Maximum Negative Pressure Research Articles

Pulmonary function testing in spinal cord injury: correlation with vital capacity.

Spinal cord injury (SCI) causes restrictive ventilatory changes, with reductions in vital capacity, functional residual capacity, and expiratory reserve volume. Vital capacity (VC) often is used as an indicator of overall pulmonary function in these patients. In an effort to determine the extent to which VC correlates with other pulmonary function tests, 52 patients with recent acute traumatic SCI underwent complete pulmonary function testing. Statistical relationships were determined between VC and nine other tests. VC was found to be significantly correlated with forced expiratory volume in 1 s, inspiratory capacity, expiratory reserve volume, functional residual capacity, residual volume (RV), total lung capacity (TLC), and RV/TLC ratio, but not with maximum positive expiratory pressure nor with maximum negative inspiratory pressure. The excellent correlations between vital capacity and nearly all of the other pulmonary function tests support the use of VC as a single global measure of overall ventilatory status in SCI patients.

A survey of the acoustic outputs of diagnostic ultrasound equipment in current clinical use

Surveys published up to 1991 have highlighted a steady increase in the acoustic outputs from diagnostic ultrasound equipment. Since 1991 we have made measurements of the maximum peak negative pressure (p−) and spatial peak temporal average intensity ( I SPTA) produced by 223 probes from 82 scanning systems in current clinical use in the Northern Region in the UK. Measurements have also been made of the maximum total acoustic power generated by 45 probes from 17 scanners. The results from these measurements are presented in this article and compared to the results of a similar survey of equipment from both the Northern and Wessex Regions in the UK and published in 1991. The comparison shows that measured I SPTA values have increased approximately sixfold in B mode and approximately threefold in colour Doppler mode. Also, measured total acoustic power values have doubled in pulsed Doppler mode. The present survey also draws attention to some particularly high I SPTA values obtained from a number of probes and scanning systems. This survey has shown that measurements of acoustic outputs from diagnostic ultrasound scanners in current clinical use are substantially higher than reported in earlier surveys and, for certain scanners, the acoustic outputs from scanned beam modes of operation can reach levels hitherto only found in pulsed Doppler mode.

建物内特殊継手排水システムの開発プロセスに関する技術報告

This report introduces development of a drainage system equipped with special fitting inside buildings and verification of permissible drain flow rate in the system by adapting to an existing building design as follows. (1)The basic performance of the fitting is obtained making maximum negative pressure in drain pipe and air velocity in stack vent pipe as indexes through an experiment at 10 floors high tower. (2)The permissible drain flow rate is defined by giving steady and fixture drain flows from multiple floors. (3)The verification test of permissible drain flow rate is conductted by using the drainage system in super-high rise apartment.

Long-term results of fat transplantation: clinical and histologic studies.

Nine cases of idiopathic constitutional subcutaneous fat atrophy in the cheek area during the years 1988-1992 were treated by the autologous transplantation of fat for purely aesthetic reasons. The fat graft suspension was obtained by the low-power aspiration technique with the use of a vacuum pump. The contour defects were initially overcorrected by approximately 50 percent more volume than required. The patients were followed up for 1.5 to 4.5 (mean, 3.5) years. Contrary to the experience of others, only the partial resorption of the transplanted fat occurred. This result was verified by six biopsy specimens obtained in the time range of 7 to 36 months after transplantation. The additional injections of fat were not necessary. Delicate tissue handling and the small total amount of fat transplanted by careful distribution in the recipient tissues are probably the factors responsible for the long-lasting improvement in these patients. As an experiment, suction of fat under -0.5 atm and -0.95 atm was performed in five patients undergoing abdominal liposuction. Aspiration under maximum negative pressure caused partial breakage and vaporization of the fatty tissue. The diameter of the fat cells in the remaining beads of fat was in all five cases mechanically distended and thus was larger than in the lipocytes extracted at -0.5 atm.

A column study of static nonequilibrium fluid pressures in sand during prolonged drainage

In the design of layered soil systems, such as the design of liners or covers over unsaturated soil, a key design concern is the magnitude of negative fluid pressure that will develop along the base of the liner or cover. In the absence of evaporation or vapour migration, the maximum negative fluid pressures will develop near the cessation of drainage. Previous theoretical analyses and numerical modelling of these systems have indicated that this pressure will be the pressure at which an underlying sand reaches its residual water content. The hydraulic conductivity of the sand at these pressures is so small that "static" nonequilibrium pressures are sustained over long periods of time. In this note, laboratory verification is provided for the magnitude of these pressures based on drainage of a fine and coarse sand column. Key words : covers, liners, air-entry value, residual saturation, layering, drainage.

Bronchospirometry and Separate Measurement of Occlusion Pressure Before and After Lung Resection Using a Double-Lumen Endotracheal Tube

To assess the distribution of ventilation to each lung, we measured ventilation and maximum negative airway pressure during occluded inspiratory effort (Pmax) of the individual lungs in eight male patients immediately before and after right upper lobectomy using a double-lumen endotracheal tube at a constant depth of enflurane anesthesia (end-tidal concentration 1.7%). Compared with the breathing pattern observed immediately before surgery, minute ventilation, Pmax, and respiratory frequency significantly increased immediately after the surgery, whereas tidal volume was unchanged. Bronchospirometry revealed that tidal volumes on the nonoperated side significantly increased after the operation. In contrast, tidal volumes on the operated side significantly decreased after the operation and were associated with significantly smaller Pmax obtained from unilateral airway than those of the nonoperated side postoperatively. These results indicate that there are considerable differences in ventilatory function between the lungs on the operated side and nonoperated side. The lung on the nonoperated side can partially compensate for the impaired ventilatory function on the operated side.

Efficacy of pressure support in compensating for apparatus work.

Breathing through an endotracheal tube, connector, and ventilator demand valve imposes an added load on the respiratory muscles. As respiratory muscle fatigue is thought to be a frequent cause of ventilator dependence, we sought to examine the efficacy of five different ventilators in reducing this imposed work through the application of pressure support ventilation. Using a model of spontaneous breathing, we examined the apparatus work imposed by the Servo 900-C, Puritan Bennett 7200a, Engstrom Erica, Drager EV-A or Hamilton Veolar ventilators, a size 7.0 and 8.0 mm endotracheal tube, and inspiratory flow rates of 40 and 60 l/min. Pressure support of 0, 5, 10, 15, 20 and 30 cm H2O was tested at each experimental condition. Apparatus work was greater with increased inspiratory flow rate and decreased endotracheal tube size, and was lowest for the Servo 900-C and Puritan Bennett 7200a ventilators. Apparatus work fell in a curvilinear fashion when pressure support was applied, with no major difference noted between the five ventilators tested. At an inspiratory flow rate of 40 l/min, a pressure support of 5 and 8 cm H2O compensated for apparatus work through size 8.0 and 7.0 endotracheal tubes and the Servo 900-C and Puritan Bennett 7200a ventilators. However, the maximum negative pressure was greater for the Servo 900-C. The added work of breathing through endotracheal tubes and ventilator demand valves may be compensated for by the application of pressure support. The level of pressure support required depends on inspiratory flow rate, endotracheal tube size, and type of ventilator.

Inspiratory work imposed by continuous positive airway pressure (CPAP) machines: the effect of CPAP level and endotracheal tube size.

Inspiratory work imposed by Continuous Positive Airway Pressure (CPAP) machines has been a matter of concern. The imposed inspiratory work of CPAP machine circuits (Wcir) and the effect of the total breathing apparatus with endotracheal tube (ETT) and connector included in the circuit (Wapp), were measured in three continuous flow (CF) and various configurations of three demand flow (DF) CPAP machines. The performance was assessed at 0, 5, 10 and 15 cmH2O CPAP using a Michigan Instruments Test Lung Model 1600, internal compliance set at 50 ml/cmH2O, driven at square wave inspiratory flows (VI) of 20, 40 and 60 l/min at a tidal volume of 500 ml. Work, expressed in mJ/l, was calculated from the area of pressure-volume loops. Inspiratory work, Wcir and Wapp, was dependent upon the particular CPAP machine, VI and ETT size, but not upon CPAP level, being maximum at VI 601/min and with ETT 7.0 mm i.d. Work values (Wcir) varied from 50 to 325 mJ/l with both CF and DF machines and up to 1100 mJ/l with ETT and connector (Wapp). No consistent advantage of CF over DF machines was demonstrated. There was little advantage of high gas flows (greater than 5 l/min) in various DF circuits. Within an individual machine maximum negative pressures generated during inspiration correlated with both Wcir and Wapp.

Measurement of intra-oral negative air pressure during dummy sucking in human newborn

Non-nutritive sucking on a dummy was studied in 23 clinically normal full-term infants with a mean gestational age of 40 weeks (SD 1.5). The intra-oral negative air pressure was measured by a miniature air pressure transducer inside a commercial dummy. The sucking pattern in these infants was always composed of periodical changes between sucking burst and interburst periods with a mean rate of 5.3 (SD 1.6) bursts per minute. The mean rate of sucks within a sucking burst was 1.7 (SD 0.2) sucks/sec. The mean value of maximum intra-oral negative air pressure among newborn was 58 mbar (SD 14.6) during dummy sucking. During interburst periods the negative air pressure remained at a mean value of 8.4 mbar (SD 5.8).

Correlation between integrated evoked EMG and respiratory function following atracurium administration in unanaesthetized humans

In six healthy volunteers, integrated evoked electromyography (IEEMG) measured in response to ulnar nerve stimulation was correlated with respiratory function-tidal volume (VT), forced vital capacity (FVC), forced expiratory volume in one second (FEV1), maximum negative inspiratory pressure (NIP), hand grip (HG) and head-lift during steady-state infusion of subparalytic doses of atracurium. Studies were carried out at train-of-four T4/T1 = 0.2 and T4/T1 = 0.6. When T4/T1 = 0.2, all subjects had difficulty with swallowing and phonation, none could sustain any head-lift and HG was 26 per cent of control. However, VT was normal, FVC was 80 per cent, FEV1 was 82 per cent, and NIP was 50 per cent of control. AT T4/T1 = 0.6, all assessments of peripheral strength were normal, and all respiratory measurements were not significantly different from control, except for NIP which was 73 per cent of control (P less than 0.05). We conclude that an IEEMG of 0.6, recorded from the hypothenar muscles, in unanaesthetized subjects is consistent with near normal respiratory function.

A novel method to control P+/P- ratio of the shock wave pulses used in the extracorporeal piezoelectric lithotripsy (EPL)

There is growing evidence that acoustic cavitation plays an important role in stone fragmentation during extracorporeal shock wave lithotripsy (ESL) treatment. In addition, side effects of the treatment, such as the hemorrhage and destruction of the tissue in the vicinity of the stone are also ascribed to cavitation phenomenon. Since cavitation is associated with the maximum negative pressure in the shock pulse, it would thus appear that possibility of controlling this pressure would be desirable in ESL applications. This paper describes a novel technique developed to control the ratio of compressional peak (P+) to rarefactional peak pressure (P-) of the shock wave for use in lithotripsy treatment. The procedure is based on the finite amplitude wave generation by focused piezoelectric transducers and subsequent interaction of the shocked waves in the common focal region. The highly asymmetrical shock wave is produced in the focal region by providing an appropriate time delay to each of the high voltage electrical excitation signals which drive the transducers. The degree of relative reduction of negative halfcycles and the corresponding positive halfcycles amplification increases with the number of the acoustic sources used. The practical implementation of the shock wave generator was obtained by using 5 cm diameter, focused 1 MHz transmitter, and additional transducers of identical construction having frequencies corresponding to the harmonics and subharmonics of the 1 MHz frequency. The importance of the results for the future development of lithotripters, and stone treatment efficiency is pointed out.

Inspiratory work and response times of a modified pediatric volume ventilator during synchronized intermittent mandatory ventilation and pressure support ventilation.

Volume ventilation by demand flow ventilators significantly increases work of breathing during inspiration. Although various ventilator modifications and different modes of ventilation have been developed, there have been few studies regarding imposed work of breathing in infants and children. This study was designed to evaluate several modifications of a commercially available demand flow ventilator designed to shorten response time (tr) and decrease the imposed work (Wi) involved in opening the demand valve. Minimum withdrawal volume (Vmin), maximum negative pressure (P mneg), and tr were measured. Wi was defined as the product of Vmin and P mneg. Seven Siemens Servo 900C ventilators were tested under 16 different trial conditions with four variables: 1) mode of ventilation (synchronized intermittent mandatory ventilation [SIMV] vs. pressure support ventilation [PSV]); 2) caliber of circuit tubing (adult vs. pediatric); 3) location of airway pressure monitor (distal vs. proximal); and 4) ventilator trigger sensitivity (0 cm H2O--high vs. -2 cm H2O--low). Vmin, Pmneg, and Wi were all decreased (P less than .05) while tr was unaffected by changing ventilator trigger sensitivity from low to high. Wi was decreased by pediatric tubing and proximal airway pressure monitoring only when low trigger sensitivity was used. PSV and proximal airway monitoring shortened tr. The authors conclude that the use of pediatric circuit tubing and proximal airway pressure monitoring with a Siemens Servo 900C ventilator significantly improved ventilator performance.

滲出性中耳炎と耳管

The pathogenesis of otitis media with effusion (OME) in relation to the eustachian tube was investigated clinically and experimentally. Clinical observations revealed the follow i ng characteristic pathophysiological state of OME:1. Among 300 ears with OME, organic obstruction or stenosis was rare (16%), but 95% of the patients could not equilibrate middle ear negative pressure by swallowing.2. Even in the convalescent stage, most of the OME patients (91 %) could not equilibrate middle ear nagative pressure by swallowing, and this dysfunction of th e eustachian tube was thought to be a predisposing factor for OME.3. Middle ear pressure of 30 ears of OME children measured transtubally using a catheter pressure transducer were slight negative, being within 100 m mH2O in m ost cases ( -54.0±58.9mmH2O).4. After releasing middle ear negative pressure by myringotomy, middle ear effusion was excreted transtubally within one day in 24 of 30 ears with OME (80% ). Experimental studies using cats revealed the following results:1. Abolishment of the active ventilatory function of the eustachian tube by transecting the tensor veli palatini muscle and pterygoid hammulotomy rarely caused OME (7.1%), indicating that the ‘Hydrops ex vacuo’ theory can not adquately explain the etiology of OME.2. Mean negative middle ear pressure of -150.7 mmH2O was induced by ciliary clearance function of the eustachian tube within a few hours and -27.2 mmH2O was induced by muscular clearance function within three to four minutes when there was fluid in the closed middle ear space.3. Transtubal clearance of middle ear fluid was significantly impaired in ears with tubal ventilatory dysfunction compared with normal ears.4. Experimental OME induced by intratympanic injection of E. coli endotoxin was long-lasting when the tubal ventilatory function was impaired. From these clinical and experimental studies, the development of OME was not considered to be initiated from tubal obstruction but from fluid production within the middle ear. As a next step, negative pressure develops in the middle eardue to the tubal clearance function of the fluid. The important thing is that the eustachian tube of OME patients can not release this negative middle ear pressure, therefore, negative pressure progresses to be a state where the maximum negative pressure and fluid retention coexist within the closed middle ear space. This irreversible pathophysiological state continues until transtympanic ventilation such as myringotomy is performed.In conclusion, the eustachian tube dysfunction in OME patients is not the primary etiological factor of OME, but plays an important role in the characteristic long-lasting course of OME.

Priming with Atracurium

Priming with atracurium was evaluated by dividing 39 patients into 2 groups. All received 0.2 mg IV glycopyrrolate and fentanyl, 50 micrograms IV. Group 1 received saline, group 2 received 0.06 mg/kg atracurium and a stop watch was started. After 3.5 min the patients were asked to lift their heads and maximum negative inspiratory pressure (MIP) was measured. Anesthesia then commenced with thiopental and a twitch monitor was applied to the ulnar nerve. At 5 min group 1 received 0.36 mg/kg atracurium and group 2 was given 0.30 mg/kg atracurium. At 6.5 min intubation was accomplished in all but one patient in group 1 and all but one in group 2. Mean T4/T1 ratios at 90 sec were 0.73 in group 1 and 0.51 in group 2. This difference was statistically significant (P less than 0.001). Bucking on the endotracheal tube occurred in 72% of patients in group 1 and 62% of those in group 2 (not significant). Intubating conditions were "excellent" in 56% of those in group 1 and 75% in group 2 (not significant). "Good" conditions were seen in 33% of group 1 and 15% of group 2 patients (not significant). "Fair" conditions were noted in 6% of patients in group 1 and 5% of group 2 patients (not significant). The time to maximum twitch depression was 11.3 min and 11.5 min in groups 1 and 2 respectively (not significant). All patients in group 1 could sustain head lift whereas four patients in group 2 could not (not significant).(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement and Correlation of the Striations in a Liquid Film During Sudden Separation

Experiments are described of the separation at known velocity of uniformly thick oil films of various viscosities and initial thicknesses. Separation of the film occurred in patterned striations or in un-patterned direct cleavage. The width of the striations correlated approximately with the square root of the initial film thickness. This correlation includes other data in the literature. The calculated negative pressures in the striations suggest that the separation mode changed from striations to tensile cleavage at tensile stresses greater than about four atmospheres. It appears that the rate of damage and the damage pattern in ASTM cavitation erosion tests can be correlated with the maximum negative pressure occurring in the striations.

Effect of respiratory loading on the relationship between occlusion pressure and diaphragm EMG during hypoxia and hypercapnia.

In 7 conscious, unsedated goats with chronically implanted diaphragm electrodes, the effect of respiratory loading on the relationship between occlusion pressure and diaphragm EMG was studied. Diaphragm electrical activity (ED) quantified by the moving average technique was measured in separate trials during progressive hyperoxic hypercapnia and progressive isocapnic hypoxia, both before and after inspiratory resistance had been increased by externally applied loads. Airway occlusion was performed during inspiration on random breaths at functional residual capacity, and the maximum negative pressure (Pmax) was measured. In all 7 goats, occlusion pressure was greater with external loads (EL) than control. The peak ED of unoccluded breaths was greater with EL than control in all animals during hypoxia but in only 3 of the animals during hypercapnia. In half of the trials, the ratio of Pmax to ED of occluded or unoccluded breaths was higher with EL than control. In the remaining studies, the ratio was the same. FRC was unaffected by EL. In the one goat in which it was measured, intercostal EMG was also greater during EL than control. These results suggest that the inspiratory muscles other than the diaphragm are recruited during EL causing the Pmax to ED ratio to rise even if neuromechanical coupling remains unchanged. It is speculated that in conscious, unsedated animals, acute increases in the resistance to air flow affect the distribution of respiratory motor activity.

Negative pressure in the middle ear by ciliary propulsion of mucus through the eustachian tube

Mucus was placed in the middle ears of 11 cats. A needle and stop-clock placed in the bulla communicated with the tympanic cavity. The pressure changes in the needle were transcribed on a flowing graph via a transducer in communication with the stop-clock. Negative pressure developed in each test ear. The average maximum negative pressure was 12 mm Hg with a minimum of 2 mm Hg and maximum of 24 mm Hg. The peak negative pressure, reached in 30 to 60 min. in most ears, occurred in 10 min. in one and in 3 hrs. in another. The qualitative results show all ears developed a negative pressure when mucus was in the tympanic cavity. The quantitative data suggest an average maximum negative pressure of 12 mm Hg reached at about 1 hr.

The Use of Airway Occlusion in Infants

The Use of Airway Occlusion in Infants

The aetiology of otitis externa—A new concept

This paper reports the results of middle ear pressure measurements on 33 patients with recurrent otitis externa and compares the results with those of 21 normal subjects. The maximum negative pressure in the control group was -50 mm. of water, while 17 patients (52%) with recurrent otitis externa recorded measurements of -100 mm. of water or more. It is postulated that chronic Eustachian tube dysfunction may interfere with the normal migration of epithelium from the tympanic membrane along the external auditory meatus leading to irritation and chronic infection. The treatment in these cases should be directed at the underlying cause of the Eustachian tube dysfunction.

Dynamic response of a fluid-filled spheroidal shell—An improved model for studying head injury

The human head is modelled by considering the skull to be an elastic prolate spheroidal shell enclosing an acoustic medium which represents the brain. A suddenly applied, uniformly distributed, pressure is applied to the shell surface. Time histories of the distribution of stress in the shell and pressure in the fluid are obtained for material and geometrical parameters representative of a human head. It is found that there is a significant difference in the results obtained using this model from those obtained when the assumption of zero eccentricity, i.e. spherical geometry, is made, but not in the important maximum negative pressure developed in the fluid.