During the past few years, respiration has come in for a bountiful share of physiologic and clinical research, but all of the research has been directed toward gaining some understanding of the exquisitely nicely balanced relations of excitatory and inhibitory influences which modify the rate, rhythm and amplitude of respiration.
Chemistry of the blood in its relation to respiratory function has also been the subject of much research, but the simpler problem of lung ventilation and its clinical analysis has been neglected. In every clinical examination we should form some definite idea about the volume, density and extensibility of the upper and lower lobes of the lungs. An understanding of these three physical attributes is the goal toward which most methods of physical examination of the lungs have been directed. Density of the lung, with some adventitious signs, has occupied the attention of clinicians much more than volume and extensibility
HOOVER CF. DIAGNOSTIC SIGNS FROM THE SCALENI, INTERCOSTAL MUSCLES AND THE DIAPHRAGM IN LUNG VENTILATION. Arch Intern Med (Chic). 1917;XX(5):701-715. doi:10.1001/archinte.1917.00090050062003