Comparative morphology of the trachea in newborn mammals.

Tracheal dimensions have been measured in a variety of newborn mammals ranging in body mass (M) from mouse to dolphin. Both tracheal diameter and tracheal length are nearly proportional to the cube root of M (M0.36 and M0.34, respectively). Tracheal volume is proportional to M1.07, and assuming that dead space volume (VD) is proportional to tracheal volume, VD is found to be proportional to FRC. Resting breathing frequency is proportional to M-0.21, therefore dead space ventilation (VD) can be calculated to be proportional to M0.86. This value is very close to the proportionality between oxygen consumption (VO2) and body weight reported in newborns (M0.88, Bartlett and Areson, 1977); since alveolar ventilation (VA) is proportional to VO2, VD is proportional to VA. From this, it can also be inferred that alveolar PCO2 and PO2 are nearly the same in newborns of different species.