Muscle Tissue Oxygenation Research Articles

Induced Blood Flow Oscillations at 0.1 Hz Protects Oxygenation of Severely Ischemic Tissue

Background: Early interventions that improve vital organ perfusion will reduce the number of lives lost from blood loss injuries. We have shown that generating 10 second (~0.1 Hz) fluctuations or “oscillations” in arterial pressure and blood flow during simulated hemorrhage protects cerebral tissue oxygenation. Lower body negative pressure (LBNP) was used to both simulate hemorrhage, and induce the hemodynamic oscillations in these previous studies. However, the magnitude of cerebral tissue ischemia is limited to 20-30% with LBNP due to the onset of pre-syncopal symptoms. To examine the effect of 0.1 Hz hemodynamic oscillations on blood flow delivery and tissue oxygenation of severely ischemic tissues, we developed a limb ischemia model. Hypothesis: Oscillatory arterial pressure and blood flow will attenuate reductions in brachial artery blood flow and forearm tissue oxygenation in a severely ischemic limb. Methods: Nine healthy human subjects (5M, 4F; 27.2 ± 4.1 y) completed two experimental protocols separated by ≥48 h. In both conditions, ischemia of the forearm was induced with a pneumatic cuff on the upper arm to decrease brachial artery (BA) blood velocity by ~70-80% from baseline. In the oscillation condition (OSC), 0.1 Hz oscillations in mean arterial pressure (MAP) and BA blood flow were then induced by inflating and deflating bilateral thigh cuffs every 10 seconds (0.1 Hz) throughout the forearm ischemia period. In the control condition (CON), the thigh cuffs were in place, but were inactive throughout the forearm ischemia period. BA blood flow was measured via duplex ultrasound, forearm muscle tissue oxygenation (SmO2) was measured via near infrared spectroscopy, and arterial pressure was measured via finger photoplethysmography. Results: The magnitude of forearm ischemia, indexed by the reduction in BA blood velocity, was matched between protocols (CON: -75.2 ± 8.4 % vs. OSC: -78.3 ± 7.8 %, p=0.20). Power spectral density of 0.1 Hz oscillations in MAP (CON: 19.4 ± 22.8 mmHg2 vs. OSC: 716.8 ± 514.6 mmHg2; p<0.001) and BA blood velocity (CON: 0.7 ± 1.0 cm/s2 vs. OSC: 10.6 ± 7.1 cm/s2, p=0.02) were greater with oscillatory thigh cuff compression compared with the control condition. While oscillatory thigh cuff compression during forearm ischemia had no effect on absolute MAP (CON: 94.3 ± 6.6 mmHg vs. OSC: 94.4 ± 10.8 mmHg, p=0.99), BA blood flow (CON: 9.7 ± 5.8 ml/min vs. OSC: 9.5 ± 7.3 ml/min, p=0.82), or BA conductance (CON: 0.10 ± 0.06 ml/min/mmHg vs. OSC: 0.09 ± 0.06 ml/min/mmHg, p=0.39), the reduction in SmO2 was attenuated (CON: -38.7 ± 8.3 % vs. OSC: -28.4 ± 9.7 %; p=0.04). These data provide further evidence for the use of 0.1 Hz hemodynamic oscillations as a therapeutic intervention for conditions associated with severe vital organ ischemia such as hemorrhage, stroke, myocardial infarction, and sepsis. National Institutes of Health/National Institute on Aging T32 Ruth Kirschstein Institutional National Research Service Award (T32AG020494); American Heart Association Transformational Project Award (19TPA34910073) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Functional Evaluation of Microcirculation in Response to Fluid Resuscitation in Hypovolemic Adult Post-cardiac Surgical Patients

Objectives: Microcirculation is bound to be altered during cardiac surgery due to multiple factors, mainly the intense systemic inflammatory response syndrome which peaks in the first 24-h postoperatively. Decreased microvascular flow associated with increased postoperative morbidity has been reported. The literature suggests a potential independence of macrocirculation and microcirculation during fluid loading. The present study was conducted to assess thenar muscle tissue oxygen saturation (StO2) changes during vascular occlusion test (VOT) in response to hypovolemia and to assess the dynamic responses of the StO2 variables post-volume expansion (VE). Material and Methods: Thirty-five adult post-cardiac surgical patients, with stroke volume (SV) variation >12% were included in the study. Fifty-two fluid challenges were studied. Functional evaluation of microcirculation using VOT and near infrared spectroscopy (NIRS) variables along with monitoring of macrocirculatory indices was performed before and after VE. Statistical analysis was done using Student t-test. Results: Post-VE, 34 were responders with increase in SV ≥15% and 18 were non-responders (SV <15%). Rate of resaturation was significantly faster in responders compared to non-responders after VE (P = 0.0293 vs. P = 0.1480). However, macrocirculatory indices including cardiac output, SV, and delivery of oxygen showed significant improvement in both responders and non-responders. Conclusion: Preload dependence is associated with significant change in the StO2 recovery slope measured at the thenar eminence in volume responders. Functional evaluation of microcirculation using VOT and StO2 can be a useful complimentary tool along with the macrocirculatory indices for optimal fluid rescuscitaion in adult post-cardiac surgical patients.

Effects of Press Needle Intervention on Knee Flexion and Extension Movements: A Randomized Trial

Objective: Knee flexion exercise is a type of exercise therapy for improving knee-joint muscle strength. Among the knee extensors, the vastus medialis muscle is less active and prone to disuse atrophy. The effects of press needle acupuncture include vasodilation, which may affect blood flow in the vastus medialis. This study examined the effects of exercise stimulation + press needle stimulation on muscle blood flow. Materials and Methods: Conducted in Teikyo Heisei University, Tokyo, Japan, this randomized controlled trial involved 30 healthy adults in 3 groups (10 who did not receive stimulation, 10 who received exercise stimulation only, and 10 who received press needle stimulation + exercise stimulation). The stimulations were applied once per week, for 3 weeks. After resting for 10 minutes, the nonstimulated group rested for 2 additional minutes, and the other 2 groups performed knee flexion and extension exercises considered to be “very very hard on the Borg rating.” After this activity, the 2 stimulation groups rested for 10 minutes. Press needle stimulation was applied on the vastus medialis muscles of both thighs in the combination stimulation group. Results: The combination group had a smaller decrease in muscle tissue oxygen saturation and an increase in total hemoglobin, compared to the exercise only stimulation group. Conclusions: Press needle stimulation during exercise may dilate muscle blood vessels. Future studies should examine the effectiveness of this stimulation for age-specific and knee diseases.

Non-invasive assessment of fatigue and recovery of inspiratory rib cage muscles during endurance test in healthy individuals.

Fatigue is defined as loss of capacity to develop muscle force and/or velocity that is reversible at rest. We assessed non-invasively the fatigue and recovery of inspiratory rib cage muscles during two respiratory endurance tests in healthy individuals. The sniff nasal inspiratory pressure (SNIP) was assessed before and after two respiratory endurance tests: normocapnic hyperpnea (NH) and inspiratory pressure threshold loading (IPTL). Contractile (maximum rate of pressure development and time to peak pressure) and relaxation parameters (maximum relaxation rate [MRR], time constant of pressure decay [τ], and half relaxation time) obtained from sniff curves and shortening velocity and mechanical power estimated using optoelectronic plethysmography were analyzed during SNIP maneuvers. Respiratory muscle activity (electromyography) and tissue oxygenation (near-infrared spectroscopy-NIRS) were obtained during endurance tests and SNIP maneuvers. Fatigue development of inspiratory rib cage muscles was assessed according to the slope of decay of median frequency. Peak pressure during SNIP decreased after both protocols (p <0.05). MRR, shortening velocity, and mechanical power decreased (p <0.05), whereas τ increased after IPTL (p <0.05). The median frequency of inspiratory rib cage muscles (i.e., sum of sternocleidomastoid, scalene, and parasternal) decreased linearly during IPTL and exponentially during NH, mainly due to the sternocleidomastoid. Fatigue development behaved differently between protocols and relaxation properties (MRR and τ), shortening velocity, and mechanical power changed only in the IPTL.

Post-Exertion Rate of Reperfusion vs Point-by-Point analysis of skeletal tissue near-infrared spectroscopy during repeated fatigue recovery under normoxia and hypoxemia

ObjectiveNear-Infrared Spectroscopy (NIRS) analysis techniques can often be complex to perform and interpret resulting in a barrier for wide-spread clinical use. The traditional Point-by-Point analysis methodology and our Post-Exertion Rate of Reperfusion method were examined during the recovery phases following repeated bouts of physical exertion to determine the physiological processes and information captured by each methodology under normal exertion conditions (FiO2: 0.210) and when in hypoxic conditions (FiO2: 0.129). MethodsTo achieve this, a total of n = 15 participants performed 3 sets of leg extensions to failure at 70 % their maximal effort. A 1-min rest was performed following each set where the Point-by-Point analysis means were calculated at every 6-s time to recovery for a total of 10 mean values. The Post-Exertion Rate of Reperfusion examined the linear slopes for the entire 60-s. The near-infrared spectroscopy device was placed over the vastus lateralis and measure for muscle tissue oxygen saturation, oxygenated hemoglobin, deoxygenated hemoglobin, and total hemoglobin were obtained for both the Point-by-Point and Post-Exertion Rate of Reperfusion analysis. ResultsPost-Exertion Rate of Reperfusion slopes were significantly different between normoxia and hypoxia for muscle tissue oxygen saturation (Normoxia: 0.151–0.171; Hypoxia: 0.068–0.116), oxygenated hemoglobin (Normoxia: 0.127 – 0.134; Hypoxia: 0.045 – 0.076), deoxygenated hemoglobin (Normoxia: −0.142 to −0.152; Hypoxia: −0.054 to −0.100), and total hemoglobin (Normoxia: −0.011 to 0.0250; Hypoxia: −0.009 to 0.024). Point-by-Point analysis identified significant differences between muscle tissue oxygen saturation and oxygenated hemoglobin, but not deoxygenated hemoglobin and total hemoglobin. ConclusionPoint-by-Point analysis and Post-Exertion Rate of Reperfusion can each provide distinctly unique information during exertional recovery. Point-by-Point analysis was ideal for detecting the onset of change in muscle oxygen status. Post-Exertion Rate of Reperfusion identified overall rates of change and was shown to be more sensitive at identifying changes in overall recovery of skeletal tissue reperfusion rates. Point-by-Point analysis and Post-Exertion Rate of Reperfusions may be utilized individually or separately to improve the interpretability of skeletal NIRS metrics within research or clinical settings.

The effects of inspiratory muscle fatigue on subsequent high-intensity exercise performance and muscle tissue oxygenation

The effects of inspiratory muscle fatigue on subsequent high-intensity exercise performance and muscle tissue oxygenation

Changes in Muscle Quality after Physical Rehabilitation Reduce Blood Pressure in Weightlifters with Arterial Hypertension: Randomized Controlled Trial

Hypertension is a frequent diagnosis in power athletes. Aim. To assess the effect of increased muscle oxidative capacity on blood pressure in athletes with arterial hypertension from power sports, heavy weight categories. Material and methods. The study was conducted at the Department of Sports Medicine of the Russian State University of Physical Culture, Sports, Youth and Tourism and lasted 180 days. The study involved 65 representatives of strength sports (weightlifting), heavy weight categories with arterial hypertension. Athletes were randomized into two main groups: the HIIT (High Intensity Interval Training, n=23) group, the MICE (Moderate Intensity Continuous Exercise, n=22) group and the RT (Resistance Training, n=20) control group. The following methods were used to achieve the aim of the study: ergospirometry, muscle tissue oxygenation level measurement, blood pressure measurement and methods of mathematical statistics. Athletes in the main groups trained for 180 days (3 times per week) on a cycle ergometer using a high-intensity interval and uniform protocol, and participants in the control group trained for 180 days (3 times per week) according to their traditional strength protocol. Results. After 180 days of physical rehabilitation, participants of the main groups had increased oxygen consumption at the anaerobic threshold, decreased thigh muscle oxygenation and increased maximum oxygen consumption, resulting in an average decrease in systolic blood pressure of 11.1 mm Hg and diastolic blood pressure of 11.2 mm Hg in the intervention groups. Conclusion. The physical rehabilitation systems we have developed for power athletes allow us to effectively and safely influence the oxidative capacity of working muscles and blood pressure, but the time spent by athletes on non-specific training activities in the HIIT system is 38% less.

Mechanomyography and tissue oxygen saturation during electrically-evoked wrist extensor fatigue in people with tetraplegia.

Repetitive electrically-evoked muscle contractions lead to the early onset of muscle fatigue. This study assessed the relationship between muscle mechanomyography (%RMS-MMG) and tissue oxygen saturation (%TSI) in extensor carpi radialis (ECR) during electrically-evoked fatiguing exercise in individuals with tetraplegia. Skin-surface mechanomyography (MMG) and near-infrared spectroscopy (NIRS) sensors were placed on the ECR of seven individuals with tetraplegia. All participants performed repetitive electrically-evoked wrist extension to fatigue while their muscle MMG and NIRS responses were monitored against their power output (PO). One out of seven participants showed no changes in %TSI throughout the repeated wrist FES-evoked contraction. The other six participants' %TSI was positively correlated with %PO before fatigue onset. At 50%POpeak , %TSI was negatively correlated (0.489) significantly with declining %PO as the ability of the muscle to take up oxygen became limited. The %RMS-MMG behaved analogously during pre and post-fatigue against declining %PO, whereby both displayed positive correlations of 0.443 and 0.214, respectively, (%RMS-MMG decreased) throughout the exercise session. Regression analysis revealed that %TSI was proportional to pre-fatigue and inversely proportional to %RMS-MMG during post-fatigue. The significant changes in muscle mechanomyography and tissue oxygenation correlations after 50%POpeak implied that the muscle contraction mechanical-and-physiological behavior association had been altered following FES-evoked fatigue.

Muscle oxygenation during normoxic and hypoxic cycling exercise in humans with high-affinity haemoglobin.

What is the central question of this study? Do humans with high-affinity haemoglobin (HAH) demonstrate attenuated skeletal muscle deoxygenation during normoxic and hypoxic exercise? What is the main finding and its importance? Examination of near-infrared spectroscopy-derived muscle oxygenation profiles suggests that fractional oxygen extraction is blunted during hypoxic exercise in humans with HAH compared with control subjects. However, muscle tissue oxygen saturation levels were higher in humans with HAH during exercise in normoxia compared with control subjects. These alterations in fractional oxygen extraction in humans with HAH might influence blood flow regulation and exercise capacity during hypoxia. Recently, researchers in our laboratory have shown that humans with genetic mutations resulting in high-affinity haemoglobin (HAH) demonstrate better maintained aerobic capacity and peak power output during hypoxic exercise versus normoxic exercise in comparison to humans with normal-affinity haemoglobin. However, the influence of HAH on tissue oxygenation within exercising muscle during normoxia and hypoxia is unknown. Therefore, we examined near-infrared spectroscopy-derived oxygenation profiles of the vastus lateralis during graded cycling exercise in normoxia and hypoxia among humans with HAH (n=5) and control subjects with normal-affinity haemoglobin (n=12). The HAH group elicited a blunted increase of deoxygenated haemoglobin+myoglobin during hypoxic exercise compared with the control group (P = 0.03), suggesting reduced fractional oxygen extraction in the HAH group. In addition, the HAH group maintained a higher level of muscle tissue oxygen saturation during normoxic exercise (HAH, 75 ± 4% vs. controls, 65 ± 3%, P = 0.049) and there were no differences between groups in muscle tissue oxygen saturation during hypoxic exercise (HAH, 68 ± 3% vs. controls, 68 ± 2%, P = 0.943). Overall, our results suggest that humans with HAH might demonstrate divergent patterns of fractional oxygen extraction during hypoxic exercise and elevated muscle tissue oxygenation during normoxic exercise compared with control subjects.

Effects of Forearm Compression Sleeves on Muscle Hemodynamics and Muscular Strength and Endurance Parameters in Sports Climbing: A Randomized, Controlled Crossover Trial.

Purpose: Wearing compression garments is a commonly used intervention in sports to improve performance and facilitate recovery. Some evidence supports the use of forearm compression to improve muscle tissue oxygenation and enhance sports climbing performance. However, evidence is lacking for an effect of compression garments on hand grip strength and specific sports climbing performance. The purpose of this study was to evaluate the immediate effects of forearm compression sleeves on muscular strength and endurance of finger flexor muscles in sports climbers. Materials and Methods: This randomized crossover study included 24 sports climbers who performed one familiarization trial and three subsequent test trials while wearing compression forearm sleeves (COMP), non-compressive placebo forearm sleeves (PLAC), or no forearm sleeves (CON). Test trials consisted of three performance measurements (intermittent hand grip strength and endurance measurements, finger hang, and lap climbing) at intervals of at least 48 h in a randomized order. Muscle oxygenation during hand grip and finger hang measurements was assessed by near-infrared spectroscopy. The maximum blood lactate level, rate of perceived exertion, and forearm muscle pain were also determined directly after the lap climbing trials. Results: COMP resulted in higher changes in oxy[heme] and tissue oxygen saturation (StO2) during the deoxygenation (oxy[heme]: COMP –10.7 ± 5.4, PLAC –6.7 ± 4.3, CON –6.9 ± 5.0 [μmol]; p = 0.014, ηp 2 = 0.263; StO2: COMP –4.0 ± 2.2, PLAC –3.0 ± 1.4, CON –2.8 ± 1.8 [%]; p = 0.049, ηp 2 = 0.194) and reoxygenation (oxy [heme]: COMP 10.2 ± 5.3, PLAC 6.0 ± 4.1, CON 6.3 ± 4.9 [μmol]; p = 0.011, ηp 2 = 0.274; StO2: COMP 3.5 ± 1.9, PLAC 2.4 ± 1.2, CON 2.3 ± 1.9 [%]; p = 0.028, ηp 2 = 0.225) phases of hand grip measurements, whereas total [heme] concentrations were not affected. No differences were detected between the conditions for the parameters of peak force and fatigue index in the hand grip, time to failure and hemodynamics in the finger hang, or performance-related parameters in the lap climbing measurements (p ≤ 0.05). Conclusions: Forearm compression sleeves did not enhance hand grip strength and endurance, sports climbing performance parameters, physiological responses, or perceptual measures. However, they did result in slightly more pronounced changes of oxy [heme] and StO2 in the deoxygenation and reoxygenation phases during the hand grip strength and endurance measurements.

Polyethylene glycol‐20 ameliorates tissue ischemia and improves renal function following traumatic shock

The “Golden Hour” policy used for US Troops in Iraq and Afghanistan has contributed to the highest survival rates for combat injury in history. Anticipated future combat operations require more options to optimize combat casualty care by extending “the Golden Hour” to “the Golden Day.” Low volume resuscitation with polyethylene glycol‐20K (PEG) has been shown to decrease mortality following hemorrhagic shock, however, the effect of PEG on tissue perfusion and renal function has not been determined. We hypothesized that PEG can ameliorate ischemia and prevent renal injury during prolonged traumatic shock. Anesthetized rats received extremity trauma (soft tissue injury and fracture in one hindlimb) and pressure‐controlled hemorrhage, with mean arterial pressure (MAP) maintained at 55mmHg. MAP, heart rate, renal blood flow (RBF, perivascular ultrasonic transit time flow probe), peripheral skeletal muscle microcirculatory flow and tissue oxygen partial pressure (OxyLite needle probes), blood gases, and electrolytes were monitored throughout the experiment. Glomerular filtration rate (GFR) was recorded using a non‐invasive Fluorescein isothiocyanate‐sinistrin transcutaneous technique. After 45 minutes of shock with MAP at 55mmHg, rats were randomly treated with an intravenous bolus of either 7.5% PEG or saline (1.3 ml/kg, n = 5/group). Measurements were continued from the 45th to the 165th minute without MAP control or any other treatment. Compared with saline, PEG markedly improved MAP recovery (P &lt; 0.001) and survival (P &lt; 0.01) (Figures 1A and 1B). Microcirculatory perfusion and oxygen partial pressure were markedly decreased after hemorrhage and saline treatment elicited no additional effect. However, with PEG, the decreases in capillary flow and tissue oxygen levels were significantly attenuated (P = 0.04 and 0.03, respectively) (Figure 2A). Moreover, blood lactate levels continuously increased in the saline group but returned to levels comparable to baseline within 30 minutes after PEG treatment (P &lt; 0.001) (Figure 2B). In the saline group, RBF markedly decreased concomitantly with a sustained increase in renal vascular resistance (RVR) during the shock period. PEG treatment rapidly restored RBF (P &lt; 0.001) to levels comparable to baseline along with a normalized RVR. GFR was diminished in the saline‐treated rats but was improved in the PEG‐treated group (0.07 ± 0.05 vs. 0.67 ± 0.06 ml/min/100g, respectively; P &lt; 0.001). These results provide strong evidence that PEG rapidly improves macro‐ and microcirculatory hemodynamics ameliorates tissue ischemia, and minimize renal injury and mortality following prolonged traumatic shock.

New Porcine Model of Arteriovenous Fistula Documents Increased Coronary Blood Flow at the Cost of Brain Perfusion.

Background: Arteriovenous fistulas (AVF) represent a low resistant circuit. It is known that their opening leads to decreased systemic vascular resistance, increased cardiac output and other hemodynamic changes. Possible competition of AVF and perfusion of other organs has been observed before, however the specific impact of AVF has not been elucidated yet. Previous animal models studied long-term changes associated with a surgically created high flow AVF. The aim of this study was to create a simple AVF model for the analysis of acute hemodynamic changes. Methods: Domestic female pigs weighing 62.6 ± 5.2 kg were used. All the experiments were held under general anesthesia. The AVF was created using high-diameter ECMO cannulas inserted into femoral artery and vein. Continuous hemodynamic monitoring was performed throughout the protocol. Near-infrared spectroscopy sensors, flow probes and flow wires were inserted to study brain and heart perfusion. Results: AVF blood flow was 2.1 ± 0.5 L/min, which represented around 23% of cardiac output. We observed increase in cardiac output (from 7.02 ± 2.35 L/min to 9.19 ± 2.99 L/min, p = 0.0001) driven dominantly by increased heart rate, increased pulmonary artery pressure, and associated right ventricular work. Coronary artery flow velocity rose. On the contrary, carotid artery flow and brain and muscle tissue oxygenation measured by NIRS decreased significantly. Conclusions: Our new non-surgical AVF model is reproducible and demonstrated an acute decrease of brain and muscle perfusion.

A Novel Methodology for the Synchronous Collection and Multimodal Visualization of Continuous Neurocardiovascular and Neuromuscular Physiological Data in Adults with Long COVID.

Background: Reports suggest that adults with post-COVID-19 syndrome or long COVID may be affected by orthostatic intolerance syndromes, with autonomic nervous system dysfunction as a possible causal factor of neurocardiovascular instability (NCVI). Long COVID can also manifest as prolonged fatigue, which may be linked to neuromuscular function impairment (NMFI). The current clinical assessment for NCVI monitors neurocardiovascular performance upon the application of orthostatic stressors such as an active (i.e., self-induced) stand or a passive (tilt table) standing test. Lower limb muscle contractions may be important in orthostatic recovery via the skeletal muscle pump. In this study, adults with long COVID were assessed with a protocol that, in addition to the standard NCVI tests, incorporated simultaneous lower limb muscle monitoring for NMFI assessment. Methods: To conduct such an investigation, a wide range of continuous non-invasive biomedical sensing technologies were employed, including digital artery photoplethysmography for the extraction of cardiovascular signals, near-infrared spectroscopy for the extraction of regional tissue oxygenation in brain and muscle, and electromyography for assessment of timed muscle contractions in the lower limbs. Results: With the proposed methodology described and exemplified in this paper, we were able to collect relevant physiological data for the assessment of neurocardiovascular and neuromuscular functioning. We were also able to integrate signals from a variety of instruments in a synchronized fashion and visualize the interactions between different physiological signals during the combined NCVI/NMFI assessment. Multiple counts of evidence were collected, which can capture the dynamics between skeletal muscle contractions and neurocardiovascular responses. Conclusions: The proposed methodology can offer an overview of the functioning of the neurocardiovascular and neuromuscular systems in a combined NCVI/NMFI setup and is capable of conducting comparative studies with signals from multiple participants at any given time in the assessment. This could help clinicians and researchers generate and test hypotheses based on the multimodal inspection of raw data in long COVID and other cohorts.

Structural change of myoglobin structure after binding with spermidine

Myoglobin is the iron-rich protein of 153 or 154 amino acid residues, comprising a prosthetic group of heme (iron-containing porphyrin). It is responsible for the reversible binding and transporting of molecular oxygen in muscle tissue. There are proximal and distal histidine groups. The proximal His group joined specifically to the iron center and a distal histidine group on the inverse confront, not bonded to the iron. Horse heart myoglobin contains two tyrosine residues and two tryptophan residues. Multi-spectroscopic, thermodynamic, molecular docking, and molecular dynamics simulations were used in the present study to investigate the variations instability, structure, and function of horse heart myoglobin (Mb) in the presence of polyamine spermidine. Reports from the different experiments have shown that spermidine is bound to myoglobin. Steady-state fluorescence analysis showed a static quenching system as the primal quenching mechanism in the myoglobin − spermidine interaction, which is confirmed by UV − Visible and molecular docking studies. Thermodynamic and molecular docking findings demonstrate spermidine binding to myoglobin is driven mainly by van der Waals force and hydrogen bonding forces. The CD spectrum showed the secondary variation in myoglobin structure with a rise in α-helicity after ligand binding and a small decrease in myoglobin β-sheet after.

Non-invasively Measured Venous Oxygen Saturation as Early Marker of Impaired Oxygen Delivery in Preterm Neonates.

IntroductionAdequate oxygen supply for preterm neonates may be defined through non-invasive measurement of venous oxygen saturation (SvO2) and fractional oxygen extraction using near-infrared spectroscopy (NIRS). We investigated whether there was a difference in peripheral muscle SvO2 (pSvO2) and peripheral fractional oxygen extraction (pFOE) in preterm neonates with early inflammation/infection compared to healthy subjects during the first 72 h after birth.Materials and MethodsWe retrospectively analyzed secondary outcome parameters of prospective observational studies, including preterm neonates at risk of infection in whom peripheral NIRS measurements were performed in combination with venous occlusions. Early neonatal inflammation/infection was diagnosed by clinical signs and laboratory parameters. Peripheral muscle tissue oxygenation index (pTOI) was measured using either NIRO 300 or NIRO 200-NX (both Hamamatsu Photonics, Japan) on the patients' lower legs. Using 20-s venous occlusions, pSvO2 and pFOE were calculated incorporating simultaneous measurements of arterial oxygen saturation (SpO2).ResultsWe analyzed measurements from 226 preterm neonates (median gestational age 33.9 weeks), 64 (28.3%) of whom were diagnosed with early neonatal inflammation/infection. During the first 24 h after birth, pSvO2 (66.9% [62.6–69.2] vs. 69.4% [64.6–72.0]; p = 0.04) and pTOI (68.6% [65.3–71.9] vs. 71.7% [67.3–75.1]; p = 0.02) were lower in those neonates with inflammation/infection, while there was no such difference for measurements between 24–48 and 48–72 h.DiscussionNIRS measurement of pSvO2 and pFOE is feasible and may be utilized for early detection of impaired peripheral oxygen delivery. As pTOI was also significantly lower, this parameter may serve as substitute for diminished regional oxygen supply.

Test-retest reliability of skeletal muscle oxygenation measurement using near-infrared spectroscopy during exercise in patients with sport-related iliac artery flow limitation.

The ankle‐brachial index is an accurate tool for detecting claudication in atherosclerotic patients. However, this technique fails to identify subtle flow limitations of the iliac arteries (FLIA) in endurance athletes. Near‐infrared spectroscopy (NIRS) is a noninvasive technique that measures skeletal muscle tissue oxygenation status. The aim of the present study is to examine the absolute and relative test–retest reliability of NIRS and evaluate its potential as a diagnostic tool in FLIA. NIRS‐derived exercise variables were analyzed during exercise and recovery in FLIA 17 patients and 19 healthy controls. The relative reliability of absolute variables (such as the maximal value) were slight to yet predominantly substantial (intraclass correlation coefficient [ICC], ICC range: 0.06–0.76) with good to excellent absolute reliability (absolute limits of agreement [ALoA], ALoA range: 0.8 ± 10.2 to 0.7 ± 13.1; coefficient of variation [CV], CV range: 5%–11%). Absolute values encompassing signal amplitudes showed moderate to almost perfect relative reliability (ICC range: 0.51–0.89) and poor to good absolute reliability (ALoA range: −1.3 ± 7.0 to −2.5 ± 15.7; CV range: 15%–32%). Kinetic variables showed moderate to almost perfect relative reliability for most recovery kinetics variables (ICC range: 0.54–0.86) with fair to good absolute reliability (ALoA range: 0.4 ± 12.2 to 3.9 ± 37.9; CV range: 18%–27%). Particularly, kinetic variables showed significant differences between patients and healthy subjects. NIRS is found to be a reliable method for examining muscle tissue oxygenation variables. Given the significant differences in especially recovery kinetics between normal subjects and patients, NIRS may contribute to diagnosing FLIA in endurance athletes.

Benefits of Concurrent Aerobic-Resistance Interval Exercise in Patients with Chronic Obstructive Pulmonary Disease

Physical training of lower leg skeletal muscle has been shown to increase exercise tolerance in Chronic Obstructive Pulmonary Disease (COPD) patients. The objective of this study was to measure the effect of concurrent aerobic-resistance interval exercise on lower leg muscle function and local muscle tissue oxygenation in the vastus lateralis muscle (VLM) of COPD patients.

Effect of oxygen therapy on exercise performance in patients with cyanotic congenital heart disease: Randomized-controlled trial

BackgroundPatients with unrepaired cyanotic congenital heart disease (CHD) suffer from aggravated hypoxemia during exercise. We tested the hypothesis that supplemental oxygen improves exercise performance in these patients. MethodsIn this randomized, sham-controlled, single-blind, cross-over trial cyanotic CHD-patients underwent four cycle exercise tests to exhaustion, while breathing either oxygen-enriched (FiO2 0.50, oxygen) or ambient air (FiO2 0.21, air) using incremental (IET) or constant work-rate (CWRET) exercise test protocols (75% of maximal work rate achieved under FiO2 0.21). Pulmonary gas-exchange, electrocardiogram, arterial blood gases, oxygen saturation (SpO2), cerebral and quadriceps muscle tissue oxygenation (CTO and QMTO) by near-infrared spectroscopy were measured. ResultsWe included seven patients with cyanotic CHD (4 Eisenmenger syndrome, 3 unrepaired cyanotic defects, 4 women) median (quartiles) age 36 (32;50) years, BMI 23 (20;26) kg/m2 and SpO2 at rest 87 (83;89) %. When comparing supplemental oxygen with air during exercise, maximal work-rate in IET increased from 76 (58;114) Watts to 83 (67;136) Watts, median difference 9 (0;22) W (p = 0.046) and CWRET-time increased from 412 s (325;490) to 468 s (415;553), median increase 56 (39;126) s (p = 0.018). In both IET and CWRET SpO2 was significantly higher and ventilatory equivalent for carbon dioxide significantly lower at end-exercise with oxygen compared to air, whereas CTO and QMTO did not significantly differ. ConclusionsPatients with cyanotic CHD significantly improved their exercise performance, in terms of maximal work-rate and endurance time along with an improved arterial oxygenation and ventilatory efficiency with supplemental oxygen compared to air.

Exercise Training Increases Resting Calf Muscle Oxygen Metabolism in Patients with Peripheral Artery Disease.

Exercise training can mitigate symptoms of claudication (walking-induced muscle pain) in patients with peripheral artery disease (PAD). One adaptive response enabling this improvement is enhanced muscle oxygen metabolism. To explore this issue, we used arterial-occlusion diffuse optical spectroscopy (AO-DOS) to measure the effects of exercise training on the metabolic rate of oxygen (MRO2) in resting calf muscle. Additionally, venous-occlusion DOS (VO-DOS) and frequency-domain DOS (FD-DOS) were used to measure muscle blood flow (F) and tissue oxygen saturation (StO2), and resting calf muscle oxygen extraction fraction (OEF) was calculated from MRO2, F, and blood hemoglobin. Lastly, the venous/arterial ratio (γ) of blood monitored by FD-DOS was calculated from OEF and StO2. PAD patients who experience claudication (n = 28) were randomly assigned to exercise and control groups. Patients in the exercise group received 3 months of supervised exercise training. Optical measurements were obtained at baseline and at 3 months in both groups. Resting MRO2, OEF, and F, respectively, increased by 30% (12%, 44%) (p < 0.001), 17% (6%, 45%) (p = 0.003), and 7% (0%, 16%) (p = 0.11), after exercise training (median (interquartile range)). The pre-exercise γ was 0.76 (0.61, 0.89); it decreased by 12% (35%, 6%) after exercise training (p = 0.011). Improvement in exercise performance was associated with a correlative increase in resting OEF (R = 0.45, p = 0.02).

Effects of changes in end-tidal carbon dioxide tension on oral tissue blood flow and tissue oxygen tension during remifentanil infusion in rabbits.

The aim of this study was to investigate the effects of end-tidal carbon dioxide tension (ETCO2) changes during remifentanil infusion on mandibular bone marrow tissue blood flow (BBF), masseter muscle tissue blood flow (MBF), mandibular bone marrow tissue oxygen tension (PbO2) and masseter muscle tissue oxygen tension (PmO2) in rabbits. Ten male tracheotomized Japan White rabbits were anesthetized and ventilated with sevoflurane. ETCO2 was adjusted to 30mmHg. After baseline measurement, CO2 was added to the inhaled air, and ETCO2 was increased to 40 and 60mmHg. Heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), BBF, MBF, PbO2, and PmO2 were recorded with and without remifentanil infusion at 0.4µg/kg/min. Two-way repeated measures analysis of variance showed no interaction between ETCO2 and remifentanil in all variables. Remifentanil infusion produced decreases in HR, SBP, MAP, BBF and MBF compared with those without remifentanil infusion, while it did not affect DBP, PbO2 and PmO2. Elevation of ETCO2 from 30 to 60mmHg produced decreases in HR and MBF, and increases in SBP, DBP, MAP and BBF, while it did not affect PbO2 and PmO2. PbO2 and PmO2 remained unchanged despite changes in BBF and MBF during ETCO2 change with or without remifentanil infusion.