The effect of a single closed-circuit rebreather decompression dive in extremely cold water to cardiac function.

PURPOSE: Dive-induced cardiac and hemodynamic changes are caused by various mechanisms, and they are aggravated by cold water. Therefore, aging divers with pre-existing cardiovascular conditions may be at risk of acute myocardial infarction, heart failure, or arrhythmias while diving. The aim of this study was to assess the effect of a single decompression CCR dive in arctic cold water on cardiac function in Finnish technical divers. METHODS: Thirty-nine divers performed one identical 45 mfw CCR dive in 2-4 °C water. Hydration and cardiac functions were assessed before and after the dive. Detection of venous gas embolization was performed within 120 min after the dive. RESULTS: The divers were affected by both cold-water-induced hemodynamic changes and immersion-related fluid loss. Both systolic and diastolic functions were impaired after the dive although the changes in cardiac functions were subtle. Venous inert gas bubbles were detected in all divers except for one. Venous gas embolism did not affect systolic or diastolic function. CONCLUSION: A single trimix CCR dive in arctic cold water seemed to debilitate both systolic and diastolic function. Although the changes were subtle, they appeared parallel over several parameters. This indicates a real post-dive deterioration in cardiac function instead of only volume-dependent changes. These changes are without a clinical significance in healthy divers. However, in a population with pre-existing or underlying heart problems, such changes may provoke symptomatic problems during or after the dive.

A 15-Year Longitudinal Study of Body Composition in Finnish Military Divers.

INTRODUCTION: Finnish military divers perform a great variety of tasks all year round, all of which require good physical health and fitness. Poor physical fitness can hinder the ability to cope with different situations. A high body fat percentage has been suggested to increase the risk of decompression sickness, whereas low muscle mass has been associated with an increased risk of musculoskeletal disorders and trauma. However, a low-fat composition may render divers vulnerable to cold and hypothermia during a dive in cold Arctic conditions. The aim of this study was to evaluate possible changes in body composition of Finnish military divers during a 15-year follow-up period (2007-2021). MATERIALS AND METHODS: We used body composition measures from military divers' fit-to-dive evaluations from the Finnish Defence Forces' Diving Medical Centre. Measurements were taken with two bioimpedance devices that function based on the electrical conductivity properties of the human body. The data from both devices were compared with Bland-Altman plots to show that the devices produced congruent data and the results from both devices could be included in the study. Possible changes in body composition were evaluated with a linear mixed model with random intercepts and slopes for each variable. RESULTS: Results from the two bioimpedance devices showed no significant differences. This allowed us to combine the results in the same data analysis. There were no apparent differences in the age of the divers between the years during the follow-up. The majority of the divers were between 25 and 30 years of age. Age correlated significantly with most measures, the clinically most significant being a higher fat percentage in older divers. However, all measures were within target values defined by the Diving Medical Centre. The divers were able to retain sufficient muscle mass in all age groups. DISCUSSION AND CONCLUSIONS: According to this study, Finnish military divers have managed to maintain a surprisingly good muscle mass in all age groups despite body composition changes due to aging in older subjects. A slight increase in fat mass can be observed with increasing age; nevertheless, the values have remained within fit-to-dive target levels. The current training routines of Finnish military divers are adequate for maintaining solid physical fitness and body composition over the course of the diving career.

Delayed treatment for decompression illness: factors associated with long treatment delays and treatment outcome.

INTRODUCTION: Effectiveness of delayed hyperbaric oxygen treatment (HBOT) for decompression illness (DCI) and factors affecting treatment delays have not been studied in large groups of patients. METHODS: This retrospective study included 546 DCI patients treated in Finland in the years 1999-2018 and investigated factors associated with recompression delay and outcome. Treatment outcome was defined as fully recovered or presence of residual symptoms on completion of HBOT. The symptoms, use of first aid oxygen, number of recompression treatments needed and characteristics of the study cohort were also addressed. RESULTS: Delayed HBOT (> 48 h) remained effective with final outcomes similar to those treated within 48 h. Cardio-pulmonary symptoms were associated with a shorter treatment delay (median 15 h vs 28 h without cardiopulmonary symptoms, P < 0.001), whereas mild sensory symptoms were associated with a longer delay (48 vs 24 h, P < 0.001). A shorter delay was also associated with only one required HBOT treatment (median 24 h vs 34 h for those requiring multiple recompressions) ( P = 0.002). Tinnitus and hearing impairment were associated with a higher proportion of incomplete recoveries (78 and 73% respectively, P < 0.001), whereas a smaller proportion of cases with tingling/itching (15%, P = 0.03), nausea (27%, P = 0.03), motor weakness (33%, P = 0.05) and visual disturbances (36%, P = 0.04) exhibited residual symptoms. Patients with severe symptoms had a significantly shorter delay than those with mild symptoms (median 24 h vs 36 h respectively, P < 0.001), and a lower incidence of complete recovery. CONCLUSIONS: Delayed HBOT remains an effective and useful intervention. A shorter delay to recompression is associated with fewer recompressions required to achieve recovery or recovery plateau.

Decompression illness in Finnish technical divers: a follow-up study on incidence and self-treatment.

INTRODUCTION: Technical diving is increasing in popularity in Finland, and therefore the number of decompression illness (DCI) cases is also increasing among technical divers. Although hyperbaric oxygen treatment (HBOT) remains the standard of care, there are anecdotal reports of technical divers treating mild DCI symptoms themselves and not seeking a medical evaluation and possible recompression therapy. This study aimed to make an epidemiologic inventory of technical diving-related DCI symptoms, to establish the incidence of self-treatment and to determine the apparent effectiveness of different treatment methods. METHODS: A one-year prospective survey with online questionnaires was conducted. Fifty-five experienced and highly trained Finnish technical divers answered the survey and reported their diving activity, DCI symptoms, symptom treatment, and treatment outcome. RESULTS: Of the reported 2,983 dives, 27 resulted in symptoms of DCI, which yielded an incidence of 91 per 10,000 dives in this study. All of the reported DCI symptoms were mild, and only one diver received HBOT. The most common self-treatments were oral hydration and rest. First aid oxygen (FAO2) was used in 21% of cases. Eventually, none of the divers had residual symptoms. CONCLUSIONS: The incidence of self-treated DCI cases was 27 times higher than that of HBO-treated DCI cases. There is a need to improve divers' awareness of the importance of FAO2 and other recommended first aid procedures and to encourage divers to seek medical attention in case of suspected DCI.

Inner ear decompression sickness in Finland: a retrospective 20-year multicenter study.

Introduction: Inner ear decompression sickness (IEDCS) is a condition from which only a minority of patients recover completely, the majority ending up with mild to moderate residual symptoms. IEDCS has been reported after deep technical dives using mixed breathing gases, and moderate recreational dives with compressed air as the breathing gas. Considering this and the high proportion of technical diving in Finland, a comparison between IEDCS cases resulting from technical and recreational dives is warranted. Methods: This is a retrospective examination of IEDCS patients treated at Hyperbaric Center Medioxygen or National Hyperbaric Centre of Turku University Hospital from 1999 to 2018. Patients were included if presenting with hearing loss, tinnitus, or vertigo and excluded if presenting only with symptoms of middle ear or cerebellar involvement. Patients were divided into technical and recreational divers, based on incident dive. Results: A total of 89 (15.6%) of all DCS patients presented with IEDCS, two-thirds treated during the latter decade. The most common predisposing factors were consecutive days of diving (47.2%), multiple dives per day (53.9%), and factors related to an increase in intrathoracic pressure (27.0%). The symptoms were cochlear in 19.1% and vestibular in 93.3% of cases, symptoms being more common and severe in technical divers. Complete recovery was achieved in 64.5% of technical and 71.4% of recreational divers. Conclusion: The incidence of IEDCS in Finland is increasing, most likely due to changing diving practices. A comprehensive examination should be carried out after an incident of IEDCS in all cases, irrespective of clinical recovery.

Assessment of Alertness and Cognitive Performance of Closed Circuit Rebreather Divers With the Critical Flicker Fusion Frequency Test in Arctic Diving Conditions.

Introduction: Cold water imposes many risks to the diver. These risks include decompression illness, physical and cognitive impairment, and hypothermia. Cognitive impairment can be estimated using a critical flicker fusion frequency (CFFF) test, but this method has only been used in a few studies conducted in an open water environment. We studied the effect of the cold and a helium-containing mixed breathing gas on the cognition of closed circuit rebreather (CCR) divers. Materials and Methods: Twenty-three divers performed an identical dive with controlled trimix gas with a CCR device in an ice-covered quarry. They assessed their thermal comfort at four time points during the dive. In addition, their skin temperature was measured at 5-min intervals throughout the dive. The divers performed the CFFF test before the dive, at target depth, and after the dive. Results: A statistically significant increase of 111.7% in CFFF values was recorded during the dive compared to the pre-dive values (p < 0.0001). The values returned to the baseline after surfacing. There was a significant drop in the divers' skin temperature of 0.48°C every 10 min during the dive (p < 0.001). The divers' subjectively assessed thermal comfort also decreased during the dive (p = 0.01). Conclusion: Our findings showed that neither extreme cold water nor helium-containing mixed breathing gas had any influence on the general CFFF profile described in the previous studies from warmer water and where divers used other breathing gases. We hypothesize that cold-water diving and helium-containing breathing gases do not in these diving conditions cause clinically relevant cerebral impairment. Therefore, we conclude that CCR diving in these conditions is safe from the perspective of alertness and cognitive performance.

Diving Responses in Experienced Rebreather Divers: Short-Term Heart Rate Variability in Cold Water Diving.

INTRODUCTION: Technical diving is very popular in Finland throughout the year despite diving conditions being challenging, especially due to arctic water and poor visibility. Cold water, immersion, submersion, hyperoxia, as well as psychological and physiological stress, all have an effect on the autonomic nervous system (ANS). MATERIALS AND METHODS: To evaluate divers' ANS responses, short-term (5 min) heart rate variability (HRV) during dives in 2-4°C water was measured. HRV resting values were evaluated from separate measurements before and after the dives. Twenty-six experienced closed circuit rebreather (CCR) divers performed an identical 45-meter decompression dive with a non-physical task requiring concentration at the bottom depth. RESULTS: Activity of the ANS branches was evaluated with the parasympathetic (PNS) and sympathetic (SNS) indexes of the Kubios HRV Standard program. Compared to resting values, PNS activity decreased significantly on immersion with face out of water. From immersion, it increased significantly with facial immersion, just before decompression and just before surfacing. Compared to resting values, SNS activity increased significantly on immersion with face out of water. Face in water and submersion measures did not differ from the immersion measure. After these measurements, SNS activity decreased significantly over time. CONCLUSION: Our study indicates that the trigeminocardiac part of the diving reflex causes the strong initial PNS activation at the beginning of the dive but the reaction seems to decrease quickly. After this initial activation, cold seemed to be the most prominent promoter of PNS activity - not pressure. Also, our study showed a concurrent increase in both SNS and PNS branches, which has been associated with an elevated risk for arrhythmia. Therefore, we recommend a short adaptation phase at the beginning of cold-water diving before physical activity.

Decompression illness (DCI) in Finland 1999-2018: Special emphasis on technical diving.

INTRODUCTION: This is the first published study on decompression illness (DCI) and its treatment in Finland. Diving conditions are demanding, as even in the summer the water temperature below 20 meters' sea/fresh water (msw/mfw) is 4-10°C. Technical diving has become more popular over the years, so the emphasis of this study was to describe DCI in technical divers and compare it with non-technical recreational divers. METHODS: This study includes by estimation over 95% of all hyperbaric oxygen-treated DCI patients during the years 1999-2018 (n = 571). The cases were divided into technical divers (n = 200) and non-technical divers (n = 371). We focused on the differences between these two groups. Technical diving was defined as the usage of mixed breathing gases, closed circuit rebreather diving or planned decompression diving. RESULTS: The mean annual number of treated DCI cases in Finland was 29 (range 16-38). The number of divers treated possibly indicate a shift towards technical diving. Technical dives were deeper and longer and were mainly performed in cold water or an overhead environment. Technical divers were more likely to utilize first aid 100% oxygen (FAO2) and sought medical attention earlier than non-technical divers. Symptom profiles were similar in both groups. Recompression was performed using USN Treatment Table Six in the majority of the cases and resulted in good final outcome. Eighty two percent were asymptomatic on completion of all recompression treatment(s). CONCLUSION: This 20-year observational study indicates a shift towards technical diving, and hence a more demanding and challenging style of diving among Finnish divers, with a surprisingly constant number of DCI cases over the years. There is still need for improvement in divers' education in use of FAO2 for DCI symptoms. Fortunately, the outcome after recompression therapy is generally successful.

Diving in the Arctic: Cold Water Immersion's Effects on Heart Rate Variability in Navy Divers.

INTRODUCTION: Diving close to the Arctic circle means diving in cold water regardless of the time of year. The human body reacts to cold through autonomous nervous system (ANS)-mediated thermoregulatory mechanisms. Diving also induces ANS responses as a result of the diving reflex. MATERIALS AND METHODS: In order to study ANS responses during diving in Arctic water temperatures, we retrospectively analyzed repeated 5-min heart rate variability (HRV) measures and the mean body temperature from dives at regular intervals using naval diving equipment measurement tests in 0°C water. Three divers performed seven dives without physical activity (81-91 min), and two divers performed four dives with physical activity after 10 min of diving (0-10 min HRV recordings were included in the study). RESULTS: Our study showed a significant increase in parasympathetic activity (PNS) at the beginning of the dives, after which PNS activity decreased significantly (measure 5-10 min). Subsequent measurements (15-20 min and onward) showed a significant increase in PNS activity over time. CONCLUSION: Our results suggest that the first PNS responses of the human diving reflex decrease quickly. Adverse effects of PNS activity should be considered on long and cold dives. To avoid concurrent sympathetic (SNS) and PNS activity at the beginning of dives, which in turn may increase the risk of arrhythmia in cold water, we suggest a short adaptation phase before physical activity. Moreover, we suggest it is prudent to give special attention to cardiovascular risk factors during pre-dive examinations for cold water divers.