Atemwiderstand

Atemwiderstand, in physiology often referred to as airway resistance, is the opposition to airflow within the respiratory tract during breathing. It results from friction between the moving air and the airway walls and, in parts of the system, from turbulence. The overall resistance depends on the size and geometry of the airways as well as the flow regime.

In principle, airway resistance can be described by the relationship Raw = ΔP / V̇, where ΔP is the pressure difference between the mouth and the alveoli and V̇ is the airflow. In healthy adults during quiet breathing, Raw usually falls within a low range (roughly 0.5 to 2 cm H2O·s/L). Larger airways contribute most of the resistance, while many small airways collectively have a smaller single‑airway impact but can still influence total resistance, especially when narrowed.

Several factors can increase Atemwiderstand: bronchoconstriction, inflammation, mucus accumulation, edema, tumors, external compression, or dynamic airway compression during expiration. Airway diameter changes with lung volume, so resistance typically rises at lower lung volumes and with certain disease states. Conversely, bronchodilators or anti‑inflammatory therapies can reduce resistance by widening airways and decreasing mucosal swelling.

Measurement and clinical relevance: resistance can be assessed indirectly by spirometry and plethysmography or directly by measuring pressure–flow relationships with pneumotachography. Clinically, elevated Atemwiderstand is a hallmark of asthma, chronic obstructive pulmonary disease, and other obstructive conditions, and it has implications for work of breathing and ventilator settings.