Search PubMed⌕ Search

Biomedical subjects

J Dvorak

Publications and source records attributed to J Dvorak.

At least 37 records · Page 2Linked to original sources
PubMed2005

Heading in football. Part 2: biomechanics of ball heading and head response.

OBJECTIVES: Controversy surrounding the long term effects of repeated impacts from heading has raised awareness among the public and the medical community. However, there is little information about the human response to the impacts and what measures can be taken to alter their effect. The objective of the current study was to gain a better understanding of heading biomechanics through the implementation of a numerical model and subsequent investigation of parameters related to heading technique and ball characteristics. METHODS: A controlled laboratory study was carried out with seven active football players, aged 20-23 years who underwent medical screening and were instrumented with accelerometers mounted in bite plates and electromyographic electrodes on the major neck muscle groups. Balls were delivered at two speeds (6 m/s and 8 m/s) as the subjects demonstrated several specific heading manoeuvres. Photographic targets were tracked via high speed video to measure heading kinematics. One subject demonstrating reasonably averaged flexion-extension muscle activity phased with head acceleration data and upper torso kinematics was used to validate a biofidelic 50th percentile human numerical model with detailed representation of the head and neck. RESULTS: Heading kinematics and subject responses were used with a detailed numerical model to simulate impact biomechanics for a baseline heading scenario. Changes to heading techniques and ball characteristics which mitigated head impact response were identified. CONCLUSION: A numerical model combined with biomechanical measurement techniques is an important tool for parametric investigation of strategies to reduce head impact severity via changes in heading technique or the physical properties of the ball.

Adult↗
PubMed2005

Heading in football. Part 3: effect of ball properties on head response.

OBJECTIVES: Head impacts from footballs are an essential part of the game but have been implicated in mild and acute neuropsychological impairment. Ball characteristics have been noted in literature to affect the impact response of the head; however, the biomechanics are not well understood. The present study determined whether ball mass, pressure, and construction characteristics help reduce head and neck can impact response. METHODS: Head responses under ball impact (6-7 m/s) were measured with a biofidelic numerical human model and controlled human subject trials (n = 3). Three ball masses and four ball pressures were investigated for frontal heading. Further, the effect of ball construction in wet/dry conditions was studied with the numerical model. The dynamic ball characteristics were determined experimentally. Head linear and angular accelerations were measured and compared with injury assessment functions comprising peak values and head impact power. Neck responses were assessed with the numerical model. RESULTS: Ball mass reductions up to 35% resulted in decreased head responses up to 23-35% for the numerical and subject trials. Similar decreases in neck axial and shear responses were observed. Ball pressure reductions of 50% resulted in head and neck response reductions up to 10-31% for the subject trials and numerical model. Head response reductions up to 15% were observed between different ball constructions. The wet condition generally resulted in greater head and neck responses of up to 20%. CONCLUSION: Ball mass, pressure, and construction can reduce the impact severity to the head and neck. It is foreseeable that the benefits can be extended to players of all ages and skill levels.

Biomechanical Phenomena↗
PubMed2005

Effectiveness of headgear in football.

OBJECTIVES: Commercial headgear is currently being used by football players of all ages and skill levels to provide protection from heading and direct impact. The clinical and biomechanical effectiveness of the headgear in attenuating these types of impact is not well defined or understood. This study was conducted to determine whether football headgear has an effect on head impact responses. METHODS: Controlled laboratory tests were conducted with a human volunteer and surrogate head/neck system. The impact attenuation of three commercial headgears during ball impact speeds of 6-30 m/s and in head to head contact with a closing speed of 2-5 m/s was quantified. The human subject, instrumented to measure linear and angular head accelerations, was exposed to low severity impacts during heading in the unprotected and protected states. High severity heading contact and head to head impacts were studied with a biofidelic surrogate headform instrumented to measure linear and angular head responses. Subject and surrogate responses were compared with published injury assessment functions associated with mild traumatic brain injury (MTBI). RESULTS: For ball impacts, none of the headgear provided attenuation over the full range of impact speeds. Head responses with or without headgear were not significantly different (p>0.05) and remained well below levels associated with MTBI. In head to head impact tests the headgear provided an overall 33% reduction in impact response. CONCLUSION: The football headgear models tested did not provide benefit during ball impact. This is probably because of the large amount of ball deformation relative to headband thickness. However, the headgear provided measurable benefit during head to head impacts.

Adult↗
PubMed2005

Biomechanical investigation of head impacts in football.

OBJECTIVES: This study sought to measure the head accelerations induced from upper extremity to head and head to head impact during the game of football and relate this to the risk of mild traumatic brain injury using the Head Impact Power (HIP) index. Furthermore, measurement of upper neck forces and torques will indicate the potential for serious neck injury. More stringent rules or punitive sanctions may be warranted for intentional impact by the upper extremity or head during game play. METHODS: Game video of 62 cases of head impact (38% caused by the upper extremity and 30% by the head of the opposing player) was provided by F-MARC. Video analysis revealed the typical impact configurations and representative impact speeds. Upper extremity impacts of elbow strike and lateral hand strike were re-enacted in the laboratory by five volunteer football players striking an instrumented Hybrid III pedestrian model crash test manikin. Head to head impacts were re-enacted using two instrumented test manikins. RESULTS: Elbow to head impacts (1.7-4.6 m/s) and lateral hand strikes (5.2-9.3 m/s) resulted in low risk of concussion (<5%) and severe neck injury (<5%). Head to head impacts (1.5-3.0 m/s) resulted in high concussion risk (up to 67%) but low risk of severe neck injury (<5%). CONCLUSION: The laboratory simulations suggest little risk of concussion based on head accelerations and maximum HIP. There is no biomechanical justification for harsher penalties in this regard. However, deliberate use of the head to impact another player's head poses a high risk of concussion, and justifies a harsher position by regulatory bodies. In either case the risk of serious neck injury is very low.

Acceleration↗
PubMed2005

Effects of heading exposure and previous concussions on neuropsychological performance among Norwegian elite footballers.

BACKGROUND: Cross-sectional studies have indicated that neurocognitive performance may be impaired among football players. Heading the ball has been suggested as the cause, but recent reviews state that the reported deficits are more likely to be the result of head injuries. OBJECTIVE: To examine the association between previous concussions and heading exposure with performance on computer based neuropsychological tests among professional Norwegian football players. METHODS: Players in the Norwegian professional football league (Tippeligaen) performed two consecutive baseline neuropsychological tests (Cogsport) before the 2004 season (90.3% participation, n = 271) and completed a questionnaire assessing previous concussions, match heading exposure (self-reported number of heading actions per match), player career, etc. Heading actions for 18 players observed in two to four matches were counted and correlated with their self-reported values. RESULTS: Neither match nor lifetime heading exposure was associated with neuropsychological test performance. Nineteen players scored below the 95% confidence interval for one or more subtasks, but they did not differ from the rest regarding the number of previous concussions or lifetime or match heading exposure. The number of previous concussions was positively associated with lifetime heading exposure (exponent (B) = 1.97(1.03-3.75), p = 0.039), but there was no relation between previous concussions and test performance. Self-reported number of headings correlated well with the observed values (Spearman's rho = 0.77, p < 0.001). CONCLUSION: Computerised neuropsychological testing revealed no evidence of neuropsychological impairment due to heading exposure or previous concussions in a cohort of Norwegian professional football players.

Adult↗
PubMed2005

Head injuries.

Explore the source record for details and available documents.

Biomechanical Phenomena↗
PubMed2004

The interaction of oxygen with TiC(001): photoemission and first-principles studies.

High-resolution photoemission and first-principles density-functional slab calculations were used to study the interaction of oxygen with a TiC(001) surface. Atomic oxygen is present on the TiC(001) substrate after small doses of O(2) at room temperature. A big positive shift (1.5-1.8 eV) was detected for the C 1s core level. These photoemission studies suggest the existence of strong O<-->C interactions. A phenomenon corroborated by the results of first-principles calculations, which show a CTiTi hollow as the most stable site for the adsorption of O. Ti and C atoms are involved in the adsorption and dissociation of the O(2) molecule. In general, the bond between O and the TiC(001) surface contains a large degree of ionic character. The carbide-->O charge transfer is substantial even at high coverages (>0.5 ML) of oxygen. At 500 K and large doses of O(2), oxidation of the carbide surface occurs with the removal of C and formation of titanium oxides. There is an activation barrier for the exchange of Ti-C and Ti-O bonds which is overcome only by the formation of C-C or C-O bonds on the surface. The mechanism for the removal of a C atom as CO gas involves a minimum of two O adatoms, and three O adatoms are required for the formation of CO(2) gas. Due to the high stability of TiC, an O adatom alone cannot induce the generation of a C vacancy in a flat TiC(001) surface.

Journal Article↗
PubMed2004

[Epidural injections. What is certain?].

Injection of 17-20 ml of local anesthetic combined with corticosteroids via hiatus canalis sacralis or epidural between spinal processes in the lumbar region leads to distribution up to the level of the thoracolumbar junction. The indication for therapeutic peridual or epidural injections are radicular symptoms as a result of disc herniation, foraminal stenosis as well as neurogenic claudication. Contraindications are anticoagulation or local infection. Complications and side effects occur extremely seldom. There is only one RCT for radiculopathy and epidural steroids.

Adrenal Cortex Hormones↗
PubMed2004

Liposomal doxorubicin combined with regional hyperthermia: reducing systemic toxicity and improving locoregional efficacy in the treatment of solid tumors.

Incorporation of doxorubicin into polyethylene glycol-coated (pegylated) liposomes increases the therapeutic index, prolongs circulation time and enhances tumor localization. Pegylated liposomal doxorubicin (PLD) is an established therapeutic agent in epithelial ovarian carcinoma (EOC), breast carcinoma or Kaposi's sarcoma, and PLD administration results in reduction of toxicity. Addition of regional hyperthermia increases liposome extravasation, induces the doxorubicin release from the liposomes, and the combination of hyperthermia and doxorubicin itself may be supra-additive, resulting in enhanced antitumor efficacy in the heated region. Encouraging results have been reported for the combination of PLD and hyperthermia in EOC, breast carcinoma and hepatocellular carcinoma.

Antibiotics, Antineoplastic↗
PubMed2004

Injuries in youth amateur soccer and rugby players--comparison of incidence and characteristics.

OBJECTIVES: In reviewing the literature on sports injuries, few studies could be found in which exposure related incidences of injury in different types of sport were compared. These studies indicated that ice hockey, handball, basketball, soccer, and rugby are popular team sports with a relatively high risk of injury. The aim of the study was to compare the characteristics and incidence of injuries in male youth amateur soccer and rugby players. METHODS: This prospective cohort study comprised an initial baseline examination to ascertain the characteristics of the players and their level of performance, and a one season observation period during which a physician visited the team weekly and documented all occurring injuries. Twelve soccer and 10 rugby school teams with male amateur players aged 14-18 years were selected for the study. 145 soccer and 123 rugby players could be followed up over one season. RESULTS: Comparison of the incidence of soccer and rugby injuries indicated that rugby union football was associated with a significantly higher rate of injury than soccer. The differences were pronounced for contact injuries, injuries of the head, neck, shoulder, and upper extremity, as well as for concussion, fractures, dislocations, and strains. Rugby players incurred 1.5 times more overuse and training injuries in relation to exposure time, and 2.7 times more match injuries than soccer players. Three rugby players but no soccer players had to stop their participation in sport because of severe injury. CONCLUSION: The incidence of injury in New Zealand school teams playing soccer or rugby union is high, probably in part because of the low ratio of hours spent in training relative to hours spent playing matches. The development and implementation of preventive interventions to reduce the rate and severity of injury is recommended.

Adolescent↗
PubMed2004

Complete response of multiple melanoma brain metastases after treatment with temozolomide.

BACKGROUND: Inoperable melanoma brain metastases are usually uniformly fatal, and complete response after cytotoxic therapy is rare. CASE REPORT: A patient with multiple inoperable melanoma brain metastases was treated with 6 cycles of oral temozolomide (300 mg once daily over 5 days every 28 days). A complete response was documented by magnetic resonance. CONCLUSIONS: The present observation suggests that temozolomide may be an active and well tolerated treatment for malignant melanoma brain metastases.

Antineoplastic Agents, Alkylating↗
PubMed2003

Serum S-100B protein levels in young amateur soccer players after controlled heading and normal exercise.

BACKGROUND: Repeated impacts by heading might lead to significant head injuries in soccer players comparable to those of patients with accidental minor traumatic brain injury (TBI). The neuroprotein S-100B released into the circulation is suggested to be a reliable marker indicating brain damage. The objective was to evaluate the neuroprotein S-100B serum levels in young amateur soccer players early after controlled heading compared to early measurements after normal exercise as well as in other patients after minor TBI. MATERIAL AND METHODS: Sixty-one male amateur soccer players (median age 15.3 years) performed controlled heading aimed at the forehead for 55 minutes. Data were compared to 58 male amateur soccer players (15.9 years) performing 61 minutes of normal exercise training without head contact and 81 young male patients early after TBI who underwent computed tomography (CCT) for detection of intracranial lesions. First venous blood samples were drawn before the training sessions, second and third samples 60 and 360 minutes after heading or 64 and 355 minutes after exercise, respectively, 65 and 366 minutes after TBI. RESULTS: Median S-100B serum levels of the heading group only slightly increased from 0.15 ng/ml to 0.18 ng/ml 60 minutes after end of training. Within 360 minutes S-100B values decreased again to 0.15 ng/ml reaching the initial values. S-100B serum values of the exercise group showed a similar transient increase exhibiting significant lower levels before exercise (0.10 ng/ml) as well as 64 minutes (0.11 ng/ml) and 355 minutes after exercise (0.09 ng/ml) compared to the heading group. According to age stratification in the heading group, starting median S-100B levels were significantly higher in subjects with 12-13 years (0.22 ng/ml) and 14-15 years (0.17 ng/ml) compared to those with 16-17 years of age (0.06 ng/ml). None of the subcollectives did reach median S-100B levels of the CCT+ group (n = 20) at admission (0.62 ng/ml) or 366 minutes later (0.32 ng/ml), which were significantly elevated compared to those of the CCT group (n = 61) at admission (0.10 ng/ml) or 370 minutes later (0.08 ng/ml). CONCLUSIONS: Controlled repetitive heading in young amateur soccer players leads to a transient increase between 60 to 360 min after training, but does not appear to evoke a longer lasting S-100B release into serum indicating cellular brain damage. After heading S-100B levels are significantly elevated compared to normal exercise. Although soccer players with 12-13 years and 14-15 years revealed significantly higher S-100B values than with 16-17 years of age, the transient increase is independent of the age-related starting values. However, since brain damage due to abrupt heading a ball of high speed or accidental trauma during regular soccer games cannot be excluded, S-100B measurements in soccer players are initiated during video-controlled soccer games.

Adolescent↗
PubMed2003

Development and application of quantum dots for immunocytochemistry of human erythrocytes.

Recent developments in quantum dot technology have resulted in the introduction of new fluorescence immunocytochemical probes. In contrast to organic fluorophores, which are not photostable, the high quantum yield and remarkable photostability of quantum dots solve major problems associated with immunocytochemical studies of erythrocytes. We report here the first application of quantum dots to immunocytochemical studies of human erythrocytes capable of being used in high-magnification, three-dimensional erythrocyte reconstruction techniques. The procedure consists of stabilizing human erythrocytes with a homofunctional imidoester cross-linker to minimize fixative-induced autofluorescence followed by reacting with a quantum dot - monoclonal antibody complex to label band 3 protein. Our new procedure clearly showed a non-homogeneous, raft-like distribution of band 3 protein in the erythrocyte membrane. We also demonstrate the applicability of our technique to studies of erythrocyte membrane modifications occurring during the invasion of a malaria parasite.

Animals↗
PubMed2001

Detection of nandrolone metabolites in urine after a football game in professional and amateur players: a Bayesian comparison.

Nandrolone (19-nortestosterone) is a widely used anabolic steroid in sports where strength plays an essential role. Once nandrolone has been metabolised, two major metabolites are excreted in urine, 19-norandrosterone (NA) and 19-noretiocholanolone (NE). In 1997, in France, quite a few sportsmen had concentrations of 19-norandrosterone very close to the IOC cut off limit (2ng/ml). At that time, a debate took place about the capability of the human male body to produce by itself these metabolites without any intake of nandrolone or related compounds. The International Football Federation (FIFA) was very concerned with this problematic, especially because the World Cup was about to start in France. In this respect, a statistical study was held with all football players from the first and second divisions of the Swiss Football National League. All players gave a urine sample after effort and around 6% of them showed traces of 19-norandrosterone. These results were compared with amateur football players (control group) and around 6% of them had very small amounts of 19-norandrosterone and/or 19-noretiocholanolone in urine after effort, whereas none of them had detectable traces of one or the other metabolite before effort. The origin of these compounds in urine after a strenuous physical activity is still unknown, but three hypotheses can be put forward. First, an endogenous production of nandrolone metabolites takes place. Second, nandrolone metabolites are released from the fatty tissues after an intake of nandrolone, some related compounds or some contaminated nutritive supplements. Finally, the sportsmen may have taken something during or just before the football game.

Adult↗
PubMed2001

Chemistry of NO2 on oxide surfaces: formation of NO3 on TiO2(110) and NO2<-->O vacancy interactions.

Synchrotron-based high-resolution photoemission, X-ray absorption near-edge spectroscopy, and first-principles density functional (DF) slab calculations were used to study the interaction of NO(2) with a TiO(2)(110) single crystal and powders of titania. The main product of the adsorption of NO(2) on TiO(2)(110) is surface nitrate with a small amount of chemisorbed NO(2). A similar result is obtained after the reaction of NO(2) with polycrystalline powders of TiO(2) or other oxide powders. This trend, however, does not imply that the metal centers of the oxides are unreactive toward NO(2). An unexpected mechanism is seen for the formation of NO(3). Photoemission data and DF calculations indicate that the surface nitrate forms through the disproportionation of NO(2) on Ti sites (2NO(2,ads) --> NO(3,ads) + NO(gas)) rather than direct adsorption of NO(2) on O centers of titania. Complex interactions take place between NO(2) and O vacancies of TiO(2)(110). Electronic states associated with O vacancies play a predominant role in the bonding and surface chemistry of NO(2). The adsorbed NO(2), on its part, affects the thermochemical stability of O vacancies, facilitating their migration from the bulk to the surface of titania. The behavior of the NO(2)/titania system illustrates the importance of surface and subsurface defects when using an oxide for trapping or destroying NO(x)() species in the prevention of environmental pollution (DeNOx operations).

Environmental Pollutants↗
PubMed2001

Active therapy for chronic low back pain part 1. Effects on back muscle activation, fatigability, and strength.

DESIGN: Randomized prospective study of the effects of three types of active therapy on back muscle function in chronic low back pain patients. OBJECTIVES: To quantify the effects of 3 months active therapy on strength, endurance, activation, and fatigability of the back entensor muscles. SUMMARY OF BACKGROUND DATA: Many studies have documented an association between chronic low back pain and diminished muscular performance capacity. Few studies have quantified the changes in these measures following interventions using objective measurement techniques or related them to changes in clinical outcome. METHODS: A total of 148 individuals (57% women) with chronic low back pain (age, 45.0 +/- 10.0 years; duration of low back pain, 10.9 +/- 9.5 years) were randomized to a treatment that they attended for 3 months: active physiotherapy, muscle reconditioning on devices, or low-impact aerobics. Before and after therapy, assessments were made of the following: trunk muscle strength (in flexion, extension, lateral bending, and axial rotation), erector spinae activation (maximal, and during forward bending movements), back extensor endurance (Biering-Sørensen test), and erector spinae fatigability (determined from changes in the median frequency of the surface electromyographic signal) during isometric and dynamic tests. RESULTS: A total of 132 of 148 patients (89%) completed the therapy. Isometric strength in each movement direction increased in all groups post-therapy (P < 0.0008), most notably in the devices group. Activation of the erector spinae during the extension tests also increased significantly in all groups and showed a weak, but significant, relationship with increased maximal strength (P = 0.01). Pretherapy 55% of the subjects showed no relaxation of the back muscles at L5 when in the fully flexed position; no changes were observed in any group post-therapy. Endurance time during the Biering-Sørensen test increased significantly post-therapy in all groups (P = 0.0001), but there were no significant changes in EMG-determined fatigability. Fatigability of the lumbar muscles at L5 (EMG median frequency changes) during the dynamic test increased post-therapy (P = 0.0001) without group differences. CONCLUSION: Significant changes in muscle performance were observed in all three active therapy groups post-therapy, which appeared to be mainly due to changes in neural activation of the lumbar muscles and psychological changes concerning, for example, motivation or pain tolerance.

Adult↗