In an normal adult, the ratio of physiological and anatomical dead space is:

In a normal healthy person physiological dead space almost equals anatomic dead space. Therefore the ratio is 1:1. In some respiratory disorders with non functioning alveoli the physiologic dead space may be ten times the anatomic dead space. Anatomic dead space refers to volume of air present in the conducting zone of respiratory passage i.e from nose to terminal bronchioles. It contains 150ml of air. Alveolar dead space refers to volume of air present in those alveoli which do not take pa in gas exchange. Normally, all the alveoli take pa in gas exchange but in some lung diseases some alveoli does not take pa in gas exchange. Physiologic dead space refers to total dead space which includes both anatomic and alveolar. Ref: Essentials Of Medical Physiology By Khurana PAGE 245.