Cardiovascular Responses during Free-Diving in the Sea

Cardiac output has never been assessed during free-diving diving in the sea. Knowledge of human diving response in this setting is therefore scarce. 3 immersions were performed by 7 divers: at depths of 10 m, 20 m and 30 m. Each test consisted of 3 apnea phases: descent, static and ascent. An impedance cardiograph provided data on stroke volume, heart rate and cardiac output. Mean blood pressure, arterial O-2 saturation and blood lactate values were also collected. Starting from a resting value of 4.5 +/- 1.6 L.min(-1), cardiac output at 10 m showed an increase up to 7.1 +/- 2.2 L.min(-1) (p < 0.01) during the descent, while conditions during the static and ascent phases remained unchanged. At 20 m cardiac output values were 7.3 +/- 2.4 L.min(-1) and 6.7 +/- 1. 2 L.min(-1) during ascent and descent, respectively (p < 0.01), and 4.3 +/- 0.9 L.min(-1) during static phase. At 30 m cardiac output values were 6.5 +/- 1.8 L.min(-1) and 7.5 +/- 2 L.min(-1) during descent and ascent, respectively (p < 0.01), and 4.7 +/- 2.1 L.min(-1) during static phase. Arterial O-2 saturation decreased with increasing dive depth, reaching 91.1 +/- 3.4 % (p < 0.001 vs. rest) upon emergence from a depth of 30 m. Blood lactate values increased to 4.1 +/- 1.2 mmol.L-1 at the end of the 30 m dive (p < 0.001 vs. rest). Results seem to suggest that simultaneous activation of exercise and diving response could lead to an absence of cardiac output reduction aimed at an oxygen-conserving effect.