ESI is the outcome of clinical research aimed to evaluate the relative contribution of emphysema to the airflow obstruction measured by standard spirometry. The expiratory airflow obstruction of patients with Chronic Obstructive Pulmonary Disease (COPD) results in morphologic changes of the flow/volume curve.
ESI method, based on fluid-dynamic modeling of the airways, describes the shape of the expiratory fraction of the flow/volume curve whose inflexion is widely held as an index of emphysema presence.
The mathematical model permits to evaluate the contribute of emphysema to the measured obstruction using as input variables: Peak Expiratory Flow (PEF), Forced Vital Capacity (FVC) and the Forced Expiratory Flows (FEF) at 25%, 50% e 75% of FVC. All input variables are in absolute value.
The computation, indeed, being based only on the morphology of the flow/volume curve of each subject, independently of its own ethnic and anthropometric characteristics, does not necessitate of input variables expressed as percent predicted of a reference population.
The addition to spirometry of the novel functional parameter ESI allows to define in each patient what portion of the airflow obstruction measured by the standard spirometric indexes has to be attributed to inflammatory narrowing of the conductive airways (chronic bronchitis, bronchiolitis, small airway disease) or to emphysematous destruction of lung parenchyma.
Patients with the same obstruction (FEV1) level, but different ESI value should be considered different from the pathophysiologic, therapeutic and prognostic point of view. See the accompanying figure (Figure1) referring to two patients with 45% and 44% FEV1 and very different values of ESI. A standard spirometry with ESI computation allows obtaining clinical information comparable to that obtainable with complete pulmonary function testing and in close agreement with the parenchymal destruction quantitatively evaluated by chest CT.
ESI could also be of great relevance for the evaluation of the results of large scale epidemiologic, clinical, and pharmacologic trials in which, usually, standard spirometry is the only available pulmonary function examination.
ESI adds to standard spirometry the ability to discriminate whether emphysema or conductive airway disease is the predominant mechanism of airway obstruction and, consequently, it could be a valuable means in clinical practice in terms of more individualized prognosis and treatment alternatives.
In this connection, ESI could be considered a simple tool to advance Respiratory Medicine towards the new concept of 4P Medicine (Preventive, Predictive, Precise, Personalized).
Indeed, ESI could be used to incentivize smoking cessation (Preventive), to derive prognostic information (Predictive), to identify the main mechanism underlying airway obstruction (Precise), and to select the most individualized pharmacologic treatment (Personalized).
As an exclusive support of this revolutionary achievement in clinical, therapeutic, and prognostic fields are the latest generation spirometers of MIR Plus line, the only ones in the national and international market that will implement this parameter by adding to Spirometry the power to support the diagnosis of emphysema by means of numerical values comparable with the measurements obtained by CT analysis and in line with the results published in scientific journals.