Usefulness of Hyperemic Microvascular Resistance Index as a Predictor of Clinical Outcomes in Patients with ST-Segment Elevation Myocardial Infarction

BACKGROUND AND OBJECTIVES

Microvascular function is a useful predictor of left ventricular functional changes in patients with ST-segment elevation myocardial infarction (STEMI). We evaluated the usefulness of the hyperemic microvascular resistance index (hMVRI) for predicting long-term major adverse cardiovascular events (MACEs) in patients with STEMI assessed immediately after primary percutaneous coronary intervention (PCI).

SUBJECTS AND METHODS

hMVRI were evaluated in 145 patients with first acute STEMI treated with primary PCI using an intracoronary Doppler wire. hMVRI was defined as the ratio of mean aortic pressure over hyperemic averaged peak velocity of infarct-related artery. Major adverse cardiovascular events (MACEs) included cardiac death and re-hospitalization for congestive heart failure.

RESULTS

During the mean follow-up of 85±43 months, MACEs occurred in 17.2% of patients. Using a receiver-operating characteristics analysis, hMVRI >2.82 mm Hg·cm-1·sec (sensitivity: 87%; specificity: 69%; and area under curve: 0.818) was the best cut-off values for predicting future cardiac events. The Cox proportional hazard analysis showed that hMVRI was an independent predictor for long-term MACEs (hazard ratio 1.741, 95% confidence interval 1.348-2.264, p<0.001). The Kaplan-Meier survival analysis showed a higher incidence of MACEs in patients with hMVRI >2.82 mm Hg·cm-1·sec (p<0.001).

CONCLUSION

hMVRI was a strong predictor of long-term MACEs in patients with STEMI treated with primary PCI.

Reduced red blood cell deformability over time is associated with a poor outcome in septic patients

BACKGROUND

To investigate changes in red blood cell (RBC) rheology over time in critically ill patients with sepsis and their relationship with outcome.

METHODS

In this prospective, non-interventional study, RBC rheology was assessed using the Laser-assisted Optical Rotational Cell Analyzer in a convenience sample of intensive care unit (ICU) patients with (n=64) and without (n=160) sepsis. Results were compared to measures in healthy volunteers (n=20). RBC rheology was also assessed on days 1 and 3 of the ICU stay in 32 of the non-septic and 19 of the septic patients. RBC deformability was determined by the elongation index (EI) in relation to the shear stress (0.3 to 50Pa) applied to the RBC membrane. An aggregation index (AI) was assessed simultaneously with the same device.

RESULTS

The ICU mortality rate of the septic patients was 31%. RBC deformability was already reduced in septic patients at ICU admission, an effect that persisted during the study period and worsened in the non-survivors for the large majority of shear stresses studied (e.g., EI for 50Pa of shear stress was 0.527±0.064 in non-survivors vs. 0.566±0.034 in survivors, p<0.05). These changes were not observed in non-septic patients. The AI was more elevated in septic than in non-septic patients at ICU admission, but had no prognostic value.

CONCLUSIONS

Alterations in RBC rheology, including reduced deformability and increased aggregation, occur early in septic patients and reductions in RBC deformability over time are associated with a poor outcome.

Retinal microvascular network attenuation in Alzheimer's disease

INTRODUCTION

Cerebral small-vessel disease has been implicated in the development of Alzheimer's disease (AD). The retinal microvasculature enables the noninvasive visualization and evaluation of the systemic microcirculation. We evaluated retinal microvascular parameters in a case-control study of AD patients and cognitively normal controls.

METHODS

Retinal images were computationally analyzed and quantitative retinal parameters (caliber, fractal dimension, tortuosity, and bifurcation) measured. Regression models were used to compute odds ratios (OR) and confidence intervals (CI) for AD with adjustment for confounders.

RESULTS

Retinal images were available in 213 AD participants and 294 cognitively normal controls. Persons with lower venular fractal dimension (OR per standard deviation [SD] increase, 0.77 [CI: 0.62-0.97]) and lower arteriolar tortuosity (OR per SD increase, 0.78 [CI: 0.63-0.97]) were more likely to have AD after appropriate adjustment.

DISCUSSION

Patients with AD have a sparser retinal microvascular network and retinal microvascular variation may represent similar pathophysiological events within the cerebral microvasculature of patients with AD.

An effective model of blood flow in capillary beds

In this article we derive applicable expressions for the macroscopic compliance and resistance of microvascular networks. This work yields a lumped-parameter model to describe the hemodynamics of capillary beds. Our derivation takes into account the multiscale nature of capillary networks, the influence of blood volume and pressure on the effective resistance and compliance, as well as, the nonlinear interdependence between these two properties. As a result, we obtain a simple and useful model to study hypotensive and hypertensive phenomena. We include two implementations of our theory: (i) pulmonary hypertension where the flow resistance is predicted as a function of pulmonary vascular tone. We derive from first-principles the inverse proportional relation between resistance and compliance of the pulmonary tree, which explains why the RC factor remains nearly constant across a population with increasing severity of pulmonary hypertension. (ii) The critical closing pressure in pulmonary hypotension where the flow rate dramatically decreases due to the partial collapse of the capillary bed. In both cases, the results from our proposed model compare accurately with experimental data.

Takotsubo cardiomyopathy in two patients with microvascular angina

We present two cases in which takotsubo cardiomyopathy (TC) developed immediately after a diagnosis of microvascular angina had been established. One patient who had been diagnosed as having endothelium-dependent microvascular angina (microvascular spasm) developed TC three weeks after the initial admission. The other patient was diagnosed as having endothelium-independent microvascular angina (decreased coronary flow reserve) and subsequently developed TC after the discontinuation of nicorandil treatment. These cases may provide insight into the possible mechanisms underlying the pathophysiological findings of TC. <Learning objective: Impaired coronary microcirculation has been recently reported in many cases during the acute phase of takotsubo cardiomyopathy. However, the exact mechanism responsible for the coronary microvascular dysfunction associated with this entity remains unclear. This report highlights the importance of microvascular angina, which may play a role in the development of this cardiomyopathy.>.

Insights and limits of translational research in critical care medicine

Experimental research has always been the cornerstone of pathophysiological and therapeutic advances in critical care medicine, where clinical observations and basic research mutually fed each other in a so-called translational approach. The objective of this review is to address the different aspects of translational research in the field of critical care medicine. We herein highlighted some demonstrative examples including the animal-to-human approach to study host-pathogen interactions, the human-to-animal approach for sepsis-induced immunosuppression, the still restrictive human approach to study critical illness-related neuromyopathy, and the technological developments to assess the microcirculatory changes in critically ill patients. These examples not only emphasize how translational research resulted in major improvements in the comprehension of the pathophysiology of severe clinical conditions and offered promising perspectives in critical care medicine but also point out the obstacles to translate such achievements into clinical practice.

Adhesion of platelets through thromboxane A₂ receptor signaling facilitates liver repair during acute chemical-induced hepatotoxicity

AIMS

Platelets have been suggested to play an important role in liver regeneration and repair after hepatic resection and acute liver injury. However, the underlying mechanisms of liver repair remain elusive. Signaling through thromboxane prostanoid (TP) receptor participates in inflammation and tissue injury through platelet aggregation. On the other hand, TP receptor signaling also is involved in tissue repair and tumor growth through angiogenesis. The present study was examined whether or not TP receptor signaling contributes to liver repair and sinusoidal restoration from acute liver injury through platelet adhesion to the hepatic sinusoids.

MAIN METHODS

Carbon tetrachrolide (CCl4) was used to induce acute liver injury in TP receptor knockout mice (TP(-/-) mice) and their wild-type littermates (WT mice).

KEY FINDINGS

Compared with WT mice, TP(-/-) mice exhibited delayed in liver repair and sinusoidal restoration after CCl4 treatment, which were associated with attenuated hepatic expression of pro-angiogenic factors. Intravital microscopic observation revealed that adhering platelets to the sinusoids was increased in WT livers during the repair phase as compared with TP(-/-) livers, and platelet adhesion was dependent on TP receptor signaling. The levels of hepatocyte growth factor (HGF) in platelets from WT mice treated with CCl4 for 48h were greater than those form TP(-/-) mice, and HGF enhanced the expression of angiogenic factors in cultured human umbilical vein endothelial cells (HUVECs).

SIGNIFICANCE

These results suggested that TP receptor signaling facilitates liver repair and sinusoidal restoration from acute liver injury through HGF release from platelets adhering to the sinusoids.

Sleep apnea and retinal signs in cardiovascular disease: the Multi-Ethnic Study of Atherosclerosis

PURPOSE

The aim of the study was to examine the relationship between sleep apnea, retinal vascular caliber and retinopathy, and their impact on cardiovascular disease (CVD) risk.

METHODS

A multi-ethnic cohort of 5,803 participants was examined based on standardized grading of retinal vascular caliber and retinopathy from digital fundus photographs, self-reported physician-diagnosed sleep apnea (PDSA), and incident cardiovascular events.

RESULTS

In women, PDSA was associated with narrower arterioles (regression coefficient [β] -5.76; 95 % confidence Interval [CI] -8.51, -3.02) after adjusting for cardio-metabolic risk factors. The incident rate ratio (IRR) of CVD was also associated with narrower arterioles (IRR for highest versus lowest tertile 1.91; 95 % CI 1.08, 3.38). In men, PDSA was not associated with arteriolar caliber. However, incident CVD was associated with narrower arterioles (IRR 1.67; 95 % CI 1.10, 2.52), wider venules (IRR 1.71; 95 % CI 1.13, 2.59) and PDSA (IRR 2.03, 95 % CI 1.17, 3.51). The IRR of CVD in men with PDSA increased minimally to 2.06 (95 % CI 1.18, 3.56) after adjustment for retinal arteriolar and venular caliber. Combining women and men, the IRR of CVD was 3.41 (95 % CI 1.79, 6.50) in those with both PDSA and narrower retinal arterioles.

CONCLUSIONS

Sleep apnea was associated with narrower retinal arterioles in women but not in men. However, sleep apnea was also associated with incident CVD in men. These suggest potential gender differences in susceptibility to microvascular disease in association with sleep apnea.

[Periungueal capillaroscopy: an easy and reliable method to evaluate all microcirculation diseases]

Periungueal capillaroscopy is a simple and reliable non-invasive technique allowing evaluation of cutaneous microcirculation. It was promoted for decades in patients with Raynaud's phenomenon in order to differentiate between the benign primary Raynaud's phenomenon and the secondary form in connective tissue diseases, especially systemic sclerosis. Nevertheless, the value of this procedure has also been shown in numerous pathologies such as diabetes or cardiovascular diseases. This literature review points to the versatility of this useful exam and its results in a large spectrum of diseases with microvascular involvement.

Regarding the quantification of peripheral microcirculation--Comparing responses evoked in the in vivo human lower limb by postural changes, suprasystolic occlusion and oxygen breathing

The human skin is an interesting model to explore microcirculation, particularly if using noninvasive technologies such as LDF (Laser Doppler Flowmetry) and tc (transcutaneous) gasimetry and methods as near as possible from the normal physiological state. In this study, we combined those technologies with three classical approaches--leg raising from supine, suprasystolic occlusion (in the ankle), and normobaric oxygen breathing to explore distal peripheral circulation in the foot. These methods are often cited, but a comparative assessment has not been done. The goal of this study was to identify relevant flow related descriptors, method-related advantages and pitfalls, and eventually, to find the best experimental approach. Volunteers (both genders, 22.1 ± 3.7 years old) were subjected to these methods and variables registered during basal, challenge and stabilization phases. Descriptive and comparative statistics were obtained, adopting a 95% confidence level. All flow-related quantitative descriptors potentially useful for the analysis were identified and compared. As expected, male patients consistently showed higher LDF levels and transepidermal water loss (TEWL) and lower tcpO2 values. However, lower results were recorded in the supine position, suggesting a postural dependence. Both leg raising and suprasystolic occlusion produced a hyperemic response after provocation, although different in magnitude, significantly reducing LDF and tcpO2 during provocation. The oxygen breathing method provided the most patient-friendly protocol, consistently reducing LDF (potentially by the inhibition of production of local vasodilators). TEWL increased during the provocation phase in all protocols, although not significantly. Baseline tcpO2 was found to correlate positively with the peak tcpO2 during oxygen breathing and basal LDF with peak flow during leg raising and suprasystolic occlusion. No statistical correlation between TEWL and LDF could be demonstrated under the current experimental conditions. We conclude that although equally useful considering the purpose, these methods involve very different practicalities and do not provide the same information. Also noteworthy, LDF is a highly sensitive indicator that could be further explored to look deeper into blood flow regulating mechanisms.

Design and conduct of Xtreme Everest 2: An observational cohort study of Sherpa and lowlander responses to graduated hypobaric hypoxia

Objective: Oxygen availability falls with ascent to altitude and also as a consequence of critical illness. Because cellular sequelae and adaptive processes may be shared in both circumstances, high altitude exposure (‘physiological hypoxia’) assists in the exploration of the response to pathological hypoxia. We therefore studied the response of healthy participants to progressive hypobaric hypoxia at altitude. The primary objective of the study was to identify differences between high altitude inhabitants (Sherpas) and lowland comparators.

Methods: We performed an observational cohort study of human responses to progressive hypobaric hypoxia (during ascent) and subsequent normoxia (following descent) comparing Sherpas with lowlanders. Studies were conducted in London (35m), Kathmandu (1300m), Namche Bazaar (3500m) and Everest Base Camp (5300m). Of 180 healthy volunteers departing from Kathmandu, 64 were Sherpas and 116 were lowlanders. Physiological, biochemical, genetic and epigenetic data were collected. Core studies focused on nitric oxide metabolism, microcirculatory blood flow and exercise performance. Additional studies performed in nested subgroups examined mitochondrial and metabolic function, and ventilatory and cardiac variables. Of the 180 healthy participants who left Kathmandu, 178 (99%) completed the planned trek. Overall, more than 90% of planned testing was completed. Forty-four study protocols were successfully completed at altitudes up to and including 5300m. A subgroup of identical twins (all lowlanders) was also studied in detail.

Conclusion: This programme of study (Xtreme Everest 2) will provide a rich dataset relating to human adaptation to hypoxia, and the responses seen on re-exposure to normoxia. It is the largest comprehensive high altitude study of Sherpas yet performed. Translational data generated from this study will be of relevance to diseases in which oxygenation is a major factor.

Retinal arteriolar narrowing and incidence of knee replacement for osteoarthritis: a prospective cohort study

OBJECTIVES

The role of the microcirculation in the pathogenesis of osteoarthritis (OA) remains unclear. This prospective cohort study examined the association between retinal vascular calibre and incidence of knee replacement for OA.

DESIGN

1838 participants of the Australian Diabetes, Obesity and Lifestyle (AusDiab) Study had retinal vascular calibre measured using a nonmydriatic digital fundus camera in 1999-2000 and were aged ≥ 40 years at joint replacement data collection commencement. The incidence of knee replacement for OA during 2002-2011 was determined by linking cohort records to the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR).

RESULTS

77 participants underwent knee replacement for OA. They had narrower retinal arteriolar calibre compared with those without knee replacement (166.1 ± 24.8 μm vs 174.3 ± 24.5 μm, P = 0.004). For every one standard deviation reduction in retinal arteriolar calibre, the incidence of knee replacement increased by 25% (HR 1.25, 95% confidence interval (CI) 1.00-1.56). Participants in the narrower two-thirds of arteriolar calibre had twice the risk of knee replacement compared with those in the widest one-third (HR 2.00, 95% CI 1.07-3.74, P = 0.03) after adjustment for sex, body mass index (BMI), physical activity and HbA1c. There was no association for retinal venular calibre.

CONCLUSIONS

Retinal arteriolar narrowing is associated with increased risk of knee replacement for OA suggesting that further work is warranted to determine the role of the microcirculation in the pathogenesis of knee OA.

The effect of plasma-derived activated protein C on leukocyte cell-death and vascular endothelial damage

INTRODUCTION

The role of leukocyte and its death in the progression in inflammation attracts attention nowadays. The purpose of this study is to examine the effects of activated protein C (APC) on leucocyte cell death and vascular endothelial damage in sepsis.

METHODS

Wistar rats were infused with lipopolysaccharide (8.0mg/kg) concomitantly with either a low dose (0.5mg/kg), a high dose (5.0mg/kg) of plasma-derived APC or albumin. One and 3hours after the injections, the mesenteric microcirculation was observed by intravital microscopy. The serum levels of nucleosome and High Mobility Group Box 1 (HMGB1) were measured in each group. In another series, cultured leukocyte cell-death in the medium supplemented with serum obtained from each group was examined in vitro.

RESULTS

Microcirculatory disturbance was significantly suppressed in both the high-dose and low-dose groups compared to the control group (P<0.01, 0.05, respectively). The bleeding area was significantly increased in the control and high-dose groups (P<0.05, 0.01, respectively). Serum levels of cell death markers such as nucleosome and HMGB1 were significantly decreased in the treatment groups (P<0.01), and the protective effect was more pronounced in high-dose group. Cell death suppression was most prominent in high-dose group and the formation of neutrophil extracellular traps (NETs) was significantly suppressed in the treatment groups.

CONCLUSION

Low-dose plasma-derived APC exerted protective effects on the microcirculation without increasing the risk of bleeding. The protective effect against leukocyte cell death and the suppressive effect on NETs formation of APC might be related to its beneficial effects.

Tissue microcirculation measured by vascular occlusion test during anesthesia induction

Tissue microcirculation measured by vascular occlusion test is impaired during septic shock. However, it has not been investigated extensively during anesthesia induction. The aim of the study is to evaluate tissue microcirculation during anesthesia induction. We hypothesized that during anesthesia induction, tissue microcirculation measured by vascular occlusion test might be enhanced with peripheral vasodilation during anesthesia induction. We conducted a prospective observational study of 50 adult patients undergoing cardiac surgery. During anesthesia induction, we measured and analyzed tissue oxygen saturation, vascular occlusion test, cerebral oximetry, forearm-minus-fingertip skin temperature gradients and hemodynamic data in order to evaluate microcirculation as related to alterations in peripheral vasodilation as reflected by increased Tforearm-finger thermal gradients. During anesthesia induction, recovery slope during vascular occlusion test and cerebral oxygen saturation increased from 4.0 (1.5) to 4.7 (1.3) % s(-1) (p = 0.02) and 64.0 (10.2) to 74.2 (9.2) % (p < 0.001), respectively. Forearm-minus-fingertip skin temperature gradients decreased from 1.9 (2.9) to -1.4 (2.2) °C (p < 0.001). There was an inverse correlation between changes in the skin temperature gradients and changes in cerebral oximetry (r = 0.33; p = 0.02). During anesthesia induction, blood pressure and forearm-minus-fingertip skin temperature gradients decrease while cerebral oximetry and vascular occlusion test recovery slope increase. These findings suggest that anesthesia induction increases tissue microcirculation with peripheral vasodilation.

Microvascular blood flow resistance: Role of red blood cell migration and dispersion

Microvascular blood flow resistance has a strong impact on cardiovascular function and tissue perfusion. The flow resistance in microcirculation is governed by flow behavior of blood through a complex network of vessels, where the distribution of red blood cells across vessel cross-sections may be significantly distorted at vessel bifurcations and junctions. In this paper, the development of blood flow and its resistance starting from a dispersed configuration of red blood cells is investigated in simulations for different hematocrit levels, flow rates, vessel diameters, and aggregation interactions between red blood cells. Initially dispersed red blood cells migrate toward the vessel center leading to the formation of a cell-free layer near the wall and to a decrease of the flow resistance. The development of cell-free layer appears to be nearly universal when scaled with a characteristic shear rate of the flow. The universality allows an estimation of the length of a vessel required for full flow development, lc ≲ 25D, for vessel diameters in the range 10 μm < D < 100 μm. Thus, the potential effect of red blood cell dispersion at vessel bifurcations and junctions on the flow resistance may be significant in vessels which are shorter or comparable to the length lc. Aggregation interactions between red blood cells generally lead to a reduction of blood flow resistance. The simulations are performed using the same viscosity for both external and internal fluids and the RBC membrane viscosity is not considered; however, we discuss how the viscosity contrast may affect the results. Finally, we develop a simple theoretical model which is able to describe the converged cell-free-layer thickness at steady-state flow with respect to flow rate. The model is based on the balance between a lift force on red blood cells due to cell-wall hydrodynamic interactions and shear-induced effective pressure due to cell-cell interactions in flow. We expect that these results can also be used to better understand the flow behavior of other suspensions of deformable particles such as vesicles, capsules, and cells.

Effect of continuous vs pulsed iontophoresis of treprostinil on skin blood flow

INTRODUCTION

Systemic sclerosis (SSc) is a rare disease affecting digital microcirculation, leading to finger ulcers and in some cases to amputation. Prostacyclin analogues can be used intravenously but their therapeutic effect is counterbalanced by potentially serious vasodilatation-induced side effects. Iontophoresis of treprostinil could be a promising local therapeutic alternative for SSc-related digital ulcers. Iontophoretic drug delivery is complex, and whether continuous or periodic current should be used remains debated. The objective of the present work is to compare the effect of continuous vs pulsed iontophoresis of treprostinil in rats.

MATERIALS AND METHODS

Treprostinil (0.64 mM and 0.064 mM) and NaCl were delivered by cathodal iontophoresis onto the hindquarters of anaesthetized rats. Three protocols delivering the same quantity of current were compared: one was continuous (100 μA during 20 min) and two were periodic (B: twenty 1-min cycles with 200 μA during 30 s followed by 30 s Off; and C: twenty 1-min cycles with 600 μA during 10s followed by 50s Off) (n=8 for each protocol with each concentration). Skin blood flow was quantified using laser Doppler imaging and skin resistance was calculated with Ohm's law.

RESULTS

All protocols induced a significant increase in skin blood flow. At the lower concentration (0.064 mM treprostinil) the pulsed 10/50 sequence significantly enhanced cutaneous blood flow (Table 1; Fig. 1B) compared to continuous iontophoresis or the 30/30 sequence. We noted that the pulsed iontophoresis of NaCl (10/50 sequence) induced a significant early increase in cutaneous blood flow in comparison with continuous iontophoresis. Skin resistance measures were negatively correlated with current intensity delivered.

CONCLUSION

In conclusion, pulsed iontophoresis of treprostinil with a 10 s/50 s (On/Off) protocol at 600 μA increases the efficacy of iontophoresis at 0.064 mM but not at a tenfold higher concentration. Pulsed iontophoresis could be used to optimize treprostinil iontophoresis, to provide similar efficacy with decreased costs, and should now be tested on humans.

Thoracic epidural anesthesia: Effects on splanchnic circulation and implications in Anesthesia and Intensive care

AIM: To evaluate the currently available evidence on thoracic epidural anesthesia effects on splanchnic macro and microcirculation, in physiologic and pathologic conditions.

METHODS: A PubMed search was conducted using the MeSH database. Anesthesia, Epidural was always the first MeSH heading and was combined by boolean operator AND with the following headings: Circulation, Splanchnic; Intestines; Pancreas and Pancreatitis; Liver Function Tests. EMBASE, Cochrane library, ClinicalTrials.gov and clinicaltrialsregister.eu were also searched using the same terms.

RESULTS: Twenty-seven relevant studies and four ongoing trials were found. The data regarding the effects of epidural anesthesia on splanchnic perfusion are conflicting. The studies focusing on regional macro-hemodynamics in healthy animals and humans undergoing elective surgery, demonstrated no influence or worsening of regional perfusion in patients receiving thoracic epidural anesthesia (TEA). On the other hand most of the studies focusing on micro-hemodynamics, especially in pathologic low flow conditions, suggested that TEA could foster microcirculation.

CONCLUSION: The available studies in this field are heterogeneous and the results conflicting, thus it is difficult to draw decisive conclusions. However there is increasing evidence deriving from animal studies, that thoracic epidural blockade could have an important role in modifying tissue microperfusion and protecting microcirculatory weak units from ischemic damage, regardless of the effects on macro-hemodynamics.

Effect of caffeine contained in a cup of coffee on microvascular function in healthy subjects

Recent epidemiological studies have demonstrated that coffee drinking is associated with reduced mortality of cardiovascular disease. However, its precise mechanisms remain to be clarified. In this study, we examined whether single ingestion of caffeine contained in a cup of coffee improves microvascular function in healthy subjects. A double-blind, placebo-controlled, crossover study was performed in 27 healthy volunteers. A cup of either caffeinated or decaffeinated coffee was drunk by the subjects, and reactive hyperemia of finger blood flow was assessed by laser Doppler flowmetry. In an interval of more than 2 days, the same experimental protocol was repeated with another coffee in a crossover manner. Caffeinated coffee intake slightly but significantly elevated blood pressure and decreased finger blood flow as compared with decaffeinated coffee intake. There was no significant difference in heart rate between caffeinated and decaffeinated coffee intake. Importantly, caffeinated coffee intake significantly enhanced post-occlusive reactive hyperemia of finger blood flow, an index of microvascular endothelial function, compared with decaffeinated coffee intake. These results provide the first evidence that caffeine contained in a cup of coffee enhances microvascular function in healthy individuals.

Tissue perfusion and oxygenation to monitor fluid responsiveness in critically ill, septic patients after initial resuscitation: a prospective observational study

Fluid therapy after initial resuscitation in critically ill, septic patients may lead to harmful overloading and should therefore be guided by indicators of an increase in stroke volume (SV), i.e. fluid responsiveness. Our objective was to investigate whether tissue perfusion and oxygenation are able to monitor fluid responsiveness, even after initial resuscitation. Thirty-five critically ill, septic patients underwent infusion of 250 mL of colloids, after initial fluid resuscitation. Prior to and after fluid infusion, SV, cardiac output sublingual microcirculatory perfusion (SDF: sidestream dark field imaging) and skin perfusion and oxygenation (laser Doppler flowmetry and reflectance spectroscopy) were measured. Fluid responsiveness was defined by a ≥5 or 10 % increase in SV upon fluids. In responders to fluids, SDF-derived microcirculatory and skin perfusion and oxygenation increased, but only the increase in cardiac output, mean arterial and pulse pressure, microvascular flow index and relative Hb concentration and oxygen saturation were able to monitor a SV increase. Our proof of principle study demonstrates that non-invasively assessed tissue perfusion and oxygenation is not inferior to invasive hemodynamic measurements in monitoring fluid responsiveness. However skin reflectance spectroscopy may be more helpful than sublingual SDF.

Constriction and dysfunction of pial arterioles after regional hemorrhage in the subarachnoid space

Increasing evidence indicates that poor outcomes after brain hemorrhage, especially after subarachnoid hemorrhage (SAH), can be attributed largely to dysfunction of the cerebral microcirculation. However, the cause of this dysfunction remains unclear. Here, we investigated changes in the cerebral microcirculation after regional hemorrhage in the subarachnoid space using the closed cranial window technique in mice. A single pial arteriole on the surface of the brain was punctured to induce a regional hemorrhage in the subarachnoid space. Physiological parameters were monitored during the procedure, and microvessel diameter was measured after hemorrhage. The vasoreactivity of the arterioles in response to hypercapnia as well as to topical application of the vasodilator acetylcholine (ACh) and S-nitroso-N-acetyl-penicillamine (SNAP) were assessed. The constriction of pial arterioles was detected without changes in other physiological parameters. Decreased reactivity of pial arterioles to all of the applied vasodilatory stimuli was observed after hemorrhage. Our results indicate that regional hemorrhage in the subarachnoid space can induce the vasospasm of microvessels and also reduce the vasoreactivity of pial arterioles.

Decreased numbers of endothelial progenitor cells in patients in the early stages of systemic sclerosis

INTRODUCTION

Microangiopathy and endothelial dysfunction are present in the early stages of systemic sclerosis (SSc). Defective vasculogenesis mediated by bone marrow-derived endothelial progenitor cells (EPCs) might be involved in the vascular abnormalities found in SSc.

OBJECTIVES

To evaluate the circulating EPC levels and EPC subtypes via flow cytometry and early outgrowth colony-forming units (CFUs) in patients with SSc compared to healthy subjects.

METHODS

Thirty-nine female SSc patients (30 in the early stages of SSc) and 44 age-matched healthy women were included. Peripheral blood EPCs were quantified using flow cytometry and by counting the early outgrowth CFUs.

RESULTS

The EPCs quantified with flow cytometry and the CFU numbers were significantly lower in SSc patients than in control subjects (155.1 ± 95.1 vs. 241.3 ± 184.2 EPC/10(6) lymphomononuclear cells, p=0.011; 15.4 ± 8.6 vs. 23.5 ± 10.9 CFU, p<0.001; respectively), as well as in the group of patients in the early stages of SSc compared to the controls. Patients with digital ulcers had significantly higher CFU counts than those without ulcers (p=0.013). Among patients with the scleroderma pattern on nailfold capillaroscopy, patients with the late pattern had significantly lower EPC levels than those with the early and active patterns (p=0.046). There were no significant correlations of EPCs or CFU levels with RP duration.

CONCLUSIONS

The present study revealed decreased EPCs in SSc patients, including those with early disease onset. These findings suggest that defective vasculogenesis occurs in the early phases of the disease. Therefore, EPCs might be an important therapeutic target for the prevention of vascular complications in SSc patients.

Microvascular blood flow monitoring with laser speckle contrast imaging using the generalized differences algorithm

Laser speckle contrast imaging (LSCI) is a full-field optical technique to monitor microvascular blood flow with high spatial and temporal resolutions. It is used in many medical fields such as dermatology, vascular medicine, or neurosciences. However, LSCI leads to a large amount of data: image sampling frequency is often of several Hz and recordings usually last several minutes. Therefore, clinicians often perform regions of interest in which a spatial averaging of blood flow is performed and the result is followed with time. Unfortunately, this leads to a poor spatial resolution for the analyzed data. At the same time, a higher spatial resolution for the perfusion maps is wanted. To get over this dilemma we propose a new post-acquisition visual representation for LSCI perfusion data using the so-called generalized differences (GD) algorithm. From a stack of perfusion images, the procedure leads to a new single image with the same spatial resolution as the original images and this new image reflects perfusion changes. The algorithm is herein applied on simulated stacks of images and on experimental LSCI perfusion data acquired in three different situations with a commercialized laser speckle contrast imager. The results show that the GD algorithm provides a new way of visualizing LSCI perfusion data.

Microvascular reactivity in women with gestational diabetes mellitus studied during pregnancy

AIM

To compare microvascular reactivity assessed in the skin using laser Doppler fluximetry (LDF) in women with gestational diabetes mellitus (GDM) and gestational age-matched control during pregnancy.

METHODS

110 pregnant women at ~33 weeks gestation participated in the study. Skin microvascular reactivity was evaluated by LDF, at rest, during the response to brief arterial occlusion (post occlusive hyperaemic response) and during sympathetically mediated vasoconstrictor response to deep inspiratory breath hold.

RESULTS

No statistically significant differences were found in the microvascular variables studied (resting and maximum rate flux, post-ischaemic reactive hyperaemia and deep inspiratory breath holds) between +GDM and -GDM groups women. In women with GDM there was a negative correlation between resting flux and the response to the oral glucose tolerance test (OGTT), r = -0.282 (p = 0.037). There was also a negative correlation between the response to the OGTT and the sympathetically mediated constrictor response to inspiratory breath holds (r = -.298, p = .030) but not in women with GDM (r = .102, r = .468).

CONCLUSION

Attenuated microvascular reactivity as an early marker of endothelial dysfunction is not present in women with GDM when assessed during pregnancy.

Dissociation between sublingual and gut microcirculation in the response to a fluid challenge in postoperative patients with abdominal sepsis

Background

This study was performed to compare intestinal and sublingual microcirculation and their response to a fluid challenge.

Methods

Twenty-two septic patients in the first postoperative day of an intestinal surgery, in which an ostomy had been constructed, were evaluated both before and 20 min after a challenge of 10 mL/kg of 6% hydroxyethylstarch 130/0.4. We measured systemic hemodynamics and sublingual and intestinal microcirculation. Correlations between variables were determined through the Pearson test.

Results

Fluid administration increased the cardiac index (2.6 ± 0.5 vs. 3.3 ± 1.0 L/min/m², P < 0.01) and mean arterial blood pressure (68 ± 11 vs. 82 ± 12 mm Hg, P < 0.0001). The sublingual but not the intestinal red blood cell (RBC) velocity increased (912 ± 270 vs. 1,064 ± 200 μm/s, P < 0.002 and 679 ± 379 vs. 747 ± 419 μm/s, P = 0.12, respectively). The sublingual and intestinal perfused vascular density (PVD) did not change significantly (15.2 ± 2.9 vs. 16.1 ± 1.2 mm/mm² and 12.3 ± 6.7 vs. 13.0 ± 6.7 mm/mm²). We found no correlation between the basal sublingual and intestinal RBC velocities or between their changes in response to the fluid challenge. The individual changes in sublingual RBC velocity correlated with those in cardiac index and basal RBC velocity. Individual changes in intestinal RBC velocity did not correlate with either the cardiac index modifications or the basal RBC velocity. The same pattern was observed with the sublingual and the intestinal PVDs. The sublingual RBC velocities and PVDs were similar between survivors and nonsurvivors. But the intestinal RBC velocities and PVDs were lower in nonsurvivors.

Conclusions

In this series of postoperative septic patients, we found a dissociation between sublingual and intestinal microcirculation. The improvement in the sublingual microcirculation after fluid challenge was dependent on the basal state and the increase in cardiac output. In contrast, the intestinal microcirculation behaved as an isolated territory.