To obtain interpretable results from spirometry, it is essential that the patient give full effort during testing. At least 3 tests of acceptable effort are performed to ensure reproducibility of results. Flow volume loops provide a graphic illustration of a patient's spirometric efforts. Flow is plotted against volume to display a continuous loop from inspiration to expiration. The overall shape of the flow volume loop is important in interpreting spirometric results. The volume versus time curve is an alternative way of plotting spirometric results and is another useful illustration of the patient’s performance.