The Erlangen micro-lightguide spectrophotometer EMPHO I

The Effect of Revascularization on Lower Limb Circulation Parameters in Symptomatic Peripheral Arterial Disease

Background: The prevalence of peripheral arterial disease and the number of revascularization procedures performed in symptomatic patients are steadily increasing. However, uncertainties remain regarding hemodynamic monitoring after revascularization and the prediction of clinical outcomes. This study aimed to investigate hemodynamic parameters with a focus on the microvasculature. Methods: This prospective, single-center study included 29 patients (15 with intermittent claudication [IC] and 14 with chronic limb-threatening ischemia [CLTI]). Before and after the revascularization procedure, in addition to the ankle-brachial index (ABI), microperfusion parameters, including microvascular blood flow, capillary oxygen saturation (SO2), and relative hemoglobin content (rHb), were assessed with lightguide spectrophotometry combined with laser Doppler flowmetry using an oxygen-to-see (O2C) device in the horizontal and elevated leg positions. Results: At baseline, SO2 in the elevated leg position was significantly lower in patients with CLTI than in those with IC (p = 0.0189), whereas the other microcirculatory parameters and ABI values were not significantly different. Patients with diabetes mellitus had a higher flow rate than those without in the horizontal leg position (p = 0.0162) but not in the elevated leg position. After successful revascularization, the flow increased immediately and significantly in both positions, whereas SO2, rHb, and the ABI did not. Conclusions: Elevated leg SO2 was significantly lower in CLTI than in clinically compensated peripheral arterial disease, whereas microvascular flow was a suitable surrogate parameter indicating successful revascularization. In studies using surgical or interventional revascularization procedures, noninvasive hemodynamic monitoring of the microcirculation at the foot level might be beneficial.

The impact of class I compression stockings on the peripheral microperfusion of the lower limb: A prospective pilot study

OBJECTIVE

The use of medical compression stockings (MCS) in patients with peripheral arterial disease (PAD) and diabetes is the subject of an ongoing critical debate. While reducing leg edema of various origins by improving venous back flow, there is a concern about additional arterial flow obstruction when compression therapy is applied in pre-existing PAD. The aim of this study is to obtain further information on the use of class I MCS in patients with advanced PAD and to evaluate the framework conditions for a safe application.

METHODS

The total collective (n = 55) of this prospective, clinical cohort study consisted of 24 patients with PAD Fontaine stage IIb and higher studied before revascularization, of whom 16 patients were examined again after revascularization, and 15 healthy participants included for reference. The microperfusion of the lower extremity of all participants was examined in a supine, elevated, and sitting position using the oxygen to see (O2C) method.

RESULTS

The results indicate that leg positioning had the strongest influence on microcirculation (SO2 and flow: p = 0.0001), whereas MCS had no significant effect on the perfusion parameters (SO2: p = 0.9936; flow: p = 0.4967) and did not lead to a deterioration of values into critical ranges.

CONCLUSION

Mild medical compression therapy appears to be feasible even in patients with advanced PAD. Larger studies are warranted to observe any long-term effects, in particular for the treatment of reperfusion edema after revascularization.

Tolerability safety and effectiveness of enhanced external counterpulsation versus individual shear rate therapy in patients with lower extremity atherosclerotic disease: A prospective pilot clinical trial

AIMS

We aimed to investigate the tolerability, safety, and effectiveness of enhanced external counterpulsation therapy (EECP) versus individual shear rate therapy (ISRT) in patients with lower extremity atherosclerotic disease (LEAD).

METHODS

Eighteen patients (age: 73.1 ± 6 years) underwent EECP and ISRT, each daily over five consecutive days in a cross-over design with a 1 week resting period in between the two regimens. A quality-of-life questionnaire was used to assess the therapy experience. Oxygen saturation (SO₂ ), relative hemoglobin amount (rHb) and blood flow (Flow) in the capillary-venous-system (microcirculation) of the skin were monitored continuously during all therapy sessions using the micro-lightguide spectrophotometer, also known as oxygen to see (O2C). The effects of EECP and ISRT on the renal function and skeletal muscles were evaluated using serial blood and urine tests.

RESULTS

EECP therapy had to be terminated early before the end of the 5th session in 10 patients (55.6%) because of discomfort. Four patients (22.2%) experienced signs of critical limb ischaemia under EECP. The total score of the quality-of-life questionnaire was significantly higher (= better tolerated) post-ISRT compared with EECP. Microcirculation monitoring revealed that ISRT significantly increased the SO₂ , blood flow and rHb during the therapy. All three parameters remained significantly increased in the observation period after ISRT. The serum levels of creatin kinase and myoglobin increased significantly under EECP.

CONCLUSIONS

ISRT significantly improves tolerability, safety, and effectiveness over EECP in patients with LEAD.

Muscle Oxygenation Level Might Trigger the Regulation of Capillary Venous Blood Filling during Fatiguing Isometric Muscle Actions

The regulation of oxygen and blood supply during isometric muscle actions is still unclear. Recently, two behavioral types of oxygen saturation (SvO2) and relative hemoglobin amount (rHb) in venous microvessels were described during a fatiguing holding isometric muscle action (HIMA) (type I: nearly parallel behavior of SvO2 and rHb; type II: partly inverse behavior). The study aimed to ascertain an explanation of these two regulative behaviors. Twelve subjects performed one fatiguing HIMA trial with each arm by weight holding at 60% of the maximal voluntary isometric contraction (MVIC) in a 90° elbow flexion. Six subjects additionally executed one fatiguing PIMA trial by pulling on an immovable resistance with 60% of the MVIC with each side and same position. Both regulative types mentioned were found during HIMA (I: n = 7, II: n = 17) and PIMA (I: n = 3, II: n = 9). During the fatiguing measurements, rHb decreased initially and started to increase in type II at an average SvO2-level of 58.75 ± 2.14%. In type I, SvO2 never reached that specific value during loading. This might indicate the existence of a threshold around 59% which seems to trigger the increase in rHb and could explain the two behavioral types. An approach is discussed to meet the apparent incompatibility of an increased capillary blood filling (rHb) despite high intramuscular pressures which were found by other research groups during isometric muscle actions.

Reduced pre-operative skin oxygen saturation predicts revision after open reduction and internal fixation in calcaneal fractures : A reduced pre-operative oxygen saturation as measured by laser-Doppler spectrophotometry in 8 mm depth is associated with revision surgery after open reduction and internal fixation of calcaneal fractures through an extended lateral approach

PURPOSE

To assess which pre-operative parameters correlate with wound revisions after an extended lateral approach to the calcaneus.

METHODS

Pre-operative laser-Doppler spectrophotometry was applied in patients undergoing open reduction and internal fixation. The number of wound revisions was recorded during pos-toperative follow-up. Spearman rho analysis was used to identify factors associated with wound revision and receiver operator characteristics curves were calculated for the identified factors.

RESULTS

Thirty-four patients (29 men, 5 women; 37 calcanei) with a mean patient age of 43 ± 14 years were analyzed. The minimal oxygen saturation value at the five measurement locations as well as the minimal value for flow correlated negatively with wound revisions (p value = 0.025 and 0.038, respectively). The area under the curve for the pre-operative minimal value of oxygen saturation was 0.841 (95%CI 0.64-1.00, p = 0.028), indicating a good accuracy as a test to predict wound revision.

CONCLUSION

A pre-operative oxygen saturation of at least 20.5% across five measurement points along the anticipated incision identified all patients not needing a wound revision (negative predictive value 100%). On the other hand, patients with at least one measurement below 20.5% were at risk for wound revision surgery (sensitivity 100%, specificity 48.5%). ClinicalTrials.gov NCT01264146.

Laser Doppler Flowmetry and Visible Light Spectroscopy of the Gastric Tube During Minimally Invasive Esophagectomy

Introduction

Ischemia is considered as the main reason for thoracic gastroesophageal anastomotic leaks after esophagectomy. Microcirculatory monitoring with laser Doppler flowmetry and visible light spectroscopy may provide valuable intraoperative real-time information about the gastric tube’s tissue perfusion and circulation.

Patients and Methods

Ten patients with esophageal cancer operated with minimally invasive esophagectomy participated in this single-center, prospective, observational pilot study. A single probe with laser Doppler flowmetry and visible light spectroscopy was used to perform transserosal microcirculation assessment of the gastric tube at predefined anatomical sites during different operation phases. Group comparison and changes were evaluated using the paired sample t-test.

Results

A reduction in StO2 was found at all measuring sites after the gastric tube formation compared with the baseline measurements. The mean StO2 reduction from baseline to gastric tube formation and after anastomosis was 16% (range 4%–28%) and 42% (range, 35%–52%), respectively. A statistically significant increase in the rHb concentration, representing venous congestion, was detected at the most cranial part of the gastric tube (P = 0.04). Three patients developed anastomotic leaks.

Conclusion

Intraoperative real-time laser Doppler flowmetry and visible light spectroscopy are feasible and may provide insight to microcirculatory changes in the gastric tube and at the anastomotic site. Patients with anastomotic leaks seem to have critical local tissue StO2 reduction and venous congestion that should be further evaluated in studies with larger sample sizes.

Behavior of oxygen saturation and blood filling in the venous capillary system of the biceps brachii muscle during a fatiguing isometric action

The objective of the study was to develop a better understanding of the capillary circulation in contracting muscles. Ten subjects were measured during a submaximal fatiguing isometric muscle action by use of the O2C spectrophotometer. In all measurements the capillary-venous oxygen saturation of hemoglobin (SvO2) decreased immediately after the start of loading and leveled off into a steady state. However, two different patterns (type I and type II) emerged. They differed in the extent of deoxygenation (-10.37 ±2.59 percent points (pp) vs. -33.86 ±17.35 pp, p = .008) and the behavior of the relative hemoglobin amount (rHb). Type I revealed a positive rank correlation of SvO2 and rHb (ρ = 0.735, p <.001), whereas a negative rank correlation (ρ = -0.522, p <.001) occurred in type II, since rHb decreased until a reversal point, then increased averagely 13% above the baseline value and leveled off into a steady state. The results reveal that a homeostasis of oxygen delivery and consumption during isometric muscle actions is possible. A rough distinction in two types of regulation is suggested.

Anaemia and Haemoglobin Status: A New Concept and a New Method of Assessment

Traditionally, anaemia has been determined and interpreted by the magnitude and severity of iron deficiency and the impact of intervention strategies. Internationally, it is defined as a state in which the quality and/or quantity of circulating red cells are reduced below a normal level The body employs several mechanisms during the development of anaemia to maintain the oxygen supply to the tissues. Thus, applying any quantitative cut-off point as an indicator for anaemia may lead to misclassification, since haemoglobin concentration does not necessarily reflect the level of tissue oxygen supply. Ideally, an assessment strategy should be able to determine both the degree of haemoglobin oxygenation and the haemoglobin concentration at a tissue level. The Erlangen microlight-guide spectrophotometer is a non-invasive instrument that can assess both capillary blood oxygenation and relative haemoglobin concentration.

Noninvasive measurements of tissue perfusion in critical limb ischemia

Critical limb ischemia (CLI) remains a challenge for an interdisciplinary therapeutic team due to chronic nonhealing wounds. Against this background, there is a necessity of quality control after revascularization. Beside the isolated evaluation of the macrocirculation by Ankle-Brachial or Toe-Brachial Index measurements, the microcirculation as an additional important factor of wound healing often remains underestimated. The following article gives an overview about the current investigation methods for noninvasive perfusion control of the CLI patient. Therefore, transcutaneous oxygen pressure (tcpO₂), the “oxygen-to-see” method which is a combination of white light tissue spectrometry and laser-Doppler flowmetry, fluorescence angiography with indocyanine green, and multispectral optoacoustic tomography will be described.

Melatonin pretreatment improves gastric mucosal blood flow and maintains intestinal barrier function during hemorrhagic shock in dogs

OBJECTIVE

Melatonin improves hepatic perfusion after hemorrhagic shock and may reduce stress-induced gastric lesions. This study was designed to investigate whether pretreatment with melatonin may influence gastric mucosal microcirculatory perfusion (μflow), oxygenation (μHbO₂ ), or intestinal barrier function during physiological and hemorrhagic conditions in dogs.

METHODS

In a randomized crossover study, five anesthetized foxhounds received melatonin 100 μg kg^-1 or vehicle (ethanol 5%) intravenously in the absence or presence of hemorrhagic shock (60 minutes, -20% blood volume). Systemic hemodynamic variables, gastric mucosal perfusion, and oxygenation were recorded continuously; intestinal barrier function was assessed intermittently via xylose absorption.

RESULTS

During hemorrhagic shock, melatonin significantly attenuated the decrease in μflow, compared with vehicle (-19±9 vs -43±10 aU, P<.05), without influence on μHbO₂ . A significant increase in xylose absorption was detected during hemorrhage in vehicle-treated dogs, compared with sham-operated animals (13±2 vs 8±1 relative amounts, P<.05); this was absent in melatonin-treated animals (6±1 relative amounts). Melatonin did not influence macrocirculation.

CONCLUSIONS

Melatonin improves regional blood flow suggesting improved oxygen delivery in gastric mucosa during hemorrhagic shock. This could provide a mechanism for the observed protection of intestinal barrier function in dogs.

Activation of HIF-1α and its downstream targets in rat hippocampus after long-term simulated microgravity exposure

Microgravity has many detrimental impact on brain functions, however the underlying mechanism remain unclear. In present study, 28 days of tail-suspension (30°) was used to simulate microgravity in rats. We showed that oxidative stress in hippocampus was increased after 28 days of simulated microgravity in consideration of the decreased expression of NF-E2-related factor 2 (Nrf2) and the declined activities of total superoxide dismutase (T-SOD), CuZn-SOD, glutathione peroxidase (GSH-PX) and total antioxidant capacity (T-AOC). Using RNA-seq, we further investigated the effect of simulated microgravity on the expression of genes in hippocampus, and 849 genes were found to be differentially expressed. According to pathway analysis, the differentially expressed genes involved in cytoskeleton, metabolism, immunity, transcription regulation, etc. It is interesting to note that the differentially expressed genes were involved in hypoxia-associated pathway. In agreement with this, the expression of hypoxia induced factor-1α (HIF-1α), the master regulator of oxygen homeostasis, was significantly increased. Meanwhile, HIF-2α, a HIF-1α paralog, was elevated compared with the control group. The expression of pyruvate dehydrogenase kinase 1 (PDK1), lactate dehydrogenase A (LDHA) and vascular endothelial growth factor (VEGF), three well-defined downstream targets of HIF-1α, were up-regulated in hippocampus after 28 days of simulated microgravity exposure. Additionally, brain oxygen saturation (SO₂) and blood flow analyzed by the tissue oxygen analysis system were also significantly reduced. These findings indicate that simulated microgravity might cause an alteration in oxygen homeostasis, providing novel insight into better understanding of how simulated microgravity affects the function of hippocampus and a new direction to the development of countermeasure for brain dysfunction during spaceflight (actual microgravity).

Immediate Dose-Response Effect of High-Energy Versus Low-Energy Extracorporeal Shock Wave Therapy on Cutaneous Microcirculation

Elucidation of the precise mechanisms and therapeutic options of extracorporeal shock wave therapy (ESWT) is only at the beginning. Although immediate real-time effects of ESWT on cutaneous hemodynamics have recently been described, the dose response to different ESWT energies in cutaneous microcirculation has never been examined. Thirty-nine Sprague-Dawley rats were randomly assigned to three groups that received either focused high-energy shock waves (group A: total of 1000 impulses, 10 J) to the lower leg of the hind limb, focused low-energy shock waves (group B: total of 300 impulses, 1 J) or placebo shock wave treatment (group C: 0 impulses, 0 J) using a multimodality shock wave delivery system (Duolith SD-1 T-Top, Storz Medical, Tägerwilen, Switzerland). Immediate microcirculatory effects were assessed with the O2C (oxygen to see) system (LEA Medizintechnik, Giessen, Germany) before and for 20 min after application of ESWT. Cutaneous tissue oxygen saturation increased significantly higher after high-energy ESWT than after low-energy and placebo ESWT (A: 29.4% vs. B: 17.3% vs. C: 3.3%; p = 0.003). Capillary blood velocity was significantly higher after high-energy ESWT and lower after low-energy ESWT versus placebo ESWT (group A: 17.8% vs. group B: -22.1% vs. group C: -5.0%, p = 0.045). Post-capillary venous filling pressure was significantly enhanced in the high-energy ESWT group in contrast to the low-energy ESWT and placebo groups (group A: 25% vs. group B: 2% vs. group C: -4%, p = 0.001). Both high-energy and low-energy ESWT affect cutaneous hemodynamics in a standard rat model. High-energy ESWT significantly increases parameters of cutaneous microcirculation immediately after application, resulting in higher tissue oxygen saturation, venous filling pressure and blood velocity, which suggests higher tissue perfusion with enhanced oxygen saturation, in contrast to low-energy as well as placebo ESWT. Low-energy ESWT also increased tissue oxygen saturation, albeit to a lower extent, and decreases both blood velocity and venous filling pressure. Low-energy ESWT reduced tissue perfusion, but improved oxygen saturation immediately after the application.

Cerebral blood flow reactivity in patients undergoing selective amygdalohippocampectomy for epilepsy of mesial temporal origin. A prospective randomized comparison of the trans-Sylvian and the transcortical approach

OBJECTIVE

The aim of this study was to assess (1) whether vasoreactivity is altered in patients with epilepsy and (2) whether the two most commonly used approaches, the trans-Sylvian (TS) and the trans-cortical (TC) route, differ in their impact on cortical blood flow.

METHODS

Patients were randomized to undergo selective amygdalohippocampectomy (selAH) through a TC or TS route. Before and after selAH, we recorded microcirculation parameters on the superficial cortex surrounding the surgical corridor. Blood flow and velocity were measured using laser Doppler flowmetry and micro-Doppler, respectively. Cortical oxygen saturation (SO2) was measured using remission spectrophotometry under hypocapnic and normocapnic conditions.

RESULTS

Ten patients were operated using the TS approach, and eight were operated via the TC approach. Vasomotor reactivity patterns measured with micro-Doppler were physiologically prior to selAH in both groups. After completion of surgery, a significant increase in SO2-values occurred in the TS group (before: 56.7 ± 2.2, after: 65.5 ± 3.0%SO2), but not in the TC group (before: 52.9 ± 5.2, after: 53.0 ± 3.7%SO2). The rate of critical SO2 values below 25% was significantly higher after the TC approach (12.3%) compared to the TS approach (5.2%; p < 0.05).

DISCUSSION

Our findings provide the first invasively measured evidence that patients with mesial temporal lobe epilepsy have preserved cerebral blood flow responses to alterations in CO2. In addition, local cortical SO2 was higher in the TS group than in the TC group after selAH. This may be a sign of reactive cortical vessel dilation after proximal vessel manipulation associated with the TS approach. In contrast, the lower values of SO2 after the TC approach indicate tissue ischaemia surrounding the surgical corridor surrounding the corticotomy.

Optical Measurement of Tissue Oxygen Saturation

Advances in opto-electronic systems have meant that optical spectroscopy can now be used for noninvasive measurements in tissue in patients. A number of techniques have evolved over the last 15 years that make use of the characteristic differences in the absorption spectrum of deoxygenated and oxygenated hemoglobin to measure oxygen saturation. This article summarizes, in particular, those techniques that may prove to be applicable to measurements relating to lower extremity wounds. A short introduction is given about existing electrode methods before describing applications of near infrared and visible wavelength spectroscopy to measurements in tissue. The advantages and limitations of these methods are discussed. An example of an area where tissue spectroscopy is now in routine clinical use for tissue healing viability assessment is presented.

Influence of thoracic epidural anesthesia on gastric oxygenation during hypothermia and hemorrhage

OBJECTIVE

Hypothermia preserves gastric mucosal microvascular oxygenation (μHbO2) during hemorrhagic shock. Additionally, hypothermia activates the sympathetic nervous system that leads to the release of vasopressin. The aim of this study was to evaluate whether the effect of hypothermia is mediated via the sympathetic nervous system and/or via vasopressin.

METHODS

In prospective and randomized experiments on five anesthetized dogs (foxhounds, cross-over design, 6 groups with n=5 per group) we analyzed the effects of hemorrhage on μHbO2 during mild hypothermia (HT, 34 °C), during additional thoracic epidural anesthesia (HT/TEA) and during additional vasopressin V1 receptor blockade (HT/VB). As control groups, effects of hemorrhage were studied under normothermia alone (NT), during additional thoracic epidural anesthesia (NT/TEA) and during additional vasopressin V1 receptor blockade (NT/VB).

RESULTS

Hemorrhage decreased μHbO2 from 81 ± 3 to 49 ± 8%. In contrast, in the presence of hypothermia, μHbO2 was significantly higher during hemorrhagic shock (from 79 ± 3 to 66 ± 9%) despite a similar decrease in DO2. The effect of hypothermia on μHbO2 was reduced in the presence of thoracic epidural anesthesia or vasopressin receptor blockade.

CONCLUSIONS

Hypothermia preserves μHbO2 during hemorrhagic shock. This effect is partially abolished during thoracic epidural anesthesia or during vasopressin receptor blockade. The sympathetic nervous system and the vasopressin V1 receptor are partially involved in mediating the effect of hypothermia on gastric oxygenation during hemorrhage.

Relation between blood flow and tissue blood oxygenation in human fingertip skin

BACKGROUND

Tissue blood flow (BF) is thought to be involved in the regulation of tissue blood oxygenation (StO2). The purpose of the present study was to show the relation between BF and StO2 by measuring them simultaneously under different conditions.

METHODS

Twenty-one healthy subjects (age 21-30years) participated in this study. We measured BF and StO2 in a small area of skin (fingertip, palm, forearm) simultaneously using a laser Doppler flowmeter and a tissue oxygenation monitor. Three measurements were made at rest while performing mental arithmetic and during constriction of the ipsilateral upper arm.

RESULTS

At rest, BF and StO2 were higher in the fingertip than in the palm or forearm (p<0.01). Performing mental arithmetic produced significant decreases in BF, oxygenated hemoglobin, and StO2 in the fingertip (p<0.05). Constriction of the ipsilateral upper arm produced significant decreases in BF and StO2 (p<0.05) and an increase in oxygenated hemoglobin (p<0.05). Both procedures produced significant increases in deoxygenated hemoglobin (p<0.05), which was in antiphase to the decrease in StO2.

CONCLUSIONS

BF decrease produced a significantly decreased StO2 in fingertip skin. The results show that simultaneous measurement of BF and StO2 is beneficial for showing the close relation between them.

Fractionated Repetitive Extracorporeal Shock Wave Therapy: A New Standard in Shock Wave Therapy?

Background. ESWT has proven clinical benefit in dermatology and plastic surgery. It promotes wound healing and improves tissue regeneration, connective tissue disorders, and inflammatory skin diseases. However, a single treatment session or long intervals between sessions may reduce the therapeutic effect. The present study investigated the effects of fractionated repetitive treatment in skin microcirculation. Methods. 32 rats were randomly assigned to two groups and received either fractionated repetitive high-energy ESWT every ten minutes or placebo shock wave treatment, applied to the dorsal lower leg. Microcirculatory effects were continuously assessed by combined laser Doppler imaging and photospectrometry. Results. In experimental group, cutaneous tissue oxygen saturation was increased 1 minute after the first application and until the end of the measuring period at 80 minutes after the second treatment (P < 0.05). The third ESWT application boosted the effect to its highest extent. Cutaneous capillary blood flow showed a significant increase after the second application which was sustained for 20 minutes after the third application (P < 0.05). Placebo group showed no statistically significant differences. Conclusions. Fractionated repetitive extracorporeal shock wave therapy (frESWT) boosts and prolongs the effects on cutaneous hemodynamics. The results indicate that frESWT may provide greater benefits in the treatment of distinct soft tissue disorders compared with single-session ESWT.

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

Background

After 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 Methods

Severe 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.

Results

Directly 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.

Conclusions

In 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.

A pilot study of a new spectrophotometry device to measure tissue oxygen saturation

Tissue oxygen saturation (SO2) measurements have the potential for far wider use than at present but are limited by device availability and portability for many potential applications. A device based on a small, low-cost general-purpose spectrophotometer (the Harrison device) might facilitate wider use. The aim of this study was to compare the Harrison device with a commercial instrument, the LEA O2C.Measurements were carried out on the forearm and finger of 20 healthy volunteers, using a blood pressure cuff on the upper arm to induce different levels of oxygenation. Repeatability of both devices was assessed, and the Bland-Altman method was used to assess agreement between them.The devices showed agreement in overall tracking of changes in SO2. Test-retest agreement for the Harrison device was worse than for O2C, with SD repeatability of 10.6% (forearm) or 18.6% (finger). There was no overall bias between devices, but mean (SD) difference of 1.2 (11.8%) (forearm) or 4.4 (11.5%) (finger) were outside of a clinically acceptable range.Disagreements were attributed to the stability of the Harrison probe and the natural SO2 variations across the skin surface increasing the random error. Therefore, though not equivalent to the LEA O2C, a probe redesign and averaged measurements may help establish the Harrison device as a low cost alternative.

Hypothermia improves oral and gastric mucosal microvascular oxygenation during hemorrhagic shock in dogs

Hypothermia is known to improve tissue function in different organs during physiological and pathological conditions. The aim of this study was to evaluate the effects of hypothermia on oral and gastric mucosal microvascular oxygenation (μHbO₂) and perfusion (μflow) under physiological and hemorrhagic conditions. Five dogs were repeatedly anesthetized. All animals underwent each experimental protocol (randomized cross-over design): hypothermia (34°C), hypothermia during hemorrhage, normothermia, and normothermia during hemorrhage. Microcirculatory and hemodynamic variables were recorded. Systemic (DO₂) and oral mucosal (μDO₂) oxygen delivery were calculated. Hypothermia increased oral μHbO₂ with no effect on gastric μHbO₂. Hemorrhage reduced oral and gastric μHbO₂ during normothermia (−36 ± 4% and −27 ± 7%); however, this effect was attenuated during additional hypothermia (−15 ± 5% and −11 ± 5%). The improved μHbO₂ might be based on an attenuated reduction in μflow during hemorrhage and additional hypothermia (−51 ± 21 aU) compared to hemorrhage and normothermia (−106 ± 19 aU). μDO₂ was accordingly attenuated under hypothermia during hemorrhage whereas DO₂ did not change. Thus, in this study hypothermia alone improves oral μHbO₂ and attenuates the effects of hemorrhage on oral and gastric μHbO₂. This effect seems to be mediated by an increased μDO₂ on the basis of increased μflow.

Hypercapnia counteracts captopril-induced depression of gastric mucosal oxygenation

Hypercapnia (HC) increases systemic oxygen delivery (DO2) and gastric mucosal oxygenation. However, it activates the renin-angiotensin-aldosterone system (RAAS), which conversely reduces mesenteric perfusion. The aims of this study were to evaluate the effect of RAAS inhibition during normocapnia and HC on oral and gastric mucosal oxygenation (μHbO2) and to assess the effect of blood pressure under these circumstances. Five dogs were repeatedly anesthetized to study the effects of ACE inhibition (ACE-I; 5 mg/kg captopril, followed by 0.25 mg/kg per h) on μHbO2 (reflectance spectrophotometry) and hemodynamic variables during normocapnia (end-tidal CO2=35 mmHg) and HC (end-expiratory carbon dioxide (etCO2)=70 mmHg). In the control group, the dogs were subjected to HC alone. To exclude the effects of reduced blood pressure, in one group, blood pressure was maintained at baseline values via titrated phenylephrine (PHE) infusion during HC and additional captopril infusion. ACE-I strongly reduced gastric μHbO2 from 72±2 to 65±2% and mean arterial pressure (MAP) from 64±2 to 48±4 mmHg, while DO2 remained unchanged. This effect was counteracted in the presence of HC, which increased gastric μHbO2 from 73±3 to 79±6% and DO2 from 15±2 to 22±4 ml/kg per min during ACE-I without differences during HC alone. However, MAP decreased similar to that observed during ACE-I alone from 66±3 to 47±5 mmHg, while left ventricular contractility (dPmax) increased from 492±63 to 758±119 mmHg/s. Titrated infusion of PHE had no additional effects on μHbO2. In summary, our data suggest that RAAS inhibition reduces gastric mucosal oxygenation in healthy dogs. HC not only abolishes this effect, but also increases μHbO2, DO2, and dPmax. The increase in μHbO2 during ACE-I under HC is in accordance with our results independent of blood pressure.

Enhanced spectral analysis of blood flow during post-occlusive reactive hyperaemia test in different tissue depths

The objective of this study was to investigate the impairment of microcirculation in schizophrenic patients by means of spectral analysis of blood flow signals and to determine if microcirculation is unequally altered in different tissue depths. Furthermore, the impact of gender and age on the spectral parameters of the Laser Doppler Flowmetry (LDF) signal in healthy and diseased microcirculation are to be analysed. The segmented spectral analysis (SSA) algorithm was applied to LDF signals of a provoked post-ischemic stage and compared to the traditional total spectral analysis, hypothesizing that SSA reveals more detailed information on the dynamic behaviour of the blood flow. 15 healthy subjects (CON, mean age 32.4 years) and 15 patients (PAT, mean age 33.0 years) were enrolled. Spectral analysis was performed on two LDF signals at a depth of 2mm and 6-8mm. Features in five frequency subintervals were determined. Our results indicate that microcirculation is strongly impaired in patients. SSA of blood flow revealed differences between CON and PAT in all three frequency intervals referring to local vasomotion (endothelial p=0.03; sympathetic p=0.02, myogenic p=0.03) as well as the respiratory (p=0.02) and cardiac (p=0.006) bands in the deeper tissue. In contrast, in the near-surface tissue only the endothelial (p=0.006) and cardiac (p=0.006) components were altered. Furthermore, SSA determined a gender- and age dependency regarding blood flow. In conclusion, we could demonstrate that microcirculation in schizophrenic patients is significantly impaired, depending on its location in the near-surface skin or in the superficial muscle tissue. These alterations of microcirculation are more pronounced in the deeper tissue depth of about 6-8mm and are influenced by gender and age.

A postoperative analysis of perfusion dynamics in deep inferior epigastric perforator flap breast reconstruction: a noninvasive quantitative measurement of flap oxygen saturation and blood flow

BACKGROUND

The blood supply of microvascular free flaps is rated as very critical, particularly in the first postoperative days. Only a timely recognition of a complication and its treatment can ensure the survival of the flap. To quantify the postoperative perfusion dynamics, we measured the oxygen supply and blood flow of the deep inferior epigastric perforator (DIEP) flaps.

METHOD

A total of 23 patients undergoing DIEP flap breast reconstruction were involved in this study. Noninvasive measurements were performed with the O2C-device, which combines the determination of hemoglobin oxygenation and blood flow using white light and laser light. The first measurement was performed immediately after the flap anastomosis. Further measurements were carried out on the first, third, fifth, and seventh postoperative days.

RESULTS

The preoperative value represents our baseline. With the exception of the third day, all postoperative measurements were above the baseline. On the third postoperative day, there was a decrease in the cutaneous oxygen saturation of 22% and a decrease in blood flow of 18% on average, regardless of the individual fluctuations of patient's blood pressure.

CONCLUSIONS

The postoperative perfusion characteristics of the DIEP flap showed a critical drop in the cutaneous oxygen supply and blood flow on the third postoperative day. This represents a potential risk and should be considered in the postoperative management of the DIEP flap.

Vasopressin V(1A) 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.

PaO2 oscillations caused by cyclic alveolar recruitment can be monitored in pig buccal mucosa microcirculation

BACKGROUND

Cyclic alveolar recruitment and derecruitment play a role in the pathomechanism of acute lung injury and may lead to arterial partial pressure of oxygen (PaO(2) ) oscillations within the respiratory cycle. It remains unknown, however, if these PaO(2) oscillations are transmitted to the microcirculation. The present study investigates if PaO(2) oscillations can be detected in the pig buccal mucosa microcirculation.

METHODS

Respiratory failure was induced by surfactant depletion in seven pigs. PaO(2) oscillations caused by cyclic recruitment and derecruitment were measured in the thoracic aorta by fast fluorescence quenching of oxygen technology. Haemoglobin oxygen saturation, haemoglobin amount and blood flow in the buccal mucosa microcirculation were determined by combined fast white light spectrometry and laser Doppler flowmetry additionally to systolic arterial pressure. Measurements were performed during baseline conditions and during cyclic recruitment and derecruitment.

RESULTS

Measurements remained stable during baseline. Respiratory-dependent oscillations occurred in the systemic circulation [PaO(2) oscillations 92 (69-172) mmHg; systolic arterial pressure oscillations 33 (13-35) %] and were related to the respiratory rate (5.0 ± 0.2/min) as confirmed by Fourier analysis. Synchronised oscillations were detected to the pig buccal mucosa microcirculation [haemoglobin oxygen saturation oscillations 3.4 (2.7-4.9) %; haemoglobin amount oscillations 8.5 (2.3-13.3) %; blood flow oscillations 66 (18-87) %]. The delay between PaO(2) -\ and microcirculatory oxygen oscillations was 7.2 ± 2.8 s.

CONCLUSION

The present study suggests that PaO(2) oscillations caused by cyclic recruitment and derecruitment were transmitted to the buccal mucosa microcirculation. This non-invasive approach of measuring oxygen waves as a surrogate parameter of cyclic recruitment and derecruitment could be used to monitor PaO(2) oscillations at the bedside.

Shedding light on mitochondrial function by real time monitoring of NADH fluorescence: I. Basic methodology and animal studies

Normal mitochondrial function in the process of metabolic energy production is a key factor in maintaining cellular activities. Many pathological conditions in animals, as well as in patients, are directly or indirectly related to dysfunction of the mitochondria. Monitoring the mitochondrial activity by measuring the autofluorescence of NADH has been the most practical approach since the 1950s. This review presents the principles and technological aspects, as well as typical results, accumulated in our laboratory since the early 1970s. We were able to apply the fiber-optic-based NADH fluorometry to many organs monitored in vivo under various pathophysiological conditions in animals. These studies were the basis for the development of clinical monitoring devices as presented in accompanying article. The encouraging experimental results in animals stimulated us to apply the same technology in patients after technological adaptations as described in the accompanying article. Our medical device was approved for clinical use by the FDA.

Diabetes and peripheral arterial occlusive disease impair the cutaneous tissue oxygenation in dorsal hand microcirculation of elderly adults: implications for hand rejuvenation

BACKGROUND

In spite of potential implications for anti-aging therapy regarding the selection of the most suitable therapeutical method and potential perinterventional complications, cutaneous microcirculation of the aging hand in healthy individuals as well as in those with diabetes mellitus or peripheral arterial occlusive disease (PAOD) has never been evaluated.

HYPOTHESIS

Functional microcirculation of the dorsal hand differs between healthy individuals and individuals with diabetes or PAOD at the same age.

MATERIALS AND METHODS

Prospective controlled cohort study. One hundred ten individuals were allocated to group A (healthy individuals, n = 37), group B (diabetes mellitus, n = 36), and group C (PAOD, n = 37). Microcirculatory data were obtained using combined laser-Doppler and photospectrometry.

RESULTS

Cutaneous oxygen saturation at the dorsal hand of healthy individuals was 11.1% higher than of those with diabetes mellitus (p = .04) and 18.8% higher than of those with PAOD (p = .001). Cutaneous capillary blood flow in participants with PAOD was 20% higher than in healthy individuals (p = .047).

CONCLUSION

This is the first study demonstrating that capillary microcirculation of the dorsal hand differs between healthy individuals and those with diabetes or PAOD of the same age. Further studies should explore whether ameliorating cutaneous tissue oxygen saturation could emerge as a viable antiaging strategy for elderly hands.

Compartmental and muscular response to closed soft tissue injury in rats investigated by oxygen-to-see and intravital fluorescence microscopy

BACKGROUND

Closed soft tissue injury (CSTI) induces local inflammation and progressive microvascular dysfunction. The aim of the study was to evaluate and compare the microvascular changes systematically in a precompartmental tissue injury by oxygen-to-see (O2C), a combined laser Doppler flowmetry and spectrophotometry system, and intravital fluorescence microscopy (IVM).

METHODS

Fourteen Wistar rats were subjected to a trauma and a control group (both n = 7). CSTI was performed on the left lower limb by means of a standardized impact device. Controls received a sham CSTI. Capillary blood flow (QRBC), oxygen saturation (sO2), and postcapillary filling pressure (rHb) were measured noninvasively by O2C assessed in 2-mm and 8-mm depth underneath the skin. Measurements were done before and after trauma and hourly up to 24 hours. IVM of the soleus muscle was performed after 24 hours.

RESULTS

Before CSTI, O2C parameters did not reveal a difference between both groups. Up to 2 hours after trauma, QRBC was significantly increased in 8-mm tissue depth. No significant changes of sO2 and rHb were noted compared with controls. In 2-mm depth, significantly reduced QRBC and rHb levels were observed compared with 8 mm but with no significant changes after CSTI. IVM showed a significant increase of postcapillary blood flow with decreased functional capillary density, increased macromolecular leakage, and increased nicotinamide adenine dinucleotide hydride.

CONCLUSIONS

After CSTI in rats, there was an immediate increase of compartmental capillary blood flow with a slight increase of muscle oxygen saturation and unchanged postcapillary venous filling pressures as sign of a redistribution of blood between soft and muscle tissue. The severity of pathologic changes in the compartment was not reflected by O2C but by IVM.

Micro-lightguide spectrophotometry for tissue perfusion in ischemic limbs

OBJECTIVE

To validate micro-lightguide spectrophotometry (O2C) in patients with lower limb ischemia and to compare results with those obtained from toe blood pressure.

METHODS

We prospectively examined 59 patients, 24 of whom complained of claudication, 31 had critical ischemia, and four were asymptomatic. Diabetes was present in 19 (32%) patients. Saturation (SO(2)) and flow measured with O2C were determined with the limb in the horizontal position followed by a 55-cm elevation. Toe pressures were determined in the horizontal position only. In addition, 13 patients were examined before and, on average, 3 days after revascularization.

RESULTS

Median SO(2) was 62% (25%-75% percentile: 37%-75%) with the limb in the horizontal position and 16% (3%-41%) with the limb elevated. Comparing the individual toe pressures with SO(2) values measured in the horizontal position and elevated position revealed a significant correlation (r(s) = 0.40; P < .01 and r(s) = 0.56; P < .01, respectively). A low SO(2) (ie, <40% in the horizontal position and <20% in the elevated position) was highly predictive of a toe pressure of 40 mm Hg or less. In the horizontal position, the positive predictive value was 100%, whereas the negative predictive value was 47%. The similar figures in the elevated position were a positive predictive value of 97% and a negative predictive value of 68%. Postoperatively, SO(2) increased significantly from 27% (P25%-75%: 11%-75%) to 79% (68%-87%) in the horizontal position (P = .008) and from 14% (P25%-75%: 2%-39%) to 55% (30%-73%) in the elevated position (P = .011), respectively. Looking at the individual 13 cases in which revascularization was performed, three patients had a partial reconstruction (ie, superficial femoral artery occlusion distal to a central reconstruction or reconstruction to a popliteal blind segment). These patients had significantly lower postoperative SO(2) as well as toe pressure compared with the 10 patients with unobstructed flow to the foot.

CONCLUSIONS

O2C was easy to use, fast, and painless. The most useful finding was the high predictive value of a low saturation and the rise in O2C values after successful revascularization.

Acute effects of remote ischemic preconditioning on cutaneous microcirculation--a controlled prospective cohort study

Background

Therapeutic strategies aiming to reduce ischemia/reperfusion injury by conditioning tissue tolerance against ischemia appear attractive not only from a scientific perspective, but also in clinics. Although previous studies indicate that remote ischemic intermittent preconditioning (RIPC) is a systemic phenomenon, only a few studies have focused on the elucidation of its mechanisms of action especially in the clinical setting. Therefore, the aim of this study is to evaluate the acute microcirculatory effects of remote ischemic preconditioning on a distinct cutaneous location at the lower extremity which is typically used as a harvesting site for free flap reconstructive surgery in a human in-vivo setting.

Methods

Microcirculatory data of 27 healthy subjects (25 males, age 24 ± 4 years, BMI 23.3) were evaluated continuously at the anterolateral aspect of the left thigh during RIPC using combined Laser-Doppler and photospectrometry (Oxygen-to-see, Lea Medizintechnik, Germany). After baseline microcirculatory measurement, remote ischemia was induced using a tourniquet on the contralateral upper arm for three cycles of 5 min.

Results

After RIPC, tissue oxygen saturation and capillary blood flow increased up to 29% and 35% during the third reperfusion phase versus baseline measurement, respectively (both p = 0.001). Postcapillary venous filling pressure decreased statistically significant by 16% during second reperfusion phase (p = 0.028).

Conclusion

Remote intermittent ischemic preconditioning affects cutaneous tissue oxygen saturation, arterial capillary blood flow and postcapillary venous filling pressure at a remote cutaneous location of the lower extremity. To what extent remote preconditioning might ameliorate reperfusion injury in soft tissue trauma or free flap transplantation further clinical trials have to evaluate.

Trial registration

ClinicalTrials.gov: NCT01235286

Mitochondrial function and tissue vitality: bench-to-bedside real-time optical monitoring system

BACKGROUND

The involvement of mitochondria in pathological states, such as neurodegenerative diseases, sepsis, stroke, and cancer, are well documented. Monitoring of nicotinamide adenine dinucleotide (NADH) fluorescence in vivo as an intracellular oxygen indicator was established in 1950 to 1970 by Britton Chance and collaborators. We use a multiparametric monitoring system enabling assessment of tissue vitality. In order to use this technology in clinical practice, the commercial developed device, the CritiView (CRV), is tested in animal models as well as in patients.

METHODS AND RESULTS

The new CRV enables the optical monitoring of four different parameters, representing the energy balance of various tissues in vivo. Mitochondrial NADH is measured by surface fluorometry/reflectometry. In addition, tissue microcirculatory blood flow, tissue reflectance and oxygenation are measured as well. The device is tested both in vitro and in vivo in a small animal model and in preliminary clinical trials in patients undergoing vascular or open heart surgery. In patients, the monitoring is started immediately after the insertion of a three-way Foley catheter (urine collection) to the patient and is stopped when the patient is discharged from the operating room. The results show that monitoring the urethral wall vitality provides information in correlation to the surgical procedure performed.

Dynamic microvascular blood flow analysis during post-occlusive reactive hyperemia test in patients with schizophrenia

Patients suffering from schizophrenia have an increased mortality risk due to cardiovascular events. Recently the analysis of peripheral circulation has revealed interesting results in the study of vascular pathological conditions assuming that the state of microcirculation of the skin is at least partly representative for the constitution of other vascular beds including those of the cardiac muscle and arteries. The objective of this study was to investigate the microcirculation in patients with acute schizophrenia (PAT, n = 15, mean age 33.0 years, 7 male, 8 female) to identify whether spectral features from blood flow signals derived through laser Doppler spectrometry are significantly altered compared to healthy subjects (CON, n = 15, mean age 32.4 years, 7 male, 8 female) by means of the post-occlusive reactive hyperemia test. It was also explored if a segmentation of the post-ischemic stage can disclose more detailed and additional information about the dynamic behavior of the blood flow during hyperemic response. For this reason, time-frequency analyses were performed to observe the course of the blood flow frequency components over time. Our results indicate significant differences in the patients group, already detectable under baseline conditions but also in the hyperemic phase. The main modifications affect the respiratory (p = 0.006) as well as the cardiac (p = 0.001) activity. It was further shown that the application of a segmented analysis of the post-ischemic state considerably improves the differentiation between both groups. Only with the introduced segmentation algorithm using a window length of 2048 samples and a shift of 128 and 256 samples we could demonstrate influences of the disease on the endothelial (p = 0.029), the sympathetic (p = 0.019) and the myogenic (p = 0.029) mechanisms. These information provide further insights into the appearance of schizophrenia and could lead to an improvement of the patients' treatment to avoid the occurrence of cardiovascular events.

Measurement of Cortical Microcirculation During Intracranial Aneurysm Surgery by Combined Laser-Doppler Flowmetry and Photospectrometry

BACKGROUND:

Accidental vessel occlusion is one major risk of intracranial aneurysm surgery potentially causing cerebral ischemia. The intraoperative assessment of cerebral ischemia remains a technological challenge.

OBJECTIVE:

As a novel approach, cortical tissue integrity was monitored using simultaneous measurements of regional capillary-venous cerebral blood flow (rvCBF), oxygen saturation (Srvo2), and hemoglobin amount (rvHb) during aneurysm surgery.

METHODS:

Fifteen patients scheduled for aneurysm surgery of the anterior and posterior circulation were included. A fiber optic probe was placed on the cortex associated with the distal branch of the aneurysmatic vessel. Blinded measurements by combined laser-Doppler flowmetry (rvCBF) and photospectrometry (Srvo2, rvHb) were performed before and after surgical clipping or trapping of the aneurysm. Data were correlated with postoperative imaging and neurological outcome.

RESULTS:

Cortical measurements could be successfully performed in all patients. Significant increase (&gt;25% change from baseline) or decrease (&lt;25% change from baseline) of rvCBF, Srvo2, and rvHb was detectable in 33 to 46% of patients after surgical intervention. Severe decrease (&gt;50% change from baseline) of all parameters or solitary of rvCBF was correlated to reduced cerebral perfusion and neurological deficits in 2 patients.

CONCLUSION:

Combined laser-Doppler flowmetry and photospectrometry provides real-time information on cortical microcirculation. Intraoperative alterations of parameters (rvCBF, Srvo2, rvHb) might reflect changes of cerebral tissue integrity during intracranial aneurysm surgery.

Intraoperative monitoring of cerebral microcirculation and oxygenation--a feasibility study using a novel photo-spectrometric laser-Doppler flowmetry

BACKGROUND

The present study assesses the utility of a novel invasive device (O2C-, oxygen-to-see-device) for intraoperative measurement of the cerebral microcirculation. CO2 vasoreactivity during 2 different propofol concentrations was used to investigate changes of capillary venous cerebral blood flow (rvCBF), oxygen saturation (srvO2), and hemoglobin concentration (rvHb) during craniotomy.

METHODS

Thirty-four patients were randomly assigned to a low propofol (4 mg/kg/h) versus a high propofol (6 mg/kg/h) group. A fiberoptic probe was applied on the cortex next to the surgical site. Measurements were performed during lower (35 mm Hg) and higher (45 mm Hg) levels of partial pressure of carbon dioxide (paCO2). Arterio-venous difference in oxygen concentration (avDO2) and approximated cerebral metabolic rate of oxygen (aCMRO2) were calculated for each paCO2 state. Linear models were fitted to test changes of end points in response to paCO2 and propofol concentration.

RESULTS

In comparison to the lower levels of paCO2, higher levels of paCO2 increased rvCBF (P<0.001), and srvO2 (P=0.002). RvHb remained unchanged during measurements (P=0.325). Calculated avDO2 decreased with increasing paCO2 (P<0.001), whereas aCMRO2 did not change during the study (P=0.999). Propofol concentration had no effect on measured or calculated end points.

CONCLUSIONS

Increase of rvCBF by paCO2 indicates a preserved CO2 reactivity independent of propofol anesthesia. The consecutive rise in srvO2 implies enhanced oxygen availability due to vasodilatation. Unchanged rvHb represents constant venous hemoglobin concentration. As expected, calculated avDO2 decreases with increased paCO2, whereas aCMRO2 remains unchanged. Despite the promising technical approach, the technology needs validation and further investigation for usage during neurosurgery.

Achilles tendon suture deteriorates tendon capillary blood flow with sustained tissue oxygen saturation - an animal study

BACKGROUND

Treatment of ruptured Achilles tendons currently constitutes of conservative early functional treatment or surgical treatment either by open or minimal invasive techniques. We hypothesize that an experimental Achilles tendon suture in an animal model significantly deteriorates Achilles tendon microcirculation immediately following suturing.

METHODS

Fifteen Achilles tendons of eight male Wistar rats (275-325 g) were included. After preparation of the Achilles tendon with a medial paratendinous approach, Achilles tendon microcirculation was assessed using combined Laser-Doppler and spectrophotometry (Oxygen-to-see) regarding:- tendinous capillary blood flow [arbitrary units AU]- tendinous tissue oxygen saturation [%]- tendinous venous filling pressure [rAU]The main body of the Achilles tendon was measured in the center of the suture with 50 Hz. 10 minutes after Achilles tendon suture (6-0 Prolene), a second assessment of microcirculatory parameters was performed.

RESULTS

Achilles tendon capillary blood flow decreased by 57% following the suture (70 +/- 30 AU vs. 31 +/- 16 AU; p < 0.001). Tendinous tissue oxygen saturation remained at the same level before and after suture (78 +/- 17% vs. 77 +/- 22%; p = 0.904). Tendinous venous filling pressure increased by 33% (54 +/- 16 AU vs. 72 +/- 20 AU; p = 0.019) after suture.

CONCLUSION

Achilles tendon suture in anaesthetised rats causes an acute loss of capillary perfusion and increases postcapillary venous filling pressures indicating venous stasis. The primary hypothesis of this study was confirmed. In contrast, tendinous tissue oxygen saturation remains unchanged excluding acute intratendinous hypoxia within the first 10 minutes after suture. Further changes of oxygen saturation remain unclear. Furthermore, it remains to be determined to what extent reduced capillary blood flow as well as increased postcapillary stasis might influence tendon healing from a microcirculatory point of view in this animal setting.

Microcirculatory parameters after isotonic and hypertonic colloidal fluid resuscitation in acute hemorrhagic shock

BACKGROUND

Volume resuscitation is one of the primary therapeutic goals in hemorrhagic shock, but data on microcirculatory effects of different colloidal fluid resuscitation regimen are sparse. We investigated sublingual mucosal microcirculatory parameters during hemorrhage and after fluid resuscitation with gelatin, hydroxyethyl starch, or hypertonic saline and hydroxyethyl starch in pigs.

METHODS

To induce hemorrhagic shock, 60% of calculated blood volume was withdrawn. Microvascular blood flow was assessed by laser Doppler velocimetry. Microcirculatory hemoglobin oxygen saturation was measured with a tissue reflectance spectrophotometry, and side darkfield imaging was used to visualize the microcirculation and to quantify the flow quality. Systemic hemodynamic variables, systemic acid base and blood gas variables, and lactate measurements were recorded. Measurements were performed at baseline, after hemorrhage, and after fluid resuscitation with a fixed volume regimen.

RESULTS

Systemic hemodynamic parameters returned or even exceeded to baseline values in all three groups after fluid resuscitation, but showed significantly higher filling pressures and cardiac output values in animals treated with isotonic colloids. Microcirculatory parameters determined in gelatin and hydroxyethyl starch resuscitated animals, and almost all parameters except microvascular hemoglobin oxygen saturation in animals treated with hypertonic saline and hydroxyethyl starch, were restored after treatment.

DISCUSSION

Hemorrhaged pigs can be hemodynamically stabilized with either isotonic or hypertonic colloidal fluids. The main finding is an adequate restoration of sublingual microcirculatory blood flow and flow quality in all three study groups, but only gelatin and hydroxyethyl starch improved microvascular hemoglobin oxygen saturation, indicating some inadequate oxygen supply/demand ratio maybe due to a better restoration of systemic hemodynamics in isotonic colloidal resuscitated animals.

Reliability of lightguide spectrophotometry (O2C) for the investigation of skin tissue microvascular blood flow and tissue oxygen supply in diabetic and nondiabetic subjects

BACKGROUND AND AIMS

Skin microvascular assessment has progressed to an important evaluation in patients with diabetes mellitus. This study was done to evaluate a new device using micro-lightguide spectrophotometry in the assessment of skin microvascular function.

MATERIAL AND METHODS

Twenty nondiabetic subjects (age 46.6 +/- 14.8 years; mean +/- SD) and 20 diabetic patients (age 59.4 +/- 8.4 years) participated in repeated microvascular measurements using micro-lightguide spectrophotometry. This technique allows simultaneous, noninvasive measurement of microvascular blood flow and hemoglobin oxygenation (SO(2)) at the same anatomical area in different tissue layers. A skin probe was placed on nonhairy skin at the thenar eminence of the left hand for the measurement of SO(2), and the postischemic reactive hyperemia response (PRH) was measured in skin and underlying muscle tissue.

RESULTS

Repeated measurements in PRH revealed a good correlation at the superficial skin layer (r = 0.97, p < 0.0001) with a coefficient of variation at 9.2 +/- 1.7% and at the superficial muscle layer (r = 0.80, p < 0.0002) with a coefficient of variation at 9.7 +/- 1.5%. A slightly weaker correlation was observed for the SO(2) measurement at the skin layer (r = 0.69 +/- p < 0.0001) with a coefficient of variation at 17.5 +/- 3.8% and at the muscle layer (r = 0.48; p = 0.0016) with a coefficient of variation at 18.1 +/- 10.5%.

CONCLUSIONS

Lightguide spectrophotometry is an easy, noninvasive, and reliable method for simultaneous measurement of superficial microvascular blood flow by laser Doppler fluxmetry and skin oxygenation by spectrophotometry. Further studies are required to clarify the validity of these measures in special patient populations such as diabetes mellitus with specified microvascular complications.