The Origin of Adaptive Support Ventilation

This letter concerns an article which was published in the August 2004 issue of your journal. I developed a system for closed loop control of mechanical ventilation in the late 1980’s that was issued as US Patent No. 4,986,268 in January 1991 (1). In the system originally disclosed in my patent, the frequency and tidal volume of breaths of a patient on a ventilator were automatically controlled based on the patient’s requirements. The lung mechanics were used to adjust the depth and rate of breathing to minimize the work of breathing. A modified version of an equation derived by Otis et al (2) was used to calculate the optimum frequency of mechanical ventilation in the system. The rationale was to provide a natural and comfortable breathing pattern for the patient to stimulate spontaneous breathing and thereby reduce the weaning time. A brief comparison shows that this method is the same as the one used later in a commercial ventilation mode known as Adaptive Support Ventilation (ASV). I published a paper on my patent in 1991 (3) and a review paper on closed loop mechanical ventilation that gave a description of my invention was also published in 1996 (4). Later, I authored three papers that described the patented system in combination with other ventilatory controllers (5-7). Recently, a more advanced and modified closed loop system, which utilizes the patented technique and includes an additional automatic controller for adjustment of the inspired fraction of oxygen of the patient, was evaluated and the results were published (8, 9). In the recent article “Evaluation of adaptive support ventilation in paralyzed patients and in a physical lung model,” by Belliato et al, published in the August 2004 issue of your journal, the authors referred to 20 articles regarding ASV, its roots, and applications, without referencing any of my articles or my patent. To preserve the integrity of scientific publications, it is essential that the original references of the reported and evaluated methods not be left out. Also bearing on this issue is that ASV was the subject of a lawsuit that was settled in 2004 (10).