Peak Working Research Articles

Patients with cystic fibrosis can preserve peak working capacity, even if lung function is substantially impaired

Patients with cystic fibrosis can preserve peak working capacity, even if lung function is substantially impaired

Interface Pressure and Stiffness of Various Elastic Stockings during Posture Changes and Exercise

The importance of measuring interface pressure and stiffness to characterize the elastic properties of materials has been stressed with regard to elastic stockings and elastic bandages. The objective of this study was to compare the pressure profiles of nine different elastic stockings and to quantify the effects of posture changes and exercise on compression. Using a pressure transducer (Air Pack Type Analyzer), the interface pressure associated with nine different elastic stockings was measured at level B1 during supine resting, standing, and exercise. The elastic stockings examined could be divided into two categories according to extensibility: short stretch (< 105% extensibility) and long stretch (> 105% extensibility). Short-stretch stockings include thick round-knitted stockings, firm round-knitted stockings, and flat-knitted stockings. Short-stretch stockings showed a higher peak working pressure and a larger pressure amplitude during exercise than long-stretch stockings. Short-stretch stockings can be expected to have more pronounced benefits for augmenting muscle pumping in the same way as short-stretch bandages. In selecting suitable elastic stockings for patients, the stiffness should be taken into account in addition to interface pressure.

Aerobic Capacity in Children with Hemophilia

To determine whether aerobic capacity is normal in boys with different types of hemophilia compared with healthy peers and whether the level of aerobic capacity correlates with the amount of physical activity, joint health status, muscle strength, and anthropometrics. 47 patients (mean [SD] age, 12.9 [3.2] years; age range, 8.2-17.4 years) from the "Van Creveldkliniek" of the University Medical Center Utrecht, participated. Anthropometry, muscle strength, joint impairment, functional ability, and aerobic capacity were measured. The amount of energy expenditure during daily living was assessed. All boys were able to perform at maximal or near-maximal level on exercise tests, and none of them reported bleeds or other adverse events. Relative peak oxygen, peak heart rate, and peak working capacity were significantly lower compared with healthy control subjects. 30% had Z-scores >2 for weight. Total muscle strength was normal, and almost no joint impairment and no decrease in functional ability were found. The aerobic capacity of children with hemophilia is still lower than the normal population, whereas their overall muscle strength is comparable with healthy peers. The functional ability does not differ from healthy peers, and joint health status showed very minor impairments. A substantial proportion of Dutch children with hemophilia was overweight, without showing a reduction in the amount of self-reported physical activities.

A finite horizon inventory model: An operational framework

We present a simulation based decision support system motivated by a real life situation to decide the inventory ordering policy in the context of a single commodity, multipack, and finite horizon situation. The multiple objectives include (a) minimizing the end of the season inventory, (b) maximizing the operating profit, and (c) minimizing the peak working capital requirements during the season. Stochastic demand and positive lead time add to the complexity of the problem context. In addition, multiple partners in the supply chain with distinct and conflicting set of objectives necessitate the need for a formal approach. The problem can be formulated as a multiperiod dynamic programing problem with stochastic demand with an objective to optimize the expected operating profit, subject to specific constraints on working capital requirement, service level, order fill rate, and end of the season inventory. Such a formulation is hard to solve analytically and does not lend itself to analyze several ordering policies (what-if analysis). Based on simulation experiments, we propose an ordering policy which optimizes the overall objective(s) of supply chain partners. The model is simple and easy to use and is designed with adequate flexibility to conduct what-if analysis.

Spontaneous alpha peak frequency predicts working memory performance across the age span

Working memory capacity has been consistently shown to decline with increasing age. Mechanisms underlying this decline are poorly understood. One index that has been found to predict performance on memory tests is alpha peak frequency, the peak of spectral alpha power of the EEG. Activity in the alpha band has been also associated with higher cognitive functions including attention and anticipation and has been shown to slow with age. Few studies, however, have examined whether there might be a relationship between WM decline and alpha peak frequency. The present study specifically investigated this relationship. Digit span was used as the index of WM function. The study made use of 550 normal subjects aged between 11 and 70 years in the Brain Resource International Database. The data were acquired from six laboratories located in the USA (2), Europe (2) and Australia (2). Forward and reverse digit span were found to be lower in older relative to younger age groups. Spontaneous alpha peak frequency slowed with age and more so at anterior than posterior sites. Frontal alpha peak frequency was found to be a significant predictor of reverse digit span, with each 1 Hz increase in frequency associated with a 0.21 increase in reverse digit span score and this was independent of age, indicating a positive relationship between alpha peak frequency and working memory performance.

72 HEMODYNAMIC RESPONSES TO EXERCISE IN CHILDREN WITH CYANOTIC FORMS OF HEART DISEASE

Myocardial oxygen supply during exercise may be impaired in patients with cyanotic heart disease; myocardial fibrosis secondary to chronic hypoxia may prevent normal exercise capacity post-operatively. We performed continuous, graded, maximal cycle ergometer exercise tests on 87 children and young adults. There were 66 with tetralogy of Fallot (TF)(5 pre-repair), 13 with d-transposition(TGA) (all post-repair), and 8 with tricuspid atresia (TA)(1 post-repair). The patients were compared to 405 healthy subjects by analysis of covariance with respect to race, sex, age, and body surface area. The maximal values of the following were measured: heart rate, systolic blood pressure, workload, and peak working capacity index. *=p<.05 compared to control; †=p<.05 compared to TA Ischemia on ECG was seen in 6/8 TA, 4/13 TGA, and 1/5 pre-repair TF patients. In the 61 post-repair TF patients, there was no statistical correlation between age at surgery, years since surgery, pre-repair O2 saturation or hemoglobin, or post-repair, RV/LV pressure ratio and any exercise variable. The TF patients improved post-op, suggesting non-fibrotic myocardium.

73 HEMODYNAMIC RESPONSES TO ERGOMETER EXERCISE IN CHILDREN WITH ASD OR VSD

Our previous maximal exercise studies performed on patients with left ventricular volume or pressure overload or cyanotic lesions revealed decreases of heart rate(HR), systolic blood pressure(BP), workload(Wmax), and peak working capacity index(PWCI)in comparison to 405 healthy controls. We sought to define these data in children with ASD (n=35) or VSD (n=79). The data were compared by analysis of covariance, controlling for age, sex, race, and body surface area.Age and body surface area were significant covariates for the BP, Wmax, and PWCI variables. There were strong main effects of race on HR and BP values, and both race and sex on the 2 workload indices. The ASD and VSD patients had decreased values of maximal HR; the ASD patients had low values of PWCI. As in almost all other patient groups, the BP response to exercise for ASD or VSD patients did not differ from control. Racial influences on BP were significant; in each comparison, the black children had higher values than their white counterparts.

HEMODYNAMIC RESPONSES TO EXERCISE IN CHILDREN WITH CONGENITAL HEART DISEASE

Myocardial oxygen supply during exercise may be impaired in children with cyanotic heart disease (CHD); post-operatively there may be ventricular dysfunction to prevent normal exercise capacity. To assess these hypotheses, we exercised 82 patients (pts) with CHD, 25 pre-op tetralogy of Fallot (TOF), 40 post-op TOF, 10 d-transposition (TGA), and 7 tricuspid atresia (TA). We utilized a continuous protocol on a cycle ergometer with three minute stages to exhaustion. The pts' data were compared to analysis of covariance to 383 healthy normals (N) controlling for race, sex, age, and body surface area. Variables measured were: maximal heart rate (HR), systolic blood pressure (SBP), maximal workload (MWL), and peak working capacity index (PWCI). All pt HR values were lower than N, with the TGA and TA pts significantly lower than TOF. The MWL and PWCI values for TGA and both TOF groups were normal; the TA pts were significantly lower. All SBP means were normal, but within groups, black children had higher SBP values than whites. TA pts have the most severely impaired exercise responses. TOF and TGA pts have selective abnormalities of HR but not SBP or work.

Hemodynamic responses to ergometer exercise in children and young adults with left ventricular pressure or volume overload

This study determines (1) the hemodynamic responses to exercise in groups of young patients with either left ventricular (LV) pressure or volume overload, (2) whether these responses differed from healthy subjects when the variables of sex, age, race and body surface area were controlled (analysis of covariance), and (3) whether any of the exercise variables could predict noninvasively the severity of the gradient in aortic valve stenosis (AS). We tested 137 patients, including 70 with AS, 25 with aortic isthmic coarctation, 20 with aortic regurgitation and 22 with mitral regurgitation, and compared them with a control population of 405 healthy children. The children underwent a continuous, graded, maximal test with 3-minute stages. The variables evaluated were peak heart rate, systolic blood pressure, maximal work load (kgm/min), peak working capacity index (kg-m/min/ kg body weight) and ischemia on electrocardiography. In patients with pressure overload, the maximal exercise values for work load, heart rate and peak working capacity index were significantly different (p < 0.05) from control values. The patients with volume overload had higher blood pressure values than either control subjects or patients with pressure overload. Similarly, the values for heart rate in patients with volume overload were lower than values for control subjects and patients with pressure overload. No exercise variable was predictive of severity of AS. These data confirm some previous investigators' findings with respect to LV volume and pressure overload, but do not support the concept that exercise test results are sensitive and specific for the prediction of severity in AS.

The Vacuum-Insulated, Varying-Capacitance Machine

The prospects for a varying-capacitance, vacuum-insulated, rotating machine have been examined analytically for the generation of HVDC power. Such a machine offers two potential advantages over conventional rotating machinery: 1. It is capable of very high efficiency (losses in the machine itself - excluding diodes or thyristors which might be necessary in some applications - would be less than 0.1%). 2. It is inherently suitable to high voltage operation. It appears that these machines, utilizing the best present-day techniques, are not an advantageous alternative to conventional magnetic synchronous machines for power frequency applications. For the generation of HVDC power, however, the situation is quite different: the vacuum-insulated, varying- capacitance machine would be comparable in size to the conventional magnetic machine and would possess the important advantages of producing HVDC power directly, and with higher efficiency. Assuming that 10 kV/mm could be insulated across the rotor-to-stator gap, such an HVDC machine would be 30-50% larger than a conventional synchronous alternator, but would, in effect, replace not only the alternator, but the power transformer and rectifying equipment. Losses in the vacuum-insulated HVDC machine would be 1/3 the losses of the conventional alternator-transformer -rectifier combination. If gradients of 25 kV/mm could be supported in the vacuum-insulated machine, it would be 20-30% smaller than the conventional alternative of a combination of magnetic synchronous machine, high voltage transformer, and rectifier. The design of a 7,000 kW,200 kV, dc generator, based on peak working gradients of 25 kV/mm, is discussed as an example.