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PubMed1993

The critical power concept. A review.

The basis of the critical power concept is that there is a hyperbolic relationship between power output and the time that the power output can be sustained. The relationship can be described based on the results of a series of 3 to 7 or more timed all-out predicting trials. Theoretically, the power asymptote of the relationship, CP (critical power), can be sustained without fatigue; in fact, exhaustion occurs after about 30 to 60 minutes of exercise at CP. Nevertheless, CP is related to the fatigue threshold, the ventilatory and lactate thresholds, and maximum oxygen uptake (VO2max), and it provides a measure of aerobic fitness. The second parameter of the relationship, AWC (anaerobic work capacity), is related to work performed in a 30-second Wingate test, work in intermittent high-intensity exercise, and oxygen deficit, and it provides a measure of anaerobic capacity. The accuracy of the parameter estimates may be enhanced by careful selection of the power outputs for the predicting trials and by performing a greater number of trials. These parameters provide fitness measures which are mode-specific, combine energy production and mechanical efficiency in 1 variable, and do not require the use of expensive equipment or invasive procedures. However, the attractiveness of the critical power concept diminishes if too many predicting trials are required for generation of parameter estimates with a reasonable degree of accuracy.

Anaerobic Threshold↗

PubMed1998

Differential diagnosis of small hepatocellular carcinoma and adenomatous hyperplasia with power Doppler sonography.

OBJECTIVE: The aim of this study was to compare the ability of power Doppler sonography and color Doppler sonography to differentiate hepatocellular carcinoma (HCC) from adenomatous hyperplasia (AH). SUBJECTS AND METHODS: In 48 patients with cirrhosis of the liver, color Doppler sonography and power Doppler sonography were performed on 53 hepatic nodules smaller than 20 mm in diameter (32 nodules were HCC; 21 nodules were AH). We evaluated the detectability of the pulsatile and continuous flows in the nodules at each hepatic segment. RESULTS: Thirty-four percent of nodules produced color signal on color Doppler sonography; 77%, on power Doppler sonography (p < .01). The identification rate of nodules in the left lateral segment was significantly lower than in other segments. Continuous flow was seen in the nodules of both HCC and AH. However, only in HCC did we see pulsatile flow. For HCC, pulsatile flow was seen with color Doppler sonography in 25% of the nodules smaller than 10 mm in diameter and in 50% of the nodules between 10 and 20 mm. With power Doppler sonography, pulsatile flow was seen in 67% (p < .05) of the nodules smaller than 10 mm and in 90% (p < .01) of the nodules between 10 and 20 mm. Sensitivity and negative predictive value in the differentiation of HCC from AH were significantly higher with power Doppler sonography than with color Doppler sonography (81% versus 41%, respectively, for sensitivity and 78% versus 53%, respectively, for negative predictive value). Specificity, positive predictive value, and efficacy of both color Doppler sonography and power Doppler sonography were 100%, 100%, 60%, respectively. CONCLUSION: On the basis of our results, power Doppler sonography is more sensitive than color Doppler sonography in revealing small HCC and in differentiating HCC from AH under physiologic hemodynamic conditions.

Aged↗

PubMed2000

Power Doppler sonography: evaluation of hepatocellular carcinoma after treatment with transarterial embolization or percutaneous ethanol injection therapy.

OBJECTIVE: The aim of this study was to compare tumor detectability by assessing the vascularity on power and color Doppler sonography and CT after transarterial embolization or percutaneous ethanol injection therapy or both in hepatocellular carcinoma. SUBJECTS AND METHODS: Forty-seven nodules of hepatocellular carcinoma (size, 28 +/- 7 mm [mean +/- standard deviation]; range, 20-40 mm) in 38 patients were treated with transarterial embolization (n = 6), percutaneous ethanol injection therapy (n = 23), and transarterial embolization plus percutaneous ethanol injection therapy (n = 9). Power Doppler sonography, color Doppler sonography, and CT were performed before and 2 weeks, 3 months, and 6 months after the treatments. The existence of hepatocellular carcinoma was confirmed by positive findings for color signals on both Doppler sonography techniques and for tumor stains on CT. All the tumors were determined to be malignant by microscopic examination of biopsy specimens. RESULTS: Before the treatments, power Doppler sonography (100%) and CT (100%) were significantly more effective than color Doppler sonography (61.7%) (p < 0.001, for both). Six months after the treatments, the sensitivity of power Doppler sonography (87.5%) was significantly better than that of color Doppler sonography (12.5%) but was not significant in comparison with CT (66.6%). However, power Doppler sonography detected color signals in two of three tumors in which iodized oil was accumulated and no tumor stain appeared on CT, and the two lesions detected with power Doppler sonography were carcinomas. CONCLUSION: Power Doppler sonography can be considered the most sensitive technique in assessing the viability of hepatocellular carcinoma treated with transarterial embolization or percutaneous ethanol injection therapy or both.

Adult↗

PubMed2001

Radiofrequency thermal ablation of hepatocellular carcinoma: using contrast-enhanced harmonic power doppler sonography to assess treatment outcome.

OBJECTIVE: We evaluated the accuracy of contrast-enhanced harmonic power Doppler sonography in assessing the outcome of radiofrequency thermal ablation of hepatocellular carcinoma. SUBJECTS AND METHODS: Fifty patients with 65 hepatocellular carcinoma nodules (1-5 cm in diameter; mean diameter, 2.5 cm) were studied using unenhanced and contrast-enhanced harmonic power Doppler sonography before and after IV administration of a microbubble contrast agent. The examinations were repeated after treatment of the tumors with radiofrequency ablation. Findings of the Doppler studies were compared with those of dual-phase helical CT, which were used as points of reference for assessing treatment outcome. RESULTS: Before radiofrequency treatment, intratumoral blood flow was revealed by unenhanced power Doppler sonography in 48 (74%) of 65 hepatocellular carcinoma nodules. After injection of the contrast agent, intratumoral enhancement was observed in 61 (94%) of 65 hepatocellular carcinomas (p < 0.01). After radiofrequency treatment, all 51 (84%) of the 61 hepatocellular carcinomas found to be necrotic on helical CT scans failed to show enhancement on power Doppler sonograms. In nine of the 10 lesions that showed a residual viable tumor on helical CT scans, persistent intratumoral enhancement-matching the enhancing areas on helical CT images-was revealed by power Doppler sonography. These nine hepatocellular carcinomas were subjected to repeated radiofrequency thermal ablation with the guidance of contrast-enhanced power Doppler sonography. Complete necrosis was seen after the second treatment session in six of the nine lesions. CONCLUSION: Contrast-enhanced harmonic power Doppler sonography is an accurate technique for assessing the outcome of radiofrequency thermal ablation of hepatocellular carcinoma and may be useful in guiding additional treatment in patients with incomplete response to initial efforts.

Aged↗

PubMed2006

Comparison of power spectrum characteristics of body sway during a static upright standing posture in healthy elderly people and young adults.

This study was designed to compare peak frequency, mean power frequency, and power spectrum of each frequency band of body-sway time series and velocity time series power spectra between 30 healthy elderly people and 30 young adults and to clarify their frequency characteristics. Peak frequency and mean power frequency differed between groups, being higher for elderly persons, and the difference was marked in the front-back direction. When comparing power spectra of three domains (A: 0.02-0.2 Hz, B: 0.2-2.0 Hz, and C: 2.0-10.0 Hz) of an international standard, a significant age-group difference was found only in the front-back direction. Young adults were higher in the low frequency band (A domain) in sway time series, and the elderly group was higher in the high frequency band (C domain) in body-sway velocity time series. However, almost all power spectra of both groups appeared in the low frequency band. The present results suggested frequency characteristics of healthy people occur in the low frequency band, but the elderly group compared with the young adults had more characteristics in the high frequency band. Their frequency characteristics cannot be properly evaluated by the international standard established to screen disorders. It may be necessary for healthy people to have new evaluation frequency sections when considering power spectrum characteristics of sway time series and sway-velocity time series.

Aged↗

PubMed2001

Lateral dominance of legs in maximal muscle power, muscular endurance, and grading ability.

The purpose of this study was to examine lateral dominance in maximal muscle power, muscular endurance, and grading ability, using isokinetic mulscular strength in knee extension and flexion. The subjects were 50 healthy male students whose ages ranged from 19 to 23 years (M height: 173.6+/-6.2 cm, M weight: 67.2+/-6.8 kg). Their dominant legs for power exertion and for functional use were based on questionnaire items selected from those used in previous studies. The angular velocities of extension and flexion for exerting maximal muscle power were 60, 180, and 300 x sec.(-1). A continuous exertion 30 times at an angular velocity of 180 sec.(-1) was used as the load for muscular endurance. For grading ability, 25%, 50% and 75% of the maximal muscle strength at angular velocities of 60 and 180 x sec.(-1) were the required values, and the difference between these values and the exerted muscular strength was evaluated. The dominant leg and nondominant leg were compared for both power exertion and functional use. There was no lateral dominance in maximal muscle power and muscular endurance. In muscular endurance, especially, some subjects showed one leg superior in power exertion and some superior in functional use. Lateral dominance was noted across maximal muscle power and muscular endurance in grading ability. The dominant leg tended to be better than the nondominant leg in functional use. However, lateral dominance was not remarkable for flexing motion and in exertion for a short time.

Adult↗

PubMed2005

Mechanical impedance and absorbed power of hand-arm under x(h)-axis vibration and role of hand forces and posture.

The biodynamic responses of the hand-arm system under x(h)-axis vibration are investigated in terms of the driving point mechanical impedance (DPMI) and absorbed power in a laboratory study. For this purpose, seven healthy male subjects are exposed to two levels of random vibration in the 8-1,000 Hz frequency range, using three instrumented cylindrical handles of different diameters (30, 40 and 50 mm), and different combinations of grip (10, 30 and 50 N) and push (0, 25 and 50 N) forces. The experiments involve grasping the handle while adopting two different postures, involving elbow flexion of 90 degrees and 180 degrees, with wrist in the neutral position for both postures. The analyses of the results revealed peak DPMI magnitude and absorbed power responses near 25 Hz and 150 Hz, for majority of the test conditions considered. The frequency corresponding to the peak response increased with increasing hand forces. Unlike the absorbed power, the DPMI response was mostly observed to be insensitive to variations in the excitation magnitude. The handle diameter revealed obvious effects on the DPMI magnitude, specifically at frequencies above 250 Hz, which was not evident in the absorbed power due to relatively low velocity at higher frequencies. The influence of hand forces was also evident on the DPMI magnitude response particularly at frequencies. above 100 Hz, while the effect of hand-arm posture on the DPMI magnitude was nearly negligible. The magnitude of power absorbed within the hand and arm was observed to be strongly dependent upon the excitation level over the entire frequency range, while the influence of hand-arm posture on the total absorbed power was observed to be important. The effect of variations in the hand forces on the absorbed power was relatively small for the bent elbow posture, while an increase in either the grip or the push force coupled with the extended arm posture resulted in considerably higher energy absorption. The results suggested that the handle size, hand-arm posture and hand forces, produce coupled effect on the biodynamic response of the hand-arm system.

Arm↗

PubMed1983

Circadian acrophases of powers and frequencies in the waking EEG.

Circadian changes in frequencies and powers of the close-eyed EEG were measured over six days in 12 healthy volunteers living in a regular rest-activity cycle. EEGs were recorded every two hours and the probands were awakened for the recordings during the period of rest. Circadian rhythms occurred in powers and frequencies with diurnal amplitudes differing between individuals and locally on the scalp. Acrophases of peak frequencies and beta-power coincide with those of body temperature between 5 and 7 p.m., however, the crests of the diurnal rhythms in delta-, theta- and alpha-power varied more between individuals and covered systematically different times of the day. Acrophases of delta- and theta-powers occurred during the second half of the rest period and during the first half of the waking period. Only powers in the alpha-band showed locally different acrophases on the scalp. This could be observed in single individuals, too. In the central and parietal leads, acrophases of alpha-power were found during rest, whereas in the occipital leads of some probands acrophases occurred in the second half of the waking period.

Adolescent↗

PubMed2002

Comparison of IOL powers by corrected method in eyes after PRK and LASIK.

The purpose of this study is to compare, by statistical analysis, intraocular lens (IOL) powers by SRK/T formula using autorefractokeratometer-measured keratometric (K) values (SRK/T-ARK-mK), by SRK/T formula using refraction-derived K values (SRK/T-R-dK), and by refraction corrected method (RCM), in eyes treated with photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) for myopia. Thirty-eight consecutive eyes of 23 patients with PRK for mild to moderate myopia and 35 consecutive eyes of 25 patients with LASIK for high myopia were followed up for more than 1 year. In the two groups, IOL powers by SRK/T-ARK-mK, by SRK/T-R-dK, and by RCM were compared by statistical analysis. In PRK group, the mean value of IOL powers by RCM was statistically higher than that obtained by the other two methods (p < 0.05), while there was no significant statistical difference between the mean values of IOL powers by SRK/T-ARK-mK and by SRK/T-R-dK (p > 0.05). However, in LASIK group, the mean values of IOL powers by RCM and by SRK/T-R-dK, which did not differ statistically (p > 0.05), were both statistically higher than that by SRK/T-ARK-mK (p < 0.05). In conclusion, there is a statistical difference in IOL powers by the methods used for IOL calculation, as there is according to the level of myopia in patients with PRK and LASIK treatment. We suggest that, in IOL power calculation in eyes with previous corneal refractive surgery, correction methods such as RCM and SRK/T-R-dK are more effective at higher levels of myopia.

Adult↗

PubMed2000

Statistical power for the two-factor repeated measures ANOVA.

Determining a priori power for univariate repeated measures (RM) ANOVA designs with two or more within-subjects factors that have different correlational patterns between the factors is currently difficult due to the unavailability of accurate methods to estimate the error variances used in power calculations. The main objective of this study was to determine the effect of the correlation between the levels in one RM factor on the power of the other RM factor. Monte Carlo simulation procedures were used to estimate power for the A, B, and AB tests of a 2 x 3, a 2 x 6, a 2 x 9, a 3 x 3, a 3 x 6, and a 3 x 9 design under varying experimental conditions of effect size (small, medium, and large), average correlation (.4 and .8), alpha (.01 and .05), and sample size (n = 5, 10, 15, 20, 25, and 30). Results indicated that the greater the magnitude of the differences between the average correlation among the levels of Factor A and the average correlation in the AB matrix, the lower the power for Factor B (and vice versa). Equations for estimating the error variance of each test of the two-way model were constructed by examining power and mean square error trends across different correlation matrices. Support for the accuracy of these formulae is given, thus allowing for direct analytic power calculations in future studies.

Analysis of Variance↗

PubMed2000

The power law repealed: the case for an exponential law of practice.

The power function is treated as the law relating response time to practice trials. However, the evidence for a power law is flawed, because it is based on averaged data. We report a survey that assessed the form of the practice function for individual learners and learning conditions in paradigms that have shaped theories of skill acquisition. We fit power and exponential functions to 40 sets of data representing 7,910 learning series from 475 subjects in 24 experiments. The exponential function fit better than the power function in all the unaveraged data sets. Averaging produced a bias in favor of the power function. A new practice function based on the exponential, the APEX function, fit better than a power function with an extra, preexperimental practice parameter. Clearly, the best candidate for the law of practice is the exponential or APEX function, not the generally accepted power function. The theoretical implications are discussed.

Data Interpretation, Statistical↗

PubMed2002

[Examination of the validity of RF power determination by auto prescan in T(1)-weighted images].

In the sequence of spin echo MRI systems, RF power selects the output value from which the signal intensity of the whole photography volume changes to the maximum as a 90-degree pulse in auto tuning during prescanning by the SIGNA HORIZON LX 1.0 Tesla ver. 8.3. When it consists of two or more organizations like a human body, although the RF power to which signal intensity serves as the maximum is in agreement with the RF power of a 90-degree pulse if it is a uniform phantom, the RF power from which signal intensity reaches the maximum differs for every organization. When we determined RF power by the signal intensity of two or more whole organizations in this experiment, it was found that RF power was strongly influenced by a high signal organization. Moreover, if CNR in two or more organizations is considered, T(1) contrast will be emphasized for the direction of an angle less than 90 degrees. It was possible for the same effect to be acquired by lowering the power of the RF pulse and emphasizing T(1) contrast.

Magnetic Resonance Imaging↗

PubMed2002

Correlation between color power Doppler sonographic measurement of breast tumor vasculature and immunohistochemical analysis of microvessel density for the quantitation of angiogenesis.

OBJECTIVE: To record the correlation between color power Doppler sonographic measurement of breast tumor vasculature and immunohistochemical analysis of microvessel density for the quantitation of angiogenesis. METHODS: Women with palpable breast masses scheduled for excision biopsy were scanned with two- and three-dimensional color power Doppler sonography before and after the administration of a sonographic contrast agent. Vessel counts were performed on two- and three-dimensional sonographic images before and after contrast agent administration. All tumors were surgically removed and underwent immunohistochemical analysis for microvessel density assessment. The sonographic measure of tumor vascularity was correlated with microvessel density. RESULTS: Pathologic examination showed 43 breast cancers and 14 benign breast masses. Higher microvessel density was noted in malignant than benign breast masses (P < .0005). Color power Doppler sonographic measurement of tumor vessel number showed a significant positive correlation with tumor size (P < .05) and progesterone receptor negativity (P < .05). A significant positive correlation was observed between microvessel density and the number of intratumoral blood vessels assessed by both two- and three-dimensional color power Doppler sonography (P < .05). Regression models showed three-dimensional color power Doppler sonography to have a significantly higher correlation with microvessel density when compared with two-dimensional color power Doppler sonography at baseline (P < .005). The administration of a sonographic contrast agent did not improve correlation with microvessel density. CONCLUSIONS: A significant correlation was shown between color power Doppler sonographic measurement of tumor vascularity and microvessel density by immunohistochemical analysis. Further improvement in Doppler sonographic techniques to map capillary vessel flow should be explored to improve the current association with pathologic findings.

Adult↗

PubMed1999

The power of association studies to detect the contribution of candidate genetic loci to variation in complex traits.

The statistical power of five association study test statistics (two haplotype-based tests, two marker-based tests, and the Transmission Disequilibrium Test-Q5) to detect single nucleotide polymorphism (SNP)/phenotype associations in a linkage-disequilibrium-based candidate gene scan employing a number of SNPs is examined. Power is estimated as a function of realistic parameters expected to affect the likelihood of detecting a significant association: the number of SNPs examined, the scaled recombination size of the region examined, the proportion of variance in the trait attributable to a hidden causative polymorphism within the region, and the number of individuals or families examined. For the different combinations of parameter values, power is estimated from a large number of realizations of a simulated coalescent describing a single random mating population with mutation, random genetic drift, and recombination. This explicit population genetics model results in a distribution of DNA marker heterozygosities and linkage disequilibria that are likely to resemble those expected in actual population samples. The study concludes that (1) marker-based permutation tests are more powerful than simple haplotype-based tests, (2) there is sufficient power to detect the presence of causative polymorphisms of small effect if on the order of 500 individuals are sampled, (3) greater power is achieved by increasing the sample size than by increasing the number of polymorphisms, (4) association studies are generally more powerful than transmission disequilibrium-based tests, and (5) for the range of parameters considered association studies have a low repeatability unless sample sizes are on the order of 500 individuals. Estimates of 4Nc for a number of gene regions and human populations will be of use in determining the density of SNPs that are likely to be required for successful association studies.

Computational Biology↗

PubMed2000

[Comparison between scintigraphy, B-mode, and power Doppler sonography in acute pyelonephritis in children].

PURPOSE: Comparing Power Doppler imaging versus technetium-dimercapto-succinic-acid (Tc-DMSA) scintigraphy in acute pyelonephritis of childhood. PATIENTS AND METHODS INCLUSION CRITERIA: First episode of urinary tract infection, clinical and biological findings suggesting an upper lesion, absence of urological malformation or obstruction, absence of reflux (or vesico-ureteral reflux inferior to grade 3). Number of patients: 49, length of the study: 26 months (from November 95 to January 98). METHODS: Tc99m-DMSA scintigraphy (after five days), B mode and Power Doppler imaging (on the day of admission or the following day). Systematic cystography (day 5 to day 30). RESULTS: In terms of positive diagnosis, scintigraphy was superior to Power Doppler, and the latter was superior to B mode ultrasonography. Sensitivity (scintigraphy being the gold standard) was equal for both B mode and Power DopplerUS imaging, but combined Power Doppler and B mode US provided improved results. CONCLUSION: Currently, the results with Power Doppler imaging are insufficient to replace DMSA scintigraphy. However, Power Doppler is a good complement to B mode US.

Acute Disease↗

PubMed2000

What do contrast media add to three-dimensional power Doppler evaluation of adnexal masses?

AIM: To investigate the potential usefulness of contrast-enhanced three-dimensional (3D) power Doppler sonography in the differentiation of benign and malignant adnexal lesions. METHODS: Thirty one patients with complex adnexal lesions of uncertain malignancy at transvaginal B-mode and/or color Doppler sonography were prospectively evaluated with three-dimensional power Doppler sonography before and after injection of a contrast agent. Presence of a penetrating pattern and a mixed penetrating and/or peripheral pattern suggested adnexal malignancy. The results were compared with histopathologic findings. RESULTS: There were 10 cases of ovarian malignancy and 21 benign adnexal lesions. Of 10 ovarian cancers, 6 showed vascular distribution suggestive of malignancy at nonenhanced 3D power Doppler sonography. After injection of contrast agent, a penetrating vascular pattern and/or mixed penetrating and peripheral pattern were detected in all cases of ovarian malignancy as well as in 2 benign lesions (fibroma and cystadenofibroma), which were misdiagnosed as malignant. The use of contrast agent with three-dimensional power Doppler sonography showed diagnostic efficiency of 96.7%, superior to that of nonenhanced 3D power Doppler sonography (93.5%). CONCLUSION: Contrast-enhanced 3D power Doppler sonography provides better visualization of tumor vascularity in complex adnexal masses. If used together with 3D morphological ultrasound assessment, enhanced 3D power Doppler imaging may precisely discriminate benign from malignant adnexal lesions.

Adnexa Uteri↗

PubMed2001

A series of studies on the training of high-intensity muscle power in rugby league football players.

Maximal power (Pmax) levels and the effects of the manipulation of training variables on power output in rugby league football players were investigated in 5 studies. In study 1, players of 3 different ability levels were assessed for Pmax during explosive bench press throws. Pmax levels were a significant descriptor of playing ability within the sport. In study 2, the effect of contrast loading was investigated during jump squats. The result was a significant (p < 0.05) increase in power output in the investigated load. In study 3, the effect of an ascending vs. descending order of loads during explosive bench press throws was investigated. An ascending order resulted in a significantly higher power output for the heaviest load, whereas the descending order resulted in a significantly higher power output for the lightest load. In study 4, the relationship between measures of upper-body strength, power, and speed was investigated in athletes from 3 different levels of playing ability. Strength, power, and speed were significantly correlated overall; however, the relationships were greater in the more experienced training group. In study 5, it was found that stronger athletes utilized a lower percentage of 1 repetition maximum (1RM; 46-51%) to attain Pmax than less strong athletes (58-69%).

Adolescent↗

PubMedDate not supplied

Power spectral analysis of heart rate variability in children with aortic stenosis.

Aortic stenosis is a progressive disorder and can be the cause of serious arrhythmias and possibly sudden death. Evaluation and follow-up of the autonomic nervous system may provide some useful information for management of the disease. Our study aimed to examine heart rate variability in children with aortic stenosis in the supine position and to detect the changes in autonomic activity during head-up tilt testing. Sixteen patients and 11 healthy controls participated in the study. In the supine position, seven minutes of continuous echocardiographic (ECG) recording was performed, followed by four consecutive ECG recordings, each consisting of seven minutes in 70 degrees tilt position. To obtain power spectrums, the tachograms were taken on the autoregressive mode. The mean RR interval duration, standard deviation of RR interval, central frequencies of low and high frequency oscillations, their powers, total power and percents of normalized low and high frequency powers were accepted for statistics. There were no significant differences between the groups in the supine position. In tilt position, mean RR interval and its standard deviation were decreased in both groups. The central frequency of low freuquency power significantly (p<0.05) shifted to left, normalized low frequency power increased and normalized high frequency power decreased in the control group at the beginning of tilt position, but at the second phase of tilt position in the patient group. We conclude from the results that children with mild-to-moderate aortic stenosis reflect delayed response to sympathetic provocation.

Adolescent↗