The key or just a cog in the wheel to operability assessment?

T he ability to measure the hydrostatic pressure in a capillary bed (Pc) was an impetus for the development of the arterial occlusion method [1]. The relevance of Pc in pulmonary circulation is its role in pulmonary oedema formation. In order to accurately measure Pc, the isogravimetric method and the double occlusion technique have served as standards [2, 3]. However, both techniques require surgical isolation of the organ. The pulmonary artery occlusion technique was developed for in vivo use with a standard fluid-filled pulmonary artery catheter. When incorporated, the technique enabled Pc measurements as part of a standard right heart catheterisation procedure. But interest in this technique appeared to wane after discovering that the pulmonary artery occlusion technique, rather than measuring Pc, was measuring a pre-capillary pressure in the .80–100 mm calibre range [1, 4]. Although this limited its application in pulmonary oedema research, the technique would later find renewed interest in the field of pulmonary hypertension (PH) [4, 5].