Horizontal Posture Research Articles

The motor vertical in the absence of gravicentric cues

When participants are asked to flip an omnidirectional switch “down”, the direction of their responses depends mainly on gravicentric, less so on egocentric and least on visual cues about the vertical (Lackner and DiZio, Exp. Brain Res. 130:2−26, 2000). Here we evaluate response direction when gravicentric cues are not available. Participants flipped an omnidirectional switch “down” when gravito-inertial force acted orthogonally to the response plane on earth (session E), and when it was near zero during parabolic flights (session P). We found that the relative weight of visual cues was similar in both sessions, and it was similar to that in an earlier study where participants stood upright. Across all three data sets, the weight of visual cues averaged 0.09. The relative weight of egocentric cues was also similar in both sessions, averaging 0.87; however, it was significantly lower in the earlier study with upright participants, where it averaged 0.43. We further found that informative and noninformative tactile stimulation had no substantial effects on response direction, which suggests that the earlier reported anchoring effect of tactile signals for the perceived vertical may not extend to the motor vertical. We conclude that the absence of gravicentric cues is compensated by a higher weight of egocentric cues, but not by a higher weight of visual cues. As a consequence, astronauts, divers and persons who work on ground in a horizontal body posture may mishandle equipment because of their strong reliance on egocentric cues.

Numerical simulation study on penetration performance of depleted Uranium (DU) alloy fragments

Due to its high strength, high density, high hardness and good penetration capabilities, Depleted uranium alloys have already shined in armor-piercing projectiles. There should also be a lot of room for improvement in the application of fragment killing elements. Therefore, regarding the performance of the depleted uranium alloy to penetrate the target plate, further investigation is needed to analyze its advantages and disadvantages compared to tungsten alloy. To study the difference in penetration performance between depleted uranium alloy and tungsten alloy fragments, firstly, a theoretical analysis of the adiabatic shear sensitivity of DU and tungsten alloys was given from the perspective of material constitutive model. Then, taking the cylindrical fragment penetration target as the research object, the penetration process and velocity characteristics of the steel target plates penetrated by DU alloy fragment and tungsten alloy fragment were compared and analyzed, by using finite element software ANSYS/LS-DYNA and Lagrange algorithm. Lastly, the influence of different postures when impacting target and different fragment shapes on the penetration results is carried out in the research. The results show that in the penetration process of the DU and tungsten alloy fragments, the self-sharpening properties of the DU alloy can make the fragment head sharper and the penetrating ability enhance. Under the same conditions, the penetration capability of cylindrical fragment impacting target in vertical posture is better than that in horizontal posture, and the penetration capability of the spherical fragment is slightly better than that of cylindrical fragment.

"It's all in their head": hierarchical exploration of a three-dimensional layered pyramid in rats.

Wayfinding in a three-dimensional (3D) environment is intricate, and surface-bounded animals may overcome this complexity by breaking it down into horizontal layers along with the vertical location of each layer. Here, we examined how rats explored a layered pyramid placed in a large open field. We found that exploration presented a hierarchical (or fractal) shape of three types of roundtrips: (1) from the primary home-base to the open-field floor; (2) from the floor up and down the pyramid levels; and (3) from local home-base on each pyramid level. Ascent was slow and interrupted, whereas descent was fast. This difference was a result of level altitude, remaining after data were normalized proportionally to level area. In contrast, the time spent and the distance traveled on each level were dependent on level area, not on level altitude. This structure of spatial behavior accords with multilevel exploration, presenting a relatively independent exploration of each level. The vertical dimension in this experiment thus did not alter the typical spatiotemporal behavior, and the 3D environment was explored by application of the same spatiotemporal approach as that of a horizontal open field. We suggest that this lack of alteration is due to the horizontal posture of the animal's head and trunk during progression on the pyramid. This behavior also seems to fit the bicoding hypothesis, in which the vertical information is virtually contextual (non-metric), and so, when the rat progresses to a new level, it explores it as a newly accessed horizontal floor area.

Sleep Is Compromised in -12° Head Down Tilt Position.

Recent studies are elucidating the interrelation between sleep, cranial perfusion, and cerebrospinal fluid (CSF) circulation. Head down tilt (HDT) as a simulation of microgravity reduces cranial perfusion. Therefore, our aim was to assess whether HDT is affecting sleep (clinicaltrials.gov; identifier NCT 02976168). 11 male subjects were recruited for a cross-over designed study. Each subject participated in two campaigns each comprising 3 days and 2 nights. Intervention started on the second campaign day and consisted of maintenance of horizontal position or −12° HDT for 21 h. Ultrasound measurements were performed before, at the beginning and the end of intervention. Polysomnographic measurements were assessed in the second night which was either spent in horizontal posture or at −12° HDT. Endpoints were sleep efficiency, sleep onset latency, number of sleep state changes and arousals, percentages of N3, REM, light sleep stages and subjective sleep parameters. N3 and REM sleep reduced by 25.6 and 19.1 min, respectively (P = 0.002, g = -0.898; P = 0.035, g = -0.634) during −12° HDT. Light sleep (N1/2) increased by 33.0 min at −12° HDT (P = 0.002, g = 1.078). On a scale from 1 to 9 subjective sleep quality deteriorated by 1.3 points during −12° HDT (P = 0.047, g = -0.968). Ultrasonic measurement of the venous system showed a significant increase of the minimum (P = 0.009, P < 0.001) and maximum (P = 0.004, P = 0.002) cross-sectional area of the internal jugular vein at −12° HDT. The minimum cross-sectional area of the external jugular vein differed significantly between conditions over time (P = 0.001) whereas frontal skin tissue thickness was not significantly different between conditions (P = 0.077, P = 0.811). Data suggests venous congestion at −12° HDT. Since subjects felt comfortable with lying in −12° HDT under our experimental conditions, this posture only moderately deteriorates sleep. Obviously, the human body can almost compensate the several fold effects of gravity in HDT posture like an affected CSF circulation, airway obstruction, unusual patterns of propioception and effects on the cardiovascular system.

Validation of StrabisPIX, a Mobile Application for Home Measurement of Ocular Alignment.

PurposeStrabisPIX is a smartphone application that allows clinicians to prescribe a series of self-obtained images of head position and eye alignment in nine positions of gaze that are uploaded onto a secure platform for clinician review. This study evaluates the clinical utility of this application.MethodsIn this prospective, nonmasked, cross-sectional study, 30 strabismus patients aged ≥2 years were evaluated. Participants received standardized instructions, used StrabisPIX to obtain images as prompted, and completed a satisfaction survey. During the same visit, an orthoptist obtained standard clinical images with a professional camera. All 60 image sets were evaluated by three observers.ResultsStrabisPIX image quality was similar to that of clinic photographs. Clinic photographs had significantly higher acceptability for horizontal versions (81% vs. 67%), vertical versions (76% vs. 60%), and head posture (93% vs. 81%). Abnormalities were detected at a similar rate for versions, head posture, eyelid position, and pupil size. StrabisPIX had significantly higher detection of alignment abnormalities (89% vs. 77% for clinical photos). Interrater/intrarater agreements were moderate to high (κ = 0.44–1.00) for all parameters except pupil abnormality, which had poor to fair agreement. Most patients reported that StrabisPIX was easy to learn and use.ConclusionsOverall, StrabisPIX images had similar quality and were as useful as images obtained in the clinic in detecting abnormalities.Translational RelevanceThe StrabisPIX application will enhance the use of telemedicine by allowing physicians to prescribe self-obtained images documenting strabismus.

Investigation of the stability and hydrodynamics of Tetrosomus gibbosus carapace in different pitch angles

In this paper, stability properties of Tetrosomus gibbosus have been experimentally and numerically studied in pitching movements. This fish lives in southern offshores of Iran. Boxfishes usually live in extremely turbulent parts of seas and oceans, with high stability and maneuverability that has caught the attention of scientists. Their body shape let them swim with a quite rapid speed. Studies on Boxfishes have had influences on automotive and marine industries. The CAD file of the boxfish was created using optical CMM. Also a model was built and tested in a subsonic wind tunnel and a numerical study was conducted in virtual wind tunnel. The experimental results are consistent with the numerical ones and also support the findings of other studies on similar boxfishes. These results show that the flow around the fish, which is a consequence of its body shape, tries to maintain the stable position of the fish by resisting against the external force tilting the fish from its stable horizontal posture. The ventral and dorsal keels of the boxfish generate column-like vortices in horizontal direction which play an imperative role in maintaining the stability of the fish.

Notes on the breeding behavior of the Bumblebee Hummingbird (Atthis heloisa), an endemic species of Mexico: nest, courtship displays, and altitudinal movements

ABSTRACT The Bumblebee Hummingbird (Atthis heloisa) is an endemic bird to Mexico. Its natural history is poorly known, particularly its breeding biology. We provide novel and complementary information that enriches the biological knowledge on the species. We describe a nest of the Bumblebee Hummingbird found in Northern Oaxaca and characterize the nest site. The nest was mainly assembled with mosses and lichens; however, we recorded females transporting hairs of the invasive fern Pteridium sp. and seeds of the bromeliad Catopsis sp. for nest construction. Males were noisy and conspicuous while females were secretive; thus, we suggest considering differences in detectability among sexes when studying the species. Males exhibited courtship displays that consisted of several vertical movements over females while adopting a horizontal posture, erecting the tail, emitting a bee-like sound, and fanning out the feathers of the throat toward the females. The Bumblebee Hummingbird is considered a sedentary species...

Development of a walking algorithm on the uneven terrain for a hexapod robot Little Crabster200

In Korea, the underwater robot Crabster200 was developed to perform missions such as accident correspondence, artifact exploration, and resource extraction. To explore the shallow sea successfully, it was designed to walk and swim with six legs. Besides, to develop the walking algorithm efficiently, a small model of Crabster200, Little Crabster200, was developed as well. This article describes the development of a walking algorithm on the uneven terrain for the hexapod robot Little Crabster200. The main purpose of the algorithm is for the robot to maintain a horizontal posture while it walks on uneven terrain. The pattern generator makes a trajectory of normal walking on the flat ground, and the online controller helps Little Crabster200 maintain stable walking on uneven terrain. The proposed algorithm was verified by experiments using the Little Crabster200 on a treadmill equipped with obstacles such as wood boards and bricks. The Little Crabster200 walked stably on the uneven terrain while maintaining a horizontal posture in the experiments.

Cardiac performance is influenced by rotational changes of position in the transversal plane, both in the horizontal and in the 60̊ head-up postures.

Echocardiography is usually performed with the subject/patient lying in the left lateral position (LLP), because the acoustic window is better in this than in the supine position (SP). The aim was to investigate cardiac responses to rotational changes of position in the transversal plane, from SP to LLP while horizontal, and from leaning on the back (HUT-LB) to leaning on the left side (HUT-LL) while tilted 60° head-up from the horizontal. Healthy men (n=12) underwent 10-min HUT provocations. Cardiac variables were measured using two-dimensional echocardiography, Doppler, tissue Doppler imaging and arterial pressures using a volume-clamp method. In horizontal posture, cardiac volumes were smaller in SP than in LLP: end-diastolic volume (EDV) by 14%, end-systolic volume (ESV) by 13%, stroke volume (SV) by 14%, and cardiac output (CO) by 16% (P<0·03). In addition, the mitral annular plane systolic excursion (MAPSE) was 11% smaller (P=0·001) and the left ventricle isovolumic relaxation time (IVRT) 27% longer in SP than in LLP. The ejection fraction, heart rate, arterial pressure and pulmonary ventilation were similar in SP and LLP. During HUT, EDV, SV, CO and MAPSE were smaller, and IVRT was longer, in HUT-LB than in HUT-LL, by -19%, -20%, -17%, -18% and +35%, respectively (P<0·04). Cardiac performance is enhanced in LLP versus SP and in HUT-LL versus HUT-LB, which can be attributed to improved venous return, conceivably, wholly or in part, due to increased hydrostatic pressure gradients between the caval veins and the heart in the LLP and HUT-LL positions.

The role of educator in food and nutrition by health professionals in the context of Family Health Care

ABSTRACT Objective This study aimed to understand the role of health professionals in educational groups that have food and nutrition as their theme. Methods Qualitative research was conducted in the city of São Paulo, with professionals from the Family Health Strategy. Interviews were conducted to understand the professionals’ perceptions of the roles played in groups. These were analyzed using the Discourse of the Collective Subject technique. The groups’ observations on the performance of the professionals in their mediations were analyzed, based on the following items: meeting organization, communication, support, participation, confirmation of messages, and encouragement to ask questions. Results Twenty-two professionals from different backgrounds were interviewed, and 23 groups of different configurations were observed. The speeches showed that the professionals recognize themselves as organizers, mediators, and evaluators of the groups. Under the topic of organization, teamwork was highlighted. In mediation, there was an assumption of different types of performance that are inserted in conceptions of banking education and dialogical education. In the theme of evaluation, conflict and contradiction arose, pointing out the complexity of approaching a group theme when professionals seek a more horizontal posture with users. Observation of the groups revealed a duality between discourse and professional practice, which is surrounded by contradictions inserted into academic formation and the work process of the teams. Conclusion It was possible to understand the complexity of the practice of professionals when approaching the theme in groups, evidencing the need for spaces of care and for permanent education, especially when regarding professionals who use problematic and active approaches.

Posture Used in fMRI-PET Elicits Reduced Cortical Activity and Altered Hemispheric Asymmetry with Respect to Sitting Position: An EEG Resting State Study.

Horizontal body position is a posture typically adopted for sleeping or during brain imaging recording in both neuroscience experiments and diagnostic situations. Recent literature showed how this position and similar ones with head down are associated to reduced plasticity, impaired pain and emotional responses. The present study aimed at further understanding the decrease of cortical activity associated with horizontal body position by measuring high-frequency EEG bands – typically associated with high-level cognitive activation – in a resting state experimental condition. To this end, two groups of 16 female students were randomly assigned to either sitting control (SC) or 2-h horizontal Bed Rest condition (hBR) while EEG was recorded from 38 scalp recording sites. The hBR group underwent several body transitions, from sitting to supine, and from supine to sitting. Results revealed a clear effect of horizontal posture: the hBR group showed, compared to its baseline and to SC, reduced High-Beta and Gamma EEG band amplitudes throughout the 2-h of hBR condition. In addition, before and after the supine condition, hBR group as well as SC exhibited a greater left vs. right frontal activation in both EEG bands while, on the contrary, the supine position induced a bilateral and reduced activation in hBR participants. The cortical sources significantly more active in SC compared with hBR participants included the left Inferior Frontal Gyrus and left Insula. Results are discussed in relation to the differences among neuroimaging methods (e.g., fMRI, EEG, NIRS), which can be partially explained by posture-induced neural network changes.

Menos profissionais, mais sujeitos: formação para a educação popular no Sistema Único de Saúde (SUS)

The current social dynamics demand a new paradigm of action in health, which must recreate its fundamentals conceptions, the concepts of human being, health and education, in order to overcome existing difficulties in the present moment and trace new paths. For this reason, it is necessary that those involved in this process (teachers, students and professionals) abandon old habits, based on the conception of health as an exclusive and authoritarian act of the professional categories, aiming to recreate the education and practices, making people involved in a dialogical, collaborative, inclusive and horizontal posture, capable of being interested in people, their realities and knowledge. It is perceived that only with a deeply change in the basic aspects of health education and practices, it will be possible to overcome the gaps in the attention devices of the SUS (Brazilian Unified Health System) in the direction of popular health education and dialogical exercise, which is an essential instrument for change this reality.

Orientation Preferences and Motion Sickness Induced in a Virtual Reality Environment.

Astronauts' orientation preferences tend to correlate with their susceptibility to space motion sickness (SMS). Orientation preferences appear universally, since variable sensory cue priorities are used between individuals. However, SMS susceptibility changes after proper training, while orientation preferences seem to be intrinsic proclivities. The present study was conducted to investigate whether orientation preferences change if susceptibility is reduced after repeated exposure to a virtual reality (VR) stimulus environment that induces SMS. A horizontal supine posture was chosen to create a sensory context similar to weightlessness, and two VR devices were used to produce a highly immersive virtual scene. Subjects were randomly allocated to an experimental group (trained through exposure to a provocative rotating virtual scene) and a control group (untrained). All subjects' orientation preferences were measured twice with the same interval, but the experimental group was trained three times during the interval, while the control group was not. Trained subjects were less susceptible to SMS, with symptom scores reduced by 40%. Compared with untrained subjects, trained subjects' orientation preferences were significantly different between pre- and posttraining assessments. Trained subjects depended less on visual cues, whereas few subjects demonstrated the opposite tendency. Results suggest that visual information may be inefficient and unreliable for body orientation and stabilization in a rotating visual scene, while reprioritizing preferences for different sensory cues was dynamic and asymmetric between individuals. The present findings should facilitate customization of efficient and proper training for astronauts with different sensory prioritization preferences and dynamic characteristics.Chen W, Chao J-G, Zhang Y, Wang J-K, Chen X-W, Tan C. Orientation preferences and motion sickness induced in a virtual reality environment. Aerosp Med Hum Perform. 2017; 88(10):903-910.

A potential link between lateral semicircular canal orientation, head posture, and dietary habits in extant rhinos (Perissodactyla, Rhinocerotidae).

Extant rhinoceroses share the characteristic nasal horn, although the number and size of horns varies among the five species. Although all species are herbivores, their dietary preferences, occipital shapes, and common head postures vary. Traditionally, to predict the "usual" head posture (the most used head posture of animals during normal unstressed activities, i.e., standing) of rhinos, the occipital shape was used. While a backward inclined occiput implies a downward hanging head (often found in grazers), a forward inclined occiput is related to the horizontal head posture in browsing rhinos. In this study, the lateral semicircular canal (LSC) of the bony labyrinth was virtually reconstructed from µCT-images in order to investigate a possible link between LSC orientation and head posture in extant rhinoceroses. The usual head posture was formerly reconstructed for several non-rhinoceros taxa with the assumption that the LSC of the inner ear is held horizontal (parallel to the ground) during normal activity of the living animal. The current analysis of the LSC orientation resulted in a downward inclined usual head posture for the grazing white rhinoceros and a nearly horizontal head posture in the browsing Javan rhinoceros. The other three browsing or mixed feeding species show subhorizontal (closer to horizontal than a downgrade inclination) head postures. The results show that anatomical and behavioral aspects, like occipital shape, presence and size of horns/tusk-like lower incisors, as well as feeding and feeding height preferences influence the usual head posture. Because quantitative behavioral data are lacking for the usual head postures of the extant rhinos, the here described relationship between the LSC orientation and the resulting head posture linked to feeding preferences gives new insights. The results show, that the inner ear provides additional information to interpret usual head postures linked to feeding preferences that can easily be adapted to fossil rhinoceroses.

New evaluation index for the retainability of a swimmer's horizontal posture.

This study aims to investigate the effect of changes in buoyancy when a swimmer respires in a horizontal posture. We attempted to evaluate the levelness of swimmers’ streamline posture by simultaneously measuring the lung capacity and buoyancy under water. The buoyancy was measured based on the changes in the vertical loads of the upper and lower limbs on the subjects’ streamline posture under water. The horizontal x-axis as lung ventilation and the vertical y-axis as buoyancy forms a linear equation y = ax + b. The relation between hand (upper-limb) buoyancy and lung ventilation is defined as y = a1x + b1 and that between foot (lower-limb) buoyancy and lung ventilation as y = a2x + b2. Horizontal levelness was calculated as a ratio by dividing a2 by a1 using the inclination (a) values from these formulas for an underwater streamline posture. We defined this ratio as the breathing–balance (BB) ratio. Although the performance levels in the present study did not show any difference in the absolute quantity of air that humans can inhale in a streamline posture, the BB ratio was higher in a statistically significant manner in junior swimmers competing at international levels compared with the other groups of subjects (P < 0.001). This statistical difference in horizontal levelness, despite the absence of a noticeable difference in the absolute quantity of inhaled air, may be attributable to the way in which each person inhales and exhales air. Top-level junior swimmers that exhibited a high BB ratio might have inhaled in a way that would counteract the sinking of the lower limbs, for example, through abdominal respiration. When exhaling, on the other hand, they might have let out air gradually to mitigate the acceleration force involved in submerging the lower limbs.

Vibration-related extrusion of capillary blood from the calf musculature depends upon directions of vibration of the leg and of the gravity vector.

In this study, we investigated the effects of vibration of the whole lower leg on the content and the oxygenation of hemoglobin in the unloaded relaxed lateral gastrocnemius muscle. Vibration was applied orthogonal to and in parallel with leg axis to examine whether the extrusion of blood depends on an alignment of main vessel direction, axis of vibration and gravity. The blood volume in the muscles was altered by horizontal and 30° upright body posture. Fifteen male subjects were exposed to 4 sets of experiments with both vibration directions and both tilt angles applied in permutated order. The absence of voluntary muscular activity and the potential occurrence of compound action potentials by stretch reflexes were monitored using electromyography. Total hemoglobin and tissue saturation index were measured with near infrared spectroscopy. Changes of lower leg circumference were measured with strain gauge system placed around the calf. Vibration caused decrease in tHb and increase in TSI indicating extrusion of predominantly venous blood from the muscle. In 30° tilted position, muscles contained more blood at baseline and vibration ejected more blood from the muscle compared with horizontal posture (p < 0.01). At 30° tilting deeper drop in tHb and steeper increase in TSI (p < 0.01) were observed when vibration was applied in parallel with the length axis of muscle. It is concluded that the vibration extrudes more blood in 30° head up posture and the vibration applied in parallel with the length axis of the muscle is more effective than orthogonal vibration.

Numerical and experimental investigation of a six DOF scaled model of a swimmer posed in streamlined posture

Abstract To better understand the gliding posture of a swimmer, a scaled model of a swimmer in standard gliding posture was tested in the lab and its six degrees of freedom (6-DOF) movement in the water was simulated and analyzed. In the experiment, the scaled model was positioned at a depth of 60 mm from the water surface and ejected at various scaled initial velocities. High speed camera recorded the entire sequence of gliding movement at 200 frames per-second. The displacements and attack angles of the model were extracted from the experimental data within 0.5 s after ejection, and were used to verify the numerical results, which provided details of the 6-DOF movements of the scaled model. The hydrodynamic characteristics, including the drag force, lift force, pitching moment and surrounding vortex structure etc., of the scaled model at different launch speeds were compared and analyzed. It is generally agreed that the higher the initial velocity, the better the gliding efficiency. However, the present study shows that if the swimmer's 6-DOF motion is considered, the greater the initial velocity, the sooner the swimmer will start to change the orientation. This will cost the swimmer more energy to return to the horizontal streamline posture. Thus, the greater the initial velocity, the shorter the gliding stage. For future research, it is worthwhile to determine an efficient gliding interval duration to increase the competitiveness of the swimmer.

Is posture-related craniospinal compliance shift caused by jugular vein collapse? A theoretical analysis

BackgroundPostural changes are related to changes in cerebrospinal fluid (CSF) dynamics. While sitting up leads to a decrease in cranial CSF pressure, it also causes shifts in the craniospinal CSF volume and compliance distribution. We hypothesized that jugular vein collapse in upright posture is a major contributor to these shifts in CSF volume and compliance.MethodsTo test this hypothesis, we implemented a mathematical lumped-parameter model of the CSF system and the relevant parts of the cardiovascular system. In this model, the CSF and the venous system are each divided into a cranial and a spinal part. The pressures in these cranial and spinal portions differ by the posture-dependent hydrostatic pressure columns in the connecting vessels. Jugular collapse is represented by a reduction of the hydrostatic pressure difference between cranial and spinal veins. The CSF pressure–volume relationship is implemented as a function of the local CSF to venous pressure gradient. This implies that an increase in CSF volume leads to a simultaneous displacement of blood from adjacent veins. CSF pulsations driven by the cardiovascular system are introduced through a pulsating cranial arterial volume.ResultsIn upright posture, the implemented CSF pressure–volume relationship shifts to lower cranial CSF pressures compared to the horizontal position, leading to a decrease in cranial CSF pressure when sitting up. Concurrently, the compliance of the spinal compartment decreases while the one of the cranial compartment increases. With this, in upright posture only 10% of the CSF system’s compliance is provided by the spinal compartment compared to 35% in horizontal posture. This reduction in spinal compliance is accompanied by a caudal shift of CSF volume. Also, the ability of the spinal CSF compartment to compensate for cerebral arterial volume pulsations reduces in upright posture, which in turn reduces the calculated craniospinal CSF flow pulsations.ConclusionThe mathematical model enabled us to isolate the effect of jugular collapse and quantify the induced shifts of compliance and CSF volume. The good concordance of the modelled changes with clinically observed values indicates that jugular collapse can be considered a major contributor to CSF dynamics in upright posture.

Estimation of blood pressure variability during orthostatic test using instantaneous photoplethysmogram frequency and pulse arrival time

Abstract The beat-to-beat blood pressure and heart rate variability provide information about the dynamic features of cardiovascular control mechanisms. Pulse arrival time can be used for assessment of blood pressure and is inversely related to it. The hypothesis of this study is that pulse arrival time and changes in photoplethysmogram signal waveform (instantaneous photoplethysmogram signal frequencies) could be used as the surrogate parameters for blood pressure variability estimation. The aims are: (1) to present instantaneous photoplethysmogram signal frequencies extraction algorithm; (2) to quantify variability of heart rate, systolic and diastolic blood pressure, pulse arrival time and instantaneous photoplethysmogram frequencies during orthostatic test and assess their interrelation. The experimental protocol by using orthostatic test was designed to stimulate autonomic nervous system of the body and observe its reaction. The data were recorded from fourteen healthy subjects. During exercise, physiological and motion signals (electrocardiogram, photoplethysmogram, accelerometer, and continuous arterial blood pressure) were recorded. Two systems for synchronous recordings of physiological data were used: Cardioholter 6.2-8E78 and Portapres Model-2. Classical signal processing algorithms were applied to obtain R–R intervals, systolic, and diastolic blood pressure. Hilbert transform was used for pulse arrival time estimation and Hilbert–Huang transform for instantaneous photoplethysmogram signal frequencies extraction. Time-domain and frequency-domain parameters show that heart rate, blood pressure, pulse arrival time, and instantaneous photoplethysmogram signal frequencies have different variability in different postures of the body (vertical and horizontal). Variability of R–R intervals is higher in horizontal posture, meanwhile, variability of blood pressure, pulse arrival time, and instantaneous photoplethysmogram signal frequencies are higher in vertical posture. Pulse arrival time and instantaneous photoplethysmogram signal frequencies have the same trends as blood pressure. Results showed that the differences between vertical and horizontal (supine and standing) positions are statistically significant (p Changes of blood pressure, pulse arrival time, and instantaneous photoplethysmogram signal frequencies variability are interrelated during orthostatic test. The results support the assumption that pulse arrival time and instantaneous photoplethysmogram signal frequencies can be used as the surrogate parameters for blood pressure variability estimation.

Nuchal ligament reconstructions in diplodocid sauropods support horizontal neck feeding postures

Historically, sauropods have been largely perceived as having vertical, ‘S’-curved necks which were hypothesised to allow them to feed from the canopy of trees. Within the past two decades, this popular perception has been questioned, resulting in a debate over neck posture. The osteological differences between sauropods with horizontal neck posture (Diplodocus), and less horizontally inclined necks (Brachiosaurus) suggest differing life and feeding styles. One differing vertebral feature between these polarised bauplans is the bifurcated neural spine. Regardless of the spine condition, sauropods with and without bifurcated spines have been reconstructed exhibiting the same neck posture. Corroborating histology and morphology in extant taxa highlights the presence of modified vertebral ligaments associated with bifurcated spines. Using these extant taxa to better understand the biomechanics of bifurcated spines, this study proposes alternative soft tissue reconstructions. Previous depictions had the bifurcation trough entirely open or harbouring pneumatic diverticula or muscles; conversely this study proposes that the apices of the bifurcated spines were the anchoring points for a split nuchal ligament, and that the trough of bifurcation was predominantly filled with interspinal ligaments. Ligaments provide energy-efficient elastic rebound, and a paired ligament in the cervical series would aid in prolonged, lateral movement in a horizontal plane (i.e. feeding).