Effects of Hook Maneuver on Oxygen Saturation Recovery After −40 m Apnea Dive—A Randomized Crossover Trial

To reduce the risk of syncope, trained breath-hold divers (BHDs) use a specialized breathing technique after surfacing called “hook breathing” (HB). It consists of a full inspiration followed by a Valsalva-like maneuver and with subsequent exhalation performed against resistance to generate continuous positive airway pressure during exhalation. This study analyzed the influence of HB on oxygen saturation recovery after a −40 m depth apnea dive in trained BHDs. Thirteen BHDs performed two dives to −40 m at different days, one followed by HB after a dive and the other using usual breathing (UB). To detect signs of lung edema, ultrasound B-line measurements were conducted before, 10 min after the dive, and within 1 h after the dive. To detect oxygen saturation recovery, pulse oximetry was recorded before and immediately after surfacing. Both groups exhibited significant increases in SpO2 over time (UB: F (2.25, 24.7) = 22.1, p < 0.001, ηg2 = 0.612; HB: F (2.11, 23.2) = 29.0, p < 0.001, ηg2 = 0.688). Significant differences in SpO2 were observed between the HB and UB groups at 30–45 s post-apnea, with higher SpO2 values in the HB group; between 1.64 and 5.08% of SpO2 in favor of the HB intervention. Four participants showed ultrasound B-lines within ten minutes post-dive. After a 40 m apnea dive, the results revealed significant SpO2 recovery from 30 s to 45 s, with the HB recovering more rapidly. No differences were found at earlier (10–25 s) or later time points (50–60 s).