Diving response after a one-week diet and overnight fasting

Background: We hypothesized that overnight fasting after a short dietary period, especially with carbohydrates, could allow performing breath-hold diving with no restraint for diaphragm excursion and blood shift and without any increase of metabolism, and in turn improve the diving response. Methods: During two separate sessions, 8 divers carried out two trials: (A) a 30-m depth dive, three hours after a normal breakfast and (B) a dive to the same depth, but after following a diet and fasting overnight. Each test consisted of 3 apnea phases: descent, static and ascent whose durations were measured by a standard chronometer. An impedance cardiograph, housed in an underwater torch, provided data on trans-thoracic fluid index (TFI), stroke volume (SV), heart rate (HR) and cardiac output (CO). Mean blood pressure (MBP), arterial O-2 saturation (SaO(2)), blood glucose (Glu) and blood lactate (BLa) were also collected. Results: In condition B, duration of the static phase of the dive was longer than A (37.8 +/- 7.4 vs. 27.3 +/- 8.4 s respectively, P < 0.05). In static phases, mean Delta SV value (difference between basal and nadir values) during fasting was lower than breakfast one (-2.6 +/- 5.1 vs. 5.7 +/- 7.6 ml, P < 0.05). As a consequence, since mean. HR values were equally decreased in both metabolic conditions, mean. CO value during static after fasting was lower than the same phase after breakfast (-0.4 +/- 0.5 vs. 0.4 +/- 0.5 L . min(-1) respectively, P < 0.05). At emersion, despite the greater duration of dives during fasting, SaO(2) was higher than A (92.0 +/- 2.7 vs. 89.4 +/- 2.9 % respectively, P < 0.05) and BLa was lower in the same comparison (4.2 +/- 0.7 vs. 5.3 +/- 1.1 mmol L-1, P < 0.05). Conclusions: An adequate balance between metabolic and splancnic status may improve the diving response during a dive at a depth of 30 m, in safe conditions for the athlete's health