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This paper aims at reviewing linear and nonlinear approaches to study the stability of fluid flows. We provide a concise but self-contained exposition of the main concepts and specific numerical methods designed for global stability studies, including the classical linear stability analysis, the adjoint-based sensitivity, and the most recent nonlinear developments. Regarding numerical implementation, a number of ideas making resolution particularly efficient are discussed, including mesh adaptation, simple shift-invert strategy instead of the classical Arnoldi algorithm, and a simplification of the recent nonlinear self-consistent (SC) approach proposed by Mantič-Lugo et al. (2014, “Self-Consistent Mean Flow Description of the Nonlinear Saturation of the Vortex Shedding in the Cylinder Wake,” Phys. Rev. Lett., 113(8), p. 084501). An open-source software implementing all the concepts discussed in this paper is provided. The software is demonstrated for the reference case of the two-dimensional (2D) flow around a circular cylinder, in both incompressible and compressible cases, but is easily customizable to a variety of other flow configurations or flow equations.

Losartan, an angiotensin II type 1 receptor antagonist, reduces blood pressure values by counteracting the angiotensin II actions at many levels, among them autonomic nervous system could be involved; so, we have evaluated the effects of this drug on sympatho-vagal balance of 7 hypertensive subjects, aged 52.1 ± 11.98 yrs, never treated with dietary renstrinction or drug administration, without signs of left ventricular hypertrophy at Doppler echocardiographic evaluation. All patients were studied, by a 24-hour blood pressure (BP) monitoring, a 24-hour ambulatory ECG monitoring (AEM) and an evaluation of autonomic nervous system by cardiovascular test (CT), carried out according to the Ewings protocol followed by an autoregressive analysis of heart rate variability (HRV), with measurement of low frequency (LF) and high frequency (HF) power in spectral components. All patients were observed before treatment and after 3 month of Losartan administration, at a dosage of 50 mg a day. In all cases, Losartan administration was associated with a significant decrease of 24-hour systolic BP values (142.0 ± 11.27 vs 131.86 ± 9.9 mm Hg, p < 0.05), 24-hour diastolic BP (89.19 ± 7.36 vs 83.5 ± 7.16 mm Hg, p < 0.05), 24-hour systolic BP load (61.14% ± 26.45 vs 28.14% ± 25.77, p < 0.05) and 24-hour diastolic BP load (57.0% ± 26.65 vs 31.86% ± 22.31, p < 0.05). Not significant differences of mean 24-hour heart rate were observed (73.57 bpm ± 11.34 vs 71.14 bpm ± 8.57, p = ns); HRV analysis, clinostatic LF power showed a not significant decrease after treatment (48.01 ± 16.94 vs 58.77 ± 26.33 nu, p = ns) with a not significant increase of clinostatic HF power (31.99 ± 24.45 vs 41.23 ± 13.66 nu, p = ns); moreover, at cardiovascular tests, we found a significantly lower values of systolic BP increase at the sustained handgrip (192.71 ± 21.31 vs 164.14 ± 24.67 mm Hg, p < 0.005). These findings suggest that Losartan may display an hypotensive effect associated to a low sympatholithic action, that need to be confirmed by a broader long-term observed population; this observation, if confirmed, could justify recent observations concerning a cardiovascular protective effects of this kind of drugs.

The endothelial function (EF), as evaluated by maximum vasodilation induced by acethylcoline during plethysmography, seems to be weakly related to office blood pressure but much more with ambulator blood pressure monitoring (ABPM) values in the hypertensive patient. In the present study we examined the relationship between EF, assessed with non-invasive echo-Doppler, and to daytime and nighttime blood pressure load (BPL). We studied 13 untreated hypertensive subjects (BP = 140/90 mm Hg) and 21 normotensive subjects (BP = 140/90 mm Hg) matched for age (mean 42.0 ± 7.0 years vs 45.0 ± 9.4 years, p = ns). All subjects were non smokers, non dislipidemic. BP was evaluated both with sphygmomanometry and by ABPM, (Spacelabs 90207). EF was evaluated measuring internal diameter and arterial flow in basal conditions. during reactive hyperemia and after sublingual nitrate administration of the brachial artery with an echo-Doppler and a 7.5 MHz probe. We found a reduced increase of internal diameter of the brachial artery during reactive hyperemia (?%RH) in hypertensive subjects compared to normotensive subjects (6.6 ± 5.8% vs 11.9 ± 5.3% respectively: p = <0.05). The ?%RH was related to office diastolic (D) BP values (r = -0.379. p < 0.05) but not to office s stolic (S) BP values (r = -0.288; p = ns) in both groups. An inverse correlation was found in all subjects comparing ?%RH to 24-h SBP values (r = -0.561; p < 0.001), 24-h DBP values (r = -0.451; p < 0.005), daytime SBPL (r = -0.501; p < 0.001), daytime DBPL (r = -0.406; p < 0.01), nighttime SBPL (r = -0.398; p < 0.01) and nighttime DBPL (r = -0.391; p < 0.01). The finding that an abnormally high BPL is constantly associated to a reduced ?%RH, suggest that the endothelial damage is a consequence and not a cause of hypertension.