http://repub.eur.nl/res/aut/16116/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/28415/ 2010-10-01T00:00:00Z Objective: The statistical method of motor unit number estimation (MUNE) assumes that all motor unit potentials (MUPs) have the same size. The present study aims to evaluate the consequences of this assumption as well as its implications for the validity of statistical MUNEs. Methods: We performed statistical and multiple point stimulation (MPS) MUNE with an array of 120 electrodes on the thenar muscles of 15 healthy subjects. These recordings allow isolation and quantification of the effect of non-uniform MUP size on MUNE, because the differences in submaximal CMAP size (and, hence, in MUNE) between electrodes are due almost entirely to differences in (summed) MUP size. Results: We found no correlation between statistical and MPS MUNEs. Statistical MUNEs proved very sensitive to small variations in the "bandwidth" (variance) of the response series; MUNEs from electrodes only 8 mm apart could deviate by as much as 60%. This variation in bandwidth resulted from spatial (and, hence, size) differences between the contributing MUPs. Conclusions: Statistical MUNEs are very sensitive to violation of the uniform MUP-size assumption, to an extent that blurs any correlation with MPS MUNE in healthy subjects. Significance: Statistical MUNE cannot be used to detect mild to moderate motor unit losses. http://repub.eur.nl/res/pub/14111/ 2008-12-01T00:00:00Z Following (tracking) individual motor units over time can provide important new insights, both into the relationships among various motor unit (MU) morphological and functional properties and into how these properties are influenced by neuromuscular disorders or interventions. The present study aimed to determine whether high-density surface EMG (HD-sEMG) recordings, which use an array of surface electrodes over a muscle, can increase the yield of MU tracking studies in terms of the number of MUs that can be tracked. For that purpose, four HD-sEMG recording sessions were performed on the thenar muscles of ten healthy subjects. Decomposition of the recorded composite responses yielded a study total of 2849 motor unit action potentials (MUAPs). MUAPs that were found in both of the first two sessions, performed on the same day, were defined as trackable MUAPs. Our results show that 22 (median value; range, 13-34) MUAPs per nerve were trackable, which represented approximately 5% of the total MU population. Of these trackable MUAPs, 16 (11-26) could also be found in one or both of the third and fourth sessions, which were performed between 1 and 13 weeks after the initial studies. Nine (4-18) MUAPs were found in all four sessions. Many of the characteristic MUAP shapes matched well between sessions, even when these sessions were several weeks apart. However, some MUAPs seem very sensitive to changes in arm position or in the muscle's morphology (e.g., to changes in muscle fiber length due to variable degrees of thumb flexion or extension), particularly those from larger and/or superficial MUs. Standardization is, therefore, essential to detect even small MUAP changes, as may occur with pathology or interventions. If this is accomplished, MU tracking with HD-sEMG may prove to be a powerful tool for a promising type of neurophysiological investigation. http://repub.eur.nl/res/pub/30240/ 2008-10-01T00:00:00Z http://repub.eur.nl/res/pub/30279/ 2008-01-01T00:00:00Z Objective: To present a motor unit number estimation (MUNE) technique that resolves alternation by means of high-density surface EMG. Methods: High-density surface EMG, using 120 EMG channels simultaneously, is combined with elements of the increment counting technique (ICT) and the multiple-point stimulation technique. Alternation is a major drawback in the ICT. The spatial and temporal information provided by high-density surface EMG support identification and elimination of the effects of alternation. We determined the MUNE and its reproducibility in 14 healthy subjects, using a grid of 8 × 15 small electrodes on the thenar muscles. Results: Mean MUNE was 271 ± 103 (retest: 290 ± 109), with a coefficient of variation of 22% and an intra-class correlation of 0.88. On average, 22 motor unit potentials (MUPs) were collected per subject. The representativity of this MUP sample was quantitatively assessed using the spatiotemporal information provided by high-density recordings. Conclusions: MUNE values are relatively high, because we were able to detect many small MUPs. Reproducibility was similar to that of other MUNE techniques. Significance: Our technique allows collection of a large MUP sample non-invasively by resolving alternation to a large extent and provides insight into the representativity of this sample. The large sample size is expected to increase MUNE accuracy. http://repub.eur.nl/res/pub/26285/ 1973-12-12T00:00:00Z Reeds in 1937 stelden McCance en Widdowson (1937) dat de zeer beperkte ijzerafgifte een karakteristiek aspect van de ijzerhuishouding van de mens is. Het sindsdien verrichte onderzoek heeft dit vele malen bevestigd. Het inzicht dat het vermogen om ijzer uit te scheiden in kwantitatieve zin zeer beperkt is, heeft ertoe geleid dat de studie van de regulatiemechanismen zich voornamelijk heeft gericht op het ijzeropnamesysteem. Verschillende regulatiemechanismen voor de ijzerabsorptie zijn geponeerd. Het bekendste mechanisme is de regulatie door middel van het in de darmmucosacellen aanwezige (apo)ferritine (mucosa blok-theorie, Granick, 1946). De ijzerhuishouding bij de mens is bijzonder storingsgevoelig. Enerzijds blijkt dit uit het veelvuldig voorkomen van ijzergebreksanemieën, anderzijds uit het regionaal voorkomen van hemochromatosen. Op grond van de gemeten ijzerverliezen van de normale man en van de normale nietzwangere vrouw, wordt de dagelijkse ijzerbehoefte van de normale man gesteld op 1 mg en die van de normale vrouw op 1, 5 mg, dus op 18 en 27 u-mol respectievelijk. Uit de verschillende studies die zijn gepubliceerd over het dagelijks voedsel-ijzer aanbod (Hall berg et al., 1970), kan worden geconcludeerd dat - althans in de westeuropese landen - in principe ruimschaats aan de gestelde eisen wordt voldaan. Gemiddeld wordt evenwel slechts 5% van het met het voedsel aangeboden ijzer door het lichaam geabsorbeerd. Op grond van deze geringe absorptie, kan worden gesteld, dat in vele gevallen de voeding - wat het ijzer betreft - marginaal tot submarginaal is.