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Biomedical subjects

M Intaglietta

Publications and source records attributed to M Intaglietta.

At least 19 recordsLinked to original sources
PubMed2001

Effect of erythrocyte aggregation on velocity profiles in venules.

A recent whole organ study in cat skeletal muscle showed that the increase in venous resistance seen at reduced arterial pressures is nearly abolished when the muscle is perfused with a nonaggregating red blood cell suspension. To explore a possible underlying mechanism, we tested the hypothesis that red blood cell aggregation alters flow patterns in vivo and leads to blunted red blood cell velocity profiles at reduced shear rates. With the use of fluorescently labeled red blood cells in tracer quantities and a video system equipped with a gated image intensifier, we obtained velocity profiles in venous microvessels (45-75 microm) of rat spinotrapezius muscle at centerline velocities between 0.3 and 14 mm/s (pseudoshear rates 3-120 s(-1)) under normal (nonaggregating) conditions and after induction of red blood cell aggregation with Dextran 500. Profiles are nearly parabolic (Poiseuille flow) over this flow rate range in the absence of aggregation. When aggregation is present, profiles are parabolic at high shear rates and become significantly blunted at pseudoshear rates of 40 s(-1) and below. These results indicate a possible mechanism for increased venous resistance at reduced flows.

Algorithms↗
PubMed2001

Effects of erythrocyte aggregation and venous network geometry on red blood cell axial migration.

Axial migration of red blood cells in small glass tubes can cause blood viscosity to be effectively independent of shear rate. However, this phase separation may not occur to the same degree in the venous network due to infusion of cells and aggregates at branch points. To investigate this hypothesis, we followed trajectories of fluorescently labeled red blood cells in the venular network of the rat spinotrapezius muscle at normal and reduced flow with and without red blood cell aggregation. Cells traveling near the wall of an unbranched venular segment migrated approximately 1% of the longitudinal path length without aggregation and migrated slightly more with aggregation. Venular segment length between branch points averaged three to five times the diameter. Cells in the main vessel were shifted centrally by up to 20% of diameter at branch points, reducing the migration rate of cells near the opposite wall to <1% even in the presence of aggregation. We conclude that formation of a cell-free marginal layer in the venular network is attenuated due to the time dependence of axial migration and the frequent branching of the network.

Animals↗
PubMed2001

Erythrocyte margination and sedimentation in skeletal muscle venules.

Previous studies in skeletal muscle of the dog and cat have shown that venous vascular resistance changes inversely with blood flow and may be due mainly to red blood cell aggregation, a phenomenon present in these species. To determine whether red blood cell axial migration and sedimentation contribute to this effect, we viewed either vertically or horizontally oriented venules of the rat spinotrapezius muscle with a horizontally oriented microscope during acute arterial pressure reduction. With normal (nonaggregating) rat blood, reduction of arterial pressure did not significantly change the relative diameter of the red blood cell column with respect to the venular wall. After induction of red blood cell aggregation in the rat by infusion of Dextran 500, red blood cell column diameter decreased up to 35% at low pseudoshear rates (below approximately 5 s(-1)); the magnitude was independent of venular orientation. In vertically oriented venules, the plasma layer was symmetrical, whereas in horizontally oriented venules, the plasma layer formed near the upper wall. We conclude that, although red blood cell axial migration and sedimentation develop in vivo, they occur only for larger flow reductions than are needed to elicit changes in venous resistance.

Animals↗
PubMed2001

High viscosity plasma expanders: Volume restitution fluids for lowering the transfusion trigger.

Hemorheological studies lead to the axiom that high plasma viscosity is detrimental and that it is beneficial to lower blood viscosity, a precept embodied in the practice of hemodilution, where improved perfusion is attributed to the lowering of blood viscosity. Hemodilution is limited by the transfusion trigger, hemoglobin content of blood of about 7-8 g/dl, which indicates when further volume replacements must restore oxygen carrying capacity with red blood cells (RBC). However, oxygen consumption and delivery are not compromised upon passing this landmark. The reduced blood viscosity does not transmit adequate pressure to the capillaries, causing functional capillary density (FCD) to decrease, jeopardizing organ function through the inadequate extraction of products of metabolism from the tissue by the capillaries. Studies in hemorrhagic shock show that survival is primarily determined by the maintenance of FCD and secondarily by tissue oxygenation. FCD is maintained as hematocrit is reduced beyond the transfusion trigger by increasing plasma viscosity, which transmits systemic pressure to the capillaries and induces vasodilatation through the increased shear stress dependent release of vasodilators. Consequently the transfusion trigger is also a "viscosity trigger" indicating when blood and plasma viscosity are too low. In this condition increasing plasma viscosity is beneficial and extends the transfusion trigger reducing the use of blood transfusions.

Animals↗
PubMed2001

Rheological effects of red blood cell aggregation in the venous network: a review of recent studies.

It has long been recognized that understanding the rheological properties of blood is essential to a full understanding of the function of the circulatory system. Given the difficulty of obtaining carefully controlled measurements in vivo, most of our current concepts of the flow behavior of blood in vivo are based on its properties in vitro. Studies of blood rheology in rotational and tube viscometers have defined the basic properties of blood and pointed to certain features that may be especially significant for understanding in vivo function. At the same time, differences between in vivo and in vitro systems combined with the complex rheological properties of blood make it difficult to predict in vivo blood rheology from in vitro studies. We have investigated certain flow properties of blood in vivo, using the venular network of skeletal muscle as our model system. In the presence of red blood cell aggregation, venous velocity profiles become blunted from the parabolic as in Poiseuille flow, as pseudo-shear rate (= mean fluid velocity/vessel diameter) is decreased from approximately 100 s(-1) to 5 s(-1). At control flow rates, the short distance between venular junctions does not appear to permit significant axial migration and red cell depletion of the peripheral fluid layer before additional red cells and aggregates are infused from a feeding tributary. Formation of a cell-free plasma layer at the vessel wall and sedimentation in vivo are evident only at very low pseudo-shear rates (<5 s(-1)). These findings may explain in large part observations in whole organs of increased venous resistance with reduction of blood flow.

Blood Flow Velocity↗
PubMed2000

Constriction of resistance arteries determines l-NAME-induced hypertension in a conscious hamster model.

The influence of infusion of a nitric oxide (NO) synthase inhibitor, N(omega)-nitro-l-arginine methyl ester (l-NAME), on resistance arteries (diameter, 150 +/- 8 microm) and its relationship with hypertension were examined in conscious hamsters fitted with a dorsal skinfold window. After infusing l-NAME (10 and 30 mg/kg), hamsters showed immediate hypertension of +13 +/- 9 and +21 +/- 9 mm Hg, respectively, relative to basal values, and a maximum of +44 +/- 4 mm Hg at 30 min for the high-dose group. There was simultaneous significant vasoconstriction of the resistance arteries (A(0)) which reduced to 60 +/- 5% of baseline diameter at 3 h; however, there was no significant vasoconstriction in large and small arterioles with diameters diameters less than 70 microm. Blood flow rate in all the vessels decreased in consonance with the vasoconstriction of the resistance artery, irrespective of microvessel classification. These results indicate that the resistance artery plays a key role as a regulator and microvascular resistance in determining blood flow distribution and hypertension when a NO synthase inhibitor is infused.

Animals↗
PubMed2000

Diameter changes in skeletal muscle venules during arterial pressure reduction.

Previous studies in skeletal muscle have shown a substantial (>100%) increase in venous vascular resistance with arterial pressure reduction to 40 mmHg, but a microcirculatory study showed no significant venular diameter changes in the horizontal direction during this procedure. To examine the possibility of venular collapse in the vertical direction, a microscope was placed horizontally to view a vertically mounted rat spinotrapezius muscle preparation. We monitored the diameters of venules (mean diameter 73. 8 +/- 37.0 microm, range 13-185 microm) oriented horizontally and vertically with a video system during acute arterial pressure reduction by hemorrhage. Our analysis showed small but significant (P < 0.0001) diameter reductions of 1.0 +/- 2.5 microm and 1.8 +/- 3. 1 microm in horizontally and vertically oriented venules, respectively, upon reduction of arterial pressure from 115.0 +/- 26. 3 to 39.8 +/- 12.3 mmHg. The venular responses were not different after red blood cell aggregation was induced by Dextran 500 infusion. We conclude that diameter changes in venules over this range of arterial pressure reduction are isotropic and would likely increase venous resistance by <10%.

Animals↗
PubMed2000

Molecular dimensions of Hb-based O(2) carriers determine constriction of resistance arteries and hypertension.

The effect of molecular dimension of hemoglobin (Hb)-based O(2) carriers on the diameter of resistance arteries (A(0), 158 +/- 21 microm) and arterial blood pressure were studied in the conscious hamster dorsal skinfold model. Cross-linked Hb (XLHb), polyethylene glycol (PEG)-conjugated Hb, hydroxyethylstarch-conjugated XLHb, polymerized XLHb, and PEG-modified Hb vesicles (PEG-HbV) were synthesized. Their molecular diameters were 7, 22, 47, 68, and 224 nm, respectively. The bolus infusion of 7 ml/kg of XLHb (5 g/dl) caused an immediate hypertension (+34 +/- 13 mmHg at 3 h) with a simultaneous decrease in A(0) diameter (79 +/- 8% of basal value) and a blood flow decrease throughout the microvascular network. The diameter of smaller arterioles did not change significantly. Infusion of larger O(2) carriers resulted in lesser vasoconstriction and hypertension, with PEG-HbV showing the smallest changes. Constriction of resistance arteries was found to be correlated with the level of hypertension, and the responses were proportional to the molecular dimensions of the O(2) carriers. The underlying mechanism is not evident from these experiments; however, it is likely that the effects are related to the diffusion properties of the different Hb molecules.

Animals↗
PubMed1999

Tumour necrosis factor-alpha cytokine promoter gene polymorphism in Hodgkin's disease and chronic lymphocytic leukaemia.

Regulation of cytokine levels has been shown to be under genetic control through the coding and promoter sequences of genetic polymorphisms. We elucidated the prevalence of a previously described G to A transition polymorphism at position -308 of the tumour necrosis factor-alpha (TNF-alpha) promoter region in a population of patients with Hodgkin's disease (HD) (n = 36) and chronic lymphocytic leukaemia (CLL) (n = 49) and healthy volunteers (n = 51). The DNA fragment containing this polymorphism was amplified by PCR and sequenced by solid-phase minisequencing. The frequency of the TNF-alpha promoter polymorphism was not significantly different between CLL patients and HD patients compared to controls.

Adult↗
PubMed1999

Haemodynamics and oxygen tension in the microcirculation of ischaemic skin flaps after neural blockade and haemodilution.

The aim of this study was to evaluate the effects of neural blockade and extended normovolaemic haemodilution on haemodynamics and oxygenation in the microcirculation of ischaemic skin flaps using a recently developed island flap on the back of Syrian golden hamsters. One part of the flap was made ischaemic by inducing a random perfusion pattern following interruption of the axial blood supply. The model permitted quantitative assessment of the microhaemodynamics and oxygen tension in all microvascular segments by the use of intravital microscopy. Oxygen tension was measured with the phosphorescence decay method. Neural blockade was induced by applying 2% lidocaine to the neurovascular flap pedicle. Haemodilution was achieved by isovolaemic exchange of 50% of the total blood volume with dextran 70. One hour after surgery (baseline), centreline velocity was significantly reduced to 20-44% in all the microvessels in the randomly as compared to the axially perfused part, whereas the diameters were slightly larger (ns). In the control group, blood flow declined by 20-75% (P< 0.01 vs. baseline) over time in the entire flap. Flow reduction was significantly attenuated by haemodilution in the entire flap, but more pronounced in the ischaemic part. Neural blockade caused marked vasodilatation and significantly improved blood flow in the axially but not in randomly perfused microvessels. After 8 h, oxygen tension ranged from 4.0 to 6.1 mmHg in the axial part (means, ns between groups), whereas in the ischaemic part, it was 0.8-1.0 mmHg (P< vs. axial) in the control and neural blockade groups, and 1.7 mmHg (ns vs. axial and between groups) after haemodilution. Our findings indicate that neural blockade does not improve microcirculation and oxygenation in randomly perfused flap tissue because the sympathetic regulation of its microcirculation is overruled by autoregulatory mechanisms. Normovolaemic haemodilution, even after a 50% exchange, augments oxygenation in ischaemic flap tissue due to increased blood flow particularly in the randomly perfused tissue.

Analysis of Variance↗
PubMed1999

Quantitative assessment of microhemodynamics in ischemic skin flap tissue by intravital microscopy.

Skin flaps are susceptible to ischemia, which may result in tissue necrosis particularly in areas deprived of their original anatomic blood supply. The pathophysiology of skin flap failure has been debated for many years, but due to methodological insufficiencies, every proposed theory has remained hypothetical. The aim of this study was to gain more evidence for the mechanisms involved in flap ischemia by assessing quantitatively hemodynamic parameters such as diameter, flow velocity, and volume flow in the microcirculation of a flap. To this end the authors developed a new island flap on the back of Syrian golden hamsters that allowed intravital microscopic investigation. The flap included an extended portion, which was deprived of its original anatomic blood supply. One hour after flap dissection, blood flow was 42% to 66% lower in all microvessels in the extended area than in the anatomically perfused part of the flap (p<0.05). In the entire microvasculature, a significant gradual decline of blood flow was observed over time. Any blood flow reduction was caused to a major extent by diminished flow velocity. At all times, microvascular diameters were slightly larger in the extended portion of the flap than in the anatomically perfused portion of the flap. The authors conclude that their new model is a unique tool for investigating microhemodynamic mechanisms involved in flap ischemia. This study reveals hypoperfusion of extended flap tissue, which is attributed to diminished arterial perfusion pressure but not to vasoconstriction or arteriovenous shunting.

Animals↗
PubMed1999

Microvascular responses to hemodilution with Hb vesicles as red blood cell substitutes: influence of O2 affinity.

Phospholipid vesicles encapsulating purified hemoglobin (HbV) were developed to provide O2-carrying capacity to plasma expanders. Microvascular perfusion was determined for HbV with different O2 affinity (P50 = 9, 16, and 30 mmHg) prepared by coencapsulating pyridoxal 5'-phosphate (PLP) at the molar ratios of [PLP]/[Hb] = 0, 0.5, and 3, respectively (cf. hamster blood, P50: 28 mmHg), and suspended in 8 g/dl human serum albumin (HSA). Eighty percent of the red blood cell (RBC) mass of conscious Syrian golden hamsters fitted with dorsal skinfold windows was substituted with either of the HbV-HSA suspensions, washed hamster RBC suspended in HSA (RBC-HSA), and HSA alone. All three HbV-HSA groups and RBC-HSA groups showed stable blood pressure and heart rate, which could not be sustained with HSA alone. Only the HbV (P50 = 9)-HSA group showed an increase in arterial O2 tension (89.8 +/- 14.7 mmHg, baseline 58.4 +/- 4.0 mmHg) because of hyperventilation, and microvascular perfusion was decreased, indicating that facilitated O2 unloading of HbV by decreasing the O2 affinity (increasing P50) with PLP as an allosteric effector is important. Microvascular perfusion and microvascular and interstitial O2 tensions in the HbV (P50 = 16 and 30)-HSA groups were significantly higher than those in the HSA group. The O2 release rate from the HbV was 18-32 s-1 vs. 4.4 s-1 for RBC. Functional capillary density was improved from 17 to 41% on average by decreasing P50 from 30 to 16 mmHg, which appears to be an optimal value for the P50 in this system.

Animals↗
PubMed1999

Changes in resistance vessels during hemorrhagic shock and resuscitation in conscious hamster model.

The unanesthetized hamster dorsal skinfold preparation was used to monitor diameters and blood flow rates in resistance arteries (small arteries, A0: diameter, 156 +/- 23 micrometers) and capacitance vessels (small veins, V0: 365 +/- 64 micrometers), during 45 min of hemorrhagic shock at 40 mmHg mean arterial pressure (MAP) and resuscitation. A0 and V0 vessels constricted significantly to 52 and 70% of the basal values, respectively, whereas precapillary arterioles (A1-A4, 8-60 micrometers) and collecting venules (VC-VL, 26-80 micrometers) did not change or tended to dilate. Blood flow rates in the microvessels declined to <20% of the basal values. Resuscitation with shed autologous blood (SAB) showed incomplete recovery of A0 and V0 diameters even 2 h after resuscitation (71 +/- 14% and 81 +/- 18%, respectively, of basal value), whereas other vessels did not change significantly. The behavior of A0 diameter coincided with the incomplete recovery of blood flow rates in all the vessels (ca. 50%) according to Poiseuille's law, and the incomplete recovery of functional capillary density (ca. 75%). Resuscitation with 8% human serum albumin in saline (HSA) tended to show higher levels of A0 constriction and A4 dilation and lowered blood flow rates. Resuscitation with SAB restored tissue PO2 27 +/- 10 mmHg after 2 h, which was near control levels (28 +/- 5 mmHg), whereas resuscitation with HSA caused tissue PO2 to remain significantly depressed (6 +/- 2 mmHg), and flow rates were significantly lower than resuscitation with SAB. These results indicate that response of the A0 vessels is the crucial determinant of blood flow in the observed area. The constriction of A0 may help sustain MAP, and constriction of V0 may enhance blood redistribution from the skin to the vital organs under the hypotensive condition.

Animals↗
PubMed1999

Systemic and microcirculatory effects of autologous whole blood resuscitation in severe hemorrhagic shock.

Systemic and microcirculatory effects of autologous whole blood resuscitation after 4-h hemorrhagic shock with a mean arterial pressure (MAP) level of 40 mmHg were investigated in 63 conscious Syrian golden hamsters. Microcirculation of skeletal skin muscle and subcutaneous connective tissue was visualized in a dorsal skinfold. Shed blood was retransfused within 30 min after 4 h. Animals were grouped into survivors in good (SG) and poor condition (SP) and nonsurvivors (NS) according to 24-h outcome after resuscitation and studied before shock, during shock (60, 120, and 240 min), and 30 min and 24 h after resuscitation. Microvascular and interstitial PO2 values were determined by phosphorescence decay. Shock caused a significant increase of arterial PO2 and decrease of PCO2, pH, and base excess. In the microcirculation, there was a significant decrease in blood flow (QB), functional capillary density (FCD; capillaries with red blood cell flow), and interstitial PO2 [1.8 +/- 0.8 mmHg (SG), 1.3 +/- 1.3 mmHg (SP), and 0.9 +/- 1.1 mmHg (NS) vs. 23.0 +/- 6.1 mmHg at control]. Blood resuscitation caused immediate MAP recompensation in all animals, whereas metabolic acidosis, hyperventilation, and a significant interstitial PO2 decrease (40-60% of control) persisted. In NS (44.4% of the animals), systemic and microcirculatory alterations were significantly more severe both in shock and after resuscitation than in survivors. Whereas in SG (31.8% of the animals) there was only a slight (15-30%) but still significant impairment of microscopic tissue perfusion (QB, FCD) and oxygenation at 24 h, SP (23.8% of the animals) showed severe metabolic acidosis and substantial decreases (>/=50%) of FCD and interstitial PO2. FCD, interstitial PO2, and metabolic state were the main determinants of shock outcome.

Animals↗
PubMed1999

Microcirculatory basis for the design of artificial blood.

Artificial blood or blood substitutes are being developed using molecular solutions of modified free hemoglobin. When these products are used and the red blood cell mass is reduced below the transfusion trigger, there is a condition of extreme hemodilution which is characterized by a significant reduction of blood viscosity and NO production, reflex vasoconstriction, decreased functional capillary density, and impaired microvascular function. This combination of events may be lethal because decreased NO availability may also increase the intrinsic oxygen consumption of the tissue. Current developments in the understanding of the physiology of the microcirculation in extreme hemodilution, and the physical events associated with the substitution of red blood cells with molecular hemoglobin solutions show that a viable "artificial blood" can be obtained from a new formulation of the product, where viscosity is such that when introduced in the circulation the resulting viscosity of blood is close to normal, the dissociation curve is left shifted and the concentration of hemoglobin is in the range of 3-5 g Hb/dl. This formulation redistributes viscous losses in the circulation causing higher capillary pressure which maintains functional capillary density, a key parameter in tissue survival. Furthermore the increased plasma viscosity increases shear stress in the microcirculation, enhancing the production shear dependent vasodilators, thus counteracting the vasoconstrictor effects due to NO scavenging by free hemoglobin solutions. A principal feature of this formulation is that it maintains microvascular function when the transfusion trigger is passed and the circulation is subjected to extreme hemodilution.

Animals↗
PubMed1998

Microvascular and tissue oxygen gradients in the rat mesentery.

One of the most important functions of the blood circulation is O2 delivery to the tissue. This process occurs primarily in microvessels that also regulate blood flow and are the site of many metabolic processes that require O2. We measured the intraluminal and perivascular pO2 in rat mesenteric arterioles in vivo by using noninvasive phosphorescence quenching microscopy. From these measurements, we calculated the rate at which O2 diffuses out of microvessels from the blood. The rate of O2 efflux and the O2 gradients found in the immediate vicinity of arterioles indicate the presence of a large O2 sink at the interface between blood and tissue, a region that includes smooth muscle and endothelium. Mass balance analyses show that the loss of O2 from the arterioles in this vascular bed primarily is caused by O2 consumption in the microvascular wall. The high metabolic rate of the vessel wall relative to parenchymal tissue in the rat mesentery suggests that in addition to serving as a conduit for the delivery of O2 the microvasculature has other functions that require a significant amount of O2.

Animals↗