Air flow - the rate @ which air moves from point of higher pressure to point of lower pressure a function of the

- Magnitude of driving pressure (the difference between the pressure at the beginning of the tube and the pressure at the end of the tube)
- Resistance to gas flow in communicating pathway (influenced by radius, shape of pathway)

- Density and viscosity of gas
- Type of flow pattern:

Flow – measurement of fluid volume per unit of time (L/min or L/sec) and symbolized by

, the V representing volume, and the dot above the V representing the unit of time, and can be expressed as L/min or L/sec.

Formula for calculating resistance to flow in the airway (aw):

Resistance in the airway is equal to the difference in pressure (also called pressure gradient) divided by the flow.

Three types of flow patterns occur simulataneously in the respiratory tract, under the influence of airway resistance, which contribute to the work of breathing, and influence the distribution of gases in the lung.