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Background and Objectives : Scuba divers often experience persistent inert gas narcosis (IGN) even after surfacing. This study aimed to test the hypothesis that breathing oxygen (O 2 ) before surfacing can reduce postdive IGN. Materials and Methods : A group of 58 experienced divers underwent a 5 min dive at a depth of 50 m in a multi-place hyperbaric chamber. They were decompressed using air (air group). Another group of 28 divers (O 2 group) breathed 100% O 2 during the end of decompression. Prior to and after the dive, all participants performed the Sharpened Romberg test (SRT) and a modified tweezers test. Results : In the air group, the number of positive SRT results increased postdive (47% vs. 67%), indicating a greater impairment in the vestibular system (Cohen's d = 0.41). In the O 2 group, the percentage of positive SRT results remained constant at 68% both before and after the dive. In terms of the modified tweezers test, the air group showed no significant change in the number of picked beads (40 ± 9 vs. 39 ± 7), while the O 2 group demonstrated an increase (36 ± 7 vs. 44 ± 10) (Cohen's d = 0.34). Conclusion : The results reveal that the SRT revealed a negative effect of nitrogen (N 2 ) on the vestibular system in the air group. The increased number of beads picked in the O 2 group can be attributed to the learning effect, which was hindered in the air group. Consistent with our hypothesis, breathing O 2 during decompression appears to reduce postdive IGN.

Background: It is currently still not clarified whether diving using a self-contained breathing apparatus (SCUBA) is associated with intraocular pressure (IOP) fluctuations of clinical relevance and whether intensive diving could exacerbate the damage in glaucoma patients., Objective: This study aimed to evaluate the effect of SCUBA diving on IOP in healthy volunteers without prior eye injuries or surgery., Hypothesis: recreational diving does not lead to significant increases or fluctuations of the IOP., Material and Methods: The study included 16 divers (5 female) who performed a total of 96 dives with air or nitrox32 to a depth of 20-30 m for an average of 50 min. The central cornea thickness was measured using ultrasonic pachymetry Pocket II TM (Quantel Medical Pocket II™, Quantel Medical, Clermont-Ferrand, France), and the IOP was measured using an Icare® PRO (Icare® PRO, Icare Finland Oy, Espoo, Finland) directly before the dive and 10 min after surfacing., Results: All data refer to the right eye. Average IOP values ranged from 15.6 to 19.2 mm Hg pre-dive and 16.8 to 18.2 mm Hg post-dive. The range of IOP values was 2.2-11.5 mm Hg pre-dive (∆ = 9.3 mm Hg) and 2.7-14.8 mm Hg post-dive (∆ = 12.1 mm Hg). Of the divers 11.5% vs. 18.8% had increased IOP values > 21 mm Hg (pre-dive vs. post-dive)., Conclusion: This study found no significant differences in IOP values between pre-dive and post-dive measurements in healthy SCUBA divers. Therefore, recreational SCUBA diving is unlikely to affect the IOP in healthy individuals., (© 2023. The Author(s).)

The critical flicker fusion frequency (cFFF) refers to the frequency at which a regularly recurring change of light stimuli is perceived as steady. The cFFF threshold is often assessed in clinics to evaluate the temporal characteristics of the visual system, making it a common test for eye diseases. Additionally, it serves as a helpful diagnostic tool for various neurological and internal diseases. In the field of diving/hyperbaric medicine, cFFF has been utilized to determine alertness and cognitive functions. Changes in the cFFF threshold have been linked to the influence of increased respiratory gas partial pressures, although there exist inconsistent results regarding this effect. Moreover, the use of flicker devices has produced mixed outcomes in previous studies. This narrative review aims to explore confounding factors that may affect the accuracy of cFFF threshold measurements, particularly in open-field studies. We identify five broad categories of such factors, including (1) participant characteristics, (2) optical factors, (3) smoking/drug use, (4) environmental aspects, and (5) breathing gases and partial pressures. We also discuss the application of cFFF measurements in the field of diving and hyperbaric medicine. In addition, we provide recommendations for interpreting changes in the cFFF threshold and how they are reported in research studies.

Purpose: Scuba diving is a complex condition including elevated ambient pressure, limited air supply, increased breathing work, and unfamiliar fin-swimming. Earlier approaches to assess diving specific data did not comprehensively address these aspects. We first present an underwater ergospirometry system and then test the hypothesis that both breathing characteristics and fin-swimming style affect the air consumption., Methods/participants: A suspended-weights ergospirometry system was mounted inside a hyperbaric chamber. Ergo group: 25 divers (24.6 ± 4.1 years); three set-ups: dry normobaric cycling (75-225 W), dry cycling at 20 m simulated depth (75-225 W), fin-swimming at 20 m (5-8 kg suspended weights). Style group: 20 other divers (24.6 ± 4.1 years): fin-swimming at 20 m (5-8 kg) with regard to ventilation ([Formula: see text]E) and fin-swimming style., Results: Ergo group: linear heart rate and oxygen uptake ([Formula: see text]O 2 ) increases with both 50 W-bicycle steps and suspended-weights ergometry (r = 0.97). During hyperbaric conditions, [Formula: see text]E was less increased versus normobaric conditions. Style group: the more efficient hip/thigh-oriented style shifted towards the knee/calf-oriented style. [Formula: see text]E and [Formula: see text]O 2 were higher in beginners (< 100 dives) versus advanced divers (≥ 100 dives). Significant differences on the 5 kg-step: [Formula: see text]E: 31.5 ± 7.1 l/min vs. 23.7 ± 5.9 l/min and [Formula: see text]O 2 : 1.6 ± 0.3 l/min vs. 1.2 ± 0.3 l/min. A comparison is presented, in addition to illustrate the impact of differences in breathing characteristics and fin-swimming style., Conclusions: Diving ergospirometry with suspended weights in a hyperbaric chamber allows for comprehensive studies. Little diving experience in terms of breathing characteristics and fin-swimming style significantly increases [Formula: see text]E thereby increasing the risk of running-out-of-air., (© 2022. The Author(s).)

Hyperoxia has been described to induce bradycardia by direct stimulation of the parasympathetic nervous system. Also, hyperoxia has been found to increase blood pressure by an elevation of vascular resistance. However, the latter effect itself would induce bradycardia by baroreceptor stimulation. This single-arm monocentric retrospective study aims to evaluate the correlation between these effects by investigating the relation between oxygen (O 2 ) administration and heart rate over time. Data were collected from 23 patients without cardiovascular problems undergoing hyperbaric oxygen therapy (2.4 bar) retrospectively. During single oxygen bouts, transcutaneously measured partial pressure of O 2 was increased. During this surge of oxygen pressure, the arterial blood pressure was increased while the heart rate was decreased. Respiration rate was maintained independently from breathing 100% O 2 or air. During single oxygen bouts, the half-life of transcutaneously measured partial pressure of O 2 was 5.4 ± 2.1 mmHg/s, and the half-life of heart rate was 0.45 ± 0.19 beats/min. It has been shown that hyperbaric oxygen therapy increases the transcutaneously measured partial pressure of O 2 . This increase was rather fast, followed by a rather slow decrease in HR. This finding does not support direct vagal activation. Heart rate is not decreased due to a direct vagal activation during hyperbaric oxygen therapy. Our single-arm, retrospective study has additionally confirmed that oxidative stress injures the endothelium, and the reduced endothelial-derived vasodilators cause vasoconstriction. As a consequence, blood pressure increases, and heart rate is then further decreased via the baroreceptor reflex.

Objectives . Fire departments train divers for search, rescue and recovery in and under water. Their tasks likely exert major physical and psychological stress. This study hypothesizes that training is well balanced, following a learning spiral. Methods . Seven firefighters participated, performing 272 dives in different waters. Measurements included pulmonary function (body plethysmography); heart rate (HR) and air consumption during dives; personality variables with the state-trait anxiety inventory (STAI) and psychological stress with the task load index (NASA-TLX). Results . Pulmonary function was maintained at the end of training dives. During the dives, mean HR was 108 ± 23 bpm and mean air consumption 37 ± 15 L/min. Both values remained unchanged during training. The three highest STAI stanines (severe trait anxiety) were not considered, but median stanines and very low values were over-represented. Demands within the seven NASA-TLX areas were perceived differently. Sum of the scales 'very low', 'low' and 'mean' was ≥60%. In turn, the scale 'very high' was in none of the demands >10%. Conclusion . Physiological values remained unaltered throughout training, i.e. workload and increase in competence properly matched. The moderate manifestation of psychomental stress speaks for a group of highly selected individuals. Both candidate selection and design of the learning spiral was successful.

Oxygen-enriched air is commonly used in the sport of SCUBA-diving and might affect ventilation and heart rate, but little work exists for applied diving settings. We hypothesized that ventilation is decreased especially during strenuous underwater fin-swimming when using oxygen-enriched air as breathing gas. Ten physically-fit divers (age: 25±4; 5 females; 67±113 open-water dives) performed incremental underwater fin-swimming until exhaustion at 4 m water depth with either normal air or oxygen-enriched air (40% O 2 ) in a double-blind, randomized within-subject design. Heart rate and ventilation were measured throughout the dive and maximum whole blood lactate samples were determined post-exercise. ANOVAs showed a significant effect for the factor breathing gas (F(1, 9)=7.52; P=0.023; η 2 p =0.455), with a lower ventilation for oxygen-enriched air during fin-swimming velocities of 0.6 m·s -1 (P=0.032) and 0.8 m·s -1 (P=0.037). Heart rate, lactate, and time to exhaustion showed no significant differences. These findings indicate decreased ventilation by an elevated oxygen fraction in the breathing gas when fin-swimming in shallow-water submersion with high velocity (>0.5 m·s -1 ). Applications are within involuntary underwater exercise or rescue scenarios for all dives with limited gas supply., Competing Interests: The authors declare that they have no conflict of interest., (The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial-License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/).)

Owing to the unfamiliar environment, recreational and professional diving is confronted with several challenges. Usage of self-contained under-water breathing apparatuses during the dive provides the indispensable breathing gas supply for the diver. Instead of air, oxygen-enriched breathing gases (EANx or nitrox) are used with increasing frequency. Unfortunately, their usage implies negative effects because the elevated oxygen partial pressure (pO 2 ) increases oxidative stress. As a result, the increased formation of reactive oxygen species exerts negative effects on the central nervous system, lungs, vasculature and eyes. However, these disadvantages can be avoided if appropriate rules are followed, e.g. a pO 2 <1.4 bar. EANx breathing gases have, on the other hand, major advantages as they help reducing narcotic nitrogen effects and bubble formation. Several land-based studies had proven a reduced ventilation of exercising subjects if EANx was used instead of air. As breathing gas is the most valuable under-water good, we wanted to translate the on-land results into under-water results. Appropriate studies now demonstrate a novel EANx property as under-water ventilation is also reduced with EANx. In this short communication, we present this additional advantage of EANx-breathing. This benefit seems to be of particular importance as it delays unforeseen running-out-of-gas and thus, contributes to further improving diving safety., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2022 The Authors.)

Many recreational divers suffer medical conditions, potentially jeopardizing their safety. To scale down risks, medical examinations are mandatory and overwhelmingly performed using bicycle ergometry, which overlooks some important aspects of diving. Searching ergometric systems that better address the underwater environment, a systematic literature search was conducted using the keywords 'diving', 'fitness', 'ergometry', and 'exertion'. All presented alternative systems found convincingly describe a greatly reduced underwater physical performance. Thus, if a diver's workload in air should already be limited, he/she will suffer early from fatigue, risking a diving incident. How to assess fitness? Performance diagnostics in sports is always specific for a modality or movement. Therefore, professional scuba divers should be tested when fin-swimming underwater. For the vast number of recreational divers, the current screening can likely not be replaced. However, to prevent accidents, divers need to understand and be able to improve factors that limit their physical performance underwater. Other systems, presented here, will continue to be important tools in underwater research.

Effects of the hyperbaric environment on the autonomic nervous system (ANS) in recreational divers are not firmly settled. Aim of this exploratory study was to (1) assess ANS changes during scuba diving via recordings of electrocardiograms (ECG) and to (2) study whether nitrox40 better improves sympathovagal balance over air. 13 experienced divers (~40yrs) performed two open-water dives each breathing either air or nitrox40 (25m/39min). 3-channel ECGs were recorded using a custom-made underwater Holter-monitor. The underwater Holter system proved to be safe. Air consumption exceeded nitrox40 consumption by 12% (n = 13; p < 0.05). Both air and nitrox40 dives reduced HR (10 vs 13%; p < 0.05). The overall HRV (pNN50: 82 vs 126%; p < 0.05) and its vagal proportion (RMSSD: 33 vs 50%; p < 0.05) increased during the dive. Moreover, low (LF: 61 vs 47%) and high (HF: 71 vs 140%) frequency power were increased (all p < 0.05), decreasing the ratio of LF to HF (22 vs 34%). : Conventional open-water dives distinctly affect the ANS in experienced recreational divers, with sympathetic activation less pronounced than vagal activation thereby improving the sympathovagal balance. Nitrox40 delivered two positive results: nitrox40 consumption was lower than air consumption, and nitrox40 better improved the sympathovagal balance over air.

Introduction: Scuba diving likely has an impact on the autonomic nervous system (ANS). In the course of conducting trials of underwater ECG recording for measurement of heart rate variability, there was an unexpected stressful event; one participant's regulator iced and began to free-flow., Methods: A custom-made, water- and pressure-tight aluminum housing was used to protect a portable Holter monitor. ECGs were recorded in three experienced divers who witnessed an unplanned moderately stressful incident during diving. The ECG signals were analysed for measures of heart rate variability (HRV)., Results: Analysis for different short-term HRV measures provided consistent results if periods of interest were appropriately time-aligned. There was improvement in sympatho-vagal balance. One diver unexpectedly exhibited an increase in both sympathetic and vagal activity shortly after the incident., Conclusions: A conventional open-water dive affected the ANS of experienced recreational divers as measured by HRV which provides a global evaluation of the ANS and alterations in its two branches. The heart rate variability data gathered from several participating divers around the time of this event illustrate the potential utility of this variable in quantifying stress during diving. HRV data may be useful in addressing relevant diving related questions such as effects of cold, exercise or different breathing gases on ANS function., (Copyright: This article is the copyright of the authors who grant Diving and Hyperbaric Medicine a non-exclusive licence to publish the article in electronic and other forms.)

This short review focuses on pulmonary injury in breath-hold (BH) divers. When practicing their extreme leisure sport, they are exposed to increased pressure on pulmonary gas volumes, hypoxia, and increased partial gas pressures. Increasing ambient pressures do present a serious problem to BH deep divers, because the semi-rigid thorax prevents the deformation required by the Boyle-Mariotte law. As a result, a negative-pressure barotrauma (lung squeeze) with acute hemoptysis is not uncommon. Respiratory maneuvers such as glossopharyngeal insufflation (GI) and glossopharyngeal exsufflation (GE) are practiced to prevent lung squeeze and to permit equalizing the paranasal sinuses and the middle ear. GI not only impairs venous return, thereby provoking hypotension and even fainting, but also produces intrathoracic pressures likely to induce pulmonary barotrauma that is speculated to induce long-term injury. GE, in turn, further increases the already negative intrapulmonary pressure, thereby favoring alveolar collapse (atelectasis). Finally, hypoxia seemingly not only induces brain injury but initiates the opening of intrapulmonary shunts. These pathways are large enough to permit transpulmonary passage of venous N2 bubbles, making stroke-like phenomena in deep BH divers possible., (© 2019 S. Karger AG, Basel.)

Background: Impending cardiac surgery presents an existential experience that may induce psychological trauma. Moreover, quality of life long after successful coronary artery bypass graft surgery (CABG) can be impaired., Aim: The aim of this study was to describe the time course of anxiety and depression in patients undergoing mitral valve surgery and compare it with our earlier results of patients undergoing CABG, a disease that is likely to be related to psychosomatic disorders. We hypothesized that patients undergoing mitral valve surgery can better manage stresses of cardiac surgery than patients undergoing CABG., Patients and Methods: Of 117 patients undergoing mitral valve surgery, 100 patients (22 to 87 years; 53 females) completed the study and were interviewed before (pre), 1 week after (early), and 6 months after (late) surgery. The Hospital Anxiety and Depression Scale (HADS) was employed., Results: The proportion of patients with elevated anxiety scores (AS ≥ 8) was higher than normal (19.8%): pre, 33.0%; early, 28.0%; and was normalized late (18.0%). Similarly, depression scores (DS ≥ 8) were increased: pre, 15.0%; early, 20.0%; and late 14.0%, respectively (normal: 3.2%)., Conclusion: Coronary heart disease of CABG patients is presented as a systemic disorder, associated with both higher and postoperatively increased distress levels than in mitral valve patients. Anxiety and depression should be recognized as possible symptoms of psychosomatic disorders necessitating psychotherapeutic intervention to prevent postoperative depression and warrant patient-perceived surgical outcome that is additionally affected by expectations with respect to treatment and individual coping capacities. HADS is recommended to screen for vulnerable patients in the clinical routine, and psychosomatic support should be provided., Competing Interests: The authors confirm that there is no conflict of interests in relation to this article., (Georg Thieme Verlag KG Stuttgart · New York.)

Bubble formation during scuba diving might induce decompression sickness. This prospective randomised and double-blind study included 108 advanced recreational divers (38 females). Fifty-four pairs of divers, 1 breathing air and the other breathing nitrox28 undertook a standardised dive (24 ± 1 msw; 62 ± 5min) in the Red Sea. Venous gas bubbles were counted (Doppler) 30-<45 min (early) and 45-60 min (late) post-dive at jugular, subclavian and femoral sites. Only 7% (air) vs. 11% (air28®) (n.s.) were bubble-free after a dive. Independent of sampling time and breathing gas, there were more bubbles in the jugular than in the femoral vein. More bubbles were counted in the air-group than in the air28-group (pooled vein: early: 1845 vs. 948; P = 0.047, late: 1817 vs. 953; P = 0.088). The number of bubbles was sex-dependent. Lastly, 29% of female air divers but only 14% of male divers were bubble-free (P = 0.058). Air28® helps to reduce venous gas emboli in recreational divers. The bubble number depended on the breathing gas, sampling site and sex. Thus, both exact reporting the dive and in particular standardising sampling characteristics seem mandatory to compare results from different studies to further investigate the hitherto incoherent relation between inert gas bubbles and DCS.

About 50% of scuba divers have suffered from barotrauma of the ears and about one-third from barotrauma of paranasal sinuses. The sphenoid sinuses are rarely involved. Vital structures, as internal carotid artery and optic nerve, adjoin the sphenoid sinus. Thus, barotrauma could lead to serious neurologic disorders, including blindness. After searching the literature (Medline) and other sources (Internet), we present some cases of sphenoid sinus barotrauma, because these injuries may be underreported and misdiagnosed due to the lack of awareness and knowledge. Therefore, information is provided, e.g. on anatomical and pathophysiological features. Divers and physicians should have in mind that occasional headache during or after diving sometimes signals serious neurological disorders like vision loss. We show that injuries can develop from both negative and positive pressures in the sinuses. Because visual recovery depends on prompt diagnosis and proper therapy, physicians like otolaryngologists, ophthalmologists and neurologists need to closely collaborate.

Backround: Nitrogen narcosis impairs cognitive function, a fact relevant during SCUBA-diving. Oxygen-enriched air (nitrox) became popular in recreational diving, while evidence of its advantages over air is limited., Aim: Compare effects of nitrox28 and air on two psychometric tests., Methods: In this prospective, double-blind, open-water study, 108 advanced divers (38 females) were randomized to an air or a nitrox-group for a 60-min dive to 24 m salt water. Breathing gas effects on cognitive performance were assessed during the dive using a short- and long-term memory test and a number connection test., Results: Nitrox28 divers made fewer mistakes only on the long-term memory test (p = 0.038). Female divers remembered more items than male divers (p < 0.001). There were no significant differences in the number connection test between the groups., Conclusion: Likely owing to the comparatively low N 2 reduction and the conservative dive, beneficial nitrox28 effects to diver performance were moderate but could contribute to diving safety.

Context: It has been widely believed that tissue nitrogen uptake from the lungs during breath-hold diving would be insufficient to cause decompression stress in humans. With competitive free diving, however, diving depths have been ever increasing over the past decades., Methods: A case is presented of a competitive free-diving athlete who suffered stroke-like symptoms after surfacing from his last dive of a series of 3 deep breath-hold dives. A literature and Web search was performed to screen for similar cases of subjects with serious neurological symptoms after deep breath-hold dives., Case Details: A previously healthy 31-y-old athlete experienced right-sided motor weakness and difficulty speaking immediately after surfacing from a breathhold dive to a depth of 100 m. He had performed 2 preceding breath-hold dives to that depth with surface intervals of only 15 min. The presentation of symptoms and neuroimaging findings supported a clinical diagnosis of stroke. Three more cases of neurological insults were retrieved by literature and Web search; in all cases the athletes presented with stroke-like symptoms after single breath-hold dives of depths exceeding 100 m. Two of these cases only had a short delay to recompression treatment and completely recovered from the insult., Conclusions: This report highlights the possibility of neurological insult, eg, stroke, due to cerebral arterial gas embolism as a consequence of decompression stress after deep breath-hold dives. Thus, stroke as a clinical presentation of cerebral arterial gas embolism should be considered another risk of extreme breath-hold diving.