Maximum Peak Pressure Research Articles

The Effect of Breathing Frequency on Inspiratory Muscle Endurance During Incremental Threshold Loading

We tested whether there were differences in measures of respiratory muscle endurance between tests with spontaneously chosen breathing patterns and tests with fixed breathing rates in normal volunteers. Measures of respiratory muscle endurance-maximum load tolerated, mean mouth pressure at maximum load and peak pressure at maximum load were reproducible over three tests with the spontaneously chosen breathing pattern. There was no difference in these measurements between the three tests with fixed breathing frequency. There was no difference in tidal volume, inspiratory time, and the ratio of inspiratory time to total breath duration between the tests in which breathing pattern was spontaneously chosen; there was a difference in these measurements between the tests with a fixed breathing frequency. We conclude that regulation of breathing frequency is unnecessary in the two-minute threshold loading test to obtain reproducible results for measures of respiratory muscle endurance.

Squeeze and Entraining Motion in Nonconformal Line Contacts. Part II—Elastohydrodynamic Lubrication

A fast numerical approach to the solution of elastohydrodynamic lubrication (EHL) of line contacts in combined entraining and normal squeeze motion is developed. The initial conditions for the pressure profile, the central normal squeeze velocity, and the location of the outlet boundary at any specified dimensionless load and dimensionless entraining velocity were obtained from the hydrodynamic lubrication study in Lee and Hamrock (1988). The pressure and film thickness were obtained by solving the transient Reynolds, elasticity, rheology, and time-dependent central squeeze velocity equations. The squeeze effect on this transient EHL problem has been proved in that the maximum peak pressure was always higher than the maximum pressure calculated at the steady-state condition. The needle-shaped pressure profile during the transient process produced a dimpled shape near the center of the contacts. In general, the maximum peak pressure increased with increasing dimensionless load, decreasing dimensionless entraining velocity, and increasing dimensionless materials parameter. The dynamic performance parameters were plotted and are a function not only of the dimensionless velocity parameter (as described in Lee and Hamrock, (1988)), but also of the dimensionless load, the dimensionless entraining velocity, and the dimensionless materials parameter. The major factor causing the pressure gradient to be infinity during the transient process was the viscosity. A non-Newtonian fluid is suggested to execute the problem for high load and low entraining velocity.

Mechanism of action of neurotensin at the ileocecal sphincter region

Neurotensin, a neuropeptide identified in the distal small intestine, plays an unclear role in ileocecal sphincter regional function. The purpose of this study was to determine the effect and mechanism of action of neurotensin on the feline ileocecal sphincter (ICS), proximal colon, and distal ileum. Intraluminal pressures were recorded at these sites in anesthetized cats after superior mesentric artery injection of neurotensin. Dose dependent tonic and phasic contractions were seen at all sites. Peak pressure responses were seen at the maximal dose used and were greater for the ICS than the distal ileum and the proximal colon. The threshold dose for peak pressures for neurotensin was 0.05 μg/kg for all sites with the maximal peak pressures occurring at the maximal dose used (100 μg/kg). The motility index (MI [number of contractions × mean amplitude of contractions]) was determined for three minutes before and after neurotensin injection. The change in the motility index after neurotensin increased at doses above 0.05 μg/kg for the ileum and the ICS and 0.25 μg/kg for the colon. Maximal responses for the motility index were seen at 1 μg/kg for the distal ileum, and 10 μg/kg for the ICS and the proximal colon, with the greatest response seen at the ICS. Neurotensin-induced ICS relaxation was seen at 1 μg/kg (50 ± 10%, p < 0.01) in 33% of cats. The contractile responses of the distal ileum and the proximal colon were not inhibited by naloxone, trimethaphan, tetrodotoxin, or atropine. The ICS contractile response was decreased by tetrodotoxin by 53%, p < 0.05. The alpha 2 antagonist, yohimbine reduced the neurotensin induced ICS contraction from 31.6 ± 3.4 to 21.9 ± 3.3 mm Hg, p < 0.05. Prazosin had no effect on neurotensin-induced contractions. In the presence of cimetidine and diphenhydramine, trimethaphan did not affect the neurotensin-induced contractile response at all three sites. However, neurotensin inhibited contractions induced by trimethaphan alone at all three sites. Conclusions: 1. Neurotensin causes a dose-dependent contractile response at the distal ileum, ICS, and proximal colon. 2. Neurotensin has an inhibitory effect at all three sites. 3. The contractile response at the distal ileum and the proximal colon is mediated via smooth muscle receptors. 4. The contractile response of neurotensin at the ICS is mediated partly via alpha 2 receptors and partly via smooth muscle receptors.

A study of the vapor explosion mechanism with single drops of high temperature liquids and volatile liquids. (2nd report Temperature effect of cold liquid and experiments with plural drops)

Vapor explosion after the collapse of vapor film around a single drop and plural drops of hot LiNO3 submerged in tapped ethanol, whose degree of subcooling is widely changed, are studied by photographic observation and pressure measurement. At small degree of subcooling the vapor bubble region expands rather gradually and the pressure curve has only a small peak which is correspond to the vapor film collapse. At large degree of subcooling the curve has three typical peaks, and the third peak is generally the maximum. The propagation phenomenon is photographed by plural drops experiments. Since the pressure curve of plural drops is similar with that of a single drop, the coherence of the phenomenon during the whole process is confirmed. A model for vapor explosion mechanism is proposed and discussed. The maximum pressure peak is considered to be depend on the same mechanism with that of the cavitation which generates at the collapse and reexpansion of cavitation bubbles.

モデルビンの壁圧 ＩＩ マスフロー排出速度と流動壁圧

The problems of predicting the dynamic peak pressures during mass flow have been investigated. In a portion of a vertical-sided silo, the stress fields adjacent to a wall have been derived by the observation of a flow pattern which shows simultaneous yield within the solids layer along the wall. An equation on the local passive yielding is presented in order to predict the peak pressures.Measurements of the wall pressure show that the equation predicts accurately the maximum peak pressures. In a portion of a convergent hopper, the stress condition during emptying has been examined by measurement of the static rearranged wall pressure distribution after flow, and the dynamic surcharge for the transition to be emplyed is predicted experimentally.

Percutaneous balloon valvuloplasty for treatment of congenital pulmonary valvular stenosis in children

Percutaneous balloon pulmonary valvuloplasty was performed in seven children with moderate to severe valvular pulmonary stenosis (right ventricular to pulmonary artery pressure gradient greater than 50 mm Hg). All patients experienced a decrease in right ventricular peak systolic pressure from 108 +/- 30 to 60 +/- 5.6 mm Hg (p less than 0.001), decrease in right ventricular to pulmonary artery gradient from 90.1 +/- 30 to 38.8 +/- 5 mm Hg (p less than 0.001) and increase in pulmonary valve area from 0.33 +/- 0.06 to 0.55 +/- 0.15 cm2/m2 (p less than 0.001). In the two patients who underwent supine bicycle exercise before and after valvuloplasty, a significant decrease in both the maximal right ventricular peak systolic pressure (212 to 140 and 175 to 125 mm Hg, respectively) and in right ventricular to pulmonary artery peak pressure gradient (185 to 110 and 151 to 85 mm Hg, respectively) occurred. All patients tolerated the procedure well and no serious complications were observed. It is concluded that percutaneous balloon valvuloplasty is a safe and effective method for relief of right ventricular obstruction due to moderate or severe valvular pulmonary stenosis. However, long-term results remain unknown.

Bronchopulmonary Dysplasia

In their detailed study of the long-term survivors of bronchopulmonary dysplasia (BPD) Smyth and colleagues1 contrast their findings of a high incidence of abnormal pulmonary function in early childhood with the commonly held view that pulmonary function becomes normal in most children surviving BPD.2 However, they do not give us detailed parameters of the mode of intermittent positive pressure ventilation (IPPV) used on their patients, in particular maximum peak pressures, inspiratory: expiratory ratios and rates, or type of pressure wave curves generated by the ventilators used.

The diffraction of short duration impulsive sound waves by an artificial head

The acoustical effects of the human head, the pinna, and the auditory canal, separately and when combined, were obtained by means of an artificial head. In addition to the well known resonance at about 3·1 kHz caused by the auditory canal, two broad resonances caused by the concha and the pinna were observed at higher frequencies. The pinna contributes to an increase of the monaural loudness of the shock waves when the sound source is behind the head. The opposite is true when the head is turned towards the sound source. The maximum peak pressure gain and the maximum loudness by monaural hearing is obtained when the sound waves are impinging on the head at an angle of 40 to 50 degrees from the frontal direction. In the high frequency range the results reflect the advantage of using impulsive sound waves in preference to continuous sound waves even in rather good anechoic rooms.

Bedside Criteria for Discontinuation of Mechanical Ventilation

The purpose of this study was to determine bedside criteria for discontinuation of mechanical ventilation. The resting minute ventilation (MV), maximal voluntary ventilation (MVV) and peak negative pressure on maximal inspiration (PNP) were studied in 100 consecutive patients receiving assisted ventilation. Seventysix patients (Group 1) had MV less than 10 L/min and could double the MV with an MVV maneuver. All Group 1 patients could have mechanical ventilation discontinued. Seventeen patients (Group 2) could not double their resting MV with an MVV maneuver and required further ventilatory assistance. Seven patients (Group 3) could not double their resting MV with an MVV maneuver but did not require further mechanical ventilation. Patients whose PNP was greater than 30 cm H2O less than atmospheric were always able to have mechanical ventilation discontinued. The ease with which these measurements can be performed at the bedside and their high degree of predictability make them useful in acute respiratory care. The purpose of this study was to determine bedside criteria for discontinuation of mechanical ventilation. The resting minute ventilation (MV), maximal voluntary ventilation (MVV) and peak negative pressure on maximal inspiration (PNP) were studied in 100 consecutive patients receiving assisted ventilation. Seventysix patients (Group 1) had MV less than 10 L/min and could double the MV with an MVV maneuver. All Group 1 patients could have mechanical ventilation discontinued. Seventeen patients (Group 2) could not double their resting MV with an MVV maneuver and required further ventilatory assistance. Seven patients (Group 3) could not double their resting MV with an MVV maneuver but did not require further mechanical ventilation. Patients whose PNP was greater than 30 cm H2O less than atmospheric were always able to have mechanical ventilation discontinued. The ease with which these measurements can be performed at the bedside and their high degree of predictability make them useful in acute respiratory care.

New Test Techniques for Evaluating the Compatibility of Materials with Liquid Oxygen under Impact

The current drop-weight test methods for evaluating the compatibility of materials with liquid oxygen under impact are briefly discussed, with particular emphasis upon the characteristically poor repeatability of the “threshold value” impact sensitivity ratings yielded by these methods. It is pointed out that this trait is primarily due to the poor statistics of the test procedures used. It is further shown that impact sensitivity alone, even when measured by the most accurate and reliable technique, is not an adequate description of the potential fire or explosion hazard of a material; reaction intensity must also be considered. With this background, typical results from two new test techniques are presented and discussed. In one of these, impact sensitivity is measured in terms of the drop height at which a material has a 50% probability of reaction. In the other, reaction intensity is measured in terms of the maximum peak pressure of the air shock wave generated by the reaction. Presented at the 23rd A...