Haemodynamic and cerebrovascular effects of intermittent lower-leg compression as countermeasure to orthostatic stress

Macrovascular and microvascular responses to prolonged sitting with and without bodyweight exercise interruptions: A randomized cross-over trial

Exposure to uninterrupted prolonged sitting leads to macro- and microvascular complications, which can contribute to increased cardiovascular disease risk. This study investigated the macrovascular and microvascular responses to 3 h of sitting that was: (i) uninterrupted (CON); and (ii) interrupted every 20 min with 1 min light intensity half squats plus calf raises (EX). Twenty healthy participants (21 [SD: 2] years; 21.5 [SD: 1.6] kg/m²) were recruited to participate in this randomized cross-over trial. Macrovascular function was quantified using brachial-ankle pulse wave velocity (baPWV) and the lower- and upper-limb arterial stiffness index (ASI). Microvascular function was quantified as the medial gastrocnemius tissue oxygen saturation (StO₂) area under the curve (AUC) during reactive hyperemia. The baPWV did not significantly change with time (p = 0.594) or by condition (p = 0.772). The arm ASI increased by 3.6 (95% CI: 0.7 to 6.6, effect size [ES] = 0.27) with a nonsignificant condition effect (p = 0.219). There was a significant interaction effect for leg ASI (p = < 0.001), with ASI increasing (impairment) by 18.7 (95% CI: 12.1 to 25.3, ES = 0.63) for CON and decreasing (improvement) by -11.9 (95% CI: -18.5 to -5.3, ES = 0.40) for EX compared to presitting. Similarly, the AUC decreased (detrimental) by 18% (Δ = -321, 95% CI: -543 to -100, ES = 0.32) for CON and increased by 32% (Δ = 588, 95% CI: 366 to 809, ES = 0.59) for EX. The leg ASI was inversely associated with StO₂ AUC (interclass correlation coefficient: -0.66, 95% CI: -0.51 to -0.77). These preliminary findings suggest that regularly interrupting prolonged sitting with simple bodyweight exercises may help to preserve lower-limb vascular function.

Intermittent compression of the calf muscle as a countermeasure to protect blood pressure and brain blood flow in upright posture in older adults

PURPOSE

Orthostatic hypotension, leading to cerebral hypoperfusion, can result in postural instability and falls in older adults. We determined the efficacy of a novel, intermittent pneumatic compression system, applying pressure around the lower legs, as a countermeasure against orthostatic stress in older adults.

METHODS

Data were collected from 13 adults (4 male) over 65 years of age. Non-invasive ultrasound measured middle cerebral artery blood velocity (MCAv) and finger photoplethysmography measured mean arterial blood pressure (MAP). Intermittent lower leg compression was applied in a peristaltic manner in the local diastolic phase of each cardiac cycle to optimize venous return during 1-min of seated rest and during a sit-to-stand transition to 1-min of quiet standing with compression initiated 15 s before transition.

RESULTS

During seated rest, compression resulted in a 4.5 ± 6.5 mmHg increase in MAP, and 2.3 ± 2.1 cm/s increase in MCAv (p < 0.05). MAP and MCAv increased during the 15 s of applied compression before the posture transition (2.3 ± 7.2 mmHg and 2.1 ± 4.0 cm/s, respectively, p < 0.05) with main effects for both variables confirming continued benefit during the transition and quiet stand periods.

CONCLUSIONS

Application of carefully timed, intermittent compression to the lower legs of older adults increased MAP and MCAv during seated rest and maintained an elevated MAP and MCAv during a transition to standing posture. Future research could assess the benefits of this technology for persons at risk for orthostatic hypotension on standing and while walking in an effort to reduce injurious, unexplained falls in older adults.

Lower body positive pressure affects systemic but not cerebral haemodynamics during incremental hyperthermia

Hyperthermia produces profound redistribution of blood and circulatory reflex function. We investigated the potential for lower body positive pressure (LBPP) to maintain or restore haemodynamics during graded hyperthermia. Eight healthy adults rested supine in a custom-made LBPP box, sealed distal to the iliac crest. Following 5 min of normothermic rest, 20 mmHg of LBPP was applied and repeated when core temperature (T_core ) had increased passively by +0.5 and +1°C. Primary dependent variables included mean middle cerebral artery blood velocity (MCAv_mean , transcranial Doppler), mean arterial blood pressure (MAP, finger photoplethysmography), heart rate (HR) and partial pressure of end-tidal carbon dioxide (P_ET CO₂ ). The absolute increase in MAP during LBPP was lower at T_core +1°C (2 ± 3 mmHg), compared with normothermia (7 ± 3 p = .01). The modest increase in MCAv_mean was unchanged by T_core (normothermia, 2 ± 3 cm/s; +0.5°C, 3 ± 3 cm/s and +1°C, 3 ± 4 cm/s, p = .74). By design, P_ET CO₂ was unchanged in all conditions from normothermic baseline (42 ± 1, p = .81). LBPP-induced changes in HR were greater at +0.5°C (-13 ± 4 b/min) and +1°C (-12 ± 6 b/min) compared with normothermia (-3 ± 3 b/min, p = .01 and p = .01, respectively). These data indicate that despite a significant attenuation in MAP to LBPP with moderate hyperthermia, MCAv_mean dynamics were unchanged among the thermal manipulations.