An ambulatory patient monitoring system (100) is provided for measuring and storing predetermined diagnostic parameters of a patient. The monitoring system includes a personal type computer (120) which may be selectively coupled to the portable portion (102) of system (100). Portable portion (102) may include one or more monitoring modules, such as ECG monitoring unit (110) and blood pressure monitoring unit (210). When ECG monitoring unit (110) and blood pressure monitoring unit (210) are disposed in side-by-side relationship and with respective optical interfaces (50, 254) in optical alignment, the two units operate in concert. ECG monitoring unit (110) supplies an R-wave gating signal to blood pressure monitoring unit (210) for establishing a window in which the receipt of a Korotkoff sound is expected. Additionally, the ECG unit (110) may trigger the blood pressure unit (210) to take a reading responsive to unit (110) identifying a predetermined abnormality in the ECG signal. Alternately, ECG monitoring unit (110) and blood pressure monitoring unit (210) may be used independently of one another as separate monitoring devices.