Kuniyuki Takai

Fluctuating fluid forces acting on two circular cylinders in a tandem arrangement at a subcritical Reynolds number

Aerodynamic characteristics of two circular cylinders in a tandem arrangement were investigated experimentally in a uniform flow at a Reynolds number of 6.5 × 10 4 . This Reynolds number is within the range in which fluid forces acting on a single cylinder are comparatively insensitive to change in the Reynolds number. Mutual interference between the two cylinders at close proximity, however, caused significant change in parameters of the aerodynamic characteristics, such as fluctuating lift and drag forces, time-averaged and fluctuating pressure distributions, Strouhal number, and vortex-shedding patterns, when the spacing between the cylinders was changed. The changes in these aerodynamic characteristics were systematically analyzed in this study.

Effects of milrinone on systemic capacitance vessels in relation to venous return and right ventricular pump function

To investigate the effect of milrinone (MIL) on systemic capacitance vessels, we measured the mean circulatory filling pressure (MCP) in anesthetized open chest dogs. We measured hemodynamic parameters (a) at baseline blood volume (BV), (b) immediately after bloodletting (5 ml/kg), and (c) immediately after dextran injection (5 ml/kg). These measurements were taken in a control group (n = 8) and in a MIL group (n = 8), where MIL (100 + 2.5 micrograms/kg/min) was administered i.v. The extra volume (EV) was obtained by extrapolating the straight line that was fit to the MCP-BV plot. MIL significantly decreased the EV, from 22.8 +/- 1.0 to 19.1 +/- 0.4 ml/kg, indicating that MIL dilates the systemic capacitance vessels. MIL shifted the right ventricular output curve to the left and upward and shifted the venous return curve to the left and rotated it clockwise. Thus, venous return was increased by decreasing the resistance to venous return and by improving right ventricular pump function. Next we evaluated the effects of MIL (100 micrograms/kg) on systemic capacitance and resistance vessels from changes seen in the MCP and the total peripheral resistance (TPR), respectively. In the untreated dogs, MIL decreased TPR significantly without affecting MCP. In dogs pretreated with total spinal anesthesia or phenoxybenzamine, MIL significantly decreased both MCP and TPR. This suggests that the intrinsic venodilator action of MIL is modified by the baroreflex in untreated animals. MIL decreased the MCP and TPR elevated previously by norepinephrine. One would, therefore, predict that MIL would dilate the systemic capacitance vessels in patients with congestive heart failure.

Comparative effect of candesartan and amlodipine, and effect of switching from valsartan, losartan, telmisartan and olmesartan to candesartan, on early morning hypertension and heart rate

Abstract Early morning hypertension and a high heart rate are risk factors for cardiovascular disease. The DOHSAM study was designed to evaluate the effect of candesartan on early morning blood pressure (BP) and heart rate in hypertensives. We used a prospective, randomized, open-label design. Protocol 1: Patients with early morning BP more than 135/85 mmHg who were not on any antihypertensive drug or on candesartan were given amlodipine 2.5 mg/day (amlodipine group, n = 22) or added candesartan 4 mg/day (candesartan group, n = 36). Candesartan or amlodipine was added when BP did not fall lower than 135/85 mmHg. Protocol 2: Early morning hypertensives who were on other angiotensin receptor blockers (ARBs) (n = 50) such as valsartan, losartan, telmisartan and olmesartan were switched to candesartan. Early morning BP significantly decreased in the candesartan group compared with the amlodipine group 9 and 12 months after treatment. Switching other ARBs except for olmesartan to candesartan significantly decreased early morning systolic and diastolic BP 3, 6, 9 and 12 months after treatment. Heart rate in the office significantly decreased by switching to candesartan 6, 9 and 12 months after treatment. In conclusion, candesartan significantly decreased early morning hypertension more than amlodipine or other ARBs except olmesartan in early morning hypertensives.

Baroreflex Modifies the Effect of Vasodilators on Systemic Capacitance Vessel in Dogs

We examined whether the vasodilating effect of vasodilators on systemic capacitance vessels is modified by the baroreflex when a fall in arterial blood pressure was induced by the vasodilators in dogs. We estimated the dilation of the systemic capacitance vessels from the fall in mean circulatory pressure (MCP), proposed by Guyton et al. and the dilation of the systemic capacitance vessels from the fall in the total peripheral resistance (TPR). The dose-response curve for percent change in TPR to graded doses of nitroglycerin (NG, 0.8–200 µg/kg) in the untreated group was not different from that in the total spinal anesthesia (TSA) group in which the baroreflex was eliminated. The TSA group gave a dose-response curve for percent change in MCP to NG on the low dose side of NG as compared with the untreated group. NG increased both plasma levels of nor-epinephrine (NA) and epinephrine (A) in the untreated group. However, NG hardly affected plasma levels of NA or A in the TSA group. Milrinone significantly decreased the TPR and there was no significant difference in the percent change in TPR between the untreated and TSA groups. Milrinone did not change the MCP in the untreated group, but decreased it in both TSA group and the group pretreated with α-blocker, suggesting that baroreflex-mediated vasoconstriction is mediated through α-adrenoceptors in the capacitance vessels. Milrinone also increased plasma levels of NA and A in the untreated group but not in the TSA group.

Nicardipine inhibits the endothelin-1-induced constriction of systemic capacitance and resistance vessels

We estimated the effects of intravenous injection of endothelin-1 (ET-1; 400 pmol/kg) on the systemic capacitance and resistance vessels in anesthetized mongrel dogs by measuring changes in the mean circulatory pressure (MCP) and total peripheral resistance (TPR), respectively. In addition, the present study investigated the inhibiting action of nicardipine (NIC; 10 micrograms/kg bolus injection followed by 1.0-2.0 micrograms/kg/min continuous infusion) against the vasoconstrictor action of ET-1. We examined the effects of ET-1 (30 to 1,000 pmol/0.1 ml) on the femoral arterial system by measuring the percent changes in the perfusion pressure (% delta PP) of the femoral artery perfused with a constant flow, and investigated the effect of NIC on the vasoconstrictor action of ET-1 in this preparation. We obtained the following results: (a) Intravenous injection of ET-1 raised both TPR and MCP. However, in the presence of NIC, ET-1 raised TPR without influencing MCP. (b) Intra-arterial injection of ET-1 caused a dose-dependent increase in % delta PP. NIC shifted the dose-response curve of ET-1 for % delta PP to the right in a parallel fashion.