Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:have mitral regurgitation secondary to congestive heart failure have a unique pattern of flow across the mitral valve in systole which consists of early systolic accentuation of mitral regurgitant flow with lesser flow in the latter two-thirds of systole (15).
Category: