Cheyne-Stokes respiration: hypoxia plus a deep breath that interrupts hypoxic drive, initiating cyclic breathing

In the 19th Century, Cheyne and Stokes independently reported cycles of respiration in patients with heart failure, beginning with apnea, followed by a few breaths. However Cheyne–Stokes respiration (C–SR) can also occur in healthy individuals with sleep, and was demonstrated in 1908 with voluntary hyperventilation, followed by apnea that Haldane blamed on hypoxia, subsequently called post-hyperventilation apnea. Additional theories explaining C–SR did not appear until 1954, based on control theory, specifically a feed-back regulator controlling CO₂. This certainly describes control of normal respiration, but to produce an unstable state such as C–SR requires either a very long transit time (3½ min) or an increase of the controller gain (13 times), physiologically improbable. There is general agreement that apnea initiates C–SR but that has not been well explained except for post-hyperventilation apnea, and that explanation is not compatible with a study by Nielsen and Smith in 1951. They plotted the effects of diminished oxygen on ventilation (V) in relation to CO₂ (Fig. 1). They found that the slope of V/CO₂ (gain) increased with hypoxia, but it flattened at a moderate CO₂ level and had nointercept with zero (apnea). It is also incompatible with our published findings in 1975 that showed that apnea did not occur until an extreme level of hypoxia occurred (the PO₂ fell below 10 mmHg), followed shortly by gasping. Much milder hypoxia underlies most cases of C–SR, when hypoxic drive replaces the normal CO₂-based respiratory drive, in a failsafe role. I hypothesize that the cause of apnea is a brief interruption of hypoxic drive caused by a pulse of oxygen from a stronger than average breath, such as a sigh. The rapidity of onset of apnea in response to a pulse of oxygen, reflects the large pressure gradient for oxygen from air to lung with each breath, in contrast to CO₂. With apnea, there is a gradual fall in oxygen, resulting in a resumption of hypoxic drive, and the cycle of C–SR continues until the next large breath. This novel theory, that a pulse of oxygen interrupts hypoxic drive to cause the initiating apnea of C–SR, is compatible with the known causes of C–SR: onset of sleep, mild hypoxia with congestive heart failure, and neurologic disorders. It is also compatible with factors known to abolish C–SR: waking, oxygen supplementation, and drugs that increase alertness such as caffeine.Testing of the hypothesis would require beat by beat recording of respiration, and arterial oxygen with a response time fast enough to demonstrate the rapid suppression of hypoxic drive. Alternatively, using a different theoretical approach such as limit-cycle oscillators instead of control theory.