Does Your Baseline Heart Rate Predict Your Diving Reflex Response?
Yes. This study of 65 healthy volunteers found that your resting heart rate strongly predicts how your heart responds to cold water facial immersion. People with lower minimum heart rates at rest showed stronger cardiodepressive (heart-slowing) responses during the simulated diving test.
The diving response varies dramatically between individuals. Some people experience mild heart slowing, while others may have bradycardia below 30 beats per minute or even brief asystole (heart stopping). This 2023 study from Medical University of Gdansk explored whether baseline heart rate characteristics could help predict these responses.
Dr. Kumar’s Take
This is an important finding for anyone using cold water immersion therapeutically. The unpredictability of the diving response has always been a concern. Strong vagal activation can slow the heart dangerously in some individuals. This study suggests we might be able to identify who’s at higher risk by simply measuring their resting heart rate before they get in the water. That’s a practical, low-cost screening approach that could improve safety.
Study Design
Researchers tested 65 healthy volunteers:
- 37 women, 28 men
- Average age 21 years (range 20-27)
- Average BMI 21.49 kg/m²
The cold-water face-immersion test involved:
- Maximum inhalation
- Breath-holding
- Voluntary facial immersion in cold water (8-10°C)
- Immersion maintained as long as possible
Heart rate was measured at rest (minimum, average, maximum) and during the test (minimum and maximum).
Key Findings
Minimum resting heart rate predicts diving response: There was a strong relationship between the lowest heart rate at rest and the heart-slowing response during facial immersion.
Maximum heart rate correlation: The maximum heart rate during the test related to the maximum resting heart rate before the test.
Neurogenic regulation matters: Heart rate variability measures suggested that the autonomic nervous system’s baseline tone influences the diving response.
Anticipatory effect: Heart rate typically increases for several seconds before and after immersion begins. This reflects emotional arousal and the body’s stress response.
Why This Happens
The diving response activates both divisions of the autonomic nervous system simultaneously:
Parasympathetic activation: The vagus nerve slows the heart, sometimes dramatically. In extreme cases, heart rate can drop below 30 bpm. The sinoatrial node (the heart’s main pacemaker) may be suppressed.
Sympathetic activation: Blood vessels constrict in the arms, legs, and gut. Blood pressure rises. Blood is redirected to the brain and heart.
This dual activation is why responses vary so much. The net effect depends on how strongly each system responds and which predominates.
The Risk Factor
The study notes that strong cardiodepressive reactions can be dangerous. In extreme cases, the vagus nerve activation can cause:
- Severe bradycardia (very slow heart rate)
- Brief asystole (heart temporarily stops)
- Cardiac arrhythmias
Such events are documented in divers. The ability to predict who might have stronger responses could help prevent accidents.
The Cold Shock Connection
The trigeminal nerve in facial skin detects cold water. This triggers the trigeminocardiac reflex, which works together with the chemoreceptor reflex (triggered by breath-holding) to produce the full diving response. The colder the water (this study used 8-10°C), the stronger the trigeminal stimulation.
Practical Takeaways
- Your resting heart rate may predict how strongly you respond to cold water
- People with lower minimum resting heart rates may have stronger diving reflexes
- Heart rate measurement before cold exposure could serve as a simple screening tool
- The diving response varies dramatically between individuals
- Strong vagal activation during cold water immersion can be potentially dangerous
Related Studies and Research
- Related Podcast Episode
- ENDOCRINE, CATECHOLAMINES, AND “ENDORPHINS” (OPEN FULL TEXT WHERE AVAILABLE)
- Systematic review/meta-analysis: CWI and post-match recovery in soccer players
- Cold water immersion and depression
- Limitations of facial immersion as a test of parasympathetic function
FAQs
Why does the heart slow down when you put your face in cold water?
Cold water on the face stimulates the trigeminal nerve, which triggers a reflex that activates the vagus nerve. The vagus nerve slows the heart. This is part of the diving reflex, an oxygen-conserving mechanism found in all mammals.
Can the diving reflex be dangerous?
In extreme cases, yes. Strong vagal activation can cause severe bradycardia (heart rate below 30 bpm) or brief asystole (heart stopping for a few seconds). While rare, these events can be life-threatening, especially in people with underlying heart conditions.
Can you predict how someone will respond to cold water?
This study suggests yes, to some degree. People with lower minimum resting heart rates tend to have stronger cardiodepressive responses during cold water facial immersion. Measuring resting heart rate before exposure could serve as a simple screening tool.
Bottom Line
This study demonstrates that resting heart rate characteristics can predict the cardiac response to cold water facial immersion. People with lower minimum heart rates at rest tend to have stronger heart-slowing responses during the diving reflex. This finding has practical implications for safety screening before cold water exposure. Since the diving response varies dramatically between individuals and can occasionally cause dangerous cardiac events, having simple predictive tools could help identify those at higher risk.
