Aims: 

Sleep-disordered breathing is extremely common and is characterized by intermittent hypoxia/asphyxia due to recurrent apnoea during sleep. We sought to determine the effects of chronic intermittent hypoxia (CIH) and asphyxia (CIA) on respiratory control in conscious animals.

Methods: 

Adult male Wistar rats were exposed to either 1) alternating periods of air and hypoxia, twice per minute, 8 hours a day for 5 weeks (CIH-treated, n = 16) or 2) alternating periods of air and asphyxia, twice per minute, 8 hours a day for 5 weeks (CIA-treated, n = 16). Control rats (n = 32) were exposed to an air/air cycle under identical experimental conditions. At the end of the study, ventilation during normoxia and acute hypoxia [FiO2 = 0.12] was assessed in animals by barometric plethysmography.

Results: 

After the 5-week treatment period, normoxic and hypoxic ventilation was elevated in CIH-treated rats compared to control. The hypoxic ventilatory response was similar in the two groups. Thus, VE was 42.1 ± 4.6 and 52.0 ± 4.1 in air and hypoxia respectively in control animals and 49.3 ± 4.3* and 61.3 ± 6.4* in CIH-treated rats; mean±SEM, ml/min/100g, *P < 0.05 ANOVA. Baseline normoxic ventilation was unaffected by CIA treatment (37.1 ± 1.5 vs. 40.2 ± 1.5) although the pattern of respiration was different following CIA. However, there was a significant blunting of the hypoxic ventilatory response in CIA-treated rats compared to controls (VE in hypoxia was 76.6 ± 4.1 vs. 46.1 ± 1.6*; control vs. CIA, *P < 0.05 ANOVA).

Conclusions: 

These results indicate that chronic intermittent hypoxia and asphyxia elicit plasticity in the respiratory control system. These changes have potentially adaptive and maladaptive consequences for respiratory homeostasis.