Mohammed Mousa

• The relationship between spleen volume and arterial blood pressure (BP) in the general population is not well understood. This dissertation contributed to understand the associations using a population-based approach, including 1,095 German adults. Importantly, this might be the first large-scale study to explore the links between spleen volume, arterial hypertension, and body composition markers Using MRI instead of ultrasound for spleen volume measurement enhanced the precision of these observations compared to previous studies. The findings revealed a positive association between spleen volume and BP parameters, specifically systolic blood pressure (SBP) and pulse pressure (PP) at rest and during exercise, but not with diastolic blood pressure (DBP). These associations were sex-specific, present only in men, suggesting the potential influence of sex hormones, particularly the cardioprotective role of estrogen in women. We also examined associations of body composition markers such as body fat mass (FM), skeletal muscle mass (FFM), and visceral adipose tissue (VAT) with spleen volume. We found stronger associations between spleen volume and FM/SAT in men, while FFM and VAT were more strongly associated with spleen volume in women. BMI was strongly associated with spleen volume in men and women. An elevated estimated total blood volume (eTBV) and plasma volume, driven by increased FFM, may explain the association between body composition and spleen size. Prior research aligns with these findings, highlighting the role of FFM in regulating TBV and plasma volume, which may place an increased volume load on the spleen. These results suggest that spleen volume could be an important biomarker for hypertension and body composition dynamics, particularly in men To conclude, this dissertation on a cohort of German adults found that higher spleen volume was associated with increased systolic and pulse pressure in men, but not in women, indicating a possible link to arterial hypertension in men. Furthermore, obesity-related markers and absolute fat-free mass (FFM) were significantly correlated with larger spleen volume in both sexes.