Gas flow in the airways is governed by the relation F = ΔP / R, in which flow is directly proportional to the pressure gradient between the atmosphere and the alveoli and inversely proportional to airway resistance. The pressure term expresses the diffusion principle — gases move passively from regions of higher pressure to regions of lower pressure, so a zero gradient yields no net flow and a reversed gradient reverses the direction of flow — while the resistance term is dominated by friction, the principal non-elastic source of resistance, which varies with airway diameter under bronchial smooth muscle control (sympathetic adrenergic dilation, parasympathetic cholinergic and inflammatory constriction). The concept belongs to respiratory physiology within human anatomy and physiology and is the airway analogue of the general flow-pressure-resistance law used throughout fluid dynamics and cardiovascular physiology, linking the mechanics of breathing to the exchange processes downstream.
Gas flow in the airways is governed by the relation F = ΔP / R, in which flow is directly proportional to the pressure gradient between the atmosphere and the alveoli and inversely proportional to ai…