Ok Tyler I will take some of your bait.
The mammalian diving reflex is a real phenomenon. Scientifically sound..done deal. I think everyone agrees with this. The diversity of human experiences, personal attributes, conditions and situations will greatly affect how this reflex is provoked, to what degree or if even at all. How do we measure if someone is experiencing the diving reflex? I guess the objective way is to plug them into monitors and measure a physiological response. Here are some thoughts I have that lead me to believe that we are close to the diving reflex. We may not be aware that it is there or to what degree, just as we aren't aware of every beat of our heart, or the digestion process of our bowels.
We see the diving reflex very early in our mortal existence. In fact, as a child being born our bodies used the diving reflex to survive the hypoxic episodes of each uterine contraction as we were expelled from our mother's womb. This bradycardia and peripheral vasoconstriction that occurs in the fetus during this time is called in the medical field the "diving reflex".
The diving reflex is provoked by increased stimulation of the parasympathetic nervous system (this is the side that does everything opposite of the fight or flight sympathetic system). In particular the vagus nerve, is our friend that slows the heart.
The diving reflex is so handy at slowing electrical conduction of the heart that it can be used to halt some dangerous arrhythmias, specifically SVT - a type of tachycardia. When some one presents to an Emergency room with SVT, "vagal maneuver's" are attempted to elicit the diving reflex and return the heart rate to a normal rhythm. If this is not successful then further measures are employed.
Vagal maneuver's are done to try and stimulate the vagus nerve or generally speaking increase the parasympathetic nervous system stimulation.
What are the vagal maneuver's? Typically, the major ones in adults are
Valsalva (sound familiar
) and carotid body massage.
Valsalva - by straining against a closed glottis during a held breath there is an abrupt increase in intrathoracic and intra-abdominal pressure....long story short....increases vagal tone....decreases heart rate. Increase in intrathoracic and intraabdominal pressure (subsequent intra-arterial pressure changes is an important part of the process) from diving pressure depths will also reinforce the process. This is essentially what happens in the birthing child mentioned previously with the forceful uterine contractions increasing pressure on the child.
In little kids with certain arrhythmias, since it is hard to tell them to "bear down" and perform valsalva, ice packs or cold water cloth
can be placed on the face in an attempt to elicit the diving reflex. This is where we Canadian divers might have some advantage
....probably voided by the 15 lbs of lead and 7mm suits to get down
.
As far as what other experiences people are having that aren't the diving reflex? I don't really know, other than good relaxation, which would probably be a biofeedback type of turning down one's own sympathetic nervous system?
lee
