EMS Anatomy & Physiology - Mammalian Diving Response Syndrome

EMS Providers should be familiar with the Mammalian Diving Response Syndrome as it is a physiological reflex that can have critical implications during emergency scenarios, especially those involving drowning, cold-water immersion, or apnea. 

Here are some key points to know:

Definition:

The Mammalian Diving Response Syncdrome is a reflex primarily triggered by submersion in cold water or holding one’s breath. 

It is characterized by specific physiological changes that help conserve oxygen and protect vital organs during hypoxia. 

This response is more pronounced in children and is part of an evolutionary adaptation found in many mammals.

Physiological Mechanisms:

The diving response involves three primary components:

- Bradycardia: The heart rate slows down significantly to reduce oxygen consumption by non-essential tissues.

- Peripheral Vasoconstriction: Blood vessels in the extremities constrict, redirecting blood flow to vital organs like the brain and heart.

- Blood Shift (during deep dives): In humans, blood is directed away from the lungs and limbs to maintain pressure and prevent lung collapse during deep dives.

Triggers:

Submersion of the face in water, especially cold water.

Holding breath (apnea).

Psychological stress, such as fear or panic.

Clinical Implications for EMS: 

Understanding the diving response is crucial because it affects how a patient may present and how to manage their condition:

- Bradycardia Management: EMS providers might encounter significantly reduced heart rates in drowning or near-drowning victims.

Bradycardia could be misinterpreted as a sign of severe hypoxia, but it’s a protective mechanism rather than a sign of complete cardiac failure.

Avoid aggressive measures to increase heart rate unless the patient shows other signs of instability.

- Respiratory Considerations: The diving response may cause prolonged breath-holding, so patients might appear apneic or have delayed hypoxic symptoms.

Observe for hypoxia carefully and administer oxygen as indicated.

- Pediatric Considerations: The diving response is more prominent in children, which is why some drowning victims can survive prolonged submersion with relatively less neurological damage.

Cold water can extend the safe resuscitation window in pediatric patients.

- Cardiac Arrest in Cold Water: During cold water submersion, the body’s metabolic rate decreases significantly, which can potentially improve resuscitation outcomes even after prolonged submersion.

Follow hypothermia protocols and prolonged resuscitation efforts in cases of drowning in cold water.

Treatment and Management:

- ABC Approach: Focus on Airway, Breathing, and Circulation.

Hypothermia Management: Consider hypothermia treatment protocols as the mammalian diving response is often accompanied by cold water immersion.

Consider ECLS/ECMO in severe cases: In cases of cardiac arrest with diving reflex activation, specialized centers might use Extracorporeal Life Support (ECLS) or Extracorporeal Membrane Oxygenation (ECMO).

Key Takeaways:

Do not confuse bradycardia with imminent cardiac arrest. It can be a protective adaptation.

Cold-water submersion can improve survival outcomes—keep in mind for prolonged resuscitation in cold environments.

Children are more likely to benefit from the diving response due to their physiology.

Understanding this reflex allows EMS providers to better assess, treat, and manage patients exposed to cold water or other scenarios that can induce the diving response.

Who Discovered The Mammalian Diving Response Syndrome?

The mammalian diving response was first described by Edmund Goodwyn in 1786. However, it was extensively studied and popularized by Paul Bert and later Johan E. Severin Nilsson in the late 19th and early 20th centuries.

Goodwyn, a British physician, observed physiological changes in animals and humans during submersion. His initial work laid the foundation for understanding the reflex, but it was Paul Bert who made significant contributions by studying the effects of breath-holding and diving on the heart rate and blood flow.

Johan E. Severin Nilsson, a Swedish physiologist, further refined the concept, investigating how immersion and apnea affected circulation and oxygen usage in various mammals. His research solidified the understanding of the mammalian diving reflex as a protective adaptation seen across multiple species, including humans.

Further Reading

Alexander, M. & Belle, R. (2017) Advanced EMT: A Clinical Reasoning Approach (2nd Ed). Hoboken, New Jersey: Pearson Education

Bledsoe, B. E., Cherry, R. A. & Porter, R. S (2023) Paramedic Care: Principles and Practice (6th Ed) Boston, Massachusetts: Pearson

Godek, D., & Freeman, A. M. (2022) Physiology, Diving Reflex. Treasure Island, Florida: StatPearls Publishing

Mistovich, J. J. & Karren, K. J. (2014) Prehospital Emergency Care (11th Ed). Hoboken, New Jersey: Pearson Education

Panneton, W. M. (2013) The Mammalian Diving Response: An Enigmatic Reflex To Preserve Life? Physiology 28(5): 284-97. Accessed October 6, 2024

Peate, I. & Sawyer, S (2024) Fundamentals of Applied Pathophysiology for Paramedics. Hoboken, New Jersey:  Wiley Blackwell