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PubMed2002

Selecting passive and active materials for 1.3 composite power transducers.

1.3 PZT-polymer composites were fabricated using the dice and fill method with various PZT types and volume fractions. These composites were evaluated for power underwater transducer applications with an air backed and no matching layer configuration. Electrical input and acoustical output powers were monitored as a function of the drive level. Total acoustic power densities of 30 W/cm2 were obtained with a P189/epoxy piezocomposite vibrating at 350 kHz with a low duty cycle (1-5%) and with a 90% efficiency. Power densities up to 20 W/cm2 were measured with a 50% duty cycle. Evolution and destruction of the transducers were monitored versus increasing averaged power. It was observed that better efficiencies were obtained with low volume fraction configurations allowing natural acoustic impedance matching to water. It was found that hard PZT type (Navy III) are optimal compositions even for piezocomposite transducers. It is shown that, unlike a common belief, the polymer mechanical losses are comparable to those of the active ceramic justifying that 1.3 piezocomposites are suited for low-cost power applications. In fact, the main limitation induced by the polymer phase is a strong thermal breakdown when the temperature of the transducer approaches the glass transition region of the polymer. Measurements of the polymer losses as a function of the temperature were obtained confirming this point and offering interesting new alternatives for future composite power transducers.

Journal Article↗

PubMed2003

The detection of stage I ovarian cancer by three-dimensional sonography and power Doppler.

OBJECTIVE: The objective was to determine the diagnostic accuracy of three-dimensional (3D) sonography and 3D power Doppler imaging, used together with standard 2D transvaginal grayscale and color/power Doppler modalities, for preoperative sonographic assessment of suspected ovarian lesions. METHODS: Five-year retrospective analysis was performed by our experts on ultrasonography and surgery on the reports from 43 referred patients with suspected stage I ovarian cancer. All patients were evaluated during the week prior to surgery at our department. Preoperative sonographic assessment included careful examination of ovarian volume, morphology, and vascularity by four complementary sonographic methods. Scoring systems combining morphological and Doppler parameters were adopted for 2D and 3D sonographic examinations. Final diagnosis was confirmed by a histopathologist. RESULTS: Out of the 43 stage I ovarian cancers, 42 cases were successfully detected preoperatively by four complementary sonographic methods. Only 30 (69.8%) and 37 (86.1%) cases of stage I ovarian cancer were detected by 2D grayscale and combined 2D grayscale and color Doppler sonography, respectively. Morphological analysis obtained by 3D sonography alone detected 32 of 43 ovarian malignancies, reaching a diagnostic rate of 74.4%. Qualitative analysis of tumor vascularity architecture by 3D power Doppler significantly improved the sonographic management process and successfully detected 41 cases of stage I ovarian cancer (95.4%). When morphological features obtained by 3D sonography were added to 3D power Doppler findings, we achieved an even higher diagnostic accuracy of 97.7%. We found a statistically significant difference (P </= 0.01) in diagnostic rates of 3D power Doppler, and especially the combined use of 3D sonography and 3D power Doppler in comparison to those obtained with transvaginal 2D grayscale (P </= 0.002 and P </= 0.001, respectively) or 3D sonography (P </= 0.006 and P </= 0.002, respectively). CONCLUSIONS: In comparison to transvaginal 2D grayscale or 3D sonography, 3D power Doppler and especially the combined use of 3D sonography and power Doppler imaging significantly improve diagnostic accuracy in preoperative sonographic assessment of suspected ovarian lesions.

Female↗

PubMed1998

Effect of power settings versus temperature change at the root surface when using multiple fiber sizes with a Holmium YAG laser while enlarging a root canal.

The aim of this study was to determine if there is an increase in temperature at the root surface as the canal is enlarged when using a Holmium:YAG laser. An increase might be expected because, as the canal is enlarged, there is less dentin between the canal walls and the outer cementum surface of the root to absorb the heat. Sixty single-rooted human teeth were randomly assigned to 1 of 3 groups according to laser power settings: 0.50, 0.75, and 1.00 W. Each tooth in each power group was subjected to lasing using fiber sizes of 140, 245, 355, and 410 microns. The dependent variables in these analyses included: (a) change in temperature, measured with T-type thermocouples placed 2 mm from the coronal and apical ends of the root; (b) depth of laser in the tooth; (c) depth that a conventional fiber could be inserted after lasing; and (d) tooth physical dimensions. ANOVA for coronal temperature showed no interaction between fibers and power settings. Repeated-measures ANOVA for apical temperature showed a significant difference between fibers, but not between power settings. No interaction between fibers and power settings was observed. For the depth of tooth during lasing (how far the fiberoptic guide penetrated into the tooth), no interaction between fibers and power settings was observed. Pairwise contrasts revealed that all fibers were different from one another, with depth decreasing as fiber size increased. Depth files could be inserted that showed the depth significantly decreased as file size increased from 50 through 70. ANOVAs illustrated that there were no significant differences between power settings for any of the five tooth physical dimensions. All temperature differences observed apically and coronally were between 0 degree to 10 degrees C, with the majority (> 98%) being between 0 degree to 5 degrees C. After lasing with the 410-micron fiber, the root canals were widened to at least 45 or 50 K-files (450 or 500 microns). However, by using a 410-micron fiber, the laser did not seem to widen the canal beyond a 500-micron diameter.

Analysis of Variance↗

PubMed1990

Effect of corneal hydration and intraocular pressure on keratometric power after experimental radial keratotomy.

Persistent diurnal fluctuations in vision are common after radial keratotomy (RK), associated with a myopic change in refraction and keratometric power as the day progresses. A possible relation between keratometric power and either intraocular pressure (IOP) or corneal hydration was investigated in a cadaver eye model. First, keratometric power was measured before and after RK while IOP was varied from less than 0.5 to 20 mmHg. A nonlinear relation was found; in particular, changes in IOP in the physiologic range had no effect on keratometric power after RK. In a second set of experiments, keratometric power was measured after RK as the dehydrated corneas were gradually hydrated with balanced salt solution. After RK, keratometric power decreased markedly as corneal hydration increased (0.33 diopters [D] per 10-microns increase in thickness). The keratometric power of control corneas was not affected by changes in IOP or hydration. The author concludes that diurnal fluctuations in refraction after RK are probably caused by diurnal fluctuations in corneal hydration rather than changes in IOP.

Body Fluids↗

PubMed2002

Estimating sample size in functional MRI (fMRI) neuroimaging studies: statistical power analyses.

Estimation of statistical power in functional MRI (fMRI) requires knowledge of the expected percent signal change between two conditions as well as estimates of the variability in percent signal change. Variability can be divided into intra-subject variability, reflecting noise within the time series, and inter-subject variability, reflecting subject-to-subject differences in activation. The purpose of this study was to obtain estimates of percent signal change and the two sources of variability from fMRI data, and then use these parameter estimates in simulation experiments in order to generate power curves. Of interest from these simulations were conclusions concerning how many subjects are needed and how many time points within a scan are optimal in an fMRI study of cognitive function. Intra-subject variability was estimated from resting conditions, and inter-subject variability and percent signal change were estimated from verbal working memory data. Simulations derived from these parameters illustrate how percent signal change, intra- and inter-subject variability, and number of time points affect power. An empirical test experiment, using fMRI data acquired during somatosensory stimulation, showed good correspondence between the simulation-based power predictions and the power observed within somatosensory regions of interest. Our analyses suggested that for a liberal threshold of 0.05, about 12 subjects were required to achieve 80% power at the single voxel level for typical activations. At more realistic thresholds, that approach those used after correcting for multiple comparisons, the number of subjects doubled to maintain this level of power.

Adult↗

PubMed1997

Abnormal passive head-up tilt test in subjects with symptoms of anxiety power spectral analysis study of heart rate and blood pressure.

Previous reports that subjects with anxiety symptoms are at higher risk of sudden death may imply that anxiety induces stable sympathetic hyperactivity. To address this subject, in persons with and without anxiety symptoms, we evaluated autonomic nervous system activity by power spectral analysis of heart-rate and arterial-pressure variability at baseline (rest) and after sympathetic stress (tilt). The 117 subjects selected (56 men and 61 women, age range 23-87 years) were subdivided by questionnaire into three groups: 49 subjects (mean age 55.8+/-2.8 years) had no anxiety symptoms; 36 (mean age 56.8+/-3.6 years) had one anxiety symptom; and 32 (mean age 55.0+/-2.9 years) had two or more anxiety symptoms. Power spectral analysis recognizes three main components: high frequency (HF), chiefly reflecting vagal efferent activity; low frequency (LF), reflecting sympathetic activity; and very-low-frequency (VLF). The ratio of low- to high-frequency powers (LF:HF) of heart rate variability provides a measure of sympathovagal balance. Power spectral analysis showed that subjects with two or more anxiety symptoms had significantly lower resting values for all power spectral components of heart rate variability: total power (TP), VLF, LF, and HF than did symptomless controls (P<0.05). The highest anxiety-score groups also had a higher baseline LF:HF than the other two groups (P<0.05). Their resting LF:HF ratio correlated positively with anxiety symptom scores (r=0.72, P<0.0001). Tilt induced opposite results: the highest anxiety-score groups had a significantly lower LF:HF ratio; the ratio correlated inversely with their anxiety scores (r=-0.69; P<0.0001). Recordings of resting systolic arterial pressure variability showed that the group with two or more anxiety symptoms had significantly higher LF power (P<0.05) than symptomless controls. Our findings suggest that persons with high anxiety scores have baseline cardiac sympathetic hyperactivity. They also have low heart-rate variability, possibly explaining their susceptibility to sudden cardiac death.

Adult↗

PubMed1997

Chemical response of the lichen Punctelia subrudecta (Nyl.) Krog transplanted close to a power station in an urban-industrial environment.

The lichen Punctelia subrudecta (Nyl.) Krog was transplanted to 22 biomonitoring sites in a northwestern area of Córdoba city, Argentina and tested for chlorophyll a, chlorophyll b, phaeophytin a, soluble protein, hydroperoxy conjugated dienes (HPCD), malondialdehyde (MDA) concentration and sulphur accumulation. A pollution index (PI) was calculated for each biomonitoring site. The biomonitoring sites were set according to (1) traffic levels, (2) industrial density and (3) distance of the power station close to each site. The biomonitor's chemical response was associated with industries as well as power stations. Significant differences were observed in sulphur content, MDA concentration and PI values in lichen material transplanted to sites with different industrial densities. The higher values for these parameters were found at sites with high industrial levels. At the same time, significant differences were detected for sulphur content in samples at different distances from the power station, with higher accumulation in samples located far from the power plant. For MDA concentration, effect of different levels of industrial density was observed only at points close to the power station, probably because of higher levels of humidity near the power plant. For PI significantly higher values were observed in samples at points far from the power station and with high industrial density. This shows the additive effect of the principal emission sources that act on the response of P. subrudecta to air pollutants.

Journal Article↗

PubMed1998

In situ measurements of Doppler power vs. flow turbulence intensity in red cell suspensions.

Whereas previous studies have shown that ultrasonic backscatter and Doppler power from blood are affected by flow turbulence, turbulence level has only been inferred from the flow Reynolds number and not directly measured. In this study, both ultrasonic Doppler power and flow turbulence intensity were measured in situ to quantify the relationship between Doppler power and flow turbulence. Three grid meshes of different geometries were used in a steady-flow mock loop to generate controlled levels of flow turbulence in porcine red blood cell saline suspensions. Doppler power was measured by a 10-MHz PW Doppler flowmeter, and the turbulence intensity by using constant-temperature hot film anemometry. We showed that Doppler power is affected by turbulence and hematocrit in a complex way. At a fixed hematocrit, Doppler power increases nonlinearly with turbulence intensity and, at fixed turbulence intensity, Doppler power peaks at an optimal hematocrit level that increases with turbulence level. The shape factor, introduced by Lucas and Twersky (1987) to take into account effects of shape and orientation of the scatterers in a dense distribution of small and tenuous scatterers, was estimated by fitting the experimental data to the theoretical model. The results indicate that shape factor decreases with increasing turbulence intensity.

Animals↗

PubMed2001

Improved prediction of intraocular lens power using partial coherence interferometry.

PURPOSE: To evaluate the feasibility of using a new optical biometry technique, dual-beam partial coherence interferometry (PCI), to improve intraocular lens (IOL) power prediction in cataract surgery. SETTING: Department of Ophthalmology, Vienna General Hospital, and Institute of Medical Physics, University of Vienna, Vienna, Austria. METHODS: Preoperative axial length (AL) data obtained with PCI biometry and applanation ultrasound (US) biometry in 77 eyes of 51 patients was applied to 4 commonly used IOL power formulas. The refractive outcome and the mean absolute error (MAE) were calculated for each formula using both biometry methods. A linear multiple-regression model based on preoperative PCI biometry data was derived to predict the postoperative anterior chamber depth (ACD). The predictive power of this regression model was assessed by adding the predicted ACD to the SRK/T formula. Predicted residuals were calculated to evaluate the feasibility and stability of this modified IOL power formula. RESULTS: Using PCI instead of US biometry significantly improved the refractive outcome with all 4 IOL power formulas. The Holladay I and SRK/T formulas yielded an MAE of 0.44 diopter (D) using PCI AL data and 0.56 D and 0.57 D, respectively, using US biometry data. The SRK/T formula combined with the PCI regression model for postoperative ACD prediction performed slightly better (MAE 0.42 D) than the conventional SRK/T formula alone. Predicted residuals revealed an MAE of 0.46 D, proving the predictive performance of the new formula. CONCLUSIONS: Partial coherence interferometry biometry applied to several widely used IOL power formulas yielded significantly better IOL power prediction and therefore refractive outcome in cataract surgery than US biometry. Further improvement can be achieved by applying PCI to a modified SRK/T formula that predicts the postoperative ACD using PCI biometry data.

Biometry↗

PubMed2003

Implantation of a single-piece, hydrophilic, acrylic, minus-power foldable posterior chamber intraocular lens in a rabbit model: clinicopathologic study of posterior capsule opacification.

PURPOSE: To compare the extent of posterior capsule opacification (PCO) after implantation of a standard-power biconvex Centerflex intraocular lens (IOL) and a newly introduced biconcave high-minus-power Centerflex design in rabbit eyes. SETTING: The Center for Research on Ocular Therapeutics and Biodevices, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, and the David J. Apple, MD, Laboratories for Ophthalmic Devices Research, John A. Moran Eye Center, University of Utah School of Medicine, Salt Lake City, Utah, USA. METHODS: Twelve rabbits had phacoemulsification and implantation of 2 foldable single-piece hydrophilic acrylic Centerflex posterior chamber IOLs. The right eyes received a standard-power (+21.00 diopters [D]) biconvex-optic lens and the left eyes, a minus-power (-7.00 D) biconcave-optic IOL. Formation of PCO was evaluated 3 weeks after surgery using the Miyake-Apple posterior photography technique. Histological sections from each globe were prepared to analyze capsular bag status and assess postsurgical intracapsular lens epithelial cell (LEC) proliferation, especially ingrowth of LECs across the visual axis. The data were analyzed using the Kruskal-Wallis 1-way analysis of variance for nonparametric measurements and the Mann-Whitney rank sum test. RESULTS: There was no significant difference in Soemmering's ring formation between the 2 IOL models. The biconcave minus-power IOL showed significantly lower central and peripheral PCO scores than the biconvex standard-power lens (P<.05). Pathological evaluations revealed that the effective site of blockage of LECs was at the truncated optic edge of both lenses, even in the presence of retained and/or regenerative cortical material. CONCLUSIONS: This study confirms the efficacy of a truncated IOL optic in helping reduce the incidence of PCO. Both IOL designs have optic geometries that create clear-cut barrier effects. However, the biconcave minus-power IOL, which has a thicker, square, truncated optic edge with a ridge that encircles the periphery of the optic for 360 degrees, appears to have an enhanced barrier effect, especially at the optic-haptic junction. This further minimizes the ingrowth of migrating LECs toward the visual axis.

Acrylic Resins↗

PubMed1997

Intraocular lens power formula based on vergence calculation and lens design.

PURPOSE: To present a new method of intraocular lens (IOL) power calculation that takes into account the power-dependent variation in lens design. SETTING: Department of Ophthalmology, Aalborg, Denmark. METHODS: Information on exact IOL design is derived from the manufacturers' cutting cards. These data were built into an IOL calculation formula based on exact ray tracing and vergence calculation. All algorithms are demonstrated. RESULTS: The method is optically correct as all refractive surfaces are characterized with respect to both position and refractive power. In simulation models, the Naeser and the Holladay formulas performed similarly, while the SRK/T formula predicted higher postoperative refractions for low-power IOLs. CONCLUSION: It is possible to incorporate the exact IOL design into an IOL power calculation formula. Theoretically, the Naeser formula should increase the accuracy of IOL power calculation; however, this has yet to be proved from empirical data. The formula provides an advantage in analysis of postoperative pseudophakia for experimental/scientific purposes because all intraocular distances and powers may be measured or calculated.

Algorithms↗

PubMed2000

Towards a neurobiology of dysfunctional arousal in depression: the relationship between beta EEG power and regional cerebral glucose metabolism during NREM sleep.

This study sought to clarify the neurobiological basis of variations in one aspect of central nervous system 'arousal' in depression by characterizing the functional neuroanatomic correlates of beta electroencephalographic (EEG) power density during non-rapid eye movement (NREM) sleep. First, nine healthy (n=9) subjects underwent concurrent EEG sleep studies and [18F]2-fluoro-2-deoxy-D-glucose ([18F]FDG) positron emission tomography (PET) scans during their first NREM period of sleep in order to generate hypotheses about specific brain structures that show a relationship between increased beta power and increased relative glucose metabolism. Second, brain structures identified in the healthy subjects were then used as a priori regions of interest in similar analyses from identical studies in 12 depressed subjects. Statistical parametric mapping was used to identify the relationship between beta power and relative regional cerebral glucose metabolism (rCMRglu) during NREM sleep. Regions that demonstrated significant correlations between beta power and relative cerebral glucose metabolism in both the healthy and depressed subjects included the ventromedial prefrontal cortex and the right lateral inferior occipital cortex. During a baseline night of sleep, depressed patients demonstrated a trend toward greater beta power in relation to a separate age- and gender-matched healthy control group. In both healthy and depressed subjects, beta power negatively correlated with subjective sleep quality. Finally, in the depressed group, there was a trend for beta power to correlate with an indirect measure of absolute whole brain metabolism during NREM sleep. This study demonstrates a similar relationship between electrophysiological arousal and glucose metabolism in the ventromedial prefrontal cortex in depressed and healthy subjects. Given the increased electrophysiological arousal in some depressed patients and the known anatomical relations between the ventromedial prefrontal cortex and brain activating structures, this study raises the possibility that the ventromedial prefrontal cortex plays a significant role in mediating one aspect of dysfunctional arousal found in more severely aroused depressed patients.

Adult↗

PubMed1998

The role of power Doppler sonography in the evaluation of superficial soft tissue abscesses.

OBJECTIVE: To evaluate the efficacy of power doppler ultrasonography in depicting increased vasculature and hyperemia around the superficial soft tissue abscess. MATERIALS AND METHODS: 21 patients with soft tissue abscess were evaluated with gray scale imaging, color doppler sonography, power doppler sonography and computed tomography. In each case attempts were made using power doppler sonography to demonstrate any areas of increased vascularity around the lesion. The results were compared with computed tomographic findings. RESULTS: Peripheral hyperemia and increased vasculature were demonstrated with power doppler sonography in 19 of 21 patients with soft tissue abscess. The hyperemic area demonstrated around the wall of the abscess by power doppler sonography was similar to the enhanced area shown by computed tomography performed after contrast administration. CONCLUSION: Power doppler sonography shows increased vasculature and hyperemia in the wall of abscesses. Therefore, power doppler sonography can be used to assist with the diagnosis of superficial soft tissue abscess.

Abscess↗

PubMed2002

Statistical power in observer-performance studies: comparison of the receiver operating characteristic and free-response methods in tasks involving localization.

RATIONALE AND OBJECTIVES: Statistical power, defined as the probability of detecting real differences between imaging modalities, determines the cost in terms of readers and cases of conducting receiver operating characteristic (ROC) studies. Neglect of location information in lesion-detection studies analyzed with the ROC method can compromise power. Use of the alternative free-response ROC (AFROC) method, which considers location information, has been discouraged, because it neglects intraimage correlations. The relative statistical powers of the two methods, however, have not been tested. The purpose of this study was to compare the statistical power of ROC and AFROC methods using simulations. MATERIALS AND METHODS: A new model including intraimage correlations was developed to describe the decision variable sampling and to simulate data for ROC and AFROC analyses. Five readers and 200 cases (half of which contained one signal) were simulated for each trial. Two hundred trials, equally split between the null hypothesis and alternative hypothesis, were run. Ratings were analyzed with the Dorfman-Berbaum-Metz method, and separation of the null hypothesis and alternative hypothesis distributions was calculated. RESULTS: The AFROC method yielded higher power than the ROC method. Separation of the null hypothesis and alternative hypothesis distributions was larger by a factor of 1.6 regardless of the presence or absence of intraimage correlations. The effect of the incorrect localizations during ROC analysis of localization data is believed to be the major reason for the enhanced power of the AFROC method. CONCLUSION: The AFROC method can yield higher power than the ROC method for studies involving lesion localization. Greater consideration of this methodology is warranted.

Computer Simulation↗

PubMed2004

Red muscle recruitment during steady swimming correlates with rostral-caudal patterns of power production in trout.

Rainbow trout (Oncorhynchus mykiss) and brook trout (or charr, Salvelinus fontinalis) display different rostral-caudal patterns of power production by the red or aerobic muscle during steady swimming. The anterior muscle of rainbow trout produces much less power for swimming than the posterior, while in brook trout there is no variation in power output. To determine if red muscle recruitment is associated with anterior-posterior patterns of power production, electromyography (EMG) was used to record red muscle activity at three body positions across a range of swimming speeds in fish of each species. The initial recruitment of the anterior red muscle in swimming rainbow trout was predicted to lag behind, i.e. occur at higher speeds, that of the posterior due to the variation in power production, but no variation in recruitment was expected for brook trout. Burst of red muscle EMG activity occurring with each tailbeat was analyzed for frequency (tailbeat frequency), duty cycle (DC) (duration of burst relative to the period of the tailbeat) and burst intensity (BI) (magnitude of the measured EMG activity). Brook trout swam with higher tailbeat frequencies and longer values of DC than rainbow trout. Both species showed a pattern of longitudinal variation in DC, with longer DC values in the anterior red muscle. BI also differed significantly along the length of rainbow trout but not brook trout. In the former, BI of anterior muscle was significantly less than the posterior at lower steady swimming speeds. The EMG data suggest that power production and muscle recruitment are related. In rainbow trout, where there is longitudinal variation in muscle power output, there are also significant rostral-caudal differences in red muscle recruitment.

Analysis of Variance↗

PubMed2001

Power output of legs during high intensity cycle ergometry: influence of hand grip.

Traditionally, leg cycle ergometry is used to assess the power output of the lower limbs. However, it is suspected that the upper body makes a significant, albeit as yet unknown, contribution to the measured power output, and as such, the lean mass of the whole body should be considered during ergometric assessment. To test this idea, indices of mechanical power output were obtained from 11 subjects during high intensity leg cycle ergometry tests (20 second duration; 75 grams per kilogram total body mass) using two protocols: one with a standard handle-bar grip (with grip) and one with supinated wrists (without-grip). Peak mechanical power, mean mechanical power, fatigue index and total mechanical work values were calculated for each subject during each test and the sample mean differences associated with the two protocols were compared using paired Student t-tests. The with-grip protocol yielded significantly greater peak mechanical power output than the without-grip protocol (886+/-124 W and 815+/-151 W, respectively), suggesting a significant upper body contribution to the maximum power output measured for the legs. As a first step towards quantifying the upper body involvement during leg cycle ergometry, surface electromyography of the forearm musculature was measured in a twelfth subject whilst performing each of the test protocols. During the with-grip ergometer tests, the intensity of electrical activity in the forearm musculature was similar, if not greater than, the intensity of electrical activity recorded for the forearm musculature during 100% maximum voluntary hand grip-dynamometer contractions, suggesting maximum isometric-type forearm muscle contraction during the with-grip leg ergometry tests. These findings suggest that the performance of traditional-style leg cycle ergometry requires a muscular contribution from the whole body. As such, researchers should be mindful of this, both in terms of the allocation of ergometer loads, and in the analysis of blood-borne metabolites.

Adult↗

PubMed1998

The relationship between aerobic fitness and both power output and subsequent recovery during maximal intermittent exercise.

The primary aim of the study was to establish a link between aerobic adaptation and both the recovery from maximal short duration exercise, and the ability to maintain power output in a subsequent bout. The question as to whether the aerobic adaptations facilitating recovery are centrally or peripherally located was also examined. Male university level rugby and soccer players (n=20) volunteered for the study. Mean (SD) age, mass and maximal oxygen uptake (VO2 max) was 21.9 (1.8) years, 84.7 (12.7) kg and 52.7 (6.9) ml x kg(-1) x min(-1) respectively. Subjects completed six 15s maximal intensity sprints (90s active recovery) on a Monark friction braked cycle ergometer. A significant relationship (r=-.49, P=0.03) was obtained between VO2 max (mL x kg(-1) x min(-1)) and the percent drop-off in mean power in bouts 5 and 6 compared with bout 1. A correlation of r=-.62 (P=0.002) was obtained between VO2 max (mL x kg(-1) x min(-1)) and the percent drop off in peak power in bouts 5 and 6 compared with bout 1. A significant correlation was obtained between arterial venous oxygen difference and the drop in mean power (r=-.54, P=0.02) but not with the drop in peak power (r=-.22, P=.36). There was no significant relationship between cardiac output and the drop in mean power (r=-.16, P=.51) or the drop in peak power (r=-.02, P=.94). Percent drop-off in oxygen consumption, when compared with the first, in the second (RVO2(30-60)), third (RVO2(60-90)), fourth (RVO2(90-120)) and fifth (RVO2(120-150)) 30s time periods of recovery following the intermittent protocol was calculated. Correlations between VO2 max (ml x kg(-1) x min(-1)) and these variables were (r=.51, P=-0.03), (r=.44, P=0.06), (r=.63, P=-0.003) and (r=.6, P=0.007) respectively. Consequently it was concluded that maximal oxygen uptake particularly the peripheral component, is an important determinant of the ability to perform intermittent exercise of this nature and to recover between bouts.

Adaptation, Physiological↗

PubMed2004

Relevance of the Pediatric Powered Wheelchair Screening Test for children with cerebral palsy.

In a previous study we developed a cognitive assessment battery called the Pediatric Powered Wheelchair Screening Test (PPWST) to help clinicians determine a young child's readiness to drive a powered wheelchair. The current multicenter study sought to determine: (1) whether the PPWST is appropriate for use in a population of children with cerebral palsy (CP) who use joysticks to drive their wheelchair; (2) whether two additional factors (symbolic representation and coping) would increase the predictive power of the PPWST for this group and for children with orthopedic or neuromuscular disabilities only; and (3) whether the test was appropriate for children with severe motor impairments who use switches to control their wheelchair. Fifty children (27 males, 23 females) between the ages of 21 months and 6 years 11 months participated. Twenty-six children (mean age 4 years 4 months, SD 15 months) had triplegic or tetraplegic CP and 24 children (mean age 27 months, SD 5 months) had orthopedic or neuromuscular disabilities. Sixty-nine per cent of children had some limited form of mobility (such as rolling or scooting) but none was a functional ambulator. Each child was assessed with the PPWST and with measures of symbolic representation and coping. After six wheelchair training sessions, driving ability was scored. The PPWST was found to be predictive of functional driving ability for children with CP who used a joystick to control their wheelchair. Assessment of symbolic representation skills increased the predictive power for this group but not for children with orthopedic or neuromuscular disabilities; coping scores did not increase the predictive power for either group. The PPWST accounted for only 20% of the variance in overall driving skills for switch users, and thus is not yet considered an adequate screening device for this group. The PPWST is designed to help clinicians determine whether a child currently has the specific cognitive skills found to be related to powered wheelchair driving but is not intended to be used exclusively to determine whether or not a child is ultimately a candidate for powered mobility.

Adaptation, Psychological↗