Because the performance of the chest bellows deteriorates with age, the elderly may be more dependent than the young on compensatory adjustments of the respiratory controller to forestall respiratory failure. However, sensorimotor function also declines with advancing years, and this may interfere with the adequate operation of the respiratory control system. For these reasons, the risk of respiratory failure in the elderly is great. In the proposed project, the operation of the respiratory control system will be compared in persons over 65 years of age and under 35 years of age. The studies will include evaluation of respiratory responses to chemical stimuli (hypoxia and hypercapnia) exercise, flow resistive and elastic loads. Respiratory responses will be assessed from measurements of ventilation, occlusion pressures, and respiratory muscle electrical activity. The ability of the elderly as compared to younger individuals to detect and appreciate changes in respiratory system mechanics and ventilation will be assessed by standard psychophysical techniques, and will be related to respiratory responses. Measurements of ventilation and the occurrence of apneic periods during sleep will be related to waking responses to mechanical and chemical stimuli. We expect that the data obtained will allow: 1) the identification of any specific defects in respiratory control that occur with age so that remedial measures can be instituted and 2) the development of tests which could be used to select elderly individuals who are at greatest risk of developing respiratory insufficiency because of controller defects.