Diaphragm Ultrasound in Cardiac Surgery: State of the Art

In cardiac surgery, patients are at risk of phrenic nerve injury, which leads to diaphragm dysfunction and acute respiratory failure. Diaphragm dysfunction (DD) is relatively frequent in cardiac surgery and particularly affects patients after coronary artery bypass graft. The onset of DD affects patients’ prognosis in term of weaning from mechanical ventilation and hospital length of stay. The authors present a narrative review about diaphragm physiology, techniques used to assess diaphragm function, and the clinical application of diaphragm ultrasound in patients undergoing cardiac surgery.

An implantable ventilator augments inspiration in an in vivo porcine model

Severe diaphragm dysfunction can lead to respiratory failure, requiring permanent mechanical ventilation. Permanent tethering to a mechanical ventilator via a patient’s mouth or tracheostomy can interfere with quality of life and autonomy by hindering activities like speech and swallowing. We present a diaphragm assist system that intervenes internally at the diaphragm as opposed to the mouth. By implanting contractile, soft robotic actuators above the diaphragm to push downwards and augment diaphragm motion during inspiration, this diaphragm assist system functions as an implantable ventilator. We demonstrate the proof-of-concept feasibility of this system to augment physiological metrics of ventilation in an in vivo porcine model of varied respiratory insufficiency. Synchronized actuation of the assist system with native respiratory effort augmented the tidal volume by up to a 100 mL increase and was capable of improving minute ventilation into a normal range. The diaphragm assist system has the potential to provide a new therapeutic ventilation option that aims to restore respiratory performance without sacrificing quality of life.

Characterisation of hemidiaphragm dysfunction using dynamic chest radiography: a pilot study

ObjectivesDynamic chest radiography (DCR) is a novel real-time digital fluoroscopic imaging system that produces clear, wide field-of-view diagnostic images of the thorax and diaphragm in motion, alongside novel metrics on moving structures within the thoracic cavity. We describe the use of DCR in the measurement of diaphragm motion in a pilot series of cases of suspected diaphragm dysfunction.MethodsWe studied 21 patients referred for assessment of diaphragm function due to suspicious clinical symptoms or imaging (breathlessness, orthopnoea, reduced exercise tolerance, and/or an elevated hemidiaphragm on plain chest radiograph). All underwent DCR with voluntary sniff manoeuvres.ResultsParadoxical motion on sniffing was observed in 14 patients, and confirmed in 6 who also underwent fluoroscopy or ultrasound. In 4 patients, DCR showed reduced hemidiaphragm excursion but no paradoxical motion; in 3, normal bilateral diaphragm motion was demonstrated. DCR was quick to perform, well-tolerated in all cases and with no adverse events reported. DCR was achieved in around five minutes per patient, with images available to view by the clinician immediately within the clinical setting.ConclusionDCR is a rapid, well-tolerated and straightforward X-ray technique that warrants further investigation in the assessment of diaphragm dysfunction.

Ultrasound Imaging of the Diaphragm

The diaphragm is the major muscle of respiration and its dysfunction is associated with problems ranging from orthopnea to prolonged recovery from surgery or ventilator management. Common causes of diaphragm dysfunction include phrenic neuropathy, motor neuron disease, neuromuscular junction disorders, and myopathy. This article reviews sonographic findings of normal diaphragm, including key quantitative ultrasound measurements that are helpful in the evaluation of diaphragm. It also discusses various clinical application of this technique in diagnosis of neuromuscular diseases.

Positive end-expiratory pressure affects geometry and function of the human diaphragm

We demonstrate that PEEP causes changes in diaphragm geometry, especially muscle shortening, and decreases in vivo diaphragm contractile function. Thus prerequisites for the development of diaphragm longitudinal muscle atrophy are present with the acute application of PEEP. Once confirmed in ventilated critically ill patients, this could provide a new mechanism for ventilator-induced diaphragm dysfunction and ventilator weaning failure in the intensive care unit (ICU).

Altered expression of microRNAs in the rat diaphragm in a model of ventilator-induced diaphragm dysfunction after controlled mechanical ventilation

Background Ventilator-induced diaphragm dysfunction (VIDD) is a common complication of life support by mechanical ventilation observed in critical patients in clinical practice and may predispose patients to severe complications such as ventilator-associated pneumonia or ventilator discontinuation failure. To date, the alterations in microRNA (miRNA) expression in the rat diaphragm in a VIDD model have not been elucidated. This study was designed to identify these alterations in expression. Results Adult male Wistar rats received conventional controlled mechanical ventilation (CMV) or breathed spontaneously for 12 h. Then, their diaphragm tissues were collected for RNA extraction. The miRNA expression alterations in diaphragm tissue were investigated by high-throughput microRNA-sequencing (miRNA-seq). For targeted mRNA functional analysis, gene ontology (GO) analyses and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were subsequently conducted. qRT-PCR validation and luciferase reporter assays were performed. We successfully constructed a model of ventilator-induced diaphragm dysfunction and identified 38 significantly differentially expressed (DE) miRNAs, among which 22 miRNAs were upregulated and 16 were downregulated. GO analyses identified functional genes, and KEGG pathway analyses revealed the signaling pathways that were most highly correlated, which were the MAPK pathway, FoxO pathway and Autophagy–animal. Luciferase reporter assays showed that STAT3 was a direct target of both miR-92a-1-5p and miR-874-3p and that Trim63 was a direct target of miR-3571. Conclusions The current research supplied novel perspectives on miRNAs in the diaphragm, which may not only be implicated in diaphragm dysfunction pathogenesis but could also be considered as therapeutic targets in diaphragm dysfunction.