The Mammalian Diving Response, An Enigmatic Reflex to Preserve Life?
Authors: W. Michael Panneton
DOI / Source: https://doi.org/10.1152/physiol.00020.2013
Date: 01 September 2013
Reading level: Intermediate
Why This Matters for Freedivers
This paper explains the “core engine” behind freediving: the automatic reflex that slows the heart, tightens blood vessels in the limbs, and forces oxygen to be spent on the brain and heart first. Knowing what triggers it (especially nose/face stimulation and calm control) and what can mess with it (stress, panic, over-effort) helps you train smarter and dive safer.
Synopsis
The mammalian diving response is one of the strongest survival reflexes we have. It’s often taught in freediving as a simple trio—apnea, bradycardia, and peripheral vasoconstriction—but this review goes deeper and argues something important: these are not one single “switch,” but an amalgam of three reflexes that can be activated together and can even override normal “homeostasis” (the usual rules your body follows on land).
The logic is simple. Underwater, you can’t breathe. So survival depends on how well you conserve and manage your internal oxygen stores—mainly oxygen bound to hemoglobin in blood and myoglobin in muscle. When oxygen stores are used up, the diver crosses the aerobic dive limit (ADL) and starts relying more on anaerobic metabolism (with lactate rising later, often after resurfacing when circulation to the limbs returns).
The review separates two big themes:
1) Adaptations vs. Reflexes
Large aquatic mammals (seals, whales, dolphins) have special adaptations that make long dives possible: larger blood volume, higher hemoglobin and myoglobin, spleens that can release stored red blood cells, and even anatomical features that help manage blood flow under extreme conditions. But the key point is that the basic diving response itself is shared across mammals, including rodents and humans. In other words: elite “marine mammal” dive capacity comes from extra hardware, but the reflex control system is widespread and ancient.
2) What triggers it and how the brain runs it
A major emphasis of this paper is that the trigger is strongly linked to facial/nasal stimulation. Research in rodents suggests the paranasal region (nose area) is especially important, with sensory input traveling via branches of the trigeminal nerve, particularly the anterior ethmoidal nerve—described here as a kind of “gatekeeper” for sensing water/irritants entering the nasal passages.
From there, the review outlines how brainstem circuits appear to coordinate the three main outputs: - Apnea: diving animals remain apneic even with extreme low O₂ and high CO₂—meaning the normal “breathe now!” chemoreflex is being overridden. - Bradycardia: largely driven by the vagus nerve via cardiac control regions near the nucleus ambiguus. - Vasoconstriction / blood pressure control: driven by sympathetic output, involving brainstem regions like the rostral ventrolateral medulla (RVLM), with selective blood flow reduction to limbs/skin/splanchnic areas while protecting flow to the brain and heart.
A practical section is the discussion of voluntary vs. forced dives. In some species, forced submersion looks more stressful and can bring more rhythm disturbances—suggesting stress and “top-down” brain influence can change the pattern. The review also highlights that higher mammals can show anticipatory changes (heart rate dropping before submersion, rising before surfacing), hinting that the diving response is not purely automatic: it can be shaped by behavior, training, and the brain’s control systems.
Overall, this is a big-picture “wiring diagram” paper: it frames the diving response as a powerful life-preserving reflex, explains why it exists, and maps the sensory triggers and brainstem control pathways that make it happen.
Abstract
The mammalian diving response is a powerful survival reflex seen across mammals (and broadly across vertebrates). It is characterized by apnea, a rapid vagally mediated bradycardia, and a strong peripheral vasoconstriction that redistributes blood flow to protect the brain and heart while conserving intrinsic oxygen stores. Aquatic mammals have additional physiological adaptations that expand oxygen storage and reduce oxygen use, but the core diving response is neurally mediated and shared with terrestrial mammals. This review summarizes key diving adaptations (oxygen stores, spleen effects, hypometabolism/hypothermia) and emphasizes evidence from rodent studies describing how nasal/facial trigeminal pathways and brainstem circuits coordinate the cardiorespiratory changes during diving.