Postural Stress Research Articles

Exploring the Short-Term Memory of Heart Rate Variability through Model-Free Information Measures.

In this work, we perform a comparative analysis of discrete- and continuous-time estimators of information-theoretic measures quantifying the concept of memory utilization in short-term heart rate variability (HRV). Specifically, considering heartbeat intervals in discrete time we compute the measure of information storage (IS) and decompose it into immediate memory utilization (IMU) and longer memory utilization (MU) terms; considering the timings of heartbeats in continuous time we compute the measure of MU rate (MUR). All measures are computed through model-free approaches based on nearest neighbor entropy estimators applied to the HRV series of a group of 15 healthy subjects measured at rest and during postural stress. We find, moving from rest to stress, statistically significant increases of the IS and the IMU, as well as of the MUR. Our results suggest that both discrete-time and continuous-time approaches can detect the higher predictive capacity of HRV occurring with postural stress, and that such increased memory utilization is due to fast mechanisms likely related to sympathetic activation.

Decomposing the Mutual Information Rate of Heart Period and Respiration Variability Series to Assess Cardiorespiratory Interactions.

Heart rate variability results from the coupled activity of the cardiovascular and cardiorespiratory systems, which have their own internal regulation mechanisms but also interact with each other and with the autonomic nervous system to maintain homeostasis. In this work, the assessment of these physiological mechanisms is carried out decomposing the Mutual Information Rate (MIR), an information-theoretic measure of the interdependence between coupled processes, into terms of entropy rate or conditional mutual information related respectively to complexity and causality measures. These measures are computed using a non-parametric approach based on nearest-neighbors. The proposed framework is first tested on simulated autoregressive processes and then applied to experimental data consisting of heart period and respiratory time series measured in healthy subjects monitored at rest and during head-up tilt. Our results evidence that MIR decomposition is able to highlight the interdependence of short-term physiological mechanisms of cardiorespiratory interactions during postural stress.

A Combined Exoscopic and Endoscopic Approach for Radical Temporal Bone Resection and Usefulness of the Endoscopic Approach to the Medial Aspect of the Temporal Bone.

Radical temporal bone resection (TBR) for lateral skull base malignancies is technically challenging because of the vital anatomical structures located at the medial part of the temporal bone and their limited exposure. A possible solution is to adopt an additional endoscopic approach for medial osteotomy to reduce blind spots. The authors aimed to describe a combined exoscopic and endoscopic approach (CEEA) for cranial dissection in radical TBR and to determine the usefulness of the endoscopic approach to the medial aspect of the temporal bone. Having utilized the CEEA in for cranial dissection in radical TBR since 2021, the authors included 5 consecutive patients who underwent the procedure between 2021 and 2022. All surgeries were successful and resulted in no significant complications. The additional use of an endoscope improved visualization of the middle ear in 4 patients and that of the inner ear and carotid canal in 1 patient, enabling precise and safe cranial dissection. Furthermore, surgeons experienced reduced intraoperative postural stress with CEEA than with a microscopic approach. The main advantage of CEEA in radical TBR was the extension of the viewing angles of the endoscope, which allowed observation of the medial aspect of the temporal bone and limited tumor exposure and injury to vital structures. Given the other benefits of exoscopes and endoscopes, including compact size, ergonomics, and surgical field accessibility, CEEA proved to be an efficient treatment option for cranial dissection in radical TBR.

Sex-specific differences in the circulatory response to postural stress among young adults with adverse childhood experiences (ACEs)

Adverse childhood experiences (ACEs)—a highly prevalent assortment of traumatic childhood events (e.g., abuse)—are strongly linked to adult cardiovascular disease (CVD), though differently among males and females. Biological sex differences in the circulatory response to physiological stress (e.g., postural stress) have been well-characterized; however, whether ACEs affect this response differently among males and females remains unclear. This study tested the hypothesis that ACEs affect the circulatory response to head-up tilt (HUT; postural stress) differently among males and females. Three hundred ( n = 156 female; 22.4 ± 1.8 years) young adults recruited through the Niagara Longitudinal Heart Study (NLHS) were included in the current analyses. ACEs were assessed (Childhood Trust Events Survey 2.0) and participants were dichotomized into high (≥4 ACEs) and low (<4 ACEs) exposure groups. Beat-by-beat mean arterial pressure (MAP; finger photoplethysmography) and heart rate (HR; electrocardiogram) were recorded during 10-minutes of supine rest and 5-minutes of 60° HUT. Sex-stratified, mixed-model regression analyses assessed the effect of ACEs on changes (Δ) in MAP and HR from supine rest to HUT, adjusting for age, body mass index, physical activity, and smoking status. During HUT, MAP increased to a similar extent in males with high and low ACEs exposure (ΔMAP: 11.5 ± 10.8 mmHg vs. 10.1 ± 10.9 mmHg, respectively; p > 0.05). In contrast, MAP increased to a greater extent in females with high ACEs exposure compared to females with low ACEs exposure (ΔMAP: 11.3 ± 10.4 mmHg vs. 5.9 ± 9.8 mmHg, respectively; p = 0.003). HR increased during HUT in males with both high and low ACEs exposure; however, it increased to a lesser extent in males with high ACEs exposure compared to males with low ACEs exposure (ΔHR: 14.7 ± 7.5 bpm vs. 18.7 ± 8.1 bpm, respectively; p = 0.015). In females, HR increased to a similar extent during HUT in those with high and low ACEs exposure (ΔHR: 16.5 ± 8.1 bpm vs. 17.6 ± 8.9 bpm, respectively; p > 0.05). These data suggest that ACEs affect the circulatory response to postural stress differently in males and females. Further, these data imply that sex-specific differences in circulatory regulation can be observed as early as young adulthood in those reporting high ACEs exposure. This work was supported by the Canadian Institute of Health Research (CIHR) and Brock University This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

CARPEL TUNNEL SYNDROME: AN OCCUPATIONAL DISEASE

Carpal tunnel syndrome (CTS) is a common problem in certain occupations. Many etiological factors have been suggested for CTS which include repetitive, prolonged hand and intensive activities, forceful exertions, awkward or static posture, vibration, temperature extremes and localised mechanical stress. The references were taken from Grays` anatomy and B.D.Chourasiya which we are supplemented by systematic searches on Google and Pubmed with keywords, occupation incidence, carpal tunnel syndrome, repetitive activities, several specic occupations including cutting metal, dealing with meat and sh processing, slaughter house, manufacturing and construction workers, musicians, repetitive industrial work groups, frozen, food factory employees, grocery store workers, footwear factory workers, etc. In summary, this study concludes that certain occupations involving wrist activities increases the risk of carpal tunnel syndrome. It is recommended that prolonged exposure to highly repetitive action of wrist (i.e. exion and extension) movements should be avoided.

The The Observed Pre and Post-Intervention Changes to Movement Potentiation Scale (MPS) Scores and How That Impacts Pain, Balance & Coordination - A Case Series

Musculoskeletal (MSK) injuries are a major leading burden of disease worldwide, making up 77% of all injury healthcare visits, totaling around 65.8 million people annually in the US alone. There is a clear demand to optimize conservative treatment strategies for improved clinical outcomes. Three Case Reports were conducted with three different female participants (of whom each presented with different primary complaints). Each participant was scored pre and post-intervention using the Movement Potentiation Scale™ (MPS), designed by Williams & Horschig (2022). Additionally, a Visual Analog Pain Scale (VAS) was used to determine each participant’s pain levels, and a comprehensive history was conducted prior to the commencement of the program. The MPS model consists of 6 fundamental movement challenges worth a total value of 26 points. Following the MPS assessment, each participant underwent a consecutive 5-day Functional Movement Training Program. The program prioritized movement Quality over Quantity, an inherent characteristic of Movement Therapy, focusing on proprioception, balance, coordination, and proper biomechanics under tolerable loads. Primary provocative movements and day-to-day activities were identified. Each participant was educated about spinal hygiene, postural stress, and safe movement strategies such as hip hinging, squats, lifting overhead, and the coordination of the core and bracing. On day 6, post-intervention data was collected. Each participant displayed a drastic improvement in pain and MPS score, reflecting increased Movement Quality and joint stability. Improvements in strength, neural control, and connective tissue integrity were observed with reduced nociception and inflammation. Participant 1, awaiting surgery for ongoing chronic Low Back Pain (LBP), scored a low MPS score of 5/26 on day 1. Post-intervention on Day 6, she presented with 0/10 pain and a 15/26 MPS score. It was noted that “for the first time in years,” she had pain-free sleep and zero pain. Participant 2 entered the study with a low MPS score of 7/26 and chronic ongoing shoulder pain and paresthesia down the left arm. On day 6, she presented with 0/10 pain, no paresthesia, and an improved 14/26 MPS score. Participant 3 presented an MPS score of 8/26 and a primary complaint of Urinary Incontinence (UI). Referrals were made from her doctor (GP) to multiple physiotherapists, including postpartum specialists. However, they were unsuccessful. On day 6, she presented an improved MPS score of 18/26 with a 10-day follow-up of zero urinary incontinence issues. This case series is a small step in the right direction; however, further high-caliber studies are required to add further validation to the utility of The MPS Model and Movement Quality focused Rehabilitation – Functional Movement Therapy.

Comparison of discretization strategies for the model-free information-theoretic assessment of short-term physiological interactions

This work presents a comparison between different approaches for the model-free estimation of information-theoretic measures of the dynamic coupling between short realizations of random processes. The measures considered are the mutual information rate (MIR) between two random processes X and Y and the terms of its decomposition evidencing either the individual entropy rates of X and Y and their joint entropy rate, or the transfer entropies from X to Y and from Y to X and the instantaneous information shared by X and Y. All measures are estimated through discretization of the random variables forming the processes, performed either via uniform quantization (binning approach) or rank ordering (permutation approach). The binning and permutation approaches are compared on simulations of two coupled non-identical Hènon systems and on three datasets, including short realizations of cardiorespiratory (CR, heart period and respiration flow), cardiovascular (CV, heart period and systolic arterial pressure), and cerebrovascular (CB, mean arterial pressure and cerebral blood flow velocity) measured in different physiological conditions, i.e., spontaneous vs paced breathing or supine vs upright positions. Our results show that, with careful selection of the estimation parameters (i.e., the embedding dimension and the number of quantization levels for the binning approach), meaningful patterns of the MIR and of its components can be achieved in the analyzed systems. On physiological time series, we found that paced breathing at slow breathing rates induces less complex and more coupled CR dynamics, while postural stress leads to unbalancing of CV interactions with prevalent baroreflex coupling and to less complex pressure dynamics with preserved CB interactions. These results are better highlighted by the permutation approach, thanks to its more parsimonious representation of the discretized dynamic patterns, which allows one to explore interactions with longer memory while limiting the curse of dimensionality.

Postural stress and risk conditions in manual load handling of Chilean industrial workers

Introduction: Although, there is a current regulatory framework for optimal manual handling of loads to preserve health conditions in the industrial sector, technical assessment and the use of certain instruments are still required for the diagnosis of occupational hazards. This study aimed to identify the occupational hazards associated with manual load handling in industry workers and estimate those resulting from postural stress. Methods: Fifty-two (52) industry workers took part in this cross-sectional study. All participants were evaluated using the Manual Handling Guide and the Reba assessment tool. Subjects were characterized, and risks associated with different tasks were detected. Results: 59.6% of workers were between 18 and 45 years old. Lifting, lowering, and transporting loads activities had a repetitive task risk of 94%, exceeding the weight limit in 85.7% of cases. Pushing and pulling activities, mostly showed a working postural risk of 82% and a high perception of initial effort (Borg> 8). Reba score warned to intervene immediately in both types of tasks. Conclusion: Risk from the manual handling of loads found in this study constitutes an alert that suggests reviewing compliance with the current regulation, as well as effective use of working pauses and the improvement of strategies to minimize physical efforts used by workers.

Assessment of quality of life among dental practitioners using magnification devices during nonsurgical root canal treatment in the Kingdom of Saudi Arabia

Introduction: This study was conducted to assess the effect of magnification devices (MDs) during nonsurgical root canal treatment (RCT) on quality of life ( QOL) among dental professionals of the Kingdom of Saudi Arabia. The dental practitioners performing endodontic treatment were evaluated for ergonomic, postural, psychological, and financial issues associated with and without the use of MDs. Materials and Methodology: A total of 1650 dental professionals (general dentists and endodontists) were recruited from public and private sectors of Saudi Arabia from October 2021 to December 2021. The World Health Organization's QOL assessment questionnaire (WHOQOL-BREF) was administered to conduct the study. The questionnaire addressed four domains of QOL which included physical, psychological, procedural, and financial. Statistical analysis was done by SPSS software® version 23.0. Descriptive analysis, ANOVA test, and unpaired t-test were used. Results: All dental professionals completed the survey. 41.5% reported the use of MDs out of which dental loupe was most commonly used. Work-related musculoskeletal disorders were the most frequent physical difficulty which was faced by 61.5% of dental practitioners while performing RCT. 80% of DPs revealed that MDs improve manual abilities while performing RCT. MDs also relieved psychological, physical, and postural stress by 49.2%, 64.6%, and 63%, respectively. Further 72% of the dental professionals reported improved quality of work after the usage of MD. Conclusion: MDs are commonly used by dental professionals during RCT in Saudi Arabia. It is believed that its use can lead to a better ergonomic, postural, and psychological state of these dental professionals.

POSTURAL STRESS AND MUSCULOSKELETAL DISORDERS OF FARM WOMEN IN UPROOTING OF PADDY SEEDLINGS FROM MAT NURSERY

– Uprooting of paddy seedlings from wet bed is one of the most drudgery prone farm activities of Assam. Raising paddy seedlings in mat nursery is a solution for reduction of drudgery of farm women. A study was carried out to assess postural stress and incidence of musculoskeletal problems of farm women while uprooting in mat nursery. Angle of deviation in lower lumber region was measured with Flexi curve. Body Map was used to identify pains in different parts of the body. Angle of deviation at lumbar region was higher in wet bed and reported more ‘severe’ pain in shoulder joints, back, legs due to prolonged bending posture adopted in uprooting deep rooted seedlings. Mat nursery is a suitable alternative to wet bed for reducing drudgery, muscular stress, and labor cost. It is important to bring resilience in Indian agriculture to climate change

Feasibility of Ultra-Short-Term Analysis of Heart Rate and Systolic Arterial Pressure Variability at Rest and during Stress via Time-Domain and Entropy-Based Measures.

Heart Rate Variability (HRV) and Blood Pressure Variability (BPV) are widely employed tools for characterizing the complex behavior of cardiovascular dynamics. Usually, HRV and BPV analyses are carried out through short-term (ST) measurements, which exploit ~five-minute-long recordings. Recent research efforts are focused on reducing the time series length, assessing whether and to what extent Ultra-Short-Term (UST) analysis is capable of extracting information about cardiovascular variability from very short recordings. In this work, we compare ST and UST measures computed on electrocardiographic R-R intervals and systolic arterial pressure time series obtained at rest and during both postural and mental stress. Standard time-domain indices are computed, together with entropy-based measures able to assess the regularity and complexity of cardiovascular dynamics, on time series lasting down to 60 samples, employing either a faster linear parametric estimator or a more reliable but time-consuming model-free method based on nearest neighbor estimates. Our results are evidence that shorter time series down to 120 samples still exhibit an acceptable agreement with the ST reference and can also be exploited to discriminate between stress and rest. Moreover, despite neglecting nonlinearities inherent to short-term cardiovascular dynamics, the faster linear estimator is still capable of detecting differences among the conditions, thus resulting in its suitability to be implemented on wearable devices.

Spectral decomposition of cerebrovascular and cardiovascular interactions in patients prone to postural syncope and healthy controls

We present a framework for the linear parametric analysis of pairwise interactions in bivariate time series in the time and frequency domains, which allows the evaluation of total, causal and instantaneous interactions and connects time- and frequency-domain measures. The framework is applied to physiological time series to investigate the cerebrovascular regulation from the variability of mean cerebral blood flow velocity (CBFV) and mean arterial pressure (MAP), and the cardiovascular regulation from the variability of heart period (HP) and systolic arterial pressure (SAP). We analyze time series acquired at rest and during the early and late phase of head-up tilt in subjects developing orthostatic syncope in response to prolonged postural stress, and in healthy controls. The spectral measures of total, causal and instantaneous coupling between HP and SAP, and between MAP and CBFV, are averaged in the low-frequency band of the spectrum to focus on specific rhythms, and over all frequencies to get time-domain measures. The analysis of cardiovascular interactions indicates that postural stress induces baroreflex involvement, and its prolongation induces baroreflex dysregulation in syncope subjects. The analysis of cerebrovascular interactions indicates that the postural stress enhances the total coupling between MAP and CBFV, and challenges cerebral autoregulation in syncope subjects, while the strong sympathetic activation elicited by prolonged postural stress in healthy controls may determine an increased coupling from CBFV to MAP during late tilt. These results document that the combination of time-domain and spectral measures allows us to obtain an integrated view of cardiovascular and cerebrovascular regulation in healthy and diseased subjects.

Sympathetic Action Potential Firing and Recruitment Patterns Are Abnormal in Gestational Hypertension.

We tested the hypothesis that women who develop gestational hypertension (GH) display abnormal sympathetic action potential (AP) discharge patterns during late pregnancy (32-36 weeks), both at supine rest and during postural stress. Thirteen nonpregnant, female controls (nonpregnant controls [CTRL]) and 32 pregnant women participated; 14 had low-risk (no personal history of GH) normal pregnancies (LR-NP), 10 had high-risk (personal history of GH) normal pregnancies (HR-NP), and 8 developed GH. We measured heart rate, blood pressure, and muscle sympathetic nerve activity (microneurography) at supine rest and 60° head-up tilt. Sympathetic AP patterns were studied using wavelet-based methodology. At rest, muscle sympathetic nerve activity burst frequency was elevated in LR-NP, HR-NP, and GH versus CTRL (all P≤0.01); however, the AP content per integrated burst was augmented only in GH (20±5 spikes/burst), compared with CTRL (8±3 spikes/burst), LR-NP (9±2 spikes/burst) and HR-NP (11±4 spikes/burst; all P<0.0001). Thus, total AP firing frequency was greater in GH versus each of CTRL, LR-NP, and HR-NP (all P<0.0001). In pregnancy, AP frequency is related directly to systolic (R2=46%) and diastolic (R2=20%) blood pressure (both P≤0.01). Unlike CTRL (both P<0.01), women who developed GH were unable to increase within-burst AP firing (P=0.71) or recruit latent subpopulations of larger-sized APs (P=0.72) in response to head-up tilt, perhaps related to a ceiling-effect; however, total AP firing frequency in the upright posture was elevated in the GH cohort versus CTRL, LR-NP, and HR-NP (all P<0.05). Women who develop GH display aberrant sympathetic AP firing patterns in both the supine and upright postures.

Multiscale partial information decomposition of dynamic processes with short and long-range correlations: theory and application to cardiovascular control

Objective. In this work, an analytical framework for the multiscale analysis of multivariate Gaussian processes is presented, whereby the computation of Partial Information Decomposition measures is achieved accounting for the simultaneous presence of short-term dynamics and long-range correlations. Approach. We consider physiological time series mapping the activity of the cardiac, vascular and respiratory systems in the field of Network Physiology. In this context, the multiscale representation of transfer entropy within the network of interactions among Systolic arterial pressure (S), respiration (R) and heart period (H), as well as the decomposition into unique, redundant and synergistic contributions, is obtained using a Vector AutoRegressive Fractionally Integrated (VARFI) framework for Gaussian processes. This novel approach allows to quantify the directed information flow accounting for the simultaneous presence of short-term dynamics and long-range correlations among the analyzed processes. Additionally, it provides analytical expressions for the computation of the information measures, by exploiting the theory of state space models. The approach is first illustrated in simulated VARFI processes and then applied to H, S and R time series measured in healthy subjects monitored at rest and during mental and postural stress. Main Results. We demonstrate the ability of the VARFI modeling approach to account for the coexistence of short-term and long-range correlations in the study of multivariate processes. Physiologically, we show that postural stress induces larger redundant and synergistic effects from S and R to H at short time scales, while mental stress induces larger information transfer from S to H at longer time scales, thus evidencing the different nature of the two stressors. Significance. The proposed methodology allows to extract useful information about the dependence of the information transfer on the balance between short-term and long-range correlations in coupled dynamical systems, which cannot be observed using standard methods that do not consider long-range correlations.

Application of the predicted biomechanics approach in assessing work-related musculoskeletal discomfort among female brickfield workers in West Bengal, India.

Manual brick manufacturing units in West Bengal, India are mostly unorganized sectors employing many migrant female workers in manual material handling tasks as brick moulders and brick carriers. The study estimated the biomechanical postural stress developed due to manual load handling, carriage and brick transportation. Body Part Discomfort Scale was used to assess the subjective pain felt by 18 adult female brick moulders and 12 brick carriers during work. Video recordings were taken during the actual field work and the images were analyzed for two-dimensional prediction kinetics and kinematics. Results show that the horizontal distance of the load from the body was 59.95±3.74 cm during the initial lifting of bricks by the brick carriers and so their biomechanical trunk angle inclination was significantly detrimental. The bending moment at the lumbosacral disc was much higher during the squatting posture while initial brick lifting. Moreover, the trunk and the neck pain of the brick carriers were caused by carrying 18% of body weight load. The brick carriers were the more vulnerable group in terms of work-related musculoskeletal disorders. Therefore, ergonomic interventions such as relay brick carrying and pole supported balanced brick carrying, may be implemented to reduce the prevalence of pain. This study is the first of its kind that validates the extent or the prevalence of work-related musculoskeletal disorders among the female brickfield workers through approaches of predicted biomechanics.

Comparison of LEBA and RULA Based on Postural Load Criteria and Epidemiological Data on Musculoskeletal Disorders.

Various observational methods have been developed and applied in industrial settings with the aim of preventing musculoskeletal disorders (MSDs). This study aimed to compare the Rapid Upper Limb Assessment (RULA), a representative observational method, and the Loading on the Entire Body Assessment (LEBA), a newly developed tool for assessing postural loads and their association with MSDs. The two methods were compared in various categories, including general characteristics, risk levels, postural load criteria, association with MSDs, influencing factors, and inter- and intra-rater reliabilities based on relevant previous studies. The results showed that compared to the RULA, the LEBA was better at evaluating various factors affecting postural loads and assessing musculoskeletal loadings, was better correlated with various postural load criteria, could predict the association with MSDs more accurately, and had higher inter- and intra-rater reliabilities. Based on these comparisons, it seems that the LEBA may be better than the RULA for estimating postural stress and predicting the association with MSDs.

Cardiovascular Responses to Squatting Postural Stress among Non-Diabetic and Type-2 Diabetic Nigerian Black Africans.

A change in posture brings about a significant alteration in cardiovascular functions. The squat test has been used to study autonomic function in White Europeans but not Black Africans. The aim of this study is to determine the cardiovascular effects of postural stress in Black African non-diabetics and Type-2 diabetics. Blood pressure (BP) and heart rate (HR) was measured in 40 non-diabetics and 40Type-2 diabetics in sitting, standing from sitting, squatting and standing from squatting positions Difference in BP and HR between consecutive positions was tested using 2- way mixed ANOVA. Proportions of those who showed orthostatic hypotension and hypertension were compared with Fishers exact test. Significance was set at p <0.05. BP and HR changes evoked by standing from sitting were not different, however squatting evoked greater increase in BP in diabetics(change (Δ) SBP: 5.85±9.95 vs 17.40±13.75mmHg: Δ DBP: 0.15 ± 6.89 vs 5.10 ± 7.59 mmHg:Δ MABP:2.02 ± 6.98 vs 8.63 ± 9.34 mmHg ,p <0.05) and standing from squatting evoked greater fall BP in diabetics (ΔSBP: -9.80±13.89 vs -24.35±16.03 mmHg; Δ MABP:-2.02±6.98 vs -8.63±9.34 mmHg: Δ PP: -2.28 ±15.35 vs -14.50 ±11.96 mmHg, p < 0.05) while Δ HR did not differ. A higher proportion of diabetics showed SBP and DBP orthostatic hypertension. Relative to the non-diabetics, diabetics showed greater BP but not HR responses to postural stress.

Measuring the Rate of Information Exchange in Point-Process Data With Application to Cardiovascular Variability.

The amount of information exchanged per unit of time between two dynamic processes is an important concept for the analysis of complex systems. Theoretical formulations and data-efficient estimators have been recently introduced for this quantity, known as the mutual information rate (MIR), allowing its continuous-time computation for event-based data sets measured as realizations of coupled point processes. This work presents the implementation of MIR for point process applications in Network Physiology and cardiovascular variability, which typically feature short and noisy experimental time series. We assess the bias of MIR estimated for uncoupled point processes in the frame of surrogate data, and we compensate it by introducing a corrected MIR (cMIR) measure designed to return zero values when the two processes do not exchange information. The method is first tested extensively in synthetic point processes including a physiologically-based model of the heartbeat dynamics and the blood pressure propagation times, where we show the ability of cMIR to compensate the negative bias of MIR and return statistically significant values even for weakly coupled processes. The method is then assessed in real point-process data measured from healthy subjects during different physiological conditions, showing that cMIR between heartbeat and pressure propagation times increases significantly during postural stress, though not during mental stress. These results document that cMIR reflects physiological mechanisms of cardiovascular variability related to the joint neural autonomic modulation of heart rate and arterial compliance.

Tropocollagen springs allow collagen fibrils to stretch elastically

The mechanical properties of connective tissues are tailored to their specific function, and changes can lead to dysfunction and pathology. In most mammalian tissues the mechanical environment is governed by the micro- and nano-scale structure of collagen and its interaction with other tissue components, however these hierarchical properties remain poorly understood. In this study we use the human cornea as a model system to characterise and quantify the dominant deformation mechanisms of connective tissue in response to cyclic loads of physiological magnitude. Synchronised biomechanical testing, x-ray scattering and 3D digital image correlation revealed the presence of two dominant mechanisms: collagen fibril elongation due to a largely elastic, spring-like straightening of tropocollagen supramolecular twist, and a more viscous straightening of fibril crimp that gradually increased over successive loading cycles. The distinct mechanical properties of the two mechanisms suggest they have separate roles in vivo. The elastic, spring-like mechanism is fast-acting and likely responds to stresses associated with the cardiac cycle, while the more viscous crimp mechanism will respond to slower processes, such as postural stresses. It is anticipated that these findings will have broad applicability to understanding the normal and pathological functioning of other connective tissues such as skin and blood vessels that exhibit both helical structures and crimp. Statement of significanceThe tropocollagen spring mechanism allows collagen fibrils from some tissues to elongate significantly under small loads, and its recent discovery has the potential to change our fundamental understanding of how tissue deforms. This time-resolved study quantifies the contribution of the spring mechanism to the local strain in stretched tissue and compares it to the contribution associated with the straightening of fibril waviness, the widely accepted primary low-load strain mechanism. The spring mechanism contributed more to the local tissue strain than fibril straightening, and was found to be elastic while fibril straightening was more viscous. The results suggest that the viscoelastic behaviour of a biomaterial is controlled, at least in part, by the relative amount of fibril-scale crimp and tropocollagen supramolecular twist.

Central Hypovolemia Detection During Environmental Stress-A Role for Artificial Intelligence?

The first step to exercise is preceded by the required assumption of the upright body position, which itself involves physical activity. The gravitational displacement of blood from the chest to the lower parts of the body elicits a fall in central blood volume (CBV), which corresponds to the fraction of thoracic blood volume directly available to the left ventricle. The reduction in CBV and stroke volume (SV) in response to postural stress, post-exercise, or to blood loss results in reduced left ventricular filling, which may manifest as orthostatic intolerance. When termination of exercise removes the leg muscle pump function, CBV is no longer maintained. The resulting imbalance between a reduced cardiac output (CO) and a still enhanced peripheral vascular conductance may provoke post-exercise hypotension (PEH). Instruments that quantify CBV are not readily available and to express which magnitude of the CBV in a healthy subject should remains difficult. In the physiological laboratory, the CBV can be modified by making use of postural stressors, such as lower body “negative” or sub-atmospheric pressure (LBNP) or passive head-up tilt (HUT), while quantifying relevant biomedical parameters of blood flow and oxygenation. Several approaches, such as wearable sensors and advanced machine-learning techniques, have been followed in an attempt to improve methodologies for better prediction of outcomes and to guide treatment in civil patients and on the battlefield. In the recent decade, efforts have been made to develop algorithms and apply artificial intelligence (AI) in the field of hemodynamic monitoring. Advances in quantifying and monitoring CBV during environmental stress from exercise to hemorrhage and understanding the analogy between postural stress and central hypovolemia during anesthesia offer great relevance for healthy subjects and clinical populations.