Assessment of diaphragm dysfunction during cardiac rehabilitation after heart surgery: the role of ultrasound imaging
Authors: Maranta F , Rizza V , Cartella I , Pellegrino S , Bonaccorso A , Meloni C , Avitabile M , Castiglioni A , De Bonis M , Alfieri O , Cianflone D 
Published: November 2020

Abstract

Background
Diaphragm dysfunction is a frequent and underdiagnosed complication of cardiac surgery. It can cause dyspnoea, decreased exercise performance and, in more severe cases, respiratory failure. Ultrasonography (US) is a valuable, non-invasive technique for the assessment of diaphragm function. Only few trials have been conducted using US to evaluate diaphragm functional recovery after cardiovascular rehabilitation (CR).

Purpose
The aim of the study was to assess with US the incidence of diaphragm dysfunction after heart surgery and to define the impact of an inpatient CR programme on diaphragm functional recovery.

Methods
We performed a single-centre prospective cohort study, enrolling 185 patients hospitalized in our CR unit: 99 patients underwent mitral valve repair or replacement, 28 tricuspid valve repair or replacement, 53 aortic valve replacement, 30 coronary artery bypass grafting, 59 combined surgery and 14 other surgical procedures. Diaphragm US was performed at admission and after 10 rehabilitative sessions. We assess the following parameters on quiet breathing: excursion, time of inspiration, time of a respiratory cycle and contraction velocity (slope) in M-mode on the right anterior subcostal projections and thickening fraction (TF) in B-mode on the right intercostal projections. TF was defined as [(thickness at end inspiration–thickness at end expiration)/thickness at end expiration].

Results
The median excursion at admission was 1.6 cm. Patients with excursion &lt;2 cm (lower limit for the general population) were considered with diaphragm dysfunction. Following cardiac surgery, the incidence of diaphragm dysfunction was 70.8%. Patients with excursion &lt;2 cm at admission gained an important benefit from CR, with a significant improvement in TF (p&lt;0.001), excursion (p&lt;0.001), time of inspiration (p&lt;0.001), time of a respiratory cycle (p&lt;0.001) and slope (p&lt;0.001). Conversely, in patients with excursion ≥2 cm there was no significant improvement in slope (p=0.539) and excursion (p=0.179). At the final assessment, diaphragm function recovered in 50.5% of the patients, whilst 49.5% had a failure of recovery (excursion relative change between admission and discharge &lt;33%). The multivariate analysis identified combined surgery (OR 3.08; 95% CI 1.59–5.99, p=0.001) and post-surgical pneumothorax (OR 3.05; 95% CI 1.23–7.55, p=0.036) as independent predictors of failure of diaphragm function recovery.

Conclusions
US might be a valuable tool for initial and follow-up assessment of patients after cardiac surgery. CR has been shown to be an effective strategy to improve diaphragm parameters in patients with post-surgical dysfunction. Patients undergoing combined surgery or developing post-surgical pneumothorax might benefit from a personalised rehabilitation programme to improve diaphragm function.

Funding Acknowledgement
Type of funding source: None