Willy Colier

• Doctor of Medicine
• Radboud University

Sleep, notably active sleep (AS) and quiet sleep (QS), plays a pivotal role in the brain development and gradual maturation of (pre) term infants. Monitoring their sleep patterns is imperative, as it can serve as a tool in promoting neurological maturation and well-being, particularly important in preterm infants who are at an increased risk of imm...

Background: Near-infrared spectroscopy (NIRS) relative concentration signals contain ‘noise’ from physiological processes such as respiration and heart rate. Simultaneous assessment of NIRS and respiratory rate (RR) using a single sensor would facilitate a perfectly time-synced assessment of (cerebral) physiology. Our aim was to extract respiratory...

Objective: The employment of wearable systems for continuous monitoring of vital signs is increasing. However, due to substantial susceptibility of conventional bio-signals recorded by wearable systems to motion artifacts, estimation of the respiratory rate (RR) during physical activities is a challenging task. Alternatively, functional Near-Infra...

Near-infrared spectroscopy (NIRS) intensity signals provide useful additional physiological information of which the most prominent one is the pulsatile fluctuation by heartbeats. This allows for the extraction of heart rate (HR), one of the primary clinical indicators of health in neonates. In this study, we propose a novel algorithm, NHR (NIRS HR...

Objective: Respiration is recognized as a systematic physiological interference in functional near-infrared spectroscopy (fNIRS). However, it remains unanswered as to whether it is possible to estimate the respiratory rate (RR) from such interference. Undoubtedly, RR estimation from fNIRS can provide complementary information that can be used alon...

Recent studies have established that cardiac and respiratory phases can modulate perception and related neural dynamics. While heart rate and respiratory sinus arrhythmia possibly affect interoception biomarkers, such as heartbeat-evoked potentials, the relative changes in heart rate and cardiorespiratory dynamics in interoceptive processes have no...

Recent studies have established that cardiac and respiratory phases can modulate perception and related neural dynamics. While heart rate and respiratory sinus arrhythmia are possibly affecting interoception biomarkers, such as heartbeat-evoked potentials, the relative changes in heart rate and cardiorespiratory dynamics in interoceptive processes...

We propose the signal quality index (SQI) algorithm as a novel tool for quantitatively assessing the functional near infrared spectroscopy (fNIRS) signal quality in a numeric scale from 1 (very low quality) to 5 (very high quality). The algorithm comprises two preprocessing steps followed by three consecutive rating stages. The results on a dataset...

Investigation of marine mammal dive-by-dive blood distribution and oxygenation has been limited by a lack of noninvasive technology for use in freely diving animals. Here, we developed a noninvasive near-infrared spectroscopy (NIRS) device to measure relative changes in blood volume and haemoglobin oxygenation continuously in the blubber and brain...

Purpose Cerebral oxygenation as measured by near-infrared spectroscopy (NIRS) might be useful to discriminate between physiological and pathological responses after standing up in individuals with orthostatic hypotension. This study addressed the physiological sensitivity of the cerebral oxygenation responses as measured by NIRS to different types...

Combining electrophysiological and hemodynamic features is a novel approach for improving current performance of brain switches based on sensorimotor rhythms (SMR). This study was conducted with a dual purpose: to test the feasibility of using a combined electroencephalogram/functional near-infrared spectroscopy (EEG-fNIRS) SMR-based brain switch i...

Motor-impaired individuals such as tetraplegics could benefit from Brain-Computer Interfaces with an intuitive control mechanism, for instance for the control of a neuroprosthesis. Whereas BCI studies in healthy users commonly focus on motor imagery, for the eventual target users, namely patients, attempted movements could potentially be a more pro...

Standing up shifts blood to dependent parts of the body, and blood vessels in the leg become filled. The orthostatic blood volume accumulation in the small vessels is relatively unknown, although these may contribute significantly. We hypothesized that in healthy humans exposed to the upright posture, volume accumulation in small blood vessels cont...

Exposure to vibration has traditionally been associated with compromised perfusion. This study investigated whether blood supply during whole body vibration (WBV), as an exercise modality, is in proportion to the metabolic demand by the contracting musculature. As a secondary aim, serum levels of vascular endothelial growth factor (VEGF) were asses...

Leg crossing increases arterial pressure and combats symptomatic orthostatic hypotension in patients with sympathetic failure. This study compared the central and cerebrovascular effects of leg crossing in patients with sympathetic failure and healthy controls. We addressed the relationship between MCA Vmean (middle cerebral artery blood velocity;...

When healthy subjects stand up, it is associated with a reduction in cerebral blood velocity and oxygenation although cerebral autoregulation would be considered to prevent a decrease in cerebral perfusion. Aging is associated with a higher incidence of falls, and in the elderly falls may occur particularly during the adaptation to postural change....

For adequate development and functioning of the neonatal brain, sufficient oxygen (O2) should be available. With a fast sampling (fs ≫ 50 Hz) continuous wave NIRS device, arterial (SaO2) and venous (SvO2) saturation can be measured using the physiological fluctuations in the oxyhemoglobin (O2Hb) and total hemoglobin (tHb) concentrations due to hear...

Despite the social impact of repetitive strain injury (RSI), little is known about its pathophysiological mechanism. The main objective of this study was to assess the local muscle oxygenation (mVO2) and blood flow (mBF) of the forearm in individuals with RSI during isometric contractions of the forearm. We employed the non-invasive optical techniq...

Near infrared spectroscopy (NIRS) is a non-invasive method to monitor cerebral haemodynamics. Used either alone or in combination with other non-invasive methods such as transcranial Doppler sonography, this technique is well suited for use in cerebrovascular research in ageing. Reproducibility of NIRS, however, has only been determined in neonates...

The purpose of this study was to assess if chronic low back pain patients have impaired paraspinal muscle O(2) turnover and endurance capacity as compared to healthy control subjects during dynamic exercise. Middle-aged healthy male subjects (n=12, control) and male patients with chronic low back pain (n=17, CLBP) participated in the study. L4-L5 l...

Impaired oxidative phosphorylation is a crucial factor in the pathogenesis of Friedreichs ataxia (FA). L-carnitine and creatine are natural compounds that can enhance cellular energy transduction. We performed a placebo-controlled triple-phase crossover trial of L-carnitine (3g/d) and creatine (6.75g/d) in 16 patients with genetically confirmed FA....

Impaired oxidative phosphorylation is a crucial factor in the pathogenesis of Friedreich’s ataxia (FA). L-carnitine and creatine are natural compounds that can enhance cellular energy transduction. We performed a placebo-controlled triple-phase crossover trial of L-carnitine (3 g=d) and creatine (6.75 g=d) in 16 patients with genetically confirmed...

Local oxygen consumption in a muscle (VO(2)) can be determined by near infrared spectroscopy (NIRS). In principle it should be possible to use this measure to validate musculoskeletal models. However, the relationship between VO(2) and external force, or between VO(2) and surface EMG, as a measure for muscle activity, is hardly known. The aim of th...

Background: Repetitive Strain Injury (RSI) is a major problem in nowadays health care and creates high financial costs and personal distress. Average prevalence rates in the Netherlands vary from 20-40% of the working population. Insight into the patho-physiological mechanism of RSI is important in order to establish adequate treatment and preventi...

The aim of this study was to investigate local muscle oxygen consumption (mVO2) during various protocols of isometric handgrip exercise. mVO2was measured by near-infrared spectroscopy (NIRS) during sustained, rhythmic, and intermittent isometric handgrip exercise. Whereas rhythmic handgrip exercise has the advantage that local muscle metabolism can...

Patients with left ventricular dysfunction may have different orthostatic responses of blood pressure (BP) and cerebral oxygenation than healthy elderly subjects. We investigated orthostatic changes in systemic haemodynamic variables and cerebral oxygenation in 21 elderly patients with heart failure New York Heart Association class I–III in stable...

Near Infrared Spectroscopy (NIRS) analyzes infrared light having traveled through tissue, for its oxygenation status. The main chromophore analyzed is hemoglobin (Hb), but in muscle tissue also myoglobin (Mb) is present. Since NIRS cannot discern between these two species experimentally, we did model calculation studies using general data for human...

Evaluation of the cerebrovascular response (delta CBV/delta PaCO2) during baseline metabolic conditions and acute metabolic acidosis. 15 healthy subjects, 5 m, 10 f, 56 +/- 10 yrs were investigated. For acidification, NH4Cl was given orally. CBV was measured using Near Infrared Spectroscopy (OXYMON) during normo-, hyper- and hypocapnia. Acute metab...

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 tomogr...

Elderly patients with heart failure are at risk of postprandial hypotension (PPH), orthostatic hypotension (OH), and concomitant cerebral oxygenation changes because of altered cardiovascular balance and the use of cardiovascular medications, such as furosemide and captopril. In 24 patients with heart failure (New York Heart Association class II to...

Near-infrared spectroscopy (NIRS) is a direct, non-invasive optical method for measuring local oxygenation and haemodynamics in muscle tissue. Although measurement of local oxygenation by NIRS has been used for the diagnosis of metabolic myopathies, the technique has not previously been applied to inflammatory myopathies. Dermatomyositis is a muscl...

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 (mVO2) in the human flexor digitorum superficialis muscle at rest and during rhythmic isometric handgrip exercise in a broad rang...

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 deoxyhemog...

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 deoxyhemog...

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 deoxyhemog...

Effects of chronic metabolic alkalosis and acidosis and their relation to central chemoregulation may differ between normocapnic and chronic hypercapnic patients with COPD. The relationship between responses of inspired ventilation (VI), mouth occlusion pressure (P(0.1)), and cerebral blood volume (CBV), to short-term changes in arterial PCO(2) was...

The authors investigated the effect of acclimatization to high altitude on cerebral blood flow and oxidative metabolism at rest and during exercise. Nine healthy, native sea-level residents were studied 3 weeks after arrival at Chacaltaya, Bolivia (5,260 m) and after reacclimatization to sea level. Global cerebral blood flow at rest and during exer...

Spinal cord-injured (SCI) individuals, having a sympathetic nervous system lesion, experience hypotension during sitting and standing. Surprisingly, they experience few syncopal events. This suggests adaptations in cerebrovascular regulation. Therefore, changes in systemic circulation, cerebral blood flow, and oxygenation in eight SCI individuals w...

Single location muscle monitoring does not reflect the heterogeneous activation of the muscle group(s) during a given exercise. Vastus lateralis and rectus femoris O2 consumption (VO2) was investigated, noninvasively, at rest and during maximal voluntary contractions (MVC) using a 12-channel near-infrared continuous wave spectroscopy (NIR(CWS)) sys...

This study investigated the hypothesis that hypercapnia in some chronic obstructive pulmonary disease (COPD) patients may be related to a high cerebrovascular response to carbon dioxide (CO 2 ). The relationship between responses of ventilation and of cerebral blood volume (CBV) to acute changes in carbon dioxide tension in arterial blood ( P a,CO...

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 su...

The monitoring of a single muscle location does not reflect the heterogeneity of the muscle groups activation during exercise. In the past, measurements of oxygen consumption (VO2) at single muscle locations could be carried out non-invasively by near-infrared continuous wave spectroscopy (NIRCWS) at rest or during isometric contractions. In the pr...

In some circumstances, cerebral blood volume (CBV) can be used as a measure for cerebral blood flow. A new near infrared spectroscope was used for determining the reproducibility of CBV measurements assessed by the O2-method. Twenty-seven healthy subjects were investigated. An intrasubject coefficient of variation (CV) was calculated, based on four...

The aim of this study was to investigate local muscle O(2) consumption (muscV(O(2))) and forearm blood flow (FBF) in resting and exercising muscle by use of near-infrared spectroscopy (NIRS) and to compare the results with the global muscV(O(2)) and FBF derived from the well-established Fick method and plethysmography. muscV(O(2)) was derived from...

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 conf...

The relationship between alterations in cerebral blood volume (CBV) and central chemosensitivity regulation was studied under neutral metabolic conditions and during metabolic acidosis. Fifteen healthy subjects (56+/-10 years) were investigated. To induce metabolic acidosis, ammonium chloride (NH(4)Cl) was given orally. CBV was measured using Near...

In the elderly, standing can frequently be accompanied by blood pressure (BP) changes and cerebral symptoms such as dizziness, fall, or even syncope, but this may vary from day-to-day. Therefore, we aimed to investigate the reproducibility of orthostatic responses of cerebral cortical oxygenation and systemic haemodynamics in elderly subjects. In 2...

It is not known to what extent effects in extracerebral tissue influence non-invasive near infra-red optical measurement of cerebral arterial oxygenation saturation. Measurements were made at different positions on the forehead of six healthy adult male volunteers with arterial saturation near to 100%. The optical ratios between the pulse heights a...

Patients with orthostatic hypotension due to sympathetic failure become symptomatic when standing, although their capability to maintain cerebral blood flow is reported to be preserved. We tested the hypothesis that in patients with sympathetic failure, orthostatic symptoms reflect reduced cerebral perfusion with insufficient oxygen supply. This st...

With increasing age, assuming the upright position is more often accompanied by symptoms such as dizziness and lightheadedness, possibly as a result of a diminished oxygen supply to the brain due to impaired cerebral autoregulation. We aimed to quantify postural changes in cerebral oxygenation and systemic hemodynamics in healthy elderly and young...

To compare tilt-induced alterations in cardiovascular homeostasis and cerebral oxygenation of spinal cord-injured (SCI) to able-bodied (AB) individuals. Subjects underwent 10 min supine rest followed by 10 min 70 degrees head-up tilt. The last 5 min of supine rest and head-up tilt were analyzed, provided a steady state existed. SCI individuals (n=...

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...

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...

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 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 (19)F-MR relaxometry, using perfluoro-15-crown-...

In the past, the measurement of O(2) consumption ((2)) by the muscle could be carried out noninvasively by near-infrared spectroscopy from oxyhemoglobin and/or deoxyhemoglobin measurements only at rest or during steady isometric contractions. In the present study, a mathematical model is developed allowing calculation, together with steady-state le...

The aim of this study was to induce acute metabolic acid/base changes of > or = 2 mequiv.l-1 change in base excess (BE) to aid future investigations of respiratory parameters under these conditions. Ammonium chloride (NH4Cl) was administered to induce acidification and furosemide was used to induce alkalization. Nine healthy volunteers (six men and...

Cardiovascular stability, as affected by several diseases, may be assessed by head-up tilt testing. Follow-up studies are essential in both evaluating interventions and assessing progression. However, data on the reproducibility of the changes in circulatory status and cerebral oxygenation provoked by head-up tilt testing are fundamental to follow-...

In the last few years near infrared spectroscopy (NIRS) has become a more widespread tool to map the human brain function, in particular the motor cortex areas (Gratton et al., 1995; Hirth et al., 1996; Obrig et al., 1996; Colier et al., 1997) and visual cortex areas (Kato et al., 1993; Hoshi et al., 1993; Meek et al., 1995; Wenzel et al., 1996; Gr...

Near Infrared Spectroscopy (NIRS) can be used to measure cerebral blood volume (CBV), and its reactivity to changes in PaCO2. NIRS is a promising technique, which offers continuous measurements of CBV at bedside and is relatively cheap. Moreover, invasiveness is not necessary, which makes NIRS a very interesting tool for clinical use.KeywordsChroni...

Five patients with chronic progressive external ophthalmoplegia (CPEO) and 27 healthy controls were examined by near-infrared spectroscopy (NIRS) for the non-invasive and direct quantitative measurement of muscle oxygen consumption during rest as well as during static isometric handgrip exercise at 10% of their maximum voluntary contraction. In pat...

Theoretically, Near Infrared Spectroscopy (NIRS) can be used as a non-invasive and fast method to quantify cerebral blood flow (CBF) in neonates (Wyatt et al., 1990) and adults (Elwell et al., 1994). In contrast to current methods such as 133Xe washout, positron emission tomography (PET) or magnetic resonance imaging (MRI), repeated measurements ar...

Near infrared spectroscopy (NIRS) has been used to monitor oxygenation changes in muscle. Quantitative values for O2 consumption, blood flow and venous saturation have been reported by several investigators. The amount of these measurements is, however, still limited and complete validation has not yet been established. The aim of this study was to...

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 i...

The purpose of this study was to explore the application of near-infrared spectroscopy (NIRS) to the assessment of peripheral arterial occlusive disease (PAOD). Muscle blood flow, oxygen consumption, arterial inflow capacity, O2 resaturation, and recovery times were determined at rest, under ischemic and hyperemic conditions, and continuously durin...

In the last four years near infrared spectroscopy (NIRS) has been used in cerebral functional activation studies to monitor changes in concentration of oxy-, deoxy- and total hemoglobin [(O2Hb), (HHb) and (tHb) respectively] in response to different stimuli. Previous studies were performed with a 1 - 2 Hz temporal resolution and a poor signal-to-no...

Near infrared spectroscopy (NIRS) is an optical technique that provides information on cerebral tissue oxygenation and hemodynamics on a continuous, direct, and noninvasive basis. It is used to determine cerebral blood volume (CBV) and cerebrovascular CO 2 reactivity during normoxic hyper- and hypocapnia in a group of 28 healthy volunteers aged 20...

Vasovagal syncope is usually described as a sudden and transient loss of consciousness that resolves spontaneously. Cardiocirculatory changes are well described during and before syncope. However, changes in the cerebral oxygenation are not well defined. In this study, near-infrared spectroscopy (NIRS) was used to assess the cerebral oxygenation di...

Conventional near infrared spectroscopy (NIRS), introduced by Jöbsis in 1977, can be considered as a reliable trend monitor for cerebral oxygenation. Quantisation, however, is complex and cumbersome. Recently a relatively simple system for cerebral oximetry (INVOS 3100, Somanetics Corporation, USA) was developed, measuring the regional oxygen satur...

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 1...

Cryptorchidism is the most common male sexual disorder. In the case of an abdominal testis there is no objective criterion to choose between autotransplantation or orchiopexy after ligation of the spermatic vessels with subsequent development of collateral blood supply. By combining near infrared spectroscopy (NIRS) with pulse oximetry the active t...

Near-infrared spectroscopy has been applied to the study of cerebral oxygenation and hemodynamics in the newborn. Fetal Hb is present in high concentrations in these infants. Because spectral absorption curves in the near-infrared range for fetal Hb are not identical to those for adult Hb, there is a potential for the measurements to be affected. T...