Pressure Artifacts Research Articles

Shale Preservation and Testing Techniques for Borehole-Stability Studies

Summary Shale rocks are known to be the primary troublesome formation that has plagued drillers for many years. Attempts have been made to investigate the characteristics of shales, but results are limited because of the scarcity of test samples. Rapid deterioration of cuttings and cores has made data collection limited at best and a complete failure in many cases. It now appears that the shales become unsaturated as they dry out because of poor storage conditions, which result in false test results owing to the incorporation of capillary pressure artifacts. This paper discusses results obtained with a specially preserved, highly reactive shale core obtained at a depth of 4,500 ft in the North Sea. A previously developed method was used for the evaluation of shale cores to determine their level of saturation. This study shows that shales must be preserved at their native water content if accurate physical measurements are to be made. Swelling data show that shales that are altered during handling (hydrated or dehydrated) do not respond properly even when restored to their native hydration conditions. They tend to experience excessive swelling compared to cores kept at their native water content. Results also showed that the North Sea core used in this study was maintained in a fully saturated condition during coring, retrieval, and storage. The technique used is discussed here.

Filtration artifacts caused by overloading membrane filters.

The conventional practice of using 0.45 or 0.40 microm membranes to distinguish between the particulate and dissolved phases in natural waters neglects the importance of colloids. Many of the colloids in natural waters pass through 0.45 or 0.40 microm membranes, but a significant fraction at the upper end of the colloidal particle size range is retained. Membrane clogging during filtration decreases the effective pore size and can cause the retention of increasing amounts of colloids. This filtration artifact can cause serious errors in sampling and in assigning trace metals to various particle size classes. We evaluated the effect of membrane loading for two common membrane types (0.45 microm Millipore Durapore and 0.40 microm Nuclepore) on the retention of colloidal Fe, Al, Mn, and OM in three Connecticut rivers. In addition, we used a 1.0 microm Nuclepore membrane to estimate the amount of colloids in the 0.40-1.0 microm size fraction that are retained by membranes during conventional filtration. All samples were collected with clean techniques, and all filtrations were carried out in a class 100 clean room. A peristaltic pump, set at an initial flow rate of 120 mL/min, was used to pump samples through 47 mm diameter inline Teflon filter holders. Back pressure and flow rate were monitored during filtration, and both are good indicators for the onset of membrane clogging. The results show a consistent correlation between increasing back pressure and decreasing concentration of colloidal Fe and sometimes Al, Mn, and OM in the filtrate for all membrane types. Although the shape of the loading-retention curves varied dramatically by site and by membrane type, the essential relationship between back pressure, flow rate, and filtration artifacts during membrane clogging remained the same.

Measurement of intracompartmental pressure with use of a new electronic transducer-tipped catheter system.

Laboratory and clinical tests were carried out to determine the clinical usefulness, validity, and safety of a new self-calibrating, battery-powered monitoring system for the measurement of intramuscular pressure with use of an electronic transducer-tipped catheter. The eight probes accurately recorded applied pressures ranging from zero to 160 millimeters of mercury (zero to 21.33 kilopascals). The system registered little temperature-induced drift (maximum, 1.25 millimeters of mercury [0.17 kilopascal]) between dry room temperature and 40 degrees Celsius. There were also minimum variations (range, -0.14 to 0.81 millimeter of mercury [0.02 to 0.11 kilopascal]) in the pressures recorded during a twenty-four-hour period. The resting pressure in the tibialis anterior muscle of twenty volunteers who had normal limbs was a mean (and standard deviation) of 13.1+/-8.3 millimeters of mercury (1.75+/-1.11 kilopascals). There was a good correlation between externally applied pressures (zero, twenty, forty, sixty, eighty, and 100 millimeters of mercury [zero, 2.67, 5.33, 8.00, 10.66, and 13.33 kilopascals] applied with use of antishock trousers) and the pressures measured in the tibialis anterior muscle of four volunteers (r = 0.997 to 0.999). The injection of sterile saline solution into the tibialis anterior muscle of a volunteer and the use of high-frequency recording during muscular activity showed a high degree of responsiveness and sensitivity to changes in intramuscular pressure. We also prospectively evaluated the clinical usefulness of the system and found it to be easy to assemble, calibrate, and use. Thus, this reusable, electronic transducer-tipped catheter system, which is based on a noninfusion technique, is simple, minimally traumatic, and highly precise. It is free of hydrostatic pressure artifacts and provides dynamic responses to changes in intramuscular pressure.

Removal of pressure and free energy artifacts in charged periodic systems via net charge corrections to the Ewald potential

A uniform neutralizing background plasma is employed by default in standard Ewald calculations for net-charged systems. We show here that this plasma leads to serious artifacts in both system energy and pressure, which lead to unrealistic behavior. These artifacts are especially critical to simulations where either net charge or volume is allowed to change. To correct these problems we institute a net-charge correction term that consists of subtracting off the Ewald sum for a single particle with charge equal to the net charge of the full system and an optional Born or Poisson–Boltzmann term. This correction decreases pressure artifacts by three orders of magnitude and allows rapid energy convergence as the cell size increases. The correction term is general, in that it applies to systems of any shape or net charge. The net-charge correction was tested for systems in all three phases of matter: gas, solid, and liquid, and found to be markedly superior to standard Ewald in all three cases. In the gas phase, isolated molecular energies are quickly achieved as the cell size increases. In the solid phase the vaporization energy of the NaCl crystal is reproduced using free energy perturbation techniques where a single atom is removed. In the liquid phase, the solvation free energy of Na+ was investigated. It is demonstrated that both the net-charge correction and an energy term twice the size of a Born term is required to obtain optimal free energies of ionic hydration.

Basic principles for measurement ofintramuscular pressure

We review historical and methodological approaches to measurements of intramuscular pressure (IMP) in humans. These techniques provide valuable measures of muscle tone and activity as well as diagnostic criteria for evaluation of exertional compartment syndrome. Although the wick and slit catheter techniques provide accurate measurements of IMP at rest, their value for exercise studies and diagnosis of exertional compartment syndrome is limited because of low frequency response and hydrostatic (static and inertial) pressure artifacts. Presently, most information on diagnosis of exertional compartment syndromes during dynamic exercise is available using the Myopress catheter. However, future research and clinical diagnosis using IMP can be optimized by the use of a miniature transducer-tipped catheter such as the Millar Mikro-tip.

Regulation of melatonin-sensitivity and firing-rate rhythms of hamster suprachiasmatic nucleus neurons: constant light effects

Rhythms of spontaneous firing rate and of responsiveness to pressure ejection of melatonin were recorded from neurons in the Syrian hamster suprachiasmatic nuclei (SCN) in a slice preparation. In animals taken from light-dark cycles (LD 14:10), SCN cells had high firing rates during the projected day and lower rates during the projected night. The proportion of melatonin-suppressed cells (35% overall) was also high during the day and fell during the night, while melatonin activated ∼23% of cells at all phases. To assess the source of the melatonin-responsiveness rhythm, hamsters were exposed for ∼48 h to constant illumination (LL) to suppress melatonin secretion. LL exposure before slice preparation altered both firing-rate and melatonin-responsiveness rhythms. Firing rates failed to show a morning peak and remained at low levels, with no indication of daily rhythmicity. Melatonin responsiveness also failed to show the usual rhythm and even tended to rise at night. Overall melatonin responsiveness rose after LL exposure so that 50% of cells were suppressed and 21% activated. LL exposure also increased the proportions of cells which showed regular baseline firing rates. Control studies indicated that pressure artifacts did not account for either suppression or activation by melatonin, while the composition of the saline vehicle appeared to be responsible for the activations recorded. The results indicate that brief LL exposure alters SCN sensitivity to melatonin and SCN rhythmicity in Syrian hamsters, perhaps as a result of the loss of the daily melatonin secretion rhythm. Physiological melatonin patterns may have important effects on the rodent circadian pacemaker.

Instant of vascular occlusion defined with laser-Doppler flowmetry.

Derivation of capillary pressure from tracings postarterial (AO) or -venous (VO) occlusion requires back extrapolation to an instant near the time of occlusion. This instant is difficult to identify because of pressure artifacts created by the occlusion maneuver. Theoretically, when the flow in the main artery (or veins) is stopped instantaneously, the flow in the arterioles (or venule) will stop after a short time delay (perhaps less than 100 ms). When flow had stopped in the main artery and in the arteriole, the pressure in the main artery at that instant would equal the pressure in the arterioles. We sought to identify the instant when flow stops in the arterioles and venules after AO and VO, respectively. In an isolated perfused dog left lower lobe preparation flow in the main vessels were monitored with inline flow probes, whereas flow in the microcirculation was monitored with laser-Doppler flow (LDF) probe placed on the lung surface. A sudden decline in arterial flow was detected by the LDF probe after 54 ms, while a sudden decline in venous flow was detected in the venules after 35 ms. These time delays were used as wave transmission time across the arterial and venous trees. Consequently, it was concluded that after AO, flow in the arterioles would stop 54 ms after it had become zero in the main artery, while after VO flow in the venules would stop 35 ms after it had become zero in the main vein. The pressure post-AO and post-VO was read at these instants (54 and 35 ms after flow in the main vessel reached zero).(ABSTRACT TRUNCATED AT 250 WORDS)

A new “transducer‐tipped” fiber optic catheter for measuring intramuscular pressures

Laboratory and clinical tests were used to determine the efficacy of a new fiber optic "transducer-tipped" catheter for measuring intramuscular pressures. When pressures ranging from 0 to 250 mm Hg were applied by a mercury manometer, the fiber optic system accurately recorded the pressures. In addition, the fiber optic system showed long-term stability by accurately recording the manometer pressure over a 3 day period. The Slit system showed a higher magnitude of hydrostatic pressure artifacts with catheter tip movement as compared to the fiber optic system. The two catheters showed no difference when measuring pressures in pig muscle at rest or when being compressed throughout a range of 0 to 250 mm Hg. In human volunteers, both catheters measured essentially equal pressures at rest, during venous stasis, and during a combination of venous stasis and compression. For long-term assessment, the Slit system required as many as three saline flushes, whereas the fiber optic system measured pressures continuously without manipulation. We conclude that the fiber optic system is as accurate as the Slit catheter for measuring tissue fluid pressures at rest. In addition, the fiber optic system offers distinct advantages over conventional fluid-filled systems for measuring intramuscular pressures due to a lack of hydrostatic pressure artifacts caused by limb position and to the lack of flushing for long-term measurements.

Microwave Fixation of the Lung

A technique for microwave fixation of inflated rat lung is described. Conventional intratracheal fixation with instillation of fixative into the airways at a constant pressure results in pressure artifacts as well as flushing and disruption of cells and exudates. Microwave fixation fixes these elements in situ without disruption and thus is valuable when evaluating the distribution of inflammatory infiltrates. Exudative pneumonitis was produced in the rat using intratracheal instillations of either endotoxin or silica and comparisons were made between histologic sections fixed using either standard formalin fixation or microwave fixation.

Computer-aided oesophageal manometry: Prospects and problems

We describe a method in which computer-aided analysis has been applied to oesophageal manometry, and address some of the major problems which were encountered. The elimination of pressure artefacts caused by respiration and normal cardiac function is necessary in order to define accurately the parameters required from the analysis. The most promising method of solving this signal/noise problem is to include a fast Fourier transform in the analytical program.

Corona discharge photography of human breast tumour biopsies.

Corona discharge photography of human breast carcinoma biopsies was directly compared with normal adjacent breast tissue from the same patient by photographing the samples simultaneously with a split grounding electrode. Samples were immersed in saline and adjusted to the same weight to ensure identical conditions and to eliminate moisture and pressure artifacts. Tumour samples always showed an increased corona discharge intensity and contained characteristic regions of high intensity light as compared with normal tissue. The technique may therefore be useful as a new non-invasive diagnostic technique for early detection of surface tumours. The results are discussed in terms of a possible contribution of ultra-weak photon emission since this technique gives similar results to those reported here.

A comparison of some extra‐renal effects of spironolactone and canrenone.

1 Measurement of changes in trans-mural rectal potential difference (t.m.r.p.d.) and plasma aldosterone levels have been used in a comparison of the extra-renal activities of spironolactone and its major metabolite canrenone. 2 A characteristic pressure artifact was observed during measurement of t.m.r.p.d. When pressure artifacts were eliminated, there was a log-linear relationship between increasing doses of intravenous aldosterone and maximum increase in t.m.r.p.d. 3 Pre-treatment for 5 days with spironolactone or canrenone produced a similar attenuation of the increase in t.m.r.p.d. produced by infused aldosterone, suggesting that canrenone is the active metabolite of spironolactone in the rectum. This is in contrast to the significantly greater renal activity of spironolactone that has been demonstrated after a similar treatment period. Neither antagonist treatment produced significant changes in pre-infusion plasma aldosterone concentrations. 4 The need for assay of the extra-renal activities of aldosterone antagonists in the assessment of their therapeutic potential is discussed.

Artifact production with micromanometers used to record intracardiac pressure and sound.

In horses experimental right and left heart catheterization using a catheter with two microtransducers 9 cm apart, usually in a transvalval position produced pressure and sound artifacts that confounded the diagnosis. Most were probably due to malpositioning resulting in movement through a valve during recording or impingement on the valve cusps or the chordae tendineae or lodgement in the apex of the heart. The recognition of these artifacts is particularly important in studies of large animals in which catheter siting cannot be monitored by radiography.

A pressure- and flow-insensitive reference electrode liquid junction.

The design and construction of a pressure- and flow-insensitive reference liquid junction for use in ion concentration electrode measuring systems is described. The junction is inexpensive, is very easily and rapidly constructed, is rugged, and is adaptable to various applications. When used in a pH-measuring system, drift, pressure artifacts, and flow artifacts are negligible. The response time of the system appears to be less than 10 ms. Using the pH electrode device as described, the dissociation reaction rate constant of H2CO3 at 24 degrees C was determined to be 22 s-1.

A method for ventilatory measurements in subjects 1 month--5 years of age: Normal results and observations in disease.

Extract: Using the total body plethysmograph, a method for the measurement of lung volume and airway resistance was developed for infants and young children of 1 month-5 years of age. The subjects were studied in a supine position using a reproducible method of sedation. The procedure providing the most consistent results involved use of a Rendell-Baker mask directly controlled by the operator while the subjects were breathing through the nose. Availability of an oscilloscope permitted immediate detection of pressure leaks, artifacts, and abnormal patterns during each determination and minimized potential errors during the study of each subject. Care was required to avoid pressure on the tip of the nose because an abnormally high airway resistance resulted.The logarithmic relation of thoracic gas volume (TGV) at functional residual capacity (FRC) to body length for 52 normal subjects compared well with results obtained on newborn infants and with those obtained on older subjects. The equation was: TGV at FRC, litters = 1.57 × 10-5 × length, cm2.238 (correlation coefficient = 0.948). The logarithmic relation of airway conductance to TGV was: conductance, liters/sec/cm H2O = 0.1431 TGV, liters0.6441 (correlation coefficient = 0.835). Comparison with older subjects was limited by the difference in airflow rates at which the airway conductance was determined (0.06-0.28 liters/sec versus about 0.5 liters/sec for adults) and by the use of sedation and nasal breathing in this study; adults are studied a wake and during mouth breathing. Comparison of our conductance values with those obtained on unsedated newborns suggests that either sedation alters the airway resistance or that some change occurs in the airway size-lung volume relation during the first weeks of life.Examples of the application of this method to patients with asthmatic bronchitis and cystic fibrosis of the pancreas are provided.Speculation: It is possible that an airflow-lung voliume-airway resistance relation exists throughout life; however, the results presented in this study, combined with those previously presented on newborns for airway resistance, suggest that a change may occur in the relation of the size of the airways to lung volume during early infancy, or that sedation alters airway resistance. Development of this and other methodology should permit more adequate studies of the early changes in pulmonary physiology associated with growth and the acute and chronic pulmonary conditions seen during the first 5 years of life.

Retrograde pulmonary venous pressure measurement-Fact or artifact?

Retrograde pulmonary venous pressure measurement-Fact or artifact?

Airway resistance and lung volume in the newborn infant.

Extract: The total body plethysmograph method of DuBois et al. [7] for measurement of lung volume and airway resistance was adapted to the study of newborn infants. A Rendell-Baker mask directly controlled by the operator proved by trial and error to minimize the chances of pressure leaks and undesirable pressure on the nose and allowed the mandible to be pulled forward to minimize pharyngeal obstruction. Use of an oscilloscope for direct visualization of flow and pressure tracings was essential in order to detect immediately pressure leaks, artifacts, and abnormal patterns during measurements of both lung volume and airway resistance. Interpretation of the measurements of airway resistance and of the relation of conductance to lung volume over a wide range of age and lung volumes requires that the flow rates at which measurements are made be recorded, along with lung volumes. In 51 newborn infants, an airway resistance value of 19.2±5.6 cm H2O/l/s was observed. Thoracic gas volume at functional residual capacity was 89.9±15.5 ml. The resulting mean value for conductance (reciprocal of airway resistance), 0.052 l/s/cm H2O, fell above the calculated regressions of conductance versus lung volume determined by Briscoe and DuBois [3], who used data obtained from older children and adults. Direct comparison is limited since airway resistance in the older subjects was usually obtained using panting flow rates of 0.5 l/s, while the infants in this study had flow rates of approximately 0.1 l/s at the time airway resistance was measured. Speculation: Confirmation of the presence of the major expiratory flow-limiting segment in the nasal airway of newborn and small infants is needed. This location suggests a physiologic means for slowing expiratory flow and thus maintaining expiratory intraluminal pressure in the tracheobronchial tree, which might protect the compliant trachea and major bronchi from compression by positive intrapleural pressure in obstructive pulmonary disease. It is possible that there is an airflow-lung volume-airway resistance relation throughout life; however, a wide range of control data will be required to establish such a relation.

Location of radioactively labelled extracellular fluid indicators in nervous tissue by autoradiography.

ABSTRACT The location of three radioactively labelled extracellular-space indicators ([3H]methoxyinulin, [3H]-D-mannitol and sodium [MS]sulphate) in the superior cervical sympathetic and nodose ganglia of cats was studied using an autoradiographic technique. The technique was designed to eliminate movement of soluble, diffusible substances in tissues after excision, and to provide high autoradiographic resolution. Ganglia were rapidly excised after administration of the radioactive compounds in vivo, and frozen in liquid propane. Frozen sections were cut at – 60 °C at a thickness of 0·7–0·8 μ. The frozen sections were freeze-dried, dry-mounted on dried, photographic emulsion-coated microscope slides, and exposed at – 15 °C until development. The highest densities of silver grains in the autoradiographs were associated with regions of the tissue containing the greatest amounts of connective tissue. Lowest densities occurred beneath neurons and myelinated nerve fibres. The silver grain density beneath neuron peri-karya was between 10% and 15% of that associated with plasma. Attempts were made to determine the source of these subneuronal silver grains. The results suggested that they could not be ascribed to the following: background; chemographs and pressure artefacts; spread of radiation from radioactive material outside the perikarya; and in vitro translocation of radio-active material into the neurons or into the emulsion beneath the neurons. It was concluded that the subneuronal grains reflected a small amount of intraneuronal penetration of the compounds in vivo. There was very little difference between inulin, mannitol and sulphate with regard to the proportion of intracellular activity. Except for this small amount of intracellular radioactivity, the findings accord with the view that inulin, mannitol and sulphate are confined predominantly to the extracellular fluid.

Direct Comparison of Subglottal and Esophageal Pressure during Speech

Subglottal air pressure during speech was measured by two methods: (1) by recording from a tracheal catheter, and (2) by recording from a 10-cm-long balloon positioned in the middle third of the esophagus and correcting for the pressure developed by the elastic recoil of the lungs. A simple linear elastic-recoil correction factor was devised. The two measures of subglottal air pressure yielded similar results. Some of the conditions that can produce pressure artifacts in esophageal balloons are discussed. The data also show that peaks in subglottal air pressure are not always associated with phonetic prominence, particularly when several noncontiguous words are emphasized in the same breath group.

Cardiac Pressures and Pulses.

This small book by Luisada and Liu summarizes in 109 pages aspects of hemodynamic cardiac phenomena obtained by cardiac catheterization with the Fick principle for recording variations in cardiac output and pressure. The monograph includes a discussion, in more or less conventional fashion, of the cardiac cycle, technique of catheterization, normal patterns of pressure in the chambers and large vessels, abnormal pressure patterns, artifacts, and formulas used in cardiac catheterization. There is a bibliography of 77 references and an index. There is nothing really unique about the monograph or anything new. It contains the ideas and methods of approach and thinking of Luisada and his associates, which have been published already. This book does accumulate them however, so that it can serve as a source of this information for others. The monograph will serve beginners best, provided they realize it is a condensed version of the problem and the authors'