Time-resolved Near-infrared Spectroscopy Research Articles

Continuous non-invasive optical monitoring of cerebral blood flow and oxidative metabolism after acute brain injury

Rapid detection of ischemic conditions at the bedside can improve treatment of acute brain injury. In this observational study of 11 critically ill brain-injured adults, we employed a monitoring approach that interleaves time-resolved near-infrared spectroscopy (TR-NIRS) measurements of cerebral oxygen saturation and oxygen extraction fraction (OEF) with diffuse correlation spectroscopy (DCS) measurement of cerebral blood flow (CBF). Using this approach, we demonstrate the clinical promise of non-invasive, continuous optical monitoring of changes in CBF and cerebral metabolic rate of oxygen (CMRO2). In addition, the optical CBF and CMRO2 measures were compared to invasive brain tissue oxygen tension (PbtO2), thermal diffusion flowmetry CBF, and cerebral microdialysis measures obtained concurrently. The optical CBF and CMRO2 information successfully distinguished between ischemic, hypermetabolic, and hyperemic conditions that arose spontaneously during patient care. Moreover, CBF monitoring during pressor-induced changes of mean arterial blood pressure enabled assessment of cerebral autoregulation. In total, the findings suggest that this hybrid non-invasive neurometabolic optical monitor (NNOM) can facilitate clinical detection of adverse physiological changes in brain injured patients that are otherwise difficult to measure with conventional bedside monitoring techniques.

Cerebral oxygenation and blood flow in term infants during postnatal transition: BabyLux project

ObjectivesA new device that combines, for the first time, two photonic technologies (time-resolved near-infrared spectroscopy and diffuse correlation spectroscopy) was provided and tested within the BabyLux project. Aim was to...

BabyLux device: a diffuse optical system integrating diffuse correlation spectroscopy and time-resolved near-infrared spectroscopy for the neuromonitoring of the premature newborn brain.

The BabyLux device is a hybrid diffuse optical neuromonitor that has been developed and built to be employed in neonatal intensive care unit for the noninvasive, cot-side monitoring of microvascular cerebral blood flow and blood oxygenation. It integrates time-resolved near-infrared and diffuse correlation spectroscopies in a user-friendly device as a prototype for a future medical grade device. We present a thorough characterization of the device performance using test measurements in laboratory settings. Tests on solid phantoms report an accuracy of optical property estimation of about 10%, which is expected when using the photon diffusion equation as the model. The measurement of the optical and dynamic properties is stable during several hours of measurements within 3% of the average value. In addition, these measurements are repeatable between different days of measurement, showing a maximal variation of 5% in the optical properties and 8% for the particle diffusion coefficient on a liquid phantom. The variability over test/retest evaluation is . The integration of the two modalities is robust and without any cross talk between the two. We also perform in vivo measurements on the adult forearm during arterial cuff occlusion to show that the device can measure a wide range of tissue hemodynamic parameters. We suggest that this platform can form the basis of the next-generation neonatal neuromonitors to be developed for extensive, multicenter clinical testing.

Unaltered V̇o2 kinetics despite greater muscle oxygenation during heavy-intensity two-legged knee extension versus cycle exercise in humans.

Relative perfusion of active muscles is greater during knee extension ergometry (KE) than cycle ergometry (CE). This provides the opportunity to investigate the effects of increased O2 delivery (Q̇o2) on deoxygenation heterogeneity among quadriceps muscles and pulmonary oxygen uptake (V̇o2) kinetics. Using time-resolved near-infrared spectroscopy, we hypothesized that compared with CE the superficial vastus lateralis (VL), superficial rectus femoris, and deep VL in KE would have 1) a smaller amplitude of the exercise-induced increase in deoxy[Hb + Mb] (related to the balance between V̇o2 and Q̇o2); 2) a greater amplitude of total[Hb + Mb] (related to the diffusive O2 conductance); 3) a greater homogeneity of regional muscle deoxy[Hb + Mb]; and 4) no difference in pulmonary V̇o2 kinetics. Eight participants performed square-wave KE and CE exercise from 20 W to heavy work rates. Deoxy[Hb + Mb] amplitude was less for all muscle regions in KE (P < 0.05: superficial, KE 17-24 vs. CE 19-40; deep, KE 19 vs. CE 26 μM). Furthermore, the amplitude of total[Hb + Mb] was greater for KE than CE at all muscle sites (P < 0.05: superficial, KE, 7-21 vs. CE, 1-16; deep, KE, 11 vs. CE, -3 μM). Although the amplitude and heterogeneity of deoxy[Hb + Mb] were significantly lower in KE than CE during the first minute of exercise, the pulmonary V̇o2 kinetics was not different for KE and CE. These data show that the microvascular Q̇o2 to V̇o2 ratio, and thus tissue oxygenation, was greater in KE than CE. This suggests that pulmonary and muscle V̇o2 kinetics in young healthy humans are not limited by Q̇o2 during heavy-intensity cycling.

Compression Stockings Suppressed Reduced Muscle Blood Volume and Oxygenation Levels Induced by Persistent Sitting

This study quantitatively analyzed the effects of 3 h of constant sitting on skeletal muscle oxygenation in the lower extremities, using near-infrared time-resolved spectroscopy (NIRTRS). The effects of compression stockings were also evaluated. Eleven healthy men (age, 30.0 ± 6.7 years) maintained their knee joints at 90° flexion during 3 h of constant sitting and wore a compression stocking on either the right or left leg. The side the stocking was worn was chosen randomly. Subsequently, leg circumference and extracellular water were measured. After 3 h of sitting, both factors increased significantly in uncompressed limbs. Furthermore, intracellular water and muscle oxygenation had significantly decreased. In contrast, extracellular water had not increased in the limbs wearing compression stockings. Furthermore, the increased circumference of compressed limbs was significantly smaller than that of uncompressed limbs. Decreases in oxygenated hemoglobin and total hemoglobin were significantly smaller in compressed limbs than in uncompressed limbs (oxy-Hb; p = 0.021, total-Hb; p = 0.013). Three hours of sitting resulted in decreased intracellular water and increased extracellular water in the lower extremities, leading to reduced blood volume and oxygenation levels in skeletal muscle. Compression stockings successfully suppressed these negative effects.

Accuracy and precision of tissue optical properties and hemodynamic parameters estimated by the BabyLux device: a hybrid time-resolved near-infrared and diffuse correlation spectroscopy neuro-monitor

We have investigated the accuracy and precision of "the BabyLux device", a hybrid time-resolved near-infrared (TRS) and diffuse correlation spectroscopy (DCS) neuro-monitor for the pre-term infant. Numerical data with realistic noise were simulated and analyzed using the BabyLux device as a reference system and different experimental and analysis parameters. The results describe the limits for the precision and the accuracy to be expected. The dependence of these limits on different experimental conditions and choices of the analysis method is also described. Experiments demonstrate comparable values for precision with respect to the simulation results.

Abstract TP168: Impairment of Cerebral Blood Flow Autoregulation in Patients With Acute Cerebral Infarction Recovered Within 7-10 Days After Onset

InIntroduction: Cerebral blood flow (CBF) autoregulation is impaired after acute cerebral infarction (AIS). Although previous studies revealed that changes in cerebral oxygenation occurred when head-of-bed raised from flat to head-up position within 72hr after onset, chronological changes of this phenomenon had never been evaluated. Hypothesis: We hypothesized that the impairment of CBF autoregulation improved within 7-10 days after onset of AIS. We aimed to evaluated the chronological changes in oxygenated- (ΔHbO 2 ), deoxygenated- (ΔHb) and total-hemoglobin (ΔtHb) concentration in response to passive sitting between &lt;72hr and 7-10 days after onset of AIS. Method: We repeatedly measured forehead ΔHbO2, ΔHb and ΔtHb in response to raise the head-of-bed to 30 degrees from spine within 72hr (1 st measurement) and 7-10 days (2 nd measurement) after onset of AIS by using time-resolved near-infrared spectroscopy. Difference in the ΔHbO2, ΔHb and ΔtHb values between two measurements were compared. We also evaluated Spearman Rank Correlation Coefficient of those values between affected and unaffected side in each measurement. Results: A total of 37 participants (mean age, 70.4±12.5 years; 13 females) with a first AIS hospitalization in the Seirei Mikatahara General Hospital, Hamamatsu, Japan, were enrolled. No significant differences of ΔHbO 2, ΔHb or ΔtHb in either affected or unaffected side were observed between two measurements. The ΔHbO 2, ΔHb or ΔtHb of the affected side did not correlate with those in the unaffected side at the first measurement (ΔHbO 2 ; r=0.197, p=0.282, ΔHb; r=0.065, p=0.695. and ΔtHb; r=0.193, p=0.245, respectively). Interestingly, the correlation coefficients of the ΔHbO 2, ΔHb and ΔtHb between affected and unaffected side at the 2 nd measurement were statistically significant (ΔHbO 2 ; r=0.420, p=0.011, ΔHb; r=0.398, p=0.017. and ΔtHb; r=0.490, p=0.003, respectively). Conclusion: Although cerebral oxygenation changes in relation to posture change did not correlate between affected or unaffected side within 72hr after onset, this difference was improved in 7-10 days after onset. Our result suggested that the impairment of CBF autoregulation improved, at least partially, within 7-10 days after onset of AIS.

Eight-Wavelength, Dual Detection Channel Instrument for Near-Infrared Time-Resolved Diffuse Optical Spectroscopy

In this paper, we present an innovative instrument for near-infrared time-resolved spectroscopy. The system is based on eight custom-designed pulsed diode lasers emitting at different wavelengths in the near-infrared region (635–1050 nm), all exhibiting an average optical power higher than 1 mW at 40 MHz pulse repetition rate, two custom-made single-photon detectors based on wide-area silicon photomultipliers and two time-measurement units based on a custom time-to-digital converter with 10 ps timing resolution. The system instrument response function has a width narrower than 160 ps (fullwidth at half-maximum) and stability better than ±1% for several hours for all the wavelengths. All the components of the instrument were designed in order to be compact. The entire system will be hosted in a standard 19 inches, 5U rack case (size 48 × 38 × 20 cm3 ). The system communicates with the external computer through a USB 2.0 link and is designed to be employed in a clinical environment. The proposed instrument, thanks to the reduction of its cost and dimensions, paves the way to a wider diffusion of multiwavelengths near-infrared time-resolved spectroscopy systems.

Effect of Source-Detector Distance on the Measurement of Hemoglobin Using Near-Infrared Spectroscopy in Breast Cancer.

We measured total hemoglobin concentrations in breast tumors by near-infrared time-resolved spectroscopy. Muscles interfere with measurement when the probe is close to the chest wall. Since the target area of measurement depends on the distance between the light source and probe detector, we inferred that this issue could be solved by reducing the source-detector distance. The purpose of this study was to examine the effects of the source-detector distance on the measurement of total hemoglobin concentration in the breast. We examined 26 patients with breast tumors. Total hemoglobin concentration was measured in tumors and the contralateral normal breasts at source-detector distances of 20 and 30 mm. The difference in total hemoglobin concentration between each tumor and the contralateral breast was calculated. The normal breast total hemoglobin concentration was significantly smaller for the source-detector distance of 20 mm than for the source-detector distance of 30 mm. Differences in source-detector distance did not significantly affect tumor total hemoglobin. The difference in total hemoglobin concentration between the tumor and the contralateral breast obtained at the source-detector distance of 20 mm was significantly higher than that obtained at the source-detector distance of 30 mm. From these results, we considered that measurement with a source-detector distance of 20 mm is less affected by the chest wall than with a source-detector distance of 30 mm and that the difference in total hemoglobin concentration between the tumor and the contralateral breast at a source-detector distance of 20 mm can better reflect the net total hemoglobin concentrations of the breast tumors. In conclusion, using a probe with a source-detector distance of 20 mm can more accurately evaluate the total hemoglobin concentration in breast tumors.

Correction by the skin-to-chest wall distance in near-infrared spectroscopy and assessment of breast cancer responses to neoadjuvant chemotherapy

The measurement of hemoglobin (Hb) concentrations in breast cancer by near-infrared spectroscopy is useful for the assessment of responses to neoadjuvant chemotherapy (NAC). However, the chest wall muscles may affect this measurement. We corrected Hb concentrations based on the skin-to-chest wall distance. Corrected Hb was compared with uncorrected Hb as a marker of treatment responses in breast cancer patients. We measured total Hb (tHb) in breast cancer using a near-infrared time-resolved spectroscopy system in 10 patients before chemotherapy and after the first and second courses of NAC. To assess the skin-to-chest wall distance and thickness of tumors, ultrasound images were obtained using an ultrasonography probe with the spectroscopic probe. Net tHb (tHbnet) was calculated by subtracting tHb in normal breast tissue from cancer tHb. Patients underwent positron emission tomography with [18F] fluorodeoxyglucose (FDG) before chemotherapy and after the second course of NAC. FDG uptake was evaluated using the maximum standardized uptake value (SUVmax). tHb, tHbnet, and SUVmax in cancer significantly decreased in the course of chemotherapy. The change in tHbnet was larger than that in tHb. Although a correlation was not observed between the change in tHb and that in SUVmax, a positive correlation was noted between the change in tHbnet and that in SUVmax. Corrections by the skin-to-chest wall distance in spectroscopy led to the change in Hb concentrations being more similar to that in FDG uptake after NAC in breast cancer. tHbnet has potential as a reliable biomarker of breast cancer.

Physiological Effects of Touching the Wood of Hinoki Cypress (Chamaecyparis obtusa) with the Soles of the Feet.

We clarified the physiological effects of tactile stimulation of the soles of the feet with the wood of the Hinoki cypress (Chamaecyparis obtusa) based on measurements of prefrontal cortex and autonomic nervous activities. Nineteen female university-attending students (age: 21.2 ± 0.3 years) were included. Oxy-hemoglobin (oxy-Hb) concentrations in the prefrontal cortex were determined by using near-infrared time-resolved spectroscopy. The high frequency (HF) indicating parasympathetic nervous activity and the ratio of low frequency (LF)/HF indicating sympathetic nervous activity were measured using heart rate variability. To evaluate the psychological effects caused by contact with the materials, the modified semantic differential method was used. The soles of the participants’ feet were touched to a 600 × 600-mm plate made of Hinoki, which was finished in non-coating and brushing for 90 s. A marble plate served as the control. Next, subjective evaluation tests were administered to the participants. Compared with touching marble, touching Hinoki significantly (1) decreased the oxy-Hb concentrations in the left and right prefrontal cortices, which indicates decreased prefrontal cortex activity, (2) increased ln(HF), which indicates increased parasympathetic nervous activity, (3) decreased ln(LF/HF) ratio, which indicates decreased sympathetic nervous activity. Additionally, (4) according to subjective evaluations, the participants perceived themselves as being more “comfortable,” “relaxed,” “natural,” “warm,” “uneven,” “dry,” and “soft” after touching Hinoki. Thus, our cumulative findings indicate that touching Hinoki with the soles of the feet induces physiological relaxation.

A Quantitative Comparison of Hemoglobin Concentration and BOLD Signal using Time-Resolved Near-Infrared Spectroscopy

A Quantitative Comparison of Hemoglobin Concentration and BOLD Signal using Time-Resolved Near-Infrared Spectroscopy

Human Brown Adipose Tissue Density Assessed by Near-Infrared Time-Resolved Spectroscopy Inversely Correlates with the Body Mass Index in Patients with Type 2 Diabetes

Background: Near-infrared time-resolved spectroscopy is a non-invasive method that facilitates analysis of human brown adipose tissue (BAT) density. We measured BAT density in middle-aged patients who had type 2 diabetes by this method and examined the relationship using clinical parameters. Methods: We studied 33 Japanese middle-aged diabetic patients (30 male and 3 female, age 53.8±10.1 years, BMI 25.4±4.5, and HbA1c 7.2±1.1%). Tissue hemoglobin concentration (tHb) of the supraclavicular region was measured using near-infrared time-resolved spectroscopy, and normalized by subcutaneous fat thickness at the measurement sites. Results: The average tHb concentration was 51.1±17.7 μM and lower than 77.8 μM—the value equivalent to the detection threshold of BAT by standard FDG-PET in young adults. Univariate regression analysis showed that the tHb of the supraclavicular region was inversely correlated with BMI (r = −0.55, p=0.0009), but the tHb of the deltoid region was not (r = 0.04, p = 0.31). Other parameters showing significant correlations with BAT mass included systolic blood pressure (r = −0.47, p = 0.01) and insulin treatment (r=0.45, p=0.01). Multivariate regression analysis suggested that BMI (β=−0.42, p=0.005), systolic blood pressure (β=−0.29, p=0.042), and insulin treatment (β=0.34, p=0.015) independently account for BAT density. Conclusion: Our findings suggest that BAT density in middle-aged diabetic patients may relate to obesity more closely than previously thought. Disclosure H. Waki: Research Support; Self; MSD K.K., Novartis Pharma K.K., Boehringer Ingelheim Pharmaceuticals, Inc., Sanofi K.K., Ono Pharmaceutical Co., Ltd., Kyowa Hakko Kirin Co., Ltd., Takeda PHarmaceutical Co., Ltd.. N. Watanabe: None. S. Fuse: None. Y. Kurosawa: None. T. Yamauchi: Research Support; Self; Novo Nordisk Inc., Daiichi Sankyo Company, Limited, Sanofi, Takeda, Tanabe-Mitsubishi. R. Kime: None. T. Hamaoka: None. T. Kadowaki: Consultant; Self; Novo Nordisk A/S, AstraZeneca, Merck Sharp &amp; Dohme Corp.. Research Support; Self; Kissei Pharmaceutical Co., Ltd., Taisho Pharmaceutical Co., Ltd., Sanofi, Kyowa Hakko Kirin Co., Ltd., Novo Nordisk A/S, Astellas Pharma, Daiichi Sankyo Company, Limited, Takeda, Mitsubishi Tanabe Pharma Corporation, Ono Pharmaceutical Co., Ltd., Merck Sharp &amp; Dohme Corp., Nippon Boehringer Ingelheim Co. Ltd.. Speaker's Bureau; Self; Astellas Pharma, AstraZeneca, Merck Sharp &amp; Dohme Corp., Ono Pharmaceutical Co., Ltd., Takeda, Eli Lilly and Company, Nippon Boehringer Ingelheim Co. Ltd., Novo Nordisk A/S.

Brown adipose tissue density measured by near-infrared time-resolved spectroscopy in Japanese, across a wide age range.

F18-fluorodeoxyglucose (FDG)-positron emission tomography (PET) along with computed tomography (CT) is a standard method for assessing brown adipose tissue (BAT) activity. We tested the usefulness of near-infrared time-resolved spectroscopy (NIRTRS) as a simple and noninvasive method for evaluating BAT density (BAT-d) by examining the effects of some factors known to influence BAT activity. The total hemoglobin concentration as a parameter of BAT-d was evaluated using NIRTRS in the supraclavicular region in 413 Japanese individuals. The associations were analyzed between BAT-d and sex, age, the percentages of body fat (%BF), visceral fat (VF), and the seasonal ambient temperature (AmT) fluctuations. Age was associated with decreased BAT-d (P < 0.05). There was no sex difference in the BAT-d, except for those in their twenties. Multivariate analyses revealed that %BF and VF were correlated with BAT-d, and the lower AmT (around 4°C or 5°C) for 4 and 6 weeks prior to the measurement day was associated with an increase in the BAT-d. Our NIRTRS results were analogous to those reported with FDG18-PET / CT, indicating the usefulness of NIRTRS. BAT-d might increase during the 4 and 6 weeks after the AmT decreases to lower than 4°C or 5°C.

Multiwavelength time-resolved near-infrared spectroscopy of the adult head: assessment of intracerebral and extracerebral absorption changes.

An optical technique based on diffuse reflectance measurement combined with indocyanine green (ICG) bolus tracking is extensively tested as a method for the clinical assessment of brain perfusion at the bedside. We report on multiwavelength time-resolved diffuse reflectance spectroscopy measurements carried out on the head of a healthy adult during the intravenous administration of a bolus of ICG. Intracerebral and extracerebral changes in absorption were estimated from an analysis of changes in statistical moments (total number of photons, mean time of flight and variance) of the distributions of times of flight (DTOF) of photons recorded simultaneously at 16 wavelengths from the range of 650-850 nm using sensitivity factors estimated by diffusion approximation based on a layered model of the studied medium. We validated the proposed method in a series of phantom experiments and in-vivo measurements. The results obtained show that changes in the concentration of the ICG can be assessed as a function of time of the experiment and depth in the tissue. Thus, the separation of changes in ICG concentration appearing in intra- and extracerebral tissues can be estimated from optical data acquired at a single source-detector pair of fibers/fiber bundles positioned on the surface of the head.

Relationship between prolonged neural suppression and cerebral hemodynamic dysfunction during hypothermia in asphyxiated piglets

ObjectivesHypothermia (HT) improves the outcome of neonatal hypoxic-ischemic encephalopathy. Here, we investigated changes during HT in cortical electrical activity using amplitude-integrated electroencephalography (aEEG) and in cerebral blood volume (CBV) and cerebral hemoglobin oxygen saturation using near-infrared time-resolved spectroscopy (TRS) and compared the results with those obtained during normothermia (NT) after a hypoxic-ischemic (HI) insult in a piglet model of asphyxia. We previously reported that a greater increase in CBV can indicate greater pressure-passive cerebral perfusion due to more severe brain injury and correlates with prolonged neural suppression during NT. We hypothesized that when energy metabolism is suppressed during HT, the cerebral hemodynamics of brains with severe injury would be suppressed to a greater extent, resulting in a greater decrease in CBV during HT that would correlate with prolonged neural suppression after insult. MethodsTwenty-six piglets were divided into four groups: control with NT (C-NT, n = 3), control with HT (C-HT, n = 3), HI insult with NT (HI-NT, n = 10), and HI insult with HT (HI-HT, n = 10). TRS and aEEG were performed in all groups until 24 h after the insult. Piglets in the HI-HT group were maintained in a hypothermic state for 24 h after the insult. ResultsThere was a positive linear correlation between changes in CBV at 1, 3, 6, and 12 h after the insult and low-amplitude aEEG (<5 µV) duration after insult in the HI-NT group, but a negative linear correlation between these two parameters at 6 and 12 h after the insult in the HI-HT group. The aEEG background score and low-amplitude EEG duration after the insult did not differ between these two groups. Discussion and conclusionA longer low-amplitude EEG duration after insult was associated with a greater CBV decrease during HT in the HI-HT group, suggesting that brains with more severe neural suppression could be more prone to HT-induced suppression of cerebral metabolism and circulation.

Confirmation of brain death using optical methods based on tracking of an optical contrast agent: assessment of diagnostic feasibility

We aimed to determine whether optical methods based on bolus tracking of an optical contrast agent are useful for the confirmation of cerebral circulation cessation in patients being evaluated for brain death. Different stages of cerebral perfusion disturbance were compared in three groups of subjects: controls, patients with posttraumatic cerebral edema, and patients with brain death. We used a time-resolved near-infrared spectroscopy setup and indocyanine green (ICG) as an intravascular flow tracer. Orthogonal partial least squares-discriminant analysis (OPLS-DA) was carried out to build statistical models allowing for group separation. Thirty of 37 subjects (81.1%) were classified correctly (8 of 9 control subjects, 88.9%; 13 of 15 patients with edema, 86.7%; and 9 of 13 patients with brain death, 69.2%; p < 0.0001). Depending on the combination of variables used in the OPLS-DA model, sensitivity, specificity, and accuracy were 66.7–92.9%, 81.8–92.9%, and 77.3–89.3%, respectively. The method was feasible and promising in the demanding intensive care unit environment. However, its accuracy did not reach the level required for brain death confirmation. The potential usefulness of the method may be improved by increasing the depth of light penetration, confirming its accuracy against other methods evaluating cerebral flow cessation, and developing absolute parameters for cerebral perfusion.

Blood flow occlusion-related O2 extraction "reserve" is present in different muscles of the quadriceps but greater in deeper regions after ramp-incremental test.

It was recently demonstrated that an O2 extraction reserve, as assessed by the near-infrared spectroscopy (NIRS)-derived deoxygenation signal ([HHb]), exists in the superficial region of vastus lateralis (VL) muscle during an occlusion performed at the end of a ramp-incremental test. However, it is unknown whether this reserve is present and/or different in magnitude in other portions and depths of the quadriceps muscles. We tested the hypothesis that an O2 extraction reserve would exist in other regions of this muscle but is greater in deep compared with more superficial portions. Superficial (VL-s) and deep VL (VL-d) as well as superficial rectus femoris (RF-s) were monitored by a combination of low- and high-power time-resolved (TRS) NIRS. During the occlusion immediately post-ramp-incremental test there was a significant overshoot in the [HHb] signal ( P < 0.05). However, the magnitude of this increase was greater in VL-d (93.2 ± 42.9%) compared with VL-s (55.0 ± 19.6%) and RF-s (47.8 ± 14.0%) ( P < 0.05). The present study demonstrated that an O2 extraction reserve exists in different pools of active muscle fibers of the quadriceps at the end of a ramp exercise to exhaustion. The greater magnitude in the reserve observed in the deeper portion of VL, however, suggests that this portion of muscle may present a greater surplus of oxygenated blood, which is likely due to a greater population of slow-twitch fibers. These findings add to the notion that the plateau in the [HHb] signal toward the end of a ramp-incremental exercise does not indicate the upper limit of O2 extraction. NEW & NOTEWORTHY Different portions of the quadriceps muscles exhibited an untapped O2 extraction reserve during a blood flow occlusion performed at the end of a ramp-incremental exercise. In the deeper portion of the vastus lateralis muscle, this reserve was greater compared with superficial vastus lateralis and rectus femoris. These data suggest that the O2 extraction reserve may be dependent on the vascular and/or oxidative capacities of the muscles.

The Effect of Caffeine on Peak Torque, Muscle Fatigue and Prefrontal Cortex Blood Flow

PURPOSE: The purpose of this study was to assess the effect of caffeine consumption on prefrontal cortex (PFC) hemodynamics and muscular fatigue during maximal isokinetic exercise testing. METHODS: Six active (exercise >3x/week, >1 hour per bout for >3 months) individuals (age 20.6+2.3yrs, body weight 72.1 +7.3kg, height 172.6 + 14.5cm) participated in a double-blind placebo controlled study. Participants attended three separate exercise sessions on the Humac Norm Isokinetic Dynamometer. Each exercise session included three sets of 30 maximal knee extensions at 180° per second using their dominant leg. Exercise sessions were separated by one week and participants were instructed to refrain from consumption of caffeine 36 hours prior to testing. One hour prior to testing, participants were administered a placebo (NC), low caffeine (LC) (3mg/kg body weight) or high caffeine (HC) (6mg/ kg body weight) dose. Time-resolved near-infrared spectroscopy monitoring (TRS0-21, Hamamatsu) was utilized throughout testing to measure hemodynamics in the PFC. Peak torque and fatigue index were analyzed. RESULTS: The fatigue index for HC (42.78%) and LC (42.82%) was lower when compared to the NC condition (47.39%; p<0.05). Peak torque per exercise session was found to increase during LC (124.17 N*m) compared to both NC (120.00 N*m) and HC (116.75 N*m). Additionally, LC showed a significant increase in total hemoglobin levels (141.21uM) compared to NC (101.05uM) and HC (97.618uM) in the PFC. CONCLUSION: The results of the study indicate that both high and low doses of caffeine were found to reduce fatigue across the bout of fatiguing exercise, but only LC resulted in increased peak torque and total hemoglobin to the PFC. Further examination of both PFC and local muscle hemodynamics should be explored to further understand the differential response between LC and HC.

Factors affecting measurement of optic parameters by time-resolved near-infrared spectroscopy in breast cancer.

The purpose of this study was to evaluate the effects of the thickness and depth of tumors on hemoglobin measurements in breast cancer by optical spectroscopy and to demonstrate tissue oxygen saturation (SO2) and reduced scattering coefficient (μs') in breast tissue and breast cancer in relation to the skin-to-chest wall distance. We examined 53 tumors from 44 patients. Total hemoglobin concentration (tHb), SO2, and μs' were measured by time-resolved spectroscopy (TRS). The skin-to-chest wall distance and the size and depth of tumors were measured by ultrasonography. There was a positive correlation between tHb and tumor thickness, and a negative correlation between tHb and tumor depth. SO2 in breast tissue decreased when the skin-to-chest wall distance decreased, and SO2 in tumors tended to be lower than in breast tissue. In breast tissue, there was a negative correlation between μs' and the skin-to-chest wall distance, and μs' in tumors was higher than in breast tissue. Measurement of tHb in breast cancer by TRS was influenced by tumor thickness and depth. Although SO2 seemed lower and μs' was higher in breast cancer than in breast tissue, the skin-to-chest wall distance may have affected the measurements.