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Should Tech Divers Be Thinking More About Equalization—Like Freedivers Do?
Compared to Frenzel equalization used by freedivers, Valsalva equalization can be hard on the ears and eustachian tubes, and could cause problems for tech divers with undetected PFOs. Here scuba instructor turned freediver Charly Stringer argues the case for Frenzel and greater equalization awareness. Community comments included.
By Charly Stringer
Header photo by Derk Remmers
Technical divers plan out their dives extensively before entering the water, they think of every small detail, from gas percentages to time limits.
Freedivers plan too, they plan how deep they will go in the session and they plan out their long term training goals. But, what freedivers focus on probably the most is equalisation. This is something that scuba divers rarely have to think about, but in freediving, bad equalisation can ruin a dive session and stop you in your tracks when trying to get deeper.
But, should technical divers be taking a leaf out of their bubble-less friends’ books and thinking more about their equalisation? What if I was to tell you that the way you’re equalising during a tech dive could affect your likelihood of getting bent?
Your first response might be: “Don’t talk crazy, what has equalising the ears got to do with decompression illness (DCI)?”
Good question, but hear me out…
Equalisation techniques in freediving vs scuba diving
First, let’s explore the differences in equalisation techniques used by freedivers and scuba divers. Some people don’t know that there are different ways to equalise the ears and sinuses, it’s something they just do, without paying much attention to which body parts they are using. But actually, there are two main ways to equalise, and they are very different:
The Valsalva maneuver involves blocking the airways and pushing with the abdominals to create enough pressure to equalise the ears. This technique can be quite forceful and can put strain on the respiratory muscles and the heart.
It is the most common equalisation technique with scuba divers and with beginner freedivers because it is the simplest to perform. For scuba diving, the Valsalva technique is adequate because the diver has time to stop, breathe, and take their time.
For freediving, however, Valsalva is not desirable for equalising the ears. Firstly, it’s not very relaxing because of how strenuous it is. Secondly, pressure increases as the freediver gets deeper, it becomes almost impossible to perform the Valsalva technique because it requires a good amount of air in the lungs to be performed. As the diver gets deeper, the air in the lungs compresses and therefore can’t be used to Valsalva, unlike in scuba where the diver can simply breathe more air to the lungs.
Valsalva can sometimes be ineffective as it doesn’t activate muscles which open the Eustachian tubes, so it may not work if the tubes are already locked by a pressure differential.
The Frenzel maneuver is a bit more technical. It involves bringing air up into the throat, closing the glottis, and then contracting the throat. This creates pressure in the nasal cavity, which opens the eustachian tubes, and equalises the middle ear pressure. This technique is a little trickier but is much easier on the body, assuming that the diver can keep up with the descent. As all the work is done in the throat area, and it doesn’t require the lungs to be so full, it can be performed a lot deeper underwater. It’s also much easier to stay relaxed this way, making it perfect for freedivers.
Some people will perform the Frenzel technique naturally, however it is less common. A lot of people who have scuba dived for many years, come to freediving with confidence that their equalisation will not be a problem, because they have been Valsalvaing successfully for all that time. As they have had almost unlimited air, and the luxury of taking their time to equalise before moving deeper, Valsalva has been good to them. But when your body has a history of autopilot Valsalva, it’s hard to break that habit when switching to Frenzel for freediving, and they can struggle.
So Frenzel has become the technique of choice for freediving. Many freedivers that want to improve, and get deeper in their diving spend hours practicing equalisation. Those that naturally Valsalva have to really create an awareness to switch over to Frenzel and for some people this comes very quickly, for others it can take time. There are coaches that specialise in teaching equalisation. This is something that scuba divers never really have to practice or focus on.
Decompression illness, Valsalva, and PFOs
We know that most tech divers are using Valsalva, and we know that Valsalva can put pressure on the heart. But could this be a factor in getting bent? Well, it could if they also have a PFO…
Patent foramen ovale (PFO) is a hole in the heart between the upper right and left chambers. This is something we all have while we’re in the womb, but for most people it closes up after birth.
Studies have shown that divers who suffer from decompression illness (DCI) have a PFO prevalence twice that of the general population, and most of those divers have a PFO that is a centimeter in diameter or larger.
You might be surprised to learn that over a quarter of people have a PFO, though in some cases these are small and not psychologically relvant. Most of which will never have symptoms, and it will never cause them any health issues. However, for scuba divers, the risk of getting DCI increases five to 13-fold (some researchers place this risk at closer to 3-5 times) by having a PFO because of an increased risk of inert gas shunting (bubbles moving from the right heart chamber to the left).
For recreational scuba divers that stick to their no decompression limits, the risk of DCI is higher with a PFO, but it’s still very low. However, technical divers have a higher risk of DCI because of the depths they are diving to and the amount of time in which they are staying at those depths i.e. greater gas loading. There is less room for error in tech; every detail needs to be planned out and stuck to… make a mistake and you’re likely to get into trouble.
So where does Valsalva come into play?
A study funded by DAN Europe on PFOs and decompression sickness in sport divers found that divers who suffered cerebral DCS (in which a large number of grade 2 PFOs were found) frequently induced sustained and severely strained Valsalva maneuvers to equalise their ears whilst diving. Of course, since Valsalva is the most commonly used equalizing technique for scuba, there are likely many divers are using it without incident.
A PFO can be determined by using something called a “bubble study”. During this study the physician will inject the patient’s vein with air and get the patient to perform the Valsalva maneuver. This raises the pressures in the right side of the heart and will show bubbles in the left atrium if the patient has a PFO.
So the fact that they are using the Valsalva technique to prove that a patient has a PFO by deliberately pushing bubbles through it, is a possible indication that we shouldn’t be using it at depth; because we know that inert gas being shunted through the PFO causes a higher risk of DCI when diving. [Ed.note: However, bubbles more likely to form on ascent not at depth]
So, it seems that the way tech divers are equalising could actually be a risk factor to consider when it comes to preventing DCI.
Based on the knowledge that over a quarter of people have a PFO and that most don’t know that they have one, we can assume that over a quarter of tech divers have a PFO, and may not find out until they potentially suffer from DCI in cases where they are psychologically relevant. Few divers will likely consult their doctor to check to see if they might have a PFO in the absence of symptoms.
So, what could tech divers do to reduce the risk of getting DCI, in addition to planning their dives extensively and diving conservatively? They could switch their equalisation technique from Valsalva to Frenzel as a preventative measure. There are really no negative points to switching over: Frenzelling is easy when you get the hang of it, it could potentially lower your risk of DCI, and has other benefits too, such as being gentler on the ears, conserving more energy, and requiring less air to perform.
To be clear, I am in no way suggesting that switching to Frenzel is circumvent to surgical procedures if you do have a PFO. If you know that you do have one, you should follow your doctor’s advice when it comes to diving.
As mentioned earlier, there are freediving coaches that specialise in teaching people how to Frenzel, as well as Youtube videos and articles. With some practice, Frenzel can become the new autopilot equalisation when diving, causing a lot less strain on the heart and therefore, reducing the risk of getting bent.
Comments from The Field:
We asked a few people we thought were knowledgeable to respond to Charly’s piece. Here is what they had to say.
Instructor Development Programs Specialist, PADI Americas
“The author’s rationale for avoiding Valsalva as a means to lessen the risk of DCO in cases where the diver has a PFO seems to make sense given how forceful the procedure actually is (can be) relative to other techniques. Even DAN states that with Valsalva there’s risk of other injuries occurring—See Beat the Squeeze: Equalize Like a Pro
In my view, everyone can benefit from transitioning from Valsalva to Frenzel, or similar technique, simply because not only is it generally easier to do regardless of head orientation, but it’s generally viewed as gentler on the ears and as divers, whether tech, rec, freediver or airplane flyers, we should be as gentle as possible on our ears if we want to keep diving as much as possible. I also found this WebMD page that alleges the gentler aspect of Frenzel. May your ears, mask and visibility always be clear.”
Performance Freediving Academy CEO/Founder, Performance Freediving International President/Founder
“I agree with what Charly wrote. Frenzel is superior to Valsalva and has many benefits as described including the advantage regarding PFO’s. The main advantage is it provides superior pressure that’s more immediate without straining the chest wall and thereby compressing the heart as it is all conducted at the throat. Essential you’re compressing a volume of air the size of your thumb vs almost two gallons which helps create higher pressure. Think of a thee stage air compressor. The first stage is the low pressure (0-1500psi) and the piston is quite large and slow whereas the third stage (2500-3000) is quite large and fast.
Additionally, it’s somewhat simple to learn and I’d say most professional scuba divers naturally move to this type of equalization because the body will tend to find efficiency. For those that don’t use Frenzel it can be a short and simple online course.”
Training Director, RAID Inc.
“Bold statements but no citations except for the related DAN study on PFO, which doesn’t make the case. By all means use the Frenzel technique (I do at times) but not to circumvent dealing surgically with a hole in your heart.”
Principal & Founder Immersion Freediving
“Frenzel is a superior equalizing method in every way. The only downside is that for the people that don’t naturally do it, it’s tricky to learn. If the tech diver or scuba diver has ZERO issues equalizing than I would just keep doing what they are doing, but I know lots of scuba divers have equalization issues, that would be fixed with switching to Frenzel but so few people in the scuba industry really understand the differences between the two. I honestly look at this article as yet even another reason to use Frenzel over Valsalva!”
DAN Europe: EqualEasy – Equalisation Awareness
DAN US Smart Guide to Ear Equalization: Beat the Squeeze: Equalize Like a Pro (Downloadable)
Instagram Live: EqualizationsTechniques from Ted Harty
YouTube: How to Frenzel Equalize: an equalisation tutorial from a Professional Freediver by Adam Stern
Ted Harty’s Immersion Freediving OnLine Course: Make your equalizing problems a thing of the past.
FreeDive Passion (Dahab): Personal Coaching
PFOs AND DCI:
Journal of Applied Physiology: Patent foramen ovale and decompression sickness in sports divers (DAN Europe)
VerywellHealth.com (Discusses PFOs and Valsalva): The “Bubble Study” for Patent Foramen Ovale
Charly is a writer who’s originally from the UK but has been based in Dahab, Egypt for the past four years. She taught scuba diving for three years in Cyprus, Thailand, and Egypt before discovering her love of freediving. She still scuba dives for fun but these days she’s more focused on her freediving training. When she’s not in the water, diving, she’s on her laptop, writing about diving.
The SOS Automatic Decompression Meter: Bend-O-Matic or Game Changer?
Introduced in 1959, the Italian SOS Deco Meter—the forerunner of modern dive computers—was the first decompression device used by sports divers that automatically tracked users’ dive profiles. Here former French mine clearance diver, instructor, and historian Stephane Eyme takes us on a deep dive into SOS’s analog technology, compares its decompression prescriptions with those of the US Navy and French air diving tables for single and repetitive dives, and offers his perspective on its impact on the market.
Text by Stephane Eyme. Photos and illustrations courtesy of Stephane Eyme. This story was first published on vintagescubadiving.com.
SOS Automatic Decompression Meter was the first mechanical analog dive computer.
The SOS Automatic Decompression Meter (“DeComPressimetro,” or DCP) was introduced in 1959 by Italians Victor Aldo De Sanctis—a known U/W cinematographer at the time—and engineer Carlo Alinari, both co-founders of Strumenti Ottici Subacquei (SOS), a Torino, Italy-based company specializing in scuba diving instrumentation.
DCP provided a decompression profile to scuba divers during an actual dive.
The device was very simply manufactured. It consisted of a waterproof deformable chamber filled with gas connected to a smaller, rigid chamber through a semi-porous ceramic cartridge.
The rigid chamber was equipped with a bourdon tube to measure the inside pressure. A calibrated indicator interpreted these data to provide divers with a decompression status. The whole mechanism was enclosed in a metal and plastic housing.
Straightforward dive operation mode
During the dive:
Ascent and deco stops:
Quite a hit!
The device was distributed by SOS itself and many notable dive equipment companies. Throughout the US and Europe, Scubapro, Healthway, Beuchat, Sporasub, Nemrod, Barakuda and others, all sold the DCP at some point until the 1970s.
And so, the SOS DCP became the first successful decompression instrument sold at large scale to divers around the world. Scripps Institution of Oceanography reported more than 50,000 units sold.
A mind-blowing concept?
When the SOS DCP came out, the diving world already knew quite a bit about the decompression process.
J.C. Haldane published his perfusion parallel compartments model in 1908, and a boom in decompression research followed..
We knew that human body tissues became saturated from a few minutes to several hours depending on the tissue, that saturation followed a logarithmic curve, and that it was symmetric with the desaturation process.
We knew supersaturation ratios decreased linearly with increased ambient pressure (M-values), and that they were different for each compartment.
Based on this knowledge, divers created and used several sets of deco diving tables, for example; US Navy 1956 and the GERS 65.
While it was true that , the diving community had long been aware that decompression was complex and had to account for a wide variety of factors,even with all those considerations, deco tables remained an approximation—a model that would probably differ slightly from diver to diver.
Still, some questions were bothering me
How could an engineer and a famous U/W photographer imagine a system like the DCP?
And, once they settled on the concept, how did they nail the exact piece of ceramic that rendered the entire human body a piece of clay?
And, furthermore, why did we trust them with our lives?
Below is an extract of the SOS DCP user manual. The device is compared to an “electronic brain.” Remember, this was in the sixties, and this “electronic brain” was at the forefront of technology!
I would have thought that, if SOS’s DCP manual was unmistakably indicating—in 1959—that the DCP was extrapolating decompression data from a piece of ceramic, lots of divers would have said, “WHAT?!” and kept using the dive tables. But then, in 1966, Scubapro essentially said the same in its DCP’s user manual, and still sold countless models!
“The mechanism is a pressure-sensitive sealed bourdon tube in a sealed chamber. The only passageway into and out of the sealed chamber is through a porous ceramic element. The element precisely controls the flow of gas into and out of the chamber.
The gas is contained in a collapsible plastic bag which is protected by the stainless-steel case. An ambient pressure entry port and the strap slots allow for transmission of pressure to the collapsible bag. This differential forces the gas through the flow-controlling porous ceramic element into the sealed chamber.
As the pressure builds up within the sealed chamber, the Bourdon tube response causes the indicating needle to move in a clockwise direction. This movement simulates the nitrogen absorption by the diver’s tissues. Upon ascending, the process is reversed.”
(Scubapro’s DCP Manual user 1966)
The results are here
On the other hand, and very surprisingly, DCP deco procedure profiles were not too terrible. On the first dive of the day, they actually weren’t too far from the profiles given by GERS65 or the NAVY56 table.
The GERS (Groupe d’Études et de Recherche Sous-marine) was created in April, 1945, by Cousteau, Tailliez, and Dumas. GERS was a unit of the French Navy in charge of clearing harbors and coast waters of WWII mines.
In 1965, the GERS expanded its previous dive table span from 45 m/147 ft to 85 m/277 ft. These tables were calculated on a Haldanian model with three and four tissues. They also considered two sets of constant supersaturation coefficients throughout the ascent.
Almost every diver in France until 1990 used these tables. They were the “official dive tables” of the French Federation for recreational diving.
The French Navy conducted a statistical evaluation of the safety of the GERS65 tables between 1966 and 1987, using human guinea pigs—err, young, fit, trained, and monitored military divers—and reported a not-insignificant number of accidents following the deco procedures indicated. This was one of a few other motivators for the Navy’s production of new tables—MN90.
I’ll use the GERS65 as a reference alongside the US NAVY56 table to evaluate the DCP deco profiles.
What happened on the first dive?
The following table compares DCP, NAVY56, and GERS65. The time indicated is the maximum bottom time allowed in minutes with no decompression stop on the first dive. GERS65 comes in meters only, rounded to the next meter depth to translate to feet.
Even if the concept of the SOS DCP is really mind-blowing, the results actually are not too far from the tables available at that time.
Looking more closely, DCP was, in fact, more conservative than NAVY56 and GERS65 up to 18 m/60 ft. It was pretty much the same as NAVY56 from 18 m/60 ft to 28 m/90 feet. Less conservative than the NAVY56, but still more conservative than GERS65 from 28 m/90 ft to 37 m/120 ft. Clearly less conservative than both tables after 37 m/120 ft—all for non-decompression dive profiles.
So, saying SOS DCP was not safe… Well, the maths don’t lie. Down to 28 m/90 ft, it was more safe than—or as safe as—the US NAVY56 tables during the first dive. The same happens with GERS65 down to 37 m/120 ft.
It is noticeable during deep dives—37 m/120 ft+—that the DCP became much less conservative than the two other tables. That might be an indicator that the DCP was well-calibrated for long compartments (and long, shallow dives) but not as well-calibrated for quick/medium ones (short, deep dives).
What happened on repetitive dives?
The time indicates the bottom time allowed with no Deco Stop on a consecutive dive.
I won’t get into too many details—I would need much more data to do the experiment justice—but the situation on a consecutive dive is a bit different than on a single dive.
The DCP’s deco profile is almost always located between NAVY56 and GERS65. This means we almost never encounter the situation where DCP is safer than NAVY56. It seems to be less conservative than on the previous first dive scenario for non-deco dive profiles, but it is still safer than GERS65 in any case.
This is possibly why the manufacturer introduced the recommendation to make a deco stop for at least 5 minutes at 3 m/10 ft when diving to more than 45 m/150 ft. This seems a bit like a patch, doesn’t it?
Divers also applied other tricks for repetitive dives: “Move the safe-to-come-up point two ticks to the left for each dive that day.” Of course, the manufacturer did not indicate this rule in its user manual.
Different opinions about the DCP
Amazingly, it is difficult to clearly assess how good or bad the DCP was.
On one hand,
The very device looks like the result of a large experimental attempt to provide safe deco indications. It is not a scientific application based on multi-compartment Haldanian theory.
But DCP forgets serious deco parameters
SOS didn’t consider a few very serious parameters. Not even mentioned, for instance, was water temperature’s impact on deco schedules. Moreover, it approached the problem the wrong way—as cold water increased the viscosity of the gas in the deformable chamber, it diffused slower into the rigid chamber, incorrectly—and hazardously—giving the diver more no-deco bottom time.
Deco surface should differ according to air temperature for the same reasons. Divers sometimes used this factor to decrease surface time by setting the DCP close to the cooling fan of the air compressor!
In addition, different DCPs recommended considerably conflicting decompression schedules for dives with identical depth and time factors. Thus, the DCP’s no-deco limits given by the single dive table fluctuates—sometimes up to seven minutes!
Finally, the DCP’s recommended decompression schedules, in some cases, were more conservative (time-wise) than corresponding US Navy tables. But, in others, the recommendations were far outside the limits of staging according to the tables. Now we know why.
There is no failure warning
The manufacturer provided zero warnings about DCP failure. One potential failure is a needle that does not move or doesn’t start in the blue area, which is easy to check at the beginning of the dive. Another is a malfunctioning device—the needle moved toward the deco-stop zone, but much too slowly.
Don’t forget, this is a mechanical device and, as such, it can’t be expected to be failure-free. But, you had no way to anticipate the problem aside from checking the device right before you dived. Or perhaps attaching it to a line, immersing it to 30 m/100 ft depth for 30 minutes, checking that the needle is about to enter the deco-stop zone, and then waiting six hours to erase its nitrogen memory. Not too practical indeed!
Hence, you could potentially be diving with a malfunctioning device without knowing it, effectively risking your life.
No deco time scheduling
Lastly, the device didn’t provide a time schedule at the deco stop. The DCP only showed that you need to stop, but didn’t tell you for how long. This complicates consumption schedules, which stipulated air. You could easily find yourself with 50 bars in the tank and, without knowing it, beginning a 30 minute deco-stop… breathe shallow!
Scientists say IT IS NOT SAFE!
Scientists conducted very significant studies far beyond what a simple diver like me can understand. Their conclusions included:
“The meter’s performance is compared with the US Navy’s no decompression limits. It is concluded that use of the meter by recreational divers should be discouraged.” S. Howard, H. Bradner, K. Schmitt, Scripps Institution of Oceanography, La Jolla, Calif. 92093, USA Medical and Biological Engineering, September 1976
“Certainly, these techniques will make diving more complex for ‘fools’—but anyone who dives to depths in excess of 30 m/100 ft and thinks all is rosy when following a DCM is a fool. Deep diving in a hostile environment requires careful planning and thoughtful techniques, and no mechanical mechanism exists which can always reliably predict decompression schedules for divers at various depths for variable periods. Surely, it is safer to err conservatively and stick to the ‘deepest depth X longest time’ method. There are many ex-patients who can recommend this practice from personal experience with DCMs which failed.” Carl Edmonds, Automatic decompression meters. SPUMS J . 1973; 3: 9
On the other hand,
There is a cadre of probably tens—if not hundreds—of thousands of dives using the DCP with no decompression incidents at all [See companion story by Bret Gilliam]. A huge number of divers can testify to using this device for many years with no problem. I probably used mine on a couple hundred dives. I’m still here to tell the tale!
Why? Let’s travel back in time to the 60s—when sex was safe, and diving was dangerous…
Equipment was emerging
The scuba equipment industry was in a very embryonic stage. Double hose scuba regulators were introduced no more than 15 years earlier. The first prototype of Maurice Fenzy ABLJ was developed in 1961—so until then you were diving on your legs—and Georges Beuchat introduced its Tarzan wetsuit in 1963 and the Jet Fins in 1964.
Equipment in the 60s was, indeed, still very much emerging and would take time to penetrate the market; as a result, there were diving mandates to be in good physical shape, and divers are fit. In comparison, today’s equipment is far easier to use and even, sometimes, gives us the false impression that diving doesn’t require good physical condition.
Another kind of diver
In the 60s, divers simply weren’t the same as they are today! Scuba diving was still quite new and enjoyed by a very limited number of divers. A lot of them were former Navy—they were trained divers, fit and very experienced. This is one of the reasons why almost all national diving federations used a military-like training plan for new divers in the beginning.
This is mainly because instructors were former Navy divers, and it was the only way they knew. The long swims, the hard training sessions, the 5 minutes lifting a weight belt over your head while paddling… It came from the Navy.
As a result, the profile of the average diver back in the 60s was probably much closer to the military divers who were using the GERS65 tables than it is today. I guess if today’s divers were using the SOS DCP instead of electronic dive computers, results would be far more disastrous.
A large number of dives were done across Europe in federal clubs, with depth limits based on certification levels.
Another consideration is the dive profile itself: SOS’s DCP deco profile, when used shallower than 28 m/90 ft, was safer than (or as safe as) the US NAVY tables. In federal clubs, we did most of our recreational dives in this range due to certification level limits. Consequently, DCP guided numerous club divers with no problematic decompression outcomes during dives to less than a 30 m/100 ft.
What were the key benefits supporting its success?
The DCP was a piece of cake to operate. No need to understand the table, thoroughly plan your dive, or remember your deco parameters. It was freedom. You just had to follow the guide and enjoy the dive!
Even the DCP’s user guide was only a seven-page booklet, of which three were useless for operational purposes! With just a quick read, you could strap it on and dive right away. It was extremely intuitive.
The DCP was very practical for calculating desaturation during surface-time between consecutive dives. DCP was doing everything for you. No nitrogen factor to calculate, no additional minutes on bottom time. You just dived, and DCP would do the rest for you.
Most importantly, the DCP was following your dive profile! That was quite a revolution in a square-dive-profile-world. Suddenly, you could dive much longer by slowly ascending a cliff and get more time to enjoy the dive! That was a true difference compared to table-based diving (at least for multilevel dives).
Was the DCP a bendomatic, or a game changer?
I think it is fair to say that the SOS DCP was a game changer in this emerging scuba world. The DCP would eventually bring a new perspective to diving. It was a brilliant idea, though probably a bit incomplete on the development side.
Yet, the device laid out a genius concept—that we could design a device to do the math for us and change the way we dive. This probably inspired equipment manufacturers to look into electronic dive computers, the very same ones that appeared on the market during the 80s, but this time with a far more advanced scientific basis.
See Companion story: Diving the SOS: A Practical Discussion by Bret Gilliam
Eyme’s website offers a wealth of historical resources and tools and tips: VintageScubaDiving.com
InDepth: Oh Deco, Oh Doppler, O’Dive: Assessing the World’s First Personal Deco Safety Tool by Michael Menduno
As a former clearance diver with the French Navy, Stephane Eyme’s scuba diving experience includes running his own dive centre in the Canary Islands, supervising underwater archaeological excavations, and working for the largest dive shop in Paris. He has more than 30 years’ experience as instructor for the French Scuba Diving Federation (FFESSM) and is a PADI Master Instructor in teaching status. He runs the website VintageScubaDiving.com and often organises vintage try-dive events and participates in vintage equipment gatherings to share his passion with the diving community. He lives in Valencia on the Spanish Mediterranean coast, and lives by a motto: “What matters is being under [water].”