Asymmetrical action of the canine diaphragm after single-lung inflation

Improvements of the shape and strength of the diaphragm after endoscopic lung volume reduction

RATIONALE

Endoscopic lung volume reduction improves lung function, quality of life and exercise capacity in severe emphysema patients. However, its effect on the diaphragm function is not well understood. We hypothesised that endoscopic lung volume reduction increases its strength by modifying its shape.

OBJECTIVES

To investigate changes in both diaphragm shape and strength induced by the insertion of endobronchial valves.

METHODS

In 19 patients, both the diaphragm shape and strength were investigated respectively by 3D Slicer software applied on CT scans acquired at functional residual capacity and by transdiaphragmatic pressure measurements by bilateral magnetic stimulation of the phrenic nerves before and 3 months after unilateral valves insertion.

MEASUREMENTS AND MAIN RESULTS

After lung volume reduction (median (IQR), 434 mL (-597 to -156], p<0.0001), diaphragm strength increased (transdiaphragmatic pressure: 3 cmH2O (2.3 to 4.2), p<0.0001). On the treated side, this increase was associated with an increase in the coronal (16 mm (13 to 24), p<0.0001) and sagittal (26 mm (21 to 30), p<0.0001) lengths as well as in the area of the zone of apposition (62 cm2 (3 to 100), p<0.0001) with a decrease in the coronal (8 mm (-12 to -4), p<0.0001) and sagittal (9 mm (-18 to -2), p=0.0029) radii of curvature.

CONCLUSIONS

Endoscopic lung volume reduction modifies the diaphragm shape by increasing its length and its zone of apposition and by decreasing its radius of curvature on the treated side, resulting in an increase in its strength.

TRIAL REGISTRATION NUMBER

NCT05799352.

Diaphragm efficiency estimated as power output relative to activation in chronic obstructive pulmonary disease

Muscle efficiency increases with fiber length and decreases with load. Diaphragm efficiency (Eff(di)) in healthy humans, measured as power output (Wdi) relative to the root mean square of diaphragm electromyogram (RMS(di)), increases with hyperpnea due to phasic activity of abdominal muscles acting to increase diaphragm length at end expiration (L(di ee)) and decrease inspiratory load. In chronic obstructive pulmonary disease (COPD), hyperpnea may decrease Eff(di) if L(di ee) decreases and load increases due to airflow obstruction and dynamic hyperinflation. To examine this hypothesis, we measured Eff(di) in six COPD subjects (mean forced expiratory volume in 1 s: 54% predicted) when breathing air and at intervals during progressive hypercapnic hyperpnea. Wdi was measured as the product of mean inspiratory transdiaphragmatic pressure (ΔPdi(mean)), diaphragm tidal volume measured fluoroscopically, and 1/inspiratory duration. Results were compared with those of six healthy subjects reported previously. In COPD, L(di ee) was normal when breathing air. ΔPdi(mean) and Wdi increased normally, and RMS(di) increased disproportionately (P = 0.01) with hyperpnea, and, unlike health, inspiratory capacity (IC), L(di ee), and Eff(di) did not increase. IC and L(di ee) were constant with hyperpnea because mean expiratory flow increased as expiratory duration decreased (r(2) = 0.65), and because expiratory flow was terminated actively by the balance between expiratory and inspiratory muscle forces near end expiration, and these forces increased proportionately with hyperpnea (r(2) = 0.49). At maximum ventilation, diaphragm radius of curvature at end inspiration increased in COPD (P = 0.04) but not controls; diaphragm radius of curvature at end inspiration and ln(Eff(di)) were negatively correlated (P = 0.01). Thus in COPD with modest airflow obstruction, Eff(di) did not increase normally with hyperpnea due to a constant L(di ee) and inspiratory flattening of the diaphragm.