An observational assessment of the sublingual microcirculation of pregnant and non-pregnant women

Investigating the blood rheology in the first trimester pregnancies with high risk for preeclampsia

BACKGROUND

Pregnancy is a dynamic process associated with changes in vascular and rheological resistance. Maternal maladaptation to these changes is the leading cause of pregnancy complications such as preeclampsia.

OBJECTIVE

This study aimed to assess the hemorheological alterations in pregnancies with a high risk for preeclampsia in the first trimester.

METHODS

Ninety-two pregnant women were allocated into the high preeclampsia risk group (37 cases) and control groups (55 cases). Plasma and whole blood viscosity and red blood cell morphodynamic properties, including deformability and aggregation were assessed by Brookfield viscometer and laser-assisted optical rotational cell analyzer (LORRCA) at 11-14 gestational weeks.

RESULTS

Whole blood viscosity was significantly higher in the high-risk group at all shear rates. Plasma viscosity and hematologic factors showed no differences between the groups. Hematocrit levels positively correlated with high blood viscosity only in the high-risk group. There were no significant changes in the other deformability and aggregation parameters.

CONCLUSIONS

Changes in the whole blood viscosity of pregnant women with high preeclampsia risk refer to impaired microcirculation beginning from the early weeks of gestation. We suggest that the whole blood viscosity is consistent with the preeclampsia risk assessment in the first trimester, and its measurement might be promising for identifying high-preeclampsia-risk pregnancies.

The Nine Month Stress Test: Pregnancy and Exercise - Similarities and Interactions

Of all physiological systems, the cardiovascular system takes on the most profound adaptation in pregnancy to support fetal growth and development. The adaptations that arise are systemic and involve structural and functional changes that can be observed at the cerebral, central, peripheral, and microvascular beds. This includes, although is not limited to increased heart rate, stroke volume and cardiac output with negligible change to blood pressure, reductions in vascular resistance and cerebral blood flow velocity, systemic artery enlargement, enhanced endothelial function. All of this takes place to accommodate blood volume expansion and ensure adequate fetal and maternal oxygen delivery. In some instances, the demand placed on the vasculature can manifest as cardiovascular maladaptation and thus, cardiovascular complications can arise. Exercise is recommended in pregnancy because of its powerful ability to reduce the incidence and severity of cardiovascular complications in pregnancy. However, the mechanism by which it acts is poorly understood. The first aim of this review is to describe the systemic adaptations that take place in pregnancy. Secondly, this review aims to describe the influence of exercise on these systemic adaptations. It is anticipated that this review can comprehensively capture the extent of knowledge in this area while identifying areas that warrant further investigation.

Possible Impact of Spinal Anesthesia and Phenylephrine on Sublingual Microcirculation of Cesarean Delivery Patients

Background

This study was a proof of concept of a novel means to evaluate microcirculatory changes during spinal anesthesia for cesarean delivery. It sought to examine the distributive circulatory effects of spinal anesthesia and evaluate the impact of phenylephrine administration on the microcirculation of these women.

Methods

After Research Ethics Board approval, healthy, non-laboring pregnant women with singleton, term pregnancies scheduled for elective cesarean delivery were recruited. Participants were randomly assigned to receive either phenylephrine infusion or phenylephrine bolus. Spinal anesthesia was standardized. A sidestream dark-field (SDF) MicroScan^® video microscope was applied to the sublingual mucosa to obtain microcirculation videos in five different visual fields. Videos were made before and after spinal anesthesia. The resultant videos were analyzed randomly and blindly. The mean microvascular flow index (MFI) values were compared before and after spinal anesthesia. The difference in MFI following spinal anesthesia was compared between phenylephrine infusion and bolus groups.

Results

Thirty-two patients were recruited for the study; 22 patients had complete video sets for analysis. Baseline characteristics were similar between the two groups, including preoperative hemodynamics. There were no significant differences between pre- and post-spinal MFI. The post-spinal MFI within the infusion group (mean ± standard deviation: 2.74 ± 0.21) was not significantly different from the bolus group (2.56 ± 0.42, P = 0.22).

Conclusion

Despite theoretical physiological implications of spinal anesthesia and phenylephrine on the microcirculation, significant alteration of the MFI was not observed between pre- and post-spinal anesthesia (within group). Additionally, despite an eight-fold larger phenylephrine dose for continuous infusion prophylaxis used in this group of women, this did not result in a significant alteration of the microcirculation compared to those who received phenylephrine treatment for hypotension (between groups).

Monitoring microcirculation in critical illness

PURPOSE OF REVIEW

Critical illness includes a wide range of conditions from sepsis to high-risk surgery. All these diseases are characterized by reduced tissue oxygenation. Macrohemodynamic parameters may be corrected by fluids and/or vasoactive compounds; however, the microcirculation and its tissues may be damaged and remain hypoperfused. An evaluation of microcirculation may enable more physiologically based approaches for understanding the pathogenesis, diagnosis, and treatment of critically ill patients.

RECENT FINDINGS

Microcirculation plays a pivotal role in delivering oxygen to the cells and maintains tissue perfusion. Negative results of several studies, based on conventional hemodynamic resuscitation procedures to achieve organ perfusion and decrease morbidity and mortality following conditions of septic shock and other cardiovascular compromise, have highlighted the need to monitor microcirculation. The loss of hemodynamic coherence between the macrocirculation and microcirculation, wherein improvement of hemodynamic variables of the systemic circulation does not cause a parallel improvement of microcirculatory perfusion and oxygenation of the essential organ systems, may explain why these studies have failed.

SUMMARY

Critical illness is usually accompanied by abnormalities in microcirculation and tissue hypoxia. Direct monitoring of sublingual microcirculation using hand-held microscopy may provide a more physiological approach. Evaluating the coherence between macrocirculation and microcirculation in response to therapy seems to be essential in evaluating the efficacy of therapeutic interventions.

Sidestream Dark Field Imaging of the Microcirculation to Assess Preeclampsia Microvascular Dysfunction

Background

Development of predictive models of preeclampsia has only yielded modest results. We hypothesized that impaired indices of microcirculatory function could be detected using sidestream dark field imaging. The objective of this study was to examine microvascular function in women at high risk for preeclampsia at mid-gestation.

Methods

Women between 16 and 22 weeks of gestation were screened for eligibility. Patients were recruited if they met eligibility criteria indicating high risk for preeclampsia. Investigators performed non-invasive sidestream dark field imaging of the sublingual microcirculation. Images were analyzed to determine microcirculatory parameters (microvascular flow index, perfused vessel density, total vessel density, and proportion of perfused vessels). After delivery, charts were reviewed to determine if they developed gestational hypertension, preeclampsia or severe preeclampsia.

Results

Twelve of 66 participants (18.2%) developed preeclampsia or severe preeclampsia during the course of their pregnancy. Microvascular flow index was not significantly different between participants with normal pregnancies and participants with preeclampsia or severe preeclampsia (2.75 ± 0.38 vs. 2.80 ± 0.34, respectively; P = 0.459). Similarly, there were no significant differences between groups in the remaining microcirculatory parameters.

Conclusions

Sidestream dark field imaging of the sublingual microcirculation may remain an appropriate tool to identify women at risk for preeclampsia, albeit later in pregnancy.

Capillaroscopy in pregnancy

INTRODUCTION

In pregnancy, the circulatory system undergoes profound adaptation to meet the requirements in blood supply for the mother and the foetus. With the development of new techniques, research of the microcirculatory changes becomes available. This expert review gives an overview of the current evidence in the field of capillaroscopy. The aim of this review is to summarize the available techniques in the assessment of the microcirculation during pregnancy. Areas covered: A literature search was done, using the strategy: (microcirculation OR capillary OR capillaries OR capillaroscopy) AND pregnancy AND (density OR diameter OR count OR number). All articles were screened and all English articles were considered, when containing information regarding imaging of capillaries. Only structural parameters were considered, functional parameters (e.g. flow velocity) were not considered. Reference search was undertaken after reading full text articles. Articles from reference search underwent same selection criteria as in the primary search. Expert commentary: With growing insight in microcirculatory changes in hypertensive pregnancy conditions, the field of capillaroscopy will become more important in future. The technique is feasible and easy to use in clinical practice as well as in research setting. The first step, necessary to perform further research in this field in future, is to get consensus in technique to perform capillaroscopy and in methods to quantitatively and qualitatively describe the observed changes in microvasculature.

Effects of haemoglobin levels on the sublingual microcirculation in pregnant women

Anemia in pregnant women is associated with increased maternal and perinatal mortality and represents an important economic burden in many developing countries. Our goal was to evaluate the impact of anemia on the capillary network during pregnancy. Therefore, we compared microcirculatory parameters of anemic pregnant study participants to that of non-anemic pregnant women employing sublingual microcirculation video imaging technology and novel automated video analysis software.Non-anemic (n = 7) and anemic (n = 44) pregnant women were enrolled in the study at second and third trimesters. Video imaging was applied to the sublingual mucosal surface in five visual fields. The resultant videos were analyzed automatically, avoiding observer bias. Total vessel density (TVD), perfused vessel density (PVD) and proportion of perfused vessels (PPV) were calculated by the software. Both, mean TVD and PVD were significantly increased in the anemic pregnant group, while the PPV was not significantly different. Significant negative correlations were observed between haemoglobin (Hb) levels and both, TVD and PVD. Haemoglobin level seems to play an important determinant role in restructuring the capillary network. An effect that could compensate the impaired tissue oxygen delivery associated with anemia during pregnancy.

Maternal microcirculation and sidestream dark field imaging: a prospective assessment of the association between labour pain and analgesia on the microcirculation of pregnant women

BACKGROUND

Pregnancy places significant demands on the cardiovascular system leading to measurable changes in the macrocirculation and potentially the microcirculation. During labour, both uterine contractions and labour pain can further impact cardiovascular status. The objective of this observational study was to compare sublingual microcirculation in labouring parturients before and after epidural analgesia.

METHODS

Healthy pregnant, labouring women requesting epidural analgesia were approached to participate. Participants with cardiovascular disease, diabetes, obesity, smoking or caffeine intake were excluded. The sidestream dark field device was applied to the sublingual mucosa obtaining images of at least 20 seconds in 5 visual fields before and after epidural analgesia. Video clips were analyzed randomly and blindly. The primary outcome was mean microvascular flow index (MFI).

RESULTS

Twelve participants completed this study. The results demonstrate no statistically significant difference in the MFI during labour pain (2.9±0.1) compared to after epidural analgesia (3.0±0.04, p = 0.31). Furthermore, there were no statistically significant differences in any secondary outcomes.

CONCLUSION

Our findings indicate that epidural analgesia may not impact sublingual microcirculation in labouring women. This agrees with literature supporting epidural analgesia as a safe, appropriate method of pain relief during labour with limited impact on peripheral macro or microcirculation.

Reduced uterine perfusion pressure decreases functional capillary density in skeletal muscle

The purpose of this study was to examine the functional and structural capillary density in the reduced uterine perfusion pressure (RUPP) model, which when performed during pregnancy is an established animal model of preeclampsia. We hypothesized that the RUPP model would be associated with capillary rarefaction and impaired capillary perfusion, which would be more pronounced in the pregnant state. Female Sprague-Dawley rats (n = 32) were randomized to nonpregnancy (Nonpregnant) or breeding (Pregnant) at 12 wk of age and again to RUPP or SHAM surgeries on gestational day (GD) 14 (or equivalent age in nonpregnant rats). On GD 20 (or equivalent), capillary structure and perfusion of the extensor digitorum longus were imaged using digital intravital video microscopy. Functional videos were analyzed by a blinded observer to measure capillary density, expressed as capillaries per millimeter intersecting three staggered reference lines (200 μm). Flow was scored as the percentage of capillaries having 1) continuous, 2) intermittent, or 3) stopped flow. Total capillary density was not different between groups. There was a main effect of RUPP surgery resulting in decreased continuous flow vessels (P < 0.01) and increased stopped flow (P < 0.01), which was driven by differences between pregnant animals (Continuous flow: pregnant SHAM 80.1 ± 7.8% vs. pregnant RUPP 67.8 ± 11.2%, P < 0.05) (Stopped flow: pregnant SHAM 8.7 ± 3.2% vs. pregnant RUPP 17.9 ± 5.7%, P < 0.01). Our results demonstrate that the RUPP surgery is associated with a decrease in functional capillary density in skeletal muscle that is more pronounced in the pregnant state, which may contribute to the vascular pathophysiology observed in preeclampsia.

Microcirculation in Pregnancy

The microcirculation, like all physiological systems undergoes modifications during the course of pregnancy. These changes aid the adaption to the new anatomical and physiological environment of pregnancy and ensure adequate oxygen supply to the fetus. Even though the microcirculation is believed to be involved in major pregnancy related pathologies, it remains poorly understood. The availability of safe and non-interventional technologies enabling scientists to study the intact microcirculation of the pregnant patient will hopefully expand our understanding. In this article we review the physiological changes occurring in the microcirculation during pregnancy and the role of the microcirculation in gestational related pathologies. We will also describe the available techniques for the measurement and evaluation of the microcirculation. Lastly we will highlight the possible fields in which these techniques could be utilized to help provide a clearer view of the microcirculation in the pregnant woman.