Inflight leg cuff test does not identify the risk for orthostatic hypotension after long-duration spaceflight

Landing day symptoms from orthostatic hypotension after prolonged spaceflight can be debilitating, but severity of these symptoms can be unpredictable and highly individual. We tested the hypothesis that an impaired baroreflex response to an inflight leg cuff test could predict orthostatic intolerance on return to Earth. Eight male astronauts (44 ± 7 years of age (mean ± SD); mean mission length: 167 ± 12 days) participated in a standardized supine-to-sit-to-stand test (5 min–30s–3 min) pre- and postflight, and a 3 min thigh cuff occlusion test pre- and inflight with continuous monitoring of heart rate and arterial blood pressure. The arterial baroreflex was not changed inflight as shown by similar reductions in mean arterial pressure (MAP) response to leg cuff deflation (preflight −19 ± 2 mmHg vs. inflight −18 ± 5 mmHg). With the sit/stand test, the nadir of MAP was lower postflight (−17 ± 9 mmHg) than preflight (−11 ± 6 mmHg, p < 0.05). A greater increase in heart rate (25 ± 7; 16 ± 3 bpm) and decrease in stroke volume (−24 ± 11; −6 ± 4 mL) occurred with sit/stand postflight than leg cuffs inflight (p < 0.001). Inflight testing was influenced by elevated cardiac output resulting in a smaller drop in total peripheral resistance. Two of eight subjects exhibited orthostatic hypotension during the postflight stand test; their responses were not predicted by the inflight leg cuff deflation test. These results suggest that the baroreflex response examined by inflight leg cuff deflation was not a reliable indicator of postflight stand responses.

Integrated Multi-channel PPG and ECG System for Cardiovascular Risk Assessment

Photoplethysmography (PPG) is a non-invasive technique that employs near infrared light to estimate periodic oscillations in blood volume within arteries caused by the pulse pressure wave. Importantly, combined Electrocardiography (ECG) and PPG can be employed to quantify arterial stiffness. The capabilities of a home-made multi-channel PPG-ECG device (7 PPG probes, 4 ECG derivations) to evaluate arterial ageing were assessed. The high numerosity of channels allowed to estimate arterial stiffness at multiple body locations, without supra-systolic cuff occlusion, providing a fast and accurate examination of cardiovascular status and potentially allowing large scale clinical screening of cardiovascular risk.

Leg blood flow and skeletal muscle microvascular perfusion responses to submaximal exercise in peripheral arterial disease

Peripheral arterial disease (PAD) is characterized by stenosis and occlusion of the lower limb arteries. Although leg blood flow is limited in PAD, it remains unclear whether skeletal muscle microvascular perfusion is affected. We compared whole leg blood flow and calf muscle microvascular perfusion after cuff occlusion and submaximal leg exercise between patients with PAD ( n = 12, 69 ± 9 yr) and healthy age-matched control participants ( n = 12, 68 ± 7 yr). Microvascular blood flow (microvascular volume × flow velocity) of the medial gastrocnemius muscle was measured before and immediately after the following: 1) 5 min of thigh-cuff occlusion, and 2) a 5-min bout of intermittent isometric plantar-flexion exercise (400 N) using real-time contrast-enhanced ultrasound. Whole leg blood flow was measured after thigh-cuff occlusion and during submaximal plantar-flexion exercise using strain-gauge plethysmography. Postocclusion whole leg blood flow and calf muscle microvascular perfusion were lower in patients with PAD than control participants, and these parameters were strongly correlated ( r = 0.84, P < 0.01). During submaximal exercise, total whole leg blood flow and vascular conductance were not different between groups. There were also no group differences in postexercise calf muscle microvascular perfusion, although microvascular blood volume was higher in patients with PAD than control participants (12.41 ± 6.98 vs. 6.34 ± 4.98 arbitrary units, P = 0.03). This study demonstrates that the impaired muscle perfusion of patients with PAD during postocclusion hyperemia is strongly correlated with disease severity and is likely mainly determined by the limited conduit artery flow. In response to submaximal leg exercise, microvascular flow volume was elevated in patients with PAD, which may reflect a compensatory mechanism to maintain muscle perfusion and oxygen delivery during recovery from exercise. NEW & NOTEWORTHY This study suggests that peripheral arterial disease (PAD) has different effects on the microvascular perfusion responses to cuff occlusion and submaximal leg exercise. Patients with PAD have impaired microvascular perfusion after cuff occlusion, similar to that previously reported after maximal exercise. In response to submaximal exercise, however, the microvascular flow volume response was elevated in patients with PAD compared with control. This finding may reflect a compensatory mechanism to maintain perfusion and oxygen delivery during recovery from exercise.

The effect of cuff occlusion on the pulse wave transit time from the heart to the cuff

Background: Pulse wave transit time (PWTT) is widely used to characterize the dynamic properties of the arteries. PWTT is most often calculated as the time interval from the R peak in the electrocardiogram (start of the pulse wave) to the rise in the finger photoplethysmogram (arrival of the pulse wave). This is the PWTTHF. The aim of this study was to analyse the effect of cuff occlusion on PWTT, and using this information to improve the reliability of cuff-based indirect blood pressure (BP) measurement.Methods: PWTT was measured with a home health monitoring device that inflates and deflates the cuff slowly (6 mmHg/s). The change in the arterial wall rigidity caused by cuff occlusion is different in the parts of the arterial section proximal and distal to the cuff. Accordingly, PWTT was divided into two parts: PWTT from the heart to the cuff (PWTTHC) and PWTT from the cuff to the fingertip (PWTTCF). Seven patients with various cardiovascular diseases (55–66 years old), seven healthy senior subjects (55–65 years old) and seven healthy young subjects (22–26 years old) were included in the research.Results: Changes in PWTT characterise appropriately the effect of cuff occlusion on BP measurement. Cuff occlusion affected PWTTHC and PWTTCF differently; it increased the former and decreased the latter. Increased PWTTHC reflects a less rigid arterial wall, resulting in an underestimation of BP. The changes in PWTT values are person-specific and not group-specific (patient, healthy senior, and healthy youth).Conclusion: Occlusion with the cuff is an excitation to the cardiovascular system, causing a temporary change in the dynamic properties of the arteries from the heart to the cuff. The change influences the result of indirect BP measurement. Arterial rigidity in the part proximal to the cuff can be characterized by PWTTHC, which provides different information about the arteries than the widely used PWTTHF.