This work presents the development and experimental validation of a low-cost inertial acquisition framework for postural stability analysis. The system consists of three custom inertial measurement units (IMU), positioned on pelvis, right thigh and right shank, and a dedicated processing pipeline that includes sensor fusion, sensor-to-segment calibration, and joint angle computation. The system was validated against stereophotogrammetry and a commercial IMU reference, achieving high accuracy in hip and knee flexion-extension (RMSE

Non-invasive assessment of the volemic status is still an open and urgent clinical need. The pulse wave velocity in the venous compartment (vPWV) has recently been re-proposed as a possible indicator but still needs to be tested in different settings including hypovolemic conditions. The present study aims at investigating the response of the vPWV to hypovolemic changes of different magnitude, as provided by the lower body negative pressure (LBNP) and using the ultrasound monitoring of the inferior vena cava (IVC) as a reference. In 28 healthy subjects, vPWV was measured at the arm during exposure to short (90 s at -10, -20, -30, -40 mmHg) and long (5 min at -30 mmHg) exposure to LBNP, along with arterial blood pressure (ABP) and heart rate (HR). In a subgroup of 17 subjects IVC was successfully monitored and the full-time course of IVC diameter (dIVC) and collapsibility indices were extracted from the recording. While collapsibility indices were little responsive, vPWV and dIVC were significantly affected by LBNP, decreasing by 19.5 ± 9.7 and 20.9 ± 21.3

This study investigates the vascular effect of hemispheric lateralization during active and imagined elbow flexion-extension (EFE), using transcranial Doppler ultrasound (TCD). In order to assess the potential impact of the working side and of task repetition on the magnitude and time course of hemodynamic responses. Nineteen healthy right-handed participants were bilaterally monitored for cerebral blood flow velocity (CBFV) in the middle cerebral arteries (MCAs) during both active and imagined EFE. Significant lateralization during active movement, particularly with the left arm, were detected while imagined movements showed reduced lateralization and a delayed hemodynamic response. No effect of task repetition was observed but a left-ward trend of lateralization was observed during repeated motor imagery tasks, compared to active movements, suggesting that active engagement may influence cerebral activation and hemispheric lateralization. These findings offer insights into the neural correlates of motor tasks and have potential applications in brain-computer interfaces (BCIs) and neurorehabilitation.

Balance control can be evaluated by studying the displacement of the center of pressure (CoP) during dynamic posturographic trials. However, differences in anthropometric characteristics may affect the measurement and increase intersubject variability, possibly leading to misinterpretation. This study evaluates how sex, age, and anthropometric characteristics (weight, height, and foot length) influence the CoP displacement to postural perturbations. Seventy-two healthy subjects, 31 women and 41 men, were subjected to five small impulsive perturbations applied to their back. Balance performance was quantified by three CoP parameters: the ratio between the maximum CoP displacement and the impulse of the perturbation (ΔCoPn), the latency (Lat), and the duration (Dur) of the CoP response. A linear regression analysis evidenced that body weight and height exhibited a negative and positive relation with ΔCoPn, respectively, which explained 48

Stroke-surviving patients may present a wide range of neurological deficits affecting both sensory and motor functions as well as the cognitive and the emotional domains, with an impact on independence on daily activities and quality of life in general. Assessment scales are essential tools for evaluating all these aspects of a patient’s condition and for monitoring their evolution in time, attempting to provide a quantitative index to complex and sometimes indirectly observable parameters. In fact, the use of these scales entails methodological and interpretative challenges that can limit their applicability and effectiveness. This narrative review explores the current state and limitations of assessment scales used in the rehabilitative evaluation of post-stroke patients. Common neurorehabilitation techniques and traditionally used assessment scales for measuring patient progress are reviewed, highlighting their main limitations. As an alternative to the observational approach, direct assessment of the effect of the ongoing rehabilitative process on the functional recovery of the damaged neurological network, based on the recording of their electric signaling or on the modification in regional cerebral blood flow, have been recently proposed. Innovative rehabilitation assessment methods based on quantitative data are reviewed, with a special focus on ultrasound-based techniques, aiming to improve accuracy and sensitivity in clinical assessment.

Stress significantly impacts our society, making strategies for its mitigation necessary. A possible approach may involve binaural beats (BBs), i.e., an auditory stimulation obtained by presenting pure tones with slightly different frequencies to the user’s ears, resulting in a third phantom beat (fBB). While studies in the literature investigate the effects of BBs at a constant stimulation frequency, with this pilot study, we present an innovative approach that adapts the beat frequency in real time within the theta range (4.0–8.0 Hz) to reduce acute mental stress. A stress index, obtained from the predictions of a random forest regressor, was considered to adjust the stimulation. The regressor considered features from an electrocardiogram (ECG) and the ECG-derived respiratory signal. Thirteen healthy subjects underwent a stressful protocol involving multiple mental arithmetic tasks during which constant (CBB) or adapted (ABB) stimulation occurred. Task performances like accuracy and reaction times were recorded. The results show that ABBs significantly lowered the average stress index (p<0.05) and heart rate (p<0.05) compared to CBBs. No statistically significant differences were detected in task performance. The results support the importance of adaptive and personalized approaches for mitigating stress. Future research is necessary to assess the goodness of our proposal, considering a larger sample, different stressors, and an objective and external assessment of stress (e.g., cortisol levels).

BackgroundIPC has been suggested to boost skeletal muscle performance, though its effectiveness remains controversial. This study evaluates whether IPC influences local hemodynamic responses and surface electromyographic (sEMG) activity during non-fatiguing voluntary sustained and intermittent contractions.MethodsTen male participants were subjected to IPC (3 cycles, 5-min ON/5-min OFF right arm ischemia, cuff pressure: 250 mmHg) and SHAM (same protocol at 20 mmHg) in two different sessions. Near-infrared spectroscopy was used to monitor tissue oxygenation (TOI) and deoxy-hemoglobin (HHb) in extensor and flexor forearm muscles. sEMG was also recorded. Measurements were taken during sustained (20-s duration) and intermittent (5 s ON/5 s OFF) isometric contractions at 20, 30, and 40% of the maximal voluntary contraction. These non-fatiguing exercise tasks were performed before and 30 min after the IPC/SHAM intervention.ResultssEMG exhibited a significant increase post vs. pre-treatment in both IPC and SHAM in extensors. A significant decrease in TOI at rest was noted pre vs. post-treatment for both IPC and SHAM (p < 0.01). In general, no main effect of treatment was observed, except for HHb changes during contraction in extensor muscles, associated with no effect of time and no time-treatment interaction. All variables exhibited a main effect of force level (p < 0.05), with no interaction with treatment or time.ConclusionIPC had no effect on hemodynamic and electromyographic variables during sustained and intermittent handgrip. These results do not support IPC-related ergogenic effects at the muscle level, aligning with previous findings on electrically stimulated contractions.

Brainwave entrainment (BWE) through Binaural Beats (BBs) has been proposed as a non-invasive method to modulate cortical activity by enhancing oscillatory power at specific frequencies. Despite growing interest, empirical evidence regarding the efficacy of BBs remains inconsistent. This study aimed to assess long-term effects of BBs stimulation using a personalized protocol. Eleven healthy university students (7 males, 4 females; mean age 24.8 ± 1.6 years) participated in three EEG acquisition sessions over two weeks, each including Baseline, Stimulation, and Post-Stimulation phases. Personalized audio tracks were created based on each participant's Individual Alpha Frequency (IAF) and applied daily during a 10-day training period. EEG signals were analysed in time and frequency domains using linear and complexity-based metrics. Multivariate processing combining Principal Component Analysis and K-means clustering revealed high classification accuracy distinguishing Baseline from Stimulation (>81%) and Baseline from Post-Stimulation (>89%) phases, with consistent results across sessions and in pooled data. Statistical significance was confirmed via non-parametric permutation testing. Alpha rhythm analysis showed significant frontal effects (F3, F4), including increased spindle incidence, reduced duration, decreased alpha power, and lowered α exponent via Detrended Fluctuation Analysis. Although the dataset was relatively small, these findings suggest that BBs may modulate brain activity, with sustained effects observable post-stimulation, particularly in frontal regions.

The passive leg raising (PLR) manoeuvre is an accepted method for assessing fluid responsiveness without the risks associated with direct fluid infusion. The present study aimed to investigate whether two consecutive PLR manoeuvres could influence fluid response, measured in terms of the diameter and collapsibility of the inferior vena cava (IVC). A cohort of thirteen healthy subjects (five men and eight women, age of 27 ± 9.5 years) participated. The assessment of each manoeuvre was structured around three key events: the pre–manoeuvre (baseline) state, the PLR interventions, and the immediate post–manoeuvre assessments. To evaluate the hemodynamic changes associated with the PLR, segmentation of the IVC was conducted utilizing specialized software developed by VIPER s.r.l. This segmentation process enabled the detailed analysis of various parameters indicative of the hemodynamic behaviour, including IVC diameter and caval index (CI). During the first manoeuvre, the mean diameter of the IVC, averaged over all subjects, was observed to increase from a baseline measurement of 14.4 ± 4.7 mm to 16.6 ± 4.1 mm during PLR. Coming back to the initial posture, there was a subsequent decrease in the IVC diameter to 14.9 ± 5.1 mm. The CI decreased from 0.35 ± 0.13 (baseline) to 0.26 ± 0.01 (PLR phase), before returning to 0.34 ± 0.12 upon removing the manoeuvre. In the second manoeuvre, the initial mean IVC diameter, between all subjects, was 13.7 ± 5.0 mm. This measurement increased significantly to 16.8 ± 5.3 mm during the PLR phase, followed by a reduction to 13.3 ± 4.4 mm afterward. The CI decreased from 0.33 ± 0.13 to 0.26 ± 0.01 during PLR, with a subsequent recovery to 0.34 ± 0.13 post–manoeuvre. Two–sample t–tests revealed significant differences between parameters measured during both PLR manoeuvres and their respective baseline values, as well as between measurements taken immediately following the manoeuvres. However, no significant differences were identified between parameters recorded during the two PLR manoeuvres themselves. In conclusion, these findings suggest that the PLR manoeuvre does not induce physiological adaptation, reinforcing its status as a consistent and reliable assessment tool.

In recent years, the Pupil Accommodative Response (PAR) has emerged as a promising communication strategy in Human-Computer Interaction (HCI) and augmentative and alternative communication devices. In fact, the PAR is a repetitive, high-magnitude and low-noise innate response. Previous studies exploited the far-to-near focus switch that induces the PAR to extract a binary output. This preliminary study has introduced the potential for detecting intermediate levels of response, with the aim of extracting a non-binary output from pupil size variations induced by shifts in focus between multiple targets. In the current context, this strategy was applied to a music machine, where the pupil size is continuously monitored and converted into musical notes resulting in a jazz melody. This article aims to present the preliminary results of the developed system and to explore the challenges and limitations associated with this type of application. In addition to entertainment, usefulness of this approach includes enhancing user awareness about the physiological function and the voluntary control of pupil size. In perspective, the approach adopted for the music machine may be exploited in pupil-based HCIs to achieve higher information transfer rates.

Functional transcranial Doppler (fTCD) ultrasound can detect cerebral blood flow lateralization to the left/right hemisphere during different tasks. This study aims to test the effectiveness of neurofeedback in improving the individual capacity to lateralize blood flow with mental activity. Bilateral monitoring of blood velocity (CBV) in the middle cerebral arteries was performed in 14 subjects engaged in 15 min of training, followed by a 15 min test in each of four sessions. A ball, displayed on a screen, moved right or left, according to the current right/left difference in normalized CBVs, thus providing a visual neurofeedback of lateralization. The subjects were invited to control the left/right movement of the depicted ball by appropriately orienting their mental activity, freely exploring different strategies. These attempts were completely free and unsupervised during training, while during the test, the subjects were required to follow randomized left/right cues lasting 35 s. Performance was assessed using receiver operating characteristic (ROC) analysis. With training, responses to left and right cues diverged more rapidly and consistently. Accuracy improved significantly from 0.51 to 0.65, and the area under the ROC increased from 0.55 to 0.69. These results demonstrate the effectiveness of neurofeedback in improving lateralization capacity, with implications for the development of fTCD-based brain–computer interfaces.

Sex differences in response to hypovolemia are still an open issue, which is readdressed here by exploiting the potential of near-infrared spectroscopy (NIRS) to monitor the response of lower body negative pressure (LBNP) in upper and lower limbs. In 28 subjects in a supine position, non-invasive arterial blood pressure was continuously monitored along with NIRS parameters from the forearm and thigh during randomized 90 s exposure to LBNP at −10, −20, −30, and −40 mmHg, followed by one 5 min exposure to −30 mmHg. LBNP did not affect arterial blood pressure, slightly increased the heart rate, and affected blood volume in both limbs (p < 0.005). Slopes of tissue oxygenation and deoxy-hemoglobin revealed pressure (p < 0.001) and sex (p < 0.05) dependences for the vasoconstrictive response to LBNP in both arms and legs, with some evidence of larger vasoconstriction in legs. Most variables reached a stable value within 90 s in the arm, while longer time courses were observed in the leg. NIRS is a valuable methodology to detect early LBNP-induced hemodynamic changes, providing that blood volume and blood flow contribution are discriminated. A comparative analysis of time courses proved useful in revealing stronger vasoconstrictive responses in males than in females and in lower limbs than in upper limbs. The same approach could be applied to other experimental contexts.

Ischemic pre-conditioning (IPC) offers protection against future ischemic events and may improve sports performance due to several mechanisms at local and systemic levels. This study investigates the local effects on muscle contractility in electrically induced muscle contractions, thus effectively excluding any uncontrolled change in the motor drive. Twenty-one subjects were divided into two groups: 12 subjects in the IPC group (3 × 5/5 min right arm ischemia/reperfusion; cuff pressure 250 mmHg) and 9 subjects in the SHAM group (same treatment at 20 mmHg). The adductor pollicis was contracted by supramaximal stimulation of the ulnar nerve with single pulses, trains of stimuli (5, 8, 10 and 12 Hz, 1-s duration) and bursts (4 pulses, 25 Hz), all separated by 5-s intervals. The stimulation sequence was delivered before and 15 and 30 min after IPC/SHAM treatment. The isometric contraction force, the superficial electromyographic signal, and tissue oxygenation were continuously monitored. A significant force decrease in time was observed at 8, 10 (p < 0.01) and 12 Hz (p < 0.05) along with a decrease in half-relaxation time in single twitches and bursts (p = 0.01), regardless of treatment. This general time-related weakening was more marked in IPC than SHAM at 5-Hz stimulation. No effects were observed on the magnitude of the superficial electromyographic signal. Data indicate that IPC does not increase muscle force during electrically stimulated contractions, supporting the idea that IPC’s ergogenic effects are not due to increased muscle contractility.

Objective Volume status assessment of a patient by ultrasound (US) imaging of the inferior vena cava (IVC) is important for the diagnosis and prognosis of various clinical conditions. In order to improve the clinical investigation of IVC, which is mainly based on unidirectional US (in M-mode), automated processing of 2-D US scans (in B-mode) has enabled tissue movement tracking on the visualized plane and can average this in various directions. However, IVC geometry outside of the visualized plane is not under control and could result in errors that have not yet been evaluated. Methods We used a method that integrates information from long- and short-axis IVC views (simultaneously acquired in the X-plane) to assess challenges in IVC diameter estimations using 2-D US scans in eight healthy subjects. Results Relative movements between the US probe and IVC induced the following problems when assessing IVC diameter via 2-D view: a median error (i.e., absolute difference with respect to diameter measured in the X-plane) of 17% using 2-D US scans in the long-axis view of the IVC affected by medio-lateral displacements (median: 4 mm); and a median error of 7% and 9% when measuring the IVC diameter from a short-axis view in the presence of pitch angle (median: 0.12 radians) and cranio-caudal movement (median: 15 mm), respectively. Conclusion Relative movements in the IVC that are out of view of B-mode scans cannot be detected, which results in challenges in IVC diameter estimation.

This study proposes a TCD-based neurofeedback system designed to visualize interhemispheric hemodynamic imbalance based on the bilateral monitoring of middle cerebral arteries (MCAs). The difference between cerebral blood velocities collected from the right and left side is calculated in real time and used to drive the horizontal position of the ball displayed on a screen. With this visual feedback, the user may see how different thoughts impact on the position of the ball and possibly acquire and improve control of the ball through progressive training. Four healthy volunteers participated in a preliminary assessment conducted over four training sessions, on average demonstrating increased control over the ball movement. The results provide a proof of concept of the methodology, confirm the feasibility of the approach. The system’s novelty lies in its simplicity, cost-effectiveness, and focus on cerebral lateralization, which make TCD an intriguing alternative to other neurofeedback systems, typically based on EEG, fMRI or fNIRS. The results encourage larger sample size, investigations on the TCD-based neurofeedback's therapeutic and rehabilitative potential.

Background and Objectives: Atrial fibrillation (AF) results in systemic hemodynamic perturbations which impact cerebral circulation, possibly contributing to the development of dementia. However, evidence documenting effects in cerebral perfusion is scarce. The aim of this study is to provide a quantitative characterization of the magnitude and time course of the cerebral hemodynamic response to the short hypotensive events associated with long R-R intervals, as detected by near-infrared spectroscopy (NIRS). Materials and Methods: Cerebral NIRS signals and arterial blood pressure were continuously recorded along with an electrocardiogram in twelve patients with AF undergoing elective electrical cardioversion (ECV). The top 0.5–2.5% longest R-R intervals during AF were identified in each patient and used as triggers to carry out the triggered averaging of hemodynamic signals. The average curves were then characterized in terms of the latency, magnitude, and duration of the observed effects, and the possible occurrence of an overshoot was also investigated. Results: The triggered averages revealed that long R-R intervals produced a significant drop in diastolic blood pressure (−13.7 ± 6.1 mmHg) associated with an immediate drop in cerebral blood volume (THI: −0.92 ± 0.46%, lasting 1.9 ± 0.8 s), followed by a longer-lasting decrease in cerebral oxygenation (TOI: −0.79 ± 0.37%, lasting 5.2 ± 0.9 s, p < 0.01). The recovery of the TOI was generally followed by an overshoot (+1.06 ± 0.12%). These effects were progressively attenuated in response to R-R intervals of a shorter duration. Conclusions: Long R-R intervals cause a detectable and consistent cerebral hemodynamic response which concerns both cerebral blood volume and oxygenation and outlasts the duration of the systemic perturbation. These effects are compatible with the activation of dynamic autoregulatory mechanisms in response to the hypotensive stimulus.

Objective . Altered temporal muscle perfusion is implicated in several painful disorders afflicting orofacial and head regions, including temporomandibular joint dysfunctions, bruxism, and headache. Knowledge about the regulation of blood supply to the temporalis muscle is limited, due to methodological difficulties. The study aimed to test the feasibility of near-infrared spectroscopy (NIRS) monitoring of the human temporal muscle. Approach . Twenty-four healthy subjects were monitored with a 2-channel NIRS: a muscle probe placed over the temporal muscle and a brain probe placed on the forehead. A series of teeth clenching at 25, 50, and 75% of maximum voluntary contraction for 20 s and hyperventilation for 90 s at 20 mmHg of end-tidal CO 2 were performed, to elicit hemodynamic changes in muscle and brain, respectively. Main results . In twenty responsive subjects, NIRS signals from both probes were consistently different during both tasks. The absolute change in tissue oxygenation index (ΔTOI) as detected by muscle and brain probes was −9.40 ± 12.28 and 0.29 ± 1.54% during teeth clenching ( p < 0.01) at 50% maximum voluntary contraction, while −1.03 ± 2.70 and −5.11 ± 3.81% during hyperventilation ( p < 0.01), respectively. Significance . Distinct response patterns were observed from the temporal muscle and prefrontal cortex which proves that this technique is adequate to monitor tissue oxygenation and hemodynamic changes in human temporal muscle. Noninvasive and reliable monitoring of hemodynamics in this muscle will help to extend basic and clinical investigations about the peculiar control of blood flow in head muscles.

Autonomic control of orofacial areas is an integral part of the stress response, controlling functions such as pupil dilatation, salivation, and skin blood flow. However, the specific control of blood flow in head muscles during stress is unknown. This study aims to investigate the hemodynamic response of temporalis and masseter muscles in response to five different stressors. Sixteen healthy individuals were subjected to a randomized series of stressors, including cold pressor test, mental arithmetic test, apnea, isometric handgrip, and post-handgrip muscle ischemia, while in the sitting posture. Finger-pulse photoplethysmography was used to measure arterial blood pressure, heart rate, and cardiac output. Near-infrared spectroscopy was used to measure changes in tissue oxygenation and hemoglobin indices from the temporalis and masseter muscles. All stressors effectively and significantly increased arterial blood pressure. Tissue oxygenation index significantly increased in both investigated head muscles during mental arithmetic test (temporalis: 4.22 ± 3.52