Biomedical subjects

J P Micallef

Publications and source records attributed to J P Micallef.

At least 19 recordsLinked to original sources

PubMed2006

Failed excitability of spinal motoneurons induced by prolonged running exercise.

The main purpose of this study was to investigate the modulations in H-reflex and V-wave responses (spinal loop properties) induced by prolonged locomotion activities. The second purpose was to compare the development of central fatigue between continuous and intermittent running modes. Eleven males randomly performed two 90-min running exercises either continuously (CONT, first ventilatory threshold) or intermittently (INT, 150 s at a velocity 20% higher than that during CONT/30 s of recovery). Neuromuscular tests of the plantar flexors [including M-wave and H-reflex at rest and M-wave and V-wave during maximal voluntary contraction (MVC)] were performed before and 5 and 30 min after the running exercises. During MVC, the torque significantly decreased (P < 0.05) from preexercise to 5 and 30 min postexercise (-11 and -9%, respectively), as did the RMS/M ratio (-11 and -13%, respectively) and the V/M ratio (-19 and -37%, respectively) for the soleus muscle. At rest, the H/M ratio also decreased significantly (P < 0.001) from preexercise to 5 and 30 min postexercise (-61 and -55%, respectively). Last, no difference in the alteration of spinal loop properties was noted between CONT and INT. In conclusion, the results regarding H-reflex and V-wave suggest for the first time a modulation in spinal loop properties after prolonged running.

Action Potentials↗

PubMed2006

Specific incremental field test for aerobic fitness in tennis.

OBJECTIVES: To compare metabolic and cardiorespiratory responses between subjects undergoing incremental treadmill (non-specific) and tennis field based (sport specific) tests. METHODS: Nine junior competitive tennis players randomly performed two incremental protocols to exhaustion: a treadmill test (TT) and a tennis specific fitness test (FT). The FT consisted of repeated displacements replicating the game of tennis at increasing speed on a court. In both tests, ventilatory variables and heart rate (HR) were determined at the ventilatory threshold (VT), respiratory compensation point (RCP), and maximal loads (max). Blood lactate concentration was determined at the point of volitional fatigue. RESULTS: Percentage (mean (SD)) maximal HR (83.6 (5.1) v 83.0 (2.8) and 92.1 (2.1) v 92.3 (2.1)%, respectively) and percentage maximal oxygen uptake (VO2max) (69.4 (8.1) v 73.5 (6.1) and 84.4 (6.5) v 85.5 (8.7)%, respectively) at the VT and RCP were not different between the FT and TT subjects, whereas VO2max was higher in the FT than in the TT (63.8 (3.0) v 58.9 (5.3) ml/min/kg; p<0.05). Blood lactate concentration (10.7 (3.0) v 10.6 (4.3) mmol/l) did not differ between the TT and FT. CONCLUSIONS: Although cardiorespiratory variables were not different at submaximal intensities between the two tests, VO2max values derived from laboratory measurements were underestimated. Using field testing in addition to treadmill testing provides a better measurement of a player's individual fitness level and may be routinely used to accurately prescribe appropriate aerobic exercise training.

Adolescent↗

PubMed2006

The intensity level of physical exercise and the bone metabolism response.

This study investigated the short-term effects of the intensity level of physical exercise on bone metabolism and related hormones. The responses of calciotropic hormones and bone biochemical markers were evaluated in seven male cyclists (mean age 24.4 years, range 20-39) during two 50-min cycling tests performed 15% below (-VT) and 15% above (+VT) the ventilatory threshold. In each test, venous blood samples were drawn at rest, at the 30th and 50th min of exercise, and after 15 min of recovery. For both intensity levels, no significant variation in calcium, 25-hydroxyvitamin D, 1.25-dihydroxyvitamin D, or cortisol level was observed. Intact parathyroid hormone (iPTH) level increased significantly after the last minute of the test (41%, p < 0.05) and peaked during the recovery (80%, p < 0.05) only in response to exercise performed at +VT. Serum phosphorus concentration rose during both tests, while albumin levels increased only at +VT. Concerning bone cell activity, osteocalcin, and type I-C telopeptide breakdown products transiently increased only in response to exercise performed at +VT (11% and 16.8%, respectively; p < 0.05). Bone alkaline phosphatase increased similarly for both intensity levels after 30 min (12%, p < 0.05) and 50 min (12% for -VT vs. 14% for +VT, p < 0.05). All markers of bone turnover returned to initial values during the recovery. In conclusion, a no-impact but intense and sustained exercise performed at +VT transiently stimulated bone turnover and iPTH secretion, suggesting the existence of a bone stimulation threshold. In addition to the well known effect of mechanical constraints, both the duration and intensity of exercise may induce changes in bone turnover.

Adult↗

PubMed2004

Competitive season of triathlon does not alter bone metabolism and bone mineral status in male triathletes.

This longitudinal study evaluated the effects of a triathlon season on bone metabolism and hormonal status. Seven male competitive triathletes (mean age 19.3 years, range 18 - 20) with 5.0 +/- 0.3 years of competition experience were tested twice during the season: at the beginning of training and 32 weeks later. Total and regional bone mineral density (BMD) was determined by dual-energy X-ray absorptiometry, while bone turnover was evaluated by specific biochemical markers: bone-specific alkaline phosphatase (B-ALP), osteocalcin, and urinary type I collagen C-telopeptide. In addition, sexual, calciotropic and somatotropic hormones were also analyzed. After 32 weeks, a BMD increase was found at the lumbar spine (1.9 %; p = 0.031) and skull (3.1 %; p = 0.048), while no variation was observed for total body or at the proximal femur. The B-ALP level decreased (-23.2 %; p = 0.031), but no variation was found for the other bone markers. 1.25 (OH) (2)D3, IGF-1 and the bioavailability IGF-1 index (IGF-1/IGFBP-3) increased by 18.3 % (p = 0.047), 29 % (p = 0.048), 33 % (p = 0.011), respectively, while PTH, testosterone, IGFBP-3 and cortisol concentrations were unchanged. In conclusion, the triathlon season had a moderately favourable effect on BMD, although a slowing down of bone formation activity was observed. No variation in hormonal levels was observed that could have limited the effects of exercise on bone tissue.

Absorptiometry, Photon↗

PubMed2004

Effects of physical activities that induce moderate external loading on bone metabolism in male athletes.

Sports characterized by little or moderate weight bearing or impact have a low osteogenic effect. However, the action of such sports on bone turnover remains unclear. The objective of this study was to determine the effect on bone remodelling of physical activities that induce moderate external loading on the skeleton. Thirty-eight male athletes aged 18-39 years (cyclists, n = 11; swimmers, n = 13; triathletes, n = 14) and 10 age-matched sedentary controls aged 22-35 years participated in the study. The study combined measurement of bone mineral density by dual-energy X-ray absorptiometry and bone turnover assessment from specific biochemical markers: serum bone-specific alkaline phosphatase, osteocalcin, urinary type I collagen C-telopeptide and calcium. Compared with the controls and swimmers, adjusted bone mineral density was higher (P < 0.05) in triathletes at the total proximal femur and lower limbs. No differences in bone mineral density were found between cyclists, swimmers and controls. Compared with controls, osteocalcin was higher (P < 0.05) in triathletes and swimmers and urinary type I collagen C-telopeptide was higher in swimmers only. Serum bone-specific alkaline phosphatase was lower (P < 0.05) in cyclists than in all other groups. In conclusion, an osteogenic effect was found only in triathletes, mainly at bone sites under high mechanical stress. Bone turnover differed in athletes compared with controls, suggesting that bone turnover may be sport-practice dependent. Despite some encouraging observations, it was not possible to show that changes in the bone remodelling process were sport-discipline dependent.

Absorptiometry, Photon↗

PubMed2003

[Retinaculum flexors: clinical and experimental anatomic bases in favor of reconstruction in carpal tunnel surgery].

The goal of this anatomical study is to prove that reconstruction of the flexor retinaculum in carpal tunnel syndrome surgery is a reliable procedure and can improve the results of this procedure. In the first static study, we noted that when left to heal spontaneously, after 3 months the gap between the two edges of the cut retinaculum remained equal to or even larger than the gap created at the time of the surgery. A special Canaletto implant was created to achieve this reconstruction. It is technically possible to do this reconstruction by a 2 to 3 cm surgical approach in the palm. In another, dynamic study, we used a transducer to analyse the forces borne by the retinaculum during flexor tendon contraction. We compared these forces in a normal retinaculum, a reconstructed retinaculum with the Canaletto implant and a retinaculum opened endoscopically. This reconstruction conserves the anterior continuity of the retinaculum, allows excellent carpal tunnel decompression and immediately permits near-physiological forces. We discuss the advantages and the limits of this reconstruction. We think that this new surgical technique in the Carpal Tunnel Syndrome (CTS) will be able to improve the results, particularly in recurrences, in wrist malunion with CTS, in cases with severe electromyographic change with a sensory conduction speed of under 15 m.s-1 and in metabolic CTS. As always, his implant needs to be evaluated through a mid and long term clinical follow-up. By recovering better grip strength and reducing postoperative pain, this surgical technique can decrease the time needed to return to work and hence the economic costs of CTS surgery.

Arthroscopy↗

PubMed2003

Analysis of mechanical preparations in extracted teeth using ProTaper rotary instruments: value of the safety quotient.

The purpose of this study was to apply the Endographe to analyze the vertical forces and torque developed during mechanical preparations in extracted teeth. The data collected in this study may be used to calculate the safety quotient (SQ) as proposed by J.T. McSpadden. The SQ formula is defined as the torque required to break a file at D3 divided by the mean working torque required to cut dentin. The Endographe is a unique force-analyzer device equipped to measure, record, and generate graphs of the vertical forces and torque exerted during root canal preparation. All preparations were performed by endodontists in roots with narrow, more restrictive canals, larger, more open canals, or in roots sectioned in two halves. All canals, including the sectioned canals, were prepared with ProTaper files in accordance with the manufacturer's guidelines for use. For narrow canals, the mean values of the generated vertical forces (g) and torque (g.cm) varied from 80 (+/- 20) g (SX) to 232 (+/- 60) g (F2) and from 80 (+/- 24) g x cm (F1) to 150 (+/- 45) g x cm (S2), respectively. For large canals, the mean values of the generated vertical forces (g) and torque (g x cm) varied from 80 (+/- 20) g (SX) to 340 (+/- 20) g (F1) and from 31 (+/- 9) g x cm (S2) to 96 (+/- 35) g x cm (SX), respectively. The SQ varied from 0.93 to 7.95 for narrow canals and from 1.58 to 14.50 for large canals. The SQ is intended to provide values that can be analyzed to predict whether a rotary file will have a tendency to break or will work safely during clinical use. However, if the formula is going to provide useful information, it must index the "rotation to failure torque" with the "mean working torque" at a specific location along the cutting blades of a file. Additionally, this mathematical formula does not account for factors such as the concentration of forces, the way the instruments are used, or the wear of the instruments. A precise protocol for canal preparation should emphasize using small flexible stainless steel hand files to create or verify that within any portion of a root canal there is sufficient space for rotary instruments to follow. When there is a confirmed smooth, reproducible glide path, then a "secured" space exists to safely guide the more flexible terminal extent of a rotary NiTi file. Endogrammes provide an innovative approach to the analysis of mechanical preparations and suggest that the ProTaper shaping files are best used with lateral forces to decrease the coronal screwing effect. The ProTaper finishing files should be used with slow penetration and be introduced only into canals that have a confirmed smooth and reproducible glide path. When any part of the overall length of a canal has been secured, then the number of instruments, the time spent utilizing each instrument, and the overall time progressing through a sequence of instruments to shape this region of the canal is reduced.

Dental Alloys↗

PubMed2002

Insulin-like growth factor-binding protein 1 and blood rheology in athletes.

The GH-IGF axis has been recently suggested to modulate blood rheology in trained athletes, via GH effects on body water status and a possible action of IGF-I on erythrocyte deformability and aggregability. Another potential candidate for such a rheologic effect of the GH-IGF axis is insulin-like growth factor binding protein-1 (IGF-BP1) which is increased in trained people and correlated to fitness: IGF-BP1 is elevated in patients with polycythemia vera and stimulates erythroid burst formation in vitro. We investigated the statistical relationships between IGF-BP1 and blood rheology in athletes. 21 soccer players, age 24.5+/-1.13 yr; body mass index 23.7+/-0.38 kg/m(2); VO2max 44.8+/-7 ml.min(-1).kg(-1)). The major statistical determinant of IGFBP1 (measured at rest after overnight fast) was age (r=0.752, p=0.00013) which was not correlated with rheological parameters. IGF BP1 was negatively correlated with blood viscosity eta (high shear rate r=-0.516, p=0.024) and positively correlated with the percentage of extracellular water in total body water (ECW/TBW) (r=0.488, p=0.039). The previously reported correlations between IGF-I and both eta (r=0.637, p=0.003) and red cell rigidity "Tk" (r=0.696, p=0.0137) were observed, but IGF-I and IGF-BP1 were not correlated to each other (r=-0.176 ns) and their correlations with eta and Tk appeared to be independent when studied by multivariate analysis. Consistent with these correlations, subjects in the upper tertile of IGF-BP1 (>23.4 ng/ml) compared to those in the lower (<7.5 ng/ml) had a higher percentage of ECW/TBW (40.8+/-0.4 vs 38+/-0.8%, p=0.033), a lower eta (2.7+/-0.05 vs 2.97+/-0.06 mPa.s, p=0.016), and a lower Tk (0.54+/-0.05 vs 0.63+/-0.01, p=0.027). Thus, beside GH and IGF-I, IGF-BP1, which is reported to act on erythroid progenitors, exhibits statistical relationships with blood fluidity and erythrocyte flexibility that may suggest a physiological role in improving blood rheology.

Adult↗

PubMed2002

Postexercise red cell aggregation is negatively correlated with blood lactate rate of disappearance.

In three separate studies, we have observed that the rise in blood lactate during exercise is correlated to blood viscosity and red cell aggregation. Whether these results were related to an effect of blood rheology on lactate production by muscles or on lactate disappearance remains unknown. The modelling of postexercise lactate kinetics allows a fair evaluation of lactate production by muscles (gamma1) and lactate disappearance (gamma2), the latter being easily measurable with simplified protocols. We thus investigated the relationships between pre- and postexercise blood rheology and gamma2. Ten subjects (2 female and 8 males; age 16-45 yr, weight 62-106.5 kg) exhibiting a wide range of gamma2 (from 2 to 7.7x10(-2) min(-1)) underwent a maximal exercise-test with postexercise calculation of gamma2 with the simplified formula gamma2=0.0724+0.755(Lac8-Lac20)/(Lac8.Deltat)-0.00684Lac20 where Lac8 and Lac20 are lactate concentrations 8 and 10 min after exercise stop at the level of VO2max, as previously reported. During exercise whole blood viscosity eta(b) increased (+15%, p<0.01) due to a rise in hematocrit (p<0.05) and plasma viscosity (+0.08+/-0.03 mPa.s, p<0.05), while red cell rigidity was unchanged. Red cell aggregation (Myrenne M1) increased by 11% (p<0.05). Postexercise M1 (measured at VO2max) was the only hemorheologic parameter correlated to gamma2 (r=-0.697, p=0.037). We find once again a statistical relationship between lactate at exercise and red cell aggregation. Microcirculatory adaptations influenced by red cell aggregation may influence lactate disposal (as reflected by gamma2), adding its effect to that of the balance between carbohydrates and fat oxidation which is the major determinant of blood lactate concentrations at exercise in physiological conditions.

Adult↗

PubMed2001

Transcutaneous electric nerve stimulation reduces neglect-related postural instability after stroke.

OBJECTIVE: To test the existence of a neglect-related component of postural imbalance in some stroke patients to determine whether neglect patients (1) show worse postural control compared with nonneglect patients and healthy subjects and (2) have latent postural capacities that could be unmasked by an appropriate somatosensory manipulation. DESIGN: Intervention study with and without transcutaneous electric nerve stimulation (TENS). SETTING: Rehabilitation center research laboratory. PARTICIPANTS: Twenty-two stroke patients (mean age, 58.3 +/- 2.5yr; average days since stroke, 83.2d) and 14 age-matched healthy subjects. Stroke patients were subdivided into 3 groups: 6 with spatial neglect and 16 without (8 with left lesion, 8 with right lesion). INTERVENTIONS: All participants were subjected to a dynamic balance task, performed while sitting for 8 seconds on a laterally rocking platform. Seated on this mobile support, they were asked to maintain actively an erect posture, sitting as still as possible. In patients, TENS was applied on the contralesional side of the neck during the postural task. An effective stimulation (intensity corresponding to the threshold of perception, TENS+) was compared with a placebo stimulation (.01 x threshold of perception, TENS-). MAIN OUTCOME MEASURES: Postural performance in each trial was monitored by using 2 criteria: the number of aborted trials caused by loss of balance, and the angular dispersion of the support oscillations in roll. The latter criterion, which increased with body instability, was defined as 2 standard deviations of the angular distribution. RESULTS: Patients showing neglect displayed pronounced postural instability compared with other patients and controls. Although dramatic postural instability in the neglect patients was spectacularly and systematically reduced with TENS, no effect was observed in patients without neglect. CONCLUSION: This is among the first studies to provide clinical evidence supporting the "postural body scheme" concept.

Adult↗

PubMed2001

Qualitative description of a new preparation technique: the balanced-force motion using the Endographe.

The forces and torque applied during the balanced-force motion technique of root canal preparation were measured with the Endographe. Five endodontists prepared 100 extracted teeth, all straight and with similar root anatomy. The assignment of "tooth practitioner" was randomized. Gates-Glidden burs were used to prepare the coronal part and ensure apical patency for the other instruments. The balanced-force technique with conventional instruments was then used for the body of the canal. For the apical part either the watch-winding pull with conventional instruments or the reversed balanced-force technique with manual GT files was used. The Endogrammes were similar among endodontists for the coronal phase and showed low vertical forces in contrast with the lateral forces. For the body the Endogrammes were highly specific and described perfectly the different steps of instrument work. For the apical part the Endogrammes of the conventional instruments showed a lack of vertical forces. The Endogrammes of the manual GT files showed that torque was applied inversely to that of the conventional instruments. Force application was similar. In conclusion these objective data indicate the correct way of working with the different techniques incorporated into the balanced-force motion technique.

Dental Stress Analysis↗

PubMed2001

Analysis of the endogrammes developed during obturations on extracted teeth using system B.

The ability of an obturation technique to fill the root canal system tridimensionally depends partially on the timing and intensity of force applications. The aim of this study was to use the Endographe to analyze the forces and wedging effects developed in the root canal using a new obturation technique: System B. This system uses a heat plugger that simultaneously heats and pushes gutta-percha. The plugger was used to soften and move the gutta-percha apically during the down-pack stage. Two different methods, however, were used to withdraw the plugger from the compacted gutta-percha. One used the burst heat method, and the other was cold withdrawal. Five endodontists performed 50 obturations of prepared extracted teeth and 50 obturations of the "wedging effect" holder of the Endographe. The practitioner-obturation assignment was randomized. For each obturation the biggest plugger possible in relationship to the shape of the canal was chosen. For the obturation of the special holder the same tip was chosen. Endogrammes showed the force application and wedging effect sequences. The mean values for the vertical and horizontal forces and the wedging effect were, respectively, 16 +/- 2 N, 5 +/- 1 N, and 9 +/- 1 N. These results suggest that System B is one of the best techniques in terms of the developed vertical forces (low values) and the resulting wedging effect (high values) in relationship to the plasticity of the gutta-percha. The Endogrammes provide a new approach to the analysis of obturation techniques and a means to demonstrate correct and optimal manipulation of the new System B plugger.

Analysis of Variance↗

PubMed2000

Electrical stimulation-induced changes in double-wrapped muscles for dynamic graciloplasty.

HYPOTHESIS: Treatment of fecal incontinence has been greatly improved by electrical stimulation of gracilis muscle transposed around the anal canal. Various configurations of the muscle have been used: single alpha, gamma, epsilon muscle loops, split sling, or double wrap. We report herein experimental data on muscle transformation and damage induced by the latter surgical approach. DESIGN, INTERVENTIONS, AND MAIN OUTCOME MEASURES: This study was conducted on 4 groups of New Zealand white rabbits. Group 1 had unstimulated transposed gracilis muscles. Group 2 had left transposed gracilis muscles stimulated only. Group 3 had both right and left transposed gracilis muscles stimulated. Group 4 were the controls (not operated on). Muscle properties were studied by electrophysiological,immunohistochemical,and biochemical techniques. RESULTS: Transformation from fast-contractile glycolytic muscle fibers into fast-intermediate to slow-contractile oxidative muscle fiber types induced a fatigue resistance of the transposed muscle that has undergone long-term stimulation and muscle alterations characterized by fiber atrophy and fibrosis. CONCLUSIONS: Whatever technique of dynamic graciloplasty is used, muscle degeneration associated with mobilization might result primarily from the surgical dissection, whereby collateral blood supply to the gracilis is interrupted and exacerbated by long-term stimulation.

Animals↗

PubMed2000

The polymodal sensory cortex is crucial for controlling lateral postural stability: evidence from stroke patients.

In modern literature, internal models are considered as a general neural process for resolving sensory ambiguities, synthesising information from disparate sensory modalities, and combining efferent and afferent information. The polymodal sensory cortex, especially the temporoparietal junction (TPJ), is thought to be a nodal point of the network underlying these properties. According to this view, a pronounced disruption of the TPJ functioning should dramatically impair body balance. Surprisingly, little attention has been paid to this possible relationship, which was the subject of investigation in this study. Twenty-two brain-damaged patients and 14 healthy subjects were subjected to a self-regulated lateral balance task, performed while sitting for 8 s on a rocking platform. Their lateral body balance was analysed both with and without vision (darkness). Support displacements in the frontal plane were recorded by means of an accelerometer. Two criteria were taken into account to evaluate body stability in each trial: the number of aborted trials due to balance loss and the angular dispersion of the supporting surface. Lesions involving the temporoparietal junction were found to markedly increase body instability, both with and without vision. Therefore, the temporoparietal junction plays a pivotal role in lateral body stabilisation, irrespective of the sensory condition in which the task is performed. This suggests that body stability is controlled throughout internal model(s).

Adult↗

PubMed2000

Relationships between blood viscosity and insulin-like growth factor I status in athletes.

Exercise training is known (1) to enhance the function of the GH-IGF-I system, which has profound effects on body fluid status; (2) to increase blood fluidity. Thus, we investigated during an exercise-test in 39 male elite sportsmen (age 23.7+/-0.72 years; body mass index 23.7+/-0.28 kg/m2) the possible relationships between GH and IGF-I status and the rheological properties of blood. Two correlations indicate a relationship between body hydration and fitness: isometric handgrip strength is correlated with the percentage of extracellular water in total body water (r = 0.432, p = 0.02) and the aerobic working capacity W170 is negatively correlated with hematocrit (r = -0.341, p = 0.039). Water loss during exercise appears to be inversely related to fitness as evaluated by W170 (r = -0.529, p = 0.05), and is positively correlated with the score of signs of overtraining (r = 0.725, p = 0.003) and with the red blood cell aggregation index (r = 0.584, p = 0.036). Finally, while the GH peak value is correlated with the extracellular water volume (r = 0.393, p = 0.02), IGF-I is correlated with blood viscosity (r = 0.546, p = 0.0003), suggesting that when IGF-I values are within the upper quintile (>340 ng/ml) IGF-I may unfavourably affect blood rheology. Among factors of blood viscosity, IGF-I exhibits a borderline correlation (p = 0.05) with "Tk" and the ratio IGF1/IGFBP3 which reflects free circulating IGF-I is correlated with red cell aggregability measured with the Myrenne "M" (r = 0.485, p = 0.014) and S60 (r = 0.396, p = 0.494). These findings confirm the importance of hydration and dehydration as determinants of both blood rheology and exercise performance. Moreover, they suggest that values of IGF-I within the upper quintile are associated with an impairment of blood fluidity, possibly due to a direct effect of IGF-I on red cell deformability and aggregability.

Adult↗

PubMed2000

The paradox of hematocrit in exercise physiology: which is the "normal" range from an hemorheologist's viewpoint?

The paradox of hematocrit in exercise physiology is that artificially increasing it by autotransfusion or erythropoietin doping improves VO2 max and performance, while in normal conditions there is a strong negative correlation between hematocrit and fitness, due to a training-induced "autohemodilution". We aimed at investigating: (a) which is the physiological range of hematocrit in highly trained professional footballers; (b) what are the characteristics of athletes with high vs low hematocrit? We determined in 77 healthy male footballers the physiological range (mean +/- sd) of hematocrit: 42.3+/-2.74, (range -2sigma/+2sigma = 36.8-47.8%) thus defining boundaries of quintiles of distribution for this parameter: 40, 41.6, 42.9, 44.6. In another sample of 42 male footballers we compared three groups: lowest quintile (n = 8), highest quintile (n = 5) and the three middle quintiles considered together (n = 29). Athletes in the lowest quintile compared to those in the four other quintiles had a lower value of blood viscosity (-8%, p < 0.01) but this difference disappeared after correction for hematocrit. These subjects with low hematocrit had also higher values of the following parameters: aerobic working capacity (p < 0.01); isometric adductor strength (p = 0.02); crossover point of carbohydrate oxidation (70% carbohydrates/30% lipids) (p < 0.05); insulin like growth factor binding protein 1 (p < 0.0001). Athletes in the highest quintile had higher red cell aggregability (Myrenne index "M1" 8.45+/-0.38 vs 6.82+/-0.62, p < 0.04) and a higher disaggregability threshold gammaD (72.6+/-22.63 vs 44.49+/-1.37, p < 0.01) and a lower percentage of water in fat-free mass (p < 0.02). On the whole sample hematocrit was negatively correlated with aerobic working capacity (W170 r = -0.329, p = 0.007; Wmax (% of expected value) r = -0.552, p = 0.008; VO2 max (% of expected value) r = -0.543, p = 0.009) and with ferritin (r = -0.33, p = 0.031), and positively correlated with the overtraining score (r = 0.352, p = 0.019) which was in turn negatively correlated with ferritin r = -0.312, p = 0.02). Besides, hematocrit behaves as a major determinant of blood viscosity (correlation with blood viscosity r = 0.997, p < 10(-7)) and erythrocyte disaggregability gammaD (r = 0.384, p = 0.03), but the hematocrit/viscosity ratio (h/eta index of O2 delivery) remains maintained almost constant over the range of values studied. These results show that (a) physiological values of hematocrit in these athletes are comprised between 36 and 48%; (b) "low" hematocrit (<40%) was associated with a higher aerobic capacity; (c) subjects with the higher hematocrits (>44.6%) were frequently overtrained and/or iron-deficient, and their blood viscosity (and red cell disaggregability) tended to be increased.

Adaptation, Physiological↗

PubMed1999

Location of contact areas on rotary Profile instruments in relationship to the forces developed during mechanical preparation on extracted teeth.

AIM: The aim of this study was to locate the areas of direct instrument contact with dentine in the root canal system during rotary preparation and to analyse the relationship between these areas and the vertical forces and torque developed during the preparation. METHODOLOGY: Canal preparations were performed by endodontists either with the step-back (SB) or the crown-down (CD) technique. In order to locate the areas of contact, the instruments were coated with two layers of gold by electro-deposition. They were photographed before and after use, and a coding system, based on mm from the instrument tip, was devised to designate areas of gold removal or instrument wear due to friction. To standarise the conditions of instrument manipulation, the teeth were fixed in the Endographe holder, and this device was used to measure vertical forces and torque. RESULTS: The results showed that the first series of instruments used for the CD technique (taper 0.06) left 2 +/- 1 mm of the tip with the gold intact, indicating that these instruments and this step of the CD technique are the safest part of the preparation. For all other instruments (taper 0.04 series), the areas of gold removal involved the 3 mm around the tip and this finding was independent of the order of instrument use and preparation technique (SB or CD). The differences between the two techniques were significant in terms of the mean area of decolouration and the mean force and torque values. For the SB and CD techniques, the contact areas were, respectively, 10 +/- 3 and 7 +/- 2 mm. The forces and torque values were correspondingly higher for SB vs. CD; the mean values were, respectively, 19 and 21 N for vertical forces and 16 10(5) and 13 10(5) Nm for torque. CONCLUSIONS: The recorded torque values and the location on the instruments of the areas of contact with dentine during this development of torque i.e. at or near the tip, indicate that great caution should be used with the rotary technique, particularly with the taper 0.04 instruments, regardless of preparation technique.

Analysis of Variance↗

PubMed1999

Analysis of forces developed during mechanical preparation of extracted teeth using Profile NiTi rotary instruments.

AIM: The aim of this study was to analyse the vertical forces and torque developed in the root canal system of extracted teeth during mechanical preparation using ProFile NiTi instruments. METHODOLOGY: Instrument wear and fracture is in great part due to the repeated application of forces and torque during the course of root-canal preparation but research into the direct relationship has been hampered by the lack of adequate measuring devices. Measurements of these forces and torque were made with a new force analyser device, the Endographe, that was equipped with a holder to record and generate graphs of the vertical forces and torque exerted during the preparations. These preparations was performed by endodontists or students either with a series of instruments of increasing size or with the crown-down pressureless technique. RESULTS: The mean values for the endodontists of the generated vertical forces and torque varied, respectively, from 4 to 6N and from 7.105 to 12.105 Nm for the step-back technique and from 2.9 to 4.2 N and from 18.105 to 20.105 Nm for the crown-down technique. This suggested that the crown-down technique generated lower stresses (lower torque and lower vertical forces), although these findings also depend on the shape of individual canals. The students initially showed wide variations in generated forces, with significantly lower vertical force the torque values. By the end of the experimental sessions their values were similar to those of the endodontists, which indicated improvement in the efficiency of manipulation. CONCLUSIONS: Further work is needed to investigate the relationship between the force and the torque data from this study and the incidence of instrument fracture with the two techniques, as the clinical implications are considerable. It must be noted, however, that the Endographe is unable to take into account the cutting efficiency of the instruments. The use of graphs provides a new approach to the analysis of mechanical preparation.

Analysis of Variance↗