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 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Since activity of the genioglossus muscle plays a primary role in maintaining upper airway patency during sleep, its strength and endurance characteristics are of potential importance. The purpose of this study was 2-fold. First, to define the strength and endurance characteristics of the normal human genioglossus. Second, we hypothesized that because the genioglossus has a high proportion of fast glycolytic muscle fibers, brief periods of increased activity would make it more susceptible to fatigue. In five normal male subjects strength of the tongue was evaluated by measuring maximal anterior force using a transducer (Fmax). In each subject tongue endurance was then tested at 100%, 80%, and 50% Fmax. To test the effect of a short-term increase in genioglossal activity on its endurance, an inspiratory flow-resistive load with mild hypercapnia was presented to the upper airway for 10 min, after which genioglossal endurance at 80% Fmax was repeated. On a separate day the effect of inspiratory loading plus hypercapnia on thoracic inspiratory muscle endurance was also tested. Our results showed that mean Fmax was 1,267 +/- 125 (SEM) g. Endurance time (Tlim) decreased progressively during 50%, 80% and 100% Fmax trials. Short-term activation of the genioglossus caused a reduction in Tlim at 80% Fmax to 51.4 +/- 4.8% of its value before loading (p < 0.05). Tlim for the inspiratory muscles, however, was unaffected. We conclude that, like other skeletal muscles, genioglossal endurance is reduced as the force of contraction increases. In addition, genioglossal endurance is significantly reduced by short-term activation insufficient to fatigue the thoracic inspiratory muscles.
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PMID:Strength and endurance characteristics of the normal human genioglossus. 831 95

The effect of L-carnitine on energy metabolism at a high lipolytic flux was studied. Nine healthy male subjects received L-carnitine (CARN) (3 g.d-1) for 7 d, or a placebo (CONT), both with Ca pentothenate. The treatment increased resting nitrogen excretion slightly (+15%, P < 0.02). After an overnight fast, the subjects were submitted successively to 20 min bicycle exercise at 43 +/- 2 (SEM) %VO2max, a glycogen depletion routine involving high intensity bouts to exhaustion, 1-2 h of rest, again 20 min at the initial load, and finally 20 min at 57 +/- 3 %VO2max. After glycogen depletion, blood short-chain acylcarnitine concentrations increased 5 times as much in CARN as in CONT (P < 0.02). Fat oxidation estimated from respiratory gas exchange doubled after glycogen depletion for the same exercise intensity. However, there were no treatment differences in nonprotein RQ, heart rate, perceived fatigue, and blood parameters. It is concluded that during submaximal exercise after glycogen depletion (i.e., at a high lipid flux) substrate metabolism is not influenced by L-carnitine supplementation.
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PMID:Effect of L-carnitine on submaximal exercise metabolism after depletion of muscle glycogen. 832 Nov 12

Patients with neuromuscular disease can display paradoxic motion of the rib cage (RC) and abdomen (AB), which increases the work of breathing and predisposes to respiratory muscle fatigue. Long-term mechanical ventilation can reverse chronic hypercapnea and decrease the work of breathing in these patients. Changes in chest wall motion (CWM) that occur during mechanical ventilation have not been studied. We have assessed CWM using a calibrated respiratory inductive plethysmograph before and during mechanical ventilation in 5 children and young adults with neuromuscular disease and paradoxic breathing at rest. Asynchrony of CWM was quantitated by measuring the phase shift, theta, between RC and AB motion (0 degree = synchronous motion, 180 degrees = paradoxic motion). The volume contribution of the paradoxing compartment to tidal volume (PC/VT) was calculated. Before mechanical ventilation, mean +/- SEM VT was 122 +/- 17 mL, theta was 131 +/- 15 degrees C, and PC/VT was -27 +/- 6%. During mechanical ventilation, VT increased to 274 +/- 47 mL (P < 0.05), theta decreased to 41 +/- 14 degrees (P < 0.05), and PC/VT increased to +39 +/- 9% (P < 0.02). We conclude that mechanical ventilation improves RC/AB asynchrony and reverses the negative contribution to tidal volume of the paradoxing compartment in children and young adults with neuromuscular disease. This implies that mechanical ventilation assumes most or all the role of the respiratory pump in these patients, which provides a rationale for the use of chronic or nighttime ventilation in the treatment of respiratory muscle fatigue. Assessment of CWM may be useful in the determination of optimal ventilator settings in this population.
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PMID:Chest wall motion before and during mechanical ventilation in children with neuromuscular disease. 836 22

The pharmacokinetics and pharmacodynamics of the ACE inhibitor quinaprilat have been studied in six chronic haemodialysis (HD) patients and in six patients undergoing continuous ambulatory peritoneal dialysis (CAPD) after a single oral dose of 2.5 mg quinapril. Mean tmax and Cmax values (SEM) for quinaprilat in interdialytic HD patients were 4.0 (0) h and 84 (8.4) ng.ml-1 respectively, and they did not differ significantly from those in CAPD patients (4.7 (0.7) h and 64 (5.7) ng.ml-1). Elimination half lives were 30 (10.1) h (HD) and 34 (7.3) h (CAPD). Cmax, tmax, t1/2, and AUC were increased and CL was decreased compared to data reported previously after giving 2.5 mg to healthy subjects. Peritoneal clearance was calculated as 0.1 (0.1) ml.min-1, thus less than 0.5% of the dose were removed within 24 h by CAPD. ACE activity was suppressed by more than 93% between 4 and 24 h postdose (P < 0.001). It decreased in both groups with increasing plasma quinaprilat levels. Angiotensin II concentration compared to baseline was significantly decreased at 4 hours (-30.4 +/- 10%) and 24 h (-30 +/- 9.9%) (P < 0.05, n = 11), while active plasma renin concentration was still significantly increased at 48 h postdose (+ 60.2 +/- 14.5%, P < 0.01). Mean arterial pressure 24 h postdose was significantly (P < 0.05) decreased in HD (-12 mmHg) and CAPD patients (-20 mm Hg). Only two patients reported unwanted effects (fatigue, dizziness, nausea, and weakness). In conclusion, due to its long lasting effect on ACE activity and on blood pressure in terminal renal failure a starting dose of quinapril 2.5 mg o.d. may be used in hypertensive HD and CAPD patients.
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PMID:Pharmacokinetics and pharmacodynamics of quinaprilat after low dose quinapril in patients with terminal renal failure. 838 27

The purpose of this study was to compare a gravimetric method and an impression technique in the evaluation of occlusal substance loss. The wear of gold, porcelain, and microfilled resin was studied in vivo. The gravimetric method showed lower substance loss for porcelain than for gold, whereas the microfilled resin had the highest substance loss. To obtain a higher accuracy for the measurement of occlusal substance loss of restorative materials with an impression technique, the test area has to be restricted, the antagonizing occlusal contacts carefully recorded before the test period, and the number of cuts increased. The observed structure of wear facets (SEM) corroborated with previous findings of the wear mechanism of these materials; that is, gold has mainly abrasive wear in contact with porcelain, whereas porcelain has a fatigue type and microfilled resin a tribochemical type of wear.
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PMID:Wear resistance of some prosthodontic materials in vivo. 849 67

Postoperative fatigue as defined by a 10-point scale (1 = fit, 10 = fatigued) was determined prospectively in 84 patients undergoing major surgery. Results from this scale correlated well with standard psychological assessment of fatigue (Profile of Mood States Questionnaire) (r = 0.767; p < 0.0001). Fatigue values were 3.46 +/- 0.19 arbitrary units (mean +/- SEM) preoperatively; and postoperatively they were 5.61 +/- 0.24 at day 7, 5.02 +/- 0.24 at day 14, 3.74 +/- 0.19 at day 28, and 2.77 +/- 0.18 at day 90. Fatigue during the postoperative period was integrated to give a total fatigue score (332 +/- 14 arbitrary units, range 90-664), and this score was correlated with preoperative and early postoperative factors. The best predictor of postoperative fatigue was preoperative fatigue (r = 0.545; p = 0.001), with lesser correlations with diagnosis (especially cancer); preoperative weight, particularly total body protein (r = 0.317; p = 0.01); and weight loss (r = 0.29; p = 0.03), grip strength (r = 0.352; p = 0.01), and age (r = 0.267; p = 0.01). Postoperative fatigue was not correlated with preoperative anxiety, depression, or hostility, involuntary muscle function, gender, preoperative stress, or changes in total body protein or fat over the two postoperative weeks. It is concluded that patients who present for surgery already fatigued are the ones who are most likely to suffer from prolonged postoperative fatigue, particularly so if they are elderly, suffer from cancer, or have few extra reserves of body protein.
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PMID:Predicting postoperative fatigue: importance of preoperative factors. 851 18

Patients with congestive heart failure (CHF) suffer from respiratory muscle weakness which may contribute to dyspnea. Nasal continuous positive airway pressure (NCPAP) can improve left ventricular ejection fraction (LVEF) and reduce dyspnea in patients with CHF and Cheyne-Stokes respiration with central sleep apnea (CSR-CSA) but its effects on respiratory muscle strength are not known. We therefore studied the effects of NCPAP on maximal inspiratory and expiratory pressures (MIP and MEP, respectively), LVEF, dyspnea, and fatigue in patients with chronic CHF and CSR-CSA over 3 mo. Eight patients were randomized to control and nine to nightly NCPAP. There were no significant changes in any of these factors in the control group during the study. In contrast, among the NCPAP group, MIP increased from 79.3 +/- 8.1 to 90.7 +/- 10.4 cm H2O (mean +/- SEM; p < 0.02), LVEF increased from 24.0 +/- 4.0 to 32.6 +/- 6.6% (p < 0.02) and symptoms of dyspnea and fatigue were alleviated. However, MEP did not change. In addition, the number of apneas and hypopneas decreased from 49 +/- 11 to 17 +/- 7 per hour of sleep (p < 0.001) and mean low Sao2 during sleep increased from 87.9 +/- 1.0 to 93.0 +/- 1.0% (p < 0.01). Our data indicate that nightly application of NCPAP in patients with CHF and CSR-CSA improves inspiratory muscle strength and LVEF, and relieves dyspnea and fatigue.
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PMID:CPAP improves inspiratory muscle strength in patients with heart failure and central sleep apnea. 854 29

Sodium bicarbonate given by nasogastric tube has been used by some trainers as the key ingredient in a 'milkshake'. It has been suggested that such treatment given 3-5 h prior to racing may enhance a horse's racing performance by increasing the blood buffering capacity and enhancing lactate clearance from skeletal muscle, thereby delaying the onset of fatigue. Several experiments were conducted to examine the effects on fluid, electrolyte and acid-base values of 0.5 g kg-1 dose of sodium bicarbonate, were examined. The effects of fasting, the simultaneous administration of glucose (0.5 g kg-1) or the withholding of water were also examined to determine whether they influenced the uptake and elimination of sodium bicarbonate. Six Thoroughbred horses were used, each wearing a urine and faecal collection harness. Prior to sodium bicarbonate administration, venous blood, urine and faecal samples were collected for 24 h to establish control values. After administration of sodium bicarbonate (0.5 g kg-1) in 2 l of water, samples were collected at various times for up to 46 h. There were significant increases in water consumption, from 0.5-2.3 l h-1 at 2 h post-administration. Urine output increased by approximately three fold and did not return to control levels until 18 h post-administration. Urinary sodium concentration increased from 95 +/- 16 mmol l-1 (mean +/- SEM) to peak values of 349 +/- 12 mmol l-1 at 12 h. In the 24 h after sodium bicarbonate administration, approximately 80% of the sodium intake (NaHCO3+feed) was excreted in the urine. There was no significant change in the total urinary potassium and chloride excretion. Faecal water content did not change following sodium bicarbonate administration, but there was an increase in faecal sodium content. The mean increase in venous blood bicarbonate concentration was 7.6 +/- 0.4 mmol l-1 after the 0.5 kg-1 dose. Water deprivation for 6 h after sodium bicarbonate administration, fasting or the co-administration of glucose did not affect the peak blood bicarbonate concentration or the time to peak concentration. However, the withholding of water did result in a faster rate of decrease in blood bicarbonate concentration when water was resupplied.
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PMID:Effects of sodium bicarbonate on fluid, electrolyte and acid-base balance in racehorses. 855 10

Previously, we examined the effects of carbohydrate (CHO) ingestion on glucose kinetics during exercise at 70% of maximum O2 uptake (VO2, max). Here we repeat those studies in heavier cyclists (n = 6 per group) cycling for 3 h at a similar absolute O2 uptake but at a lower (55% of VO2, max) relative exercise intensity. During exercise, the cyclists were infused with a 2-3H-glucose tracer and ingested U-14C glucose-labelled solutions of either flavoured water (H2O) or 10 g/100 ml glucose polymer, at a rate of 600 ml/h. Two subjects in the H2O trial fatigued after 2.5 h of exercise. Their rates of glucose appearance (Ra) declined from 2.9 +/- 0.6 to 2.0 +/- 0.1 mmol/min (mean +/- SEM) and, as their plasma glucose concentration [Glu] declined from 4.7 +/- 0.2 to below 3.5 +/- 0.2 mM, their rates of glucose oxidation (Rox) and fat oxidation plateaued at 2.7 +/- 0.4 and 1.7 +/- 0.1 mmol/min respectively. In contrast, all subjects completed the CHO trial. Although CHO ingestion during exercise reduced the final endogenous Ra from 3.4 +/- 0.6 to 0.9 +/- 0.3 mmol/min at the end of exercise, it increased total Ra to 5.5 +/- 0.5 mmol/min (P < 0.05). A higher total Ra with CHO ingestion raised [Glu] from 4.3 +/- 0.3 to 5.3 +/- 0.1 mM and accelerated Rox from 3.5 +/- 0.2 to 5.9 +/- 0.2 mmol/min after 180 min of exercise (P < 0.05). The increased contribution to total energy production from glucose oxidation (34 +/- 1 vs. 20 +/- 1%) decreased energy production from fat oxidation from 51 +/- 2 to 40 +/- 5% (P = 0.08) and produced patterns of glucose, muscle glycogen (plus lactate) and fat utilisation similar to those during exercise at 70% of (V&dot;O2, max). Thus, CHO ingestion is necessary to sustain even prolonged, low to moderate intensity exercise and when ingested, it suppresses the higher relative rates of fat oxidation usually observed at exercise intensities less than 60% of VO2, max.
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PMID:Fuel utilisation during prolonged low-to-moderate intensity exercise when ingesting water or carbohydrate. 859 50

In recent years, titanium has become a material of major interest in prosthetic dentistry. Due to its chemical properties, titanium has to be processed differently from conventional alloys. In this paper, two different methods of welding were investigated. Specimens machined from pure titanium rods were fused either by laser welding or plasma welding. Hardness profiles and light microscopy images were taken in the region of the weld. The mechanical properties were tested by alternating bending fatigue tests up to 3 million cycles. Light microscopy images and hardness profiles showed a larger heat-affected zone after plasma welding compared to laser welding. No significant differences comparing fatigue strength could be found between the two methods of welding. However, extreme loads led to earlier fatigue in the plasma-welded specimens. SEM images of the laser-welded joints showed fractures in the welding zone, while the plasma-welded specimens fractured mostly beyond the heat-affected zone. From these results, it can be assumed that both methods are suitable for welding titanium. At the moment, laser welding is the more suitable technique in dentistry because of its lower thermal alteration of the workpieces.
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PMID:Studies on laser- and plasma-welded titanium. 859 37


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