Fig. 7. Influences of different magnitude of respiratory loop gain on breathing stability. Different ventilatory responses to reduced tidal volume are illustrated. Height of an arrow represents tidal volume. Dotted line represents optimal ventilation level. An individual with a high respiratory loop gain (A ) will instantaneously respond to the abnormal breathing but overshoot the ventilatory response, resulting in rapid decline in the ventilation. Waxing and waning pattern of unstable breathing continues in this person. In contrast, an individual with low respiratory loop gain ( C ) will slowly respond to the abnormal breathing and fail to establish a desired ventilation level. Breathing stability can be accomplished in an individual with an optimal loop gain ( B ).