Microvascular Hemoglobin Research Articles

Timing of capillary enlargement after adenoviral VEGF gene transfer does not support post-ischemic skeletal muscle recovery in hyperlipidemic mice

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Finish Academy (Clinical Researcher 324070 and Research Project 339560). Finnish Foundation for Cardiovascular Research Background Transient capillary enlargement has been shown to be essential for successful post-ischemic tissue recovery as it may facilitate the return of arterial driving pressure by supporting collateral maturation. It also leads to an intussusceptive increase in capillary density that supports efficient oxygen delivery and muscle regeneration. Hyperlipidemia has been shown to blunt post-ischemic capillary reactivity and hinder skeletal muscle recovery from ischemia. Therefore, it can be hypothesized that correction of capillary reactivity might improve post-ischemic muscle recovery under hyperlipidemia. Purpose The aim of this study was to test the ability of angiogenic VEGF gene therapy in improving post-ischemic muscle recovery under hyperlipidemia. Methods AdVEGF gene transfer was performed into the calf muscles of aged, hyperlipidemic LDLR-/-ApoB100/100 mice after acute ischemia induction. The effects of AdVEGF on capillary phenotype, tissue edema, restoration of blood flow parameters, microvascular hemoglobin oxygenation and tissue damage/regeneration were evaluated for up to 29 days post-procedure as compared to AdLacZ control using immuno- and histological analyses, magnetic resonance, contrast-enhanced ultrasound and photoacoustic imaging, respectively. Results AdVEGF gene therapy was able to promote capillary enlargement that led to recovery of arterial driving pressure in ischemic LDLR-/-ApoB100/100 muscles. However, capillary enlargement induced by AdVEGF appeared late, lasted up to 29 days and did not promote intussusception. Consequently, the negative effect of long-lasting enlargement, i.e., massive tissue edema, delayed blood flow recovery and aggravated ischemic tissue damage. Conclusion Proper time of induction and duration of capillary enlargement are crucial to yield a functional vascular response supporting post-ischemic tissue recovery.

Temporal Pattern of Cortical Hypoxia in Multiple Sclerosis and Its Significance on Neuropsychological and Clinical Measures of Disability.

Multiple sclerosis (MS) is a degenerative disease of the central nervous system (CNS) characterized by inflammation, demyelination, and axonal damage. It has been hypothesized that hypoxia plays a role in the pathogenesis of MS. This study was undertaken to investigate the reproducibility of non-invasively measured cortical microvascular hemoglobin oxygenation (St O2 ) using frequency domain near-infrared spectroscopy (fdNIRS), investigate its temporal pattern of hypoxia in people with MS (pwMS), and its relationship with neurocognitive function and mood. We investigated the reproducibility of fdNIRS measurements. We measured cortical hypoxia in pwMS, and the relationships between St O2 , neurocognitive function, fatigue, and measures of physical disability. Furthermore, we cataloged the temporal pattern of St O2 measured at 1-week intervals for 4 weeks, and at 8 weeks and ~1 year. We show that fdNIRS parameters were highly reproducible in 7 healthy control participants measured over 6 days (p > 0.05). There was low variability between and within subjects. In line with our previous findings, we show that 33% of pwMS (n = 88) have cortical microvascular hypoxia. Over 8 weeks and at ~1 year, St O2 values for normoxic and hypoxic groups did not change significantly. There was no significant association between cognitive function and St O2 . This conclusion should be revisited as only a small proportion of the relapsing-remitting MS group (21%) was cognitively impaired. The fdNIRS parameters have high reproducibility and repeatability, and we have demonstrated that hypoxia in MS is a chronic condition, lasting at least a year. The results show a weak relationship between cognitive functioning and oxygenation, indicating future study is required. ANN NEUROL 2023;94:1067-1079.

Increased brain microvascular hemoglobin concentrations in children with cerebral malaria.

Brain swelling is associated with death from cerebral malaria, but it is unclear whether brain swelling is caused by cerebral edema or vascular congestion-two pathological conditions with distinct effects on tissue hemoglobin concentrations. We used near-infrared spectroscopy (NIRS) to noninvasively study cerebral microvascular hemoglobin concentrations in 46 Malawian children with cerebral malaria. Cerebral malaria was defined by the presence of the malaria parasite Plasmodium falciparum on a blood smear, a Blantyre coma score of 2 or less, and retinopathy. Children with uncomplicated malaria (n = 33) and healthy children (n = 29) were enrolled as comparators. Cerebral microvascular hemoglobin concentrations were higher among children with cerebral malaria compared with those with uncomplicated malaria [median (25th, 75th): 145.2 (95.2, 190.0) μM versus 82.9 (65.7, 105.4) μM, P = 0.008]. Cerebral microvascular hemoglobin concentrations correlated with brain swelling score determined by MRI (r = 0.37, P = 0.03). Fluctuations in cerebral microvascular hemoglobin concentrations over a 30-min time period were characterized using detrended fluctuation analysis (DFA). DFA determined self-similarity of the cerebral microvascular hemoglobin concentration signal to be lower among children with cerebral malaria compared with those with uncomplicated malaria [0.63 (0.54, 0.70) versus 0.91 (0.82, 0.94), P < 0.0001]. The lower self-similarity of the hemoglobin concentration signal in children with cerebral malaria suggested impaired regulation of cerebral blood flow. The elevated cerebral tissue hemoglobin concentration and its correlation with brain swelling suggested that excess blood volume, potentially due to vascular congestion, may contribute to brain swelling in cerebral malaria.

BIO2: Microcirculation Perfusion is Impaired up to 24 Hours after Veno-arterial Extracorporeal Circulation.

Extracorporeal circulation (ECC) procedures, such as extracorporeal membrane oxygenation (ECMO) and cardiopulmonary bypass (CPB), are used to replace the function of the heart and lung, but they induce complications in the form of acute kidney failure, bleeding, heart arrhythmias or thromboembolic complications. This study aimed to quantify the changes in microvascular perfusion and oxygenation that occur after veno-arterial ECC (VA-ECC). Male Golden Syrian hamsters were instrumented with a dorsal window chamber to study their microcirculation and an exteriorized carotid artery catheter for blood pressure and blood gas measurements. After baseline (BL) measurements were taken, the hamster underwent surgery under isoflurane to insert a drainage catheter into the jugular vein. A heparin bolus (0.05 IU/g) was then provided, and the animal was connected to the VA-ECC circuit, which consists of a peristaltic pump and bubble trap. The VA-ECC circuit was primed with either lactated ringers (LR) or 5% human serum albumin in saline (HSA). Blood flow was ramped up over 15 minutes, maintained at 15% of the animal’s cardiac output for 60 minutes, then ramped down over 15 minutes. Sham animals underwent cannulation surgery and heparinization but were not connected to the VA-ECC circuit. The animals were surgically closed, placed on a heating pad, and allowed at least 30 minutes to wake up from the anesthetic plane before taking measurements at 1, 2, and 24 hours after VA-ECC. Results show that flow in arterioles and venules (Figure 1) at all post-ECC timepoints statistically decreased in LR and HSA groups compared to Sham. LR and HSA failed to recover flow in arterioles and venules back to BL levels post-ECC. Interestingly, venule perfusion statistically increased at 1 and 2 hrs in the HSA group compared to the LR group. Functional capillary density (FCD, Figure 2) showed a statistical reduction in capillary perfusion for both ECC groups, with the HSA group maintaining higher levels compared to the LR group. Microvascular hemoglobin (Hb) oxygen (O2) saturation (Figure 3), in venules was statistically reduced post-ECC for both LR and HSA compared to Sham and BL. The microvascular perfusion results, combined with the consistent drop in hematocrit (Hct) post-ECC suggest an imbalance in oncotic pressure that slowly rectifies after ECC. Via Starling’s law of filtration, the priming volume dilutes protein content within the blood, causing the intravascular oncotic pressure to drop, resulting in ultrafiltration at the capillary level. Additionally, the drop in venule Hb O2 saturation and the reduced microvascular perfusion suggest a reduced O2 delivery and potentially a repayment of an O2 debt post-ECC. This study shows that microvascular sequelae could potentially cause ischemic injury in ECC procedures, which can lead to organ damage and inflammation.Figure 1. Microcirculatory hemodynamics. Diameter, velocity, and volumetric blood flow are shown from top to bottom, while arterioles (Sham: n = 38, LR: n = 33; HSA: n = 33) and venules (Sham: n = 38, LR: n = 30, HSA: n = 33) are shown from the left to right columns. All values are normalized to baseline (BL, before ECC) measurements for each vessel. * P < 0.05, ** P < 0.01, *** P < 0.001, **** P < 0.0001 between groups at each timepoint. † P<0.05 compared to BL, within each group.Figure 2. Functional capillary density (FCD). * P < 0.05, ** P < 0.01, *** P < 0.001, **** P < 0.0001 between groups. † P<0.05 compared to baseline (BL). N = 6 for all groups.Figure 3. Microvascular Hemoglobin Oxygen Saturation Changes. The top row shows arterioles (Sham: n = 19, LR: n = 13, HSA: n = 16), while the bottom row shows venules (Sham: n = 21, LR: n = 19, HSA: n = 22). * P < 0.05, ** P < 0.01, *** P < 0.001, **** P < 0.0001 between groups. † P<0.05 compared to baseline (BL).

BIO18: Hemoglobin and Heme Scavenger Proteins Reduce Free Hemoglobin During Venovenous Extracorporeal Circulation and Preserves Microvascular Function.

Extracorporeal circulation procedures often utilize a blood pump to drive flow through an external circuit, which can cause hemolysis due to high shear conditions and foreign surface contact. The purpose of this study was to determine whether priming fluids containing proteins to sequester hemoglobin (Hb) and heme could be used in venovenous extracorporeal circulation (VV-ECC) to reduce their toxicity. A day prior to the experiment, male Golden Syrian hamsters were instrumented with a dorsal window chamber to monitor the microcirculation. The day of the experiment, both jugular veins were then cannulated under isoflurane anesthesia. Baseline (BL) microvascular oxygenation was measured using a hyperspectral camera. The animals were then heparinized (2.5 IU/g) and connected to the VV-ECC circuit, consisting of a peristaltic pump and bubble trap. The ECC circuit was primed with either 5% human serum albumin (HSA), ApoHb-Hp (62.01 mg/mL), or a protein solution containing hemopexin, transferrin, and Hp (protein cocktail, 84.50 mg/mL). Haptoglobin (Hp), hemopexin, and transferrin are native proteins that bind to Hb, heme, and iron respectively. Apohemoglobin (apoHb) is a synthetic scavenger produced by removing heme from Hb. ApoHb binds to haptoglobin (Hp) forming the apoHb-Hp complex that retains its ability to bind heme and scavenge free Hb. The experiment lasted a total of 2 hrs (Table 1), in which first the animals were hemodiluted, and the flow rate through the circuit was ramped up to 50% of the animal’s cardiac output. This max flow rate was then maintained for 35 minutes before being ramped down to 0.2 mLPM. The circuit was maintained at this flow rate for 15 minutes, allowing the animal and the circuit to equilibrate before the circuit flow was stopped. While mean arterial pressure (MAP, Figure 1a) showed differences at baseline (BL) between HSA and both other groups, there was no significance observed after hemodilution and the ramp up phase of the experiment. This difference in MAP between HSA and the two other solutions returned at all timepoints after the ramp up phase. Hb oxygen saturation (sO2, Figure 2) within the microvasculature showed a drop for both arterioles and venules in both the protein cocktail and ApoHb-Hp groups at the full VV-ECC timepoint. The plasma Hb (Figure 3) for the protein cocktail and ApoHb-Hp groups were significantly lower than the HSA control from the start of VV-ECC to the equilibration stage when compared to the HSA control. These results confirm that the ApoHb and protein cocktail solutions have the capability to bind and sequester free Hb, which has the potential to reduce the extravasation of Hb from the circulatory compartment into tissues, preserves the vascular nitric oxide (NO) signaling pathway, and reduce Hb and heme toxicity. Future work is needed to determine impact on organs, especially the kidneys, and to quantify the binding efficiency of these proteins to free hemoglobin.Figure 1. Hemodynamic parameters measured via the carotid artery: a) Mean arterial pressure (MAP) and b) heart rate (HR). bl = baseline, dil = hemodilution, up = ramp up, ecc = VV-ECC at max flow rate (50% of cardiac output), down = ramp down, equ = equilibration, off = off pump. * P < 0.05, ** P < 0.01, *** P < 0.001 between groups. N = 6 for all groups.Figure 2. Changes in microvascular hemoglobin oxygen saturation. The top row shows arterioles, while the bottom row shows venules. Arterioles and venules were analyzed for 4 hamsters per group. bl = baseline, dil = hemodilution, up = ramp up, ecc = VV-ECC at max flow rate (50% of cardiac output), down = ramp down, equ = equilibration, off = off pump. * P < 0.05, ** P < 0.01, *** P < 0.001, **** P < 0.0001 between groups. † P<0.05 compared to baseline (BL).Figure 3. a) Hematocrit (Hct) and b) plasma hemoglobin (pHb). 0 = baseline (BL), 25 = hemodilution, 45 = VV-ECC (start), 75 = VV-ECC (end), 105 = equilibrate, 120 = off pump. * P < 0.05, ** P < 0.01, *** P < 0.001, **** P < 0.0001 between groups. † P<0.05 compared to BL. Table 1. - Experimental timeline highlight the blood flow through the circuit. Baseline Hemodilution Ramp Up VV-ECC Ramp Down Equilibrate Off Pump Duration 15 min 15 min 15 min 35 min 15 min 15 min 10 min Blood Flow 0 mLPM 0.2 mLPM 0.2 mLPM → 50% CO 50% CO 50% CO → 0.2 mLPM 0.2 mLPM 0 mLPM Hyperspectral images were taken every 5 minutes. mLPM = milliliters per minute, CO = cardiac output, VV-ECC = full venovenous extracorporeal circulation.

Aortic stiffness and impairments in cerebrovascular function in cancer survivorship

An established consequence of anti-cancer treatment is increased aortic stiffness, which impairs the aortic damping of cardiac-generated pulsatile pressure and blood flow. These increased pulsations may result in vascular injury in the microcirculation of target end organs like the brain. The aim of the present study was to determine the ramifications of elevated aortic stiffness on cerebral macro- and microvascular pulsatility and autoregulatory function in cancer survivors. We hypothesized that cerebrovascular pulsatility would be enhanced, and cerebrovascular reactivity (CVR) to elevations in arterial CO 2 would be impaired, both in the large and small cerebral vessels in patients with a history of cancer and anti-cancer treatment versus healthy age- and sex-matched non-cancer controls. Aortic arch pulse wave velocity (aaPWV), a regional measure of stiffness in the proximal aorta, was calculated from echocardiographic views of the aortic valve and the descending aortic arch. Subjects then breathed room air for 60s followed by ~2 minutes of rebreathing with simultaneous collection of end-tidal pressure of CO 2 (P ET CO 2 ). Middle cerebral artery blood flow velocity (MCAv) was assessed using transcranial doppler. Oxygenated (oxy-[Hb]) and deoxygenated (deoxy-[Hb]) cerebral microvascular hemoglobin concentrations were monitored using two near-infrared spectroscopy probes placed over the prefrontal cortices. Pulsatility was assessed at baseline using Gosling’s Pulsatility Index (PI) for both the microvasculature and MCA. To account for changes in perfusion pressure, MAP was collected via finger plethysmography and cerebrovascular conductance indices were calculated for both oxy-[Hb] (CVCi oxy ) and MCAv (CVCi MCA ). CVR was calculated as the slope of CVCi oxy and CVCi MCA over P ET CO 2 during rebreathing. Six women were recruited (n = 3/group). Age was similar between the healthy non-cancer controls (HC) and patients with a history of cancer and anti-cancer treatment (CS) (31.0 ± 7 vs. 32.7 ± 13 years). Baseline ventilatory (P ET CO 2 ), central and cerebral hemodynamics were also similar (all p &gt; 0.05). aaPWV was significantly elevated in CS compared to HC (5.3 ± 0.6 vs. 3.1 ± 1.1 m/s, p = 0.04). Cerebral microcirculation PI in CS was significantly elevated (0.04 ± 0.01 vs. 0.02 ± 0.01, p = 0.02), but MCA PI was not different (p &gt; 0.05). CVR-CVCi oxy was impaired in CS (-3.6 ± 2.8 vs. 1.5 ± 0.5 nM·mmHg -1 /mmHg, p = 0.03), and CVR-CVCi MCA was similarly reduced (-0.05 ± 0.06 vs. 0.15 ± 0.01 mm/sec·mmHg -1 /mmHg, p &lt; 0.01). The increase in MAP during hypercapnia was similar between groups. Consistent with our hypothesis, both CVR-CVCi oxy and CVR-CVCi MCA were attenuated in patients with a history of anti-cancer treatment. Additionally, the microvascular pulsatility was greater in CS. This suggests an impaired cerebrovascular function, possibly related to increased transmission of pulsatility into the brain, in the years following cancer diagnoses and treatment. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Hyperspectral wide-field-of-view imaging to study dynamic microcirculatory changes during hypoxia.

Hyperspectral imaging (HSI) provides a fast, reliable, and noninvasive way for the study of vascular microcirculation in animal models. Rapid hyperspectral imaging of large portions of the microcirculatory preparation is critical for understanding the function and regulation of vascular microcirculatory networks. This report presents the application of an off-the-shelf benchtop HSI linear scanning system to acquire larger field-of-view images of microcirculatory preparations. The HSI line detector was displaced perpendicular to the scanning direction to map larger areas, with a rate of displacement determined by the scanning rate and the exposure time. Analysis of the collected image was used to assess dynamic changes in the microcirculation. The system records dynamic changes in microvascular hemoglobin oxygen (HbO2) saturation and vascular morphology during hypoxia and reoxygenation and has similar acquisition speeds to commonly referenced spectral-scanning HSI systems. In addition, the HbO2 saturations collected via HSI closely correlate with those collected by phosphorescence quenching microscopy. The reported system enables dynamic functional imaging of the microcirculation for broad experimental and clinical applications.NEW & NOTEWORTHY This study presents a novel bench setup and algorithm to measure intravascular hemoglobin oxygen saturation in microcirculation. Wide-field hyperspectral imaging allows for rapid quantification of intravascular changes in hemoglobin saturation. The method described in this manuscript can expand the understanding of oxygen delivery to tissues in vivo.

Spectroscopy detects skeletal muscle microvascular dysfunction during onset of sepsis in a rat fecal peritonitis model

Sepsis is a dysregulated host inflammatory response to infection potentially leading to life-threatening organ dysfunction. The objectives of this study were to determine whether early microvascular dysfunction (MVD) in skeletal muscle can be detected as dynamic changes in microvascular hemoglobin (MVHb) levels using spectroscopy and whether MVD precedes organ histopathology in septic peritonitis. Skeletal muscle of male Sprague–Dawley rats was prepared for intravital microscopy. After intraperitoneal injection of fecal slurry or saline, microscopy and spectroscopy recordings were taken for 6 h. Capillary red blood cell (RBC) dynamics and SO2 were quantified from digitized microscopy frames and MVHb levels were derived from spectroscopy data. Capillary RBC dynamics were significantly decreased by 4 h after peritoneal infection and preceded macrohemodynamic changes. At the same time, low-frequency oscillations in MVHb levels exhibited a significant increase in Power in parts of the muscle and resembled oscillations in RBC dynamics and SO2. After completion of microscopy, tissues were collected. Histopathological alterations were not observed in livers, kidneys, brains, or muscles 6 h after induction of peritonitis. The findings of this study show that, in our rat model of sepsis, MVD occurs before detectable organ histopathology and includes ~ 30-s oscillations in MVHb. Our work highlights MVHb oscillations as one of the indicators of MVD onset and provides a foundation for the use of non-invasive spectroscopy to continuously monitor MVD in septic patients.

Dynamic tracking of microvascular hemoglobin content for continuous perfusion monitoring in the intensive care unit: pilot feasibility study.

Purpose: There is a need for bedside methods to monitor oxygen delivery in the microcirculation. Near-infrared spectroscopy commonly measures tissue oxygen saturation, but does not reflect the time-dependent variability of microvascular hemoglobin content (MHC) that attempts to match oxygen supply with demand. The objective of this study is to determine the feasibility of MHC monitoring in critically ill patients using high-resolution near-infrared spectroscopy to assess perfusion in the peripheral microcirculation. Methods: Prospective observational cohort of 36 patients admitted within 48 h at a tertiary intensive care unit. Perfusion was measured on the quadriceps, biceps, and/or deltoid, using the temporal change in optical density at the isosbestic wavelength of hemoglobin (798 nm). Continuous wavelet transform was applied to the hemoglobin signal to delineate frequency ranges corresponding to physiological oscillations in the cardiovascular system. Results: 31/36 patients had adequate signal quality for analysis, most commonly affected by motion artifacts. MHC signal demonstrates inter-subject heterogeneity in the cohort, indicated by different patterns of variability and frequency composition. Signal characteristics were concordant between muscle groups in the same patient, and correlated with systemic hemoglobin levels and oxygen saturation. Signal power was lower for patients receiving vasopressors, but not correlated with mean arterial pressure. Mechanical ventilation directly impacts MHC in peripheral tissue. Conclusion: MHC can be measured continuously in the ICU with high-resolution near-infrared spectroscopy, and reflects the dynamic variability of hemoglobin distribution in the microcirculation. Results suggest this novel hemodynamic metric should be further evaluated for diagnosing microvascular dysfunction and monitoring peripheral perfusion.Electronic supplementary materialThe online version of this article (10.1007/s10877-020-00611-x) contains supplementary material, which is available to authorized users.

Visible light optical coherence tomography angiography (vis-OCTA) facilitates local microvascular oximetry in the human retina.

We report herein the first visible light optical coherence tomography angiography (vis-OCTA) for human retinal imaging. Compared to the existing vis-OCT systems, we devised a spectrometer with a narrower bandwidth to increase the spectral power density for OCTA imaging, while retaining the major spectral contrast in the blood. We achieved a 100 kHz A-line rate, the fastest acquisition speed reported so far for human retinal vis-OCT. We rigorously optimized the imaging protocol such that a single acquisition took < 6 seconds with a field of view (FOV) of 3×7.8 mm2. The angiography enables accurate localization of microvasculature down to the capillary level and thus enables oximetry at vessels < 100 µm in diameter. We demonstrated microvascular hemoglobin oxygen saturation (sO2) at the feeding and draining vessels at the perifoveal region. The longitudinal repeatability was assessed by < 5% coefficient of variation (CV). The unique capabilities of our vis-OCTA system may allow studies on the role of microvascular oxygen in various retinal pathologies.

Effect of differential muscle activation patterns on muscle deoxygenation and microvascular haemoglobin regulation.

What is the central question of this study? Does the presence and extent of heterogeneity in the ratio of O2 delivery to uptake across human muscles relate specifically to different muscle activation patterns? What is the main finding and its importance? During ramp incremental knee-extension and cycling exercise, the profiles of muscle deoxygenation (deoxy[haemoglobin+myoglobin]) and diffusive O2 potential (total[haemoglobin+myoglobin]) in the vastus lateralis corresponded to different muscle activation strategies. However, this was not the case for the rectus femoris, where muscle activation and deoxygenation profiles were dissociated and might therefore be determined by other structural and/or functional attributes (e.g. arteriolar vascular regulation and control of red blood cell flux). Near-infrared spectroscopy has revealed considerable heterogeneity in the ratio of O2 delivery to uptake as identified by disparate deoxygenation {deoxy[haemoglobin+myoglobin] (deoxy[Hb+Mb])} values in the exercising quadriceps. However, whether this represents a recruitment phenomenon or contrasting vascular and metabolic control, as seen among fibre types, has not been established. We used knee-extension (KE) and cycling (CE) incremental exercise protocols to examine whether differential muscle activation profiles could account for the heterogeneity of deoxy[Hb+Mb] and microvascular haemoconcentration (i.e. total[Hb+Mb]). Using time-resolved near-infrared spectroscopy for the quadriceps femoris (vastus lateralis and rectus femoris) during exhaustive ramp exercise in eight participants, we tested the following hypotheses: (i) the deoxy[Hb+Mb] (i.e. fractional O2 extraction) would relate to muscle activation levels across exercise protocols; and (ii) KE would induce greater total[Hb+Mb] (i.e. diffusive O2 potential) at task failure (i.e. peak O2 uptake) than CE irrespective of muscle site. At a given level of muscle activation, as assessed by the relative integrated EMG normalized to maximal voluntary contraction (%iEMGmax ), the vastus lateralis deoxy[Hb+Mb] profile was not different between exercise protocols. However, at peak O2 uptake and until 20% iEMGmax for CE, rectus femoris exhibited a lower deoxy[Hb+Mb] (83.2±15.5 versus 98.2±19.4μm) for KE than for CE (P<0.05). The total[Hb+Mb] at peak O2 uptake was not different between exercise protocols for either muscle site. These data support the hypothesis that the contrasting patterns of convective and diffusive O2 transport correspond to different muscle activation patterns in vastus lateralis but not rectus femoris. Thus, the differential deoxygenation profiles for rectus femoris across exercise protocols might be dependent upon specific facets of muscle architecture and functional haemodynamic events.

Impact of shear rate pattern on post-occlusive near-infrared spectroscopy microvascular reactivity

The primary aim of the present study was to determine the impact of acute changes in shear rate patterns, in particular retrograde shear rate, on microvascular function in 15 healthy, young men and women as determined via the post-occlusive near-infrared spectroscopy (NIRS) microvascular reactivity response. Microvascular reactivity, via NIRS-derived measurements of post-occlusion tissue saturation index (TSI%) and total microvascular hemoglobin+myoglobin concentration ([Hb]total), were assessed in each participant before and immediately after exposure to a 30min retrograde shear treatment. Retrograde shear was achieved via a blood pressure cuff placed below the knee inflated to 75mmHg. One leg was exposed to the retrograde shear (Treatment leg) and the contralateral leg served as a non-treatment control. In the Treatment leg, significant increases in retrograde shear rate occurred during the retrograde intervention. Following the intervention, the area under the TSI% post-occlusion response curve, which represents the total microvascular reactivity response, and the absolute peak TSI% response were significantly increased compared to pre-intervention in the Treatment leg, but not the Control leg. The absolute peak [Hb]total response was significantly increased post-intervention in both legs. These results are in contrast to our hypothesis that 75mmHg cuff inflation, designed to increase retrograde shear rate in the femoral artery would negatively affect post-occlusive microvascular reactivity. These data suggest that the current method of increasing retrograde shear rate in the intact human does not adversely impact NIRS derived measurements of microvascular reactivity.

The impact of endotoxin on jejunal tissue oxygenation.

We examined the effects of systemic ETX on jejunal mucoal microcirculatory parameters in anesthetized pigs. Jejunal mucosal tissue PO2 was measured employing Clark-type surface oxygen electrodes. Oxygen saturation of jejunal microvascular hemoglobin was determined by tissue reflectance spectrophotometry. Jejunal microcirculatory blood flow was assessed by laser Doppler flowmetry. Microvascular conductance and rhythmical oscillation of the tissue PO2 were calculated. Systemic hemodynamic variables, mesenteric venous and systemic acid base and blood gas variables, and lactate measurements were recorded. Measurements were taken at BL and after Escherichia coli LPS administration in 20minutes intervals for 110minutes. ETX infusion led to a significant (P<.05) decrease of PO2 muc (from 24±4 to 8±4mmHg) and microvascular HbO2 (from 41±13 to 24±12%). Microcirculatory conductivity increased in ETX animals, microvascular blood flow remained unchanged (PU; from 228±45 to 232±58). ETX induced an increase in oscillation frequency of mucosal tissue oxygenation. Endotoxinemia resulted in a significant depression of mucosal tissue oxygenation despite a constant microcirculatory blood flow. This impairment of tissue oxygenation resulted in an increase in the vasomotion pattern in a futile attempt to counteract the undersupply of oxygen to the jejunal tissue.

Abstract WP99: Neuroprotective Therapy for Ischemia-Reperfusion Injury by Hemoglobin-albumin-cluster(Hemoact Tm )

Background: A hemoglobin-albumin cluster designated as “HemoAct” was developed as a red blood cell substitute. It is composed of one core hemoglobin center wrapped covalently by three albumin shells. Since its particle size with a diameter of 10 nm is far smaller than red blood cell, it is expected to maintain good perfusion in the cerebral microvessels, leading to neuroprotective effects on ischemia-reperfusion (I/R) injury. Purpose: We aim to examine whether HemoAct have neuroprotective effects in rat transient middle cerebral artery occlusion (tMCAO) model, without toxic effects of hemoglobin, by administering it though the recanalized artery just before the onset of reperfusion. Subjects and Methods: Male Sprague-Dawley rats were subjected to 2-hour tMCAO by suture occlusion and then divided into four groups with respective treatments: (1) control group; no infusion, (2) vehicle group; infusion of PBS as the solvent (3) 0.5х HemoAct group; infusion of one-half diluted HemoAct (4) HemoAct group; infusion of undiluted HemoAct. Physical and neurological states, infarct and edema volumes, reactive oxygen species (ROS) and protease immunoblot levels were compared between the four groups after 24 hours of reperfusion. Microvascular hemoglobin perfusion and morphological states were compared between the control and HemoAct groups with immunohistochemical technique. Results: No significant changes were observed in blood pressure, pH, and blood gas after HemoAct infusion. Neurological symptoms were significantly less severe in the HemoAct group than in the other groups. Infarct and edema volumes were significantly smaller in the 0.5х HemoAct group (27.1%/15.2%) and the HemoAct group (20.2%/14.1%) than in the control group (55.2%/26.4%) and the vehicle group (53.2%/27.1%). ROS (4-HNE) and protease (MMP-9) immunoblot levels were significantly reduced in HemoAct group compared with the control and vehicle groups. Microvascular hemoglobin perfusion was more and microvascular narrowing changes was less in the HemoAct group than in the control group. Conclusion: HemoAct exhibited strong neuroprotective effects on I/R injury without toxic effects of hemoglobin. Superior microvascular perfusion of HemoAct may be a possible neuroprotective mechanism.

Reduced cortical microvascular oxygenation in multiple sclerosis: a blinded, case-controlled study using a novel quantitative near-infrared spectroscopy method.

Hypoxia (low oxygen) is associated with many brain disorders as well as inflammation, but the lack of widely available technology has limited our ability to study hypoxia in human brain. Multiple sclerosis (MS) is a poorly understood neurological disease with a significant inflammatory component which may cause hypoxia. We hypothesized that if hypoxia were to occur, there should be reduced microvascular hemoglobin saturation (StO2). In this study, we aimed to determine if reduced StO2 can be detected in MS using frequency domain near-infrared spectroscopy (fdNIRS). We measured fdNIRS data in cortex and assessed disability of 3 clinical isolated syndrome (CIS), 72 MS patients and 12 controls. Control StO2 was 63.5 ± 3% (mean ± SD). In MS patients, 42% of StO2 values were more than 2 × SD lower than the control mean. There was a significant relationship between StO2 and clinical disability. A reduced microvascular StO2 is supportive (although not conclusive) that there may be hypoxic regions in MS brain. This is the first study showing how quantitative NIRS can be used to detect reduced StO2 in patients with MS, opening the door to understanding how microvascular oxygenation impacts neurological conditions.

Postural change in volunteers: sympathetic tone determines microvascular response to cardiac preload and output increases.

PurposeMicrovascular perfusion may be a non-invasive indicator of fluid responsiveness. We aimed to investigate which of the microvascular perfusion parameters truly reflects fluid responsiveness independent of sympathetic reflexes.MethodsFifteen healthy volunteers underwent a postural change from head up tilt (HUT) to the supine position, diminishing sympathetic tone, followed by a 30° passive leg raising (PLR) with unaltered tone. Prior to and after the postural changes, stroke volume (SV) and cardiac output (CO) were measured, as well as sublingual microcirculatory perfusion (sidestream dark field imaging), skin perfusion, and oxygenation (laser Doppler flowmetry and reflectance spectroscopy).ResultsIn responders (subjects with >10 % increase in CO), the HUT to supine change increased CO, SV, and pulse pressure, while heart rate, systemic vascular resistance, and mean arterial pressure decreased. Additionally, microvascular flow index, laser Doppler flow, and microvascular hemoglobin oxygen saturation and concentration also increased.ConclusionWhen preload and forward flow increase in association with a decrease in sympathetic activity, microvascular blood flow increases in the skin and in the sublingual area. When preload and forward flow increase with little to no change in sympathetic activity, only sublingual functional capillary density increases. Therefore, our results indicate that sublingual functional capillary density is the best parameter to use when evaluating fluid responsiveness independent of changes in sympathetic tone.

Severe blunt muscle trauma in rats: only marginal hypoxia in the injured area.

BackgroundAfter severe muscle trauma, hypoxia due to microvascular perfusion failure is generally believed to further increase local injury and to impair healing. However, detailed analysis of hypoxia at the cellular level is missing. Therefore, in the present work, spectroscopic measurements of microvascular blood flow and O2 supply were combined with immunological detection of hypoxic cells to estimate O2 conditions within the injured muscle area.Materials and MethodsSevere blunt muscle trauma was induced in the right Musculus gastrocnemius of male Wistar rats by a standardized “weight-drop” device. Microvascular blood flow, relative hemoglobin amount, and hemoglobin O2 saturation were determined by laser Doppler and white-light spectroscopy. Hypoxic cells were detected by histologic evaluation of covalent binding of pimonidazole and expression of HIF-1α.ResultsDirectly after trauma and until the end of experiment (480 minutes), microvascular blood flow and relative hemoglobin amount were clearly increased. In contrast to blood flow and relative hemoglobin amount, there was no immediate but a delayed increase of microvascular hemoglobin O2 saturation. Pimonidazole immunostaining revealed a hypoxic fraction (percentage area of pimonidazole-labelled muscle cells within the injured area) between 8 to 3%. There was almost no HIF-1α expression detectable in the muscle cells under each condition studied.ConclusionsIn the early phase (up to 8 hours) after severe blunt muscle trauma, the overall microvascular perfusion of the injured area and thus its O2 supply is clearly increased. This increased O2 supply is obviously sufficient to ensure normoxic (or even hyperoxic) conditions in the vast majority of the cells.

Detection of reduced interhemispheric cortical communication during task execution in multiple sclerosis patients using functional near-infrared spectroscopy.

Multiple sclerosis (MS) impairs brain activity through demyelination and loss of axons. Increased brain activity is accompanied by increases in microvascular hemoglobin oxygen saturation (oxygenation) and total hemoglobin, which can be measured using functional near-infrared spectroscopy (fNIRS). Due to the potentially reduced size and integrity of the white matter tracts within the corpus callosum, it may be expected that MS patients have reduced functional communication between the left and right sides of the brain; this could potentially be an indicator of disease progression. To assess interhemispheric communication in MS, we used fNIRS during a unilateral motor task and the resting state. The magnitude of the change in hemoglobin parameters in the motor cortex was significantly reduced in MS patients during the motor task relative to healthy control subjects. There was also a significant decrease in interhemispheric communication between the motor cortices (expressed as coherence) in MS patients compared to controls during the motor task, but not during the resting state. fNIRS assessment of interhemispheric coherence during task execution may be a useful marker in disorders with white matter damage or axonal loss, including MS.

Evaluation of Multiple Modes of Oximetry Monitoring as an Index of Splanchnic Blood Flow in a Newborn Lamb Model of Hypoxic, Ischemic, and Hemorrhagic Stress

Early and aggressive treatment of circulatory failure is associated with increased survival, highlighting the need for monitoring methods capable of early detection. Vasoconstriction and decreased oxygenation of the splanchnic circulation are a sentinel response of the cardiovasculature during circulatory distress. Thus, we measured esophageal oxygenation as an index of decreased tissue oxygen delivery caused by three types of ischemic insult, occlusive decreases in mesenteric blood flow, and hemodynamic adaptations to systemic hypoxia and simulated hemorrhagic stress. Five anesthetized lambs were instrumented for monitoring of mean arterial pressure, mesenteric artery blood flow, central venous hemoglobin oxygen saturation, and esophageal and buccal microvascular hemoglobin oxygen saturation (StO2). The sensitivities of oximetry monitoring to detect cardiovascular insult were assessed by observing responses to graded occlusion of the descending aorta, systemic hypoxia due to decreased FIO2, and acute hemorrhage. Decreases in mesenteric artery flow during aortic occlusions were correlated with decreased esophageal StO2 (R = 0.41). During hypoxia, esophageal StO2 decreased significantly within 1 min of initiation, whereas buccal StO2 decreased within 3 min, and central venous saturation did not change significantly. All modes of oximetry monitoring and arterial blood pressure were correlated with mesenteric artery flow during acute hemorrhage. Esophageal StO2 demonstrated a greater decrease from baseline levels as well as a more rapid return to baseline levels during reinfusion of the withdrawn blood. These experiments suggest that monitoring esophageal StO2 may be useful in the detection of decreased mesenteric oxygen delivery as may occur in conditions associated with hypoperfusion or hypoxia.

Vasopressin V1A receptors mediate the increase in gastric mucosal oxygenation during hypercapnia

Hypercapnia (HC) improves systemic oxygen delivery (DO₂) and microvascular hemoglobin oxygenation of the mucosa (μHbO₂). Simultaneously, HC increases plasma levels of vasopressin. Although vasopressin is generally regarded a potent vasoconstrictor particularly in the splanchnic region, its effects on splanchnic microcirculation during HC is unclear. The aim of this study was to evaluate the role of endogenous vasopressin on gastric mucosal oxygenation and hemodynamic variables during physiological (normocapnia) and hypercapnic conditions. Five dogs were repeatedly anesthetized to study the effect of vasopressin V(1A) receptor blockade ([Pmp¹,Tyr(Me)²]-Arg⁸-Vasopressin, 35 μg/kg) on hemodynamic variables and μHbO₂ during normocapnia or HC (end-tidal CO₂ 70 mmHg). In a control group, animals were subjected to HC alone. μHbO₂ was measured by reflectance spectrophotometry, systemic DO₂ was calculated from intermittent blood gas analysis, and cardiac output was measured by transpulmonary thermodilution. Data are presented as mean±s.e.m. for n=5 animals. During HC alone, DO₂ increased from 12±1 to 16±1 ml/kg per min and μHbO₂ from 70±4 to 80±2%. By contrast, additional vasopressin V(1A) receptor blockade abolished the increase in μHbO₂ (80±2 vs. 69±2%) without altering the increase in DO₂ (16±1 vs. 19±2 ml/kg per min). Vasopressin V1A receptor blockade (VB) during normocapnia neither affected DO₂ (13±1 vs. 14±1 ml/kg per min) nor μHbO₂ (75±3 vs. 71±5%). Vasopressin V(1A) receptor blockade abolished the increase in μHbO₂ during HC independent of DO₂. Thus, in contrast to its generally vasoconstrictive properties, the vasopressin V1A receptors seem to mediate the increase in gastric microcirculatory mucosal oxygenation induced by acute HC.