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PubMed2006

Carotid artery stent implantation: evaluation with multi-detector row CT angiography and virtual angioscopy--initial experience.

Approval for this HIPAA-compliant study was obtained from the institutional review board; informed consent was not required for retrospective review of patient studies that had been performed for clinical evaluation. The purpose of this study was to retrospectively compare the accuracy of intrastent luminal diameter, as measured on transverse computed tomographic (CT) angiograms and virtual angioscopic views, with the manufacturer's specifications for phantom diameter and with digital subtraction angiographic (DSA) measurements of stent diameter obtained in patients. Intrastent diameter was measured by using standard and stent-optimized reconstruction kernels with three window settings. Endoluminal virtual angioscopic views of the stent-containing vessels were also generated. Measurements at CT angiography were compared with known specifications for the phantom and with DSA measurements in patients. Erroneous measurements of intrastent diameter occurred when a standard kernel and nonoptimized window settings were used. A set of parameters that minimized error relative to measurements obtained at DSA was also identified. Virtual angioscopy helped demonstrate morphologic aspects of stenosis that were otherwise difficult to appreciate.

Aged↗

PubMed1977

Measurement of body temperature in neonatal mice.

A simple method is described for obtaining repeated measurements of body temperature in young mice with minimal error introduced through stress. Temperatures are measured by an external thermocouple attached to the thorax in the region of the heart. A sling around the animal's thorax provides insulation for the thermocouple from surrounding air and mild restraint of the animal during measurement. Comparison with temperatures obtained in other locations indicates that external thoracic temperature as described gives a reliable estimate of true body temperature in mice up to 21 days old. Typical results with normal mice aged 1 day to 6 wk postpartum are included, together with a brief discussion of the technique's applicability.

Age Factors↗

PubMed1982

Increased pulmonary microvasuclar permeability induced by alpha-naphthylthiourea.

The effects of alpha-naphthylthiourea (ANTU) on lung microvascular permeability to plasma proteins were studied in anesthetized open-chest dogs. Lymph flow (Jv) was recorded, and total protein in plasma and lymph was analyzed after cannulating a small prenodal lung lymphatic. The protocol involved four experimental periods. Period 1. During this base-line period the preparation stabilized and steady states were reached in Jv, lymph total protein, pulmonary arterial pressure (Ppa), and left atrial pressure (Pla). Period 2. Pla was increased to approximately 20 cmH2O and maintained at that level until Jv and protein measurements attained a new steady state. Period 3. After Pla was lowered to control levels, ANTU (5 mg/kg body wt) was infused intravenously and parameters were measured for 3 h. Period 4 Pla was again raised to the pre-ANTU levels of period 2 and maintained for an additional 2-3 h. The lymphatic total protein clearance increased 8.6-fold for an equivalent increase in pulmonary capillary pressure after ANTU. Vascular permeability was assessed by estimating the osmotic reflection coefficient (sigma d) for total protein at the pulmonary capillary membrane. Sigma d decreased from 0.65 to 0.40 following ANTU. From plasma protein fractions in four experiments, equivalent pore radii for the capillary membrane of 95 and 280 A were calculated after ANTU compared with 80 and 200 A for normal lung capillaries. In addition, extravascular lung water increased from 3.8 +/- 0.16 to 5.87 +/- 0.25 following ANTU and to 7.55 +/- 0.55 (g/g blood-free dry wt) when Pla was elevated with ANTU. The experimental design allowed quantitative assessment of the vascular permeability increase after ANTU by use of lymph protein fluxes that had minimal errors due to changes in surface area or lymph contamination from nonpulmonary structures.

Animals↗

PubMed1991

Short-term effect of tidal pleural pressure swings on pulmonary blood flow during rest and exercise.

Because pleural pressure (Ppl) has important effects on venous return and left ventricular function, it is possible that the magnitude of respiratory fluctuations in Ppl importantly influences cardiac output (pulmonary blood flow, QL) during exercise. To examine this question, we increased (+15 cmH2O) and decreased (-11 cmH2O) the amplitude of fluctuations in Ppl by elastic loading and unloading, respectively, during steady-state exercise (50 W) and estimated the corresponding changes in QL from measurement of breath-by-breath alveolar O2 consumption [(Vo2)A] by a modification of the technique of Beaver et al. (J. Appl. Physiol. 51: 1662-1675, 1981). Load changes were applied for three breaths. Using oscilloscopic volume feedback, subjects maintained constant breathing pattern and end-expiratory volume during control and experimental breaths. This procedure minimized errors in computing (Vo2)A. Furthermore, because over the brief period of load change (especially the first 1 or 2 breaths) mixed venous and arterial O2 contents were not likely to have changed, changes in (Vo2)A reflected changes in QL according to the Fick principle. In six normal subjects, neither loading nor unloading had any effect on (Vo2)A in the first, second, or third breath (P greater than 0.5). Additional studies at rest produced equally negative results. We conclude that the magnitude of respiratory fluctuations in Ppl has no short-term effect on pulmonary blood flow at rest or during mild exercise.

Adult↗

PubMed1990

Determination of right ventricular mass in humans and dogs with ultrafast cardiac computed tomography.

There is currently no clinical approach to precisely measure right ventricular (RV) mass. We postulated that the radiological mode of ultrafast computed tomography (CT) of 3-mm-thick slices with 0.7-mm resolution would allow sufficient resolution to accurately estimate RV mass. Using this radiological mode, we serially imaged the entire right ventricle from apex to base, gated to end diastole, and applied Simpson's rule to calculate mass of the RV free wall. Thirteen mongrel dogs (weight, 6-30 kg) were studied. The free wall mass of the right ventricle was in the range of 12.0-47.5 g and averaged 35.4 +/- 3.7 g (mean +/- SEE). The correlation between RV mass estimated by ultrafast CT and actual RV mass was r equaling 0.85, SEE equaling 5.5 g, slope equaling 0.99, and gamma intercept equaling -1.8. Intraobserver and interobserver variability (r = 0.99 and r = 0.99, respectively) was excellent with a standard deviation (SD) equal to 1.5 and 1.8, respectively. The effect of variable RV preload (right atrial pressure, -5 to +20 mm Hg) on accuracy of RV mass measurements produced minimal error (SD = 3.6 g) in RV mass measurements. Seven normal young healthy men were also studied. The free wall mass of the right ventricle was in the range of 48.3-67.4 g and averaged 54.6 +/- 2.8 g (mean +/- SEE). The left ventricular to right ventricular (LV:RV) ratio averaged 3.2 +/- 0.2:1. These results are in agreement with human autopsy data in healthy males reporting mean RV mass equal to 46 g and an LV:RV ratio equal to 3.4:1. Because imaging every 3-mm slice from apex to base requires two contrast injections, we determined the accuracy of RV mass measurements if only every fourth 3-mm slice with interpolation was used. RV mass measurements using every slice or every fourth slice with interpolation were excellent (dogs, r = 0.99; humans, r = 0.97). It is concluded that high resolution CT imaging (3-mm tomograms) allows accurate measurements of RV mass. It is possible to add this stop-action mode of ultrafast CT, to previous CT studies, using every fourth tomographic slice for mass determinations and only one additional contrast injection of 40-60 ml. This should permit the study of progression and regression of RV mass in patients with various diseases.

Animals↗

PubMed2005

Timing and velocity randomization similarly affect anticipatory pursuit.

Smooth pursuit eye movements are guided largely by retinal-image motion. To compensate for neural conduction delays, the brain employs a predictive mechanism to generate anticipatory pursuit that precedes target motion (E. Kowler, 1990). A critical question for interpreting neural signals recorded during pursuit concerns how this mechanism is interfaced with sensorimotor processing. It has been shown that the predictor is not simply turned-off during randomization because anticipatory eye velocity remains when target velocity is randomized (E. Kowler & S. McKee, 1987; G. W. Kao & M. J. Morrow, 1994). This study was completed to compare pursuit behavior during randomized motion-onset timing with that occurring during direction or speed randomization. We found that anticipatory eye velocity persisted despite motion-onset randomization, and that anticipation onset time was between that observed in the different constant-timing conditions. This centering strategy was similar to the bias of eye velocity magnitude away from extremes observed when direction or speed was randomized. Such a strategy is comparable to least-squares error minimization, and could be used to facilitate acquisition of a target when it begins to move. Centering was in some observers accounted for by a shift of eye velocity toward that generated in the preceding trial. The results make unlikely a model in which the predictor is disengaged by randomizing stimulus timing, and suggest that predictive signals always interact with those used in sensorimotor processing during smooth pursuit.

Humans↗

PubMed1989

Diagnosis of arteriosclerosis obliterans by impedance technique with special reference to relative blood flow of the lower extremity.

Simultaneous recordings of impedance cardiography of the chest and impedance plethysmography of the lower extremity were performed on 105 limbs with or without arteriosclerosis obliterans (ASO) documented by angiography. The ratios of blood flow to the lower extremity--leg stroke volume/cardiac stroke volume--(LSV/CSV) were 11.2 +/- 3.3% in normal male subjects, 11.1 +/- 5.5% in normal female subjects, and 3.1 +/- 1.2% in lower extremities with ASO, respectively. The normal value (range) for LSV/CSV calculated from the normal groups by the percentile method was between 4.9% and 17.8%, and the diagnostic accuracy of this value was 100% for sensitivity and 97.5% for specificity. LSV/CSV is a good index for the diagnosis of ASO and makes it possible to minimize error when expressed as an absolute value.

Arteriosclerosis Obliterans↗

PubMed1993

The left ventricular end-systolic pressure and pressure-volume index. Comparison between invasive and auscultatory arm pressure measurements.

The slope of the left ventricular (LV) end-systolic pressure-volume relation (ESPVR) has been established as a valuable clinical method to assess LV contractile function independent of LV loading factors. The purpose of the present study was to evaluate whether the ESPVR could be reliably determined from auscultatory blood pressure (BP) measurements and from LV volume measurement by contrast ventriculography (CVG). Twenty-four patients with suspected or known ischemic heart disease were studied by cardiac catheterization with simultaneous, blinded, intravascular and auscultatory pressure measurements. LV volume was determined by CVG. The auscultatory mean arterial blood pressure (MAP) derived from: [formula: see text] was found to be a useful measure of the LV end-systolic pressure in this connection. The correlation between invasively measured LV end-systolic pressure (ESP) and MAP was highly significant (r = 0.82; SEE = 6.9 mmHg; p = 0.001). The correlation between invasively and semi-invasively measured ESPVR fell close to the line of identity (r = 0.99; SEE = 0.23 mmHg.mL-1; p < 0.001). The replacement of ESP by MAP induced only a minimal error in the assessment of the ESPVR. A complete noninvasive determination of the ESPVR and LV contractility therefore seems possible by using the MAP and by measuring the end-systolic volume by radionuclide ventriculography or by echocardiography.

Adult↗

PubMedDate not supplied

Incidence of Bell's palsy.

The annual incidence of Bell's palsy in three consecutive years--1984, 1985, and 1986--was investigated in Ehime Prefecture in Japan, which has a population of 1,530,000. The number of new patients with Bell's palsy was solicited from 1,377 medical institutions and their referral hospitals. The clinical records of the 15 main hospitals were examined personally by the author to confirm the exact numbers. Special care was taken to ensure minimal error in the present epidemiologic investigation. The annual incidence of Bell's palsy per 100,000 population was found to be 30, and no annual variation was noted. The ratio of male to female patients was 48:52 in all cases. There was no geographic difference in incidence.

Facial Paralysis↗

PubMedDate not supplied

Context effects in a double-weak theory of speech perception.

The present study provides an elaboration of the "double-weak" theory of speech perception proposed by Nearey (1990, 1991). In this framework, the objects of speech perception (and production) are viewed as neither primarily auditory nor primarily gestural; rather, they are abstract, symbolic elements lawfully constrained to map onto relatively simple (but not entirely transparent) patterns in both domains. Speech cannot be understood unless both articulation and acoustics are considered: Many production strategies appear to be directed at achieving acoustically-oriented goals, yet most context effects in speech perception seem to be motivated by the consequences of gestural overlap. The double-weak framework suggests that speech perception and speech production are less-than-perfect inverses of each other. Despite long-term accommodation of each for the demands of the other, real-time production and perception may operate as autonomous subsystems. A family of perceptual models is discussed that provides varying degrees of approximation to "ideal solutions" (in the sense of minimizing error rate) to classifying production data exhibiting contextual interactions. Members of this family that provide substantial, yet incomplete, compensation for the consequences of gestural overlap appear to be adequate to account for the results of many speech perception experiments. Such partial perceptual compensation allows, in principle, for the kind of imperfect "error correction" discussed by Ohala (1981, 1990) in conjunction with hypo- and hypercorrection phenomena.

Female↗

PubMed1994

Aflatoxin exposure in Singapore: blood aflatoxin levels in normal subjects, hepatitis B virus carriers and primary hepatocellular carcinoma patients.

Blood screening conducted on Singaporeans over 1991-1992 showed exposure to predominantly aflatoxin B1 and to a lesser extent G1. The extent of exposure to B1 among three groups of residents in Singapore, namely normal subjects (n = 423), hepatitis B virus carriers (n = 302) and primary hepatocellular carcinoma (PHC) patients (n = 58) were extensive as reflected by the positive rates of 15.1, 0.7 and 1.7 per cent respectively. However, the degree of individual exposure to this toxin among the three groups was considered low as shown by the low respective mean blood levels of 5.4 +/- 3.2 (range 3.0-17), 7.7 (range 7.5-7.9) and 7.5 picogrammes per ml of blood. It is not immediately clear whether or not such low levels would precipitate an undesirable health effect. The higher positive rate seen in normal subjects as compared with the other groups could be due to differences in dietary intake of aflatoxin B1, differences in metabolic patterns or both. About 70 per cent of PHC patients studied were carriers. The degree of aflatoxin B1 exposure among normal subjects in Singapore was a factor of 22.1 times less than that in Japan, 40.9 times less than that in Indonesia and 51.3 times less than that in the Philippines. Similarly, the extent of exposure among hepatitis B carriers in Singapore was a factor of 8.2 times, 39.6 times and 24.2 times less than those in the other three Asiatic countries respectively. The results reflected stringent Government control over the quality of food stuff imported into this country. As Singapore imports almost all of its dietary needs from elsewhere, it can afford to be selective at a cost. Aflatoxin M1, a metabolite of B1, was most commonly encountered in the liver tissues of deceased (n = 154) who died of causes other than sickness or disease in 1992-93, consistent with our blood findings of prevalence of aflatoxin B1. High performance liquid chromatography (HPLC) with fluorescence detection using one of the aflatoxins G2 or B2 as an internal standard was used for the detection and quantification of aflatoxins. The use of an internal standard structurally and chemically similar to those required to be quantified minimizes errors in quantifications. This is because differences in the quenching of fluorescence between specimen extracts and spiked-standard extracts were internally standardized and compensated for. The presence of an internal standard also helped to locate aflatoxins of interest more accurately.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed2006

Food composition database development for between country comparisons.

Nutritional assessment by diet analysis is a two-stepped process consisting of evaluation of food consumption, and conversion of food into nutrient intake by using a food composition database, which lists the mean nutritional values for a given food portion. Most reports in the literature focus on minimizing errors in estimation of food consumption but the selection of a specific food composition table used in nutrient estimation is also a source of errors. We are conducting a large prospective study internationally and need to compare diet, assessed by food frequency questionnaires, in a comparable manner between different countries. We have prepared a multi-country food composition database for nutrient estimation in all the countries participating in our study. The nutrient database is primarily based on the USDA food composition database, modified appropriately with reference to local food composition tables, and supplemented with recipes of locally eaten mixed dishes. By doing so we have ensured that the units of measurement, method of selection of foods for testing, and assays used for nutrient estimation are consistent and as current as possible, and yet have taken into account some local variations. Using this common metric for nutrient assessment will reduce differential errors in nutrient estimation and improve the validity of between-country comparisons.

Agriculture↗

PubMed2006

Getting causal considerations back on the right track.

In their commentary on my paper Phillips and Goodman suggested that counterfactual causality and considerations on causality like those by Bradford Hill are only "guideposts on the road to common sense". I argue that if common sense is understood to mean views that the vast majority of researchers share, Hill's considerations did not lead to common sense in the past--precisely because they are so controversial. If common sense is taken to mean beliefs that are true, then Hill's considerations can only lead to common sense in the simple and well-understood causal systems they apply to. Counterfactuals, however, are largely common sense in the latter meaning.I suggest that the road of scientific endeavour should lead epidemiologic research toward sound strategies that equip researchers with skills to separate causal from non-causal associations with minimal error probabilities. This is undeniably the right direction and the one counterfactual causality leads to. Hill's considerations are merely heuristics with which epidemiologists may or may not find this direction, and they are likely to fail in complex landscapes (causal systems). In such environments, one might easily lose orientation without further aids (e.g., defendable assumptions on biases). Counterfactual causality tells us when and how to apply these heuristics.

Comment↗

PubMed2001

A simple model based on mutation and selection explains trends in codon and amino-acid usage and GC composition within and across genomes.

BACKGROUND: Correlations between genome composition (in terms of GC content) and usage of particular codons and amino acids have been widely reported, but poorly explained. We show here that a simple model of processes acting at the nucleotide level explains codon usage across a large sample of species (311 bacteria, 28 archaea and 257 eukaryotes). The model quantitatively predicts responses (slope and intercept of the regression line on genome GC content) of individual codons and amino acids to genome composition. RESULTS: Codons respond to genome composition on the basis of their GC content relative to their synonyms (explaining 71-87% of the variance in response among the different codons, depending on measure). Amino-acid responses are determined by the mean GC content of their codons (explaining 71-79% of the variance). Similar trends hold for genes within a genome. Position-dependent selection for error minimization explains why individual bases respond differently to directional mutation pressure. CONCLUSIONS: Our model suggests that GC content drives codon usage (rather than the converse). It unifies a large body of empirical evidence concerning relationships between GC content and amino-acid or codon usage in disparate systems. The relationship between GC content and codon and amino-acid usage is ahistorical; it is replicated independently in the three domains of living organisms, reinforcing the idea that genes and genomes at mutation/selection equilibrium reproduce a unique relationship between nucleic acid and protein composition. Thus, the model may be useful in predicting amino-acid or nucleotide sequences in poorly characterized taxa.

Amino Acids↗

PubMed1996

Effects of maturation on cyclic GMP metabolism in ovine carotid arteries.

Previous studies suggest that elevated basal levels of cGMP in newborn arteries may help explain why vascular resistance is lower in newborns than adults. To explore the reasons why basal cGMP is higher in neonatal arteries, the present studies examined rates of cGMP synthesis and degradation in newborn and adult ovine common carotid arteries. The measurements were performed in both intact and homogenized arteries, and results were normalized relative to cell water to estimate intracellular concentrations and minimize errors due to compositional differences between newborn and adult arteries. Steady state levels of cGMP measured under baseline conditions averaged 0.11 +/- 0.02 microM in adult arteries and 0.59 +/- 0.11 microM in newborn arteries. These resting cGMP levels were unaffected by endothelium removal. Under baseline conditions, steady state rates of cGMP synthesis (mumol of cGMP/L of cell water/min) were higher in newborn (0.31 +/- 0.06) than in adult (0.15 +/- 0.04) arteries. Maximal rates of cGMP degradation (mumol of cGMP/L of cell water/min) measured in artery homogenates were also much higher in preparations of newborn (106 +/- 6) than of adult (78 +/- 6) arteries. Together, these data suggest that the reason resting cGMP concentrations were higher in newborn than in adult arteries was due at least in part to a higher basal rate of cGMP synthesis in the newborn. Estimates of apparent Km values for PDE were also greater in newborn (2.9 microM) than in adult (1.5 microM) preparations, suggesting that age-related differences in the Km for PDE may also contribute to the elevated basal concentration of cGMP observed in the newborn.

1-Methyl-3-isobutylxanthine↗

PubMed2000

On the science of Rorschach research.

Wood et al.'s (1999b) article contained several general points that are quite sound. Conducting research with an extreme groups design does produce effect sizes that are larger than those observed in an unselected population. Appropriate control groups are important for any study that wishes to shed light on the characteristics of a targeted experimental group and experimental validity is enhanced when researchers collect data from both groups simultaneously. Diagnostic efficiency statistics--or any summary measures of test validity--should be trusted more when they are drawn from multiple studies conducted by different investigators across numerous settings rather than from a single investigator's work. There should be no question that these points are correct. However, I have pointed out numerous problems with specific aspects of Wood et al.'s (1999b) article. Wood et al. gave improper citations that claimed researchers found or said things that they did not. Wood et al. indicated my data set did not support the incremental validity of the Rorschach over the MMPI-2 when, in fact, my study never reported such an analysis and my data actually reveal that the opposite conclusion is warranted. Wood et al. asserted there was only one proper way to conduct incremental validity analyses even though experts have described how their recommended procedure can lead to significant complications. Wood et al. cited a section of Cohen and Cohen (1983) to bolster their claim that hierarchical and step-wise regression procedures were incompatible and to criticize Burns and Viglione's (1996) regression analysis. However, that section of Cohen and Cohen's text actually contradicted Wood et al.'s argument. Wood et al. tried to convince readers that Burns and Viglione used improper alpha levels and drew improper conclusions from their regression data although Burns and Viglione had followed the research evidence on this topic and the expert recommendations provided in Hosmer and Lemeshow's (1989) classic text. Wood et al. oversimplified issues associated with extreme group research designs and erroneously suggested that diagnostic studies were immune from interpretive confounds that can be associated with this type of design. Wood et al. ignored or dismissed the valid reasons why Burns and Viglione used an extreme groups design, and they never mentioned how Burns and Viglione used a homogeneous sample that actually was likely to find smaller than normal effect sizes. Wood et al. also overlooked the fact that Burns and Viglione identified their results as applying to female nonpatients; they never suggested their findings would characterize those obtained from a clinical sample. Wood et al. criticized composite measures although some of the most important and classic findings in the history of research on personality recommend composite measures as a way to minimize error and maximize validity. Wood et al. also were mistaken about the elements that constitute an optimal composite measure. Wood et al. apparently ignored the factor-analytic evidence that demonstrated how Burns and Viglione created a reasonable composite scale, and Wood et al. similarly ignored the clear evidence that supported the content and criterion related validity of the EMRF. With respect to the HEV, Wood et al. created a z-score formula that used the wrong means and standard deviations. They continued to use this formula despite being informed that it was incorrect. Subsequently, Wood et al. told readers that their faulty z-score formula was "incompatible" with the proper weighted formula and asserted that the two formulas "do not yield identical results" and "do not yield HEV scores that are identical or even very close." These published claims were made even though Wood et al. had seen the results from eight large samples, all of which demonstrated that their wrong formula had correlations greater than .998 with the correct formula. At worst, it seems that Wood et al. (199

Female↗

PubMed1999

The Tourette syndrome diagnostic confidence index: development and clinical associations.

BACKGROUND: The clinical characteristics of Tourette syndrome (TS) present challenges for the systematic determination of whether individuals are affected and severity. Vocal and motor tics wax and wane, decrease over time, and may be voluntarily suppressible, and therefore may be absent at interview. Current instruments measure symptoms at interview or rate symptom severity only. METHOD: To minimize error in case ascertainment and produce an instrument measuring lifetime likelihood of having had TS, clinical members of the American Tourette Syndrome Association International Genetic Collaboration developed the Diagnostic Confidence Index (DCI). The expert group worked collaboratively with progressive revision in consensus workshops using existing diagnostic criteria as guidelines. The DCI produces a score from 0 to 100 that is a measure of the likelihood of having or ever having had TS. RESULTS: The DCI was administered to 280 consecutive patients with TS attending a TS clinic; 264 (94%) completed it, indicating high feasibility and acceptability. Its correlation with other instruments and associations with psychopathology provide support for its being a lifetime measure of TS. CONCLUSIONS: The DCI is a useful, practicable instrument in the clinic or research practice allowing an assessment of lifetime likelihood of TS. Further work is needed to test the DCI's psychometric properties, such as its validity and reliability in populations of interest.

Adolescent↗

PubMed2004

Sensitivity of finite helical axis parameters to temporally varying realistic motion utilizing an idealized knee model.

Various uses of the screw or helical axis have previously been reported in the literature in an attempt to quantify the complex displacements and coupled rotations of in vivo human knee kinematics. Multiple methods have been used by previous authors to calculate the axis parameters, and it has been theorized that the mathematical stability and accuracy of the finite helical axis (FHA) is highly dependent on experimental variability and rotation increment spacing between axis calculations. Previous research has not addressed the sensitivity of the FHA for true in vivo data collection, as required for gait laboratory analysis. This research presents a controlled series of experiments simulating continuous data collection as utilized in gait analysis to investigate the sensitivity of the three-dimensional finite screw axis parameters of rotation, displacement, orientation and location with regard to time step increment spacing, utilizing two different methods for spatial location. Six-degree-of-freedom motion parameters are measured for an idealized rigid body knee model that is constrained to a planar motion profile for the purposes of error analysis. The kinematic data are collected using a multicamera optoelectronic system combined with an error minimization algorithm known as the point cluster method. Rotation about the screw axis is seen to be repeatable, accurate and time step increment insensitive. Displacement along the axis is highly dependent on time step increment sizing, with smaller rotation angles between calculations producing more accuracy. Orientation of the axis in space is accurate with only a slight filtering effect noticed during motion reversal. Locating the screw axis by a projected point onto the screw axis from the mid-point of the finite displacement is found to be less sensitive to motion reversal than finding the intersection of the axis with a reference plane. A filtering effect of the spatial location parameters was noted for larger time step increments during periods of little or no rotation.

Algorithms↗