Influence of the diving wetsuit on standard spirometry

INTRODUCTION A well-fitting wetsuit exerts a pressure on the body that may influence spirometry. This pressure is expected to reduce the forced vital capacity (FVC) due to hampered inspiration. Since the shape of the spirometric flow curve should not be changed by the pressure effects of the wetsuits, FVC, the forced expiratory volume during the first second of expiration (FEV₁), the peak expiratory flow (PEF) and the flow between 25 and 75% of FVC (FEF25-75) should change to the same degree. This study investigates the influence of a wetsuit on spirometric variables using age, suit thickness and suit type as the parameters. Spirometry (dry) was performed in 28 volunteers (12 women), aged 27-69 years. The wetsuit (3.8 mm, range 2-7 mm) resulted in a change in FVC of -4.0% (P = 2∙E-08 〈 0.001), in FEV₁ of -3.6% (P = 3∙E-05 〈 0.001) and in PEF of -2.4% (P = 0.03); the FEF25-75 may also diminish. The FEV₁/FVC ratio did not change. The decreases can be regarded as a quasi-ageing effect of about 3.5 years. No influence of age, suit thickness and suit type was found. The wetsuit appears to impair ventilatory mechanics. Both the medical examiner and the diver should be aware that a too-thick or too-tight suit might be a potential pulmonary risk factor in divin

Correction for adiabatic effects in lethe calculated instantaneous gas consumption of scuba dives

Introduction: In scuba-diving practice, instantaneous gas consumption is generally calculated from the fall in cylinder pressure without considering the effects of water temperature (heat transfer) and adiabatic processes. We aimed to develop a simple but precise method for calculating the instantaneous gas consumption during a dive. Methods: With gas thermodynamics and water/gas heat transfer, the instantaneous released gas mass was modelled. In addition, five subjects made an open-water, air, open-circuit scuba dive to 32 metres' sea water. Depth, cylinder pressure and water temperature were recorded with a dive computer and gas consumption was calculated and compared using different methods. Results: After descent in open-water dives, the calculated gas mass in the cylinder was the same as calculated from cylinder data, suggesting that the model is adequate. Modelled dives showed that adiabatic effects can result in considerable overestimate of the gas consumption, depending on the dive profile, exercise-dependent pulmonary ventilation and the cylinder volume. On descending, gas thermodynamics are predominantly adiabatic, and the adiabatic correction of ventilation is substantial. During the dive, the adiabatic process (at the start 100%) decreases steadily until the end of the dive. Adiabatic phenomena are substantially different between square and saw-tooth profiles. In the emergency situation of a nearly empty cylinder after a square-wave dive involving heavy physical exertion, the adiabatic effect on the cylinder pressure is generally > 20%. Then, with a strongly reduced consumption at the start of the ascent, heat inflow produces an increase of cylinder pressure and so more gas becomes available for an emergency ascent. Conclusion: Adiabatic effects, being indirectly dependent on exercise, the profile and other conditions, can be substantial. The developed method seems sufficiently accurate for research and possibly for reconstruction of fatalities and is implementable in dive computer

Body fat does not affect venous bubble formation after air dives of moderate severity: theory and experiment

For over a century, studies on body fat (BF) in decompression sickness and venous gas embolism of divers have been inconsistent. A major problem is that age, BF, and maximal oxygen consumption (Vo2max) show high multicollinearity. Using the Bühlmann model with eight parallel compartments, preceded by a blood compartment in series, nitrogen tensions and loads were calculated with a 40 min/3.1 bar (absolute) profile. Compared with Haldanian models, the new model showed a substantial delay in N2 uptake and (especially) release. One hour after surfacing, an increase of 14-28% in BF resulted in a whole body increase of the N2 load of 51%, but in only 15% in the blood compartment. This would result in an increase in the bubble grade of only 0.01 Kisman-Masurel (KM) units at the scale near KM = I-. This outcome was tested indirectly by a dry dive simulation (air breathing) with 53 male divers with a small range in age and Vo2max to suppress multicollinearity. BF was determined with the four-skinfold method. Precordial Doppler bubble grades determined at 40, 80, 120, and 160 min after surfacing were used to calculate the Kisman Integrated Severity Score and were also transformed to the logarithm of the number of bubbles/cm(2) (logB). The highest of the four scores yielded logB = -1.78, equivalent to KM = I-. All statistical outcomes of partial correlations with BF were nonsignificant. These results support the model outcomes. Although this and our previous study suggest that BF does not influence venous gas embolism (Schellart NAM, van Rees Vellinga TP, van Dijk FH, Sterk W. Aviat Space Environ Med 83: 951-957, 2012), more studies with different profiles under various conditions are needed to establish whether BF remains (together with age and Vo2max) a basic physical characteristic or will become less important for the medical examination and for risk assessmen

Hyperbaric oxygen treatment improved neurophysiologic performance in brain tumor patients after neurosurgery and radiotherapy: a preliminary report

Cognitive performance often is impaired permanently in long-term brain tumor survivors after neurosurgery and radiotherapy. Hyperbaric oxygen treatment (HBOT) stimulates neovascularization of hypoperfused tissue and may result in improved functionality of damaged tissue. In this pilot study, clinical neurophysiologic tests were used to assess the effect of HBOT on brain performance. Ten long-term brain tumor survivors received HBOT for severe cognitive deficits after neurosurgery and radiosurgery. Patients were tested before HBOT and at 6 weeks and 4 months after HBOT. The tests comprised a quantitative electroencephalographic (EEG) examination, the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) for memory performance, and 2 cognitive tests, the number connection test (NCT) and the continuous reaction time test (CRTT). Late event-related components (LERCs) of averaged evoked EEG responses to a visual odd-ball stimulus were analyzed from whole-head activity maps. For comparison, a control group of healthy individuals (no HBOT) also were investigated. After HBOT, the amplitude of the LERC with the longest latency, P3b (involved in object interpretation) was improved significantly (P = .02). The amplitudes of the N200 (occipital, negative) and the intermediate P3a (centroparietal, positive), LERCs with shorter latencies, and of a small, positive, occipital visual component did not change. Neither latencies nor reaction times changed after HBOT. However, P3a and P3b (parietal, positive) latencies were longer in survivors than in healthy individuals. The NCT produced inconclusive results, but the IQCODE revealed an improvement. When outcomes of the NCT, CRTT, IQCODE, and P3b amplitudes were evaluated in common tests, HBOT appeared to provide substantial improvement (P <.006). On the basis of the current results, the authors concluded tentatively that HBOT improves neurophysiologic performance in long-term brain tumor survivor

Doppler Bubble Grades After Diving and Relevance of Body Fat

SCHELLART NAM, VAN REES VELLINGA TP, VAN DIJK FJ, STERK W. Doppler bubble grades after diving and relevance of body fat. Aviat Space Environ Med 2012; 83:951-7. Background: From the literature on venous gas embolism (VGE) and decompression sickness (DCS), it remains unclear whether body fat is a predisposing factor for VGE and DCS. Therefore, this study analyses body fat (range 16-44%) in relation to precordial VGE measured by Doppler bubble grades. Also examined is the effect of age (range 34-68 yr), body mass index (BMI; range 17-34 kg . m(-2)), and a model estimate of (V) over dotO(2max) (maximal oxygen uptake; range 24-54 ml . kg(-1) . min(-1)), Methods:, (maximal oxygen uptake; range 24-54 ml . kg(-1) . min(-1)), Methods: Bubble grades were determined in 43 recreational divers after an open sea air dive of 40 min to 20 m. Doppler bubble grade scores were transformed to the logarithm of the number of bubbles/cm(2), logB, and the logarithm of the Kissman Integrated Severity Score (KISS) to allow numerical analysis. Statistical analyses were performed with Pearson's regular and partial correlations, and uni- and multivariate linear regressions. Results: For divers in their midlife (and older), the analyses indicate that neither body fat nor BMI stimulate bubble formation, since correlations were nonsignificant. In contrast, age and especially (V) over dotO(2max) appeared to determine VGE. For these types of dives it was found that logB = -1.1 + 0.02age - 0.04(V) over dotO(2max). Conclusion: Based on these data we conclude that body fat and BMI seem less relevant for diving. We recommend that medical examinations pay more attention to (V) over dotO(2max) and age, acid that international dive institutions come to a consensus regarding (V) over dotO(2max) criteri