Role of bronchial basement membrane in airway collapse

Bronchial basement membrane is an elastic structure that has the potential to be load bearing and thus to contribute to the mechanical stiffness of the bronchus. To investigate this possible role, the membrane was modeled as a thin-walled linearly elastic tube surrounded by a uniform liquid on the outside and by air on the inside. When the external pressure on such a tube exceeds the internal pressure by a critical amount, the tube buckles reversibly into two or more folds. The critical buckling pressure varies as the square of the number of folds. The analysis was used to investigate the collapse behavior of the model tube into patterns ranging from 2 to 24 folds. This showed that the resistance to collapse increases rapidly as the number of folds increases. Data in the literature lead to the conclusion that the pressures involved in collapsing the tubes are probably in the physiological range. It is suggested, on the basis of the model results reported here, that bronchial hyperresponsiveness could be related to the number of folds into which the basement membrane buckles when the bronchial muscle contracts. A reduced number of folds would yield an increased response.     

Replicase proteins as determinants of phloem-dependent long-distance movement of tobamoviruses in tobacco

Summary The turgor pressure of growing pollen tubes of the lily (Lilium longiflorum Thunb.) has been recorded using a turgor pressure probe. Insertion of the probe's micropipette was routinely accomplished, providing recording periods of 20 to 30 min. Probe insertion did not affect tube growth. The stable turgor values ranged between 0.1 and 0.4 MPa, the mean value being 0.209 ± 0.064 MPa (n=106). A brief increase in turgor, generated by injection of oil through the pressure probe, caused the tube to burst at its tip. Burst pressures ranged between 0.19 and 0.58 MPa, that is, individual lily pollen tubes do not withstand turgor pressure approaching twice their regular turgor pressure. In contrast, parallel experiments using the incipient plasmolysis technique yielded a mean putative turgor pressure of 0.79 MPa either using sucrose (n=24) or mannitol (n=25). Surprisingly, turgor pressure was not significantly correlated with tube growth rate which ranged from zero to 13 m/min. Nor did it correlate with tube length over the tested range of 100 to 1600 m. In addition the influence of the medium's osmolality was surprisingly low: raising the external osmotic pressure from 0.36 to 1.08 MPa, with sucrose or mannitol, only caused mean turgor pressure to decline from 0.27 to 0.18 MPa. We conclude that growing lily pollen regulates its turgor pressure remarkably well despite substantial variation in tube growth rate, tube length, and osmotic milieu.     

Die Cnidogenese der Octocorallia (Anthozoa,Cnidaria): I. Sekretionund Differenzierung von Kapsel und Schlauch

The ultrastructural differentiation of capsule and its relation to tube development is described in several Octocorallia species(Alcyonaria: Alcyonium digitatum, Parerythropodium coralloides, Cornularia cornucopiae, Paralcyonium elegans; Pennatularia: Pteroeides spinosum, Veretillum cynomorium; Gorgonaria: Pseudopterogorgia aerosa), all of which have only one type nematocyst. In the Octocorallia, capsule and tube are secreted successively by the Golgi apparatus associated with a primary centriolar complex. During the secretion of the external tube, the outer capsular wall (sclera) is structurally differentiated; inside the capsule the material of the inner capsular wall is separated from the later capsular content (matrix). The primary wall differentiation enables the capsules to grow after capsular secretion has been completed. Following tube secretion, the external tube is completely transferred into the capsule, without the tube wall being transformed into capsular wall, as previously suggested (Westfall, 1966; Ivester, 1977). During early invagination of the tube wall, the coarse, granulated matrix of the external tube is transferred into the internal tube. From this material the spines are developed, which are observed before the tube is completely transferred into the capsule. By a secondary wall differentiation the previously structureless inner capsular wall changes to a complex structure, extending again the capsule, thus mixing the capsular content and enabling the tube to shift to a position, which corresponds with that of mature capsules. These observations demonstrate for the first time the differentiation of the capsule and its close relationship to the differentiation of the tube in nematocysts of Octocorallia.     

Effect of vessel compliance on the in-vitro performance of a pulsating respiratory support catheter

Intravena caval respiratory support (or membrane oxygenation) is a potential therapy for patients with acute respiratory insufficiency. A respiratory support catheter is being developed that consists of a bundle of hollow fiber membranes with a centrally positioned pulsating balloon to enhance gas exchange. This study examined the influence of vessel compliance on the gas exchange performance of the pulsating respirator, support catheter. Polyurethane elastic tubes were fabricated with compliance comparable to that measured in bovine vena cava specimens. The gas exchange performance of the respiratory catheter was studied in an in-vitro flow loop using either the model compliant tube or a rigid tube as a "mock" vena cava. Balloon pulsation enhanced gas exchange comparably in both rigid and model compliant vessels up to 120 bpm pulsation frequency. Above 120 bpm gas exchange increased with further pulsation in the rigid tube, but no additional increase in gas exchange was seen in the compliant tube. The differences above 120 bpm may reflect differences in the compliance of the elastic tube versus the natural vena cava.     

Catheterization of pulmonary artery in rats with an ultraminiature catheter pressure transducer

Utilizing new materials and miniaturization techniques, an ultraminiature catheter pressure transducer for catheterization of the pulmonary artery (PA) has been developed and applied in intact, spontaneously breathing, anesthetized rats. The catheter arrangement consists of three components: 1) an SPR-671 ultraminiature pressure transducer (measuring catheter), 2) a plastic introducer (sheath) that is slipped over the measuring catheter, and 3) an external wire mounted on the outside of the introducer for bending its tip. The measuring catheter is first inserted through the right jugular vein into the right ventricle. The introducer is then slipped over it. The tip of the introducer is bent so that there is an angle of approximately 90 degrees or less to the shaft. The measuring catheter is advanced across the pulmonary valve into the PA. Measurements of pulmonary arterial pressure were made in five male Long Evans (364 +/- 7 g body wt) and five female Sprague-Dawley (244 +/- 7 g body wt) rats under control conditions. The effects of infusion of norepinephrine (0.1 mg.kg(-1).h(-1) iv for 20-min duration) were tested in Long Evans rats. Pulmonary arterial systolic pressure measurements were 34.0 +/- 0.8 and 29.5 +/- 0.4 mmHg, and diastolic pressure values were 23.6 +/- 0.8 and 18.1 +/- 0.6 mmHg in male Long Evans and female Sprague-Dawley rats, respectively. Norepinephrine induced an increase in pulmonary arterial systolic (40.8 +/- 0.1 mmHg) and diastolic (28.6 +/- 0.4 mmHg) pressures and an elevation in pulmonary vascular resistance from a control value of 0.093 +/- 0.003 to 0.103 +/- 0.004 mmHg.kg.min.ml(-1).     

An alternative method of endotracheal intubation of common marmosets (Callithrix jacchus)

Endotracheal intubation was carried out in 11 common marmosets (Callithrix jacchus). A commercially available tilting stand and a Miller laryngoscope blade were used to visualize the larynx. Anaesthesia was induced with alphaxalone (10.6 ± 1.6 mg/kg intramuscularly, followed by 3.2 ± 1.2 mg/kg intravenously). The diameter of the proximal trachea easily fitted an endotracheal tube made from readily available material (a 12 G 'over the needle' catheter). Once the tip of the endotracheal tube was at the level of the vocal folds, the tube had to be gently rotated through a 180° angle in order to pass through the larynx into the trachea. Assessment of the dimensions of the larynx and trachea, and comparison with external anatomical features of the animals (n = 10) showed that the length of the trachea could be predicted by multiplying the craniosacral length of the marmoset by a factor of 0.42.     

A Method for Collection of Bile in the Conscious Sheep

A method to collect bile directly from the hepatic duct is described for use in the sheep. The technique is a combination of the intestinal re-entrant cannulae and a catheter from the duodenal lumen to the hepatic duct. The cystic duct is ligated near its junction with the common bile duct. The catheter is fixed in the proximal visible end of the hepatic duct. One plastic cannula is fixed to the duodenum opposite to the opening of the common bile duct and the other is fixed in the same way about 15 cm posterior to the first one. The two plastic cannulae fixed together with a plastic tube serve as an extra-abdominal anastomosis. During the collection periods the bile duct catheter is passed through an opening in the wall of the connection tube into a collection bag that is fixed to the plastic cannulae. Between the collection periods the catheter ends in the lumen of the anastomosis.     

The Influence of Drag on Nonlinear Oscillatory Flow through Concentric Annulus

A mathematical model has been developed to study the effect of particle drag parameter and frequency parameter on velocity and pressure gradient in nonlinear oscillatory two phase flow. The main purpose is to apply the model to study the combined effect of introduction of the catheter and elastic properties of the arterial wall on the pulsatile nature of the blood flow. We model the artery as an isotropic thin walled elastic tube and the catheter as a coaxial flexible tube. Blood is modeled as an incompressible particulate viscous Newtonian fluid. Perturbation technique has been applied to find the approximations for velocity and pressure gradient up to second order. Numerical solutions are investigated with graphical presentations to understand the effects of drag parameter, frequency parameter and phase angle on velocity along radial direction and pressure gradient along axial directions. As the drag parameter increases, mean pressure gradient and mean velocity will be decreased. As frequency parameter increases mean velocity profile bends near the outer wall. Due to elastic nature of artery wall, a thin catheter experience small oscillations and a thick catheter remains stationary inside the artery. Finally, the effect of catheterization on various physiologically important flow rate characteristics—mean velocity, mean pressure gradient are studied for a range of different catheter sizes, particle drag parameter and frequency parameters.     

Functional morphology of regular echinoid tests (Echinodermata,Echinoida): a finite element study

Functional morphology of the calcareous test ofEchinus esculentus was investigated by parametric finite element analysis, an engineering technique developed for numerical analysis of the behaviour of complex structures responding to external forces. Finite element models of the test were generated by methods of Computer Aided Geometric Design (CAGD) to calculate the mechanical responses to different types of loading. The load cases included vertical, concentrated load at the apex, vertical, distributed load on the upper third of the test, internal pressure and tensile forces as introduced into the test by tube feet activity. The objectives were the shape of the test, the distribution of material and the alternating zones of porous and non-porous plates within the test.—Echinoid tests resist external loading without showing any specific points of failure. The thickened margins of the periproct and peristome apertures account for load-bearing capacity as well as the thickned meridional structures which carry a greater portion of stress than the thinner parts of the test. Distribution of material is not a response to concentrated loads on the apex nor to self-weight. Taken strictly, echinoid tests are not thin (or membrane) shells. Under loading, bending moments occur which influence the stress state in the entire test. The pneu hypothesis could not be confirmed. Adaptation of the test shape or of the distribution of material as a response to internal pressure does not exist. Tests of regular echinoids are especially well adapted to the mechanical activity of the ambulacral tube feet, i.e. the shape of the test, its flattening towards the substrate, the outward bulge of the ambulacra and the differential distribution of material within the test.     

In vivo quantitative assessment of catheter patency in rats

Formation of fibrin sleeves around catheter tips is a central factor in catheter failure during chronic implantation, and such tissue growth can occur despite administration of anticoagulants. We developed a novel method for monitoring catheter patency. This method recognizes the progressive nature of catheter occlusion, and tracks this process over time through measurement of changes in catheter resistance to a standardized 1 mL bolus infusion from a pressurized reservoir. Two indirect measures of catheter patency were used: (a) reservoir residual pressure and (b) reservoir discharge time. This method was applied to the study of catheter patency in rats comparing the effect of catheter material (silastic, polyurethane, Microrenathanetrade mark), lock solution (heparin, heparin/dexamethasone) and two different cannulation sites (superior vena cava via the external jugular vein, inferior vena cava via the femoral vein). Our findings reveal that application of flexible smaller-size silastic catheters and a dexamethasone lock solution resulted in prolonged catheter patency. Patency could be maintained over nine weeks with the femoral vein catheters, compared with five weeks with the external jugular vein catheters. The current method for measuring catheter patency provides a useful index for the assessment of tissue growth around the catheter tip. The method also provides an objective and quantitative way of comparing changes in catheter patency for different surgical methods and catheter types. Our method improves on the conventional method of assessing catheter occlusion by judging the ability to aspirate from the catheter.     

Anatomical and functional characteristics of carotid sinus stimulation in humans

Transmission characteristics of pneumatic pressure to the carotid sinus were evaluated in 19 subjects at rest and during exercise. Either a percutaneous fluid-filled (n = 12) or balloon-tipped catheter (n = 7) was placed at the carotid bifurcation to record internal transmission of external neck pressure/neck suction (NP/NS). Sustained, 5-s pulses, and rapid ramping pulse protocols (+40 to -80 Torr) were recorded. Transmission of pressure stimuli was less with the fluid-filled catheter compared with that of the balloon-tipped catheter (65% vs. 82% negative pressure, 83% vs. 89% positive pressure; P < 0.05). Anatomical location of the carotid sinus averaged 3.2 cm (left) and 3.6 cm (right) from the gonion of the mandible with a range of 0-7.5 cm. Transmission was not altered by exercise or Valsalva maneuver, but did vary depending on the position of the carotid sinus locus beneath the sealed chamber. These data indicate that transmission of external NP/NS was higher than previously recorded in humans, and anatomical variation of carotid sinus location and equipment design can affect transmission results.     

Regulation of stretch-activated ANP secretion by chloride channels

This study was aimed to define roles of stretch-activated ion channels (SACs), especially Cl(-) channels, in regulation of atrial natriuretic peptide (ANP) secretion using isolated perfused beating atria. The volume load was achieved by elevating height of outflow catheter connected to isolated rat atria and the pressure load was achieved by decreasing diameter of outflow catheter. Both methods increased atrial contractility similarly although volume load was different (736microl for volume load vs. 129microl for pressure load). Atrial stretch by volume load markedly increased ECF translocation and ANP secretion but the pressure load slightly increased. The ANP secretion was positively correlated to workload generated by volume or pressure load. Treatment of atria with gadolinium, a blocker for SACs, attenuated the ECF translocation and the ANP secretion induced by volume load. A blocker for Ca2+-activated Cl(-) channel, niflumic acid (NFA), accentuated the ANP secretion induced by volume load whereas a blocker for swelling-activated Cl(-) channel, diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS), attenuated the ANP secretion. The ANP secretion of hypertrophied atria by volume load was markedly reduced and the augmented effect of NFA on volume load-induced ANP secretion was not observed. These results indicate that Cl(-) channels may differently regulate stretch-activated ANP secretion.     

Chronic double lumen intravenous cannulation of the unrestrained rat

Chronic double lumen intravenous cannulation was performed on the rat. The cannulation system consisted of a pulley assembly, protective tube, mounting post, and a double lumen cannula. Using a double lumen expanded catheter, a two-channel connection was made with the rat's vascular system through a single entry into the external jugular vein. The cannulation system permitted free animal movement in a large cage and simultaneous measurement of behavioral and physiologic variables. The procedure minimized stress and provided a simple alternative to other systems using two cannulas.     

Thermal sensation at index finger while applying external pressure at upper arm

In this study we focused on thermal sensation at fingertip under the influence of applied external pressure via a tourniquet at the upper arm. The perceived thermal sensation has found to be closely related to the skin temperature (Tsk) that is regulated by the skin blood flow (SkBF), whereas SkBF is easily influenced by external pressure. We thus hypothesized that the perceived thermal sensation, the Tsk and SkBF form such a cross-coupled triad that jointly affects our feeling of thermal comfort. Such interconnections among them were examined in this study using two protocols to investigate the perceived thermal sensation from a given heat stimulus under an exerted external pressure: (1) the SkBF and Tsk, at the right hand index finger under different external pressures at the right upper arm of one male subject, were monitored by a laser-Doppler flowmeter (LDF); (2) subjective thermal feelings (cold, normal and warm) at the right index fingertip of 10 test takers were recorded, while contacting a glass tube filled with water at different temperatures, with/without 50 mm Hg external pressure at the upper arm, while the temperatures of the glass tube and the index fingertip were recorded by an infrared camera. First, it is found that the SkBF and Tsk at the index fingertip reduced significantly with high external pressure applied at the upper arm, while the pressure from our daily clothing is not large enough to generate such an effect. Next, the applied pressure suppresses the variations in subjective sensory responses towards the thermal stimuli. Our hypothesis on the interconnections among the perceived thermal sensation, the Tsk and SkBF is thus confirmed. Overall, females appear more discerning to temperature change under the given conditions compared to males.     

Longitudinal tension variation in collapsible channels: a new mechanism for the breakdown of steady flow.

There are several mechanisms potentially involved in the breakdown of steady fluid flow in a collapsible tube under external pressure. Here we investigate one that has received little attention in the past: the fact that the longitudinal tension in the tube wall, T, decreases with distance downstream as a consequence of the viscous shear stress exerted by the fluid. If the tube is long enough, or the initial tension small enough, T may fall to zero before the end of the collapsible tube, and unsteady motion would presumably then ensue; this is what we mean by "breakdown." We study the phenomenon theoretically, when the flow Reynolds number is of order one, using lubrication theory in a symmetric two-dimensional channel in which the collapsible tube is replaced by membranes occupying a segment of each wall. The resulting nonlinear ordinary differential equations are solved numerically for values of the dimensionless parameters that cover all the qualitatively different types of solution (e.g., in which the channel is distended over all its length, collapsed over all its length, or distended in the upstream part and collapsed downstream). Reducing the longitudinal tension has a marked effect on the shape of the collapsible segment, causing it to become much more deformed for the same flow rate and external pressure. Indeed, the wall slope is predicted to become very large when the downstream tension is very small, so the model is not self-consistent then. Nevertheless, the parameter values for which T becomes zero are mapped out and are expected to be qualitatively useful.(ABSTRACT TRUNCATED AT 250 WORDS)     

SURGICAL DECOMPRESSION OF THE BOWEL IN PERITONITIS

In some circumstances peritoneal infection causes distention and crowding of the bowel to such an extent that the effect is that of intestinal obstruction and it is impossible to introduce a tube far enough by physiologic routes to bring about deflation. The pressure upon the diaphragm then may cause pain in breathing, with the result that the patient does not fully expand the lungs and atelectasis develops in the lower lobes. In such circumstances surgical intervention to relieve the pressure in the bowel may be indicated.An ordinary urethral catheter introduced through an incision in the intestine cannot be extended far enough to relieve pressure in more than a few loops.A method of using a Foley catheter and of advancing it for greater distances inside the bowel was used in five cases with good results and without complications.     

右心导管法测大鼠肺动脉压力的改良

目的:目前常用的测量大鼠肺动脉压力的右心导管法存在一定的缺陷,且很难得到典型的压力曲线图。本实验对大鼠经颈外静脉插管与测压的方法进行改良,同时与已有报道的实验结果进行比较,并提供正常SD大鼠右心房、右心室及肺动脉的压力参考值及典型的压力曲线图,以协助研究人员判断导管位置,及时调整导管的深度和方向,快速测出肺动脉压力。方法:雌雄不分的清洁级SD大鼠共30只,体重180~230 g,6~7周龄。应用自制的末端呈一弧形的PE-10管,采用改良后的右心导管法,经颈外静脉插入大鼠心腔及肺动脉,检测并计算大鼠右心房、右心室和肺动脉的收缩压、舒张压及肺动脉平均压。结果:右心房压力波动较平缓,呈小波浪形;右心室压力曲线波动大,骤升骤降;肺动脉压力曲线有重搏波。正常SD大鼠右心房舒张压为(2.03±2.56)mmHg,收缩压为(2.82±1.85)mmHg;右心室舒张压为(5.72±3.99)mmHg,收缩压为(18.73±4.80)mmHg;肺动脉舒张压为(15.27±2.64)mmHg,收缩压为(18.49±2.53)mmHg,肺动脉平均压为(16.34±2.32)mmHg。右心室收缩压与肺动脉收缩压无明显差异(P0.05)。结论:改良后的方法可准确到达大鼠肺动脉,提供的压力参考值及曲线图有助于研究人员顺利完成测压实验。     

A computational study on the influence of catheter-delivered intravascular probes on blood flow in a coronary artery model

Catheter-delivered intravascular probes are widely used in clinical practice to measure coronary arterial velocity and pressure, but the artefactual effect of the probe on the variables being measured is not well characterised. A coronary artery was simulated with a 180 degrees curved tube 3mm in diameter and the effect of catheters of different diameters was modelled numerically under pulsatile flow conditions. The presence of a catheter increased pressure by 1.3-4.3 mmHg depending on its diameter, and reduced velocity-pressure phase-lag. For an ultrasound sample volume 5mm downstream from the probe tip, the underestimation in velocity measurement attributed to catheter blockage is approximately 15-21% for an average inlet velocity of 0.1m/s. The velocity measurement error is lower at higher mean flow velocity. Accuracy of clinical velocity measurements could be improved by moving the sample volume farther downstream from the probe tip, because the centrifugal pressure gradient intrinsic to the curvature promotes re-development of flow.     

Straining urethral reflex: description of a reflex and its clinical significance. Preliminary report

The present communication describes a reflex, which I call 'straining urethral reflex', and discusses its clinical significance. The study was performed on 17 healthy volunteers with a mean age of 39.6 years. The intrarectal pressure (representative of the intra-abdominal pressure) was measured by means of a balloon-tipped catheter introduced into the rectum and connected to a pressure transducer. A concentric needle electrode was introduced into the external urethral sphincter. The subject was asked to strain, and the urethral sphincter electromyographic activity and the intrarectal pressure were recorded. Two types of straining were investigated: sudden and slow. The procedure was repeated in 10 subjects after urethral sphincter infiltration with xylocaine or saline. On sudden straining, the external urethral sphincter contracted. The anesthetized sphincter did not respond, while the saline-infiltrated sphincter responded to sudden straining. Slow sustained straining did not evoke the reflex response. The latency of the reflex was calculated. The external urethral sphincter contraction on sudden straining guards against the involuntary opening of the vesical neck and urinary leak under stress conditions of a sudden increase in the intra-abdominal pressure. The reflex may prove significant in the diagnosis of micturition control disorders. It can thus be included as an investigative tool in urologic practice.     

Measurement of oscillatory flow pressure gradient in an elastic artery model

In vitro experiments were conducted to measure the oscillatory flow pressure gradient along an elastic tube in order to assess the recent nonlinear theory of Wang and Tarbell. According to this theory, in an elastic tube with oscillatory flow, the mean (time-averaged) pressure gradient cannot be calculated using Poiseuille's law. The effect of wall motion creates a nonlinear convective acceleration, and an induced mean pressure gradient is required to balance the convective acceleration. The induced mean pressure gradient depends on the diameter variation over a cycle, the pulsatility and unsteadiness of the flow, and the phase difference between the pressure wave form and the flow wave form. The amplitude of the pressure gradient also depends on these parameters and may deviate significantly from Womersley's rigid tube theory. A flow loop was constructed to produce oscillatory flow in an elastic tube. Flow wave forms were measured with an ultrasonic flow probe, and ultrasonic diameter crystals were used to measure wall movement. A special device for pressure drop measurement was constructed using Millar catheter tip transducers to obtain both forward and backward pressure drops that were then averaged. This averaging method eliminated the static error of the pressure transducers. The pressure-flow phase angle was varied by clamping a distal elastic section at various locations. Pressure gradients were obtained for a range of phase angles between −55 ° and +49 °. The mean and amplitude of the measured pressure gradient were compared to theoretical values. Both positive and negative induced mean pressure gradients were measured over the range of phase angles. The measured pressure gradient amplitudes were always lower than predicted by Womersley's rigid tube theory. The experimental means and amplitudes are in good agreement with the elastic tube theoretical values. Thus, the experiments verify the theory of Wang and Tarbell.