Functional impact of diaphragm muscle sarcopenia in both male and female mice

Abstract

To perform a range of ventilatory and nonventilatory behaviors, the diaphragm muscle (DIAm) must be able to generate sufficient forces throughout the lifespan. We hypothesized that sarcopenia impacts DIAm force generation and thus limits performance of expulsive, higher force, nonventilatory behaviors. Male and female mice (n = 79) at 6 and 24 mo of age (100 vs. 70-75% survival, respectively) were used to examine transdiaphragmatic pressure (Pdi) generation across motor behaviors in vivo and in vitro DIAm specific force. We found a significant effect of age on maximum Pdi (20-41% decline during tracheal occlusion and bilateral phrenic nerve stimulation), maximum DIAm specific force (30% decline), and DIAm fatigue resistance (15% increase). There were no differences between sexes in these age effects on DIAm performance. These results support our hypothesis that sarcopenia primarily impacts higher force, nonventilatory motor behaviors of the DIAm. Such functional limitations may have negative implications in the ability of the DIAm to generate forces needed for airway clearance in old age and thereby contribute to age-related respiratory complications.

Keywords: aging; respiratory muscles; sex differences; transdiaphragmatic pressure.

Fig. 1.

Representative transdiaphragmatic pressure (Pdi) tracings from young and old mice (male) across motor behaviors: eupnea, hypoxia (10% O₂)-hypercapnia (5% CO₂), spontaneously occurring deep breaths, sneezing, tracheal occlusion, and bilateral maximal phrenic nerve stimulation. Bar represents 10 cmH₂O.

Fig. 2.

Pdi generated across motor behaviors: eupnea, hypoxia (10% O₂)-hypercapnia (5% CO₂), spontaneously occurring deep breaths, sneezing, tracheal occlusion, and bilateral maximal phrenic nerve stimulation for both male (A) and female (B) mice at 6 and 24 mo of age, young (open bars) and old (solid bars), respectively (n = 9/group). Data analyzed by 3-way ANOVA: interaction P = 0.988; main effect of age P = 0.001; main effect of sex P = 0.153; main effect of behavior P < 0.001. Significant main effect of behavior: eupnea and hypoxia-hypercapnia less than deep breaths and sneezing; and eupnea, hypoxia-hypercapnia, deep breaths, and sneezing less than tracheal occlusion and nerve stimulation. *Significant main effect of age different from young at same behavior.

Fig. 3.

Diaphragm muscle (DIAm) force is decreased at 24 mo of age (n = 8/group). Specific force of the DIAm is normalized for the physiological cross-sectional area of the muscle. Data analyzed by 2-way ANOVA: interaction P = 0.145; main effect of age P < 0.001; main effect of sex P = 0.363. *Significantly different from young.

Fig. 4.

DIAm fatigue resistance following 2 min of repetitive stimulation calculated as the ratio of force after 2 min of repetitive stimulation to that of the initial force (2-way ANOVA: main effect of age P = 0.036; main effect of sex P = 0.063; interaction P = 0.882). *Significantly different from young.