Cardiopulmonary Bypass Blood Flow Rates and Major Adverse Kidney Events in Cardiac Surgery: A Propensity Score-adjusted Before-After Study.

OBJECTIVES: Cardiac surgery associated-acute kidney injury is a common and serious postoperative complication of cardiac surgery, which is associated with increased postoperative morbidity and mortality. This study aimed to explore the association between cardiopulmonary bypass (CPB) blood flow rate (BFR), and major adverse kidney events (MAKEs) at day 30. DESIGN: Retrospective single-center before-after observational study. Patients were divided in 2 groups according to CPB flow rates: a first group with an institutional protocol targeting a CPB-BFR of >2.2 L/min/m² (low CPB-BFR group), and a second group with a modified institutional protocol targeting a CPB-BFR of >2.4 L/min/m² (high CPB-BFR group). The primary outcome was MAKE at 30 days, defined as the composite of death, renal replacement therapy or persistent renal dysfunction. SETTING: The data were collected from clinical routines in university hospital. PARTICIPANTS: Adult patients who underwent elective and urgent cardiac surgery without severe chronic renal failure, for whom CPB duration was ≥90 minutes. INTERVENTIONS: We included 533 patients (low CPB-BFR group, n = 270; high CPB-BFR group, n = 263). MEASUREMENTS AND MAIN RESULTS: A significant decrease in MAKE at 30 days was observed in the high CPB-BFR group (3% v 8%; odds ratio [OR], 0.779; 95% confidence interval [CI], 0.661-0.919; p < 0.001) mainly mediated by a lower 30-day mortality in the high CPB-BFR group (1% v 5%; OR, 0.697; 95% CI, 0.595-0.817; p = 0.001), as was renal replacement therapy (1% v 4%; OR, 0.739; 95% CI, 0.604-0.904; p = 0.016). CONCLUSIONS: In patients undergoing cardiac surgery, increased CPB-BFR was associated with a decrease in MAKE at 30 days including mortality and renal replacement therapy.

Relationship between effective blood flow rate and clinical outcomes in maintenance hemodialysis patients: a single-center study.

The association between blood flow rate (BFR) and clinical outcomes in patients undergoing maintenance hemodialysis (MHD) is inconclusive. This retrospective study included 175 patients undergoing MHD treatment between July 2015 and March 2022, divided into two groups based on time-averaged effective blood flow rate (eBFR) median value. We investigated arteriovenous fistula (AVF) outcomes and the association of eBFR with all-cause mortality and new major adverse cardiovascular events (MACE). Mean ± SD and median time-averaged eBFR values were 276 ± 24 and 275 mL/min, respectively. After adjusting for relevant factors including age, sex, vintage, diabetes, CVD, receiving hemodiafiltration (HDF) treatment and spKt/V, Cox models indicated a low time-averaged eBFR (≤ 275 ml/min) was associated with increased risks of all-cause mortality (hazard ratio [HR] 14.18; 95% confidence interval [CI], 3.14-64.1) and new MACE (HR 3.76; 95% CI, 1.91-7.40) in MHD patients. Continuous Cox models demonstrated each 20 ml/min increase in eBFR linked to a 63% decrease in the risk of all-cause mortality (HR: 0.37, 95% CI: 0.23-0.59) and a 38% decrease in the occurrence of new MACE (HR: 0.62, 95% CI: 0.46-0.84). There was no significant difference in AVF outcomes between the two groups. Our study noted higher eBFR (>275 mL/min) is associated with lower risks of both all-cause mortality and new MACE compared with low eBFR (≤275 mL/min). Increased eBFR is not associated with a higher risk of AVF failure.

Effect of Blood Flow Rate on the Accuracy of Central Venous Pressure Measurement during Continuous Renal Replacement Therapy.

BACKGROUND: The objective of this study was to study the influence of extracorporeal blood flow rate (BFR) on the accuracy of central venous pressure (CVP) measurement during continuous renal replacement therapy (CRRT). METHODS: Eligible patients were randomly divided into 3 groups based on the location of catheters used for their CRRT and CVP measurement. CVP levels measured at increased extracorporeal BFR (from 0 to 300 mL/min) in the normal and reverse positions of inlet and outlet lines connected to the CV catheter (CVC) in the course of the CRRT session were collected. RESULTS: CVP levels measured at different extracorporeal BFRs did not significantly differ between and among the 3 groups. Inversion of inlet and outlet lines connected to the catheters did not affect the accuracy of CVP measurement. BFR had a negative correlation with inflow/access pressure but a positive correlation with outflow/return pressure. Neither inflow pressure nor outflow pressure was correlated with CVP. CONCLUSIONS: Extracorporeal BFR has no influence on the accuracy of CVP measurement during CRRT with the net machine balance adjusted to zero regardless of the location of the catheter and the connection method between catheters and CRRT lines. Thus, CRRT does not need to be discontinued to obtain an accurate CVP measurement.

Temperature Dynamics in Rat Brains Exposed to Near-Field Waveguide Outputs at 2.8 GHz.

Biological effects in the microwave band of the radiofrequency (RF) spectrum are thermally mediated. For acute high-power microwave exposures, these effects will depend on transient time-temperature histories within the tissue. In this article, we summarize the transient temperature response of rats exposed to RF energy emanating from an open-ended rectangular waveguide. These exposures produced specific absorption rates of approximately 36 and 203 W/kg in the whole body and brain, respectively. We then use the experimentally measured thermal data to infer the baseline perfusion rate in the brain and modify a custom thermal modeling tool based upon these findings. Finally, we compare multi-physics simulations of rat brain temperature against empirical measurements in both live and euthanized subjects and find close agreement between model and experimentation. This research revealed that baseline brain perfusion rates in rat subjects could be larger than previously assumed in the RF thermal modeling literature, and plays a significant role in the transient thermal response to high-power microwave exposures. © 2021 Bioelectromagnetics Society.

Another route of CO2 gas excretion independent of red blood cells in human lungs.

We demonstrated pulmonary arteriolar blood flow-mediated CO2 gas excretion in rabbit lungs. The shear stress stimulation produced CO2 gas in cultured human endothelial cells of pulmonary arterioles via the activation of F1/Fo ATP synthase. To confirm the findings in human subjects undergoing the operation with heart-lung machines, we aimed to evaluate the effects of a stepwise switch, from a partial to a complete cardiopulmonary bypass, of the circulatory blood volume (BV, 100% = 2.4 × cardiac index), on the end-expiratory CO2 pressure (PetCO2), maximal flow velocity in the pulmonary artery (Max Vp), the inner diameter (ID) of pulmonary artery, pulmonary arterial CO2 pressure (P mix v CO2), pulmonary arterial O2 pressure (P mix v O2), hematocrit (Hct), pH, the concentration of HCO3-, and base excess (BE) in mixed venous blood in 9 patients with a mean age of 72.3 ± 3.4 years. In addition, the effects of the decrease in Hct infused with physiological saline solution (PSS) on PetCO2 were investigated in the human subjects. An approximately linear relationship between the PetCO2 and Max Vp was observed. The pumping out of 100% BV produced little or no change in the Hct, pH, P mix v CO2, and P mix v O2, respectively. The hemodilution produced by intravenous infusion of PSS caused a significant decrease in the Hct, but not in the PetCO2. In conclusion, another route of CO2 gas excretion, independent of red blood cells, may be involved in human lungs.

Dynamic diagnosis of early gastric cancer with microvascular blood flow rate using magnifying endoscopy (with video): A pilot study.

BACKGROUND AND AIM: Magnifying endoscopy (ME) diagnostic algorithm for early gastric cancer (EGC) relies on qualitative features such as microvascular (MV) architecture and microsurface structure; however, it is a "static" diagnostic algorithm that uses still images. ME can visualize red blood cell flow within subepithelial microvessels in real time. Here, we evaluated the utility of using the MV blood flow rate in combination with ME for the diagnosis of EGC as a retrospective study. METHODS: Patients with differentiated-type EGC (n = 10) or patchy redness (n = 10) underwent ME with blue laser imaging. The mean MV blood flow rates of EGC, patchy redness, and background mucosa were calculated by the mean movement distance of one tagging red blood cell using split images of ME with blue laser imaging videos. We compared the mean MV blood flow rate between EGC, patchy redness, and background mucosa and also calculated the MV blood flow imaging ratio (inside lesion/background mucosa) between EGC and patchy redness. RESULTS: Mean MV blood flow rate was significantly lower in EGC (1481 µm/s; range 1057-1762) than in patchy redness (3859 µm/s; 2435-5899) or background mucosa (4140.6 µm/s; 2820-6247) (P < 0.01). The MV blood flow imaging ratio was significantly lower in EGC (0.39; 0.27-0.62) than in patchy redness (0.90; 0.78-1.1) (P < 0.01). CONCLUSIONS: Dynamic diagnosis with MV blood flow rate using ME may be useful for the differential diagnosis of EGC and patchy redness. Endoscopic assessment of dynamic processes within the gastric mucosa may facilitate the diagnosis of EGC.

How to Reduce the Risk of Arteriovenous Fistula Dysfunction by Observing Prepump Arterial Pressure during Hemodialysis: A Multicenter Retrospective Study.

OBJECTIVE: Prepump arterial (Pa) pressure indicates the ease or difficulty with which the blood pump can draw blood from the vascular access (VA) during hemodialysis. Some studies have suggested that the absolute value of the Pa pressure to the extracorporeal blood pump flow (Qb) ratio set on the machine (|Pa/Qb|) can reflect the dysfunction of VA. This study was conducted to explore the impact of arteriovenous fistula (AVF) dysfunction and to explore the clinical reference value of |Pa/Qb|. METHODS: We retrospectively identified adults who underwent hemodialysis at 3 hospitals. Data were acquired from electronic health records. We evaluated the pattern of the association between |Pa/Qb| and AVF dysfunction during 1 year using a Cox proportional hazards regression model with restricted cubic splines. Then, the patients were grouped based on the results, and hazard ratios were compared for different intervals of |Pa/Qb|. RESULTS: A total of 490 patients were analyzed, with an average age of 55 (44, 66) years. There were a total of 85 cases of AVF dysfunction, of which 50 cases were stenosis and 35 cases were thrombosis. There was a U-shaped association between |Pa/Qb| and the risk of AVF dysfunction (p for nonlinearity <0.001). |Pa/Qb| values <0.30 and >0.52 increased the risk of AVF dysfunction. Compared with the group with a |Pa/Qb| value between 0.30 and 0.52, the groups with |Pa/Qb| <0.30 and |Pa/Qb| >0.52 had a 4.04-fold (p = 0.002) and 3.41-fold (p < 0.001) greater risk of AVF dysfunction, respectively. CONCLUSIONS: The appropriate range of |Pa/Qb| is between 0.30 and 0.52. When |Pa/Qb| is <0.30 or >0.52, the patient's AVF function or Qb setting should be reevaluated to prevent subsequent failure.

Effect of increased blood flow rate on renal anemia and hepcidin concentration in hemodialysis patients.

BACKGROUND: Increasing the blood flow rate (BFR) is a useful method for increasing Kt/V and the clearance for low molecular solutes. Hemodialysis patients are often anemic due to hypoerythropoiesis and their chronic inflammatory state. Hepcidin, a hormone that regulates iron homeostasis, is considered as an indicator of iron deficiency in patients with end-stage renal disease. This study aimed to investigate the effects of an increased BFR during hemodialysis on serum hepcidin levels and anemia. METHODS: Between April 2014 and March 2016, 22 chronic dialysis patients (11 men [50.0 %]; mean [± standard deviation] age, 72 ± 12 years) undergoing maintenance hemodialysis treatment, thrice weekly, were enrolled and followed prospectively for 24 months. In April 2014, the BFR was 200 mL/min; in April 2015 this was increased to 400 mL/min, which was within acceptable limits. The dialysate flow rate remained stable at; 500mlL/min. Blood samples were collected in March 2015 and 2016. The primary endpoint was the comparison of the amounts of erythropoiesis-stimulating agent (ESA) required. RESULTS: The increased BFR increased the Kt/V and contributed to significantly decreased urea nitrogen (UN) (p = 0.015) and creatinine (Cr) (p = 0.005) levels. The dialysis efficiency was improved by increasing the BFR. Ferritin (p = 0.038), hepcidin (p = 0.041) and high-sensitivity interleukin-6 (p = 0.038) levels were also significantly reduced. The ESA administered was significantly reduced (p = 0.004) and the Erythropoietin Resistant Index (ERI) significantly improved (p = 0.031). The reduction rates in UN (p < 0.001), Cr (p < 0.001), and beta-2 microglobulin (p = 0.017) levels were significantly greater post the BFR increase compared to those prior to the BFR increase. However, hepcidin was not affected by the BFR change. CONCLUSIONS: Increasing BFR was associated with hemodialysis efficiency, and led to reduce inflammatory cytokine interleukin-6, but did not contribute to reduce C-reactive protein. This reduced hepcidin levels, ESA dosage and ERI. Hepcidin levels were significantly correlated with ferritin levels, and it remains to be seen whether reducing hepcidin leads to improve ESA and iron availability during anemia management.

Changes in practice patterns in Japan from before to after JSDT 2013 guidelines on hemodialysis prescriptions: results from the JDOPPS.

BACKGROUND: The Japanese Society for Dialysis Therapy (JSDT) published in 2013 inaugural hemodialysis (HD) guidelines. Specific targets include 1.4 for single-pool Kt/V (spKt/V) with a minimum dose of 1.2, minimum dialysis session length of 4 hours, minimum blood flow rate (BFR) of 200 mL/min, fluid removal rate no more than 15 mL/kg/hr, and hemodiafiltration (HDF) therapy for certain identified symptoms. We evaluated the effect of these guidelines on actual practice in the years spanning 2005 - 2018. METHODS: Analyses were carried out to describe trends in the above HD prescription practices from December 2005 to April 2013 (before guideline publication) to August 2018 based on prevalent patient cross-sections from approximately 60 randomly selected HD facilities participating in the Japan Dialysis Outcomes and Practice Patterns Study. RESULTS: From April 2006 to August 2017 continual rises occurred in mean spKt/V (from 1.35 to 1.49), and percent of patients having spKt/V>1.2 (71% to 85%). Mean BFR increased with time from 198.3 mL/min (April 2006) to 218.4 mL/min (August 2017) , along with percent of patients with BFR >200 ml/min (65% to 85%). HDF use increased slightly from 6% (April 2006 and August 2009) to 8% by April 2013, but increased greatly thereafter to 23% by August 2017. In contrast, mean HD treatment time showed little change from 2006-2017, whereas mean UFR declined from 11.3 in 2006 to 8.4 mL/Kg/hour in 2017. CONCLUSIONS: From 2006 - 2018 Japanese HD patients experienced marked improvement in reaching the spKt/V target specified by the 2013 JSDT guidelines. This may have been due to moderate increase in mean BFR even though mean HD session length did not change much. In addition, HDF use increased dramatically in this time period. Other HD delivery changes during this time, such as increased use of super high flux dialyzers, also merit study. While we cannot definitively conclude a causal relationship between the publication of the guidelines and the subsequent practice changes in Japan, those changes moved practice closer to the recommendations of the guidelines.

A systematic review and meta-analysis of the comparison of performance among step-tip, split-tip, and symmetrical-tip hemodialysis catheters.

OBJECTIVE: Patients with end-stage renal disease need vascular access to ensure sufficient blood flow during hemodialysis (HD). Patients who are poor candidates for arteriovenous access creation require long-term catheter placement. Problems such as dialysate recirculation, thrombosis, catheter-related infections, and malfunction can occur with HD catheters. Different tip designs (step, split, and symmetrical) have been developed to ameliorate the catheter-related problems. The aim of the study was to compare the efficacy and safety of split-tip, step-tip, and symmetrical-tip HD catheters. METHODS: The PubMed, Embase, Cochrane Library, and Scopus databases and the ClinicalTrials.gov registry were searched for studies published before November 2017. Studies comparing the clinical and rheologic outcomes of step-, split-, or symmetrical-tip catheters in patients undergoing HD were included in this meta-analysis. We conducted meta-analyses using random-effects models. The primary outcomes were catheter survival time and incidence of functioning catheters. The secondary outcomes were delivered blood flow rate, blood recirculation rate, and incidence of catheter-related complications. RESULTS: Seven randomized controlled trials and one retrospective study with a total of 988 patients were included. No significant differences were observed in the delivered blood flow rate (weighted mean difference, -5.37 mL/min; 95% confidence interval [CI], -23.75 to 13.02), incidence of catheter-related infections (risk ratio [RR], 1.18; 95% CI, 0.63-2.22), or incidence of catheter-related thrombosis (RR, 1.29; 95% CI, 0.64-2.59) between step-tip catheters and advanced (both split-tip and symmetrical-tip) catheters. Moreover, a meta-analysis of the incidence of functioning catheters at 1 month, 6 months, and 12 months revealed that the outcome of step-tip catheter use was better than that of split-tip catheter use, but with a significant difference only at 6 months (RR, 1.22; 95% CI, 1.02-1.46). CONCLUSIONS: None of the catheter types exhibited unique features that can enhance their suitability for application. Hence, catheters can be selected by also considering different factors, including costs, ease of procedures, expertise of the clinician, and education and preference of the patient.

Interspecific scaling of blood flow rates and arterial sizes in mammals.

This meta-study investigated the relationships between blood flow rate (Q̇; cm3 s-1), wall shear stress (τw; dyn cm-2) and lumen radius (ri; cm) in 20 named systemic arteries of nine species of mammals, ranging in mass from 23 g mice to 652 kg cows, at rest. In the dataset, derived from 50 studies, lumen radius varied between 3.7 µm in a cremaster artery of a rat and 11.2 mm in the aorta of a human. The 92 logged data points of [Formula: see text] and ri are described by a single second-order polynomial curve with the equation: [Formula: see text] The slope of the curve increased from approximately 2 in the largest arteries to approximately 3 in the smallest ones. Thus, da Vinci's rule ([Formula: see text]) applies to the main arteries and Murray's law ([Formula: see text]) applies to the microcirculation. A subset of the data, comprising only cephalic arteries in which [Formula: see text] is fairly constant, yielded the allometric power equation: [Formula: see text] These empirical equations allow calculation of resting perfusion rates from arterial lumen size alone, without reliance on theoretical models or assumptions on the scaling of wall shear stress in relation to body mass. As expected, [Formula: see text] of individual named arteries is strongly affected by body mass; however, [Formula: see text] of the common carotid artery from six species (mouse to horse) is also sensitive to differences in whole-body basal metabolic rate, independent of the effect of body mass.

Carotid foramen size in the human skull tracks developmental changes in cerebral blood flow and brain metabolism.

OBJECTIVES: In humans, neuronal processes related to brain development elevate the metabolic rate of brain tissue relative to the body during early childhood. This phenomenon has been hypothesized to contribute to slow somatic growth in preadolescent Homo sapiens. The uncoupling of the brain's metabolic rate from brain size during development complicates the study of the evolutionary emergence of these traits in the fossil record. Here, we extend a method previously developed to predict interspecific differences in cerebral blood flow (a correlate of cerebral glucose use) to predict ontogenetic changes in human brain metabolism. MATERIALS AND METHODS: Radii of the carotid foramen from an ontogenetic series of modern human crania were used to predict blood flow rates through the internal carotid arteries (ICA), which were compared to empirically measured ICA flow and brain metabolism values. RESULTS: Predictions of both absolute ICA blood flow rates and perfusion (ICA blood flow rates relative to brain size) generally match measured values in infancy and childhood. Maximum predicted ICA blood flow rates and perfusion were found to occur between ages 5 and 8, which roughly correspond to the age of maximum measured ICA blood flow rate and absolute and brain mass-specific rate of whole brain glucose uptake. DISCUSSION: These findings suggest that, during human growth and development, the size of the carotid foramen corresponds well to blood flow requirements through the ICA, and the method tested here may provide new opportunities for studying developmental changes in brain metabolism using osteological samples, including fossil hominins.

Color Doppler imaging of ocular hemodynamic changes in patients with rheumatoid arthritis unrelated to disease activity.

We aimed to investigate how orbital blood flow rates in patients with rheumatoid arthritis (RA) are affected by the active and remission phase of the disease. This prospective study included a total of 56 patients with RA (study group) and 24 control individuals (control group). All RA patients were divided into two groups, as active (Group 1) and remission (Group 2) according to the disease activity index (DAS 28) score. For each eye, retrobulbar vascular structures were evaluated [central retinal artery (CRA), posterior ciliary artery (PCA), and ophthalmic artery (OA)], respectively. The peak systolic velocity (PSV) and end-diastolic velocity (EDV) values were obtained for each artery and the vascular resistance index (RI) measurement was calculated. The median RI of the OA was 0.70 (0.57; 0.79) in the control group, 0.77 (0.55; 0.87) in group 1, and 0.73 (0.47; 0.87) in group 2. The median RI in the PCA was 0.70 (0.56; 0.82) in the control group, 0.76 (0.52; 0.88) in the group 1, and 0.74 (0.52; 0.86) in the group 2. The median RI of CRA was 0.73 (0.48; 0.81) in the control group, 0.71 (0.64; 0.81) in group 1, and 0.68 (0.61; 0.85) in group 2. The RI value was a significant difference between control and group 1 (p < 0.05). Active and remission RA patients had different effects on the flow rate of eye blood vessels.

The Effect of Increasing Blood Flow Rate on Severity of Uremic Pruritus in Hemodialysis Patients: A Single Clinical Trial.

BACKGROUND: Although the prevalence of uremic pruritus has decreased compared to the past, the problem still remains as a matter of health and a major challenge of research in medical field, and has no effective treatment at present. This study aimed to investigate the effect of increasing blood flow rate on severity of uremic pruritus in hemodialysis patients in Iran. METHODS: This clinical trial was performed on 60 hemodialysis patients that referred to hospitals affiliated to Tehran University of Medical Sciences and these patients were selected through the convenience method and were treated for four weeks. They were divided into two groups of experimental and control as random allocation block, and studied for 4 weeks. Information on pruritus severity was collected using a researcher-made questionnaire in three steps of before intervention and two and four weeks after start of intervention. The rate of blood flow was increased in the first two weeks and the second two weeks by 25 and 50 rounds per minute (rpm) compared to the mean rate of blood flow of hemodialysis device in the last two sessions before intervention. Data were analyzed using the tests Mann-Whitney, Fisher, and t-test. RESULTS: Analysis of data from 50 persons in both groups who completed the study revealed a significant difference between the groups in the severity of pruritus between the two sessions of hemodialysis (pruritus at home) at the end of the first two weeks of the intervention (<0.05) and the number of cases of pruritus (<0.05) at the end of the study. CONCLUSIONS: Increasing blood flow for hemodialysis machine can induce significant statistical and clinical reduction in the severity and the frequency of pruritus in hemodialysis patients and can be help to be improve the quality of life of these persons by increased the blood flow rate.

Endovascular Proximal Forearm Arteriovenous Fistula for Hemodialysis Access: Results of the Prospective, Multicenter Novel Endovascular Access Trial (NEAT).

BACKGROUND: Hemodialysis arteriovenous fistulas (AVFs) are suboptimally used primarily due to problems with maturation, early thrombosis, and patient nonacceptance. An endovascular approach to fistula creation without open surgery offers another hemodialysis vascular access option. STUDY DESIGN: Prospective, single-arm, multicenter study (Novel Endovascular Access Trial [NEAT]). SETTINGS & PARTICIPANTS: Consecutive adult non-dialysis-dependent and dialysis-dependent patients referred for vascular access creation at 9 centers in Canada, Australia, and New Zealand. INTERVENTION: Using catheter-based endovascular technology and radiofrequency energy, an anastomosis was created between target vessels, resulting in an endovascular AVF (endoAVF). OUTCOMES: Safety, efficacy, functional usability, and patency end points. MEASUREMENTS: Safety as percentage of device-related serious adverse events; efficacy as percentage of endoAVFs physiologically suitable (brachial artery flow ≥ 500mL/min, vein diameter ≥ 4mm) for dialysis within 3 months; functional usability of endoAVFs to provide prescribed dialysis via 2-needle cannulation; primary and cumulative endoAVF patencies per standardized definitions. RESULTS: 80 patients were enrolled (20 roll-in and 60 participants in the full analysis set; the latter are reported). EndoAVFs were created in 98% of participants; 8% had a serious procedure-related adverse event (2% device related). 87% were physiologically suitable for dialysis (eg, mean brachial artery flow, 918mL/min; endoAVF vein diameter, 5.2mm [cephalic vein]). EndoAVF functional usability was 64% in participants who received dialysis. 12-month primary and cumulative patencies were 69% and 84%, respectively. LIMITATIONS: Due to the unique anatomy and vessels used to create endoAVFs, this was a single-arm study without a surgical comparator. CONCLUSIONS: An endoAVF can be reliably created using a radiofrequency magnetic catheter-based system, without open surgery and with minimal complications. The endoAVF can be successfully used for hemodialysis and demonstrated high 12-month cumulative patencies. It may be a viable alternative option for achieving AVFs for hemodialysis patients in need of vascular access.

Total uterine artery blood volume flow rate in nulliparous women is associated with birth weight and gestational age at delivery.

OBJECTIVES: To investigate the relationship between total uterine artery blood volume flow rate (TVFR) and birth weight and gestational age at delivery, and to establish normal ranges of TVFR throughout pregnancy. METHODS: This was a prospective cohort study of 334 nulliparous women booking antenatal care at University College London Hospital between August 2008 and September 2009. Women underwent a transabdominal ultrasound examination of uterine arteries for measurement of TVFR at 12, 20 and 24 weeks' gestation. Pregnancy outcomes were recorded and linear regression was used to study the relationship between TVFR and gestational age at delivery and birth weight. RESULTS: A total of 551 ultrasound scans were performed. There was a significant, positive correlation between TVFR at 11-13 weeks (TVFR1) and at 22-26 weeks (TVFR3) and birth weight. For every 100-mL/min increase in TVFR1 and TVFR3, there was an increase in birth weight of 45 g and 27 g, respectively. There was also a positive association between TVFR1 and gestational age at delivery, with a 1.4-day increase in gestational age for every 100-mL/min increase of TVFR1. CONCLUSION: Ultrasound measurement of TVFR in the first trimester is significantly associated with both birth weight and gestational age at delivery. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Interactive retinal blood flow analysis of the macular region.

The study of retinal hemodynamics plays an important role to understand the onset and progression of diabetic retinopathy. In this work, we developed an interactive retinal analysis tool to quantitatively measure the blood flow velocity (BFV) and blood flow rate (BFR) in the macular region using the Retinal Function Imager (RFI). By employing a high definition stroboscopic fundus camera, the RFI device is able to assess retinal blood flow characteristics in vivo. However, the measurements of BFV using a user-guided vessel segmentation tool may induce significant inter-observer differences and BFR is not provided in the built-in software. In this work, we have developed an interactive tool to assess the retinal BFV and BFR in the macular region. Optical coherence tomography data was registered with the RFI image to locate the fovea accurately. The boundaries of the vessels were delineated on a motion contrast enhanced image and BFV was computed by maximizing the cross-correlation of pixel intensities in a ratio video. Furthermore, we were able to calculate the BFR in absolute values (µl/s). Experiments were conducted on 122 vessels from 5 healthy and 5 mild non-proliferative diabetic retinopathy (NPDR) subjects. The Pearson's correlation of the vessel diameter measurements between our method and manual labeling on 40 vessels was 0.984. The intraclass correlation (ICC) of BFV between our proposed method and built-in software was 0.924 and 0.830 for vessels from healthy and NPDR subjects, respectively. The coefficient of variation between repeated sessions was reduced significantly from 22.5% to 15.9% in our proposed method (p<0.001).

Physiological responses to changes in relative humidity under thermally neutral, warm and hot conditions.

Four hypothetical thermophysiological responses to changes in relative humidity (Rh) under thermally neutral, warm, and hot conditions were proposed for a person at rest. Under thermally neutral and warm conditions, the first hypothetical response to an increase in Rh was a decrease in mean skin temperature (T¯sk) due to increase in mean evaporation rate (E¯sk), and the second hypothetical response to a decrease in Rh was a decrease, an increase, or no change in T¯sk, depending on changes in the E¯sk. Under hot conditions, the third hypothetical response to an increase in the Rh was an increase in T¯sk or decrease in T¯sk upon decrease in the Rh due to changes in E¯sk, and the forth hypothetical response to an increase in Rh was an increase in T¯sk due to increase in the peripheral blood flow rate (SkBF). To test these hypotheses, the T¯sk and E¯sk of four young male volunteers were measured at 28°C, 30°C, or 32°C while the Rh was maintained at 40% or 80% Rh for 60min after 20min exposure at 60% Rh (control condition). In a second experiment, the T¯sk, E¯sk, and SkBF of five young male volunteers were measured at 34°C-40% Rh or 36°C-40% Rh, or 34°C-70% Rh or 36°C-70% Rh for 60min after 20min exposure at 28°C-60% Rh (control condition). The first hypothesis was partly supported by the findings that the T¯sk was lower than the control values at 28°C-80% Rh and the E¯sk was higher than the control values at 80% Rh at any tested temperature. The second hypothesis was partly supported by the findings that the T¯sk was lower than the control values at 28°C-40% Rh, and there were small changes in both T¯sk and E¯sk at 30°C-40% Rh. The third and fourth hypotheses were supported by the findings that the T¯sk at 36°C-70% Rh was significantly higher (p<0.01) than at 36°C-40% Rh, the E¯sk was significantly higher (p<0.01) at 70% Rh than at 40% Rh, and SkBF was positively correlated with T¯sk.

Parameters of Blood Flow in Great Arteries in Hypertensive ISIAH Rats with Stress-Dependent Arterial Hypertension.

Magnetic resonance angiography was used to examine blood flow in great arteries of hypertensive ISIAH and normotensive Wistar rats. In hypertensive ISIAH rats, increased vascular resistance in the basin of the abdominal aorta and renal arteries as well as reduced fraction of total renal blood flow were found. In contrast, blood flow through both carotid arteries in ISIAH rats was enhanced, which in suggests more intensive blood supply to brain regulatory centers providing enhanced stress reactivity of these rats characterized by stress-dependent arterial hypertension.

Impact of extracorporeal blood flow rate on blood pressure, pulse rate and cardiac output during haemodialysis.

BACKGROUND: If blood pressure (BP) falls during haemodialysis (HD) [intradialytic hypotension (IDH)] a common clinical practice is to reduce the extracorporeal blood flow rate (EBFR). Consequently the efficacy of the HD (Kt/V) is reduced. However, only very limited knowledge on the effect of reducing EBFR on BP exists and data are conflicting. The aim of this study was to evaluate the effect and the potential mechanism(s) involved by investigating the impact of changes in EBFR on BP, pulse rate (PR) and cardiac output (CO) in HD patients with arteriovenous-fistulas (AV-fistulas). METHODS: We performed a randomized, crossover trial in 22 haemodynamically stable HD patients with AV-fistula. After a conventional HD session each patient was examined during EBFR of 200, 300 and 400 mL/min in random order. After 15 min when steady state was achieved CO, BP and PR were measured at each EFBR, respectively. RESULTS: Mean (SD) age was 71 (11) years. Systolic BP was significantly higher at an EBFR of 200 mL/min as compared with 300 mL/min [133 (23) versus 128 (24) mmHg; P < 0.05], but not as compared with 400 mL/min [133 (23) versus 130 (19) mmHg; P = 0.20]. At EBFR of 200, 300 and 400 mL/min diastolic BP, mean arterial pressure, PR and CO remained unchanged. CONCLUSION: Our study does not show any consistent trend in BP changes by a reduction in EBFR. Reduction in EBFR if BP falls during IDH is thus not supported. However, none of the patients experienced IDH. Further studies are required to evaluate the impact of changes in EBFR on BP during IDH.