I participated in a physiology experiment once that aimed to elicit this primitive reflex. We were set up with large basins of cold water (cold is important) and asked to place our entire face to the hairline and earline into it. Meanwhile our responses of heart rate, BP and SaO2 were recorded. Almost all recorded a drop in BP, HR and only a gradual rise in pCO2 after a few practices. After many practices we could hold our breath longer, and our respiratory drive (CO2) grew weaker while our pulse stayed lower for longer. We were then asked to imagine the event, and those who had practised most could elicit the same responses. (Repeated practices at lengthy submersions, particularly in cold water, have been associated with unexplained drownings I have been told.)
It is thought this primitive response is at the bottom of the lowered BMR and decreased respiratory drive that occurs with prolonged submersion in very cold water and subsequent 'miracle' survivals of drowning. So though the 'diving response' in infants that leads to resumption of fetal circulation in neonatal life and the lovely baby swimmers is thought to disappear, it doesn't really. We all have it to an extent. It is why we shouldn't expose newborns to very cold water, submerge their face or blow cold air onto their face, as it stimulates the breathholding (after the gasp of surprise) that leads to resumption of fetal circulation. Sorry, no refs, am accessing offsite. Trish -- This mailing list is sponsored by ACE Graphics. Visit <http://www.acegraphics.com.au> to subscribe or unsubscribe.
