Impact of advancing age on diaphragm thickness and maximal inspiratory pressure: Comparison with peripheral skeletal muscle.

Aging is associated with deleterious effects on skeletal muscle size and function, known as sarcopenia. Less understood is the impact of advancing age specific to the size and function of the diaphragm. The purpose of this study was to determine the extent to which structural and functional responses of the diaphragm to advancing age are similar or unique to those observed in peripheral muscle. Ten young (22 ± 1 yr, 5 M, 5 F) and ten old (69 ± 3, 4 M, 6 F) healthy individuals volunteered for this study. Diaphragm thickness (end exhalation, end-tidal inhalation, end-maximal inhalation) and thickness of the thigh (vastus lateralis, vastus intermedius) were assessed via ultrasound. Inspiratory muscle strength was evaluated using maximal inspiratory pressure (MIP) and thigh muscle strength was assessed using peak isometric (extension) force. Thigh muscle thickness and peak isometric force were ~35% and 44%, respectively, lower in old compared to young (p < 0.05). All measures of diaphragm thickness were similar between old and young (p > 0.05). Despite similar diaphragm thickness, MIP was ~24% lower in old compared to young (p < 0.05). Linear regression analysis revealed that diaphragm thickness at end exhalation was a predictor of MIP in old (r2 = 0.42, p < 0.05). These preliminary data suggest that while aging contributes to reduced respiratory and peripheral muscle function, diaphragm thickness, as assessed via ultrasound, appears less impacted by advancing age compared to peripheral skeletal muscle thickness. These data provide further insight for muscle-specific responses to advancing age and a basis for the development of diaphragm muscle-specific therapeutic strategies.