where CDif,TAC represents alveolar properties when the alveoli are
fully inflated and f is an exponent that describes how CDif is proportional
to VA. Only the overall effect on ˙D due to changes in VA
were estimated and we did not attempt to quantify the magnitude
of ˙D. For comparison with previous modeling attempts where gas
exchange abruptly ceases at Pcoll we assume ˙D is proportional to
P when Pamb < Pcoll and ˙D = 0 when Pamb ≥Pcoll.