Changes In Tissue Oxygenation Research Articles

Tissue Perfusion Changes after Direct and Indirect Angiosome Revascularization in Critical Limb Ischemia

Background. Blood flow restore in critical limb ischemia according to angiosomes is becoming very popular. This method allows to restore blood flow precisely to the artery supplying the ischemic zone, based on the angiosome concept. However, angiosome revascularization is not a gold standard because of the lack of evidence supporting this approach. The aim of this study was to compare tissue oxygenation changes in ischemic zone during endovascular revascularization procedure either following angiosome concept or performing indirect revascularization. Methods. A prospective observational study was performed. Patients with critical limb ischemia and tissue loss due to chronic total occlusion of below the knee arteries were included. Endovascular revascularization was performed in all cases. Tissue oxygen saturation was observed intraoperatively using near-infrared spectroscopy. Tissue oxygenation changes near the ischemic wound were compared between direct and indirect revascularization groups. Results. This clinical trial included 30 patients with critical limb ischemia (Rutherford 5) and occluded below the knee arteries intended to treat. In 15 patients the procedure was performed according to angiosome, while the other half underwent indirect revascularization. Tissue oxygenation near the wound was monitored during the intervention. Greater oxygen saturation increase was observed in the group with direct revascularization (29% and 23% accordingly), however the difference between groups was not statistically significant (t-test for independent group, p = 0,544). Conclusions. The increase in tissue oxygen saturation differed very slightly in direct and indirect revascularization groups and the difference was statistically insignificant.

Myocardial Tissue Oxygenation and Microvascular Blood Volume Measurement Using a Contrast Blood Oxygenation Level-Dependent Imaging Model.

We propose a method of quantitatively measuring drug-induced microvascular volume changes, as well as drug-induced changes in blood oxygenation using calibrated blood oxygen level-dependent magnetic resonance imaging (MRI). We postulate that for MRI signals there is a contribution to R2* relaxation rates from static susceptibility effects of the intravascular blood that scales with the blood volume/magnetic field and depends on the oxygenation state of the blood. These may be compared with the effects of an intravascular contrast agent. With 4 R2* measurements, microvascular blood volume (MBV) and tissue oxygenation changes can be quantified with the administration of a vasoactive drug. The protocol examined 12 healthy rats in a prospective observational study. R2* maps were acquired with and without infusion of adenosine, which increases microvascular blood flow, or dobutamine, which increases myocardial oxygen consumption. In addition, R2* maps were acquired after the intravenous administration of a monocrystalline iron oxide nanoparticle, with and without adenosine or dobutamine. Total microvascular volume was shown to increase by 10.8% with adenosine and by 25.6% with dobutamine ( P < 0.05). When comparing endocardium versus epicardium, both adenosine and dobutamine demonstrated significant differences between endocardial and epicardial MBV changes ( P < 0.05). Total myocardial oxygenation saturation increased by 6.59% with adenosine and by 1.64% with dobutamine ( P = 0.27). The difference between epicardial and endocardial oxygenation changes were significant with each drug (adenosine P < 0.05, dobutamine P < 0.05). Our results demonstrate the ability to quantify microvascular volume and oxygenation changes using calibrated blood oxygen level-dependent MRI, and we demonstrate different responses of adenosine and dobutamine. This method has clinical potential in examining microvascular disease in various disease states without the administration of radiopharmaceuticals or gadolinium-based contrast agents.

Impact of Medical Treatment of Hemodynamically Significant Patent Ductus Arteriosus on Cerebral and Renal Tissue Oxygenation Measured by Near-Infrared Spectroscopy in Very Low-Birth-Weight Infants.

Background and objective: Hemodynamically significant patent ductus arteriosus (hsPDA) can cause ductal steal and contribute to poor outcomes in preterm infants. Near-infrared spectroscopy (NIRS) allows us to continuously evaluate regional tissue oxygenation (rSpO2) and perfusion changes in underlying organs. The aim of this study was to evaluate the effect of medical treatment for hsPDA on cerebral and renal rSpO2 in infants less than 32 weeks of gestational age, and older than 72 h of life. Materials and methods: Infants with a gestational age of <32 weeks with hsPDA were prospectively studied before and during medical treatment. Two-site (cerebral and renal) rSpO2 monitoring by NIRS was performed 1 h before treatment (T0) and 24 h (T1), 24–48 h (T2), 48–72 h (T3) after the infusion of the first drug dose. Results: A total of 21 infants were studied. The mean day of life at treatment initiation was 8.2 (SD, 2.75). The DA diameter, LA/Ao ratio, and resistive index in the anterior cerebral artery (RI ACA) were significantly lower after treatment (p < 0.05). There were no significant differences in cerebral rSpO2, cerebral fractional tissue oxygen extraction (FTOE), and SpO2 comparing different time points. A significantly higher renal SpO2 value was recorded at T2 as compared with T0 (75.0%, SD 4.9%, vs. 69.4%, SD 7.6%; p < 0.013), while for renal FTOE, a tendency to lower values at T2 was observed (0.18, SD 0.05, vs. 0.24, SD 0.09; p = 0.068). Conclusions: Late (later than 7 days postpartum) hsPDA medical treatment with paracetamol or ibuprofen completely closed the duct only in a small proportion of preterm infants, despite a statistically significant reduction in the DA diameter, LA/Ao ratio, and RI ACA. Continuous renal, not cerebral, NIRS measurements can help to anticipate the efficacy of medical treatment of hsPDA in preterm infants. Large-scale prospective studies are needed to ascertain that renal and cerebral NIRS can be used as a reliable tool for evaluating the effectiveness of medical treatment for hsPDA.

Factors Associated With Brain Tissue Oxygenation Changes After RBC Transfusion in Acute Brain Injury Patients.

Anemia is common after acute brain injury and can be associated with brain tissue hypoxia. RBC transfusion (RBCT) can improve brain oxygenation; however, predictors of such improvement remain unknown. We aimed to identify the factors associated with PbtO2 increase (greater than 20% from baseline value) after RBCT, using a generalized mixed model. This is a multicentric retrospective cohort study (2012-2020). This study was conducted in three European ICUs of University Hospitals located in Belgium, Switzerland, and Austria. All patients with acute brain injury who were monitored with brain tissue oxygenation (PbtO2) catheters and received at least one RBCT. Patients received at least one RBCT. PbtO2 was recorded before, 1 hour, and 2 hours after RBCT. We included 69 patients receiving a total of 109 RBCTs after a median of 9 days (5-13 d) after injury. Baseline hemoglobin (Hb) and PbtO2 were 7.9 g/dL [7.3-8.7 g/dL] and 21 mm Hg (16-26 mm Hg), respectively; 2 hours after RBCT, the median absolute Hb and PbtO2 increases from baseline were 1.2 g/dL [0.8-1.8 g/dL] (p = 0.001) and 3 mm Hg (0-6 mm Hg) (p = 0.001). A 20% increase in PbtO2 after RBCT was observed in 45 transfusions (41%). High heart rate (HR) and low PbtO2 at baseline were independently associated with a 20% increase in PbtO2 after RBCT. Baseline PbtO2 had an area under receiver operator characteristic of 0.73 (95% CI, 0.64-0.83) to predict PbtO2 increase; a PbtO2 of 20 mm Hg had a sensitivity of 58% and a specificity of 73% to predict PbtO2 increase after RBCT. Lower PbtO2 values and high HR at baseline could predict a significant increase in brain oxygenation after RBCT.

Abstract 89: Nimodipine-induced Blood Pressure Reductions Below Personalized Limits Of Autoregulation Are Associated With Worse Outcomes After Subarachnoid Hemorrhage

Background: Impairment of cerebral autoregulation after subarachnoid hemorrhage (SAH) makes patients vulnerable to changes in blood pressure (BP). While oral nimodipine is recommended for improving neurological outcomes, its administration is frequently associated with reductions in BP. In this observational study, we examined the effect of nimodipine-induced BP reductions below personalized limits of autoregulation on outcome after aneurysmal SAH. Methods: Autoregulatory function was continuously measured by interrogating changes in near-infrared spectroscopy-derived tissue oxygenation (a cerebral blood flow surrogate) in response to changes in mean arterial pressure (MAP). The resulting autoregulatory index was used for trending the BP range at which autoregulation was most preserved. Cerebral hypoperfusion was defined as episodes with at least 30 minutes of MAP reductions below the lower limit of autoregulation (LLA) following nimodipine administration (Fig. 1). Functional outcome was measured with the modified Rankin Scale at 90 days. Results: We identified 593 occurrences of nimodipine administration with simultaneous recording of continuous physiologic data for 60 minutes before and after the intervention among 26 SAH patients (mean age 57 + 14, 21 F). Following nimodipine administration, the mean MAP decreased from 103 to 98 mmHg (p&lt;0.001), and the time with MAP below the LLA increased from 9.5 to 21.7% (p&lt;0.001). Moreover, the proportion of episodes with cerebral hypoperfusion was associated with worse 90-day outcomes after adjusting for age and SAH severity (OR for 10% increase 1.5, 95% CI 1.2-2.2, P=0.038). Conclusions: Nimodipine-induced BP reductions below the LLA may increase the risk of secondary brain injury and poor functional outcomes. A more personalized treatment approach accounting for cerebral autoregulation status could help identify vulnerable patients and maximize the benefit from current clinical interventions.

Oxyhaemoglobin Level Measured Using Near-Infrared Spectrometer Is Associated with Brain Mitochondrial Dysfunction After Cardiac Arrest in Rats.

Cerebral blood oxygenation (CBO), measured using near-infrared spectroscopy (NIRS), can play an important role in post-cardiac arrest (CA) care as this emerging technology allows for noninvasive real-time monitoring of the dynamic changes of tissue oxygenation. We recently reported that oxyhaemoglobin (oxy-Hb), measured using NIRS, may be used to evaluate the quality of chest compressions by monitoring the brain tissue oxygenation, which is a critical component for successful resuscitation. Mitochondria are the key to understanding the pathophysiology of post-CA oxygen metabolism. In this study, we focused on mitochondrial dysfunction, aiming to explore its association with CBO parameters such as oxy-Hb and deoxyhaemoglobin (deoxy-Hb) or tissue oxygenation index (TOI). Male Sprague-Dawley rats were used in the study. We applied NIRS between the nasion and the upper cervical spine. Following 10 min of CA, the rats underwent cardiopulmonary resuscitation (CPR) with a bolus injection of 20μg/kg epinephrine. At 10 and 20 min after CPR, brain, and kidney tissues were collected. We isolated mitochondria from these tissues and evaluated the association between CBO and mitochondrial oxygen consumption ratios. There were no significant differences in the mitochondrial yields (10 vs. 20 min after resuscitation: brain, 1.33±0.68 vs. 1.30±0.75mg/g; kidney, 19.5±3.2 vs. 16.9±5.3mg/g, respectively). State 3 mitochondrial oxygen consumption rates, known as ADP-stimulated respiration, demonstrated a significant difference at 10 vs. 20 min after CPR (brain, 170±26 vs. 115±17nmol/min/mg protein; kidney, 170±20 vs. 130±16nmol/min/mg protein, respectively), whereas there was no significant difference in ADP non-dependent state 4 oxygen consumption rates (brain, 34.0±6.7 vs. 31.8±10nmol/min/mg protein; kidney, 29.8±4.8 vs. 21.0±2.6nmol/min/mg protein, respectively). Consequently, the respiratory control ratio (RCR=state 3/state 4) showed a significant difference over time, but this was only noted in the brain (brain, 5.0±0.29 vs. 3.8±0.64; kidney, 5.8±0.53 vs. 6.2±0.25nmol/min/mg protein, respectively). The oxy-Hb levels had a dynamic change after resuscitation, and they had a significant association with the RCR of the brain mitochondria (r=0.8311, p=0.0102), whereas deoxy-Hb and TOI did not (r=-0.1252, p=0.7677; r=0.4186, p=0.302, respectively). The RCRs of the kidney mitochondria did not have a significant association with CBO (oxy-Hb, r=-0.1087, p=0.7977; deoxy-Hb, r=0.1565, p=0.7113; TOI, r=-0.1687, p=0.6896, respectively). The brain mitochondrial respiratory dysfunction occurred over time, and it was seen at the time points between 10 and 20 min after CPR. The oxy-Hb level was associated with brain mitochondrial dysfunction during the early post-resuscitation period.

Upper Trapezius Muscle Tonicity, Assessed by Palpation, Relates to Change in Tissue Oxygenation and Structure as Measured byTime-Domain Near Infrared Spectroscopy.

Palpation is a diagnostic tool widely used by manual therapists despite its disputed reliability and validity. Previous studies have usually focused on the detection of myofascial trigger points (MTrPs), i.e., the points within muscles thought to have undergone molecular composition, oxygenation and structural changes, altering their tonicity. Time-domain near-infrared spectroscopy (TD-NIRS) could provide new insights into soft tissue oxygenation and structure, in order to objectively assess the validity and reliability of palpation. This pilot study aims at (1) assessing the ability of TD-NIRS to detect a difference between palpably normal and hypertonic upper trapezius (UT) muscles, and (2) to estimate the reproducibility of the TD-NIRS measurement on UT muscles. TD-NIRS measurements were performed on 4 points of the UT muscles in 18 healthy participants (10F, mean age: 27.6years), after a physical examination by a student osteopath to locate these points and identify the most and least hypertonic. From TD-NIRS, the most hypertonic points had a higher concentration in deoxy- ([HHb]) (0.887±0.253μM, p<0.001) and total haemoglobin ([HbT]) (1.447±0.772μM, p<0.001), a lower tissue oxygen saturation (StO2) (-0.575±0.286%, p<0.001), and a greater scattering amplitude factor (AF) (0.2238±0.1343 cm-1, p=0.001) than the least hypertonic points. Moreover, the intraclass correlation coefficient one-way random-effects model (ICC (1,1)) calculated for each TD-NIRS parameter and for each point revealed an excellent reliability of the measurement (Mean±SD, 0.9253±0.0678). These initial results, showing that changes in TD-NIRS parameters correlate with changes in muscle tonicity as assessed by palpation, are encouraging and show that TD-NIRS could help to further assess the validity of palpation as a diagnostic tool in manual therapy.

Comparison of functional activation responses from the auditory cortex derived using multi-distance frequency domain and continuous wave near-infrared spectroscopy.

.Significance: Quantitative measurements of cerebral hemodynamic changes due to functional activation are widely accomplished with commercial continuous wave (CW-NIRS) instruments despite the availability of the more rigorous multi-distance frequency domain (FD-NIRS) approach. A direct comparison of the two approaches to functional near-infrared spectroscopy can help in the interpretation of optical data and guide implementations of diffuse optical instruments for measuring functional activation.Aim: We explore the differences between CW-NIRS and multi-distance FD-NIRS by comparing measurements of functional activation in the human auditory cortex.Approach: Functional activation of the human auditory cortex was measured using a commercial frequency domain near-infrared spectroscopy instrument for 70 dB sound pressure level broadband noise and pure tone (1000 Hz) stimuli. Changes in tissue oxygenation were calculated using the modified Beer–Lambert law (CW-NIRS approach) and the photon diffusion equation (FD-NIRS approach).Results: Changes in oxygenated hemoglobin measured with the multi-distance FD-NIRS approach were about twice as large as those measured with the CW-NIRS approach. A finite-element simulation of the functional activation problem was performed to demonstrate that tissue oxygenation changes measured with the CW-NIRS approach is more accurate than that with multi-distance FD-NIRS.Conclusions: Multi-distance FD-NIRS approaches tend to overestimate functional activation effects, in part due to partial volume effects.

2.5 Hz sample rate time-domain near-infrared optical tomography based on SPAD-camera image tissue hemodynamics.

Time-domain near-infrared optical tomography (TD NIROT) techniques based on diffuse light were gaining performance over the last years. They are capable of imaging tissue at several centimeters depth and reveal clinically relevant information, such as tissue oxygen saturation. In this work, we present the very first in vivo results of our SPAD camera-based TD NIROT reflectance system with a temporal resolution of ∼116 ps. It provides 2800 time of flight source-detector pairs in a compact probe of only 6 cm in diameter. Additionally, we describe a 3-step reconstruction procedure that enables accurate recovery of structural information and of the optical properties. We demonstrate the system's performance firstly in reconstructing the 3D-structure of a heterogeneous tissue phantom with tissue-like scattering and absorption properties within a volume of 9 cm diameter and 5 cm thickness. Furthermore, we performed in vivo tomography of an index finger located within a homogeneous scattering medium. We employed a fast sampling rate of 2.5 Hz to detect changes in tissue oxygenation. Tomographic reconstructions were performed in true 3D, and without prior structural information, demonstrating the powerful capabilities of the system. This shows its potential for clinical applications.

Hyperspectral Imaging for the Evaluation of Microcirculatory Tissue Oxygenation and Perfusion Quality in Haemorrhagic Shock: A Porcine Study.

Background: The ultimate goal of haemodynamic therapy is to improve microcirculatory tissue and organ perfusion. Hyperspectral imaging (HSI) has the potential to enable noninvasive microcirculatory monitoring at bedside. Methods: HSI (Tivita® Tissue System) measurements of tissue oxygenation, haemoglobin, and water content in the skin (ear) and kidney were evaluated in a double-hit porcine model of major abdominal surgery and haemorrhagic shock. Animals of the control group (n = 7) did not receive any resuscitation regime. The interventional groups were treated exclusively with either crystalloid (n = 8) or continuous norepinephrine infusion (n = 7). Results: Haemorrhagic shock led to a drop in tissue oxygenation parameters in all groups. These correlated with established indirect markers of tissue oxygenation. Fluid therapy restored tissue oxygenation parameters. Skin and kidney measurements correlated well. High dose norepinephrine therapy deteriorated tissue oxygenation. Tissue water content increased both in the skin and the kidney in response to fluid therapy. Conclusions: HSI detected dynamic changes in tissue oxygenation and perfusion quality during shock and was able to indicate resuscitation effectivity. The observed correlation between HSI skin and kidney measurements may offer an estimation of organ oxygenation impairment from skin monitoring. HSI microcirculatory monitoring could open up new opportunities for the guidance of haemodynamic management.

Hyperspectral imaging for perioperative monitoring of microcirculatory tissue oxygenation and tissue water content in pancreatic surgery \u2014 an observational clinical pilot study

BackgroundHyperspectral imaging (HSI) could provide extended haemodynamic monitoring of perioperative tissue oxygenation and tissue water content to visualize effects of haemodynamic therapy and surgical trauma. The objective of this study was to assess the capacity of HSI to monitor skin microcirculation and possible relations to perioperative organ dysfunction in patients undergoing pancreatic surgery.MethodsThe hyperspectral imaging TIVITA® Tissue System was used to evaluate superficial tissue oxygenation (StO2), deeper layer tissue oxygenation (near-infrared perfusion index (NPI)), haemoglobin distribution (tissue haemoglobin index (THI)) and tissue water content (tissue water index (TWI)) in 25 patients undergoing pancreatic surgery. HSI parameters were measured before induction of anaesthesia (t1), after induction of anaesthesia (t2), postoperatively before anaesthesia emergence (t3), 6 h after emergence of anaesthesia (t4) and three times daily (08:00, 14:00, 20:00 ± 1 h) at the palm and the fingertips until the second postoperative day (t5–t10). Primary outcome was the correlation of HSI with perioperative organ dysfunction assessed with the perioperative change of SOFA score.ResultsTwo hundred and fifty HSI measurements were performed in 25 patients. Anaesthetic induction led to a significant increase of tissue oxygenation parameters StO2 and NPI (t1–t2). StO2 and NPI decreased significantly from t2 until the end of surgery (t3). THI of the palm showed a strong correlation with haemoglobin levels preoperatively (t2:r = 0.83, p < 0.001) and 6 h postoperatively (t4: r = 0.71, p = 0.001) but not before anaesthesia emergence (t3: r = 0.35, p = 0.10). TWI of the palm and the fingertip rose significantly between pre- and postoperative measurements (t2–t3). Higher blood loss, syndecan level and duration of surgery were associated with a higher increase of TWI. The perioperative change of HSI parameters (∆t1–t3) did not correlate with the perioperative change of the SOFA score.ConclusionThis is the first study using HSI skin measurements to visualize tissue oxygenation and tissue water content in patients undergoing pancreatic surgery. HSI was able to measure short-term changes of tissue oxygenation during anaesthetic induction and pre- to postoperatively. TWI indicated a perioperative increase of tissue water content. Perioperative use of HSI could be a useful extension of haemodynamic monitoring to assess the microcirculatory response during haemodynamic therapy and major surgery.Trial registrationGerman Clinical Trial Register, DRKS00017313 on 5 June 2019

Feasibility of umbilical cord blood as a source of red blood cell transfusion in preterm infants.

Preterm infants born earlier than 32 weeks of gestational age (GA) often need red blood cell (RBC) transfusions, which have been associated with an increased incidence of complications of prematurity, due to changes in tissue oxygenation. Transfusion of umbilical cord blood (UCB) could be beneficial for this group. The aims of this study were: (i) to determine the RBC transfusion needs in infants <32 weeks in Hospital Clinic of Barcelona; (ii) to identify the target GA group that would benefit most from UCB transfusion; and (iii) to assess the current availability of UCB as a potential source of RBC transfusion for these premature infants in our tertiary referral blood bank. A retrospective observational study was performed on infants born at <32 weeks GA, divided into two groups: (i) extremely low gestational age neonates (ELGAN) (from 230 to 276 weeks) and (ii) very preterm neonates (VPN) (from 280 to 316 weeks). Their complications and transfusion rates were compared. Processing and availability of UCB samples in the reference blood bank were assessed. Overall, 1,651 infants <32 weeks GA were admitted in the study period. While 12.5% of VPN received at least one RBC transfusion, the percentage increased to 60% among the ELGAN. Retinopathy of prematurity and bronchopulmonary dysplasia were diagnosed more frequently in the ELGAN group (p<0.001) than in the VPN group. The annual average volume of RBC transfusion in our study group was 1.35 L (95% CI: 1.07-1.64). The reference blood bank was able to produce 16 L (95% CI: 14-18) of UCB-RBC per year. Considering the data obtained about RBC transfusion needs and morbidities, the ELGAN group has been identified as the target group that would benefit most from UCB-RBC transfusions. We have demonstrated that our blood bank is able to produce enough RBC from UCB. Randomised control trials are warranted to study the potential benefits of UCB compared to adult blood for RBC transfusions.

Geoff Burnstock, purinergic signalling, and chemosensory control of breathing.

This article is the authors' contribution to the tribute issue in honour of Geoffrey Burnstock, the founder of this journal and the field of purinergic signalling. We give a brief account of the results of experimental studies which at the beginning received valuable input from Geoff, who both directly and indirectly influenced our research undertaken over the last two decades. Research into the mechanisms controlling breathing identified ATP as the common mediator of the central and peripheral chemosensory transduction. Studies of the sources and mechanisms of chemosensory ATP release in the CNS suggested that this signalling pathway is universally engaged in conditions of increased metabolic demand by brain glial cells - astrocytes. Astrocytes appear to function as versatile CNS metabolic sensors that detect changes in brain tissue pH, CO2, oxygen, and cerebral perfusion pressure. Experimental studies on various aspects of astrocyte biology generated data indicating that the function of these omnipresent glial cells and communication between astrocytes and neurons are governed by purinergic signalling, - first discovered by Geoff Burnstock in the 70's and researched through his entire scientific career.

Impact of Stellate Ganglion Block on Tissue Blood Flow/Oxygenation and Postoperative Mandibular Nerve Hypoesthesia: A Cohort Study

Although a stellate ganglion block (SGB) increases tissue blood flow in the mandibular region, the change in tissue oxygenation after SGB and therapeutic effect of SGB for postoperative mandibular nerve hypoesthesia remain to be established. The study aim was to measure the change in tissue oxygenation in the mandibular region after SGB. To determine the variation in tissue oxygenation in the mandibular region, the tissue oxygen index (TOI; percentage of oxygenated hemoglobin in the total hemoglobin) was measured at the skin near the mental foramen bilaterally, at the primary site of unilateral SGB, achieved using 6 mL of 1% lidocaine hydrochloride, for the treatment of bilateral postoperative mandibular nerve injury. The primary outcome of this study is the temporal variation in TOI after SGB (0.5, 1, 5, 10, 15, 20, and 25 minutes after SGB), and the control group in this study is the TOI at the end of SGB injection (0 minute). All data are expressed as the mean ± standard deviation and 95% confidence interval (CI). Repeated-measures analysis of variance with Dunnett's test was used to determine parametric statistical significance. A P-value <.05 was considered statistically significant. Thirteen patients were enrolled in this study. On both the blocked and contralateral side, the TOI was significantly increased compared to that before SGB (ΔTOI at 15 minute after SGB, 5.87 ± 2.89%, P < .001, 95% CI: 4.122 to 7.617% in the blocked side, 1.88 ± 2.73%, P=.005, 95% CI: 1.877 to 2.725% in the contralateral side). Unilateral SGB using 6 mL of 1% lidocaine hydrochloride results in an increase in tissue oxygenation in the mandibular region. Based on these findings, we hypothesize that a series of SGBs may contribute to a more rapid recovery of postoperative trigeminal nerve injury.

A physiological and biomechanical investigation of three passive upper-extremity exoskeletons during simulated overhead work

The objective of this study was to evaluate three passive upper-extremity exoskeletons relative to a control condition. Twelve subjects performed an hour-long, simulated occupational task in a laboratory setting. Independent measures of exoskeleton, exertion height (overhead, head height), time, and their interactions were assessed. Dependent measures included changes in tissue oxygenation (ΔTSI) in the anterior deltoid and middle trapezius, peak resultant lumbar spine loading, and subjective discomfort in various body regions. A statistically significant reduction in ΔTSI between exoskeleton and control was only observed in one instance. Additionally, neither increases in spinal loading nor increases in subjective discomfort ratings were observed for any of the exoskeletons. Ultimately, the exoskeletons offered little to no physiological benefit for the conditions tested. However, the experimental task was not highly fatiguing to the subjects, denoted by low ΔTSI values across conditions. Results may vary for tasks requiring constant arm elevation or higher force demands. Practitioner summary This study quantified the benefits of upper-extremity exoskeletons using NIRS, complementary to prior studies using EMG. The exoskeletons offered little to no physiological benefit for the conditions tested. However, the experimental task was not highly fatiguing, and results may vary for an experimental task with greater demand on the shoulders. Abbreviations: WMSD: work-related musculoskeletal disorder; EMG: electromyography; NIRS: near-infrared spectroscopy; NIR: near-infrared; Hb: haemoglobin; Mb: myoglobin; TSI: tissue saturation index; ATT: adipose tissue thickness

Post-Operative Monitoring of Intestinal Tissue Oxygenation Using an Implantable Microfabricated Oxygen Sensor.

Anastomotic leakage (AL) is a common and dangerous post-operative complication following intestinal resection, causing substantial morbidity and mortality. Ischaemia in the tissue surrounding the anastomosis is a major risk-factor for AL development. Continuous tissue oxygenation monitoring during the post-operative recovery period would provide early and accurate early identification of AL risk. We describe the construction and testing of a miniature implantable electrochemical oxygen sensor that addresses this need. It consisted of an array of platinum microelectrodes, microfabricated on a silicon substrate, with a poly(2-hydroxyethyl methacrylate) hydrogel membrane to protect the sensor surface. The sensor was encapsulated in a biocompatible package with a wired connection to external instrumentation. It gave a sensitive and highly linear response to variations in oxygen partial pressure in vitro, although over time its sensitivity was partially decreased by protein biofouling. Using a pre-clinical in vivo pig model, acute intestinal ischaemia was robustly and accurately detected by the sensor. Graded changes in tissue oxygenation were also measurable, with relative differences detected more accurately than absolute differences. Finally, we demonstrated its suitability for continuous monitoring of tissue oxygenation at a colorectal anastomosis over a period of at least 45 h. This study provides evidence to support the development and use of implantable electrochemical oxygen sensors for post-operative monitoring of anastomosis oxygenation.

(IMCS First Place Best Paper Award) Local Hypoxia System as a Sensing Interface of Cellular Responses

Oxygen concentration is one of the critical factors tightly controlled in each part of an organism to regulate the cells’ role and function. Yet, changes in tissue oxygenation often occur in small focal areas with aging or as a result of an injury. Despite the serious health implications of focal hypoxia, no methodologies exist that can model oxygen supply system accordingly in animal models or in vitro models. Therefore, we designed a novel local hypoxia system as a sensing interface for in vitro cell culture. The oxygen removal efficiencies measured by Clark electrodes showed that O2 concentration can be reduced from 20.9% / 140mmHg or 5% / 35mmHg and maintained at hypoxia (< 1.5% / 10mmHg) in 15 or 8 minutes respectively, compared with 3 hours needed by conventional incubator and hypoxic chambers. The induced hypoxia stimulated localized time-dependent HIF-1α transcription factor nuclear accumulation at the region of interest on human neural progenitor cells. This new culture system can robustly generate a hypoxia gradient in the same culture dish for the first time and provides the opportunity to decipher the impact of focal hypoxia, the function of localised oxygen homeostasis and the pathophysiology of multiple diseases.

Quantifying the Effect of Topical Nitroglycerin on Random Pattern Flap Perfusion in a Rodent Model: An Application of the ViOptix Intra.Ox for Dynamic Flap Perfusion Assessment and Salvage.

Near-infrared spectroscopy can detect changes in tissue oxygenation postoperatively that predict flap necrosis. The authors hypothesized that this technology can be applied along with topical nitroglycerin to measure an improvement in tissue oxygenation that correlates with tissue salvage. Dorsal, random pattern flaps measuring 10 × 3 cm were raised using Sprague-Dawley rats. Tissue oxygenation was measured after flap elevation in 10 locations using the ViOptix Intra.Ox. Animals were divided into three groups that received 30 mg of topical nitroglycerin daily, twice-daily, or not at all. Oxygenation measurements were repeated on postoperative day 1 and animals were euthanized on day 7 and evaluated for tissue necrosis. Tissue necrosis was greatest in controls (51.3 mm) compared to daily (28.8 mm) and twice-daily nitroglycerin (18.8 mm; p = 0.035). Three flap perfusion zones were identified: healthy (proximal, 50 mm), necrotic (distal, 20 mm), and watershed. Immediate postoperative tissue oxygenation was highest in healthy tissue (57.2 percent) and decreased to 33.0 and 19.3 percent in the watershed and necrotic zones, respectively (p < 0.001). One day after treatment with nitroglycerin, oxygenation in the healthy zone did not increase significantly (mean difference, -1.5 percent). The watershed (17.8 percent; p < 0.001) and necrotic zones (16.3 percent; p <0.001) did exhibit significant improvements that were greater than those measured in control tissues (7.9 percent; both p < 0.001). Serial perfusion assessment using the ViOptix Intra.Ox measured a significant improvement in flap oxygenation after treatment with topical nitroglycerin. Within the watershed area of the flap, this increase in tissue oxygenation was associated with the salvage of ischemic tissue.

Wireless Wearable Sensor Paired With Machine Learning for the Quantification of Tissue Oxygenation

The accurate knowledge of tissue oxygenation can be decisive for diagnostic applications in burns, limb injuries, and surgical interventions. Medical devices created for oxygenation measurements require extensive research and complex electronic, optical, and/or chemical techniques that typically result in nonmobile and expensive equipment. We have designed a wireless prototype that can detect changes in tissue oxygenation ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$pO_{2}$ </tex-math></inline-formula> ) making use of simple off-the-shelf electronic components and 3-D printing by measuring the phosphorescence intensity of an oxygen-sensing phosphor. The quantification of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$pO_{2}$ </tex-math></inline-formula> was initially carried out by a phenomenological algorithm composed of a color-compensation matrix, a modified Stern–Volmer relation adding temperature dependence and an explicit photobleaching term. We improved the accuracy of measurement by employing a machine learning approach, which yields readings that are independent of changes in temperature and photobleaching, can be implemented into our data logging software, and potentially into the device’s firmware.

Renal tissue oxygenation after caffeine administration in preterm neonates.

Caffeine has been associated with reduced rates of acute kidney injury (AKI) in preterm neonates. The effect of caffeine on preterm neonatal renal regional saturation of oxygen (RrSO2) is unknown. RrSO2 was recorded continuously in neonates < 32 weeks' gestation until 7 days of age with INVOS™ neonatal near-infrared spectroscopy (NIRS) sensors. Baseline RrSO2 values were established by averaging the saturations in the 20 min prior to caffeine administration. Subgroup analysis was performed based on pre-caffeine RrSO2 averages. Change in RrSO2 was recorded at 0.5, 1, 2, 3, 4, 6, and 12 h after maintenance caffeine administration. Of 35 eligible neonates, 31 (median gestational age 28.4 weeks) received 156 caffeine doses (median 8 mg/kg). Analysis of combined doses showed no significant changes in RrSO2 after caffeine administration at any time. However, neonates with baseline 20-29.9% had significant increases from 1 to 12 h (range of increase 5.9-13.9%), and those with baseline 30-39.9 had significant increases at 1 h (8.06%, p < 0.05). Maintenance caffeine dosing increased RrSO2 in neonates with low RrSO2 in the first week. Further research is needed to determine the effect of loading doses of caffeine and if increases in RrSO2 correlate with improved clinical kidney outcomes. Caffeine administration is associated with increased renal tissue oxygenation in preterm neonates with low baseline values under 40%. The most significant renal tissue oxygenation changes occur in the first 3 h after IV caffeine administration. With recent studies suggesting low RrSO2 values in preterm neonates are associated with AKI, caffeine should be studied as a potential therapeutic for this common and complex morbidity in preterm neonates.