Inspiratory Effort Assessed Through Nasal Pressure Measurement in Patients With Idiopathic Pulmonary Fibrosis

Idiopathic Pulmonary Fibrosis (IPF) is a fibrosing progressive interstitial lung disease with unknown etiology, with a median survival of 3 years since first diagnosis. The typical radiologic pattern of the disease is usual interstitial pneumonia (UIP) defined by basal and peripheral (subpleural) predominance and a typical cystic degeneration of lung parenchyma (honeycombing), interstitial fibrotic thickening and traction bronchiectasis. Despite the recent introduction of two antifibrotic treatments (Pirfenidone and Nintendanib) which proved to be successful in slowing the decline of pulmonary function in patients with IPF, a benefit of these therapies on average survival remains yet to be demonstrated.

A significant part of patients affected by IPF die due to progressive worsening of respiratory failure, often accelerated by the insurgence of acute events, like acute exacerbations. Processes leading to the development and progression of IPF are not yet completely understood. We might hypothesize a regenerative deficit in the lungs of subjects affected, due to a dysregulation of repair mechanism in response to repeated damage (inflammatory, mechanics, infectious, chemical) to the alveolar and vascular epithelium. Moreover, mechanism of damage caused by aging in tissues, with a dysfunction in resident stem cell, might contribute to progression. Patients with IPF undergo mechanical alterations of respiratory system due to progressive restrictive deficit caused by reduction in total lung capacity. This functional alteration generates an ineffective and superficial ventilation due to the waste of the majority inspiratory effort spent in ventilating dead anatomical space. When physical effort occurs, the increased ventilatory necessity and the inability to compensate due to functional impairment leads to increased inspiratory effort and subsequent increase in negative intrathoracic pressure. Recent studies have demonstrated how exerting a pressure (for example when the patient is mechanically ventilated) on lung tissue of subjects with IPF and UIP pattern can generate damage due to unfavorable mechanism of mechanotransduction caused by the pathological behavior of fibrotic lung (''squishy ball lung''). Studies investigating inspiratory effort during spontaneous breathing and respiratory failure highlighted how negative values of intrathoracic pressure might induce self induced lung injury.

Respiratory effort can be quantified measuring esophageal pressure through a pressure transducer inserted with a nasogastric tube in the inferior third part of the esophagus. Measuring esophageal pressure is a precise and accurate way of quantifying inspiratory effort, however its use in daily clinical practice is limited by invasiveness of the maneuver, high cost and need for specific clinical training. Physiological studies show that nasal pressure measured at the entrance of the nostril might correlate with esophageal pressure and therefore estimate inspiratory effort of the patient in a noninvasive way.

The goal of our study is to evaluate the role of respiratory effort during spontaneous breathing as a potential source of mechanical damage (hence favoring disease progression) in subjects with IPF and UIP pattern. The study aims to identify patient with an unfavorable mechanical phenotype defined by the simultaneous presence of UIP pattern and elevated inspiratory effort after physical activity.