Intravital sidestream dark-field (SDF) imaging is used in a rabbit model for continuous noninvasive monitoring and quantification of mucosal capillary regeneration during wound healing in the oral cavity: A pilot study

Time of dissociation between microcirculation, macrocirculation, and lactate levels in a rabbit model of early endotoxemic shock

Background

The relationship between macrocirculation and microcirculation remains controversial. The loss of coherence between microcirculation and macrocirculation has already been found in late-stage sepsis shock. The objective of this study was to determine the earliest possible time of detecting the loss of coherence between microcirculation and macrocirculation in early-stage endotoxemic shock.

Methods

We randomized 24 female New Zealand white rabbits into two groups: endotoxemic shock group (n = 14) and control group (n = 10). Rabbits in the endotoxemic shock group were equipped with arterial and venous catheters and received an intravenous infusion of Escherichia coli lipopolysaccharide (LPS, 2 mg/kg over 10 min). Rabbits in the control group received the same dose of saline infusion. Microcirculatory perfusion parameters were assessed in the sublingual mucosa using sidestream dark-field video microscopy. Systemic hemodynamics and blood lactate levels were measured at baseline and over a 120-min period.

Results

Ninety minutes after completing LPS infusion, all animals in the endotoxemic shock group developed a hypodynamic septic condition, characterized by low cardiac output and increased systemic vascular resistance; 120 min after completing LPS infusion, the mean arterial pressure decreased by 25% (P = 0.01), confirming ongoing endotoxemic shock. However, significant decreases in sublingual microcirculatory parameters of small vessels (microvascular flow index, perfused vessel density, and proportion of small perfused vessels) were observed 30 min after completing LPS infusion (P = 0.01, for all), and threshold decreases of 30% were found 60 min after completing LPS infusion (P = 0.001, for all) in the endotoxemic shock group. Lactate levels significantly increased to more than 2 mm/L at 90 min and more than 4 mm/L at 120 min in the endotoxemic shock group (P = 0.02 and P = 0.01, respectively).

Conclusions

Changes in microcirculatory perfusion precede changes in macrocirculation and lactate levels in a rabbit model of endotoxemia shock. Microcirculation, macrocirculation, and oxygen metabolism are distinct in early-stage endotoxic shock.

The use of sentinel skin islands for monitoring buried and semi-buried micro-vascular flaps. Part I: Summary and brief description of monitoring methods

Micro-vascular flaps have been used for the repair of challenging defects for over 45 years. The risk of failure is reported to be around 5-10% which despite medical and technical advances in recent years remains essentially unchanged. Precise, continuous, sensitive and specific monitoring together with prompt notification of vascular compromise is crucial for the success of the procedure. In this review, we provide a classification and brief description of the reported methods for monitoring the micro-vascular flap and a summary of the benefits over direct visual monitoring. Over 40 different monitoring techniques have been reported but their comparative merits are not always obvious. One looks for early detection of a flap's compromise, improved flap salvage rate and a minimal false-positive or false-negative rate. The cost-effectiveness of any method should also be considered. Direct visualisation of the flap is the method most generally used and still seems to be the simplest, cheapest and most reliable method for flap monitoring. Considering the alternatives, only implantable Doppler ultrasound probes, near infrared spectroscopy and laser Doppler flowmetry have shown any evidence of improved flap salvage rates over direct visual monitoring.

Epinephrine penetrates through gingival sulcus unlike keratinized gingiva and evokes remote vasoconstriction in human

Background

It has been demonstrated in non-oral tissues that the locally evoked vasoconstriction could elicit remote vasoconstriction. This study aimed to investigate the spreading vasoconstrictor effects of epinephrine in the gingiva.

Methods

Gingival blood flow (GBF) was measured by laser speckle contrast imager in 21 healthy volunteers. In group A, two wells were fabricated from orthodontic elastic ligature and placed 2 mm apically to the free gingival margin at the mid buccal line of 12 (test side) and 21 (control side) teeth. The GBF was measured in the wells and tightly apical, coronal, distal and mesial to the wells. In group B, the wells were made on the buccal surface of the same teeth, including the gingival sulcus. Four regions were selected for measurement from the gingival margin reaching the mucogingival line (coronal, midway1, midway2 and apical). After the baseline recording, 3 µg epinephrine was applied into the test, and physiological saline into the control well. The GBF was recorded for 14 min. The gingival thickness was measured with a PIROP Ultrasonic Biometer.

Results

In group A, the GBF did not increase or decrease after the application of epinephrine. In group B, the GBF significantly decreased in all regions of the test side and remained low for the observation period. The vasoconstriction appeared with delays in more apical regions (at min 1 in the coronal and the midway1, at min 2 in the midway2, at min 4 in the apical region). Similarly, the amount of the decrease at 14 min was the largest close to sulcus (− 53 ± 2.9%), followed by the midway1 (− 51 ± 2.8%) and midway2 (− 42 ± 4.2%) and was the lowest in the apical region (− 32 ± 5.8%). No correlation was found between GBF and gingival thickness.

Conclusion

Epinephrine could evoke intense vasoconstriction propagating to the mucogingival junction, indicating the presence of spreading vasoconstriction in the human gingiva. The attached gingiva is impermeable to epinephrine, unlike the gingival sulcus.

This trial was registered in ClinicalTrials.gov titled as Evidence of Spreading Vasoconstriction in Human Gingiva with the reference number of NCT04131283 on 16 October 2019. https://clinicaltrials.gov/show/NCT04131283

Evidence of spreading vasodilation in the human gingiva evoked by nitric oxide

BACKGROUND AND OBJECTIVE

Spreading vasodilation is an important means of increasing local blood flow effectively during increased metabolic demands or in case of vascular injury. Our aim was to develop a technique proving the presence of spreading vasodilation in the human keratinized gingiva.

METHODS

Local vasodilation was evoked by the application of nitric oxide (NO) donor nitroglycerin into a well, fixed 2 mm above the marginal gingiva, in 20 subjects with healthy periodontal tissue. Either 1 or 8 mg/mL nitroglycerin solutions were dropped into the test well at the upper right second incisor, and saline was applied into the control well at the upper left first incisor. The gingival blood flow (GBF) was recorded for 15 minutes by a laser speckle contrast imager below the well and in the surrounding area in the mesial, distal, apical and coronal directions. Gingival thickness was measured by an ultrasonic biometer.

RESULTS

Peak GBF increase was similar after 1 mg/mL and after 8 mg/mL nitroglycerin application in the well (51% ± 12% vs 42% ± 8%) and in the apical region (33 ± 9% vs 55% ± 13%). While the lower dose of nitroglycerin increased GBF only in the apical region around the well, the higher dose induced significant elevations in all surrounding regions, with apical prominence. Hyperaemia lasted 10-14 minutes in the low-dose group whereas it extended beyond the observation period in the high-dose group. Neither the baseline nor the NO-induced peak GBF were correlated with gingival thickness.

CONCLUSION

The role of the direct effect of NO in the regulation of perfusion was demonstrated in the human gingiva as well as the propagation of local vasodilation to distant, especially apical areas, probably by the mechanism of flow-mediated dilation. This mechanism may have a clinical importance for flap survival or wound healing.

Evaluation of Laser Speckle Contrast Imaging for the Assessment of Oral Mucosal Blood Flow following Periodontal Plastic Surgery: An Exploratory Study

The laser speckle contrast imaging (LSCI) is proved to be a reliable tool in flap monitoring in general surgery; however, it has not been evaluated in oral surgery yet. We applied the LSCI to compare the effect of a xenogeneic collagen matrix (Geistlich Mucograft®) to connective tissue grafts (CTG) on the microcirculation of the modified coronally advanced tunnel technique (MCAT) for gingival recession coverage. Gingival microcirculation and wound fluid were measured before and after surgery for six months at twenty-seven treated teeth. In males, the flap microcirculation was restored within 3 days for both grafts followed by a hyperemic response. During the first 8 days the blood flow was higher at xenogeneic graft comparing to the CTG. In females, the ischemic period lasted for 7–12 days depending on the graft and no hyperemic response was observed. Females had more intense and prolonged wound fluid production. The LSCI method is suitable to capture the microcirculatory effect of the surgical intervention in human oral mucosa. The application of xenogeneic collagen matrices as a CTG substitute does not seem to restrain the recovery of graft bed circulation. Gender may have an effect on postoperative circulation and inflammation.

A novel method for in vivo visualization of the microcirculation of the mandibular periosteum in rats

OBJECTIVE

The periosteum plays an important role in bone physiology, but observation of its microcirculation is greatly limited by methodological constraints at certain anatomical locations. This study was conducted to develop a microsurgical procedure which provides access to the mandibular periosteum in rats.

METHODS

Comparisons of the microcirculatory characteristics with those of the tibial periosteum were performed to confirm the functional integrity of the microvasculature. The mandibular periosteum was reached between the facial muscles and the anterior surface of the superficial masseter muscle at the external surface of the mandibular corpus; the tibial periosteum was prepared by dissecting the covering muscles at the anteromedial surface. Intravital fluorescence microscopy was used to assess the leukocyte-endothelial interactions and the RBCV in the tibial and mandibular periosteum. Both structures were also visualized through OPS and fluorescence CLSM.

RESULTS

The microcirculatory variables in the mandibular periosteum proved similar to those in the tibia, indicating that no microcirculatory failure resulted from the exposure technique.

CONCLUSION

This novel surgical approach provides simple access to the mandibular periosteum of the rat, offering an excellent opportunity for investigations of microcirculatory manifestations of dentoalveolar and maxillofacial diseases.

Sidestream dark field images of the microcirculation: intra-observer reliability and correlation between two semi-quantitative methods for determining flow

Background

Since analysis of Sidestream Dark Field images still requires subjective interpretation, we wanted to determine intra-observer repeatability and to estimate the correlation between different evaluation methods.

Methods

Fifty-four Sidestream Dark Field videos were analyzed twice by the same blinded observer using validated software. Vessels were detected, generating the parameter Total Vessel Density (TVD), and flow was determined by (i) classifying each vessel separately, generating the parameters Perfused Vessel Density (PVD) and Proportion of Perfused Vessels (PPV), and by (ii) the “Boerma” method, generating a Microvascular Flow Index (MFI) by quadrants.

Results

Intraclass Correlation Coefficients (ICCs) were above 0.9 for TVD and above 0.8 for PDV and PPV. MFI_{by quadrants} had the lowest reliability (ICC = 0.52 for capillaries and ICC = 0.59 for all vessels), significantly lower than for PVD (ICC = 0.89, p < 0.001 for capillaries and ICC = 0.90, p < 0.001 for all vessels) and PPV (ICC = 0.82, p = 0.003 for capillaries and ICC = 0.83, p = 0.01 for all vessels). Correlation coefficient (r) between PPV and MFI_{by quadrants} corrected for measurement error was 0.39 (0.10 – 0.64) for capillaries and 1.01 (0.85 – 1.16) for all vessels.

Conclusions

Intra-observer reliability for full evaluation of Sidestream Dark Field images was good for vessel detection and for flow classification but significantly poorer for the faster “Boerma” method. Furthermore, the Boerma method is likely to estimate different aspects of capillary flow than do the standard methods.

Hyperbaric oxygen therapy accelerates vascularization in keratinized oral mucosal surgical flaps

BACKGROUND

Hyperbaric oxygen therapy (HBOT) is thought to promote vascular regeneration in wounds. The purpose of this study was to investigate the role of HBOT in advancing vascular regeneration in healing oral mucosal surgical flaps.

METHODS

A palatine partial-thickness mucosal flap was raised in 10 male-specific pathogen-free New Zealand White rabbits. Randomized into 2 groups of 5 animals each (control and HBOT), functional capillary density was measured preoperatively (baseline), and immediately postoperatively until day 21 using sidestream dark-field video microscopy. Ten HBOT sessions were administered over the course of 2 weeks at 2.5 atmospheres (2.5 bar O2 /90 minutes).

RESULTS

Repeated measures analysis of variance was used to compare the HBOT and control group on the sequential functional capillary density measurements. A significant interaction effect was present between time and group (F [8, 64] = 9.60; p < .0001) resulting from a significant increase in microcirculation in the HBOT group relative to the control group on days 7, 9, and 11.

CONCLUSION

Our results suggest that HBOT is capable of advancing wound vascular regeneration in healing keratinized oral mucosal flaps.

The influence of zoledronic acid and cyclophosphamide on microcirculation regeneration in healing oral mucosal flaps

The use of intravenous nitrogenous bisphosphonates and antineoplastic agents as postoperative adjuvant cancer management strategies may influence the course of oral wound healing by altering tissue vascularisation kinetics. The aim of this study was to investigate if single or combined zoledronic acid (ZOL) and cyclophosphamide (CTX) would influence microcirculation regeneration in healing oral mucosal flaps. Twenty female specific-pathogen free New Zealand white rabbits were randomised into four groups. In all animals a mucosal flap was raised; three groups were treated each separately with intravenous infusions of 0.14mg/kg ZOL, 100mg/kg CTX, or both, respectively. The fourth group was used as a control. Capillary density measurements, expressed as the mean number of capillaries±SD per mm(2) (cpll/mm(2)), was performed preoperatively using sidestream dark-field (SDF) imaging and repeated immediately postoperatively and on days 2, 4, 7, 9, 11, 14, and 21. Whole blood count and body weight was assessed in each group to monitor pharmacotherapeutic responses. Preoperative mean capillary density was 74±8cpll/mm(2) and 40±11cpll/mm(2) directly after surgery (P<0.0001). Post hoc comparisons of follow-up SDF measurements on days 9-21 between control and ZOL vs. CTX and ZOL+CTX were statistically significant (P<0.05). The present study demonstrates that ZOL did not alter capillary regeneration in healing mucosal flaps. However, although the early healing phase is generally characterised by rapid progression of capillary regeneration, interventions with CTX and ZOL+CTX significantly altered capillary regeneration and persisted beyond the third postoperative week.