Impact of 14 Days of Bed Rest in Older Adults and an Exercise Countermeasure on Body Composition, Muscle Strength, and Cardiovascular Function: Canadian Space Agency Standard Measures.

INTRODUCTION: Head-down bed rest (HDBR) has long been used as an analog to microgravity, and it also enables studying the changes occurring with aging. Exercise is the most effective countermeasure for the deleterious effects of inactivity. The aim of this study was to investigate the efficacy of an exercise countermeasure in healthy older participants on attenuating musculoskeletal deconditioning, cardiovascular fitness level, and muscle strength during 14 days of HDBR as part of the standard measures of the Canadian Space Agency. METHODS: Twenty-three participants (12 males and 11 females), aged 55-65 years, were admitted for a 26-day inpatient stay at the McGill University Health Centre. After 5 days of baseline assessment tests, they underwent 14 days of continuous HDBR followed by 7 days of recovery with repeated tests. Participants were randomized to passive physiotherapy or an exercise countermeasure during the HDBR period consisting of 3 sessions per day of either high-intensity interval training (HIIT) or low-intensity cycling or strength exercises for the lower and upper body. Peak aerobic power (V̇O2peak) was determined using indirect calorimetry. Body composition was assessed by dual-energy X-ray absorptiometry, and several muscle group strengths were evaluated using an adjustable chair dynamometer. A vertical jump was used to assess whole-body power output, and a tilt test was used to measure cardiovascular and orthostatic challenges. Additionally, changes in various blood parameters were measured as well as the effects of exercise countermeasure on these measurements. RESULTS: There were no differences at baseline in main characteristics between the control and exercise groups. The exercise group maintained V̇O2peak levels similar to baseline, whereas it decreased in the control group following 14 days of HDBR. Body weight significantly decreased in both groups. Total and leg lean masses decreased in both groups. However, total body fat mass decreased only in the exercise group. Isometric and isokinetic knee extension muscle strength were significantly reduced in both groups. Peak velocity, flight height, and flight time were significantly reduced in both groups with HDBR. CONCLUSION: In this first Canadian HDBR study in older adults, an exercise countermeasure helped maintain aerobic fitness and lean body mass without affecting the reduction of knee extension strength. However, it was ineffective in protecting against orthostatic intolerance. These results support HIIT as a promising approach to preserve astronaut health and functioning during space missions, and to prevent deconditioning as a result of hospitalization in older adults.

Effects of Posture and Walking on Tibial Vascular Hemodynamics Before and After 14 Days of Head-Down Bed Rest.

Human skeletal hemodynamics remain understudied. Neither assessments in weight-bearing bones during walking nor following periods of immobility exist, despite knowledge of altered nutrient-artery characteristics after short-duration unloading in rodents. We studied 12 older adults (8 females, aged 59 ± 3 years) who participated in ambulatory near-infrared spectroscopy (NIRS) assessments of tibial hemodynamics before (PRE) and after (POST) 14 days of head-down bed rest (HDBR), with most performing daily resistance and aerobic exercise countermeasures during HDBR. Continual simultaneous NIRS recordings were acquired over the proximal anteromedial tibial prominence of the right lower leg and ipsilateral lateral head of the gastrocnemius muscle during supine rest, walking, and standing. During 10 minutes of walking, desaturation kinetics in the tibia were slower (time to 95% nadir values 125.4 ± 56.8 s versus 55.0 ± 30.1 s, p = 0.0014). Tibial tissue saturation index (TSI) immediately fell (-9.9 ± 4.55) and did not completely recover by the end of 10 minutes of walking (-7.4 ± 6.7%, p = 0.027). Upon standing, total hemoglobin (tHb) kinetics were faster in the tibia (p < 0.0001), whereas HDBR resulted in faster oxygenated hemoglogin (O2Hb) kinetics in both tissues (p = 0.039). After the walk-to-stand transition, changes in O2Hb (p = 0.0022) and tHb (p = 0.0047) were attenuated in the tibia alone after bed rest. Comparisons of NIRS-derived variables during ambulation and changes in posture revealed potentially deleterious adaptations of feed vessels after HDBR. We identify important and novel tibial hemodynamics in humans during ambulation before and after bed rest, necessitating further investigation. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

High-intensity exercise does not protect against orthostatic intolerance following bedrest in 55- to 65-yr-old men and women.

Prolonged bedrest provokes orthostatic hypotension and intolerance of upright posture. Limited data are available on the cardiovascular responses of older adults to head-up tilt following bedrest, with no studies examining the potential benefits of exercise to mitigate intolerance in this age group. This randomized controlled trial of head-down bedrest (HDBR) in 55- to 65-yr-old men and women investigated if exercise could avert post-HDBR orthostatic intolerance. Twenty-two healthy older adults (11 female) underwent a strict 14-day HDBR and were assigned to either an exercise (EX) or control (CON) group. The exercise intervention included high-intensity, aerobic, and resistance exercises. Head-up tilt-testing to a maximum of 15 minutes was performed at baseline (Pre-Bedrest) and immediately after HDBR (R1), as well as 6 days (R6) and 4 weeks (R4wk) later. At Pre-Bedrest, three participants did not complete the full 15 minutes of tilt. At R1, 18 did not finish, with no difference in tilt end time between CON (422 ± 287 s) and EX (409 ± 346 s). No differences between CON and EX were observed at R6 or R4wk. At R1, just 1 participant self-terminated the test with symptoms, while 12 others reported symptoms only after physiological test termination criteria were reached. Finishers on R1 protected arterial pressure with higher total peripheral resistance relative to Pre-Bedrest. Cerebral blood velocity decreased linearly with reductions in arterial pressure, end-tidal CO2, and cardiac output. High-intensity interval exercise did not benefit post-HDBR orthostatic tolerance in older adults. Multiple factors were associated with the reduction in cerebral blood velocity leading to intolerance.

Prediction of oxygen uptake kinetics during heavy-intensity cycling exercise by machine learning analysis.

Nonintrusive estimation of oxygen uptake (V̇o2) is possible with wearable sensor technology and artificial intelligence. V̇o2 kinetics have been accurately predicted during moderate exercise using easy-to-obtain sensor inputs. However, V̇o2 prediction algorithms for higher-intensity exercise with inherent nonlinearities are still being refined. The purpose of this investigation was to test if a machine learning model can accurately predict dynamic V̇o2 across exercise intensities, including slower V̇O2 kinetics normally observed during heavy- compared with moderate-intensity exercise. Fifteen young healthy adults (seven females; peak V̇o2: 42 ± 5 mL·min-1·kg-1) performed three different pseudorandom binary sequence (PRBS) exercise tests ranging in intensity from low-to-moderate, low-to-heavy, and ventilatory threshold-to-heavy work rates. A temporal convolutional network was trained to predict instantaneous V̇o2, with model inputs including heart rate, percent heart rate reserve, estimated minute ventilation, breathing frequency, and work rate. Frequency domain analyses between V̇o2 and work rate were used to evaluate measured and predicted V̇o2 kinetics. Predicted V̇o2 had low bias (-0.017 L·min-1, 95% limits of agreement: [-0.289, 0.254]), and was very strongly correlated (rrm = 0.974, P < 0.001) with the measured V̇o2. The extracted indicator of kinetics, mean normalized gain (MNG), was not different between predicted and measured V̇o2 responses (main effect: P = 0.374, ηp2 = 0.01), and decreased with increasing exercise intensity (main effect: P < 0.001, ηp2 = 0.64). Predicted and measured V̇o2 kinetics indicators were moderately correlated across repeated measurements (MNG: rrm = 0.680, P < 0.001). Therefore, the temporal convolutional network accurately predicted slower V̇o2 kinetics with increasing exercise intensity, enabling nonintrusive monitoring of cardiorespiratory dynamics across moderate- and heavy-exercise intensities.NEW & NOTEWORTHY Machine learning analysis of wearable sensor data with a sequential model, which utilized a receptive field of approximately 3 min to make instantaneous oxygen uptake estimations, accurately predicted oxygen uptake kinetics from moderate through to higher-intensity exercise. This innovation will enable nonintrusive cardiorespiratory monitoring over a wide range of exercise intensities encountered in vigorous training and competitive sports.

Loss of cardiorespiratory fitness and its recovery following two weeks of head-down bed rest and the protective effects of exercise in 55- to 65-yr-old adults.

Cardiorespiratory fitness declines with age and this decline can be accelerated by inactivity and bed rest. Recovery of fitness is possible, but the timeline in 55- to 65-yr-old adults is unknown. Furthermore, the effectiveness of exercise to prevent deconditioning during bed rest is unexplored in this age group. Twenty-two adults (11 women, 59 ± 3 yr) completed 2 wk of strict 6° head-down bed rest (HDBR). Half of the participants performed approximately 1 h of daily exercises, including high-intensity interval cycling, aerobic cycling, and upper- and lower-body resistance training, whereas control participants were inactive. Step-incremental cycling tests to exhaustion were conducted pre-HDBR and at three times during the recovery phase (day 1 or 2, day 6, and 4 wk) to assess peak oxygen uptake (V̇o2). Peak V̇o2 was reduced in the control group throughout the first 6 days of recovery, but did return to pre-HDBR levels by the 4-wk recovery time point (interaction: P = 0.002). In the exercise group, peak V̇o2 was not different at any time point during recovery from pre-HDBR. Ventilatory threshold V̇o2 (interaction: P = 0.002) and heart rate at 15 W (interaction: P = 0.055) mirrored the changes in peak V̇o2 in each respective group. Overall, this study showed that approximately 1 h of daily exercise effectively protected 55- to 65-yr-old adults' cardiorespiratory fitness during 2 wk of HDBR. HDBR without exercise countermeasures caused substantial reductions in cardiorespiratory fitness, but fitness recovered within 4 wk of resuming daily activities. These findings highlight the importance of physical activity in late middle-age adults.NEW & NOTEWORTHY We report the complete time-course of cardiorespiratory fitness recovery back to baseline levels following 2 wk of head-down bed rest in 55- to 65-yr-old adults and found that multimodal training, consisting of high-intensity interval, aerobic and resistive exercises, performed throughout the 2 wk of head-down bed rest prevented reductions in cardiorespiratory fitness.

Ambulatory Monitoring of Cerebrovascular Responses to Upright Posture and Walking in Older Adults With Heart Failure.

Background: Insufficient cardiac output in individuals with heart failure (HF) limits daily functioning and reduces quality of life. Although lower cerebral perfusion, secondary to limitations in cardiac output, has been observed during moderate-intensity efforts, individuals with HF also may be at risk for lower perfusion during even low-intensity ambulatory activities. Methods: We determined whether HF is associated with an altered cerebrovascular response to low-intensity activities representative of typical challenges of daily living. In this study, we monitored central hemodynamics and middle cerebral artery blood velocity (MCAv) and cerebral tissue oxygenation (near-infrared spectroscopy) in 10 individuals with HF (aged 78 ± 4 years; left ventricular ejection fraction 20%-61%) and 13 similar-aged controls (79 ± 8 years; 52%-73%) during 3 randomized transitions, as follows: (i) supine-to-standing; (ii) sitting-to-slow-paced over-ground walking; and (iii) sitting-to-normal-paced over-ground walking. Results: Throughout supine, sitting, standing, and both walking conditions, individuals with HF had lower cardiac index and cerebral tissue oxygenation than controls (P < 0.05), and MCAv was lower across the range of blood pressure in HF patients (P = 0.051) and during walking only (P = 0.011). Individuals with HF had an attenuated increase in stroke volume index and cardiac index during normal-paced walking, compared to controls (P < 0.01). Conclusions: The indices of cerebral perfusion from MCAv and cerebral oxygenation were lower during ambulatory activities in individuals with HF; however, relationships between MCAv and blood pressure were not different between those with HF and controls, indicating no difference in static cerebral autoregulation.

Contexte: Un débit cardiaque insuffisant chez les personnes atteintes d'insuffisance cardiaque limite les activités quotidiennes et affecte la qualité de vie. Par exemple, des efforts d'intensité modérée ont été associés à une perfusion cérébrale affaiblie chez ces personnes. Or, il semble que même des activités ambulatoires de faible intensité soient susceptibles d'avoir les mêmes conséquences. Méthodologie: Nous voulions déterminer si l'insuffisance cardiaque est associée à une altération de la réponse cérébrovasculaire à des activités de faible intensité qui sont typiques de la vie quotidienne. Dans le cadre de cette étude, nous avons surveillé l'hémodynamique centrale et la vitesse du sang dans l'artère cérébrale moyenne (VACM), ainsi que l'oxygénation tissulaire cérébrale (par spectroscopie dans le proche infrarouge) chez 10 personnes atteintes d'insuffisance cardiaque (âge : 78 ± 4 ans; fraction d'éjection du ventricule gauche de 20 à 61 %) et 13 témoins d'âge similaire (79 ± 8 ans; de 52 à 73 %) lors de 3 transitions réparties de façon aléatoire, soit : i) de la position couchée à debout; ii) de la position assise à une marche lente et iii) de la position assise à une marche à vitesse normale. Résultats: En position couchée, assise ou debout et avec les deux vitesses de marche, l'index cardiaque et l'oxygénation tissulaire cérébrale étaient plus faibles chez les personnes atteintes d'insuffisance cardiaque que chez les témoins (p < 0,05); la VACM était plus faible dans toutes les plages de pression artérielle chez les personnes atteintes d'insuffisance cardiaque (p = 0,051) et durant la marche seulement (p = 0,011). Les personnes atteintes d'insuffisance cardiaque présentaient une plus faible augmentation du volume d'éjection systolique et de l'index cardiaque durant la marche à vitesse normale, comparativement aux témoins (p < 0,01). Conclusions: Les indices de la perfusion cérébrale selon la VACM et l'oxygénation cérébrale étaient réduits durant les activités ambulatoires chez les personnes atteintes d'insuffisance cardiaque; cependant, les relations entre la VACM et la pression artérielle n'étaient pas différentes entre les personnes atteintes d'insuffisance cardiaque et les témoins, ce qui indique que l'autorégulation cérébrale statique n'est pas un facteur de différenciation.

Cuffless Blood Pressure Estimation During Moderate- and Heavy-Intensity Exercise Using Wearable ECG and PPG.

OBJECTIVE: To develop and evaluate an accurate method for cuffless blood pressure (BP) estimation during moderate- and heavy-intensity exercise. METHODS: Twelve participants performed three cycling exercises: a ramp-incremental exercise to exhaustion, and moderate and heavy pseudorandom binary sequence exercises on an electronically braked cycle ergometer over the course of 21 minutes. Subject-specific and population-based nonlinear autoregressive models with exogenous inputs (NARX) were compared with feedforward artificial neural network (ANN) models and pulse arrival time (PAT) models. RESULTS: Population-based NARX models, (applying leave-one-subject-out cross-validation), performed better than the other models and showed good capability for estimating large changes in mean arterial pressure (MAP). The models were unable to track consistent decreases in BP during prolonged exercise caused by reduction in peripheral vascular resistance, since this information is apparently not encoded in the employed proxy physiological signals (electrocardiography and forehead PPG) used for BP estimation. Nevertheless, the population-based NARX model had an error standard deviation of 11.0 mmHg during the entire exercise window, which improved to 9.0 mmHg when the model was periodically calibrated every 7 minutes. CONCLUSION: Population-based NARX models can estimate BP during moderate- and heavy-intensity exercise but need periodic calibration to account for the change in vascular resistance during exertion. SIGNIFICANCE: MAP can be continuously tracked during exercise using only wearable sensors, making monitoring exercise physiology more convenient and accessible.

Longitudinal assessment of cardiorespiratory fitness and body mass of young healthy adults during COVID-19 pandemic.

Physical activity was reduced during the COVID-19 pandemic, especially when lockdowns were mandated; however, little is known about the impact of these lifestyle changes on objective measures of cardiorespiratory fitness. To address this knowledge gap, we evaluated the cardiorespiratory fitness of 14 young healthy adults (4 women, age: 27 ± 6 yr) just before the pandemic and after ∼1 yr of public health measures being in place. During fitness assessments, participants performed submaximal pseudorandom cycling exercise to assess cardiorespiratory kinetics, and a 25 W·min-1 ramp-incremental cycling test to determine peak oxygen uptake (V̇o2). Cluster analysis identified two subgroups of participants: those who had reduced peak V̇o2 at the 1-yr follow-up (-0.50 ± 0.17 L·min-1) and those whose peak V̇o2 was maintained (0.00 ± 0.10 L·min-1). Participants with reduced peak V̇o2 also exhibited slower heart rate kinetics (interaction: P = 0.01), reduced peak O2 pulse (interaction: P < 0.001), and lower peak work rate (interaction: P < 0.001) after 1 yr of the pandemic, whereas these variables were unchanged in the group of participants who maintained peak V̇o2. Regardless of changes in peak V̇o2, both subgroups of participants gained body mass (main effect: P = 0.002), which was negatively correlated with participants' level of self-reported physical activity level at the follow-up assessment (mass: ρ = -0.59, P = 0.03) These findings suggest that some young healthy individuals lost cardiorespiratory fitness during the pandemic, whereas others gained weight, but both changes could potentially increase the risk of adverse health outcomes and disease later in life if left unaddressed.NEW & NOTEWORTHY Some young healthy adults experienced cardiovascular deconditioning during the COVID-19 pandemic, with measurable reductions in cardiorespiratory fitness, whereas others experienced no change in fitness but gained body mass, which was related to self-reported physical activity during the pandemic.

Implementation of exercise countermeasures during spaceflight and microgravity analogue studies: Developing countermeasure protocols for bedrest in older adults (BROA).

Significant progress has been made in the development of countermeasures to attenuate the negative consequences of prolonged exposure to microgravity on astronauts' bodies. Deconditioning of several organ systems during flight includes losses to cardiorespiratory fitness, muscle mass, bone density and strength. Similar deconditioning also occurs during prolonged bedrest; any protracted time immobile or inactive, especially for unwell older adults (e.g., confined to hospital beds), can lead to similar detrimental health consequences. Due to limitations in physiological research in space, the six-degree head-down tilt bedrest protocol was developed as ground-based analogue to spaceflight. A variety of exercise countermeasures have been tested as interventions to limit detrimental changes and physiological deconditioning of the musculoskeletal and cardiovascular systems. The Canadian Institutes of Health Research and the Canadian Space Agency recently provided funding for research focused on Understanding the Health Impact of Inactivity to study the efficacy of exercise countermeasures in a 14-day randomized clinical trial of six-degree head-down tilt bedrest study in older adults aged 55-65 years old (BROA). Here we will describe the development of a multi-modality countermeasure protocol for the BROA campaign that includes upper- and lower-body resistance exercise and head-down tilt cycle ergometry (high-intensity interval and continuous aerobic exercise training). We provide reasoning for the choice of these modalities following review of the latest available information on exercise as a countermeasure for inactivity and spaceflight-related deconditioning. In summary, this paper sets out to review up-to-date exercise countermeasure research from spaceflight and head-down bedrest studies, whilst providing support for the proposed research countermeasure protocols developed for the bedrest study in older adults.

Repeatability and reproducibility of changes in thoracoabdominal compartmental volumes and breathing pattern during low-, moderate- and heavy-intensity exercise.

PURPOSE: To determine how repeatable thoracoabdominal compartmental contributions to tidal volume (VT) are across different intensities of exercise, and to examine if the pattern of breathing for a given minute ventilation (V̇E) is reproducible between constant-load and ramp exercise tests. METHODS: Ten healthy adults (age: 27 ± 6 yr, peak oxygen uptake: 42 ± 5 mL min-1 kg-1) completed a 25 W·min-1 ramp cycling test to exhaustion and two repetitions of a step cycling test on separate days. VT, breathing rate (BR), and V̇E were assessed using a bi-directional turbine, and thoracic and abdominal contributions to VT were measured using respiratory inductance plethysmography. Repeatability (step vs. step) and reproducibility (step vs. ramp) of responses were assessed using the intra-class correlation coefficient (ICC). RESULTS: The relative compartment contributions to VT during step exercise were highly repeatable for low (ICC = 0.87, p = 0.003), moderate (ICC = 0.89, p = 0.002) and heavy (ICC = 0.93, p = 0.001) exercise. Inter-individual differences in response to higher intensity exercise were observed, as two participants had significant relationships between VT and their percent compartmental contributions to VT, but five others did not. No differences were identified between ramp and step exercise tests for VT (main effect: p = 0.61) or BR (main effect: p = 0.77) at matched V̇E for each intensity, and the pattern of breathing was reproducible for each intensity. CONCLUSION: These findings suggest the way young healthy adults breathe for a given V̇E is repeatable day-to-day and reproducible between different exercise protocols.

Temporal convolutional networks predict dynamic oxygen uptake response from wearable sensors across exercise intensities.

Oxygen consumption ([Formula: see text]) provides established clinical and physiological indicators of cardiorespiratory function and exercise capacity. However, [Formula: see text] monitoring is largely limited to specialized laboratory settings, making its widespread monitoring elusive. Here we investigate temporal prediction of [Formula: see text] from wearable sensors during cycle ergometer exercise using a temporal convolutional network (TCN). Cardiorespiratory signals were acquired from a smart shirt with integrated textile sensors alongside ground-truth [Formula: see text] from a metabolic system on 22 young healthy adults. Participants performed one ramp-incremental and three pseudorandom binary sequence exercise protocols to assess a range of [Formula: see text] dynamics. A TCN model was developed using causal convolutions across an effective history length to model the time-dependent nature of [Formula: see text]. Optimal history length was determined through minimum validation loss across hyperparameter values. The best performing model encoded 218 s history length (TCN-VO2 A), with 187, 97, and 76 s yielding <3% deviation from the optimal validation loss. TCN-VO2 A showed strong prediction accuracy (mean, 95% CI) across all exercise intensities (-22 ml min-1, [-262, 218]), spanning transitions from low-moderate (-23 ml min-1, [-250, 204]), low-high (14 ml min-1, [-252, 280]), ventilatory threshold-high (-49 ml min-1, [-274, 176]), and maximal (-32 ml min-1, [-261, 197]) exercise. Second-by-second classification of physical activity across 16,090 s of predicted [Formula: see text] was able to discern between vigorous, moderate, and light activity with high accuracy (94.1%). This system enables quantitative aerobic activity monitoring in non-laboratory settings, when combined with tidal volume and heart rate reserve calibration, across a range of exercise intensities using wearable sensors for monitoring exercise prescription adherence and personal fitness.

Influence of intermittent pneumatic compression on foot sensation and balance control in chemotherapy-induced peripheral neuropathy patients.

BACKGROUND: Chemotherapy-induced peripheral neuropathy, a side effect of cancer treatment, presents several issues to patients, including reduced sensation and increased fall risk. Previously, massage therapy has been shown to improve chemotherapy-induced peripheral neuropathy symptoms, possibly through increased blood flow. A custom built intermittent pneumatic compression device, previously shown to increase lower leg blood flow, was tested as a plausible treatment modality. METHODS: Seven cancer survivors suffering from chemotherapy-induced peripheral neuropathy were recruited. Foot sensation (Semmes-Weinstein test) as well as static (dual and tandem stance) and dynamic (timed-up-and-go) balance control tests were performed both pre and post a 5-min intermittent pneumatic compression intervention. Self-reported feedback was provided by participants following testing and 24-h later. FINDINGS: Five participants reported positive changes in their feet immediately following intermittent pneumatic compression treatment while four of those participants reported positive changes up to 24 h after intervention. Foot sensation was unchanged regardless of location tested (P ≥ 0.23). Postural sway path length and sway area were unchanged following intervention during dual stance (P ≥ 0.14), but path length was significantly reduced (~19.9%) following intervention during tandem stance (P = 0.033). Timed-up-and-go duration was also significantly reduced (~7.0%, P = 0.012). INTERPRETATION: Overall, these findings demonstrate that intermittent pneumatic compression may be a plausible treatment modality for improving self-reported foot sensation as well as static and dynamic balance control. As a pilot study, this study provides sufficient context for further research exploring the efficacy of intermittent pneumatic compression as a treatment using a randomized control trial design.

Accurate Blood Pressure Estimation During Activities of Daily Living: A Wearable Cuffless Solution.

The objective is to develop a cuffless method that accurately estimates blood pressure (BP) during activities of daily living. User-specific nonlinear autoregressive models with exogenous inputs (NARX) are implemented using artificial neural networks to estimate the BP waveforms from electrocardiography and photoplethysmography signals. To broaden the range of BP in the training data, subjects followed a short procedure consisting of sitting, standing, walking, Valsalva maneuvers, and static handgrip exercises. The procedure was performed before and after a six-hour testing phase wherein five participants went about their normal daily living activities. Data were further collected at a four-month time point for two participants and again at six months for one of the two. The performance of three different NARX models was compared with three pulse arrival time (PAT) models. The NARX models demonstrate superior accuracy and correlation with "ground truth" systolic and diastolic BP measures compared to the PAT models and a clear advantage in estimating the large range of BP. Preliminary results show that the NARX models can accurately estimate BP even months apart from the training. Preliminary testing suggests that it is robust against variabilities due to sensor placement. This establishes a method for cuffless BP estimation during activities of daily living that can be used for continuous monitoring and acute hypotension and hypertension detection.

Continuous forearm cooling attenuates gastrointestinal temperature increase during cycling.

Hot environmental conditions can challenge thermoregulation resulting in exacerbated heat strain. This study evaluated the influence of continuous inner forearm cooling on gastrointestinal temperature (TGI) and physiological responses to exercise in hot (30°C) and humid (relative humidity: 70%) conditions. Eleven trained cyclists (seven male age: 37±12 years; four female age: 41±15 years; mean±standard deviation) performed two experimental trials, cycling at 66% of their self-reported functional threshold power (average work rate over an hour of maximum effort cycling; 175±34W) for 45 minutes in an environmental chamber. One trial employed continuous inner forearm cooling (COOL) with 5°C water passing through aluminum heat exchangers, while the other had no cooling (CONTROL). Heat was removed from the body at an average rate of 30.3±6.6W during the COOL trial resulting in an attenuation of TGI rise (CONTROL: 2.46±0.70, COOL: 2.03±0.63°C·h-1; p=0.002). The change in heart rate from the 10th minute to the end of exercise, as an indicator of cardiovascular drift, was reduced (CONTROL: 20±7, COOL: 17±6beats·min-1; p=0.050) and end-exercise thermal comfort was improved in the COOL trial with a trend for reduced rating of perceived exertion (p=0.055). Findings suggest that continuous cooling of the inner forearms can attenuate the rise of TGI and help mitigate the risk of heat injury during exercise in hot and humid conditions.

Frequency domain analysis to extract dynamic response characteristics for oxygen uptake during transitions to moderate- and heavy-intensity exercises.

At the onset of an exercise transition, exponential modeling to calculate a time constant (τ) is the conventional method to analyze pulmonary oxygen uptake (V̇O2p) kinetics for moderate and heavy exercises. A new frequency domain analysis technique, mean normalized gain (MNG), has been used to analyze V̇O2p kinetics during moderate exercise, but has not been evaluated for its ability to detect differences in kinetics between moderate and heavy exercises. This study tested the hypothesis that MNG would detect smaller amplitude V̇O2p responses in the heavy-exercise domain compared with moderate-exercise domain. Eight young healthy adults (3 female; age: 27 ± 6 yr; peak V̇O2p: 43 ± 6 mL·min-1·kg-1; means ± SD) performed three bouts of pseudorandom binary sequence (PRBS) exercise for frequency analysis, with the work rate (WR) changing between 25 W and 90% ventilatory threshold (VT; L → MPRBS), 25 W and 50% of the difference between VT and peak V̇O2p (Δ50%; L → HPRBS), and VT to Δ50% (VT → HPRBS). Step exercise tests with equivalent changes in WR to the PRBS tests were performed to facilitate the comparison between MNG and τ. MNG was the highest for L → MPRBS (59 ± 7%), then L → HPRBS (52 ± 6%), and the lowest for VT → HPRBS (38 ± 7%, F(2,14) = 129.755, P < 0.001) exercise conditions indicating slower kinetics with increasing exercise intensity that correlated strongly in repeated measures with τ from step transitions (rrm = -0.893). These results indicate that frequency domain analysis and MNG reliably detect differences in V̇O2p kinetics observed across exercise intensity domains.NEW & NOTEWORTHY Mean normalized gain is able to detect differences in V̇O2p kinetics between moderate-, heavy-, and heavy-intensity exercises from a raised WR within the same individuals. This new method of kinetic analysis may be advantageous compared with conventional V̇O2p curve fitting, as it is less sensitive to breath-by-breath noise, it can provide useful information from a single exercise testing session, and it can be applied to nonconstant work rate exercise situations.

Cuffless Blood Pressure Estimation for Activities of Daily Living.

This work presents a modelling approach to predict the blood pressure (BP) waveform time series during activities of daily living without the use of a traditional pressure cuff. A nonlinear autoregressive model with exogenous inputs (NARX) is implemented using artificial neural networks and trained to predict the BP waveform time series from electrocardiography (ECG) and forehead photoplethysmography (PPG) input signals. To broaden the range of blood pressures present in the training set, a protocol was implemented that included sitting, standing, walking, Valsalva manoeuvers, and static handgrip exercise. A five-minute interval of data in the sitting position at the end of the day was also used for training. The efficacy of the cuffless BP method for continuous BP estimation over 4.67 hours was evaluated on 3 participants for varying training data segments. A mean absolute error of 6.3 and 5.2 mmHg were achieved for systolic BP and diastolic BP estimates, respectively. Including static handgrips and Valsalva manoeuvers in the training dataset leads to better estimation of the higher ranges of BP observed throughout the day. The proposed method shows potential for estimating the range of BP experienced during activities of daily living.Clinical Relevance- Establishes a method for cuffless continuous blood pressure estimation during activities of daily living that can be used for continuous monitoring and acute hypertension detection.

Monocular 3D Sway Tracking for Assessing Postural Instability in Cerebral Hypoperfusion During Quiet Standing.

Postural instability is prevalent in aging and neurodegenerative disease, decreasing quality of life and independence. Quantitatively monitoring balance control is important for assessing treatment efficacy and rehabilitation progress. However, existing technologies for assessing postural sway are complex and expensive, limiting their widespread utility. Here, we propose a monocular imaging system capable of assessing sub-millimeter 3D sway dynamics during quiet standing. Two anatomical targets with known feature geometries were placed on the lumbar and shoulder. Upper and lower trunk 3D kinematic motion were automatically assessed from a set of 2D frames through geometric feature tracking and an inverse motion model. Sway was tracked in 3D and compared between control and hypoperfusion conditions in 14 healthy young adults. The proposed system demonstrated high agreement with a commercial motion capture system (error [Formula: see text], [-0.52, 0.52]). Between-condition differences in sway dynamics were observed in anterior-posterior sway during early and mid stance, and medial-lateral sway during mid stance commensurate with decreased cerebral perfusion, followed by recovered sway dynamics during late stance with cerebral perfusion recovery. This inexpensive single-camera system enables quantitative 3D sway monitoring for assessing neuromuscular balance control in weakly constrained environments.