SELF-CONTROL AND EXTERNAL CONTROL OF MECHANICAL VENTILATION GIVE EQUAL AIR HUNGER RELIEF

Elevated end-tidal partial pressure of CO2 (PETCO2) causes air hunger; this sensation becomes intense with a relatively small rise in PETCO2 if ventilation is held constant. Spontaneously breathing subjects inc rease ventilation in response to CO2 thereby greatly diminishing air h unger. In healthy subjects and ventilator-dependent patients, experime nter-induced increases in ventilator tidal volume (VT) relieve air hun ger even if PETCO2 is kept elevated. We addressed two questions: (1) C an paralyzed, ventilator-dependent patients use the sensation of air h unger to effectively control ventilator VT using nonrespiratory motor pathways; and (2) Do subjects obtain more relief when in control of th eir own ventilator? Four subjects were trained to increase ventilator Vr using a mouth-operated switch. Subjects' ratings of air hunger inte nsity in response to elevated PETCO2 were compared during three condit ions: (1) constant VT; (2) subject-controlled VT; and (3) experimenter -controlled VT. When given control of their ventilator, all subjects i ncreased VT in response to increased PETCO2, thereby relieving air hun ger. Air hunger relief was similar when the experimenter mimicked thes e VT changes. These results suggest that: (1) ventilator-dependent pat ients can use sensation, conscious decisions, and nonrespiratory motor pathways to achieve an appropriate respiratory response to increased P-CO2 and (2) control of one's own ventilation is unimportant in these circumstances.