During expiration (step 4), the first 150 mL of air emerging from the body is the fresh air left in the conducting airways from the previous inspiration. By the end of inspiration, the 500 mL of air that entered the alveoli (150 mL of stale air plus 350 mL of fresh air) has mixed by diffusion with the pre-existing alveolar air (see Fig.

However, the first 150 mL is stale air previously in the conducting airways only the final 350 mL is fresh air. During inspiration, ~500 mL of air also enters the alveoli. However, only the first 350 mL reaches the alveoli the final 150 mL remains in the conducting airways (i.e., nose, pharynx, larynx, trachea, and other airways without alveoli)-that is, the anatomical dead space. These figures are typical for a 70-kg person V T and V D are roughly proportional to body size. During inspiration, ~500 mL of “fresh” atmospheric air (high /low ) enters the body (step 2). Thus, for someone with a tidal volume of 0.5 L, breathing 12 breaths/min,īecause total ventilation usually is reported in L/min, it is sometimes called minute ventilation.īefore an inspiration, the conducting airways are filled with “stale” air having the same composition as alveolar air ( Fig. A practical definition is that is the product of tidal volume (TV or V T) and the respiratory frequency (f).

Here V is the volume of air exiting the lungs during a series of breaths. Note that we are using differently than in Chapter 27, where represented flow through an airway at a particular instant in time. Total ventilation ( ) is the volume of air moved out of the lungs per unit of time: Medical Physiology, 3rd Edition VentilationĪbout 30% of total ventilation in a respiratory cycle is wasted ventilating anatomical dead space (i.e., conducting airways)

Anatomical dead space gravity