Sympathetic And Cardiovascular Responses To Glossopharyngeal Insufflation In Trained Apnea Divers
Authors: Karsten Heusser, Gordan Dzamonja, Toni Breskovic, Craig D. Steinback, André Diedrich, Jens Tank, Jens Jordan, Zeljko Dujic
DOI / Source: 10.1152/japplphysiol.00522.2010
Date: 23 September 2010
Reading level: Intermediate
Why This Matters for Freedivers
Packing doesn’t just “add air” — it can change your nervous system and circulation immediately. This study shows that even moderate packing can trigger a stronger sympathetic (fight-or-flight) response early in the breath-hold while blood pressure rises less than expected, which helps explain why some divers feel unstable or light-headed and why “more packing” can come with a real physiological cost.
Synopsis
Glossopharyngeal insufflation (lung packing) is a technique where a diver uses the mouth and throat like a pump to force extra air into the lungs after a full inhale. It’s common among experienced freedivers, but it can also disrupt cardiovascular stability. This paper looked at why that happens by measuring not only heart rate and blood pressure, but also direct nerve signals controlling blood vessel tone.
Fourteen trained apnea divers performed maximal breath-holds lying down, once with a normal full inhale and once after moderate packing (on average adding about 0.8 liters). The researchers measured heart rate, blood pressure, cardiac output, total peripheral resistance, oxygen saturation, and—most importantly—muscle sympathetic nerve activity (MSNA) using microneurography (a technique that records sympathetic nerve bursts in a peripheral nerve).
The main finding was that packing did not change the overall apnea duration, the degree of oxygen desaturation, or the size of the cardiac output drop during the breath-hold. In other words, in this study moderate packing didn’t give measurable “more apnea time” or “more oxygen reserve,” and it didn’t make the cardiac output collapse worse than it already does during a full-inhale apnea.
But packing did change the early cardiovascular control pattern in a surprising way. About one minute into the breath-hold (the “easy-going” phase before strong struggle contractions), divers showed: - Higher sympathetic activation after packing (more MSNA bursts and greater total nerve activity). - Smaller increases in mean arterial pressure and smaller increases in vascular resistance than during the non-packed breath-hold.
That combination looks paradoxical: if the nervous system is sending a stronger “constrict blood vessels” signal, why don’t pressure and resistance rise more? The authors suggest that packing might trigger the release of vasodilating substances from the lungs when they’re stretched and pressurized, which could partially cancel out the constrictor effect of the sympathetic nerves. They discuss candidates like nitric-oxide-related signaling or prostacyclin-type pathways as plausible explanations.
Later in the breath-hold (near the end), the differences between packed and non-packed apneas largely disappeared. Sympathetic activity became extremely high in both conditions as asphyxia built, and the end-stage autonomic pattern looked similar. This again points to packing’s biggest “signature” being early-phase instability rather than late-phase effects.
The practical safety message is important: the divers here used moderate packing, and even that was enough to create a distinct autonomic and vascular response. The authors caution that these results cannot be extrapolated to aggressive packing (“overpacking”), which may have much more dramatic hemodynamic consequences and could contribute to presyncope/syncope in real-world settings.
Abstract
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 during maximal breath-holds without and with prior moderate packing in trained divers. Packing did not change apnea time, hemoglobin oxygen desaturation, or the reduction in CO. On the other hand, packing dampened the early increase in mean arterial pressure and total peripheral resistance but augmented the concomitant rise in MSNA. We conclude that the early sympathoactivation after moderate packing is due to mechanisms other than excessive reduction in CO, and we speculate that lower arterial pressure despite increased MSNA after packing might be explained by vasodilator substances released by the lungs.