Final answer:
An analog-to-digital converter is required to interface a water-sealed spirometer to a computer, as it converts the analog signals into digital format for computer processing.
Step-by-step explanation:
To interface a water-sealed spirometer to a computer, the required component would be an analog-to-digital converter. This device converts the analog signals from the spirometer, which measure lung capacity and function, into digital signals that a computer can process and record.
The options provided such as a pneumotachometer and a flow transducer are used for measuring the rate of airflow, and while they could be part of a spirometry system, they are not specifically for interfacing with a computer. A barometric pressure sensor is not directly required for interfacing purposes but may be used to adjust readings for atmospheric pressure variations.