Of course, there's some degree of proprietary knowledge involved in designing a ventilator.

The most basic vents decades ago were programmed to be a breath in, breath out based primarily on a patient's weight; tidal volume. As vents moved beyond basic, they were designed to deliver differing fractions of inspired oxygen, PEEP (positive end expiratory pressure, which helps to keep the alveoli open at the end of inspiration so the alveoli do not completely collapse at the end of exhalation, benefiting the diffusion of oxygen and carbon dioxide), the ability to deliver volumes beyond the tidal volume that mimic the deep sighs that humans typically take to hyperinflate the lungs, and various alarm systems to alert medical staff of any reason the volume of air isn't being delivered or accidental disconnect.