3D analysis of sexual dimorphism in size, shape and breathing kinematics of human lungs

Abstract

Sexual dimorphism in the human respiratory system has been previously reported at the skeletal (cranial and thoracic) level, but also at the pulmonary level. Regarding lungs, foregoing studies have yielded sex-related differences in pulmonary size as well as lung shape details, but different methodological approaches have led to discrepant results on differences in respiratory patterns between males and females. The purpose of this study is to analyse sexual dimorphism in human lungs during forced respiration using 3D geometric morphometrics. Eighty computed tomographies (19 males and 21 females) were taken in maximal forced inspiration (FI) and expiration (FE), and 415 (semi)landmarks were digitized on 80 virtual lung models for the 3D quantification of pulmonary size, shape and kinematic differences. We found that males showed larger lungs than females (P < 0.05), and significantly greater size and shape differences between FI and FE. Morphologically, males have pyramidal lung geometry, with greater lower lung width when comparing with the apices, in contrast to the prismatic lung shape and similar widths at upper and lower lungs of females. Multivariate regression analyses confirmed the effect of sex on lung size (36.26%; P < 0.05) and on lung shape (7.23%; P < 0.05), and yielded two kinematic vectors with a small but statistically significant angle between them (13.22°; P < 0.05) that confirms sex-related differences in the respiratory patterns. Our 3D approach shows sexual dimorphism in human lungs likely due to a greater diaphragmatic action in males and a predominant intercostal muscle action in females during breathing. These size and shape differences would lead to different respiratory patterns between sexes, whose physiological implications need to be studied in future research.

Three‐dimensional analysis of sexual dimorphism in ribcage kinematics of modern humans

“…Since abdominal breathing with diaphragmatic action is more predominant in males (Kaneko & Horie, ; Ragnarsdóttir & Kristinsdóttir, ; Verschakelen & Demedts, ), we can infer that the larger thoracic size increase of males and their large TLC are caused by differences in the ways that intercostal muscles and the diaphragm act to increase thoracic volume (the so‐called breathing pattern) between males and females. In this regard, recent research on human lungs (Torres‐Tamayo et al, ) observed that the base of the lungs, which largely tracks the diaphragmatic domes, undergoes a larger expansion in males than in females, also pointing to a larger diaphragmatic contribution to breathing kinematics in males than in females. However, it is important to note that differences in the kinematics of the diaphragmatic domes are not directly quantified by our measures of rib cage form and kinematics.…”

“…Differences in kinematic patterns were explored in a form space principal component analysis (form space PCA) (Mitteroecker, Gunz, Windhager, & Schaefer, ) and thorax shape differences associated with variations along the PC1‐2 axes were visualized using EVAN Toolkit (version 1.71; http://www.evan-society.org/). Kinematic differences were statistically tested by computing a dummy regression of shape on the kinematic state for each sex and calculating the angle between those regressions (Torres‐Tamayo et al, ), the significance being assessed via a permutation test ( N = 1,000).…”

“…However, if we assume that the sexes differ in ventilatory advantage (in terms of a greater tidal volume) and diaphragmatic contributions to breathing kinematics, we should also expect different kinematic breathing patterns. In this regard, recent research (Torres‐Tamayo et al, ) found sex‐related differences in the breathing kinematics of human lungs, which is also supported by physiological data (Guenette, Witt, McKenzie, Road, & Sheel, ; Hopkins & Harms, ). However, it is important to note that many of the sex‐related kinematic differences in lungs are due to differences in cranio‐caudal movements of the inferior portions of the lungs directly related to the diaphragm.…”

Sex and Height Influence Neck Posture When Using Electronic Handheld Devices

“…Various studies have used GM to assess sexual dimorphism, character displacement, craniofacial shape, and beyond in both extant and extinct species (Adams and Rohlf, ; Franklin et al, ; Kaliontzopoulou et al, ; Pierce et al, ) to attempt to discern relationships and/or evolutionary trends. No study at present has used these techniques to assess cervical spinal morphology and head/neck postures in humans, and the use of GM in biomechanical and/or kinematic analyses has been limited (but see Manfreda et al, ; Arlegi et al, ; Torres‐Tamayo et al, ). With such a drastic increase in handheld device usage in the past decade, further investigation into its effect on bone morphology is warranted.…”

3D geometric morphometric analysis of variation in the human lumbar spine

“…Sexual shape dimorphism and inter‐population shape variation of the lumbar vertebrae were both explored by carrying out a principal components analysis (PCA) in shape space (Mitteroecker et al, ; Zelditch et al, ). To determine statistically whether sex or inter‐population factors are associated with the shape variation of the lumbar spine explained by each principal component (PC), two dummy multivariate regressions of PC1 and PC2 shape variation were calculated (dummy variables: sex or population; 1,000 permutations, significance level 0.05) (Bastir et al, ; García‐Martínez et al, ; Monteiro, ; Rosas & Bastir, ; Torres‐Tamayo et al, ) using MorphoJ software (Klingenberg, ). Dummy (or indicator) variables are created to represent an attribute which may have an impact on the sample's variability (i.e., sex or population ) in a binary form (e.g., males = 1; females = −1) in order to identify which factor influences the shape variation summarized in each PC.…”