Voluntary apnea evokes diving responses in obstructive sleep apnea patients

Two potentially protective responses to apnea were studied in obstructive sleep apnea (OSA) patients; the diving response and the increase in Hb concentration [Hb] via spleen contraction. Eight OSA patients and ten healthy controls performed apneas in air (A) and apneas with facial immersion in 15 A degrees C water (FIA) after inspiration and without prior hyperventilation. In each condition, subjects performed three apneas of maximal voluntary duration spaced by 2 min of rest. Cardiorespiratory parameters were measured non-invasively, and venous blood samples for [Hb] analysis were drawn before and after apneas. Mean (SD) apnea durations were similar between groups (NS). In controls, the heart rate (HR) reduction was 10 +/- A 10 % at apnea and 19 +/- A 10 % in FIA (P < 0.05). In OSA patients, however, the fall in HR was the same in both conditions, 13 +/- A 10 and 14 +/- A 8 % for A and FIA, respectively (NS). In controls, the [Hb] increase was the same in A and FIA (2.2 +/- A 2.9 and 2.1 +/- A 2.2 %), while in OSA the [Hb] increase was greater during FIA compared to A (3.3 +/- A 2.2 and 1.4 +/- A 0.9 %; P < 0.05). Apnea induces a diving response and [Hb] increase in both groups. OSA patients did not show the typical training effect of the diving response seen in apnea divers despite their frequent nocturnal apneas. However, they also deviated from normal controls in response pattern; face immersion enhanced the cardiovascular diving response in controls but not in OSA, while the hematological response was enhanced by face immersion only in OSA patients.