Changes In Hydrostatic Pressure Research Articles

Laboratory and field investigations on freeze and gravity core sampling and assessment of coring disturbances with implications on gas bubble characterization

AbstractThe quantification of greenhouse gas emissions from aquatic ecosystems requires knowledge about the spatial and temporal dynamics of free gas in sediments. Freezing the sediment in situ offers a promising method for obtaining gas‐bearing sediment samples, unaffected by changes in hydrostatic pressure and sample temperature during core withdrawal and subsequent analysis. This article presents a novel freeze coring technique to preserve the in situ stratigraphy and gas bubble characteristics. Nondestructive X‐ray computed tomography (CT) scans were used to identify and characterize coring disturbances of gravity and freeze cores associated with gassy sediment, as well as the effect of the freezing process on the gas bubble characteristics. Real‐time X‐ray CT scans were conducted to visualize the progression of the freezing process. Additional experiments were conducted to determine the freezing rate to assess the probability of sediment particle/bubble migration, and gas bubble nucleation at the phase transition of pore water to ice. The performance of the freeze coring technique was evaluated under field conditions in Olsberg and Urft Reservoir (Germany). The results demonstrate the capability of the freeze coring technique for the preservation of gas‐bearing sediments and the analysis of gas bubble distribution pattern in both reservoirs. Nevertheless, the obtained cores showed that nearly all gravity and freeze cores show some degree of coring disturbances.

Color Doppler ultrasound twinkling in pathological biomineralizations

The color Doppler ultrasound twinkling artifact has been observed on some kidney stones as well as various sites in the body where pathological biomineralization can occur. On kidney stones, twinkling was recently attributed to stabilized crevice microbubbles, which suggests that microbubbles may also be present on other minerals. However, it is unknown how crystal structure, composition, and the surrounding environment influences the presence and location of microbubbles and twinkling. Here, crystals found in pathological biomineralization (i.e., uric acid, cholesterol, calcium phosphate, and calcium oxalate), were grown in vitro, embedded in a tissue-mimicking phantom, and imaged with a research ultrasound system at 5 and 18.5 MHz. Doppler power was quantified and compared between crystal composition (n = 5 per type). We found twinkling was strongest in cholesterol crystals and weakest in calcium phosphate crystals. Micro-computed tomography (µCT) of an ex vivo calcium oxalate kidney stone (i.e., a heterogeneous crystal) submerged in water revealed the presence of gas within internal microcracks, which was confirmed by reducing the hydrostatic pressure in a subsequent µCT scan. Future work includes exposing pure in vitro crystals to µCT and ultrasound with changes in hydrostatic pressure to evaluate for internal gas pockets that may contribute to twinkling.

Microbubbles on kidney stones contribute to the twinkling artifact in humans

The color Doppler ultrasound twinkling artifact, a rapid color change that highlights kidney stones, was recently attributed to surface crevice microbubbles on ex vivo stones because twinkling was affected by changes in hydrostatic pressure. However, it was unclear whether crevice bubbles existed on in situ human kidney stones, and, if so, how smooth-surfaced stones could harbor the crevice bubbles that give rise to twinkling. Here, 8 human subjects with known kidney stones were exposed to 4 atmospheres absolute (ATA) while breathing air inside a hyperbaric chamber; twinkling was monitored and quantified with a research ultrasound system. At 3 and 4 ATA, twinkling was significantly reduced by an average of 35% and 39%, respectively (p = 0.04). Then, ex vivo kidney stones that twinkled were exposed to micro-computed tomography (μCT) and hypobaric pressures while submerged in water. Regions of low x-ray attenuation within the stone (i.e., microcracks) at 1 ATA expanded when the pressure was reduced to 0.1 ATA. These results support the theory that microbubbles are present on kidney stones in the human body and that microbubbles may be internal as well as external to the kidney stone. [Work supported by NSBRI through NASA NCC 9-58 and NIH DK043881.]

Environmental controls on mid-ocean ridge hydrothermal fluxes

High temperature hydrothermal fluxes at mid-ocean ridges are thought to be an important component of oceanic biogeochemical cycles. However, little consideration has been given to how these fluxes vary as a consequence of changing environmental conditions over Earth history. Here we consider how changes in sea level and ocean chemistry are likely to have impacted on-axis, high-temperature, hydrothermal fluxes focusing on Phanerozoic conditions. Changes in sea level lead to changes in hydrostatic pressure near the base of hydrothermal systems where both peak fluid-rock reaction temperatures and phase separation occur. In general, higher global sea level will lead to higher peak temperatures of fluid-rock reaction. Additionally, phase separation at higher pressure tends to lead to formation of a more Cl-rich vapor, that constitutes a larger mass fraction of the system. These combined factors may serve to significantly modify hydrothermal fluxes even for sea level changes on the scale of 100 m. Changes in ocean chemistry can also affect axial hydrothermal fluxes in several ways. Seawater sulfate contents control the amount of anhydrite that forms, which has both physical (porosity filling) and chemical effects. The most important aspect of ocean chemistry in controlling the composition of high-temperature vent fluids may be ocean salinity. If evaporite formation and dissolution has changed ocean salinity substantially over the Phanerozoic, hydrothermal fluxes could have been greatly modified. Ocean chemistry also plays a large role in controlling processes operating in hydrothermal plumes and hence the net flux of elements into and out of the ocean associated with hydrothermal systems. We conclude that there is a need for substantial further work to quantify the effects of sea level and ocean chemistry on high-temperature hydrothermal fluxes, including the development of more robust models that integrate field, laboratory and theoretical observations.

Giant and Reversible Inverse Barocaloric Effects near Room Temperature in Ferromagnetic MnCoGeB0.03.

Hydrostatic pressure represents an inexpensive and practical method of driving caloric effects in brittle magnetocaloric materials, which display first-order magnetostructural phase transitions whose large latent heats are traditionally accessed using applied magnetic fields. Here, moderate changes of hydrostatic pressure are used to drive giant and reversible inverse barocaloric effects near room temperature in the notoriously brittle magnetocaloric material MnCoGeB0.03 . The barocaloric effects compare favorably with those observed in barocaloric materials that are magnetic. The inevitable fragmentation provides a large surface for heat exchange with pressure-transmitting media, permitting good access to barocaloric effects in cooling devices.

Evaluation of a novel flow-controlled syringe infusion pump for precise and continuous drug delivery at low flow rates: a laboratory study.

Syringe infusion pumps are used for the administration of short-acting drugs in anaesthesia and critical care medicine, but are prone to flow irregularities at low flow rates. A flow-controlled syringe infusion pump using an integrated flow sensor for feedback control represents a new approach to overcoming these limitations. This study compares the performance of a prototype flow-controlled syringe pump both at start-up, and during vertical displacement manoeuvres, with that of a standard infusion syringe pump. The novel pump almost completely eliminated delays at start-up and flow irregularities during hydrostatic pressure changes. Related fluctuations in plasma drug concentration were minimised and the known disadvantages of standard syringe infusion pumps currently used in clinical practice were reduced. Besides providing fast start-up to steady-state flow and precise continuous drug delivery at low flow rates during hydrostatic pressure changes, the new pump offers the potential for the development of target-controlled infusion algorithms for short-acting cardiovascular and other drugs.

Early-Stage Dynamics in Vascular Endothelial Cells Exposed to Hydrostatic Pressure.

Blood pressure is an important factor both in maintaining body homeostasis and in its disruption. Vascular endothelial cells (ECs) are exposed to varying degrees of blood pressure and therefore play an important role in these physiological and pathological events. However, the effect of blood pressure on EC functions remains to be elucidated. In particular, we do not know how ECs sense and respond to changes in hydrostatic pressure even though the hydrostatic pressure is known to affect the EC functions. Here, we hypothesized that the cellular responses, leading to the reported pressure effects, occur at an early stage of pressure exposure and observed the early-stage dynamics in ECs to elucidate mechanisms through which ECs sense and respond to hydrostatic pressure. We found that exposure to hydrostatic pressure causes an early actomyosin-mediated contraction of ECs without a change in cell morphology. This response could be caused by water efflux from the ECs following exposure to hydrostatic pressure. Although only a limited study, these findings do explain a part of the mechanism through which ECs sense and respond to hydrostatic pressure.

Adaptation of Systemic and Pulmonary Circulation to Acute Changes in Gravity and Body Position.

INTRODUCTION: Changes in gravity or body position provoke changes in hydrostatic pressure in the arterial system and in venous return. Potential asymmetries between left (QLV) and right ventricular (QRV) cardiac output during transient gravity changes were investigated. It was hypothesized that blood volume is temporarily stored in the pulmonary vessels, with amount and duration depending on the level and directions of gravity.METHODS: Eight healthy, male subjects (32 ± 3 yr, 182 ± 7 cm, 82 ± 6 kg) were tested on a tilt seat (TS), in a long arm human centrifuge (laHC), and during parabolic flights (PF). The gravitational changes during PF were reconstructed by changing gravity in a laHC and different body positions on a TS. All participants were tested in the seated, resting position. Heart rate and blood pressure were recorded continuously and QLV was calculated, applying the Modelflow Algorithm. Gas exchange was measured breath-by-breath. QRV was calculated from these data according to the Fick Principle. Four sequences were superimposed and analyzed by ANOVA with the factors Time, Ventricle (QRV, QLV), and Mode (TS, PF, laHC).RESULTS: After reductions in gravity QRV and QLV were transiently desynchronized. ANOVA showed no main effect for Mode, but significant changes were found for Time and Ventricle and all interactions.DISCUSSION: Phases of reduced gravity seem to lead to transiently increased storage of blood volume inside the pulmonary vascular system. A more detailed understanding of these mechanisms might help to describe the compliance of the pulmonary vascular system in diseases of the pulmonary circulation.Hoffmann U, Koschate J, Appell Coriolano H-J, Drescher U, Thieschäfer L, Dumitrescu D, Werner A. Adaptation of systemic and pulmonary circulation to acute changes in gravity and body position. Aerosp Med Hum Perform. 2019; 90(8):688-695.

Verification and spatial mapping of TRPV1 and TRPV4 expression in the embryonic and adult mouse lens

The transient receptor protein vanilloid channels, TRPV1 and TRPV4, have recently been shown to be mechanosensors in the ocular lens that act to transduce physical changes in lens volume and internal hydrostatic pressure into the activation of signalling pathways in lens epithelial cells. These pathways in turn regulate ion and water transport to ensure that the optical properties of the lens remain constant. Despite the functional evidence that implicate the roles of TRPV1 and TRPV4 in the lens, their respective cellular expression patterns in the different regions of the lens has to date not been fully characterised. Using Western blotting we have confirmed that TRPV1 and TRPV4 are expressed throughout all regions (epithelium, outer cortex, inner cortex/core) of the adult mouse lens. Subsequent immunolabeling of lens cryosections confirmed that TRPV1 and TRPV4 are expressed throughout all regions of the lens, but revealed differentiation-dependent differences in the subcellular expression of the two channels in the different regions. In the epithelium and outer cortex, intense TRPV1 and TRPV4 labeling was predominately associated with the cytoplasm. In a discrete zone in the inner cortex, labeling for both proteins was greatly diminished, but could be enhanced by incubating sections with the detergent Triton X-100 to reveal TRPV1 and TRPV4 labelling that was associated with the membrane. This suggests that in this region of the lens there is a potential interacting protein that masks the binding of the TRPV1 and TRPV4 antibodies to their respective epitopes in the lens inner cortex. In the core of the lens, which contains the embryonic nucleus, TRPV1 and TRPV4 labelling was associated exclusively with fibre cell membranes. This labelling in the lens core of the adult mouse lens appeared to originate in early development as a similar membrane labelling was observed at embryonic day 10 (E10) of the cells in the lens vesicle that subsequently forms the embryonic nucleus in the adult lens. During subsequent stages of embryonic development TRPV1 and TRPV4 remained membranous in the inner cortex and core, while showing labelling that was associated with the cytoplasm in the superficial outer cortical region. The extent of cytoplasmic labelling for TRPV4, but not TRPV1, in this cortical region could however be dynamically regulated by cutting the zonules that normally attach the lens to the ciliary body. We have shown an early onset and continuous expression of TRPV1 and TRPV4 across all lens regions, and that TRPV4 can be dynamically trafficked into the membranes of differentiating fibre cells, results that suggests that these mechanosensitive channels may also be functionally active in lens fibre cells.

Is increased plasma TMAO a compensatory response to hydrostatic and osmotic stress in cardiovascular diseases?

Recent clinical studies show a positive correlation between elevated plasma TMAO and increased cardiovascular risk. However, the mechanism of the increase and biological effects of TMAO in the circulatory system are obscure.Plasma TMAO level depends mostly on the following three factors. First, the liver produces TMAO from TMA, a gut bacteria metabolite of dietary choline and carnitine. Second, plasma TMAO increases after ingestion of dietary TMAO from fish and seafood. Finally, plasma TMAO depends on TMAO and TMA excretion by the kidneys.Ample evidence highlights protective functions of TMAO, including the stabilization of proteins and cells exposed to hydrostatic and osmotic stresses, for example in fish exposed to hydrostatic stress (deep water) and osmotic stress (salty water).Osmotic stress and hydrostatic stresses are augmented in cardiovascular diseases such as hypertension. In hypertensive subjects a diastole-systole change in hydrostatic pressure in the heart may exceed 220 mmHg with a frequency of 60–220/min. This produces environment in which hydrostatic pressure changes over 100,000 times per 24 h. Furthermore, cardiovascular diseases are associated with disturbances in water-electrolyte balance which produce changes in plasma osmolarity. Perhaps, the increase in plasma TMAO in cardiovascular diseases is analogous to increased level of plasma natriuretic peptide B, which is both a cardiovascular risk marker and a compensatory response producing beneficial effects for pressure/volume overloaded heart. In this regard, there is some evidence that a moderate increase in plasma TMAO due to TMAO supplementation may be beneficial in animal model of hypertension-related heart failure. Finally, increased plasma TMAO is present in humans consuming seafood-rich diet which is thought to be health-beneficial.We hypothesize that increased plasma TMAO serves as a compensatory response mechanism which protects cells from hydrostatic and osmotic stresses.

Ventilasi dan Perfusi, serta Hubungan antara Ventilasi dan Perfusi

Lung is a place for gas exchange where ventilation and perfusion occurs. Ventilation is the first step where sequential process of inhalation and exhalation take place. Meanwhile perfusion as the other step facilitates the gas exchange and tissue supply need. Blood flows through the lungs are equals as the amount of cardiac output where the factors that control cardiac output are mainly peripheral factors, also control pulmonary blood flow. In general condition, pulmonary blood vessels act as a passive tube, which can be increased with the increasing pressure and narrowed the pressure drop. Oxygen absorption level from lungs into bloodstream is a critical determinant for functional capacity, and an important factor wheter in normal conditions (including exercise) or even in illness state. Lung diffusion capacity is influenced by several geometric and functional factors. Gravitation influence systematic gradient in ventilation and perfusion distribution. Ventilation and blood flow variations at horizontal level also occur due to intrinsic anatomic variations and vascular geometry, as well as the differences in airway and vascular smooth muscle response which modifies the distribution. The change of integrity intrapleural chamber, hydrostatic pressure and osmotic imbalance, malfunction of surfactants, other intrinsic weakness of the branching system in the form of a progressive airway, and all the things that could potentially damage the structure of the lung can cause ventilation and diffusion dysfunction.

High pressure-induced relaxation of electrical resistance in weakly doped НоBa2Cu3O7–x single crystals

The relaxation of high-temperature resistance, ρ(300 K t), in HoBa2Cu3O7–x single crystals after a sharp change in hydrostatic pressure is investigated. A comparison of the electrical resistance relaxation against the relaxation of the superconducting transition critical temperature Тс under the same experimental conditions points to the existence of anisotropy in vacancy cluster relaxation: cluster coalescence is dominant in the Сu–О planes; however, the generation of new clusters and coalescence of existing clusters both occur in the sample volume.

Molecular and histological characteristics of bovine caudal nucleus pulposus by combined changes in hydrostatic and osmotic pressures in vitro.

ABSTRACTIntervertebral disc degeneration is ubiquitous among aging patients, and altered matrix homeostasis is one of the key features of this condition. Physicochemical stresses have a significant impact on matrix homeostasis as they lead to progressive degeneration and may be associated with spinal pain and dysfunction. Thus, it is important to understand the cellular and matrix characteristics of nucleus pulposus in response to these stresses, which include hydrostatic and osmotic pressures during alternate loading conditions. We hypothesized that a combination of changes in hydrostatic pressure and in osmotic pressure that mimic normal, daily spinal stress would stimulate anabolic function, whereas a non‐realistic combination of those stresses would stimulate catabolic function in nucleus pulposus cells. We examined the effects of these combined stresses, represented by 12 systematic conditions, on the metabolic activities of enzymatically isolated bovine caudal nucleus pulposus in vitro. We measured the gene expression of extracellular matrix (ECM) molecules and proliferating cell nuclear antigen (PCNA) and evaluated the quality of the matrix and the capability of cell proliferation immunohistologically. Combined cyclic hydrostatic pressure at 0.5 MPa, 0.5 Hz, and high osmotic pressure at 450 mOsm upregulated the aggrecan core protein and collagen type‐II gene expression significantly (p < 0.05), and showed trends of upregulation of chondroitin sulfate N‐acetylgalactosaminyltransferase 1, matrix metalloproteinase‐13, and PCNA. ECM, however, contained empty spaces at a high osmotic pressure with and without hydrostatic pressure. Since ECM has highly specialized physicochemical properties, homeostasis should involve not only phenotypic cellular behavior but also turnover of ECM. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 37:466–476, 2019.

Quality changes in high hydrostatic pressure and thermal pasteurized grapefruit juice during cold storage.

This study evaluated the effects of high hydrostatic pressure (HHP) and thermal pasteurization (TP) on microbial counts, physicochemical properties, antioxidant characteristics, naringin and naringenin contents, and naringinase activity of grapefruit juice during 21 days cold storage period. Results showed that HHP and TP significantly decreased the total microbial, coliform, and yeast counts. No significant differences between HHP-treated grapefruit juice (600MPa/5min) and untreated fruit juice with respect to physicochemical properties such as total titratable acidity, pH, and total soluble solids was observed after 21 days of storage. Although HHP affected the colour and antioxidant characteristics of grapefruit juice, the extent of effect was significantly lower than that for TP-treated fruit juice. This demonstrated that HHP could better maintain the original flavour and quality of grapefruit juice compared to TP. In addition, 92% naringinase activity was maintained in HHP-600 group on Day 21, which increased the degradation of bitter naringin into non-bitter naringenin during the cold storage of grapefruit juice. In summary, HHP can simultaneously maintain the microbiological safety of grapefruit juice along with its original quality characteristics. HHP can effectively extend the storage period and safety during cold chain transport, and hence highly applicable in the grapefruit juice industry.

Pathophysiology and symptoms of renal colic in children - a case report.

Urolithiasis is a disease characterized by the presence of stones in the kidney or urinary tract. It is often detected accidentally during an ultrasound or an abdominal x-ray performed for other reasons. However, the first symptom of kidney stone disease can be severe pain called renal colic. Pain caused by a colic attack is characterized by sudden onset. In half of the cases it is associated with nausea or vomiting and can lead to hypotension and fainting. The exact location and radiation of the pain depends on the location of the stone in the urinary tract. The first most commonly performed study is abdominal ultrasound with estimation of the deposit size and evaluation of urinary tract obstruction. Alternative or complementary studies are: an abdominal x-ray where radiopaque deposits can be shown, or unenhanced helical computed tomography of the abdomen. The severity of pain depends on the individual pain threshold and on the change in hydrostatic pressure in the part of the urinary system above the obstruction. Prolonged deposition of the stone in one place causes the activation of autoregulatory mechanisms to lower the pressure of the upper urinary tract, which limits the pain. The basic treatment for renal colic is analgetic therapy. The most commonly used drugs are NSAIDs and opiates. Another important component of renal colic treatment are medications that facilitate urinary stone passage by reducing oedema or limiting urethral contractions, such as: calcium channel blockers, alpha blockers, phosphodiesterase inhibitors. Intensive hydration is not currently recommended. Patients who are unlikely to spontaneously excrete the stone are eligible for minimally invasive treatment. The risk of urolithiasis recurring is high, reaching up to 40% in 5 years and up to 50% in 10 years. However, it can be reduced by proper prevention. The paper describes the pathophysiology of pain in renal colic, the treatment methods, and the case of a boy with recurrent renal colic.

Under pressure: biomechanical limitations of developing pneumatocysts in the bull kelp (Nereocystis luetkeana, Phaeophyceae).

Maintaining buoyancy with gas-filled floats (pneumatocysts) is essential for some subtidal kelps to achieve an upright stature and compete for light . However, as these kelps grow up through the water column, pneumatocysts are exposed to substantial changes in hydrostatic pressure, which could cause complications as internal gases may expand or contract, potentially causing them to rupture, flood, and lose buoyancy. In this study, we investigate how pneumatocysts of Nereocystis luetkeana resist biomechanical stress and maintain buoyancy as they develop across a hydrostatic gradient. We measured internal pressure, material properties, and pneumatocyst geometry across a range of thallus sizes and collection depths to identify strategies used to resist pressure-induced mechanical failure. Contrary to expectations, all pneumatocysts had internal pressures less than atmospheric pressure, ensuring that thalli are always exposed to a positive pressure gradient and compressional loads, indicating that they are more likely to buckle than rupture at all depths. Small pneumatocysts collected from depths between 1 and 9m (inner radius=0.4-1.0cm) were demonstrated to have elevated wall stresses under high compressive loads and are at greatest risk of buckling. Although small kelps do not adjust pneumatocyst material properties or geometry to reduce wall stress as they grow, they are ~3.4 times stronger than they need to be to resist hydrostatic buckling. When tested, pneumatocysts buckled around 35m depth, which agrees with previous measures of lower limits due to light attenuation, suggesting that hydrostatic pressure may also define the lower limit of Nereocystis in the field.

Alterations of blood pulsations parameters in carotid basin due to body position change

The velocity of the pulse wave (PWV) propagating through the vascular tree is an essential parameter for diagnostic the state of the cardiovascular system especially when it is measured in the pool of carotid arteries. In this research, we showed for the first time that the time of the blood-pressure-wave propagation from the heart to the face is a function of the body position. Significant asymmetry and asynchronicity of blood pulsations in the facial area were found in a recumbent position. Parameters of blood pulsations were measured by an advanced camera-based photoplethysmography system in 73 apparently healthy subjects. Most likely, observed changes of the blood-pulsation parameters are caused by variations of the arterial blood pressure due to hydrostatic pressure changes, and secondary reaction of blood vessels in response to these variations. Demonstrated feasibility of PWV measurements in the pool of carotid arteries provides considerable advantages over other technologies. Moreover, possibilities of the method to estimate physiological regulation of the peripheral blood flow (particularly, as a response to the gravitational changes) have been demonstrated. The proposed concept allows development of non-invasive medical equipment capable of solving a wide range of scientific and practical problems related to vascular physiology.

Cyclophane‐Based Fluorescence Tuning Induced by Hydrostatic Pressure Changes

AbstractIn contrast to a standard steady fluorescence intensity increase of a chloroform solution of a linear chromophore unit under high pressure, a fluorescent cyclophane solution shows significant fluorescence quenching under elevated pressure. A pressure‐induced enhancement of the formation of an intramolecular π‐stacked conformation is proposed to be responsible.

Filler and Water Reducer Effects on Sedimentation, Bleeding and Zeta-Potential of Cement Paste

Abstract Bleeding and sedimentation quantify the stability of fresh cement paste, whereas the addition of fillers and water reducers affect the stability. The effect of various types of fillers and water reducers was investigated by measuring bleeding, hydrostatic pressure and electroacoustic zeta-potential. Depending on their characteristics and use, fillers can improve stability by reducing sedimentation rate and bleeding. The combined effects of fillers and water reducers on the sedimentation rates, quantified as time-dependent hydrostatic pressure changes (dp/dt) in fresh matrix, correspond to their effects on zeta-potentials. The influence of the water reducers on sedimentation and bleeding exceed that of filler type.

Venous compliance and clinical implications

Compliance is a characteristic of every deformable system. Compliance is very clear concept in physics and mechanics but in clinics, perhaps, is not the same. However, in veins compliance fits perfectly with the function of drainage of the venous system. Volumetric increase (dV) of the content is correlated with pressure increase (dP) inside the vein according to the equation C’= dV/dP. In humans 75% of the blood is located in the venous system, primarily because the molecular components of a vein media layer is significantly more compliant to that of arteries. This property is fundamental to understanding the change in blood volume in response to a change in posture. Measurements of venous compliance in clinical practice can be done by the means of ultrasound, as well as with the plethysmography. Ultrasound methods assimilate the cross sectional area to the volume of the vein, because it reflects the blood content. Changes in cross sectional area can be reliably measured in response to a change in posture, while pressure can be derived from the hydrostatic pressure changes. Venous compliance is of paramount importance also in pulsatile veins such as the inferior or superior vena cava and the jugular veins, where high resolution ultrasound may accurately derive the cross sectional area. Clinical implications of the mechanical properties of the venous wall are extensively discussed, including the need of dedicated venous stenting, which takes into account venous compliance as the main parameter of the venous function. In addition, venous compliance is the interpretative key for a better understanding of plethysmography curves, as well as of varicose veins and of their return to normal cross sectional area following ambulatory venous pressure reduction.