Ultrasound and Respiratory Physiological Signals in Lung Diseases

Overview

The use of lung ultrasound is instrumental in the evaluation of many chest pathologies and its ability to detect pleuro-pulmonary pathology is widely accepted. However, the use of ultrasound to explore the state of the peripheral lung parenchyma, when the organ is still aerated, is a relatively new application. Horizontal and vertical artifacts are separate and distinct artifacts that can be seen during ultrasound examination of the lungs. While the practical role of lung ultrasound artifacts is accepted to detect and monitor many conditions, further research is needed for the physical interpretation of ultrasound artifacts. These artifacts are diagnostic signs, but we don't fully understand their origin. The artifactual information deriving from the surface acoustic interaction, beyond the pleural line, in the ultrasound images of the normally aerated and non-deflated lung, represents the final result of complex interactions of acoustic waves with a specific three-dimensional structure of the biological tissue. Thus, the umbrella term "vertical artifacts" oversimplifies many physical phenomena associated with a pathological pleural plane. There is growing evidence that vertical artifacts are caused by physiological and pathological changes in the superficial lung parenchyma. Therefore, the need emerges to explore the physical phenomena underlying the artifactual ultrasound information deriving from the surface acoustic interaction of ultrasound with the pleuro-pulmonary structures.

In the last years, lung ultrasonography has gained ever-growing clinical interest and curiosity because of its peculiar ability to acquire clinical information at bedside, its non-invasiveness and low cost. In particular settings (emergency medicine, intensive care unit) its utility has been well demonstrated. Clinicians use chest ultrasound for detecting pleural diseases, consolidations, bronchiolitis, interstitial lung pathology and critical pulmonary conditions of adults, children, and infants. However, the development of lung ultrasonography for exploring non-consolidated organs, has been not supported by a strong knowledge of the physical mechanisms that underlie pulmonary artifacts. Lung ultrasonography is comparable to a standard morphological sonography only when assessing a pulmonary consolidation, a tissue without air, which is in direct contact with the visceral pleural. In this case, the clinicians evaluate anatomic images, representing the real structure of the diseased organ. Differently, when the lung surface is denser but not yet consolidated, the large acoustic impedance gradient between the chest wall and the pulmonary tissue containing air prevents every anatomic representation, and the scan results in the visualization of many kinds of vertical artifacts known as B-Lines. Even though the practical role of lung ultrasound artifacts is accepted for detecting and monitoring many conditions, many of the published studies are empirical and further research is needed to clarify the physical genesis of vertical artifacts. These artifacts are diagnostic signs, but we do not fully understand their origin. The artifactual information beyond the pleura line in ultrasonographic images of the normal and of the not critically deflated lung represents the ultimate outcome of complex interactions of a specific acoustic wave with a specific three-dimensional structure of the biological tissue. There is growing evidence that vertical artifacts are caused by physiological and pathological changes in the superficial lung parenchyma. The study intends to explore the relationship among ultrasound, tomographic and patch-based cardio-respiratory data, obtained from a heterogeneous population of patients suffering from: 1) pre-consolidative pulmonary changes such as diffuse interstitial lung diseases during exacerbation, 2) infectious interstitial pneumonia and 3) chronic obstructive pulmonary disease during both stable phase and exacerbations.