Diving reflex: can the time course of heart rate reduction be quantified?

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System Function
• Human Diving Response

Background:

• The diving reflex, characterized by bradycardia, is a physiological response to breath-holding and facial immersion.
• Understanding the temporal dynamics of heart rate reduction is crucial for assessing autonomic control.

Purpose of the Study:

• To quantify the time course of heart rate reduction during the diving reflex using a mathematical model.
• To evaluate the applicability of a monoexponential function in describing diving bradycardia.
• To assess the utility of the diving reflex in diagnosing cardiovascular autonomic pathway integrity.

Main Methods:

• A meta-analysis of studies investigating diving bradycardia was performed.
• A mathematical function (HR=c+aexp(-(t-t(0))/τ)) was used to fit heart rate data over time.
• Data from comparable studies were analyzed, focusing on apneic facial immersion and breathing air.

Main Results:

• Apneic facial immersion led to a heart rate decrease with a time constant (τ) of 10.4 s.
• Breathing air without facial immersion showed a slower heart rate decrease (τ=16.2 s).
• A monoexponential function accurately described heart rate decrease during apnea (r²>0.93), but less so during exercise.

Conclusions:

• The diving reflex follows a quantifiable monoexponential time course during apnea.
• The mathematical model effectively quantifies the early phase of diving bradycardia.
• The diving reflex serves as a valuable tool for assessing the integrity of cardiovascular autonomic pathways.