"The First Mathematical Description of the Pressure-Volume Diagram 

"Not until 60 years after 1899 Otto Frank's mathematical formulation of the volume-pressure diagram and his concept of the mechanism of the cardiac work of the left ventricle cardio-physiologists began to rediscover Frank's work systematically. Frank's scientific development proves his constant commitment to and deep interest in understanding and analysing physiological problems mathematically. Consequently Frank worked on the quality and theory of physiological instruments and the problems of measurement, to calculate the influence in experimental research of the cardio-vascular system. Besides Frank's publications on different types of manometers his theory of "Windkessel" function as a model of the mechanics of the left ventricle and the different energies of the cardiac work are of importance even today, although we know only few details of his life as a pupil of Carl Ludwig and Carl von Voit and as a professor of physiology in Giessen and Munich." (B. Lohff, https://pubmed.ncbi.nlm.nih.gov/10705804/) Translated into English by K. Sagawa K, R.K. Lie, J. Schaefer, J Mol Cell Cardiol 22 (1990) 253-277.