Obesity and Decompression Illness

There is a considerable body of work relating an increased incidence of DCS to increased percentage of body fat. Higher DCS rates have been noted in the older diver, due in part, to the gradual increase in skin fold thickness (% body fat) and possibly to the increased incidence of cardiovascular disease, commonly noted in the obese.

Michael Powell, PhD describes the effects of diving in the obese as follows: “From the standpoint of
decompression, when one dives, nitrogen dissolves in all tissues of the body in proportion to the gas solubility and the blood flow to the tissue. As far as joint pain DCS is concerned (“the bends”), this arises primarily in tissues that contain water. However, nitrogen is very soluble in adipose (fat) tissue and, in
overweight people, the fraction of this tissue in the body is high. In some cases, nitrogen loads can rise in adipose tissue and bubble formation can be extensive. While one would not develop pain DCS from this, these gas bubbles would be dumped into the venous system where they are carried to the heart and lungs. If the gas bubble loads to these organs is high, the lung capillaries become blocked, blood pressures rise in the pulmonary artery, and bubbles can pass through the lung vasculature (or a PFO, patent foramen ovale in the heart) and embolize the brain. We end up with a vein-to-artery “stroke” and neurological DCS.”

Below are some selected abstracts from the literature regarding obesity as a factor in scuba divers.

Undersea Biomed Res 1984 Dec;11(4):395-406
Health risk factors for the development of decompression sickness among U.S. Navy divers.
Dembert ML, Jekel JF, Mooney LW

185 U.S. Navy divers who did experience decompression sickness either before or after examination had significantly higher measures of skin fold thickness and weight when compared to those who remained free of decompression sickness. These findings suggest that obesity may be a contributory factor to the occurrence of decompression sickness.

Aviat Space Environ Med 1984 May;55(5):391-5

Weight/height indices and percent body fat among U.S. Navy divers.
Dembert ML, Jekel JF, Mooney LW

Weight, height, and other anthropometric measurements were obtained on a cohort of 194 U.S. Navy divers 20-42 years old. Among the divers, weight, weight/height indices, and percent body fat increased across age strata. The body mass index (W/H2) was the best predictor of adiposity, as it had the highest correlation with percent body fat and the lowest correlation with height.

Br J Ind Med 1984 May;41(2):275-8
Optimum weights for commercial divers.
McCallum RI, Petrie A

Obesity is one of the factors which increase the risk of decompression sickness. It has been suggested that any diver whose weight is more than 20% in excess of that derived from currently accepted tables should therefore be stopped from diving until he has lost enough weight. Analysis of weight measurements of 1520 divers whose records are in the Decompression Sickness Central Registry in Newcastle upon Tyne suggests that divers as a group are substantially heavier than other populations on whom height/weight tables have been based.

Clin Orthop 1978 Jan-Feb;(130):94-106
Dysbaric osteonecrosis. Etiological and pathogenetic concepts.
Chryssanthou CP
Dysbaric osteonecrosis appears to be independent of decompression sickness. The 2 conditions, however, may share etiologic and pathogenetic factors. The incidence of osteonecrosis is influenced by the number of hyperbaric exposures, extent of pressure, decompression profile and possibly by the rate of compression and degree of obesity.

Int J Sports Med 1999 Aug;20(6):410-4
Circulating venous bubbles in recreational diving: relationships with age, weight, maximal oxygen uptake and body fat percentage.
Carturan D, Boussuges A, Burnet H, Fondarai J, Vanuxem P, Gardette B
Faculte des Sciences du Sport, Luminy, Marseille, France
Decompression sickness (DCS) is recognized as a multifactorial phenomenon depending on several individual factors, such as age, adiposity, and level of fitness. The detection of circulating venous bubbles is considered as a useful index for the safety of a decompression, because of the relationship between bubbles and DCS probability. The variables investigated were: age, weight, maximal oxygen uptake (VO2max) and percentage of body fat (%BF). The effects of age, weight and VO2max are more significant than the effect of %BF.

Aviat Space Environ Med 1997 Aug;68(8):695-8
Relationship between age and susceptibility to altitude decompression sickness.
Sulaiman ZM, Pilmanis AA, O’Connor RB
Armstrong Laboratory, Crew Technology Division, Brooks AFB, TX 78235-5104, USA.

Susceptibility to altitude decompression sickness (DCS) is influenced by a multitude of factors including, potentially, an individual’s age. Previous attempts by authors to determine the effect of age on DCS susceptibility have produced conflicting results. There is a trend toward increased DCS susceptibility with increasing age, with a particularly strong trend for individuals over 42 yr. of age.

Cardiovascular Disease Risk Increase

BMI
In some areas of the world where medical fitness is more stringently regulated than the US, a high BMI (body mass index) would deter one from diving. Complicating conditions of adiposity include diabetes mellitus, dyslipidemia or hypertension and their associations with coronary artery disease. The BMI is important to divers due to the fact that people with high BMI are more prone to coronary artery disease and an untoward coronary event while diving. A BMI above 30 kg/m2 is thought to be excessively risky for diving. Of course, measured %BF can sometimes show that the diver is quite large and muscular and this needs to be taken into consideration.

Appetite Suppressants

Medications given for appetite suppression also have a risk for diving in that most have psychotropic effects and can cause elevated blood pressures. The possible ill effects of nitrogen added to the drugs are not known.

DAN ‘s Report on DCI and Diving Fatalities for 2000 shows a high incidence of cardiovascular disease fatalities in divers over the past 9 years, surpassed only by AGE in 1998.

Diabetes

The overweight person as also at increased risk for diabetes. Unknown and untreated diabetics are at risk for wide swings in blood sugar levels, often brought on by stressful situations such as diving and cold water. Low blood sugar (hypoglycemia) is a risk factor for divers, known to cause drowning and gas embolism on ascent.

Decreased pulmonary function (hypoxia, CO2 retention)

The obese diver would be at risk for carbon dioxide retention and hypoxia due to decrease in all parameters of pulmonary function. This would be highly variable with the individual and would require PFTs to determine the real risk. Pulmonary function tests that are more than two standard deviations from normal would indicate high risk. Low vital capacity and FEV1 would be indicators of possible increased risk.

Decreased physical fitness
Increased DCS
Decreased ability for Self rescue
Decreased Buddy rescue ability
Increased risk of panic in stressful situations