The orthostatic tolerance of service personnel of the Household Division of the British Army

Reflex syncope is common among UK Armed Forces (UKAF) personnel in the Household Division, particularly during ceremonial duties involving prolonged orthostatic stress. This study aimed to (1) assess orthostatic tolerance (OT) using head-up tilt combined with lower body negative pressure (HUT/LBNP), (2) evaluate the retrospective diagnostic accuracy of HUT/LBNP based on syncope trigger, and (3) examine test repeatability. Seventy-three service personnel were categorized into ORTHOSTATIC (27 %), NON-ORTHOSTATIC (16 %), or CONTROL (56 %) groups based on prior syncopal history. OT was measured to presyncope using a standardized HUT/LBNP protocol with continuous cardiovascular monitoring. Repeatability was assessed in a subset of 17 participants one week apart. Mean OT across participants was 32 ± 12 min. The ability of HUT/LBNP-derived OT to identify prior reflex syncope yielded an AUC of 0.75 (p = 0.0003), improving to 0.85 (p < 0.0001) in the ORTHOSTATIC group but was non-significant in NON-ORTHOSTATIC participants (p = 0.44). HUT/LBNP demonstrated high repeatability (bias: 1.1 ± 4.2 min; 3 ± 11 %). UKAF personnel with orthostatic-mediated syncope had significantly lower OT compared to both non-fainters and those with non-orthostatic syncope. HUT/LBNP is a reproducible tool that can discriminate between syncope subtypes and may be useful in monitoring intervention efficacy and guiding management in high-risk occupational settings.