Changes in blood volume and oxygenation level in a working muscle during a crank cycle

PURPOSE: This study examined circulatory and metabolic changes in a working muscle during a crank cycle in a pedaling exercise with near-infrared spectroscopy (NIRS). METHODS: NIRS measurements sampled under stable metabolic and cadence conditions during incremental pedaling exercise were reordered according to the crank angles whose signals were obtained in eight male subjects. RESULTS: The reordered changes in muscle blood volume during a crank cycle demonstrated a pattern change that corresponded to changes in pedal force and electrical muscle activity for pedal thrust. The top and bottom peaks for muscle blood volume change at work intensities of 180 W and 220 W always preceded (88 +/- 32 and 92 +/- 23 ms, respectively) those for muscle oxygenation changes. Significant differences in the level of NIRS parameters (muscle blood volume and oxygenation level) among work intensities were noted with a common shape in curve changes related to pedal force. In addition, a temporary increase in muscle blood volume following a pedal thrust was detected at work intensities higher than moderate. This temporary increase in muscle blood volume might reflect muscle blood flow restriction caused by pedal thrusts. CONCLUSION: The results suggest that circulatory and metabolic conditions of a working muscle can be easily affected during pedaling exercise by work intensity. The present method, reordering of NIRS parameters against crank angle, serves as a useful measure in providing additional findings of circulatory dynamics and metabolic changes in a working muscle during pedaling exercise.     

The use of near infrared spectroscopy in sports medicine

In the last 15 years the study of the human muscle energetics in sports medicine underwent a radical change thanks to the progressive introduction of non-invasive techniques, including near infrared (NIR) spectroscopy (NIRS). NIR light (700-1000 nm) penetrates skin, subcutaneous fat and underlying muscle, and is either absorbed (by oxy- and deoxy-haemoglobin) or scattered within the tissue. NIRS is a non-invasive and relatively low cost optical technique that is becoming a widely used instrument for measuring muscle O(2) saturation and changes in haemoglobin volume. Muscle O(2) saturation represents a dynamic balance between O(2) supply and O(2) consumption in the small vessels such as the capillary, arteriolar and venular bed. NIRS offers the advantage of being less restrictive than (31)P-magnetic resonance spectroscopy with regard to muscle performance and more comfortable and suitable for the monitoring, with high temporal resolution (up to 10 Hz), of multiple muscle groups. The aim of this review is to summarise the NIRS instrumentation and the measurable parameters, the role of NIRS in muscle exercise physiology, and the applications in sports medicine. The advantages and the problems of NIRS measurements, in resting and exercising skeletal muscles, are reported. The results of several studies suggest that NIRS is a powerful tool for being applied successfully in sports medicine. NIRS can objectively evaluate muscle oxidative metabolism in athletes and its modifications following potential therapeutic strategies and specific training programs.     

Effect of cycling experience and pedal cadence on the near-infrared spectroscopy parameters

PURPOSE: Previously we demonstrated that the method to reorder near-infrared spectroscopy (NIRS) parameters against crank angle could serve as a useful measure in providing circulatory dynamics and metabolic changes in a working muscle during pedaling exercise. To examine further applicability of this method, we investigated the effects of cycling experience and pedal cadence on the NIRS parameters. METHODS: Noncyclists (NON), triathletes (TRI), and cyclists (CYC) performed pedaling exercises at a work intensity of 75% VO2max while changing pedal cadence (50, 75, 85, and 95 rpm). Physiological and biomechanical responses and NIRS parameters were measured. RESULTS: NIRS measurements determined with the reordered NIRS change demonstrated significant differences depending on the factors. The bottom peak of reordered NIRS changes in muscle blood volume and oxygenation level shifted upward with an increase in pedal cadence in NON but remained unchanged in CYC. The reordered NIRS change demonstrated a temporary increase at the crank angle corresponding to the relaxation phase of the working muscle. This temporary increase was observed even in the highest pedal cadence in CYC. The difference in levels between the peak of the temporary increase and the bottom peak of reordered NIRS change (LPB-diff) for CYC at 85 rpm was significantly larger than that for NON. The results with NIRS parameters corresponded to changes in pedal force and myoelectric activity during pedal thrust. CONCLUSIONS: The bottom peak level of the reordered NIRS changes and LPB-diff determined for blood volume are available to detect noninvasively the differences in circulatory dynamics and metabolic change during pedaling exercises performed at different pedal cadences and also to estimate the difference of physiological and technical developments for endurance cycling in athletes.     

Pilot cerebral oxygen status during air-to-air combat maneuvering

BACKGROUND: Successful monitoring of in-flight cerebral oxygen status (COS; cerebral hemoglobin concentration changes and oxygenation changes under dynamic flight conditions) was recently achieved using near-infrared spectroscopy (NIRS). In this study, we examined the effects of air-to-air combat maneuvering on COS. METHOD: Six F-15 fighter pilots performed 2-vs.-1 air-to-air combat one to three times in each of eight sorties. We took continuous measurements of the pilots' in-flight COS using a commercial NIRS system. We measured the direct effects of G-forces on COS as evidenced by relative concentrations of oxy- and deoxy-hemoglobin. RESULTS: With respect to the G-levels reached during air combat maneuvering (Gz range of -0.4 to + 9.5), oxyhemoglobin concentration (O2Hb) and tissue oxygenation index (TOI, the ratio of oxygenated to total tissue hemoglobin) decreased with increasing G-forces during aerial combat maneuver (ACM). Maximum changes in relative O2Hb ranged from -4.2 to -26 micromol x L(-1). Subjects' experience as measured by total fighter time was an independent determinant of the magnitude of decrease in relative oxygenation. CONCLUSIONS: 1. Pilots' COS declined with dynamic G-forces experienced under aerial combat conditions. 2. Fighter pilots with more flying hours maintained a higher cerebral oxygen level at the same level of G-forces than pilots with less flying time. 3. NIRS technology in the form of the NIRO-300G has matured for continuous monitoring of in-flight cerebral oxygen status under vigorous field conditions.     

In-flight cerebral oxygen status: continuous monitoring by near-infrared spectroscopy

BACKGROUND: Little is known about the in-flight cerebral oxygen status (COS) of fighter pilots. The purpose of this study was to evaluate the COS of fighter pilots during an F-15DJ flight. METHODS: Three male F-15DJ fighter pilots volunteered to serve as test subjects during aerial gunnery training (AGT) missions. During the flight, the pilots' COS was continuously monitored from the right forehead using a NIRO-300G near-infrared spectrophotometer. This new instrument is capable of measuring the concentration changes in the brain of oxygenated hemoglobin (O2Hb), reduced hemoglobin (HHb), total hemoglobin (cHb, O2Hb + HHb), and the tissue oxygenation index (TOI, O2Hb/cHb). RESULTS: Continuous changes of COS within the brain were clearly demonstrated using NIRO-300G, the changes included reductions in O2Hb, cHb, and TOI with increased +Gz, in a mirror image fashion. The maximum decreased concentration of hemoglobin during flight ranged from 12.8 to 25.6 micromol x L(-1) (of brain tissue). CONCLUSIONS: We believe this study is the first monitoring of COS during F-15 actual flight. The monitoring of COS during F-15 flight showed that the effect of +Gz was to simultaneously lower blood flow in a mirror image fashion. Our results demonstrated that near-infrared spectroscopy (NIRO-300G) provides a reliable and sensitive method for the monitoring of pilots' COS during flight.     

Use of near-infrared reflection spectroscopy to study the effects of X-ray contrast media on renal tolerance in rats: effects of a prostacyclin analogue and of phosphodiesterase inhibitors

RATIONALE AND OBJECTIVES: Use of near-infrared reflection spectroscopy (NIR-RS) as a new model to assess renal tolerance of contrast agents and determination of the effects of a prostacyclin analogue and of two phosphodiesterase inhibitors on renal tolerance. MATERIALS AND METHODS: NIR-RS was used to measure total hemoglobin, oxygenated hemoglobin and tissue oxygen saturation in the renal cortex of rats and the effect of diatrizoate, iopromide and iotrolan injected at 1 g iodine/kg alone or together with the prostacyclin derivative, iloprost, or the phosphodiesterase inhibitors, rolipram and mesopram, on these parameters. RESULTS: Injection of the contrast media alone resulted in a 10% to 35% depression of total hemoglobin, oxygenated hemoglobin, and tissue oxygen saturation approximately 40 to 100 seconds after administration, whereas saline showed no effect and mannitol solution only a minor effect. Coadministration of iloprost or pretreatment with the phosphodiesterase inhibitors, rolipram or mesopram, significantly attenuated the contrast media-induced effects. CONCLUSION: NIR-RS might be useful for the determination of contrast media-induced side effects. Stable prostacyclin analogues or phosphodiesterase inhibitors have the potential to mitigate these side effects.     

Comparison of oxygenation kinetics measured by different placements of the NIRS probe during sustained isometric gripping

The purpose of this study was to compare oxygenation kinetics measured by slightly different placements of a near-infrared spectroscopy (NIRS) probe during sustained isometric gripping. Oxygenation kinetics of sixteen young adult males was measured with two NIRS probes attached to the flexor carpiradialis muscle during gripping for 3 min. One probe (channel 1) was attached at one-third the length of a line from the medial epicondyle of the humerus to the styloid process of radius. Another probe (channel 2) was attached at the palmaris longus. Although the cross-correlation coefficients for the two probe placements regarding oxygenated hemoglobin (oxy-Hb/Mb), deoxygenated hemoglobin (deoxy-Hb/Mb) and tissue oxygenation saturation (StO₂) were low (r_xy, 0.119–0.405), Pearson’s correlation coefficients for the times to reach almost steady state for these parameters were very high (oxy-Hb/Mb, r=0.878; deoxy-Hb/Mb, r=0.769; StO₂, r=0.843; p<0.05). The difference of oxygenation kinetics between the probe placements may reflect the difference of fiber recruitment characteristics in the flexion muscle group. In conclusion, to obtain a stable measurement, it is important that the NIRS probe is placed at the same anatomical point.     

A brief review of the use of near infrared spectroscopy with particular interest in resistance exercise

There is growing interest in resistance training, but many aspects related to this type of exercise are still not fully understood. Performance varies substantially depending on how resistance training variables are manipulated. Fatigue is a complex phenomenon usually attributed to central (neuronal) and/or peripheral (muscular) origin. Cerebral oxygenation may be associated with the decision to stop exercise, and muscle oxygenation may be related to resistance training responses. Near infrared spectroscopy (NIRS) is a non-invasive optical technique used to monitor cerebral and muscle oxygenation levels. The purpose of this review is to briefly describe the NIRS technique, validation and reliability, and its application in resistance exercise. NIRS-measured oxygenation in cerebral tissue has been validated against magnetic resonance imaging during motor tasks. In muscle tissue, NIRS-measured oxygenation was shown to be highly related to venous oxygen saturation and muscle oxidative rate was closely related to phosphocreatine resynthesis, measured by (31)P-magnetic resonance spectroscopy after exercise. The test-retest reliability of cerebral and muscle NIRS measurements have been established under a variety of experimental conditions, including static and dynamic exercise. Although NIRS has been used extensively to evaluate muscle oxygenation levels during aerobic exercise, only four studies have used this technique to examine these changes during typical resistance training exercises. Muscle oxygenation was influenced by different resistance exercise protocols depending on the load or duration of exercise, the number of sets and the muscle being monitored. NIRS is a promising, non-invasive technique that can be used to evaluate cerebral and muscle oxygenation levels simultaneously during exercise, thereby improving our understanding of the mechanisms influencing performance and fatigue.     

Near-infrared spectroscopy: what can it tell us about oxygen saturation in skeletal muscle?

Near-infrared spectroscopy (NIRS) measures hemoglobin saturation in small vessels. A number of interesting studies have used this method. However, difficulties with signal quantification and studies in which NIRS oxygen saturation did not behave as expected raise concerns. NIRS remains promising for studies of skeletal muscle, but a better understanding of the method is needed.     

Evaluation of BA1112 rhabdomyosarcoma oxygenation with microelectrodes, optical spectrophotometry, radiosensitivity, and magnetic resonance spectroscopy.

We studied tumor tissue oxygenation in the BA1112 rhabdomyosarcoma using micro-electrode pO2 measurements, optical spectrophotometry, analyses of cell survival after irradiation, and 31P magnetic resonance spectroscopy (MRS). Studies were carried out in WAG/Rij/Y rats breathing normoxic, hypoxic, and hyperoxic gas mixtures with and without iv administration of perfluorochemical. Significant changes in tissue oxygenation and metabolic status were found when pO2 values, optical measurements of hemoglobin saturation and cytochrome a, a3 reduction-oxidation, radiation cell survival determinations, and MRS measurements of phosphometabolite ratios were obtained in rats breathing different gas mixtures. Inhalation of 100% O2 caused increases in tumor pO2, hemoglobin saturation, cytochrome a, a3 oxidation, tumor radiosensitivity, and PCr/Pi, NTP/Pi, and PDE/Pi ratios. Such changes were augmented by pretreatment with iv perfluorochemicals. Inhalation of hypoxic gas mixtures resulted in reductions in the above parameters. These results indicate that tissue oxygenation can be manipulated reproducibly in the BA1112 rhabdomyosarcoma and suggest that 31P MRS can be used to monitor changes in tumor oxygenation in this model system.     

Noninvasive hemodynamic monitoring for combat casualties

The aims of this study were to develop and to test a noninvasive hemodynamic monitoring system that could be applied to combat casualties to supplement conventional vital signs, to use an advanced information system to predict outcomes, and to evaluate the relative effectiveness of various therapies with instant feedback information during acute emergency conditions. In a university-run inner city public hospital, we evaluated 1,000 consecutively monitored trauma patients in the initial resuscitation period, beginning shortly after admission to the emergency department. In addition to conventional vital signs, we used noninvasive monitoring devices (cardiac index by bioimpedance with blood pressure and heart rate to measure cardiac function, arterial hemoglobin oxygen saturation by pulse oximetry to reflect changes in pulmonary function, and tissue oxygenation by transcutaneous oxygen tension indexed to fractional inspired oxygen concentration and carbon dioxide tension to evaluate tissue perfusion). The cardiac index, mean arterial pressure, pulse oximetry (arterial hemoglobin oxygen saturation), and transcutaneous oxygen tension/fractional inspired oxygen concentration were significantly higher in survivors, whereas the heart rate and carbon dioxide tension were higher in nonsurvivors. The calculated survival probability was a useful outcome predictor that also served as a measure of severity of illness. The rate of misclassification of survival probability was 13.5% in the series as a whole but only 6% for patients without severe head injuries and brain death. Application of noninvasive hemodynamic monitoring to acute emergency trauma patients in the emergency department is feasible, safe, and inexpensive and provides accurate hemodynamic patterns in continuous, on-line, real-time, graphical displays of the status of cardiac, pulmonary, and tissue perfusion functions. Combined with an information system, this approach provided an early outcome predictor and evaluated, with an objective individualized method, the relative efficacy of alternative therapies for specific patients.     

In vivo hemoglobin and water concentrations, oxygen saturation, and scattering estimates from near-infrared breast tomography using spectral reconstruction

RATIONALE AND OBJECTIVES: Near-infrared (NIR) imaging has its niche in quantifying and characterizing functional changes in tissue relating to vascularity and metabolic status. Here, NIR tomography was applied to study mammographically normal breast tissue in vivo by evaluating relationships between functional parameters so obtained to clinical representers in an effort to understand factors influencing tissue compositional changes. MATERIALS AND METHODS: A new spectral reconstruction method that is considered to provide the most accurate estimates of hemoglobin level, oxygen saturation, water fraction, scattering power, and amplitude was used to assess healthy breast tissue imaged in vivo by means of NIR tomography. The approach directly recovers functional parameters with inherent inclusion of spectral behavior enforced through the incorporation of a priori model assumptions. Sixty subjects were imaged by using a frequency-domain instrument followed by spectral image reconstruction and statistical analysis for significant correlations. RESULTS: The new analysis shows statistically significant inverse correlations between body mass index and breast total hemoglobin and water fractions. Water fraction also correlated inversely with age and separated certain categories of breast density. Average scatter power was indicative of breast radiographic density composition, whereas scatter amplitude varied inversely with breast diameter. Total hemoglobin correlated with water fraction, whereas water correlated with scatter power. CONCLUSION: The changes observed here are attributable to volume fraction alterations and provide some of the most comprehensive data on breast composition variations with demographic factors.     

A near-infrared spectrophotometric method for studying brain O2 sufficiency in man during +Gz acceleration

A technique for the noninvasive monitoring of cerebral oxygen status was evaluated on volunteer subjects on the USAF School of Aerospace Medicine centrifuge. By using multiwavelength near-infrared spectrophotometry, the instrumentation measured changes in the quantities of reduced and oxygenated hemoglobin (and their sum, an indicator of cerebral blood volume), and the quantity of oxidized cytochrome c oxidase within the forebrain. Tests used acceleration of up to 9 G with onset rates from 0.1 to 5.0 G.s-1, anti-G suits and straining maneuvers, and hyperoxic and hypoxic breathing mixtures. In general, +Gz acceleration produced a fall in blood volume within the cerebral microcirculation with a relative increase in the content of reduced hemoglobin and a tendency towards reduction of cytochrome c oxidase. These findings are discussed in relation to accepted changes in arterial blood pressure, cerebral blood flow, and arterial oxygen saturation caused by acceleration exposure.     

Monitoring blood oxygen state in muscle microcirculation with transverse relaxation.

Oxygen uptake from the microcirculation is a direct measure of tissue function. Magnetic resonance is capable of detecting differences between oxygenated and deoxygenated blood due to the paramagnetic properties of deoxyhemoglobin. At the level of the microcirculation, however, imaging methods cannot directly visualize the vessels. Instead, bulk MR parameters are investigated for their ability to monitor blood oxygen saturation (%O(2)) changes in the microcirculation of tissue, specifically skeletal muscle. Experiments in an in vitro model verified the feasibility of detecting changes in exponential decay signals, and also verified the prediction of only two distinct decay components. Experiments in a rabbit model demonstrate that T(2)' and monoexponential T(2) decay are not sensitive to blood oxygen changes, but that the long-T(2) component in a biexponential fit is correlated to the blood oxygen state. Assuming a two-pool model for water protons in muscle, and with knowledge of the T(2)-%O(2) relation, estimates of the microcirculation blood oxygen state can be made with some reasonable assumptions. Magn Reson Med 45:662-672, 2001.     

Red blood cell-derived ATP as a regulator of skeletal muscle perfusion

Blood flow to skeletal muscle is a complex process designed to provide adequate, yet not excessive, amounts of oxygen to meet the ever-changing metabolic needs of the tissue. To accomplish this goal, a mechanism must exist that couples the oxygen needs of the tissue with the oxygen delivery system. A number of mechanisms have been investigated that have focused primarily on the vessel or tissue supplied. However, because none of these was able to adequately explain the precision inherent in oxygen supply, we began to investigate the potential role of the mobile oxygen carrier itself, the red blood cell. This review will provide evidence in support of the idea that the red blood cell is able to both sense oxygen need and evoke changes in blood flow to meet that need. In this scheme, as a red blood cell enters a region of increased metabolic demand relative to supply, the fall in hemoglobin oxygen saturation evokes the release of ATP, found within the red blood cell in mM amounts. The released ATP binds to purinergic receptors located on the vascular endothelium and induces a vasodilation that is conducted upstream increasing oxygen supply to the region of tissue supplied by the vessel. Although this mechanism is likely only one component of a complex system, which precisely regulates blood flow, we suggest that it plays a vital role in the regulation of perfusion distribution within tissue.     

脑氧代谢相关参数在中枢神经系统疾病中的应用进展

颅内静脉血氧饱和度、氧摄取分数、脑氧代谢率是一组反映脑组织氧的利用及代谢情况的指标,可间接评估脑功能及脑组织发育程度。多种医学成像技术可测量静脉血氧饱和度,包括如血氧水平依赖成像（BOLD）、自旋标记下T2弛豫成像（TRUST）、磁敏感加权成像（SWI）、定量磁敏感图（QSM）等。综述血氧饱和度及其相关代谢参数的测量在脑梗死、创伤性脑损伤、多发性硬化、肝性脑病、肾性脑病及镰状细胞贫血疾病中的应用及研究。     

Exercise-induced skeletal muscle deoxygenation in O-supplemented COPD patients

This study was designed to assess quadriceps oxygenation during symptom-limited and constant-load exercise in patients with chronic obstructive pulmonary disease (COPD) and healthy age-matched controls. Thirteen male COPD patients [FEV(1): 43 +/- 5% predicted (mean +/- SEM)] and seven healthy male controls performed an incremental exercise test at peak work rate (WR) and a constant-load test at 75% peak WR on a cycle ergometer. Quadriceps hemoglobin saturation (StO2) was measured by continuous-wave near-infrared spectrophotometry throughout both exercise tests. StO2 is the ratio of oxygenated hemoglobin to total hemoglobin and reflects the relative contributions of tissue O2 delivery and tissue O2 utilization. Oxygen was supplemented to all patients in order to maintain arterial O2 saturation normal (> 95%). The StO2 decreased during symptom-limited exercise, reaching the nadir at peak WR. The decrease in StO2 was greater (P < 0.05) in healthy subjects (from 74 +/- 2% to 38 +/- 6%) compared with that in COPD patients (from 61 +/- 5% to 45 +/- 4%). However, when StO2 was normalized relative to the WR, the slope of change in StO2 during exercise was nearly identical between COPD patients and healthy subjects (0.47 +/- 0.10%/W and 0.51 +/- 0.04%/W, respectively). During constant-load exercise, the kinetic time constant of StO2 desaturation after the onset of exercise (i.e., equivalent to time to reach approximately 63% of StO2 decrease) was not different between COPD patients and healthy subjects (19.0 +/- 5.2 and 15.6 +/- 2.5 s, respectively). In O2-supplemented COPD patients, peripheral muscle oxygenation for a given work load is similar to that in healthy subjects, thus suggesting that skeletal muscle O2 consumption becomes normal for a given O2 delivery in COPD patients     

Helicopter cockpit seat side and trapezius muscle metabolism with night vision goggles

INTRODUCTION: Documented neck strain among military helicopter aircrew is becoming more frequent and many militaries use helicopters that provide pilots with the option of sitting in the left or right cockpit seat during missions. PURPOSE: The purpose of this study was to use near infrared spectroscopy (NIRS) to investigate the physiological changes in trapezius muscle oxygenation and blood volume during night vision goggle (NVG) flights as a function of left and right cockpit seating. METHODS: There were 25 pilots who were monitored during NVG flight simulator missions (97.7 +/- 16.1 min). Bilateral NIRS probes attached to the trapezius muscles at C7 level recorded total oxygenation index (TOI, %), total hemoglobin (tHb), oxyhemoglobin (Hbo2), and deoxyhemo-globin (HHb). RESULTS: No significant differences existed between variables for pilots seated in the right cockpit seat as compared with the pilots seated in the left cockpit seat in either trapezius muscle (pTOI = 0.72; ptHb = 0.72; pHbo2 = 0.57; pHHb = 0.21). CONCLUSION: Alternating cockpit seats on successive missions is not a means to decrease metabolic stress for helicopter pilots using NVG. This suggests that cockpit layout and location of essential instruments with respect to the horizontal and the increased head supported mass of the NVG may be important factors influencing metabolic stress of the trapezius muscle.     

Accuracy and precision of MR blood oximetry based on the long paramagnetic cylinder approximation of large vessels

An accurate noninvasive method to measure the hemoglobin oxygen saturation (%HbO₂) of deep‐lying vessels without catheterization would have many clinical applications. Quantitative MRI may be the only imaging modality that can address this difficult and important problem. MR susceptometry–based oximetry for measuring blood oxygen saturation in large vessels models the vessel as a long paramagnetic cylinder immersed in an external field. The intravascular magnetic susceptibility relative to surrounding muscle tissue is a function of oxygenated hemoglobin (HbO₂) and can be quantified with a field‐mapping pulse sequence. In this work, the method's accuracy and precision was investigated theoretically on the basis of an analytical expression for the arbitrarily oriented cylinder, as well as experimentally in phantoms and in vivo in the femoral artery and vein at 3T field strength. Errors resulting from vessel tilt, noncircularity of vessel cross‐section, and induced magnetic field gradients were evaluated and methods for correction were designed and implemented. Hemoglobin saturation was measured at successive vessel segments, differing in geometry, such as eccentricity and vessel tilt, but constant blood oxygen saturation levels, as a means to evaluate measurement consistency. The average standard error and coefficient of variation of measurements in phantoms were <2% with tilt correction alone, in agreement with theory, suggesting that high accuracy and reproducibility can be achieved while ignoring noncircularity for tilt angles up to about 30°. In vivo, repeated measurements of %HbO₂ in the femoral vessels yielded a coefficient of variation of less than 5%. In conclusion, the data suggest that %HbO₂ can be measured reproducibly in vivo in large vessels of the peripheral circulation on the basis of the paramagnetic cylinder approximation of the incremental field. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Changes in superficial blood distribution in thigh muscle during LBNP assessed by NIRS

INTRODUCTION: The present study was designed to determine how superficial blood distributed in the lower limb muscle during graded lower body negative pressure (LBNP). METHODS: Near-infrared spectroscopy (NIRS) was used to evaluate the blood volume change in the thigh muscles of seven volunteers during 35 min graded LBNP (rest, -10, -20, -30, -40, -50 mm Hg, and recovery). RESULTS: Deoxygenated and total hemoglobin (Hb) increased in proportion to the magnitude of LBNP applied to the thigh muscles. Oxygenated Hb rose significantly at -10 mm Hg LBNP, although the increase leveled off during subsequent increments of LBNP. Systolic pressure significantly decreased from 120 mm Hg at rest, to a value of 108 at -50 mm Hg LBNP. In contrast, mean and diastolic pressures were well maintained during graded LBNP. The increased total and deoxygenated Hb might indicate that blood was held in venous space, and the magnitude of rise in blood volume corresponded to the change in LBNP. On the other hand, oxygenated Hb change seems to reflect mainly blood accumulated in arterial space by interacting between mechanical stretch induced by LBNP and vasoconstriction caused by augmented sympathetic nerve activity. CONCLUSION: From these results, blood distribution in thigh muscles was different and was affected by the strength of LBNP. The data assessing oxygenation sites of Hb were found to be useful as indices of estimating superficial blood pooling in the muscle during LBNP.