Skeletal Muscle Oxygen Saturation Research Articles

Population pharmacokinetic modelling and simulation of tranexamic acid in adult trauma patients.

The aim of this study is to describe the disposition of tranexamic acid (TXA) in adult trauma patients and derive a dosing regimen that optimizes exposure based on a predefined exposure target. We performed a population pharmacokinetic (popPK) analysis of participants enrolled in the Tranexamic Acid Mechanisms and Pharmacokinetics in Traumatic Injury (TAMPITI) trial (≥18 years with traumatic injury, given ≥1 blood product and/or requiring immediate transfer to the operating room) who were randomized to a single dose of either 2 or 4g of TXA ≤2h from time of injury. PopPK analysis was conducted using nonlinear mixed-effects modelling (NONMEM). Simulations were then performed using the final model to generate estimated plasma TXA concentrations in 1000 simulated participants. Dosing schemes were evaluated to determine maintenance of TXA plasma concentrations >10mg/L for ≥8h after administration of the initial dose. TXA PK was best described by a two-compartment model with proportional residual error and allometric scaling on all parameters. Platelet count, skeletal muscle oxygen saturation measured by near-infrared spectroscopy and interleukin-8 concentration were significant covariates on TXA clearance. Based on simulations, a 2g IV bolus dose, repeated 3h later, best achieved the target exposure. According to simulations from a popPK model of TXA, a 2g IV bolus with a repeated dose 3h later would be most likely to maintain concentrations >10mg/L for 8h in >95% of adult trauma patients and should be considered for patients with ongoing haemorrhage.

Reactive hyperemia half-time response is associated with skeletal muscle oxygen saturation changes during cycling exercise.

We investigated the relationship between muscle microvascular responses during reactive hyperemia as assessed using near-infrared spectroscopy (NIRS) with changes in skeletal muscle oxygen saturation during exercise. Thirty young untrained adults (M/W: 20/10; 23±5years) completed a maximal cycling exercise test to determine exercise intensities performed on a subsequent visit separated by seven days. At the second visit, post-occlusive reactive hyperemia was measured as changes in NIRS-derived tissue saturation index (TSI) at the left vastus lateralis muscle. Variables of interest included desaturation magnitude, resaturation rate, resaturation half-time, and hyperemic area under the curve. Afterwards, two 4-minute bouts of moderate intensity cycling followed by one bout of severe intensity cycling to fatigue took place while TSI was measured at the vastus lateralis muscle. TSI was averaged across the last 60-s of each moderate intensity bout then averaged together for analysis, and at 60-s into severe exercise. The change in TSI (∆TSI) during exercise is expressed relative to a 20W cycling baseline. On average, the ΔTSI was -3.4±2.4% and -7.2±2.8% during moderate and severe intensity cycling, respectively. Resaturation half-time was correlated with the ΔTSI during moderate (r=-0.42, P=0.01) and severe (r=-0.53, P=0.002) intensity exercise. No other reactive hyperemia variable was found to correlate with ΔTSI. These results indicate that resaturation half-time during reactive hyperemia represents a resting muscle microvascular measure that associates with the degree of skeletal muscle desaturation during exercise in young adults.

Muscle oxygen saturation rates coincide with lactate-based exercise thresholds.

Monitoring muscle metabolic activity via blood lactate is a useful tool for understanding the physiological response to a given exercise intensity. Recent indications suggest that skeletal muscle oxygen saturation (SmO2), an index of the balance between local O2 supply and demand, may describe and predict endurance performance outcomes. We tested the hypothesis that SmO2 rate is tightly related to blood lactate concentration across exercise intensities, and that deflections in SmO2 rate wouldcoincide with established blood lactate thresholds (i.e., lactate thresholds 1 and 2). Ten elite male soccer players completed an incremental running protocol to exhaustion using 3-min work to 30s rest intervals. Blood lactate samples were collected during rest and SmO2 was collected continuously via near-infrared spectroscopy from the right and left vastus lateralis, left biceps femoris and the left gastrocnemius. Muscle O2 saturation rate (%/min) was quantified after the initial 60s of each 3-min segment. The SmO2 rate was significantly correlated with blood lactate concentrations for all muscle sites; RVL, r = -0.974; LVL, r = -0.969; LG, r = -0.942; LHAM, r = -0.907. Breakpoints in SmO2 rate were not significantly different from LT1 or LT2 at any muscle sites (P > 0.05). Bland-Altman analysis showed speed threshold estimates via SmO2 rate and lactate are similar at LT2, but slightly greater for SmO2 rate at LT1. Muscle O2 saturation rate appears to provide actionable information about maximal metabolic steady state and is consistent with bioenergetic reliance on oxygen and its involvement in the attainment of metabolic steady state.

Interrater reliability of a customized submaximal cycle ergometer test.

Graded exercise testing (GXTs) is used to determine maximum oxygen uptake ([Formula: see text]). Recently, customized submaximal exercise testing (CSET) completed on both treadmill and cycle ergometry were validated. Interrater reliability of the CSET for cycle ergometry was examined. Thirteen participants (age 31 ± 10.2 y, weight 77.9 ± 10.5kg, height 176.2 ± 9.9cm, body mass index 25.1 ± 2.9) completed the 2-stage × 3-min CSET protocol performed by two separate testers. True [Formula: see text] was determined using the highest value derived by a GXT and verification bout. Skeletal muscle oxygen saturation ([Formula: see text]), measured using near-infrared spectrometry on the medial gastrocnemius muscle, and [Formula: see text] were monitored during each CSET; whereby, [Formula: see text] kinetics were modeled breath-by-breath data for each 3-min stage. Measurement agreement was quantified using intraclass coefficient (ICC), typical error (TE), and coefficient of variation (CV). "True" [Formula: see text] (ml·kg-1·min-1) between the GXT (41.3 ± 10.5) and verification (42.5 ± 11.5) was established (ICC = 0.98, TE: 0.98, CV 2.1%). Estimated [Formula: see text] by tester 1 (42.5 ± 9.8) and tester 2 (42.7 ± 8.9) did not differ from "true" [Formula: see text] (F2,36 = 0.02, p = 0.98, ηp2 = 0.00). The second stage evoked a [Formula: see text] slow component of 194 ± 124ml·min-1 that corresponded with a time-dependent decline of [Formula: see text]. The mean [Formula: see text] from the two CSET testers were highly correlated (ICC = 0.91, TE: 4.1%, CV = 8.9%). The CSET is a reliable and valid procedure and [Formula: see text] is a useful tool for corroborating the second stage is in the heavy-intensity domain.

A Comparative Analysis On Aerobically- And Anaerobically-trained Individuals’ Skeletal Muscle Oxygen Saturation

Skeletal muscle oxygen saturation (SmO2) is an important measure of how well muscles uptake oxygen from the blood and has been shown to correlate to exercise load. Maximal rate of oxygen consumption (VO2max) has been used to measure cardiorespiratory fitness which influences how much oxygen is being carried in the blood. What is not fully elucidated is if there is a difference in SmO2 and VO2max between aerobically trained individuals (runners) and anaerobically trained individuals (CrossFitters). Purpose: To determine if CrossFit-trained individuals and runners have differences in SmO2 during and after VO2 max test. Methods: Seventeen Crossfitters (n = 12 male; n = 5 female, Age 28.6 ± 7.6 years, VO2max 43.6 ± 7.2 ml/kg/min) and 18 endurance runners (n = 10 male; n = 8 female, Age 43.1 ± 12.3 years, VO2max 41.1 ± 7.6 ml/kg/min) completed a single VO2 max ramp protocol treadmill test while wearing a MOXY Sensor to assess SmO2. The MOXY Sensor was placed on the lateral-posterior belly of the gastrocnemius. The high, average, and low measures of SmO2 were obtained at baseline, during exercise, and post-exercise. In addition, total hemoglobin (THb) was also measured at all time points. The data was analyzed using a paired sample t-test to compare SmO2 measures, VO2max, THb, and time to recovery (secs). In addition, a linear regression was performed to show differences between groups. All analyses were performed using SAS (v.9.3). Results: There was a significant difference between the highest point of baseline SmO2 data between groups (p = 0.0330) with Crossfit individuals having a higher baseline SMO2. However, no significant difference was found for VO2max, THb, and time to recovery between groups. Additionally, we controlled for age and gender by running a linear regression. For gender, we did not find any statistical significance; however, we found that age had a significant effect on VO2 max (p = 0.0358). Conclusion: Analysis of the data indicated that aerobically-trained and anaerobically-trained individuals did not have a significant difference in SmO2 during the VO2 max test. Due to our disproportionate gender and age sample size, future research is needed in order to determine the full extent of whether there is a significant difference in SmO2 between anaerobically- and aerobically-trained individuals.

Capsaicin supplementation did not increase skeletal muscle oxygen saturation and muscular endurance during resistance exercise: a randomized and crossover study

Capsaicin supplementation did not increase skeletal muscle oxygen saturation and muscular endurance during resistance exercise: a randomized and crossover study

Impact of supervised exercise on skeletal muscle blood flow and vascular function measured with MRI in patients with peripheral artery disease.

Supervised exercise is a common therapeutic intervention for patients with peripheral artery disease (PAD), however, the mechanism underlying the improvement in claudication symptomatology is not completely understood. The hypothesis that exercise improves microvascular blood flow is herein tested via temporally resolved magnetic resonance imaging (MRI) measurement of blood flow and oxygenation dynamics during reactive hyperemia in the leg with the lower ankle-brachial index. One hundred and forty-eight subjects with PAD were prospectively assigned to standard medical care or 3 mo of supervised exercise therapy. Before and after the intervention period, subjects performed a graded treadmill walking test, and MRI data were collected with Perfusion, Intravascular Venous Oxygen saturation, and T2* (PIVOT), a method that simultaneously quantifies microvascular perfusion, as well as relative oxygenation changes in skeletal muscle and venous oxygen saturation in a large draining vein. The 3-mo exercise intervention was associated with an improvement in peak walking time (64% greater in those randomized to the exercise group at follow-up, P < 0.001). Significant differences were not observed in the MRI measures between the subjects randomized to exercise therapy versus standard medical care based on an intention-to-treat analysis. However, the peak postischemia perfusion averaged across the leg between baseline and follow-up visits increased by 10% (P = 0.021) in participants that were adherent to the exercise protocol (completed >80% of prescribed exercise visits). In this cohort of adherent exercisers, there was no difference in the time to peak perfusion or oxygenation metrics, suggesting that there was no improvement in microvascular function nor changes in tissue metabolism in response to the 3-mo exercise intervention.NEW & NOTEWORTHY Supervised exercise interventions can improve symptomatology in patients with peripheral artery disease, but the underlying mechanism remains unclear. Here, MRI was used to evaluate perfusion, relative tissue oxygenation, and venous oxygen saturation in response to cuff-induced ischemia. Reactive hyperemia responses were measured before and after 3 mo of randomized supervised exercise therapy or standard medical care. Those participants who were adherent to the exercise regimen had a significant improvement in peak perfusion.

Associations Between Heart Rate and Skeletal Muscle Oxygen Saturation (SmO₂) in Upper and Lower Extremities During Self‐Paced Walking

This study aims to determine the association between heart rate and skeletal muscle oxygen saturation (SmO₂) during 30 minutes of self‐paced walking on 4 different days. It was hypothesized that there would be a significant association between heart rate and SmO₂, as increased exercise intensity would result in increased peripheral muscle O₂ consumption and increased heart rate. Participants (age= 18‐40) were recruited from Clarkson University as part of an ongoing larger study and informed consent was signed. Heart rate was measured using a pulse oximeter after every five minute interval of the 30 minute walking period and was recorded in an online survey on surveymonkey.com. The muscle oxygen monitor (MOXY) near infrared sensors were placed on the left and right medial gastrocnemius heads as well as on the left biceps brachii muscle to record SmO₂ levels. Data was analyzed using a bivariate Pearson correlation to determine if there was a significant correlation between SmO₂ and heart rate while walking. Heart rate was negatively associated with SmO₂ in the left medial gastrocnemius head (R= ‐0.139, p= 0.044, n= 211) while there was no significant relationship seen in the right medial gastrocnemius head (p&gt; 0.05). In the left biceps brachii muscle, there was a positive association between heart rate and SmO₂ (R= 0.148, p= 0.035, n= 204). The findings of our study suggest that as walking intensity increases, O₂ consumption in the upper and lower extremities has a weak, but significant association with heart rate. These findings suggest that as blood is shunted from the upper extremity to lower extremity to meet lower extremity demands during walking, O₂ utilization by muscles in the upper extremity is decreased. Further research is needed to elucidate how these relationships change when performing activities that require both upper and lower extremity muscles as well as with varying intensities of exercise.

Young healthy adults with a family history of hypertension have increased microvascular reactivity but decreased macrovascular function.

To determine whether, like hypertensives, normotensive adults with a family history of hypertension (+FHH) display lower microvascular reactivity and conduit artery function than normotensive adults without a family history of hypertension (-FHH). A forearm vascular occlusion test was performed on healthy normotensive adults while resting in the supine position. A near-infrared spectroscopy sensor placed on the forearm measured skeletal muscle oxygen saturation kinetics to determine microvascular reactivity. Simultaneously, an ultrasound probe placed on the brachial artery above the occlusion cuff was used to assess flow-mediated dilation; a test of macrovascular function. Twenty-two participants were included in this investigation (-FHH n=13, +FHH n=9). Following cuff release, the resaturation slope (1st 10s median±SD, -FHH 2.76±2.10, +FHH 5.59±2.47%/s; p=.036) was greater in +FHH when accounting for the magnitude and rate of the decrease in skeletal muscle oxygen saturation during occlusion. Conversely, flow-mediated dilation (median±SD, -FHH 5.96±5.22, +FHH 4.10±3.17%∆; p=.031) was lower in +FHH when accounting for baseline artery diameter and shear rate. Young +FHH adults have altered microvascular and macrovascular reactivity compared with young -FHH adults.

Thenar oxygen saturation (StO2) alterations during a spontaneous breathing trial predict extubation failure

BackgroundWeaning from mechanical ventilation (MV) is a cardiovascular stress test. Monitoring the regional oxygenation status has shown promising results in predicting the tolerance to spontaneously breathe in the process of weaning from MV. Our aim was to determine whether changes in skeletal muscle oxygen saturation (StO2) measured by near-infrared spectroscopy (NIRS) on the thenar eminence during a vascular occlusion test (VOT) can be used to predict extubation failure from mechanical ventilation.MethodsWe prospectively studied 206 adult patients with acute respiratory failure receiving MV for at least 48 h from a 30-bed mixed ICU, who were deemed ready to wean by their physicians. Patients underwent a 30-min spontaneous breathing trial (SBT), and were extubated according to the local protocol. Continuous StO2 was measured non-invasively on the thenar eminence. A VOT was performed prior to and at 30 min of the SBT (SBT30). The rate of StO2 deoxygenation (DeO2), StO2 reoxygenation (ReO2) rate and StO2 hyperemic response to ischemia (HAUC) were calculated.ResultsThirty-six of the 206 patients (17%) failed their SBT. The remainder 170 patients (83%) were extubated. Twenty-three of these patients (13.5%) needed reinstitution of MV within 24 h. Reintubated patients displayed a lower HAUC at baseline, and higher relative changes in their StO2 deoxygenation rate between baseline and SBT30 (DeO2 Ratio). A logistic regression-derived StO2 score, combining baseline StO2, HAUC and DeO2 ratio, showed an AUC of 0.84 (95% CI 0.74–0.91) for prediction of extubation failure.ConclusionsExtubation failure was associated to baseline and dynamic StO2 alterations during the SBT. Monitoring StO2-derived parameters might be useful in predicting extubation outcome.

Effect of Acute Creatine Supplementation on Arterial Stiffness and Muscle Oxygen Saturation

ObjectiveTo determine the effects of acute creatine monohydrate supplementation on arterial stiffness (AS) and skeletal muscle oxygen saturation (SmO2). There is a void in our knowledge on the impact of acute creatine monohydrate supplementation on AS in the major elastic arteries. In addition, there is a dearth of findings on the effects of creatine supplementation on SmO2 in the lower leg. Data have indicated that creatine supplementation can result in an increase in lower leg anterior compartment pressure at rest and post exercise. Although the increased pressures seen during these studies were not pathological, this and additional factors associated with creatine supplementation could possibly effect SmO2 during exercise and recovery.Methods20 male, physically active participants were randomized in a double‐blind fashion to placebo (PL) (n=10, 22.9±3.1 yrs.) or creatine (CM) (n=10, 21.3±1.8 yrs.) groups. Subjects received 0.3 g/kg/day creatine monohydrate or placebo in gelatin capsules for 7 days. Ultrasonography of the carotid artery, applanation tonometry, submaximal exercise tests (10 minute treadmill activity at 3.7 mph and 9% incline), SmO2, and lower leg pain (analog visual scale and pain test algometer) assessments were conducted at baseline and on day 7 of the study period.ResultsThere were baseline differences in central systolic blood pressure (cSBP) (mean difference, 109; 95% confidence interval (CI) 105 to 113, vs. mean difference, 130; 95% CI 114 to 146, p &lt; 0.05) between the PLA and CM groups, respectively. Following the intervention, there were no significant differences between PL and CM in arterial stiffness indices between the groups. There was a significant group effect (P&lt;0.03) but no significant effect of supplementation (P&gt;0.05) on the % change in SmO2 during the exercise tests (CM: pre 66.49 ± 30.54; post 59.61 ± 23.87 vs. PL: pre 39.87 ± 16.72; post 38.51 ± 26.95 % change SmO2; M ± SD). Percent fat free mass (FFM) was significantly increased (mean, 68.5±7.5%; 95% CI 62.1% to 72.9%, to mean 69.3±7.5% 95% CI 62.9% to 73.6%, P&lt;0.05) in the CM group only. There were no other significant changes in anthropometric measurements.ConclusionsUsing a randomly controlled, double‐blind trial with validated measurements of AS and SmO2, acute creatine supplementation does not appear to impact vascular compliance or oxygen saturation in skeletal muscle in young, healthy males.

Skeletal muscle oxygenation and regional blood volume during incremental limb loading in interstitial lung disease.

IntroductionIndividuals with interstitial lung disease (ILD) exhibit reduced exercise capacity and exertional hypoxaemia. The role of peripheral (muscle) limitation to exercise tolerance in ILD is not well studied to date.MethodsA prospective cross-sectional study examined skeletal muscle oxygen saturation (SmO2) and regional blood volume of the knee extensors and elbow flexors during incremental limb loading in healthy people and people with varying severity of ILD. Isotonic concentric exercise was performed on an isokinetic dynamometer. SmO2 and regional blood volume were measured by near-infrared spectroscopy over the vastus lateralis and biceps.ResultsThirteen people who were dependent on oxygen, candidates for lung transplant and with severe ILD (forced vital capacity (FVC) 59±20% predicted), 10 people who were not oxygen dependent with mild ILD (FVC 81±17% predicted) and 13 healthy people (FVC 101±14% predicted) were included. Total haemoglobin, a marker of regional blood volume, was lower at task failure in the knee extensors in participants with severe ILD compared to healthy participants (p=0.05). At task failure for both knee-extensor loading and elbow-flexor loading, SmO2 was decreased to similar levels across all groups, but occurred at lower total workloads in the ILD groups (all p<0.01).ConclusionsOverall, people with severe ILD had lower levels of total work and experienced less increase in blood volume in the knee extensors after knee-extensor loading compared to healthy people. Peripheral muscle dysfunction in severe ILD may have contributed to muscle deoxygenation at lower workloads.

Interpretation of Near-Infrared Spectroscopy (NIRS) Signals in Skeletal Muscle.

Near-infrared spectroscopy (NIRS) uses the relative absorption of light at 850 and 760 nm to determine skeletal muscle oxygen saturation. Previous studies have used the ratio of both signals to report muscle oxygen saturation. Purpose: The purpose of this pilot study is to assess the different approaches used to represent muscle oxygen saturation and to evaluate the pulsations of oxygenated hemoglobin/myoglobin (O2heme) and deoxygenated hemoglobin/myoglobin (Heme) signals. Method: Twelve participants, aged 20–29 years, were tested on the forearm flexor muscles using continuous-wave NIRS at rest. Measurements were taken during 2–3 min rest, physiological calibration (5 min ischemia), and reperfusion. Ten participants were included in the study analysis. Results: There was a significant difference in pulse size between O2heme and Heme signals at the three locations (p < 0.05). Resting oxygen saturation was 58.8% + 9.2%, 69.6% + 3.9%, and 89.2% + 6.9% when calibrated using O2heme, the tissue oxygenation/saturation index (TSI), and Heme, respectively. Conclusion: The difference in magnitude of O2heme and Heme pulses with each heartbeat might suggest different anatomical locations of these signals, for which calibrating with just one of the signals instead of the ratio of both is proposed. Calculations of physiological calibration must account for increased blood volume in the tissue because of the changes in blood volume, which appear to be primarily from the O2heme signal. Resting oxygen levels calibrated with Heme agree with theoretical oxygen saturation.

Evaluating Near Infrared Spectroscopy Signals From Skeletal Muscle

Near Infrared Spectroscopy (NIRS) uses the relative absorption of light at 850 and 760nm to determine skeletal muscle oxygen saturation. There are currently disagreements in the literature over how to report oxygen saturation and the relative contributions of hemoglobin and myoglobin. PURPOSE: 1) Compare the separate 850nm (HbO2) and 760nm (HHb)signals during rest, ischemia, and reperfusion, and 2) test whether electrical stimulation to increase metabolic rate changes oxygen saturation values during 5-6 minutes of complete ischemia. METHOD: Ten participants ages = 20-29 years were measured. NIRS measurements were made in the forearm flexor muscles at rest, after 30 seconds of 6 Hz electrical stimulation, during and after 5-6 minutes of complete ischemia produced by arterial occlusion preceded by 30 seconds of 6 Hz electrical stimulation. After 5-6 minutes of ischemia 30 seconds of 6 Hz electrical stimulation was performed. RESULTS: Six Hz stimulation for 30 s increased metabolic rate for HbO2 and HHb; 6.2+3.1 and 5.5+2.7 fold over rest, respectively. Six Hz stimulation during cuff ischemia did not change either the HHb or HbO2 values (p>0.05). There was significantly greater (p<0.05) pulsitility associated with heart rate in the HbO2 (0.78+0.41% range) compared to HHb (0.16+0.09% range). Pulse size increased during reperfusion; HbO2 (2.37+0.38% range) compared to HHb (0.96+0.32% range). CONCLUSIONS: The difference in the magnitude of pulsitility between HbO2 and HHb signals suggests different anatomical locations for these signals, further suggesting that using various ratios of HbO2 and HHb signals should be performed with caution. Increasing metabolic rate with electrical stimulation during complete ischemia did not further change the NIRS signals, suggesting complete ischemia is obtained with 5-6 minutes of complete cuff occlusion. Keywords: Skeletal Muscle, Near Infrared Spectroscopy (NIRS), Oxygen consumption, Hemoglobin, Myoglobin

Blood pressure and leg deoxygenation are exaggerated during treadmill walking in patients with peripheral artery disease.

The purpose of this study was to investigate blood pressure (BP) and leg skeletal muscle oxygen saturation (Smo2) during treadmill walking in patients with peripheral artery disease (PAD) and healthy subjects. Eight PAD patients (66 ± 8 yr, 1 woman) and eight healthy subjects (65 ± 7 yr, 1 woman) walked on a treadmill at 2 mph (0.89 m/s). The incline increased by 2% every 2 min, from 0 to 15% or until maximal discomfort. BP was measured every 2 min with an auscultatory cuff. Heart rate (HR) was recorded continuously with an ECG. Smo2 in the gastrocnemius muscle was measured on each leg using near-infrared spectroscopy. The change in systolic BP from seated to peak walking time (PWT) was greater in PAD (healthy: 23 ± 9 vs. PAD: 44 ± 19 mmHg, P = 0.007). HR was greater in PAD patients compared with controls at PWT (P = 0.011). The reduction in Smo2 (PWT - seated) was greater in PAD (healthy: 15 ± 12 vs. PAD: 49 ± 5%, P < 0.001) in the most affected leg and in the least affected leg (healthy: 12 ± 11 vs. PAD: 32 ± 18%, P = 0.003). PAD patients have an exaggerated decline in leg Smo2 during walking compared with healthy subjects, which may elicit the exaggerated rise in BP and HR during walking in PAD.NEW & NOTEWORTHY This is the first study to simultaneously measure skeletal muscle oxygen saturation and blood pressure (BP) during treadmill exercise in patients with peripheral arterial disease. We found that BP and leg deoxygenation responses to slow-paced, graded treadmill walking are greater in patients with peripheral arterial disease compared with healthy subjects. These data may help explain the high cardiovascular risk in patients with peripheral arterial disease.

Microvascular response to transfusion in elective spine surgery.

AIMTo investigate the microvascular (skeletal muscle tissue oxygenation; SmO2) response to transfusion in patients undergoing elective complex spine surgery.METHODSAfter IRB approval and written informed consent, 20 patients aged 18 to 85 years of age undergoing > 3 level anterior and posterior spine fusion surgery were enrolled in the study. Patients were followed throughout the operative procedure, and for 12 h postoperatively. In addition to standard American Society of Anesthesiologists monitors, invasive measurements including central venous pressure, continual analysis of stroke volume (SV), cardiac output (CO), cardiac index (CI), and stroke volume variability (SVV) was performed. To measure skeletal muscle oxygen saturation (SmO2) during the study period, a non-invasive adhesive skin sensor based on Near Infrared Spectroscopy was placed over the deltoid muscle for continuous recording of optical spectra. All administration of fluids and blood products followed standard procedures at the Hospital for Special Surgery, without deviation from usual standards of care at the discretion of the Attending Anesthesiologist based on individual patient comorbidities, hemodynamic status, and laboratory data. Time stamps were collected for administration of colloids and blood products, to allow for analysis of SmO2 immediately before, during, and after administration of these fluids, and to allow for analysis of hemodynamic data around the same time points. Hemodynamic and oxygenation variables were collected continuously throughout the surgery, including heart rate, blood pressure, mean arterial pressure, SV, CO, CI, SVV, and SmO2. Bivariate analyses were conducted to examine the potential associations between the outcome of interest, SmO2, and each hemodynamic parameter measured using Pearson’s correlation coefficient, both for the overall cohort and within-patients individually. The association between receipt of packed red blood cells and SmO2 was performed by running an interrupted time series model, with SmO2 as our outcome, controlling for the amount of time spent in surgery before and after receipt of PRBC and for the inherent correlation between observations. Our model was fit using PROC AUTOREG in SAS version 9.2. All other analyses were also conducted in SAS version 9.2 (SAS Institute Inc., Cary, NC, United States).RESULTSPearson correlation coefficients varied widely between SmO2 and each hemodynamic parameter examined. The strongest positive correlations existed between ScvO2 (P = 0.41) and SV (P = 0.31) and SmO2; the strongest negative correlations were seen between albumin (P = -0.43) and cell saver (P = -0.37) and SmO2. Correlations for other laboratory parameters studied were weak and only based on a few observations. In the final model we found a small, but significant increase in SmO2 at the time of PRBC administration by 1.29 units (P = 0.0002). SmO2 values did not change over time prior to PRBC administration (P = 0.6658) but following PRBC administration, SmO2 values declined significantly by 0.015 units (P < 0.0001).CONCLUSIONIntra-operative measurement of SmO2 during large volume, yet controlled hemorrhage, does not show a statistically significant correlation with either invasive hemodynamic, or laboratory parameters in patients undergoing elective complex spine surgery.

Skeletal Muscle Oxygen Saturation (StO2) Measured by Near-Infrared Spectroscopy in the Critically Ill Patients

According to current critical care management guidelines, the overall hemodynamic optimization process seeks to restore macrocirculatory oxygenation, pressure, and flow variables. However, there is increasing evidence demonstrating that, despite normalization of these global parameters, microcirculatory and regional perfusion alterations might occur, and persistence of these alterations has been associated with worse prognosis. Such observations have led to great interest in testing new technologies capable of evaluating the microcirculation. Near-infrared spectroscopy (NIRS) measures tissue oxygen saturation (StO2) and has been proposed as a noninvasive system for monitoring regional circulation. The present review aims to summarize the existing evidence on NIRS and its potential clinical utility in different scenarios of critically ill patients.

The Effects of Chronic Betaine Supplementation on Exercise Performance, Skeletal Muscle Oxygen Saturation and Associated Biochemical Parameters in Resistance Trained Men

Trepanowski, JF, Farney, TM, McCarthy, CG, Schilling, BK, Craig, SA, and Bloomer, RJ. The effects of chronic betaine supplementation on exercise performance, skeletal muscle oxygen saturation, and associated biochemical parameters in resistance trained men. J Strength Cond Res 25(12): 3461-3471, 2011-We examined the effects of chronic betaine supplementation on exercise performance and associated parameters in resistance trained men. Men were randomly assigned in a double-blind manner using a crossover design to consume betaine (2.5 g of betaine mixed in 500 ml of Gatorade®) or a placebo (500 ml of Gatorade®) for 14 days, with a 21-day washout period. Before and after each treatment period, tests of lower- and upper-body muscular power and isometric force were conducted, including a test of upper-body muscular endurance (10 sets of bench press exercise to failure). Muscle tissue oxygen saturation (StO2) during the bench press protocol was measured via near infrared spectroscopy. Blood samples were collected before and after the exercise test protocol for analysis of lactate, nitrate/nitrite (NOx), and malondialdehyde (MDA). When analyzed using a repeated measures analysis of variance, no significant differences were noted between conditions for exercise performance variables (p > 0.05). However, an increase in total repetitions (p = 0.01) and total volume load (p = 0.02) in the 10-set bench press protocol was noted with betaine supplementation (paired t-tests), with values increasing approximately 6.5% from preintervention to postintervention. Although not of statistical significance (p = 0.14), postexercise blood lactate increased to a lesser extent with betaine supplementation (210%) compared with placebo administration (270%). NOx was lower postintervention as compared with preintervention (p = 0.06), and MDA was relatively unchanged. The decrease in StO2 during the bench press protocol was greater with betaine vs. placebo (p = 0.01), possibly suggesting enhanced muscle oxygen consumption. These findings indicate that betaine supplementation results in a moderate increase in total repetitions and volume load in the bench press exercise, without favorably impacting other performance measures.

Comparison of pre-workout nitric oxide stimulating dietary supplements on skeletal muscle oxygen saturation, blood nitrate/nitrite, lipid peroxidation, and upper body exercise performance in resistance trained men

BackgroundWe compared Glycine Propionyl-L-Carnitine (GlycoCarn®) and three different pre-workout nutritional supplements on measures of skeletal muscle oxygen saturation (StO2), blood nitrate/nitrite (NOx), lactate (HLa), malondialdehyde (MDA), and exercise performance in men.MethodsUsing a randomized, double-blind, cross-over design, 19 resistance trained men performed tests of muscular power (bench press throws) and endurance (10 sets of bench press to muscular failure). A placebo, GlycoCarn®, or one of three dietary supplements (SUPP1, SUPP2, SUPP3) was consumed prior to exercise, with one week separating conditions. Blood was collected before receiving the condition and immediately after exercise. StO2 was measured during the endurance test using Near Infrared Spectroscopy. Heart rate (HR) and rating of perceived exertion (RPE) were determined at the end of each set.ResultsA condition effect was noted for StO2 at the start of exercise (p = 0.02), with GlycoCarn® higher than SUPP2. A condition effect was also noted for StO2 at the end of exercise (p = 0.003), with SUPP1 lower than all other conditions. No statistically significant interaction, condition, or time effects were noted for NOx or MDA (p > 0.05); however, MDA decreased 13.7% with GlycoCarn® and increased in all other conditions. Only a time effect was noted for HLa (p < 0.0001), with values increasing from pre- to post-exercise. No effects were noted for HR, RPE, or for any exercise performance variables (p > 0.05); however, GlycoCarn® resulted in a statistically insignificant greater total volume load compared to the placebo (3.3%), SUPP1 (4.2%), SUPP2 (2.5%), and SUPP3 (4.6%).ConclusionNone of the products tested resulted in favorable changes in our chosen outcome measures, with the exception of GlycoCarn® in terms of higher StO2 at the start of exercise. GlycoCarn® resulted in a 13.7% decrease in MDA from pre- to post-exercise and yielded a non-significant but greater total volume load compared to all other conditions. These data indicate that 1) a single ingredient (GlycoCarn®) can provide similar practical benefit than finished products containing multiple ingredients, and 2) while we do not have data in relation to post-exercise recovery parameters, the tested products are ineffective in terms of increasing blood flow and improving acute upper body exercise performance.

Skeletal muscle oxygen saturation estimates mixed venous oxygen saturation in patients with severe left heart failure

Low cardiac output states, such as left heart failure, are characterized by a preserved oxygen extraction ratio compared with severe sepsis. Near-infrared spectroscopy (NIRS) allows noninvasive estimation of skeletal muscle tissue oxygenation (StO2). The aim of study was to determine relationship between StO2 and mixed venous oxygen saturation (SvO2) in patients with severe left heart failure with or without additional severe sepsis or septic shock.