A flow model of respiration in health and disease

Summary. Respiratory functions operating to transport O₂ are depicted by a flow diagram which consists of eight consecutive units, each depending on the preceding one. All the units are characterized by three features: applicable drive, special capability and outgoing flow. The flows are: respiratory centre output for breathing; effects of respiratory motor nerves; contractions of respiratory muscles; ventilation movements of abdomen and thorax wall; ventilation movements of lungs and air; O₂ taken up during ventilation transport; O₂ flow through alveolar membrane; and O₂ consumed during blood transport. Equations describe connections of the units. The magnitude of the pleural pressure swing during the ventilation cycle apparently estimates the respiratory drive if the functional connection from the respiratory centre to pleural pressure is normal. Data from the literature are used to evaluate some unit parameters, at rest and during exercise. Breathlessness in somatic disease appears to originate from a low special capability of one or several units, raising, as does exercise, respiratory drive and effort.