W.N.J.M. Colier

Adipose tissue thickness affects in vivo quantitative near-IR spectroscopy in human skeletal muscle

The influence of adipose tissue thickness (ATT) on near-IR spectroscopy (NIRS) measurements in vivo was studied in the human flexor digitorum superficialis muscle at rest and during sustained isometric handgrip exercise. NIRS was used for the quantitative measurement of muscle O(2) consumption (mV.O(2)) and forearm blood flow (FBF) in 78 healthy subjects. Skinfold thickness ranged from 1.4 to 8.9 mm within the group. Resting mV.O(2) was 0.11+/-0.04 ml of O(2).min(-1).100 g(-1), and FBF was 1.28+/-0.82 ml.min(-1).100 ml(-1). There was a negative correlation (r=-0.70, P< or =0.01), indicating a decrease in mV.O(2) with increasing ATT. mV.O(2) in the 10 leanest subjects appeared to be twice as high as that in the 10 subjects with the highest ATT. A poor correlation (r=0.29, P< or =0.01) was found between ATT and FBF. The gender difference that we found for mV.O(2) was due to the difference in ATT between female and male subjects. No correlation was found between maximum voluntary contraction and mV.O(2), nor between maximum voluntary contraction and ATT, indicating that the contraction force did not confound our results. These results show that ATT has a substantial confounding influence on in vivo NIRS measurements, and that it is essential to incorporate this factor into future NIRS muscle studies in order to justify comparisons between different groups. To facilitate such comparisons, upper and lower boundaries for normal values of mV.O(2) and FBF in relation to ATT are presented.

Simultaneous measurements of cerebral oxygenation changes during brain activation by near‐infrared spectroscopy and functional magnetic resonance imaging in healthy young and elderly subjects

Near infrared spectroscopy (NIRS) and functional magnetic resonance imaging (fMRI) both allow non‐invasive monitoring of cerebral cortical oxygenation responses to various stimuli. To compare these methods in elderly subjects and to determine the effect of age on cortical oxygenation responses, we determined motor‐task‐related changes in deoxyhemoglobin concentration ([HHb]) over the left motor cortex in six healthy young subjects (age 35 ± 9 years, mean ± SD) and five healthy elderly subjects (age 73 ± 3 years) by NIRS and blood‐oxygen‐level‐dependent (BOLD) fMRI simultaneously. The motor‐task consisted of seven cycles of 20‐sec periods of contralateral finger‐tapping at a rate as fast as possible alternated with 40‐sec periods of rest. Time‐locked averages over the seven cycles were used for further analysis. Task‐related decreases in [HHb] over the motor cortex were measured by NIRS, with maximum changes of −0.83 ± 0.38 μmol/L (P < 0.01) for the young and −0.32 ± 0.17 μmol/L (P < 0.05) for the elderly subjects. The BOLD‐fMRI signal increased over the cortex volume under investigation with NIRS, with maximum changes of 2.11 ± 0.72% (P < 0.01) for the young and 1.75 ± 0.71% (P < 0.01) for the elderly subjects. NIRS and BOLD‐fMRI measurements showed good correlation in the young (r = −0.70, r2 = 0.48, P < 0.001) and elderly subjects (r = −0.82, r2 = 0.67, P < 0.001). Additionally, NIRS measurements demonstrated age‐dependent decreases in task‐related cerebral oxygenation responses (P < 0.05), whereas fMRI measurements demonstrated smaller areas of cortical activation in the elderly subjects (P < 0.05). These findings demonstrate that NIRS and fMRI similarly assess cortical oxygenation changes in young subjects and also in elderly subjects. In addition, cortical oxygenation responses to brain activation alter with aging. Hum. Brain Mapping 16:14–23, 2002.

Human motor-cortex oxygenation changes induced by cyclic coupled movements of hand and foot

Abstract Near-infrared spectroscopy (NIRS) was used to assess human motor-cortex oxygenation changes in response to cyclic coupled movements of hand and foot. Using a highly sensitive NIRS instrument, we showed that it was possible to detect reproducible oxygenation patterns using single cycles (20 s) of easy and difficult association tasks. No significant differences in the time corresponding to the maximal changes in concentration of oxy- and deoxyhemoglobin ([O2Hb] and [HHb], respectively) were found during easy and difficult association as well as cycles. Only [O2Hb] showed a significantly higher value at the end of the difficult association during the first cycle. No significant differences were found for [O2Hb] and [HHb] in the other cycles. We conclude that NIRS is a useful addition to functional magnetic resonance imaging in investigating the time course of cortical activation.

In vivo quantitative near‐infrared spectroscopy in skeletal muscle during incremental isometric handgrip exercise

The aim of this study was to investigate the performance of in vivo quantitative near‐infrared spectroscopy (NIRS) in skeletal muscle at various workloads. NIRS was used for the quantitative measurement of O2 consumption (mV˙O2) in the human flexor digitorum superficialis muscle at rest and during rhythmic isometric handgrip exercise in a broad range of work intensities (10–90% MVC=maximum voluntary contraction force). Six subjects were tested on three separate days. No significant differences were found in mV˙O2 measured over different days with the exception of the highest workload. The within‐subject variability for each workload measured over the three measurements days ranged from 15·7 to 25·6% and did not increase at the high workloads. The mV˙O2 was 0·14 ± 0·01 mlO2 min–1 100 g–1 at rest and increased roughly 19 times to 2·68 ± 0·58 mlO2 min–1 100 g–1 at 72% MVC. These results show that local muscle oxygen consumption at rest as well as during exercise at a broad range of work intensities can be measured reliably by NIRS, applied to a uniform selected subject population. This is of great importance as direct local measurement of mV˙O2 during exercise is not possible with the conventional techniques. The method is robust enough to measure over separate days and at various workloads and can therefore contribute to a better understanding of human physiology in both the normal and pathological state of the muscle.

New and highly sensitive continuous-wave near-infrared spectrophotometer with multiple detectors

For a long time continuous wave near infrared instruments have been used to detect oxygenation changes in tissue. These instruments have proven to be reliable. The new generation of instruments, such as phase-modulated systems, or time-of-flight instruments, is not yet reliable enough for clinical applications. Most available continuous wave near infrared instruments have low temporal resolution and low signal-to-noise ratio. For functional brain imaging, for example, a sensitive and fast instrument is needed. Therefore we developed the OXYMON, an instrument with a sample frequency up to 50 Hz and for optical densities up to 9 OD. The instrument uses 3 laser diodes, and is equipped with 1 or 2 avalanche photo detectors. Modular building techniques make maintenance easy.

Determination of oxygen consumption in muscle during exercise using near infrared spectroscopy.

The aim of this study was to determine oxygen consumption (VO2) during isometric exercise in human muscles using near infrared spectroscopy (NIRS). The technique was used to study the relationship between VO2 in the soleus muscle and the level of isometric exercise expressed as percentages of the maximum voluntary contraction (MVC). For the study 11 healthy male volunteers were recruited. Reproducibility was studied in 6 subjects. The subjects were seated in a chair with the knee joint at an angle of 90°. The optodes of the NIRS instrument were attached to the lateral aspect of the soleus muscle. A horizontal bar above the knee was connected to a dynamometer. Subjects applied isometric force to the bar by producing a torque at the ankle joint. Firstly the MVC was determined. Secondly the VO2 at rest and at 5 levels of isometric exercise, ranging from 5% to 25% of MVC and increasing by 5% each stage, was measured. In all cases the VO2 at rest or during isometric contraction was determined from the decrease of the oxyhaemoglobin (O2Hb) signal immediately after arterial occlusion of the thigh. Repeated measurements showed no significant difference between trials, indicating that the measurements were reproducible. At rest a VO2 of 6.7 ± 1.1 μMO2Hb min‐1 (mean ± S.E.M.) was found, a result comparable with other studies. In all subjects a linear relationship was found between the VO2 and the level of exercise. The average slope of the regression lines of all individuals was 0.85 ± 0.22 μuMO, Hb min‐1 MVC‐1 (mean ± S.E.M.). Inter‐individual variation of the slopes was high and ranged from 0.28 to 2.29 μuMO2 Hb‐ min‐1 %MVC‐1, which can be explained by differences in fat percentage and in the measuring volume of the NIRS instrument. NIRS appeared to be a reproducible and reliable method for the non‐invasive measurement of VO2 in human muscles. The method could be used to investigate regional differences as well as changes in time between muscle groups as a function of training.

Effect of carbogen breathing on the physiological profile of human glioma xenografts.

The aim of this study was to evaluate the effect of carbogen breathing on the physiological profile of human glioma xenografts. Near infrared spectroscopy was used to investigate changes in oxy‐ and deoxyhemoglobin concentrations in tumor blood. Oxygen tension changes in tumor tissue were evaluated by 19F‐MR relaxometry, using perfluoro‐15‐crown‐5‐ether, and modifications of tumor blood perfusion (TBP) were analyzed by fast dynamic 1H‐MR imaging of Gd‐DTPA uptake. Finally, changes of the bioenergetic status and pH of tumor cells were analyzed by 31P‐MRS. After 5 to 8 min of carbogen breathing, the average oxygen tension increase in tumor tissue was 4.6 ± 1.3 mm Hg, which is in agreement with an increase of the oxyhemoglobin concentration in tumor blood (Δ[O2Hb] = 9.2 ± 3 μM). However, simultaneously the TBP was reduced, the bioenergetic status was diminished, and pH was decreased. As 100% O2 breathing alone did not result in a detectable increase of oxyhemoglobin in tumor blood, the increase of the tumor oxygenation by carbogen appears to be mediated by its CO2 content. This component may cause a nutrient‐limited decrease of oxidative energy metabolism, indirectly via a steal‐effect and/or by inhibition of the glycolytic rate resulting from tissue acidification. Magn Reson Med 42:490–499, 1999.

Lateral frontal cortex oxygenation changes during translation and language switching revealed by non-invasive near-infrared multi-point measurements

The organisation of language in the brain of multilingual people remains controversial. Using a high temporal resolution 12-channel near-infrared continuous wave spectroscopy system, we have demonstrated that it is possible to monitor non-invasively, comfortably and, without the interferences due to intrinsic limitations of positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), cortical oxygenation changes in the Brocas area in response to translation of short sentences and language switching. Eight Dutch students proficient in English translated aloud from their native language into English or vice versa or alternating (switching) short visually presented sentences. These tasks provoked, in the left inferior frontal cortex which includes the Brocas area, a consistent and incremental rise in oxyhaemoglobin accompanied by a smaller decrease in deoxyhaemoglobin. The investigated cortical areas surrounding the Brocas area showed no uniform and consistent oxygenation changes upon the three different translation tasks. These results confirm that Brocas area is involved in the translation process and its so called activation is unaffected by the direction of the translation. In addition, these results strengthen the role of near-infrared multi-point measurements as a powerful tool for investigating the spatial and temporal features of the cortical oxygenation changes during language processing.

Simultaneous near-infrared spectroscopy monitoring of left and right occipital areas reveals contra-lateral hemodynamic changes upon hemi-field paradigm

In this study we have shown that in humans it is possible to monitor non-invasively and simultaneously both hemispheres revealing cortical oxygenation changes in the occipital area in response to a contra-lateral hemi-field paradigm. A novel multi-channel near infrared spectroscopy approach with a high temporal resolution was used. The results confirm previous findings obtained by functional magnetic resonance imaging and positron emission tomography with the advantage to measure directly not only concentration changes in deoxyhemoglobin as measured by functional magnetic resonance imaging (MRI), but also in oxyhemoglobin with low cost instrumentation potentially useful to investigate the pathophysiology of vision.

Quantitative near-infrared spectroscopy discriminates between mitochondrial myopathies and normal muscle.

Five patients with chronic progressive external ophthalmoplegia (CPEO) and 27 healthy controls were examined by near‐infrared spectroscopy (NIRS) for the noninvasive and direct quantitative measurement of muscle oxygen consumption and forearm blood flow. NIRS measurements were obtained in rest and during static isometric handgrip exercise at 10% of the maximum voluntary contraction (MVC) force. A significantly decreased oxygen consumption at rest as well as during exercise was found in patients with CPEO. Our results suggest that NIRS is able to discriminate between CPEO patients and healthy controls, which makes NIRS a valuable tool in the diagnostic workup of patients suspected to have a mitochondrial myopathy.