Target Alveolar Ventilation - ResMed VPAP ST-A User Manual

Target alveolar ventilation

iVAPS targets alveolar ventilation. Alveolar ventilation was chosen because it is at the level of the alveoli
that gas exchange occurs. Total ventilation includes the ventilation devoted to the conducting airways,
whereas alveolar ventilation best represents the useful portion of ventilation that reaches the alveoli.
Alveolar ventilation cannot be measured directly, so iVAPS estimates it using a height approximated value
of anatomical deadspace as shown in the graph below. Anatomic deadspace is the amount of breath
that remains in the conducting airways, which does not reach alveoli and does not contribute to gas
exchange. Its contribution is proportional to breath rate. By using alveolar ventilation as a servoventilation
target, as opposed to tidal volume or minute ventilation, the effect of respiratory rate change on effective
ventilation is negated.
Anatomical Deadspace Estimation
225
200
175
150
125
100
75
50
25
35 35 40
Adapted from Hart MC et al. Journal Applied Physiology.18(3), p519-522. 1963
iVAPS Deadspace
Estimation
45 50 55 60 65 70 75
Height (in)
80
7
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