Capillary Red Blood Cell Velocity Research Articles

Endothelin-A Receptor in Rat Skeletal Muscle Microvasculature

Although the effect of endothelin-1 (ET-1) on vascular tone has been studied extensively at the arterial/arteriolar level, little is known about the direct effect of ET-1 at the level of the capillary. Using intravital microscopy, we determined capillary red blood cell velocity and arteriolar diameter responses to ET-1, ETA-receptor blocker BQ-123, and ETB-receptor blocker BQ-788 applied locally on capillaries in rat extensor digitorum longus (EDL) muscle. Using immunohistochemistry, we examined capillaries in this muscle and microvascular endothelial cells isolated from this muscle for immunoreactivity with ETA-receptor antibody. ET-1 (10−9 to 10−5 M in micropipette) caused quick reductions (i.e., within several seconds), whereas BQ-123 (10−8 to 10−4 M) and BQ-788 (10−6 and 10−4 M) caused quick increases, in both velocity and diameter. Capillaries and endothelial cells showed ETA-receptor immunoreactivity. We conclude that the microvasculature of the rat EDL muscle is sensitive to ET-1 and its receptor blockers and that the ETA receptor may be present in the capillary wall of this muscle, including the endothelium.

Protective effect of ketoprofen lysine salt on interleukin-1beta and bradykinin induced inflammatory changes in hamster cheek pouch microcirculation.

The purpose of this study was to assess the efficacy of topically applied ketoprofen lysine salt (KLS), a cyclooxygenase inhibitor, against the inflammatory changes induced by interleukin-1beta (IL-1beta) and bradykinin (BK) in hamster cheek pouch microcirculation. In addition, we characterised the pharmacological regulation of IL-1beta activity in this model. Male Syrian hamsters were used. Microcirculation was visualised by fluorescent microscopy. Leukocyte adhesion, permeability, perfused capillary length (PCL) and capillary red blood cell (RBC) velocity were evaluated. KLS (25 microg/ml/min to 1.6 mg/ml/min) was topically applied for 3 min before topically administered IL-1beta (1microg/ml) and BK (10(-4) M). Monoclonal anti-mouse IL-1beta receptor antagonist (200 ng/ml), BK-B2 receptor antagonist (10(-6) M), PAF inhibitor (10(-5) M) and cycloheximide (10 microg/ml) were added topically 15, 10, 15 and 60 min, respectively, before IL-1beta (1 microg/ml). IL-1beta caused a significant increase in microvascular permeability, a decrease in capillary RBC velocity followed by increased leukocyte adhesion in postcapillary venules. BK caused a marked increase in leukocyte adhesion and no decrease in PCL and RBC velocity. Treatment with KLS significantly inhibited both the leukocyte adhesion and microvascular leakage induced by the two mediators. The inflammatory effects induced by IL-1beta were reduced by blockade of IL-1beta receptors and by a BK-B2 receptor antagonist but were not affected by a PAF antagonist and protein synthesis inhibition. These results demonstrate that KLS is effective in preventing early inflammatory changes induced by both IL-1beta and BK in the capillary network. Prostaglandin release and BK are essential components for IL-beta mediated responses, whereas neither PAF nor new protein synthesis appear to be linked to the early inflammatory changes induced by IL-1beta.

L-Arginine and Antineutrophil Serum Enable Venular Control of Capillary Perfusion in Hypercholesterolemic Rats

Objective: The purpose of this study was to investigate and counteract dysfunctional control of capillary flow in hypercholesterolemia. Capillary flow is controlled by arteriolar tone, which in turn is influenced by mediators released from closely paired venules in a mechanism that involves nitric oxide (NO). However, venular control of capillary flow is altered with hypercholesterolemia. Methods: Rats were given a normal or high-cholesterol diet before measurements of mesenteric capillary red blood cell velocity. The arteriolar pathway leading to the capillary was videotaped to measure the percent of the surrounding area (within 15 µm) that was occupied by a venule (% pairing). Results: Venule-paired arterioles were significantly smaller in hypercholesterolemia compared with normocholesterolemia, corresponding to slower capillary flow. A positive correlation between capillary velocity and % pairing observed in normocholesterolemia was not observed during NO synthase inhibition or in hypercholesterolemic rats. However, positive correlations between the two parameters were found in hypercholesterolemia when the rats were given drinking water supplementation of L-arginine or an injection of antineutrophil serum, both of which tended to improve velocity in capillaries branching from venulepaired arteriolar pathways. Conclusions: Dysfunctional venular control of capillary perfusion in hypercholesterolemia may be a consequence of a neutrophil-mediated deficiency of NO.

Association between Shear Stress, Angiogenesis, and VEGF in Skeletal Muscles In Vivo

ABSTRACTObjective: To investigate the hypothesis that capillary proliferation in skeletal muscles, induced by a long‐term increase in blood flow which elevates capillary shear stress, is associated with capillary expression of vascular endothelial growth factor (VEGF).Methods: Adult rats received prazosin in drinking water (∼2 mg per day) or had extensor digitorum longus (EDL) muscles stimulated by implanted electrodes for up to 14 days. At intervals, serial frozen sections of EDL were stained for alkaline phosphatase to identify capillaries, proliferating cell nuclear antigen (PCNA), and VEGF‐A protein. Shear stress was estimated from capillary red blood cell velocities and diameters, measured by direct observation of epiilluminated EDL.Results: Chronic stimulation and prazosin treatment both increased capillary: fiber ratio by ∼40% after 14 days. In stimulated muscles, the percentage of capillaries positively stained for VEGF increased within 3 to 4 days, while the density of PCNA‐positive capillaries had increased 20‐fold after 2 days. With prazosin, VEGF‐positive capillaries increased after 2 and 4 days, accompanied by a threefold increase in PCNA. By 14 days, PCNA labeling and VEGF were still high in stimulated muscles, but no longer different from controls with prazosin. After 3 to 4 days of treatment, capillary shear stress in resting muscle was 57% higher than in controls as a result of stimulation, but 4 times higher with prazosin.Conclusions: Higher capillary shear stress with prazosin than with stimulation may upregulate VEGF expression in the early stages of treatment. Greater proliferation of capillaries preceding a higher proportion of VEGF‐positive capillaries in stimulated muscles, in the presence of a modest increase in shear stress, suggests that angiogenesis was initiated by other factors in addition to shear stress.

Temporary pancreatic duct occlusion by ethibloc: cause of microcirculatory shutdown, acute inflammation, and pancreas necrosis.

Temporary obliteration of the pancreatic duct has been suggested to be beneficial in chronic pancreatitis, segmental pancreatic transplantation, and following Roux-Y pancreaticojejunostomy. Little is known, however, as to whether obliteration of the duct alters exocrine pancreatic physiology. Therefore we studied in male inbred Lewis rats the immediate effects of Ethibloc-induced duct obliteration (Ethibloc: Ethicon, Norderstedt, Germany) on pancreatic microcirculation, inflammation, and tissue injury (n = 8), and compared these effects with those caused by experimental pancreatitis (4% sodium taurocholate; n = 8). Animals receiving an intraductal infusion of saline served as controls (n = 8). Duct occlusion with Ethibloc resulted in a marked decrease (p < 0.05) in capillary red blood cell (RBC) velocity and functional capillary density (FCD) to 88 +/- 39 microm/s (baseline 716 +/- 40 microm/s) and 72 +/- 33 cm(-1) (baseline 493 +/- 21 cm(-1)), respectively, which was even more pronounced when compared with that observed in experimental pancreatitis (333 +/- 62 microm/s and 195 +/- 44 cm(-1), respectively). In parallel, the manifestation of tissue damage was found to be more severe after Ethibloc; and chloracetate esterase staining showed a larger number of infiltrating leukocytes [555 +/- 86/high power field (HPF) versus pancreatitis: 160 +/- 12/HPF; p < 0.05). We conclude that intraductal application of Ethibloc induces significant microcirculatory failure and a marked inflammatory response, which are even more pronounced when compared with the changes observed with experimental pancreatitis. Based on these results and the fact that there is no direct proof for a benefit of temporary duct occlusion by Ethibloc, it is proposed that the procedure be reevaluated for its use in pancreatic surgery.

Local heat-shock priming-induced improvement in microvascular perfusion in osteomyocutaneous flaps is mediated by heat-shock protein 32.

Stress conditioning is thought to improve microvascular free flap survival but the mechanisms of protection are not clear. The aim of this study was to determine whether local induction of heat-shock protein (HSP) 32 improves microvascular perfusion in transferred osteomyocutaneous flaps. The hindlimb harvest region of osteomyocutaneous flaps in Wistar rats was subjected to stress conditioning by local heating (30 min, 42.5 degrees C) 24 h before microvascular flap transfer. In a second group of animals, after heat-shock priming, the action of HSP-32 was inhibited by tin protoporphyrin IX. Animals with unconditioned flaps served as controls. After transfer, the microcirculation of the muscle, cutaneous, subcutaneous and periosteal tissue of the flap was analysed quantitatively for 6 h using intravital fluorescence microscopy. Immunohistochemistry revealed that HSP-32 was detectable only after priming and not in unconditioned flaps. Priming did not alter functional capillary density or capillary red blood cell velocity compared with that in unconditioned flaps. However, heat-shock priming induced significant capillary dilatation (P < 0.05) and thus a substantial increase in capillary blood flow volume (P < 0.05) in all tissues of the transferred flaps. Inhibition of HSP-32 by tin protoporphyrin IX completely abolished the priming-induced improvement in capillary perfusion, as indicated by the lack of increased capillary diameters and volumetric blood flow. The present study demonstrated that stress conditioning by local heat-shock priming improves nutritive perfusion in osteomyocutaneous flaps by capillary dilatation, probably mediated through the vasoactive action of HSP-32.

Microvascular flow and tissue PO(2) in skeletal muscle of chronic reduced renal mass hypertensive rats.

This study determined whether arteriolar blood flow, capillary red blood cell (RBC) velocity, capillary hematocrit (Hct(cap)), and tissue PO(2) are altered in cremaster muscles of rats with chronic reduced renal mass hypertension (RRM-HT) relative to normotensive rats on high- or low-salt (NT-HS vs. NT-LS) diet. The blood flow in first- through third-order arterioles was not different between NT and HT rats, either at rest or during maximal relaxation of the vessels with 10(-4) M adenosine. Capillary RBC velocity was similar between the groups at rest but was elevated in RRM-HT and NT-HS rats during adenosine superfusion. Hct(cap) was reduced at rest in RRM-HT and NT-HS rats compared with NT-LS and was reduced in RRM-HT rats during adenosine-induced dilation. Tissue PO(2) was reduced in RRM-HT and NT-HS rats compared with NT-LS rats during control conditions and was lower in RRM-HT than in NT-LS rats during adenosine-induced dilation. These results indicate that both RRM-HT and chronic exposure of normotensive rats to a high-salt diet lead to reduced tissue oxygenation, despite the maintenance of normal arteriolar blood flow.

Detrimental effects of octreotide on intestinal microcirculation.

Octreotide (OCT) is used for the protection of pancreato-intestinal anastomoses and for treatment of acute pancreatitis. Its effect on jejunal microcirculation after ischemia-reperfusion has not been investigated. Intestinal ischemia was induced in Wistar rats (n = 8) by occlusion of the superior mesenteric artery for 40 min. Prior to reperfusion infusion of OCT (7.5 microgram/h) was started (n = 8). Microvascular perfusion of the jejunal mucosal and muscle layers was assessed and compared with that of groups without intervention (n = 16) by means of intravital microscopy. Ischemia-reperfusion decreased mucosal functional capillary density from 838.4 +/- 12.6 to 418.9 +/- 9.6 cm(-1). Mucosal capillary red blood cell velocity was reduced from 0.53 +/- 0.01 to 0.35 +/- 0.01 mm/s (P < 0.05). Permanent leukocyte adherence was increased. OCT without ischemia-reperfusion decreased functional capillary density (735.4 +/- 13.5 cm(-1)) and red blood cell velocity (0.46 +/- 0.01 mm/s). After reperfusion OCT led to perfusion heterogeneity demonstrated by villous stasis (26 +/- 4%) and a decrease in the index of mucosal perfusion (0.38 +/- 0.02). Functional capillary density was further decreased compared with ischemic controls (234.0 +/- 11.8 cm(-1)). Capillary red blood cell velocity was lower (0.30 +/- 0.01 mm/s) than in ischemic controls. OCT impairs microvascular perfusion of the jejunum both under physiological conditions and after ischemia-reperfusion.

Spinal cord stimulation in the treatment of severe peripheral vascular and vasospastic disorders of the upper extremity

Objective: To evaluate the technique and results of spinal cord stimulation in patients who have intractable ischemic pain due to peripheral vascular disease, and vasospastic disorders of the upper extremity. Design: Clinical case series. The cohort underwent diagnostic evaluation and surgical intervention, and had a mean postoperative follow-up of 18.3 months. Patients and Methods: A consecutive, referred sample. Four patients had severe ischemic pain due to peripheral vascular disease and six had vasospastic disorders. Six were women and four were men, with a mean age of 45 years. All patients underwent implantation of a spinal cord stimulation system. The technique is performed under local anesthesia, using epidural puncture for electrode placement. Main outcome measures were relief of the ischemic pain for which the patient was referred, and microcirculatory skin blood flow parameters. Results: Pain relief was significant in all patients and remained significant throughout follow-up in 80% of the patients. TcPO2 values increased significantly, capillary red blood cell velocity and capillary density improved also significantly. Effects on macrocirculatory parameters were not observed. Conclusion: It is concluded that treatment of intractable ischemic pain of the upper extremities with spinal cord stimulation provides significant pain relief mainly due to effects on the microcirulatory skin blood flow.

Altered peripheral vascular response of women with and without pelvic pain due to congestion.

To test the hypothesis that women with pelvic venous congestion have a reduction of reactivity of their peripheral circulation. Comparison was made between 20 women with chronic pelvic pain due to congestion and a control group of 15 pain-free women matched for age, parity and body weight. A comparison of these results was made with those from six postmenopausal women taking hormone replacement therapy. Study and control groups were investigated during the mid-follicular phase of the menstrual cycle (days 5-9) and the mid-luteal phase (days 19-23). The study group was also investigated during the fifth month of treatment with suppression of ovarian activity with leuprorelin or medroxyprogesterone acetate or six months after hysterectomy and bilateral salpingo-oophorectomy. Head-up tilt sufficient to increase intra-vascular pressure in the toe by a standard 40 mmHg was used as a means of raising venous pressure in the lower limb. Skin capillary red blood cell velocity (flux) was measured using a laser Doppler flow probe placed over the pulp of the big toe. Heart rate and blood pressure were also recorded. The change in skin blood flow following head-up tilt was expressed as a percentage of baseline flow in the supine position. Percentage change in skin red blood cell flux, heart rate and blood pressure in response to 40 degrees head-up tilt. In the control group the median response to head-up tilt in the follicular phase was one of a reduction in flux, whereas in the luteal phase it was more variable ranging from an increase to a decrease in flux. The responses in the pelvic congestion group in both the follicular and luteal phases were similar to those of the control group in the luteal phase. A small but significant increase in heart rate in response to tilt in the pelvic pain group, compared with the control group, was interpreted as being due to a fall in venous return. Treatment of the pelvic congestion group by medical suppression of ovarian activity or total hysterectomy with bilateral salpingo-oophorectomy resulted in a significant change in response to head-up tilt from the variable type of luteal response to one of a more constant reduction in flux, similar to that of the control group in the follicular phase. A reduction in flux was also found consistently in postmenopausal women. The study confirms the hypothesis that women with pelvic pain due to congestion show a change in peripheral vascular reactivity which returns to normal after suppression of ovarian activity. It seems likely that some alteration of normal ovarian function is responsible for the observed changes in peripheral blood flow in response to a rise in venous pressure in women with pelvic congestion.

Impact of Gastrin-Releasing Peptide on Intestinal Microcirculation after Ischemia-Reperfusion in Rats

We investigated the effect of gastrin-releasing peptide (GRP) and its antagonist RC-3095 on intestinal microcirculation after ischemia-reperfusion. Intestinal ischemia was induced in female Wistar rats by occlusion of the superior mesenteric artery for 40 min. Ten minutes prior to reperfusion, infusion of GRP or RC-3095 was started. A jejunal segment was exteriorized and the microhemodynamics of the mucosa and submucosa were examined by intravital microscopy and compared both with normal and ischemic controls (without application of the regulatory peptide). Ischemia-reperfusion significantly decreased functional capillary density from 891.2 ± 14.1 to 398.3 ± 11.4 cm^–1. Capillary red blood cell velocity was reduced from 0.46 ± 0.01 to 0.37 ± 0.01 mm/s (p < 0.05). Furthermore, both sticking and rolling of leukocytes were enhanced. 3.4 ± 1.1% of the villi were not perfused at all. GRP infusion reversed the microcirculatory ischemia-reperfusion injury by increasing functional capillary density to 669.8 ± 8.3 cm^–1 and red blood cell velocity to 0.62 ± 0.01 mm/s (p < 0.05). In addition, application of GRP resulted in a complete absence of stasis (0%) in the villi. Leukocyte-endothelium adherence remained unchanged when compared to the ischemic controls. In contrast, application of RC-3095 caused an aggravation of microcirculatory disturbances demonstrated by a markedly increased number of non-perfused villi (42.5 ± 4.2%; p < 0.05 vs. ischemic controls) and a significantly reduced functional capillary density (346.2 ± 8.4 cm^–1, p < 0.05 vs. ischemic controls). In addition, RC-3095 led to an increased permanent leukocyte adherence in postcapillary venules whereas rolling was significantly reduced when compared to normal controls. We conclude that GRP in pharmacological doses has a protective effect on intestinal microcirculation during reperfusion. Furthermore, these data suggest that endogenous GRP may play a decisive role in the maintenance of microvascular integrity during reperfusion.

Attenuation of microvascular reperfusion injury in rat pancreas transplantation by L-arginine.

Despite improving results, exocrine complications remain a major challenge in clinical pancreas transplantation. The etiology of posttransplantation pancreatitis relates almost certainly to cold ischemia/reperfusion-induced microvascular injury with an imbalance of vasoconstricting and vasodilating mediators due to endothelial dysfunction. We therefore studied the effectiveness of a nitric oxide donor on postischemic microvascular reperfusion injury after pancreas transplantation. Heterotopic isogeneic pancreaticoduodenal transplantation was performed in spontaneously breathing, chloralhydrate-anesthetized Sprague Dawley rats after 16 hr (n=5) of cold storage of the graft in 4 degrees C histidine-tryptophane-ketoglutarate solution. An additional five animals received L-arginine immediately before (50 mg/kg i.v.) and during the first 30 min of reperfusion (100 mg/kg i.v.). Five animals that did not undergo transplantation served as controls. Intravital fluorescence microscopy was used for analysis of functional capillary density, capillary diameters, and capillary red blood cell velocity in exocrine pancreatic tissue during 120 min of reperfusion. Histology served for quantitative assessment of inflammatory response (leukocytic tissue infiltration) and endothelial disintegration (edema formation). In L-arginine-treated animals, functional capillary density of exocrine tissue of pancreatic grafts was found slightly higher after 30 and 60 min, and significantly higher after 120 min of postischemic reperfusion compared with untreated pancreatic grafts. This was accompanied by a significant increase of capillary diameters. In parallel, pancreatic histology revealed significant attenuation of both leukocytic tissue infiltration and edema formation in the L-arginine-treated animals when compared with the nontreated controls. Besides reduction of leukocyte-dependent microvascular injury, L-arginine improves postischemic microvascular reperfusion, supposedly by capillary dilatation. Thus, our results suggest that supplement of nitric oxide during reperfusion is effective in attenuating exocrine microvascular reperfusion injury.

Hemodynamics in Nailfold Capillaries of Patients with Systemic Scleroderma: Synchronous Measurements of Capillary Blood Pressure and Red Blood Cell Velocity

There is increasing evidence that endothelial damage occurs at a very early stage during the course of systemic scleroderma. Endothelial damage is accompanied by impaired microvascular function, which has clearly failed in patients with systemic scleroderma, as evidenced by necrosis of the fingertips in severe cases. We investigated two important determinants of microvascular function, namely capillary blood pressure and capillary red blood cell velocity, simultaneously in the same capillary. In patients with systemic scleroderma and in healthy volunteers matched for age and sex, capillary blood pressure was measured by direct cannulation and capillary red blood cell velocity by video microscopy. Capillary blood pressure and capillary red blood cell velocity were significantly lower in patients (14.27 +/- 4.34 mmHg, 230 +/- 310 microm per s) than in healthy controls (19.06 +/- 3.69 mmHg, p < 0.008, and 910 +/- 240 microm per s, p < 0.003) at an ambient temperature of 22 degrees C, whereas no significant difference in skin temperature was observed (23.7 +/- 0.9 degrees C vs 24.7 +/- 1.9 degrees C) and no occlusion of finger arteries was detected. Capillary blood pressure in enlarged capillaries did not differ from that in normal-shaped capillaries in the patients (correlation of diameter and capillary blood pressure, R2 = 0.04), which was also the case with capillary red blood cell velocity (R2 = 0.13). Capillary pulse pressure amplitude and capillary red blood cell velocity showed a strong correlation (R2 = 0.81), suggesting that the pressure gradient across the capillary loop, which is the driving force for capillary red blood cell velocity, was mainly dependent on precapillary resistance. These observations reflect the inadequate microvascular function in systemic scleroderma, which may be due mainly to a pathophysiologic functional increase in precapillary resistance, even at comfortable ambient temperatures.

Comparison of CapiFlow and frame by frame analysis for the assessment of capillary red blood cell velocity

CapiFlow (CF), a new fully computerized system for the measurement of capillary blood velocity (CBV) was compared to manual frame by frame analysis (a) in a model system, and (b) in finger nailfold capillaries recorded on video tape. In the model the overall agreement between the two methods was very good (figure 1), with no significant differences being noted between the two sets of results and the calculated velocities. However, when comparing frame by frame and CapiFlow directly, CapiFlow read on average 4.50 + 5.21 % higher than frame by frame analysis (figure 2). The in vivo results obtained by the two methods showed similar dynamic changes although some differences between the overall mean CBVs were noted (capillary I, manual 0.13+0.59 mm s−1 versus CF 0.12+0.02 mms−1, (mean + SD), p = 0.354; capillary 2, manual 0.66 +0.23 mms−1 versus CF 0.47+0.09 mm s−1, p <0.001; capillary 3, manual 2.53 + 0.73 mm s−1 versus CF 2.35 +0.34 mm s−1, p = 0.062). Further analyses established the optimum settings of delta limit and cross correlation. Investigations into the effects of changes in window size, window distance or video settings on CBV results obtained by CapiFlow, indicated that only settings radically different from the optimum had a significant effect on the results obtained.

In vivo microvascular structural and functional consequences of muscle length changes.

As muscles are stretched, blood flow and oxygen delivery are compromised, and consequently muscle function is impaired. We tested the hypothesis that the structural microvascular sequellae associated with muscle extension in vivo would impair capillary red blood cell hemodynamics. We developed an intravital spinotrapezius preparation that facilitated direct on-line measurement and alteration of sarcomere length simultaneously with determination of capillary geometry and red blood cell flow dynamics. The range of spinotrapezius sarcomere lengths achievable in vivo was 2.17 +/- 0.05 to 3.13 +/- 0.11 microns. Capillary tortuosity decreased systematically with increases of sarcomere length up to 2.6 microns, at which point most capillaries appeared to be highly oriented along the fiber longitudinal axis. Further increases in sarcomere length above this value reduced mean capillary diameter from 5.61 +/- 0.03 microns at 2.4-2.6 microns sarcomere length to 4.12 +/- 0.05 microns at 3.2-3.4 microns sarcomere length. Over the range of physiological sarcomere lengths, bulk blood flow (radioactive microspheres) decreased approximately 40% from 24.3 +/- 7.5 to 14.5 +/- 4.6 ml.100 g-1.min-1. The proportion of continuously perfused capillaries, i.e., those with continuous flow throughout the 60-s observation period, decreased from 95.9 +/- 0.6% at the shortest sarcomere lengths to 56.5 +/- 0.7% at the longest sarcomere lengths and was correlated significantly with the reduced capillary diameter (r = 0.711, P < 0.01; n = 18). We conclude that alterations in capillary geometry and luminal diameter consequent to increased muscle sarcomere length are associated with a reduction in mean capillary red blood cell velocity and a greater proportion of capillaries in which red blood cell flow is stopped or intermittent. Thus not only does muscle stretching reduce bulk blood (and oxygen) delivery, it also alters capillary red blood cell flow dynamics, which may further impair blood-tissue oxygen exchange.

The effect of acetylcholine on finger capillary pressure and capillary flow in healthy volunteers.

1. Constitutive nitric oxide (NO) synthase has been demonstrated in human skin microvascular endothelial cells; however, the physiological significance of this finding is not known. The aim of this study was to investigate the effects of acetylcholine (ACh), which stimulates the release of NO from endothelial cells, on skin capillary pressure, capillary pulse pressure amplitude (CPPA) and capillary red blood cell velocity (CBV) in healthy volunteers. 2. Finger nailfold capillary pressure was measured in five healthy volunteers. CBV was measured in capillaries of the dorsal middle phalangeal area of the finger in six subjects using a recently developed capillary anemometer. In each case the responses to ionophoretically applied ACh and vehicle were measured on two separate fingers on the left hand. 3. Application of vehicle did not significantly change either capillary pressure, CPPA or CBV. ACh significantly increased capillary pressure (from 15.8 +/- 2.2 mmHg under basal conditions to 27.7 +/- 3.8 mmHg at the plateau of the ACh response; P < 0.008), CPPA (from 2.4 +/- 2.4 mmHg at baseline to 8.4 +/- 2.4 mmHg at the plateau of the drug response; P < 0.013) and CBV (from 0.54 +/- 0.22 mm s-1 at baseline to 2.46 +/- 1.12 mm s-1 after ACh; P < 0.008). 4. The increases in capillary pressure, CPPA and CBV following the application of ACh suggest that the overall effect of ACh was to induce a reduction in the pre- to postcapillary resistance ratio.

Synchronous Oscillations in Cerebrocortical Capillary Red Blood Cell Velocity after Nitric Oxide Synthase Inhibition

Low-frequency (4–12 cpm) spontaneous oscillations in cerebral blood flow are well known and their augmentation after nitric oxide synthase inhibition has recently been described. However, the presence of these oscillations in blood flow velocity in the capillary network of the brain has not been demonstrated. In this paper, low-frequency oscillations in red blood cell flow velocity in cortical capillaries using intravital video microscopy were studied before and after infusion of the nitric oxide synthase inhibitor Nω-nitro-L-arginine methyl ester (L-NAME). Fluorescein isothiocyanate-labeled red blood cells were injected intravenously and served as markers of capillary flow. Red cell velocity was measured by off-line image tracking. After infusion ofL-NAME (30 mg/kg), red cell velocity decreased from an average of 1.0 ± 0.1 mm/sec to 0.53 ± 0.1 mm/sec. Simultaneously, low-frequency oscillations in velocity emerged as indicated by an 81 ± 17% increase in standard deviation of the 4- to 8-cpm frequency components. There was a significant temporal correlation (r= 0.58,P< 0.01) in red cell velocity between neighboring capillaries afterL-NAME. Principal component analysis suggested that the high temporal correlation was a consequence of low-frequency oscillations rather than phase. These results are consistent with a model in which low-frequency spontaneous oscillations in flow velocity are brought about by precapillary vasomotion. This study provides for the first time direct evidence for low-frequency synchronous oscillations of red cell flow velocity in the cerebral capillary network.

Synchronous Measurements of Blood Pressure and Red Blood Cell Velocity in Capillaries of Human Skin

We have devised a system for analyzing the temporal coherence of capillary pressure (CP) and capillary red blood cell velocity (CBV) variations in humans. The system is designed to measure human blood pressure in skin capillaries by direct cannulation while simultaneously measuring red blood cell velocity in the same capillary by video microscopy. The servo-nulling pressure measurement system allows the dynamic recording of capillary pressure with a flat frequency response of about 12 Hz. Computerized data acquisition is synchronized with the frame code of a U-matic video recorder, which records the capillaroscopic picture for later computerized off-line analysis of capillary red blood cell velocity. Measurements of simultaneously recorded CP and CBV in healthy volunteers show synchronized pulsation. Minimal pulsatile variations in CP values result in marked variations of CBV. In addition, minor fluctuations (3-4 cycles per minute) in CP are accompanied by marked changes in CBV. This system may help provide information about microvascular pathophysiology in skin diseases before and after treatment.

A new technique for controlling the finger skin temperature in microcirculatory research demonstrated in a local cold stress test in healthy controls and patients with Raynaud's phenomenon.

Changes in skin temperature cause great changes in blood flow and capillary blood pressure. The new technique presented here makes it possible to control the temperature of the finger during nailfold capillaroscopy. Automatic temperature control, both for warming and cooling, is made possible with the aid of a temperature-controlled finger holder. The temperature of the finger holder can be automatically matched to the spontaneous skin temperature of the examined finger, or the finger holder temperature and temperature change velocity can be set digitally to a desired value. We used this new technique in a local cold stress test on 9 healthy controls (3 men, 6 women) and 9 patients (3 men, 6 women) with Raynaud's phenomenon due to systemic sclerosis. We simultaneously measured capillary red blood cell velocity (CBV) and laser Doppler flux (LDF) in adjacent areas of the finger nailfold with three different cooling procedures (8, 10, 12 degrees C for 5 min). CBV and LDF values showed the most pronounced differences between patients and controls at 12 degrees C. This new technique supplements capillaroscopy with full temperature control and defined temperature changes. It can also be combined with measurements of LDF and capillary blood pressure. In view of the disadvantages of other cooling methods we recommend this new and easy-to-handle technique for clinical practice and research.

Control of renal medullary blood flow by vasopressin V1 and V2 receptors.

Experiments were performed in anesthetized renal-denervated rats to determine the contribution of renal medullary vasopressin V1 and V2 receptor stimulation in the regulation of renal medullary blood flow. Renal medullary interstitial infusion of the selective V1 agonist [Phe2,Ile3,Orn8]vasopressin (2 ng.kg-1.min-1) significantly decreased outer medullary blood flow by 15% and inner medullary blood flow by 35%, as measured with implanted optical fibers for laser-Doppler flowmetry. Medullary interstitial infusion of equimolar doses of arginine vasopressin (AVP) also decreased outer medullary blood flow by 15% but decreased inner medullary blood flow by only 17%, a decrease significantly less than that during the infusion of the V1 agonist. These results were confirmed in videomicroscopy experiments on the exposed papilla, which demonstrated that the V1 agonist and AVP decreased descending and ascending vasa recta capillary red blood cell velocity and calculated blood flow, with greater decreases during infusion of the V1 agonist. In further laser-Doppler flowmetry studies, stimulation of V2 receptors by medullary interstitial infusion of 1-desamino-8-D-arginine vasopressin (2 ng.kg-1.min-1) or AVP in rats pretreated with the vasopressin V1 receptor antagonist d(CH2)5[Tyr(Me)2,Ala-NH2]AVP increased renal medullary blood flow by 16 +/- 3 and 27 +/- 8%, respectively. The present experiments indicate that vasopressin V1 receptor stimulation serves to decrease renal medullary blood flow while V2 receptor stimulation appears to increase renal medullary blood flow; however, the net effect of AVP is to decrease renal medullary blood flow.