Abstract: A diagnostic system and methods for detecting abnormalities in central and peripheral respiratory control chemoreceptors is provided. The system and methods are based on distinguishing between relative sensitivities of chemoreceptors of individuals with normal and compromised chemoreceptors. Predetermined combined carbon dioxide and oxygen levels are provided to a subject for a specified period of time, during which physiological parameters are measured as an indication of response to the chemoreceptors relative sensitivities. A preferred method provides higher than normal combined concentrations of carbon dioxide and oxygen, and lower than normal combined concentrations of carbon dioxide and oxygen, and measures physiological parameters to calculate an index, taking into account the basic parameters of the patient such as age, cardio-pulmonological condition and BMI, and provide a diagnosis regarding the function of the respiratory control chemoreceptors.