White Blood Cell Flux Research Articles

Interaction between leukocytes and erythrocytes in the human retina: Effects of pentoxifylline on hyperoxia‐induced vasoconstriction during increased neutrophil counts

AbstractPurpose We have previously shown that under states of vasoconstriction an interaction between circulating erythrocytes and leukocytes may play a role in the control of blood flow. In the present study we hypothesized that pentoxifylline may alter this interaction during oxygen‐induced vasoconstriction.Methods 24 healthy male subjects participated in this double masked, randomized, placebo‐controlled 2 way cross over trail. In order to increase white blood cell count (WBC) count, 300 μg of G‐CSF was administered intravenously. Vasoconstriction of retinal vessels was induced by oxygen inhalation. 400mg of pentoxifylline or placebo was infused at two different study days. White blood cell flux was assessed with the blue‐field entoptic technique. Vessel calibers were measured with a dynamic vessel analyzer (DVA) and red blood cell velocity (RBCV) was determined with laser Doppler velocimetry (LDV). Retinal blood flow was calculated based on retinal vessel diameters and RBCV.Results Retinal vessel diameter, RBCV, calculated retinal blood flow and white blood cell flow were not altered by administration of pentoxifylline. Hyperoxia induced a pronounced decrease in retinal blood flow parameters. No difference was observed between groups during oxygen breathing in vessel diameters (p=0.54), RBCV (p=0.34), calculated retinal blood flow (p=0.3) and white blood cell flow (p=0.26).Conclusion Our data indicate that short time administration of pentoxifylline does not alter the oxygen‐induced effect on ocular blood flow parameters during leukocytosis.

Interaction between leukocytes and erythrocytes in the human retina: Effects of pentoxifylline on hyperoxia-induced vasoconstriction during increased neutrophil counts

PurposePentoxifylline, a nonselective phosphodiesterase inhibitor, shows vasodilator effects in certain vascular beds and reduces blood viscosity. We have previously shown that under states of vasoconstriction an interaction between circulating erythrocytes and leukocytes may play a role in the control of blood flow. The reason for this observation is not entirely clear but may be related to a mechanical interaction between red and white blood cells. In the present study we hypothesized that pentoxifylline may alter this interaction during oxygen-induced vasoconstriction. Methods24 healthy male subjects participated in this double masked, randomized, placebo-controlled 2 way cross over trail. In order to increase white blood cell count (WBC) count, 300μg of G-CSF was administered intravenously. Vasoconstriction of retinal vessels was induced by oxygen inhalation. 400mg of pentoxifylline or placebo was infused at two different study days. White blood cell flux was assessed with the blue-field entoptic technique. Vessel calibers were measured with a dynamic vessel analyzer (DVA) and red blood cell velocity (RBCV) was determined with laser Doppler velocimetry (LDV). Retinal blood flow was calculated based on retinal vessel diameters and RBCV. ResultsAdministration of G-CSF induced a significant increase in WBC, both in the placebo and the pentoxifylline group (p<0.01 for both groups). Retinal vessel diameter, RBCV, calculated retinal blood flow and white blood cell flow were not altered by administration of pentoxifylline. Hyperoxia induced a pronounced decrease in retinal blood flow parameters. No difference was observed between groups during oxygen breathing in vessel diameters (p=0.54), RBCV (p=0.34), calculated retinal blood flow (p=0.3) and white blood cell flow (p=0.26). ConclusionOur data indicate that short time administration of pentoxifylline does not alter the oxygen-induced effect on ocular blood flow parameters during leukocytosis. Whether long-term treatment could improve retinal blood flow under states of vasoconstriction remains to be investigated.

Retinal white blood cell flux and systemic blood pressure in patients with type 1 diabetes

There is evidence that altered retinal blood flow and altered retinal blood flow regulation play a role in the development and progression of diabetic retinopathy. We compared the association between systemic blood pressure and retinal white blood cell flux in patients with type 1 diabetes and healthy control subjects. The study was performed in 100 patients with type 1 diabetes with no or minimal diabetic retinopathy and a group of 313 age-matched healthy controls. Inclusion criteria were systolic blood pressure ≤ 160 mmHg and diastolic blood pressure ≤ 95 mmHg. None of the subjects took vasoactive medication except insulin. The blue field entoptic technique was used to assess retinal white blood cell flux, velocity and density in the perimacular region. Pressure-flow relationships were calculated for both groups to assess differences in blood flow regulation. Retinal white blood cell flux was comparable between the two study groups. Both type 1 diabetic patients and healthy subjects showed a significant positive correlation between retinal white blood cell flux and mean arterial pressure (diabetic patients: r=0.48; p<0.05, healthy subjects r=0.28). The correlation coefficients between mean arterial pressure and white blood cell flux were significantly higher in patients with diabetes than in the healthy control group (p=0.0459). Retinal white blood cell flux, as assessed with the blue-field entoptic technique, is not significantly different between type 1 diabetic patients with no or minimal retinopathy and healthy control subjects. Type 1 diabetic subjects do, however, show an abnormal association between systemic blood pressure and retinal white blood cell flux. This indicates altered autoregulation in early diabetic retinopathy.

Effects of increased white blood cell count on retinal perfusion during hyperoxia-induced vasoconstriction

PurposeSeveral studies have shown that administration of granulocyte-colony stimulating factor (G-CSF) is followed by an increase of white blood cell (WBC) count. There is evidence from other vascular beds that an increase in WBC count impairs blood flow regulation especially in the microcirculation. Whether this also holds true for the ocular circulation is yet unknown. In the following trial we investigated whether an increase in WBC count alters the oxygen induced vasoconstriction of retinal vessels. MethodsThe study design was randomized, double-masked, placebo-controlled with two parallel groups. 24 healthy, male subjects were included. Measurements of retinal white blood cell flux with the blue-field entoptic technique, red blood cell velocity using the laser Doppler velocimeter and retinal vessel diameter using a Retinal Vessel Analyzer, were assessed at baseline and after breathing of 100% oxygen over 20min. Thereafter 300μg of G-CSF or placebo was administered. Measurements were repeated after another inhalation of 100% oxygen 8h later. ResultsG-CSF did not show any influence on systemic hemodynamics. WBC count increased significantly from 5.7±1.6×109/L at baseline up to 19.5±4.8×109/L 8h after G-CSF administration. As expected, oxygen breathing induced a pronounced vasoconstriction and a decrease red and white cell flux in both, the placebo and the G-CSF group (p<0.01 for both groups). Administration of G-CSF increased WBC flux, but did not affect red blood cell flux. The response of red blood cell flux and retinal vessel diameters to hyperoxia was not altered by G-CSF administration. However, leukocytosis leads to a more pronounced oxygen induced reduction in red blood cell velocity compared to the placebo group (p=0.024). ConclusionOur data indicate that increased WBC count as induced with G-CSF, leads to a more pronounced reduction in retinal red blood cell flux during states of vasoconstriction. This indicates that, as in other vascular beds, an increase in WBC leads to an altered blood flow regulation.

Effects of increased neutrophile count on ET1 – induced changes in erythrocyte and leukocyte movements

AbstractPurpose It is known that granulocyte‐colony stimulating factor (G‐CSF) increases white blood cell (WBC) count. There is evidence from other vascular beds that an increase in WBC count impairs blood flow regulation in the microcirculation. Whether this also holds true for the ocular circulation is yet unknown. In the following trial we investigated whether an increase in WBC count alters the endothelin‐1 (ET‐1) induced vasoconstriction.Methods 24 healthy male subjects entered this randomized, placebo‐controlled, double masked, two‐way cross over study. 300µg G‐CSF or placebo were applied intravenously to increase WBC count on two study days. Thereafter, ET‐1 (5ng/kg/min) was infused for 30 minutes. Ocular hemodynamic variables were measured before and after G‐CSF treatment and during the last 10 minutes of ET‐1 infusion. Measurements of retinal WBC flux were performed with the blue‐field entoptic technique, blood flow (BF) velocity using a laser Doppler velocimeter and retinal vessel diameter using a Retinal Vessel Analyzer.Results Neither G‐CSF nor ET‐1 had any consistent effect on blood pressure, pulse rate or IOP. G‐CSF induced an increase in retinal WBC density (p&lt;.01). As expected ET‐1 lowered choroidal BF (p&lt;.01), retinal BF (p&lt;.01)and WBC velocity (p=.01). Changes in choroidal BF and WBC velocity in response to ET‐1 were not altered by pre‐treatment with G‐CSF. Contrary, the decrease in retinal BF was more pronounced during leukocytosis (p=.02) as compared to placebo.Conclusion During vasoconstriction, induced by ET‐1, vascular regulation can be altered by the number of circulating leukocytes. Whether this is caused by an interaction of red and white blood cells or by another mechanism is yet unknown.

Reactivity of white blood cell flux to hyperoxia in patients infected with human immunodeficiency virus

The aetiology of the apparently vasoocclusive phenomena in human immunodeficiency virus (HIV)-related retinopathy is not well understood. Several hypotheses, including infectious damage of the retinal vasculature and altered retinal haemodynamics, have been postulated. Direct measurement of oxygen tension in the retina is not possible in vivo and indirect methods have to be employed. The objective of this study was to investigate the retinal vascular response to 100% oxygen breathing in patients with HIV. Twelve patients infected with HIV and 12 healthy individuals, matched for age, sex and smoking habits, were studied in an open study using the blue-field entoptic technique for the measurement of retinal white blood cell (WBC) flux. Reactivity in retinal blood flow during 100% O(2) breathing over 15 min was measured and expressed as percentage change over baseline. WBC velocity during oxygen inhalation decreased over baseline by 9.0 ± 5.8% in HIV-infected patients and by 18.6 ± 5.4% in healthy participants (p < 0.04 between groups, ANOVA). The decrease in WBC velocity was paralleled by a decrease in WBC density. This decrease tended to be more pronounced in healthy participants (13.6 ± 7.9%) than in HIV-infected patients (8.0 ± 10.8%), but the difference was not statistically significant (p = 0.1 between groups, ANOVA). WBC flux decrease was 16.2 ± 11.4% in HIV-infected patients and 29.5 ± 9.5% in the control group and was significant between groups (p = 0.007 between groups, ANOVA). Our results indicate a reduced reactivity of WBC flux to systemic hyperoxia in patients with HIV. Whether abnormal retinal haemodynamics in HIV-infected persons contributes to the pathogenesis of HIV-related microvascular diseases or is a consequence of the structural changes associated with the disease is unknown.

Twelve‐hour reproducibility of retinal and optic nerve blood flow parameters in healthy individuals

The aim of the present study was to investigate the reproducibility and potential diurnal variation of optic nerve head and retinal blood flow parameters in healthy individuals over a period of 12 hr. We measured optic nerve head and retinal blood flow parameters in 16 healthy male non-smoking individuals at five time-points during the day (08:00, 11:00, 14:00, 17:00 and 20:00 hr). Outcome parameters were perimacular white blood cell flux (as assessed with the blue field entoptic technique), blood velocities in retinal veins (as assessed with bi-directional laser Doppler velocimetry), retinal arterial and venous diameters (as assessed with the retinal vessel analyser), optic nerve head blood flow, volume and velocity (as assessed with single point and scanning laser Doppler flowmetry) and blood velocities in the central retinal artery (as assessed with colour Doppler imaging). The coefficient of variation and the maximum change from baseline in an individual were calculated for each outcome parameter. No diurnal variation in optic nerve head or retinal blood flow was observed with any of the techniques employed. Coefficients of variation were between 1.6% and 18.5% for all outcome parameters. The maximum change from baseline in an individual was much higher, ranging from 3.7% to 78.2%. Our data indicate that in healthy individuals the selected techniques provide adequate reproducibility to be used in clinical studies. However, in patients with eye diseases and reduced vision the reproducibility may be considerably worse.

Pioglitazone does not Affect Vascular or Inflammatory Responses after Endotoxemia in Humans

PPARgamma agonists have been proposed to exert more than metabolic benefits, particularly by anti-inflammatory mechanisms. We hypothesized that pioglitazone might modulate inflammatory and vascular responses to lipopolysaccharide (LPS). In a placebo-controlled parallel-group study in 18 healthy male subjects, the E. coli endotoxin model of inflammation (20 IU/kg i. v.) was employed to test the effect of 60 mg pioglitazone over nine days on inflammatory cytokines. Macrovascular function and microvascular blood flow were assessed by brachial artery ultrasound and retinal blood flow parameters, respectively. Pioglitazone increased brachial artery diameter by 5.6% but had no effect on other outcome parameters under resting conditions. LPS increased cytokine levels to peak concentrations of 91.3+/-22.5 ng/ml (IL-6), 261.4+/-60.0 ng/ml (TNFalpha), and 524.5+/-15.3 ng/ml (VCAM-1). The endotoxin caused microvascular vasodilation and increased retinal white blood cell flux, while baseline brachial artery diameter remained unchanged. Pioglitazone had no effect on inflammatory cytokine or adhesion molecule release but mitigated LPS-induced hypotension (p<0.05). Neither brachial artery function nor microvascular blood flow was altered by pioglitazone. In conclusion, acute immune reactions to LPS are not affected by pioglitazone, which exerts subtle vascular effects alone and during endotoxemia. The anti-inflammatory properties of short-term pioglitazone to endotoxins in healthy subjects are therefore limited.

Reactivity of retinal blood flow to 100% oxygen breathing after lipopolysaccharide administration in healthy subjects

Administration of low doses of Escherichia coli endotoxin (LPS) to humans enables the study of inflammatory mechanisms. The purpose of the present study was to investigate the retinal vascular reactivity after LPS infusion. In a randomized placebo-controlled cross-over study, 18 healthy male volunteers received 20 IU/kg LPS or placebo as an intravenous bolus infusion. Outcome parameters were measured at baseline and 4 h after LPS/placebo administration. At baseline and at 4 h after administration a short period of 100% oxygen inhalation was used to assess retinal vasoreactivity to this stimulus. Perimacular white blood cell velocity, density and flux were assessed with the blue-field entoptic technique, retinal branch arterial and venous diameters were measured with a retinal vessel analyzer and red blood cell velocity in retinal branch veins was measured with laser Doppler velocimetry. LPS is associated with peripheral blood leukocytosis and increased white blood cell density in ocular microvessels ( p < 0.001). In addition, retinal arterial ( p = 0.02) and venous ( p < 0.01) diameters were increased. All retinal hemodynamic parameters showed a decrease during 100% oxygen breathing. This decrease was significantly blunted by LPS for all retinal outcome parameters except venous diameter ( p = 0.04 for white blood cell velocity, p = 0.0002 for white blood cell density, p < 0.0001 for white blood cell flux, p = 0.01 for arterial diameter, p = 0.02 for red blood cell velocity and p = 0.006 for red blood cell flux). These data indicate that LPS-induced inflammation induces vascular dysregulation in the retina. This may provide a link between inflammation and vascular dysregulation. Further studies are warranted to investigate whether this model may be suitable to study inflammation induced vascular dysregulation in the eye.

Response of Retinal Blood Flow to CO2-Breathing in Humans

To investigate the effect of systemic hypercapnia on retinal hemodynamics in humans. We studied the effect of breathing a mixture of normal air with 5% CO2 for 13 minutes in ten healthy young male volunteers, using the Zeiss retinal vessel analyzer for continuous measurement of retinal vessel diameter and the blue-field entoptic technique to quantify retinal white blood cell flux. In eight other subjects the effect of hypercapnia was measured with the Zeiss retinal vessel analyzer and by laser Doppler velocimetry to establish retinal blood flow velocity. Retinal arterial and venous vessel diameters increased by a maximum of 4.2% and 3.2%, respectively. Peak effect was observed after 3 minutes of breathing the mixture of normal air with 5% CO2. During hypercapnia red blood cell velocity increased 11.7% and, accordingly, retinal blood flow increased 19.1%. White blood cell density and velocity rose significantly during hypercapnia, resulting in an increase in white blood cell flux (19.2%). Our data indicate that CO2 induces vasodilation in retinal arteries and retinal veins. Retinal blood flow and perimacular white blood cell flux increased to the same extent in subjects breathing a mixture of normal air with 5% CO2.

Ocular hyperperfusion following onset of intensified insulin therapy is inversely correlated with plasma endothelin-1 in Type I diabetes

It has been reported that improvement of metabolic control by intensified insulin therapy in patients with Type I (insulin-dependent) diabetes mellitus is associated with alterations in ocular blood flow. We hypothesized that these changes in ocular blood flow could be associated with alterations of plasma insulin, glucose or endothelin concentration. In 16 patients with Type I diabetes ocular haemodynamic parameters were assessed daily during the first 5 days of institution of intensified insulin therapy and plasma concentrations of glucose, insulin, and endothelin-1 plasma were measured. Retinal white blood cell flux was estimated with the blue field entoptic technique. Pulsatile choroidal blood flow was assessed by laser interferometric measurement of fundus pulsation amplitude. Retinal white blood cell flux ( p=0.0015) and ocular fundus pulsation amplitude ( p<0.001) increased during institution of strict metabolic control. Changes in ocular haemodynamic variables were inversely correlated with concentrations of plasma ET-1, but not with that of insulin or glucose. These data indicate that institution of improved metabolic status is paralleled by rapid changes in the production of ET-1, which could in turn affect ocular perfusion.

Age dependence of perimacular white blood cell flux during isometric exercise

Purpose. To investigate the age dependence of perimacular white blood cell flux (WBCF) during isometric exercise. Methods. Fourteen healthy young (age range: 21–29 years; 24 ± 3 years, mean ± SD, 12 male and 2 female) and 15 healthy middle-aged (age range: 45–57 years; 53 ± 4 years, mean ± SD; 5 male and 10 female) volunteers were studied. Subjects performed isometric handgrip for 10 minutes and squatting for 6 minutes. WBCF was assessed with the blue field entoptic technique, mean arterial pressure (MAP) was measured with an automated oscillometric device, intraocular pressure (IOP) was measured by Goldmann applanation tonometry and ocular perfusion pressure (OPP) was calculated as 2/3 MAP – IOP. Results. Baseline WBCF was significantly higher in young subjects than in middle-aged subjects (191 ± 28 vs 142 ± 23; p = 0.001). Isometric handgrip induced a significant increase in WBCF in the middle-aged subjects (23 ± 24%; p = 0.005), but not in the young subjects. Squatting significantly increased WBCF in both groups (young: 42 ± 23%; p = 0.004 and middle aged: 51 ± 27%; p < 0.001). A significant deviation from baseline WBCF was observed when OPP increased by 42 ± 4% (p = 0.003) and 35 ± 4% (p < 0.001) for the young and middle-aged subjects, respectively. The OPP-WBCF relationship was not different between the two study groups. Conclusion. Altered retinal autoregulation as observed in vascular ocular disease appears to be unrelated to the normal physiological aging process.