Renovascular reactivity measured by near-infrared spectroscopy

Hypotension and shock are risk factors for death, renal insufficiency, and stroke in preterm neonates. Goal-directed neonatal hemodynamic management lacks end-organ monitoring strategies to assess the adequacy of perfusion. Our aim is to develop a clinically viable, continuous metric of renovascular reactivity to gauge renal perfusion during shock. We present the renovascular reactivity index (RVx), which quantifies passivity of renal blood volume to spontaneous changes in arterial blood pressure. We tested the ability of the RVx to detect reductions in renal blood flow. Hemorrhagic shock was induced in 10 piglets. The RVx was monitored as a correlation between slow waves of arterial blood pressure and relative total hemoglobin (rTHb) obtained with reflectance near-infrared spectroscopy (NIRS) over the kidney. The RVx was compared with laser-Doppler measurements of red blood cell flux, and renal laser-Doppler measurements were compared with cerebral laser-Doppler measurements. Renal blood flow decreased to 75%, 50%, and 25% of baseline at perfusion pressures of 60, 45, and 40 mmHg, respectively, whereas in the brain these decrements occurred at pressures of 30, 25, and 15 mmHg, respectively. The RVx compared favorably to the renal laser-Doppler data. Areas under the receiver operator characteristic curves using renal blood flow thresholds of 50% and 25% of baseline were 0.85 (95% CI, 0.83-0.87) and 0.90 (95% CI, 0.88-0.92). Renovascular autoregulation can be monitored and is impaired in advance of cerebrovascular autoregulation during hemorrhagic shock.     

Evaluation of laser-Doppler flowmetry as a measure of tissue blood flow

In this study the technique of laser-Doppler flowmetry was evaluated for the measurement of tissue blood flow by comparing laser-Doppler flow (LDF) signal in the renal cortex, gracilis muscle, and cremaster muscle of anesthetized rats to whole-organ blood flow measured with an electromagnetic flowmeter or radioactive microspheres. In vitro, LDF signal was closely correlated (r = 0.99) to changes in erythrocyte velocity generated with a rotating wheel. Although individual LDF readings varied in situ, mean LDF signal calculated from multiple readings on the tissue surface were significantly correlated (r = 0.74-0.95) with tissue blood flows measured at various perfusion pressures. However, significant differences in the slope of the LDF signal vs. blood flow relationship were observed in different tissues and with different methods of measurement in the same tissue. This study indicates that mean laser-Doppler flow signal provides a good estimate of tissue blood flow, provided a sufficient number of points is scanned. However, there appears to be no universal calibration factor for the method.     

Renal tissue NO and intrarenal haemodynamics during experimental variations of NO content in anaesthetised rats.

Direct renal nitric oxide (NO) measurements were infrequent and no simultaneous measurements of renal cortical and medullary NO and local perfusion. Large-surface NO electrodes were placed in renal cortex and medulla of anaesthetised rats; simultaneously, renal blood flow (RBF, index of cortical perfusion) and medullary laser-Doppler flux (MBF) were determined. NO synthase inhibitors: nonselective (L-NAME) or selective for neuronal NOS (nNOS) (S-methyl-thiocitrulline, SMTC), and NO donor (SNAP), were used to manipulate tissue NO. Baseline tissue NO was significantly higher in medulla (703+/-49 NM) than in cortex (231+/-17 nM). Minimal cortical and medullary NO current measured after maximal L-NAME dose (2.4 mg kg(-1) i.v.) was taken as tissue NO zero kevel. This dose decreased RBF and MBF significantly (-43%). SMTC, 1.2 mg kg(-1) h(-1) i.v., significantly decreased tissue NO by 105+/-32 nM in cortex and 546+/-64 nM in medulla, RBF and MBF decreased 30% and 20%, respectively. Renal artery infusion of SNAP, 0.24 mg kg(-1) min(-1) significantly increased tissue NO by 139+/-18 nM in cortex and 948+/-110 nM in medulla. Since inhibition of nNOS decreased medullary NO by 80% and MBF by 20% only, this isoform has probably minor role in the maintenance of medullary perfusion.     

Circadian periodicity of cerebral blood flow revealed by laser-Doppler flowmetry in awake rats: relation to blood pressure and activity

Cardiovascular parameters such as arterial blood pressure (ABP) and heart rate display pronounced circadian variation. The present study was performed to detect whether there is a circadian periodicity in the regulation of cerebral perfusion. Normotensive Sprague-Dawley rats (SDR, approximately 15 wk old) and hypertensive (mREN2)27 transgenic rats (TGR, approximately 12 wk old) were instrumented in the abdominal aorta with a blood pressure sensor coupled to a telemetry system for continuous recording of ABP, heart rate, and locomotor activity. After 5-12 days, a laser-Doppler flow (LDF) probe was attached to the skull by means of a guiding device to measure changes in brain cortical blood flow (CBF). After the animals recovered from anesthesia, measurements were taken for 3-4 days. The time series were analyzed with respect to the midline estimating statistic of rhythm (i.e., mean value of a periodic event after fit to a cosine function), amplitude, and acrophase (i.e., phase angle that corresponds to the peak of a given period) of the 24-h period. The LDF signal displayed a significant circadian rhythm, with the peak occurring at around midnight in SDR and TGR, despite inverse periodicity of ABP in TGR. This finding suggests independence of LDF periodicity from ABP regulation. Furthermore, the acrophase of the LDF was consistently found before the acrophase of the activity. From the present data, it is concluded that there is a circadian periodicity in the regulation of cerebral perfusion that is independent of circadian changes in ABP and probably is also independent of locomotor activity. The presence of a circadian periodicity in CBF may have implications for the occurrence of diurnal alterations in cerebrovascular events in humans.     

Laser-Doppler flowmetry reveals rapid perfusion changes in adipose tissue of lean and obese females

The present study aimed to evaluate adipose tissue blood flow (ATBF) by means of laser-Doppler flowmetry (LDF) in humans. Lower body negative pressure (LBNP) and straining known to affect epidermal blood flow through the autonomic nervous system were performed in 11 lean and 11 obese female volunteers. ATBF changes were compared between both groups and also discriminated from skin blood flow (SBF) responses of the immediate vicinity. Additionally, LDF measurements were compared with flow measurements using (133)xenon washout in 10 lean subjects during whole body cooling. LDF estimations of SBF and ATBF showed a positive correlation to (133)Xe during cooling. SBF and ATBF were reduced to the same extent in both lean and obese subjects during LBNP. Straining induced divergent changes in SBF and ATBF: initially SBF decreased while ATBF increased, but toward the end of straining SBF increased above baseline and ATBF returned down to baseline level. Those changes were similar in both weight groups. Interestingly, only in obese subjects, both LBNP and straining were followed by ATBF augmentation, while SBF levels remained stable. In conclusion, LDF compares with (133)Xe washout in monitoring ATBF during tonic perfusion changes. Its strength, however, lies in the detection of rapid flow alterations within the subcutaneous tissue, allowing the evaluation of reflex responses of the subcutaneous microcirculation. Interestingly, those rapid changes in SBF and ATBF can be both concordant and discordant. With regard to ATBF, vasoconstrictor components of the reflex responses were similar in lean and obese subjects, whereas vasodilatory responses were more pronounced in obese volunteers.     

Adaptation of laser-Doppler flowmetry to measure cerebral blood flow in the fetal sheep.

The purpose of this study was to devise a means to use laser-Doppler flowmetry to measure cerebral perfusion before birth. The method has not been used previously, largely because of intrauterine movement artifacts. To minimize movement artifacts, a probe holder was molded from epoxy putty to the contour of the fetal skull. A curved 18-gauge needle was embedded in the holder. At surgery, the holder, probe, and skull were fixed together with tissue glue. Residual signals were recorded after fetal death and after maternal death 1 h later. These averaged <5% of baseline flow signals, indicating minimal movement artifact. To test the usefulness of the method, cerebral flow responses were measured during moderate fetal hypoxia induced by giving the ewes approximately 10% oxygen in nitrogen to breathe. As fetal arterial PO(2) decreased from 21.1 +/- 0.5 to 10.7 +/- 0.4 Torr during a 30-min period, cerebral perfusion increased progressively to 56 +/- 8% above baseline. Perfusion then returned to baseline levels during a 30-min recovery period. These responses are quantitatively similar to those spot observations that have been recorded earlier using labeled microspheres. We conclude that cerebral perfusion can be successfully measured by using laser-Doppler flowmetry with the unanesthetized, chronically prepared fetal sheep as an experimental model. With this method, relative changes of perfusion from a small volume of the ovine fetal brain can be measured on a continuous basis, and movement artifacts can be reduced to 5% of measured flow values.     

Delayed distribution of active vasodilation and altered vascular conductance in aged skin.

Reflex vasodilation is attenuated in aged skin during hyperthermia. We used laser-Doppler imaging (LDI) to test the hypothesis that the magnitude of conductance and the spatial distribution of vasodilation are altered with aging. LDI of forearm skin was compared in 12 young (19- to 29-yr-old) and 12 older (64- to 75-yr-old) men during supine passive heating. Additionally, iontophoresis of bretylium tosylate was performed in a subset of subjects to explore the involvement of sympathetic vasoconstriction in limiting skin blood flow. Passive heating with water-perfused suits clamped mean skin temperature at 41.0 +/- 0.5 degrees C, causing a ramp increase in esophageal temperature (T(es)) to 相似文献   

Use of a modified oxygen microelectrode and laser-Doppler flowmetry to monitor changes in oxygen tension and microcirculation in a flap

Flap failure is a clinical problem in free tissue transfer, and there is no reliable device for monitoring the tissue. Differentiating between an arterial occlusion and venous congestion is also a problem. A study was undertaken to monitor viability in a pedicled groin flap and to compare two different monitoring methods. The oxygen tension in the flap, measured with a modified Clark-type microelectrode (tip diameter = 3 to 8 microm; 90 percent response within 2.6 +/- 0.5 seconds), was compared with changes in blood flow in the flap, measured with a laser-Doppler probe. In 11 Sprague-Dawley rats, the changes in oxygen tension and blood flow in the pedicled groin flap were studied after clamping and subsequent reperfusion of the artery or vein. After occlusion of the artery to the flap, oxygen tension decreased to a stable value (i.e., the recording level remained unchanged for 30 seconds), from 19.7 +/- 1.8 to 0.3 +/- 0.1 mmHg, after 193 +/-25 seconds; blood flow decreased to a stable value, from 117 +/- 21 to 54 +/- 18 perfusion units, after 26 +/- 6 seconds. Clamping of the vein resulted in a decrease in oxygen tension, from 17.1 +/- 1.8 to 1.4 +/- 0.7 mmHg, after 416 +/- 67 seconds, and blood flow decreased to a stable value, from 90 +/- 14 to 35 +/- 6 perfusion units, after 107 +/- 27 seconds. The results of this study show that there is a difference in oxygen tension and blood flow responses between arterial and venous occlusion and that it may be possible with both methods to distinguish arterial from venous occlusion. However, although oxygen tension measurements are slightly slower in response than laser-Doppler measurements, the values are more reliable as a diagnostic tool for interpretation of a vessel occlusion.     

Suppression of cortical functional hyperemia to vibrissal stimulation in the rat by epoxygenase inhibitors

Application of glutamate to glial cell cultures stimulates the formation and release of epoxyeicosatrienoic acids (EETs) from arachidonic acid by cytochome P-450 epoxygenases. Epoxygenase inhibitors reduce the cerebral vasodilator response to glutamate and N-methyl-D-aspartate. We tested the hypothesis that epoxygenase inhibitors reduce the somatosensory cortical blood flow response to whisker activation. In chloralose-anesthetized rats, percent changes in cortical perfusion over whisker barrel cortex were measured by laser-Doppler flowmetry during whisker stimulation. Two pharmacologically distinct inhibitors were superfused subdurally: 1) N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide (MS-PPOH), an epoxygenase substrate inhibitor; and 2) miconazole, a reversible cytochrome P-450 inhibitor acting on the heme moiety. Superfusion with 5 micromol/l MS-PPOH decreased the hyperemic response to whisker stimulation by 28% (from 25 +/- 9 to 18 +/- 7%, means +/- SD, n = 8). With 20 micromol/l MS-PPOH superfusion, the response was decreased by 69% (from 28 +/- 9% to 9 +/- 4%, n = 8). Superfusion with 20 micromol/l miconazole decreased the flow response by 67% (from 31 +/- 6% to 10 +/- 3%, n = 8). Subsequent superfusion with vehicle restored the response to 26 +/- 11%. Indomethacin did not prevent MS-PPOH inhibition of the flow response, suggesting that EET-related vasodilation was not dependent solely on cyclooxygenase metabolism of 5,6-EET. Neither MS-PPOH nor miconazole changed baseline flow, reduced the blood flow response to an adenosine A(2) agonist, or decreased somatosensory evoked potentials. The marked reduction of the cortical flow response to whisker stimulation with two different types of epoxygenase inhibitors indicates that EETs play an important role in the physiological coupling of blood flow to neural activation.     

Real-time cortical cerebral blood flow follow-up in conscious,freely moving rats by laser Doppler flowmetry

This article describes a laser Doppler flowmetry (LDF) system that enables repeated measurements and thereby long-term followup of cortical cerebral blood flow (CBF) in awake and freely moving rats. The system consists of a specially designed flow probe adapter, a flow probe connector, and a LDF flow probe, which may thereby rotate through its own axis. During the experiment, the flow adapter is permanently mounted onto the rat's skull bone. A thin layer of skull bone is left intact at the site for cortical CBF measurements. The probe connector and the flow probe may be repeatedly detached and remounted to the adapter, which allows for cortical cerebral blood flow recording from exactly the same anatomical location. The laser Doppler flowmetry system enables stable cortical CBF recordings in the conscious rat while it moves freely in a bowl cage.     

Laser-Doppler measurement of tracheal mucosal blood flow: comparison with tracheal arterial flow

Blood flow in the tracheal mucosa (Qm) has been measured by laser-Doppler flowmetry in anesthetized sheep and dogs. The values have been compared with tracheal arterial inflow (Qtr) by use of an electromagnetic flow probe and with tracheal arterial perfusion pressure (Ptr) produced by mechanical perfusion. Changes in blood flow were caused by injections of methacholine, phenylephrine, and histamine into the perfusion circuit. These interventions produced a range of measurements for each animal. Correlations of Qm against Qtr were significant in two of five animals (R = 0.03-0.93); correlations of Qm against Ptr were significant in two of four animals (R = 0.56-0.96). Percent changes in Qtr were generally much larger than those of Qm, and there was considerable variability between Qm and either Qtr or Ptr. Qm reflected the same vascular changes as Ptr or Qtr in 28 interventions and showed an opposing change in 4 cases. In 11 interventions, changes measured by Ptr or Qtr were not reflected by any changes in Qm. Thus qualitative changes in tracheal perfusion measured with these methods were usually the same; quantitatively the three methods showed great differences. These differences may reflect different regulatory mechanisms in various components of the tracheal vasculature or different technical aspects of the methods used.     

Peak muscle perfusion and oxygen uptake in humans: importance of precise estimates of muscle mass.

The knee extensor exercise model was specifically developed to enable in vivo estimates of peak muscle blood flow and O(2) uptake in humans. The original finding, using thermodilution measurements to measure blood flow in relation to muscle mass [P. Andersen and B. Saltin. J. Physiol. (Lond.) 366: 233-249, 1985], was questioned, however, as the measurements were two- to threefold higher than those previously obtained with the (133)Xe clearance and the plethysmography technique. As thermodilution measurements have now been confirmed by other methods and independent research groups, we aimed to address the impact of muscle mass estimates on the peak values of muscle perfusion and O(2) uptake. In the present study, knee extensor volume was determined from multiple measurements with computer tomography along the full length of the muscle. In nine healthy humans, quadriceps muscle volume was 2.36 +/- 0.17 (range 1. 31-3.27) liters, corresponding to 2.48 +/- 0.18 (range 1.37-3.43) kg. Anthropometry overestimated the muscle volume by approximately 21-46%, depending on whether quadriceps muscle length was estimated from the patella to either the pubic bone, inguinal ligament, or spina iliaca anterior superior. One-legged, dynamic knee extensor exercise up to peak effort of 67 +/- 7 (range 55-100) W rendered peak values for leg blood flow (thermodilution) of 5.99 +/- 0.66 (range 4.15-9.52) l/min and leg O(2) uptake of 856 +/- 109 (range 590-1,521) ml/min. Muscle perfusion and O(2) uptake reached peak values of 246 +/- 24 (range 149-373) and 35.2 +/- 3.7 (range 22.6-59. 6) ml. min(-1). 100 g muscle(-1), respectively. These peak values are approximately 19-33% larger than those attained by applying anthropometric muscle mass estimates. In conclusion, the present findings emphasize that peak perfusion and O(2) uptake in human skeletal muscle may be up to approximately 30% higher than previous anthropometric-based estimates that use equivalent techniques for blood flow measurements.     

Mechanism of Protection by Soluble Epoxide Hydrolase Inhibition in Type 2 Diabetic Stroke

Inhibition of soluble epoxide hydrolase (sEH) is a potential target of therapy for ischemic injury. sEH metabolizes neuroprotective epoxyeicosatrienoic acids (EETs). We recently demonstrated that sEH inhibition reduces infarct size after middle cerebral artery occlusion (MCAO) in type 1 diabetic mice. We hypothesized that inhibition of sEH would protect against ischemic injury in type 2 diabetic mice. Type 2 diabetes was produced by combined high-fat diet, nicotinamide and streptozotocin in male mice. Diabetic and control mice were treated with vehicle or the sEH inhibitor t-AUCB then subjected to 60-min MCAO. Compared to chow-fed mice, high fat diet-fed mice exhibited an upregulation of sEH mRNA and protein in brain, but no differences in brain EETs levels were observed between groups. Type 2 diabetic mice had increased blood glucose levels at baseline and throughout ischemia, decreased laser-Doppler perfusion of the MCA territory after reperfusion, and sustained larger cortical infarcts compared to control mice. t-AUCB decreased fasting glucose levels at baseline and throughout ischemia, improved cortical perfusion after MCAO and significantly reduced infarct size in diabetic mice. We conclude that sEH inhibition, as a preventative treatment, improves glycemic status, post-ischemic reperfusion in the ischemic territory, and stroke outcome in type 2 diabetic mice.     

An application of nanoindentation technique to measure bone tissue Lamellae properties

Measuring the microscopic mechanical properties of bone tissue is important in support of understanding the etiology and pathogenesis of many bone diseases. Knowledge about these properties provides a context for estimating the local mechanical environment of bone related cells thait coordinate the adaptation to loads experienced at the whole organ level. The objective of this study was to determine the effects of experimental testing parameters on nanoindentation measures of lamellar-level bone mechanical properties. Specifically, we examined the effect of specimen preparation condition, indentation depth, repetitive loading, time delay, and displacement rate. The nanoindentation experiments produced measures of lamellar elastic moduli for human cortical bone (average value of 17.7 +/- 4.0 GPa for osteons and 19.3 +/- 4.7 GPa for interstitial bone tissue). In addition, the hardness measurements produced results consistent with data in the literature (average 0.52 +/- 0.15 GPa for osteons and 0.59 +/- 0.20 GPa for interstitial bone tissue). Consistent modulus values can be obtained from a 500-nm-deep indent. The results also indicated that the moduli and hardnesses of the dry specimens are significantly greater (22.6% and 56.9%, respectively) than those of the wet and wet and embedded specimens. The latter two groups were not different. The moduli obtained at a 5-nm/s loading rate were significantly lower than the values at the 10- and 20-nm/s loading rates while the 10- and 20-nm/s rates were not significantly different. The hardness measurements showed similar rate-dependent results. The preliminary results indicated that interstitial bone tissue has significantly higher modulus and hardness than osteonal bone tissue. In addition, a significant correlation between hardness and elastic modulus was observed.     

Effects of induced hypothermia on organ blood flow in a hibernator and a nonhibernator

Regional blood flow and hemodynamic variables during induced hypothermia were compared in six guinea pigs and four hedgehogs. Tracer microspheres were used for blood flow measurements, since this technique is more accurate than the earlier method (86Rb+ distribution) used for cardiac output distribution measurements in hibernators. Heart rate and blood pressure decreased with reduced temperature in a comparable fashion in the two species, while cardiac output was less affected in the hedgehogs than in the guinea pigs. Total peripheral resistance increased in both species. At 34 degrees C the hedgehogs had a higher myocardial blood flow per gram tissue than the guinea pigs and it was not reduced in the hedgehogs when the body temperature was lowered to 22 degrees C, whereas in the guinea pigs it was markedly reduced. The brown adipose tissue of the hedgehogs showed a fourfold increase in blood perfusion at 22 degrees C when compared with 34 degrees C. In the hedgehogs the fractional distribution of cardiac output to the myocardium increased with decreasing body temperature, while the renal fraction decreased. In the guinea pigs, on the other hand, the fractional distribution of cardiac output to the myocardium remained unchanged but increased to the kidneys.     

Effects of permanent magnets on resting skin blood perfusion in healthy persons assessed by laser Doppler flowmetry and imaging

Effects on skin blood perfusion of permanent ceramic magnets [0.1 T (1000 G) surface field], individually (disk shaped, 4 cm diameter x 1 cm thick) or in the form of a 11 x 7 in pad ( approximately 28 x 17.8 cm) with an array of 16 rectangular magnets (4.5 x 2.2 cm), were investigated in 16 female volunteers (27.4 +/- 1.7 years, range 21-48 years) using three separate protocols. In protocol A, a disk magnet was placed on the palmar surface of the hand in contact with the thenar eminence (n = 5). In protocol B, the magnet was placed on the hand dorsum overlying the thenar eminence (n = 5). In protocol C, the entire palm and fingers rested on the magnetic pad (n = 6). Magnets were in place for 36 min on one hand, and a sham was in place on the other hand. Blood perfusion was measured on the middle finger dorsum by laser Doppler flowmetry (LDF) and on the index finger by laser Doppler imaging (LDI). Perfusion measurements were simultaneously taken in sham and magnet exposed hands, before and during the entire magnet exposure interval. Magnetic field effects were tested by comparing skin blood perfusion sequences in magnet and sham exposed regions. Results showed no significant changes in either LDF or LDI perfusion at magnet or sham sites during exposure, nor were there any significant differences between sham and magnet sites for any protocol. Measurements of skin temperature at the LDF measurement sites also showed no significant change. It is concluded that in the healthy subjects studied with normal, unstressed circulation, magnets of the type and for the duration used, showed no detectible effect on skin blood perfusion in the anatomical area studied.     

Spatial correlation of regional pulmonary perfusion.

Despite the heterogeneous distribution of pulmonary blood flow, perfusion appears to be spatially ordered, with neighboring regions of lung having similar magnitudes of flow. This premise was tested by determining the spatial correlation of regional flow [rho(d)] as a function of distance (d) between regions. Regional pulmonary perfusion was measured in both supine and prone positions in seven anesthetized mechanically ventilated dogs with radiolabeled microspheres. After excision and drying, the lungs were cubed into pieces 1.2 cm on a side, with a three-dimensional coordinate assigned to each piece. The microsphere-determined flow to each piece was measured by radioactive counts, and rho(d) was calculated for all paired pieces within the same lobe. rho(d) was greatest for adjacent pieces (d = 1.2 cm) and decreased with increasing d, becoming negative at large distances in all dogs and positions. The spatial correlation of flow between adjacent pieces, rho(1.2 cm), was greater in the supine than in the prone position (0.66 vs. 0.72, P less than 0.05). The observations for each dog and position were fit to the equation rho(d) = d(a)+b.d+c, and the coefficients were used to compare rho(d) in the supine and prone positions. rho(d) differed in the two positions (P less than 0.05), with rho(d) falling off more rapidly with distance in the supine position. When trends in flow due to gravity were mathematically removed, differences between supine and prone positions were no longer observed. The spatial correlation of regional pulmonary perfusion was anisotropic in both supine and prone positions. The observation that regional pulmonary perfusion is highly correlated over large spatial distances has important implications for models of flow distribution.     

Assessment of Renal Function in Patients with Unilateral Ureteral Obstruction Using Whole-Organ Perfusion Imaging with 320-Detector Row Computed Tomography

Background

Obstructed nephropathy is a common complication of several disease processes. Accurate evaluation of the functional status of the obstructed kidney is important to achieve a good outcome. The purpose of this study was to investigate renal cortical and medullary perfusion changes associated with unilateral ureteral obstruction (UUO) using whole-organ perfusion imaging with 320-detector row computed tomography (CT).

Methodology/Principle Findings

Sixty-four patients with UUO underwent whole-organ CT perfusion imaging. Patients were divided into 3 groups, mild, moderate, and severe, based on hydronephrosis severity. Twenty sex- and age-matched patients without renal disease, who referred to abdominal CT, were chosen as control subjects. Mean cortical and medullary perfusion parameters of obstructed and contralateral kidneys were compared, and mean perfusion ratios between obstructed and contralateral kidneys were calculated and compared. Mean cortical or medullary blood flow (BF) and blood volume (BV) of the obstructed kidneys in the moderate UUO and BF, BV, and clearance (CL) in the severe UUO were significantly lower than those of the contralateral kidneys (p < 0.05). The mean cortical or medullary BF of the obstructed kidney in the moderate UUO, and BF, BV, and CL in the severe UUO were significantly lower than those of the kidneys in control subjects (p < 0.05). Mean cortical or medullary BF of the non-obstructed kidneys in the severe UUO were statistically greater than that of normal kidneys in control subjects (p < 0.05). An inverse correlation was observed between cortical and medullary perfusion ratios and grades of hydronephosis (p < 0.01).

Conclusions/Significance

Perfusion measurements of the whole kidney can be obtained with 320-detector row CT, and estimated perfusion ratios have potential for quantitatively evaluating UUO renal injury grades.     

Role of prostaglandins in the cortical distribution of renal blood flow following reductions in renal perfusion pressure

The purpose of this study was to examine the role of prostaglandins in the redistribution of renal cortical blood flow that occurs following reductions in renal perfusion pressure. The distribution of blood flow to the renal cortex was examined using radio-labeled microspheres (15 +/- 1 micron). It was found that in animals not treated with a prostaglandin synthesis inhibitor a decrease in renal perfusion pressure to the limit of renal blood flow autoregulation was associated with a decrease in fractional flow to the outer cortex (Zone I) and an increase in fractional flow to the inner cortex (Zones III and IV). A further decrease in renal perfusion pressure below the limit of autoregulation produced a further decrease in the fractional flow to Zone I and a further increase in fractional flow to Zones III and IV. In contrast, in animals treated with the prostaglandin synthesis inhibitor meclofenamate (5 mg/kg, i.v. bolus) a reduction in renal perfusion pressure to the limit of renal blood flow autoregulation produced no change in fractional blood flow to any of the 4 cortical zones. A further decrease in renal perfusion pressure, however, did produce a fall in fractional blood flow to Zone I and an increase in fractional flow to Zones III and IV. In conclusion, the results of this study indicate that within, but not below, the limit of renal blood flow autoregulation prostaglandin synthesis is an important factor in the regulation of renal cortical blood flow distribution.     

Autoregulation of renal medullary blood flow in rabbits

We examined the extent of renal medullary blood flow (MBF) autoregulation in pentobarbital-anesthetized rabbits. Two methods for altering renal arterial pressure (RAP) were compared: the conventional method of graded suprarenal aortic occlusion and an extracorporeal circuit that allows RAP to be increased above systemic arterial pressure. Changes in MBF were estimated by laser-Doppler flowmetry, which appears to predominantly reflect erythrocyte velocity, rather than flow, in the kidney. We compared responses using a dual-fiber needle probe held in place by a micromanipulator, with responses from a single-fiber probe anchored to the renal capsule, to test whether RAP-induced changes in kidney volume confound medullary laser-Doppler flux (MLDF) measurements. MLDF responses were similar for both probe types and both methods for altering RAP. MLDF changed little as RAP was altered from 50 to >or=170 mmHg (24 +/- 22% change). Within the same RAP range, RBF increased by 296 +/- 48%. Urine flow and sodium excretion also increased with increasing RAP. Thus pressure diuresis/natriuresis proceeds in the absence of measurable increases in medullary erythrocyte velocity estimated by laser-Doppler flowmetry. These data do not, however, exclude the possibility that MBF is increased with increasing RAP in this model, because vasa recta recruitment may occur.