Hand Held Doppler

***ScubaDadMiami*** · 17th December 2007, 04:13

It is (or at least has been) a course, and I have taken it. It was one of the most interesting courses I have ever taken.

After learning how to detect, part of the course included a list of items so that the attendees could actually build their own monitoring equipment. I recently thought about building my own station and starting to conduct these studies for divers. I just didn't think there would be enough demand out there for this type of service. (At most, a few divers would pay for such a study once, which is not enough to support a going business.)

The problem with many of these portable doppler monitors is that their probes and design do not work well enough because they pick up too much background noise to be much good. There are better units that can be made fairly portable for the field though.

By recording the bubbling, this can be studied and compared after return from the trip. This is helpful because it helps to better measure against agreed upon standards. It also allows the user to hear what is going on without background noise that will be encountered on dive boats or otherwise in the field.

john56 · 17th December 2007, 16:07

I bought a hand-held doppler in the early '90's and took a course of sorts with Mike Emmerman and 2 other experts (can't remember their names, but I think one was his girlfriend). One of the things they mentioned was that, to an untrained ear, using a doppler was near useless as we couldn't understand what we were hearing. They then pointed out that the 3 of them, all trained, gave 3 different interpretations of a recording of a doppler check on a diver!

I used to bring mine out on the boat and use it on willing divers before and after deep dives to see if we could hear bubbles. Having a baseline prior to diving is important, so you can see if anything has changed. To be honest, we often thought we heard bubbles before we even went diving, and although I think we might have heard post-dive changes once or twice, it would be a stretch to say we thought it was a valuable tool in decompression planning, even though we were pushing the envelope with some of our profiles.

The technology may have gotten better since then, but I would think the training necessary to understand the results remains the same. We got better results inviting a trained technician out on trips to doppler the divers. It is important to make sure the tech take some sort of seasickness preventative if you want to get anything out of him though...

John Yurga

zzzzzzzz · 17th December 2007, 17:19

Hi John,

What sort of doppler were you using and which probes?

The unit referred to in my case is a Huntleight Diagnostics Dopplex II, fitted with a 5 MHz probe. This probe is for shallow yet focused probing. The usual target is the subclavian artery and vein. These are very easy to find since everybody has a clavicle, and the curved part is where you can easily locate these conduits on just about every body type. For fleshy types, a lower frequency probe may be advised.

Using the probe, it is quite easy to find and differentiate the vein and the artery. Arteries are pulsatile while veins sound like wind.

One can carry several probes to increase coverage. Naturally, one must use gel to match impedance between the probe and the subject. An air interface just doesn't work.

Using some other probes, you can hear all the way to the heart with ease. There is a combination of probe position and angle, as well as the use of some of Gray's anatomy references that can be of help.

Bubbles show up quite clearly, don't need a PhD for sure! If you hear a POP, you're there. If there is more than one bubble once in a while, you go into a exponential scale, 10's, 100's, 1000's, 10000's... per minute. If you sound like a popcorn machine, you are experiencing decompression stress. Feeling strange, not quite yourself maybe?

Usually, one looks for bubbles in the veinous supply on the assumption that bubbles are forming in the tissue at the extremeties and are being shunted by the lungs. If one finds bubbles in the arterial supply this isn't great news since it either means you have a PFO or there is excessive decompression stress that is bypassing the lungs. This accentuates bubble growth since they grow when they run the circuit. This can lead to irregular pulses through the arteries and can also be heard during an ultrasonic examination.

One can also test for sensitivity by squeezing the forearm of the patient or by having him clasp his first rapidly. This creates a rush of blood toward the heart, the wave front can be heard with the doppler device. If saturation is high, bubbles can form near the edges of this wave front and be heard using the ultrasonic device. Again, the very distinctive POP is unmistakeable.

Audiograms can be found on the net easily with detailed descriptions of what one is hearing. What is even more stunning though is when you hear such things in real life. It's one thing to hear an audio file of distorted arterial pulses resulting from decompression stress, it is quite another when it's your buddy who decided he was going to shave 5-10 minutes from his schedule to not look like a decompression panzy on a dive. Also curious when folks matching the decompression conservatism decline an ultrasonic examination. Sometimes it's better not to know.

z

john56 · 17th December 2007, 17:44

Sorry, it's been at least 10 years since I last used the doppler, so I don't remember the brand. I know we listened at the subclavian vein; the sound was like a river, or like wind. The unit came with 3 tips, if I remember, (one was for fetal use?) but we only used the one recommended when I took the course. We used the gel to aid in conductivity.

The big problem for us seemed to be that we would hear the occasional pop when doing our baseline recordings, before we had gotten in the water. I think the worst post-dive incidence we ever got was on the order of 10 pops per minute, and there was disagreement on whether we were actually hearing bubbles or not. I never got the opportunity to use the unit on a diver who had badly violated his or her decompression, so other than a recording in the course I never heard a real case of bubbles in the veins, as far as I know. It sounds like the units may have gotten better if you can easily distinguish bubbles with your unit.

When the doppler guy was well enough to test us, he calculated that, diving to 220' on air he should see 2.3 cases of the bends and bubbling in all divers, or some such. We all wanted to be the .3 guy... He found very few bubbles, and actually called one of the divers a "freak of nature" because he didn't get bent on his profile.

John Yurga

Simon Mitchell · 17th December 2007, 18:12

Quote: (Originally Posted by zzzzzzzz)

Everybody who is heavily invested in diving should have one. Dopplers are virtually useless in the hands of hyperbaric personel, since the damage is usually done and the bubbles long gone by the time a victim reaches the chamber.

Validating decompression conservatism and correcting for future dives is an absolutely valid use of these portables.

z

Hello,

I would suggest that to say "everyone should have one" and that their use in evaluating decompression is "absolutely valid" is a significant overstatement of the case. This is, in fact, a very controversial topic; mostly for reasons that others on this thread have already mentioned. Those reasons can be divided up into two broad headings: the technical difficulties of Doppler monitoring, and the meaning of Doppler bubble counts after dives.

Technical difficulties.

As others have mentioned, interpretation of the Doppler-shifted signal is usually not as straight forward as you have portrayed. I would have to agree that training could circumvent this problem to some extent, but it would still be difficult to get everyone "singing from the same songbook". You could argue that this does not matter, and that so long as everyone interprets their own signals consistently (even if inaccurately) that might still be useful. I suppose there is some merit in that, but it remains likely that divers will hear bubbles where they don't exist, or miss bubbles that do.

The meaning of the counts.

This is the biggest problem. As has been pointed out, the correlation between venous bubble counts / grades and clinical DCS is weaker than you might expect. Your implication that these counts are useful in a diagnostic sense is quite wrong. Staff at hyperbaric units would not bother to do bubble counts, even if seeing a diver immediately after a dive, simply because the count would not change what they do. If a diver has symptoms the diagnosis is made irrespective of a bubble count; if the diver didn't have symptoms the diagnosis would not be made even if the bubble count was high.

Despite this, many researchers continue to use Doppler as an imperfect tool to evaluate decompression stress, mainly because the alternative end point (clinical DCS) would not be acceptable to many IRBs / Ethics Committees. However, doing this in large studies with multiple subjects, trials, and using statistical techniques to analyse the results is quite different to the individual trying to make sense of changes in their own counts from dive to dive. There are almost certainly many things that can affect the count other than simply depth / time / ascent protocol. Thus, it is conceivable that you could adjust your profile to be more conservative and yet hear even more bubbles on your next dive because some other factor was at play. You would then be faced with difficult decisions around the interpretation of your numbers.

To summarise, I am definitely not opposed to divers owning Doppler units and self monitoring after diving. With training and care in interpretation of the findings some useful insights might be gained. But I think that your slightly evangelical interpretation of their usefulness needs to be tempered with some realism!

Warm regards,

Simon M

zzzzzzzz · 17th December 2007, 18:39

Hi John,

What you communicate reflects much of what the experience is like. Until the first time I heard distorted arterial pulsing I thought the doppler was nice to have. Using conservative profiles is a factor in doppler fatigue.

What you describe is doppler fatigue. Nice to read your decompression was effective in spite of some adventuresome activities. It does seem as though there was a lot of investment and planning. Often preparation and planning are key factors.

Nowdays, there is an easy cure: hang out with decompression hounds. There are a lot of super-divers out there now, and these folks can be a lot of ''fun'' post-dive.

Only by chance did I find myself with a group that was deliberately or unknowingly pushing a little past the limits. Without a huge statistical base, a few factors were observed, the most significant seemed to be work at depth. Some of these folks were making some significant physical effort at the bottom, you should have just seen some of the swimming. Couple that with shaving 10% from the decompression schedule, cold water and presto: popcorn machines.

It is something to hear recording of such things, and then to actually be talking to someone who is right there before you experiencing such decompression stress. There were no DCI symptoms in these cases, except perhaps over time some have curtailed their diving activities substantially.

Most people do go about their diving without over-exerting at depth. Every once in a while, you will see somebody really put in a swim at depth this would be your candidate especially if this person dialed down the conservatism. Also look for cold water, lack of proper thermal protection, dehydration...

It is still not really obvious and it is unlikely that a sure fire method will ever be possible given that so many variables can intervene. Even with the benefit of substantial use of the doppler, historical data and experience, one will never be able to predict that over-exertion is going to happen on one or another dive and that it will become the factor.

Decompression will remain a field where vigilance may no even guarantee success. In any case, it is handy to have around for those times that one doesn't feel that great after a dive, or where there was some event.

The takeway for me is that Doppler fatigue is a factor among users. The interest is there, seeing no action is an issue. This is also most curious. The lack of incidents in these diving circles is itself interesting. It would be interesting to have more such evaluations to determine what those factors might be.

z

brandonmc · 18th December 2007, 17:08

Hand held Doppler units can be found pretty cheaply on eBay for around $100 since they are now pretty commonly used as fetal heart rate monitors. Obviously these are not as sensitive as a high end unit but for the price they are a cool toy to play with. My buddy has one and we played with it this past summer on dives in the 50-75m range. I would not recommend these as a way to track decompression sickness but with a consistent baseline it is possible to detect signs of bubbling, and get at least a semi-quantitative idea of your own personal tolerance for computer generated decompression tables.

Example on ebay (no, its not mine)

AD_ward9 · 18th December 2007, 17:19

Some are really cheap: New Fetal Heart Doppler detector Prenatal Baby Monitor on eBay, also, Monitors Dopplers, Maternity Pregnancy, Baby (end time 19-Dec-07 17:31:51 GMT)

Watch those shipping costs though

!

Alex

Tyler S. · 18th March 2008, 19:17

I have an el cheapo doppler and it is useful for detecting bubbles however I would not use it to judge the efficency of a particular profile or algorithm. Sometime there is a dcs case with no bubbles or there are bubbles and no dcs. Be careful about that....

17th December 2007, 04:13	#11 (permalink)
*ScubaDadMiami* Moderator Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2005 Location: Florida, USA Posts: 1,896	Re: Hand Held Doppler It is (or at least has been) a course, and I have taken it. It was one of the most interesting courses I have ever taken. After learning how to detect, part of the course included a list of items so that the attendees could actually build their own monitoring equipment. I recently thought about building my own station and starting to conduct these studies for divers. I just didn't think there would be enough demand out there for this type of service. (At most, a few divers would pay for such a study once, which is not enough to support a going business.) The problem with many of these portable doppler monitors is that their probes and design do not work well enough because they pick up too much background noise to be much good. There are better units that can be made fairly portable for the field though. By recording the bubbling, this can be studied and compared after return from the trip. This is helpful because it helps to better measure against agreed upon standards. It also allows the user to hear what is going on without background noise that will be encountered on dive boats or otherwise in the field. __________________ Howard Packer IANTD CCR Instructor Miami Beach, Florida CCRDiveTraining.com
(Offline)

17th December 2007, 16:07	#12 (permalink)
john56 New Member Current Rebreather/s: Evolution Other Rebreather/s: Megalodon Join Date: Jan 2007 Location: New Jersey Posts: 7	Re: Hand Held Doppler I bought a hand-held doppler in the early '90's and took a course of sorts with Mike Emmerman and 2 other experts (can't remember their names, but I think one was his girlfriend). One of the things they mentioned was that, to an untrained ear, using a doppler was near useless as we couldn't understand what we were hearing. They then pointed out that the 3 of them, all trained, gave 3 different interpretations of a recording of a doppler check on a diver! I used to bring mine out on the boat and use it on willing divers before and after deep dives to see if we could hear bubbles. Having a baseline prior to diving is important, so you can see if anything has changed. To be honest, we often thought we heard bubbles before we even went diving, and although I think we might have heard post-dive changes once or twice, it would be a stretch to say we thought it was a valuable tool in decompression planning, even though we were pushing the envelope with some of our profiles. The technology may have gotten better since then, but I would think the training necessary to understand the results remains the same. We got better results inviting a trained technician out on trips to doppler the divers. It is important to make sure the tech take some sort of seasickness preventative if you want to get anything out of him though... John Yurga
(Offline)

17th December 2007, 17:19	#13 (permalink)
zzzzzzzz New Member Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Dec 2006 Location: Earth Posts: 68	Re: Hand Held Doppler Hi John, What sort of doppler were you using and which probes? The unit referred to in my case is a Huntleight Diagnostics Dopplex II, fitted with a 5 MHz probe. This probe is for shallow yet focused probing. The usual target is the subclavian artery and vein. These are very easy to find since everybody has a clavicle, and the curved part is where you can easily locate these conduits on just about every body type. For fleshy types, a lower frequency probe may be advised. Using the probe, it is quite easy to find and differentiate the vein and the artery. Arteries are pulsatile while veins sound like wind. One can carry several probes to increase coverage. Naturally, one must use gel to match impedance between the probe and the subject. An air interface just doesn't work. Using some other probes, you can hear all the way to the heart with ease. There is a combination of probe position and angle, as well as the use of some of Gray's anatomy references that can be of help. Bubbles show up quite clearly, don't need a PhD for sure! If you hear a POP, you're there. If there is more than one bubble once in a while, you go into a exponential scale, 10's, 100's, 1000's, 10000's... per minute. If you sound like a popcorn machine, you are experiencing decompression stress. Feeling strange, not quite yourself maybe? Usually, one looks for bubbles in the veinous supply on the assumption that bubbles are forming in the tissue at the extremeties and are being shunted by the lungs. If one finds bubbles in the arterial supply this isn't great news since it either means you have a PFO or there is excessive decompression stress that is bypassing the lungs. This accentuates bubble growth since they grow when they run the circuit. This can lead to irregular pulses through the arteries and can also be heard during an ultrasonic examination. One can also test for sensitivity by squeezing the forearm of the patient or by having him clasp his first rapidly. This creates a rush of blood toward the heart, the wave front can be heard with the doppler device. If saturation is high, bubbles can form near the edges of this wave front and be heard using the ultrasonic device. Again, the very distinctive POP is unmistakeable. Audiograms can be found on the net easily with detailed descriptions of what one is hearing. What is even more stunning though is when you hear such things in real life. It's one thing to hear an audio file of distorted arterial pulses resulting from decompression stress, it is quite another when it's your buddy who decided he was going to shave 5-10 minutes from his schedule to not look like a decompression panzy on a dive. Also curious when folks matching the decompression conservatism decline an ultrasonic examination. Sometimes it's better not to know. z
(Offline)

17th December 2007, 17:44	#14 (permalink)
john56 New Member Current Rebreather/s: Evolution Other Rebreather/s: Megalodon Join Date: Jan 2007 Location: New Jersey Posts: 7	Re: Hand Held Doppler Sorry, it's been at least 10 years since I last used the doppler, so I don't remember the brand. I know we listened at the subclavian vein; the sound was like a river, or like wind. The unit came with 3 tips, if I remember, (one was for fetal use?) but we only used the one recommended when I took the course. We used the gel to aid in conductivity. The big problem for us seemed to be that we would hear the occasional pop when doing our baseline recordings, before we had gotten in the water. I think the worst post-dive incidence we ever got was on the order of 10 pops per minute, and there was disagreement on whether we were actually hearing bubbles or not. I never got the opportunity to use the unit on a diver who had badly violated his or her decompression, so other than a recording in the course I never heard a real case of bubbles in the veins, as far as I know. It sounds like the units may have gotten better if you can easily distinguish bubbles with your unit. When the doppler guy was well enough to test us, he calculated that, diving to 220' on air he should see 2.3 cases of the bends and bubbling in all divers, or some such. We all wanted to be the .3 guy... He found very few bubbles, and actually called one of the divers a "freak of nature" because he didn't get bent on his profile. John Yurga
(Offline)

17th December 2007, 18:12	#15 (permalink)
Simon Mitchell New Member Current Rebreather/s: MK 15.X Other Rebreather/s: Join Date: May 2005 Location: New Zealand Posts: 156	Re: Hand Held Doppler Quote: (Originally Posted by zzzzzzzz) Everybody who is heavily invested in diving should have one. Dopplers are virtually useless in the hands of hyperbaric personel, since the damage is usually done and the bubbles long gone by the time a victim reaches the chamber. Validating decompression conservatism and correcting for future dives is an absolutely valid use of these portables. z Hello, I would suggest that to say "everyone should have one" and that their use in evaluating decompression is "absolutely valid" is a significant overstatement of the case. This is, in fact, a very controversial topic; mostly for reasons that others on this thread have already mentioned. Those reasons can be divided up into two broad headings: the technical difficulties of Doppler monitoring, and the meaning of Doppler bubble counts after dives. Technical difficulties. As others have mentioned, interpretation of the Doppler-shifted signal is usually not as straight forward as you have portrayed. I would have to agree that training could circumvent this problem to some extent, but it would still be difficult to get everyone "singing from the same songbook". You could argue that this does not matter, and that so long as everyone interprets their own signals consistently (even if inaccurately) that might still be useful. I suppose there is some merit in that, but it remains likely that divers will hear bubbles where they don't exist, or miss bubbles that do. The meaning of the counts. This is the biggest problem. As has been pointed out, the correlation between venous bubble counts / grades and clinical DCS is weaker than you might expect. Your implication that these counts are useful in a diagnostic sense is quite wrong. Staff at hyperbaric units would not bother to do bubble counts, even if seeing a diver immediately after a dive, simply because the count would not change what they do. If a diver has symptoms the diagnosis is made irrespective of a bubble count; if the diver didn't have symptoms the diagnosis would not be made even if the bubble count was high. Despite this, many researchers continue to use Doppler as an imperfect tool to evaluate decompression stress, mainly because the alternative end point (clinical DCS) would not be acceptable to many IRBs / Ethics Committees. However, doing this in large studies with multiple subjects, trials, and using statistical techniques to analyse the results is quite different to the individual trying to make sense of changes in their own counts from dive to dive. There are almost certainly many things that can affect the count other than simply depth / time / ascent protocol. Thus, it is conceivable that you could adjust your profile to be more conservative and yet hear even more bubbles on your next dive because some other factor was at play. You would then be faced with difficult decisions around the interpretation of your numbers. To summarise, I am definitely not opposed to divers owning Doppler units and self monitoring after diving. With training and care in interpretation of the findings some useful insights might be gained. But I think that your slightly evangelical interpretation of their usefulness needs to be tempered with some realism! Warm regards, Simon M
(Offline)

17th December 2007, 18:39	#16 (permalink)
zzzzzzzz New Member Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Dec 2006 Location: Earth Posts: 68	Re: Hand Held Doppler Hi John, What you communicate reflects much of what the experience is like. Until the first time I heard distorted arterial pulsing I thought the doppler was nice to have. Using conservative profiles is a factor in doppler fatigue. What you describe is doppler fatigue. Nice to read your decompression was effective in spite of some adventuresome activities. It does seem as though there was a lot of investment and planning. Often preparation and planning are key factors. Nowdays, there is an easy cure: hang out with decompression hounds. There are a lot of super-divers out there now, and these folks can be a lot of ''fun'' post-dive. Only by chance did I find myself with a group that was deliberately or unknowingly pushing a little past the limits. Without a huge statistical base, a few factors were observed, the most significant seemed to be work at depth. Some of these folks were making some significant physical effort at the bottom, you should have just seen some of the swimming. Couple that with shaving 10% from the decompression schedule, cold water and presto: popcorn machines. It is something to hear recording of such things, and then to actually be talking to someone who is right there before you experiencing such decompression stress. There were no DCI symptoms in these cases, except perhaps over time some have curtailed their diving activities substantially. Most people do go about their diving without over-exerting at depth. Every once in a while, you will see somebody really put in a swim at depth this would be your candidate especially if this person dialed down the conservatism. Also look for cold water, lack of proper thermal protection, dehydration... It is still not really obvious and it is unlikely that a sure fire method will ever be possible given that so many variables can intervene. Even with the benefit of substantial use of the doppler, historical data and experience, one will never be able to predict that over-exertion is going to happen on one or another dive and that it will become the factor. Decompression will remain a field where vigilance may no even guarantee success. In any case, it is handy to have around for those times that one doesn't feel that great after a dive, or where there was some event. The takeway for me is that Doppler fatigue is a factor among users. The interest is there, seeing no action is an issue. This is also most curious. The lack of incidents in these diving circles is itself interesting. It would be interesting to have more such evaluations to determine what those factors might be. z
(Offline)

18th December 2007, 17:08	#17 (permalink)
brandonmc New Member Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Oct 2006 Location: Philadelphia Posts: 75	Re: Hand Held Doppler Hand held Doppler units can be found pretty cheaply on eBay for around $100 since they are now pretty commonly used as fetal heart rate monitors. Obviously these are not as sensitive as a high end unit but for the price they are a cool toy to play with. My buddy has one and we played with it this past summer on dives in the 50-75m range. I would not recommend these as a way to track decompression sickness but with a consistent baseline it is possible to detect signs of bubbling, and get at least a semi-quantitative idea of your own personal tolerance for computer generated decompression tables. Example on ebay (no, its not mine) __________________ http://mcjangles.blogspot.com/
(Offline)

18th December 2007, 17:19	#18 (permalink)
AD_ward9 So much more to learn Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Jun 2005 Location: Scotland Posts: 1,553	Re: Hand Held Doppler Some are really cheap: New Fetal Heart Doppler detector Prenatal Baby Monitor on eBay, also, Monitors Dopplers, Maternity Pregnancy, Baby (end time 19-Dec-07 17:31:51 GMT) Watch those shipping costs though ! Alex
(Offline)

18th March 2008, 19:17	#19 (permalink)
Tyler S. rEject Current Rebreather/s: rEvo Other Rebreather/s: rEvo Join Date: Nov 2005 Location: San Diego Posts: 165	Re: Hand Held Doppler I have an el cheapo doppler and it is useful for detecting bubbles however I would not use it to judge the efficency of a particular profile or algorithm. Sometime there is a dcs case with no bubbles or there are bubbles and no dcs. Be careful about that....
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