With the increasing number of premature infants surviving to reach BPD units, one wonders how long the system can survive the extremely high cost of long term care (about $700,000/year in the BPD unit and $300,000/year for home care). One possible answer is reliable monitoring of physiological variables which permit 1) more effective respiratory management and 2) management by less sophisticated care givers (including parents), which could have a large impact toward moving patients to home care much earlier as well as further reducing the cost of home care. However, because of the unavailability of needed noninvasive monitoring (P(a)CO2 in particular), and the lack of reasonable access to arterial blood, these patients are managed on ventilators in the hospital and later in the home without access to the guidance normally provided by P(a)CO2 (as well as P(v)-O(2) and C.O.) monitoring. This proposal addresses the development of a noninvasive P(a)CO2, P(v)- CO2, and cardiac output (C.O.) monitor designed to overcome both physiological and technical problems of current systems which prevent their effect utilization for monitoring of patients such as those described. The proposed technique utilizes an inert gas technique applied to the lung for monitoring the V/Q distribution of gas exchanging units to provide data for relating continuously expired CO2 (P(E)CO2) measurements to P(a)CO2 values. A key to practical implementation of the method for home use is the adaptation of small, economical sensors - newly developed for environmental uses - to serve as the system's gas analyzer. The method imposes no additional recumberance for patients on ventilators.