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Biomedical subjects

M Intaglietta

Publications and source records attributed to M Intaglietta.

At least 91 records · Page 5Linked to original sources
PubMed1990

Capillary narrowing in hemorrhagic shock is rectified by hyperosmotic saline-dextran reinfusion.

Previously, we showed that skeletal muscle capillaries narrow during hemorrhagic shock due to swelling of endothelial cells. The present study investigated if these narrowed capillaries affected reflow and compared the effects of fluid reinfusion with iso- and hyperosmotic solutions, in particular 7.5% NaCl/6% dextran 70 (HSD) and Ringer's lactate (RL). Intravital microscopy was used to visualize capillaries in the rabbit tenuissimus muscle during 1 h of shock (40% hemorrhage) and subsequent reinfusion period. Changes in capillary lumenal diameter were inferred by changes in the width of red blood cells traversing the capillary. At the end of the shock period, the capillary diameter was reduced by 20.4 +/- 8.0% (N = 24). With infusion of HSD (dose equal to one-seventh of the shed blood volume; N = 7), there was a sustained flow resurgence and complete return of the capillary diameter to control values after 30 min. The response appears to result from both the hypertonic saline and dextran components. Reinfusion with RL (dose equal to the shed blood volume; N = 7) caused only a transient increase in flow and no change in the lumenal narrowing. We conclude that HSD surpasses conventional RL treatment in reestablishing capillary hemodynamics owing to a decreased hydraulic resistance from osmotically induced endothelium shrinkage.

Animals↗
PubMed1990

Hemodynamic responses in rabbit tenuissimus muscle arterioles during local reduction in perfusion pressure.

Transverse (TR) and terminal (TE) arteriolar diameters and TR pressure were measured in the rabbit tenuissimus muscle during steady state reductions in perfusion pressure. An inflatable occluder was positioned on the abdominal aorta proximal to the bifurcation to alter perfusion pressure. In the control conditions, TEs exhibited highly regular cyclic activity (20 +/- 4 cpm). In contrast, TRs seldom exhibited regular vasomotor activity. Pressure reductions from 76 +/- 1 to 40-50 mm Hg caused no significant change in the observed hemodynamic variables. Reductions below this level caused proportional dilations of TRs and a change in vasomotion pattern of TEs; i.e. the fundamental frequency was unaltered, but periods without vasomotion increased in duration. At an arterial pressure of 30-40 mm Hg, vasomotion in the TEs completely disappeared. Pressure in the distal TR was autoregulated at 40 +/- 4 mm Hg until a threshold (40-50 mm Hg) was reached; thereafter TR pressure decreased in proportion to the arterial pressure decrements. These results suggest that the TRs are the last generation of arterioles involved in the autoregulation of microvascular pressure. Furthermore, the basic frequency and maximal amplitude of vasomotion in TEs are not affected by pressure reductions.

Animals↗
PubMed1989

Confocal laser tomographic analysis of the retina in eyes with macular hole formation and other focal macular diseases.

To study the retinal surface in the human eye in normal and diseased states we used laser scanning tomography. The confocal arrangement of the laser tomographic scanner permits examination of retinal topography in the axis perpendicular to the retinal surface. The eyes examined with the laser tomographic scanner included normal eyes, eyes with macular holes, impending macular holes, radiation retinopathy, macular edema, photocoagulation scars, subfoveal scars, and serous detachment of the fovea associated with subretinal neovascularization. The laser tomographic scanner is a new method that allows measurements of the topography of the internal limiting membrane in the macular area and may improve our understanding of the pathophysiologic characteristics and treatment of a variety of disorders of the macula.

Adult↗
PubMed1989

Volume changes of an endothelial cell monolayer on exposure to anisotonic media.

The osmotic process plays an important role in controlling the distribution of water across cell membranes and thus the cell volume. A system was designed to detect the volume changes of an endothelial cell monolayer when cells were exposed to media with altered osmolalities. Electrodes housed in a flow chamber measured the resistance of ionic media flowing over a cultured cell layer. Assuming the cell membrane acts as an electrical insulator, volume changes of the cell layer can be calculated from the corresponding changes in chamber resistance. The media used in the experiments had osmolalities in the range 120-630 mmol/kg. When cells were exposed to hypertonic media, there was rapid shrinkage with an approximate 30% reduction in total cell volume for a twofold increase in osmolality. On exposure to hypotonic media, the cells initially swelled with an approximate 20% volume increase for a decrease in osmolality by half. With sustained exposure to low osmolality media, there was a gradual and partial return of cell volume towards isotonic values that started 10 minutes after and was complete within 30 minutes of the osmolality alteration. This finding suggests regulatory volume decrease (RVD); however, no regulatory volume increase (RVI) was observed with the continued exposure to hypertonic media over 45 minutes.

Cells, Cultured↗
PubMed1989

Central effects of angiotensin II in conscious hamsters: drinking, pressor response, and release of vasopressin.

The effects of intracerebroventricular (icv) injections of angiotensin II (ANG II) on water intake, blood pressure, heart rate, and plasma arginine-vasopressin (AVP) concentration were studied in chronically instrumented adult male Syrian golden hamsters (Mesocricetus auratus). Furthermore, the effects of pharmacological ganglionic blockade, and of vascular AVP receptor blockade, on central ANG II-induced cardiovascular responses were investigated. ANG II (1, 10, and 100 ng, icv) elicited dose-dependent increases in water intake and arterial blood pressure. Heart rate showed a biphasic response with a short initial non dose-dependent tachycardic and a subsequent longer lasting bradycardic phase. Plasma AVP concentration was increased two and a half fold with 100 ng ANG II icv. Both ganglionic blockade and vascular AVP receptor blockade significantly attenuated the central ANG II-induced pressor response. The tachycardic phase of the heart rate response was abolished by ganglionic blockade and the bradycardic phase was significantly diminished by AVP receptor blockade. The results support the hypothesis that brain ANG II may participate in the central control of body fluid volume and in central cardiovascular regulation in conscious hamsters.

Angiotensin II↗
PubMed1989

Central angiotensin II stimulates arteriolar vasomotion in conscious hamsters.

The effects of intracerebroventricular (icv) injections of 10 ng angiotensin II (ANG II) on mean arteriolar diameter and spontaneous arteriolar vasomotion were studied in subcutaneous tissue of conscious, restrained hamsters, using the skin fold window chamber preparation. Angiotensin II caused a significant decrease in mean arteriolar diameter which was associated with a significant elevation in the amplitude of vasomotion. The frequency of vasomotion did not change significantly. The central ANG II-induced effects on arteriolar vasomotion were not significantly altered by continuous intravenous (iv) infusion of hexamethonium (1 mg.kg-1.min-1). In contrast, iv bolus injection of the vascular vasopressin receptor antagonist d(CH2)5Tyr(Me)AVP (10 micrograms.kg-1) 5 min prior to icv injection of ANG II significantly attenuated the effects of the neuropeptide on mean arteriolar diameter and the amplitude of vasomotion. These data indicate that central ANG II stimulation enhances arteriolar vasomotion in peripheral subcutaneous tissue of conscious hamsters and that this effect may be mediated by release of vasopressin.

Angiotensin II↗
PubMed1989

Local tissue oxygenation during constant red blood cell flux: a discrete source analysis of velocity and hematocrit changes.

Tissue oxygenation in the proximity of single capillaries was investigated mathematically, with the red blood cells (RBC) modeled as discrete oxygen sources separated by plasma gaps. The variables studied are the simultaneous change of capillary RBC flow velocity, and hematocrit (Hct), during constant flux (e.g., RBC velocity x Hct), with an oxygen tension-dependent tissue oxygen consumption rate. The model was used to analyze isovolemic hemodilution under the assumption that the decrease of capillary Hct is compensated by the increase of RBC velocity. The results show that during constant flux conditions, changes in the RBC velocity are directly related to the distance along the capillary to which oxygen is delivered and inversely related to the radial penetration of oxygen into the tissue. Therefore during isovolemic hemodilution, there is a redistribution of the volume of tissue oxygenated whereby a greater volume of tissue becomes oxygenated at an oxygen tension above the critical limit, but at a lower time averaged value. Hypothermia is stimulated and its added effect on constant flux assessed. Tissue oxygenation at low capillary hematocrit was found to be highly sensitive to capillary spacing, suggesting that one of the mechanisms for the maintenance of tissue oxygenation during hemodilution is the recruitment of capillaries.

Blood Flow Velocity↗
PubMed1989

Changes of activated partial thromboplastin time during constant intravenous and fixed intermittent subcutaneous administration of heparin.

Marked circadian variations in the activated partial thromboplastin time (APTt) during continuous heparin infusions for thromboembolic episodes have been reported in a French study. The aim of the present study was to test if these variations could be reproduced in a Swedish population. The frequency spectrum variations in APTt values were analysed with the Prony and the statistical Pearson product momentum correlation coefficient methods. In seven patients with pulmonary embolism, APTt was checked every fourth hour during 48 h of continuous, constant heparin treatment. In only one patient was a distinct circadian variation of APTt values seen. In six patients with venous leg thromboses, treated with s.c. heparin, marked variations in APTt were noticed over periods of 12 h. These variations paralleled the regular s.c. injections of heparin every twelfth hour. The results of the present study could not confirm the marked circadian variations in APTt reported in an earlier French study during continuous heparin infusions, except in one patient.

Adult↗
PubMed1989

Shunting of leukocytes in rabbit tenuissimus muscle.

Leukocyte distribution was studied in 58 arterioles and capillaries constituting eight networks in the fascia adjacent to the rabbit tenuissimus muscle. Fluorescence video microscopy (acridine red) and digital image processing were used to visualize the leukocytes. Leukocyte concentration in the transverse arterioles leaving the muscle proper to irrigate the fascia was significantly elevated to 143 +/- 13% (mean +/- SE) of the systemic count. Leukocytes were found to further accumulate along the arteriolar tree, reaching 244 +/- 16% of systemic in the most remote branches. Leukocyte accumulation in the connective tissue can be calculated to lead to a decrease of leukocyte concentration in muscle capillaries to 89% of the systemic value. This shunting effect may be important in preventing leukocyte-induced capillary obstruction. At individual arteriolar bifurcations, leukocytes were found to preferentially enter the downstream branch with higher flow rate (regression coefficient 1.11 +/- 0.04, n = 100). This preferential distribution is quantitatively sufficient to account for the observed leukocyte distribution in the network.

Algorithms↗
PubMed1989

Capillary fluxmeter: the simultaneous measurement of hematocrit, velocity and flux.

An automated technique was developed for the measurement of capillary hematocrit in vivo. The method is based on the photometric detection of the passage of the red blood cells (RBC) through video photometric windows. Red blood cell flux is derived from the primary measurement of opacity and velocity, as opposed to frequency of cell passage and cell transit time. Consequently the technique is less prone to errors caused by the detection of joined cells. Tests in muscle capillaries, compared with hand count frame-by-frame analysis shows that the difference in measured flux is of the order of 16%. Fluctuations due to vasomotion are easily recorded by this approach.

Animals↗
PubMed1989

Vascular resistance vs. perfusate osmolarity: the short term microvascular effect of hypotonic and hypertonic perfusion in the isolated kidney.

Vascular resistance changes were measured in response to alteration in perfusate osmolarity in isolated rabbit kidneys perfused at 10 degrees C. The data obtained were found to fit a simple mathematical model of the vascular resistance of the microcirculation in which it was assumed that variation in this parameter depended solely upon osmotic alterations in the size of the cells within and around the blood vessel walls. The model predicts that the volumetric changes due to the different osmolarities are produced in a tissue layer whose thickness is 30% relative to a fixed outer radius. This result is compatible with the hypothesis that the effects are predominantly due to changes of endothelial cell volume and other perivascular capillary cells. The analysis illustrates the significance of perfusate osmolarity as a determinant of vascular resistance, can be used to investigate the hemodynamic effects that occur during the introduction and removal of cryoprotective agents, and is relevant to the interpretation of results obtained with hypertonic solutions in blood volume restoration after hypovolemic shock.

Animals↗
PubMed1989

Computer assisted leukocyte adhesion measurement in intravital microscopy.

The pathogenetic role of the leukocytes in the development of postischemic injury is not yet understood. Therefore a model was developed which allows for in vivo quantification of leukocyte-endothelium interaction in the awake animal. The velocity of leukocytes was measured by means of intravital microscopy and interactive digital image analysis. An adhesion coefficient (AC) was calculated which characterizes the degree of the leukocyte-endothelium interaction. A special procedure of automatically taking image samples for the leukocyte velocity measurement reduces observer bias. As shown in a validation experiment, this procedure yields reproducible results and therefore allows to quantify the influence of prophylactic and therapeutic measures on postischemic leukocyte-endothelium interaction.

Animals↗
PubMed1989

Lumenal narrowing and endothelial cell swelling in skeletal muscle capillaries during hemorrhagic shock.

Capillary lumenal narrowing in hemorrhagic shock was investigated using intravital microscopy to visualize capillaries directly in the rabbit tenuissimus muscle after a rapid single-withdrawal of 40% of the blood volume. The ensuing 1 hr shock period in the animals was marked by a protracted systemic hypotension and metabolic acidosis. Changes in capillary lumen diameter were inferred by changes in the width and length of red blood cells (RBCs) as they traversed the capillary. By the end of the shock period, RBC flux from nine experiments decreased over 60% with a -24.3 +/- 9.3% and +22.8 +/- 6.4% change in RBC width and length, respectively. The narrowed capillary lumen resulting from endothelial cell swelling elevates hydraulic resistance which may hinder resuscitation efforts to restore shock-impaired flow.

Animals↗
PubMed1988

Vasomotion patterns in skeletal muscle arterioles during changes in arterial pressure.

The effects of stepwise reductions of arterial pressure on arteriolar diameter and on vasomotion patterns in the rabbit tenuissimus muscle were investigated in eight New Zealand White rabbits (0.8-1.2 kg) anesthetized with 20% urethane. The vasomotor activity of 13 bifurcations, where first-order terminal arterioles branch from a transverse arteriole, was recorded by video microscopy and related to the pressures in the femoral artery. The arterial pressure was lowered in steps by partial occlusion of the abdominal aorta. Changes of mean diameter due to reduced perfusion pressures were most pronounced in transverse arterioles. Dilation in terminal arterioles at reduced arterial pressures did not exceed resting condition vasomotion peak diameters. Regular vasomotion in the terminal arterioles was intercalated with periods of no vasoactivity which became progressively longer when perfusion pressure was reduced. The oscillation frequency was maintained during the periods with regular vasomotion. Vasomotion ceased in transverse and terminal arterioles at arterial pressures between 50 and 30 mm Hg. During reactive hyperemia vasomotion reappeared after 0.5 to 4 min with the original fundamental frequency. We postulate that vasomotion in terminal arterioles is due to a vascular pacemaker which acts as a local oscillator that can be influenced by perfusion pressure in an on/off-type fashion. The pacemaker oscillation frequency is constant and independent of myogenic factors.

Animals↗
PubMed1988

Increase in capillary blood flow and relative haematocrit in rabbit skeletal muscle following acute normovolaemic anaemia.

The effect of acute normovolaemic haemodilution on microvascular red blood cell flow was studied by intravital microscopy in the tenuissimus muscle of the rabbit. Blood was substituted isovolaemically with equal volumes of a 6% solution of dextran 70 (MW 70,000). The systemic haematocrit (Hsys) decreased from 36 +/- 4% (mean +/- SD) to 17 +/- 2%. Following haemodilution capillary haematocrit (Hcap), as measured by video densitometric methods, decreased by 20 +/- 9%. The reduction of Hcap was significantly smaller than that of Hsys, and Hcap normalized with respect to Hsys increased from 0.39 +/- 0.07 in the control situation to 0.62 +/- 0.18 after haemodilution. Red blood cell velocity (vrbc) increased by 45 +/- 20% and compensated for the decrease in Hcap in such a way that the red blood cell flux, calculated from vrbc and Hcap, remained unchanged. Measurements of volume flow in the feeding arterioles in the muscle revealed a fractional redistribution of blood flow in favour of the muscle capillaries following haemodilution at the expense of vessels in adjacent connective tissue supplied by the same arterioles. This fractional flow redistribution was likely the basis for the relative increase in capillary haematocrit seen after haemodilution. The present data demonstrate that an acute reduction of the systemic haematocrit is compensated for in an active regulating vascular bed by a proportionally smaller decrease in capillary haematocrit and by an increased capillary red cell velocity. Microvascular haematocrit was found not to be a constant fraction of the systemic value, which supports the view of capillary haematocrit as a 'controlled' physiological variable.

Anemia↗
PubMed1988

Effects of hemodilution on skin microcirculation.

Red blood cell (RBC) velocity, capillary hematocrit (Hctcap), RBC flux, and arteriolar diameter were studied in the subcutaneous connective tissue of the Syrian hamster skinfold window preparation during successive normovolemic hemodilutions with 6% solutions of Dextran 70. The experiments were carried out in the unanesthetized animal. Heart rate (HR), mean systemic arterial pressure (Psys), and systemic hematocrit (Hctsys) were monitored throughout the procedure to ensure that normovolemia was maintained and hemodilution caused no adverse effects. The changes of RBC flux in the hemodiluted state, up to 50% hemodilution (Hctsys = 25% +/- 4), were not statistically significant when compared with control (t test, P less than 0.5). At this Hctsys, capillary RBC velocity increased by 60% and Hctcap decreased by 30%. Both of these changes were statistically significant relative to control. The arteriolar diameter did not change significantly during the reduction of Hctsys. The animals were studied during subsequent days to determine the chronic effects of hemodilution. Hctsys increased by approximately 12% per day after the experiment, and the systemic parameters returned to the prehemodiluted state in direct proportion to the reestablishment of the Hctsys.

Animals↗
PubMed1988

Beta-adrenergic control of resistance in individual vessels in rabbit tenuissimus muscle.

The microvascular responses to topically applied isoproterenol and to epinephrine in the intact and beta-adrenoceptor-blocked microcirculation were studied in the rabbit tenuissimus muscle by direct intravital microscopy. The main feeding arterioles in this muscle supply two vascular areas, the muscle capillaries and the adjacent connective tissue. beta-Adrenergic stimulation with isoproterenol and epinephrine dilated the transverse arterioles that supply muscle and connective tissues, whereas their first-order side branches (terminal arterioles), which only supply the muscle capillaries, were little affected. Flow measurements were made at two different sites in the transverse arterioles to determine the relative changes in muscle capillary flow and connective tissue flow. These measurements showed that beta-adrenergic stimulation caused a fractional redistribution of microvascular blood flow from the muscle tissue proper to the adjacent connective tissue.

Animals↗