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Continuous measurement of bladder urine oxygen tension (Po2) is a method to potentially detect renal medullary hypoxia in patients at risk of acute kidney injury (AKI). To assess its practicality, we developed a computational model of the peristaltic movement of a urine bolus along the ureter and the oxygen exchange between the bolus and ureter wall. This model quantifies the changes in urine Po2 as urine transits from the renal pelvis to the bladder. The model parameters were calibrated using experimental data in rabbits, such that most of the model predictions are within ±1 SE of the reported mean in the experiment, with the average percent difference being 7.0%. Based on parametric experiments performed using a model scaled to the geometric dimensions of a human ureter, we found that bladder urine Po2 is strongly dependent on the bolus volume (i.e., bolus volume-to-surface area ratio), especially at a volume less than its physiological (baseline) volume (<0.2 mL). For the model assumptions, changes in peristaltic frequency resulted in a minimal change in bladder urine Po2 (<1 mmHg). The model also predicted that there exists a family of linear relationships between the bladder-urine Po2 and pelvic urine Po2 for different input conditions. We conclude that it may technically be possible to predict renal medullary Po2 based on the measurement of bladder urine Po2, provided that there are accurate real-time measurements of model input parameters.

Using a case-control design, we determined risk factors associated with hypertension in a disadvantaged rural population in southern India. Three hundred adults with hypertension and 300 age- and sex-matched controls were extensively phenotyped. Underweight (29%, body mass index < 18.0 kg m-2), chronic kidney disease (25%, estimated glomerular filtration rate <60 ml min-1 1.73 m-2) and anemia (82%) were highly prevalent. The ratio of sodium to potassium excretion was high (8.2). In multivariable conditional logistic regression of continuous variables dichotomized by their median value, hypertension was independently associated with greater abdominal adiposity as assessed by waist-hip ratio [odds ratio (95% confidence interval), 1.89 (1.21-2.97)], lesser protein intake as assessed by 24 h urea excretion [0.39 (0.24-0.65)], and lesser plasma renin activity [0.54 (0.35-0.84)]. Hypertension tended to be independently associated with lesser serum potassium concentration [0.66 (0.44-1.01), P = 0.06]. Furthermore, those with hypertension reported less frequent intake of vegetables and urinary sodium-potassium ratio correlated positively with serum sodium-potassium ratio (r = 0.18). Hypertension was also independently associated with lesser blood hemoglobin concentration [0.48 (0.26-0.88)]. Blood hemoglobin concentration was positively associated with serum iron (r = 0.41) and ferritin (r = 0.25) concentration and negatively associated with total iron binding capacity (r = -0.17), reflecting iron-deficiency anemia. Our findings indicate potential roles for deficient intake of potassium and protein, and iron-deficiency anemia, in the pathophysiology of hypertension in a setting of disadvantage in rural India. Imbalanced intake of potassium and sodium may be driven partly by deficient intake of vegetables or fruit.Copyright © 2021, The Author(s), under exclusive licence to Springer Nature Limited part of Springer Nature.

Acute kidney injury (AKI) is a common and serious post-operative complication of cardiac surgery. The value of a predictive biomarker is determined not only by its predictive efficacy, but also by how early this prediction can be made. For a biomarker of cardiac surgery-associated AKI, this is ideally during the intra-operative period. Therefore, in 82 adult patients undergoing cardiac surgery requiring cardiopulmonary bypass (CPB), we prospectively compared the predictive efficacy of various blood and urinary biomarkers with that of continuous measurement of urinary oxygen tension (UPO2) at pre-determined intra- and post-operative time-points. None of the blood or urine biomarkers we studied showed predictive efficacy for post-operative AKI when measured intra-operatively. When treated as a binary variable (<= or > median for the whole cohort), the earliest excess risk of AKI was predicted by an increase in urinary neutrophil gelatinase-associated lipocalin (NGAL) at 3 h after entry into the intensive care unit (odds ratio [95% confidence limits], 2.86 [1.14-7.21], p = 0.03). Corresponding time-points were 6 h for serum creatinine (3.59 [1.40-9.20], p = 0.008), and 24 h for plasma NGAL (4.54 [1.73-11.90], p = 0.002) and serum cystatin C (6.38 [2.35-17.27], p = 0.001). In contrast, indices of intra-operative urinary hypoxia predicted AKI after weaning from CPB, and in the case of a fall in UPO2 to <=10 mmHg, during the rewarming phase of CPB (3.00 [1.19-7.56], p = 0.02). We conclude that continuous measurement of UPO2 predicts AKI earlier than plasma or urinary NGAL, serum cystatin C, or early post-operative changes in serum creatinine.Copyright © 2021 John Wiley & Sons Australia, Ltd

Background--Various indicators of socioeconomic position (SEP) may have opposing effects on the risk of hypertension in disadvantaged settings. For example, high income may reflect sedentary employment, whereas greater education may promote healthy lifestyle choices. We assessed whether education modifies the association between income and hypertension in 3 regions of South India at different stages of epidemiological transition. Methods and Results--Using a cross-sectional design, we randomly selected villages within each of rural Trivandrum, West Godavari, and Rishi Valley. Sampling was stratified by age group and sex. We measured blood pressure and anthropometry and administered a questionnaire to identify lifestyle factors and SEP, including education, literacy, and income. Logistic regression was used to assess associations between various components of SEP and hypertension, and interaction analyses were used to determine whether educational attainment modified the association between income and hypertension. Trivandrum, the region of highest SEP, had the greatest prevalence of hypertension, whereas Rishi Valley, the lowest SEP region, had the least. Overall, greater income was associated with greater risk of hypertension. In interaction analyses, there was no evidence that educational attainment modified the association between income and hypertension. Conclusions--Education is widely considered to ameliorate the risk of hypertension in high-income countries. Why this effect is absent in rural India merits investigation. ( J Am Heart Assoc. 2020;9:e014486. DOI: 10.1161/JAHA.119.014486.).Copyright © 2020 The Authors.

Aim: Renal tissue hypoxia during cardiopulmonary bypass could contribute to the pathophysiology of acute kidney injury. We tested whether renal tissue hypoxia can be alleviated during cardiopulmonary bypass by the combined increase in target pump flow and mean arterial pressure. Method(s): Cardiopulmonary bypass was established in eight instrumented sheep under isoflurane anaesthesia, at a target continuous pump flow of 80 mL.kg-1 min-1 and mean arterial pressure of 65 mmHg. We then tested the effects of simultaneously increasing target pump flow to 104 mL.kg-1 min-1 and mean arterial pressure to 80 mmHg with metaraminol (total dose 0.25-3.75 mg). We also tested the effects of transitioning from continuous flow to partially pulsatile flow (pulse pressure ~15 mmHg). Result(s): Compared with conscious sheep, at the lower target pump flow and mean arterial pressure, cardiopulmonary bypass was accompanied by reduced renal blood flow (6.8 +/- 1.2 to 1.95 +/- 0.76 mL.min-1 kg-1) and renal oxygen delivery (0.91 +/- 0.18 to 0.24 +/- 0.11 mL.O2 min-1 kg-1). There were profound reductions in cortical oxygen tension (PO2) (33 +/- 13 to 6 +/- 6 mmHg) and medullary PO2 (31 +/- 12 to 8 +/- 8 mmHg). Increasing target pump flow and mean arterial pressure increased renal blood flow (to 2.6 +/- 1.0 mL.min-1 kg-1) and renal oxygen delivery (to 0.32 +/- 0.13 mL.O2 min-1kg-1) and returned cortical PO2 to 58 +/- 60 mmHg and medullary PO2 to 28 +/- 16 mmHg; levels similar to those of conscious sheep. Partially pulsatile pump flow had no significant effects on renal perfusion or oxygenation. Conclusion(s): Renal hypoxia during experimental CPB can be corrected by increasing target pump flow and mean arterial pressure within a clinically feasible range.Copyright © 2020 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd

Introduction: The renal medulla is susceptible to hypoxia during cardiopulmonary bypass (CPB), which may contribute to the development of acute kidney injury. But the speed of onset of renal medullary hypoxia remains unknown. Method(s): We continuously measured renal medullary oxygen tension (MPO2) in 24 sheep, and urinary PO2 (UPO2) as an index of MPO2 in 92 patients, before and after induction of CPB. Result(s): In laterally recumbent sheep with a right thoracotomy (n = 20), even before CPB commenced MPO2 fell from (mean +/- SEM) 52 +/- 4 to 41 +/-5 mmHg simultaneously with reduced arterial pressure (from 108 +/- 5 to 88 +/- 5 mmHg). In dorsally recumbent sheep with a medial sternotomy (n = 4), MPO2 was even more severely reduced (to 12 +/- 12 mmHg) before CPB. In laterally recumbent sheep in which a crystalloid prime was used (n = 7), after commencing CPB, MPO2 fell abruptly to 24 +/-6 mmHg within 20-30 minutes. MPO2 during CPB was not improved by adding donor blood to the prime (n = 13). In patients undergoing cardiac surgery, UPO2 fell by 4 +/- 1 mmHg and mean arterial pressure fell by 7 +/- 1 mmHg during the 30 minutes before CPB. UPO2 then fell by a further 12 +/- 2 mmHg during the first 30 minutes of CPB but remained relatively stable for the remaining 24 minutes of observation. Conclusion(s): Renal medullary hypoxia is an early event during CPB. It starts to develop even before CPB, presumably due to a pressure-dependent decrease in renal blood flow. Medullary hypoxia during CPB appears to be promoted by hypotension and is not ameliorated by increasing blood hemoglobin concentration.Copyright © The Author(s) 2021.

Objective: To determine whether there is an interaction between knowledge about hypertension and awareness of hypertension on the treatment and control of hypertension in three regions of South India at different stages of epidemiological transition (see Video, Supplemental Digital Content 1, http://links.lww.com/HJH/B426). Method(s): Using a cross-sectional design, we randomly selected villages within each of rural Trivandrum, West Godavari, and Chittoor. Sampling was stratified by age group and sex. We measured blood pressure and administered a questionnaire to determine knowledge and awareness of hypertension. Logistic regression was used to assess associations of awareness and knowledge about hypertension with its treatment and control in participants with hypertension, while examining for statistical interaction. Result(s): Among a total of 11 657 participants (50% male; median age 45 years), 3455 had hypertension. In analyses adjusted for age and sex, both knowledge score [adjusted odds ratio (aOR) 1.14 [95% confidence interval (CI) 1.12- 1.17)] and awareness [aOR 104 (95% CI 82-134)] were associated with treatment for hypertension. Similarly, both knowledge score [aOR 1.10; 95% CI (1.08-1.12)] and awareness [aOR 13.4; 95% CI (10.7-16.7)], were positively associated with control of blood pressure in those with hypertension, independent of age and sex. There was an interaction between knowledge and awareness on both treatment and control of hypertension (P of attributable proportion <0.001 for each). Conclusion(s): Health education to improve knowledge about hypertension and screening programs to improve awareness of hypertension may act in an additive fashion to improve management of hypertension in rural Indian populations.Copyright © 2021 Lippincott Williams and Wilkins. All rights reserved.

Background: To improve the control of hypertension in low- and middle-income countries, we trialed a community-based group program co-designed with local policy makers to fit within the framework of India's health system. Trained accredited social health activists (ASHAs), delivered the program, in three economically and developmentally diverse settings in rural India. We evaluated the program's implementation and scalability. Method(s): Our mixed methods process evaluation was guided by the United Kingdom Medical Research Council guidelines for complex interventions. Meeting attendance reports, as well as blood pressure and weight measures of attendees and adherence to meeting content and use of meeting tools were used to evaluate the implementation process. Thematic analysis of separate focus group discussions with participants and ASHAs as well as meeting reports and participant evaluation were used to investigate the mechanisms of impact. Result(s): Fifteen ASHAs led 32 community-based groups in three rural settings in the states of Kerala and Andhra Pradesh, Southern India. Overall, the fidelity of intervention delivery was high. Six meetings were delivered over a 3-month period to each of the intervention groups. The mean number of meetings attended by participants at each site varied significantly, with participants in Rishi Valley attending fewer meetings [mean (SD) = 2.83 (1.68)] than participants in West Godavari (Tukeys test, p = 0.009) and Trivandrum (Tukeys test, p < 0.001) and participants in West Godavari [mean (SD) = 3.48 (1.72)] attending significantly fewer meetings than participants in Trivandrum [mean (SD) = 4.29 (1.76), Tukeys test, p < 0.001]. Culturally appropriate intervention resources and the training of ASHAs, and supportive supervision of them during the program were critical enablers to program implementation. Although highly motivated during the implementation of the program ASHA reported historical issues with timely remuneration and l

Glomerular filtration rate (GFR) is acutely increased following a high-protein meal or systemic infusion of amino acids. The mechanisms underlying this renal functional response remain to be fully elucidated. Nevertheless, they appear to culminate in preglomerular vasodilation. Inhibition of the tubuloglomerular feedback signal appears critical. However, nitric oxide, vasodilator prostaglandins, and glucagon also appear important. The increase in GFR during amino acid infusion reveals a "renal reserve,"which can be utilized when the physiological demand for single nephron GFR increases. This has led to the concept that in subclinical renal disease, before basal GFR begins to reduce, renal functional reserve can be recruited in a manner that preserves renal function. The extension of this concept is that once a decline in basal GFR can be detected, renal disease is already well progressed. This concept likely applies both in the contexts of chronic kidney disease and acute kidney injury. Critically, its corollary is that deficits in renal functional reserve have the potential to provide early detection of renal dysfunction before basal GFR is reduced. There is growing evidence that the renal response to infusion of amino acids can be used to identify patients at risk of developing either chronic kidney disease or acute kidney injury and as a treatment target for acute kidney injury. However, large multicenter clinical trials are required to test these propositions. A renewed effort to understand the renal physiology underlying the response to amino acid infusion is also warranted.Copyright © 2020 the American Physiological Society.

Background: Acute kidney injury (AKI) is common after cardiac surgery requiring cardiopulmonary bypass. Renal hypoxia may precede clinically detectable AKI. We compared the efficacy of two indices of renal hypoxia, (i) intraoperative urinary oxygen tension (UPO2) and (ii) the change in plasma erythropoietin (pEPO) during surgery, in predicting AKI. We also investigated whether the performance of these prognostic markers varies with preoperative patient characteristics. Method(s): In 82 patients undergoing on-pump cardiac surgery, blood samples were taken upon induction of anesthesia and upon entry into the intensive care unit. UPO2 was continuously measured throughout surgery. Result(s): Thirty-two (39%) patients developed postoperative AKI. pEPO increased during surgery, but this increase did not predict AKI, regardless of risk of postoperative mortality assessed by EuroSCORE-II. For patients categorized at higher risk by EuroSCORE-II >1.98 (median score for the cohort), UPO2 <=10 mmHg at any time during surgery predicted a 4.04-fold excess risk of AKI (p =.04). However, UPO2 did not significantly predict AKI in lower-risk patients. UPO2 significantly predicted AKI in patients who were older, had previous myocardial infarction, diabetes, lower preoperative serum creatinine, or shorter bypass times. pEPO and UPO2 were only weakly correlated. Conclusion(s): Intraoperative change in pEPO does not predict AKI. However, UPO2 shows promise, particularly in patients with higher risk of operative mortality. The disparity between these two markers of renal hypoxia may indicate that UPO2 reflects medullary oxygenation whereas pEPO reflects cortical oxygenation.Copyright © 2021 Wiley Periodicals LLC

We assessed the association of hypertension with markers of inflammation and infection in a rural and disadvantaged Indian population. In a case-control study, we age- and gender-matched 300 cases with hypertension to 300 controls without hypertension. Blood pressure was measured according to a strict protocol. We measured markers of inflammation and infection including serum high-sensitivity C-reactive protein (hs-CRP), blood lymphocyte count, serum homocysteine, tooth loss, overcrowding and exposure to fecal contamination. Multivariable conditional logistic regression was used to determine their association with hypertension. Median serum hs-CRP was 42% greater in cases than controls, while median serum homocysteine was 10% greater. In multivariable conditional logistic regression, elevated homocysteine (OR 1.75, 95% CI 1.09-2.82), greater lymphocyte count (OR 1.49, 95% CI 1.01-2.01) and exposure to fecal contamination, defined as a distance from the field used for toilet purposes to the household of <=50 m (OR 2.38, 95% CI 1.07-5.29), were independently associated with hypertension in this rural population. In separate analyses for each gender, elevated hs-CRP (OR 2.62, 95% CI 1.04-6.58) was associated with hypertension in men, whereas edentulism (OR 4.75, 95% CI 1.62-13.96) was associated with greater odds of hypertension in women. Our findings demonstrate specific associations between hypertension and markers of inflammation and infection including hs-CRP, homocysteine, lymphocyte count, edentulism and exposure to fecal contamination. Thus, strategies aimed at reducing inflammation and infection may reduce the burden of hypertension in such settings of disadvantage in rural India.Copyright © 2021, The Author(s), under exclusive licence to Springer Nature Limited.

Renal medullary hypoxia may contribute to the pathophysiology of acute kidney injury, including that associated with cardiac surgery requiring cardiopulmonary bypass (CPB). When performed under volatile (isoflurane) anesthesia in sheep, CPB causes renal medullary hypoxia. There is evidence that total intravenous anesthesia (TIVA) may preserve renal perfusion and renal oxygen delivery better than volatile anesthesia. Therefore, we assessed the effects of CPB on renal perfusion and oxygenation in sheep under propofol/fentanyl-based TIVA. Sheep (n = 5) were chronically instrumented for measurement of whole renal blood flow and cortical and medullary perfusion and oxygenation. Five days later, these variables were monitored under TIVA using propofol and fentanyl and then on CPB at a pump flow of 80 mL*kg-1*min-1 and target mean arterial pressure of 70 mmHg. Under anesthesia, before CPB, renal blood flow was preserved under TIVA (mean difference +/- SD from conscious state: -16 +/- 14%). However, during CPB renal blood flow was reduced (-55 +/- 13%) and renal medullary tissue became hypoxic (-20 +/- 13 mmHg versus conscious sheep). We conclude that renal perfusion and medullary oxygenation are well preserved during TIVA before CPB. However, CPB under TIVA leads to renal medullary hypoxia, of a similar magnitude to that we observed previously under volatile (isoflurane) anesthesia. Thus use of propofol/fentanyl-based TIVA may not be a useful strategy to avoid renal medullary hypoxia during CPB.Copyright © 2020 the American Physiological Society

Background New methods are required to manage hypertension in resource-poor settings. We hypothesised that a community health worker (CHW)-led group-based education and monitoring intervention would improve control of blood pressure (BP). Methods and findings We conducted a baseline community-based survey followed by a cluster randomised controlled trial of people with hypertension in 3 rural regions of South India, each at differing stages of epidemiological transition. Participants with hypertension, defined as BP >= 140/90 mm Hg or taking antihypertensive medication, were advised to visit a doctor. In each region, villages were randomly assigned to intervention or usual care (UC) in a 1:2 ratio. In intervention clusters, trained CHWs delivered a group-based intervention to people with hypertension. The program, conducted fortnightly for 3 months, included monitoring of BP, education about hypertension, and support for healthy lifestyle change. Outcomes were assessed approximately 2 months after completion of the intervention. The primary outcome was control of BP (BP < 140/90 mm Hg), analysed using mixed effects regression, clustered by village within region and adjusted for baseline control of hypertension (using intention-to-treat principles). Of 2,382 potentially eligible people, 637 from 5 intervention clusters and 1,097 from 10 UC clusters were recruited between November 2015 and April 2016, with follow-up occurring in 459 in the intervention group and 1,012 in UC. Mean age was 56.9 years (SD 13.7). Baseline BP was similar between groups. Control of BP improved from baseline to follow-up more in the intervention group (from 227 [49.5%] to 320 [69.7%] individuals) than in the UC group (from 528 [52.2%] to 624 [61.7%] individuals) (odds ratio [OR] 1.6, 95% CI 1.2-2.1; P = 0.001). In secondary outcome analyses, there was a greater decline in systolic BP in the intervention than UC group (-5.0 mm Hg, 95% CI -7.1 to -3.0; P < 0.001) and a greater decline in diast

BACKGROUND: There are few available data regarding the prevalence of diabetes in the sub-Himalayan region of India. The aim of this study was to determine the prevalence of pre-diabetes and diabetes in rural Garhwal based on glycosylated hemoglobin. METHOD(S): In a cross-sectional survey of 500 adults from five randomly selected villages in Chamba, a mountainous Tehri Garhwal district in Uttarakhand in north-west India, we determined the prevalence of diabetes (hemoglobin (Hb) A1c>=6.5%) and pre-diabetes (5.7%<=HbA1c<=6.4%). In a sub-sample of those diagnosed with diabetes or pre-diabetes (n=140), fasting blood glucose (FBG, n=117) or postprandial blood glucose (PBG, n=23), and blood hemoglobin concentration, was measured at follow-up. RESULT(S): Based on HbA1c, 10.0% had diabetes and 56.4% pre-diabetes. Of those diagnosed as diabetic by HbA1c, 10 of 16 (62.5%) were diagnosed as diabetic by FBG (>125mg/dL) or PBG (>=200mg/dL). In those diagnosed as pre-diabetic by HbA1c, only 55 of 124 (44.4%) were diagnosed as pre-diabetic by FBG (100-125mg/dL) or PBG (140-199mg/dL). A large proportion of these 140 individuals (67.1%) were moderately to severely anemic (Hb <11.4mg/dL). The diagnostic gap for pre-diabetes between HbA1c and FBG/PBG was similar for the groups with and without moderate to severe anemia. CONCLUSION(S): HbA1c and FBG/PBG have similar diagnostic performance for diabetes in this population. However, many individuals were diagnosed with pre-diabetes by HbA1c but not FBG/PBG. The relative excess diagnosis of pre-diabetes with HbA1c does not appear to be explained by anemia, an endemic condition in India. The prognostic significance of diagnosis of pre-diabetes by HbA1c but not FBG/PBG remains unknown, but merits investigation.

OBJECTIVE: To determine whether there is an interaction between knowledge about hypertension and awareness of hypertension on the treatment and control of hypertension in three regions of South India at different stages of epidemiological transition (see Video, Supplemental Digital Content 1, http://links.lww.com/HJH/B426). METHOD(S): Using a cross-sectional design, we randomly selected villages within each of rural Trivandrum, West Godavari, and Chittoor. Sampling was stratified by age group and sex. We measured blood pressure and administered a questionnaire to determine knowledge and awareness of hypertension. Logistic regression was used to assess associations of awareness and knowledge about hypertension with its treatment and control in participants with hypertension, while examining for statistical interaction. RESULT(S): Among a total of 11 657 participants (50% male; median age 45 years), 3455 had hypertension. In analyses adjusted for age and sex, both knowledge score [adjusted odds ratio (aOR) 1.14 [95% confidence interval (CI) 1.12--1.17)] and awareness [aOR 104 (95% CI 82--134)] were associated with treatment for hypertension. Similarly, both knowledge score [aOR 1.10; 95% CI (1.08--1.12)] and awareness [aOR 13.4; 95% CI (10.7--16.7)], were positively associated with control of blood pressure in those with hypertension, independent of age and sex. There was an interaction between knowledge and awareness on both treatment and control of hypertension (P of attributable proportion <0.001 for each). CONCLUSION(S): Health education to improve knowledge about hypertension and screening programs to improve awareness of hypertension may act in an additive fashion to improve management of hypertension in rural Indian populations.

Computational models have made a major contribution to the field of physiology. As the complexity of our understanding of biological systems expands, the need for computational methods only increases. But collaboration between experimental physiologists and computational modellers (ie theoretical physiologists) is not easy. One of the major challenges is to break down the barriers created by differences in vocabulary and approach between the two disciplines. In this review, we have two major aims. Firstly, we wish to contribute to the effort to break down these barriers and so encourage more interdisciplinary collaboration. So, we begin with a “primer” on the ways in which computational models can help us understand physiology and pathophysiology. Second, we aim to provide an update of recent efforts in one specific area of physiology, renal oxygenation. This work is shedding new light on the causes and consequences of renal hypoxia. But as importantly, computational modelling is providing direction for experimental physiologists working in the field of renal oxygenation by: (a) generating new hypotheses that can be tested in experimental studies, (b) allowing experiments that are technically unfeasible to be simulated in silico, or variables that cannot be measured experimentally to be estimated, and (c) providing a means by which the quality of experimental data can be assessed. Critically, based on our experience, we strongly believe that experimental and theoretical physiology should not be seen as separate exercises. Rather, they should be integrated to permit an iterative process between modelling and experimentation.

Per gram of tissue, the kidneys are among our most highly perfused organs. Yet the renal cortex and, in particular, the renal medulla are susceptible to hypoxia. In turn, hypoxia is a major pathophysiological feature of both acute kidney injury and chronic kidney disease. We identify seven factors that render the kidney susceptible to hypoxia: (1) the large metabolic demand imposed by active reabsorption of sodium; (2) limitations on oxygen delivery to cortical tissue imposed by the density of peritubular capillaries; (3) the poor capacity for angiogenesis in the adult kidney; (4) the limited ability of the renal vasculature to dilate in response to hypoxia; (5) diffusive oxygen shunting between arteries and veins in the cortex and descending and ascending vasa recta in the medulla; (6) the physiological requirement for low medullary blood flow to facilitate urinary concentration; and (7) the topography of vascular‐tubular arrangements in the outer medulla that limit oxygen delivery to the thick ascending limb of Henle's loop. Recent collaborative efforts between anatomists, physiologists, and mathematicians have improved our understanding of the roles of these factors in both physiological regulation of intrarenal oxygenation and development of renal hypoxia under pathophysiological conditions. We are also better able to understand these apparent maladaptations in the context of evolution. That is, they can be explained by the combined effects of historical contingency (our ancestral life in the sea) and selection pressures imposed by the multiple functions of the kidney to regulate extracellular fluid volume, retain water, and control erythrocyte production. Anat Rec, 2019. © 2019 American Association for Anatomy

Aim: Blood transfusion may improve renal oxygenation during cardiopulmonary bypass (CPB). In an ovine model of experimental CPB, we tested whether increasing blood haemoglobin concentration [Hb] from ~7 g dL-1 to ~9 g dL-1 improves renal tissue oxygenation. Method(s): Ten sheep were studied while conscious, under stable isoflurane anaesthesia, and during 3 hours of CPB. In a randomized cross-over design, 5 sheep commenced bypass at a high target [Hb], achieved by adding 600 mL donor blood to the priming solution. After 90 minutes of CPB, PlasmaLyte was added to the blood reservoir to achieve low target [Hb]. For the other 5 sheep, no blood was added to the prime, but after 90 minutes of CPB, 800-900 mL of donor blood was given to achieve a high target [Hb]. Result(s): Overall, CPB was associated with marked reductions in renal oxygen delivery (-50 +/- 12%, mean +/- 95% confidence interval) and medullary tissue oxygen tension (PO2, -54 +/- 29%). Renal fractional oxygen extraction was 17 +/- 10% less during CPB at high [Hb] than low [Hb] (P =.04). Nevertheless, no increase in tissue PO2 in either the renal medulla (0 +/- 6 mmHg change, P >.99) or cortex (-19 +/- 13 mmHg change, P =.08) was detected with high [Hb]. Conclusion(s): In experimental CPB blood transfusion to increase Hb concentration from ~7 g dL-1 to ~9 g dL-1 did not improve renal cortical or medullary tissue PO2 even though it decreased whole kidney oxygen extraction.Copyright © 2020 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd

Introduction: Urinary oxygen tension (PO2) may provide a useful estimate of renal medullary PO2 and thus risk of acute kidney injury (AKI). However, the relationship between urinary PO2 and medullary PO2 could be confounded by variations in urine flow and arterial PO2. In the current study we exploited data we had previously generated, from experimental studies in ovine septic AKI and in patients undergoing cardiac surgery requiring cardiopulmonary bypass (CPB), to perform a detailed analysis of the influences of urine flow and arterial PO2 on urinary PO2. We also investigated the potential for simultaneous measurement of urine flow and urinary PO2, during CPB, to improve prediction of AKI over that provided by measurement of each variable on its own. Method(s): In ovine septic AKI urine flow, urinary PO2, arterial PO2, and medullary PO2 were measured. In human patients undergoing cardiac surgery requiring CPB urinary PO2 and arterial PO2 were measured continuously and urine flow was estimated every 5 minutes. Result(s): In 28 conscious septic sheep breathing room air, urinary PO2 was more closely correlated with medullary PO2 (r2=0.29) than with arterial PO2 (r2=0.06) or urine flow (r2=0.03). The difference between medullary PO2 and urinary PO2 varied little with urine flow or arterial PO2. In 20 patients, urine flow increased abruptly from 2.81 +/- 0.24 mL/min to 6.53 +/- 0.30 mL/min upon commencement of CPB, usually coincident with a fall in urinary PO2 (Fig. 1). During hyperoxic CPB high values of urinary PO2 were often observed at low urine flow. In 65 patients, low urinary PO2 during CPB (<10 mmHg at any time during CPB) was associated with greater (4.5-fold) risk of AKI. However, the level of urine flow on bypass was not significantly associated with risk of AKI. [Figure presented] Conclusion(s): We developed a method for virtually continuous measurement of urine flow in the operating theatre. We found that urinary PO2 provides a relatively robust estimate of

Renal medullary hypoxia may contribute to cardiac surgery-associated acute kidney injury (AKI). However, the effects of cardiopulmonary bypass (CPB) on medullary oxygenation are poorly understood. Here we tested whether CPB causes medullary hypoxia and whether medullary oxygenation during CPB can be improved by increasing pump flow or mean arterial pressure (MAP). Twelve sheep were instrumented to measure whole kidney, medullary, and cortical blood flow and oxygenation. Five days later, under isoflurane anesthesia, CPB was initiated at a pump flow of 80 mL kg-1min-1 and target MAP of 70 mm Hg. Pump flow was then set at 60 and 100 mL kg-1min-1, while MAP was maintained at approximately 70 mm Hg. MAP was then increased by vasopressor (metaraminol, 0.2-0.6 mg/min) infusion at a pump flow of 80 mL kg-1min-1. CPB at 80 mL kg-1min-1 reduced renal blood flow (RBF), -61% less than the conscious state, perfusion in the cortex (-44%) and medulla (-40%), and medullary PO2 from 43 to 27 mm Hg. Decreasing pump flow from 80 to 60 mL kg-1min-1 further decreased RBF (-16%) and medullary PO2 from 25 to 14 mm Hg. Increasing pump flow from 80 to 100 mL kg-1min-1 increased RBF (17%) and medullary PO2 from 20 to 29 mm Hg. Metaraminol (0.2 mg/min) increased MAP from 63 to 90 mm Hg, RBF (47%), and medullary PO2 from 19 to 39 mm Hg. Thus, the renal medulla is susceptible to hypoxia during CPB, but medullary oxygenation can be improved by increasing pump flow or increasing target MAP by infusion of metaraminol.Copyright © 2019 International Society of Nephrology

Introduction: Continuous measurement of bladder urinary oxygen tension (PO2) may provide a real-time surrogate measure of oxygenation in the renal medulla. Therefore, urinary PO2 may be a useful tool for early prediction of acute kidney injury (AKI) and potentially also the management of renal oxygenation in patients with AKI. We examined the relationship between urinary PO2, measured in the intensive care unit (ICU), and development of AKI in patients who had undergone cardiac surgery requiring cardiopulmonary bypass (CPB). Method(s): In 74 patients undergoing on-pump cardiac surgery, bladder urinary PO2 was measured continuously in the ICU using a fibre optic probe placed in the patient's bladder catheter. AKI was diagnosed by modified 'Kidney Disease: Improving Global Outcomes' (KDIGO) criteria, excluding the urine flow criterion. Result(s): Twenty-eight out of 74 patients (37.8%) developed post-operative AKI (18 Stage 1, 7 Stage 2, and 3 Stage 3). The median time to first diagnosis of AKI, using serum creatinine, was 16.9 hours after entry into the ICU (interquartile range (IQR): 13, 32 h). The median duration of monitoring of urinary PO2 was 37.8 hours (IQR: 24.0, 47.3 h). During the first 3 hours after arrival in the ICU, overall mean urinary PO2 (AKI: 19.4 +/- 9.3 vs. non-AKI: 25.3 +/- 9.7 mmHg, p = 0.01), and the nadir (lowest recorded) urinary PO2 (AKI: 12.1 +/- 6.8 vs. non-AKI: 16.0 +/- 5.7 mmHg, p = 0.01) were lower in patients who developed AKI than those who did not. Furthermore, within the first 3 hours of entry to the ICU, 17 of the 28 patients (61%) who developed AKI had urinary PO2 less than or equal to 15 mmHg while this threshold was only reached in 16 of the 46 patients (35%) who did not develop AKI. Patients who developed AKI also experienced longer periods with urinary PO2 less than or equal to 15 mmHg (median time of 10.9 min per hour of measurement) than those who did not (median 0.0 min per hour), p = 0.01. If urinary PO2 fell to 10 mmHg or

Background. Acute kidney injury (AKI) is common after cardiac surgery and profoundly affects postoperative mortality and morbidity. There are no validated methods to assess risk of AKI intraoperatively. Methods. We determined the association between postoperative AKI and intraoperative urinary oxygen tension (PO2), measured via a fiber optic probe in the tip of the urinary catheter, in 65 patients undergoing high-risk cardiac surgery requiring cardiopulmonary bypass (CPB). AKI was diagnosed by modified Kidney Disease: Improving Global Outcomes criteria. Results. Urinary PO2 fell during the operation, often reaching its nadir during rewarming or after weaning from CPB. Nadir urinary PO2 was lower in the 26 patients who developed AKI (mean 6 SD, 8.9 6 5.6 mmHg) than in the 39 patients who did not (14.9 6 10.2 mmHg, P 1/4 0.008). Patients who developed AKI had longer periods of urinary PO2 15 and 10 mmHg than patients who did not. Odds of AKI increased when urinary PO2 fell to 10 mmHg {3.60 [95% confidence interval (CI) 1.27-10.21]} or 5 mmHg [3.60 (95% CI 1.04-12.42), P 1/4 0.04] during the operation. When urinary PO2 fell to 15 mmHg, for more than or equal to the median duration for all patients (4.8 min/h surgery), the odds of AKI were 4.85 (95% CI 1.64-14.40), P 1/4 0.004. The area under the receiver-operator curve for this parameter alone was 0.69, and was 0.89 when other variables with P 0.10 in univariable analysis were included in the model. Conclusion. Low urinary PO2 during adult cardiac surgery requiring CPB predicts AKI, so may identify patients in which intervention to improve renal oxygenation might reduce the risk of AKI.Copyright © The Author(s) 2018.

Introduction: Continuous measurement of urinary oxygen tension (PO2) in patients undergoing cardiac surgery may allow prediction of post-operative acute kidney injury (AKI). The predictive efficacy of urinary PO2 may be because it provides a good estimate of renal medullary PO2. Medications given during the perioperative period, particularly diuretics, could potentially alter medullary and/or urinary PO2. Thus, administration of furosemide may reduce the utility of urinary PO2 in predicting AKI. Therefore, we tested the effects of furosemide on urinary PO2 in patients recovering in the intensive care unit (ICU) after open heart surgery requiring cardiopulmonary bypass. Method(s): Bladder urinary PO2 was measured using a fibre optic probe, placed in the patient's bladder catheter at the time of induction of anaesthesia in the operating theatre. Urinary PO2 was measured in the ICU in 66 patients for up to 48 h (mean +/- SEM 38.9 +/- 2.6 h) after admission to the ICU. Of these, 39 patients received a bolus intravenous dose of furosemide (10-80 mg). Result(s): Urine flow in the hour before furosemide administration averaged 0.83 +/- 0.11 mL/min (mean +/- SEM) in the 23 patients who did not develop AKI during the five days after surgery (KDIGO criteria excluding urine flow criterion) and 0.57 +/- 0.11 mL/min in the 16 patients who did develop AKI (Figure 1A). In the two hours following administration of furosemide, urine flow increased to 2.10 +/- 0.37 mL/min in patients who did not develop AKI, and 1.97 +/- 0.44 mL/min in patients who did develop AKI. Urinary PO2 before administration of furosemide was lower in patients who developed AKI (20.2 +/- 2.0 mmHg) than those who did not (26.3 +/- 2.6 mmHg) (Figure 1B). Urinary PO2 did not change significantly in the first two hours following administration of furosemide in patients who did develop AKI (21.9 +/- 2.3 mmHg), or in patients who did not develop AKI (25.9 +/- 1.8 mmHg). There was also no significant relationship bet

Objectives: Acute kidney injury (AKI) develops in ~30% of patients following cardiac surgery on cardiopulmonary bypass (CPB). There are no interventions to prevent post-operative AKI, because its pathophysiology remains unclear. Our aims are (1) to determine the effects of CPB on the renal macro-and micro-circulation and (2) to determine the effects of altering pump flow on global and regional-kidney perfusion and oxygenation during CPB. Method(s): We implanted a flow probe on the renal artery and laser Doppler/oxygen-sensing probes in the cortex and medulla in sheep (N = 10). After baseline recordings in conscious sheep, animals were anesthetized, then placed on CPB with inspired oxygen fraction (FiO2) maintained at 0.6. From a baseline level of 80 mL/kg/min, pump flow was altered to 60, 80 and 100 mL/kg/min in random order. Result(s): During CPB, renal blood flow (RBF; 287 +/- 21 to 109 +/- 19 mL/ min), medullary perfusion (720 +/- 127 to 222 +/- 42 BPU) and medullary oxygenation (48 +/- 5 to 22 +/- 7 mmHg) were all reduced, compared with conscious sheep. Cortical oxygenation increased during CPB (46 +/- 3 to 70 +/- 17 mmHg), despite reduced perfusion (1954 +/- 378 to 872 +/- 112 BPU). Reducing pump flow exacerbated medullary hypoxia (to 11 +/- 3 mmHg), while increasing pump flow tended to improve medullary oxygenation (to 29 +/- 7 mmHg). Conclusion(s): CPB had detrimental effects on RBF, medullary and cortical perfusion and medullary oxygenation. Cortical oxygenation was maintained by the high FiO2. Medullary hypoxia may be a crucial mediator of post-CPB AKI. Thus, avoiding medullary hypoxia, by optimizing perfusion conditions on CPB, may be a feasible strategy to mitigate post-operative AKI.

Aim: Urinary oxygen tension (uPO2) may provide an estimate of renal medullary PO2 (mPO2) and thus risk of acute kidney injury (AKI). We assessed the potential for variations in urine flow and arterial PO2 (aPO2) to confound these estimates. Method(s): In 28 sheep urine flow, uPO2, aPO2 and mPO2 were measured during development of septic AKI. In 65 human patients undergoing cardiac surgery requiring cardiopulmonary bypass (CPB) uPO2 and aPO2 were measured continuously during CPB, and in a subset of 20 patients, urine flow was estimated every 5 minutes. Result(s): In conscious sheep breathing room air, uPO2 was more closely correlated with mPO2 than with aPO2 or urine flow. The difference between mPO2 and uPO2 varied little with urine flow or aPO2. In patients, urine flow increased abruptly from 3.42 +/- 0.29 mL min-1 to 6.94 +/- 0.26 mL min-1 upon commencement of CPB, usually coincident with reduced uPO2. During hyperoxic CPB high values of uPO2 were often observed at low urine flow. Low urinary PO2 during CPB (<10 mm Hg at any time during CPB) was associated with greater (4.5-fold) risk of AKI. However, low urine flow during CPB was not significantly associated with risk of AKI. Conclusion(s): uPO2 provides a robust estimate of mPO2, but this relationship is confounded by the simultaneous presence of systemic hyperoxia and low urine flow. Urine flow increases and uPO2 decreases during CPB. Thus, CPB is probably the best time to use uPO2 to detect renal medullary hypoxia and risk of post-operative AKI.Copyright © 2019 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd

We have previously developed a three-dimensional computational model of oxygen transport in the renal medulla. In the present study, we used this model to quantify the sensitivity of renal medullary oxygenation to four of its major known determinants: medullary blood flow (MBF), medullary oxygen consumption rate (V̇o2,M), hemoglobin (Hb) concentration in the blood, and renal perfusion pressure. We also examined medullary oxygenation under special conditions of hydropenia, extracellular fluid volume expansion by infusion of isotonic saline, and hemodilution during cardiopulmonary bypass. Under baseline (normal) conditions, the average medullary tissue Po2 predicted for the whole renal medulla was ~30 mmHg. The periphery of the interbundle region in the outer medulla was identified as the most hypoxic region in the renal medulla, which demonstrates that the model prediction is qualitatively accurate. Medullary oxygenation was most sensitive to changes in renal perfusion pressure followed by Hb, MBF, and V̇o2,M, in that order. The medullary oxygenation also became sensitized by prohypoxic changes in other parameters, leading to a greater fall in medullary tissue Po2 when multiple parameters changed simultaneously. Hydropenia did not induce a significant change in medullary oxygenation compared with the baseline state, while volume expansion resulted in a large increase in inner medulla tissue Po2 (by ~15 mmHg). Under conditions of cardiopulmonary bypass, the renal medulla became severely hypoxic, due to hemodilution, with one-third of the outer stripe of outer medulla tissue having a Po2 of <5 mmHg.

Erythropoietin is released from the kidney in response to tissue hypoxia. Montero and Lundby found that increases in plasma erythropoietin induced by reducing arterial oxygen content in healthy humans were independent of arterial oxygen tension. Their observations accord with the established physiology of kidney oxygenation and can be predicted by a computational model of renal oxygen transport. However, model simulations indicate that the interpretation implicit in the title of their paper may be an oversimplification.

Acute kidney injury (AKI) is a common complication following cardiac surgery performed on cardiopulmonary bypass (CPB) and has important implications for prognosis. The aetiology of cardiac surgery-associated AKI is complex, but renal hypoxia, particularly in the medulla, is thought to play at least some role. There is strong evidence from studies in experimental animals, clinical observations and computational models that medullary ischaemia and hypoxia occur during CPB. There are no validated methods to monitor or improve renal oxygenation during CPB, and thus possibly decrease the risk of AKI. Attempts to reduce the incidence of AKI by early transfusion to ameliorate intra-operative anaemia, refinement of protocols for cooling and rewarming on bypass, optimization of pump flow and arterial pressure, or the use of pulsatile flow, have not been successful to date. This may in part reflect the complexity of renal oxygenation, which may limit the effectiveness of individual interventions. We propose a multi-disciplinary pathway for translation comprising three components. Firstly, large-animal models of CPB to continuously monitor both whole kidney and regional kidney perfusion and oxygenation. Secondly, computational models to obtain information that can be used to interpret the data and develop rational interventions. Thirdly, clinically feasible non-invasive methods to continuously monitor renal oxygenation in the operating theatre and to identify patients at risk of AKI. In this review, we outline the recent progress on each of these fronts.Copyright © 2017 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd

BACKGROUND: Hypertension is a major risk factor for cardiovascular disease, a leading cause of premature death and disability in India. Since access to health services is poor in rural India and Accredited Social Health Activists (ASHAs) are available throughout India for maternal and child health, a potential solution for improving hypertension control is by utilising this available workforce. We aimed to develop and implement a training package for ASHAs to identify and control hypertension in the community, and evaluate the effectiveness of the training program using the Kirkpatrick Evaluation Model. METHOD(S): The training program was part of a cluster randomised feasibility trial of a 3-month intervention to improve hypertension outcomes in South India. Training materials incorporated details on managing hypertension, goal setting, facilitating group meetings, and how to measure blood pressure and weight. The 15 ASHAs attended a five-day training workshop that was delivered using interactive instructional strategies. ASHAs then led community-based education support groups for 3 months. Training was evaluated using Kirkpatrick's evaluation model for measuring reactions, learning, behaviour and results using tests on knowledge at baseline, post-training and post-intervention, observation of performance during meetings and post-intervention interviews. RESULT(S): The ASHAs' knowledge of hypertension improved from a mean score of 64% at baseline to 76% post-training and 84% after the 3-month intervention. Research officers, who observed the community meetings, reported that ASHAs delivered the self-management content effectively without additional assistance. The ASHAs reported that the training materials were easy to understand and useful in educating community members. CONCLUSION(S): ASHAs can be trained to lead community-based group educational discussions and support individuals for the management of high blood pressure. TRIAL REGISTRATION: The feasibility tria