Microvascular oxygen distribution in awake hamster window chamber model during hyperoxia

2003 ◽  
Vol 285 (4) ◽  
pp. H1537-H1545 ◽  
Author(s):  
Amy G. Tsai ◽  
Pedro Cabrales ◽  
Robert M. Winslow ◽  
Marcos Intaglietta
Keyword(s):  
Capillary Density ◽  
Microvascular Blood Flow ◽  
Oxygen Distribution ◽  
Microvascular Network ◽  
Normobaric Hyperoxia ◽  
Arterial Blood ◽  
Hyperoxic Condition ◽  
Direct Measurements ◽  
Chamber Model ◽  
Window Chamber

The microvascular effects and hemodynamic events following exposure to normobaric hyperoxia (because of inspiration of 100% O2) were studied in the awake hamster window chamber model and compared with normoxia. Hyperoxia increased arterial blood Po2 to 477.9 ± 19.9 from 60.0 ± 1.2 mmHg ( P < 0.05). Heart rate and blood pressure were unaltered, whereas cardiac index was reduced from 196 ± 13 to 144 ± 31 ml · min–1 · kg–1 ( P < 0.05) in hyperoxia. Direct measurements in the microcirculation showed there was arteriolar vasoconstriction, reduction of microvascular flow (83% of control, P < 0.05), and functional capillary density (FCD, 74 ± 16% of control), the latter change being significant ( P < 0.05). Calculations of oxygen delivery and oxygen consumption based on the measured changes in microvascular blood flow velocity and diameter and estimates of oxygen saturation corrected for the Bohr effect due to the lowered pH and increased Pco2 showed that oxygen transport in the microvascular network did not change between normal and hyperoxic condition. The congruence of systemic and microvascular hemodynamics events found with hyperoxia suggests that the microvascular findings are common to most tissues in the organism, and that hyperoxia, due to vasoconstriction and the decrease of FCD, causes a maldistribution of perfusion in the microcirculation.

Plasma viscosity regulates systemic and microvascular perfusion during acute extreme anemic conditions

2006 ◽  
Vol 291 (5) ◽  
pp. H2445-H2452 ◽  
Author(s):  
Pedro Cabrales ◽  
Amy G. Tsai
Keyword(s):  
Flow Distribution ◽  
Capillary Density ◽  
High Viscosity ◽  
Plasma Viscosity ◽  
Functional Capillary Density ◽  
Microvascular Perfusion ◽  
Arterial Blood ◽  
Chamber Model ◽  
Kidney Liver ◽  
Window Chamber

The hamster window chamber model was used to study systemic and microvascular hemodynamic responses to extreme hemodilution with low- and high-viscosity plasma expanders (LVPE and HVPE, respectively) to determine whether plasma viscosity is a factor in homeostasis during extreme anemic conditions. Moderated hemodilution was induced by two isovolemic steps performed with 6% 70-kDa dextran until systemic hematocrit (Hct) was reduced to 18% ( level 2). In a third isovolemic step, hemodilution with LVPE (6% 70-kDa dextran, 2.8 cP) or HVPE (6% 500-kDa dextran, 5.9 cP) reduced Hct to 11%. Systemic parameters, cardiac output (CO), organ flow distribution, microhemodynamics, and functional capillary density, were measured after each exchange dilution. Fluorescent-labeled microspheres were used to measure organ (brain, heart, kidney, liver, lung, and spleen) and window chamber blood flow. Final blood and plasma viscosities after the entire protocol were 2.1 and 1.4 cP, respectively, for LVPE and 2.8 and 2.2 cP, respectively, for HVPE (baseline = 4.2 and 1.2 cP, respectively). HVPE significantly elevated mean arterial pressure and CO compared with LVPE but did not increase vascular resistance. Functional capillary density was significantly higher for HVPE [87% (SD 7) of baseline] than for LVPE [42% (SD 11) of baseline]. Increases in mean arterial blood pressure, CO, and shear stress-mediated factors could be responsible for maintaining organ and microvascular perfusion after exchange with HVPE compared with LVPE. Microhemodynamic data corresponded to microsphere-measured perfusion data in vital organs.

scholarly journals Increased hemoglobin O2 affinity protects during acute hypoxia

2012 ◽  
Vol 303 (3) ◽  
pp. H271-H281 ◽  
Author(s):  
Ozlem Yalcin ◽  
Pedro Cabrales
Keyword(s):  
Blood Flow ◽  
Acute Hypoxia ◽  
Severe Hypoxia ◽  
Microvascular Blood Flow ◽  
Vehicle Group ◽  
Control Group ◽  
Arterial Blood ◽  
Partial Pressures ◽  
Chamber Model ◽  
Window Chamber

Acclimatization to hypoxia requires time to complete the adaptation mechanisms that influence oxygen (O2) transport and O2 utilization. Although decreasing hemoglobin (Hb) O2 affinity would favor the release of O2 to the tissues, increasing Hb O2 affinity would augment arterial O2 saturation during hypoxia. This study was designed to test the hypothesis that pharmacologically increasing the Hb O2 affinity will augment O2 transport during severe hypoxia (10 and 5% inspired O2) compared with normal Hb O2 affinity. RBC Hb O2 affinity was increased by infusion of 20 mg/kg of 5-hydroxymethyl-2-furfural (5HMF). Control animals received only the vehicle. The effects of increasing Hb O2 affinity were studied in the hamster window chamber model, in terms of systemic and microvascular hemodynamics and partial pressures of O2 (Po2). Pimonidazole binding to hypoxic areas of mice heart and brain was also studied. 5HMF decreased the Po2 at which the Hb is 50% saturated with O2 by 12.6 mmHg. During 10 and 5% O2 hypoxia, 5HMF increased arterial blood O2 saturation by 35 and 48% from the vehicle group, respectively. During 5% O2 hypoxia, blood pressure and heart rate were 58 and 30% higher for 5HMF compared with the vehicle. In addition, 5HMF preserved microvascular blood flow, whereas blood flow decreased to 40% of baseline in the vehicle group. Consequently, perivascular Po2 was three times higher in the 5HMF group compared with the control group at 5% O2 hypoxia. 5HMF also reduced heart and brain hypoxic areas in mice. Therefore, increased Hb O2 affinity resulted in hemodynamics and oxygenation benefits during severe hypoxia. This acute acclimatization process may have implications in survival during severe environmental hypoxia when logistic constraints prevent chronic acclimatization.

Extreme hemodilution with PEG-hemoglobin vs. PEG-albumin

2005 ◽  
Vol 289 (6) ◽  
pp. H2392-H2400 ◽  
Author(s):  
Pedro Cabrales ◽  
Amy G. Tsai ◽  
Robert M. Winslow ◽  
Marcos Intaglietta
Keyword(s):  
Base Excess ◽  
Microvascular Blood Flow ◽  
Oxygen Release ◽  
Capillary Perfusion ◽  
Isovolemic Hemodilution ◽  
Arterial Blood ◽  
Dextran 70 ◽  
Chamber Model ◽  
Plasma Expanders ◽  
Window Chamber

Isovolemic hemodilution to 11% systemic hematocrit was performed in the hamster window chamber model using 6% dextran 70 kDa (Dx 70) and 5% human serum albumin (HSA). Systemic and microvascular effects of these solutions were compared with polyethylene glycol (PEG)-conjugated 5% albumin (MPA) and PEG-conjugated 4.2% Hb (MP4). These studies were performed for the purpose of comparing systemic and microvascular responses of PEG vs. non-PEG plasma expanders and similar oxygen-carrying vs. noncarrying blood replacement fluids. Mean arterial blood pressure was statistically significantly reduced for all groups compared with baseline ( P < 0.05), HSA, MPA, and MP4 higher than Dx 70 ( P < 0.05). MP4 and MPA had a significantly higher cardiac index than HSA and Dx 70, in addition to a positive base excess. Microvascular blood flow and capillary perfusion were significantly higher for the PEG compounds compared with HSA and Dx 70. Intravascular Po2 for MP4 and MPA was higher in arterioles ( P < 0.05) compared with HSA and Dx 70, but there was no difference in either tissue or venular Po2 between groups. Total Hb in the MP4 group was 4.8 ± 0.4 g/dl, whereas the remaining groups had a range of 3.6–3.8 g/dl. The hemodilution results showed that PEG compounds maintained microvascular conditions with lower concentrations than conventional plasma expanders. Furthermore, microvascular oxygen delivery and extraction in the window chamber tissue were significantly higher for the PEG compounds. MP4 was significantly higher than MPA ( P < 0.05) and was not statistically different from baseline, an effect due to the additional oxygen release to the tissue by the Hb MP4.

scholarly journals Tissue oxidative metabolism after extreme hemodilution with PEG-conjugated hemoglobin

2010 ◽  
Vol 109 (6) ◽  
pp. 1852-1859 ◽  
Author(s):  
Pedro Cabrales ◽  
Fantao Meng ◽  
Seetharama A. Acharya
Keyword(s):  
Energy State ◽  
Capillary Density ◽  
Functional Capillary Density ◽  
Acid Base Balance ◽  
Noninvasive Technique ◽  
Isovolemic Hemodilution ◽  
Blood Flows ◽  
Arterial Blood ◽  
Base Balance ◽  
Chamber Model

NADH-localized fluorometry was used as a noninvasive technique to monitor changes in the energy state of intact tissue (muscle and connective tissue), without anesthesia, as a function of blood plasma O2-carrying capacity in the hamster window chamber model. Acute moderate isovolemic hemodilution was induced by two isovolemic hemodilution steps: in the first step, 6% 70-kDa dextran (Dex70) was used to induce an acute anemic state (18% Hct); in the second step, exchange transfusion of polyethylene glycol (PEG) maleimide-conjugated Hb (4 g/dl, PEG-Hb) or Dex70 (6 g/dl) was used to reduce erythrocytes to 75% of baseline (11% Hct). PEG-Hb had six copies of PEG (5 kDa) conjugated to each human Hb (0.48 g PEG/g Hb) through extension arm-facilitated chemistry. Systemic parameters, microvascular perfusion, functional capillary density, intravascular and interstitial Po2, and intracellular NADH fluorescence were monitored. Mean arterial blood pressure after extreme hemodilution was statistically significantly reduced for Dex70 compared with PEG-Hb. The presence of PEG-Hb in the circulation maintained positive acid-base balance. While microvascular blood flows were not different, functional capillary density was significantly higher for PEG-Hb than Dex70. Arteriolar Po2 was higher in the presence of PEG-Hb than Dex70, but tissue and venular Po2 were not different. Cellular energy metabolism (intracellular O2) in the tissues was improved with PEG-Hb. Moderate hemodilution to 18% Hct (6.4 g Hb/dl) brings tissue O2 delivery to the verge of inadequacy. Extreme hemodilution to 11% Hct (3.7 g Hb/dl) produces tissue anoxia, and high-O2-affinity PEG-Hb (Po2 at which blood is 50% saturated with O2 = 4 Torr, 1.1 g Hb/dl) only partially decreases anaerobic metabolism without increasing tissue Po2.

Increased tissue Po2and decreased O2delivery and consumption after 80% exchange transfusion with polymerized hemoglobin

2004 ◽  
Vol 287 (6) ◽  
pp. H2825-H2833 ◽  
Author(s):  
Pedro Cabrales ◽  
Amy G. Tsai ◽  
Marcos Intaglietta
Keyword(s):  
Blood Cells ◽  
Exchange Transfusion ◽  
Blood Substitute ◽  
Capillary Density ◽  
Bovine Hemoglobin ◽  
Velocity Data ◽  
Blood Exchange ◽  
Chamber Model ◽  
Window Chamber ◽  
Arteriolar Diameter

The O2-carrying blood substitute based on polymerized bovine hemoglobin (PBH) was used to determine efficacy in maintaining tissue Po2after an 80% isovolemic blood exchange leading to a hematocrit of 19% [5.4 g Hb/dl from red blood cells (RBCs) and 6.3 g Hb/dl from PBH]. Effects were studied in terms of O2delivery, O2extraction, and tissue Po2at the microcirculatory level at 1, 12, and 24 h after exchange transfusion in awake hamsters prepared with a window chamber model. At 1 h after exchange, arteriolar and venular diameters were decreased compared with baseline. Arteriolar diameter did not fully recover at 12 h after exchange, but venular diameter returned to normal. At 24 h after exchange, arteriolar and venular diameters were not different from baseline. Combining diameter and flow velocity data allowed us to calculate arteriolar and venular flows. At 1 h after exchange, arteriolar and venular flow was reduced compared with baseline. Arteriolar flow was lower at 12 h after exchange and recovered after 24 h. The number of capillaries with RBC passage [functional capillary density (FCD)] at 1 h after exchange with PBH was significantly lower than baseline. FCD remained decreased at 12 h; at 24 h after exchange transfusion, FCD was fully recovered. Tissue Po2was maximal at 1 h after exchange and decreased progressively at 12 and 24 h after exchange. O2release to the tissue was minimal at 1 h and increased at 12 and 24 h after exchange. These results suggest the impairment of tissue O2metabolism after introduction of PBH into the circulation, which is mitigated as PBH concentration declines.

Measurement of the Platelet Response to Laser- induced Microvascular Injury

1974 ◽  
Vol 32 (02/03) ◽  
pp. 704-713 ◽  
Author(s):  
F. N McKenzie ◽  
K.-E Arfors ◽  
N. A Matheson
Keyword(s):  
Inhibitory Effect ◽  
Microvascular Blood Flow ◽  
Platelet Response ◽  
High Concentration ◽  
Platelet Activity ◽  
Microvascular Injury ◽  
Arterial Blood ◽  
Proximal Site ◽  
Adenosine Phosphates

SummaryA study has been made of the biochemical factors underlying the platelet response to laser-induced microvascular injury. A platelet aggregating substance is produced at sites of laser-induced injury which markedly stimulates platelet activity at a site of injury inflicted a short distance downstream. Distal sites of injury are not similarly influenced if the distance between the injuries is increased or if the proximal site no longer shows platelet-stimulating activity. The stimulating effect of an adjacent proximal injury on platelet activity at a distal site is inhibited by local intra-arterial infusion of adenosine. Measurements of arterial blood pressure and microvascular blood flow velocity during adenosine infusion showed that its inhibitory effect on platelet activity is largely independent of its vasodilator properties. The effect of infusion of different adenosine phosphates (AMP, ADP, ATP) was also studied. Very small amounts of ADP markedly stimulated platelet activity and the emboli formed were similar to those normally produced at sites of laser injury. At high concentration AMP inhibited while ATP stimulated platelet activity in vivo. The results emphasise the fundamental role of ADP as a mediator of the platelet response at sites of laser- induced microvascular injury.

scholarly journals A METHOD TO DETERMINE THE PERIPHERAL ARTERIAL BLOOD PRESSURE IN THE MOUSE

1941 ◽  
Vol 74 (1) ◽  
pp. 29-40 ◽  
Author(s):  
Philip D. McMaster
Keyword(s):  
Blood Pressure ◽  
Systolic Blood Pressure ◽  
Arterial Blood Pressure ◽  
Close Agreement ◽  
Carotid Arteries ◽  
Systolic Pressure ◽  
Arterial Blood ◽  
Relative Transparency ◽  
Direct Measurements ◽  
Peripheral Arterial

Advantage has been taken of the relative transparency of the claw of the mouse to devise a method, here described, to measure the blood pressure in the animal's leg. Direct measurements of the systolic blood pressure from the carotid arteries of anesthetized mice have also been made. Simultaneous blood pressure readings by both these methods applied to the same animal showed close agreement. The systolic pressure ranged from 60 to 126 mm. Hg, according to the conditions.

scholarly journals Apohemoglobin-haptoglobin complex attenuates the pathobiology of circulating acellular hemoglobin and heme

2020 ◽  
Vol 318 (5) ◽  
pp. H1296-H1307 ◽  
Author(s):  
Carlos J. Munoz ◽  
Ivan S. Pires ◽  
Jin Hyen Baek ◽  
Paul W. Buehler ◽  
Andre F. Palmer ◽  
...  
Keyword(s):  
Therapeutic Strategy ◽  
Capillary Density ◽  
Microvascular Blood Flow ◽  
Systemic Hypertension ◽  
Proof Of Concept ◽  
Heme Transfer ◽  
Ligand Transfer ◽  
Novel Therapeutic

This study highlights the apoHb-Hp complex as a novel therapeutic strategy to attenuate the adverse systemic and microvascular responses to intravascular Hb and heme exposure. In vitro and in vivo Hb exchange and heme transfer experiments demonstrated proof-of-concept Hb/heme ligand transfer to apoHb-Hp. The apoHb-Hp complex reverses Hb- and heme-induced systemic hypertension and microvascular vasoconstriction, preserves microvascular blood flow, and functional capillary density. In summary, the unique properties of the apoHb-Hp complex prevent adverse systemic and microvascular responses to Hb and heme-albumin exposure and introduce a novel therapeutic approach to facilitate simultaneous removal of extracellular Hb and heme.

Dexmedetomidine Attenuates the Microcirculatory Derangements Evoked by Experimental Sepsis

2015 ◽  
Vol 122 (3) ◽  
pp. 619-630 ◽  
Author(s):  
Marcos L. Miranda ◽  
Michelle M. Balarini ◽  
Eliete Bouskela
Keyword(s):  
Blood Gases ◽  
Capillary Density ◽  
Sepsis Syndrome ◽  
In Vivo Studies ◽  
Experimental Sepsis ◽  
Leukocyte Rolling ◽  
Capillary Perfusion ◽  
Arterial Blood ◽  
Baseline Values

Abstract Background: Dexmedetomidine, an α-2 adrenergic receptor agonist, has already been used in septic patients although few studies have examined its effects on microcirculatory dysfunction, which may play an important role in perpetuating sepsis syndrome. Therefore, the authors have designed a controlled experimental study to characterize the microcirculatory effects of dexmedetomidine in an endotoxemia rodent model that allows in vivo studies of microcirculation. Methods: After skinfold chamber implantation, 49 golden Syrian hamsters were randomly allocated in five groups: (1) control animals; (2) nonendotoxemic animals treated with saline; (3) nonendotoxemic animals treated with dexmedetomidine (5.0 μg kg−1 h−1); (4) endotoxemic (lipopolysaccharide 1.0 mg/kg) animals treated with saline; and (5) endotoxemic animals treated with dexmedetomidine. Intravital microscopy of skinfold chamber preparations allowed quantitative analysis of microvascular variables and venular leukocyte rolling and adhesion. Mean arterial blood pressure, heart rate, arterial blood gases, and lactate concentrations were also documented. Results: Lipopolysaccharide administration increased leukocyte rolling and adhesion and decreased capillary perfusion. Dexmedetomidine significantly attenuated these responses: compared with endotoxemic animals treated with saline, those treated with dexmedetomidine had less leukocyte rolling (11.8 ± 7.2% vs. 24.3 ± 15.0%; P &lt; 0.05) and adhesion (237 ± 185 vs. 510 ± 363; P &lt; 0.05) and greater functional capillary density (57.4 ± 11.2% of baseline values vs. 45.9 ± 11.2%; P &lt; 0.05) and erythrocyte velocity (68.7 ± 17.6% of baseline values vs. 54.4 ± 14.8%; P &lt; 0.05) at the end of the experiment. Conclusions: Dexmedetomidine decreased lipopolysaccharide-induced leukocyte–endothelial interactions in the hamster skinfold chamber microcirculation. This was accompanied by a significant attenuation of capillary perfusion deficits, suggesting that dexmedetomidine yields beneficial effects on endotoxemic animals’ microcirculation.

A model of anemic tissue perfusion after blood transfusion shows critical role of endothelial response to shear stress stimuli

2021 ◽  
Author(s):  
Weiyu Li ◽  
Amy G. Tsai ◽  
Marcos Intaglietta ◽  
Daniel M. Tartakovsky
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Blood Transfusion ◽  
Critical Role ◽  
Cardiovascular Responses ◽  
Arterial Blood Flow ◽  
Microvascular Blood Flow ◽  
No Production ◽  
Arterial Blood ◽  
Transfusion Requirements

­­ ­Although some of the cardiovascular responses to changes in hematocrit (Hct) are not fully quantified experimentally, available information is sufficient to build a mathematical model of the consequences of treating anemia by introducing RBCs into the circulation via blood transfusion. We present such a model, which describes how the treatment of normovolemic anemia with blood transfusion impacts oxygen (O2) delivery (DO2, the product of blood O2 content and arterial blood flow) by the microcirculation. Our analysis accounts for the differential response of the endothelium to the wall shear stress (WSS) stimulus, changes in nitric oxide (NO) production due to modification of blood viscosity caused by alterations of both hematocrit (Hct) and cell free layer thickness, as well as for their combined effects on microvascular blood flow and DO2. Our model shows that transfusions of 1- and 2-unit of blood have a minimal effect on DO2 if the microcirculation is unresponsive to the WSS stimulus for NO production that causes vasodilatation increasing blood flow and DO2. Conversely, in a fully WSS responsive organism, blood transfusion significantly enhances blood flow and DO2, because increased viscosity stimulates endothelial NO production causing vasodilatation. This finding suggests that evaluation of a patients' pre-transfusion endothelial WSS responsiveness should be beneficial in determining the optimal transfusion requirements for treating anemic patients.

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