Arterial oxygen saturation and heart rate variation during breath-holding:: comparison between breath-hold divers and controls

Breath-holding induces cardiovascular responses, notably bradycardia and peripheral vasoconstriction, which are known collectively as the diving response. This response is oxygen-conserving, i.e. an augmented response attenuates arterial oxygen desaturation, and is enhanced by apnoea training. To test this hypothesis, we compared heart rate (HR) and arterial oxygen saturation (SaO(2)) in breath-hold divers (BHD) and non-divers (ND). Nine BHD and nine healthy ND performed two static apnoeas (for 30s and 45s) and two dynamic apnoeas (for 30s and 45s) while swimming underwater at 0.7 m circle s(-1). The pool temperature was 26 degrees C. The apnoeas were performed at 60% of forced vital capacity. Heart rate (HR) and SaO(2) were recorded before breath-holding and at its end and are expressed in % change from rest values (Delta HR and Delta SaO(2)). Comparisons between BHD and ND showed that Delta SaO(2) were lower in divers after both static apnoeas for 30s and 45s (-2.8% vs. -5.5%; -3.2% vs. 6.3%; p < 0.05, respectively) and dynamic apnoeas (-6% vs. -10.1%; -7.2% vs. -12.3%; p < 0.05, respectively). The change in HR did not differ between the two groups and negative linear relations were found between Delta HR and Delta SaO(2) in both divers and ND (r = 0.66 and 0.61, respectively; p < 0.001). Moreover, the slope was lower for the divers (- 0.785 vs. -0.1429; p < 0.001). Our results suggest that apnoea training explained the greater oxygen conservation seen in the divers in both static and dynamic conditions.