Biomedical subjects

A de Haan

Publications and source records attributed to A de Haan.

At least 37 records · Page 2Linked to original sources

PubMed2004

The value of prospective monitoring of Epstein-Barr virus DNA in blood samples of pediatric liver transplant recipients.

UNLABELLED: Post-transplant lymphoproliferative disease (PTLD) is one of the major causes of morbidity and mortality in transplantation patients. A primary Epstein-Barr virus (EBV) infection is a major risk factor for developing PTLD. The aim of this study was to determine circulating EBV DNA after liver transplantation in pediatric patients in relation to primary EBV infection and development of PTLD. EBV serology was performed before transplantation. Every 4 weeks after transplantation a competitive quantitative polymerase chain reaction (PCR) assay for EBV nuclear antigen-1 was performed in 13 patients. Patients were followed for development of a PTLD. Before transplantation four patients were EBV seropositive and nine patients were EBV seronegative. In one of the four patients who were EBV seropositive before transplantation, EBV DNA became detectable after transplantation, with a peak load of 3600 copies/mL. None of these four patients developed a PTLD. Eight of the nine patients who were EBV seronegative before transplantation developed positive EBV DNA samples. EBV DNA was first detected at a mean of 64 days after transplantation (range 38-89). The mean peak EBV DNA load was 79,700 copies/mL (3600-446,000). Two of these patients developed PTLD, but they could not be identified based on prior or concomitant EBV PCR results. CONCLUSIONS: In pediatric liver transplantation EBV DNA load is higher in patients with a primary infection than in patients who were EBV seropositive before transplantation. The EBV PCR cannot be used to identify individual patients who develop PTLD. However, elevated EBV DNA load can be used to detect a group of patients at increased risk for PTLD.

Adolescent↗

PubMed2003

Voluntary drive-dependent changes in vastus lateralis motor unit firing rates during a sustained isometric contraction at 50% of maximum knee extension force.

The purpose of the present study was to relate the expected inter-subject variability in voluntary drive of the knee extensor muscles during a sustained isometric contraction to the changes in firing rates of single motor units. Voluntary activation, as established with superimposed electrical stimulation was high (range: 91-99%, n=8) during a short maximal contraction, but was lower (range: 69-100%) in most subjects at the point of force failure during a sustained (49.1+/-10.1 s) fatiguing contraction at 50% of maximum force. On a different experimental day the firing behaviour of 27 single motor units was recorded with wire electrodes in the vastus lateralis muscle, 24 of which could be monitored from the time of recruitment to the point of force failure (53.6+/-9.8 s). Motor unit firing behaviour differed considerably among subjects. During the second half of the sustained, fatiguing contraction the changes in firing rate firing rate variability of early recruited units ranged from -10% to +100% and from -50% to +160% respectively among subjects. There were significant positive linear relations between voluntary activation, on the one hand, and rectified surface electromyogram (rsEMG, r=0.82), the changes in motor unit firing rate ( r=0.49) and firing rate variability ( r=0.50) towards the point of force failure on the other. The present data suggest that differences in voluntary drive that appear among subjects during fatigue may be an important determinant of motor unit firing behaviour.

Action Potentials↗

PubMed2003

Low-frequency fatigue is fibre type related and most pronounced after eccentric activity in rat medial gastrocnemius muscle.

Effects of fibre type composition and type of contraction on low-frequency fatigue (LFF) were investigated in isolated rat medial gastrocnemius (GM) muscle. Fast oxidative or fast glycolytic GM muscle parts of anaesthetised male Wistar rats (n=18) were activated selectively by maximal electrical stimulation of the nerve after selective cutting of sub-branches. LFF was induced by a series of 40 isometric, concentric or eccentric contractions. Post exercise (55 min), the force-frequency curves differed significantly from the pre-exercise curves. Decreased forces were exerted mainly at the lower frequencies. This effect was significantly greater for glycolytic than oxidative muscle parts and following eccentric compared to isometric and concentric exercise. Seventy minutes following eccentric exercise, the relative values of the 60:200 Hz force ratios for the oxidative compared to the glycolytic parts were 65.6+/-2.2% and 43.6+/-4.6% (mean+/-SE) of the pre-fatigue values (=100%), respectively. In conclusion, for conditions of identical activation, eccentric exercise led to significantly more LFF than isometric and concentric exercise. In addition, and independent of the exercise type, fast glycolytic muscle parts were more susceptible to LFF than fast oxidative muscle parts.

Animals↗

PubMed2003

The effects of 11 weeks whole body vibration training on jump height, contractile properties and activation of human knee extensors.

The purpose of the present study was to investigate whether 11 weeks of whole body vibration (WBV) training applied in a way that is commonly seen in practice, i.e. without additional loads, would improve muscle activation and/or contractile properties of the knee extensor muscles and counter movement jump height in healthy subjects. Ten subjects belonging to the experimental group trained three times a week and stood bare-foot with a 110 degrees knee angle on a vibration platform (30 Hz, 8 mm amplitude). They underwent five to eight sets of 1-min vibration with 1 min rest in between. Ten control subjects followed the same training programme but stood (110 degrees knee angle) beside the platform. Before, during and following the training period the subjects were tested. Values [mean (SEM)] obtained in the last test were expressed as percentages of the baseline value and presented for control and experimental groups. Quadriceps femoris isometric muscle force [105.4 (6.2)%, 99.9 (2.0)%; P=0.69], voluntary activation [107.1 (6.0)%, 101.1 (2.3)%; P=0.55] and maximal rate of voluntary force rise [95.4 (6.0)%, 103.3 (7.7)%; P=0.57] did not improve. The maximal rate of force rise during electrical stimulation was increased [102.3 (4.5)%, 123.6 (7.5)%; P=0.02]. Counter movement jump height was not affected by WBV [103.7 (1.8)%, 103.0 (2.8)%; P=0.71]. In conclusion, 11 weeks of standard two-legged WBV training without additional training loads did not improve functional knee extensor muscle strength in healthy young subjects.

Adult↗

PubMed2003

Effect of antagonist muscle fatigue on knee extension torque.

The effect of hamstring fatigue on knee extension torque was examined at different knee angles for seven male subjects. Before and after a dynamic flexion fatigue protocol (180 degrees s(-1), until dynamic torque had declined by 50%), maximal voluntary contraction extension torque was measured at four knee flexion angles (90 degrees, 70 degrees, 50 degrees and 30 degrees ). Maximal torque generating capacity and voluntary activation of the quadriceps muscle were determined using electrical stimulation. Average rectified EMG of the biceps femoris was determined. Mean dynamic flexion torque declined by 48+/-11%. Extensor maximal voluntary contraction torque, maximal torque generating capacity, voluntary activation and average rectified EMG at the four knee angles were unaffected by the hamstring fatigue protocol. Only at 50 degrees knee angle was voluntary activation significantly lower (15.7%) after fatigue ( P<0.05). In addition, average rectified EMG before fatigue was not significantly influenced by knee angle. It was concluded that a fatigued hamstring muscle did not increase the maximal voluntary contraction extension torque and knee angle did not change coactivation. Three possible mechanisms may explain the results: a potential difference in recruited fibre populations in antagonist activity compared with the fibres which were fatigued in the protocol, a smaller loss in isometric torque generating capacity of the hamstring muscle than was expected from the dynamic measurements and/or a reduction in voluntary activation.

Adult↗

PubMed2003

Association between macrophage activation and function of micro-encapsulated rat islets.

AIMS/HYPOTHESIS: Survival of microencapsulated islet grafts is limited, even when inflammatory reactions against the capsules are restricted to a small portion of less than 10%. METHODS: This study investigates both in vivo in rat recipients and in vitro whether cellular overgrowth on this minority of the capsules contributes to limitations in the functional survival of the 90% of the encapsulated islets which remain free of any cellular overgrowth. RESULTS: In successful rat recipients of an allogenic microencapsulated islet graft we found that the vast majority of cells in the capsular overgrowth were activated ED-1 and ED-2 positive macrophages which were found in numbers of approximately 1500 per capsule. Co-culture of encapsulated islets with 1500 (nr8383) rat-macrophages per capsule showed that the activation of macrophages was caused by islet-derived bioactive factors since TNF-alpha and IL-1beta secretion by macrophages was induced by islet-containing capsules and not by empty capsules. This activation of macrophages was associated with a decrease in function of the encapsulated islets as evidenced by a quantitatively reduced (35%) insulin response in static incubation and a slower response in perifusion. CONCLUSION/INTERPRETATION: Present research aims to design strategies for the temporary inhibition of macrophage activation since macrophages are predominantly present in the first two months after implantation. These strategies will serve as a pertinent basis for future clinical application of microencapsulated islets.

Animals↗

PubMed2003

Force/velocity curves of fast oxidative and fast glycolytic parts of rat medial gastrocnemius muscle vary for concentric but not eccentric activity.

The purpose of this study was to compare the force exerted by the rat medial gastrocnemius (GM) muscle with either fast oxidative or fast glycolytic parts active during concentric and eccentric contractions at different velocities. The proximal end of the GM contains mainly fast oxidative fibres and the distal end predominantly fast glycolytic fibres. Different parts of GM were activated by selective stimulation of nerve branches. Fast oxidative or fast glycolytic muscle parts of anaesthetised male Wistar rats were activated maximally. After assessment of concentric force/velocity (F/v) relations (n=11), some of the muscles were subjected to a fatiguing series of isometric contractions (n=5). Fast oxidative muscle parts showed a significantly lower mean (+/-SD) maximal power output (P(max) 0.12+/-0.06 W) and fatigability than fast glycolytic muscle parts (P(max) 0.20+/-0.06 W). The remaining muscles performed eccentric contractions. The eccentric F/v curves were not significantly different for fast oxidative and fast glycolytic muscle parts (n=6). Maximum eccentric force relative to the maximum isometric force (157+/-3% and 153+/-6% respectively,P=0.99) was reached at a velocity of 60 mm s(-1). It is concluded that eccentric F/v relations of rat GM with either fast oxidative or fast glycolytic parts active are very similar despite the differences in the concentric F/v relations.

Animals↗

PubMed2002

Short-term effects of whole-body vibration on maximal voluntary isometric knee extensor force and rate of force rise.

Whole-Body vibration (WBV) may lead to muscle contractions via reflex activation of the primary muscle spindle (Ia) fibres. WBV has been reported to increase muscle power in the short term by improved muscle activation. The present study set out to investigate the acute effects of a standard WBV training session on voluntary activation during maximal isometric force production (MVC) and maximal rate of force rise (MRFR) of the knee extensors. Twelve students underwent a single standard WBV training session: 5x1 min vibration (frequency 30 Hz, amplitude 8 mm) with 2 min rest in between. During vibration, subjects stood barefoot on the vibration platform with their knees at an angle of 110 degrees. At 90 s following vibration, maximal voluntary knee extensor force was reduced to 93 (5)% [mean (SD), P<0.05] of baseline value and recovered within the next 3 h. Voluntary activation remained significantly depressed (2-4%). Neither the electrically induced MRFR nor voluntary MRFR were significantly affected by WBV. In addition, six WBV training sessions in 2 weeks ( n=10) did not enhance either voluntary muscle activation during MVC [99 (2)% of the baseline value] or voluntary MRFR [98 (9)% of the baseline value]. It is concluded that in the short term, WBV training does not improve muscle activation during maximal isometric knee extensor force production and maximal rate of force rise in healthy untrained students.

Adult↗

PubMed2002

Shortening-induced depression of voluntary force in unfatigued and fatigued human adductor pollicis muscle.

The goals of this study were to investigate adductor pollicis muscle (n = 7) force depression after maximal electrically stimulated and voluntarily activated isovelocity (19 and 306 degrees /s) shortening contractions and the effects of fatigue. After shortening contractions, redeveloped isometric force was significantly (P < 0.05) depressed relative to isometric force obtained without preceding shortening. For voluntarily and electrically stimulated contractions, relative force deficits respectively were (means +/- SE) 25.0 +/- 3.5 and 26.6 +/- 1.9% (19 degrees /s), 7.8 +/- 2.2 and 11.5 +/- 0.6% (306 degrees /s), and 23.9 +/- 4.4 and 31.6 +/- 4.7% (19 degrees /s fatigued). The relative force deficit was significantly smaller after fast compared with slow shortening contractions, whereas activation manner and fatigue did not significantly affect the deficit. It was concluded that in unfatigued and fatigued muscle the velocity-dependent relative force deficit was similar with maximal voluntary activation and electrical stimulation. These findings have important implications for experimental studies of force-velocity relationships. Moreover, if not accounted for in muscle models, they will contribute to differences observed between the predicted and the actually measured performance during in vivo locomotion.

Adult↗

PubMed2002

Skeletal muscle of mice with a mutation in slow alpha-tropomyosin is weaker at lower lengths.

Skeletal muscle function was measured in anaesthetised transgenic mice having a mutation in the TPM3 gene (slow alpha-tropomyosin), a similar mutation as found in some patients with nemaline myopathy, and was compared with control muscles. Measurements of isometric and dynamic muscle performance were done with electrical nerve stimulation at physiological temperatures. No muscle weakness was found in the transgenic muscles when performance was measured at muscle optimum length. This was true not only with full activation but also at lower activation levels, indicating that calcium sensitivity was not affected at this length. Also, fatigability was not affected in these conditions. However, isometric force of the muscles with the mutation in TPM3 was lower at lengths below optimum, with more impairment at decreasing length. As the muscles are active over a large range of different muscle lengths during daily activities, this finding may explain, at least in part, the muscle weakness experienced by patients with nemaline myopathy.

Animals↗

PubMed2002

Calcium regulation and muscle disease.

Changes in intracellular Ca2+-concentration play an important role in the excitation-contraction-relaxation cycle of skeletal muscle. In this review we describe various inheritable muscle diseases to highlight the role of Ca2+-regulatory mechanisms. Upon excitation the ryanodine receptor releases Ca2+ in the cytosol. During and after contraction the sarcoplasmic reticulum (SR) Ca2+ATPase (SERCA) pumps Ca2+ back in the SR resulting in relaxation. An abnormal change in the intracellular Ca2+-concentration results in defective muscle contraction and/or relaxation, which is the cause of various muscle diseases. Malignant hyperthermia (MH) and central core disease (CCD) are both caused by mutations in the ryanodine receptor but show different clinical phenotypes. In MH an acute increase of Ca2+ results in excessive muscle contraction causing rigidity, while in CCD a chronic rise of cytosolic Ca2+ is seen, leading to mitochondrial damage, disorganization of myofibrils and muscle weakness. In Brody disease and also in mitochondrial myopathies, SERCA functions sub optimal causing a prolonged physiological Ca2+-elevation leading to slowing of relaxation. Defective actin-myosin interactions, as in nemaline myopathy and also in mitochondrial myopathies due to ATP-shortage, cause Ca2+-hyposensitivity and slowness of contraction. Information of Ca2+-kinetics in these inherited muscular diseases improves our understanding of the role of calcium in the physiology and pathophysiology of the skeletal muscle cell.

Animals↗

PubMed2002

Muscle function during repetitive moderate-intensity muscle contractions in myoadenylate deaminase-deficient Dutch subjects.

We investigated whether the capacity for repetitive submaximal muscle contraction was reduced in a group of subjects (n=8) with a primary deficiency of myoadenylate deaminase (MAD). Quadriceps femoris muscle fatigue was evaluated using voluntary and electrically stimulated contractions during 20 min of repetitive voluntary isometric contractions at 40% of maximal force-generating capacity (MFGC). After 5 min of exercise, MFGC had declined significantly to 70.6+/-4.1% (mean+/-S.E.M.) and 87.2+/-1.6% of baseline values in MAD-deficient and sedentary control subjects (n=8) respectively (P=0.002 between groups). After 5 min of exercise, the half-relaxation time had increased significantly to 113.4+/-6.1% of baseline in MAD-deficient muscle, but had decreased significantly to 94.1+/-1.3% in control subjects (P=0.003 between groups). All control subjects completed the 20-min exercise test. Five of the MAD-deficient subjects had to stop exercising due to early muscle fatigue; however, three of the MAD-deficient subjects were able to complete the 20-min exercise test. In conclusion, although the capacity for repetitive submaximal isometric muscle contractions for the group of MAD-deficient subjects was significantly decreased, it remains uncertain whether MAD deficiency is the sole cause of pronounced muscle fatigue.

AMP Deaminase↗

PubMed2001

Rapid decreases in donor-specific cytotoxic T lymphocyte precursor frequencies and graft outcome after liver and lung transplantation.

BACKGROUND: A decrease in donor-specific T cell precursor frequencies as seen late, one or more years, after transplantation is assumed to reflect transplantation tolerance, a condition important for long term acceptance of the allograft. However, such late decreases also occur in recipients that developed chronic transplant dysfunction questioning its relevance in transplantation tolerance. We investigated whether early, i.e., the first 6 months, decreases in donor-specific T cell precursor frequencies reflect transplantation tolerance and predict graft outcome after liver and lung transplantation. METHODS: Donor and third party specific cytotoxic (CTLp) and helper T lymphocyte precursor (HTLp) frequencies were analyzed in pretransplant and 1 (or 2) and 6-month blood samples taken from liver and lung recipients and were correlated with graft outcome. RESULTS: In liver allograft recipients with good graft function (n=7), mean donor-specific CTLp frequencies decreased as early as 1 month after transplantation and remained low thereafter. In contrast, mean CTLp frequencies did not decrease in liver allograft recipients with chronic transplant dysfunction (n=6). In lung allograft recipients, donor-specific CTLp frequencies remained relatively high and frequencies were not different between recipients without (n=6) or with (n=6) chronic transplant dysfunction. Donor-specific HTLp frequencies did not change significantly after liver or lung transplantation and did not differ between recipients without or with chronic transplant dysfunction. CONCLUSIONS: An early decrease in donor-specific CTLp correlates with good graft outcome after liver transplantation. Such rapid decreases in alloreactivity do not occur after lung transplantation illustrating the unique capacity of liver allografts to induce transplantation tolerance.

Humans↗

PubMed2001

Contractile speed and fatigue of adductor pollicis muscle in multiple sclerosis.

The purpose of the study was to investigate differences in contractile speed, force, and fatigability of the adductor pollicis muscle between 12 patients with multiple sclerosis (MS) and 8 sedentary control subjects matched for age and gender. There were no differences between the patients with MS and control subjects with respect to the percentage of maximal muscle force that could be recruited during voluntary effort (95.5 +/- 3.9% and 98.2 +/- 2.0%, respectively, P = 0.10), the stimulation frequency/force and force/velocity relationships, the rates of force development and relaxation, fatigue resistance, and the recovery rate of adductor pollicis muscle. However, previous results from the same group of MS patients showed that quadriceps femoris muscle force and resistance to fatigue were reduced. Therefore, our data support the clinical experience that, in patients with MS, lower limb muscle function is more or earlier affected than upper limb muscle function.

Adult↗

PubMed2001

Phosphocreatine and ATP content in human single muscle fibres before and after maximum dynamic exercise.

The recovery of high-energy phosphate levels in single human skeletal muscle fibres following short-term maximal (all-out) exercise was investigated. Three male volunteers exercised maximally for 25 s on an isokinetic cycling ergometer. Muscle biopsy samples from the vastus lateralis were collected at rest, immediately post-exercise and at 1.5 min of recovery. The subjects also performed a second exercise bout 1.5 min after the first, on a separate occasion. Single muscle fibres were dissected, characterized and assigned to one of four groups according to their myosin heavy chain (MyHC) isoform content; namely, type I, IIA, IIAx and IIXa (the latter two groups containing either less or more than 50% IIX MyHC). Fibres were analysed for adenosine 5'-triphosphate (ATP), inosine-5'-monophosphate (IMP), phosphocreatine (PCr) and creatine (Cr) levels. Type I fibres had a lower Cr content than type II fibres (P<0.01). Within type II fibres resting [PCr] increased with increasing MyHC IIX isoform content (r=0.59, P<0.01). Post-exercise [PCr] was very low in all fibre groups (P<0.01 versus rest) while great reductions in ATP were also observed (P<0.01 versus rest), especially in the type II fibre groups. [PCr] at 1.5 min of recovery was still lower compared to rest for all fibre groups (P<0.01) especially in the IIAx and IIXa fibres.

Adenosine Triphosphate↗

PubMed2001

Reproducibility of contractile properties of the human paralysed and non-paralysed quadriceps muscle.

This study assessed the reproducibility of electrically evoked, isometric quadriceps contractile properties in eight people with spinal cord injury (SCI) and eight able-bodied (AB) individuals. Over all, the pooled coefficients of variation (CVps) in the SCI group were significantly lower (ranging from 0.03 to 0.15) than in the AB group (ranging from 0.08 to 0.21) (P<0.05). Furthermore, in all subjects, the variability of force production increased as stimulation frequency decreased (P<0.01). In subjects with SCI, variables of contractile speed are clearly less reproducible than tetanic tension or resistance to fatigue. Contractile properties of quadriceps muscles of SCI subjects were significantly different from that of AB subjects. Muscles of people with SCI were less fatigue resistant (P<0.05) and produced force-frequency relationships that were shifted to the left, compared with AB controls (P<.01). In addition, fusion of force responses resulting from 10 Hz stimulation was reduced (P<.05) and speed of contraction (but not relaxation) was increased (P<0.05), indicating an increased contractile speed in paralysed muscles compared with non-paralysed muscles. These results correspond with an expected predominance of fast glycolytic muscle fibres in paralysed muscles. It is concluded that quadriceps dynamometry is a useful technique to study muscle function in non-paralysed as well as in paralysed muscles. Furthermore, these techniques can be reliably used, for example, to assess therapeutic interventions on paralysed muscles provided that expected differences in relative tetanic tension and fatigue resistance are larger than approximately 5% and differences in contractile speed are larger than approximately 15%.

Adult↗

PubMed2001

Peripheral vascular changes after electrically stimulated cycle training in people with spinal cord injury.

OBJECTIVE: To test whether a short period of training leads to adaptations in the cross-sectional area of large conduit arteries and improved blood flow to the paralyzed legs of individuals with spinal cord injury (SCI). DESIGN: Before-after trial. SETTING: Rehabilitation center, academic medical center. PARTICIPANTS: Nine men with spinal cord lesions. INTERVENTION: Six weeks of cycling using a functional electrically stimulated leg cycle ergometer (FES-LCE). MAIN OUTCOME MEASURES: Longitudinal images and simultaneous velocity spectra were measured in the common carotid (CA) and femoral (FA) arteries using quantitative duplex Doppler ultrasound examination. Arterial diameters, peak systolic inflow volumes (PSIVs), mean inflow volumes (MIVs), and a velocity index (VI), representing the peripheral resistance, were obtained at rest. PSIVs and VI were obtained during 3 minutes of hyperemia following 20 minutes of FA occlusion. RESULTS: Training resulted in significant increases in diameter (p < .01), PSIVs (p < .01), and MIVs (p < .05), and reduced VI (p < .01) of the FA, whereas values in the CA remained unchanged. Postocclusive hyperemic responses were augmented, indicated by significantly higher PSIVs (p <.01) and a trend toward lower VI. CONCLUSION: Six weeks of FES-LCE training increased the cross-sectional area of large conduit arteries and improved blood flow to the paralyzed legs of individuals with SCI.

Adult↗

PubMed2001

Metabolism changes in single human fibres during brief maximal exercise.

Changes in high-energy phosphate levels in single human skeletal muscle fibres after 10 s of maximal (all-out) dynamic exercise were investigated. Muscle biopsies from vastus lateralis of two volunteers were collected at rest and immediately post exercise. Single muscle fibres were dissected from dry muscle and were assigned into one of four groups according to their myosin heavy chain (MyHC) isoform content: that is type I, IIA, IIAx and IIXa (the latter two groups containing either less or more than 50% IIX MyHC). Fragments of characterised fibres were analysed by HPLC for ATP, inosine-monophosphate (IMP), phosphocreatine (PCr) and creatine levels. After 10 s of exercise, PCr content ([PCr]) declined by approximately 46, 53, 62 and 59 % in type I, IIA, IIAx and IIXa fibres, respectively (P < 0.01 from rest). [ATP] declined only in type II fibres, especially in IIAx and IIXa fibres in which [IMP] reached mean values of 16 +/- 1 and 18 +/- 4 mmol (kg dry mass)(-1), respectively. While [PCr] was reduced in all fibre types during the brief maximal dynamic exercise, it was apparent that type II fibres expressing the IIX myosin heavy chain isoform were under a greatest metabolic stress as indicated by the reductions in [ATP].

Adenosine Triphosphate↗