DCS RISK FACTORS AND LIFESTYLE

In one of the first articles on my blog we discussed about smoking and its consequences on scuba diving (https://scubadivinggoodpractices.blogspot.com/2020/04/diving-and-smoking.html).

 

For sure, smoking plays an important role as a risk factor for the development of DCS (decompression sickness). In fact, among other 1000 reasons not to smoke, I recall you that:

 

• 
  carbon monoxide, as a product of burning, interferes negatively with an efficient gas exchange, thus impeding proper oxygenation of the tissues.
• Nicotine as a vasoconstrictor reduces the blood perfusion in the body extremities, slowing down the inert gas discharge.
• Toxins in the cigarettes damage the alveoli, thus reducing pulmonary functionality and leading to hypoventilation.

What are the other DCS risk factors?

Many of them are environmental (external), others are physiological (internal), but some of them for sure can be reduced by a healthy lifestyle and an average level of fitness! Let us have a closer look.

ENVIRONMENTAL (EXTERNAL) FACTORS  

Altitude: dive table and computer are set up for use at sea level. Nevertheless, as you may know, altitude change leads to a variation in compression and decompression ratios, so prior to dive at altitudes different to sea level, make sure that your dive computer is correctly set up!
 

Water temperature: from a merely physics point of view, there is no doubt that tissue temperature can influence the gas absorption rate. In fact, lower temperature facilitate N2 absorption. However, as a matter of fact, minor body temperature variations as a consequence of diving in cold water do not seem to have significant effect on the gas absorption rate. The most relevant effect of temperature on diving physiology is rather vasoconstriction and the subsequent minor blood perfusion of the body extremities.
 

Surface intervals and off-gasing: see my previous post “off-gasing and minimum surface interval"  (https://scubadivinggoodpractices.blogspot.com/2020/05/off-gasing-minimum-surface-interval.html)
 

Reverse profiles: also on this topic I already collected some relevant information in the previous post "Reverse profiles in recreational diving"  (https://scubadivinggoodpractices.blogspot.com/2020/12/reverse-profiles-in-recreational-diving.html)

PHYSIOLOGICAL (INTERNAL) FACTORS

Gender: although many studies have been carried out on this topics, there is no concrete evidence that gender influences the incidence of DCS.
 

Age: aging itself does not play a specific role in DCS susceptibility, nevertheless by aging the cardio-vascular system tends to be less efficient, thus slowing down the gas exchange process.

Fitness and exercise: there is no doubt that an average level of fitness and physical activity carried out up to 20 to 12 hours prior to the dive has a positive effect on DCS prevention, by improving cardiovascular functionality. Nevertheless exercise carried out right before of after the dive affects blood circulation, contributing to the increase of micronuclei and tribonucleation due to blood turbulence and thus leading to a greater risk of bubble formation.

Previous injuries, illness and drugs: previous healed injuries may produce local circulation anomalies, affecting inert gas elimination from the involved body part. Also illness and the connected drug consumption may affect body circulation. Moreover empirical observations suggest that if bends occur in one part of the body, they are more likely to appear again in the same region.

Obesity: there are lots of scientific and empirical evidence for obesity as a predisposing DCS factor. This is due to the fact that N2 is more soluble in fat than other body tissues. No need to say that obesity, such as smoking, has other negative long-term implications such as heart disease, high blood pressure, diabetes and others.

Alcohol consumption: there is no doubt that dinking alcohol before a dive should be strictly forbidden! But drinking alcohol should be avoided also in the evening prior the dive and following the dive, as alcohol tends to accelerate circulation and dilate capillaries leading to unpredictable changes of inert gas absorbtion / release. Alcohol also has diuretic properties that could lead to dehydration.

Hypovolemia / Dehydration: hypovolemia can be explained as volume reduction of the blood circulating in the body. This condition is normally caused by dehydration due to many different factors such as alcohol consumption, perspiration, diarrhea or vomit. Easy to understand, a reduction of circulating blood volume results in a less efficient gas exchange process.


Personally, I try to reduce the impact of internal DCS risk factors by avoiding alcohol and cigarettes (as long as I manage, I am not a saint you know 😁), following a healthy diet and moderate exercise.

And you? How are you getting fit for diving?

HOW TO THREAD A BCD TANK STRAP

 

How many times did it happen that, arriving to the diving site, you find out that your BCD’s tank cam band is open and unconnected?

 

Did you know that you can re-thread it by yourself, without always asking a divemaster or an instructor for help? 

 

This short video shows you how to do it!

 

 

 

 

REVERSE PROFILES IN RECREATIONAL DIVING

Many of us, reading our Open Water Diver manuals (including PADI and CMAS) have been instructed and warned about the danger of diving s.c. reverse profiles.

Briefly explained, reverse profiles occur when, within a single dive, the latter portion of the dive is deeper than the earlier portion or, in the case of repetitive dives, the repeat dive is deeper than the earlier one.

 

Although the rule against reverse dive profiles has been (and apparently still is) widely accepted and taught by major recreational diving agencies, it is not clear where did this rule came from and which was the scientific motivation behind it. Sure thing, historically this limitation could be explained by the use of dive plan tables and electronic dive planner that were only in the condition of calculating bottom time and nitrogen loading only based on the maximum depth and time figures.

With this in mind, in the year 1999 the Smithsonian Institution and AAUS (American Academy of Underwater Sciences) called a Workshop with the purpose of investigating, among others,  if there is any physiological basis (read “DCS incidence”) for the rule against reverse profiles ( Reverse Dive Profiles Workshop, Washington DC, October 29 and 30, 1999).

The results of this study, that considered modern bubble decompression models, were:

• Historically neither the U.S. Navy nor the commercial sector have prohibited reverse dive profiles. 

• Reverse dive profiles are being performed in recreational, scientific, commercial, and military diving. 

• The prohibition of reverse dive profiles by recreational training organizations cannot be traced to any 
definite diving experience that indicates an increased risk of DCS. 

• No convincing evidence was presented that reverse dive profiles within the no-decompression limits 
lead to a measurable increase in the risk of DCS.

Within this research, the possible increase of DCS cases possibly connected to reverse profiles was explained with the fact that very often reverse profiles are associated to repetitive dives on multiple days activity and connected nitrogen exposure.  

The conclusion of the study was that if diving within no decompression limits and less than 40 meters, and within a maximum depth difference of 12 meters, the current evidence does not show any demonstrable increase in risk of DCS.

With this in mind, and with the generic commercial spread of dive computers with algorithms capable of adequately calculate bottom time and residual nitrogen loading for reverse profiles, today the only reason for avoiding reverse profiles in recreational diving seems to be purely based on the necessity of maximizing the dive duration.

In fact, even if apparently not relevant for DCS, reverse profiles  still significantly reduce the available bottom time, and this is for sure a valid reason for avoiding them when possible: for sure, when we are on holiday, we want to maximize our fun and to stay below water as long as we can!

One last consideration: the position of the Smithsonian Institution and AAUS is not globally shared and there have been more recent studies showing different results, even though based on animal experiments (The relative safety of forward and reverse diving profiles. S. McInnes, C. Edmonds, M. Bennett, UHM 2005: VOL 32, ISSUE #6).

Nonetheless, the results of the 1999 Workshop are still widely accepted, among others, also by Divers Alert Network (DAN).

I share this article based on my best knowledge and research on public documentation as well as literature in my possession. If any of you fellow divers out there, especially tech divers, do have any further information or authoritative source, I would be happy to further investigate and discuss with you!

 

 

CONSEQUENCES OF RAPID ASCENT AFTER THE SAFETY STOP

Many times, in my professional activity (mostly in the role of dive guide), I witness the inexplicable behavior of divers who, after a perfect safety stop at 5 meters performed in very good buoyancy, rapidly swim to the surface or even worse just inflate the BCD and pop up uncontrolled. 

These divers are probably convinced that after the safety stop there is no more risk and it’s possible to return rapidly to the surface and thus to the boat… Well this could not be more wrong! 

To perform a safety stop does not mean to eliminate every risk: in fact, the last 10 to 5 meters before surfacing are the most stressful for our body, in terms of percentage pressure change and connected gas volume differential. 

If we consider the Workman critical ratio 1,58:1, we can easily understand that a rapid ascent from 5 - 6 meters is at the very limit of this value! Moreover, the most modern VPN and RGBM decompression models imply the constant presence of bubbles in the body tissues, and in a previous article we learned that a full washout (off-gasing) of bubbles relevant for DCS only occurs in the 12 - 24 hours following the dive. So, given the presence of bubbles in the tissues while we still are underwater, the sudden pressure decrease caused by a rapid ascent from 5 meters could trigger the production and growth of bubbles potentially relevant for DCS. 

Furthermore, a rapid ascent from 5 meters is not only relevant in terms of DCS, but also with reference to pulmonary injuries and barotrauma, such as reverse squeeze. In particular we shall always keep in mind that, if we surface holding the breath with full lungs, a depth change of only 1,2 meters is sufficient to cause lungs over-expansion! 

 

Finally, considering, the massive pressure change in this delicate phase, it is recommendable to choose an ascent speed even slower than the 9 m/s recommended by many training agencies. Considering an ascent rate of 6 m/s, we should take at least one minute to surface from 5 meters! 

No need to say that in this phase, perfect buoyancy is the most important skill to be mastered, so keep training and, if necessary, join dedicated buoyancy courses.

KEEP DISTANCE!

As many of you know, this Summer I had the opportunity of working by OmniSub, one of the historical diving center of the Isle of Elba.

As a tradition in Italy, in the month of August the island was rather packed: as a consequence, also the maritime traffic has been very high.

This situation caused a lot of stress in particular for our non diving boat crew, whose main task during this crazy period was to shout and wave to unresponsible boat drivers who rushed at high speed just a few meters away from our boat, thus putting at risk the safety of the divers below who in the worst but not impossible case could be hit by the hull or even by the propeller of boats moving right above their heads.  

📸 (c) DAN Europe

 Of course generally every diver and diving center staff member is very well educated about the obligation to use a “diver-down” or “alpha” flag and a surface marker buoy. Nevertheless, the above described incident tipology is generally caused by lack of attention or ignorance: with reference to this second point, unfortunately in Italy is it possible to rent any boat up to 40hp, even without any licence, under the condition of being at least 16 years old and to remain within six miles form the coast. Surprisingly, a display of knowledge of the most basic national sea traffic regulation is not a requirement for getting the boat.

 

For this reason, I grab this opportunity to make you aware about the ITALIAN regulation about diving warning signals and minimum distance from divers and diving boats.
 The subject was originally regulated by the DPR 1639 from 02.10.1968, art. 130, that states as follows:

 

• scuba divers must use a float equipped with a red flag with a diagonal white stripe (“diver-down” flag). If diving from a boat, the flag bust be lifted on the boat;
• scuba divers can move within a range of 50 meters from the boat or from the float.

In addition, in the year 2003 a note from the Corps of the Italian Port Authorities imposed to boats and vessels a minimum distance of 100 meters from diving warning buoys and diving boats.

Nowadays the subject is regulated by the D.M. 146 from 29.07.2008, art. 91 that, in addition to the above mentioned rules, requires every diver to bring along a personal DSMB.

It is important to stress out that the violation of the rules concerning minimum distance by boat drivers lead to criminal prosecution even if no incident or injuries occur.

Eventually, here a few safety tips for divers:

• always surface as close as possible to the diving boat;
• use an SMB if you are not able to locate the boat. If you di not know how to deploy an SMB; please refer to my previous post available here: https://www.facebook.com/741846475/videos/10157262944171476/;
  
• train your buoyancy, avoid uncontrolled ascents and always look up before surfacing.

 

PERFORMING SKILLS: KNEELING OR NEUTRALLY BUOYANT?

I have being discussing many times with colleagues, friends and students whether it is better to demonstrate and learn OW skills in a neutrally buoyant position or on the knees, and I can already anticipate you that without any doubt I opt for the first solution. Here is why.

First of all, let me clarify that for me neutral buoyancy does not necessarily mean being “perfectly” neutrally buoyant from the first second we hit the water, but just horizontal position. The first skills can be comfortably achieved in slightly negative buoyant position, with the tip of the fins and belly or hands touching the bottom. Progressively, by practicing buoyancy skills as oral inflation and fin pivot, the student will improve his horizontal neutral position in the water.

📸 La Palma Diving

The above described slightly negative position offers the advantage for the student of practicing skills in a more realistic dive position, but still keeping the pool bottom as a reference in case of lost of balance. In fact, when practicing skills in a resort pool there is normally no problem in keeping the position on the knees; on the contrary, if we must teach skills in a wavy confined open water session for the students it will be easier to keep the balance in an horizontal position with the tip of the fins touching the bottom. The students in fact will have the possibility of helping themselves with the hands, e.g. by holding a big rock, and they will not be pushed away by the waves as it could happen in a knee position as a consequence of the bigger body area exposed to the waves. In consideration of the above, I do not see any problem in connection with students ratio as the group will be more compact and stable.

Moreover, being used to horizontal position, in open water environment the student will be already used to a correct horizontal trim and will not tend to put himself in a vertical position in order to perform skills. This normally works also in relation with simple DSD dives.

Furthermore, speaking about a realistic training scenario with very short time available due to holiday schedule, learning in an horizontal position is not more difficult that learning on the knees, it is just a matter of initial set up.

Of course much of this depends by how the instructor himself was trained to perform skills during his IDC: many instructors that learned to perform skills on their knees will find inconvenient to demonstrate in neutrally buoyant position, just because they never trained how to do it properly. In fact, the demonstration of some skills (think about BCD or weights system removal and replacement) changes drastically if you chose knee or an horizontal position.

For this reason, in my personal case, I decided to opt for an IDC where I could learn how to demonstrate skills in a neutrally buoyant position: switching from neutral buoyancy to kneeling position is easy, but the opposite can be tricky and needs some training.

Some last considerations:

• as the training standards of major agencies do not impose any position, the instructor must be clever enough to "read" his students and to choose the position that better adapts to his students’ water skills, in order them to complete the course having fun and without stress;

• the surrounding underwater environment and the sea bottom structure also influence the demo position: if teaching in a place full of corals where you only have available a patch of sand 3m x 3m, it will be difficult for both instructor and student to lay on their belly so the only solution, at least in the beginning, would be to perform skills in kneeing position. This is valid in particular in the case of DSD in tropical destinations where no pool is available;

• if the instructor opts for a position, he shall perform all the skills in that position. In other words, if you go for neutral buoyancy, you shall teach all the skills in neutral buoyancy and not some in one position and some in the other, otherwise this could be potentially misleading for the student.

And you? How did you learn basic skills during your Open Water Course?

If you are an instructor, how do you teach skills to your students?

DAN RELEASES NEW COVID-19 MEDICAL FORM

Following the latest MIT recommendations DAN releases a new medical statement form for diving during covid-19.

Click on the picture below for free download ⤵️