Abstract
BACKGROUND: Haemoglobin plays a crucial role in oxygen transport, and any acute deviation will trigger compensatory hemodynamic functions. While the consequences of anaemia are well documented, the effects of haemoglobin reduction in individuals without anaemia remain less explored. Patients with polycythaemia vera and healthy blood donors, who both undergo regular phlebotomies, offer a valuable model for studying these effects. METHODS: This observational case-crossover study assessed short-term physiological and quality-of-life changes following phlebotomy in five patients with polycythaemia vera and six healthy blood donors. Participants were remotely monitored using a smartwatch and completed daily quality-of-life assessments. The primary outcome was heart rate, while secondary outcomes included step count and quality-of-life measures. RESULTS: Patients with polycythaemia vera exhibited stable heart rates, with only minor variations in physical activity and quality of life after phlebotomy. In contrast, healthy blood donors experienced a significant increase in heart rate, which returned to baseline within a week. Physical activity remained clinically unchanged in both groups, and quality-of-life scores were stable. CONCLUSIONS: This pilot study demonstrates that any acute haemoglobin reduction, even within the normal range, induces measurable heart rate changes that are directly related to probably the most optimal oxygen delivery state. Moreover, our studies show that wearable technology is sensitive enough to detect these effects. Hence, this nowadays readily available telemetry allows monitoring of subtle physiological changes in a research setting, but it also offers a path towards optimising QoL for patients with anaemia, polyglobulia and for blood donors.