  All schoolchildren know how often they breathe, but even experts don't know
exactly why. The aim of this publication is to develop a model of the resting
spontaneous breathing rate using physiological, physical and mathematical
methods with the aid of the principle that evolution pushes physiology in a
direction that is as economical as possible. The respiratory rate then follows
from an equation with the parameters CO2-production rate of the organism,
resistance, static compliance and dead space of the lungs, the inspiration
duration: expiration duration - ratio and the end-expiratory CO2 fraction. The
derivation requires exclusively secondary school mathematics. Using the example
of an adult human or a newborn child, data from the literature then result in
normal values for their breathing rate at rest. The reason for the higher
respiratory rate of a newborn human compared to an adult is the relatively high
CO2-production rate together with the comparatively low compliance of the
lungs. A side result is the fact that the common alveolar pressure throughout
the lungs and the common time constant is a consequence of the economical
principle as well. Since the above parameters are not human-specific, there is
no reason to assume that the above equation could not also be applicable to
many animals breathing through lungs within a thorax, especially mammals. Not
only physiology and biology, but also medicine, could benefit: Applicability is
being discussed in pulmonary function diagnostics, including pathophysiology.
However, the present publication only claims to be a theoretical concept for
the spontaneous quiet breathing rate. In the absence of comparable animal data,
this publication is intended to encourage further scientific tests.
