Berend Oeseburg

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.

Arterial oxygen saturation in relation to metabolic acidosis in fetal lambs

OBJECTIVE We studied the relationship between preductal arterial oxygen saturation and metabolic acidosis in 18 chronically instrumented fetal lambs (gestational age 119 to 133 days) in two experimental designs. In the first group the onset of metabolic acidosis was determined. In the second group the progression of metabolic acidosis was studied as was the cardiovascular and hormonal changes resulting from hypoxemia. STUDY DESIGN In nine fetal lambs maternal fraction of inspired oxygen was lowered stepwise by increasing flows of nitrogen delivered into the trachea through a small indwelling catheter (group 1), and in nine fetal lambs maternal blood flow was reduced stepwise by means of a vascular occluder (group 2). RESULTS Baseline arterial oxygen saturation values ranged from 26% to 67% with normal pH and extracellular fluid base excess values in both groups 1 and 2. In both groups pH and extracellular fluid base excess started to decrease below 30% arterial oxygen saturation, with a progressive decrease below 20% arterial oxygen saturation to an end value for pH of 7.14. In some fetal lambs pH and extracellular fluid base excess decreased initially at 20% to 30% arterial oxygen saturation and then stabilized at the lower level. Fetal heart rate in group 1 increased during hypoxemia from 155 to 179 beats/min. In group 2 baseline fetal heart rate was 153 beats/min and fell with every step change in arterial oxygen saturation but subsequently increased to 172 beats/min by the end of the period of hypoxemia. Baseline values for epinephrine, norepinephrine, dopamine, cortisol, and mean arterial pressure were not related to baseline arterial oxygen saturation levels, and each of these variables was increased at the end of hypoxemia in group 2. CONCLUSION Preductal arterial oxygen saturation can reach values between 20% and 30% before anaerobic metabolism starts. During the progressive acidosis blood pressure was increased, which can be attributed to a strong rise in catecholamines.

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.

Changes in blood flow in the common femoral artery related to inactivity and muscle atrophy in individuals with long-standing paraplegia

A spinal cord lesion refers to a partial or total disruption of the structural and functional integrity of the spinal cord, which is often caused by some sort of trauma, and results in impairments such as paralysis, loss of sensation and autonomic dysfunctioning.

Cardiovascular responses in paraplegic subjects during arm exercise

SummaryThe purpose of this study was to examine cardiovascular responses during arm exercise in paraplegics compared to a well-matched control group. A group of 11 male paraplegics (P) with complete spinal cord-lesions between T6 and T12 and 11 male control subjects (C), matched for physical activity, sport participation and age performed maximal arm-cranking exercise and submaximal exercise at 20%, 40% and 6070 of the maximal load for each individual. Cardiac output (Qc) was determined by the CO2 rebreathing method. Maximal oxygen uptake was significantly lower and maximal heart rate (fc) was sigificantly higher in P compared to C. At the same oxygen uptakes no significant differences were observed inQc between P and C; however, stroke volume (SV) was significantly lower andfc significantly higher in P than in C. The lower SV in P could be explained by an impaired redistribution of blood and, therefore, a reduced ventricular filling pressure, due to pooling of venous blood caused by inactivity of the skeletal muscle pump in the legs and lack of sympathetic vasoconstriction below the lesion. In conclusion, in P maximal performance appears to have been limited by a smaller active muscle mass and a lower SV despite the higher ϕc,max. During submaximal exercise, however, this lower SV was compensated for by a higherfc and, thus at the same submaximal oxygen uptake,Qc was similar to that in the control group.

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.

Cardiovascular responses in persons with paraplegia to prolonged arm exercise and thermal stress

The purpose of this study was to investigate cardiovascular responses in subjects with paraplegia (P) during prolonged upper body exercise in a hot environment. In addition, the effect of the level of the lesion on cardiovascular regulation of persons with paraplegia was studied. Four P with lesions between T2-T6 (P1), five P with T7-T8 lesions (P2), four P with lesions between T9-T12 (P3), and 10 control subjects (C) performed 45-min arm-cranking exercise at 40% of the individual peak power output, in a climatic room at 35 degrees C with a 70% relative humidity. From the 15th to the 45th min, cardiac output (Q) and oxygen uptake (VO2) remained unaltered in all subjects, except a significant decrease of Q in P1. Stroke volume (SV) decreased significantly in both P (-20%) and C (-18%) during the test. Heart rate (HR) increased in compensation for P2 (56%), P3 (65%), and C (55%), whereas HR in P1 did not increase significantly. Hemoglobin concentration changes, representing total plasma volume changes, increased significantly in P2, P3, and C but not in P1. Weight loss and sweat rate increased relative to the sensate skin area and, thus, to the level of the spinal cord lesion (P < 0.01). In conclusion, P with lesions below T6 are able to maintain a stable Q by increasing HR to compensate for the declining SV during exercise in a hot environment. P with lesions above T6 cannot fully compensate for the reduction in SV by an increase in HR, therefore, Q declines.

The effect of blood transfusion and haemodilution on cerebral oxygenation and haemodynamics in newborn infants investigated by near infrared spectrophotometry

Abstract The objective of this study was to investigate the influence of blood transfusion and haemodilution on cerebral oxygenation and haemodynamics in relation to changes in cerebral blood flow velocity (CBFV) and other relevant physiological variables in newborn infants. Thirteen preterm infants with anaemia (haematocrit < 0.33) and ten infants with polycythaemia (haematocrit > 0.65) were studied during blood transfusion and haemodilution respectively using adult red blood cells and partial plasma exchange transfusion. Changes in cerebral concentrations of oxyhaemoglobin (cO2Hb), deoxyhaemoglobin (cHHb), total haemoglobin (ctHb), (oxidized - reduced) cytochrome aa3 (cCyt.- aa3) were continuously measured using near infrared spectrophotometry throughout the whole procedure. Simultaneously, changes of mean CBFV in the internal carotid artery were continuously measured using pulsed Doppler ultrasound. Heart rate, transcutaneous partial pressure of oxygen and carbon dioxide, and arterial O2 saturation were continuously and simultaneously measured. Blood transfusion resulted in increase of cO2Hb, cHHb, ctHb and red cell transport (product of CBFV and haematocrit), whereas CBFV decreased. The increase of cO2Hb exceeded that of cHHb, reflecting improvement of cerebral O2 supply. Haemodilution resulted in a decrease of cO2Hb, cHHb and ctHb, whereas CBFV increased. Red cell transport was unchanged. The decrease of cO2Hb exceeded that of cHHb, reflecting decreased cerebral O2 supply. cCyt.aa3 decreased after blood transfusion and remained unchanged after haemodilution, but the reliability of these results is uncertain. With the exception of a small, but significant increase in transcutaneous partial pressure of oxygen after blood transfusion, the other variables showed no changes. Each blood withdrawal during exchange transfusion resulted in only a significant increase in heart rate without changes in the other variables measured, suggesting unchanged cerebral perfusion. Conclusion In newborn infants blood transfusion in anaemia results in improvement of cerebral oxygenation, but haemodilution in polycythaemia does not improve cerebral oxygenation despite possible improvement of cerebral perfusion.

The effect of an anti-G suit on cardiovascular responses to exercise in persons with paraplegia.

The purpose of this study was to determine whether external pressure on legs and abdomen could prevent venous blood pooling in persons with paraplegia and thus positively affect their cardiovascular responses to arm exercise. To investigate this, five male subjects with paraplegia (P), with complete lesions between T6 and T12, and five male control subjects who were wheelchair bound (C) (due to a chronic lower extremity disability), performed submaximal arm-cranking exercise at 20%, 40%, and 60% of their maximal power output (Wmax), with and without an antigravity (anti-G) suit inflated to 52 mm Hg (1 psi). For P, higher preexercise systolic pressure (127 vs 117 mm Hg) was seen with the anti-G suit. At 40 and 60% Wmax, significantly lower heart rates (at 40% = 5.7%; at 60% = 10.6%) at similar cardiac outputs were seen for P with an anti-G suit. Although not significant, P also demonstrated higher stroke volumes at 40% (4.8%) and 60% (5.0%) Wmax with external pressure. For C, no differences in preexercise blood pressure or cardiovascular responses at all three exercise levels were seen with or without the anti-G suit. These data suggest that an inflated anti-G suit is able to prevent venous blood pooling and offers hemodynamic benefits in persons with paraplegia during submaximal arm-cranking exercise. In addition, this study reports a possible alternative to hosiery or functional neuromuscular stimulation that could be applied to all subjects with spinal cord injuries regardless of type or duration of the lesion or of muscle-atrophy.