A novel hyperbaric swimming respirometer allows the simulation of varying swimming depths in fish respirometry studies.

The understanding of swimming physiology and knowledge on the metabolic costs of swimming are important for assessing effects of environmental factors on migratory behavior. Swim tunnels are the most common experimental setups for measuring swimming performance and oxygen uptake rates in fishes; however, few can realistically simulate depth and the changes in hydrostatic pressure that many fishes experience, e.g. during diel vertical migrations. Here, we present a new hyperbaric swimming respirometer (HSR) that can simulate depths of up to 80 m. The system consists of three separate, identical swimming tunnels, each with a volume of 205 L, a control board and a storage tank with water treatment. The swimming chamber of each tunnel has a length of 1.40 m and a diameter of 20 cm. The HSR uses the principle of intermittent-flow respirometry and has here been tested with female European eels (Anguilla anguilla). Various pressure, temperature and flow velocity profiles can be programmed, and the effect on metabolic activity and oxygen consumption can be assessed. Thus, the HSR provides opportunities to study the physiology of fish during swimming in a simulated depth range that corresponds to many inland, coastal and shelf waters.

Change in Rheologic Properties of Facial Soft-Tissue Fillers across the Physiologic Angular Frequency Spectrum.

BACKGROUND: The number of soft-tissue filler injections performed in the United States is constantly increasing and reflects the high demand for enhanced facial and body attractiveness. The objective of the present study was to measure the viscoelastic properties of soft-tissue fillers when subjected to different testing frequencies. The range of tested frequencies represents clinically different facial areas with more [lips (high frequency)] or less [zygomatic arch (low frequency)] soft-tissue movement. METHODS: A total of 35 randomly selected hyaluronic acid-based dermal filler products were tested in an independent laboratory for their values of G', G″, tan δ, and G* at angular frequencies between 0.1 and 100 radian/second. RESULTS: The results of the objective analyses revealed that the viscoelastic properties of all tested products changed between 0.1 and 100 radian/second angular frequency. Changes in G' ranged from 48.5 to 3116 percent, representing an increase in their initial elastic modulus, whereas changes in G″ ranged from -53.3 percent (i.e., decrease in G″) to 7741 percent (i.e., increase in G″), indicating both an increase and a decrease in their fluidity, respectively. CONCLUSIONS: The increase in G' would indicate the transition from a "softer" to a "harder" filler, and the observed decrease in G″ would indicate an increase in the filler's "fluidity." Changes in the frequency of applied shear forces such as those occurring in the medial versus the lateral face will influence the aesthetic outcome of soft-tissue filler injections.

Electrical velocimetry has limited accuracy and precision and moderate trending ability compared with transthoracic echocardiography for cardiac output measurement during cesarean delivery: A prospective observational study.

We aimed to evaluate the accuracy and interchangeability of stroke volume and cardiac output measured by electrical velocimetry and transthoracic echocardiography during cesarean delivery.We enrolled 20 parturients in this prospective observational study. We recorded the stroke volume and cardiac output using both methods and compared the values at seven specific time points. We analyzed the data using linear regression analysis for Pearson's correlation coefficients and Bland-Altman analysis to determine percentage errors. We conducted a trending ability analysis based on the four-quadrant plot with the concordance rate and correlation coefficient.We recorded 124 paired datasets during cesarean delivery. The correlation coefficients of the measured cardiac output and stroke volume between the two methods were 0.397 (P < .001) and 0.357 (P < .001). The 95% limits of agreement were -1.0 to 8.1 L min for cardiac output and -10.4 to 90.4 ml for stroke volume. Moreover, the corresponding percentage errors were 62% and 60%. The concordance correlation coefficients were 0.447 (95% CI: 0.313-0.564) for stroke volume and 0.562 (95% CI: 0.442-0.662) for cardiac output. Both methods showed a moderate trending ability for stroke volume (concordance rate: 82% (95% CI: 72-90%)) and cardiac output (concordance rate: 85% (95% CI: 78-93%)).Our findings indicated that electrical velocimetry monitoring has limited accuracy, precision, and interchangeability with transthoracic echocardiography; however, it had a moderate trending ability for stroke volume and cardiac output measurements during cesarean delivery.

Predictive Value of Intraoperative Doppler Flowmetry for Delayed Graft Function in Kidney Transplantation: A Pilot Study.

BACKGROUND: The delayed graft function (DGF) in kidney transplantation (KT) is a risk factor for long-term poor graft survival. The pathogenesis is multifactorial but mainly related to an ischemia-reperfusion injury. However, the graft hemodynamics have been recently identified as a key aspect for early DGF risk assessment and potential therapeutic intervention. METHODS: A pilot study on 20 single kidney grafts from donor after brain death with intraoperative measurement of graft arterial flowmetry, 30 minutes after reperfusion. Exclusion criteria were grafts with multiple arteries or severe atherosclerosis of the recipient's external iliac artery. RESULTS: KT recipients with DGF (n = 4, 20%) were homogenous with controls (n = 16) in terms of cold ischemia time, donor age, recipients' hemodynamic parameters, renal artery, and recipients' external iliac artery diameters. Nonetheless, at transplant, the kidney grafts that developed DGF were characterized by a significantly higher renal artery resistive index (DGF vs no-DGF 0.96 ± 0.04 vs 0.77 ± 0.13, P = .02), as well as lower flow extraction rate (24.8% ± 11.8 vs 59.2% ± 21.1, P < .01). CONCLUSIONS: Intraoperative arterial graft flowmetry seems to be an effective tool to identify grafts at high risk of DGF.

Flow resistive forces index (QRF): Development and clinical applicability assessment of a novel measure of bladder outlet resistance, aiming to enhance the diagnostic performance of uroflowmetry.

BACKGROUND: Currently, the diagnostic ability of uroflowmetry, the most widely used urodynamic test available for initial assessment of patients with lower urinary tract symptoms (LUTS), is considered limited by its inability to accurately discriminate between the underlying mechanisms of this condition. To improve the diagnostic accuracy of uroflow, we developed a mathematical formula that calculates the flow resistive forces index (QRF), a novel measure of bladder outflow/urethral resistance, and assessed its clinical applicability compared to the maximum flow rate (Qmax ). MATERIALS AND METHODS: A cross-sectional observational study was conducted in a cohort of 61 adult men presenting with voiding dysfunction symptoms, who all underwent free uroflowmetry followed by pressure flow study. The development of the mathematical formula which contains five key uroflowmetry variables (voided volume, flow time, Qmax , average flow rate, and peak flow time) was based on the assumption that urine volume momentum changes during voiding, the concept of diphasic uroflow pattern (acceleration/deceleration), and the urethral resistance factor (URA) equation. Study subjects were classified either as obstructed or nonobstructed according to established urodynamic criteria (linearized passive urethral resistance relation, LinPURR; Abrams-Griffiths number, AGN [also called bladder outlet obstruction index, BOOI]; and URA). Univariate linear correlations, binary logistic regression model, and receiver operating characteristic (ROC) curve statistical analysis were employed (SPSS-22, MedCalc, GraphPad [P < .05]). RESULTS: Outflow obstruction was diagnosed in 50.8% (1 in 2) patients. Univariate analysis, and bivariate linear correlation, binary logistic regression, and ROC curve analyses showed that the QRF was a strong independent predictor of bladder outlet/outflow obstruction (BOO), significantly outperforming Qmax . CONCLUSIONS: QRF index accurately predicts BOO, significantly outperforming the currently widely used bladder outlet obstruction estimator Qmax . Despite potential study limitations (mainly small cohort size and lack of control group), we anticipate that with further study and proper clinical validation, QRF could become a valuable complement to uroflowmetry.

Validation of electrical velocimetry in resuscitation of patients undergoing liver transplantation. Observational study.

Major hemodynamic changes are frequently noted during liver transplantation (LT). We evaluated the performance of electrical velocimetry (EV) as compared to that of TEE in SV optimization during liver transplantation. This was an observational study in 32 patients undergoing LT. We compared SV values measured simultaneously by EV (SVEV) and TEE (SVTEE) at baseline 30 min after induction, at the end of dissection phase, 30 min after anhepatic phase, 30 min after reperfusion. We also evaluated the reliability of EV to track changes In SV before and after 49 fluid challenges. Finally, the SV variation (SVV) and pulse pressure variation (PPV) were tested as predictors for volume responsiveness, defined as an increase in SV ≥ 10% after 250 ml of colloid. For 112 paired SV data, the overall correlation was 0.76 and bias (limits of agreement) 0.3 (- 29 to 29) ml percentage error 62%. The EV was able to track changes in SV with a concordance rate of 97%, and a sensitivity and specificity of 93% to detect a positive fluid challenge. The AUC values (with 95% confidence intervals) for SVV and PPV were 0.68 (0.52-0.83) and 0.72 (0.57-0.86), respectively, indicating low predictive capacity in these setting. The absolute values of SV derived from EV did not agree with SV derived from TEE. However, EV was able to track the direction of changes in SV during hemodynamic management of patients undergoing liver transplantation.Clinical trial registration: Clinicaltrials.gov Identifier: NCT03228329 prospectively Registered on 13-July-2017.

Reliability of indocyanine green retention and clearance rates at 15 minutes calculated by dye-dilution cardiac output flowmetry in comparison to blood sampling in patients undergoing hepatic resection.

BACKGROUND: The indocyanine green retention rate at 15 min (ICGR15) is a marker of the liver function and is useful for planning hepatectomy. To clarify the ICGR15 and the related clearance value (ICGK) calculated by a dye-dilution cardiac output flowmetry (DCOF), we examined the correlation and clinical significance of the ICGR15 values determined by DCOF and those determined with the conventional blood sampling (BS) procedure. METHODS: We extracted liver function parameters, including the ICGR15 modified value and ICGK, and the extent of hepatectomy from the clinical and surgical records of 63 patients with various liver diseases in whom the ICGR15 (actual value), R15m (mean), and K (clearance rate per minute) were measured by DCOF. RESULTS: All the patients were classified as Child-Pugh grade A. Hepatic complications were observed in 10 (16%) patients, but there was no mortality. The mean values of ICGR15 determined by BS (R15-BS) and DCOF (R15-DCOF) were 12.2 ± 8.1% and 11.2 ± 8.7%, respectively. The mean R15m determined by DCOF (R15m-DCOF) was 15.7 ± 10.2%. Significant differences were observed between R15-BS and R15-DCOF (1.1 ± 4.8%; p = 0.002) and R15m-DCOF (4.0 ± 5.9%; p < 0.001). The difference between R15-BS and R15m-DCOF was greater than that between R15-BS and R15-DCOF. Correlation between R15-BS and R15-DCOF was significant r = 0.839 (p < 0.001). CONCLUSIONS: The ICGR15 measured by DCOF shows comparable reliability and stability to the BS method, which is useful for planning hepatectomy.

Fully developed slip flow in a concentric annuli via single and dual phase nanofluids models.

In the present work it is aimed to obtain closed-form exact solutions for the fully developed momentum, thermal and concentration layers through a concentric annulus filled with various nanoparticle mixtures of water-based nanofluids in the presence of wall slip nanofluid velocity. The thermal boundary conditions of either both walls at fixed temperatures or of the inner wall at prescribed temperature and of the outer wall at specified heat flux are considered. Initially, the classical single phase model is adopted leading to simple formulas for the nanofluid flow and heat transfer. Then, the two-phase model of Buongiorno is considered by modifying it to incorporate the effects of nanoparticle volume fraction distribution in the full governing equations. This complex model also yields analytical formulas with regard to the momentum and thermal transport of nanoparticles of different nanofluids flowing in the concentric annuli. The essential features of nanofluids concerning the velocity, temperature and nanoparticle concentration fields as well as the rate of heat transfer are easily captured via the presented cute formulae. Particularly, the effects of Brownian and thermophoretic diffusivities as numerically examined in the literature can be investigated analytically by means of the derived solutions here valid under two distinct thermal conditions. Both models successfully explain the enhancement of heat transfer character of nanofluids by analysing the obtained exact Nusselt numbers involving several parameters of physical interest.

A Comparison of Measurements of a Pediatric Supplement.

This study evaluated the flow properties of viscosity and flow rate for water and two common pediatric liquids. The flow properties of the test liquids are of interest to create a cup simulation model and "smart" prototype training cup. Two objective methods of determining flow properties were utilized: a rheometer to assess viscosity and a modified version of the International Dysphagia Diet Standardization Initiative (IDDSI) to assess flow rate. Rheometer results concluded that the pediatric supplements were less than 50 cP at all shear rates evaluated and exhibited shear-thinning properties, placing both liquids into the "thin" category. The IDDSI, which was performed according to standardized protocol and also with experimental modifications of varying syringe volumes, determined that all three test liquids had greater than 1 mL/s flow rate across all syringe types/sizes. The experimental modification of the IDDSI with 60 mL syringe volume was found to be the most consistent and applicable with discrete values obtained across all liquids tested. A flow rate factor equation can be determined with the use of a 60 mL syringe, with our laboratory setup, to create the cup simulation model. This computer-generated cup simulation model also aims to integrate engineering with clinical practice to develop a "smart" prototype training cup equipped with software to control flow rate.

Mathematical modelling of pressure-driven micropolar biological flow due to metachronal wave propulsion of beating cilia.

In this paper, we present an analytical study of pressure-driven flow of micropolar non-Newtonian physiological fluids through a channel comprising two parallel oscillating walls. The cilia are arranged at equal intervals and protrude normally from both walls of the infinitely long channel. A metachronal wave is generated due to natural beating of cilia and the direction of wave propagation is parallel to the direction of fluid flow. Appropriate expressions are presented for deformation via longitudinal and transverse velocity components induced by the ciliary beating phenomenon with cilia assumed to follow elliptic trajectories. The conservation equations for mass, longitudinal and transverse (linear) momentum and angular momentum are reduced in accordance with the long wavelength and creeping Stokesian flow approximations and then normalized with appropriate transformations. The resulting non-linear moving boundary value problem is solved analytically for constant micro-inertia density, subject to physically realistic boundary conditions. Closed-form expressions are derived for axial velocity, angular velocity, volumetric flow rate and pressure rise. The transport phenomena are shown to be dictated by several non-Newtonian parameters, including micropolar material parameter and Eringen coupling parameter, and also several geometric parameters, viz eccentricity parameter, wave number and cilia length. The influence of these parameters on streamline profiles (with a view to addressing trapping features via bolus formation and evolution), pressure gradient and other characteristics are evaluated graphically. Both axial and angular velocities are observed to be substantially modified with both micropolar rheological parameters and furthermore are significantly altered with increasing volumetric flow rate. Free pumping is also examined. An inverse relationship between pressure rise and flow rate is computed which is similar to that observed in Newtonian fluids. The study is relevant to hemodynamics in narrow capillaries and also bio-inspired micro-fluidic devices.

Evaluation of intra-individual test-re-test variability of uroflowmetry in healthy women and women suffering from stress, urge, and mixed urinary incontinence.

INTRODUCTION AND HYPOTHESIS: The objective was to evaluate the intra-individual variability of uroflowmetry (UFM) in healthy control subjects and women suffering from stress, urge, and mixed urinary incontinence. METHODS: A total of 35 healthy controls (group A) and 105 women suffering from urinary incontinence were enrolled in the study. Thirty-five women suffered from stress urinary incontinence (group B), 35 women suffered from mixed urinary incontinence (group C), and 35 women with overactive bladder both dry and wet (group D). All participants were asked to perform UFM measurement three times. The following parameters were analyzed: voided volume (VV), peak flow (Qmax), average flow (Qave), volume-corrected peak flow cQmax (cQmax = Qmax/2√ VV), volume-corrected average flow (cQave = Qave/2√ VV), and postvoid residual volume (PVR). Statistical analysis was performed using the analysis of variance on repeated measurements. Relative error was calculated using variation coefficients reported as a percentage of the average. All descriptive characteristics were reported as means ± standard deviation (SD). p values ≤0.05 were considered statistically significant. RESULTS: No statistically significant intra-individual difference in any of the recorded parameters was identified among the three UFM recordings in groups A, C, and D. The intra-individual variability of the following parameters reached statistical significance in patients suffering from stress urinary incontinence (group B): Qmax (p = 0.0016), Qave (p = 0.0005), and cQave (p = 0.0389). A significant difference was only observed in comparison between the first and second consecutive recordings. CONCLUSIONS: This study provides evidence supporting the high yield and good intra-individual reproducibility of UFM.

Model-based observer and feedback control design for a rigid Joukowski foil in a Kármán vortex street.

Obstacles and swimming fish in flow create a wake with an alternating left/right vortex pattern known as a Kármán vortex street and reverse Kármán vortex street, respectively. An energy-efficient fish behavior resembling slaloming through the vortex street is called Kármán gaiting. This paper describes the use of a bioinspired array of pressure sensors on a Joukowski foil to estimate and control flow-relative position in a Kármán vortex street using potential flow theory, recursive Bayesian filtering, and trajectory-tracking feedback control. The Joukowski foil is fixed in downstream position in a flowing water channel and free to move on air bearings in the cross-stream direction by controlling its angle of attack to generate lift. Inspired by the lateral-line neuromasts found in fish, the sensing and control scheme is validated using off-the-shelf pressure sensors in an experimental testbed that includes a flapping device to create vortices. We derive a potential flow model that describes the flow over a Joukowski foil in a Kármán vortex street and identify an optimal path through a Kármán vortex street using empirical observability. The optimally observable trajectory is one that passes through each vortex in the street. The estimated vorticity and location of the Kármán vortex street are used in a closed-loop control to track either the optimally observable path or the energetically efficient gait exhibited by fish. Results from the closed-loop control experiments in the flow tank show that the artificial lateral line in conjunction with a potential flow model and Bayesian estimator allow the robot to perform fish-like slaloming behavior in a Kármán vortex street. This work is a precursor to an autonomous robotic fish sensing the wake of another fish and/or performing pursuit and schooling behavior.

Outcomes and reliability of the flow coupler in postoperative monitoring of head and neck free flaps.

OBJECTIVES/HYPOTHESIS: To assess the accuracy and reliability of the flow coupler relative to the implantable arterial Doppler probe in postoperative monitoring of head and neck free flaps. STUDY DESIGN: Retrospective single-institution study, April 2015 to March 2017. METHODS: Both the venous flow coupler and arterial Doppler were employed in 120 consecutive head and neck free flap cases. When Doppler signal loss occurred, flaps were evaluated by physical exam to determine whether signal loss was a true positive necessitating operating room takeback. Sensitivity, specificity, and false positive rate (FPR) were recorded for each device. Logistic regression was conducted to identify user trends over time. RESULTS: Eleven of 120 patients (9.2%) required takeback, 10 from venous thrombosis and one from arterial thrombosis. Permanent signal loss (PSL) occurred in the flow coupler in all takebacks; PSL occurred in the arterial Doppler only in the case of arterial thrombosis. Salvage rate was 9/11 (81.8%). For the flow coupler, sensitivity was 100%, specificity 86.4%, and FPR 13.6%. For the arterial probe, sensitivity was 9.1%, specificity 97.1%, and FPR 2.9%. A 4.1% decrease in false positives with each additional flow coupler use was observed. CONCLUSIONS: Monitoring the vein via flow coupler has high sensitivity in identifying vascular compromise compared to the arterial probe, especially for venous thrombosis. There is moderate FPR; this decreases with increased usage and, when supplemented with physical examination, does not result in unnecessary takebacks. The flow coupler can be a valuable tool in postoperative monitoring of head and neck free flaps. LEVEL OF EVIDENCE: 4. Laryngoscope, 128:812-817, 2018.

Correlation of Visual Prostate Symptom Score with International Prostate Symptom Score and Uroflowmetry Parameters in Nepalese Male Patients with Lower Urinary Tract Symptoms.

INTRODUCTION: International prostate symptom score is a validated questionnaire used to evaluate the lower urinary tract symptoms in benign prostatic hyperplasia. Visual prostate symptom score is a new simplified symptom score with pictograms to evaluate the same. We evaluated the correlation of visual prostate symptom score with international prostate symptom score and uroflowmetry parameters in Nepalese male patients with lower urinary tract symptoms. METHODS: Male patients aged ≥40 years attending the Urology clinic were enrolled in the study. They were given international prostate symptom score and visual prostate symptom score questionnaires to complete providing assistance whenever needed. Demographic data, examination findings and uroflowmetry parameters were noted. Correlation and regression analysis was used to identify correlation of the two scoring systems and uroflowmetry parameters. RESULTS: Among the 66 patients enrolled, only 10 (15.15%) patients were able to understand English language. There was a statistically significant correlation between total visual prostate symptom score and international prostate symptom score (r= 0.822; P<0.01). The correlations between individual scores of the two scoring systems related to force of urinary stream, frequency, nocturia and quality of life were also statistically significant. There was also a statistically significant correlation of both scores with maximum flow rate and average flow rate. CONCLUSIONS: There is a statistically significant correlation of visual prostate symptom score with international prostate symptom score and uroflowmetry parameters. IPSS can be replaced with simple VPSS in evaluation of lower urinary tract symptoms in elderly male patients.

Heat Source/Sink in a Magneto-Hydrodynamic Non-Newtonian Fluid Flow in a Porous Medium: Dual Solutions.

This communication deals with the properties of heat source/sink in a magneto-hydrodynamic flow of a non-Newtonian fluid immersed in a porous medium. Shrinking phenomenon along with the permeability of the wall is considered. Mathematical modelling is performed to convert the considered physical process into set of coupled nonlinear mathematical equations. Suitable transformations are invoked to convert the set of partial differential equations into nonlinear ordinary differential equations which are tackled numerically for the solution computations. It is noted that dual solutions for various physical parameters exist which are analyzed in detail.

Can a quantitative means be used to predict flow patterns: Agreement between visual inspection vs. flow index derived flow patterns.

INTRODUCTION: Uroflowmetry is a first-line tool in the evaluation of children with lower urinary tract symptoms. Unfortunately, there is a tremendous amount of intra- and interobserver variation in defining the shape of curves. Regrettably, one observer can see one flow as a tower and the other can call it a bell. Here lies the major flaw with the interpretation of uroflow shapes. Previously, we have shown that there is a good correlation between the calculated flow index (FI) and the shape of a flow curve (bell, tower and plateau) in normal children. OBJECTIVE: Our hypothesis was to show that the FI-defined shapes were as good or better than the present system of grading flow curves. If so this would help remove subjectivity from the field of uroflow assessment and make studies objective and easily compared. STUDY DESIGN: Consecutive uroflows of children who were being evaluated for lower urinary tract symptoms from two centers were reviewed and compared alongside those of presumed normal voiders; the shape of the curves were read by the same experienced readers at each institution. Only curves that were read as bell, plateau, and tower were compared with the curve patterns derived from the quantitative methods derived by one of the authors. FI was derived by taking the actual Qmax/estimated Qmax. RESULTS: There were 591 males and 1039 females who had uroflow studies, of these 409 and 819, respectively were read as either bell, towers, or plateaus The highest kappa value for males was 0.71 (CI 0.64-0.79) using a 3 × 3 matrix indicating substantial agreement. In females the highest kappa was 0.52 (CI 0.46-0.59) in the group 2 patients using the receiver operating characteristic cutoffs but the 1 SD cutoff was close with a kappa value of 0.51, which indicates moderate agreement (Table). DISCUSSION: Using the FI method we saw that there was substantial to moderate agreement using a quantitative method to define flow shapes based on the kappa values that were obtained in this study. The one fundamental flaw with shape determination in both visual and FI-derived methods is that the cutoffs are arbitrary since the visual defined shapes are the basis for the FI shapes. CONCLUSION: Our findings clearly showed that a FI-derived method of defining shapes is as accurate as visual inspection or more depending on the study. The greatest disagreement occurs in those grey or transition zones between plateau, bell and tower. This system could be useful in removing much of the ambiguity and difficulty in reading flows.

A Rotational Pressure-Correction Scheme for Incompressible Two-Phase Flows with Open Boundaries.

Two-phase outflows refer to situations where the interface formed between two immiscible incompressible fluids passes through open portions of the domain boundary. We present several new forms of open boundary conditions for two-phase outflow simulations within the phase field framework, as well as a rotational pressure correction based algorithm for numerically treating these open boundary conditions. Our algorithm gives rise to linear algebraic systems for the velocity and the pressure that involve only constant and time-independent coefficient matrices after discretization, despite the variable density and variable viscosity of the two-phase mixture. By comparing simulation results with theory and the experimental data, we show that the method produces physically accurate results. We also present numerical experiments to demonstrate the long-term stability of the method in situations where large density contrast, large viscosity contrast, and backflows occur at the two-phase open boundaries.

Milk Flow Rates from bottle nipples used after hospital discharge.

PURPOSE: To test the milk flow rates and variability in flow rates of bottle nipples used after hospital discharge. STUDY DESIGN AND METHODS: Twenty-six nipple types that represented 15 common brands as well as variety in price per nipple and store location sold (e.g., Babies R' Us, Walmart, Dollar Store) were chosen for testing. Ten of each nipple type (n = 260 total) were tested by measuring the amount of infant formula expressed in 1 minute using a breast pump. Mean milk flow rate (mL/min) and coefficient of variation (CV) were calculated. Flow rates of nipples within brand were compared statistically. RESULTS: Milk flow rates varied from 1.68 mL/min for the Avent Natural Newborn Flow to 85.34 mL/min for the Dr. Brown's Standard Y-cut. Variability between nipple types also varied widely, from .03 for the Dr. Brown's Standard Level 3 to .37 for MAM Nipple 1 Slow Flow. CLINICAL IMPLICATIONS: The extreme range of milk flow rates found may be significant for medically fragile infants being discharged home who are continuing to develop oral feeding skills. The name of the nipple does not provide clear information about the flow rate to guide parents in decision making. Variability in flow rates within nipples of the same type may complicate oral feeding for the medically fragile infant who may not be able to adapt easily to change in flow rates. Both flow rate and variability should be considered when guiding parents to a nipple choice.

Validation of stroke volume and cardiac output by electrical interrogation of the brachial artery in normals: assessment of strengths, limitations, and sources of error.

The goal of this study is to validate a new, continuous, noninvasive stroke volume (SV) method, known as transbrachial electrical bioimpedance velocimetry (TBEV). TBEV SV was compared to SV obtained by cardiac magnetic resonance imaging (cMRI) in normal humans devoid of clinically apparent heart disease. Thirty-two (32) volunteers were enrolled in the study. Each subject was evaluated by echocardiography to assure that no aortic or mitral valve disease was present. Subsequently, each subject underwent electrical interrogation of the brachial artery by means of a high frequency, low amplitude alternating current. A first TBEV SV estimate was obtained. Immediately after the initial TBEV study, subjects underwent cMRI, using steady-state precession imaging to obtain a volumetric estimate of SV. Following cMRI, the TBEV SV study was repeated. Comparing the cMRI-derived SV to that of TBEV, the two TBEV estimates were averaged and compared to the cMRI standard. CO was computed as the product of SV and heart rate. Statistical methods consisted of Bland-Altman and linear regression analysis. TBEV SV and CO estimates were obtained in 30 of the 32 subjects enrolled. Bland-Altman analysis of pre- and post-cMRI TBEV SV showed a mean bias of 2.87 % (2.05 mL), precision of 13.59% (11.99 mL) and 95% limits of agreement (LOA) of +29.51% (25.55 mL) and -23.77% (-21.45 mL). Regression analysis for pre- and post-cMRI TBEV SV values yielded y = 0.76x + 25.1 and r(2) = 0.71 (r = 0.84). Bland-Altman analysis comparing cMRI SV with averaged TBEV SV showed a mean bias of -1.56% (-1.53 mL), precision of 13.47% (12.84 mL), 95% LOA of +24.85% (+23.64 mL) and -27.97% (-26.7 mL) and percent error = 26.2 %. For correlation analysis, the regression equation was y = 0.82x + 19.1 and correlation coefficient r(2) = 0.61 (r = 0.78). Bland-Altman analysis of averaged pre- and post-cMRI TBEV CO versus cMRI CO yielded a mean bias of 5.01% (0.32 L min(-1)), precision of 12.85% (0.77 L min(-1)), 95% LOA of +30.20 % (+0.1.83 L min(-1)) and -20.7% (-1.19 L min(-1)) and percent error = 24.8%. Regression analysis yielded y = 0.92x + 0.78, correlation coefficient r(2) = 0.74 (r = 0.86). TBEV is a novel, noninvasive method, which provides satisfactory estimates of SV and CO in normal humans.

The effect of needle dimensions and infusion rates on injection pressures in regional anaesthesia needles: a bench-top study.

Animal studies have shown that injection pressures > 75 kPa indicate probable intrafascicular needle tip position. This study describes the flow/pressure characteristics of seven common needle systems. A syringe pump delivered flow rates of 5, 6.67, 10, 13.3, 15 and 20 ml.min(-1) through these needle systems, while keeping the needle tips open to atmosphere. A pressure transducer connected between the syringe and needle provided a real-time graphical display for analysis. Mean plateau pressures increased linearly with flow and with decreasing needle diameter (2.7-92 kPa). Flow rates > 17 ml.min(-1) and needle sizes 22 G and smaller produced mean plateau pressures > 75 kPa. Pressure monitors upstream from the needle may produce false-positive alarms at high flow rates due to needle resistance, and unreliable readings due to non-laminar flow. We recommend injection rates ≤ 15 ml.min(-1) (0.25 ml.s(-1) ) to reduce the effect of factors upstream from the needle tip as a cause of high pressure readings.