Slow Pressure Waves Research Articles

Daytime dexmedetomidine sedation with closed-loop acoustic stimulation alters slow wave sleep homeostasis in healthy adults

BackgroundThe alpha-2 adrenergic agonist dexmedetomidine induces EEG patterns resembling those of non-rapid eye movement (NREM) sleep. Fulfilment of slow wave sleep (SWS) homeostatic needs would address the assumption that dexmedetomidine induces functional biomimetic sleep states. MethodsIn-home sleep EEG recordings were obtained from 13 healthy participants before and after dexmedetomidine sedation. Dexmedetomidine target-controlled infusions and closed-loop acoustic stimulation were implemented to induce and enhance EEG slow waves, respectively. EEG recordings during sedation and sleep were staged using modified American Academy of Sleep Medicine criteria. Slow wave activity (EEG power from 0.5 to 4 Hz) was computed for NREM stage 2 (N2) and NREM stage 3 (N3/SWS) epochs, with the aggregate partitioned into quintiles by time. The first slow wave activity quintile served as a surrogate for slow wave pressure, and the difference between the first and fifth quintiles as a measure of slow wave pressure dissipation. ResultsCompared with pre-sedation sleep, post-sedation sleep showed reduced N3 duration (mean difference of −17.1 min, 95% confidence interval −30.0 to −8.2, P=0.015). Dissipation of slow wave pressure was reduced (P=0.02). Changes in combined durations of N2 and N3 between pre- and post-sedation sleep correlated with total dexmedetomidine dose, (r=−0.61, P=0.03). ConclusionsDaytime dexmedetomidine sedation and closed-loop acoustic stimulation targeting EEG slow waves reduced N3/SWS duration and measures of slow wave pressure dissipation on the post-sedation night in healthy young adults. Thus, the paired intervention induces sleep-like states that fulfil certain homeostatic NREM sleep needs in healthy young adults. Clinical trial registrationClinicalTrials.gov NCT04206059.

Ultrasonic characterization of multi-layered porous lithium-ion battery structure for state of charge

A multi-layered porous finite element model of lithium-ion battery is proposed by using Voronoi polygons. The time domain simulation of ultrasonic transmission characteristics with different state of charge (SOC) are carried out, and the variation of acoustic parameters versus SOCs is explored. Then, in the experiment research, the ultrasonic transmission signals are obtained by employing piezoelectric ceramic transducers during the discharging step. By extracting the time domain characteristic parameters, it is discovered that the amplitude and time-of-flight (TOF) have a strong correlation with SOC, the slow pressure-wave (SPW) velocities of the experiments correspond well with the simulation results. In addition, the frequency domain analysis shows a linear link between the amplitude of the frequency spectrum and SOC. Moreover, via repeated experiments, it is found that the ultrasonic transmission method has good repeatability in probing the SOC, and the SPW velocities acquired by experiments can almost be covered by 95% confidence interval formed based on the results of the simulation. Furthermore, according to the results of the experiments, a gray model based on the particle swarm optimization-based-simulated annealing (GM-PSO-SA) is established, which realized the prediction of the SOC under the condition of small sample data. The research results can serve as a reference for creating a comprehensive finite element model of the multi-layered porous structure of lithium-ion battery. Meanwhile, it also provides a detection and evaluation tool for the monitoring of the SOC.

Inducing oscillations in positive end-expiratory pressure improves assessment of cerebrovascular pressure reactivity in patients with traumatic brain injury.

The cerebral pressure reactivity index (PRx), through intracranial pressure (ICP) measurements, informs clinicians about the cerebral autoregulation (CA) status in adult-sedated patients with traumatic brain injury (TBI). Using PRx in clinical practice is currently limited by variability over shorter monitoring periods. We applied an innovative method to reduce the PRx variability by ventilator-induced slow (1/min) positive end-expiratory pressure (PEEP) oscillations. We hypothesized that, as seen in a previous animal model, the PRx variability would be reduced by inducing slow arterial blood pressure (ABP) and ICP oscillations without other clinically relevant physiological changes. Patients with TBI were ventilated with a static PEEP for 30 min (PRx period) followed by a 30-min period of slow [1/min (0.0167 Hz)] +5 cmH2O PEEP oscillations (induced (iPRx period). Ten patients with TBI were included. No clinical monitoring was discontinued and no additional interventions were required during the iPRx period. The PRx variability [measured as the standard deviation (SD) of PRx] decreased significantly during the iPRx period from 0.25 (0.22-0.30) to 0.14 (0.09-0.17) (P = 0.006). There was a power increase around the induced frequency (1/min) for both ABP and ICP (P = 0.002). In conclusion, 1/min PEEP-induced oscillations reduced the PRx variability in patients with TBI with ICP levels <22 mmHg. No other clinically relevant physiological changes were observed. Reduced PRx variability might improve CA-guided perfusion management by reducing the time to find "optimal" perfusion pressure targets. Larger studies with prolonged periods of PEEP-induced oscillations are required to take it to routine use.NEW & NOTEWORTHY Cerebral autoregulation assessment requires sufficient slow arterial blood pressure (ABP) waves. However, spontaneous ABP waves may be insufficient for reliable cerebral autoregulation estimations. Therefore, we applied a ventilator "sigh-function" to generate positive end-expiratory pressure oscillations that induce slow ABP waves. This method demonstrated a reduced variability of the pressure reactivity index, commonly used as continuous cerebral autoregulation measure in a traumatic brain injury population.

The flame propagation characteristics and detonation parameters of ammonia/oxygen in a large-scale horizontal tube: As a carbon-free fuel and hydrogen-energy carrier

As a carbon-free fuel and a hydrogen-energy carrier, ammonia is a potential candidate for future energy utilization. Therefore, in order to promote the application of ammonia in detonation engines and to evaluate the safety of ammonia related industrial process, DDT experiments for ammonia/oxygen mixtures with different ERs were carried out in a large-scale horizontal tube. Moreover, pressure transducers and self-developed temperature sensors were applied to record the overpressure and the instantaneous flame temperature during DDT process. The results show that the DDT process in ammonia/oxygen mixtures contains four stages: Slow propagation stage, Flame and pressure wave acceleration stage, Fast propagation and detonation wave formation stage, Detonation wave self-sustained propagation stage. For stoichiometric ammonia/oxygen mixtures, flame front and the leading shock wave propagate one after another with different velocity, until they closely coupled and propagated together with one steady velocity. At the same time, it is found that an interesting retonation wave propagates backward. The peak overpressure, detonation velocity, and flame temperature of the self-sustained detonation are 2 MPa, 2000 m/s and 3500 K, respectively. With the ER increased from 0.6 to 1.6, the detonation velocities and peak overpressures ranged from 2310 m/s to 2480 m/s and 25.6 bar–28.7 bar, respectively. In addition, the detonation parameters of ammonia were compared with those of methane and hydrogen to evaluate the detonation performance and destructiveness of ammonia.

Seismic metasurfaces on porous layered media: Surface resonators and fluid-solid interaction effects on the propagation of Rayleigh waves

Seismic surface wave mitigation using metamaterials is a growing research field propelled by intrinsic theoretical value and possible application prospects. Up to date, the complexity of site conditions found in engineering practice, which can include layered stratigraphy and variable water table level, has been discarded in the development of analytical frameworks to favor the derivation of simple, yet effective, closed-form dispersion laws. This work provides a further step towards the analytical study of “seismic metasurfaces” in real site conditions considering the propagation of Rayleigh waves through a layered porous substrate equipped with local resonators. To this aim, we combine classical elasticity theory, Biot’s poroelasticity and an effective medium approach to describe the metasurface dynamics and its coupling with the poroelastic substrate. The developed framework naturally includes simpler configurations like seismic metasurfaces atop homogeneous dry or saturated soils. Apart from known phenomena like wave-resonance hybridization and surface wave band gaps, we predict the existence of an extended frequency range where surface waves are attenuated due to energy leakage in the form of slow pressure waves, as a result of the fluid-solid interaction. Besides, we demonstrate that the surface wave band gap and the related surface-to-shear wave conversion is robust to variations in the water table level. Conversely, when the dry and saturated layers have different material parameters, for example, due to different porosity ratios, the surface-to-shear wave conversion can be accompanied by the excitation of higher-order surface modes, which remain channeled below the metasurface. These analytical findings, augmented and confirmed by numerical simulations, evidence the importance of accounting for fluid-solid interaction in the dynamics of seismic metasurfaces.

Pressure diffusion wave and shear wave in gels with tunable wave propagation properties

Gels are composed of cross-linked polymer network and solvent. Gels are both ubiquitous in nature and widely applied in engineering applications. In this work, we develop a physics-based dynamic theory to investigate the tunable wave propagation properties of gels. Gels are soft and can generate large deformation. The constitutive relation takes account the coupled large deformation and diffusion of gels. The dynamic governing equations take account the relative motions between the polymer network and solvent, which leads to a pressure diffusion wave similar to the “slow pressure wave” in the classical Biot’s poroelastodynamics. It is different from the pressure wave in pure solid or pure liquid. The phase velocity, group velocity and attenuation coefficient are analyzed at different frequencies and propagating directions for both pressure wave and shear wave. We show that the wave propagation properties of gels are not only related to the material properties including the crosslink density and the interaction property between solvent and polymer, but also can be tuned by different mechanical loading conditions and chemical stimuli. It is also predicted that the constrained swollen gel exhibits anisotropic wave propagation properties, which leads to the splitting of the pressure wave and shear wave propagating through it. The theory provides a general frame for fundamental understanding and quantitative characterization of the dynamic behaviors of gels.

Influence of prucalopride on esophageal secondary peristalsis in reflux patients with ineffective motility.

Ineffective esophageal motility (IEM) is associated with gastroesophageal reflux disease. Secondary peristalsis contributes to esophageal clearance. Prucalopride promotes secondary peristalsis by stimulating 5-hydroxytrypatamine 4 receptors in the esophagus. We aimed to determine whether prucalopride would augment secondary peristalsis in gastroesophageal reflux disease patients with IEM. After a baseline recording of primary peristalsis, secondary peristalsis was stimulated by slow and rapid mid-esophageal injections of air in 15 patients with IEM. Two separate sessions with 4-mg oral prucalopride or placebo were randomly performed. Prucalopride significantly increased primary peristaltic wave amplitude (68.1±10.0 vs 55.5±8.8mmHg, P=0.02). The threshold volume for triggering secondary peristalsis was significantly decreased by prucalopride during slow (9.3±0.8 vs 12.0±0.8mL; P=0.04) and rapid air injection (4.9±0.3 vs 7.1±0.1mL; P=0.01). Secondary peristalsis was triggered more frequently after application of prucalopride (55% [43-70%]) than placebo (45% [33-50%]) (P=0.008). Prucalopride did not change pressure wave amplitudes during slow air injection (84.6±8.1 vs 57.4±13.8mmHg; P=0.19) or pressure wave amplitudes during rapid air injection (84.2±8.6 vs 69.5±12.9mmHg; P=0.09). Prucalopride enhances primary peristalsis and mechanosensitivity of secondary peristalsis with limited impact on secondary peristaltic activities in IEM patients. Our study suggests that prucalopride appears to be useful in augmenting secondary peristalsis in patients with IEM only via sensory modulation of esophageal secondary peristalsis.

Analytical analysis of slow and fast pressure waves in a two-dimensional cellular solid with fluid-filled cells.

Wave propagation in cellular and porous media is widely studied due to its abundance in nature and industrial applications. Biot's theory for open-cell media predicts the existence of two simultaneous pressure waves, distinguished by its velocity. A fast wave travels through the solid matrix, whereas a much slower wave is carried by fluid channels. In closed-cell materials, the slow wave disappears due to a lack of a continuous fluid path. However, recent finite element (FE) simulations done by the authors of this paper also predict the presence of slow pressure waves in saturated closed-cell materials. The nature of the slow wave is not clear. In this paper, an equivalent unit cell of a medium with square cells is proposed to permit an analytical description of the dynamics of such a material. A simplified FE model suggests that the fluid-structure interaction can be fully captured using a wavenumber-dependent spring support of the vibrating cell walls. Using this approach, the pressure wave behavior can be calculated with high accuracy, but with less numerical effort. Finally, Rayleigh's energy method is used to investigate the coexistence of two waves with different velocities.

Anorectal Manometry in Wistar Rats with Inexpensive Setup: A Physiological Description of the Mechanical Activity

Anorectal manometry is a common technique for investigating the performance of the anal canal. The absence of the rectosphincteric reflex may determine the existence of important pathologies. Animal models are essential to assess the efficacy of new therapies as well as to provide a better understanding of the physiological mechanisms underlying intestinal motility. This paper describes an inexpensive laboratory setup for experimental anorectal manometry that consists of a water-perfused customized catheter, a signal acquisition and processing system, and a personal computer with a software program to display biosignals. Twenty Wistar rats, ten males and ten females, were anesthetized using a ketamine–xylazine intraperitoneal injection. The basal tone of the anorectal sphincter and the rectosphincteric reflex were studied. In basal conditions, two frequency peaks were found, one at 0.015 ± 0.007 Hz and the other at 0.363 ± 0.057 Hz, corresponding to slow and ultraslow pressure waves, respectively. The maximum resting pressure varied between 37.8 and 109.0 mmHg. Anorectal relaxations derived from stimulation of the rectum wall dropped to 82.65 ± 14.61 % of the pressure level prior to stimulation. The overall period of the relaxation wave was 10.22 ± 2.91 s. Differences between genders were found: autonomous pressure oscillations were significantly slower in female rats whereas the period of the relaxation wave was significantly shorter in male subjects. Overall, the mechanical description of the anal canal in Wistar rats is similar to that in humans, especially to that in newborns. Therefore, it represents a good animal model for the investigation of anorectal motility.

Time in General Anesthesia: Depriving the Homeostat?

Time in General Anesthesia: Depriving the Homeostat?

Waves in expanding electronegative plasmas containing double layers

Expanding electronegative (EN) plasmas have been previously observed, experimentally, to generate wave activity. Using a particle-in-cell (PIC) code we have investigated these waves in expanding EN plasmas containing a double layer (DL) between an upstream source region and an expanded downstream region. Oxygen reaction rates were used but modified to correspond more closely to experimental conditions. Under a subset of pressures, for which a DL existed, waves were observed traveling upstream in the expanded region, and growing in amplitude in the direction of travel. Both slow and fast waves were observed. The fast wave existed only over part of the slow wave pressure range. The PIC results were compared to both fluid and kinetic theory, both of which assumed axial uniformity. The results of a somewhat simplified fluid theory, ignoring fast wave coupling and collisions with the background gas, gave a remarkable result: if the theory predicted a slow wave instability for any axial parameters in the downstream region, the instability was observed in the simulation. Conversely, if no instability was predicted at any axial position, no instability was observed. More accurate kinetic calculations, including electron and ion Landau damping, and also collisional damping against the background gas, gave wavelengths and growth rates that were consistent with the PIC simulations, and with the fluid results. The kinetic theory also indicated that the fast waves were always stable but became weakly damped for conditions of unstable slow waves. We postulate that nonlinear and nonuniformity effects excite the fast waves.

Effect of cushing response on systemic arterial pressure

This work investigates the complex relationships between cerebrovascular dynamics, intracranial pressure (ICP), Cushing response, and short-term systemic regulation via an original mathematical model. The model has been used to analyze the effects of Cushing response on cardiovascular and cerebrovascular quantities during constant ICP elevation and during the occurrence of ICP plateau waves and to investigate the conditions leading to system instability with the formation of slow (0.05-0.1 Hz) arterial pressure waves. The model may be of value to assist clinicians in finding the balance between clinical benefits of Cushing response and its shortcomings.

24-Hour Rectal Manometry for Overactive Bladder

We describe prolonged rectal manometry used to characterize rectal motor activity patterns and possible rectum-bladder interaction during defecation and micturition in children with nonneuropathic overactive bladder. We evaluated 10 children with a mean +/- SD age of 9.7 +/- 1.3 years with overactive bladder who underwent urodynamics and 24-hour rectal manometric recording. All records were analyzed visually. Rectal contractions were defined as pressure runs exceeding 5 cm H(2)O and lasting longer than 5 seconds. Three rectal motility patterns were noted in all children, including 1) slow tonic pressure waves with a frequency of 3 to 12 per hour, b) rectal motor complexes with a frequency of 3 to 10 per minute and c) single contractions 10 to 30 seconds in duration. The median nocturnal duration of rectal motor complexes was longer than that during the day (16.3 minutes, range 10.8 to 18.8 vs 11.0, range 8.9 to 12.6, p <0.05). As a percent of time, median total contraction time was greater at night than during the day (51.9%, range 42.6% to 56.9% vs 30.6%, range 19.4% to 49.3%, p <0.05). Characteristic rectal activity was seen during defecation and voiding but no bladder-rectum interaction was detected. We identified 3 rectal motility patterns in all children with overactive bladder. Like the upper gastrointestinal tract, the rectum shows some periodic motor activity, which is more frequent at night. No association was observed between bladder and rectal activity during micturition and defecation.

Aspects of the lateral and vertical resolution of surface electroseismic data with implications for groundwater exploration in fractured Karoo rocks

Horizontal bedding-plane fractures are of prime importance for the drilling of successful water-supply boreholes in Karoo rocks, but usually have very localized occurrences and small aperture widths. Geophysical methods conventionally used for groundwater exploration in Karoo rocks are unable to detect these fractures. Electroseismic (ES) methods make use of the fact that electromagnetic waves are radiated when seismic waves cause fluid flow across interfaces between porous media of different electrokinetic properties. Since the electrokinetic contrast between a fluid-filled fracture and its host is likely to be high, ES signal generation may occur at both the top and bottom interfaces of the fracture. The ability of surface ES methods to detect and resolve the fractures depends on the lateral and vertical resolution of ES data. The ES Fresnel zones are larger than their seismic equivalents and the lateral resolution of ES data is correspondingly poorer. Seismic velocity increases with depth have an additional negative impact on the lateral resolution of ES data. Assuming that a fracture has a measurable surface ES response, a simplified model shows that the response from a localized fracture may be observed at surface positions laterally displaced from the fracture. The presence of large localised unfractured areas occurring within fractured areas may not be detected at all. Rayleigh’s vertical resolution criterion applied to electroseismic data requires that an embedded thin layer have a minimum thickness of half the dominant wavelength of the seismic wave. Since the Biot slow wave has a much smaller wavelength than the Biot fast wave, it would seem that the limits of vertical resolution are determined by the dominant wavelength of the slow wave. The dissipative nature of the slow wave, however, may cause the practical limit of vertical resolution to be more dependent on the wavelength of the fast wave. The detection of a thin embedded layer depends on the conditions of constructive and destructive interference of signal generated at its top and bottom interfaces. For both the fast and slow wave a thin bed with a thickness less than a quarter of the dominant wavelength results in a total ES response that is weaker than the response from the top interface alone. For both fast and slow pressure waves this thickness is much larger than the aperture width of the bedding-plane fractures in Karoo rocks, and detection of these fractures with surface ES methods seems unlikely.

Novel sound phenomena in superfluid helium in aerogel and other impure superfluids

During the last decade new techniques for producing impure superfluids with unique properties have been developed. This new class of systems includes superfluid helium confined to aerogel, HeII with different impurities (D 2, N 2, Ne, Kr), superfluids in Vycor glasses, and watergel. These systems exhibit very unusual properties including unexpected acoustic features. We discuss the sound properties of these systems and show that sound phenomena in impure superfluids are modified from those in pure superfluids. We calculate the coupling between temperature and pressure oscillations for impure superfluids and for superfluid He in aerogel. We show that the coupling between these two sound modes is governed either by c∂ρ/ ∂c or σρ a ρ s (for aerogel) rather than thermal expansion coefficient ∂ρ/ ∂T, which is enormously small in pure superfluids. This replacement plays a fundamental role in all sound phenomena in impure superfluids. It enhances the coupling between the two sound modes that leads to the existence of such phenomena as the slow mode and heat pulse propagation with the velocity of first sound observed in superfluids in aerogel. This means that it is possible to observe in impure superfluids such unusual sound phenomena as slow pressure (density) waves and fast temperature (entropy) waves. The enhancement of the coupling between the two sound modes decreases the threshold values for nonlinear processes as compared to pure superfluids. Sound conversion, which has been observed in pure superfluids only by shock waves should be observed at moderate sound amplitude in impure superfluids. Čerenkov emission of second sound by first sound (which never been observed in pure superfluids) could be observed in impure superfluids.

Slow pressure waves in the cranial enclosure.

Slowly varying pressure oscillations in the cranial enclosure are well known, especially intracranial pressure waves as best described by the pioneering works of Janny and Lundberg. Nevertheless, in spite of over twenty five years research on intracranial pressure waves, their origin and regulation remain unclear but are often considered only as pathological. Our aim was to review data on these phenomena to clarify their biological status and the role that they could play in the management of patients suffering from such intracranial neurosurgical diseases as intracranial hypertension, severe head injury, and hydrocephalus. It appears that these pressure waves reveal important information on the function of the cerebral vasculature and as such have significance for influencing intracranial compliance. Pressure waves are also closely associated with autoregulation, in particular dynamic autoregulation. It seems evident that they are not only pathophysiological but also physiological, linked with other biological parameters such as the neurovegetative cardiovascular system, breathing, and sleeping. This study shows that it is not only important to continue to explore these slow waves, but also the methods of analysis in order to more fully clarify their clinical significance.

Slow pressure waves during intracranial hypertension

Intracranial pressure waves include fast waves (pulse and respiration) and slow waves. Only the latter are considered here. Since the definition of three wave types in the pioneering works of Janny (1950) and Lundberg (1960), their study of frequential characteristics shows they are included in a spectrum where three contiguous frequency bands are individualised: the B wave band (BW) between 8 x 10(-3) Hz and 50 x 10(-3) Hz; the Infra B band (IB) below 8 x 10(-3) Hz; and the Ultra B band (UB) beyond 50 x 10(-3) Hz to 200 x 10(-3) Hz. The origin of these waves is vascular and some may be physiological. They are probably generated by central neuro-pacemakers and/or cyclic phenomena of cerebral autoregulation. They are linked with slow peripheral arterial pressure waves, with biological rhythms and with biomechanics and vasomotricity in the craniospinal enclosure. They are pathological for the slowest (IB), particularly if they are plateau waves, but the physiologic-pathologic boundary is not yet established for each type of slow waves. They can cause severe consequences if they result in major cerebral perfusion pressure changes, and if they induce or worsen herniations.

A computer software for frequential analysis of slow intracranial pressure waves

A microcomputer program to analyse ICP signal in the frequential domain is described. It allows the detection and quantification of especially slow pressure waves (A, B, and C). 212 ICP data recordings were analysed with our software, and gave pertinent frequential informations. The status report and lessons learned are discussed.

Structure and dynamics of the slow pressure wave in a porous medium saturated with a liquid containing gas bubbles

Structure and dynamics of the slow pressure wave in a porous medium saturated with a liquid containing gas bubbles

Ultra slow wave pressure variations in the anal canal before and after lateral internal sphincterotomy.

Ultra slow waves (USW's) in the anal canal are discrete pressure fluctuations with a low frequency (1-2/minute) and high amplitude (> or = 10% above or below baseline resting pressure). To investigate the nature of these USW's, anorectal manometry was performed in 20 control subjects as well as in 58 patients presenting with anal fissure or symptomatic hemorrhoids, before and 2 weeks after lateral internal sphincterotomy. USW's could be demonstrated in two control subjects and in 29 patients. The median value of maximum anal resting pressure (MARP) in the two control subjects with USW's was significantly higher than the median MARP in the 18 control subjects without USW's (181.5 vs. 92 cm H2O, p < 0.001, two-tailed Mann-Whitney test). The same difference was found between MARP in patients with and without USW's (158 vs. 138 cm H2O, p < 0.05, two-tailed Mann-Whitney test). All patients were treated by means of lateral internal sphincterotomy (LIS). Two weeks after this procedure USW's had disappeared in half of the patients. The MARP in these patients was reduced to a level found in control subjects without USW's. This pressure reduction was significantly greater than in patients with persistent USW's (40% vs. 15%, p < 0.02, two-tailed Mann-Whitney test). Because USW's are associated with high MARP and disappear when such a high anal canal resting pressure is reduced by LIS to a level found in control subjects without USW's, it can be concluded that USW's are the manifestation of increased activity of the internal anal sphincter.