The novel Mechanical Ventilator Milano for the COVID-19 pandemic

Abstract

This paper presents the Mechanical Ventilator Milano (MVM), a novel intensive therapy mechanical ventilator designed for rapid, large-scale, low-cost production for the COVID-19 pandemic. Free of moving mechanical parts and requiring only a source of compressed oxygen and medical air to operate, the MVM is designed to support the long-term invasive ventilation often required for COVID-19 patients and operates in pressure-regulated ventilation modes, which minimize the risk of furthering lung trauma. The MVM was extensively tested against ISO standards in the laboratory using a breathing simulator, with good agreement between input and measured breathing parameters and performing correctly in response to fault conditions and stability tests. The MVM has obtained Emergency Use Authorization by U.S. Food and Drug Administration (FDA) for use in healthcare settings during the COVID-19 pandemic and Health Canada Medical Device Authorization for Importation or Sale, under Interim Order for Use in Relation to COVID-19. Following these certifications, mass production is ongoing and distribution is under way in several countries. The MVM was designed, tested, prepared for certification, and mass produced in the space of a few months by a unique collaboration of respiratory healthcare professionals and experimental physicists, working with industrial partners, and is an excellent ventilator candidate for this pandemic anywhere in the world.

FIG. 1.

A schematic of the MVM ventilator system (light blue box) with the connection to the patient. Dashed lines indicate electrical connections, and solid lines indicate gas connections. Thick black lines represent the breathing circuit, thin red lines are connections to pressure measurements, and the green line is the gas connection to drive the pneumatic valve at the end of the expiratory line. The direction of gas flow is indicated by the blue (inspiratory phase) and red (expiratory phase) arrows. The lines in gray indicate the breathing circuit relief lines. The beige rectangle represents the main electronics and control board, and the yellow square represents the supervisor board, which provides a redundant monitor and control.

FIG. 2.

A view of the inside of the MVM: the labels identify the components shown in Fig. 1.

FIG. 3.

The high-level software architecture.

FIG. 4.

Front view of the MVM.

FIG. 5.

The state machine of the controller software.

FIG. 6.

Schematics of the pressure controller that manages the pressure at the patient. It is based on two nested loops. The Proportional-Integral regulator of the inner loop, driven by the difference between the output of the outer loop regulator and the pressure at valve V-1 output (PI-3 sensor), actuates the V-1 valve. The Integral regulator of the outer loop ensures that the pressure at the patient (sensor PI-2) tracks the set pressure value. Pressure sensors PI-3 and PI-2 are placed at the input and output of the breathing circuit connecting the ventilator to the patient, respectively. The controller automatically identifies a simplified model of patient lungs to tune the inner loop regulator.

FIG. 7.

Software development process. It is based on the V-model, and agile practices have been integrated (circular arrow) to facilitate team collaboration, iterative development, and flexible response to changes. Each development activity on the left-hand side of the V-model corresponds to a testing activity on the right-hand side.

FIG. 8.

Example waveforms from the breathing simulator with the MVM in PCV mode, referring to test number 5 of Table 201.105 of the ISO 80601-2-12:2020 standard.

FIG. 9.

Example waveforms from the breathing simulator with the MVM in PSV mode.