“…J. Radiol. 36, 660 (1964) Thorax (1) Pulmonary Ventilation It has been shown that variations in radiographic density of the lungs during respiration and during various phases of the cardiac cycle can be recorded by photodensitometry (Marchal & Marchal 1955, Marchal et al 1959, Steiner et al 1960, Oderr 1964).…”