Acute reduction in cerebral blood velocity on supine-to-stand transition increases postural instability in young adults

Standing middle cerebral artery velocity predicts cognitive function and gait speed in older adults with cognitive impairment, and is impacted by sex differences

Upright posture challenges the cerebrovascular system, leading to changes in middle cerebral artery velocity (MCAv) dynamics which are less evident at supine rest. Chronic alterations in MCAv have been linked to hypoperfusion states and the effect that this may have on cognition remains unclear. This study aimed to determine if MCAv and oscillatory metrics of MCAv (ex. pulsatility index, PI) during upright posture are i) associated with cognitive function and gait speed (GS) to a greater extent than during supine rest, and ii) are different between sexes. Beat-by-beat MCAv (transcranial Doppler ultrasound) and mean arterial pressure (MAP, plethysmography) were averaged for 30-seconds during supine-rest through a transition to standing for 53 participants (73±6yrs, 17 females). While controlling for age, multiple linear regressions predicting MoCA scores and GS from age, supine MCAv metrics, and standing MCAv metrics, were completed. Simple linear regressions predicting Montreal Cognitive Assessment (MoCA) score and GS from MCAv metrics were performed separately for females and males. Significance was set to p<0.05. Lower standing diastolic MCAv was a significant (p = 0.017) predictor of lower MoCA scores in participants with mild cognitive impairment, and this relationship only remained significant for males. Lower standing PI was associated with slower GS (p = 0.027, r=-0.306) in both sexes. Our results indicate a relationship between blunted MCAv and altered oscillatory flow profiles during standing, with lower MoCA scores and GS. These relationships were not observed in the supine position, indicating a unique relationship between standing measures of MCAv with cognitive and physical functions.

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.

Exaggerated postural sway improves orthostatic cardiovascular and cerebrovascular control

Introduction

Healthy individuals with poor cardiovascular control, but who do not experience syncope (fainting), adopt an innate strategy of increased leg movement in the form of postural sway that is thought to counter orthostatic (gravitational) stress on the cardiovascular system. However, the direct effect of sway on cardiovascular hemodynamics and cerebral perfusion is unknown. If sway produces meaningful cardiovascular responses, it could be exploited clinically to prevent an imminent faint.

Methods

Twenty healthy adults were instrumented with cardiovascular (finger plethysmography, echocardiography, electrocardiogram) and cerebrovascular (transcranial Doppler) monitoring. Following supine rest, participants performed a baseline stand (BL) on a force platform, followed by three trials of exaggerated sway (anterior-posterior, AP; mediolateral, ML; square, SQ) in a randomized order.

Results

All exaggerated postural sway conditions improved systolic arterial pressure (SAP, p = 0.001) responses, while blunting orthostatic reductions in stroke volume (SV, p < 0.01) and cerebral blood flow (CBFv, p < 0.05) compared to BL. Markers of sympathetic activation (power of low-frequency oscillations in SAP, p < 0.001) and maximum transvalvular flow velocity (p < 0.001) were reduced during exaggerated sway conditions. Responses were dose-dependent, with improvements in SAP (p < 0.001), SV (p < 0.001) and CBFv (p = 0.009) all positively correlated with total sway path length. Coherence between postural movements and SAP (p < 0.001), SV (p < 0.001) and CBFv (p = 0.003) also improved during exaggerated sway.

Discussion

Exaggerated sway improves cardiovascular and cerebrovascular control and may supplement cardiovascular reflex responses to orthostatic stress. This movement provides a simple means to boost orthostatic cardiovascular control for individuals with syncope, or those with occupations that require prolonged motionless standing.

Counter pressure maneuvers for syncope prevention: A semi-systematic review and meta-analysis

Physical counter pressure maneuvers (CPM) are movements that are recommended to delay or prevent syncope (fainting) by recruiting the skeletal muscle pump to augment cardiovascular control. However, these recommendations are largely based on theoretical benefit, with limited data evaluating the efficacy of CPM to prevent syncope in the real-world setting. We conducted a semi-systematic literature review and meta-analysis to assess CPM efficacy, identify literature gaps, and highlight future research needs. Articles were identified through a literature search (PubMed, April 2022) of peer-reviewed publications evaluating the use of counter pressure or other lower body maneuvers to prevent syncope. Two team members independently screened records for inclusion and extracted data. From 476 unique records identified by the search, 45 met inclusion criteria. Articles considered various syncopal conditions (vasovagal = 12, orthostatic hypotension = 8, postural orthostatic tachycardia syndrome = 1, familial dysautonomia = 2, spinal cord injury = 1, blood donation = 10, healthy controls = 11). Maneuvers assessed included hand gripping, leg fidgeting, stepping, tiptoeing, marching, calf raises, postural sway, tensing (upper, lower, whole body), leg crossing, squatting, “crash” position, and bending foreword. CPM were assessed in laboratory-based studies (N = 28), the community setting (N = 4), both laboratory and community settings (N = 3), and during blood donation (N = 10). CPM improved standing systolic blood pressure (+ 14.8 ± 0.6 mmHg, p < 0.001) and heart rate (+ 1.4 ± 0.5 bpm, p = 0.006), however, responses of total peripheral resistance, stroke volume, or cerebral blood flow were not widely documented. Most patients experienced symptom improvement following CPM use (laboratory: 60 ± 4%, community: 72 ± 9%). The most prominent barrier to employing CPM in daily living was the inability to recognize an impending faint. Patterns of postural sway may also recruit the skeletal muscle pump to enhance cardiovascular control, and its potential as a discrete, proactive CPM needs further evaluation. Physical CPM were successful in improving syncopal symptoms and producing cardiovascular responses that may bolster against syncope; however, practical limitations may restrict applicability for use in daily living.

The Effects of Transcranial Direct Current Stimulation on Balance and Gait in Stroke Patients: A Systematic Review and Meta-Analysis

Objective: Balance dysfunction after stroke often results in individuals unable to maintain normal posture, limits the recovery of gait and functional independence. We explore the short-term effects of transcranial direct current stimulation (tDCS) on improving balance function and gait in stroke patients.

Methods: We systematically searched on PubMed, Web of Science, EMBASE, Cochrane Central Register of Controlled Trials, and Google Scholar for studies that explored the effects of tDCS on balance after stroke until August 2020. All involved studies used at least one measurement of balance, gait, or postural control as the outcome.

Results: A total of 145 studies were found, of which 10 (n = 246) met the inclusion criteria and included in our studies. The present meta-analysis showed that active tDCS have beneficial effects on timed up and go test (TUGT) [mean difference (MD): 0.35; 95% confidence interval (CI): 0.11 to 0.58] and Functional Ambulation Category (FAC) (MD: −2.54; 95% CI: −3.93 to −1.15) in stroke patients. However, the results were not significant on the berg balance scale (BBS) (MD: −0.20; 95% CI: −1.44 to 1.04), lower extremity subscale of Fugl-Meyer Assessment (FMA-LE) (MD: −0.43; 95% CI: −1.70 to 0.84), 10-m walk test (10 MWT) (MD: −0.93; 95% CI: −2.68 to 0.82) and 6-min walking test (6 MWT) (MD: −2.55; 95% CI: −18.34 to 13.23).

Conclusions: In conclusion, we revealed that tDCS might be an effective option for restoring walking independence and functional ambulation for stroke patients in our systematic review and meta-analysis.

Systematic Review Registration: CRD42020207565.

Older Adults' Drop in Cerebral Oxygenation on Standing Correlates With Postural Instability and May Improve With Sitting Prior to Standing

BACKGROUND

Impaired blood pressure (BP) recovery with orthostatic hypotension on standing occurs in 20% of older adults. Low BP is associated with low cerebral blood flow but mechanistic links to postural instability and falls are not established. We investigated whether posture-related reductions in cerebral tissue oxygenation (tSO2) in older adults impaired stability upon standing, if a brief sit before standing improved tSO2 and stability, and if Low-tSO2 predicted future falls.

METHOD

Seventy-seven older adults (87 ± 7 years) completed (i) supine-stand, (ii) supine-sit-stand, and (iii) sit-stand transitions with continuous measurements of tSO2 (near-infrared spectroscopy). Total path length (TPL) of the center of pressure sway quantified stability. K-cluster analysis grouped participants into High-tSO2 (n = 62) and Low-tSO2 (n = 15). Fall history was followed up for 6 months.

RESULTS

Change in tSO2 during supine-stand was associated with increased TPL (R = -.356, p = .001). When separated into groups and across all transitions, the Low-tSO2 group had significantly lower tSO2 (all p < .01) and poorer postural stability (p < .04) through 3 minutes of standing compared to the High-tSO2 group. There were no effects of transition type on tSO2 or TPL for the High-tSO2 group, but a 10-second sitting pause improved tSO2 and enhanced postural stability in the Low-tSO2 group (all p < .05). During 6-month follow-up, the Low-tSO2 group had a trend (p < .1) for increased fall risk.

CONCLUSIONS

This is the first study to show an association between posture-related cerebral hypoperfusion and quantitatively assessed instability. Importantly, we found differences among older adults suggesting those with lower tSO2 and greater instability might be at increased risk of a future fall.

The preponderance of initial orthostatic hypotension in postural tachycardia syndrome

Reduced systolic/diastolic blood pressure (BP) by >40/20 mmHg defines initial orthostatic hypotension (IOH). Rapid resolution of hypotension and lightheadedness follows, but tachycardia may be prolonged. We aimed to examine IOH in controls and patients with postural tachycardia syndrome (POTS) using indices of spontaneous fluctuations of heart rate (HR) and systolic BP as measures of cardiac baroreflex differences. We recruited otherwise healthy IOH patients without POTS (n = 20, 16 ± 3 yr), healthy volunteers (n = 32, 17 ± 3 yr), and POTS patients (n = 39, 17 ± 4 yr). Subjects were instrumented for electrocardiography and beat-to-beat BP. After 10 min supine, subjects stood for 5 min. Following supine recovery, subjects underwent 70° head-up tilt for 10 min to test for POTS. BP, HR, and time, referenced to standing, were measured at events during standing: minimum BP, BP recovery, peak HR, HR minimum, and steady state. Baseline HR and BP were higher in POTS compared with healthy groups. IOH occurred in 13% of controls and 51% of POTS patients. The BP minimum was lower in POTS. Parasympathetic modulation of cardiac baroreflex was decreased in all POTS and control-IOH subjects. Sympathetic indices were increased. Events following BP minimum occurred progressively later in all POTS and control-IOH subjects compared with non-IOH controls. IOH is more frequent in POTS than in controls with a lower minimum BP. POTS has markedly reduced heart rate variability and baroreflex, indicating reduced HR buffering of BP. POTS-IOH and control-IOH subjects had similar peak HR despite decreased minimum BP in POTS. IOH data indicate modest parasympathetic and cardiovagal baroreflex deficits in control-IOH subjects. Parasympathetic deficits are more severe in all POTS patients.NEW & NOTEWORTHY Significant initial orthostatic hypotension (IOH) occurs in ~50% of postural tachycardia syndrome (POTS) patients and 13% of controls. Heart rate and blood pressure recovery are prolonged in IOH sustaining lightheadedness; IOH is more prevalent and severe in POTS. Altered cerebral blood flow and cardiorespiratory regulation are more prevalent in POTS. Altered heart rate variability and baroreflex gain may cause nearly instantaneous lightheadedness in POTS. IOH alone fails to confer a strong probability of POTS.