Voluntary apnea evokes diving responses in obstructive sleep apnea patients.
Level 4 - case-series / case-control
Case-control physiological comparative study
PubMed 25549785 · doi:10.1007/s00421-014-3083-7
What was done
Eight obstructive sleep apnea (OSA) patients and ten healthy controls performed voluntary apneas under two experimental conditions: apnea in air (A) and apnea with facial immersion in 15 °C water (FIA) following inspiration without prior hyperventilation. In each condition, subjects completed three maximal voluntary apneas separated by 2 minutes of rest. Cardiorespiratory parameters were recorded non-invasively, and venous blood samples were collected before and after apneas to measure hemoglobin concentration ([Hb]).
What was found
Mean apnea durations did not differ significantly between groups. In healthy controls, heart rate (HR) reduction was significantly greater with facial immersion (10 ± 10% in A vs 19 ± 10% in FIA, P < 0.05). In OSA patients, HR reduction remained unchanged across conditions (13 ± 10% in A vs 14 ± 8% in FIA, not significant). For [Hb] increase, controls showed no difference between conditions (2.2 ± 2.9% in A vs 2.1 ± 2.2% in FIA), whereas OSA patients showed a significantly higher [Hb] elevation during facial immersion compared to air (3.3 ± 2.2% in FIA vs 1.4 ± 0.9% in A, P < 0.05).
Why it matters
This study shows that recurrent nocturnal apneas in OSA patients do not induce the trained cardiovascular diving response seen in elite divers, revealing an altered physiological pattern where cold-face cardiovascular reflexes are blunted while hematological responses remain responsive.
Limits
The sample size is very small (8 OSA patients, 10 controls), limiting statistical power and generalizability. Spleen contraction was inferred from venous [Hb] rather than measured directly via ultrasound. Awake, voluntary apneas under normoxic conditions do not fully replicate the pathophysiology, sleep state, or negative intrathoracic pressures of spontaneous obstructive apneas during sleep.
Cited by
- context Sleep disturbances such as mild sleep apnea trigger splenic contractions at night, causing iron biomarkers to fluctuate significantly on blood tests.