Continuous Pressure Measurement Research Articles

Construction and experimental application of a catheter for selective arterial kidney perfusion in situ

In order to improve dog kidney perfusion in situ with a protective solution, a perfusion catheter was constructed which allowed continuous pressure measurement in the center of the catheter tip during perfusion. Using this catheter, the equilibration of the extracellular space with a protective solution (HTK solution) was found to be pressure dependent. Continuous pressure and resistance control is therefore a prerequisite for reliable organ protection.

Volume control during periodic changes of blood volume in the alert rat.

Blood (3.4-13.5% of blood volume) was pumped in and out of the circulation of rats at different rates and period lengths during continuous measurements of blood conductivity (reciprocally related to hematocrit) and arterial pressure. Hct followed the same zig-zag course as the induced changes of blood volume in every case, indicating that fluid shifts (delta v) between interstitium and intravascular space closely follow blood volume changes. As the hct increase during reinfusion was not as great as the preceding decrease, hct dropped continuously during the 20-90 minutes of experimentation, so that a final volume increase (delta v) by about 4% was calculated, which was confirmed by a corresponding decrease of plasma protein concentration. Both final delta v and delta v during periodic volume change (delta % B.V.) were greater when arterial pressure dropped. delta v was directly related to delta % B.V. but not to its rate of change. Heart rate dropped slightly at the end of the reinfusion periods, whereas it rose to control at the end of the withdrawal periods. The results were regarded as evidence of blood volume regulation proportional to the absolute volume of blood lost in non-hypotensive hemorrhage.

A new type of continent ileostomy

Kock's continent ileostomy is a well-established technique, however, it is technically difficult to construct and has a high incidence of complications. This study evaluates a new type of mucosal valve constructed in continuity with an intestinal reservoir. The valve is created along the antimesenteric border of the efferent limb 0.5 cm distal to the reservoir. The seromuscular layer is "stripped" from the mucosal layer for 50 per cent of the bowel circumference and then excised. The remaining seromuscular borders are then sutured to the apex of the pouch and along the antimesenteric border of the afferent limb. In this way the valve is created and, upon distention of the afferent limb and apex of the pouch, the valve closes. In seven dogs such a continent ileostomy was constructed and all were clinically continent. The reservoirs were intubated through the ileostomy two to three times a day. The mean volume aspirated was 143 ml/day. After eight weeks, radiographic and volume-pressure studies were performed. Prior to sacrifice, increasing volumes of barium were instilled into each pouch via the afferent limb and radiographs were taken: these studies confirmed the continence in all seven ileostomies. Following this the reservoirs were intubated and the instilled barium was aspirated. Then Ringer's solution was instilled into each pouch with continuous intrapouch pressure measurements. The pressure remained at 0 cmH2O until a mean volume of 243 ml was exceeded. The mean volume at which incontinence occurred was 415 ml.

Continuous intraoperative EEG monitoring during carotid surgery.

Continuous intraoperative EEG monitoring and stump pressure measurements were studied during 85 carotid revascularizations performed in 40 symptomatic cerebrovascular patients and in 32 asymptomatic subjects with a cervical bruit. The decision to place a temporary shunt was made on the basis of intraoperative EEG abnormalities regardless of stump pressure values. 11 patients with contralateral carotid lesions showed marked EEG alterations, at the moment of clamping, which returned to normal after the placement of an indwelling shunt. Stump pressure values showed a wide variation and a poor correlation with intraoperative EEG changes. In the early postoperative period there were no deaths; no new neurological deficits were detected. In the follow-up there was only 1 asymptomatic carotid rethrombosis, not revealed by the EEG, which was suspected by Doppler sonography and confirmed by angiography. The authors conclude that EEG gives valuable information about cerebral functions during carotid revascularization and can reduce the intraoperative complications of the procedure. Stump pressure measurement cannot be used alone as a safe indicator of cerebral ischemia during carotid cross-clamping.

Homogeneous nucleation rate measurements for water over a wide range of temperature and nucleation rate

An expansion cloud chamber was used to measure the homogeneous nucleation rate for water over a wide range of temperature from 230–290 K and nucleation rates of 1–106 drops cm−3 s−1. The comprehensive and extensive nature of this data allows a much more detailed comparison between theory and experiment than has previously been possible. The expansion chamber technique employs continuous pressure measurement and an adiabatic pulse of supersaturation to give the time history of supersaturation and temperature during the nucleation. The resulting drop concentration is determined using photographic techniques. The experimental observations are presented in tabular form and from them an empirical nucleation rate formula is determined: J=S2 exp[328.124−5.582 43T+0.030 365T2−5.0319E−5T3 −(999.814−4.100 87 T+3.010 84E−3 T2)ln−2S], where J is the nucleation rate in units of drops cm−3 s−1. S is the supersaturation ratio and T is the temperature in K.

System for umbilical artery monitoring.

A simple, safe, and effective system for umbilical artery monitoring controls continuous fluid infusion to prevent fluid overinfusion and keep the catheter from clotting. Accurate and continuous pressure measurements can be recorded simultaneously with fluid infusion. A convenient method for checking dynamic response fidelity is provided. The system is easy to set up and maintain. Because it is a closed system, contamination of the neonate is minimized.

High Temperature Geothermal Well-Logging Techniques in Japan: ABSTRACT

A high temperature geothermal well-logging system has been developed by Japan Petroleum Exploration Co., under the sponsorship of the Japanese government. The tools developed on this project are: Multi-Spacing Electrical-SP Log (equivalent to Lateral Log); Microspherical-Caliper Log; Side Wall Acoustic-Caliper Log (P-S Wave Sonic Log); Steering Tool (Azimuth, Hole Deviation and Inclination); Optical Borehole TV; Production Logging Tools (Temperature, Pressure, Continuous Flow and Caliper, and Borehole Sampler). The maximum operating temperature of these tools is 325°C and they can withstand pressures of 500 kg/cm2, by the use of TFE teflon insulator armored cable. The tools have been subjected to field tests over 50 geothermal wells, since 1978, and all except the Optical Borehole TV were successfully operated where bottom-hole temperatures were as high as 210 to 275°C. The side wall acoustic tool, which consists of P and S wave transducers, is very useful for the detection of formation fractures in volcanic rocks. The Optical Borehole TV could not be used where temperatures exceeded 150°C, because of heat radiation emitted from the mud and the holewall surrounding the down-hole probe, or when the tool was focused at the surface of the semiconductor imagesensor on the TV and the temperature of the image spot exceeded 120°C, even when placed in a Dewar bottle and heat sink assembly. Super high temperature (450°C) production logging tools, using mineral insulation cable, are under construction and will be in operation by the end of August 1982. They are: Absolute and 1-meter spacing differential Temperature Survey; Continuous Pressure Measurement; Continuous Flow and Caliper Measurement; High Temperature Microphone and Accelometer, with a wall set mechanism. The diameter of these tools is 2 inches and their maximum operating time is 30 hours at 450°C. They can withstand pressures of 500 kg/cm2. The success of this system is apparent from the summary of field results and the technical report of the super high temperature production logging tools. End_of_Article - Last_Page 972------------

Effects of prazosin on reflex changes in heart rate evoked by vasopressor and vasodepressor stimuli in conscious rabbits.

In conscious rabbits prepared for continuous arterial pressure measurements by means of a catheter placed into the main ear artery, intravenous administration of prazosin (5.0 micrograms/kg, i.v. over 20 min) produced a significant decrease in arterial pressure and cardioacceleration. This dose of prazosin inhibited by approximately 70% the pressor effects of phenylephrine. However, prazosin failed to produce significant functional modifications of either the bradycardia or the tachycardia which accompanied the changes in arterial pressure evoked, respectively, by intravenous bolus injections of angiotensin II or acetylcholine. It is concluded that prazosin in the dose studied does not appear to interfere with reflex heart rate responses to vasodepressor or vasopressor stimuli in conscious rabbits.

A chronic cannula for obtaining CSF from the cisterna magna of awake dogs

We have designed a cannula system that can be chronically implanted to end above the dura of the cisterna magna of the dog. During experiments in the awake dog, a screw cap with stylet is removed from the cannula and a spinal needle inserted for the withdrawal of samples of cisternal cerebrospinal fluid (CSF) or for making continuous measurements of pressure. The system can be used for repeated experiments extending over several weeks.

Changes in cervical compliance at parturition independent of uterine activity

A new animal model has been developed to measure intrinsic changes of cervical compliance during spontaneous parturition or exposure to hormonal manipulation. Intermittent measurements of cervical compliance and continuous measurements of uterine and cervical pressure were made during the last month of gestation of nine pregnant ewes. Cervical compliance increased abruptly and dramatically during spontaneous and dexamethasone-induced parturition. Maternal progesterone supplementation at parturition inhibited uterine contractions but not the increase in cervical compliance, demonstrating the independence of the two events. The cervix was found to contract rhythmically and vigorously with a gradual decrease in activity as parturition approached.

Mechanical response of LMFBR and P1 cladding tubes under transient heating

Type 316 stainless steel tubing specimens comparable to LMFBR cladding were burst tested with relatively constant internal pressure in the 219–836 psi range and with increasing temperature. Continuous measurements of diameter change, temperature, and pressure were recorded as the samples were heated to temperatures near the melting point at rates from 10–1800°F/sec. The effects of varying initial wall thickness, cold work level, length, and thermal experience were explored. Ductile failures were observed at 10°F/sec, and stable strains at time of failure were greater than those reported by HEDL. At 200°F/sec the initially 20% cold-worked, 15-mil wall tubing produced brittle failures; while initially 40% cold worked, 10-mil wall samples displayed a mixture of ductile and brittle features. At ∼1000°F/sec the behavior of the latter material was prodominately brittle, although stable strains as large as 6% were observed. Failure temperatures were generally above 2000°F. When substantial ductility was displayed, an exponentially increasing stable strain was recorded as temperature and time progressed: from such curves temperatures corresponding to 1% strain were derived. Factors controlling the mechanical response appear to be separable by analysis based on the recorded data and the variety of materials and conditions of the tests.

Parasympathetic cholinergic control of cerebral blood flow in dogs.

SUMMARY We studied the effects of cholinergic receptor activation on cerebral blood flow in dogs anesthetized with chloralose. Continuous measurements of cerebral blood flow, arterial and cerebral spinal fluid pressure, heart rate, and respiratory carbon dioxide tension were made during parasympathetic nerve stimulation and during intraarterial infusion of acetylcholine. Multiple samples of arterial and cerebral venous blood were taken before, during, and after cholinergic vasodilation and analyzed for oxygen tension, carbon dioxide tension, and pH. Dose-response curves obtained by intra-arterial infusion of acetylcholine at 0.27-1,080 /ig/min and stimulation frequency-response curves obtained by excitation of the major petrosal nerve at 2-40 Hz demonstrated a dose or frequency-dependent cerebral vasodilation. The maximum cerebral vasodilation (171% of control flow) was obtained with an acetylcholine infusion of 1,080 /xg/min. During infusion of 27 /tg of acetylcholine/min arterial blood gases showed little or no change and thus could not have produced the observed change in cerebral blood flow. The changes in cerebral venous blood were all consistent with the observed increase in cerebral blood flow; oxygen tension rose from 30.4 to 36.0 mm Hg, carbon dioxide tension fell from 45.7 to 42.3 mm Hg, and pH rose from 7.342 to 7.360. Ipsilateral stimulation of the major petrosal nerve at 10 Hz, with a 3-msec pulse duration and 60-second stimulation period, produced an increase in cerebral blood flow to 111% of control flow. Cholinergic receptor blockade with atropine (1 mg/kg, i.v.) completely eliminated the cerebral vasodilation produced by acetylcholine infusion at 27 figlmin and significantly reduced the vasodilation resulting from major petrosal nerve stimulation. We conclude that the cerebral circulation has the capacity for significant cholinergic vasodilation. THE ABUNDANT anatomical evidence demonstrating the existence of nerve fibers on the cerebral vessels has recently been reviewed. 1 The sympathetic autonomic component of this innervation has been shown to have the capacity for marked cerebral vasoconstriction via an aadrenergic receptor mechanism. 2 - 3 A parasympathetic cerebral vasodilator mechanism was suggested by early workers when they observed pial vessel in response to cranial nerve stimulation. 4 More recently, intravertebral atropine was shown to suppress the resulting from inhalation of 5% CO2, 5 and intravertebral neostigmine enhanced cerebral vasodilator reactivity to CO2. (i Atropine was also shown to eliminate autoregulatory dilation in unanesthetized rabbits. 7 Each of these observations is consistent with a parasympathetic cholinergic vasodilator mechanism for the cerebral circulation. None of these studies demonstrates a parasympathetic cholinergic increase in cerebral blood flow. A cholinergic vasodilator mechanism to compliment the adrenergic vasoconstrictor mechanism has, therefore, not been clearly defined for the control of cerebral blood flow. In the present study, parasympathetic nerve stimulation and intra-arterial infusion of a cholinergic agonist, acetylcholine, were used to test for a possible parasympathetic cholinergic cerebral vasodilator mechanism.

A New Technique for Continuous Sphincter Pressure Measurement

The use of a constantly perfused side hole sensor (CPSH) for continuous measurement of maximal lower esophageal sphincter pressure (LESP) is associated with important but variable undermeasurement as a result of side hole displacement. A 5 cm long pressure sensor has been developed which measures maximal LESP continuously in the face of movement of the sphincter within the sensor length. This sensor, the perfused sleeve, is described, and validated by comparison with CPSH in man, the dog, and a model esophageal sphincter. The sleeve detects maximal LESP accurately, regardless of sphincter length, over the pressure range encountered in the lower esophageal sphincter. Continuous recording of LESP with the sleeve is unaffected by displacement that causes serious undermeasurement with CPSH.

SFT transducer and its clinical application for continous monitoring of epidural intracranial pressure (author's transl)

We devised a semiconductor film strain transducer (SFT) for continuous measurements of epidural or subdural intracranial pressure and blood pressure. The metal diaphragm of this transducer facing the dura mater was made of high quality stainless steel (sus 27, 30μ in thickness). A strip of SFT element is bonded on the counter surface of the diaphragm at its center, and the rim of the diaphragm is fixed at the edge of the stainless steel cylindrical housing base. The inner space is sealed except for an 1 mm diameter polyethylene tube which is used to balance the inner space pressure against the outer. For the detection of SFT resistance change a bridge method was employed. The transducer was calibrated by a comparison method, giving both positive and negative air pressure. We also developed a new telemetric system consisting of transducer bridge circuits with IC amplifier and transmitter circuits. The miniature transmitter measures only 5×1×3 cm in size, but it was still too large to be implanted. The transmitter and its receiving system utilize the pulse transmitting circuits (3 and 80 MHz), and its radius of action is approximately 10 meters. The SFT was used for continuous recording of epidural pressure (EDP) in 41 neurosu rgical patients for a period ranging from one to nine days (3.5 days on an average). No untoward complications such as infection or hemorrhage at the site of implantation were experienced. Induction of general anesthesia caused an acute rise in the EDP in almost all cases. Intraoperative recording of the EDP was performed in the supine, sitting and prone positions. The sitting position proved to be very useful in reducing the EDP for posterior fossa craniectomy. Irrespective of the positioning of the patients, the EDP was restored to a lower and adequate level as soon as an extreme flexion or rotation of the neck was corrected. In one case the development of a postoperative intracerebral hematoma was detected by monitoring the EDP. Telemetric monitoring of the EDP was performed in two patients during their daily life in the neurosurgical ward, such as eating, drinking, sitting, standing or going to stool. The EDP and systemic blood pressure were recorded simultaneously in one of them. When those patients went to stool, the EDP increased sharply at the beginning of straining and the diastolic pressure also increased at the same time, but the systolic pressure decreased. At the end of straining both the systolic and diastolic pressure increased. Of particular interest was the fact that the magnitude of the EDP rise during straining at stool differed significantly by the posture of the patients, such as lying on a bed-pan, seating on a toilet or squatting over a Japanese style toilet.

Cerebral dysregulation in tumors of the posterior, cranial fossa with hydrocephalus occlusus. (Continuous measurements of ventricular pressure, interval measurements of liquor-pulse, respiration and electroencephalographic interval-spectrum-analysis (EISA) during nocturnal hours

Cerebral dysregulation in tumors of the posterior, cranial fossa with hydrocephalus occlusus. (Continuous measurements of ventricular pressure, interval measurements of liquor-pulse, respiration and electroencephalographic interval-spectrum-analysis (EISA) during nocturnal hours

Irradiation Test of Reluctance Type Pressure Sensor for Measuring Fission Gas Pressure

A reluctance type pressure sensor for continuous measurements of the fission gas pressure in fuel pins during irradiation was developed and irradiated in the JMTR. The pressure sensor is constituted of magnetic materials and electric wire, which may be affected by the effect of heat and radiation, and this in turn may impair the accuracy of the pressure sensor. An irradiation test was performed to obtain quantitative information on the accuracy of the pressure sensor itself and for examining its viability in actual use under radiation. The test was made during three cycles of operation of the JMTR at 30 MW reactor power. The calculated neutron fluence was about 4.2×1019n/cm2 (E> 1.05MeV) and 6.8×1020n/cm2 (E<1.05 MeV). It was found that the effect of heat was larger than that of radiation to a fluence of this order, but the former effect can be reduced by correction for temperature. The error due to radiation effect is estimated to be about ±1.0% at the limiting pressure of 50kg/cm2G. The error at full po...

Determination of the hydraulic conductivity and of reflection coefficients in Nitella flexilis by means of direct cell-turgor pressure measurements

From direct and continuous measurements of the internal hydrostatic pressure ( P) in the internodes of Nitella flexilis, the reflection coefficients ( σ s) of some non-electrolytes were determined, using a zero-flow method, and were compared with those found previously on Valonia utricularis and with those obtained by Dainty and Ginzburg on other Characean internodes from transcellular osmosis experiments. The hydraulic conductivities ( Lp) of the cell membranes were determined by two independent methods, that is, using hydrostatically or osmotically induced flows. From the exponential time course of P in such experiments and from the volumetric elastic modulus (ε) of the cell wall, Lp was calculated. The effect of unstirred layers in the methods described was negligibly small. In osmotic experiments with different non-plasmolysing external sucrose concentrations (20–200 mM) the exosmotic hydraulic conductivity ( Lp ex) decreases markedly with increasing concentration, while the endosmotic hydraulic conductivity ( Lp en) shows only a weak dependence. In the hydrostatic experiments the hydraulic conductivities for single cells were constant in the pressure range for P from 2 to 7 atm. In this pressure range Lp en and Lp ex varied for different cells from 2.2·10 −5 to 2.8·10 −5 and from 1.8·10 −5 to 2.5·10 −5 cm·s −1·atm −1, respectively, with an average ratio Lp en to Lp ex of 1.1, which indicates a polarity in water movement. These values were the same as those obtained in the osmotic experiments from extrapolation to zero sucrose concentration. At internal pressures below 2 atm the Lp-values markedly increase on approaching the plasmolytic point. The results are discussed in terms of a dehydration of the membranes (or the cytoplasm) at increased solute concentrations. In addition, the strong dependence of Lp at low internal hydrostatic pressures points to a direct influence of P on the water permeability of the membranes.

Effects of norepinephrine and sympathetic stimulation on extraction of oxygen and 86Rb in perfused canine small bowel.

Previous studies have shown that sympathetic stimulation can cause a redistribution of intestinal capillary blood flow. Our computer model of the intestinal circulation predicted that the diffusion parameters (e.g., capillary surface area and mean capillaryto-cell diffusion distance) altered by precapillary sphincter closure would be sufficient to affect intestinal oxygen extraction. To test this prediction in an animal model, we made continuous measurements of arteriovenous oxygen difference (ΔO 2 ) and perfusion pressure during constant-flow perfusion of isolated loops of canine small bowel. Intraarterial infusion of norepinephrine or stimulation of sympathetic nerves for 7 minutes produced sustained increases in vascular resistance and sustained reductions in arteriovenous ΔO 2 . Maximal changes in resistance and arteriovenous ΔO 2 occurred by the second minute of norepinephrine or sympathetic nerve stimulation, and subsequently both parameters escaped somewhat. The maximal and steady-state values of these parameters were dose-dependent or frequency-dependent. In other experiments, sympathetic nerve stimulation caused synchronous decreases in arteriovenous ΔO 2 and 86 Rb extraction. These results support the hypothesis that the infusion of norepinephrine and the stimulation of sympathetic nerves cause sustained reductions in the density of the perfused capillary bed which are sufficient to reduce intestinal extraction of Rb and oxygen despite constant-flow perfusion.

Homogeneous Nucleation and Growth of Ethanol Drops in Supersonic Flow

Condensation of ethanol by homogeneous nucleation of liquid droplets has been studied in a supersonic nozzle. Continuous static pressure measurements on the nozzle centerline and light scattering measurements permit the condensation process to be resolved in detail for comparison with theory. Nucleation rates found in the present work are in general agreement with previous results obtained in diffusion and expansion cloud chambers. It is seen that the predictions of the classical theory of homogeneous nucleation or that of the statistical mechanical theory with the assumptions of Dunning roughly agree with the experimental results. Various terms entering different versions of nucleation theory are given quantitatively. The pressure variations in the flow found beyond the onset point of condensation are used to study droplet growth processes. It is shown that a simple kinetic growth law with a constant mass condensation coefficient describes the condensation process well.

The effect of increased intracranial pressure on cerebrovascular hemodynamics.

✓ Both brain edema (increased water content) and enlargement of the vascular compartment have been implicated as being responsible for intracranial hypertension following trauma. In this study pertinent cerebrovascular hemodynamic parameters have been investigated in states of increased intracranial pressure (ICP) and graded trauma to determine whether cerebral edema or vascular factors are of major importance. Utilizing the monkey-epidural balloon experimental model, continuous measurements of the mean arterial pressure (MABP) , jugular outflow pressure (MJVP), and sagittal sinus wedge pressure (SSWP) were obtained. Shulman's observations that the sagittal sinus wedge pressure accurately reflects the intracranial pressure have been confirmed. The total cerebral blood flow (CBF) and mean transit time (t̄) were determined and the total cerebral blood volume (CBV) computed. From these data the venous (Rv), arterial (Ra), and total resistances (Rt) were calculated. Analysis of these parameters during both the acute elevation of ICP and that following graded trauma has demonstrated: 1) a progressive decrease in the total cerebral blood flow and volume and a concomitant increase in the mean transit time; 2) a progressive increase in the total resistance with a shift from the arterial to the venous side; 3) a progressive decrease in the perfusion pressure (PP = MABP-SSWP); 4) impairment of CO2 reactivity pari passu with vasomotor activity and autoregulation of flow to pressure. The findings did not support the concept that increased intracranial pressure following trauma is the result of an increase in the size of the cerebrovascular compartment.