A Novel Methodology for the Synchronous Collection and Multimodal Visualization of Continuous Neurocardiovascular and Neuromuscular Physiological Data in Adults with Long COVID.

Background: Reports suggest that adults with post-COVID-19 syndrome or long COVID may be affected by orthostatic intolerance syndromes, with autonomic nervous system dysfunction as a possible causal factor of neurocardiovascular instability (NCVI). Long COVID can also manifest as prolonged fatigue, which may be linked to neuromuscular function impairment (NMFI). The current clinical assessment for NCVI monitors neurocardiovascular performance upon the application of orthostatic stressors such as an active (i.e., self-induced) stand or a passive (tilt table) standing test. Lower limb muscle contractions may be important in orthostatic recovery via the skeletal muscle pump. In this study, adults with long COVID were assessed with a protocol that, in addition to the standard NCVI tests, incorporated simultaneous lower limb muscle monitoring for NMFI assessment. Methods: To conduct such an investigation, a wide range of continuous non-invasive biomedical sensing technologies were employed, including digital artery photoplethysmography for the extraction of cardiovascular signals, near-infrared spectroscopy for the extraction of regional tissue oxygenation in brain and muscle, and electromyography for assessment of timed muscle contractions in the lower limbs. Results: With the proposed methodology described and exemplified in this paper, we were able to collect relevant physiological data for the assessment of neurocardiovascular and neuromuscular functioning. We were also able to integrate signals from a variety of instruments in a synchronized fashion and visualize the interactions between different physiological signals during the combined NCVI/NMFI assessment. Multiple counts of evidence were collected, which can capture the dynamics between skeletal muscle contractions and neurocardiovascular responses. Conclusions: The proposed methodology can offer an overview of the functioning of the neurocardiovascular and neuromuscular systems in a combined NCVI/NMFI setup and is capable of conducting comparative studies with signals from multiple participants at any given time in the assessment. This could help clinicians and researchers generate and test hypotheses based on the multimodal inspection of raw data in long COVID and other cohorts.

A Review of Heart Rate and Blood Pressure Responses to Active Standing in Healthy Adults.

OBJECTIVES: This review outlines the normal heart rate and blood pressure response to active standing, the physiological mechanisms governing these, and the effect of ageing on the responses. METHODS: A literature search was conducted to identify articles investigating the normal heart rate and/or blood pressure response to standing. RESULTS: Heart rate when standing increases and then decreases and recovers to baseline. Blood pressure responses are inverse. Skeletal muscle contraction and the baroreceptor reflex drive this. With ageing, heart rate response attenuates and the initial blood pressure response increases. DISCUSSION: Normal heart rate and blood pressure responses are attributed to the baroreceptor reflex and skeletal muscle contraction. Decreased muscle strength and baroreceptor sensitivity are associated with ageing, suggesting a possible benefit in improving skeletal muscle strength to maintain an efficient response. Understanding these responses and their variation with ageing is clinically relevant and may be beneficial in improving rehabilitation outcomes.

Orthostatic Blood Pressure Behavior in People with Mild Cognitive Impairment Predicts Conversion to Dementia.

OBJECTIVES: To compare the patterns of blood pressure (BP) behavior during orthostasis in individuals with mild cognitive impairment (MCI) with those of controls and to investigate whether orthostatic BP behavior differs between individuals with MCI who convert to dementia and those who do not. DESIGN: Longitudinal study with 3 years of follow-up. SETTING: Memory clinic in Dublin, Ireland, between 2007 and 2012. PARTICIPANTS: Community-dwelling individuals with MCI (n = 150) and controls (n = 75). MEASUREMENTS: Orthostatic BP was examined using the active standing test with a beat-to-beat continuous BP monitoring device in addition to neuropsychological testing. Hazard ratios (HRs) from parametric survival models were used to determine whether conversion to dementia was independently associated with baseline orthostatic BP variables. RESULTS: Individuals with MCI were more likely than controls to have a systolic BP (SBP) deficit of greater than 30% 30 seconds after standing (P = .01). Thirty percent of participants with MCI (n = 43) converted to dementia within the 3-year follow-up period. Individuals with MCI with a SBP deficit greater than 30% 30 seconds after standing were twice as likely to convert to dementia as those without the deficit (HR = 2.77, 95% confidence interval = 1.02-7.50). CONCLUSION: Human beings have evolved an elaborate neurological control system to maintain cerebral perfusion during orthostatic challenge. In people with MCI, this response is impaired and renders them twice as likely to convert to dementia.

Continuous noninvasive orthostatic blood pressure measurements and their relationship with orthostatic intolerance, falls, and frailty in older people.

OBJECTIVES: To identify morphological orthostatic blood pressure (BP) phenotypes in older people and assess their correlation with orthostatic intolerance (OI), falls, and frailty and to compare the discriminatory performance of a morphological classification with two established orthostatic hypotension (OH) definitions: consensus (COH) and initial (IOH). DESIGN: Cross-sectional. SETTING: Geriatric research clinic. PARTICIPANTS: Four hundred forty-two participants (mean age 72, 72% female) without dementia or risk factors for autonomic neuropathy. MEASUREMENTS: Active lying-to-standing test monitored using a continuous noninvasive BP monitor. For the morphological classification, four orthostatic systolic BP variables were extracted (delta (baseline - nadir) and maximum percentage of baseline recovered by 30 seconds and 1 and 2 minutes) using the 5-second averages method and entered in K-means cluster analysis (three clusters). Main outcomes were OI, falls (≥1 in past 6 months), and frailty (modified Fried criteria). RESULTS: The morphological clusters were small drop, fast overrecovery (n=112); medium drop, slow recovery (n=238); and large drop, nonrecovery (n=92). Their characterization revealed an increasing OI gradient (17.9%, 27.5%, and 44.6% respectively, P<.001) but no significant gradients in falls or frailty. The COH definition failed to reveal clinical differences between COH+ (n=416) and COH- (n=26) participants. The IOH definition resulted in a clinically meaningful separation between IOH+ (n=85) and IOH- (n=357) subgroups, as assessed according to OI (100% vs 11.5%, P<.001), falls (24.7% vs 10.4%, P<.001), and frailty (14.1% vs 5.4%, P=.005). CONCLUSION: It is recommended that the IOH definition be applied when taking continuous noninvasive orthostatic BP measurements in older people.

Clinical Gait assessment of older adults using open platform tools.

Gait impairment is associated with increased falls risk. The gait of 321 community dwelling elderly adults was assessed using the TRIL Gait Analysis Platform (GAP), which was specially designed for ease of use in a research clinic setting by non-experts. The GAP featured body-worn kinematic sensors, a pressure sensitive electronic walkway, and two orthogonally mounted web cameras, and was developed using open platform tools. This flexible platform was applied to objectively measure gait parameters in different gait assessments. The results from the 6 meter walk assessment are presented here. In this assessment, participants were categorized by clinical falls history as 'fallers' or 'non-fallers'. Temporal and spatial gait parameters were examined. Significant differences in spatial parameters were observed when fallers and non-fallers were compared. Temporal parameters were found to differ, though not significantly.

Using the Finometer to examine sex differences in hemodynamic responses to orthostasis in older people.

OBJECTIVES: In young and middle age, women have higher orthostatic intolerance (OI) than men, and hemodynamic differences have been found supporting this finding. In older people, these sex differences are less studied. Our aim was to contribute evidence. METHODS: Two hundred and twenty-four community-dwelling older participants were studied (154 females and 70 males, mean age 72.6, standard deviation 7.3) who were without dementia or risk factors for autonomic neuropathy. Men and women were well matched for baseline characteristics. Finometer Pro was used to noninvasively monitor participants during an active stand test. Derived hemodynamic parameters were extracted with BeatScope (5-s averages method) at different phases (baseline, nadir, and recovery at 2 minutes), and compared between men and women. OI symptoms were recorded. Subgroup analyses were conducted focusing on the presence or absence of antihypertensives. RESULTS: Men and women did not differ in OI. Men tended to drop to a lower nadir (117 vs. 128 mmHg, P=0.001) and reach lower recovery systolic blood pressure than women (161 vs. 171 mmHg, P=0.006); Women had greater total peripheral resistance (P<0.001) and a trend towards lower stroke volumes (P<0.01). However, these differences disappeared in the nonmedicated subgroup. Consistently, women had greater aortic impedance and lower arterial compliance (P<0.001), suggesting greater arterial stiffness. CONCLUSION: The Finometer is a useful tool to monitor orthostatic hemodynamics in older people, and in this study it allowed establishment of interesting sex differences. For further understanding, validation of Modelflow-derived parameters against other clinical standards is desirable.