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PubMed1995

Use of a power-consumption-controlled extruder in the development of pellet formulations.

Shape is an important characteristic of pellets that is highly influenced by the water content of the extrudate during spheronization. The power-consumption-controlled extruder (pcc-extruder) is an appropriate tool to adjust the required water content to yield round pellets. For this purpose, it is necessary to run the extruder at a specific level of power consumption. In the first part of the study, this approach was employed to screen different drugs as well as excipients to prove the concept of the pcc-extruder. Usually round pellets were obtained but a few formulations did not produce round pellets. In the second part of the study, the influence of screw speed and powder feed rate on the required level of power consumption was investigated. A correlation between the water content and the shape of pellets was evident. To account for screw speed, it was necessary to adjust net power consumption instead of total power consumption. The influence of the screw speed on water content of extrudate and consequently on the shape of pellets was not significant in the studied range. Variations of the powder feed rate affected both the water content and the shape of pellets. However, the water content was not only dependent on the level of net power consumption. The specific power is the ratio of net power consumption to extrusion rate, and it correlates well with water content and pellet shape. Using the specific power, it is possible to adjust the net power consumption in response to changes in powder feed rate.

Acetaminophen↗

PubMed1999

The effect of reinnervation on force production and power output in skeletal muscle.

Failure to fully restore contractile function after denervation and reinnervation of skeletal muscle engenders significant disability in patients suffering peripheral nerve injuries. This work tested the hypothesis that skeletal muscle denervation and reinnervation result in a deficit in normalized power (W/kg), which exceeds the deficit in specific force (N/cm2), and that the mechanisms responsible for these deficits are independent. Adult Lewis rats underwent either transection and epineurial repair of the left peroneal nerve (denervation-reinnervation, n = 13) or SHAM exposure of the peroneal nerve (SHAM, n = 13). After a 4-month recovery period, isometric force, peak power, and maximum sustained power output were measured in the left extensor digitorum longus (EDL) muscle from each animal. Isometric force measurements revealed a specific force deficit of 14.3% in the reinnervated muscles. Power measurements during isovelocity shortening contractions demonstrated a normalized peak power deficit of 25.8% in the reinnervated muscles, which is accounted for by decreases in both optimal velocity (10.5%) and average force during shortening (13.7%). Maximum sustained power was similar in both groups. These data support our working hypothesis that both whole muscle force production and power output can be impaired in reinnervated muscle and that the relative deficits in power output exceed the deficits in force production. The mechanisms responsible for the deficits in force production appear to be independent of those that result in changes in peak power output. The measurement of muscle power output may represent a clinically relevant variable for studies of the recovery of mechanical function after motor nerve injury and repair.

Animals↗

PubMed2005

Nature's strategy for optimizing power generation in insect flight muscle.

Table 1 summarizes the primary mechanisms most likely responsible for modifying wing beat frequency (WBF) and muscle power in the Drosophila mutants discussed above. The different outcomes reflect different mechanisms that come into play, depending on the protein and site of the mutation. For example, the reduced muscle power and WBF of the RLC phosphorylation site mutant Mlc2(S6sA,S67A) reflect the reduced number of myosin heads available to form working cross-bridges and the concomitant reduction in muscle stiffness. The mixed results of the other mutants are more difficult to explain. For example, while the reduced muscle stiffness of the paramyosin rod mutant pm(S18A) and the projectin mutant bent(D)/+ may in part reflect mutation-related increases in compliance of the thick filaments (pm(S18A)) or connecting filaments (bent(D)/+), the elevated WBF is unexpected because one would expect reduced muscle stiffness to lower WBF rather than raise it. Other aspects of the results are equally baffling. In the case of pm(S18A), e.g., myofilament kinetics are enhanced, opposite to what one would predict from reduced myofilament stiffness (Wang et al. 1999), but consistent with a direct effect of the mutation on cross-bridge kinetics. It is tempting to speculate that the fly increases the resonance frequency of its flight system, perhaps even over-compensating, as a mechanism for bringing the optimum frequency of power output of the flight system in line with the optimum frequency of power output of the myofilaments in order to achieve flight. The fly might accomplish this by voluntarily activating flight control muscles that change the stiffness and shape of the thoracic box (Tu and Dickinson, 1996), thereby significantly changing the basal stiffness of the resonance system. This effective strategy would serve to tune flight system kinetics to that of the actomyosin motor for optimum power transmission. Notably, of the four thick filament mutations listed in Table 1 produce no significant changes in wing beat frequency, three exhibit reduced muscle power, so these flies must make other adjustments to maintain flight competency. These may be additional cases in which the effects of marked changes in cross-bridge kinetics (MHC IFI-EC), cross-bridge deployment (Mlc2(delta2-46), or sarcomere (thick filament) stiffness (pm(S-A4) and Df(3L) fln(1)/+) are ameliorated by the intervention of direct flight muscles. In summary, it may well be that the fly's general response to mutations that alter one component of the flight system is to alter another in order to maintain optimum transmission of power and flight competency. That is, nature's strategy for optimizing power generation throughout the flight system is probably the same as that at the level of the myofibril: that is, strengthen weak links, orient parts for optimum power production, and modify power train proteins through isoform switches or post-translational modifications to assure all components are in tune with one another.

Animals↗

PubMed2007

Age-related differences in adaptation during childhood: the influences of muscular power production and segmental energy flow caused by muscles.

Acquisition of skillfulness is not only characterized by a task-appropriate application of muscular forces but also by the ability to adapt performance to changing task demands. Previous research suggests that there is a different developmental schedule for adaptation at the kinematic compared to the neuro-muscular level. The purpose of this study was to determine how age-related differences in neuro-muscular organization affect the mechanical construction of pedaling at different levels of the task. By quantifying the flow of segmental energy caused by muscles, we determined the muscular synergies that construct the movement outcome across movement speeds. Younger children (5-7 years; n = 11), older children (8-10 years; n = 8), and adults (22-31 years; n = 8) rode a stationary ergometer at five discrete cadences (60, 75, 90, 105, and 120 rpm) at 10% of their individually predicted peak power output. Using a forward dynamics simulation, we determined the muscular contributions to crank power, as well as muscular power delivered to the crank directly and indirectly (through energy absorption and transfer) during the downstroke and the upstroke of the crank cycle. We found significant age x cadence interactions for (1) peak muscular power at the hip joint [Wilks' Lambda = 0.441, F(8,42) = 2.65, p = 0.019] indicating that at high movement speeds children produced less peak power at the hip than adults, (2) muscular power delivered to the crank during the downstroke and the upstroke of the crank cycle [Wilks' Lambda = 0.399, F(8,42) = 3.07, p = 0.009] indicating that children delivered a greater proportion of the power to the crank during the upstroke when compared to adults, (3) hip power contribution to limb power [Wilks' Lambda = 0.454, F(8,42) = 2.54, p = 0.023] indicating a cadence-dependence of age-related differences in the muscular synergy between hip extensors and plantarflexors. The results demonstrate that in spite of a successful performance, children construct the task of pedaling differently when compared to adults, especially when they are pushed to their performance limits. The weaker synergy between hip extensors and plantarflexors suggests that a lack of inter-muscular coordination, rather than muscular power production per se, is a factor that limits children's performance ranges.

Adaptation, Physiological↗

PubMed2000

Intraspecific scaling of flight power in the bat Glossophaga soricina (Phyllostomidae).

Aerodynamic theory predicts that power output during flight should vary with body mass by an exponent of 1.56 when wing morphology remains constant (within an individual), and by an exponent of 1.19 when wing morphology changes with body mass (within a species or between species). I tested these predictions by estimating the power input during horizontal flight in three pregnant and two subadult Glossophaga soricina using a multivariate regression model. This analysis yielded power input during resting and flight as well as the energetic equivalent of change in body mass. A comparison of the estimated flight power for pregnant G. soricina, with published data on flight power of nonpregnant adults, revealed that energy turnover in flight is highest for pregnant G. soricina. Flight power of a 13-g pregnant G. soricina was even higher than that of a 16-g non-pregnant Glossophaga longirostris. A least-squares regression analysis yielded the following equations for the intraspecific scaling of flight power with body mass: power input during horizontal flight (Pf) = 24099 body mass (bm; kg)2.15 (r2 = 0.97) for the intra-individual allometry (pregnancy) and Pf = 113 bm(kg)0.95 (r2 = 0.99) for the inter-individual allometry (ontogeny). Both mass exponents are not significantly different from the predicted values for the scaling relationship of flight power within an individual (1.56) and within a species (1.19). This is the first measurement of power input during flight for subadult and pregnant bats.

Adaptation, Physiological↗

PubMed1989

Power spectrum analysis of the EMG pattern in normal and diseased muscles.

The diagnostic value of analogue frequency analysis of EMG from patients with neuromuscular disorders has not been convincing. Using fast Fourier transformation it is today possible to obtain the EMG power spectrum on-line and with a better resolution. We examined the power spectrum of the EMG pattern of the brachial biceps muscle in 20 control subjects, 20 patients with myopathy, and 12 with neurogenic disorders. The electrical activity was sampled with a concentric needle electrode from 10 sites in each muscle. From each spectrum, mean power frequency, the power at 140 Hz, 1400 Hz, 2800 Hz and 4200 Hz relative to total power and the high/low ratio (1400/140) were obtained. The mean power frequency was higher at 10% than at 30% of maximal force. At a force of 30% of maximum the power spectrum analysis identified 55% and 64% of the patients with myopathy and neurogenic disorders, respectively. Although the diagnostic yield of the power spectrum analysis at a force of 10% of maximum was less than that at 30%, additional patients were identified at 10% increasing the diagnostic yield to 65% and 73% for patients with myopathy and neurogenic disorders, respectively. The best diagnostic parameters were the mean power frequency and the relative power at 1400 Hz.

Adolescent↗

PubMed2004

Redistribution of power spectrum of heart rate variability during acute umbilical artery embolism and hypoxemia in late-gestation fetal sheep.

OBJECTS: Fetal heart rate variability (HRV) is subject to a number of factors, including fetal distress. The aim of this study was to investigate the power spectral distribution of fetal heart rate variability during acute hypoxemia following umbilical artery embolism and to test the hypothesis that the relative proportion of frequency domains in total power of HRV, reflects the changes in HRV during hypoxemia more closely than the absolute values. METHODS: Acute hypoxemia was induced in seven catheterized late-gestation fetal sheep by repeated injections of microspheres to cause umbilical artery embolism. The very-low, low-, middle- and high-frequency domains (0-0.025, 0.025-0.125, 0.125-0.20, and 0.20-0.50 cycles/beat, respectively) were determined by power spectral analysis. RESULTS: Umbilical artery embolism induced marked fetal hypoxemia, hypercapnia and acidosis, accompanied by an increase in heart rate and a decrease in arterial blood pressure. These changes were associated with the increase in power over the entire frequency range and in the relative power in the low-frequency range (P<0.01), and with decrease in the relative power in the high-frequency range (P<0.05). Correlations were found between the relative power in the low- and high-frequency ranges and PO2 and between the relative power in these ranges and mean arterial blood pressure (P<0.05), but not PCO2 or pH. CONCLUSIONS: The present study indicates that acute hypoxemia induced by umbilical artery embolism leads to the redistribution of power spectral density of fetal HRV and that the relative proportion of individual frequency domains may reflect the changes in HRV during acute hypoxemia more closely than the absolute power values.

Animals↗

PubMed2006

Measuring total corneal power before and after laser in situ keratomileusis with high-speed optical coherence tomography.

PURPOSE: To measure total corneal power using optical coherence tomography (OCT). SETTING: Refractive surgery practices at 2 academic eye centers in Cleveland, Ohio, and Los Angeles, California, USA. METHODS: Thirty-two eyes of 17 patients having myopic laser in situ keratomileusis (LASIK) were enrolled in a prospective observational study. Manifest refraction, OCT, and Placido ring corneal topography with the Atlas 995 (Carl Zeiss Meditec, Inc.) were performed preoperatively and 3 months after laser in situ keratomileusis (LASIK). A high-speed (2000 axial scans/second) corneal and anterior segment OCT prototype was used. The total corneal power was calculated by summation of the anterior and posterior surface powers, and the value was compared with that determined by simulated keratometry. Two methods of measuring total corneal power were tested: the direct method, which used OCT to measure both corneal surfaces directly, and the hybrid method, which combined OCT with anterior corneal topography. RESULTS: The repeatability (pooled standard deviation) of measuring total corneal power using the hybrid method was 3 times better than that using the direct method. It was 0.23 diopter (D) before LASIK and 0.26 D after LASIK. Preoperative total power was 1.13 D (2.6%) lower than the simulated keratometry. Compared to the LASIK-induced change in spherical equivalent refraction, the change in total corneal power was equivalent, while the change in simulated keratometry power was significantly smaller (-18.8%) (P<.001). CONCLUSIONS: Keratometry using the traditional index of 1.3375 overestimated the total power in preoperative corneas and underestimated LASIK-induced refractive change. Measuring both corneal surfaces using a combination of OCT and Placido ring topography provided a better measure of total corneal power that closely tracked the refractive change in post-LASIK eyes.

Anterior Eye Segment↗

PubMed1999

Underestimation of intraocular lens power for cataract surgery after myopic photorefractive keratectomy.

OBJECTIVE: To assess the validity of corneal power measurement and standard intraocular lens power (IOLP) calculation after photorefractive keratectomy (PRK). DESIGN: Nonrandomized, prospective, cross-sectional, clinical study. PARTICIPANTS: A total of 31 eyes of 21 females and 10 males with a mean age at the time of surgery of 32.3 +/- 6.6 years (range, 24.4-49.5 years). INTERVENTION: Subjective refractometry, standard keratometry, TMS-1 corneal topography analysis, and pachymetry were performed before and 15.8 +/- 10.4 months after PRK for myopia (n = 24, -1 .5 to -8.0 diopters [D], mean -5.4 +/- 1.9 D) or myopic astigmatism (n = 7, sphere -2.0 to -7.5 D, mean -4.4 +/- 1.9 D; cylinder -1.0 to -3.0 D, mean -1.9 +/- 0.7 D). The IOLP calculations were done using two different formulas (SRK/T and HAIGIS). MAIN OUTCOME MEASURES: Keratometric power (K) and topographic simulated keratometric power (TOPO) as measured (Kmeas, TOPOmeas) and as calculated according to the change of power of the anterior corneal surface or according to the spherical equivalent change after PRK (Kcalc, TOPOcalc), IOLP for emmetropia, and postoperative ametropia for calculated corneal powers were assessed in a model. RESULTS: After PRK, mean Kmeas and TOPOmeas were significantly greater (0.4-1.4 D, maximum 3.3 D) than mean KRcalc and TOPOcalc (P < 0.0001). On average, the relative flattening of the cornea after PRK was underestimated by 14% to 30% (maximum, 83%) depending on the method of calculation. The mean theoretical IOLP after PRK ranged from + 17.4 D (SRK/T, TOPOmeas) to +20.9 D (HAIGIS, Kcalc) depending on the calculation method for corneal power and IOLP calculation formula used. For both formulas, IOLP values using keratometric readings were significantly higher (>1 D) than IOLP values using topographic readings (P < 0.0001). The theoretically induced mean refractive error after cataract surgery ranged from +0.4 to +1.4 (maximum, +3.1) D. Corneal power overestimation and IOLP underestimation correlated significantly with the spherical equivalent change after PRK (P = 0.001) and the intended ablation depth during PRK (P = 0.004). CONCLUSIONS: To avoid underestimation of IOLP and hyperopia after cataract surgery following PRK, measured corneal power values must be corrected. The calculation method using spherical equivalent change of refraction at the corneal plane seems to be the most appropriate method. In comparison with this method, direct power measurements underestimate corneal flattening after PRK by 24% on average. Use of conventional topography analysis seems to increase the risk of error. However, because this study is retrospective and theoretical, there is still a need for a large prospective investigation to validate the authors' findings.

Adult↗

PubMed1997

Growth spurts in brain maturation during middle childhood as indexed by EEG power spectra.

Developmental changes in background EEG power spectra were examined in 5-12-year-old children. The results confirmed older and more recent studies that reported continuous maturation and more sudden growth spurts in power spectral amplitude. EEG power in the Delta and Theta frequency bands decreased gradually with age, while power in the Alpha and Beta bands changed very little. Changes in spectral power were relatively increased between 6 and 7 years and between 9, 10 and 11 years. Some methodological problems concerning the assessment of cross-sectional age changes in EEG power spectra were addressed. Peak frequency increased with age; between 5 and 12 years the peak in the power spectrum shifted from fast Theta via slow Alpha to fast Alpha. Transformation of absolute power into relative power produced a high degree of interdependency between the broad bands. This interdependency affected the change with age of relative Alpha. Absolute power Alpha only changed in the eldest children, but because of a substantial decrease in Delta and Theta with increasing age, the proportion of Alpha relative to the other three bands increased. Hence, relative Alpha provided a good indication of the general maturational trend.

Age Factors↗

PubMed2001

EEG power, frequency, asymmetry and coherence in male depression.

Quantitative electroencephalographic (EEG) power topography has served as a useful tool for investigating brain regional mechanisms underlying affective disorders. In an attempt to examine the role of gender and widen the scope of the measurement probes used in these investigations, the traditional power and inter-hemispheric power ratio indices were supplemented with intra-hemispheric power ratios, mean frequency and both inter and intra-hemispheric coherence indices, in the comparison of depressed male patients and healthy controls. Resting (eyes closed), vigilance controlled EEG recordings from 21 scalp sites were collected from 70 male, unmedicated, unipolar major depressive disorder outpatients and 23 normal control male subjects. Absolute and relative power, frequency, asymmetry and coherence measures derived from spectrally analyzed EEGs were subjected to univariate analyses for group comparisons as well as to discriminant function analysis to examine their utility as classification indices. Compared with controls, patients evidenced greater overall relative beta power and, at bilateral anterior regions, greater absolute beta power and faster mean total spectrum frequency. Inter-hemispheric alpha power asymmetry index differences were noted, with controls exhibiting relatively reduced left hemisphere activation, and widespread reduced delta, theta, alpha and beta coherence indices. Whereas intra-hemispheric theta power asymmetry reduction was exhibited in patients bilaterally at all regions, group differences with intra-hemispheric beta power asymmetry were unilateral, being restricted to the right hemisphere. Discriminant analysis correctly classified 91.3% of the patients and controls. Quantitative EEG measurements in male depression appear to describe a pattern of aberrant inter-hemispheric synchrony/asymmetry and a profile of frontal activation.

Adult↗

PubMed1999

EEG power changes are related to regional cerebral glucose metabolism in vascular dementia.

OBJECTIVE: In patients with vascular dementia (VD), the relationship between the EEG power within the 4 frequency bands and the regional metabolic disturbances was investigated. METHODS: Twenty-eight patients (age 69.0+/-6.54 years) with VD according to NINDS-AIREN criteria underwent quantitative EEG recording, according to the 10-20 system, and fluodeoxyglucose F18 positron emission tomography (PET) at resting condition within 24 h. EEG power FFT-analysis was performed for delta (2-3.5 Hz), theta (4-7.5 Hz), alpha (8-13 Hz) and beta (13.5-20 Hz) frequency bands. Regional EEG power bands were related to regional glucose metabolism in anatomically defined regions corresponding to locations of the 10-20 system. RESULTS: Correlation between slow frequency band power and glucose metabolism was found. A widespread inverse relationship of delta power to metabolism was found between various regions; additionally, delta power was negatively correlated to cerebral glucose metabolism in individual regions. Frontal theta power correlated especially with thalamic CMRglc. Alpha power correlated directly with metabolism in the occipital lobe. No significant relationships were found between beta power and metabolism. CONCLUSION: We conclude that EEG power in VD is linked to glucose metabolism, indicating specific regional dependencies.

Aged↗

PubMedDate not supplied

Effects of increased impeller power in a production-scale Aspergillus oryzae fermentation.

The goal in this study was to determine how increased impeller power affects enzyme expression in large-scale (80 m(3)), fed-batch Aspergillus oryzae fermentations. An approximate 50% increase in average impeller power was achieved by increasing impeller diameter approximately 10%, while operating at slightly reduced speed. Measured decreases in terminal (95%) mixing time show increased power improved bulk mixing. However, batches operated at increased power had lower recombinant enzyme productivity. Biomass assays and image analysis tests showed no significant difference between "high power" and control batches, suggesting that slower growth, altered morphology, or increased hyphal fragmentation were not the cause of reduced productivity. Off-line tests on the shear-thinning, highly viscous broth show oxygen limitation occurred after transport through the air-liquid interface and imply the limitation may involve bulk mixing. Specifically, oxygen transfer may be limited to a small zone surrounding each impeller. When this is the case, oxygen mass transfer will be determined by both impeller shear and fluid circulation, which have been characterized with the energy dissipation/circulation function (EDCF). EDCF values during control fermentations were approximately constant at 25 kW m (-3) s(-1), while EDCF values during "high power" batches fell linearly from 40 to 15 kW m (-3) s(-1). The point at which "high power" EDCF values drop below those in control fermentations corresponds almost exactly with the point at which product titer stops increasing. Thus, our findings suggest oxygen mass transfer was less efficient during the latter half of "high power" fermentations because of reductions in impeller speed and subsequent decreases in EDCF values. This observation has clear implications during the scale-up of viscous fungal fermentations, implying that not only is the level of impeller power important, but also relevant is how this power is applied.

Aspergillus oryzae↗

PubMed1999

Changes in EEG spectral power in the prefrontal cortex of conscious rats elicited by drugs interacting with dopaminergic and noradrenergic transmission.

1. The electroencephalographic (EEG) effects of drugs interacting with dopaminergic and noradrenergic systems were studied in conscious rats. Power spectra (0 - 30 Hz) were recorded from electrodes implanted bilaterally in the prefrontal cortex. Drug effects on EEG power were calculated as the spectral power following drug administration divided by the spectral power after vehicle administration. 2. Dopaminergic agonists at low doses, (apomorphine 0. 01 mg kg-1 s.c., quinpirole 0.01 mg kg-1 i.p.) and dopaminergic antagonists (haloperidol 1 mg kg-1 i.p., raclopride 2.5 mg kg-1 s.c. ), which decrease dopaminergic transmission, induced an increase of EEG power. Conversely, dopaminergic agonists at higher doses (apomorphine 0.5 mg kg-1 s.c., quinpirole 0.5 mg kg-1 i.p.) which increase activation of postsynaptic D2 and D3 receptors, induced a decrease of EEG power. 3. The alpha1-adrenoceptor antagonists (phenoxybenzamine 0.64 mg kg-1 s.c., prazosin 0.32 mg kg-1 s.c.) and the alpha2-adrenoceptor agonists (UK 14304 0.05 mg kg-1 s.c., clonidine 0.025 mg kg-1 i.p.), which decrease noradrenergic transmission, induced an increase of EEG power. Conversely, the alpha1-adrenoceptor agonist, cirazoline (0.05 mg kg-1 s.c.), the adrenergic agent modafinil (250, 350 mg kg-1 i.p.) and alpha2-adrenoceptor antagonists (RX 821002 0.01 mg kg-1 s.c., yohimbine 0.5 mg kg-1 i.p.), which increase noradrenergic transmission, induced a decrease of EEG power. The effects of prazosin (0.64 mg kg-1 s.c.) were dose-dependently antagonized by co-administration with modafinil and cirazoline, but not by apomorphine. 4. In conclusion, pharmacological modulation of dopaminergic and noradrenergic transmission may result in consistent EEG changes: decreased dopaminergic or noradrenergic activity induces an increase of EEG spectral power; while increased dopaminergic or noradrenergic activity decreases EEG spectral power.

Adrenergic Agents↗

PubMed2002

The relationship between leg power and physical performance in mobility-limited older people.

OBJECTIVES: The purpose of this study was to assess the influence of leg power and leg strength on the physical performance of community-dwelling mobility-limited older people. DESIGN: Cross-sectional analysis of baseline data from a 12-week randomized controlled exercise-intervention study. SETTING: Exercise laboratory within the Department of Health Science of an urban university. PARTICIPANTS: Forty-five community-dwelling mobility-limited people (34 women, 11 men), aged 65 to 83. MEASUREMENTS: Health status, depression, cognition, physical activity, and falls efficacy; physiological measures of lower extremity strength and power; and measures of physical performance. RESULTS: Through bivariate analyses, leg power was significantly associated with physical performance as measured by stair-climb time, chair-stand time, tandem gait, habitual gait, maximal gait, and the short physical performance battery describing between 12% and 45% of the variance (R2). Although leg power and leg strength were greatly correlated (r = .89) in a comparison of bivariate analyses of strength or power with physical performance, leg power modeled up to 8% more of the variance for five of six physical performance measures. Despite limitations in sample size, it appeared that, through quadratic modeling,the influence of leg power on physical performance was curvilinear. Using separate multivariate analyses, partial R2 values for leg power and leg strength were compared, demonstrating that leg power accounted for 2% to 8% more of the variance with all measures of physical performance. CONCLUSION: Leg power is an important factor influencing the physical performance of mobility-limited older people. Although related to strength, it is a separate attribute that may exert a greater influence on physical performance. These findings have important implications for clinicians practicing geriatric rehabilitation.

Age Factors↗

PubMed2004

Mechanically braked Wingate powers: agreement between SRM, corrected and conventional methods of measurement.

In this study, we assessed the agreement between the powers recorded during a 30 s upper-body Wingate test using three different methods. Fifty-six men completed a single test on a Monark 814E mechanically braked ergometer fitted with a Schoberer Rad Messtechnik (SRM) powermeter. A commercial software package (Wingate test kit version 2.21, Cranlea, UK) was used to calculate conventional and corrected (with accelerative forces) values of power based on a resistive load (5% body mass) and flywheel velocity. The SRM calculated powers based on torque (measured at the crank arm) and crank rate. Values for peak 1 and 5 s power and mean 30 s power were measured. No significant differences (P >0.05) were found between the three methods for 30 s power values. However, the corrected values for peak 1 and 5 s power were 36 and 23% higher (P <0.05) respectively than those for the conventional method, and 27 and 16% higher (P <0.05) respectively than those for the SRM method. The conventional and SRM values for peak 1 and 5 s power were similar (P >0.05). Power values recorded using each method were influenced by sample time (P <0.05). Our results suggest that these three measures of power are similar when sampled over 30 s, but discrepancies occur when the sample time is reduced to either 1 or 5 s.

Anaerobic Threshold↗

PubMedDate not supplied

Stability and accuracy of power and phase measurements of a VVM system designed for online quality control of the BSD-2000 (-3D) DHT system.

Accurate control of power and phase is essential for the quality assurance of hyperthermia treatments. Hereto, an external measurement device was inserted, built around a Vector Voltmeter (VVM), in order to assess online the performance of the steering capability of the BSD-2000 and later the BSD-2000-3D system. This paper only concerns the power and phase calibration of the signal in the path between the power and phase detection probes of the BSD-system and power and phase measurement point of the VVM. The calibration is performed in the frequency range of 60-120 MHz using a network analyser with a frequency range of 0.01-500 MHz. More importantly, by repeating the calibration periodically over the last 3 years, the stability and accuracy of the power and phase measurements were determined using the VVM system. The results of the power calibration show that the VVM system, concerning its power and phase measurement, is stable in time. The variation of the power measured with the VVM system is less than 0.22 dB (5.2%) for the latest configuration of the BSD-2000-3D system. The variation of the VVM-based phase measurements of the latter configurations is 1.1 degrees or less. From the results of the power and phase measurements in the BSD 2000 system reported in previous studies using other measurement systems, it follows that the uncertainties of the power and phase measurements with the currently proposed VVM system are small enough to assess accurately the performance of the BSD system concerning its steering capability.

Calibration↗

PubMed2004

Optimal power deposition patterns for ideal high temperature therapy/hyperthermia treatments.

If it were possible to achieve, an ideal high temperature therapy or hyperthermia treatment would involve a single heating session and yield a desired thermal dose distribution in the tumour that would be attained in the shortest possible treatment time without heating critical normal tissues excessively. Simultaneously achieving all of these goals is impossible in practice, thus requiring trade-offs that allow clinicians to approach more closely some of these ideal goals at the expense of others. To study the basic nature of a subset of these trade-offs, the present simulation study looked at a simple, ideal case in which the tumour is heated by a single, optimized (with respect to space) power pulse, with no power deposition in the normal tissue. Results were obtained for two different clinical strategies (i.e. trade-off approaches), including: (1) an 'aggressive' approach, wherein the desired, uniform thermal dose is completely delivered to the tumour during the power-on period. This approach gives the clinician the satisfaction of knowing that the tumour was treated completely while power was being delivered, and yields the shortest attainable tumour dose delivery time. However, that benefit is attained at the cost of both 'overdosing' the tumour during the subsequent cool down period and, paradoxically, requiring a longer, overall treatment time. Here, the treatment time is considered as that time interval from the initiation of the heating pulse to the time at which the entire tumour has decayed to a specified 'safe' temperature--below 43 degrees C for our calculations. And, (2) a 'conservative' approach is considered, wherein the desired uniform dose is attained at the post-heating time at which the complete tumour cools back down to 'basal' conditions, taken as 4 h in this study. This conservative approach requires less applied power and energy and avoids the 'overdosing' problem, but at the cost of having a tumour dose delivery time that can be significantly longer than the heating pulse duration. This approach can require that clinicians wait a significant time after the power has been turned off before being able to confirm that the desired tumour thermal dose was reached. The present findings show that: (1) for both clinical strategies, an optimal power deposition shape (with respect to position in the tumour) can always be found that provides the desired uniform thermal dose in the tumour, regardless of the heating pulse duration chosen or the tumour perfusion pattern; and (2) shorter heating pulses are preferable to longer ones in that they require less total energy, take less total time to treat the patients, and have optimal power deposition patterns less influenced by perfusion. On the other hand, shorter pulses always require higher temperatures, and for the 'aggressive' clinical approach, they give significantly larger excess thermal doses in the tumour. The aggressive approach always requires longer treatment times than comparable conservative treatments. The optimal power patterns for both strategies involve a high-power density at the tumour boundary, which frequently creates a 'thermal wave' that contributes significantly to the final thermal dose distribution attained.

Algorithms↗