Diverging Awareness of Postoperative Delirium and Cognitive Dysfunction in German Health Care Providers.

PURPOSE: Postoperative cognitive dysfunction (POCD) appears in up to 30% of patients suffering from postoperative delirium (POD). Both are associated with higher mortality and postoperative complications, prolonged hospital stays, and increased costs. Multi-modal models with pre-admission risk reduction counselling, perioperative monitoring, and training of multidisciplinary patient care providers have been shown to decrease the prevalence of both. The aim of our study is to understand how far those measures are known and implemented in routine care and to detect potential gaps in the current practice regarding risk communication and information flow between involved caregivers for patients at risk for POD/POCD. PATIENTS AND METHODS: As part of a multicenter study, seven semi-structured focus group (FG) discussions with nurses and physicians from tertiary care hospitals (surgery, anesthesiology, and orthopedics, n=31) and general practitioners (GPs) in private practice (n=7) were performed. Transcribed discussions were analyzed using qualitative content analysis. RESULTS: POD is present above all in the daily work of nurses, whereas physicians do not perceive it as a relevant problem. Physicians report that no regular risk assessment or risk communication was performed prior to elective surgery. Information about POD often gets lost during hand-offs and is not regularly reported in discharge letters. Thus, persisting cognitive dysfunction is often missed. The importance of standardized documentation and continuous education concerning risks, screening, and treatment was emphasized. The often-suggested pre-OP medication adjustment was seen as less important; in contrast, avoiding withdrawal was regarded as far more important. CONCLUSION: Altogether, it seems that standards and available best practice concepts are rarely implemented. In contrast to physicians, nurses are highly aware of delirium and ask for standardized procedures and more responsibility. Therefore, raising awareness regarding risks, screening tools, and effective preventive measures for POD/POCD seems an urgent goal. Nurses should have a central role in coordination and care of POD to prevent the risk for POCD.

Ectoine protects DNA from damage by ionizing radiation.

Ectoine plays an important role in protecting biomolecules and entire cells against environmental stressors such as salinity, freezing, drying and high temperatures. Recent studies revealed that ectoine also provides effective protection for human skin cells from damage caused by UV-A radiation. These protective properties make ectoine a valuable compound and it is applied as an active ingredient in numerous pharmaceutical devices and cosmetics. Interestingly, the underlying mechanism resulting in protecting cells from radiation is not yet fully understood. Here we present a study on ectoine and its protective influence on DNA during electron irradiation. Applying gel electrophoresis and atomic force microscopy, we demonstrate for the first time that ectoine prevents DNA strand breaks caused by ionizing electron radiation. The results presented here point to future applications of ectoine for instance in cancer radiation therapy.

Ectoine can enhance structural changes in DNA in vitro.

Strand breaks and conformational changes of DNA have consequences for the physiological role of DNA. The natural protecting molecule ectoine is beneficial to entire bacterial cells and biomolecules such as proteins by mitigating detrimental effects of environmental stresses. It was postulated that ectoine-like molecules bind to negatively charged spheres that mimic DNA surfaces. We investigated the effect of ectoine on DNA and whether ectoine is able to protect DNA from damages caused by ultraviolet radiation (UV-A). In order to determine different isoforms of DNA, agarose gel electrophoresis and atomic force microscopy experiments were carried out with plasmid pUC19 DNA. Our quantitative results revealed that a prolonged incubation of DNA with ectoine leads to an increase in transitions from supercoiled (undamaged) to open circular (single-strand break) conformation at pH 6.6. The effect is pH dependent and no significant changes were observed at physiological pH of 7.5. After UV-A irradiation in ectoine solution, changes in DNA conformation were even more pronounced and this effect was pH dependent. We hypothesize that ectoine is attracted to the negatively charge surface of DNA at lower pH and therefore fails to act as a stabilizing agent for DNA in our in vitro experiments.

Assessment of a new method for the analysis of decomposition gases of polymers by a combining thermogravimetric solid-phase extraction and thermal desorption gas chromatography mass spectrometry.

For analysis of the gaseous thermal decomposition products of polymers, the common techniques are thermogravimetry, combined with Fourier transformed infrared spectroscopy (TGA-FTIR) and mass spectrometry (TGA-MS). These methods offer a simple approach to the decomposition mechanism, especially for small decomposition molecules. Complex spectra of gaseous mixtures are very often hard to identify because of overlapping signals. In this paper a new method is described to adsorb the decomposition products during controlled conditions in TGA on solid-phase extraction (SPE) material: twisters. Subsequently the twisters were analysed with thermal desorption gas chromatography mass spectrometry (TDS-GC-MS), which allows the decomposition products to be separated and identified using an MS library. The thermoplastics polyamide 66 (PA 66) and polybutylene terephthalate (PBT) were used as example polymers. The influence of the sample mass and of the purge gas flow during the decomposition process was investigated in TGA. The advantages and limitations of the method were presented in comparison to the common analysis techniques, TGA-FTIR and TGA-MS.

Phase and amplitude patterns in DySEM mappings of vibrating microstructures.

We use a dynamic scanning electron microscope (DySEM) to analyze the movement of oscillating micromechanical structures. A dynamic secondary electron (SE) signal is recorded and correlated to the oscillatory excitation of scanning force microscope (SFM) cantilever by means of lock-in amplifiers. We show, how the relative phase of the oscillations modulate the resulting real part and phase pictures of the DySEM mapping. This can be used to obtain information about the underlying oscillatory dynamics. We apply the theory to the case of a cantilever in oscillation, driven at different flexural and torsional resonance modes. This is an extension of a recent work (Schröter et al 2012 Nanotechnology 23 435501), where we reported on a general methodology to distinguish nonlinear features caused by the imaging process from those caused by cantilever motion.

Analytical and numerical analysis of imaging mechanism of dynamic scanning electron microscopy.

The direct observation of small oscillating structures with the help of a scanning electron beam is a new approach to study the vibrational dynamics of cantilevers and microelectromechanical systems. In the scanning electron microscope, the conventional signal of secondary electrons (SE, dc part) is separated from the signal response of the SE detector, which is correlated to the respective excitation frequency for vibration by means of a lock-in amplifier. The dynamic response is separated either into images of amplitude and phase shift or into real and imaginary parts. Spatial resolution is limited to the diameter of the electron beam. The sensitivity limit to vibrational motion is estimated to be sub-nanometer for high integration times. Due to complex imaging mechanisms, a theoretical model was developed for the interpretation of the obtained measurements, relating cantilever shapes to interaction processes consisting of incident electron beam, electron-lever interaction, emitted electrons and detector response. Conclusions drawn from this new model are compared with numerical results based on the Euler-Bernoulli equation.

[Memorandum registry for health services research]. / Memorandum Register für die Versorgungsforschung.

On August 30, 2010, the German Network for Health Services Research [Deutsches Netzwerk Versorgungsforschung e. V. (DNVF e. V.)] approved the Memorandum III "Methods for Health Services Research", supported by their member societies mentioned as authors and published in this Journal [Gesundheitswesen 2010; 72: 739-748]. Registries in Health Services Research vary in their aims and research questions as well as in their designs, methods of data collection, and statistical analyses. This paper aims to provide both a methodological guideline for developers to ensure a high quality of a planned registry and, to provide an instrument for users of data from registries to assess their overall quality. First, the paper provides a definition of registries and presents an overview of objectives in Health Services Research where registries can be useful. Second, several areas of methodological importance for the development of registries are presented. This includes the different phases of a registry (i. e., conceptual and preliminary design, implementation), technical organisation of a registry, statistical analysis, reporting of results, data protection, and ethical/legal aspects. From these areas, several criteria are deduced to allow the assessment of the quality of a registry. Finally, a checklist to assess a registry's quality is presented.

Immobilization of silanized DNA on glass: influence of the silane tether on the DNA hybridization.

Two trifunctional (trimethoxy and triethoxy) and one difunctional (methyldimethoxy) 3-mercaptopropyl-alkoxysilanes were covalently tethered to thiolated DNA oligonucleotides in solution. After deposition as microarrays onto glass, the immobilized DNA probes were tested for hybridization ability by a florescence-based method. The results demonstrate a large enhancement in the fluorescence signal when the functionality of the silane tether is reduced from three to two. An XPS analyses revealed that this is not due to a higher DNA surface density. FTIR spectra of the spin-coated silanes showed that the trifunctional silanes form branched and cyclic siloxane moieties, whereas the difunctional silane generates predominantly short straight siloxane chains. Therefore, the propensity of trifunctional silanes to form more complex networks leads to conformations of the bound DNA which are less favorable for the specific interaction with the complementary strand. The data implicate that further significant improvements in the DNA hybridization ability are possible by adroit choice of the silane system.

DNA damage by low-energy electron impact: dependence on guanine content.

Single-stranded DNA oligonucleotides (33-mers) containing different numbers of guanines (n=1-4) were tethered to a gold surface and exposed to 1 eV electrons. The electrons induced DNA damage, which was analyzed with fluorescence and infrared spectroscopy methods. The damage was identified as strand breaks and found to correlate linearly with the number of guanines in the sequence. This sequence dependence indicates that the electron capture by the DNA bases plays an important role in the damage reaction mechanism.

Influence of film-substrate adhesion on the mechanical properties of thin polymer films.

The mechanical properties of mechanical double layers (thin amorphous films of poly(n-butyl methacrylate) on considerably stiffer silicon substrates) were investigated by force-displacement curves acquired with an atomic force microscope. The substrate surface was modified to provide a hydrophilic and a hydrophobic moiety. Such a modification affects the adhesion between film and substrate, since the polymer film adheres strongly on the hydrophilic side and weakly on the hydrophobic one. In this way, we were able to investigate the influence of the adhesion between the polymer film and substrate on the mechanical properties of the mechanical double layer. We were able to show that force-displacement curves on the two moieties of the sample have a different shape, and we propose an interpretation of the mechanisms determining the force-deformation curves on films with small adhesion to the substrate. This experiment can also provide an approach to the question of how the mechanical properties of a bulk material change with the volume to surface ratio, since a film with vanishing adhesion to the substrate is the only experimental accessible setup approximating a free-standing thin film.

Pharmaceutical policies: effects of cap and co-payment on rational drug use.

BACKGROUND: Growing expenditures on prescription drugs represent a major challenge to many health systems. Cap and co-payment (direct cost-share) policies are intended as an incentive to deter unnecessary or marginal utilisation, and to reduce third-party payer expenditures by shifting parts of the financial burden from the insurer to patients, thus increasing their financial responsibility for prescription drugs. Direct patient drug payment policies include caps (maximum number of prescriptions or drugs that are reimbursed), fixed co-payments (patients pay a fixed amount per prescription or drug), coinsurance (patients pay a percent of the price), ceilings (patients pay the full price or part of the cost up to a ceiling, after which drugs are free or available at reduced cost), and tier co-payments (differential co-payments usually assigned to generic and brand drugs). OBJECTIVES: To determine the effects of cap and co-payment (cost-sharing) policies on drug use, healthcare utilisation, health outcomes and costs (expenditures). SEARCH STRATEGY: We searched the following databases and web sites: Effective Practice and Organisation of Care Group Register (date of last search: 6 September 07), Cochrane Central Register of Controlled Trials (27 August 07), MEDLINE (29 August 07), EMBASE (29 August 07), NHS EED (27 August 07), ISI Web of Science (09 January 07), CSA Worldwide Political Science Abstracts (21 October 03), EconLit (23 October 03), SIGLE (12 November 03), INRUD (21 November 03), PAIS International (23 March 04), International Political Science Abstracts (09 January 04), PubMed (25 February 04), NTIS (03 March 04), IPA (22 April 04), OECD Publications & Documents (30 August 05), SourceOECD (30 August 05), World Bank Documents & Reports (30 August 05), World Bank e-Library (04 May 05), JOLIS (22 February 06), Global Jolis (22 February 06), WHOLIS(22 February 06), WHO web site browsed (25 August 05). SELECTION CRITERIA: We defined policies in this review as laws, rules, or financial or administrative orders made by governments, non-government organisations or private insurers. We included randomised controlled trials, non-randomised controlled trials, interrupted time series analyses, repeated measures studies and controlled before-after studies of cap or co-payment policies for a large jurisdiction or system of care. To be included, a study had to include an objective measure of at least one of the following outcomes: drug use, healthcare utilisation, health outcomes or costs (expenditures). DATA COLLECTION AND ANALYSIS: Two authors independently extracted data and assessed study limitations. We undertook quantitative analysis of time series data for studies with sufficient data. MAIN RESULTS: We included 30 evaluations (in 21 studies). Of these, 11 evaluated fixed co-payment, six evaluated coinsurance with a ceiling, four evaluated caps, three evaluated fixed co-payment with a ceiling, three evaluated tier co-payment, one evaluated ceiling, one evaluated fixed co-payment and coinsurance with a ceiling, and one evaluated a fixed co-payment with a cap. Most of the included evaluations were observational studies and the quality of the evidence was found to be generally low to moderate. Introducing or increasing direct co-payments reduced drug use and saved plan drug expenditures across studies. Patients responded through drug discontinuation or by cost-sharing. Investigators found reductions for life-sustaining drugs or drugs that are important in treating chronic conditions as well as other drugs. Few studies reported on the effects on health and healthcare utilisation. One study found adverse effects on health through increased healthcare utilisation when a cap was introduced in a vulnerable population. No statistically significant change in use of healthcare services was found in other studies when a cap was introduced on a drug considered over-prescribed in a vulnerable population, or following a shift from a two-tier to a three-tier system with increased co-payments for tier-1 drugs in a general population. AUTHORS' CONCLUSIONS: We found a diversity of cap and co-payment policies. Poor reporting of the intensity of interventions and differences in setting, populations and interventions made it difficult to make comparisons across studies. Cap and co-payment polices can reduce drug use and save plan drug expenditures. However, although insufficient data on health outcomes were available, substantial reductions in the use of life-sustaining drugs or drugs that are important in treating chronic conditions may have adverse effects on health, and as a result increase the use of healthcare services and overall expenditures. Direct payments are less likely to cause harm if only non-essential drugs are included or exemptions are built in to ensure that patients receive needed medical care.

Bringing electrons and microarray technology together.

Low-energy secondary electrons are the most abundant radiolysis species which are thought to be able to attach to and damage DNA via formation and decay of localized molecular resonances involving DNA components. In this study, we analyze the consequences of low-energy electron impact on the ability of DNA to hybridize (i.e., to form the duplex). Specifically, single-stranded thymine DNA oligomers tethered to a gold surface are irradiated with very low-energy electrons (E = 3 eV, which is below the 7.5 eV ionization threshold of DNA) and subsequently exposed to a dye-marked complementary strand to quantify by a fluorescence method the electron induced damage. The damage to (dT)25 oligomers is detected at quite low electron doses with only about 300 electrons per oligomer being sufficient to completely preclude its hybridization. In the microarray format, the method can be used for a rapid screening of the sequence dependence of the DNA-electron interaction. We also show for the first time that the DNA reactions at surfaces can be imaged by secondary electron (SE) emission with both high analytical and spatial sensitivity. The SE micrographs indicate that strand breaks induced by the electrons play a significant role in the reaction mechanism.

Pharmaceutical policies: effects of financial incentives for prescribers.

BACKGROUND: Pharmaceuticals, while central to medical therapy, pose a significant burden to health care budgets. Therefore regulations to control prescribing costs and improve quality of care are implemented increasingly. These include the use of financial incentives for prescribers, namely increased financial accountability using budgets and performance based payments. OBJECTIVES: To determine the effects on drug use, healthcare utilisation, health outcomes and costs (expenditures) of policies, that intend to affect prescribers by means of financial incentives. SEARCH STRATEGY: We searched the following databases and web sites: Effective Practice and Organisation of Care Group Register (August 2003), Cochrane Central Register of Controlled Trials (October 2003), MEDLINE (October 2005), EMBASE (October 2005), and other databases. SELECTION CRITERIA: Policies were defined as laws, rules, financial and administrative orders made by governments, non-government organisations or private insurers. One of the following outcomes had to be reported: drug use, healthcare utilisation, health outcomes, and costs. The study had to be a randomised or non-randomised controlled trial, interrupted time series analysis, repeated measures study or controlled before-after study evaluating financial incentives for prescribers introduced for a jurisdiction or healthcare system. DATA COLLECTION AND ANALYSIS: Two review authors independently extracted data and assessed study limitations. MAIN RESULTS: Thirteen evaluations of budgetary policies and none of performance based payments met our inclusion criteria. Ten studies evaluated general practice fundholding in the UK, one the Irish Indicative Drug Target Savings Scheme (IDTSS) and two evaluated German drug budgets for physicians in private practice. The interrupted time series analyses had some limitations. All the controlled before-after studies (all from the UK) had serious limitations. Drug expenditure (per item and per patient) and prescribed drug volume decreased with budgets in all three countries. Evidence indicated increased use of generic drugs in the UK and Ireland, but was inconclusive on the use of new and expensive drugs. We found no clear evidence of increased health care utilisation and no studies reporting effects on health. Administration costs were not reported. No studies on the effects of performance-based payments or other policies met our inclusion criteria. AUTHORS' CONCLUSIONS: Based on the evidence in this review from three Western European countries, drug budgets for physicians in private practice can limit drug expenditure by limiting the volume of prescribed drugs, increasing the use of generic drugs or both. Since the majority of studies included were found to have serious limitations, these results should be interpreted with care.

Prescribing for chronic heart failure in Europe: does the country make the difference? A European survey.

PURPOSE: International differences in prescribing patterns for chronic heart failure (CHF) have been demonstrated repeatedly. It is not clear whether these differences arise entirely from patient characteristics or factors related to the country itself, such as health care systems or culture. We aim to assess the role of countries in this international variation, aside from the role of patient characteristics. METHODS: In this European primary care practice survey (from 1999/2000) 11062 CHF patients from 14 countries were included. The influence of country (corrected for patient characteristics) on prescribed drug regimes was assessed by multinomial logistical regression. RESULTS: Prescribing of guideline-recommended drug regimes ranged from 28.1% in Turkey to 61.8% in Hungary. Including additional regimes justifiable by patients' co-morbidities, increased overall 'rational' prescribing by 11%, but differences among countries remained similar. Multivariate analysis for one-drug and two-drug regimes explained between 35% and 42% of the total variance, country contributed 7%-8% (p < 0.005). Countries determined the number of drugs used and the likelihood of individual drug regimes. For example, in Czech Republic digoxin alone was more likely to be given than the recommended ACE-inhibitors (OR: 3.45; 95%CI: 2.56-4.64), while the combination of digoxin with ACE-inhibitors was as likely as the recommended combination of ACE-inhibitors and beta-blockers (OR: 1.17; 95%CI: 0.88-1.55). CONCLUSION: Country of residence clearly influenced prescribed drug volume and choice of drug regimes. Therefore, optimal CHF management cannot be achieved without considering country specific factors. It remains to be established which factors within health-care systems are responsible for these effects.

Pharmaceutical policies: effects of reference pricing, other pricing, and purchasing policies.

BACKGROUND: Pharmaceuticals can be important for people's health. At the same time drugs are major components of health care costs. Pharmaceutical pricing and purchasing policies are used to determine or affect the prices that are paid for drugs. Examples are price controls, maximum prices, price negotiations, reference pricing, index pricing and volume-based pricing policies. The essence of reference pricing is to establish a maximum level of reimbursement for a group of drugs assumed to be therapeutically equivalent. OBJECTIVES: To determine the effects of pharmaceutical pricing and purchasing policies on drug use, healthcare utilisation, health outcomes and costs (expenditures). SEARCH STRATEGY: We searched the following databases and web sites: Effective Practice and Organisation of Care Group Register (date of last search: 22/08/03), Cochrane Central Register of Controlled Trials (15/10/03), MEDLINE (07/09/05), EMBASE (07/09/05), ISI Web of Science (08/09/05), CSA Worldwide Political Science Abstracts (21/10/03), EconLit (23/10/03), SIGLE (12/11/03), INRUD (21/11/03), PAIS International (23/03/04), International Political Science Abstracts (09/01/04), NHS EED (20/02/04), PubMed (25/02/04), NTIS (03/03/04), IPA (22/04/04), OECD Publications & Documents (30/08/05), SourceOECD (30/08/05), World Bank Documents & Reports (30/08/05), World Bank e-Library (04/05/05), JOLIS (22/08/05), Global Jolis (22/08/05 and 23/08/05), WHOLIS (29/08/05). SELECTION CRITERIA: Policies in this review were defined as laws, rules, financial and administrative orders made by governments, non-government organisations or private insurers. To be included a study had to include an objective measure of at least one of the following outcomes: drug use, healthcare utilisation, health outcomes, and costs (expenditures); the study must be a randomised controlled trial, non-randomised controlled trial, interrupted time series analysis, repeated measures study or controlled before-after study of a pharmaceutical pricing or purchasing policy for a large jurisdiction or system of care. DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and assessed study limitations. Quantitative analysis of time series data, for studies with sufficient data, and qualitative analyses were undertaken. MAIN RESULTS: We included 10 studies of reference pricing and one study of index pricing. Most of the reference pricing studies were for senior citizens in British Columbia, Canada. The use (dispensing) of reference drugs increased in five studies, between 60% and 196% immediately after introduction of reference drug pricing, whereas the use of cost sharing drugs decreased by between 19% and 42% in four studies. In three studies the reference drug group expenditures decreased (range 19% - 50%), whereas in the fourth study the expenditures increased by 5% in the short term. The results after six months of reference pricing do not show any clear pattern in relationship to the immediate effects. We found no evidence of adverse effects on health and no clear evidence of increased health care utilisation. For index pricing the evidence was much more limited than for reference drug pricing. A small reduction in drug prices was found. AUTHORS' CONCLUSIONS: We found relatively few studies of pricing policies. The majority of the studies dealt with reference pricing. They had few methodological limitations. Based on the evidence in this review, mostly from senior citizens in British Columbia, Canada, reference drug pricing can reduce third party drug expenditures by inducing a shift in drug use towards less expensive drugs. We found no evidence of adverse effects on health and no clear evidence of increased health care utilisation. The analysis and reporting of the effects on patient drug expenditures were limited in the included studies and administration costs were not reported.

Selective enhancement of motoneurone short-term synchrony during an attention-demanding task.

Recent experiments on monkeys suggest that attention-related changes in the synchronous activity of neurones occur in the motor cortex. In humans, the clinical data available suggest that the weak synchronization of the motor unit firing observed during voluntary contraction might reflect the activity of the motoneurone cortico-spinal afferents. The present study was therefore designed to investigate how the synchronous motor-unit activity might depend on the attention required in performing a motor task. Twenty-five motor unit pairs were tested in the right extensor carpi radialis muscles of five right-handed subjects, who were instructed to keep both motor units firing tonically while trying to maintain the extension force as constant as possible using visual feedback set either at low or high gain. Fifteen motor unit pairs (60%) showed a greater amount of synchronous activity, without any consistent changes in the motor unit firing rates, when the subjects were monitoring the force at high gain. In addition, the mean value and the steadiness of the force did not differ significantly between the two tasks. The amplitude of the motor units' contractile force extracted by spike-triggered averaging did not change consistently despite the slight increase in the synchronous impulse probability observed under the high-gain conditions. Changes in synchrony affected slowly contracting, low-threshold motor units as well as fast-contracting, high-threshold motor units. The most noteworthy finding was that these changes actually focused on a narrow component of the synchronous activity (within a period of less than 4 ms) in keeping with the short-term synchronization process. This suggests that common inputs, possibly of cortical origin, may have contributed more greatly to controlling the motoneurone firing pattern in the motor task which required the subjects to pay more attention.

Dual task-related changes in the synchronous activity of wrist extensor type-identified motor units in humans.

The coupling between the firings of 33 pairs of motor units tested in the extensor carpi radialis muscles was evaluated by cross-correlation analysis and compared during isometric wrist extension and hand clenching. A slightly greater amount of synchrony was observed during hand clenching (0.042 +/- 0.024 vs 0.035 +/- 0.017 synchronous impulses per trigger). This trend did not reach however the level of significance and the changes were actually found to be heterogeneous: in 15 out of the 33 pairs tested, synchronous activity with a narrow coupling (4.6 +/- 2.4 ms) consistent with short-term synchrony was greater during hand clenching whereas in nine other pairs, synchronous activity with a broader dispersion (9.0 +/- 4.5 ms) was reduced. These opposite changes could not be explained in terms of changes in the firing pattern of the motor units and were found instead to correlate with the motor units' biomechanical properties. Motor units with high recruitment thresholds and fast rising twitches showed predominantly an increase in synchrony; whereas the motor unit pairs with low recruitment thresholds and slow twitches showed either an increase or a decrease. The enhanced short-term synchrony suggests that common inputs distributed to motoneurones of all types were more effective during hand clenching whereas the decrease in weakly coupled synchronous activity suggests that other inputs synchronized at a pre-synaptic level and distributed more specifically to motor units recruited at low force levels were less effective. The possible origins of the inputs reflected in the dual changes are discussed in terms of the supra-spinal and peripheral pathways controlling the wrist extensor motoneurones during wrist extension and hand clenching.

Firing pattern of type-identified wrist extensor motor units during wrist extension and hand clenching in humans.

1. Single motor unit activity was investigated in the extensor carpi radialis muscles during voluntary isometric contraction involving either the coactivation of the wrist agonist extensor muscles (wrist extension) or the coactivation of the wrist and finger antagonist extensor and flexor muscles (hand clenching). 2. The motor units were found to be activated at a similar level of motoneurone pool drive during both wrist extension and hand clenching, as indicated by the fact that the EMG activity at which they were recruited was practically the same in both cases (mean +/- S.D.: 20 +/- 26 and 21 +/- 25 mV, respectively). In addition, the net excitatory drive exerted on the motoneurones, as assessed from the mean interspike intervals, did not differ significantly between the two tasks (mean +/- S.D.: 104.57 +/- 17.24 and 103.01 +/- 16.26 ms, for wrist extension and hand clenching, respectively). 3. However, the discharge variability, in terms of the coefficient of variation of the interspike intervals, was slightly but significantly greater during hand clenching than during wrist extension (0.213 +/- 0.049 and 0.198 +/- 0.045, respectively). This increase involved all types of motor units, regardless of their contractile force. 4. We suggest that the greater motoneurone discharge variability observed during hand clenching may be attributable to an increase in the synaptic noise. This increase might be due to the activation of numerous afferent pathways mediating reciprocal interactions between antagonist motoneurone pools, as well as to the activation of hand cutaneous receptors that play a major role in the regulation of handling and gripping motor activities.