Background: Spinal cord injury (SCI) compromises bladder function, including the ability to sense the need to void. Overdistension leads to involuntary leakage and endangers health through upper renal tract pressure damage and autonomic dysreflexia. A monitor warning the bladder is full will allow optimal use of manual expression or intermittent catheterization. Methods: The wearable interface is a silicone sheet worn over the bladder, which incorporates a grid of 4 near-infrared LED transmitters with 3 wavelengths (2 at 950 nm for water detection and 2 of 760 and 850 nm for conventional monitoring of O2Hb and HHb). The system has 8 continuous-wave measurement channels and monitors at 2 different vertical levels to detect variation in bladder fullness; IOD’s of 30 and 40mm provide information at 2 depths. Associations between optical densities during bladder emptying and then during natural filling were compared. Results: Data from 4 male and one female subject were analyzed. The optical densities recorded at the lower vertical locations showed positive correlation with the voiding rate (ratio of scale signal), and O2Hb and HHb concentration changes at higher vertical locations revealed muscle activation prior to voiding. Discussion: This pilot study provides proof of the feasibility of using a 950nm wavelength incorporated into a wearable NIRS bladder monitoring system to transcutaneously and non-invasively detect changes in bladder volume in real-time. Conclusions: Ongoing research is warranted to further evaluate the system as the bladder fills naturally; and establish the clinical value of the data obtained to patients living with spinal cord injury
KEYWORDS: Sensors, Near infrared spectroscopy, Muscles, In vivo imaging, Education and training, Oxygenation, Tissues, Oxygen, Accuracy assessment, Reproducibility
Athletes can optimize training performance by measuring the oxygenation level in their muscles using Near-infrared spectroscopy (NIRS). NIRS allows athletes to measure local muscle oxygenation changes and assess performance indicators such as optimal pace or intensity during endurance activities and optimal recovery in endurance and strength activities. A novel NIRS sensor (Train.Red FYER) was developed to enable these measurements. In this this study the stability, accuracy, intra- and inter-variability of muscle oxygenation saturation (SmO2) in 10 sensors using two different phantoms and in-vivo tests, were SmO2 was defined as the percentage of the ratio of oxygenated to total hemoglobin. Stability of three sensors was tested during 3 hours on each phantom. Intra-variability of three sensors was assessed on four different days by two different operators by repositioning the sensor over the same location on both phantoms and on the forearm during resting position. Intra-variability was also assessed during vascular occlusion tests (VOT). Intervariability was assessed between 10 sensors on both phantoms on four different days. For analysis coefficient of variance (CV) was calculated. The sensor showed to be stable on both phantoms (<1% SmO2). Precision tests showed a larger inter-variability (<2% SmO2) than intra-variability (<1% SmO2). Inter-day and inter-operator variability on phantoms were also small (<4% SmO2). In vivo tests on the forearm and VOT showed higher variability (<5% SmO2) than on phantoms. It was shown a stable and precise NIRS sensor for the measurement of SmO2.
The rest period in between strength exercises determines how the short-term energy supplies in the muscles are replenished and metabolites are cleared. Near-InfraRed Spectroscopy (NIRS) is a proven method to study oxidative recovery kinetics following exercise. The goal of this study is to develop a model that predicts the oxygenated recovery state, this can help athletes optimize the resumption of exercise. 17 healthy subjects performed a sustained isometric hold in a hand gripper until volitional exertion, Tissue Saturation Index (TSI) was continuously monitored throughout and following exercise by a NIRS sensor (Train.Red PLUS). The oxygenated recovery state was manually categorized by three independent experts into four different phases of recovery; I - a pronounced increase, II - a gentle increase, III - the maximum oxygenated state, and IV - the return to baseline. A Recurrent Neural Network, inspired by Natural Language Processing, was trained and tested on this data, resulting in a model that predicts shifts between phases of recovery. A 5-fold cross-validation analysis resulted in the following average performance: • Recurrent Neural Network: Accuracy: 55.17%, categorical cross-entropy: 1.02351. • Multi-Layer Perceptron: Accuracy: 57.16%, categorical cross-entropy: 0.95201. • XGBoost: accuracy: 44.85%, categorical cross-entropy: 10.1119. In predicting the user’s current state of oxygenated recovery the MLP and RNN are similar in performance, however, the MLP shows erratic behavior, while the RNN generally follows the shift in phases of the ground truth. These capabilities could enable athletes with different fitness goals to design goal-tailored and therefore more efficient training.
Background: Spinal cord injury (SCI) compromises muscle function; when the pelvic floor muscles (PFM) are involved continence is affected. Women with partial injury rely on PFM rehabilitation therapy (PFMT) to aid continence, but the current lack of absolute measures to quantify training effects by monitoring changes in muscle oxygenation and perfusion hampers rehabilitation. We report clinical translation of a near infrared spectroscopic (NIRS) system to enable women with partial SCI to apply transvaginal optical detection of physiologic changes during PMFT as a point of care tool to quantify the effects of their PFM rehabilitation. Methods: The NIRS interface incorporates a circumferential grid of 6 LED emitters and 4 photodiode receivers with interoptode distances of 20 and 35 mm. The system was developed iteratively by engineers working with clinicians and patient care advocates to be clinically applicable for women following spinal cord injury. The continuous wave system uses 2-wavelengths (nominal 760nm, 850nm) and a sampling rate of 50Hz. Placed in the vagina during PMFT, the system monitors changes in oxy and deoxy-hemoglobin concentration (O2Hb/HHb) in real time at multiple points in the PFM. The slope of reoxygenation recovery post contraction is a measure of muscle oxidative capacity. Results: A point of care system was successfully developed that provides a means of detecting chromophore change occurring in the PFM during muscular contraction. The chromophore changes monitored also allow an absolute measure, HbDiff half-recovery time (½RT) to be derived. Comparison of these data over time provides a means of evaluating PMFT regimens for a training effect. In preparation for application in subjects with SCI, the reproducibility of SMVCs was monitored successfully in a pilot study where a volunteer conducted a series of 4 SMVCs on 15 occasions. Discussion: Skeletal muscle recovery from exercise-induced oxygen deficit indicates oxidative capacity; this equates with muscular fitness. SMVC is a robust measure of muscle strength and endurance, and HbDiff in occlusion free ½RT analysis reflects metabolic changes within muscle better than O2Hb. This clinical translation of NIRS provides a hand held system for women to use to quantify physiologic changes in their PFM; this will aid women with partial spinal cord injury in whom PFM function may either be too weak to be detected by physical exam or manometry, and may only be present unilaterally. Hence the merit of an optical system able to provide quantifiable measures of reoxygenation recovery as a measure of PFM fitness. A quantitative physiologic measure for evaluating for PMFT training effect is currently lacking Conclusions: The collaborative development of this self-contained transvaginal NIRS system, and prior proof that optical detection of a validated quantifiable oxygenation parameter is feasible in the pelvic floor, now allows clinical evaluation using this point of care system to aid women with partial spinal cord injury. The aim is to enable them to use this system to optimize their PFM rehabilitation therapy as means of enhancing their continence and quality of life.
Motion is disruptive to neuroimaging methods. Motion artefacts range from large amplitude and short frequency spikes to drifts in amplitude causing cofounds in the analysis or completely invalidating any analysis, leading to epoch exclusion of data. However, we can only acquire ecologically robust information if subjects are engaging in natural interaction with their environment. Even more so in the case of sports, infants or motor disorder afflicted populations, where movement will happen. We proposed to study the relationship between channel location and Inertial Measuring Unit (IMU) quantified head movements, in order to better understand their effects in fNIRS data. Cerebral oxygenated (O2Hb) and deoxygenated (HHb) haemoglobin were measured bilaterally in prefrontal to frontal and occipital to temporo-parietal regions of healthy individuals. All participants performed controlled head movements in four conditions: Up, Down, measured by pitch IMU values; and Left, Right, measured by yaw IMU values, in varying degrees of movement. We analysed amplitude and coefficient of determination of O2Hb and HHb, within conditions and channel coordinates across subjects. Our results show that smaller angle magnitude movements (bellow 60 degrees in rotation) are significantly different than larger angle magnitude movements (above 75 degrees in rotation) with a p value of 0.0073; and that the Up condition is significantly different than other movement directions with a p value of 0.0001. We conclude that movement artefacts do not depend on area of measurement for the movement conditions studied. We recommend the application of threshold values for the future with the use of the IMU, by ignoring the effects of lower magnitudes of movement, while correcting or removing larger magnitudes. In future motion artefact removal, we recommend using an IMU for optimal head motion correction of cerebral oxygenation signals.
Functional near infrared spectroscopy (fNIRS) is used for brain hemodynamic assessment. Cortical hemodynamics are reliably estimated when the recorded signal has a sufficient quality. This is acquired when fNIRS optodes have proper scalp coupling. A lack of proper scalp coupling causes false positives and false negatives. Therefore, developing an objective algorithm for determining fNIRS signal quality is of great importance. In this study, we developed a machine learning-based algorithm for quantitatively rating fNIRS signal quality. Our promising results confirm the efficacy of the algorithm in determining fNIRS signal quality and hence decreasing misinterpretations.
Background: A requisite for fNIRS studies of cortical blood flow is that sufficient photons are transmitted transcutaneously for the fluctuations in cerebral hemoglobin oxygenation that occur during neuronal activation to be detected. Transmission is determined by the specifications of the fNIRS device, but also influenced by the characteristics of the skin. Epidermal pigments can attenuate photon transmission; the literature states that in dark skinned subjects some NIRS devices may not achieve sufficient photon migration to monitor cortical blood flow. Hence, as fNIRS use is spreading, we describe a simple head tilt maneuver where positional redistribution of cerebral blood volume will confirm if photon transmission is sufficient. Methods: A repetitive head tilt maneuver (bending forward from a seated position, hold for 30 seconds, returning to original position X 5) performed by a pigmented (African) subject and a non-pigmented (Caucasian) subject. A 23- channel portable fNIRS system with dual wavelength (750 and 860 nm) emitters and photodiode detectors was worn over the anterior cortex, and changes in oxy, deoxy and total hemoglobin concentration measured at 50 Hz. Results: Data from both subjects were compared and found to have a comparable pattern of change in oxyhemoglobin concentration and temporal response to the effects of head tilt; clear arterial pulsations and minimal noise were also evident. Conclusion: We suggest the head tilt maneuver described as a feasible test to confirm the adequacy of transcutaneous photon transmission where fNIRS studies are to be performed in subjects with pigmented skin to detect hemodynamic change in the cortex.
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 be measured over the full range from low- to high-intensity work, the advantage of sustained handgrip exercise is that it is less prone to movement artifacts. Intermittent isometric handgrip exercise enables
calculation of mVO2 at short time intervals providing information about the time response of local oxygen consumption in relation to the onset of exercise. Ten healthy subjects participated in this study. The different protocols were performed on separate days and in random order. mVO2 during rhythmic exercise was significantly higher than that during sustained exercise at all work intensities tested (P ≤ 0.05). However, the highest oxygen
consumption value for the three exercise protocols was measured during the steady state of intermittent exercise (P ≤ 0.05). These results show that the measurement of task-specific muscle metabolism during exercise can be measured noninvasively and with relative ease by near-infrared spectroscopy.
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 prevention programs. Objective: The aim of this study was to gain insight in muscle oxygen consumption (mVO2), blood flow (BF), and reoxygenation (ReOx) in the forearm of computer workers with stage III Repetitive Strain Injury (RSI). Method: We have used continuous wave infrared spectroscopy (NIRS) to measure these variables. Measurements were conducted on the extensor and flexor muscle in both arms as well in RSI-patients (n=10) as in control subjects (n=21). A protocol of increased isometric repetitive contraction in a handgrip ergonometer was used with increasing levels of strength. Results: mVO2 in the extensor muscle in RSI-subjects (dominant side) was increased compared to control subjects and compared to the non-dominant side (p<0.05). ReOx was not increased in RSI (dominant side-extensor muscle). However, there was a tendency towards statistical significance (p=0.065). BF in rest was equal in both groups, however after exercise it tended to be increased. Half-time recovery (T ½) was measured during only one part of the protocol and it was significantly increased (p<0.05). Conclusion: mVO2 in RSI is impaired. BF and ReOx did not show difference between both groups. Future research should aim at a microvascular dysfunction in RSI.
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 present study, human regional quadriceps (vastus lateralis and rectus femoris) VO2 was investigated at rest and during maximal voluntary contractions using a 12- channel NIRCWS system with an acquisition time of 0.1 s.
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 at different wavelengths were as expected from the spectral characteristics of hemoglobin, but showed an unacceptably large spread: the mean ratio between the 770 and 905 nm pulse heights was 0.69 (SD 0.08, range 0.50 - 0.95). We consider that this was due to pulsation of large extracranial arteries.
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 investigate the different NIRS methods to calculate O2 consumption (VO2) and forearm blood flow (FBF) and to validate the data with the accepted method of strain-gauge plethysmography and blood sampling. Thirteen subjects were tested in rest and during static isometric handgrip exercise at 10% MVC. The NIRS optodes were positioned on the flexor region of the arm. A significant correlation was found between plethysmograph data and NIRS [tHb] during venous occlusion in rest (r EQ 0.925 - 0.994, P < 0.05) as well as during exercise (r equals 0.895 - 0.990, P < 0.05). No correlation was found, however, for the calculated FBF and VO2 values between NIRS and the combination of plethysmography and blood sampling. In rest nor during exercise. It seems that although NIRS is a good qualitative monitoring technique, quantification is difficult due to the great variability that is found between the subjects.
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.
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-noise (S/N) ratio. The aim of this study was to investigate the response of the motor cortex region during a finger opposition task in single subjects using a novel continuous wave NIRS instrument with enhanced temporal resolution and S/N ratio. Six subjects performed a sequential finger opposition task with the right hand (20 s duration; 2 Hz). The optodes were positioned over the left motor cortex region using an inter-optode distance of 3.5 cm. The high S/N ratio and 0.1 s sampling time allowed clear monitoring of (O2Hb) and (HHb) changes due to heart beat as well as to respiration. The contribution of the heart pulse to the total signal was less than 0.4%. As previously shown by others using pooled data, an increase of (O2Hb) during the activation accompanied by a decrease of (HHb) was found in most subjects for every activation cycle. Our approach provides a better insight into the underlying physiological mechanisms.
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 CO2 reactivity during normoxic hyper- and hypocapnia in a group of 28 healthy volunteers aged 20 to 83 years. The main focus is on to the age dependency of the measured variables. The influence of changes in minute ventilation during normocapnia on the cerebral oxygenation was also studied. The mean CBV (6SD) in age was, for 20 to 30 years, 2.1460.51 ml/100 g of brain tissue; for 45 to 50 years, 1.9260.40 ml/100 g; and for 70 to 83 years, 1.4760.55 ml/100 g. The CBV showed a significant
decrease with advancing age. No influence was found for a change in minute ventilation on cerebral oxygenation. During hypercapnia cerebral blood flow (CBF) significantly increased in all age groups, with a factor of 1.3160.17 kPa−1, 1.6461.39 kPa−1, and 2.461.7 kPa−1, respectively, for the three age groups. The difference in change among the age groups was not statistically significant (p50.09). The trend seen was an increased change in CBF with advancing age. During hypocapnia, the CBF significantly decreased in all age groups, with a factor of 0.8960.08 kPa−1, 0.8960.04 kPa−1, and 0.8560.11 kPa−1, respectively. There was no significant
difference among the age groups (p50.50).
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