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PubMed1992

Influence of power and aerobic exercise training on haemostatic factors after coronary artery surgery.

OBJECTIVES: To determine the effects of aerobic and power exercise training on haemostatic factors after coronary artery surgery and to compare the effect of the two exercise programmes. DESIGN: A prospective randomised controlled study of six months aerobic and power exercise training in men after coronary artery surgery. SETTING: Exercise rehabilitation classes in a teaching hospital in Glasgow. PATIENTS: 55 men within 12 months of coronary artery surgery recruited from surgical centres and medical clinics and asked to participate in the study. INTERVENTIONS: Assessments, including a treadmill test, measurements of haemoglobin, platelet, fibrinogen, factor VIIc, and fibrinopeptide A concentrations, and packed cell volume, done at baseline, three months, and six months. Patients in the two exercise groups attended training sessions three times weekly for six months. Control patients had no formal exercise training but continued with their leisure time activities. MAIN OUTCOME MEASURES: Exercise performance on a treadmill, haematology, and haemostatic factor assays at baseline, three months, and six months. RESULTS: In the aerobic trained group exercise performance increased significantly over baseline at three months (interval change 146.7, 95% confidence interval (95% CI) 52.5 to 240.9 s, p = 0.003) and was maintained at six months (interval change 172.1, 95% CI 63.3 to 280.9 s, p = 0.002). In the power trained groups significant improvement in exercise performance was delayed until six months (interval change 99.9 s, 95% CI 20.3 to 170.5 s, p = 0.01). Exercise performance in the control did not change significantly. Haemoglobin, concentration, packed cell volume, and platelet counts did not change significantly at any time. Fibrinogen concentration was significantly lower in the aerobic group than the other two groups at three months (2.96 g/dl compared with 3.3 g/dl and 3.87 g/dl in the power and control groups, p = 0.01). The power group had a lower fibrinogen concentration than the control group (p = 0.04). The lower fibrinogen concentration in the aerobic group was maintained at six months. There was a gradual rise in factor VIIc concentrations in the aerobic and control groups compared with a small fall in the power group. Fibrinopeptide A concentrations showed no consistent changes. CONCLUSIONS: Aerobic exercise training after coronary artery surgery causes an early favourable change in treadmill performance and in fibrinogen concentrations, that is maintained with further training. Power exercise training causes delayed benefit in treadmill performance. It also causes a small fall in fibrinogen concentrations. These changes may be relevant in reducing cardiovascular morbidity from graft failure and occurrence of myocardial infarction after coronary artery surgery.

Adult↗

PubMed1999

Estimation of cardiac reserve by peak power: validation and initial application of a simplified index.

OBJECTIVES: To validate a simplified estimate of peak power (SPP) against true (invasively measured) peak instantaneous power (TPP), to assess the feasibility of measuring SPP during exercise and to correlate this with functional capacity. DESIGN: Development of a simplified method of measurement and observational study. SETTING: Tertiary referral centre for cardiothoracic disease. SUBJECTS: For validation of SPP with TPP, seven normal dogs and four dogs with dilated cardiomyopathy were studied. To assess feasibility and clinical significance in humans, 40 subjects were studied (26 patients; 14 normal controls). METHODS: In the animal validation study, TPP was derived from ascending aortic pressure and flow probe, and from Doppler measurements of flow. SPP, calculated using the different flow measures, was compared with peak instantaneous power under different loading conditions. For the assessment in humans, SPP was measured at rest and during maximum exercise. Peak aortic flow was measured with transthoracic continuous wave Doppler, and systolic and diastolic blood pressures were derived from brachial sphygmomanometry. The difference between exercise and rest simplified peak power (Delta SPP) was compared with maximum oxygen uptake (VO(2)max), measured from expired gas analysis. RESULTS: SPP estimates using peak flow measures correlated well with true peak instantaneous power (r = 0.89 to 0.97), despite marked changes in systemic pressure and flow induced by manipulation of loading conditions. In the human study, VO(2)max correlated with Delta SPP (r = 0.78) better than Delta ejection fraction (r = 0.18) and Delta rate-pressure product (r = 0.59). CONCLUSIONS: The simple product of mean arterial pressure and peak aortic flow (simplified peak power, SPP) correlates with peak instantaneous power over a range of loading conditions in dogs. In humans, it can be estimated during exercise echocardiography, and correlates with maximum oxygen uptake better than ejection fraction or rate-pressure product.

Animals↗

PubMed2005

Torso stabilization reduces the metabolic cost of producing cycling power.

Many researchers have used cycling exercise to evaluate muscle metabolism. Inherent in such studies is an assumption that changes in whole-body respiration are due solely to respiration at the working muscle. Some researchers, however, have speculated that the metabolic cost of torso stabilization may contribute to the metabolic cost of cycling. Therefore, our primary purpose was to determine whether a torso stabilization device would reduce the metabolic cost of producing cycling power. Our secondary purpose was to determine the validity of the ergometer used in this study. Nine male cyclists cycled on a Velotron cycle ergometer at mechanical power outputs intended to elicit 50, 75, and 100% of their ventilatory threshold at 40, 60, and 80 rpm, with and without torso stabilization. Power was controlled by the Velotron in iso-power mode and measured with an SRM powermeter. We determined metabolic cost by indirect calorimetery and recorded power output. Torso stabilization significantly reduced metabolic cost of producing submaximal power (1%), and reduction tended to be greatest at the lower pedaling rates where pedaling force was greatest (1.6% at 40 rpm, 1.2% at 60 rpm, 0.2% at 80 rpm). Power, measured with the SRM powermeter, was strongly correlated with that specified to the Velotron ergometer control unit (R(2) > 0.99). We conclude that muscular contractions associated with torso stabilization elicit significant metabolic costs, which tend to be greatest at low pedaling rates. Researchers who intend to make precise inferences regarding metabolism in the working muscles of the legs may wish to provide torso stabilization as a means of reducing variability, particularly when comparing metabolic data across a wide range of pedaling rates.

Adult↗

PubMed2006

Incorrect calculation of power outputs masks the ergogenic capacity of creatine supplementation.

This study assessed the effect of incorrect calculation of power output measurement on the ergogenic properties of creatine. Fifteen males performed repeated Wingate anaerobic tests, under baseline, placebo, and creatine conditions. Statistics showed significant differences (p < 0.05) following creatine-supplemented conditions compared with placebo conditions, whereas no significant differences existed between the baseline and placebo conditions. However, the performance enhancement effect of creatine became significant only when the corrected (for the inertia of the flywheel) method was employed for measuring peak and minimum power. Mean (+/- SD) values across all cycle sprints for placebo versus creatine were 1033 +/- 100 W versus 1130 +/- 95 W for peak power and 385 +/- 78 W versus 427 +/- 70 W for minimum power. No significant differences were shown using the uncorrected method for peak power (756 +/- 97 W versus 786 +/- 88 W) and minimum power 440 +/- 64 W pre versus 452 +/- 65 W post). In conclusion, the present study suggests that the potentiating effect of creatine might be underestimated if the inertial effects of the flywheel are not considered in power output determination.

Adult↗

PubMed2002

Radio-frequency ablation of VX2 rabbit tumors: assessment of completeness of treatment by using contrast-enhanced harmonic power Doppler US.

PURPOSE: To assess contrast material-enhanced harmonic power Doppler and fundamental color Doppler ultrasonography (US) in the detection of residual viable tumor tissue after radio-frequency (RF) ablation in tumors embedded in fat. MATERIALS AND METHODS: Twenty-eight VX2 tumors were implanted into the retroperitoneum of 14 rabbits. Tumors were examined with contrast-enhanced fundamental color Doppler US and harmonic power Doppler US before and 10 minutes after RF ablation. Saline-enhanced RF ablation (30 mL/h) was performed over 10 minutes with 28-W RF power. Follow-up included repeat US examinations. Necropsies and histopathologic assessment were performed after detection of residual untreated tumor at US or 3 weeks after ablation. RESULTS: VX2 tumors reached a mean size of 21 mm +/- 9 (SD) (size range, 6-43 mm) 25 days after implantation. All tumors larger than 31 mm showed signs of central necrosis at US. Before ablation, intense vascularity was detected in all tumors with both contrast-enhanced US modes. Histopathologic assessment at the end of the follow-up period revealed local relapses due to incomplete ablation in 14 (50%) of 28 cases. Detection of residual tumor was missed in all cases with contrast-enhanced color Doppler US. Contrast-enhanced harmonic power Doppler US depicted residual flow in 12 of the 14 cases (sensitivity, 86%) in which local relapses occurred. There was a significant (P <.005, McNemar test) improvement in detection of residual tumor when the harmonic power Doppler mode was used. CONCLUSION: Contrast-enhanced harmonic power Doppler US has greater sensitivity than contrast-enhanced color Doppler US for detecting residual VX2 tumor following ablation. Therefore, contrast-enhanced harmonic power Doppler US may be a useful additional method for the detection of residual tumors after RF ablation.

Animals↗

PubMed1997

Power Doppler US of the normal prepubertal testis: does it live up to its promises?

PURPOSE: To assess whether power Doppler ultrasound (US) improves the detection of flow in normal prepubertal testes. MATERIALS AND METHODS: Seventy-two normal testes of 38 prepubertal boys (age range, 2 weeks to 12.5 years) were scanned with color and power Doppler US (7-MHz transducer). The two modalities were compared subjectively to determine which one was more sensitive for detection of flow. Only reproducible intratesticular flow signals were considered positive; capsular flow was disregarded. RESULTS: Power Doppler US depicted flow in 50 testes (69%), while color Doppler US depicted flow in 47 testes (65%, not statistically significant). Power and color Doppler US combined depicted flow in 57 testes (79%), which was significant when compared with color Doppler US alone (P = .002). Detection of flow was subjectively easier with power Doppler US in 10 of 72 testes, while it was easier with color Doppler US in 14 of 72 testes. Motion artifacts were greater with power Doppler US. CONCLUSION: Power Doppler US was equally sensitive as conventional color Doppler US in the detection of flow in normal prepubertal testes. Combining both modalities improved detection of flow in 14% of cases and may be useful in excluding torsion in children. For a positive preoperative diagnosis of torsion in children, radionuclide scintigraphy remains the imaging modality of choice.

Artifacts↗

PubMed2000

Power Doppler imaging: initial evaluation as a screening examination for carotid artery stenosis.

PURPOSE: To evaluate power Doppler imaging as a possible screening examination for carotid artery stenosis. MATERIALS AND METHODS: In the principal pilot study, a prospective, blinded comparison of power Doppler imaging with duplex Doppler imaging, the reference-standard method, was conducted in 100 consecutive patients routinely referred for carotid artery imaging at a large, private multispecialty clinic. In the validation pilot study, a prospective, blinded comparison of power Doppler imaging with digital subtraction angiography, the reference-standard method, was conducted in 20 consecutive patients routinely referred at a teaching hospital. Using conservative assumptions, the authors performed cost-effectiveness analysis. RESULTS: Power Doppler imaging produced diagnostic-quality images in 89% of patients. When the images of the patients with nondiagnostic examinations were regarded as positive, power Doppler imaging had an area under the receiver operating characteristic curve, A(z), of 0.87, sensitivity of 70%, and specificity of 91%. The validation study results were very similar. The cost-effectiveness of screening and, as indicated, duplex Doppler imaging as the definitive diagnostic examination and endarterectomy was $47,000 per quality-adjusted life-year. CONCLUSION: The A(z) value for power Doppler imaging compares well with that for mammography, a generally accepted screening examination, and with most other imaging examinations. Power Doppler imaging is likely to be a reasonably accurate and cost-effective screening examination for carotid artery stenosis in asymptomatic populations.

Adult↗

PubMed2000

Hepatocellular carcinoma treated with percutaneous radio-frequency ablation: usefulness of power Doppler US with a microbubble contrast agent in evaluating therapeutic response-preliminary results.

PURPOSE: To evaluate the usefulness of power Doppler ultrasonography (US) with a microbubble contrast agent in assessing the therapeutic response of hepatocellular carcinomas (HCCs) treated with percutaneous radio-frequency (RF) ablation. MATERIALS AND METHODS: Forty patients with 45 nodular HCC lesions 1.0-3.8 cm in diameter underwent power Doppler US before and after intravenous injection of a microbubble contrast agent. The same procedures were repeated after US-guided percutaneous RF ablation. The results of these studies were compared with those of three-phase helical computed tomography (CT) performed immediately after RF ablation. RESULTS: Before RF ablation, nonenhanced power Doppler US demonstrated flow signals within tumor in 33 of 45 HCCs. After contrast agent administration, flow signals increased or newly appeared in all cases. After RF ablation, none of the ablated tumors showed intratumoral flow signals at nonenhanced power Doppler US, whereas six showed marginal intratumoral flow signals at contrast agent-enhanced power Doppler US. These six tumors were found to have small enhancing foci, suggestive of viable tumor, in corresponding areas at immediate follow-up CT. Additional RF ablation or transcatheter arterial chemoembolization was performed in these tumors. CONCLUSION: The results of power Doppler US with a microbubble contrast agent in HCCs treated with RF ablation correlated well with those of contrast-enhanced CT. Preliminary data suggest that contrast-enhanced power Doppler US can be a promising noninvasive technique for assessing therapeutic response.

Adult↗

PubMed2005

Beta-myosin heavy chain myocytes are more resistant to changes in power output induced by ischemic conditions.

During ischemia intracellular concentrations of P(i) and H+ increase. Also, changes in myosin heavy chain (MHC) isoform toward beta-MHC have been reported after ischemia and infarction associated with coronary artery disease. The purpose of this study was to investigate the effects of myoplasmic changes of P(i) and H+ on the loaded shortening velocity and power output of cardiac myocytes expressing either alpha- or beta-MHC. Skinned cardiac myocyte preparations were obtained from adult male Sprague-Dawley rats (control or treated with 5-n-propyl-2-thiouracil to induce beta-MHC) and mounted between a force transducer and servomotor system. Myocyte preparations were subjected to a series of isotonic force clamps to determine shortening velocity and power output during Ca2+ activations in each of the following solutions: 1) pCa 4.5 and pH 7.0; 2) pCa 4.5, pH 7.0, and 5 mM P(i); 3) pCa 4.5 and pH 6.6; and 4) pCa 4.5, pH 6.6, and 5 mM P(i). Added P(i) and lowered pH each caused isometric force to decline to the same extent in alpha-MHC and beta-MHC myocytes; however, beta-MHC myocytes were more resistant to changes in absolute power output. For example, peak absolute power output fell 53% in alpha-MHC myocytes, whereas power fell only 38% in beta-MHC myocytes in response to elevated P(i) and lowered pH (i.e., solution 4). The reduced effect on power output was the result of a greater increase in loaded shortening velocity induced by P(i) in beta-MHC myocytes and an increase in loaded shortening velocity at pH 6.6 that occurred only in beta-MHC myocytes. We conclude that the functional response to elevated P(i) and lowered pH during ischemia is MHC isoform-dependent with beta-MHC myocytes being more resistant to declines in power output.

Animals↗

PubMed1998

Regulation of skeletal muscle glycogen phosphorylase and PDH at varying exercise power outputs.

This study investigated the transformational and posttransformational control of skeletal muscle glycogen phosphorylase and pyruvate dehydrogenase (PDH) at three exercise power outputs [35, 65, and 90% of maximal oxygen uptake (VO2 max)]. Seven untrained subjects cycled at one power output for 10 min on three separate occasions, with muscle biopsies at rest and 1 and 10 min of exercise. Glycogen phosphorylase in the more active (a) form was not significantly different at any time across power outputs (21. 4-29.6%), with the exception of 90%, where it fell significantly to 15.3% at 10 min. PDH transformation increased significantly from rest (average 0.53 mmol . kg wet muscle-1 . min-1) to 1 min of exercise as a function of power output (1.60 +/- 0.26, 2.77 +/- 0.29, and 3.33 +/- 0.31 mmol . kg wet muscle-1 . min-1 at 35, 65, and 90%, respectively) with a further significant increase at 10 min (4.45 +/- 0.35) at 90% VO2 max. Muscle lactate, acetyl-CoA, acetylcarnitine, and free ADP, AMP, and Pi were unchanged from rest at 35% VO2 max but rose significantly at 65 and 90%, with accumulations at 90% being significantly higher than 65%. The results of this study indicate that glycogen phosphorylase transformation is independent of increasing power outputs, despite increasing glycogenolytic flux, suggesting that flux through glycogen phosphorylase is matched to the demand for energy by posttransformational factors, such as free Pi and AMP. Conversely, PDH transformation is directly related to the increasing power output and the calculated flux through the enzyme. The rise in PDH transformation is likely due to increased Ca2+ concentration and/or increased pyruvate. These results demonstrate that metabolic signals related to contraction and the energy state of the cell are sensitive to the exercise intensity and coordinate the increase in carbohydrate use with increasing power output.

Acetyl Coenzyme A↗

PubMed1978

Aerobic power as related to body growth and training in Japanese boys: a longitudinal study.

Maximal aerobic power was measured for 5-6 successive years in 50 Japanese schoolboys starting from the age of 9 or 13 yr. and for 2-3 yr in 6 superior junior runners from the age of 14 yr. A large increase in aerobic power was observed during the adolescent growth spurt for 7 schoolboys who trained between the ages of 9 and 14 yr. Aerobic power for 43 average schoolboys increased from 45.0 to 52.2 ml/kg.min between the ages of 13 and 17 yr. The aerobic power of 6 superior junior runners increased from 63.4 to 73.4 ml/kg.min between the ages of 14 and 17 yr. A remarkable increase in aerobic power was not observed in trained boys before the age of peak height growth velocity (PHV). Beginning approximately 1 yr prior to the age of PHV and thereafter, training effectively increased aerobic power above the normal increase attributable to age and growth. The highly developed aerobic power found in superior junior runners may have been derived from strenuous training and partially by genetically superior endowment.

Adolescent↗

PubMed1983

Power spectral analysis of the diaphragm electromyogram.

We studied the power spectrum of the diaphragm electromyogram (EMG) at frequencies between 31 and 246 Hz in four young normal subjects and five patients with chronic obstructive lung disease (COPD). Diaphragm EMGs were analyzed during spontaneous breathing and maximum inspiratory efforts to determine the effect of signal-to-noise ratio on the power spectrum and if treadmill exercise to dyspnea was associated with diaphragm fatigue. We found that the centroid frequencies of the power spectra (fc) were strongly correlated (r = 0.93) with ratios of power at high frequencies to power at low frequencies (H/L) for all subjects. Of the two indices, H/L had the largest standard deviation expressed as a percentage of the mean. The mean values of both of these decreased significantly after exercise, fc from 100.2 to 97.3 and H/L from 1.07 to 0.97. Signal-to-noise ratios were higher in maximal inspiratory efforts and after exercise in normal subjects and higher in COPD patients. The signal-to-noise ratio was correlated negatively with fc and H/L, indicating that these indices of the shape of the power spectrum are influenced by signal strength and noise levels as well as muscle function. We conclude that the fc and H/L index similar qualities of the power spectrum, that they are partially determined by the signal-to-noise ratio, and that, in some cases, exercise to dyspnea is associated with apparently mild diaphragm fatigue.

Adult↗

PubMed1994

Comparison of diaphragmatic EMG power spectra: spontaneous contractions vs. evoked compound action potentials.

The electromyogram (EMG) power spectrum from spontaneous diaphragm contractions has been used to identify the development of fatigue. However, power spectral analysis of the spontaneous diaphragmatic EMG signal is limited and subject to error. In contrast, power spectral analysis of the compound diaphragm action potential (CDAP) may be superior. The aim of the present study was to determine whether the EMG power spectra of evoked CDAPs correlate with those of spontaneous diaphragm contractions. Four anesthetized mechanically ventilated dogs with spontaneous isometric diaphragm contractions were studied using a mechanically isolated in situ diaphragm preparation. CDAPs were elicited via phrenic nerve stimulation, and intramuscular wire electrodes recorded EMG. Diaphragm temperature was changed from 40 to 30 degrees C to elicit changes in the EMG power spectra. The EMG signal from 10 spontaneous contractions and 10 CDAPs were acquired at 1 degrees C intervals. Fast Fourier transform was applied to both spontaneous and CDAP data yielding the power spectra, which were represented by their center frequencies (fc). The CDAP fc correlated well with the EMG fc obtained from spontaneous contractions (r = 0.99). We conclude that evoked CDAPs may provide an accurate alternative to spontaneous contractions for EMG power spectral analysis of the diaphragm.

Animals↗

PubMed1995

Effect of oral creatine supplementation on power output and fatigue during bicycle ergometry.

Our purpose was to determine the effect of oral creatine supplementation on exercise performance during high-intensity short-duration bicycle sprinting. Power output was recorded for 12 healthy untrained males (age 24.08 +/- 0.53 yr, weight 81.22 +/- 1.32 kg) before and after 5 days of creatine (n = 6) or placebo (n = 6) supplementation. A double-blind research design was employed. Subjects performed maximal sprints against a constant load (111.8 N) for 15 s. Each one-half pedal revolution was magnetically counted, and subsequent measurements of peak power, time to peak power, total work, and the fatigue index were digitized and stored on disk. Mean values for peak power, time to peak power, total work, and fatigue index were 958.01 +/- 40.66 W, 4.09 +/- 0.82 s, 11.28 +/- 0.46 kJ, and 32.1 +/- 1.58% decline from peak power, respectively. No significant differences were observed within or between groups before or after supplementation for any of the mechanical parameters measured (P > 0.05). These findings suggest that oral creatine supplementation does not positively affect power output or fatigue during continuous high-intensity bicycle exercise in untrained men.

Adult↗

PubMed2004

Age differences in knee extension power, contractile velocity, and fatigability.

The purposes of this study were to examine age and gender differences in knee extensor strength, power, and fatigue using open- and closed-chain testing procedures. We tested the hypothesis that specific strength (strength/unit muscle mass) would not differ by age, whereas age differences in specific power and fatigue would remain consequent to blunted maximal contractile velocity. Skeletal muscle performance was examined in 28 young (26.9 +/- 0.7 yr) and 24 older (63.6 +/- 0.8 yr) men and women. Assessments included one-repetition maximum strength for knee extension, leg press, and squat; concentric knee extensor peak power, velocity, and fatigability; and sit-to-stand power, fatigability, and relative neural activation (electromyograph activity during sit-to-stand movement normalized to electromyograph activity during isometric maximum voluntary contraction). Thigh lean mass (TLM; kg) was assessed by dual-energy X-ray absorptiometry. Specific strength (N/kg TLM) and specific power (W/kg TLM) were estimated by dividing absolute values by TLM. Age differences in specific strength were observed for knee extension only (young, 41.2 +/- 1.0 N/kg TLM; older, 32.4 +/- 1.0 N/kg TLM; P < 0.05). Adjustment for TLM did not negate age differences in knee extension specific power (25-41% lower in older; P < 0.05) across loads tested. Older adults experienced fatigue across 10 repetitions of knee extension as peak velocity fell by 24% (P < 0.05). Deficits in concentric power persist after adjustment for TLM as maximum contractile velocity falls markedly with aging. Older adults are less capable of sustaining maximum concentric velocity during repetitive contractions. These findings suggest that velocity impairments are a possible contributor to mobility loss and falls risk among older adults. Interventions for improving contractile velocity should be pursued.

Adult↗

PubMed2005

LFP power spectra in V1 cortex: the graded effect of stimulus contrast.

We recorded local field potentials (LFPs) and single-unit activity simultaneously in the macaque primary visual cortex (V1) and studied their responses to drifting sinusoidal gratings that were chosen to be "optimal" for the single units. Over all stimulus conditions, the LFP spectra have much greater power in the low-frequency band (< or = 10 Hz) than higher frequencies and can be described as "1/f." Analysis of the total power limited to the low, gamma (25-90 Hz), or broad (8-240 Hz) frequency bands of the LFP as a function of stimulus contrast indicates that the LFP power gradually increases with stimulus strength across a wide band in a manner roughly comparable to the increase in the simultaneously recorded spike activity. However, the low-frequency band power remains approximately constant across all stimulus contrasts. More specifically the gamma-band LFP power increases differentially more with respect to baseline than either higher or lower bands as stimulus contrast increases. At the highest stimulus contrasts, we report as others have previously, that the power spectrum of the LFP typically contains an obvious peak in the gamma-frequency band. The gamma-band peak emerges from the overall broadband enhancement in LFP power at stimulus contrasts where most single units' responses have begun to saturate. The temporal/spectral structures of the LFP located in the gamma band-which become most evident at the highest contrasts-provide additional constraints on potential mechanisms underlying the stimulus response properties of spiking neurons in V1.

Action Potentials↗

PubMed2002

Power Doppler ultrasonographic diagnosis of small hepatocellular carcinomas.

BACKGROUND/AIMS: Power Doppler ultrasonography can evaluate the hemodynamics of intrahepatic tumors. The ability of power Doppler ultrasonography to detect small hepatocellular carcinomas and estimate the differentiation of the tumor by the patterns of intranodular waves was assessed. METHODS: We used conventional B-mode ultrasonography, power Doppler ultrasonography, and dynamic computed tomography to examine 71 hepatocellular carcinomas (</=3 cm) before liver resection. RESULTS: The sensitivity of conventional ultrasonography, power Doppler ultrasonography, and computed tomography increased as tumor diameter increased, with little difference between modalities. Nodules up to 5 mm in diameter as well as some nodules in the lateral segment or the subphrenic area of the liver were not detected by power Doppler ultrasonography, although two nodules not detected by computed tomography were apparent from power Doppler ultrasonography. With the latter modality, the proportion of nodules with afferent pulsatile waves was higher in moderately or poorly differentiated hepatocellular carcinomas than in well-differentiated hepatocellular carcinomas. Afferent continuous waves were detectable only in well-differentiated hepatocellular carcinomas. CONCLUSION: Although the sensitivity of power Doppler ultrasonography remains unsatisfactory for minute lesions (</=5 mm) and for laterally or subphrenically situated lesions, this method can usually distinguish moderately or poorly differentiated from well-differentiated hepatocellular carcinomas, which is useful in planning treatment and predicting outcome.

Aged↗

PubMed2004

Power loss for linkage analysis due to the dichotomization of trichotomous phenotypes.

OBJECTIVES: Some traits, while naturally polychotomous, are routinely dichotomized for genetic analysis. Dichotomization, intuitively, leads to a loss of power to detect linkage, as some phenotypic variability is discarded. This paper examines this power loss in the context of a trichotomous trait. METHODS: To examine this power loss, we performed a simulation study where a trichotomous trait was simulated in a sample of 1,000 sib-pairs under various genetic models. The study was replicated 1,000 times. Linkage analysis using a variance components method, as implemented in Mx, was then performed on the trichotomous trait and compared with that on a dichotomized version of the trait. RESULTS: A comparison of the power and false positive rates of the analyses shows that power to detect linkage was increased by up to 22 percentage points simply by examining the trait as a trichotomy instead of a dichotomy. Under all models examined, the trichotomous analysis outperformed the dichotomous version. CONCLUSIONS: Comparable levels of false positive rates under both methods confirm that this power gain comes solely from the information lost upon dichotomization. Thus, dichotomizing tri- or poly-chotomous traits can lead to crippling power loss, especially in the case of many loci of small effect.

Alleles↗