Differences In Pressure Responses Research Articles

The added value of symptom analysis during a rapid drink challenge in high-resolution esophageal manometry.

Patients with esophageal symptoms often remain with an uncertain diagnosis after high-resolution manometry. To determine the added value of concomitant pressure and symptom analysis in response to a rapid drink challenge (RDC). In consecutive patients referred for esophageal manometry, a RDC consisting in free drinking of 200ml of water as quick as possible was performed after the standard single water swallows manometry. Both pressure patterns and usual symptoms induced by the RDC were analyzed. A total of 1319 patients were included, (64.7% women, mean age 58.2years, range 11-90). There were significant differences in pressure responses between patients with obstructive disorders, major hypercontractile disorders, esophageal hypomotility disorders and normal motility. The RDC provoked usual symptoms in 388 (29.4%) patients, associated with hyperpressive and obstructive patterns in 14.0% and 16.6%, respectively. Reproduction of dysphagia and regurgitation (not pain) was significantly associated with abnormal pressure responses during the RDC (p<0.001 and p=0.002, respectively). The RDC elicited both abnormal pressure patterns and symptoms in 6.2%, 1.6%, and 20.8% of patients with normal motility, ineffective esophageal motility, and esophago-gastric junction outflow obstruction, respectively. Concomitant evaluation of symptoms and pressure responses to a RDC may increase the specificity of esophageal motor testing in patients with inconclusive diagnosis or normal esophageal motility.

Impact of incubation conditions and post-treatment on the properties of bacterial cellulose membranes for pressure-driven filtration

Bacterial cellulose (BC) has shown potential as a separation material. Herein, the performance of BC in pressure-driven separation is investigated as a function of incubation conditions and post-culture treatment. The pure water flux of never-dried BC (NDBC), was found to be 9 to 16 times higher than that for dried BC (DBC), in a pressure range of 0.25 to 2.5 bar. The difference in pressure response of NDBC and DBC was observed both in cross-flow filtration and capillary flow porometry experiments. DBC and NDBC were permeable to polymers with a hydrodynamic radius of ∼60 nm while protein retention was possible by introducing anionic surface charges on BC. The results of this work are expected to expand the development of BC-based filtration membranes, for instance towards the processing of biological fluids.

Effect of L-arginine intake on exercise-induced hypotension.

to verify if one single dose of L-arginine improves post-exercise hypotension (PEH) in hypertensive. double-blind, placebo, randomized with 20 hypertensive (51.47 ± 1.24 years). Two sessions of aerobic exercise were performedproceeded for the ingestion of one dose of 7 g of L-arginine (EX-LARG) or placebo (EX-PLA), plus one session only with L-arginine ingestion(L-ARG). Blood pressure (BP) was measured at rest, and each ten minutes for a period of 60 minutes recovery after exercise. Blood samples weretaken before and after exercise for analysis of plasma concentration of nitrite and malondialdehyde (MDA). One-way ANOVA tests were used tocompare the baseline conditions and two-way ANOVA, to evaluate possible differences in pressure responses between procedures. both sessions EX-LARG and EX-PLA showed similar peak reduction for the mean systolic blood pressure (-6.58 ± 0.95 mmHg and-8.38 ± 1.29 mmHg respectively, p = 0.28). On the other hand, for the diastolic component, only L-ARG was able to promote PEH (-1.85 ±0.44 mmHg), significantly better than EX-PLA (+2.13 ± 0.62 mmHg; p < 0.01). L-ARG alone did not result in significant changes in BP. Nitriteand MDA behaved similarly between procedures. a single dose of L-arginine before exercise improves diastolic PEH.

Observation of intermediate states of the human prion protein by high pressure NMR spectroscopy

BackgroundPrions as causative agents of transmissible spongiform encephalopathies (TSEs) in humans and animals are composed of the infectious isomer, PrPSc, of the cellular prion protein, PrPC. The conversion and thus the propensity of PrPC to adopt alternative folds leads to the species-specific propagation of the disease. High pressure is a powerful tool to study the physico-chemical properties of proteins as well as the dynamics and structure of folding intermediates.ResultsConformational intermediates of the human prion protein huPrPC were characterized by a combination of hydrostatic pressure (up to 200 MPa) with two-dimensional NMR spectroscopy. All pressure effects showed to be reversible and there is virtually no difference in the overall pressure response between the folded core of the N-terminal truncated huPrPC(121–230) and the full-length huPrPC(23–230). The only significant differences in the pressure response of full-length and truncated PrP suggest that E168, H187, T192, E207, E211 and Y226 are involved in a transient interaction with the unfolded N-terminus. High-pressure NMR spectroscopy indicates that the folded core of the human prion protein occurs in two structural states N1and N2 in solution associated with rather small differences in free enthalpies (3.0 kJ/mol). At atmospheric pressure approximately 29% of the protein are already in the pressure favored conformation N2. There is a second process representing two possible folding intermediates I1 and I2 with corresponding average free enthalpies of 10.8 and 18.6 kJ/mol. They could represent preaggregation states of the protein that coexist at ambient pressure with a very small population of approximately 1.2% and less than 0.1%. Further the pressure response of the N-terminus indicates that four different regions are in a fast equilibrium with non-random structural states whose populations are shifted by pressure.ConclusionWe identified pressure stabilized folding intermediates of the human prion protein. The regions reflecting most strongly the transition to the intermediate states are the β1/α1-loop and the solvent exposed side of α3. The most pressure-sensitive region (representing mainly intermediate I1) is the loop between β-strand 1 and α-helix 1 (residue 139–141), indicating that this region might be the first entry point for the infectious conformer to convert the cellular protein.

Role of short-term regulatory mechanisms on pressure response to hemodialysis-induced hypovolemia

A large inter-subject variability exists in the arterial pressure response to hemodialysis-induced blood volume (BV) withdrawal. We investigated the hypothesis that this variability is due to the inter-subject differences in the short-term reflex capacity to compensate for hypovolemia. Mean arterial pressure (MAP), heart rate (HR) and the percentage reduction in BV (%R-BV) were recorded in 32 subjects during their regular hemodialysis sessions. On the basis of absolute MAP changes between the beginning and the end of the session with respect to %R-BV at the end of the session, three distinct pressure responses were identified: (1) hypotension-prone response; (2) unstable response with delayed hypotension; and (3) hypotension-resistant response. For each kind of response, one patient was selected and a computer model of the cardiovascular system including the main short-term reflex compensatory mechanisms was used to analyze data collected over five consecutive sessions. The %R-BV and HR were used as model inputs, while simulated arterial pressure was fitted to the measured MAP by the tuning model parameters representing the efficiency in the control of venous capacity, microvascular resistance and heart inotropism. The model-based analysis related the hypotension-prone response to a lack of efficacy in capacity and resistance regulation. In the unstable response with delayed hypotension, the control of venous capacity was not effective and resistance control alone kept the pressure stable only for a limited %R-BV reduction (<5%). In the hypotension-resistant response, an efficient compensation of capacitance vessels was evidenced, and the slightly increasing arterial pressure was referred to a prevalence of cardiopulmonary pathway in the compensatory process. The model ascribes differences in pressure response to differences in the effectiveness of reflex compensatory mechanisms.

Improvement of fecal continence through stimulation of the M. sphincter ani externus

Using the pig as a model, it was shown that stimulation of the distal nerve ending of the pudendal nerve leads to the isolated stimulation of the external anal sphincter muscle. No difference in pressure response was noted after application of between 0.5 and 1.5 mA unilateral or bilateral stimulation. Major advantages observed using between 1.5 and 2.5 mA bilateral stimulation; with a stimulation between 2.0 and 2.5 mA the pressure response was twice as high compared to unilateral stimulation. Continuous stimulation of the striated anal sphincter muscle leads to fatigue, reaching 50% fatigue after a median time between 40-90 s. In cyclic stimulation (alternation every 15 s, duration 20 min) a fatigue reaction was also seen. The peak pressure decreased after 20 min for a median of 11%, the final pressure was lowered in 15% following a logarithmic curve pattern. The experimental application of variable impulse ranges also caused pressure differences. Increasing the impulse range from 200 to 450 microseconds (peak pressure) vs. 400 microseconds (final pressure) resulted in a statistically significant pressure increase. Therefore, it was proven that selective stimulation of the external anal sphincter muscle can lead to a transient pressure increase, which possibly improves fecal continence.

Relation between intra-abdominal pressure and lumbar stress: effect of trunk posture.

The recording of intra-abdominal pressure (IAP) variations has been proposed as a tool for evaluating the biomechanical stress imposed on the low back in working tasks. Literature data are however controversial as regards the relationship between IAP and lumbar stress, some studies showing that IAP increases with trunk flexion while others indicate that IAP is greater when the trunk is kept erect. The present study was aimed at a quantification of this relation for sagittal-plane lifting activities performed at various inclinations of the trunk. Fifteen young males lifted loads ranging from 49 N to 147N from four standing postures: trunk erect and trunk flexed at 30, 60 and 90 degrees from the vertical. The force exerted at the hands, as well as intra-abdominal and intrathoracic pressures were recorded throughout the lift and the L4/L5 moment was calculated using a static biomechanical model. Results showed that the IAP-moment relation is influenced both by the trunk angle and by individual characteristics. Peak IAP increases per unit increase in lumbar moment were higher in the erect posture than in the flexed ones, and in each posture were inversely related to the subject's stature and maximal oxygen uptake. In the flexed postures, no significant general IAP-moment relation could be drawn from the 15 subjects1 data, whereas at the individual level, the relation was significant for two thirds of the subjects. The study thus shows that IAP cannot be used as an index of biomechanical stress, unless the individual IAP to lumbar moment relation is considered. It is suggested that the differences in pressure response found between erect and flexed trunk postures were related more to differences in the leverage moment acting at the shoulder than to differences in trunk angle.

Response of a Realistic Human Head-Neck Model to Impact

A structurally realistic model of the human head-neck system, consisting of a water-filled human cadaver skull and an artificial neck was subjected to pendulum impact under nondestructive conditions. The neck consisted of a series of neoprene and aluminum rings fabricated so as to faithfully reproduce the head motion of living persons in the saggital plane. Both an aluminum spherical shell and a solid steel sphere were employed to produce contact durations of the order of 1–6 ms and 0.2–1 ms, respectively, depending upon whether the impact occurred against the bare skull or against one of several scalp simulators used. Both frontal and occipital blows were produced on the system. A series of pressure transducers were suspended along the impact axis that measured the history of this parameter for the various conditions employed, and a crystal transducer arrangement ascertained the force input to the system. A displacement gage was utilized to record the excursion of the head-neck junction. Significant differences in pressure response were noted between frontal and occipital blows without protective covers that disappeared when scalp simulators were employed. The response characteristics in the present tests were much simpler than in corresponding tests using an acrylic shell for the head model, where pressures under similar impulsive loading conditions were at least an order of magnitude larger; this difference is attributed to the layering effect of the real skull relative to the homogeneous shell previously used.

Environmental Effects on Phosphorescence. VI. Matrix Site Effects for Triphenylene

The phosphorescence lifetime and spectra of triphenylene are studied in different matrices at 77°K and as a function of increasing pressure (0–30 kbar). The magnitude of the pressure shift of the spectra and the pressure coefficient of the lifetime depend upon the size of the molecules comprising the solvent cage. This difference in pressure response is attributed to the preponderance of repulsive interactions between highly symmetric triphenylene and smaller solvent molecules under pressure.

EFFECT OF AN ORAL OSMOTIC AGENT ON VENTRICULAR FLUID PRESSURE OF HYDROCEPHALIC CHILDREN

To quantitatively measure the effect of oral isosorbide on ventricular fluid pressure in hydrocephalic children, a method for continuous direct pressure recording with a closed isometric system was utilized. A baseline pressure pattern could be established for each patient, and the effect of drug could be observed with follow-through for reestablishment of baseline pressure after the last dose of drug. Fourteen hydrocephalic children have been given oral isosorbide in doses varying from 1 to 3 gm per kilogram. Significant (average 50%) reduction in ventricular fluid pressure was measured in 13 of the 14 children following a single dose of isosorbide. Rebound pressure greater than baseline was measured in 5 of the 10 children given multiple doses of isosorbide. No toxic side effects were observed during the single dose studies. Clinically significant dehydration and hypernatremia began to occur after 72 hours of continuous drug administration. Serum-CSF gradient curves for drug level and osmolarity are included to show the correlation of these gradients to the ventricular fluid pressure. Pressure curves comparing the effects of intravenous urea, intravenous mannitol, and oral acetazolamide show the quantitative differences in pressure response which can be observed when the pressures are being recorded continuously with a closed system.