Sympathetic and cardiovascular responses to glossopharyngeal insufflation in trained apnea divers

Glossopharyngeal insufflation (lung packing) is a common maneuver among experienced apnea divers by which additional air is pumped into the lungs. It has been shown that packing may compromise cardiovascular homeostasis. We tested the hypothesis that the packing-mediated increase in intrathoracic pressure enhances the baroreflex-mediated increase in muscle sympathetic nerve activity (MSNA) in response to an exaggerated drop in cardiac output (CO). We compared changes in hemodynamics and MSNA (peroneal microneurography) during maximal breath-holds without and with prior moderate packing (0.79 +/- 0.40 liters) in 14 trained divers (12 men, 2 women, 26.7 +/- 4.5 yr, body mass index 24.8 +/- 2.4 kg/m(2)). Packing did not change apnea time (3.8 +/- 1.0 vs. 3.8 +/- 1.2 min), hemoglobin oxygen desaturation (-17.6 +/- 12.3 vs. -18.7 +/- 12.8%), or the reduction in CO (1 min: -3.65 +/- 1.83 vs. -3.39 +/- 1.96 l/min; end of apnea: -2.44 +/- 1.33 vs. -2.16 +/- 1.44 l/min). On the other hand, packing dampened the early, i.e., 1-min increase in mean arterial pressure (MAP, 1 min: 9.2 +/- 8.3 vs. 2.4 +/- 11.0 mmHg, P < 0.01) and in total peripheral resistance (relative TPR, 1 min: 2.1 +/- 0.5 vs. 1.9 +/- 0.5, P < 0.05) but it augmented the concomitant rise in MSNA (1 min: 28.0 +/- 11.7 vs. 39.4 +/- 12.7 bursts/min, P < 0.001; 32.8 +/- 16.4 vs. 43.9 +/- 14.8 bursts/100 heart beats, P < 0.01; 3.3 +/- 2.1 vs. 4.8 +/- 3.2 au/min, P < 0.05). We conclude that the early sympathoactivation 1 min into apnea after moderate packing is due to mechanisms other than excessive reduction in CO. We speculate that lower MAP despite increased MSNA after packing might be explained by vasodilator substances released by the lungs. This idea should be addressed in future studies.