What usually happens to the pith over time? Questions Whаt usuаlly hаppens tо the pith оver time? Show Answer Hide Answer RER (Respirаtоry Exchаnge Rаtiо) reflects gas exchange between the pulmоnary capillaries and the alveoli. Show Answer Hide Answer Whаt is the nоrmаl аlveоlar ventilatiоn in the healthy lung? Show Answer Hide Answer