Dynamic Volume Changes Research Articles

Evidence for an increasing role of ocean heat in Arctic winter sea ice growth

AbstractWe investigate how sea ice decline in summer and warmer ocean and surface temperatures in winter affect sea ice growth in the Arctic. Sea ice volume changes are estimated from satellite observations during winter from 2002 to 2019 and partitioned into thermodynamic growth and dynamic volume change. Both components are compared to validated sea ice-ocean models forced by reanalysis data to extend observations back to 1980 and to understand the mechanisms that cause the observed trends and variability. We find that a negative feedback driven by the increasing sea ice retreat in summer yields increasing thermodynamic ice growth during winter in the Arctic marginal seas eastward from the Laptev Sea to the Beaufort Sea. However, in the Barents and Kara Seas, this feedback seems to be overpowered by the impact of increasing oceanic heat flux and air temperatures, resulting in negative trends in thermodynamic ice growth of -2 km3month-1yr-1 on average over 2002-2019 derived from satellite observations.

Quantitative MRI texture analysis in chronic active multiple sclerosis lesions

ObjectiveRecently, there has been an increasing interest in “chronic enlarging” or “chronic active” multiple sclerosis (MS) lesions that are associated with clinical disability. However, investigation of dynamic lesion volume changes requires longitudinal MRI data from two or more time points. The aim of this study was to investigate the application of texture analysis (TA) on baseline T1-weighted 3D magnetization-prepared rapid acquisition gradient-echo (MPRAGE) images to differentiate chronic active from chronic stable MS lesions. Material and methodsTo identify chronic active lesions as compared to non-enhancing stable lesions, two MPRAGE datasets acquired on a 3 T MRI at baseline and after 12 months follow-up were applied to the Voxel-Guided Morphometry (VGM) algorithm. TA was performed on the baseline MPRAGE images, 36 texture features were extracted for each lesion. ResultsOverall, 374 chronic MS lesions (155 chronic active and 219 chronic stable lesions) from 60 MS patients were included in the final analysis. Multiple texture features including “DISCRETIZED_HISTO_Energy”, “GLCM_Energy”, “GLCM_Contrast” and “GLCM_Dissimilarity” were significantly higher in chronic active as compared to chronic stable lesions. Partial least squares regression yielded an area under the curve of 0.7 to differentiate both lesion types. ConclusionOur results suggest that multiple texture features extracted from MPRAGE images indicate higher intralesional heterogeneity, however they demonstrate only a fair accuracy to differentiate chronic active from chronic stable MS lesions.

Deep Analysis of EIT Dataset to Classify Apnea and Non-Apnea Cases in Neonatal Patients

Electrical impedance tomography (EIT) is a non-invasive imaging modality that can provide information about dynamic volume changes in the lung. This type of image does not represent structural lung information but provides changes in regions over time. EIT raw datasets or boundary voltages are comprised of two components, termed real and imaginary parts, due to the nature of cell membranes of the lung tissue. In this paper, we present the first use of EIT boundary voltage data obtained from infants for the automatic detection of apnea using machine learning, and investigate which components contain the main features of apnea events. We selected 15 premature neonates with an episode of apnea in their breathing pattern and applied a hybrid classification model that combines two established methods; a pre-trained transfer learning method with a convolutional neural network with 50 layers deep (ResNet50) architecture, and a support vector machine (SVM) classifier. ResNet50 training was undertaken using an ImageNet dataset. The learnt parameters were fed into the SVM classifier to identify apnea and non-apnea cases from neonates' EIT datasets. The performance of our classification approach on the real part, the imaginary part and the absolute value of EIT boundary voltage datasets were investigated. We discovered that the imaginary component contained a larger proportion of apnea features.

Viscoelasticity and Volume of Cortical Neurons under Glutamate Excitotoxicity and Osmotic Challenges

Neural activity depends on the maintenance of ionic and osmotic homeostasis. Under these conditions, the cell volume must be regulated to maintain optimal neural function. A disturbance in the neuronal volume regulation often occurs in pathological conditions such as glutamate excitotoxicity. The cell volume, mechanical properties, and actin cytoskeleton structure are tightly connected to achieve the cell homeostasis. Here, we studied the effects of glutamate-induced excitotoxicity, external osmotic pressure, and inhibition of actin polymerization on the viscoelastic properties and volume of neurons. Atomic force microscopy was used to map the viscoelastic properties of neurons in time-series experiments to observe the dynamical changes and a possible recovery. The data obtained on cultured rat cortical neurons were compared with the data obtained on rat fibroblasts. The neurons were found to be more responsive to the osmotic challenges but less sensitive to the inhibition of actin polymerization than fibroblasts. The alterations of the viscoelastic properties caused by glutamate excitotoxicity were similar to those induced by the hypoosmotic stress, but, in contrast to the latter, they did not recover after the glutamate removal. These data were consistent with the dynamic volume changes estimated using ratiometric fluorescent dyes. The recovery after the glutamate-induced excitotoxicity was slow or absent because of a steady increase in intracellular calcium and sodium concentrations. The viscoelastic parameters and their changes were related to such parameters as the actin cortex stiffness, tension, and cytoplasmic viscosity.

Assessment of left ventricular diastolic function by three-dimensional transthoracic echocardiography.

Doppler echocardiography assessment of left ventricular (LV) filling pressures at rest and during exercise is the most widely used imaging technique to assess LV diastolic function in clinical practice. However, a sizable number of patients evaluated for suspected LV diastolic function show an inconsistency between the various parameters included in the flowchart recommended by current Doppler echocardiography guidelines and results in an undetermined LV diastolic function. Current three-dimensional echocardiography technology allows obtaining accurate measurements of the left atrial volumes and functions that have been shown to improve the diagnostic accuracy and prognostic value of the algorithms recommended for assessing both LV diastolic dysfunction and heart failure with preserved ejection fraction. Moreover, current software packages used to quantify LV size and function provide also volume-time curves showing the dynamic LV volume change throughout the cardiac cycle. Examining the diastolic part of these curves allows the measurement of several indices of LV filling that have been reported to be useful to differentiate patients with normal LV diastolic function from patients with different degrees of diastolic dysfunction. Finally, several software packages allow to obtain also myocardial deformation parameters from the three-dimensional datasets of both the left atrium and the LV providing additional functional parameters that may be useful to improve the diagnostic yield of three-dimensional echocardiography for the LV diastolic dysfunction. This review summarizes the current applications of three-dimensional echocardiography to assess LV diastolic function.

Effect of Sand Fouling on the Dynamic Properties and Volume Change of Gravel During Cyclic Loadings

Understanding the factors that influence the dynamic behavior of granular soils during cyclic loading is critical to infrastructure design. Previous research has lacked quantitative study of the effects of fouling index (FI), mean effective confining pressure, relative density, shear strain level and anisotropic consolidation, especially when the effective vertical stress is lower than the effective horizontal stress on the dynamic behavior of gravelly soils. The objective of the present study was to evaluate the dynamic behavior and volume change of both clean and fouled specimens for practical applications. To this end, cyclic triaxial tests with local strain measurements under both isotropic and anisotropic confining conditions were conducted. It is found that the fouled specimen with 50 % sand (i.e. the specimen which contains 50 % gravel and 50 % sand) has the highest shear modulus at low shear strain levels and the largest volume reduction and damping ratio at large shear strain levels. The results of tests indicate that the effect of fouling index on the shear modulus is reduced at large shear strain levels. Volumetric contraction due to the increase in mean effective confining pressure is more significant at large shear strain levels. The results also indicate that the stiffness of the specimens under anisotropic compression mode are larger than those in extension or isotropic mode.

A Flexible Patch-Type Strain Sensor Based on Polyaniline for Continuous Monitoring of Pulse Waves

A flexible, patch-type strain sensor is described for continuous monitoring of pulse waves. The proposed sensor exploits the piezo-resistivity of the conductive polymer, polyaniline (PANI), to detect dynamic volume changes in blood vessels owing to pulse waves. The proposed PANI film was fabricated through electrodeposition, which is considered as a suitable low-cost technique for mass production in the sensor manufacturing industry. Thus, it is prospective for a disposable wearable sensing system solution in remote healthcare applications. Besides, a flexible sensor packaging can be achieved by laminating the PANI films and an ECOFLEX elastomer to the film bandage. The proposed PANI sensor has high sensitivity (gauge factor of 74.28) and linearity (R 2 = 0.99). It also showed a high correlation with commercially available photoplethysmography (PPG) sensor with the small bias and confidence interval to the PPG sensor: bias <; 0.1% and confidence interval <; 3% for all subjects. Moreover, the proposed PANI sensor was tested for prospective circulatory system-related applications such as measuring heart rate, stiffness index, and pulse transit time. Finally, the proposed study suggests that the proposed PANI sensor is a promising candidate for continuous, long-term, unobtrusive pulse wave monitoring, which can provide real-time insights into an individual's health status.

Dynamic prostatic and laser-ablated lesion volume change after transperineal laser ablation in canine: preliminary observation and its clinical significance

Aim The purpose of this study is to observe the volume change of prostate and laser-ablated lesions in the canine and to explore the mechanism and clinical significance through histopathology. Materials and methods Transperineal laser ablation (TPLA) was performed under the guidance of transrectal ultrasound (TRUS) in eight canines. Two canines were sacrificed 1 day and 1 week after TPLA, respectively. The remaining six canines were sacrificed after finishing transrectal contrast-enhanced ultrasound (TR-CEUS) at three phases. Results The prostatic volumes immediately following TPLA and 1 week later were larger than before TPLA (20.1 ± 3.9 vs 17.1 ± 3.8 ml; 21.7 ± 3.6 vs 17.1 ± 3.8 ml, p < 0.05), but 1 month later, returned to the preoperative level (17.4 ± 3.2 ml). At three time points, the mean volumes of laser-ablated lesions at 3 W/600 J were 0.6 ± 0.2, 1.1 ± 0.4, and 1.7 ± 0.5 ml, respectively, while those of laser-ablated lesions at 3 W/1200 J were 1.2 ± 0.2, 1.6 ± 0.3, and 2.2 ± 0.5 ml, respectively. The mean volumes of laser-ablated lesions increased significantly over time after TPLA (p < 0.050). Conclusion The prostate volume transient enlarges after TPLA, which prompts for clinical application that it should prolong appropriately the duration of urinary catheterization to avoid acute urinary retention. Many inflammatory cells were observed in the laser-ablated lesions and adjacent normal prostate parenchyma through histopathology. It is speculated that the inflammatory response is involved in the progression of tissue damage.

Dynamic Stable Volume Changes of the Liver Maintaining its Function before and after Stereotactic Body Radiotherapy (SBRT): A Clinical Pilot Study

Dynamic Stable Volume Changes of the Liver Maintaining its Function before and after Stereotactic Body Radiotherapy (SBRT): A Clinical Pilot Study

Dynamic Volume Change Rate and Aspect Ratio Are Correlated to the Formation of an Irregular Morphology of Unruptured Intracranial Aneurysm.

The aim of this research was to study the factors influencing the formation of intracranial aneurysms with irregular morphology by observing the dynamic volume change rate of intracranial unruptured aneurysms and other aneurysm characteristics. Sixty-five unruptured intracranial aneurysms of 51 consecutive patients from 1 center were included in this study. All patients underwent a dual-source computed tomography electrocardiogram-gated 4-dimensional computed tomography angiography examination. The original data at the end of the scan were reconstructed, and 20 sets of data packages through a cardiac cycle with 5% interval were obtained. Data packages were processed by a 3-dimensional software workstation to obtain 20 sets of images and dynamic diagrams. The volume of each aneurysm in the 20 sets of images was measured, and the volume change was calculated by a specific formula. The other data features of the aneurysm such as aneurysm neck, aneurysm height, aspect ratio (AR), location at bifurcation, and clinical features such as age, sex, hypertension history, type 2 diabetes history, smoking history, family history, multiple aneurysm history, and subarachnoid hemorrhage history, were documented in detail. After single factor analysis data, logistic regression analysis of the meaningful indicator was conducted to study the predictive factors of irregular aneurysms. Of the 65 aneurysms, 25 possessed an irregular shape and 40 were of regular shape; 51 were anterior circulatory aneurysms and 14 were posterior circulatory aneurysms. Single factor analysis showed that AR (P = 0.001), volume change rate (P = 0.002), and location of aneurysm at the bifurcation (P = 0.038) of the vessel were significantly correlated with irregular aneurysms, but not correlated with age, sex, hypertension history, type 2 diabetes history, smoking history, family history, multiple aneurysm history, and subarachnoid hemorrhage history. Multifactor analysis showed that volume change rate greater than 30% (P = 0.008; odds ratio, 6.934) and AR greater than 1.4 (P = 0.004; odds ratio, 8.258) were independent correlative factors of the formation of intracranial aneurysm with irregular shape. The volume change rate and AR are independent correlative factors of the formation of intracranial aneurysm with irregular shape.

Rational design of graphitic-inorganic Bi-layer artificial SEI for stable lithium metal anode

Lithium metal batteries (LMBs) have attracted increasing attentions for their ultrahigh specific capacity (3860 mAh g−1) and the lowest electrode potential (−3.04 V vs. standard hydrogen electrode). However, the dynamic volume changes, the complex interfacial reactions, and the dendrite growth remain as the grand challenges in LMBs that prevent their practical applications. A bi-layer artificial solid electrolyte interphase (BL-SEI), which is composed of covalent graphitic materials (graphene and h-BN) and inorganic components (LiF, Li2O, Li3N, and Li2CO3), is rationally designed through comprehensive first-principles calculation to render a stable Li metal anode. Key interfacial properties, such as chemical stability, ionic conductivity, and mechanical strength, are systematically investigated to achieve a rational design of the BL-SEI. Among all the considered BL-SEI, the graphene/LiF combination is hopeful to exhibit the best interfacial stability and electrochemical performance. The protective role of BL-SEI for Li metal anode comes from the coupled effects through the anisotropic character and the defective structure. This work reveals the origin of the significant role of BL-SEI for achieving a stable Li metal anode from the atomic and electronic level, affording a paradigm for rational deign of a high-performance artificial SEI in working LMBs.

Passive Self Resonant Skin Patch Sensor to Monitor Cardiac Intraventricular Stroke Volume Using Electromagnetic Properties of Blood.

This paper focuses on the development of a passive, lightweight skin patch sensor that can measure fluid volume changes in the heart in a non-invasive, point-of-care setting. The wearable sensor is an electromagnetic, self-resonant sensor configured into a specific pattern to formulate its three passive elements (resistance, capacitance, and inductance). In an animal model, a bladder was inserted into the left ventricle (LV) of a bovine heart, and fluid was injected using a syringe to simulate stoke volume (SV). In a human study, to assess the dynamic fluid volume changes of the heart in real time, the sensor frequency response was obtained from a participant in a 30° head-up tilt (HUT), 10° HUT, supine, and 10° head-down tilt positions over time. In the animal model, an 80-mL fluid volume change in the LV resulted in a downward frequency shift of 80.16 kHz. In the human study, there was a patterned frequency shift over time which correlated with ventricular volume changes in the heart during the cardiac cycle. Statistical analysis showed a linear correlation n}{}{R} ^{2} = 0.98n and 0.87 between the frequency shifts and fluid volume changes in the LV of the bovine heart and human participant, respectively. In addition, the patch sensor detected heart rate in a continuous manner with a 0.179% relative error compared to electrocardiography. These results provide promising data regarding the ability of the patch sensor to be a potential technology for SV monitoring in a non-invasive, continuous, and non-clinical setting.

The respiratory mechanics of the yacare caiman (Caiman yacare).

The structure and function of crocodilian lungs are unique compared with those of other reptiles. We examined the extent to which this and the semi-aquatic lifestyle of crocodilians affect their respiratory mechanics. We measured changes in intratracheal pressure in adult and juvenile caiman (Caiman yacare) during static and dynamic lung volume changes. The respiratory mechanics of juvenile caiman were additionally measured while the animals were floating in water and submerged at 30, 60 and 90deg to the water's surface. The static compliance of the juvenile pulmonary system (2.89±0.22 ml cmH2O-1100 g-1) was greater than that of adults (1.2±0.41 ml cmH2O-1100 g-1), suggesting that the system stiffens as the body wall becomes more muscular and keratinized in adults. For both age groups, the lungs were much more compliant than the body wall, offering little resistance to air flow (15.35 and 4.25 ml cmH2O-1100 g-1 for lungs, versus 3.39 and 1.67 ml cmH2O-1100 g-1 for body wall, in juveniles and adults, respectively). Whole-system dynamic mechanics decreased with increasing ventilation frequency (fR), but was unaffected by changes in tidal volume (VT). The vast majority of the work of breathing was required to overcome elastic forces; however, work to overcome resistive forces increased proportionally with fR Work of breathing was higher in juvenile caiman submerged in water at 90deg because of an increase in work to overcome both elastic and flow resistive forces. The lowest power of breathing was found to occur at high fR and low VT for any given minute ventilation (V̇E) in caiman of all ages.

MR brain volumetric measurements are predictive of neurobehavioral impairment in the HIV-1 transgenic rat.

IntroductionHIV infection is known to be associated with brain volume loss, even in optimally treated patients. In this study, we assessed whether dynamic brain volume changes over time are predictive of neurobehavorial performance in the HIV-1 transgenic (Tg) rat, a model of treated HIV-positive patients.Materials and methodsCross-sectional brain MRI imaging was first performed comparing Tg and wild type (WT) rats at 3 and 19 months of age. Longitudinal MRI and neurobehavioral testing of another group of Tg and WT rats was then performed from 5 to 23 weeks of age. Whole brain and subregional image segmentation was used to assess the rate of brain growth over time. We used repeated-measures mixed models to assess differences in brain volumes and to establish how predictive the volume differences are of specific neurobehavioral deficits.ResultsCross-sectional imaging showed smaller whole brain volumes in Tg compared to WT rats at 3 and at 19 months of age. Longitudinally, Tg brain volumes were smaller than age-matched WT rats at all time points, starting as early as 5 weeks of age. The Tg striatal growth rate delay between 5 and 9 weeks of age was greater than that of the whole brain. Striatal volume in combination with genotype was the most predictive of rota-rod scores and in combination with genotype and age was the most predictive of total exploratory activity scores in the Tg rats.ConclusionThe disproportionately delayed striatal growth compared to whole brain between 5 and 9 weeks of age and the role of striatal volume in predicting neurobehavioral deficits suggest an important role of the dopaminergic system in HIV associated neuropathology. This might explain problems with motor coordination and executive decisions in this animal model. Smaller brain and subregional volumes and neurobehavioral deficits were seen as early as 5 weeks of age, suggesting an early brain insult in the Tg rat. Neuroprotective therapy testing in this model should thus target this early stage of development, before brain damage becomes irreversible.

Measurement of Pharyngo-laryngeal Volume During Swallowing Using 320-Row Area Detector Computed Tomography.

This study aimed to (1) evaluate changes in bolus and air volumes in the pharyngo-laryngeal cavity during swallowing and (2) determine how differences in these volumes during swallowing are influenced by bolus amount using 320-row area detector computed tomography (320-ADCT). Three-, 10-, and 20-ml honey-thick liquids (5% w/v) were presented to ten healthy subjects placed in a 45° reclining position. 3D images were created in 29 phases at an interval of 0.1s for 3.15s. Changes in bolus and air volumes in the pharyngo-laryngeal cavity were calculated. The two one-sided tests were used to determine equivalency of the pharyngo-laryngeal volume of each event (i.e., onset of hyoid elevation, soft palate closure, true vocal cord closure, closure of laryngeal vestibule, epiglottis inversion, pharyngo-esophageal sphincter opening) for each bolus volume. The pharyngo-laryngeal volume during swallowing was about 20ml before swallowing. The volume temporarily increased with tongue loading, but decreased to about 0ml with pharyngeal contraction. Subsequently, the volume returned to the original volume after airway opening. Most of the air was released from the pharyngo-laryngeal space before the bolus flowed into the esophagus during swallowing. As the bolus volume to be swallowed increased, the maximal pharyngo-laryngeal volume increased, but changes in air volume remained constant. 320-ADCT allowed for analysis of dynamic volume changes in the pharyngo-laryngeal cavity, which will increase our knowledge of kinematic and volumetric mechanisms during swallowing.

Lithium Metal Anodes with an Adaptive "Solid-Liquid" Interfacial Protective Layer.

Lithium metal is an attractive anode for the next generation of high energy density lithium-ion batteries due to its high specific capacity (3,860 mAh g-1) and lowest overall anode potential. However, the key issue is that the static solid electrolyte interphase cannot match the dynamic volume changes of the Li anode, resulting in side reactions, dendrite growth, and poor electrodeposition behavior, which prevent its practical applications. Here, we show that the "solid-liquid" hybrid behavior of a dynamically cross-linked polymer enables its use as an excellent adaptive interfacial layer for Li metal anodes. The dynamic polymer can reversibly switch between its "liquid" and "solid" properties in response to the rate of lithium growth to provide uniform surface coverage and dendrite suppression, respectively, thereby enabling the stable operation of lithium metal electrodes. We believe that this example of engineering an adaptive Li/electrolyte interface brings about a new and promising way to address the intrinsic problems of lithium metal anodes.

Coupling heat and mass transfer for determining individual diffusion coefficient of a hot C3H8–CO2 mixture in heavy oil under reservoir conditions

By characterizing heavy oil as multiple pseudocomponents, a generalized methodology has been developed to determine both apparent and individual diffusion coefficients by coupling heat and mass transfer for hot C3H8–CO2–heavy oil systems under reservoir conditions with consideration of swelling effect. Experimentally, a visualized PVT setup has been used to conduct diffusion tests for hot C3H8–CO2–heavy oil systems with different C3H8 concentrations under a constant pressure. The dynamic volume change of liquid-phase is monitored and recorded during the measurements. Theoretically, the volume-translated Peng–Robinson equation of state (PR EOS) with a modified alpha function has been incorporated to develop a two-dimensional heat and mass transfer model for the hot C3H8-enriched CO2–heavy oil systems, while the heavy oil sample has been characterized as three pseudocomponents for accurately predicting phase behavior of the aforementioned systems. The binary interaction parameter (BIP) correlations are tuned with the experimentally measured saturation pressures, while the tuned BIPs are validated with the measured equilibrium swelling factors. Both the individual diffusion coefficient of each component and the apparent diffusion coefficients of C3H8–CO2 mixtures are determined once the discrepancy between the measured and calculated dynamic swelling factors of heavy oil has been minimized. Compared to CO2 alone, C3H8–CO2 mixtures lead to enhanced swelling effect of heavy oil, while a higher C3H8 concentration achieves a faster dissolution and a larger dynamic swelling factor. Thus, C3H8 preferentially diffuses into heavy oil than CO2 at the same conditions for C3H8–CO2–heavy oil systems.

Current Injection Provokes Rapid Expansion of the Guard Cell Cytosolic Volume and Triggers Ca2+ Signals

High-resolution microscopy opens the door for detailed single-cell studies with fluorescent reporter dyes and proteins. We used a confocal spinning disc microscope to monitor fluorescent dyes and the fluorescent protein Venus in tobacco and Arabidopsis guard cells. Multi-barreled microelectrodes were used to inject dyes and apply voltage pulses, which provoke transient rises in the cytosolic Ca2+ level. Voltage pulses also caused changes in the distribution of Lucifer Yellow and Venus, which pointed to a reversible increase of guard cell cytosolic volume. The dynamic cytosolic volume changes turned out to be provoked by current injection of ions. A reduction of the clamp current, by blocking K+ uptake channels with Cs+, strongly suppressed the cytosolic volume changes. Cs+ not only inhibited the expansion of the cytosol, but also inhibited hyperpolarization-induced elevations of the cytosolic Ca2+ concentration. A complete loss of voltage-induced Ca2+ signals occurred when Ca2+-permeable plasma membrane channels were simultaneously blocked with La3+. This shows that two mechanisms cause hyperpolarization-induced elevation of the cytosolic Ca2+-concentration: (i) activation of voltage-dependent Ca2+-permeable channels, (ii) osmotically induced expansion of the cytosol, which leads to a release of Ca2+ from intracellular stores.

Volume change theory for syringomyelia: A new perspective.

Background:The etiopathogenesis of syringomyelia is still an enigma. The authors present a novel theory based on fluid dynamics at the craniovertebral (CV) junction to explain the genesis of syringomyelia (SM). The changes in volume of spinal canal, spinal cord, central canal and spinal subarachnoid space (SSS) in relation to the posterior fossa have been analysed, specifically during postural movements of flexion and extension. The effect of fluctuations in volume of spinal canal and its contents associated with cerebrospinal fluid (CSF) flow dynamics at the CV junction have been postulated to cause the origin and propagation of the syringomyelia. The relevant literature on the subject has been reviewed and the author's theory has been discussed.Conclusion:Volume of spinal canal in flexion is always greater than that in extension. Flexion of spine causes narrowing of the ventral subarachnoid space (SAS) and widening of dorsal SAS while extension causes reverse changes leading to fluid movement in dorsal spinal SAS in flexion and ventral spinal SAS in extension. Cervical and lumbar spinal region with maximum bulk hence maximum area and volume undergo maximum deformation during postural changes. SSS CSF is the difference between the volume of spinal canal and spinal cord, varies in flexion and extension which is compensated by changes in posterior fossa (CSF) volume in normal circumstances. Blocked SAS at foramen magnum donot permit spinal SAS CSF exchange which during postural changes is compensated by cavitatory/cystic (syrinx) change at locations in cervical and lumbar spine with propensity for maximum deformation. Augmentation of posterior fossa volume by decompression helps by normalization of this CSF exchange dynamics but immobilizing the spinal movement theoretically will cease any dynamic volume changes thereby minimizing the destructive influence of the fluid exchange on the cord. Thus, this theory strengthens the rational of treating patients by either methodology.

Dynamics of end expiratory lung volume after changing positive end-expiratory pressure in acute respiratory distress syndrome patients.

IntroductionLung recruitment maneuvers followed by an individually titrated positive end-expiratory pressure (PEEP) are the key components of the open lung ventilation strategy in acute respiratory distress syndrome (ARDS). The staircase recruitment maneuver is a step-by-step increase in PEEP followed by a decremental PEEP trial. The duration of each step is usually 2 minutes without physiologic rationale.MethodsIn this prospective study, we measured the dynamic end-expiratory lung volume changes (ΔEELV) during an increase and decrease in PEEP to determine the optimal duration for each step. PEEP was progressively increased from 5 to 40 cmH2O and then decreased from 40 to 5 cmH2O in steps of 5 cmH2O every 2.5 minutes. The dynamic of ΔEELV was measured by direct spirometry as the difference between inspiratory and expiratory tidal volumes over 2.5 minutes following each increase and decrease in PEEP. ΔEELV was separated between the expected increased volume, calculated as the product of the respiratory system compliance by the change in PEEP, and the additional volume.ResultsTwenty-six early onset moderate or severe ARDS patients were included. Data are expressed as median [25th-75th quartiles]. During the increase in PEEP, the expected increased volume was achieved within 2[2-2] breaths. During the decrease in PEEP, the expected decreased volume was achieved within 1 [1–1] breath, and 95 % of the additional decreased volume was achieved within 8 [2–15] breaths. Completion of volume changes in 99 % of both increase and decrease in PEEP events required 29 breaths.ConclusionsIn early ARDS, most of the ΔEELV occurs within the first minute, and change is completed within 2 minutes, following an increase or decrease in PEEP.