Breath reflect test => significant drop in HR. Why??

[JonVortex]

Hi there,

I recently did a breath reflex test (where I naturally exhaled to the 'point of turning') and then held my breath for as long as I can. First time was 47 seconds - second time was more like 80 seconds.

But what was interesting was that my HR pretty much dropped off a cliff. I had recently finished a run so my starting HR was around 90, but was nowhere near any water to my face. In both tests my HR basically dropped in a straight line to about 60 - a drop of over 30%.

The guy who was testingt me said he had never seen that reaction, that everyone else either goes up or stays around the same with a slight change ... mine was very different.

It made me wonder about what the physiology of that might be - and what it might mean is going on inside me.

The only other thing of note was that I have a 7l lung capacity - which isn't astounding, but not bad considering I am only just starting up my training after being a lard-arse for the last 6 months.

Any thoughts??

 

[Rik]

This is certainly not uncommon. The dive reflex has three causes: stress, hypoxia and activation of the facial receptors. In some individuals, the physical stress of holding the breath and hypoxia can also cause an remarkably drop in heartbeat.

In my case, I can drop my heart-beat from 80bpm to 32bpm, independent of holding my breath in water or not.

Some even discuss if the diving reflex actually exists, and if it is not just an hypoxia induced reflex, but I think there is sufficient evidence that the diving reflex does exist in humans. Some people just seem to get some of the effect without being actually submerged.

 

[growingupninja]

Hi there,

I recently did a breath reflex test (where I naturally exhaled to the 'point of turning') and then held my breath for as long as I can. First time was 47 seconds - second time was more like 80 seconds.

But what was interesting was that my HR pretty much dropped off a cliff. I had recently finished a run so my starting HR was around 90, but was nowhere near any water to my face. In both tests my HR basically dropped in a straight line to about 60 - a drop of over 30%.

The guy who was testingt me said he had never seen that reaction, that everyone else either goes up or stays around the same with a slight change ... mine was very different.

It made me wonder about what the physiology of that might be - and what it might mean is going on inside me.

The only other thing of note was that I have a 7l lung capacity - which isn't astounding, but not bad considering I am only just starting up my training after being a lard-arse for the last 6 months.

Any thoughts??

With a 7L lung capacity it is highly unlikely you are actually running an O2 deficit after 80 seconds, and for nondivers 'breakpoint' is typically where CO2 levels are high enough to force them to breathe. Beyond breakpoint, pulse, blood pressure and general feelings of panic rise. O2 actually starts dropping here and a little ways into this point is usually where an actual dive reaponse kicks in (hr falls well below normal resting). This for dry, and untrained individuals can't usually hold to this point. In water, especially cold water, it may begin much, much sooner (seconds into the hold). On dry land if not moving I don' experience any signifcant (by that I mean well below resting hr) drop in hr untill minutes into the hold, but neither is my O2 below normal until then either. 7L is a good lung for the general athletes but the guy running your test must not work much on swimmers.

Don't drown in the bathtub or anything but you want to work on getting HR below normal resting during a hold, which unless you have a medical condition or need some serious general fitness before you start freediving safely, should be well under 90 bpm.

 

[Herup]

Hehe, these reflexes usually makes doctors freak out. Try having him stick a fast and reading blood pressure instrument on you a long with the HR monitor. If you can hold hour breath at FRC level or lower long enough to have the meter measuring when your HR drop to around 40 or even 30, he's gonna thing you're about to blow up in his hands

Best regards
Herup

 

[Rik]

With a 7L lung capacity it is highly unlikely you are actually running an O2 deficit after 80 seconds, and for nondivers 'breakpoint' is typically where CO2 levels are high enough to force them to breathe. Beyond breakpoint, pulse, blood pressure and general feelings of panic rise. O2 actually starts dropping here and a little ways into this point is usually where an actual dive reaponse kicks in (hr falls well below normal resting).

Well, not sure where that comes from.

1. Scientific studies of the dive reflex clearly show an direct drop in heart-rate when the diver and non-diver is submerged in water. It is true that if the diver get's more hypoxic, the heart-beat initially decreases more, but this is well after the initial drop in heartbeat.

2. A large lungcapacity and a short "dive" time doesn't have to exclude early hypoxia or an strong response to an limited decrease of the oxygen levels of the individual.

Besides hypoxia, other causes of an fast drop in heart-beat could be an vasovagal mediated slow heart-beat, which can be due completely other reasons that diving related situations.

 

[growingupninja]

Rik - yeah all true but I THOUGHT the original poster was talking about a dry and what I asumed was full lung static, not an apnea sprint or exhale hold. The dry part was in my response but buried in some less than stellar grammar and sentence construction. On closer inspection I see he was talking about I think something more like an FRC hold (turning point? Is that to forced exhale?) and I stand very much corrected.

Since he was talking about total lung capacity I thought it was a full lung hold. But anyway, most anyone would get an O2 drop after 80 secs on an exhale. Any sort of exhale test would be sort of subjective as most athletes doing any sport with a cardio component would probably have a lower residual volume than general population and there is probably a genetic component as well. My pulse drops on an exhale hold as my O2 levels drop. Full lung is very different; typically O2 does not drop for a while and with 7L full lung doing a relaxed static I would imagine he could go a few minutes before his O2 level began to drop, although CO2 would trigger a 'need to breathe' feeling sooner in most cases.

OP - probably drop in HR from decreasing O2 levels; what Rik said. Pretty normal for divers. I don't know what is supposed to be 'normal' for general population on an exhale. Personally I get a fast drop in HR when I do dry exhale holds; I also get a fast drop in O2 in that case as well.

 

[Antoine]

OP - probably drop in HR from decreasing O2 levels; what Rik said. Pretty normal for divers. I don't know what is supposed to be 'normal' for general population on an exhale. Personally I get a fast drop in HR when I do dry exhale holds; I also get a fast drop in O2 in that case as well.

On an exhale I also get a a very steep and relatively early drop in heart rate. My resting HR is alrady pretty low at 56bpm and after an exhale I can get it as low as in the 30's.
I rekon, after having seen how quite a number of family and friends react in terms of HR after an exhale, the "normal" for most of the population would be to get at least a 10% drop in heart rate after the first 30-40 seconds. That means, someone with an average resting heart rate of 70bpm would lower their HR to arond the sixties in the first 30 or so seconds after an exhale.