How Free Swimming Fosters the Locomotion of a Purely Oscillating Fish-like Body.

The recoil motions in free swimming, given by lateral and angular rigid motions due to the interaction with the surrounding water, are of great importance for a correct evaluation of both the forward locomotion speed and efficiency of a fish-like body. Their contribution is essential for calculating the actual movements of the body rear end whose prominent influence on the generation of the proper body deformation was established a long time ago. In particular, the recoil motions are found here to promote a dramatic improvement of the performance when damaged fishes, namely for a partial functionality of the tail or even for its complete loss, are considered. In fact, the body deformation, which turns out to become oscillating and symmetric in the extreme case, is shown to recover in the water frame a kind of undulation leading to a certain locomotion speed though at the expense of a large energy consumption. There has been a deep interest in the subject since the infancy of swimming studies, and a revival has recently arisen for biomimetic applications to robotic fish-like bodies. We intend here to apply a theoretical impulse model to the oscillating fish in free swimming as a suitable test case to strengthen our belief in the beneficial effects of the recoil motions. At the same time, we intend to exploit the linearity of the model to detect from the numerical simulations the intrinsic physical reasons related to added mass and vorticity release behind the experimental observations.

Wave dispersion in moderate channel turbulence.

We study channel turbulence by interpreting its vorticity as a random sea of ocean wave packet analogues. In particular, we investigate the ocean-like properties of vortical packets applying stochastic methods developed for oceanic fields. Taylor's hypothesis of frozen eddies does not hold when turbulence is not weak, and vortical packets change shape as they are advected by the mean flow, altering their own speed. This is the physical manifestation of a hidden wave dispersion of turbulence. Our analysis at the bulk Reynolds number Reb = 5600 suggests that turbulent fluctuations behave dispersively as gravity-capillary waves, with capillarity being dominant near the wall region.

The fish ability to accelerate and suddenly turn in fast maneuvers.

Velocity burst and quick turning are performed by fish during fast maneuvers which might be essential to their survival along pray-predator encounters. The parameters to evaluate these truly unsteady motions are totally different from the ones for cruising gaits since a very large acceleration, up to several times the gravity, and an extreme turning capability, in less than one body length, are now the primary requests. Such impressive performances, still poorly understood, are not common to other living beings and are clearly related to the interaction with the aquatic environment. Hence, we focus our attention on the water set in motion by the body, giving rise to the relevant added mass and the associated phenomena in transient conditions, which may unveil the secret of the great maneuverability observed in nature. Many previous studies were almost exclusively concentrated on the vortical wake, whose account, certainly dominant at steady state, is not sufficient to explain the entangled transient phenomena. A simple two-dimensional impulse model with concentrated vorticity is used for the self-propulsion of a deformable body in an unbounded fluid domain, to single out the potential and the vortical impulses and to highlight their interplay induced by recoil motions.

The performance of a flapping foil for a self-propelled fishlike body.

Several fish species propel by oscillating the tail, while the remaining part of the body essentially contributes to the overall drag. Since in this case thrust and drag are in a way separable, most attention was focused on the study of propulsive efficiency for flapping foils under a prescribed stream. We claim here that the swimming performance should be evaluated, as for undulating fish whose drag and thrust are severely entangled, by turning to self-propelled locomotion to find the proper speed and the cost of transport for a given fishlike body. As a major finding, the minimum value of this quantity corresponds to a locomotion speed in a range markedly different from the one associated with the optimal efficiency of the propulsor. A large value of the feathering parameter characterizes the minimum cost of transport while the optimal efficiency is related to a large effective angle of attack. We adopt here a simple two-dimensional model for both inviscid and viscous flows to proof the above statements in the case of self-propelled axial swimming. We believe that such an easy approach gives a way for a direct extension to fully free swimming and to real-life configurations.

[The CROFF pavilion at the Policlinico Hospital in Milan: the beginnings].

This article collects the personal stories of the young doctors who in the early sixties contributed to the birth and development of the Croff pavilion at the Policlinico Hospital in Milan. Inaugurated on October 19, 1964, this has been the first institute in Italy entirely devoted to patients with kidney diseases. Since its inception, it has significantly contributed to the progress of nephrology thanks to important and pioneering investigations in the main fields of our specialty, which still continue nowadays. The different stories reported here follow the chronological order in which the young doctors arrived at Croff, each story representing a personal narrative that interweaves and integrates that of others. This gives rise to a vivid many-voiced account, from which emerge not only the figures of these young doctors, but also those of patients, nurses, and laboratory technicians.

On the feasibility of the Rayleigh cycle for dynamic soaring trajectories.

Dynamic soaring is a flight technique used by albatrosses and other birds to cover large distances without the expenditure of energy, which is extracted from the available wind conditions, as brightly perceived five centuries ago by Leonardo da Vinci. Closed dynamic soaring trajectories use spatial variations of wind speed to travel, in principle, indefinitely over a prescribed area. The application of the concept of closed dynamic soaring trajectories to aerial vehicles, such as UAVs, may provide a solution to improve the endurance in certain missions. The main limitation of dynamic soaring is its dependence on the wind characteristics. More than one century ago, Lord Rayleigh proposed a very simple model, based on the repeated crossing of a step wind profile, presently known as Rayleigh cycle, that provides a clear explanation of the physical phenomenon. The present paper studies the feasibility of closed, single-loop, energy-neutral trajectories for a broad set of wind and vehicle conditions. Through the use of trajectory optimization methods, it was possible to see how the shape of the wind profile, the initial flight conditions and the vehicle constraints influence the required wind strength to perform dynamic soaring trajectories and consequently their feasibility. It was possible to conclude that there are optimal values for the initial airspeed and initial height of the vehicle, that minimize the required wind strength. In addition, it was seen how the structural and aerodynamic constraints of the vehicle affect dynamic soaring at high and low airspeeds respectively. Finally, some new trajectories that can be performed in conditions of excess wind are proposed. The purpose is to maximize the time spent aloft and the path length while maintaining the concept of single-loop, energy-neutral trajectories, making them especially useful for aerial vehicles surveillance applications.

Neurological counterparts of hyponatremia: pathological mechanisms and clinical manifestations.

Hyponatremia, defined as a serum sodium concentration <135 mEq/L, represents the most frequent electrolyte disorder in older hospitalized patients. Early recognition of hyponatremia is mandatory, since it represents an independent risk factor that increases hospital mortality by 40 %. Delayed correction of hyponatremia may worsen brain edema, resulting in different degrees of neural damage. However, an overly rapid correction of serum sodium levels can lead to osmotic demyelination syndrome (ODS), a dreadful neurological picture. In recent years, hyponatremia and ODS have received growing attention both in terms of clinical management and pathophysiology, leading to the discovery of new drugs and treatment algorithms. In this review, we recapitulate the pathogenetic background, clinical manifestations, and treatment guidelines of hyponatremia, focusing on the neurological alterations. Neurological symptoms may be neglected when they manifest as early signs of mild hyponatremia, while brain damage can irremediably affect patients' conditions in the context of ODS.

Renal transplantation in elderly patients. How to select the candidates to the waiting list?

Today, old age does not represent a formal contraindication to kidney transplantation. Rather, there is evidence that in elderly patients renal transplantation offers longer life expectancy and better quality of life in comparison with dialysis. Yet, the results of renal transplantation in recipients older than 65years are inferior to those observed in younger adults, death with functioning graft representing a major cause of failure. Therefore, the selection of aged patients is of paramount importance. Apart from the routine clinical and biological investigations, three aspects have been relatively neglected by the transplant community and may require a careful analysis in elderly candidates to transplantation: the presence and degree of frailty, the presence of comorbidities and the adherence to prescriptions. Although there are rapid and simple tests for assessing the degree of frailty in the elderly, there is no clear cut-off value to decide whether a patient should be accepted or not. With advanced age the prevalence and severity of cardiovascular events and other diseases tend to increase. The use of combined age-comorbidity indices may be helpful to identify patients at high risk of mortality. Another critical point is the poor unintentional adherence to treatment, often caused by forgetfulness and mild cognitive impairment. These drawbacks may be further enhanced by a high number of pills to take and by changes in the dosage or type of prescriptions. A careful screening of the presence and degree of frailty, comorbidity and poor compliance to treatment is highly recommended before admitting older candidates to the waiting list for transplantation.

The dialysis scenario in patients with systemic lupus erythematosus.

Although prognosis of lupus nephritis has improved over time, a substantial amount of lupus patients still reach end-stage renal disease and require dialysis. Treatment of these patients can be challenging, since the disease poses a number of problems that can portend a poor prognosis, such as infections, lupus reactivations, vascular access thrombosis and cardiovascular complications. Consensus is lacking among investigators about the real incidence of these complications and related diagnosis and treatment. Moreover, the choice of the type of dialysis treatment and the overall prognosis are still a matter of debate. In this paper, we have reviewed the currently available literature in an attempt to answer the most controversial issues about the topic.

The humoral pattern recognition molecule PTX3 is a key component of innate immunity against urinary tract infection.

Immunity in the urinary tract has distinct and poorly understood pathophysiological characteristics and urinary tract infections (UTIs) are important causes of morbidity and mortality. We investigated the role of the soluble pattern recognition molecule pentraxin 3 (PTX3), a key component of the humoral arm of innate immunity, in UTIs. PTX3-deficient mice showed defective control of UTIs and exacerbated inflammation. Expression of PTX3 was induced in uroepithelial cells by uropathogenic Escherichia coli (UPEC) in a Toll-like receptor 4 (TLR4)- and MyD88-dependent manner. PTX3 enhanced UPEC phagocytosis and phagosome maturation by neutrophils. PTX3 was detected in urine of UTI patients and amounts correlated with disease severity. In cohorts of UTI-prone patients, PTX3 gene polymorphisms correlated with susceptibility to acute pyelonephritis and cystitis. These results suggest that PTX3 is an essential component of innate resistance against UTIs. Thus, the cellular and humoral arms of innate immunity exert complementary functions in mediating resistance against UTIs.

Renal dysfunction in acute congestive heart failure: a common problem for cardiologists and nephrologists.

The term acute heart failure (AHF) refers to a clinical syndrome with typical symptoms and signs, in which a structural or functional heart abnormality leads to defective oxygen delivery. The term cardiorenal syndrome has been proposed to outline the strict interplay between cardiac and renal function. In the setting of acute cardiac decompensation, acute kidney injury (AKI) is generally referred to as cardiorenal syndrome type 1. In this review, we summarize the fundamental pathophysiological aspects of both AHF and AHF-related AKI. We also review the latest therapeutic options, including both pharmacological ones, such as loop diuretics, potassium-sparing diuretics and vaptans, and non-pharmacological ones, such as ultrafiltration, and their impact on patients' outcome. We discuss the pathophysiology of diuretic resistance, a common occurrence in these patients, reviewing the available strategies to treat it and highlighting how a close collaboration between cardiologists and nephrologists is frequently crucial for the management of this complication. Finally, we discuss three new promising non-pharmacological tools for the prevention of AHF recurrence, including two methods that exploit sympathetic denervation and one technique that acts by increasing vagal tone.

Improvement of Erdheim-Chester disease-related renal failure after treatment with anakinra.

Erdheim-Chester disease (ECD) is a rare non-Langerhans cell histiocytosis characterized by infiltrates of lipid-laden CD68(+)/CD1a(-) histiocytes, affecting heart, lungs, central nervous system, and bones. Kidney and adjacent structures can also be affected, leading to renal failure in about 30% of cases. The diagnosis is challenging, and treatment is generally based on administration of interferon-alpha (IFNα), but preliminary results also showed the therapeutic efficacy of anakinra, an antagonist of the receptor of interleukin-1 (IL-1). We report the case of an elderly patient with ECD and severe involvement of the heart and kidneys who was successfully treated with anakinra.

Erdheim-Chester disease: from palliative care to targeted treatment.

Erdheim-Chester disease (ECD) is a life-threatening multi-systemic non-Langerhans histiocytosis with cardiovascular complications as the leading cause of death. ECD affects the kidneys in up to 30% of cases, with fibrotic tissue deposition in the perirenal fat and renal hilum. Diagnosis is usually based on histological analysis of the pathologic tissue, which typically shows xanthogranulomatous infiltrates of foamy CD68+/CD1a- histiocytes surrounded by fibrosis. A consistent percentage of patients affected by ECD develop renal failure and hypertension as a consequence of renal artery stenosis and hydronephrosis. These conditions have been generally treated with the placement of stents and nephrostomies that frequently led to disappointing outcomes. Before the introduction of interferon-alpha (IFNα) treatment, the mortality rate was as high as 57% in the long term. Recent studies have granted new insights into the pathogenesis of ECD, which seems to bear a dual component of clonal and inflammatory disease. These advances led to use specific therapies targeting either the oncogenes (BRAF(V600E)) or the effectors of the immune response implicated in ECD (IL-1, TNFα). Drugs such as anakinra (recombinant human IL-1 receptor antagonist), infliximab (monoclonal antibody against TNFα) and vemurafenib (inhibitor of mutant BRAF) showed promising results in small single-centre series. Although larger trials will be needed to address the impact of these drugs on ECD prognosis and to select the most effective treatment, targeted therapies hold the premises to drastically change the outcome of this condition.

Current and emerging treatments for idiopathic focal and segmental glomerulosclerosis in adults.

Idiopathic focal and segmental glomerular sclerosis is a frequent cause of nephrotic syndrome and end-stage renal disease. The pathogenesis is still unknown, although the body of evidence suggests that focal and segmental glomerular sclerosis is caused by a not clearly identified circulating factor that alters the permselectivity of the glomerular barrier. Proteinuria is followed by podocyte injury. Glucocorticoids, calcineurin inhibitors, cytotoxic agents and mycophenolate mofetil, either given alone or in combination, may obtain complete or partial remission of proteinuria in 50-60% of patients and protect them from end-stage renal disease, but the remaining patients are resistant to the available drugs. A number of new drugs, including rituximab, galactose and antifibrotic agents, are under investigation.

Education and counseling of renal transplant recipients.

A large number of factors can influence the clinical outcome of kidney transplant recipients, but the active role of the patient to prevent the possible complications related to transplant and its treatment is often neglected. Poor adherence to prescriptions is frequent in transplant recipients and represents a major contributor to the development of graft failure, cardiovascular disease, infection and/or malignancy. Smoking can render the patient more susceptible to cancer, cardiovascular disease and infection, and can also impair renal allograft function. The risk of malignancy is increased in transplant recipients. Therefore screening for cancer is of paramount importance. Measures that can enable prevention or early detection of cancer include self-exams and screening, physical activity, avoidance of smoking and sun exposure, and a diet rich in fruits and vegetables but limited in fats, red meats, salt and alcohol. Regular exercise can help to prevent cardiovascular disease, diabetes, obesity, osteoporosis and even some forms of cancer. Thus regular exercise is recommended. Yet, too many transplant patients remain sedentary. Weight gain is common in renal allograft recipients and may be associated with hypertension, hyperlipidemia and/or glucose intolerance or overt diabetes. To prevent these complications, patients should follow diet regimens based on low fat and normal/low caloric intake. Small amounts of alcohol may be permitted in view of its potential cardioprotective effect, but a large consumption of alcohol can be responsible for devastating side effects. Last but not least, abidance by hygienic measures may help in preventing cardiovascular and infectious complications.

Proteinuria after kidney transplantation.

The prevalence of proteinuria at 1 year after renal transplantation ranges between 11% and 45% and is even higher in patients treated with inhibitors of the mammalian target of rapamycin (mTOR). Two main mechanisms can lead to proteinuria: an inadequate reabsorption of small proteins from proximal tubular cells damaged by ischemia-reperfusion injury, rejection, or toxic agents (tubular proteinuria) or an increased passage of albumin and/or protein with higher molecular weight (MW) because of a disruption of glomerular barrier caused by recurrent or de novo glomerulonephritis, transplant glomerulopathy, chronic rejection, or CNI toxicity (glomerular proteinuria). Proteinuric patients have worse patient and graft survival rates in comparison to non proteinuric patients. The amount of proteinuria is a reliable predictor of the allograft outcome. However, even microalbuminuria may be associated with a poor outcome. Treatment of proteinuria mainly rests on the management of the etiologic cause. Inhibitors of renin-angiotensin system (RAS) are useful in reversing microalbuminuria and can reduce proteinuria, but their efficacy in interfering with patient or graft survival is not demonstrated.

Syndrome of inappropriate secretion of antidiuretic hormone in traumatic brain injury: when tolvaptan becomes a life saving drug.

OBJECTIVE: To outline the role of a new drug, tolvaptan, in treating severe and chronic hyponatraemia. Tolvaptan decreases aquaporin expression in renal collecting ducts, by inhibiting antidiuretic hormone (ADH)-V2 receptors, to promote free water clearance. Given its mechanism of action, this drug seems the ideal treatment for the syndrome of inappropriate antidiuretic hormone secretion (SIADH) when the osmotic imbalance leads to life threatening complications. DATA SOURCES: A case is described of severe hyponatraemia deriving from SIADH secondary to meningoencephalitis in a patient admitted to hospital for traumatic brain injury. DATA EXTRACTION: Clinical, laboratory and radiological data at presentation and for a 1 year of follow-up were analysed. DATA SYNTHESIS: Tolvaptan ameliorated hyponatraemia, brain oedema and consciousness, and drug withdrawal led to recurrence of hyponatraemia and coma. CONCLUSIONS: In patients with SIADH, which is not self-limited, and is associated with severe cognitive impairment, the use Tolvaptan may prove life saving and should be rigorously evaluated.

Plasma pentraxin-3 as a marker of bioincompatibility in hemodialysis patients.

INTRODUCTION: Hemodialysis (HD)-induced inflammation has a pathogenetic role in patients with end-stage renal disease (ESRD). The aim of the present study was to assess whether pentraxin-3 (PTX3) could be a reliable biomarker of HD-induced inflammation and of membrane biocompatibility. METHODS: We prospectively enrolled 31 HD patients. Blood samples for determining PTX3, C-reactive protein (CRP), leukocytes and neutrophils were drawn from the arterial needle, before dialysis after the long dialysis-free interval (time 0), at the end of the index session (time 1) and before the next dialysis session (time 2). In 22 of 31 patients, 30 minutes after start of dialysis, PTX3 and CRP plasma levels were measured in blood collected from both the arterial and venous lines (time A - time V) of the dialyzer. In 7 of 22 patients intracellular PTX3 levels in neutrophils were measured at the end of session. RESULTS: PTX3 venous levels were significantly increased at the end of the index session compared with baseline and in blood samples drawn from the venous line compared with the arterial line of the dialyzer. At time 1, a reduction of intracellular PTX3 in neutrophils was noticed. In contrast, CRP plasma levels were stable during the HD session. CONCLUSIONS: Our findings suggest that PTX3, which is rapidly produced by several cell types and released by neutrophils upon stimulation, could be a biomarker of HD-induced inflammation and of blood-membrane bioincompatibility.