Laryngeal resistance before and after minor surgery: endotracheal tube versus Laryngeal Mask Airway.
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BACKGROUND: The placement of an endotracheal tube (ETT) may promote laryngeal swelling, which is an important cause of upper airway obstruction after extubation. The authors hypothesized that laryngeal swelling after ETT placement increases laryngeal resistance and tested that hypothesis by comparing postoperative laryngeal patency between patients with ETT placement and those with a Laryngeal Mask Airway trade mark (LMA). METHODS: Fourteen adult patients who underwent elective minor surgeries were randomly allocated to two groups whose airway would be managed through ETTs (the ETT group) or LMAs (the LMA group) during the surgery. While maintaining at sevoflurane 1 minimum alveolar concentration, the authors measured laryngeal resistance before and after surgery, during both spontaneous breathing and mechanical ventilation under complete paralysis. In addition, they endoscopically measured the vocal cord angle under complete paralysis. RESULTS: In association with marked swelling of the vocal cords, the vocal cord angle significantly decreased after surgery in the ETT group, whereas the angle did not change in the LMA group. Laryngeal resistance during mechanical ventilation significantly increased only in the ETT group. Laryngeal resistance during spontaneous breathing significantly increased after surgeries in both groups. CONCLUSIONS: Postoperative laryngeal resistance increases at least in part because of laryngeal swelling in patients with ETT placement, whereas alteration of laryngeal neural control mechanisms has been also indicated. The use of the LMA trade mark has an advantage over ETT placement in order to avoid postoperative laryngeal swelling. (+info)
Neuronal sensitivity to hyperoxia, hypercapnia, and inert gases at hyperbaric pressures.
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As ambient pressure increases, hydrostatic compression of the central nervous system, combined with increasing levels of inspired Po2, Pco2, and N2 partial pressure, has deleterious effects on neuronal function, resulting in O2 toxicity, CO2 toxicity, N2 narcosis, and high-pressure nervous syndrome. The cellular mechanisms responsible for each disorder have been difficult to study by using classic in vitro electrophysiological methods, due to the physical barrier imposed by the sealed pressure chamber and mechanical disturbances during tissue compression. Improved chamber designs and methods have made such experiments feasible in mammalian neurons, especially at ambient pressures <5 atmospheres absolute (ATA). Here we summarize these methods, the physiologically relevant test pressures, potential research applications, and results of previous research, focusing on the significance of electrophysiological studies at <5 ATA. Intracellular recordings and tissue Po2 measurements in slices of rat brain demonstrate how to differentiate the neuronal effects of increased gas pressures from pressure per se. Examples also highlight the use of hyperoxia (+info)
Noninvasive measurement of the tension-time index in children with neuromuscular disease.
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Respiratory muscle weakness is common in children with neuromuscular disease (NMD). We hypothesized that weakness puts them at risk for respiratory muscle fatigue, a harbinger of chronic respiratory failure. We therefore measured a noninvasive index of respiratory muscle fatigue, the tension-time index of the respiratory muscles (TT(mus)), in 11 children with NMD and 13 control subjects. Spirometric flow rates and maximal inspiratory pressure were significantly lower in the NMD group than in controls (43 +/- 23 vs. 99 +/- 21 cmH2O, P < 0.001). The mean TT(mus) was significantly higher in the NMD group than in controls (0.205 +/- 0.117 vs. 0.054 +/- 0.021, P < 0.001). The increase in TT(mus) was primarily due to an increase in the ratio of average mean inspiratory pressure to maximal inspiratory pressure, indicating decreased respiratory muscle strength reserve. We found a significant correlation between TT(mus) and the residual volume-to-total lung capacity ratio (r = 0.504, P = 0.03) and a negative correlation between TT(mus) and forced expiratory volume in 1 s (r = -0.704, P < 0.001). In conclusion, children with NMD are prone to respiratory muscle fatigue. TT(mus) may be useful in assessing tolerance during weaning from mechanical ventilation, identifying impending respiratory failure, and aiding in the decision to institute therapies. (+info)
Lung volume effects on pharyngeal swallowing physiology.
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The experiment was a prospective, repeated-measures design intended to determine how the variation of lung volume affects specific measures of swallowing physiology. Swallows were recorded in 28 healthy subjects, who ranged in age from 21 to 40 yr (mean age of 29 yr), by using simultaneous videofluoroscopy, bipolar intramuscular electromyography, and respiratory inductance plethysmography. Each subject swallowed three standardized pudding-like consistency boluses at three randomized lung volumes: total lung capacity, functional residual capacity, and residual volume. The results showed that pharyngeal activity duration of deglutition for swallows produced at residual volume was significantly longer than those occurring at total lung capacity or at functional residual capacity. No significant differences were found for bolus transit time or intramuscular electromyography of the superior constrictor. The results of this experiment lend support to the hypothesis that the respiratory system may have a regulatory function related to swallowing and that positive subglottic air pressure may be important for swallowing integrity. Eventually, new treatment paradigms for oropharyngeal dysphagia that are based on respiratory physiology may be developed. (+info)
Randomized comparison of laryngeal tube with classic laryngeal mask airway for anaesthesia with controlled ventilation.
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BACKGROUND: Only a prototype laryngeal tube has been compared with the classic LMA for brief periods of anaesthesia. We compared the new laryngeal tube (which had several improvements in design) with the classic LMA. METHODS: We randomly allocated 72 patients to receive either the laryngeal tube or an LMA, and compared adequacy of controlled ventilation during anaesthesia (good: clear airway without complications; fair; clear airway with complications or suboptimal airway; or failed), leak pressure and the incidence of postoperative complications. RESULTS: Insertion was successful within 2 attempts in all 36 patients for the classic LMA and in 35 patients for the laryngeal tube. The mean leak pressure for the laryngeal tube (28 cm H(2)O) was significantly greater than that for the classic LMA (21 cm H(2)O) (P<0.001; 95% CI 3.6-10.0 cm H(2)O). Ventilation was good in 25 cases, fair in 11, and failed in no patients with the classic laryngeal mask airway; and good in 23, fair in 11 and failed in two for the laryngeal tube. There was no significant difference in adequacy of ventilation between the groups. The median peak airway pressure for the laryngeal tube (17.5 cm H(2)O) was greater than that for the classic LMA (16 cm H(2)O) (difference: 2 cm H(2)O; 95% CI 0-5 cm H(2)O). There was no significant difference in the incidence and severity of the postoperative complications between the two groups. CONCLUSION: The laryngeal tube was as effective as the classic LMA during anaesthesia with controlled ventilation. There were similar operative and postoperative complications. (+info)
Randomized crossover comparison of the ProSeal laryngeal mask airway with the Laryngeal Tube during anaesthesia with controlled ventilation.
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BACKGROUND: The Laryngeal Tube (LT) performs similarly to the classic laryngeal mask airway during controlled ventilation but with an improved airway seal. We compared the laryngeal tube with the ProSeal laryngeal mask airway (PLMA) throughout anaesthesia. METHODS: Thirty-two patients were studied using a randomized cross-over design. The primary outcome measure was airway seal pressure. Secondary outcome measures included peak and plateau airway pressures, time to achieve an airway, ease of insertion, airway manipulations required to achieve a patent airway and grade of fibre-optic laryngoscopy. The proportion of patients in whom good, fair or failed ventilation was achieved was also calculated. RESULTS: No significant difference was found in regard to seal pressure (PLMA, median 26.5 cm H2O, range 10-40; LT, median 24, range 6-40; P=0.7, 95% confidence interval of the difference 3.5 to -4.0). There were two failures of insertion or ventilation in the LT group and none in the PLMA group. The peak airway pressure with the PLMA was lower than with the LT but the difference was clinically unimportant (PLMA, mean 16.2 cm H2O, SD 3.52; LT, mean 17.9, SD 5.21; P=0.02, 95% confidence interval of the difference -3.1 to -0.28). The PLMA took significantly less time to insert than the LT (PLMA, median 18.5 s, interquartile range 14-26; LT, median 22, interquartile range 15-36.5; P<0.02, 95% confidence interval of the difference -21.5 to -1.0). The PLMA gave a significantly better view on fibre-optic laryngoscopy than the LT (P<0.001, 95% confidence interval of the difference in grade -2.0 to -1.0). In the 16 patients in whom the PLMA was used during maintenance of anaesthesia ventilation was good in 15, fair in none and failed in one. The equivalent figures for the LT were good in nine, fair in six and failed in one (P=0.009). There was no significant difference in the plateau airway pressure, ease of insertion of the devices, number of manipulations required to achieve or maintain an airway, or in overall complications. CONCLUSION: The two devices performed equally well in terms of seal pressure. The PLMA was quicker to insert. Efficacy of ventilation was significantly better with the PLMA than the LT. The PLMA allowed a significantly better view of the larynx with a fibre-optic laryngoscope, and may therefore be of more use in cases where visualization of the larynx is required. (+info)
Open-lung protective ventilation with pressure control ventilation, high-frequency oscillation, and intratracheal pulmonary ventilation results in similar gas exchange, hemodynamics, and lung mechanics.
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BACKGROUND: Pressure control ventilation (PCV), high-frequency oscillation (HFO), and intratracheal pulmonary ventilation (ITPV) may all be used to provide lung protective ventilation in acute respiratory distress syndrome, but the specific approach that is optimal remains controversial. METHODS: Saline lavage was used to produce acute respiratory distress syndrome in 21 sheep randomly assigned to receive PCV, HFO, or ITPV as follows: positive end-expiratory pressure (PCV and ITPV) and mean airway pressure (HFO) were set in a pressure-decreasing manner after lung recruitment that achieved a ratio of Pao2/Fio2 > 400 mmHg. Respiratory rates were 30 breaths/min, 120 breaths/min, and 8 Hz, respectively, for PCV, ITPV, and HFO. Eucapnia was targeted with peak carinal pressure of no more than 35 cm H2O. Animals were then ventilated for 4 h. RESULTS: There were no differences among groups in gas exchange, lung mechanics, or hemodynamics. Tidal volume (PCV, 8.9 +/- 2.1 ml/kg; ITPV, 2.7 +/- 0.8 ml/kg; HFO, approximately 2.0 ml/kg) and peak carinal pressure (PCV, 30.6 +/- 2.6 cm H2O; ITPV, 22.3 +/- 4.8 cm H2O; HFO, approximately 24.3 cm H2O) were higher in PCV. Pilot histologic data showed greater interstitial hemorrhage and alveolar septal expansion in PCV than in HFO or ITPV. CONCLUSION: These data indicate that HFO, ITPV, and PCV when applied with an open-lung protective ventilatory strategy results in the same gas exchange, lung mechanics, and hemodynamic response, but pilot data indicate that lung injury may be greater with PCV. (+info)
High temperature characteristics and solidification microstructures of dental metallic materials part I: silver-palladium-copper-gold alloy.
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Ag-Pd-Cu-Au alloy was subjected to a Thermo-Mechanical Analyzer to investigate high temperature properties up to its liquidus temperature. Microstructural examination and elemental analysis with EPMA were also conducted in the solid/liquid mixture region. The following conclusions were obtained. (1) The solidus temperature was 838.3 +/- 2.52 degrees C and 957.7 +/- 1.53 degrees C for the liquidus point. (2) Thermal expansion coefficients were 1.39 +/- 0.08% at the solidus, 2.338 +/- 0.13% at the liquidus, and the melting expansion coefficient was 0.932 +/- 0.058%. (3) The expansion during melting was controlled by a small amount of pressure such as 1/100 of the air pressure, therefore the fit accuracy of castings is suggested not to be influenced by the solidification shrinkage. (4) Although the softening heat treatment and casting exhibited an influence on thermal expansion behavior, casting temperature in addition to post-casting plastic deformation did not show an effect on the thermal expansion. (5) The yield strength at 750 degrees C was reduced down to about 1/400 of that at room temperature, and the modulus of elasticity was about 1/100 of the room temperature value. (+info)