The effect of doorway characteristics on freezing of gait in Parkinson's disease.

Background: Freezing of gait is a debilitating symptom in Parkinson's disease, during which a sudden motor block prevents someone from moving forward. Remarkably, doorways can provoke freezing. Most research has focused on the influence of doorway width, and little is known about other doorway characteristics influencing doorway freezing. Objective: Firstly, to provide guidelines on how to design doorways for people with freezing. Secondly, to compare people with doorway freezing to people without doorway freezing, and to explore the underlying mechanisms of doorway freezing. Methods: We designed a web-based, structured survey consisting of two parts. Part I (n = 171 responders), open to people with Parkinson's disease with freezing in general, aimed to compare people with doorway freezing to people without doorway freezing. We explored underlying processes related to doorway freezing with the Gait-Specific Attention Profile (G-SAP), inquiring about conscious movement processes occurring during doorway passing. Part II (n = 60), open for people experiencing weekly doorway freezing episodes, inquired about the influence of specific doorway characteristics on freezing. Results: People with doorway freezing (69% of Part I) had higher freezing severity, longer disease duration, and scored higher on all sub scores of the G-SAP (indicating heightened motor, attentional, and emotional thoughts when passing through doorways) than people without doorway freezing. The main categories provoking doorway freezing were: dimensions of the door and surroundings, clutter around the door, lighting conditions, and automatic doors. Conclusion: We provide recommendations on how to maximally avoid freezing in a practical setting. Furthermore, we suggest that doorways trigger freezing based on visuomotor, attentional, and emotional processes.

Capturing postural blood pressure dynamics with near-infrared spectroscopy-measured cerebral oxygenation.

Orthostatic hypotension (OH) is highly prevalent in older adults and associated with dizziness, falls, lower physical and cognitive function, cardiovascular disease, and mortality. OH is currently diagnosed in a clinical setting with single-time point cuff measurements. Continuous blood pressure (BP) devices can measure OH dynamics but cannot be used for daily life monitoring. Near-infrared spectroscopy (NIRS) has potential diagnostic value in measuring cerebral oxygenation continuously over a longer time period, but this needs further validation. This study aimed to compare NIRS-measured (cerebral) oxygenation with continuous BP and transcranial Doppler-measured cerebral blood velocity (CBv) during postural changes. This cross-sectional study included 41 participants between 20 and 88 years old. BP, CBv, and cerebral (long channels) and superficial (short channels) oxygenated hemoglobin (O2Hb) were measured continuously during various postural changes. Pearson correlations between BP, CBv, and O2Hb were calculated over curves and specific characteristics (maximum drop amplitude and recovery). BP and O2Hb only showed good curve-based correlations (0.58-0.75) in the initial 30 s after standing up. Early (30-40 s) and 1-min BP recovery associated significantly with O2Hb, but no consistent associations were found for maximum drop amplitude and late (60-175 s) recovery values. Associations between CBv and O2Hb were poor, but stronger for long-channel than short-channel measurements. BP associated well with NIRS-measured O2Hb in the first 30 s after postural change. Stronger associations for CBv with long-channel O2Hb suggest that long-channel NIRS specifically reflects cerebral blood flow during postural transitions, necessary to better understand the consequences of OH such as intolerance symptoms.

Comparison of state-of-the-art deep learning architectures for detection of freezing of gait in Parkinson's disease.

Introduction: Freezing of gait (FOG) is one of the most debilitating motor symptoms experienced by patients with Parkinson's disease (PD). FOG detection is possible using acceleration data from wearable sensors, and a convolutional neural network (CNN) is often used to determine the presence of FOG epochs. We compared the performance of a standard CNN for the detection of FOG with two more complex networks, which are well suited for time series data, the MiniRocket and the InceptionTime. Methods: We combined acceleration data of people with PD across four studies. The final data set was split into a training (80%) and hold-out test (20%) set. A fifth study was included as an unseen test set. The data were windowed (2 s) and five-fold cross-validation was applied. The CNN, MiniRocket, and InceptionTime models were evaluated using a receiver operating characteristic (ROC) curve and its area under the curve (AUC). Multiple sensor configurations were evaluated for the best model. The geometric mean was subsequently calculated to select the optimal threshold. The selected model and threshold were evaluated on the hold-out and unseen test set. Results: A total of 70 participants (23.7 h, 9% FOG) were included in this study for training and testing, and in addition, 10 participants provided an unseen test set (2.4 h, 11% FOG). The CNN performed best (AUC = 0.86) in comparison to the InceptionTime (AUC = 0.82) and MiniRocket (AUC = 0.76) models. For the CNN, we found a similar performance for a seven-sensor configuration (lumbar, upper and lower legs and feet; AUC = 0.86), six-sensor configuration (upper and lower legs and feet; AUC = 0.87), and two-sensor configuration (lower legs; AUC = 0.86). The optimal threshold of 0.45 resulted in a sensitivity of 77% and a specificity of 58% for the hold-out set (AUC = 0.72), and a sensitivity of 85% and a specificity of 68% for the unseen test set (AUC = 0.90). Conclusion: We confirmed that deep learning can be used to detect FOG in a large, heterogeneous dataset. The CNN model outperformed more complex networks. This model could be employed in future personalized interventions, with the ultimate goal of using automated FOG detection to trigger real-time cues to alleviate FOG in daily life.

Cognitive map formation supported by auditory, haptic, and multimodal information in persons with blindness.

For efficient navigation, the brain needs to adequately represent the environment in a cognitive map. In this review, we sought to give an overview of literature about cognitive map formation based on non-visual modalities in persons with blindness (PWBs) and sighted persons. The review is focused on the auditory and haptic modalities, including research that combines multiple modalities and real-world navigation. Furthermore, we addressed implications of route and survey representations. Taking together, PWBs as well as sighted persons can build up cognitive maps based on non-visual modalities, although the accuracy sometime somewhat differs between PWBs and sighted persons. We provide some speculations on how to deploy information from different modalities to support cognitive map formation. Furthermore, PWBs and sighted persons seem to be able to construct route as well as survey representations. PWBs can experience difficulties building up a survey representation, but this is not always the case, and research suggests that they can acquire this ability with sufficient spatial information or training. We discuss possible explanations of these inconsistencies.

Cognitive map formation through tactile map navigation in visually impaired and sighted persons.

The human brain can form cognitive maps of a spatial environment, which can support wayfinding. In this study, we investigated cognitive map formation of an environment presented in the tactile modality, in visually impaired and sighted persons. In addition, we assessed the acquisition of route and survey knowledge. Ten persons with a visual impairment (PVIs) and ten sighted control participants learned a tactile map of a city-like environment. The map included five marked locations associated with different items. Participants subsequently estimated distances between item pairs, performed a direction pointing task, reproduced routes between items and recalled item locations. In addition, we conducted questionnaires to assess general navigational abilities and the use of route or survey strategies. Overall, participants in both groups performed well on the spatial tasks. Our results did not show differences in performance between PVIs and sighted persons, indicating that both groups formed an equally accurate cognitive map. Furthermore, we found that the groups generally used similar navigational strategies, which correlated with performance on some of the tasks, and acquired similar and accurate route and survey knowledge. We therefore suggest that PVIs are able to employ a route as well as survey strategy if they have the opportunity to access route-like as well as map-like information such as on a tactile map.

Determinants of orthostatic cerebral oxygenation assessed using near-infrared spectroscopy.

BACKGROUND: To understand the relationship between blood pressure changes during standing up and clinical outcome, cerebral oxygenation needs to be measured, which may be performed using near-infrared spectroscopy (NIRS). However, the role of potential determinants of NIRS-derived orthostatic cerebral oxygenation, i.e., age, sex, type of postural change (i.e., standing up from sitting versus supine position), blood pressure (BP) and baroreflex sensitivity (BRS) is still unknown and needed to better interpret findings from studies using orthostatic NIRS measurements. METHODS: 34 younger (median age 25 years, inter quartile range (IQR) 22-45) and 31 older adults (median age 77 years, IQR 72-81) underwent BP, BRS and NIRS measurements during standing up from sitting and supine position. Linear regression models were used to assess the potential determinant role of age, sex, type of postural change, BP and BRS in orthostatic cerebral oxygenation drop and recovery. Orthostatic cerebral oxygenation test-retest reliability was assessed using intra class correlations. RESULTS: Younger age, male sex and standing up from supine compared to sitting position were positively associated with cerebral oxygenation drop; older age and standing up from sitting compared to supine position were associated with higher cerebral oxygenation recovery. Test-retest reliability was highest (ICC > 0.83) during standing up from supine position. CONCLUSION: Based on the findings of this study, age, sex and type of postural change are significant determinants of NIRS-derived orthostatic cerebral oxygenation and should be taken into account in the interpretation of NIRS measurements. In the design of new studies, standing up from supine position is preferable (higher reliability) over standing up from sitting position.

Validation of Soft Multipin Dry EEG Electrodes.

Current developments towards multipin, dry electrodes in electroencephalography (EEG) are promising for applications in non-laboratory environments. Dry electrodes do not require the application of conductive gel, which mostly confines the use of gel EEG systems to the laboratory environment. The aim of this study is to validate soft, multipin, dry EEG electrodes by comparing their performance to conventional gel EEG electrodes. Fifteen healthy volunteers performed three tasks, with a 32-channel gel EEG system and a 32-channel dry EEG system: the 40 Hz Auditory Steady-State Response (ASSR), the checkerboard paradigm, and an eyes open/closed task. Within-subject analyses were performed to compare the signal quality in the time, frequency, and spatial domains. The results showed strong similarities between the two systems in the time and frequency domains, with strong correlations of the visual (ρ = 0.89) and auditory evoked potential (ρ = 0.81), and moderate to strong correlations for the alpha band during eye closure (ρ = 0.81-0.86) and the 40 Hz-ASSR power (ρ = 0.66-0.72), respectively. However, delta and theta band power was significantly increased, and the signal-to-noise ratio was significantly decreased for the dry EEG system. Topographical distributions were comparable for both systems. Moreover, the application time of the dry EEG system was significantly shorter (8 min). It can be concluded that the soft, multipin dry EEG system can be used in brain activity research with similar accuracy as conventional gel electrodes.

Cognitive map formation through haptic and visual exploration of tactile city-like maps.

In this study, we compared cognitive map formation of small-scale models of city-like environments presented in visual or tactile/haptic modalities. Previous research often addresses only a limited amount of cognitive map aspects. We wanted to combine several of these aspects to elucidate a more complete view. Therefore, we assessed different types of spatial information, and consider egocentric as well as allocentric perspectives. Furthermore, we compared haptic map learning with visual map learning. In total 18 sighted participants (9 in a haptic condition, 9 visuo-haptic) learned three tactile maps of city-like environments. The maps differed in complexity, and had five marked locations associated with unique items. Participants estimated distances between item pairs, rebuilt the map, recalled locations, and navigated two routes, after learning each map. All participants overall performed well on the spatial tasks. Interestingly, only on the complex maps, participants performed worse in the haptic condition than the visuo-haptic, suggesting no distinct advantage of vision on the simple map. These results support ideas of modality-independent representations of space. Although it is less clear on the more complex maps, our findings indicate that participants using only haptic or a combination of haptic and visual information both form a quite accurate cognitive map of a simple tactile city-like map.

Cerebral autoregulation assessed by near-infrared spectroscopy: validation using transcranial Doppler in patients with controlled hypertension, cognitive impairment and controls.

PURPOSE: Cerebral autoregulation (CA) aims to attenuate the effects of blood pressure variation on cerebral blood flow. This study assessed the criterion validity of CA derived from near-infrared spectroscopy (NIRS) as an alternative for Transcranial Doppler (TCD). METHODS: Measurements of continuous blood pressure (BP), oxygenated hemoglobin (O2Hb) using NIRS and cerebral blood flow velocity (CBFV) using TCD (gold standard) were performed in 82 controls, 27 patients with hypertension and 94 cognitively impaired patients during supine rest (all individuals) and repeated sit to stand transitions (cognitively impaired patients). The BP-CBFV and BP-O2Hb transfer function phase shifts (TFφ) were computed as CA measures. Spearman correlations (ρ) and Bland Altman limits of agreement (BAloa) between NIRS- and TCD-derived CA measures were computed. BAloa separation < 50° was considered a high absolute agreement. RESULTS: NIRS- and TCD-derived CA estimates were significantly correlated during supine rest (ρ = 0.22-0.30, N = 111-120) and repeated sit-to-stand transitions (ρ = 0.46-0.61, N = 19-32). BAloa separation ranged between 87° and 112° (supine rest) and 65°-77° (repeated sit to stand transitions). CONCLUSION: Criterion validity of NIRS-derived CA measures allows for comparison between groups but was insufficient for clinical application in individuals.

Orthostatic blood pressure recovery associates with physical performance, frailty and number of falls in geriatric outpatients.

OBJECTIVE: Blood pressure (BP) recovery after orthostatic hypotension might be important to prevent cerebral hypoperfusion episodes in older adults, and be related to better clinical outcome. The objective was to study the relationship between BP recovery and clinical outcome, that is physical and cognitive performance, frailty and falls, in geriatric outpatients. METHODS: One hundred and sixty-eight geriatric outpatients underwent continuous (beat-to-beat) BP measurements during standing up, and a comprehensive geriatric assessment, including assessment of physical performance (chair stand test), cognitive performance (Mini Mental State Examination), frailty (Fried criteria) and falls in the previous year. BP recovery was evaluated at 15-30, 30-60, 60-120 and 120-180 s after standing up and defined as mean SBP and DBP in the respective time intervals minus baseline BP. Associations with clinical outcome were assessed using linear (physical and cognitive performance and frailty) and logistic (falls) regression, adjusting for age, sex, baseline BP and initial BP drop. RESULTS: SBP recovery was associated with frailty (30-60 s interval; ß = 0.013, P = 0.02) and falls (30-60 s interval; odds ratio = 1.024, P = 0.02). DBP recovery was associated with physical performance (30-60 s interval; ß = 0.215, P = 0.01), frailty (30-60 s interval; ß = 0.028, P = 0.02) and falls (30-60 s interval; odds ratio = 1.039, P = 0.04). Neither SBP nor DBP recovery was associated with cognitive performance. CONCLUSION: DBP recovery was particularly associated with clinical outcome in geriatric outpatients, suggesting BP recovery to be of clinical interest.

Virtual reality distraction for patients to relieve pain and discomfort during colonoscopy.

Background and study aims Colonoscopy is an invasive procedure that may cause patients pain and discomfort. Routine use of sedation, while effective, is expensive and requires logistical planning. Virtual reality (VR) offers immersive, three-dimensional experiences that distract the attention and might comfort patients. We performed a pilot study to investigate the feasibility of VR distraction during colonoscopy. Patients and methods Adults referred for colonoscopy were considered for inclusion and divided over two groups: with and without VR glasses. The main outcome was patient acceptance of wearing VR glasses during colonoscopy without compromising the technical success of the procedure. Secondary outcomes were patient comfort, pain, and anxiety before, during and after the procedure, using validated patient questionnaires. Patient comments were collected through a qualitative interview. Results We included 19 patients, 10 of whom were offered VR glasses. All patients accepted VR glasses without prolonging procedural time. No disadvantages of the VR glasses were reported in terms of communication or change of position of the patient. We found that patient comfort, pain, anxiety, and satisfaction in relation to the procedure were similar in both groups. Patients described a pleasant distracting effect using VR glasses. Conclusion VR glasses during colonoscopy are accepted by patients and do not compromise endoscopic technical success. Patients reported that the VR experience was pleasant and distracting.

The Beneficial Effects of Conventional Visual Cues Are Retained When Augmented Reality Glasses Are Worn.

Wearing smart glasses may be distracting and thus annihilate the beneficial effects of cues on freezing of gait in Parkinson's disease. Furthermore, augmented reality cues might be effective in reducing FOG specifically in cueing-responsive patients. We present a single-patient study in which a patient with Parkinson's disease traversed a doorway under different cueing conditions. Wearing augmented reality (AR) glasses did not deteriorate FOG nor affect the beneficial effects of cues. The AR visual cues did not improve FOG. This single-patient study implies that the current design of AR glasses does not stand in the way of the development of augmented reality visual cues. However, the effectivity of augmented reality visual cues remains to be proven.

Blood Pressure Drop Rate After Standing Up Is Associated With Frailty and Number of Falls in Geriatric Outpatients.

Background The relationship between orthostatic hypotension and clinical outcome in older adults is poorly understood. Blood pressure drop rate (ie, speed of blood pressure drop) may particularly reflect the imposed challenge to the baroreflex and the associated clinical outcome (ie, frailty and number of falls). This study aimed to compare orthostatic blood pressure drop rate and drop magnitude with regard to their association with frailty and number of falls. Methods and Results Blood pressure was measured continuously during a standardized active stand task in 168 patients (mean age 81.4±7.0; 55.4% female) who visited a geriatric outpatient clinic for cognitive or mobility problems. The association of orthostatic blood pressure drop rate, blood pressure drop magnitude, and baroreflex sensitivity (ie, increase in heart rate divided by systolic blood pressure drop magnitude) with frailty (Fried criteria and 4 frailty markers) and self-reported number of falls was assessed using linear regression models, adjusting for age and sex. Systolic blood pressure drop rate had the strongest association with frailty according to the 4 frailty markers (ß 0.30; 95% CI, 0.11-0.49; P=0.003) and number of falls (ß 1.09; 95% CI, 0.19-1.20; P=0.018); diastolic blood pressure drop magnitude was most strongly associated with frailty according to the Fried criteria (ß 0.37; 95% CI, 0.15-0.60; P<0.001). Baroreflex sensitivity was associated with neither frailty nor number of falls. Conclusions Orthostatic blood pressure drop rate was associated with frailty and falls and may reflect the challenge to the baroreflex rather than drop magnitude.

The Effects of Augmented Reality Visual Cues on Turning in Place in Parkinson's Disease Patients With Freezing of Gait.

Background: Turning in place is particularly bothersome for patients with Parkinson's disease (PD) experiencing freezing of gait (FOG). Cues designed to enforce goal-directed turning are not yet available. Objectives: Assess whether augmented reality (AR) visual cues improve FOG and turning in place in PD patients with FOG. Methods: Sixteen PD patients with FOG performed a series of 180° turns under an experimental condition with AR visual cues displayed through a HoloLens and two control conditions (one consisting of auditory cues and one without any cues). FOG episodes were annotated by two independent raters from video recordings. Motion data were measured with 17 inertial measurement units for calculating axial kinematics, scaling, and timing of turning. Results: AR visual cues did not reduce the percent time frozen (p = 0.73) or the number (p = 0.73) and duration (p = 0.78) of FOG episodes compared to the control condition without cues. All FOG parameters were higher with AR visual cues than with auditory cues [percent time frozen (p = 0.01), number (p = 0.02), and duration (p = 0.007) of FOG episodes]. The AR visual cues did reduce the peak angular velocity (visual vs. uncued p = 0.03; visual vs. auditory p = 0.02) and step height (visual vs. uncued p = 0.02; visual vs. auditory p = 0.007), and increased the step height coefficient of variation (visual vs. uncued p = 0.04; visual vs. auditory p = 0.01) and time to maximum head-pelvis separation (visual vs. uncued p = 0.02; visual vs. auditory p = 0.005), compared to both control conditions. Conclusions: The AR visual cues in this study did not reduce FOG, and worsened some measures of axial kinematics, and turn scaling and timing. Stimulating goal-directed turning might, by itself, be insufficient to reduce FOG and improve turning performance. Trial Registration: This study was registered in the Dutch trial registry (NTR6409; 2017-02-16).

Pulse transit time as a proxy for vasoconstriction in younger and older adults.

OBJECTIVES: Changes of vasoconstriction may be measured non-invasively using pulse transit time. This study assessed the sensitivity, test-retest reliability and validity of pulse transit time during vasoconstriction provocation and active standing, and the predictive value of pulse transit time for blood pressure drop. METHODS: Fifty-five younger (age < 65 years) and 31 older adults (age > 70 years) underwent electrocardiography, wrist and finger photoplethysmography and continuous blood pressure and total peripheral resistance measurements during vasoconstriction provocation using a cold pressor test (21 younger adults), or active stand tests (all other participants). Pulse transit time was defined as the time lag between the electrocardiography R-peak and the peak in the photoplethysmography first derivative; sensitivity as a significant decrease relative to baseline; test-retest reliability as the intra class correlation between different repeats of the same test; validity as the association between peripheral resistance and pulse transit time; predictive value as the association between supine resting pulse transit time and mean arterial pressure drop during active standing. RESULTS: Finger pulse transit time was sensitive and reliable (ICC 0.2-0.8) during vasoconstriction provocation, but wrist pulse transit time was poorly reliable (ICC 0-0.5); only finger pulse transit time was sensitive to and reliable (ICC 0.4-0.8) during active standing in both younger and older adults. Finger pulse transit time was not associated with total peripheral resistance. Supine resting pulse transit time had predictive value for blood pressure drop during active standing in older adults (ß -0.16; p 0.025). CONCLUSIONS: Pulse transit time was sensitive to and reliable during vasoconstriction provocation and active standing, but did not significantly differ between younger and older adults. Pulse transit time could not be demonstrated to particularly reflect vasoconstriction, but it had predictive value for blood pressure drop during active standing.

Multimodal Monitoring of Cardiovascular Responses to Postural Changes.

BACKGROUND: In the poorly understood relationship between orthostatic hypotension and falls, next to blood pressure (BP), baroreflex sensitivity (BRS) and cerebral autoregulation (CAR) may be key measures. The posture- and movement dependency of orthostatic hypotension requires continuous and unobtrusive monitoring. This may be possible using simultaneous photoplethysmography (PPG), electrocardiography (ECG), and near-infrared spectroscopy (NIRS) signal recordings, from which pulse wave velocity (PWV; potentially useful for BP estimation), BRS and CAR can be derived. The PPG, NIRS and PWV signal correlation with BP and BRS/CAR reliability and validity need to be addressed. METHODS: In 34 healthy adults (mean age 25 years, inter quartile range 22-45; 10 female), wrist and finger PPG, ECG, bifrontal NIRS (oxygenated and deoxygenated hemoglobin) and continuous BP were recorded during sit to stand and supine to stand movements. Sixteen participants performed slow and rapid supine to stand movements; eighteen other participants performed a 1-min squat movement. Pulse wave velocity (PWV) was defined as the inverse of the ECG R-peak to PPG pulse delay; PPG, NIRS and PWV signal correlation with BP as their Pearson correlations with mean arterial pressure (MAP) within 30 s after the postural changes; BRS as inter beat interval drop divided by systolic BP (SBP) drop during the postural changes; CAR as oxygenated hemoglobin drop divided by MAP drop. BRS and CAR were separately computed using measured and estimated (linear regression) BP. BRS/CAR reliability was defined by the intra class correlation between repeats of the same postural change; validity as the Pearson correlation between BRS/CAR values based on measured and estimated BP. RESULTS: The highest correlation with MAP was found for finger PPG and oxygenated hemoglobin, ranging from 0.75-0.79 (sit to stand), 0.66-0.88 (supine to stand), and 0.82-0.94 (1-min squat). BRS and CAR reliability was highest during the different supine to stand movements, ranging from 0.17 - 0.49 (BRS) and 0.42-0.75 (CAR); validity was highest during rapid supine to stand movements, 0.54 and 0.79 respectively. CONCLUSION: PPG-ECG-NIRS recordings showed high correlation with BP and enabled computation of reliable and valid BRS and CAR estimates, suggesting their potential for continuous unobtrusive monitoring of orthostatic hypotension key measures.

Opto-locomotor reflexes of mice to reverse-phi stimuli.

In a reverse-phi stimulus, the contrast luminance of moving dots is reversed each displacement step. Under those conditions, the direction of the moving dots is perceived in the direction opposite of the displacement direction of the dots. In this study, we investigate if mice respond oppositely to phi and reverse-phi stimuli. Mice ran head-fixed on a Styrofoam ball floating on pressurized air at the center of a large dome. We projected random dot patterns that were displaced rightward or leftward, using either a phi or a reverse-phi stimulus. For phi stimuli, changes in direction caused the mice to reflexively compensate and adjust their running direction in the direction of the displaced pattern. We show that for reverse-phi stimuli mice compensate in the direction opposite to the displacement direction of the dots, in accordance with the perceived direction of displacement in humans for reverse-phi stimuli.

Monocular and binocular opto-locomotor reflex biases for random dot motion in mice.

We investigated the relationship between eyes receiving visual input of large field translating random dot motion and subsequent reflexive changes in running direction in mice. The animals were head-fixed running on a Styrofoam ball and the opto-locomotor reflex (OLR) was measured in response to 2 s of dots patterns moving horizontally to the left or right. We measured the OLR in conditions with both eyes open (binocular) and one eye closed (monocular). When we covered the right or left eye in the monocular condition, we found reflexive behavior to be delayed for a few hundred milliseconds to leftward or rightward motion, respectively. After this delay, the bias disappeared and reflexive behavior was similar to responses to motion under binocular conditions. These results might be explained by different contributions of subcortical and cortical visual motion processing pathways to the OLR. Furthermore, we found no evidence for nonlinear interactions between the two eyes, because the sum of the OLR of the two monocular conditions was equal in amplitude and temporal characteristics to the OLR under binocular conditions.

Sensitivity and reliability of cerebral oxygenation responses to postural changes measured with near-infrared spectroscopy.

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 and speeds of postural changes in healthy adults and assessed the reliability of these responses. METHODS: Cerebral oxygenated hemoglobin (O2Hb), deoxygenated hemoglobin (HHb) and tissue saturation index (TSI) were measured bilaterally on the forehead of 15 healthy individuals (12 male, age range 18-27) using NIRS. Participants performed three repeats of sit to stand, and slow and rapid supine to stand movements. Responses were defined as the difference between mean, minimum and maximum O2Hb, HHb and TSI values after standing up and baseline. Test-retest, interobserver and intersensor reliabilities were addressed using intraclass correlation coefficients (ICCs). RESULTS: The minimum O2Hb response was most sensitive to postural changes and showed significant differences (- 4.09 µmol/L, p < 0.001) between standing up from sitting and supine position, but not between standing up at different speeds (- 0.31 µmol/L, p = 0.70). The minimum O2Hb response was the most reliable parameter (ICC > 0.6). CONCLUSIONS: In healthy individuals, NIRS-based cerebral oxygenation parameters are sensitive to postural change and discriminate between standing up from supine and sitting position with minimum O2Hb response as the most sensitive and reliable parameter. The results underpin the potential value for future clinical use of NIRS in individuals with orthostatic hypotension.