FIGURE 1.

Breathing phases arise from a combination of rhythm- and pattern-generating mechanisms

A–C: schematic of breathing phase coordination and reconfiguration during rest, speech, exercise, and severe hypoxia. A: during rest, breathing alternates between inspiration (purple) and postinspiration (blue). Prior to speaking, the depth of inspiration (tidal volume) is adjusted to the anticipated length of the vocalization. Vocalization occurs during an extended postinspiratory phase. B: during heavy exercise, breathing generally alternates rapidly between inspiration and active expiration (red) to match increased metabolic demands. C: during severe hypoxia, breathing reconfigures to produce a slow one-phase inspiratory rhythm. D–E: processes of rhythm and pattern generation can be independent or interdependent. D: when independent, perturbations of rhythm (purple) do not alter pattern (black), and perturbations of pattern do not alter rhythm. E: when interdependent, perturbations of rhythm also alter pattern, and perturbations of pattern also alter rhythm.