Respiratory variables, including tidal volume and respiratory rate, display significant variability or the biological variability (BV). Recent studies have suggested that the BV would contain clinical information. The author has been trying to reveal why BV can contain clinical information by application of a stochastic optimal control theory for noisy spontaneous breathing. The author has obtained a Shrödinger’s wave equation for describing noisy breathing. Regarding to Bohm’s model of quantum theory, the author has proposed a new potential field (BV), which would act to integrate cells to an organ. It is necessary to measure biological variability in order to understand what a living organ is.