Autoregulation of human retinal blood flow. An investigation with laser Doppler velocimetry

The effect of acute changes in mean retinal perfusion pressure, P (2/3 of mean brachial artery blood pressure minus IOP), on retinal volumetric blood flow rate, Q, was investigated in normal volunteers. Changes in Q were determined from Q = k X Vmax X D2, where Vmax is the center line red blood cell velocity measured from temporal veins by laser Doppler velocimetry, D is the vessel diameter obtained by monochromatic fundus photography, and k is a constant of proportionality. A suction cup was used to induce step changes in IOP and, consequently, in P. The magnitude of the steps ranged from 10-32 mmHg. During the first 30 sec after a step decrease in P, Vmax and Q were significantly smaller than at rest by an amount proportional to the decrease in P. Thereafter, Vmax and Q increased markedly towards their values at rest, although P changed comparatively little during this period of time. Time constant of the corresponding decrease in vascular resistance, R(t) = P(t)/Q(t), was approximately 45 sec. There was no significant change in D during elevated IOP. Removal of the cup induced an immediate step increase in P, Vmax, D, Q, and R. Thereafter, Vmax, D, Q, and R returned to their values at rest (time constant of the change in R was about 30 sec), while P remained nearly constant. The rapid change in vascular resistance following a step decrease and increase in P can be attributed to an active process that attempts to maintain blood flow close to normal, in spite of changes in perfusion pressure (autoregulation).(ABSTRACT TRUNCATED AT 250 WORDS)     

Laser Doppler velocimetry in retinal arteries of infants

The present study was conducted to assess the feasibility of laser Doppler velocimetry in young infants, as a prelude to ultimately undertaking such measurements in premature infants. A portable, unidirectional laser Doppler velocimeter was developed based on a Kowa RC-2 hand-held fundus camera. Six infants between 1 and 21 weeks of age were studied. Relative red blood cell velocity (f_max) at the centre of retinal arteries was measured over approximately 10 heart cycles. A pulsatility parameter (P=1–f_max.dia/f_max.sys), a summary index of vascular status, was determined from the average diastolic and systolic values of f_max. Velocity waveforms were obtained in four of the six infants. Arterial pulsatility for the group was 0.63±0.13. Precise non-invasive measurement of arterial red blood cell velocity waveforms in young infants was achieved. The high signal-to-noise ratio and temporal resolution of this data suggest that relative measurements of retinal blood flow may permit assessment of haemodynamic changes in premature infants.     

Effect of panretinal photocoagulation on retinal blood flow in proliferative diabetic retinopathy

The effect of panretinal photocoagulation (PRP) on retinal volumetric blood flow rate and its regulatory response to hyperoxia was investigated in a main temporal vein of 15 eyes with proliferative diabetic retinopathy, using bi-directional laser Doppler velocimetry and monochromatic fundus photography. At an average of 4 +/- 2 months after the beginning of PRP, retinal venous diameter decreased from an average of 174 +/- 20 micron to 162 +/- 19 micron (P less than 0.01), red blood cell velocity decreased from 1.3 +/- 0.4 cm/sec to 1.1 +/- 0.4 cm/sec (P less than 0.01), and blood flow decreased from 11.5 +/- 3.8 microliter/min to 8.4 +/- 3.3 microliter/min (P less than 0.001). The regulatory response to hyperoxia, characterized by the percentage decrease in retinal blood flow during 100% oxygen breathing, improved from 20 +/- 15% prior to treatment to 45 +/- 12% following treatment (P less than 0.001). The decrease in retinal blood flow is most likely due to a decrease in viable retinal tissue and an improvement in retinal oxygenation following PRP. The increase in the regulatory response to 100% O2 breathing following PRP may also result from such an improved retinal oxygenation.     

Postbiopsy renal transplant arteriovenous fistulas: color Doppler US characteristics

Color Doppler ultrasound (US) with point-spectral analysis was performed on eight patients with postbiopsy renal transplant arteriovenous fistulas. Waveform analysis of the supplying artery documented decreased resistive indices in all cases and increased flow velocities in seven. The peak-systolic flow velocity in the arteries supplying the fistulas ranged from 55 to 180 cm/sec (mean, 92 cm/sec), while the range in normal arteries was 20-52 cm/sec (mean, 32 cm/sec). The resistive indices of the arteries supplying the fistulas ranged from 0.31 to 0.50 (mean, 0.45), while the resistive indices of the normal arteries ranged from 0.60 to 0.92 (mean, 0.74). Arterialization of the venous waveform from the draining vein was also documented in all cases. In six cases, the increased flow velocities resulted in increased color saturation toward white in the supplying artery (n = 2) or in both the artery and the draining vein (n = 4), which was detectable on the realtime image. In six cases, flow turbulence resulted in localized tissue vibration, which appeared as random color assignment in extravascular renal parenchyma adjacent to the fistula. Knowledge of these imaging and Doppler characteristics should aid in the identification of renal transplant arteriovenous fistulas with color Doppler US.     

Chronic pancreatitis: ultrasonic features

A retrospective analysis of 84 ultrasound examinations (in 77 patients) was performed to assess the frequency of sonographic findings in chronic pancreatitis. The findings included: inhomogeneously increased echogenicity in 53% of these examinations, focal or diffuse enlargement in 41%, focal dense echoes in 40%, pseudocyst formation in 21%, and a hypoechoic head mass in 7%. Thirteen per cent of our patients had a normal sonogram. Several presentations of chronic pancreatitis not previously described in the sonographic literature included: pancreatic or common bile duct enlargement or pseudocyst formation with otherwise normal-appearing glands. There was no direct relationship between the presence of focal high-intensity echoes within the pancreatic parenchyma and the presence of radiographic calcification. There was no difference in the frequency of ultrasonic abnormalities between patients with and without clinical evidence of pancreatic insufficiency. These results indicate that the sonographic findings in chronic pancreatitis are significantly more varied than previous reports would indicate.     

糖尿病大鼠骨代谢变化与立普妥、胰岛素的干预效应

目的:近年细胞培养实验发现他汀类药物可以促进骨形成,采用动物实验观察胰岛素和他汀类药物立普妥对糖尿病大鼠骨代谢的影响,为糖尿病伴骨质疏松的治疗提供实验依据。方法:实验于2005-08/2006-01在大连医科大学病理教研室完成。①实验分组:SD雄性大鼠55只,随机选择10只为空白对照组,余45只经鼠尾静脉注射链尿佐菌素造成糖尿病大鼠模型。其中40只符合造模标准,随机分为糖尿病未治疗组、胰岛素治疗组、立普妥治疗组及胰岛素 立普妥治疗组,每组10只。②实验方法:所有大鼠皆给予相同普通饮食。胰岛素治疗组及胰岛素 立普妥治疗组于实验第4天接受中效胰岛素治疗,6～8U/d分两次颈背部皮下注射。胰岛素剂量按每只鼠每周血糖进行调整。立普妥治疗组及胰岛素 立普妥治疗组于实验第4天给予立普妥1.25mg/kg灌胃。糖尿病未治疗组和空白对照组给予等量生理盐水灌胃。③实验评估:9周末用乙醚麻醉,每组取4只大鼠去眼球取血之后处死。14周末应用同样方法处死剩余大鼠。均取腰椎骨,常规脱钙石蜡包埋,行苏木精-伊红染色。骨组织形态计量学测量平均骨小梁厚度和平均骨小梁间距或弥散度。血中Ⅰ型胶原氨基端肽测定采用竞争性放射免疫检测方法(碘标记)。结果:实验期间大鼠死亡5只,其中糖尿病未治疗组1只于第3周死亡,胰岛素组2只于第6周死亡,胰岛素 立普妥治疗组2只于第7周死亡。①骨组织病理形态学变化:9周末立普妥治疗组、胰岛素 立普妥治疗组及糖尿病未治疗组光镜下见骨质疏松表现。14周末立普妥治疗组及胰岛素治疗组骨组织微观结构恢复至空白对照组水平。②平均骨小梁厚度:9周末:糖尿病未治疗组、胰岛素治疗组、立普妥治疗组及胰岛素 立普妥治疗组均明显低于空白对照组(P<0.01)。14周末:糖尿病未治疗组及胰岛素 立普妥治疗组均明显低于空白对照组(P<0.05)。③平均骨小梁间距或弥散度:9周末:糖尿病未治疗组及胰岛素 立普妥治疗组均明显高于空白对照组(P<0.05)。14周末:糖尿病未治疗组及胰岛素 立普妥治疗组均明显高于空白对照组(P<0.05)。④Ⅰ型胶原氨基端肽水平:9周末:立普妥治疗组和胰岛素 立普妥治疗组均明显高于空白对照组(P<0.01)。14周末:胰岛素治疗组、立普妥治疗组和胰岛素 立普妥治疗组均明显高于空白对照组(P<0.01)。结论:①糖尿病大鼠造模9周出现明显的骨质疏松。②糖尿病大鼠骨质变化表现为骨吸收超过骨形成作用,主要以骨吸收增强为主。③立普妥及胰岛素可以促进糖尿病大鼠骨质的形成,抑制糖尿病大鼠骨质疏松的发生发展。