage in the mid and apical regions of the left ventricle were observed. Postmortem pathology showed a transmural scar in the apical anteroseptal regions with fibrosis in the MI region, which accounted for 14.8% and 14.2% of the total left and right ventricular myocardial area and volume, respectively. DISCUSSION: This model of MI is reliable, reproducible, has a pathophysiology similar to humans, and a lower mortality and ventricular fibrillation rates compared to other models. This model may be used to evaluate the effects of pharmacologics, gene therapy, and stem cell transplantation for the treatment of cardiovascular disease as well as studying mechanisms of cardiac remodeling.

Angiography↗
PubMed2005

Reproducible clusters from microarray research: whither?

MOTIVATION: In cluster analysis, the validity of specific solutions, algorithms, and procedures present significant challenges because there is no null hypothesis to test and no 'right answer'. It has been noted that a replicable classification is not necessarily a useful one, but a useful one that characterizes some aspect of the population must be replicable. By replicable we mean reproducible across multiple samplings from the same population. Methodologists have suggested that the validity of clustering methods should be based on classifications that yield reproducible findings beyond chance levels. We used this approach to determine the performance of commonly used clustering algorithms and the degree of replicability achieved using several microarray datasets. METHODS: We considered four commonly used iterative partitioning algorithms (Self Organizing Maps (SOM), K-means, Clutsering LARge Applications (CLARA), and Fuzzy C-means) and evaluated their performances on 37 microarray datasets, with sample sizes ranging from 12 to 172. We assessed reproducibility of the clustering algorithm by measuring the strength of relationship between clustering outputs of subsamples of 37 datasets. Cluster stability was quantified using Cramer's v2 from a kXk table. Cramer's v2 is equivalent to the squared canonical correlation coefficient between two sets of nominal variables. Potential scores range from 0 to 1, with 1 denoting perfect reproducibility. RESULTS: All four clustering routines show increased stability with larger sample sizes. K-means and SOM showed a gradual increase in stability with increasing sample size. CLARA and Fuzzy C-means, however, yielded low stability scores until sample sizes approached 30 and then gradually increased thereafter. Average stability never exceeded 0.55 for the four clustering routines, even at a sample size of 50. These findings suggest several plausible scenarios: (1) microarray datasets lack natural clustering structure thereby producing low stability scores on all four methods; (2) the algorithms studied do not produce reliable results and/or (3) sample sizes typically used in microarray research may be too small to support derivation of reliable clustering results. Further research should be directed towards evaluating stability performances of more clustering algorithms on more datasets specially having larger sample sizes with larger numbers of clusters considered.

Cluster Analysis↗
PubMed1998

Isokinetic eccentric exercise as a model to induce and reproduce pathophysiological alterations related to delayed onset muscle soreness.

Physiological alterations following unaccustomed eccentric exercise in an isokinetic dynamometer of the right m. quadriceps until exhaustion were studied, in order to create a model in which the physiological responses to physiotherapy could be measured. In experiment I (exp. I), seven selected parameters were measured bilaterally in 7 healthy subjects at day 0 as a control value. Then after a standardized bout of eccentric exercise the same parameters were measured daily for the following 7 d (test values). The measured parameters were: the ratio of phosphocreatine to inorganic phosphate (PCr/Pi), the ratio of inorganic phosphate to adenosintriphosphate (Pi/ATP), the ratio of phosphocreatine to adenosintriphosphate (PCr/ATP) (all three ratios measured with 31P-nuclear magnetic resonance spectroscopy), dynamic muscle strength, plasma creatine kinase (CK), degree of pain and "muscle" blood flow rate (133Xenon washout technique). This was repeated in experiment II (exp. II) 6-12 months later in order to study reproducibility. In experiment III (exp. III), the normal fluctuations over 8 d of the seven parameters were measured, without intervention with eccentric exercise in 6 other subjects. All subjects experienced pain, reaching a maximum 48 h after eccentric exercise in both exp. I and II. A systematic effect over time for CK (increasing 278% resp. 308%), muscle strength (decreasing more than 10%), PCr/Pi (decreasing 31% resp. 43%) and Pi/ATP (increasing 55% resp. 99%) was found in both exp. I and II (P < 0.05), but not in exp. III. No significant difference was observed between exp. I and II for CK, blood-flow rate, concentric muscle strength, PCr/Pi, Pi/ATP and PCr/ATP. It is concluded that pathophysiological alterations in m. quadriceps following eccentric exercise can be induced and can be reproduced after an interval of 6 months. Thus, this model can be used to study the effects of physiotherapy.

Adenosine Triphosphate↗
PubMed1998

Determination of right ventricular structure and function in normoxic and hypoxic mice: a transesophageal echocardiographic study.

BACKGROUND: Noninvasive cardiac evaluation is of great importance in transgenic mice. Transthoracic echocardiography can visualize the left ventricle well but has not been as successful for the right ventricle (RV). We developed a method of transesophageal echocardiography (TEE) to evaluate murine RV size and function. METHODS AND RESULTS: Normoxic and chronically hypoxic mice (F(IO2)=0.11, 3 weeks) and agarose RV casts were scanned with a rotating 3.5F/30-MHz intravascular ultrasound probe. In vivo, the probe was inserted in the mouse esophagus and withdrawn to obtain contiguous horizontal planes at 1-mm intervals. In vitro, the probe was withdrawn along the left ventricular posterior wall of excised hearts. The borders of the RV were traced on each plane, allowing calculation of diastolic and systolic volumes, RV mass, RV ejection fraction, stroke volume, and cardiac output. RV wall thickness was measured. Echo volumes obtained in vitro were compared with cast volumes. Echo-derived cardiac output was compared with measurements of an ascending aortic Doppler flow probe. Echo-derived RV free wall mass was compared with true RV free wall weight. There was excellent agreement between cast and TEE volumes (y=0.82x+6.03, r=0.88, P<0.01) and flow-probe and echo cardiac output (y=1.00x+0.45, r=0.99, P<0.0001). Although echo-derived RV mass and wall thickness were well correlated with true RV weight, echo-derived RV mass underestimated true weight (y=0.53x+2.29, r=0.81, P<0.0001). RV mass and wall thickness were greater in hypoxic mice than in normoxic mice (0.78+/-0.19 versus 0.51+/-0.14 mg/g, P<0.03, 0.50+/-0.03 versus 0.38+/-0.03 mm, P<0.04). CONCLUSIONS: TEE with an intravascular ultrasound catheter is a simple, accurate, and reproducible method to study RV size and function in mice.

Animals↗