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Figure 2 Superior vena cava Doppler from a patient with constrictive pericarditis shows little respiratory changes in systolic forward flow velocity (bottom) from inspiration to expiration (arrows), in contrast to marked phasic inspiratory augmentation of forward flow velocity in chronic obstructive pulmonary disease (COPD) (top). S, systolic forward flow; D, diastolic forward flow; ins, inspiration; exp, expiration.