Contractile capability of the diaphragm assessed by ultrasonography predicts nocturnal oxygen saturation in COPD

Diaphragm function might be useful to predict nocturnal oxygen desaturation in COPD. Ultrasonography has been widely used for the assessment of the diaphragm. We aimed to investigate the relationship between the contractile capability of the diaphragm assessed by ultrasonography and the nocturnal percutaneous arterial oxygen saturation (NSpO₂ ) in COPD.

Twenty-eight male patients with COPD (age, 73 ± 7 years; forced expiratory volume in 1 s (FEV₁ ), 54.2 ± 17.0% predicted) were included. The thickness of the diaphragm (Tdi) was assessed by ultrasonography. We calculated the change ratio of Tdi at the end of maximal inspiration and expiration (%ΔTdi). The mean value of NSpO₂ (NSpO_2mean ), the percentage of total sleep time (TST) with desaturation above 4% (DA4%) and the percentage of TST with saturation below 90% (SB90%) were measured by overnight oximetry. Daytime arterial oxygen pressure (PaO₂ ) and maximal inspiratory mouth pressure (PI_max ) were also measured.

All participants had mild or no daytime hypoxaemia (PaO₂ , 77.3 ± 8.6 mm Hg). The NSpO_2mean , DA4% and SB90% were significantly correlated with %ΔTdi, PaO₂ , %PI_max of the predicted value and the Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage. The %ΔTdi and PaO₂ were predictors of NSpO₂ mean by multiple regression analysis.

This study suggested a close relationship between the NSpO₂ and the contractile capability of the diaphragm assessed by ultrasonography in COPD. The %ΔTdi combined with PaO₂ might predict NSpO₂ in COPD patients with mild or no daytime hypoxaemia.