Accessing chemosensitivity and ventilatory stability from transient stimuli.

The degree of ventilatory stability of human subjects is inferred from the presence or absence of oscillations in ventilation in response to a brief CO2 disturbance using the method of pseudorandom stimulation. Simultaneously, chemosensitivity is measured. Stability and chemosensitivity are compared in hyperoxia between wakefulness and stage 2 non-rapid eye movement (NREM) sleep and between normoxia and hyperoxia awake. Stability is unchanged between wakefulness and sleep but chemosensitivity decreases in sleep. In contrast, stability is reduced in normoxia whereas chemosensitivity is larger than in hyperoxia. It is concluded that chemosensitivity and ventilatory stability may change independently, implying that chemosensitivity alone is not an adequate indicator of the likelihood of a subject to exhibit periodic breathing.