Time-averaged Volume Research Articles

A multicentric, international matched pair analysis of body composition in peritoneal dialysis versus haemodialysis patients

Volume status, lean and fat tissue are gaining interest as prognostic predictors in patients on dialysis. Comparative data in peritoneal dialysis (PD) versus haemodialysis (HD) patients are lacking. In a cohort of PD (EuroBCM) and HD (Euclid database) patients, matched for country, gender, age and dialysis vintage, body composition was assessed by bioimpedance spectroscopy (BCM, Fresenius Medical Care). Time-averaged volume overload (TAVO) was defined as the mean of pre- and post-dialysis volume overload (VO), and relative (%) (TA)VO as (TA)VO/ECV. Four hundred and ninety-one matched pairs (55.2% males, median age 60.0 years) were included. The body mass index (BMI, PD = 26.5 ± 4.7 versus HD = 25.9 ± 4.6 kg/m(2), P = 0.18 in males and 27.4 ± 5.8 versus 27.5 ± 6.6 kg/m(2), P = 0.75 in females) and fat tissue index (males: 11.5 ± 5.3 versus 11.4 ± 5.4 kg/m(2), P = 0.90, females: 14.8 ± 6.7 versus 15.4 ± 7.2 kg/m(2), P = 0.30) were not different in PD versus HD patients, whereas the lean tissue index (LTI) was higher in PD versus HD patients (males: 14.5 ± 3.4 versus 13.7 ± 3.1 kg/m(2), P = 0.001, females: 12.6 ± 3.3 versus 11.5 ± 2.6 kg/m(2), P < 0.0001). VO/extracellular water (ECW) was not different between PD versus just before the HD treatment (males: 10.8 ± 12.1 versus 9.2 ± 10.2%, P = 0.09; females: 6.5 ± 10.8 versus 7.7 ± 9.4%, P = 0.19). The relative TAVO was higher in PD versus HD (10.8 ± 12.1% versus 3.2 ± 11.2%, and 6.5 ± 10.8% versus 1.2 ± 10.9%, both P < 0.0001). The LTI was impaired, and this was more in males versus females, but was better preserved on PD versus HD, whereas fat tissue index (FTI) was increased, but not different between PD and HD. Volume overload was more present in PD versus HD when TAVO, but not when predialysis volume status, was used as a reference.

Reflections on dissipation associated with thermal convection

AbstractBuoyancy-driven convection is modelled using the Navier–Stokes and entropy equations. It is first shown that the coefficient of heat capacity at constant pressure, ${c}_{p} $, must in general depend explicitly on pressure (i.e. is not a function of temperature alone) in order to resolve a dissipation inconsistency. It is shown that energy dissipation in a statistically steady state is the time-averaged volume integral of $- \mathrm{D} P/ \mathrm{D} t$ and not that of $- \alpha T(\mathrm{D} P/ \mathrm{D} t)$. Secondly, in the framework of the anelastic equations derived with respect to the adiabatic reference state, we obtain a condition when the anelastic liquid approximation can be made, $\gamma - 1\ll 1$, independent of the dissipation number.

Numerical investigation of subsonic hydrogen jet release

A buoyant round vertical hydrogen jet is investigated using Large Eddy Simulations at low Mach number (M = 0.3). The influence of the transient concentration fields on the extent of the gas envelope with concentrations within the flammability limits is analyzed and their structure are characterized. The transient flammable region has a complex structure that extends up to 30% beyond the time-averaged flammable volume, with high concentration pockets that persist sufficiently long for potential ignition. Safety envelopes devised on the basis of simplified time-averaged simulations would need to include a correction factor that accounts for transient incursions of high flammability concentrations.

Analysis of the influences of gas temperature fluctuation on the soot formation and oxidation

Numerical analysis is performed to investigate the influences of gas temperature fluctuation on soot formation and oxidation. The gas flow has a time-averaged gas temperature of 1400–1700K. The instantaneous variations of soot volume fraction with time are obtained under different conditions. Obvious differences are found between the results with and without the gas temperature fluctuation. The time-averaged soot volume fraction decreases with the fluctuation amplitude of the gas temperature. The evident influences of the gas temperature fluctuation on the reaction processes of soot formation and oxidation are thus delineated.

Volume excess in chronic haemodialysis patients—effects of treatment frequency and treatment spacing

The main objective of this study was to theoretically quantify the fluctuations of fluid volume excess for different modes of intermittent ultrafiltration schedules and to compare the prediction for the typical and asymmetric thrice-weekly schedule to clinical, physiological and biophysical markers of volume expansion in a group of stable haemodialysis patients. Overall volume excess (V(OVE)) was described as the sum of a time-independent (V(0)) and a time-dependent component (V). An exact relationship was developed to relate V to variable treatment frequency, treatment spacing and net volume accumulation rate. In a single-centre haemodialysis population, body mass profiling was combined with volume state evaluation by bioimpedance analysis, N-terminal pro-B-type natriuretic peptide (NT-pro BNP) levels, clinical signs, a volume questionnaire and blood pressure levels. In 23 patients following the typical thrice-weekly schedule, the time-averaged volume excess (V) during the whole week (1.1 ± 0.5 L) was significantly larger than that during the midweek interval (0.9 ± 0.4 L) (P < 0.002) by a factor comparable to that of 1.21 obtained from the theoretical analysis. V(OVE) was 1.3 ± 1.7 L and significantly related to pre- (P < 0.001) and post-dialysis levels of NT-pro BNP (P < 0.001). Asymmetric treatment spacing such as with the typical thrice-weekly treatment schedule leads to a significant increase in time-averaged volume excess. The theoretical analysis allows for comparison of time-averaged volume excess in treatments varying with regard to treatment frequency and regularity and could be helpful to prescribe post-treatment volume (target weight) for such variable treatment modes.

Use of a novel dual-sensor probe array and electrical resistance tomography for characterization of the mean and time-dependent properties of inclined, bubbly oil-in-water pipe flows

An array of dual-sensor conductance probes, which contains a number of dual-sensor probes equispaced across the diameter of an 80 mm pipe, is introduced in this paper for characterizing bubbly oil-in-water pipe flows inclined at angles from 15° to 60° to the vertical. Each dual-sensor probe measures the local axial oil velocity and the local oil volume fraction at the position of the probe. Choosing an averaging interval of 0.05 s, values of the local oil volume fraction and the local oil velocity were measured simultaneously at the different probe positions, enabling the time-dependent structure of the two-phase flow to be investigated. After data processing, time-dependent variations of volume fraction along the pipe were found which are consistent with the presence of intermittent Kelvin–Helmholtz wave structures in the flow. A high-speed dual-plane ERT system was used to measure the axial propagation speed of these Kelvin–Helmholtz waves, using cross correlation. This paper presents results for the measured characteristics of inclined oil-in-water flows including (i) time-averaged and time-dependent oil volume fraction and velocity distributions and (ii) the Kelvin–Helmholtz wave properties including the wave speed, wave amplitude, wavelength and wave frequency.

Invited commentary

This is a well-written article by an experienced group with a relatively large number of patients treated for complicated acute type B aortic dissections. The International Registry of Acute Dissection published data noting an in-hospital mortality of 13% for all patients with acute type B dissection, with branch vessel involvement or malperfusion being an independent predictor of early death. An open surgical repair carries a mortality risk of at least 30%1Suzuki T. Mehta R.H. Ince H. Nagai R. Sakomura Y. Weber F. et al.Clinical profiles and outcomes of acute type B aortic dissection in the current era: lessons from the International Registry of Aortic Dissection (IRAD).Circulation. 2003; 108: II312-II317PubMed Google Scholar; consequently, endovascular repair has become a very attractive option. Feezor et al2Feezor R.J. Martin T.D. Hess Jr, P.J. Beaver T.M. Klodell C.T. Lee W.A. Early outcomes after endovascular management of acute, complicated type B aortic dissection.J Vasc Surg. 2009; 49 (discussion:6-7): 561-566Abstract Full Text Full Text PDF PubMed Scopus (67) Google Scholar reported their experience with thoracic endovascular aortic repair for 33 patients with acute complicated type B dissection. The 30-day in-hospital mortality for their group was 21%, with 15% having permanent spinal cord complications, 12% having renal failure requiring dialysis, and a 12% incidence of stroke. Clearly, most published results are far better than this,3Eggebrecht H. Nienaber C.A. Neuhauser M. Baumgart D. Kische S. Schmermund A. et al.Endovascular stent-graft placement in aortic dissection: a meta-analysis.Eur Heart J. 2006; 27: 489-498Crossref PubMed Scopus (435) Google Scholar and the results of this manuscript reflect this as well. Nevertheless, I find very surprising and not in line with published results, that with the authors' technique of extensive aortic coverage to the celiac artery, lack of spinal protection, and 78% of patients being American Society of Anesthesiologists IV or V (an independent risk factor for poor outcome), that they would essentially have 0% paraplegia. Persistent false lumen patency is associated with continued aortic expansion and seen in about 50% of proximally stented patients. Computed tomography (CT) imaging does not reliably identify re-entry tears and, as such, extensive coverage may not necessarily provide better long-term results if there are distal tears. The provisional extension to induce complete attachment (PETTICOAT) concept may perform better if extensive apposition of the dissection flap is required. Finally, the authors conclude that the volumetric analysis of true and false lumens using 3D CT is effective; however, there may be a potential flaw in their imaging technique. They perform CT images that are not electrocardiographically gated or dynamic; consequently, they can only get a time-averaged volume of the true and false lumens. We have published on dynamic aspects of aortic dissections4Karmonik C. Bismuth J. Davies M.G. Lumsden A.B. Computational fluid dynamics as a tool for visualizing hemodynamic flow patterns.Methodist Debakey Cardiovasc J. 2009; 5: 26-33PubMed Google Scholar, 5Karmonik C. Bismuth J. Davies M.G. Shah D.J. Younes H.K. Lumsden A.B. A computational fluid dynamics study pre- and post-stent graft placement in an acute type B aortic dissection.Vasc Endovasc Surg. 2010 Dec 13; ([Epublication ahead of print])PubMed Google Scholar, 6Karmonik C. Bismuth J. Davies M.G. Younes H.K. Lumsden A.B. An image processing algorithm for the in-vivo quantification and visualization of septum motion in type III B − aortic dissections with cine magnetic resonance imaging.Conf Proc IEEE Eng Med Biol Soc. 2009; 2009: 4391-4394PubMed Google Scholar, 7Karmonik C. Bismuth J. Redel T. Anaya-Ayala J.E. Davies M.G. Shah D.J. et al.Impact of tear location on hemodynamics in a type B aortic dissection investigated with computational fluid dynamics.Conf Proc IEEE Eng Med Biol Soc. 2010; 1: 3138-3141Google Scholar, 8Karmonik C. Bismuth J.X. Davies M.G. Lumsden A.B. Computational hemodynamics in the human aorta: a computational fluid dynamics study of three cases with patient-specific geometries and inflow rates.Technol Health Care. 2008; 16: 343-354PubMed Google Scholar and find a variation in the true/false lumen of up to 20% to 50% throughout the cardiac cycle. Additionally, the benefit of dynamic imaging goes beyond simple appreciation of a septum, but rather fundamentally how that septum acts (mobility). We have found that a septum may by age be categorized as acute, but act more chronic with a rigid septum. This has potential implications for the therapy. Finally, I think knowing the volumetric analysis for a case control group being managed medically would potentially provide many answers, and could affect the management paradigm. Aortic remodeling, volumetric analysis, and clinical outcomes of endoluminal exclusion of acute complicated type B thoracic aortic dissectionsJournal of Vascular SurgeryVol. 54Issue 2PreviewStructural changes within the aorta after thoracic endovascular aortic repair (TEVAR) for acute complicated type B thoracic aortic dissections (ABAD) remain unknown. This study reviewed and analyzed morphologic changes, volumetric data, and clinical outcomes of patients with ABAD. Full-Text PDF Open Archive

Comparison and evaluation of interphase momentum exchange models for simulation of the solids volume fraction in tapered fluidised beds

Abstract An Eulerian computational fluid dynamics (CFD) model with granular flow extension was used to simulate a gas–solid fluidised bed in a tapered reactor. Various drag coefficient models were evaluated, which are used to calculate the drag force, describing the momentum transfer between the gas and solid phases. Comparison and evaluation between time-averaged solids volume fractions obtained from experiments and from simulations with several drag coefficient models were made. The predicted results obtained by the different drag models were verified using experimental data of Depypere et al. (2009) . Initial results using a 2-phase Eulerian model showed poor agreement with experimental results. However, extending the Eulerian model to include 3 solid phases—with different mean particle diameter per phase in order to account for the particle size distribution of the fluidised solid material—yielded good agreement with experimental results. Furthermore, quantitative analyses showed that the modified Gidaspow drag model gave the best agreement between CFD simulations and experimental data.

Atmospheric Ammonia Mixing Ratios at an Open-Air Cattle Feeding Facility

Mixing ratios of total and gaseous ammonia were measured at an open-air cattle feeding facility in the Texas Panhandle in the summers of 2007 and 2008. Samples were collected at the nominally upwind and downwind edges of the facility. In 2008, a series of far-field samples was also collected 3.5 km north of the facility. Ammonium concentrations were determined by two complementary laboratory methods, a novel application of visible spectrophotometry and standard ion chromatography (IC). Results of the two techniques agreed very well, and spectrophotometry is faster, easier, and cheaper than chromatography. Ammonia mixing ratios measured at the immediate downwind site were drastically higher (∼2900 parts per billion by volume [ppbv]) than those measured at the upwind site (≤200 ppbv). In contrast, at 3.5 km away from the facility, ammonia mixing ratios were reduced to levels similar to the upwind site (≤200 ppbv). In addition, PM10 (particulate matter <10 μm in optical diameter) concentrations obtained at each sampling location using Grimm portable aerosol spectrometers are reported. Time-averaged (1-hr) volume concentrations of PM10 approached 5 × 1012 nm3 cm−3. Emitted ammonia remained largely in the gas phase at the down-wind and far-field locations. No clear correlation between concentrations of ammonia and particles was observed. Overall, this study provides a better understanding of ammonia emissions from open-air animal feeding operations, especially under the hot and dry conditions present during these measurements.

Flow Volume and Cross-Sectional Area of the Extracranial Vertebral Arteries and its Relation to Vascular Lesions or Anatomical Variations in the Posterior Circulation

We examined whether the time-averaged maximum velocity (TAMV), flow volume (FV) or cross-sectional area (CA) in the vertebral arteries (VA) as determined by ultrasonography was related to vascular lesions or variations in the intracranial part of the posterior circulation. Three hundred nine patients without severe stenosis in the carotid circulation (159 males, 150 females, mean age of 69.1 years) underwent both colour duplex ultrasonography and magnetic resonance angiography (MRA) and were thus analyzed. According to the MRA findings, the patients were divided as follows; 22 patients with severe stenosis in the bilateral PCA or VA or basilar artery (V group) and 287 patients without (N group). The N group was then further divided as follows; 144 patients with no (P0 group); 89 with one (P1) and 54 with both posterior communicating arteries (P2) detected on MRA. TAMV, FV and CA were compared among these groups. Both TAMV and FV of V group were significantly lower than those of N group (35.3 vs. 42.6 cm/sec in TAMV, 98.2 vs. 135.3 mL/min in FV, p < 0.001 and 0.0001, respectively). The FVs and CAs in the P0 through P2 groups were all significantly different according to the number of posterior communicating arteries (149.3 vs. 128.0 vs. 109.8 mL/min, 22.5 vs. 20.2 vs. 16.5 mm 2, both p < 0.001) while TAMVs in these groups did not differ substantially. The FV in both VAs were thus found to be related to the vascular lesions or variations in the posterior circulation. (E-mail: sugimori@intmed2.med.kyushu-u.ac.jp)

Numerical analysis of high frequency pulsating flows through a diffuser-nozzle element in valveless acoustic micropumps

The concept of a valveless acoustic micropump was investigated. Two-dimensional, time-varying, axisymmetric, incompressible viscous flows through a planar diffuser-nozzle element were analyzed for applications in valveless acoustic micropumps. The diffuser divergence half-angles (θ), and the maximum pressure amplitudes (P) were independently varied. The inflow was periodic and the excitation frequency (f) was varied over the range 10 kHz ≤ f ≤ 30 kHz. The net time-averaged volume flux and the rectification capability of the diffuser were found as functions of θ, f, and P. The phase difference between pressure and velocity waveforms, the life time and the size of large scale flow recirculation regions inside the microdiffuser, and energy losses were found to be strongly frequency dependent.

Comparison of fibre optical measurements and discrete element simulations for the study of granulation in a spout fluidized bed

Spout fluidized beds are frequently used for the production of granules or particles through granulation. The products find application in a large variety of applications, for example detergents, fertilizers, pharmaceuticals and food. Spout fluidized beds have a number of advantageous properties, such as a high mobility of the particles, which prevents undesired agglomeration and yields excellent heat transfer properties. A discrete element model is used describing the dynamics of the continuous gas phase and the discrete droplets and particles. For each element momentum balances are solved. The momentum transfer among each of the three phases is described in detail at the level of individual elements. The results from the discrete element model simulations are compared with local measurements of time time-averaged particle volume fractions as well as particle velocities by using a novel fibre optical probe in a fluidized bed of 400 mm I.D. Simulations and experiments were carried out for three different cases using Geldart B type aluminium oxide particles: a freely bubbling fluidized bed; a spout fluidized bed without the presence of droplets and a spout fluidized bed with the presence of droplets. It is found that the experimental and numerical results agree in a qualitative manner. It is demonstrated how the discrete element model can be used to obtain information about the interaction of the discrete phases, i.e. the growth zone in a spout fluidized bed. Additional analysis of the numerical results indicates that liquid breakthrough does not take place for the studied test case.

Experimental investigation of three-phase flow in a vertical pipe: Local characteristics of the gas phase for gas-lift conditions

Laboratory experiments have been performed on the flow of oil, water and air through a vertical pipe in order to study the gas-lift technique for oil–water flows. Special attention was paid to the phase inversion phenomenon, by which the continuous phase switches to the dispersed phase and vice versa. By using different types of gas injectors the influence of the bubble size of the injected air on the efficiency of the gas-lift technique (in particular at the point of phase inversion) was studied. Also the gas and liquid mixture velocities were varied. The air bubbles were detected by means of optical fibre probes. Local measurements of the time-averaged gas volume fraction, bubble size and bubble velocity were carried out, as well as pressure measurements. Phase inversion is associated with a sharp increase of the pressure gradient. With air injection the pressure gradient (for the oil–water–air flow) is always significantly smaller than for the case of oil–water flow, except at the point of phase inversion where the pressure drop can be even be higher than for oil–water flow. It was also found that air injection does not significantly change the critical concentration of oil and water where phase inversion occurs. An important phenomenon to explain these results is, that the presence of the dispersed (oil or water) phase has a significant influence on the bubble size. Also the influence of the gas flow rate on the distribution of the oil and water phases in a cross-section of the pipe plays a significant role.

G704 ターボポンプ用インデューサ内の非定常キャビテーション流れの数値計算(2)(GS-7 キャビテーション,一般セッション)

The unsteady cavitating flow in a turbopump inducer has been calculated using an accurate three-dimensional detached eddy simulation (DES) code, which took into account the cavitating phenomena. The three-dimensional code is based on the numerical method for compressible flow using low Mach number flow approximation and a cavitation model. Qualitative agreement between our computational result and experimental data was satisfactory. The magnitude of the fluctuation in cavity volume increased as the cavities extend and close to the throat of the blade passage. The effect of the tip-gap on the cavity volume was shown; the time-averaged volume of cavities for the inducer with the tip-gap was about five times larger than that for the inducer without the tip-gap at an operating condition. Vorticity generation in cavities due to baroclinic torque was found. Multiple blade passages calculations are under way to find unsteady phenomena such as rotating cavitation.

The effect of global mixing on soot volume fraction: measurements in simple jet, precessing jet, and bluff body flames

Measurements of soot volume fraction were performed in three different turbulent diffusion flames using laser-induced incandescence (LII) to provide insight into the effect of global mixing rate on the instantaneous local and the average soot volume fraction. The three flames, produced by simple jet, precessing jet, and bluff-body jet burners, are chosen because they span a wide range of different global mixing rates for the same fuel, nozzle diameter, and flow rate, and because global measurements of their radiation, NO x emissions, and residence times are available. The measurements reveal an inverse relationship between global mixing rate and both the total amount of soot in the flame and local instantaneous soot volume fractions, broadly consistent with trends in laminar flames. However, probability density functions reveal that the relationship between local instantaneous and time-averaged soot volume fraction is different in the lower and upper regions of each flame. In the lower regions, the instantaneous and average volume fractions increase together with distance from the burner. However, the upper regions exhibit a bi-modal distribution in local, instantaneous volume fraction. This suggests that burnout in the tip region occurs predominantly by reducing the proportion of the flame being occupied by the sheets of soot, rather than by reducing the instantaneous volume fraction within the sheets. In addition, the shape of the pdf is different for each flame, showing a dependence on the turbulent characteristics, and that care must be taken in applying measurements obtained from one class of burner to another.

Evaluation of vertebral artery hypoplasia and asymmetry by color-coded duplex ultrasonography

Distinguishing stenosis and hypoplasia of the extracranial vertebral artery (VA) is clinically important, but there is no agreement in defining VA hypoplasia. We endeavored to attain reference values for VA flow volume by color Doppler ultrasonography (CDU), analyze age and gender effects on VA flow volume and develop a definition of VA hypoplasia. CDU was performed in 447 subjects free of cerebrovascular diseases or carotid stenosis. The VA diameter, peak systolic velocity, end-diastolic velocity, time-averaged mean velocity, resistance index (RI) and flow volume were recorded bilaterally. We found significant asymmetries in diameter, flow velocities and flow volume with left-sided dominance. Diameters were different on left (0.297 ± 0.052 cm) and right (0.323 ± 0.057) sides ( p < 0.001). Flow volume was different on right (83.0 ± 36.9 mL/min) and left (96.6 ± 42.4) sides ( p < 0.001). Women had significantly smaller diameters, higher flow velocities and lower RIs than men. VA flow volume did not change with aging. We defined hypoplasia as a significant decrease in flow velocities and increase in RI for VA diameters < 0.22 cm. This definition is supported by findings of an increase in ipsilateral flow resistance (RI ≥ 0.75), contralateral diameter (side-to-side diameter difference ≥ 0.12 cm), and flow volume (side-to-side flow volume ratio ≥ 5). This definition and these reference values may lead to better differentiation between congenital variation and steno-occlusion clinically. (E-mail: jsjeng@ccms.ntu.edu.tw)

The impact of maternal plasma volume expansion and antihypertensive treatment with intravenous dihydralazine on fetal and maternal hemodynamics during pre-eclampsia: a clinical, echo-Doppler and viscometric study.

To establish the effects of plasma volume expansion (PVE) followed by intravenous dihydralazine (DH) administration on maternal whole blood viscosity (WBV) and hematocrit, uteroplacental and fetoplacental downstream impedance and umbilical venous (UV) volume flow in pre-eclampsia. In 13 pre-eclamptic women maternal and fetal hemodynamics were established by means of combined measurement of maternal arterial blood pressure (BP), WBV, hematocrit and uterine artery (UtA) resistance index (RI) in addition to umbilical artery (UA) pulsatility index (PI) and UV volume flow obtained from UV vessel area and UV time-averaged flow velocity. In each woman all parameters were measured four times at baseline, after PVE, after DH and 24 h after the start of treatment. Maternal diastolic BP, hematocrit and WBV display a significant reduction after PVE. In the fetus UA PI decreases significantly whereas a significant increase in UV cross-sectional area was detected. After maternal DH administration, arterial systolic and diastolic BP and UA PI show a significant decrease compared with the measurements following PVE. At 24 h, only maternal systolic and diastolic BP display a significant further decrease. No significant changes were established for the UtA RI, UV time-averaged velocity and UV volume flow during the entire study period. During pre-eclampsia, maternal PVE followed by DH administration results in a significant reduction in maternal diastolic BP, maternal hematocrit and WBV. Maternal PVE is associated with a significant increase in UV cross-sectional area and a non-significant rise of 11% in UV volume flow. Maternal DH administration does not result in any change in UV cross-sectional area. However, UA PI decreases significantly after both PVE and DH treatment.

Umbilical venous volume flow and fetal behavioral states in the normally developing fetus

To determine the relationship between umbilical venous (UV) volume flow and fetal behavioral states 1F (quiet sleep) and 2F (active sleep) in normal pregnancies at 36-40 weeks of gestation. Fetal behavioral states were established in 17 normal pregnancies by means of combined assessment of fetal heart rate patterns (FHRP), and fetal eye and body movements. UV vessel area (mm(2)) as obtained by tracing the inner vessel area using Labview and Imaq Vision software and UV time-averaged flow velocity (mm/s Doppler) were multiplied to calculate UV volume flow (mL/min) including flow/kg fetus. The pulsatility index (PI) in the umbilical artery was also determined. In each woman, all parameters were measured between three and five times in each behavioral state. Data are reported as mean +/- 1 SD and analyzed by paired t-test. No statistically significant behavioral-state-related changes were observed for UV time-averaged velocity and UV volume flow, resulting in UV volume flow/kg fetus of 69.1 +/- 14.9 mL/min*kg at 1F and 71.6 +/- 12.1 mL/min*kg at 2F (not significant). A statistically significant increase (P = 0.02) was established for UV cross-sectional area (46.4 +/- 8.6 mm(2) vs. 49.0 +/- 10.1 mm(2)) and for fetal heart rate (FHR) from 134.2 +/- 10.3 bpm in 1F to 144.2 +/- 7 bpm in 2F. Umbilical artery PI was not significantly different between the two behavioral states. On the basis of high venous vessel wall compliance, the significant increase in UV cross-sectional area during fetal behavioral state 2F may be determined by a rise in mean venous pressure. The significant rise in FHR may reflect increased fetal cardiac output during state 2F while the resistance at the hepato-ductal pathway remains relatively constant with the purpose of meeting raised energy demands during the active sleep state. This is further supported by the observed trend towards an increase in UV volume flow.

Acute Cigarette Smoking-Induced Hemodynamic Alterations in the Common Carotid Artery-A Transcranial Doppler Study-

Cigarette smoking has been shown to temporarily alter cerebral flow velocity and vasomotor reactivity, so the aim of this study was to assess the acute effects of smoking a single cigarette on the common carotid artery (CCA) hemodynamics in healthy nonsmokers. Using a 7.0 MHz linear transducer of a computed sonography system, the CCA hemodynamics, including the diameter of the left and right CCA, peak systolic velocity, maximum end-diastolic velocity, time-averaged maximum velocity pulsatility index, resistivity index, flow volume, diameter and area of the CCAs, were measured in 16 healthy nonsmokers before and immediately after smoking a cigarette. Compared with the baseline, heart rate and blood pressure significantly increased, the diameter, flow volume and area of each CCA were unchanged, and the pulsatility index and resistivity index were significantly altered after smoking. In addition, the peak systolic velocity, maximum end-diastolic velocity and time-averaged maximum velocity were significantly altered after smoking. Cigarette smoking significantly altered the CCA hemodynamics in nonsmokers, probably as a consequence of enhanced adrenergic activity.

Monte Carlo ray-tracing simulation for radiative heat transfer in turbulent fluctuating media under the optically thin fluctuation approximation

The Monte Carlo ray-tracing method (MCRT) based on the concept of radiation distribution factor is extended to solve radiative heat transfer problem in turbulent fluctuating media under the optically thin fluctuation approximation. A one-dimensional non-scattering turbulent fluctuating media is considered, in which the mean temperature and absorption coefficient distribution are assumed and the shape of probability density function is given. The distribution of the time-averaged volume radiation heat source is solved by MCRT and direct integration method. It is shown that the results of MCRT based on the concept of radiation distribution factor agree with these of integration solution very well, but results of MCRT based on the concept of radiative transfer coefficient do not agree with these of integration solution. The solution of time-averaged radiative transfer equation by the concept of radiative transfer coefficient should be treated with caution.