From big data to rich data: The key features of athlete wheelchair mobility performance.

Quantitative assessment of an athlete׳s individual wheelchair mobility performance is one prerequisite needed to evaluate game performance, improve wheelchair settings and optimize training routines. Inertial Measurement Unit (IMU) based methods can be used to perform such quantitative assessment, providing a large number of kinematic data. The goal of this research was to reduce that large amount of data to a set of key features best describing wheelchair mobility performance in match play and present them in meaningful way for both scientists and athletes. To test the discriminative power, wheelchair mobility characteristics of athletes with different performance levels were compared. The wheelchair kinematics of 29 (inter-)national level athletes were measured during a match using three inertial sensors mounted on the wheelchair. Principal component analysis was used to reduce 22 kinematic outcomes to a set of six outcomes regarding linear and rotational movement; speed and acceleration; average and best performance. In addition, it was explored whether groups of athletes with known performance differences based on their impairment classification also differed with respect to these key outcomes using univariate general linear models. For all six key outcomes classification showed to be a significant factor (p<0.05). We composed a set of six key kinematic outcomes that accurately describe wheelchair mobility performance in match play. The key kinematic outcomes were displayed in an easy to interpret way, usable for athletes, coaches and scientists. This standardized representation enables comparison of different wheelchair sports regarding wheelchair mobility, but also evaluation at the level of an individual athlete. By this means, the tool could enhance further development of wheelchair sports in general.

Opportunities for measuring wheelchair kinematics in match settings; reliability of a three inertial sensor configuration.

Knowledge of wheelchair kinematics during a match is prerequisite for performance improvement in wheelchair basketball. Unfortunately, no measurement system providing key kinematic outcomes proved to be reliable in competition. In this study, the reliability of estimated wheelchair kinematics based on a three inertial measurement unit (IMU) configuration was assessed in wheelchair basketball match-like conditions. Twenty participants performed a series of tests reflecting different motion aspects of wheelchair basketball. During the tests wheelchair kinematics were simultaneously measured using IMUs on wheels and frame, and a 24-camera optical motion analysis system serving as gold standard. Results showed only small deviations of the IMU method compared to the gold standard, once a newly developed skid correction algorithm was applied. Calculated Root Mean Square Errors (RMSE) showed good estimates for frame displacement (RMSE≤0.05 m) and speed (RMSE≤0.1m/s), except for three truly vigorous tests. Estimates of frame rotation in the horizontal plane (RMSE<3°) and rotational speed (RMSE<7°/s) were very accurate. Differences in calculated Instantaneous Rotation Centres (IRC) were small, but somewhat larger in tests performed at high speed (RMSE up to 0.19 m). Average test outcomes for linear speed (ICCs>0.90), rotational speed (ICC>0.99) and IRC (ICC> 0.90) showed high correlations between IMU data and gold standard. IMU based estimation of wheelchair kinematics provided reliable results, except for brief moments of wheel skidding in truly vigorous tests. The IMU method is believed to enable prospective research in wheelchair basketball match conditions and contribute to individual support of athletes in everyday sports practice.

Spring-like Ankle Foot Orthoses reduce the energy cost of walking by taking over ankle work.

In patients with central neurological disorders, gait is often limited by a reduced ability to push off with the ankle. To overcome this reduced ankle push-off, energy-storing, spring-like carbon-composite Ankle Foot Orthoses (AFO) can be prescribed. It is expected that the energy returned by the AFO in late stance will support ankle push-off, and reduce the energy cost of walking. In 10 patients with multiple sclerosis and stroke the energy cost of walking, 3D kinematics, joint power, and joint work were measured during gait, with and without the AFO. The mechanical characteristics of the AFO were measured separately, and used to calculate the contribution of the AFO to the ankle kinetics. We found a significant decrease of 9.8% in energy cost of walking when walking with the AFO. With the AFO, the range of motion of the ankle was reduced by 12.3°, and the net work around the ankle was reduced by 29%. The total net work in the affected leg remained unchanged. The AFO accounted for 60% of the positive ankle work, which reduced the total amount of work performed by the leg by 11.1% when walking with the AFO. The decrease in energy cost when walking with a spring-like energy-storing AFO in central neurological patients is not induced by an augmented net ankle push-off, but by the AFO partially taking over ankle work.

The effect of ankle foot orthosis stiffness on the energy cost of walking: a simulation study.

BACKGROUND: In stroke and multiple sclerosis patients, gait is frequently hampered by a reduced ability to push-off with the ankle caused by weakness of the plantar-flexor muscles. To enhance ankle push-off and to decrease the high energy cost of walking, spring-like carbon-composite Ankle Foot Orthoses are frequently prescribed. However, it is unknown what Ankle Foot Orthoses stiffness should be used to obtain the most efficient gait. The aim of this simulation study was to gain insights into the effect of variation in Ankle Foot Orthosis stiffness on the amount of energy stored in the Ankle Foot Orthosis and the energy cost of walking. METHODS: We developed a two-dimensional forward-dynamic walking model with a passive spring at the ankle representing the Ankle Foot Orthosis and two constant torques at the hip for propulsion. We varied Ankle Foot Orthosis stiffness while keeping speed and step length constant. FINDINGS: We found an optimal stiffness, at which the energy delivered at the hip joint was minimal. Energy cost decreased with increasing energy storage in the ankle foot orthosis, but the most efficient gait did not occur with maximal energy storage. With maximum storage, push-off occurred too late to reduce the impact of the contralateral leg with the floor. Maximum return prior to foot strike was also suboptimal, as push-off occurred too early and its effects were subsequently counteracted by gravity. The optimal Ankle Foot Orthosis stiffness resulted in significant push-off timed just prior to foot strike and led to greater ankle plantar-flexion velocity just before contralateral foot strike. INTERPRETATION: Our results suggest that patient energy cost might be reduced by the proper choice of Ankle Foot Orthosis stiffness.

A new method for evaluating ankle foot orthosis characteristics: BRUCE.

The mechanical characteristics of ankle foot orthoses (AFOs), such as the stiffness and neutral angle around the ankle and metatarsal-phalangeal (MTP) joints, are rarely quantified. Paradoxically, it is expected that these characteristics determine the function of the AFO in pathological gait. Therefore a device to determine these AFO characteristics named BRUCE was designed based on multidisciplinary consensus. The design is based on a replicated human leg that is manually driven and continuously registers joint configuration and force exerted by the AFO onto the device. From this information, neutral angles and stiffnesses around the ankle and MTP joints are determined using a linear fit. The reliability of the stiffnesses and neutral angles was studied by repeatedly measuring the mechanical characteristics of four different AFOs, and evaluating the inter-session, intra-session, and inter-observer errors. The reliability study revealed that ankle and MTP stiffness could be measured with very high reliability (ICC=0.98-1.00). Ankle and MTP neutral angles showed reasonable reliability (ICC=0.79-0.92). Measurement error in the neutral angles could mainly be attributed to the difference in testers. With a fixed tester excellent reliability was obtained (ICC=0.99-0.99). The results derived using BRUCE can help to gain insight into the role of the mechanical characteristics of AFOs in correcting pathological gait. Objective information of AFO characteristics is expected to lead to a better founded prescription of AFOs, resulting in optimal functional benefit for the patient.

Is effective force application in handrim wheelchair propulsion also efficient?

BACKGROUND: Efficiency in manual wheelchair propulsion is low, as is the fraction of the propulsion force that is attributed to the moment of propulsion of the wheelchair. In this study we tested the hypothesis that a tangential propulsion force direction leads to an increase in physiological cost, due to (1) the sub-optimal use of elbow flexors and extensors, and/or (2) the necessity of preventing of glenohumeral subluxation. METHODS: Five able-bodied and 11 individuals with a spinal cord injury propelled a wheelchair while kinematics and kinetics were collected. The results were used to perform inverse dynamical simulations with input of (1) the experimentally obtained propulsion force, and (2) only the tangential component of that force. FINDINGS: In the tangential force condition the physiological cost was over 30% higher, while the tangential propulsion force was only 75% of the total experimental force. According to model estimations, the tangential force condition led to more co-contraction around the elbow, and a higher power production around the shoulder joint. The tangential propulsion force led to a significant, but small 4% increase in necessity for the model to compensate for glenohumeral subluxation, which indicates that this is not a likely cause of the decrease in efficiency. INTERPRETATION: The present findings support the hypothesis that the observed force direction in wheelchair propulsion is a compromise between efficiency and the constraints imposed by the wheelchair-user system. This implies that training should not be aimed at optimization of the propulsion force, because this may be less efficient and more straining for the musculoskeletal system.

Farr's law applied to AIDS projections.

Farr's Law of Epidemics, first promulgated in 1840 and resurrected by Brownlee in the early 1900s, states that epidemics tend to rise and fall in a roughly symmetrical pattern that can be approximated by a normal bell-shaped curve. We applied this simple law to the reported annual incidence of cases of acquired immunodeficiency syndrome in the United States from 1982 through 1987. The 6 years of incidence data closely fit a normal distribution that crests in late 1988 and then declines to a low point by the mid-1990s. The projected size of the epidemic falls in the range of 200 000 cases. A continuing incidence of endemic cases can be expected to emerge, but we believe it will occur at a low level.

Postmarketing surveillance for neurologic adverse events reported after hepatitis B vaccination. Experience of the first three years.

In 1982, the Centers for Disease Control, the Food and Drug Administration, and the manufacturer created a surveillance system to monitor spontaneous reports of adverse events occurring after inoculation with the new plasma-derived hepatitis B vaccine (Heptavax-B, Merck Sharp and Dohme, West Point, PA). In the three years between June 1, 1982 and May 31, 1985, an estimated 850,000 persons received the vaccine. During that period, a total of 41 reports were received for one of the following neurologic adverse events: convulsions (five cases), Bell's palsy (10 cases), Guillain-Barré syndrome (nine cases), lumbar radiculopathy (five cases), brachial plexus neuropathy (three cases), optic neuritis (five cases), and transverse myelitis (four cases). Half of these occurred after the first of three required vaccine doses. There were no deaths. Calculation of the relative risks of these illnesses after hepatitis B vaccination was highly dependent on diagnostic classification of the cases, estimates of the size of the vaccinated population, background incidence of the diseases, and the length and distribution of the hypothetical at-risk interval used in the analysis. Other factors important in judging the results of the study could not be measured, including underreporting. In some analyses, Guillain-Barré syndrome was reported significantly more often than expected (p less than 0.05, Poisson probability distribution). However, no conclusive epidemiologic association could be made between any neurologic adverse event and the vaccine. Even if such an association did exist, the preventive benefits of the vaccine in persons at high risk for hepatitis B would unequivocally outweigh the risk of any neurologic adverse event.

Sample size for individually matched case-control studies.

The standard formulas used to calculate sample size for an individually matched case-control study assume a constant probability of exposure throughout the pool of possible controls. We propose new formulas that allow for heterogeneity in the probability of exposure among controls in different matched sets. Since matching factors are suspected of being confounders, they are expected to divide the total population into subgroups with different proportions exposed. Thus, the assumption of homogeneity of exposure among controls, made by the currently used formulas, is inconsistent with the assumptions used to design a matched study. The proposed formulas avoid this inconsistency. We present an example to illustrate how heterogeneity can affect the required sample size.

A model-based approach for estimating the mean incubation period of transfusion-associated acquired immunodeficiency syndrome.

The incubation period, representing the interval between the date of exposure and the date of diagnosis, can be firmly ascertained in transfusion-associated cases of acquired immunodeficiency syndrome (AIDS). However, because the observation period of all transfusion-infected persons may be short compared with the average incubation period for AIDS, many cases with long incubation periods have not yet been diagnosed. Thus, the simple average of 2.6 years tends to underestimate the true mean. To correct for this underestimation bias, we assumed that the underlying distribution of the incubation periods is a member of a broad class of probability densities. Then, by maximum likelihood techniques, the mean incubation period for transfusion-associated AIDS was estimated to be 4.5 years, with the 90% confidence interval ranging from 2.6 to 14.2 years. The long incubation period has important consequences for infected individuals and implications for public health intervention and prevention policy.

Disease manifestation among homosexual men with acquired immunodeficiency syndrome: a possible role of nitrites in Kaposi's sarcoma.

To identify risk factors that determine the major manifestations of the acquired immunodeficiency syndrome (AIDS), the authors analyzed data from three epidemiologic studies conducted by the Centers for Disease Control. The authors compared patients by outcome of disease. Eighty-seven homosexual patients (47 with Kaposi's sarcoma, 20 with Pneumocystis carinii pneumonia, and 20 with both) had participated in the earlier studies, and their interviews and laboratory test results were available. Compared with patients who have Pneumocystis carinii pneumonia only, patients with Kaposi's sarcoma and those with both diseases reported more different sexual partners, more recreational drug use, higher incomes and higher rates of non-B hepatitis. Multivariate analysis showed that the variable most strongly associated with Kaposi's sarcoma was the use of large quantities of nitrite inhalants. A multifactorial model is postulated to explain the various disease manifestations of AIDS. This study suggests that the use of nitrite inhalants may be a cofactor in the development of Kaposi's sarcoma. By identifying other cofactors, investigators may be able to define additional opportunities for prevention of the development of AIDS.

Deaths from varicella in infants.

Onset of maternal varicella up to 5 days before delivery is associated with in utero exposure to varicella and may result in severe infection in the newborn 5 to 10 days after delivery. Since up to 31% of these newborns may die, routine administration of varicella-zoster immunoglobulin to these infants is recommended. Little is known, however, about the risk of death in other infants with postnatal infection. Available epidemiologic data indicate an estimated death/case ratio for children less than 1 year of age 4 times that for 1- to 14-year-olds (8 in 100,000 vs. 2 in 100,000). Since the actual ages for the infant deaths were lacking, it has been impossible to know how many deaths were possibly related to maternal varicella contracted within the 5 days before delivery. Using National Center for Health Statistics data, we analyzed 92 deaths due to varicella in children less than 1 year old reported between 1968 and 1978 (median age, 5.5 months). Only five deaths occurred in newborns (ages 8 hours to 19 days). These data indicate that intrauterine infection accounts for few varicella deaths in infants. Since postnatal infection accounts for the observed increased risk of death in this age group, the need for preventing postnatal varicella in all infants merits further study. However, based on the small number of deaths occurring annually and the low relative risk compared to other high risk groups, routine postexposure administration of varicella-zoster immunoglobulin to all children less than 1 year of age does not seem warranted at this time.

Acquired immunodeficiency syndrome among patients attending hemophilia treatment centers and mortality experience of hemophiliacs in the United States.

The acquired immunodeficiency syndrome (AIDS) was first recognized among hemophiliacs in 1982. The authors have conducted investigations to determine the onset and incidence of AIDS among hemophiliacs and to determine trends in hemophilia mortality since the introduction of clotting-factor concentrates in the late 1960s. A survey of United States hemophilia treatment centers, supported by the Centers for Disease Control and the National Hemophilia Foundation, defined a population of hemophiliacs which was monitored for AIDS cases through June 1984. Death reports from the United States Vital Statistics System and from the hemophilia treatment center survey provided mortality trends for 1968-1979 and for 1978-1982, respectively. The results of these investigations demonstrate the following points. 1) The AIDS epidemic is a new and important cause of illness and mortality among hemophiliacs, although a very low incidence of AIDS among hemophiliacs prior to 1982 cannot be ruled out. 2) The AIDS cases who attended the surveyed hemophilia treatment centers were distributed throughout the United States and were older than hemophilia treatment center patients without AIDS. AIDS cases also used more lyophilized clotting-factor concentrate, but only a small number of cases were reported with this information. 3) Improved care for hemophilia, including the use of clotting-factor concentrates, dramatically reduced hemophilia mortality rates during the 1970s. 4) In 1982, hemorrhage was the major cause of death among hemophiliacs. Deaths from non-alcoholic liver disease were also increased. AIDS incidence among hemophilia treatment center attendees was stable at 0.6 cases per 1,000 hemophilia treatment center attendees per year during 1982 and 1983 but increased sharply to 5.4 cases per 1,000 during the first quarter of 1984.

Efficacy of influenza vaccine in nursing homes. Reduction in illness and complications during an influenza A (H3N2) epidemic.

From December 10, 1982, to March 4, 1983, when influenza A (H3N2) viruses circulated in Michigan, outbreaks of influenza-like illness were identified in seven nursing homes in Genesee County; 272 (27%) of 1,018 residents were affected. Unvaccinated residents were more likely than vaccinated residents to become ill (risk ratio [RR], 2.6; 95% confidence interval [Cl], 1.8-3.6) and were subsequently more likely to be hospitalized (RR, 2.4; 95% Cl, 1.2-4.8), develop roentgenographically proven pneumonia (RR, 2.9; 95% Cl, 1.6-5.3), or die (RR, 5.6; 95% Cl, 1.2-9.1). Similar observations were made during investigations in six of the eight remaining nursing homes in Genesee County, in which 57 (12%) of 458 residents became ill sporadically. These findings suggest that influenza vaccine can reduce the incidence and severity of influenza virus infections among the elderly and chronically ill and underscore the importance of vaccination programs for those in nursing homes and in the general community.

Epidemiologic, clinical, and laboratory features of Coxsackie B1-B5 infections in the United States, 1970-79.

In the period 1970 through 1979, the Coxsackie B1, B2, B3, B4, and B5 viruses constituted 24 percent of more than 18,000 enteroviruses isolated and reported through national surveillance. Young children, especially males, were most frequently affected: 48 percent of the national surveillance population were less than 5 years of age, including 30 percent who were less than 1 year old. Among the most frequently reported clinical syndromes associated with B infection were meningitis (in 56 percent of patients with B1-B5 infections), encephalitis (in 15 percent), and respiratory tract disease (in 14 percent). Carditis, a well-known B syndrome, was reported with only 2 percent of B1-B5 infections. Like most enteroviral agents, Group B viruses were isolated primarily during the summer: 87 percent of all these isolations were made during the 5 months from June through October. Although B2, B3, and B4 viruses were isolated at relatively uniform levels each year, B1 and B5 viral illnesses occurred nationwide as explosive epidemics only in certain years. A separate population of B-infected patients, identified by the Nassau County Medical Center (NCMC) Virus Laboratory, East Meadow, N.Y., during the same 10-year period, was studied to compare epidemiologic characteristics and to evaluate in greater detail clinical and laboratory features of B infections. Because of more active solicitation of specimens for testing, ascertainment in the NCMC system was more complete. The most frequently reported clinical findings at NCMC included fever (97 percent of cases), which was biphasic in 27 percent; pharyngitis (85 percent); vomiting (56 percent); headache (49 percent); other respiratory signs and symptoms (44 percent); diarrhea (40 percent); abdominal pain (33 percent); rash (31 percent); and otitis (28 percent). Rash was more frequently associated with younger than with older age groups (P < .01) for all B agents. Overall, throat (T) and rectal (R) swabs had the highest B-positivity rates among known infected patients(83 percent for T and 78 percent for R). Only for T was the positivity rate correlated with the interval between onset of illness and obtaining the specimen (P < .05). B agents grew most quickly from T specimens, but most reliably from R specimens. On the basis of these data,the authors recommend that both T and R specimens be obtained from every patient for whom prompt and reliable laboratory diagnosis of B infection is sought.To the authors' knowledge, these results from 10 years of national surveillance represent the largest surveillance summary of Coxsackie B viruses to date in the literature. Comparison of these results with those reported over the same 10 years by NCMC reflects differences that arise mostly because of differences in ascertainment systems.

Safety of prolonged administration of rimantadine hydrochloride in the prophylaxis of influenza A virus infections in nursing homes.

We evaluated the safety of rimantadine hydrochloride (RH) prophylaxis in a double-blind, placebo-controlled trial in three nursing homes during a community epidemic of influenza A (H3N2). Although daily monitoring of the 35 participants revealed an association between RH administration (100 mg twice a day) and the development of nausea and anxiety (P less than 0.05), these and other potential side effects were transient and were rarely considered to be clinically significant. Serum RH levels measured at the end of the trial (mean, 1,159 ng/ml) were nearly three times higher than those measured previously in younger individuals, suggesting that lower dosages may be indicated for the elderly.

An epidemiologic and clinical evaluation of Guillain-Barré syndrome reported in association with the administration of swine influenza vaccines.

As a result of a court order, computerized summaries of approximately 1,300 cases reported as Guillain-Barré syndrome by state health departments to the Centers for Disease Control during the intensive national surveillance instituted following the swine influenza vaccination program in 1976-1977 became available for further study. Although the data were not uniformly adequate to confirm the diagnosis of Guillain-Barré syndrome, they were sufficient to enable classification according to extent of motor involvement. Vaccinated cases with "extensive" paresis or paralysis occurred in a characteristic epidemiologic pattern closely approximated by a lognormal curve, suggesting a causal relationship between the disease and the vaccine. Cases with "limited" motor involvement showed no such pattern, suggesting that this group included a substantial proportion of cases which were unrelated to the vaccine. The effect attributed to the vaccine lasted for at least six weeks and possibly for eight weeks but not longer. The relative risk of acquiring "extensive" disease over a six-week period following vaccination ranged from 3.96 to 7.75 depending on the particular baseline estimate of expected normal or endemic incidence that was chosen. Correspondingly, the number of cases that could be attributed to the vaccine over the six-week period ranged from 211 to 246, or very slightly higher over an eight-week period if the lowest baseline estimate was used. The total rate of Guillain-Barré syndrome cases attributed to prior use of the vaccine was 4.9 to 5.9 per million vaccinees.

Acquired immune deficiency syndrome in the United States: the first 1,000 cases.

Between June 1981 and February 1983, the Centers for Disease Control (Atlanta) received reports of 1,000 patients living in the United States who met a surveillance definition for the acquired immune deficiency syndrome (AIDS). Seventy-three percent of these patients were diagnosed after January 1, 1982. The 1,000 patients included 284 with Kaposi's sarcoma (KS), 497 with Pneumocystis carinii pneumonia (PCP), 83 with KS and PCP, and 136 with opportunistic infections other than PCP. The overall mortality has been 39.2%. Cases have been reported from 32 states and the District of Columbia; New York, California, New Jersey, and Florida account for 82.7% of the reports. All but 61 of the patients could be classified into one or more of the following groups: homosexual or bisexual men, intravenous drug abusers, Haitian natives, or patients with hemophilia. Epidemiologic trends in AIDS cases are consistent with the gradual extension of an infectious agent into new populations.

Mortality data analysis using a multiple-cause approach.

Death certificates are the primary source for information used to define general mortality patterns in the United States. Analyses of mortality data generally are restricted to one of the conditions listed on the certificate--the underlying cause of dealth. We review principles related to the use of mortality data and describe a study using mortality tapes ("multiple-cause tapes") that list all conditions recorded on dealth certificates. Using multiple-cause tapes, we found that the number of deaths associated with seven infectious diseases in 1968, 1969, and 1970 was from 24% (diphtheria) to 81% (rubella) greater than that officially reported. Multiple-cause tapes also permitted a review of the association of deaths attributed to measles and varicella and known complications of these diseases. these observations confirm the usefulness of multiple-cause tapes in analyzing mortality data and emphasize the importance of examining all conditions listed on the death certificate.