FIG 10: In patients with heart failure and periodic breathing, the so-called loop gain (LG) plays a crucial role.^[1]  Loop gain describes the ratios of the various responses to any kind of ventilation disturbance.  For example, in an acoustic arousal or any other disturbance of the respiration the result will be hyperventilation.  The ventilatory rate increases and the CO₂ level is reduced.  This change in CO₂ is measured at the chemoreceptors in the brainstem and the carotid arteries, which then signal the brainstem either to stimulate or to stop ventilation.  Patients with CSR have a high loop gain, meaning that they respond more intensively to any change in ventilation, with a more rapid reaction of the chemoreceptors and a stronger reaction of the brain stem.  This leads to hyperventilation and also a cessation of respiration, in an overshooting and undershooting manner.