Valve Closure Time Research Articles

Optimal valve closing law for improved water hammer control: a case from a water supply pipeline in Guelma, Algeria

Abstract Finding the most suitable closing law is essential to decrease the shock wave pressure caused by transient flow and minimize the potential damage to equipment. The closure of a valve can occur instantly, rapidly, or gradually, and the appropriate law can be convex, linear, or concave, depending on various factors. These factors include the pipe's characteristics (type, diameter, roughness, and length), the conveyed fluid (nature and temperature), and operating conditions (pressure and flow rate). Other factors that receive less attention, such as the duration of slow closure and the impact of soil load on the pipe, are also considered in this study. The main focus of this article is to investigate how the optimal law evolves based on the time it takes for a valve to gradually close, specifically in the case of a valve located at the end of an underground gravity supply pipe. The findings reveal that when the slow closure time (t) exceeds 0.50 times the return period (t4), the exponent of the optimal law becomes a damped periodic function. Each closure time corresponds to a unique optimal law, and as the valve closure time increases, the range of optimal laws becomes narrower.

Study on water hammer effect and tubing string vibration in high-pressure high-production gas wells

The transient internal flow in high-pressure high-production gas wells generates severe water hammer and tubing string vibration, which accelerates fatigue damage, joint wear, thread loosening, and other wellbore integrity problems. Based on the analysis of transient flow in gas wells, a mathematical model for fluid pressure surge and the induced tubing string vibration is developed and validated by similarity experiments. This method considers fluid-structure interaction, initial loads of tubing string, and compressibility of natural gas, and can fill the gap in quantification of water hammer pressure and tubing sting dynamic load in high-pressure high-production gas wells. On this basis, the effects of valve closure time, production rate, liquid content, and tubing string structure on transient flow and tubing string characteristics are analyzed systematically. The calculations show that wellhead pressure increases rapidly, and pressure wave propagates along tubing string to induce vibrations in the string after an instantaneous shut-in at the wellhead. During this transient process, fluid pressure and axial stress at wellhead reach their maximum valves. Owing to the fixed constraint effect of wellhead and downhole packer, the lack of restrictions on tubing distant from wellhead and packer enhances the severity of axial vibration. As valve closure time increases, the maximum wellhead pressure, tubing vibration displacement, and velocity gradually decrease. Therefore, the most direct way to control water hammer effect and tubing string vibration is to extend the shut-in time or prevent a rapid shut-in of gas well. The methods used in this study and the results obtained therein can serve as both a theoretical framework and practical foundation for the prediction and control of water hammer effect and tubing string vibration in high-pressure high-production gas wells.

Cardiac cycle timing intervals in university varsity athletes

Cardiac cycle timing events in varsity athletes serve an important function for baseline assessment but are not reported in the literature. The purpose of this study was to characterize the cardiac cycle timing intervals and contractility parameters in university-level varsity athletes. 152 males and 93 females were assessed using a non-invasive seismocardiography cardiac sensor attached to the sternum for 1-minute. Shorter isovolumic relaxation time (IVRT), systolic time, mitral valve open to E-wave (MVO to E) time, rapid ejection period (REP), atrial systole to mitral valve closure (AS to MVC) time, and diastolic performance index (IVRT/systolic time) were found in females, while heart rate was lower in males. Varying differences in timing intervals were found between sports. Systolic times were longer in male and female basketball players, while diastole was shortest in male football players, who also had higher heart rates than the other male sport athletes. These results add reference cardiac cycle timing data to the literature and imply that male and female athletes show different cardiac characteristics. Team differences suggest that different training for different sports can result in unique cardiac function changes, however, these appear to be related to the sex of the participants. The addition of these cardiac cycle timing intervals adds a valuable comparative tool to better understand cardiac physiology in the varsity athletic population.

The Cut-off Value of Great Saphenous Vein Diameter at the Level of Femoral Condyle to Predict the Sapheno-Femoral Junction Incompetence

Background Varicose vein is one of the commonest problems that patients visit to a vascular out patient services (OPD). It causes a great deal of morbidity in today’s population.
 Objective To see the correlation between the size of great saphenous and Saphenofemoral junction incompetence.
 Method From January 2019 till January 2020, 396 patients with symptomatic or clinically diagnosed varicose veins were screened for Saphenofemoral junction reflux. The diameter of the saphenous vein was measured with B-mode imaging, and reflux was quantified based on valve closure time using Doppler spectral measurements. Best saphenous vein diameter cutoff for predicting reflux was determined using receiver operating characteristics curve analysis.
 Result Out of 792 limbs, the Great Saphenous Venous System was involved in 452 limbs, the Short Saphenous Venous System was involved in 151 limbs and significant perforators were present in 240 limbs. Mean great Saphenous Vein diameter of diseased limb (Reflux Positive) was 5.68 mm and 4.0 mm in control group (Reflux Negative). Mean Saphenofemoral junction diameter was 8.23 mm in diseased limbs and 6.16 mm in control limbs. Receiver operating characteristics curve showed great saphenous vein diameter at femoral condyle of 4.5 mm as best cut-off value for diagnosis of sapheno femoral junction reflux.
 Conclusion Great Saphenous Vein diameter at femoral condyle of 4.5 mm is the best cut-off value for diagnosis Saphenofemoral junction reflux. The Sensitivity and specificity of this cut off value is 81.8% and 71% respectively.

The impact of isometric handgrip testing in left atrial reservoir function

Abstract Funding Acknowledgements Type of funding sources: Public hospital(s). Main funding source(s): Fundação Adib Jatene Background Speckle tracking echocardiography (STE) allows accurate quantification of left atrial (LA) strain, thus allowing assessment of all phases of LA function (reservoir, conduit and contraction). Alterations in LA strain occur before changes in LA volumes, enabling early detection of LA dysfunction. In particular, the peak of LA strain during the reservoir phase (LASr) seems to be of prognostic value in heart failure. LASr is essential to pool enough blood volume to fill the LV during the subsequent diastole. The main determinants of LA reservoir function include blood volume arriving from the right ventricle, LA relaxation, and LA compliance. Still, changes in atrioventricular plane movement during the ventricular systole have been considered an additional factor influencing LASr. The relative contribution of left ventricular afterload to LASr, however, has yet to be clearly defined. Purpose We aimed to study the LA function during changes in LV afterload induced by the handgrip maneuver in subjects without heart disease, applying LASr and strain curve shape analysis. Material and Methods We studied 31 subjects (47 ± 15 years) without evidence of heart disease. A comprehensive 2D echocardiography was performed. We recorded 3 beat clips with standard STE views of LV and LA in baseline conditions and then during pressure overload-induced by left handgrip (42 ± 8 kg) combined with simultaneous pneumatic constriction of the right arm and both lower limbs. The LV GLS and LASr were calculated offline by a blinded examinator using commercially available software. Furthermore, we extracted the raw data of the strain curves and post-processed these signals using custom software. The global curves were split into different cardiac cycle phases using the valve opening and closure times(Figure 1). Quadratic functions estimated strain curves during the ejection phase due to the acceleration involved in the phenomenon. Quadratic function linear coefficients, a component of strain rate, were used to assess the shape of deformation curves. Results The handgrip maneuver caused mild reductions in LV strain: GLS baseline –19.07 % (±0.27) vs GLS handgrip -18.58% (±0.26) p = 0.02 (Figure 2A and C). Conversely, the LASr did not present significant changes: LASr baseline 33.82% (±0.84) vs LASr handgrip 32.96% (±0.85) p= 0.18 (Figure 2B and C). For the analysis of the shape of strain curves, we obtained data from 29 subjects. We found significant differences in LV ejection linear coefficient (ELC): LV ELC baseline –158.30 (±8.52) vs LV ELC handgrip –144.62 (±8.02) p = 0.02. For LA reservoir linear coefficient (RLC), we also found significant differences: LA RLC baseline 240.30 (±17.19) vs LA RLC handgrip 212.61 (±15.62) p = 0.03 (Figure 2D). Conclusion(s) The left atrial reservoir function is affected by changes in LV afterload induced by the handgrip maneuver. Our data suggest that LV pressure overload mainly impact the shape of LA strain curve rather than LASr. Abstract Figure 1 Abstract Figure 2

Abstract 11585: Determination of Aortic and Mitral Valve Opening and Closing Times Using Only LV Pressure Data

Background: Identification of aortic and mitral valve opening and closure timing is crucial for assessment of left ventricle (LV) function, e.g. pressure-volume loops. This is particularly problematic when simultaneous imaging (e.g. echocardiography) is not available. We hypothesize that LV pressure and its time derivatives can detect valve opening and closure times. Our aim was to determine the aortic and mitral valve opening and closures using properties of the LV pressure waveform. Methods: For this pilot study, in 3 human participants in sinus rhythm, LV pressures were recorded with a high-fidelity catheter. Echocardiographic 2D-guided M-mode images were obtained across the aortic and mitral valves in the parasternal long axis view. The timing of aortic and mitral valve events was linked to the ECG tracing, using the peak of the ECG R wave as the reference point. For each participant, two consecutive heartbeats were selected and the first (dP/dt), second (d 2 P/dt 2 ), and third derivatives (d 3 P/dt 3 ) of LV pressure calculated. Local maxima and minima from these were compared with the valve timing from M-mode. Results: The maximum of dP/dt at the beginning of the systolic phase occurred consistently with the opening of the aortic valve. Local minimum and maximum d 2 P/dt 2 occurred at the closure of the aortic valve and pre-atrial contraction timing, respectively. The early diastolic minimum of d 3 P/dt 3 and early systolic maximum of d 3 P/dt 3 coincided with M-mode mitral valve opening and closure timing, respectively. There was a strong correlation between the valve events timing that was measured using these two methods (R 2 =0.98, p<0.001). Conclusion: Aortic and mitral valve timing defined using LV pressure waveform agrees with valve opening/closure timing determined using echo M-mode as the gold standard. Determination of these valve timings is helpful for advanced analysis of LV mechanics when simultaneous echocardiography is not available.

Uncertainty Quantification and Global Sensitivity Analysis for Transient Wave Propagation in Pressurized Pipes

AbstractAccurate simulation of pipe transient wave is crucial for the design, reliability assessment, and defect detection of water supply systems. However, this is a difficult task since the wave propagation media in pipeline systems are often highly complex and involve a range of uncertainties. Experimental data show that key parameters such as valve closure time, wave speed, and pipe material coefficients are strongly uncertain and stochastic that may vary in a wide range. To analyze the transient behavior in such complex environments, surrogate models are built to realize the fast computation of uncertainty propagation. Three surrogate modeling methods, i.e., the polynomial‐chaos‐expansion, ordinary‐Kriging, and polynomial‐chaos‐Kriging, are tested and compared in terms of transient wave forecast accuracy. The global sensitivity is then analyzed via the Sobol index method, by which the most influential uncertainty sources on various transient signal features are identified.

Non-invasive Assessment of Pulmonary Hypertension Using a Small Portable Device Measuring Cardiac Intervals: Design for Telemonitoring

Background Pulmonary hypertension is a condition that pulmonary artery pressure iselevated. The diagnosis and monitoring of pulmonary artery pressure oftenrequiring invasive procedures. HEMOTAG, is a small portable device that usesmicro-sensors to capture cardiac vibrations and electrocardiogram, transducedvia thoracic electrodes. It is a viable option to measure cardiac timeintervals (CTIs), surrogate markers of intracardiac pressure. In this study,mitral valve closure (MVC) and isovolumetric contraction time (IVCT) wereassessed as valid markers for pulmonary artery pressure, compared againstintracardiac pressures measured simultaneously at the time of right heartcatheterization. Methods In 37 patients, mean pulmonary artery pressure (mPAP) was measured duringcardiac catheterization. Simultaneously, Hemotag analyzed CTIs: MVC and IVCT.The predictability value of non-invasively HEMOTAG-derived CTIs- MVC and IVCT -were assessed to determine elevated mPAP. Linear correlation analysisbetween CTIs and mPAP was performed. Sensitivity, specificity, positive, andnegative predictive values were calculated. Results Mean age was 65.40 ± 12.42years, mean ejection fraction was 54.61 ± 14.24%,48% were women, 55.2% had left valvular disease, 27.6% had systolicdysfunction, and mean mPAP was 16.10 ± 5.40 mmHg. With a paired dichotomous interpretation,sensitivity of 81% was noted for MVC and specificity of 100% was observed withIVCT. A receiver operator characteristic curve was employed to assessperformance with an AUC of 0.71 and 0.64 for MVC and IVCT, respectively. Therewere no strong correlations observed between mPAP and CTIs (Table 1). Conclusions HEMOTAG detected elevated mPAPwith good sensitivity and high specificity. This preliminary study hasdemonstrated the feasibility of estimating mPAP using a portable, non-invasivedevice that empowers patients to transmit such data from home instantaneouslyto providers. Further studies are required to validate HEMOTAG as apoint-of-care non-invasive assessment for pulmonary hypertension patients.

Evaluation of Water Hammer for Seawater Treatment System in Offshore Floating Production Unit

Water hammer can result in the rupture of pipes, and significant damage to pipe supports is inevitable during the operation of an offshore plant. In this study, the dynamic behaviors of the water hammer caused by closing valves and starting pumps for the seawater treatment system were evaluated by using the 1D numerical simulation model based on the method of characteristics. Before conducting an analysis of a complex piping network, the 1D numerical simulation tools were validated by a comparison between the numerical results and the results from both static and transient experiments that have been conducted in other studies. For the case study, the effects of valve flow characteristics and valve closing time on surge pressure were investigated, and the equal percentage butterfly valve was recommended in order to reduce the surge pressure with a shorter valve closure time and lower weight compared to other valve types.

Effect of instantaneous shut-in on well bore integrity and safety of gas wells

The instantaneous shut-in of the gas well produces a transient flow phenomenon. The repeated pressure amplitude and pressure repeated changes will cause the vibration of the tubing and equipment, resulting in damage to tubing and accessory equipment. However, it is difficult to directly adopt the conventional transient flow model due to the particularity environment of the gas well bore. Based on the classical transient flow theory and mechanism of transient flow process in a gas well, a mathematical model explaining the transient flow phenomenon of gas well is established and the method of characteristics is adopted for numerical solution. The calculation results of sample show that, after the wellhead valve is closed instantaneously, the surge pressure is transmitted and gradually attenuates under the influence of frictional resistance, and reaches the balance pressure after a period of time. With the increase of valve closure time, the maximum value of wellhead pressure is reduced, and the time of peak value occurs is also delayed. When the gas well is shut in for a short time, the propagation speed of pressure wave is faster than that in the circumstance of shutting the gas well in a longer time. The transient flow model can accurately reflect the value of surge pressure, the cycle of surge pressure and attenuation law of pressure wave, which has a high reference value for studying the transient process and pressure distribution in the gas well bore.

Effect of valve closure time on transient cavitating flow through piping systems

ABSTRACT Hydraulic transient is an unavoidable phenomenon which occurs in any piping system during a sudden change in operating conditions, and it sometimes leads to cavitation; subsequently generates very high pressure in the system. The intensity of pressure developed from sudden or gradual closure of the valves at the downstream side primarily depends on the closure time of the valve. This paper is an experimental investigation into the effect of valve closure time on transient flow characteristics in a piping system. The experiments with different flow rates of fluid and valve closure times in the piping system proved that the occurrence of cavitation in a pipe links very much with the closure time of valve and the characteristics of water hammer pressure wave.

Finite element for the dynamic analysis of pipes subjected to water hammer

An axisymmetric finite element is developed for the dynamic analysis of pipes subjected to water hammer. The analysis seamlessly captures the pipe response due to water hammer by solving first the water hammer mass and momentum conservation equations, to recover the spatial–temporal distribution of the internal pressure, and then uses the predicted pressure history to form a time-dependent energy equivalent load vector within a finite element model. The study then determines the pipe response by solving the finite element discretized equations of motion. The formulation of the pipe response is based on Hamilton’s principle in conjunction with a thin shell theory formulation, and captures inertial and damping effects. The results predicted by the model are shown to be in agreement with those based on an axisymmetric shell model in Abaqus for static, free vibration and transient responses for benchmark problems. The water hammer and structural models are seamlessly integrated to enable advancing the transient solution well into the time domain to capture the effect of reflected pressure wave due to water hammer. The results indicate that the radial stress/displacement oscillations approach those of the quasi-steady response when the valve closure time exceeds eight times the period of radial vibrations obtained for the case of instantaneous valve closure.

Statistical performance analysis of transient-based extended blockage detection in a water supply pipeline

Abstract The aim of the present research is to quantify the maximum feasible accuracy (location and size) for the transient-based blockage detection in a water supply pipeline. Owing to the randomness of transient measurements, a performance bound for the extended blockage detection exists which estimated parameters cannot exceed. The Cramér–Rao lower bound (CRLB) theorem is utilized to compute the lower bound variance of noise-induced estimation errors. It gives the minimum mean square error of any estimator according to information obtained from measurements and quantified by Fisher information. The Fisher information matrix is computed using direct differentiation of the compatibility equations obtained by the method of characteristics. The influence of relevant physical parameters including valve closure time, measurement time length and noise level on the best possible localization of blockage is investigated. The connection between the signal bandwidth, noise level and the performance limit is quantified for a typical case study. The results demonstrate trade-off between the size and the location/length of blockage estimates subject to different maneuver times, roughly offering half the wave speed times maneuver duration as the resolution limit.

Estimation and examination of linepack pressures in long liquid pipelines

In the past, many researchers have carried out water-hammer pressure analysis using Joukowsky equation. However, it has been observed that the computed pressure surge is no longer applicable based on the equation. The Joukowsky equation cannot be used even within the reflection time of the long pipeline. In such cases, the actual pressure rise due to the sudden closure of a quick acting valve will be several times more than that of the sudden increase in pressure as calculated by the Joukowsky equation. The phenomenon of rising pressure at the upstream of an instantaneously closed valve with the passage of time caused by the pipe friction is commonly called as linepacking. In this paper, various parameters affecting the linepack pressure have been thoroughly investigated. As the relative roughness increases, the resulting non-dimensional linepack pressure \( \left( {P_{LP} /P_{o} } \right) \) significantly increases and the proportionality constant was equal to 1.5. The linepack pressure was determined to be decreasing with increasing valve closure time. The dominant parameter that influences the linepack pressure is found to be the Reynolds number as compared to the Mach number, and the relative roughness. Furthermore, the linepack pressure is found to be proportional to frictional head loss \( \left( {h_{L} /D} \right) \), and inversely proportional to inlet pressure \( \left( {P_{o} /\left( {\gamma L_{o} } \right)} \right) \). Finally, a linear regression equation was developed in terms of non-dimensional variables to estimate the linepack pressure using hand calculations without undergoing numerical modeling procedures. The proposed equation was validated for sudden valve closure pressure histories available in the literature. The proposed method is applicable to long distance water supply pipelines where the linepack pressures are significant.

Heterogeneity and incorporation of chromium isotopes in recent marine molluscs (Mytilus)

The mollusc genus Mytilus is abundant in various modern marine environments and is an important substrate for palaeo‐proxy work. The redox‐sensitive chromium (Cr) isotope system is emerging as a proxy for changes in the oxidation state of the Earth's atmosphere and oceans. However, potential isotopic offsets between ambient sea water and modern biogenic carbonates have yet to be constrained. We measured Cr concentrations ([Cr]) and isotope variations (δ53Cr) in recent mollusc shells (Mytilus) from open and restricted marine environments and compared these to ambient sea water δ53Cr values. We found a large range in mollusc [Cr] (12–309 ppb) and δ53Cr values (−0.30 to +1.25‰) and in the offset between δ53Cr values of mollusc shells and ambient sea water (Δ53CrseawaterbulkMytilus, −0.17 to −0.91‰). Step digestions of cultivated Mytilus edulis specimens indicate that Cr is mainly concentrated in organic components of the shell (periostracum: 407 ppb, n = 2), whereas the mollusc carbonate minerals contain ≤3 ppb Cr. Analyses of individual Cr‐hosting phases (i.e., carbonate minerals and organic matrix) did not reveal significant differences in δ53Cr values, and thus, we suggest that Cr isotope fractionation may likely take place prior to rather than during biomineralisation of Mytilus shells. Heterogeneity of δ53Cr values in mollusc shells depends on sea water chemistry (e.g., salinity, food availability, faeces). The main control for δ53Cr values incorporated into shells, however, is likely vital effects (in particular shell valve closure time) since Cr can be partially or quantitatively reduced in sea water trapped between closed shell valves. The δ53Cr values recorded in Mytilus shells may thus be de‐coupled from the redox conditions of ambient sea water, introducing additional heterogeneity that needs to be better constrained before using δ53Cr values in mollusc shells for palaeo‐reconstructions.

Stochastic water balance dynamics of passive and controlled stormwater basins

Abstract Urbanization and changing rainfall intensities affect the performance of urban stormwater infrastructure, creating the necessity to design resilient stormwater systems. One proposed method to increase the resilience of stormwater infrastructure is the active control of system flows. To improve the understanding of actively-controlled urban water infrastructure function under variable hydro-climate, we develop a stochastic water balance model for stormwater retention and detention basins with both passive and actively-controlled outflow structures. Under active outflow control, the outflow valve is closed until the water level in the basin reaches a specified maximum at which point the valve opens and the basin empties. Using the stochastic water balance model, we develop analytical expressions for the steady-state probability density functions (PDFs) of water level and valve closure time, as well as the joint PDF of water level and valve closure time. These PDFs then are used to define water level and flow duration curves that provide a probabilistic description of the full range of basin performance. The model accurately predicts the water level PDF estimated from data collected at a retention basin with a passive outflow structure. The model provides a basis for evaluating how changes in the rainfall-runoff process, affected by land use and climate change, will impact the variability of stormwater basin water storage and pollutant removal function. We find that this variability can be managed through the adaptive updating of the active control rule for the outflow structure.

Study on factors affecting local peak strain results in automatic functional imaging of transthoracic echocardiography

To investigate the important impacting factors on the accuracy of local peak strain (RLS) in transthoracic echocardiography real-time tri-axial automatic functional imaging (AFI), to evaluate the clinical efficacy of AFI and to improve the accuracy of the results. From May 2016 to May 2017, 82 healthy volunteers were enrolled in the AFI examination, of which 22 were excluded and 60 were eligible. The excluded 22 patients were analyzed for exclusion reasons, and the results of the 60 eligible AFI results were studied focusing on the longitudinal left ventricular regional longitudinal peak systolic strain (RLS) in different methods of operation, to compare the results and accuracies of AFI by different influencing factors, and to find the most important ones. The success rate of AFI for this group of subjects is 74%, and the exclusion reason is that the left ventricular segments cannot be fully displayed. Among eligible subjects, the main influencing factors on RLS were region of interest (ROI), aortic valve closure time adjustment and image frame rate selection. The differences of results obtained by different operations were statistically significant (P<0.05). The success rate of AFI for this group of subjects is 74%. The RLS results were influenced by multiple factors, which can be effectively avoided.

Influence of connection stub parameters and valve closure time on transient measurement accuracy of a pressure transducer

Abstract Consider that a transient pressure measurement occurs at the end of the connection stub attached to a pipeline. The question arises as to whether the pressure being recorded at the end of the stub is an accurate representation of pressure in the pipeline. In this study, the influence of three parameters, including pressure transducer connection stub length, stub diameter and valve closure time, on the measurement accuracy of transient pressure is investigated through numerical simulation on a reservoir-pipe-valve-reservoir system. The results show that the larger the diameter of stub, the larger its influence both on the transient in the pipe and on measurement error; the measurement accuracy increases with an increase of the length of the stub only when the closure time of the end valve is less than the time for the water hammer wave to travel back and forth between the measurement point and the end point of stub. In contrast, when the closure time of the end valve is greater than the water hammer wave return time, the measurement accuracy will decrease with an increase of the stub length; the measurement accuracy is improved as the closure time of the end valve increases. As a result, in practice, diameter and length of connection stub for the pressure-transducer should both be selected to be as small as possible.

Aging of the venous valves as a new risk factor for venous thrombosis in the elderly: the BATAVIA study

Background Increasing age is the strongest risk factor for venous thrombosis (VT). Increasing age has been related to a thickening of the venous valves and a decreased valvular function. The association between valve thickness and the risk of VT is not known. Objectives To assess the association between increased valve thickness and valve closure time (VCT) and the risk of VT. Methods Analyses were performed in the BATAVIA study, including 70 cases aged 70 + with a first VT and 96 controls. We performed an ultrasound examination of the valves in the popliteal veins. The valves were imaged with a 9 MHz linear probe using B-mode ultrasonography. VCT was measured as an indicator for valve function using an automatic inflatable cuff. To estimate the risk of VT, valve thickness was dichotomized at the 90th percentile as measured in controls and VCT was dichotomized at 1 s. Results Mean valve thickness of controls was similar in the left (0.36 mm, 95% CI 0.34-0.37) and right (0.36 mm, 95% CI 0.35-0.38) leg. In 45 cases a valve was observed in the contralateral leg with a mean valve thickness of 0.39 mm (95% CI 0.36-0.42). Cases had an increased valve thickness compared with controls: mean difference 0.028 mm (95%CI 0.001-0.055). Valve thickness > 90th percentile increased the risk of VT 2.9-fold. Mean VCT in controls was 0.38 s, in contralateral leg of cases 0.58 s. VCT > 1 s increased the risk of VT 2.8-fold (95% CI 0.8-10.4). Conclusions Risk of VT was associated with increased valve thickness and valvular reflux of > 1 s.

A pilot study of venous duplex ultrasound parameters in healthy children.

The spectrum of chronic venous disease (CVD) in adults is well documented, whereas there is a paucity of data published commenting on pediatric CVD. We previously identified that there is often venous reflux present in cases of pediatric lower extremity edema despite an alternative confirmed diagnosis. To further assess the clinical significance of this venous reflux, this study aimed to elicit venous parameters in healthy pediatric controls. Healthy pediatric volunteers aged 5 to 17years were recruited for venous reflux study. A comprehensive venous reflux study was performed with the patient standing. Vein diameter, patterns of valvular reflux, and accessory venous anatomy were examined in the deep and superficial venous systems. Eighteen children including 10 boys and 8 girls were studied. Five volunteers were aged 5 to 8years, six volunteers were aged 9 to 12years, and seven volunteers were aged 13 to 17years. Great saphenous vein (GSV) diameter at the saphenofemoral junction significantly increased with age. Deep vein valve closure time (VCT) did not differ significantly between groups, whereas GSV VCT was significantly higher in the 9- to 12-year age group. Incidental venous insufficiency was identified in 60% of children aged 5 to 8years (n= 3), 50% of children aged 9 to 12years (n= 3), and 57% of children aged 13 to 17years (n= 4). All superficial venous reflux was confined to the GSV; there were no cases of isolated deep venous reflux. Reflux was identified at multiple GSV stations in 60% of children. There was no significant difference in incompetent GSV VCT in comparing children with and without deep venous reflux. Accessory superficial veins were identified in 20% of children aged 5 to 8years (n= 1), 50% of children aged 9 to 12years (n= 3), and 43% of children aged 13 to 17years (n= 3). The presence of an accessory saphenous vein was not associated with deep venous reflux in any patient, and only 29% of those with accessory saphenous venous anatomy had evidence of superficial venous (GSV) reflux. The GSV continues to grow in diameter through the teenage years. Incidental valvular incompetence and GSV reflux are common. The presence of accessory saphenous veins is similarly common and not associated with venous reflux. The clinical significance and natural history of this incidental venous reflux remain unclear. Future research should determine whether these changes seen in the pediatric age group lead to CVD during later years of life.