Blood volume vs. deoxygenated NIRS signal: computational analysis of the effects muscle O2 delivery and blood volume on the NIRS signals

Near-infrared spectroscopy (NIRS) signals quantify the oxygenated (ΔHbMbO2) and deoxygenated (ΔHHbMb) heme group concentrations. ΔHHbMb has been preferred to ΔHbMbO2 in evaluating skeletal muscle oxygen extraction because it is assumed to be insensitive to blood volume (BV) changes, but uncertainties exist on this assumption. To analyze this assumption a computational model of oxygen transport and metabolism is used to quantify the effect of O2 delivery and BV changes on the NIRS signals from a canine model of muscle oxidative metabolism (Med.Sci.SportsExerc.,48(10)2013-2020,2016). The computational analysis accounts for microvascular (ΔHbO2, ΔHHb) and extravascular (ΔHMb, ΔHMb) oxygenated and deoxygenated forms. Simulations predicted muscle oxygen uptake and NIRS signal changes well for blood flows ranging from resting to contracting muscle. Additional NIRS signal simulations were obtained in the absence or presence of BV changes corresponding to a heme groups concentration changes (ΔHbMb=0-48μM). Under normal delivery (Q=1.0L kg-1min-1) of contracting muscle, capillary oxygen saturation (SO2) was 62% with capillary ΔHbO2 and ΔHHb of ±41μM for ΔHbMb=0. An increase of BV (ΔHbMb =24mM) caused a ΔHbO2 decrease (16mM) almost twice as much as the increase observed for ΔHHb (9μM). When SO2 increased to more than 80%, only ΔHbO2 was significantly affected by BV changes. The analysis indicates that microvascular SO2 is a key factor in determining the sensitivity of ΔHbMbO2 and ΔHHbMb to BV changes. Contrary to a common assumption, the ΔHHbMb is affected by BV changes in normal contracting muscle and even more in the presence of impaired O2 delivery.

Near infrared spectroscopy and optical coherence tomography derived plaque characteristics associated with increased plaque progression over 12-month follow up

Background Serial intravascular ultrasound (IVUS) studies demonstrated patterns of either plaque progression, regression or stabilization during pharmacotherapy including statin. At present little is known on specific plaque characteristics that are associated with excessive plaque growth. Purpose To evaluate the utility of near infrared spectroscopy (NIRS) and optical coherence tomography (OCT) to identify characteristics of non-culprit plaques associated with an increase in wall thickness (WT). Methods In this prospective, single-center study, patients with acute coronary syndrome (ACS) underwent, after successful treatment of the culprit lesions, both NIRS-IVUS and OCT assessment of a non-culprit artery at baseline and 12-month follow-up. For each vessel, 1.5-mm segments were identified, matched and divided into 45° sectors. A sector was considered as NIRS positive or labeled as OCT-detected fibrous cap atheroma (FCA), lipid rich or fibrous plaque when >75% of the sector area exhibited NIRS signal or specific OCT-detected feature. The relationship between change in IVUS-based WT, and the presence of NIRS positive signal or OCT-detected plaque components (FCA, lipid rich, fibrous) was evaluated using mixed ANCOVA, with NIRS status and OCT plaque components as fixed factors, and patient as random factor, adjusting for clustering effect of the data. All analyses of plaque WT change were adjusted for baseline WT. To examine the value of NIRS and OCT-detected plaque components in predicting plaque progression, a logistic mixed model was built with plaque progression defined as WT increase >0.2mm over the 12-month follow-up. Results A total of 38 patients (92% male, 21% diabetic) with 9167 matched sectors were analyzed at baseline and 12 months. Mean change in WT between baseline and 12 months was 0.014mm (95% confidence interval [CI] 0.011–0.018, p<0.001). Positive NIRS sectors showed more pronounced plaque progression than NIRS negative sectors (0.057mm, 95% CI 0.032–0.084 vs 0.014mm 95% CI 0.010–0.017, p=0.001) (Figure 1). FCA showed significant progression of WT over the 12-month follow-up (0.104mm, 95% CI 0.007–0.201), whereas a decrease in WT was observed in sectors with fibrous tissue (−0.031mm, 95% CI 0.048–0.014) (p=0.022). Baseline NIRS positive (OR 1.88, 95% CI 1.34–2.64) and OCT-detected lipid rich plaque (OR 1.47, 95% CI 1.20–1.81) were associated with 12-month plaque progression (>0.2mm) by logistic regression. Conclusions Positive NIRS signal and OCT-detected lipid plaque components imaged at baseline in non-culprit coronary arteries of patients presenting with ACS could identify vessel wall regions prone to plaque progression over a 12-month period. Figure 1. Plaque progression and NIRS Funding Acknowledgement Type of funding source: Other. Main funding source(s): M. Tomaniak acknowledges funding received as a Laureate of the European Society of Cardiology Research and Training Programme in the form of the ESC 2018 Grant.

Abstract 258: The Effect of Chest Compression Location on Cerebral Oxygenation

Introduction: This study examined the effect of guideline-compliant compressions performed on two locations of the chest on changes in cerebral oxygenation as measured by NIRS. We hypothesized that compressions performed over the left ventricle (LV) would produce higher levels of cerebral oxygenation than over the left ventricular outflow tract (LVOT) despite both types of compressions being within recommended guidelines. Methods: LV and LVOT compression locations were identified on the chest using trans-esophageal ultrasound in 9 domestic swine. Following 6 minutes of untreated VF, 1-inch mechanical compressions were initiated at 100 cpm and depth was increased to 2 inches over the course of 1 min. Four 2-min periods of compressions were then performed alternating between the two chest locations, with periods separated by a 10 second pause. Animals were block randomized to start with either LV or LVOT locations. Following the fourth round of compressions, epinephrine was administered followed by up to three defibrillation attempts. Changes in cerebral oxygenation were quantified using the slope of the NIRS signal during each 2-min compression period. One animal was excluded from the analysis due to a ruptured right atrium during the first round of compressions. Results: The mean increase in the cerebral oxygenation signal was 1.8% units (95% CI: 0.9-2.7) during each 2-min period of LV compressions and 1.4% units (95% CI: 0.3 - 2.5) during LVOT compressions. Five out of nine animals achieved ROSC. The mean increase for animals that achieved ROSC was 2.4% units (95% CI: 1.2 - 3.6) during LV compressions and 2.1% units (95 CI: 0.64 - 3.6) during LVOT compressions. For those that did not achieve ROSC, the increase was 0.98% units (95% CI: -0.83 - 2.8) during LV compressions and -0.28 (95% CI: -1.6 - 1.1) during LVOT compressions. Conclusions: There does not appear to be an effect of chest compression location on cerebral oxygenation during mechanical CPR. However, increases in cerebral oxygenation appear to be greater in animals that achieved ROSC. Monitoring changes in cerebral oxygenation over a period of CPR may serve as an index of chest compression effectiveness.

Association Between Fatty Acids Profile and Cerebral Blood Flow: An Exploratory fNIRS Study on Children with and without ADHD

Polyunsaturated fatty acids (PUFAs) biostatus has been proposed as possible attention deficit hyperactivity disorder (ADHD) diagnosis biomarker. The present exploratory study aimed to investigate the association between PUFAs biostatus and cerebral cortex metabolism measured by functional Near Infrared Spectroscopy (fNIRS) in a sample of children with and without ADHD. 24 children with ADHD and 22 typically developing (TD) peers, aged 8–14, were recruited. Linoleic, arachidonic, docosahexaenoic and eicosapentaenoic acids levels were evaluated in whole blood. All children underwent fNIRS while performing an n-back working memory task. Between groups comparisons revealed lower levels of arachidonic acid in children with ADHD and stronger NIRS signal in TD participants, especially when completing more difficult tasks. Correlations conducted between fNIRS activation and PUFA biostatus revealed several associations between hemodynamic changes in the frontoparietal regions and fatty acids profile across participants. This result was also confirmed by the multiple hierarchical regression analyses that remarked an inverse effect of eicosapentaenoic acid levels on oxyhemoglobin values in right frontoparietal region. Such preliminary findings, if confirmed, would suggest that PUFAs could play a role in atypical neurodevelopment.

Psychophysiological Responses to Stress Related to Anxiety in Healthy Aging

The aim of the study was to explore the effects of situational stress and anxiety in a group of healthy elderly, both in terms of psychophysiological correlates and cognitive performance. Eighteen participants ( Mage = 70 ± 6.3; range 60–85) were assessed for anxiety and were instructed to perform a computerized math task, under both a stressful and a control condition, while near-infrared spectroscopy (NIRS) signal and electrocardiography (ECG) were recorded. NIRS results evidenced an increased activation of right PFC during the entire procedure, even if effect sizes between left and right channels were larger during the experimental condition. The amount of right activation during the stressful condition was positively correlated with anxiety. Response times (RTs) were slower in more anxious than in less anxious individuals, both during the control and stressful conditions. Accuracy was lower in more anxious than in less anxious individuals, only during the stressful condition. Moreover, heart rate (HR) was not modulated by situational stress, nor by anxiety. Overall, the present study suggests that in healthy elderly, anxiety level has a significant impact on cerebral responses, and both on the amount of cognitive resources and the quality of performance in stressful situations.