Changes In Microvascular Flow Research Articles

Optimized quantitative mapping of cardiopulmonary oscillations using hyperpolarized 129 Xe gas exchange MRI: Digital phantoms and clinical evaluation in CTEPH.

The interaction between 129 Xe atoms and pulmonary capillary red blood cells provides cardiogenic signal oscillations that display sensitivity to precapillary and postcapillary pulmonary hypertension. Recently, such oscillations have been spatially mapped, but little is known about optimal reconstruction or sensitivity to artifacts. In this study, we use digital phantom simulations to specifically optimize keyhole reconstruction for oscillation imaging. We then use this optimized method to re-establish healthy reference values and quantitatively evaluate microvascular flow changes in patients with chronic thromboembolic pulmonary hypertension (CTEPH) before and after pulmonary thromboendarterectomy (PTE). A six-zone digital lung phantom was designed to investigate the effects of radial views, key radius, and SNR. One-point Dixon 129 Xe gas exchange MRI images were acquired in a healthy cohort (n = 17) to generate a reference distribution and thresholds for mapping red blood cell oscillations. These thresholds were applied to 10 CTEPH participants, with 6 rescanned following PTE. For undersampled acquisitions, a key radius of was found to optimally resolve oscillation defects while minimizing excessive heterogeneity. CTEPH participants at baseline showed higher oscillation defect + low (32 ± 14%) compared with healthy volunteers (18 ± 12%, p < 0.001). For those scanned both before and after PTE, oscillation defect + low decreased from 37 ± 13% to 23 ± 14% (p = 0.03). Digital phantom simulations have informed an optimized keyhole reconstruction technique for gas exchange images acquired with standard 1-point Dixon parameters. Our proposed methodology enables more robust quantitative mapping of cardiogenic oscillations, potentially facilitating effective regional quantification of microvascular flow impairment in patients with pulmonary vascular diseases such asCTEPH.

Resuscitation-associated endotheliopathy (RAsE): a conceptual framework based on a systematic review and meta-analysis

IntroductionShock-induced endotheliopathy (SHINE), defined as a profound sympathoadrenal hyperactivation in shock states leading to endothelial activation, glycocalyx damage, and eventual compromise of end-organ perfusion, was first described in 2017. The aggressive resuscitation therapies utilised in treating shock states could potentially lead to further worsening endothelial activation and end-organ dysfunction.ObjectiveThis study aimed to systematically review the literature on resuscitation-associated and resuscitation-induced endotheliopathy.MethodsA predetermined structured search of literature published over an 11-year and 6-month period (1 January 2011 to 31 July 2023) was performed in two indexed databases (PubMed/MEDLINE and Embase) per PRISMA guidelines. Inclusion was restricted to original studies published in English (or with English translation) reporting on endothelial dysfunction in critically ill human subjects undergoing resuscitation interventions. Reviews or studies conducted in animals were excluded. Qualitative synthesis of studies meeting the inclusion criteria was performed. Studies reporting comparable biomarkers of endothelial dysfunction post-resuscitation were included in the quantitative meta-analysis.ResultsThirty-two studies met the inclusion criteria and were included in the final qualitative synthesis. Most of these studies (47%) reported on a combination of mediators released from endothelial cells and biomarkers of glycocalyx breakdown, while only 22% reported on microvascular flow changes. Only ten individual studies were included in the quantitative meta-analysis based on the comparability of the parameters assessed. Eight studies measured syndecan-1, with a heterogeneity index, I2 = 75.85% (pooled effect size, mean = 0.27; 95% CI − 0.07 to 0.60; p = 0.12). Thrombomodulin was measured in four comparable studies (I2 = 78.93%; mean = 0.41; 95% CI − 0.10 to 0.92; p = 0.12). Three studies measured E-selectin (I2 = 50.29%; mean = − 0.15; 95% CI − 0.64 to 0.33; p = 0.53), and only two were comparable for the microvascular flow index, MFI (I2 = 0%; mean = − 0.80; 95% CI − 1.35 to − 0.26; p < 0.01).ConclusionResuscitation-associated endotheliopathy (RAsE) refers to worsening endothelial dysfunction resulting from acute resuscitative therapies administered in shock states. In the included studies, syndecan-1 had the highest frequency of assessment in the post-resuscitation period, and changes in concentrations showed a statistically significant effect of the resuscitation. There are inadequate data available in this area, and further research and standardisation of the ideal assessment and panel of biomarkers are urgently needed.

Augmentation of Tissue Perfusion with Contrast Ultrasound: Influence of Three-Dimensional Beam Geometry and Conducted Vasodilation

Cavitation of microbubble contrast agents with ultrasound produces shear-mediated vasodilation and an increase in tissue perfusion. We investigated the influence of the size of the cavitation volume by comparing flow augmentation produced by two-dimensional (2D) versus three-dimensional (3D) therapeutic ultrasound. We also hypothesized that cavitation could augment flow beyond the ultrasound field through release of vasodilators that are carried downstream. In 11 rhesus macaques, cavitation of intravenously administered lipid-shelled microbubbles was performed in the proximal forearm flexor muscles unilaterally for 10min. Ultrasound cavitation (1.3MHz, 1.5MPa peak negative pressure) was performed with 2D or 3D transmission with beam elevations of 5 and 25mm, respectively, and pulsing intervals (PIs) sufficient to allow complete postdestruction refill (5 and 12sec for 2D and 3D, respectively). Contrast ultrasound perfusion imaging was performed before and after cavitation, using multiplane assessment within and beyond the cavitation field in 1.5-cm increments. Cavitation in the hindlimb of mice using 2D ultrasound at a PI of 1 or 5sec was performed to examine microvascular flow changes from cavitation in only arteries versus the microcirculation. In primates, the degree of muscle flow augmentation in the center of the cavitation field was similar for 2D and 3D conditions (five- to sixfold increase for both, P<.01 vs baseline). The spatial extent of flow augmentation was only modestly greater for 3D cavitation because of an increase in perfusion with 2D transmission that was detected outside of the cavitation field. In mice, cavitation in the microvascular compartment (PI 5sec) produced the greatest degree of flow augmentation, yet cavitation in the arterial compartment (PI 1sec) still produced a three- to fourfold increase in flow (P<.001 vs control). The mechanism for flow augmentation beyond the cavitation zone was investigated by invitro studies that demonstrated cavitation-related release of vasodilators, including adenosine triphosphate and nitric oxide, from erythrocytes and endothelial cells. Compared with 2D transmission, 3D cavitation of microbubbles generates a similar degree of muscle flow augmentation, possibly because of a trade-off between volume of cavitation and PI, and only modestly increases the spatial extent of flow augmentation because of the ability of cavitation to produce conducted effects beyond the ultrasound field.

High-Frequency Nonlinear Doppler Contrast-Enhanced Ultrasound Imaging of Blood Flow.

Current methods for in vivo microvascular imaging (<1 mm) are limited by the tradeoffs between the depth of penetration, resolution, and acquisition time. Ultrasound Doppler approaches combined at elevated frequencies (<7.5 MHz) are able to visualize smaller vasculature and, however, are still limited in the segmentation of lower velocity blood flow from moving tissue. Contrast-enhanced ultrasound (CEUS) has been successful in visualizing changes in microvascular flow at conventional diagnostic ultrasound imaging frequencies (<7.5 MHz). However, conventional CEUS approaches at elevated frequencies have met with limited success, due, in part, to the diminishing microbubble response with frequency. We apply a plane-wave acquisition combined with the non-linear Doppler processing of ultrasound contrast agents at 15 MHz to improve the resolution of microvascular blood flow while compensating for reduced microbubble response. This plane-wave Doppler approach of imaging ultrasound contrast agents also enables simultaneous detection and separation of blood flow in the microcirculation and higher velocity flow in the larger vasculature. We apply singular value decomposition filtering on the nonlinear Doppler signal to orthogonally separate the more stationary lower velocity flow in the microcirculation and higher velocity flow in the larger vasculature. This orthogonal separation was also utilized to improve time-intensity curve analysis of the microcirculation, by removing higher velocity flow corrupting bolus kinetics. We demonstrate the utility of this imaging approach in a rat spinal cord injury model, requiring submillimeter resolution.

Optical coherence tomography angiography analysis of macular vessel density before and after anti-VEGF therapy in eyes with diabetic retinopathy.

To evaluate changes in macular vessel density following intravitreal anti-VEGF injection in patients with diabetic macular edema (DME) and proliferative diabetic retinopathy (PDR). In this retrospective case series, optical coherence tomography angiography (OCTA) images from 55 eyes of 35 patients with either DME (46 eyes) or PDR (9 eyes) were included. Macular capillary vessel density at the level of the superficial retinal capillary plexus (SCP), deep retinal capillary plexus (DCP) and total retinal capillary plexus (TCP) before and after anti-VEGF treatment was calculated. Longitudinal changes in vessel density following serial anti-VEGF treatment were analyzed in a subset of eyes. Vessel density in the SCP, DCP or TCP was not found to be significantly different after one, two or three intravitreal injections (p > 0.05 for all time points). Subgroup analysis revealed no significant change in the DME and PDR subgroups (all p > 0.05). Multivariate analysis revealed no effect of type of injected anti-VEGF agent or presence of previous treatment on VD measurements (all p > 0.05). There was no correlation between the anatomic response of DME to treatment and VD measurements. In this study, macular vessel density remained statistically unchanged following up to three intravitreal injections of any anti-VEGF agent. This indicates that there may not be an early effect of anti-VEGF treatment on macular vessel density and its effect on macular perfusion may not be a direct change in microvascular flow.

Detection of Intestinal Tissue Perfusion by Real-Time Breath Methane Analysis in Rat and Pig Models of Mesenteric Circulatory Distress.

Methane (CH4) breath test is an established diagnostic method for gastrointestinal functional disorders. Our aim was to explore the possible link between splanchnic circulatory changes and exhaled CH4 in an attempt to recognize intestinal perfusion failure. Randomized, controlled in vivo animal study. University research laboratory. Anesthetized, ventilated Sprague-Dawley rats (280 ± 30 g) and Vietnamese minipigs (31 ± 7 kg). In the first series, CH4 was administered intraluminally into the ileum before 45 minutes mesenteric ischemia or before reperfusion in non-CH4 producer rats to test the appearance of the gas in the exhaled air. In the porcine experiments, the superior mesenteric artery was gradually obstructed during consecutive, 30-minute flow reductions and 30-minute reperfusions achieving complete occlusion after four cycles (n = 6), or nonocclusive mesenteric ischemia was induced by pericardial tamponade (n = 12), which decreased superior mesenteric artery flow from 351 ± 55 to 182 ± 67 mL/min and mean arterial pressure from 96.7 ± 18.2 to 41.5 ± 4.6 mm Hg for 60 minutes. Macrohemodynamics were monitored continuously; RBC velocity of the ileal serosa or mucosa was recorded by intravital videomicroscopy. The concentration of exhaled CH4 was measured online simultaneously with high-sensitivity photoacoustic spectroscopy. The intestinal flow changes during the occlusion-reperfusion phases were accompanied by parallel changes in breath CH4 output. Also in cardiac tamponade-induced nonocclusive intestinal ischemia, the superior mesenteric artery flow and RBC velocity correlated significantly with parallel changes in CH4 concentration in the exhaled air (Pearson's r = 0.669 or r = 0.632, respectively). we report a combination of in vivo experimental data on a close association of an exhaled endogenous gas with acute mesenteric macro- and microvascular flow changes. Breath CH4 analysis may offer a noninvasive approach to follow the status of the splanchnic circulation.

Epidermal Electronic Systems for Measuring the Thermal Properties of Human Skin at Depths of up to Several Millimeters

AbstractMonitoring the composition, blood flow properties, and hydration status of human skin can be important in diagnosing disease and tracking overall health. Current methods are largely limited to clinical environments, and they primarily measure properties of superficial layers of the skin, such as the stratum corneum (10–40 µm). This work introduces soft, skin‐like thermal depth sensors (e‐TDS) in designs that seamlessly couple with human skin and measure its thermal properties with depth sensitivity that can extend up to 6 mm beneath the surface. Guidelines for tailoring devices to enable measurements through different effective depths follow from a systematic set of experiments, supported by theoretical modeling. On‐body testing validates the physiological relevance of measurements using the e‐TDS platform, with potential to aid the diagnosis of deep cutaneous and systemic diseases. Specific demonstrations include measurements that capture responses ranging from superficial changes in skin properties that result from application of a moisturizer, to changes in microvascular flow at intermediate depths induced by heating/cooling, to detection of inflammation in the deep dermis and subcutaneous fat in an incidence of a local bacterial infection, cellulitis.

Quantitative capillary blood flow spatial analysis in skeletal muscle during sepsis

IntroductionTreatment of sepsis accounts for 23 billion healthcare dollars annually, and one in three hospitalized patients are diagnosed with sepsis. While current therapeutic strategies have been effective, sepsis‐induced mortality rates still remain greater than 10% and 40% with severe sepsis. Thus, new therapeutic approaches are needed.A defining characteristic of sepsis is that it induces hyperglycemia and an insulin resistant state. Skeletal muscle is one of the largest consumers of glucose in the body. Muscle glucose uptake can be controlled by: delivery of glucose through the vasculature, transport of glucose into the muscle, and muscle glucose metabolism. Hyperglycemia and insulin resistance may be due to a defect in one or more of these processes. Our lab and others have shown that inflammatory states cause alterations in vascular flow to the skeletal muscle. Further, changes in vascular flow have been shown to correlate with sepsis‐induced hyperglycemia and insulin resistance. Given that both sepsis and inflammation induce insulin resistance and are associated with impaired muscle blood flow, we hypothesize that protecting the endothelium from sepsis‐induced inflammation will prevent insulin resistance. We will test this hypothesis through the use of mice with a vascular specific knock down of NFκB. However, few tools exist too accurately and reproducibly measure changes in capillary flow with single‐capillary spatial resolution. To being testing the hypothesis we sought to develop and validate a method to measure capillary flow patterns to assess changes in microvascular flow and heterogeneity in the skeletal muscle.MethodIntravital microscopy was used to track fluorescent beads in mouse gastrocnemius muscle capillaries, and these data were used to build spatial capillary velocity profiles. Briefly, C57/BL6 mice with jugular vein catheters were anesthetized with isoflurane and the gastrocnemius was surgically exposed and positioned on a coverslip with warmed saline. Mice were then injected with 3 μm florescent beads and imaged at 111 frames per second. Resulting videos of binarized fluorescent beads were subjected to a positional tracking algorithm to yield a dataset of position and velocity data for tracked beads. This dataset was used to build capillary flow velocity maps for enhanced spatial visualization of flow data. Data analysis was conducted on both bead tracking data and capillary flow velocity maps using MATLAB. To assess whether the method could detect changes in capillary flow, mice were subjected to saline or lipopolysaccharide (2 mg/kg; LPS).ResultsThe average vessel track length was found to be 450 μm and the average vessel flow rate in the gastrocnemius was determined to be 1030 μm/second. To prevent tracking bead vessel selection bias, we averaged the spatial velocities of vessels, and determined the average spatial velocities of capillaries to be 970 μm/second. We calculated the sample size needed to determine a 10–50% change from baseline for all variables (Table 1). LPS decreased muscle capillary flow velocity and increased flow heterogeneity (Figure 1).ConclusionWe have developed a method to quantitate microvascular flow in the skeletal muscle of mice using flourescent beads. The average flow distribution and velocity of mice was consistent and stable. Additionally, when mice were challenged with LPS, we were able to detect a decrease in capillary flow and an increase in flow heterogeneity within the skeletal muscle.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Ultrasound and microbubbles induced extravasation in a machine-perfused pig liver

Ultrasound driven microbubbles interact with capillaries and cells and have been proposed to be beneficial for localized drug delivery and uptake. Some of the mechanisms involved is transient cell membrane permeability alteration and vessel poration which increase particle extravasation. Ex vivo machine perfusion of human-sized organs is a technique that provides an ideal environment for preclinical investigations with high physiological relevance not possible with in vitro experiments. In this work, ex vivo machine-perfused pig livers combined with an image-guided therapy system were used to investigate extravasation induced by ultrasound driven microbubbles. Local microvascular flow changes (measured by contrast enhanced ultrasound) and leakage of Evans blue dye in liver parenchyma were used to assess the degree of extravasation. 1—4 MPa peak negative pressure and 20—1000 cycles were considered. Liver areas that were exposed to long pulses (1000 cycles) and peak negative pressure >2.5 MPa showed a detec...

Microvascular Injury and Perfusion Changes Induced by Ultrasound and Microbubbles in a Machine-Perfused Pig Liver

Localized drug delivery and uptake can benefit from the combined action of ultrasound and microbubbles at a specific site. Some of the possible mechanisms suggested are vessel poration and/or cell poration, but the exact acoustic parameters that trigger those phenomena remain unknown. Ex vivo machine perfusion of human-sized organs is a technique that provides an ideal environment for pre-clinical investigations with high physiologic relevance not possible with in vitro experiments. In this work, ex vivo machine-perfused pig livers were combined with an image-guided therapy system to investigate microvascular flow changes caused by the interaction of ultrasound-driven microbubbles with the vasculature. The effects of acoustic pressure (1.7–4 MPa peak negative pressures) and number of cycles (1000 or 20 cycles) were examined. Perfusion changes caused by the action of ultrasound on microbubbles in the microcirculation were qualitatively and quantitatively assessed with contrast-enhanced ultrasound and used as a metric of the extent of vessel perforation, thus, extravasation. Areas that were exposed to peak negative pressures above 1.7 MPa underwent a detectable and irreversible perfusion change. Complete devascularization of the area exposed to ultrasound was observed at much larger acoustic pressures (∼4 MPa). Shorter acoustic pulses (20 cycles) produced markedly fewer perfusion changes than longer pulses (1000 cycles) under the same acoustic amplitude exposure.

Characterization of buccal microvascular response in patients with septic shock

Microcirculatory alterations are thought to be responsible for much of the morbidity and mortality from sepsis. The aim of the present study was to characterize the buccal microvascular response in patients with septic shock using combined laser Doppler flowmetry/visual light spectroscopy measurements. Microvascular measurements were performed daily on the buccal mucosa in 21 consecutive ICU patients within 24 h of the onset of septic shock, in 20 healthy volunteers, and in eight ICU patients after uncomplicated elective surgery (ICU controls). In ICU controls, buccal mucosal flow was higher in the superficial (231.7+/-69.5 vs. 134+/-105.3 arbitrary unit, P=0.03) and lower in the deep (235.3+/-30.8 vs. 376.2+/-107.3 arbitrary unit, P=0.001) channel compared with healthy volunteers; microvascular oxygen haemoglobin saturations (microHbO2) were similar in the two groups. Microvascular flow within 24 h of onset of shock was similar in patients with septic shock and healthy individuals; however, microHbO2 was lower in the deep channel (78.3+/-10.3 vs. 91.1+/-4.5%, P<0.001). Superficial buccal mucosal microHbO2 within 24 h of onset of septic shock was lower in nonsurvivors than in survivors. Superficial buccal mucosal flow increased during the 2nd day of septic shock in survivors and decreased thereafter; microHbO2 decreased steadily. Buccal laser Doppler flowmetry/visual light spectroscopy may be useful for tracing microvascular alterations in critically ill patients. The surgical stress response was associated with alterations in local flow with preserved microHbO2. However, in patients with septic shock, microHbO2 was reduced in the deep channel, probably muscular tissue, with no changes in microvascular flow.

The implantable Cook Doppler probe for postoperative monitoring in head and neck free flap reconstruction: a critical evaluation

Introduction: Microvascular reconstruction requires postoperative monitoring to prevent vascular occlusion and flap failure. For some head and neck reconstructions, clinical monitoring is difficult and in others impossible due to flap components or site. The Cook–Swartz implantable Doppler flow system provides continual feedback on vascular pedicle status. This provides rapid assessment of minute-to-minute changes in microvascular flow that may allow intervention before total vascular occlusion permitting expeditious re-exploration for threatened flap failure, improving flap salvage.

Comparison Of Brachial Artery Blood Flow To Total [hemoglobin+myoglobin] Response During Post-occlusive Reactive Hyperemia.

The measurement of brachial artery blood flow (BABF) during post-occlusive reactive hyperemia (PORH) demands expertise and requires specialized equipment. Near-infrared spectroscopy (NIRS) is a non-invasive technology that allows for the measurement of total [hemoglobin + myoglobin] (as t[Hb+Mb]) in tissues of interest. Changes in t[Hb+Mb] of the forearm during PORH most likely reflect changes in total tissue hemoglobin, which would arise from changes in skeletal muscle microvascular hematocrit and/or microvascular blood flow. If true, t[Hb+Mb] could be a useful window into skeletal muscle microvascular function in health and disease. PURPOSE: The purpose of this investigation was to explore the temporal relationship between t[Hb+Mb] and BABF during PORH. We hypothesized that the transient changes in brachial artery blood flow during PORH would be detectable in the downstream microvasculature as temporally similar changes in t[Hb+Mb]. METHODS: Fourteen healthy subjects of both sexes had concurrent assessment of brachial artery blood flow by Doppler ultrasound, and t[Hb+Mb] responses by NIRS, during post-occlusive reactive hyperemia. RESULTS: The average correlation between these measurements was 0.90 (range 0.697-0.999). Because many of the subjects demonstrated a significant time lag between the peak BABF and the peak t[Hb+Mb] signal, a cross correlation analysis was also run to see if altering the time displacement improved the degree of correlation between these measurements. Cross correlation analysis showed that for 3 subjects there was no lag between the peak amplitudes for both measures. For 9 subjects the BABF values peaked prior to the t[Hb+Mb] signal; average lag time was 4 seconds (range 0.7-9.7 seconds). Two subjects showed BABF peaking after the t[hb+Mb] signal with an average lag time of -2.4 seconds between the peaks. CONCLUSIONS: These data demonstrate that, in healthy subjects, there is a close temporal association between changes in t[Hb+Mb] and changes in BABF, which suggests that changes in t[Hb+Mb] during PORH may reflect changes in microvascular flow.

Epinephrine reduces cerebral perfusion during cardiopulmonary resuscitation*

Epinephrine has been the primary drug for cardiopulmonary resuscitation (CPR) for more than a century. The therapeutic rationale was to restore threshold levels of myocardial and cerebral blood flows by its alpha1 (alpha1) and alpha2 (alpha2)-adrenergic agonist vasopressor actions. On the basis of coincidental observations on changes in microvascular flow in the cerebral cortex, we hypothesized that epinephrine selectively decreases microvascular flow. Randomized prospective animal study. University-affiliated research laboratory. Domestic pigs. Four groups of five male domestic pigs weighing 40 +/- 3 kg were investigated. After induction of anesthesia, endotracheal intubation was followed by mechanical ventilation. A frontoparietal bilateral craniotomy was created. Ventricular fibrillation was induced and untreated for 3 minutes before the start of precordial compression, mechanical ventilation, and attempted defibrillation. Animals were randomized to receive central venous injections during CPR of 1) placebo, 2) epinephrine, 3) epinephrine in which both alpha1- and beta (beta)-adrenergic effects were blocked by previous administration of prazosin and propranolol, and 4) epinephrine in which both alpha2- and beta-adrenergic effects were blocked by previous administration of yohimbine and propranolol. Cerebral cortical microcirculatory blood flow (MBF) was measured with orthogonal polarization spectral imaging. Cerebral cortical carbon dioxide and oxygen tensions (Pbco2 and Pbo2) were concurrently measured using miniature tissue optical sensors. Each animal was resuscitated. No differences in the number of electrical shocks for defibrillation or in the duration of CPR preceding return of spontaneous circulation were observed. Yet when epinephrine induced increases in arterial pressure, it significantly decreased Pbo2 tension and increased Pbco2 tension. Epinephrine therefore significantly decreased MBF and increased indicators of cerebral ischemia. Reduced MBF and magnified brain tissue ischemia during and after cardiopulmonary resuscitation were traced to the alpha1-adrenergic agonist action of epinephrine. When the alpha2 effects of epinephrine were blocked, reduced MBF and tissue ischemia persisted. No differences in cardiac output, end tidal Pco2, arterial Po2 and Pco2, and brain temperature were observed before inducing cardiac arrest and following return of spontaneous circulation. In this model, epinephrine through its alpha1-agonist action had adverse effects on cerebral microvascular blood flow such as to increase the severity of cerebral ischemia during CPR.

Sickle Cell Patients Have Exagerated Autonomic Response to Transient Hypoxia

Sickle cell anemia (SCA) is a devastating disorder that results from a single amino acid substitution in the beta chain of hemoglobin causing polymerization of hemoglobin S when oxygen is removed. This causes normally flexible sickle red cells (SRBC) to become rigid, obstruct vasculature resulting in ischemic organ damage and decreased longevity. Anything which decreases microvasculature flow will promote the sickling process. Inflammation and adhesion of cellular elements to the vessel wall are known to increase the probability of vasoocclusive crisis (VOC). However, the precise event that triggers the cascade called “crisis” is not known. Microvascular flow changes rapidly in response to autonomic signals which can be assessed by measurement of heart rate variability (HRV). These autonomic signals may be the trigger that causes regional decrease in flow and initiates the events resulting in crisis.We have established a model of induced hypoxia in human subjects that was designed to mimic the transient hypoxia occuring naturally during sleep. Calibrated tidal volume, O2 saturation, and electrocardiogram, were recorded up to 200 times per second using a LifeShirt physiological monitoring garment and tissue oxygenation and microvascular blood flow was assessed by laser Doppler flowmetry or magnetic resonance imaging. The report focuses on safety and on HRV results. Subjects breathed 5 breaths of 100% N2 twice separated by a 5 to 10 minte recovery period on up to 4 separate days per subject. 15 SCA had two hypoxic exposures on 38 days.Subjects were contacted 1, 12, and 24 hrs and 7 to 14 days later and symptom questionnaires completed. On only 4 occasions, subjects reported mild transient sicklelike pain that required no or non-narcotic treatment within 24 hours of hypoxia and was deemed possibly related to the hypoxic exposure. About sixty percent of the exposures were associated with lightheadedness lasting 10 to 15 seconds at the nadir of the SpO2. The drop in SpO2 was greater in the SCA patients (p<.05) and lasted 15 to 20 seconds. However, when we used the subjects' individually measured oxyhemoglobin saturation curve to calculate change in pO2, there was no difference between SCA and normals.Using a novel algorithm we developed which allows second to second comparison of autonomic nervous system (ANS) balance to change in SaO2, we found that the high frequency component of HRV representing parasympathetic (HFP) and low frequency component representing mixed sympathetic activity (LFP) were significantly different between SCA and control (p<.001). SCA patients have a dramatic loss of parasympathetic signal in response to transient hypoxia resulting in significant loss of heart rate variability. These data suggest than SCA patients have a greatly amplified autonomic nervous system response, at least to hypoxia. Since these same ANS signals are also responsible for control of regional microvascular blood flow, it is reasonable to speculate that this hyperactive ANS response leads to regional drop in perfusion which, on a background of hyper-adhesiveness, nitric oxide depletion, inflammation, and dehydration, triggers the sickling cascade. It is important to note that loss of HRV is a powerful predicator of sudden death in several other settings of vascular disease and that 15 to 20% of SCA deaths are otherwise unexplained sudden deaths.These data demonstrate thattransient hypoxia can be safely induced in SCA subjects and used to study the relation between hypoxia and physiological responses andSCA patients have a marked abnormality in autonomic nervous system regulation in response to transient hypoxia that likely plays a role in the pathophysiology of this disorder.

Impaired sublingual microvascular perfusion during surgery with cardiopulmonary bypass: A pilot study

Complications after cardiac surgery may involve multiple organ failure, which carries a high mortality. Development of multiple organ failure may be related to impaired microcirculatory perfusion as a result of systemic inflammation. Microcirculatory blood flow alterations have been associated with impaired outcome. We investigated whether these alterations occurred before, during, and after coronary artery bypass grafting. We observed 25 consecutive patients who underwent elective coronary artery bypass grafting with cardiopulmonary bypass. The sublingual microcirculation was investigated using side-stream dark-field imaging. Side-stream dark-field imaging was performed before (baseline), during, and after surgery. Microvascular blood flow was estimated with a semiquantitative microvascular flow index in small, medium, and large microvessels. Changes in microvascular flow were tested with Wilcoxon signed rank test. Median microvascular flow index of medium blood vessels decreased after starting cardiopulmonary bypass relative to that after anesthetic induction (2.6, interquartile range 1.6-3.0, vs 3.0, interquartile range 2.8-3.0, P = .02). There was a trend toward decreased microvascular flow index of small and large vessels relative to baseline (P = .08 and P = .05, respectively). Decreases in microvascular flow index occurred irrespective of changes in systemic blood pressure. After each patient's return to the intensive care unit, microvascular flow index increased and normalized in all microvessels. For the first time, sublingual microvascular blood flow alterations have been observed during cardiopulmonary bypass-assisted coronary artery bypass grafting.

Post-Exercise Hyperemic Response Adds to Muscle Microvascular Flow Changes during Lower Body Pressure

Exercise increases muscle microvascular flow via vasodilation from both endothelial dependent and independent mechanisms. Altered transmural pressure also affects blood flow in muscle. For example, lower body negative pressure decreases and lower body positive pressure increases blood flow. PURPOSE: To determine muscle microvascular blood flow (MBF) during post-exercise hyperemia at negative and positive lower body pressure (LBP). It was hypothesized that the post-exercise hyperemic response would not be present at increased levels of positive LBP. METHODS: Eight healthy subjects (6 male, 2 female; ages 21–41) were placed supine in a LBP chamber that was sealed at the waist. Photoplethysmography was used to noninvasively measure MBF of the tibialis anterior muscle and skin microvascular blood flow (SBF) of overlying skin during exposure to a series of LBP levels (−30, −20, −10, 0, 10, 20, 30mmHg) with and without dorsiflexion exercise. At each pressure level MBF was allowed to stabilize for one minute prior to a one minute baseline data collection. Subjects then performed a one minute isometric dorsiflexion at a resistance of 41N and MBF was recorded for one minute following dorsiflexion. Subjects were given a 5 minute rest period between pressure levels to ensure MBF return to baseline. All microvascular flow data were normalized to the control value obtained at ambient pressure without exercise and presented as percentages (mean±SE) to compare between conditions. Data were analyzed using two-way repeated measures ANOVA to determine exercise effect and pressure effect on MBF. RESULTS: MBF and SBF increased at all LBP levels with exercise compared to no exercise (p=0.001 and p=0.005). MBF significantly decreased with negative pressure and increased with positive pressure (p=0.003 and p<0.001). The lowest MBF was at −30mmHg (52±9% w/o exercise, 61±9% w/ exercise) and the highest was at 10mmHg (137±15% w/o exercise, 145±12% w/ exercise). CONCLUSION: Post exercise hyperemia occurs at all lower body pressure levels studied. Elevation of microvascular flow after isometric exercise adds to changes measured at different levels of LBP. Regimens for exercise training and post-injury rehabilitation may benefit from exercise at low levels of positive LBP. Supported by NIH Training Grant 2 T32AR07484-22 to GCM.

S-nitrosoglutathione-containing hydrogel increases dermal blood flow in streptozotocin-induced diabetic rats

Endothelial dysfunction is characterized by decreased vasodilatory capacity of the arterioles mainly due to the reduced release of nitric oxide (NO). Application of NO donors may prevent or even reverse the consequences of endothelial dysfunction, such as diabetic leg ulcers. To investigate the vasodilatory capacity and the possible side-effects of topical application of an NO donor-containing hydrogel in diabetic rats. S-nitrosoglutathione (GSNO) was incorporated in Pluronic F127 hydrogel and applied on the foot sole skin of healthy and streptozotocin-induced diabetic rats. Blood flow was monitored using a laser-Doppler probe. Nitrotyrosine formation, a possible side-effect of GSNO action, was evaluated by Western blotting of skin protein extracts. Systemic circulatory side-effects were investigated by monitoring blood pressure and heart rate during the application. The hydrogel alone did not induce any changes in microvascular flow, while GSNO-containing hydrogel caused a twofold increase in perfusion. This effect was similar in diabetic and healthy animals. Topical GSNO application did not increase the nitrotyrosine content of skin proteins, nor did it have any effect on blood pressure or heart rate. Dermal application of GSNO may be an effective treatment for promoting the local vasodilation in both healthy and diabetic states, without inducing protein nitration or alterations in blood pressure or heart rate.

Spindle-shaped constriction and propagated dilation of arterioles during cortical spreading depression

A dual illumination technique was used to examine the behavior of parenchymal arterioles of the cortex during cortical spreading depression in six cats. K+ produced a wave-ring spread of optical density changes concentrically from the injection site. At locations where the wave was passing, arterioles first constricted at one or two spots (55+/-43% of control), forming a spindle-shape in the early phase of cortical spreading depression, and then markedly dilated (155+/-57% of control) within 1 min. The dilation started at the constricted spots, propagated bidirectionally and finally resulted in full-length dilation of the arteriole. Although it varied in magnitude and time-course, this arteriolar behavior was observed in all six cats. Despite these changes, no associated downstream tissue microvascular flow changes were discernable.

Fluids reverse the early lipopolysaccharide-induced albumin leakage in rodent mesenteric venules.

Volume resuscitation is clinically beneficial in patients with sepsis, but few data exist concerning the effects of fluid administration on early events in the inflammatory process. Vascular permeability, leukocyte rolling and leukocyte adhesion in the rodent mesenteric microcirculation were assessed in vivo using intravital microscopy, and the effect of fluid administration on lipopolysaccharide (LPS)-induced changes recorded. Prospective, repeated measures study. University hospital laboratory. Male Wistar rats in six groups. All animals underwent intravital microscopic examination of mesenteric post-capillary venules. LPS or vehicle was applied topically. Animals received either no additional fluids, 0.9% saline (16 ml/kg per h) or 5% human albumin (16 ml/kg per h) commencing 30 min prior to LPS/vehicle administration. Leukocyte rolling, firm adhesion and blood velocity were observed directly. Vascular permeability was assessed using the flux of fluorescently labelled albumin into the interstitium. LPS significantly increased the median (IQR) number of leukocytes rolling and firmly adherent relative to baseline (at 60 min rolling increased from 12.0 (10.3-13.8) to 40.3 (36.0-47.5) cells/min; adhesion increased from 1 (1-2) to 17 (12-26) cells/100 microm; n=5, p<0.01). Transvascular albumin flux was significantly increased 45 min after LPS application (p<0.01), but not after vehicle. Administration of either 0.9% saline (n=5) or 5% human albumin (n=6), significantly attenuated LPS-induced increases in albumin flux (p<0.05), leukocyte rolling (p<0.01) and adhesion (p<0.01). Fluid administration did not appear to alter shear rates. Pre-emptive volume administration with either saline or albumin prevented early LPS-induced microcirculatory changes by an undefined effect that is unrelated to changes in microvascular flow.