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PubMed1992

Skill acquisition and development: the roles of state-, parameter, and graph dynamics.

The development of motor skills can be portrayed as a dynamical process that involves three types of dynamics: state dynamics, parameter dynamics, and graph dynamics. The time scales associated with each type of dynamics are discussed, and an outline is provided of the role played by each type in the developing organism. In particular, the role of parameter dynamics and graph dynamics in producing qualitative, bifurcational changes in behavior is described. It is concluded that all three types of dynamics are required for a complete description of skill acquisition and development.

Journal Article↗
PubMed2004

Dynamic graciloplasty versus implant of artificial sphincter for continent perineal colostomy after Miles' procedure: Technique and early results.

Abdominoperineal resection (APR) is still the standard surgical treatment of anorectal cancers close to the dentate line. Unfortunately, a permanent iliac colostomy is a severe limitation of the quality of life. Attempts to construct a continent perineal colostomy after anorectal excision have been made over the last 15 years with uncertain benefits. We report on our early results of two different procedures consisting of a laparoscopic approach to abdominoperineal rectal excision, fashioning a perineal colostomy with dynamic graciloplasty or implant of an artificial sphincter. Between 2000 and 2004, a total of six patients underwent laparoscopic abdominoperineal resection or reversal of Miles' procedure and construction of perineal colostomy with dynamic graciloplasty (three cases) or implant of an artificial bowel sphincter (three cases). A diverting loop ileostomy was constructed in all patients to prevent contamination. Data concerning the perioperative management, postoperative morbidity and mortality and function after total anorectal reconstruction at the time of discharge, at postoperative month 1 and after ileostomy closure were collected and evaluated in a prospective non-randomised fashion. No early postoperative complications occurred in both groups. No late complication occurred in the dynamic graciloplasty group, whilst one patient of the artificial sphincter group had an ulceration of the tubing and the control pump through the suprapubic skin and the labium skin respectively on postoperative day 35. Another patient in this group, with an erosion of the transposed colon wall, died of myocardial infarction on postoperative day 75 after removal of the prosthesis. Postoperative stay after artificial sphincter implant and dynamic graciloplasty ranged from 12 to 27 days and 16 to 24 days, respectively. The loop ileostomy was closed at postoperative month 3 in all remaining patients except for one in the dynamic graciloplasty group, who died one day before hospitalization for ostomy closure because of an accidental, not disease/operation related reason. Follow-up of patients of the dynamic graciloplasty and artificial sphincter groups ranged from 3 to 24 months and 2.5 to 9.5 months, respectively. Patients in the dynamic graciloplasty group had no complications and follow-up showed satisfactory continence (SF36 form). All patients in the artificial sphincter group had late local complications with erosion of the prosthesis through the wall, its consequent removal and construction of a permanent iliac colostomy. Laparoscopic APR has been reported to be as safe as open APR. There are no published, available data on laparoscopic APR and laparoscopic reversal of Miles' procedure with total anorectal reconstruction with either dynamic graciloplasty or implant of artificial sphincter. Preliminary results showed that laparoscopic APR and APR reversal with continent perineal colostomy and dynamic graciloplasty may be a possible option in selected patients whilst the implant of an artificial sphincter should not be considered as a safe surgical option in such patients.

Journal Article↗
PubMed1986

Prediction of maximum acceptable weight of lift in the horizontal and vertical planes using simulated job dynamic strengths.

An investigation was undertaken to determine the feasibility of predicting maximum weights of lift that are acceptable to individuals by measuring the individuals' simulated job dynamic strengths. Since almost all manual materials handling jobs are dynamic in nature, it was hypothesized that correlations between maximum weights acceptable for lifting and the dynamic strengths measured under similar conditions would be high compared to isometric strengths. If so, then a relatively simple procedure can be developed to estimate what people are willing to lift safely. With the use of a specially designed and constructed three-dimensional dynamic strength simulator, 19 males and 6 females lifted loads in two vertical and two horizontal planes. Their dynamic strengths also were measured under identical conditions. The correlations between simulated job dynamic strengths and acceptable weights of lift were much higher (0.52 to 0.67) compared to correlations between isometric strengths and acceptable weights of lift (0.29 to 0.38). This also confirmed earlier findings that dynamic strengths are more suitable predictors of the maximum weights people are willing to handle. Simple equations are presented between simulated job dynamic strengths and maximum acceptable weights of lift in the horizontal and vertical planes. These equations demonstrate that dynamic strength can be used reliably when matching jobs with individuals.

Adult↗
PubMed2000

Correlation properties and complexity of perioperative RR-interval dynamics in coronary artery bypass surgery patients.

BACKGROUND: Dynamic measures of heart rate variability (HRV) may uncover abnormalities that are not easily detectable with traditional time and frequency domain measures. The purpose of this study was to characterize changes in RR-interval dynamics in the immediate postoperative phase of coronary artery bypass graft (CABG) surgery using traditional and selected newer dynamic measures of HRV. METHODS: Continuous 24-h electrocardiograph recordings were performed in 40 elective CABG surgery patients up to 72 h postoperatively. In one half of the patients, Holter recordings were initiated 12-40 h before the surgery. Time and frequency domain measures of HRV were assessed. The dynamic measures included a quantitative and visual analysis of Poincaré plots, measurement of short- and intermediate-term fractal-like scaling exponents (alpha1 and alpha2), the slope (beta) of the power-law regression line of RR-interval dynamics, and approximate entropy. RESULTS: The SD of RR intervals (P < 0.001) and the ultra-low-, very-low-, low-, and high-frequency power (P < 0.01, P < 0.001, P < 0.001, P < 0.01, respectively) measures in the first postoperative 24 h decreased from the preoperative values. Analysis of Poincaré plots revealed increased randomness in beat-to-beat heart rate behavior demonstrated by an increase in the ratio between short-term and long-term HRV (P < 0.001) after CABG. Average scaling exponent alpha1 of the 3 postoperative days decreased significantly after CABG (from 1.22 +/- 0.15 to 0.85 +/- 0.20, P < 0.001), indicating increased randomness of short-term heart rate dynamics (i.e., loss of fractal-like heart rate dynamics). Reduced scaling exponent alpha1 of the first postoperative 24 h was the best HRV measure in differentiating between the patients that had normal (</= 48 h, n = 33) or prolonged (> 48 h, n = 7) intensive care unit stay (0.85 +/- 0.17 vs. 0.68 +/- 0.18; P < 0.05). In stepwise multivariate logistic regression analysis including typical clinical predictors, alpha1 was the most significant independent predictor (P < 0.05) of long intensive care unit stay. None of the preoperative HRV measures were able to predict prolonged intensive care unit stays. CONCLUSIONS: In the selected group of patients studied, a decrease in overall HRV was associated with altered nonlinear heart rate dynamics after CABG surgery. Current results suggest that a more random short-term heart rate behavior may be associated with a complicated clinical course. Analysis of fractal-like dynamics of heart rate may provide new perspectives in detecting abnormal cardiovascular function after CABG.

Aged↗
PubMedDate not supplied

Solitary pulmonary nodules: a comparative study evaluated with contrast-enhanced dynamic MR imaging and CT.

OBJECTIVE: The aim of this prospective study was to compare the diagnostic performances of dynamic MR imaging and CT for the differentiation of benign and malignant solitary pulmonary nodules (SPNs). METHODS: Eighty-one patients with SPNs (32 malignant, 49 benign) underwent dynamic MR imaging (n=31), dynamic CT (n=27), or both (n=23). The degree of peak enhancement of benign and malignant SPNs was compared on both dynamic MR imaging and CT. Receiver operating characteristic (ROC) analysis was performed to compare the diagnostic performances of dynamic MR imaging and CT. RESULTS: The malignant SPNs revealed significantly greater degrees of peak enhancement on dynamic MR imaging (mean +/- SD [p%SI] 131.2 +/- 46.1 versus 54.2 +/- 45.3; range [p%SI] 82.6-260.0 versus -0.7-171.7; P <0.0001) and CT (mean +/- SD [DMI] 37.8 +/- 15.1 versus 17.9 +/- 21.8; range [DMI] 14.1-68.2 versus -5.4-107.6; P=0.0004). Although dynamic MR imaging was somewhat superior to dynamic CT, the diagnostic performances of the 2 modalities based on ROC analysis were not statistically significant. CONCLUSIONS: Dynamic MR imaging and CT seem to be equally well suited for the differentiation between benign and malignant SPNs.

Adolescent↗
PubMed2006

Gender and limb differences in dynamic postural stability during landing.

OBJECTIVE: To determine if gender and limb dominance affect dynamic postural stability and vertical ground reaction force data during jump landings. Secondary objective was to assess the reliability of the dynamic postural stability index (DPSI). DESIGN: A mixed model (2 genderx2 limb) repeated measures design was used to determine the effects of gender and limb dominance on dynamic postural stability. Subjects were required to perform a two-legged jump to a height equivalent of 50% of their maximum vertical leap, land on a single-leg and balance for three seconds. SETTING: Sports Medicine Research Laboratory. PARTICIPANTS: Forty healthy subjects (20 men, 20 women) participated in this investigation. MAIN OUTCOME MEASURES: The DPSI and its directional components quantified dynamic postural stability during a single-leg jump landing. Normalized vertical ground reaction force data quantified energy absorption. RESULTS: DPSI values revealed that females had significantly different dynamic postural stability as compared to males in the vertical plane [T (78)=-4.2, P<0.01], and in the composite score (dynamic postural stability index) [T (78)=-6.3, P<0.01]. In addition, females had significantly higher peak vertical ground reaction forces [T (78)=-13, P=0.01] than males. The DPSI also showed excellent reliability (ICC=0.96), with a 95% confidence interval ranging from 0.94 to 0.97. CONCLUSIONS: The results indicate that females have higher dynamic postural stability scores in the vertical direction as well as the composite score. This suggests that females used different dynamic postural stability strategies than males. There were no side-to-side dynamic postural stability differences between healthy contralateral limbs.

Adult↗
PubMed2005

Dynamic versus static splinting of simple zone V and zone VI extensor tendon repairs: a prospective, randomized, controlled study.

The authors present the first prospective, randomized, controlled study comparing postoperative dynamic versus static splinting outcomes of patients following extensor tendon repair. Patients who incurred simple and complete lacerations of their extensor tendons in zones V and VI were enrolled into the study and underwent either static splinting (n = 17) or dynamic splinting (n = 17) following primary acute repair of tendons. Total active motion was improved in the dynamic group when compared with the static group in the injured digits at 4 weeks (180.5 +/- 4 degrees versus 131.3 +/- 61 degrees; p = 0.006), at 6 weeks (239 +/- 21.9 degrees versus 205.5 +/- 53.4 degrees; p = 0.048), and at 8 weeks (247+/- 19.8 degrees versus 216.3 +/- 36 degrees; p = 0.051), but not at 6 months (253.1 +/-18.8 degrees versus 250.5 +/- 32 degrees; p = 0.562). Similarly, total active motion averaged for all digits (injured and noninjured) of the involved hand was improved in the dynamic group over the static group at 4 weeks (209.8 +/- 31.3 degrees versus 140 +/- 58.2 degrees; p < 0.001) and at 6 weeks (241.5 +/- 17.2 degrees versus 217.1 +/- 42.4 degrees; p = 0.024), but not at 8 weeks (249.6 +/- 16 degrees versus 234.8 +/- 24.5 degrees; p = 0.215) or 6 months (252.3 +/- 14 degrees versus 249.1 +/- 31 degrees; p = 0.450). Grip strength outcomes demonstrated improved grip force for the dynamic group when compared with the static group at 8 weeks (81.3 +/- 18.0 percent versus 59.2 +/- 20.4 percent; p = 0.004) but not at 6 months (89.6 +/- 5.6 percent versus 82.1 +/- 22.0 percent; p = 0.595). Patients demonstrated forceful grip greater than or equal to 80 percent of the noninjured hand in 55 percent of patients in the dynamic group versus 15 percent of patients in the static group at 8 weeks. Patients demonstrated forceful grip greater than or equal to 80 percent of the noninjured hand in 100 percent of patients in the dynamic group versus 73 percent of patients in the static group at 6 months. The authors' findings suggest that dynamic splinting of simple, complete lacerations of the extensor tendons in zones V and VI provides improved functional outcomes at 4, 6, and 8 weeks but not by 6 months when compared with static splinting. Therefore, they recommend dynamic splinting of simple, complete extensor tendon lacerations in zones V and VI only to select patients who are motivated and desire earlier return to full functional capacity.

Adult↗
PubMed2005

How to compare the efficiency of albumin-bound and nonalbumin-bound contrast agents in vivo: the concept of dynamic relaxivity.

RATIONALE AND OBJECTIVES: The objective of this study was to compare, in a rabbit experimental model that mimics a magnetic resonance (MR) angiographic protocol, the efficiency of the following types of compound on the MR signal: (1) a nonalbumin-bound blood pool contrast agent: P792; (2) a weak albumin-bound extracellular contrast agent: Gd-BOPTA; and (3) a strong albumin-bound blood pool contrast agent: MS325. METHODS: The 2 main phases of early distribution after contrast agent injection, ie, the bolus phase (0-15 seconds postinjection) and the postbolus phase (1-5 minutes postinjection) were investigated by measuring Gd blood concentrations in the first 5 minutes postinjection. In the case of MS325 and Gd-BOPTA, the percentage of the free and bound forms were calculated throughout the pharmacokinetic profile. The dynamic relaxivity at 60 MHz in plasma of each contrast agent was determined in the 2 phases after contrast agent injection, ie, the bolus phase and the postbolus phase. RESULTS: Injected under similar conditions, the 3 contrast agents had a comparable profile during the bolus phase (0-15 seconds postinjection). At 1 minute postinjection, only 38% of Gd-BOPTA remained in the blood, whereas 85% of P792 was still present in the blood. MS-325 had an intermediate position with 61% remaining in the blood. During the postbolus phase, the various compounds demonstrated similar behavior: the plasma concentration of P792 was higher than that of MS325 and Gd-BOPTA, ie, Ci/C0 (P792)>Ci/C0 (MS325)>Ci/C0 (Gd-BOPTA). At the peak of the bolus, 75% of MS325 and 93% of Gd-BOPTA was present in free form. This proportion decreased progressively during the postbolus phase, because 5 minutes postinjection, 23% of the free form remained for MS325 and 82% for Gd BOPTA. A significant decrease in dynamic r1 relaxivity was observed at 60 MHz for the products that bind to albumin (Gd-BOPTA and MS325) during the bolus phase. The dynamic relaxivity for MS325 at the bolus phase was 8.6 mMs and 5.2 mMs for Gd-BOPTA. At the postbolus phase, the dynamic relaxivity increased (17.3 mMs for MS325 and 6.7 mMs for Gd-BOPTA). The dynamic relaxivity of P792, which does not bind to albumin, was constantly equal to 26 mMs at each time point of the pharmacokinetic profile (bolus and postbolus phase). CONCLUSIONS: The physicochemical measurements of relaxivity in plasma are made in vitro at a fixed concentration of gadolinium and the value of relaxivity is not necessarily an accurate reflection of the efficiency of the contrast agent in vivo, especially for contrast agents that bind to albumin. Indeed, in vivo, the proportion of free and bound forms of albumin-binding contrast agents varies according to the pharmacokinetic profile, and the relaxivities of albumin-bound and free contrast agents are different. Consequently, the concept of dynamic relaxivity was introduced to compare the efficiency of MS325, Gd-BOPTA, and P792 in vivo. The variation of the dynamic relaxivity of MS325 and Gd-BOPTA between the bolus and postbolus phase is significant (101% for MS325 and 29% for Gd-BOPTA) as a result of the variation in the quantity of bound and free forms during the pharmacokinetic profile. The blood pool agent P792 has different properties, which result from its intravascular retention and its lack of albumin binding. Indeed, contrary to Gd-BOPTA and MS325, the dynamic relaxivity of P792 is higher at the bolus phase (26 mMs) and does not vary during the pharmacokinetic profile. The impact of these different dynamic relaxivities should be integrated in the analysis of the performance of the different classes of contrast agents in clinical MRA protocols.

Animals↗
PubMed2004

Seasonality and wildlife disease: how seasonal birth, aggregation and variation in immunity affect the dynamics of Mycoplasma gallisepticum in house finches.

We examine the role of host seasonal breeding, host seasonal social aggregation and partial immunity in affecting wildlife disease dynamics, focusing on the dynamics of house finch conjunctivitis (Mycoplasma gallisepticum (MG) in Carpodacus mexicanus). This case study of an unmanaged emerging infectious disease provides useful insight into the important role of seasonal factors in driving ongoing disease dynamics. Seasonal breeding can force recurrent epidemics through the input of fresh susceptibles, which will clearly affect a wide variety of wildlife disease dynamics. Seasonal patterns of social aggregation and foraging behaviour could change transmission dynamics. We use latitudinal variation in the timing of breeding, and social systems to model seasonal dynamics of house finch conjunctivitis across eastern North America. We quantify the patterns of seasonal breeding, and social aggregation across a latitudinal gradient in the eastern range of the house finch, supplemented with known field and laboratory information on immunity to MG in finches. We then examine the interactions of these factors in a theoretical model of disease dynamics. We find that both forms of seasonality could explain the dynamics of the house finch-MG system, and that these factors could have important effects on the dynamics of wildlife diseases generally. In particular, while either alone is sufficient to create recurrent cycles of prevalence in a population with an endemic disease, both are required to produce the specific semi-annual pattern of disease prevalence seen in the house finch conjunctivitis system.

Animals↗
PubMed1996

Detection of static and dynamic activities using uniaxial accelerometers.

Rehabilitation treatment may be improved by objective analysis of activities of daily living. For this reason, the feasibility of distinguishing several static and dynamic activities (standing, sitting, lying, walking, ascending stairs, descending stairs, cycling) using a small set of two or three uniaxial accelerometers signals can be measured with a portable data acquisition system, which potentially makes it possible to perform online detection of static and dynamic activities in the home environment. However, the procedures described in this paper have yet to be evaluated in the home environment. Experiments were conducted on ten healthy subjects, with accelerometers mounted on several positions and orientations on the body, performing static and dynamic activities according to a fixed protocol. Specifically, accelerometers on the sternum and thigh were evaluated. These accelerometers were oriented in the sagittal plane, perpendicular to the long axis of the segment (tangential), or along this axis (radial). First, discrimination between the static or dynamic character of activities was investigated. This appeared to be feasible using an rms-detector applied on the signal of one sensor tangentially mounted on the thigh. Second, the distinction between static activities was investigated. Standing, sitting, lying supine, on a side and prone could be distinguished by observing the static signals of two accelerometers, one mounted tangentially on the thigh, and the second mounted radially on the sternum. Third, the distinction between the cyclical dynamic activities walking, stair ascent, stair descent and cycling was investigated. The discriminating potentials of several features of the accelerometer signals were assessed: the mean value, the standard deviation, the cycle time and the morphology. Signal morphology was expressed by the maximal cross-correlation coefficients with template signals for the different dynamic activities. The mean signal values and signal morphology of accelerometers mounted tangentially on the thigh and the sternum appeared to contribute to the discrimination of dynamic activities with varying detection performances. The standard deviation of the signal and the cycle time were primarily related to the speed of the dynamic activities, and did not contribute to the discrimination of the activities. Therefore, discrimination of dynamic activities on the basis of the combined evaluation of the mean signal value and signal morphology is proposed.

Activities of Daily Living↗
PubMed2004

Family dynamics and postnatal depression.

Research has shown that postnatal depression (PND) affects 10-15% of mothers in Western societies. PND is not easily identified and therefore it often remains undetected. Untreated depression has a detrimental effect on the mother and child and the entire family. The purpose of this study was to ascertain the state of family dynamics after delivery and whether the mother's PND was associated with family dynamics. The study used a survey covering the catchment area of one Finnish university hospital. Both primi- and multiparas took part and data were collected using the Edinburgh Postnatal Depression Scale (EPDS) for mothers and the Family Dynamics Measure II (FDM II) for both mothers and fathers. The data were analysed using SPSS statistical programme and frequency and percentage distributions, means and standard deviations were examined. Correlations were analysed using Spearman's correlation coefficients. The significance of any differences between mothers' and fathers' scores was determined with a paired t-test. Of the families participating in the study (373 mothers and 314 partners), 13% of the mothers suffered from PND symptoms (EPDS score of 13 or more). As a whole, family dynamics in the families participating in the study were reported to be rather good. However, mothers having depressive symptoms reported more negative family dynamics compared with other families. With the exception of individuation, mothers having depressive symptoms reported more negative family dynamics than their partners. With the exception of role reciprocity, non-depressed mothers reported more positive family dynamics than their partners. Knowledge of the association of mothers' PND with family dynamics could help to develop nursing care at maternity and child welfare clinics and maternity hospitals. Depressed mothers and their families need support to be able to make family dynamics as good as possible.

Adolescent↗
PubMed2004

Beat-to-beat QT dynamics in healthy subjects.

BACKGROUND: Measures of QT dynamics express repolarization abnormalities that carry prognostic information, but the reproducibility of beat-to-beat QT dynamics has never been established. The QT interval is prolonged at night, but how the circadian rhythm and heart rate influence the dynamic QT measurements is still unsettled. The aims of the present study were: (1) to describe the reproducibility of beat-to-beat QT dynamics with respect to intrasubject, between-subject, and between-observer variability and (2) to describe the normal range, circadian variation, and heart rate dependence of QT dynamics. METHODS: Ambulatory Holter recordings were performed three times on 20 healthy volunteers and were analyzed by two experienced cardiologists. Slope and intercept of the QT/RR regression, the variability of QT and R-R intervals expressed as the standard deviation, and the relation between QT and RR variability expressed as a variability ratio were measured among other QT dynamics. RESULTS: The reproducibility of all QT dynamics was good. All QT dynamics showed circadian variation when calculated on an hourly basis. The day/night variation in slope could be explained by the differences in heart rate, whereas the day/night variation in intercept was heart rate independent. CONCLUSION: The present study shows that reliable automatic QT measurements could be performed, encouraging further evaluation of the clinical value of QT dynamics in risk stratification of cardiac patients.

Adult↗
PubMed1985

Fusimotor after-effects on responses of primary endings to test dynamic stimuli in cat muscle spindles.

Conditioning stimulation of individual dynamic fusimotor axons, either gamma or beta, leaves after-effects which enhance the responses of primary endings to test stimulation of the same axon applied during slow ramp stretch. These after-effects have a long duration, persisting well over 5 min, but are abolished by stretch of large amplitude. The dynamic after-effects also enhance frequencygrams elicited by low-frequency repetitive stimulation during slow ramp stretch, causing single stimuli to become much more effective. When several dynamic axons to the same spindle are isolated, conditioning stimulation of one leaves an after-effect to test stimulation of itself and of all other dynamic axons. When two dynamic axons are used for conditioning stimulation, facilitation or occlusion can be demonstrated in their interaction, indicating that they converge on the same intrafusal element. Dynamic after-effects persist during background static fusimotor activity of considerable amplitude, suggesting that static and dynamic actions are quite independent. Dynamic after-effects appear to result from residual changes in the bag fibre, probably from a persistent increase in the number of cross-bridges between thick and thin filaments. These after-effects produce a large increase in the response of primary endings to dynamic fusimotor activity and probably have an important functional role.

Action Potentials↗
PubMed2006

A dynamic compensation strategy to correct patient-positioning errors in conformal prostate radiotherapy.

Traditionally, pretreatment detected patient-positioning errors have been corrected by repositioning the couch to align the patient to the treatment beam. We investigated an alternative strategy: aligning the beam to the patient by repositioning the dynamic multileaf collimator and adjusting the beam weights, termed dynamic compensation. The purpose of this study was to determine the geometric range of positioning errors for which the dynamic compensation method is valid in prostate cancer patients treated with three-dimensional conformal radiotherapy. Twenty-five previously treated prostate cancer patients were replanned using a four-field technique to deliver 72 Gy to 95% of the planning target volume (PTV). Patient-positioning errors were introduced by shifting the patient reference frame with respect to the treatment isocenter. Thirty-six randomly selected isotropic displacements with magnitudes of 1.0, 2.0, 4.0, 6.0, 8.0, and 10.0 cm were sampled for each patient, for a total of 5400 errors. Dynamic compensation was used to correct each of these errors by conforming the beam apertures to the new target position and adjusting the monitor units using inverse-square and off-axis factor corrections. The dynamic compensation plans were then compared with the original treatment plans via dose-volume histogram (DVH) analysis. Changes of more than 5% of the prescription dose, 3.6 Gy, were deemed significant. Compared with the original treatment plans, dynamic compensation produced small discrepancies in isodose distributions and DVH analyses. These differences increased with the magnitudes of the initial patient-positioning errors. Coverage of the PTV was excellent: D95 and Dmean were not increased or decreased by more than 5% of the prescription dose, and D5 was not decreased by more than 5% of the prescription dose for any of the 5400 simulated positioning errors. D5 was increased by more than 5% of the prescription dose in only three of the 5400 positioning errors, all three occurring with a positioning error of 10.0 cm. Dose increases for adjacent organs at risk were more common. D33 of the rectum and the periprostatic rectum was increased by more than 5% of the prescription dose in 235 (4.4%) and 212 (3.9%) of the 5400 positioning errors, respectively. D10 of the right femoral head increased by more than 5% of the prescription dose in 444 (8.2%) positioning errors, and the degree of change was highly related to individual patient anatomy and simulation position. For the bladder D20, there were three increases of more than 5% of the prescription dose. These data demonstrate the robustness of dynamic compensation for correction of patient-positioning errors in four-field conformal prostate radiotherapy, with minimal deviation from the original treatment plans even for errors greatly exceeding those commonly encountered in the clinic. Dynamic compensation can be performed remotely, thus eliminating errors that may result from unnecessary increases in treatment time or from secondary patient motion induced by couch motion during the repositioning process. Further, the ability of dynamic compensation to correct large positioning errors has implications for the accuracy necessary during the initial patient setup and, hence, patient throughput for prostate radiotherapy.

Analysis of Variance↗
PubMed2003

Bladder dysfunction: diagnosis with dynamic US.

PURPOSE: To evaluate the role of dynamic ultrasonography (US) in the diagnosis of bladder dysfunction and to compare dynamic US with urodynamic study, which is considered to be the standard in the diagnosis of bladder dysfunction. MATERIALS AND METHODS: Images from 71 pairs of examinations in 63 patients (median age, 7.9 years; range 1.0-17.4 years) were included in the study. After the child consumed adequate fluids in an appropriate environment, natural filling of the bladder occurred, and dynamic US was used to evaluate detrusor activity, determine capacity of the bladder, and estimate residual urine volume. A urodynamic study was performed in every patient within 6 months of dynamic US and under the same treatment conditions. The paired Student t test was used to compare the maximal cystometric capacity values obtained with the two examinations. Analysis of validity was performed with the calculation of sensitivity, specificity, positive and negative predictive values, and their respective 95% confidence limits. RESULTS: The bladder capacity was not significantly different between dynamic US and urodynamic study (P =.12). Analysis of validity for the determination of the presence of clinically substantial residual urine showed 97.7% sensitivity and 100% specificity for dynamic US. The sensitivity and specificity of dynamic US in the detection of involuntary detrusor contraction were 93.0% and 88.9%, respectively. In the analysis of involuntary detrusor contraction with urine leakage, dynamic US showed sensitivity of 100% and specificity of 97.8%. CONCLUSION: Dynamic US is a sensitive method for the diagnosis of bladder dysfunction.

Adolescent↗
PubMed2000

Hemodynamic responses to static and dynamic muscle contractions at equivalent workloads.

We tested the hypothesis that static contraction causes greater reflex cardiovascular responses than dynamic contraction at equivalent workloads [i.e., same tension-time index (TTI), holding either contraction time or peak tension constant] in chloralose-anesthetized cats. When time was held constant and tension was allowed to vary, dynamic contraction of the hindlimb muscles evoked greater increases (means +/- SE) in mean arterial pressure (MAP; 50 +/- 7 vs. 30 +/- 5 mmHg), popliteal blood velocity (15 +/- 3 vs. 5 +/- 1 cm/s), popliteal venous PCO(2) (15 +/- 3 vs. 3 +/- 1 mmHg), and a greater decrease in popliteal venous pH (0.07 +/- 0.01 vs. 0.03 +/- 0.01), suggesting greater metabolic stimulation during dynamic contraction. Similarly, when peak tension was held constant and time was allowed to vary, dynamic contraction evoked a greater increase in blood velocity (13 +/- 1 vs. -1 +/- 1 cm/s) without causing any differences in other variables. To investigate the reflex contribution of mechanoreceptors, we stretched the hindlimb dynamically and statically at the same TTI. A larger reflex increase in MAP during dynamic stretch (32 +/- 8 vs. 24 +/- 6 mmHg) was observed when time was held constant, indicating greater mechanoreceptor stimulation. However, when peak tension was held constant, there were no differences in the reflex cardiovascular response to static and dynamic stretch. In conclusion, at comparable TTI, when peak tension is variable, dynamic muscle contraction causes larger cardiovascular responses than static contraction because of greater chemical and mechanical stimulation. However, when peak tensions are equivalent, static and dynamic contraction or stretch produce similar cardiovascular responses.

Animals↗
PubMed2006

Dynamic wait-listed designs for randomized trials: new designs for prevention of youth suicide.

BACKGROUND: The traditional wait-listed design, where half are randomly assigned to receive the intervention early and half are randomly assigned to receive it later, is often acceptable to communities who would not be comfortable with a no-treatment group. As such this traditional wait-listed design provides an excellent opportunity to evaluate short-term impact of an intervention. We introduce a new class of wait-listed designs for conducting randomized experiments where all subjects receive the intervention, and the timing of the intervention is randomly assigned. We use the term "dynamic wait-listed designs" to describe this new class. PURPOSE: This paper examines a new class of statistical designs where random assignment to intervention condition occurs at multiple times in a trial. As an extension of a traditional wait-listed design, this dynamic design allows all subjects to receive the intervention at a random time. Motivated by our search for increased statistical power in an ongoing school-based trial that is testing a program of gatekeeper training to identify suicidal youth and refer them to treatment, this new design class is especially useful when the primary outcome is a count or rate of occurrence, such as suicidal behavior, whose rate can fluctuate over time due to uncontrolled factors. METHODS: Statistical power is computed for various dynamic wait-listed designs under conditions where the underlying rate of occurrence is allowed to vary nonsystematically. We also present as an example a large ongoing trial to evaluate a gatekeeper training suicide prevention program in 32 schools which we initially began as a classic randomized wait-listed design. The primary outcome of interest in this study is the count of the number of children who are identified by the school system as having suicidal thoughts or behaviors who are then validated as being suicidal by mental health professionals in the community. RESULTS: A general result shows that dynamic wait-listed designs always have higher statistical power over a traditional wait-listed design. This power increase can be substantial. Efficiency gains of 33% are easy to obtain for situations where the intervention has a small effect and the variation in rate across time is quite high. When the rate variation for an outcome is very low or the intervention effect is large, efficiency gains approach 100%. A small increase in the number of times where random assignment occurs from 2 - for the standard wait-listed design, to say 4 can provide a large reduction in variance. Efficiency gains can also be high when converting standard wait-listed design to a dynamic one half-way into the study. LIMITATIONS: As with all wait-listed designs, dynamic wait-listed designs can only be used to evaluate short-term impact. Since all subjects eventually receive the intervention, no comparison can be made after the end of the random assignment period. The statistical power benefits are primarily limited to outcomes that can be treated as count or time to event data. CONCLUSIONS: A dynamic design randomly assigns units - either individuals or groups - to start the intervention at varying times during the course of the study. This design is useful in testing interventions that screen for new or existing cases, as well as testing the scalability of interventions as they are disseminated or expanded system wide. They can improve on the traditional wait-listed design both in terms of statistical power and robustness in the presence of exogenous factors. This paper demonstrates that such designs yield smaller standard errors and can achieve higher statistical power than that of a standard wait-listed design. Just as important, dynamic designs can also help reduce the logistical challenges of implementing an intervention on a wide scale. When the intervention requires that significant training resources be allocated throughout the study, the dynamic wait-listed design is likely to increase the rate of training and lead to a higher level of program implementation.

Adolescent↗
PubMed2005

Yeast kinetochore microtubule dynamics analyzed by high-resolution three-dimensional microscopy.

We have probed single kinetochore microtubule (k-MT) dynamics in budding yeast in the G1 phase of the cell cycle by automated tracking of a green fluorescent protein tag placed proximal to the centromere on chromosome IV and of a green fluorescent protein tag fused to the spindle pole body protein Spc42p. Our method reliably distinguishes between different dynamics in wild-type and mutant strains and under different experimental conditions. Using our methods we established that in budding yeast, unlike in metazoans, chromosomes make dynamic attachments to microtubules in G1. This makes it possible to interpret measurements of centromere tag dynamics as reflecting k-MT dynamics. We have examined the sensitivity of our assay by studying the effect of temperature, exposure to benomyl, and a tubulin mutation on k-MT dynamics. We have found that lowering the temperature and exposing cells to benomyl attenuate k-MT dynamics in a similar manner. We further observe that, in contrast to previous reports, the mutant tub2-150 forms k-MTs that depolymerize faster than wild type. Based on these findings, we propose high-resolution light microscopy of centromere dynamics in G1 yeast cells as a sensitive assay for the regulation of single k-MT dynamics.

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