Decline of FEV1 in Scuba Divers*
- Kay Tetzlaff, MD,
- Jens Theysohn, MD,
- Caroline Stahl,
- Sabine Schlegel, PhD,
- Andreas Koch, MD and
- Claus M. Muth, MD
+ Author Affiliations
1. *From the Medical Clinic and Polyclinic (Dr. Tetzlaff), Department of Sports Medicine, University of Tuebingen, Tuebingen; Department of Radiology (Dr. Theysohn), University of Essen, Essen; Biometrics and Medical Documentation (Ms. Stahl and Dr. Schlegel), University of Ulm, Ulm; German Naval Medical Institute (Dr. Koch), Kronshagen; and Experimental Anaesthesiology (Dr. Muth), University of Ulm, Ulm, Germany. - Correspondence to: Kay Tetzlaff, MD, Medical Clinic and Polyclinic, Department of Sports Medicine, University of Tuebingen Silcherstrasse 5, 72076 Tübingen, Germany; e-mail: Kay.Tetzlaff@med.uni-tuebingen.de
Abstract
Study objectives: Obstructive changes in lung function have been reported with cumulative scuba diving exposure. The aim of this study was to investigate the decline in FEV1 in scuba divers over time.Design: Prospective controlled cohort study.
Setting: German Naval Medical Institute.
Patients: Four hundred sixty-eight healthy, male, military scuba divers and 122 submariners (control subjects) were entered.
Measurements and results: Pulmonary function tests were performed in all subjects on at least three occasions with a minimum interval of 1 year between first and last measurement. The decline in FEV1 was investigated fitting a general linear model to FEV1 across time with a factorial main-effects model for slopes and intercepts with respect to the factors group, smoking status, and baseline FEV1. Mean baseline age of all subjects was 32 years (SD, 9.1), and mean body mass index was 24.7 kg/m2 (SD, 2.4). Subjects were followed up for 5 years (range, 1 to 9 years) on average. Baseline FEV1 exceeded the predicted values in both divers and nondiving control subjects. There was no significant difference in the decline of FEV1 between divers and control subjects. Over time, FEV1 declined more rapidly in smokers than in nonsmokers (p = 0.0064) and declined more rapidly also in subjects with a baseline FEV1 above average compared to subjects below average (p < 0.0001). The annual decline of FEV1 peaked in smoking divers who had a high FEV1 at baseline.
Conclusions: The data indicate that scuba diving is not associated with an accelerated decline in FEV1. Combined exposure to diving and smoking contributes to the fall of FEV1; therefore, smoking cessation is advised for divers.
Diving with scuba gear has become a popular recreational sport. In the United States, there are > 2 million adults and children ≥ 7 years old participating in scuba diving at least once a year.1 When diving, the lungs and airways are affected by factors related to the particular environment. Breathing cold and dry gas via the oral pathway will aggravate respiratory heat loss, and increased oxygen partial pressure at depth may elicit toxic effects on airway epithelia.2 In addition, inert gas microemboli formed in body tissues during and after decompression will impair respiratory gas exchange when floating with the venous return to the pulmonary capillary bed.3 Acute changes in lung function have eventually been shown after experimental deep saturation dives,4 open-sea bounce dives,5 and simulated hyperbaric chamber air dives.6 The unanimous pattern of lung function changes obtained was indicative of acute obstructive airway changes.
The question whether these acute adverse effects cumulate with long-term exposure remains to be addressed. Cross-sectional studies789 of lung function in divers revealed some evidence of reduced expiratory flows and volumes in divers compared with nondiving control subjects, thus supporting the assumption of the development of obstructive airways disease with cumulative diving, but there is only scarce information on longitudinal changes.
The hypothesis of the current study was that the development of chronic inflammatory airway changes from scuba diving would result in an accelerated decline in FEV1. Therefore, a controlled prospective investigation of lung function in a large cohort of healthy military scuba divers was carried out to follow up lung function over time.
Materials and Methods
Study Population and Design
The cohorts were established on the individual attendance to the German Naval Medical Institute. Only healthy male subjects were included who had either been found fit to dive or fit to serve as submariners according to navy regulations. The study had been approved by an independent review board, and subjects gave informed consent. The subjects were entered only if they had at least two follow-up examinations, in order to guarantee a minimum observation period of > 1 year. Follow-up examinations were performed on the occasion of the scheduled medicals at the Naval Institute. Smoking history and a history of atopy were assessed as nominal data (yes/no). Only subjects who had never smoked were classified as nonsmokers. Divers were employing scuba with compressed air or enriched air nitrogen mixtures as the breathing gas. They dive in predominantly cold waters (sea water; depth, 0 to 50 m). Diving experience was assessed by category in terms of the absolute number of dives (< 100, 100 to 500, > 500 dives). Both divers and control subjects participated in military sports activities on average two to three times per week.Pulmonary Function Testing
Recruitment started in 1994 when the German Naval Medical Institute was equipped with a lung function laboratory that satisfied European Respiratory Society (ERS) criteria (Masterlab; Viasys Healthcare; Hoechberg, Germany).10 Pulmonary function testing was always performed by the same two technicians. FEV1, FVC, forced expiratory flow at 25% of expired FVC (FEF25), forced expiratory flow at 50% of expired FVC (FEF50), and forced expiratory flow at 75% of expired FVC (FEF75) were measured in accordance with ERS criteria. Calibrations of the system were performed on a daily basis. Predicted values were calculated according to ERS equations.10 A subset of subjects also underwent body plethysmography if available on the occasion of their medical evaluation. In these subjects, residual volume (RV) and total lung capacity (TLC) were calculated.Statistical Analysis
The primary study end point was the decline in FEV1. For statistical analysis, a general linear model was fitted to FEV1 across time with a factorial main-effects model1112 for slopes and intercepts with respect to the factors group (divers or nondivers), smoking status (yes or no), and baseline FEV1 classified in two groups (FEV1 equal or greater than the mean of baseline FEV1, and FEV1 lower than the mean of baseline FEV1). The level of significance was chosen at α = 0.05. Statistical analysis was performed using statistical software (SAS version 8.2; SAS Institute; Cary, NC).Descriptive statistics were applied for the investigation of subgroups (novice divers, highly experienced divers, and nonsmoking subjects with large lungs). Novice divers had no diving experience at study entry. Highly experienced divers were defined by a history of > 500 dives at their last follow-up. Divers and control subjects with large lungs were selected from all subjects in whom body plethysmography had been performed. Criteria for large lungs were as follows: FEV1/FVC < 80% predicted, FVC > 100%, FEV1 ≥ 90%, and RV/TLC ratio ≤ 0.3.13
Results
Overall 10,282 subjects were enrolled. Of these, 468 divers and 122 control subjects (mean baseline age, 32 years [SD, 9.1]; mean body mass index, 24.7 kg/m2 [SD, 2.4]) presented at least three times within 5 years (observation time, 1 to 9 years). The remainder failed to enter because of loss of follow-up (attending fewer than three follow-up visits). The large majority of both divers and control subjects did not present to the institute again after one investigation due to a change in or retirement from military service. Of those attending more than twice, 308 cases had to be excluded because of an incomplete medical history or lung function not meeting ERS criteria. Fourteen divers had mild diving accidents but were included because these events did not impact on their fitness to dive.Of the eligible subjects, 43% and 7% of divers and 33% and 11% of control subjects reported a history of smoking or atopy, respectively. Baseline FEV1 did not differ significantly between divers and control subjects (Table 1 ). Lung function of both groups on average exceeded the values predicted from the ERS equations.13 Mean body weight (± SD) did not change significantly between baseline (80.1 ± 9.4 kg) and last follow-up (82.3 ± 9.7 kg).
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Table 1.
Demographics and Lung Function at Baseline*
FEV1 declined in both divers and control subjects during the observation period (Fig 1, 2 ) Subjects with a baseline age above mean age had a more rapid decline of FEV1 compared with those having a baseline age below the average (p < 0.0001). There was no significant difference in the decline of FEV1 between divers and control subjects (p = 0.32). FEV1 declined more rapidly in smokers than in nonsmokers (p = 0.0064) and declined more rapidly also in subjects with a baseline FEV1 above average compared to subjects below average (p < 0.0001) [Table 2] . 
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Figure 1.
FEV1 (left axis) in 468 divers at baseline (left, A) and at last follow-up (right, B) [mean interval, 5.1 ± 1.9 years]. Short horizontal lines indicate outliers (values between 1.5 and 3 box lengths from 75th percentile or 25th percentile).
View larger version:
Figure 2.
FEV1 (left axis) in 122 control subjects at baseline (left, A) and at last follow-up (right, B) [mean interval, 4.9 ± 1.9 years]. Short horizontal lines indicate outliers (values between 1.5 and 3 box lengths from 75th percentile or 25th percentile).
View this table:
Table 2.
Changes of FEV1 in Milliliters per Year in Subgroups Defined by the Statistical Model*
No significant association between FEV1 and the total number of dives at baseline was obtained in divers. There were 30 nonsmoking divers (6.4%) and 9 nonsmoking control subjects (7.4%) who met the criteria for large lungs (Table 3 ). In divers, the FEF50 and FEF75 were lower compared to predicted values and values in control subjects at baseline. These reductions diminished toward the last follow-up. View this table:
Table 3.
Lung Function of Subjects With Large Lungs*
A total of 225 divers (48.1%) had a history of > 500 dives at last follow-up (Table 4 ). In terms of percentage of predicted, lung volumes were maintained over time, whereas expiratory flows increased over the observation interval. View this table:
Table 4.
Lung Function of 225 Highly Experienced Divers*
There were 82 divers (mean baseline age, 24.7 ± 6.2 years; mean body mass index, 23.8 ± 2.4 kg/m2) who started their diving career during the study period. In these divers, FEV1 did not change over time (Table 5 ). View this table:
Table 5.
Lung Function of 82 Novice Divers*
Discussion
Pulmonary function tests are regularly performed in professional scuba divers, since proper function of the respiratory system is of the utmost importance to minimize the risks associated with scuba diving.14 Diving exposure itself, however, may cause alterations in lung function. Several cross-sectional studies reported that divers had large lungs in terms of greater than predicted ventilatory volumes,71516 a reduced FEV1/FVC ratio,713 and a pattern of decreased expiratory flows at smaller lung volumes indicating small airway dysfunction.78913 Some of these changes in lung function were found to be correlated with indexes of diving exposure, eventually supporting the conclusion that diving contributes to the reduction in lung function over time.The present study describes, to our knowledge, the largest cohort of divers prospectively investigated using serial lung function measurements over time. Only one prospective longitudinal study of professional scuba divers has been published; in that 6-year survey, Skogstad et al1718 obtained a significantly greater reduction in FVC, FEV1, maximal expiratory flow rates, and transfer factor for carbon monoxide in 77 Norwegian professional scuba divers, compared to 64 policemen that served as control subjects. No difference in the annual change in any of the lung function variables between smoking and nonsmoking divers was observed. In contrast to that study, we were unable to demonstrate a significant difference in the decline of FEV1 between divers and nondiving control subjects in a larger cohort of military divers employing comparable diving gear. In our study, a significant effect of smoking on the decline in FEV1 was obtained. This is in accordance with the literature reporting cigarette smoking to be an important risk factor for an accelerated decline.19 Compared to the study of Skogstad et al,1718 our divers were even older on average and more experienced in terms of the mean number of dives at last follow-up, so that any accelerated decline should have been emerged from the present cohort. It is worth mentioning that in the study of Skogstad et al,1718 five of the divers had experience in saturation diving that may have confounded the effects on lung function. Saturation diving is associated with prolonged exposure to high oxygen partial pressures at greater depth,4 and may thus harm the airways by toxic oxygen effects. During scuba diving, oxygen partial pressure may only reach toxic levels when diving with pure oxygen or nitrogen-oxygen mixtures with an elevated oxygen fraction (enriched air nitrox), but exposure time generally is too short to exert any harmful effects on airways.2 In a retrospective analysis of the records of commercial saturation divers, Watt16 obtained significant reductions in FEV1 and FVC over periods of 3 to 4 years or > 5 years. No influence of smoking on the decline in lung function was found. Moreover there was a significant correlation between the change in FVC and the initial FVC. This is in line with the more accelerated decline of FEV1 in subjects with a higher than mean baseline FEV1 detected in the present study, supporting the assumption that in subjects with large lungs the decline in volume is more rapid. Davey et al7 could demonstrate that FVC increased with deep diving even in subjects > 30 years of age indicating an effect of respiratory training with enlargement of alveolar size that was confirmed by an autopsy study.20 In our study, FEV1 increased in nonsmoking divers and control subjects who had a baseline FEV1 below the average, which may be attributable to regular sports activities performed by both groups.
There is still some debate, however, whether the large lungs in divers are due to diving exposure or selection.1321 Recently, Adir et al13 analyzed the records of 109 nonsmoking scuba divers with a low FEV1/FVC ratio who fulfilled the criteria for large lungs. The authors were unable to detect a correlation between large FVC and diving experience but obtained reduced expiratory flows at low lung volumes, a finding that has been reported previously from a number of cross-sectional studies.789 In the present study, we could not confirm reduced expiratory flows in the diving cohort as a whole. Thus, we retrospectively looked at those divers who met the criteria for large lungs as defined previously.13 In 6.4% of our divers matching those criteria, a reduction of both FEF50 and FEF75 < 80% of predicted was obvious at baseline, but this difference diminished with cumulative diving exposure. In the small group of control subjects matching the criteria for large lungs, end-expiratory flows remained largely unchanged between baseline and last follow-up. The improvement in flows at low lung volumes seen in divers may be due to repetitive diving exposure as has previously22 been shown in working divers at the Neutral Buoyancy Laboratory at Houston, TX, who employed enriched air nitrogen with an oxygen fraction of 0.46. From the 3-year follow-up data of 43 divers, it was concluded that diving with enriched air nitrox at shallow depths was not likely to impair lung function. Accordingly, in the present study we could neither find evidence of small airway dysfunction at maximum follow-up in the total divers sample nor in the subgroups of divers with large lungs or the highly experienced divers.
The annual decline in FEV1 in both divers and control subjects that was derived from the present analysis was within the normal range.19 Noteworthy, the reduction of FEV1 reported previously by Skogstad et al17 of 28.3 mL is not grossly differing from the rate of decline obtained in the present study. Bermon et al23 also reported significant reductions in FEV1 between two pulmonary function tests 9 years apart in 20 professional scuba divers aged 33 years on average at baseline. The calculated annual decline amounted to 34.4 mL. Watt16 reported a mean change in FVC of 400 mL through ≥ 5 years which is marginally significant but must be interpreted cautiously since no mean annual changes were available from that study. The significant reductions reported from previous longitudinal studies thus may not necessarily indicate pathologic changes in lung function. It is worth mentioning that in the present study the most rapid decline in FEV1 was found in smoking divers with a baseline FEV1 above average. This decline was even higher than the values reported from the cited studies but still was below the threshold of what is considered an accelerated decline. It may however indicate an additive effect of diving and smoking thus supporting to advise divers not to smoke.
The present study was designed to investigate lung function over a reasonable period of time in all available divers on military duty. A limitation to the results may be that we did not observe all divers from the beginning of their respective careers. However, no change in lung function was detected in a subgroup of 82 novice divers who started diving during the study period indicating no drop in lung function during the first years of diving.
In conclusion, there was no accelerated decline in FEV1 in military scuba divers over time when compared with nondiving control subjects. The decline was significantly more rapid in smokers than in nonsmokers. Moreover, we could not detect a reduction of flows at low lung volumes over time. Although we cannot exclude that scuba diving may have cumulative damaging effects in susceptible subjects, the present results indicate that in healthy males with normal lung function and an uneventful diving history there are no long-term deleterious respiratory effects. This may be reassuring for millions of recreational divers worldwide who regularly employ compressed air scuba.
Acknowledgments
The support of Dr. Bettinghausen, Surgeon Captain (retired), German Naval Medical Institute, is gratefully acknowledged.Footnotes
· Abbreviations: ERS = European Respiratory Society; FEF25 = forced expiratory flow at 25% of expired FVC; FEF50 = forced expiratory flow at 50% of expired FVC; FEF75 = forced expiratory flow at 75% of expired FVC; RV = residual volume; TLC = total lung capacity
· This work was performed at the German Naval Medical Institute.
· Dr. Tetzlaff is an employee of Boehringer Ingelheim Pharma GmbH & Co.
· The opinions and assertions contained in this article may not necessarily reflect those of the German Navy or the German Ministry of Defense.
·
- Received October 5, 2005.
- Accepted December 23, 2005.
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