That is, if the radius is 1 the resistance is 1. Thus any change in airway diameter will impact flow dramatically. This intrapleural pressure keeps the lungs expanded. During inspiration, the diaphragm contracts, increases the volume of the thoracic cavity thereby decreasing intrapleural pressure. Air moves into the lungs.
Expiration is a reversal of that process.
The elasticity and distensibility of the lung can be measured as compliance. The compliance is equal to the change of lung volume for a given pressure differential. Air moves into the nasal turbinates where air is conditioned by adding moisture and heat. Air moves into the pharynx. Here there is a connection to the guttural pouches.