Daniel Vena

Combined effects of auditory and visual cues on the perception of vection

Vection is the illusion of self-motion in the absence of real physical movement. The aim of the present study was to analyze how multisensory inputs (visual and auditory) contribute to the perception of vection. Participants were seated in a stationary position in front of a large, curved projection display and were exposed to a virtual scene that constantly rotated around the yaw-axis, simulating a 360° rotation. The virtual scene contained either only visual, only auditory, or a combination of visual and auditory cues. Additionally, simulated rotation speed (90°/s vs. 60°/s) and the number of sound sources (1 vs. 3) were varied for all three stimulus conditions. All participants were exposed to every condition in a randomized order. Data specific to vection latency, vection strength, the severity of motion sickness (MS), and postural steadiness were collected. Results revealed reduced vection onset latencies and increased vection strength when auditory cues were added to the visual stimuli, whereas MS and postural steadiness were not affected by the presence of auditory cues. Half of the participants reported experiencing auditorily induced vection, although the sensation was rather weak and less robust than visually induced vection. Results demonstrate that the combination of visual and auditory cues can enhance the sensation of vection.

Gait Analysis in Orthopedic Foot and Ankle Surgery—Topical Review, Part 1 Principles and Uses of Gait Analysis

Gait analysis, the systematic study of human walking, is a field that has been studied for well over 100 years. With the technological and scientific advancements of the last several decades, there has been substantial improvement in our understanding of the mechanics of human walking. Particularly important has been the advancement in understanding of the differences between normal and pathological gait. The purpose of this paper is to review the principles of gait analysis, with a particular focus on the underlying methods and science. This will assist orthopedic foot and ankle surgeons in better understanding the methods and meaning of gait research and the publications that commonly appear in the orthopedic foot and ankle surgery literature. Level of Evidence: Level V, expert opinion.

Modelling fluid accumulation in the neck using simple baseline fluid metrics: Implications for sleep apnea

Obstructive sleep apnea (OSA) is a common respiratory disorder among adults. Recently we have shown that sedentary lifestyle causes an increase in diurnal leg fluid volume (LFV), which can shift into the neck at night when lying down to sleep and increase OSA severity. The purpose of this work was to investigate various metrics that represent baseline fluid retention in the legs and examine their correlation with neck fluid volume (NFV) and to develop a robust model for predicting fluid accumulation in the neck. In 13 healthy awake non-obese men, LFV and NFV were recorded continuously and simultaneously while standing for 5 minutes and then lying supine for 90 minutes. Simple regression was used to examine correlations between baseline LFV, baseline neck circumference (NC) and change in LFV with the outcome variables: change in NC (ΔNC) and in NFV (ΔNFV90) after lying supine for 90 minutes. An exhaustive grid search was implemented to find combinations of input variables which best modeled outcomes. We found strong positive correlations between baseline LFV (supine and standing) and ΔNFV90. Models developed for predicting ΔNFV90 included baseline standing LFV, baseline NC combined with change in LFV after lying supine for 90 minutes. These correlations and the developed models suggest that a greater baseline LFV might contribute to increased fluid accumulation in the neck. These results give more evidence that sedentary lifestyle might play a role in the pathogenesis of OSA by increasing the baseline LFV. The best models for predicting ΔNC include baseline LFV and NC; they improved accuracies of estimating ΔNC over individual predictors, suggesting that a combination of baseline fluid metrics is a good predictor of the change in NC while lying supine. Future work is aimed at adding additional baseline demographic features to improve model accuracy and eventually use it as a screening tool to predict severity of OSA prior to sleep.

Factors predisposing to worsening of sleep apnea in response to fluid overload in men

OBJECTIVESnObstructive sleep apnea (OSA) is highly prevalent in patients with fluid-retaining conditions. Using bioimpedance measurements, previous studies have shown that the greater the amount of fluid redistributed from the legs to the neck overnight, the greater the severity of OSA. Our objective was to investigate factors that predispose the development or worsening of OSA in response to experimental fluid overload.nnnMETHODSnFifteen normotensive and non-obese adult men with and without OSA underwent polysomnography (PSG) during which normal saline was infused intravenously at a minimal rate to keep the vein open (control) or as a bolus of 22u2009ml/kg body weight (approximately 2u2009L) in a random order and crossed over after a week.nnnRESULTS AND CONCLUSIONSnBefore and after sleep, neck circumference and bioimpedance were measured to calculate neck resistance, reactance, phase angle, and fluid volume. Subjects who experienced more than a twofold increase in apnea-hypopnea index (AHI) or obstructive AHI from control to intervention and had an AHI>10 during intervention were considered susceptible to the development or worsening of OSA. Baseline neck circumference and phase angle before saline infusion were independently associated with increased susceptibility to developing or worsening OSA in response to saline infusion. In non-obese men, a larger neck circumference and bioimpedance phase angle of the neck, which may be associated with larger pharyngeal tissue content, is associated with increased susceptibility for worsening of OSA in response to fluid overloading.

The Evaluation of Vertical Pole Configuration and Location on Assisting the Sit-to-Stand Movement in Older Adults with Mobility Limitations

Grab-bars and transfer poles are common sit-to-stand aids for mobility limited older adults. This study investigated differences in kinetics and kinematics to characterize the lower-limb strength and dynamic balance requirements across different pole configurations and positions in nine mobility limited older adults. Poles were varied by location (near and far) and configuration (single vertical pole, double vertical poles, vertical pole with a horizontal bar). Results indicated that the far pole condition resulted in increased trunk (p < 0.001) and hip flexion (p < 0.01 and < 0.0001 for contralateral and ipsilateral sides, respectively), and a reduced peak vertical force applied to the pole (p < 0.001). Peak extension moments at the hip and knee were unchanged, and, therefore, pole position had no effect on task demands. Placing the pole unilaterally introduced a small kinetic asymmetry, which significantly increased peak knee extension moments on the ipsilateral side (p < 0.05). Finally, dynamic balance was relatively unchanged across pole conditions. These findings offer novel insight into pole use and the effect of varying pole location and configuration in a sample of older adults with mobility impairment, and provide the basis for future work.

The Effect of Electrical Stimulation of the Calf Muscle on Leg Fluid Accumulation over a Long Period of Sitting

Leg fluid accumulation during sedentary behaviours such as sitting can lead to leg edema and associated adverse health consequences. This study investigates the use calf muscle electrical stimulation (ES) to reduce seated leg fluid accumulation. Thirteen non-obese, normotensive men (mean age 51u2009yr.) with sleep apnea were enrolled in the study. Participants first lay supine for 30u2009minutes to equalize fluid distribution and then sat for 150u2009minutes. While seated, participants received either active or sham ES of the calf muscles, according to random assignment. Participants returned one-week later to cross over to the other study condition. Leg fluid was measured continuously while sitting using the bioelectrical impedance method. Fluid accumulation in the leg was reduced by more than 40% using active ES, compared to sham ES (∆u2009=u200951.9u2009±u20098.8u2009ml vs. ∆u2009=u200991.5u2009±u20098.9u2009ml, Pu2009<u20090.001). In summary, calf muscle ES is an effective method for reducing accumulation of fluid during long sedentary periods and has potential use as a device for preventing leg edema to treat associated health consequences in at-risk groups and settings.

The effect of fluid overload by saline infusion on heart rate variability in men during sleep

Fluid shift from the legs and into the neck during sleep has been shown to increase tissue pressure around the upper airway and increase sleep apnea severity. Recently, acute fluid overload via saline infusion during sleep was shown to increase sleep apnea severity in an older men (≥40 years of age) but not the younger men (<;40 years of age). The purpose of this study was to estimate the changes in the autonomic nervous system response to saline infusion in the younger and older men using well studied time- and frequency domain heart rate variability metrics (HRV). Eighteen healthy men (10 in the younger group and 8 in the older group) slept for up to 3 hours during the day while ≈2L of saline was intravenously injected during sleep. An electrocardiogram was collected continuously during the sleep period. Two five minute segments of stage 1 or 2 sleep were selected for analysis of HRV: one before saline infusion and one after completion of saline infusion. Time- and frequency domain metrics of HRV were used to characterize autonomic nervous system response. Results generally showed increased HRV as measured by time-domain statistical measures in the younger men after saline infusion. In the frequency domain, the change in high frequency power from pre- to post-saline infusion was significantly greater in the younger compared to the older men. In addition, there was a borderline significant trend showing an increase in HF power from pre- to post-saline infusion in the younger, but not the older men. These results suggest that only in the younger men and not the older men, parasympathetic nervous activity increased in response to acute fluid overload. This might be one of the mechanisms that increased the severity of OSA in older and not the younger men.

Predicting Neck Fluid Accumulation While Supine

When lying supine, fluid shifts rostrally from the legs and accumulates in the neck, which is a risk factor for obstructive sleep apnea. The objective of this study was to model neck fluid accumulation using one-time baseline measurements of body fluid, demographics, and anthropometrics. Using bioelectrical impedance, leg and neck fluid volumes (LFV and NFV) were measured continuously and simultaneously. Thirty non-obese adults (13 men) stood quietly for 5 minutes, and then lay supine for 90 minutes while fluid volumes were measured. Neck circumference (NC) was measured before and after the supine period. Results demonstrated that, compared to women, men experienced a greater increase in NC after lying supine. Furthermore, baseline LFV at the onset of lying supine was significantly correlated with ΔLFV (r = 0.44, p = 0.014) and ΔNC (r = 0.51, p = 0.008) after 90 minutes supine. The findings identify that sex and baseline LFV predict both the fluid leaving the legs and increase in NC during recumbency.

Detecting inspiratory flow limitation with temporal features of nasal airflow

BACKGROUNDnInspiratory flow limitation is a breathing pattern during sleep caused by upper airway (UA) narrowing that occurs during snoring and various degrees of obstructive sleep apnea (OSA). Clinical examination of flow limitation relies on identifying patterns of airflow contour, however this process is subjective and lacks physiological evidence of UA narrowing. Our objective is to derive the temporal features of nasal airflow contour that characterize flow limitation. The features that correlate with UA narrowing can be used to develop machine learning classifiers to detect flow limitation with physiological support.nnnMETHODSnSixteen healthy adult men underwent full daytime polysomnography where the nasal airflow was recorded. Before and after sleep, we measured UA anatomical parameters including neck circumference (NC) and upper-airway cross-sectional area (UA-XSA). We extracted various temporal features of airflow and investigated their relationships with the UA anatomical parameters.nnnRESULTSnWe found that three features were correlated with the anatomical parameters associated with UA narrowing: deviation index vs. baseline UA-XSA (rxa0=xa0-0.67, pxa0=xa00.01), peak amplitude variability vs. baseline UA-XSA (rxa0=xa0-0.69, pxa0<xa00.01), peak amplitude variability vs. ΔNC (rxa0=xa00.74, pxa0<xa00.01) and peak number vs. baseline UA-XSA (rxa0=xa0-0.54, pxa0=xa00.04).nnnCONCLUSIONSnTemporal features of airflow were associated with UA narrowing. Future studies could utilize the features to develop classifiers to detect flow limitation and assess the severity of breathing disorders during sleep in high-risk populations such as pregnant women and children.

A novel approach for acoustic estimation of neck fluid volume between men and women

Obstructive Sleep apnea can be caused by fluid shift from the legs to the neck that narrows the upper airway (UA) and contributes to changes in tracheal sound. Tracheal sound is generated from the turbulent airflow in the pharynx and respiratory airways and it has recently been used to estimate increases in neck fluid volume (NFV). However, tracheal sound is also highly variable among people, especially across the sexes. In this paper, a novel method is proposed to select tracheal sound features towards estimating NFV in men and women separately. To validate this method, it was applied to the tracheal sound data of 28 healthy individuals. Our proposed feature selection algorithm is based on sparse representations and incorporates NFV to maximize the relevance of selected features. This feature selection eliminates the dependence of the previous methods on calibrating the model for every individual. Two models, regression and Kalman filters, are then used to estimate NFV from selected features. Kalman filter obtains the highest performance, estimating NFV with more than 90% accuracy in both men and women. This algorithm can be used to develop non-invasive acoustic technologies to investigate the effects of fluid on UA anatomy in general applications. These results could be used to develop convenient devices to monitor the neck edema and its contribution to sleep apnea severity in fluid retaining patients such as heart or renal failure.