Relationship of body height to thoracic aortic length: implications for sex differences and normative values

Abstract Introduction The scaling of organ to body size is highly variable and can affect organ function in individuals of different sizes. Despite the relationship between aortic length and body size, to our knowledge, its scaling relationship has not been assessed. We assessed the allometric relationship between thoracic aortic length and body height and generated normative data for this important structural parameter. Methods Using a convolutional neural network (U-Net) we segmented the thoracic aorta among 49,282 UKBB participants who underwent magnetic resonance imaging. To define normal allometric relationships, we included a highly selected subgroup (n=3,856) without cardiovascular risk factors or prevalent cardiovascular disease. Allometric relations were estimated using sex-adjusted log-log models. Results The mean thoracic aorta centerline length was 31.68 (SD=2.50) cm. Males exhibited longer thoracic aortas than females (32.93 vs. 31.15 cm; P<0.0001). In log-log models, body height accounted for 13.4% of the population variability in thoracic aortic length (R2=0.134; P<0.0001). The allometric power relating thoracic aortic length to body height was highly sublinear (power point estimate=0.44; 95% CI:0.37, 0.50). Sex was a predictor of thoracic aortic length (β=0.02; 95%CI=0.014, 0.029; P<0.0001), indicating that for any given body height, females had slightly shorter thoracic aortas compared to males. Among males, the 5th, 25th, 50th, 75th and 95th percentiles of allometrically scaled aortic length were 2.69, 3.20, 3.36, 3.53, and 3.96, respectively. Among females, the corresponding percentiles were 2.69, 3.11, 3.29, 3.46, 4.01. Conclusions The thoracic aorta exhibits a highly sublinear length relationship with body height, suggesting that disproportionate length relationships at the extremes of body height may have an important impact on pulsatile hemodynamics. Females exhibit slightly shorter thoracic aortas than males even after accounting for body height in an allometric fashion.aorta length vs height