High-Throughput Griess Assay of Nitrite and Nitrate in Plasma and Red Blood Cells for Human Physiology Studies under Extreme Conditions.

The metabolism of nitric oxide plays an increasingly interesting role in the physiological response of the human body to extreme environmental conditions, such as underwater, in an extremely cold climate, and at low oxygen concentrations. Field studies need the development of analytical methods to measure nitrite and nitrate in plasma and red blood cells with high requirements of accuracy, precision, and sensitivity. An optimized spectrophotometric Griess method for nitrite-nitrate affords sensitivity in the low millimolar range and precision within ±2 µM for both nitrite and nitrate, requiring 100 µL of scarcely available plasma sample or less than 50 µL of red blood cells. A scheduled time-efficient procedure affords measurement of as many as 80 blood samples, with combined nitrite and nitrate measurement in plasma and red blood cells. Performance and usefulness were tested in pilot studies that use blood fractions deriving from subjects who dwelt in an Antarctica scientific station and on breath-holding and scuba divers who performed training at sea and in a land-based deep pool facility. The method demonstrated adequate to measure low basal concentrations of nitrite and high production of nitrate as a consequence of water column pressure-triggered vasodilatation in deep-water divers.

Clustering of recreational divers by their health conditions in a database of a citizen science project.

Divers Alert Network Europe has created a database with a large amount of dive-related data that has been collected since 1993 within the scope of the Diving Safety Laboratory citizen science project. The main objectives of this study are the grouping divers by their health information and revealing significant differences in diving parameters using data mining techniques. Due to the methodology of the project, data cleaning was performed before applying clustering methods in order to eliminate potential mistakes resulting from inaccuracies and missing information. Despite the fact that 63% of the data were lost during the cleaning phase, the remaining 1,169 "clean" diver data enabled meaningful clustering using the "two-step" method. Experienced male divers without any health problems are in Cluster 1. Male and female divers with health problems and high rates of cigarette smoking are in Cluster 2; healthy, overweight divers are in Cluster 3. There are significant differences in terms of dive parameters including pre- and post-dive conditions with respect to each group, such as: exercise level, alcohol consumption, thermal comfort, equipment malfunctions, and maximum depth. The study proves the usefulness of citizen science projects, while data collection methodologies can be improved to decrease potential mistakes resulting from inconsistencies, inaccuracies and missing information. It is hypothesized that if naturally occurring clusters of divers were identified it might be possible to identify risk factors arising from different clusters while merging the database with other dive accident databases in the future.

Design and Validation of a Breathing Detection System for Scuba Divers.

Drowning is the major cause of death in self-contained underwater breathing apparatus (SCUBA) diving. This study proposes an embedded system with a live and light-weight algorithm which detects the breathing of divers through the analysis of the intermediate pressure (IP) signal of the SCUBA regulator. A system composed mainly of two pressure sensors and a low-power microcontroller was designed and programmed to record the pressure sensors signals and provide alarms in absence of breathing. An algorithm was developed to analyze the signals and identify inhalation events of the diver. A waterproof case was built to accommodate the system and was tested up to a depth of 25 m in a pressure chamber. To validate the system in the real environment, a series of dives with two different types of workload requiring different ranges of breathing frequencies were planned. Eight professional SCUBA divers volunteered to dive with the system to collect their IP data in order to participate to validation trials. The subjects underwent two dives, each of 52 min on average and a maximum depth of 7 m. The algorithm was optimized for the collected dataset and proved a sensitivity of inhalation detection of 97.5% and a total number of 275 false positives (FP) over a total recording time of 13.9 h. The detection algorithm presents a maximum delay of 5.2 s and requires only 800 bytes of random-access memory (RAM). The results were compared against the analysis of video records of the dives by two blinded observers and proved a sensitivity of 97.6% on the data set. The design includes a buzzer to provide audible alarms to accompanying dive buddies which will be triggered in case of degraded health conditions such as near drowning (absence of breathing), hyperventilation (breathing frequency too high) and skip-breathing (breathing frequency too low) measured by the improper breathing frequency. The system also measures the IP at rest before the dive and indicates with flashing light-emitting diodes and audible alarm the regulator malfunctions due to high or low IP that may cause fatal accidents during the dive by preventing natural breathing. It is also planned to relay the alarm signal to underwater and surface rescue authorities by means of acoustic communication.

Continuous real-time monitoring and recording of glycemia during scuba diving: pilot study.

INTRODUCTION: Insulin-dependent diabetes has been considered a scuba diving contraindication. This is currently being reconsidered for well-controlled diabetes. We developed a real-time continuous glucose monitor (CGM) to check glycemia, or blood glucose (BG), during diving, both for prospective studies and to increase diabetic diver safety, allowing for real-time control of glycemia and hypoglycemia prevention. To ensure CGM measurement accuracy we tested the method under hyperbaric conditions. MATERIALS AND METHODS: Two experienced diabetic divers were studied during a one-week diving cruise. BG was monitored every five minutes on every dive, by a dedicated CGM, and values were visible to the divers throughout their dives. The mean of relative difference (MRD) between CGM and capillary blood glucose was calculated. Measurement accuracy was assessed according to ISO guideline 15197 and by Clarke Error Grid (CEG) analysis. RESULTS: Both divers showed gradual BG decrease during diving. Hyperbaric chamber accuracy tests showed two of 26 MRD values (7.7%) slightly exceeding the ISO-15197 allowed difference (5%). However, our data suggest that this discrepancy may have been an artefact. DISCUSSION: Our data (even limited to two subjects only) agree with the current literature showing that also in our investigated subjects diving does not imply significant risks of hypoglycemia. The use of a real-time CGM by diabetic divers during their dives can provide immediate information on BG values and trends, thus significantly improving diving safety. The accuracy tests comparing continuous glucose monitoring (CGM) and capillary blood glucose measurement (CBM) data recorded under hyperbaric conditions showed that data recorded under pressure are very close to the ISO-15197 and CEG acceptable limits.

Genetic predisposition to breath-hold diving-induced hemoptysis: Preliminary study.

INTRODUCTION: Breath-hold diving-induced hemoptysis (BH-DIH) has been reported in about 25% breath-hold divers (BHD) and is characterized by dyspnea, coughing, hemoptysis and chest pain. We investigated whether eNOS G894T, eNOS T786C and ACE insertion/deletion I/D genetic variants, are possible BH-DIH risk factors. METHODS: 108 experienced healthy instructor BHDs with the same minimum requirements (102 male, six female; mean age 43.90 ± 7.49) were studied. We looked for different eNOS G894T, eNOS T786C and ACE insertion/ deletion genetic variants between BH-DIH-positive and BH-DIH-negative subjects to identify the variants most frequently associated with BH-DIH. RESULTS: At least one BH-DIH episode was reported by 22.2% of subjects, while 77.7% never reported BH-DIH. The majority of BH-DIH-positive subjects showed eNOS G894T (p = 0.001) and eNOS-T786C (p = 0.001) genotype "TT" (high-risk profile). Prevalence of BH-DIH was higher in subjects with eNOS G894T TT genotype (50%) than in subjects with GT (9.5%, p < 0.001) and GG (24%, (p = 0.0002) genotype (low-risk profile). Similar results were observed for eNOS T786C: BH-DIH prevalence was higher in the TT genotype (41.2%) group than in the CT (15.4%, p < 0.001) and CC genotype (9.1%, p < 0.001) groups. BH-DIH prevalence was significantly higher in subjects showing ACE ID genotype (34.5%) than II (0%, p < 0.001) and DD (10.5%, p = 0.0002). Of the ACE "II" genotype group, 100% never developed BH-DIH. DISCUSSION: eNOS-G894T, eNOS-T786C and ACE influence NO availability and regulation of peripheral vascular tone and blood flow. Different genetic variants of eNOS-G894T, eNOS-T786C and ACE appear significantly related to the probability to develop BH-DIH (p < 0.001).

Flying after diving: in-flight echocardiography after a scuba diving week.

INTRODUCTION: Flying after diving may increase decompression sickness risk (DCS), but strong evidence indicating minimum preflight surface intervals (PFSI) is missing. METHODS: On return flights after a diving week on a live-aboard, 32 divers were examined by in-flight echocardiography with the following protocol: 1) outgoing flight, no previous dive; 2) during the diving week; 3) before the return flight after a 24-h PFSI; and 4) during the return flight. RESULTS: All divers completed similar multiple repetitive dives during the diving week. All dives were equivalent as to inert gas load and gradient factor upon surfacing. No bubbles in the right heart were found in any diver during the outgoing flight or at the preflight control after a 24-h PFSI following the diving week. A significant increase in the number and grade of bubbles was observed during the return flight. However, bubbles were only observed in 6 of the 32 divers. These six divers were the same ones who developed bubbles after every dive. CONCLUSIONS: Having observed a 24-h preflight interval, the majority of divers did not develop bubbles during altitude exposure; however, it is intriguing to note that the same subjects who developed significant amounts of bubbles after every dive showed equally significant bubble grades during in-flight echocardiography notwithstanding a correct PFSI. This indicates a possible higher susceptibility to bubble formation in certain individuals, who may need longer PFSI before altitude exposure after scuba diving.

Diving at altitude: from definition to practice.

Diving above sea level has different motivations for recreational, military, commercial and scientific activities. Despite the apparently wide practice of inland diving, there are three major discrepancies about diving at altitude: threshold elevation that requires changes in sea level procedures; upper altitude limit of the applicability of these modifications; and independent validation of altitude adaptation methods of decompression algorithms. The first problem is solved by converting the normal fluctuation in barometric pressure to an altitude equivalent. Based on the barometric variations recorded from a meteorological center, it is possible to suggest 600 meters as a threshold for classifying a dive as an "altitude" dive. The second problem is solved by proposing the threshold altitude of aviation (2,400 meters) to classify "high" altitude dives. The DAN (Divers Alert Network) Europe diving database (DB) is analyzed to solve the third problem. The database consists of 65,050 dives collected from different dive computers. A total of 1,467 dives were found to be classified as altitude dives. However, by checking the elevation according to the logged geographical coordinates, 1,284 dives were disqualified because the altitude setting had been used as a conservative setting by the dive computer despite the fact that the dive was made at sea level. Furthermore, according to the description put forward in this manuscript, 72 dives were disqualified because the surface level elevation is lower than 600 meters. The number of field data (111 dives) is still very low to use for the validation of any particular method of altitude adaptation concerning decompression algorithms.

Prevalence of acute respiratory symptoms in breath-hold divers.

INTRODUCTION: After repetitive deep dives, breath-hold divers are often affected by a syndrome characterized by typical symptoms such as cough, sensation of chest constriction, blood-striated expectorate (hemoptysis) and, rarely, an overt acute pulmonary edema syndrome, often together with various degrees of dyspnea. The aim of this work is an epidemiological investigation to evaluate the prevalence of acute respiratory symptoms (ARS) in breath-hold divers (BHDs) in practicing breath-hold diving. MATERIALS AND METHODS: A retrospective investigation has been performed using specific questionnaires completed by a selected sample of free-divers (212 breath-hold diving instructors--194 male, 18 female; mean age 34 +/- 6.91 years); affiliated with Apnea Academy, (International School for Education and Research of Free-Diving). We also investigated possible risk factors for post-dive acute respiratory symptoms. Furthermore, the authors report that a severe case of acute pulmonary edema occurred to a healthy and experienced breath-hold diving instructor. We reported detailed CT scan and follow-up CT scans three days later, with another scan reported 10 days later as well. RESULT: A total of 56 subjects (26.4%) reported previous events such as cough, thoracic constraint, hemoptysis, associated with various degrees of dyspnea as confirmation of pulmonary involvement. Forty-five of them (82%) reported signs of true hemoptysis and a high degrees of dyspnea. A CT scan revealed the presence of patchy bilateral lung opacities at the level of superior and parahilar zones; follow-up CT scans three days later and 10 days later are also reported. CONCLUSION: Our data show that this is a common condition among experienced BHDs. In our opinion, this is particularly interesting for the free-diving community.

Serum Amino Acid Profile Changes After Repetitive Breath-Hold Dives: A Preliminary Study.

BACKGROUND: The aim of this work was to investigate the serum amino acid (AA) changes after a breath-hold diving (BH-diving) training session under several aspects including energy need, fatigue tolerance, nitric oxide (NO) production, antioxidant synthesis and hypoxia adaptation. Twelve trained BH-divers were investigated during an open sea training session and sampled for blood 30 min before the training session, 30 min and 4 h after the training session. Serum samples were assayed for AA changes related to energy request (alanine, histidine, isoleucine, leucine, lysine, methionine, proline threonine, valine), fatigue tolerance (ornithine, phenylalanine, tyrosine), nitric oxide production (citrulline), antioxidant synthesis (cystine, glutamate, glycine) and hypoxia adaptation (serine, taurine). MAIN RESULTS: Concerning the AA used as an energy support during physical effort, we found statistically significant decreases for all the investigated AA at T1 and a gradual return to the basal value at T2 even if alanine, proline and theonine still showed a slight significant reduction at this time. Also, the changes related to the AA involved in tolerance to physical effort showed a statistically significant decrease only at T1 respect to pre-diving value and a returned to normal value at T2. Citrulline, involved in NO production, showed a clear significant reduction both at T1 and T2. Concerning AA involved in endogenous antioxidant synthesis, the behaviour of the three AA investigated is different: we found a statistically significant increase in cystine both at T1 and T2, while glycine showed a statistically significant reduction (T1 and T2). Glutamate did not show any statistical difference. Finally, we found a statistically significant decrease in the AA investigated in other hypoxia conditions serine and taurine (T1 and T2). CONCLUSIONS: Our data seem to indicate that the energetic metabolic request is in large part supported by AA used as substrate for fuel metabolism and that also fatigue tolerance, NO production and antioxidant synthesis are supported by AA. Finally, there are interesting data related to the hypoxia stimulus that indirectly may confirm that the muscle apparatus works under strong exposure conditions notwithstanding the very short/low intensity of exercise, due to the intermittent hypoxia caused by repetitive diving.

White Blood Cells, Platelets, Red Blood Cells and Gas Bubbles in SCUBA Diving: Is There a Relationship?

(1) Background: SCUBA diving can influence changes of several hematological parameters (HP) but the changes of HP in the decompression phases are still unclear. The aim of this study was to investigate any possible relationship between HP and predisposition to inert gas bubble formation after a single recreational dive. (2) Methods: Blood, obtained from 32 expert SCUBA divers, was tested for differences in white blood cells (WBC), granulocytes (GRAN), lymphocytes (LYM), and monocytes (MONO), red blood cells (RBC), and platelets (PLT) between bubblers (B) and non-bubblers (NB). (3) Results: We found inter-subject differences in bubble formation (considering the same diving profile performed by the divers) and a statistically significant higher number of total WBC, GRAN and LYM in NB as compared to the B divers in the pre and in the post diving sample, while no statistical differences were found for MONO and PLT. In addition, we did not find any statistically significant difference between NB and B in RBC. (4) Conclusions: Our results, even if in absence of investigated anti-inflammatory markers, could indicate a relationship between low WBC numbers and bubble formation. This aspect may explain a possible cause of inter-subject differences in bubble formation in divers performing the same dive profile.

Ultrasound lung "comets" increase after breath-hold diving.

The purpose of the study was to analyze the ultrasound lung comets (ULCs) variation, which are a sign of extra-vascular lung water. Forty-two healthy individuals performed breath-hold diving in different conditions: dynamic surface apnea; deep variable-weight apnea and shallow, face immersed without effort (static maximal and non-maximal). The number of ULCs was evaluated by means of an ultrasound scan of the chest, before and after breath-hold diving sessions. The ULC score increased significantly from baseline after dynamic surface apnea (p = 0.0068), after deep breath-hold sessions (p = 0.0018), and after static maximal apnea (p = 0.031). There was no statistically significant difference between the average increase of ULC scores after dynamic surface apnea and deep breath-hold diving. We, therefore, postulate that extravascular lung water accumulation may be due to other factors than (deep) immersion alone, because it occurs during dynamic surface apnea as well. Three mechanisms may be responsible for this. First, the immersion-induced hydrostatic pressure gradient applied on the body causes a shift of peripheral venous blood towards the thorax. Second, the blood pooling effect found during the diving response Redistributes blood to the pulmonary vascular bed. Third, it is possible that the intense involuntary diaphragmatic contractions occurring during the "struggle phase" of the breath-hold can also produce a blood shift from the pulmonary capillaries to the pulmonary alveoli. A combination of these factors may explain the observed increase in ULC scores in deep, shallow maximal and shallow dynamic apneas, whereas shallow non-maximal apneas seem to be not "ULC provoking".

Analysis of clinical outcomes of linear vs. deep stop decompression from 3.5 to 6 atmospheres absolute (350 - 600 kpa) in awake rats.

UNLABELLED: Recreational divers are introducing "deep stops" at half the depth (HD-DS) to reduce the risk of spinal DCS with only Doppler evidence to support it. Therefore this research was designed to show the effect of an HD-DS on spinal DCS manifestations by evaluating whether: (1) air diving-induced spinal DCS could be produced in awake, freely moving rats at 3.5-6.0 atm abs (350-600 kPa); and (2) whether the introduction of an HD-DS reduced spinal DCS in such a model. Fifty-one female, Wistar rats (221 to 450 g) underwent one-hour compression at 350 to 600 kPa with seven minutes of decompression with/without a five-minute DS (HD-DS / No-DS). Animals were observed for three hours. Outcomes were classified as: (1) asymptomatic; (2) breathing difficulties; (3) paralysis/weakness; (4) immobility; or (5) death. Eight animals, exposed to 385 kPa air breathing for 60 minutes followed by a three-staged decompression of 7.5 minutes, remained asymptomatic. The profile is known to produce spinal DCS in anesthetized rats. Eleven animals were then used to determine the threshold for DCS: 500 kPa. A total of 14 animals were compressed to 550 kPa (Group 1). Group 1-A (n = 8) No-DS; Group 1-B (n = 6) HD-DS; 18 were compressed to 600 kPa (Group 2). Group 2-A (n = 8) No-DS; Group 2-B (n = 10) HD-DS. RESULTS: (1) 385 kPa protocol did not produce visible DCS manifestations in awake rats. The binomial probability of no DCS in this sample size is 0.002818 for the proportion expected from a published report. The binomial probability of no fatalities is 0.005346). (2) No animals developed spinal DCS when assessed by visible paralysis/weakness or immobility, so no difference could be shown. Group 1-A: two deaths; two breathing abnormalities; four asymptomatic. Group 1-B: all asymptomatic. Difference recorded for breathing difficulties (p = 0.0483); none for fatalities (p = 0.2024). Group 2 mortality was 55% (n = 10). Group 2-A and 2-B: no difference for death (p = 0.6063) or breathing problems (p = 0.2084). CONCLUSIONS: This model could not evaluate HD-DS for the prevention of spinal DCS in rats.

Increased Risk of Decompression Sickness When Diving With a Right-to-Left Shunt: Results of a Prospective Single-Blinded Observational Study (The "Carotid Doppler" Study).

Introduction: Divers with a patent Foramen Ovale (PFO) have an increased risk for decompression sickness (DCS) when diving with compressed breathing gas. The relative risk increase, however, is difficult to establish as the PFO status of divers is usually only determined after a DCS occurrence. Methods: This prospective, single-blinded, observational study was designed to collect DCS data from volunteer divers after screening for right-to-left shunt (RLS) using a Carotid Doppler test. Divers were blinded to the result of the test, but all received a standardized briefing on current scientific knowledge of diving physiology and "low-bubble" diving techniques; they were then allowed to dive without restrictions. After a mean interval of 8 years, a questionnaire was sent collecting data on their dives and cases of DCS (if any occurred). Results: Data was collected on 148 divers totaling 66,859 dives. There was no significant difference in diving data between divers with or without RLS. Divers with RLS had a 3.02 times higher incidence of (confirmed) DCS than divers without RLS (p = 0.04). When all cases of (confirmed or possible DCS) were considered, the Relative Risk was 1.42 (p = 0.46). DCS occurred mainly in divers who did not dive according to "low-bubble" diving techniques, in both groups. Conclusion: This prospective study confirms that DCS is more frequent in divers with RLS (such as a PFO), with a Relative Risk of 1.42 (all DCS) to 3.02 (confirmed DCS). It appears this risk is linked to diving behavior, more specifically diving to the limits of the adopted decompression procedures.

Endothelial Nitric Oxide Production and Antioxidant Response in Breath-Hold Diving: Genetic Predisposition or Environment Related?

INTRODUCTION: Nitric oxide (NO) is an essential signaling molecule modulating the endothelial adaptation during breath-hold diving (BH-diving). This study aimed to investigate changes in NO derivatives (NOx) and total antioxidant capacity (TAC), searching for correlations with different environmental and hyperbaric exposure. MATERIALS AND METHODS: Blood samples were obtained from 50 breath-hold divers (BH-divers) before, and 30 and 60 min after the end of training sessions performed both in a swimming pool or the sea. Samples were tested for NOx and TAC differences in different groups related to their hyperbaric exposure, experience, and additional genetic polymorphism. RESULTS: We found statistically significant differences in NOx plasma concentration during the follow-up (decrease at T30 and increase at T60) compared with the pre-dive values. At T30, we found a significantly lower decrease of NOx in subjects with a higher diving experience, but no difference was detected between the swimming pool and Sea. No significant difference was found in TAC levels, as well as between NOx and TAC levels and the genetic variants. CONCLUSION: These data showed how NO consumption in BH-diving is significantly lower in the expert group, indicating a possible training-related adaptation process. Data confirm a significant NO use during BH-diving, compatible with the well-known BH-diving related circulatory adaptation suggesting that the reduction in NOx 30 min after diving can be ascribed to the lower NO availability in the first few minutes after the dives. Expert BH-divers suffered higher oxidative stress. A preliminary genetic investigation seems to indicate a less significant influence of genetic predisposition.

Serum Cardiac and Skeletal Muscle Marker Changes in Repetitive Breath-hold Diving.

BACKGROUND: Breath-hold diving (BH-diving) is associated to extreme environmental conditions, prolonged physical activity, and complex adaptation mechanisms to supply enough O2 to vital organs. Consequently, one of the biggest effects could be an increased exercise-induced muscle fatigue, in both skeletal and cardiac muscles that can induce an increase of muscles injury markers including creatine kinase (CK), aspartate transferase (AST), and alanine transferase (ALT) when concerning the skeletal muscle, cardiac creatine kinase isoenzyme (CK-MBm) and cardiac troponin I (cTnI) when concerning the cardiac muscle, and lactate dehydrogenase (LDH) as index of muscle stress. The aim of this study is to investigate serum cardiac and skeletal muscle markers before and after a BH-diving training session. RESULTS: We found statistically significant increases of CK (T0: 136.1% p < 0.0001; T1: 138.5%, p < 0.0001), CK-MBm (T0: 145.1%, p < 0.0001; T1: 153.2%, p < 0.0001) LDH (T0: 110.4%, p < 0.0003; T1: 110.1%, p < 0.0013) in both T0 and T1 blood samples, as compared to basal value. AST showed a statistically significant increase only at T0 (106.8%, p < 0.0007) while ALT did not exhibit statistically significant changes. We did not find any changes in cTnI levels between pre-dive and post-dive samples. CONCLUSIONS: Our data seem to indicate that during a BH-diving training session, skeletal and cardiac muscles react to physical effort releasing stress-related substances. Although the peculiar nature of BH-diving makes it difficult to understand if our results are related only to exercise induced muscle adaptation or whether acute hypoxia or a response to environmental changes (pressure) play a role to explain the observed changes, further studies are needed to better understand if these biomarker changes are linked to physical exercise or to acute hypoxia, or if both conditions play a role.

Heart Rate Variability During a Standard Dive: A Role for Inspired Oxygen Pressure?

Introduction: Heart rate variability (HRV) during underwater diving has been infrequently investigated because of environment limitations and technical challenges. This study aims to analyze HRV changes while diving at variable hyperoxia when using open circuit (OC) air diving apparatus or at constant hyperoxia using a closed-circuit rebreather (CCR). We used HRV analysis in time and frequency domain adding nonlinear analysis which is more adapted to short-time analysis and less dependent on respiratory rate (Sinus respiratory arrhythmia). Materials and Methods: 18 males, 12 using OC (30 mfw for 20 min) and 6 using CCR (30 mfw for 40 min.). HRV was recorded using a polar recorder. Four samples of R-R intervals representing the dive were saved for HRV analysis. Standard deviation of normal-to-normal intervals (SDNN), square root of the mean squared differences between successive RR intervals (rMSSD), and average RR intervals (RR) in time-domain; low frequency (LF) and high frequency (HF) in frequency domain were investigated. Nonlinear analysis included fractal dimension (FrD). Results: SDNN and rMSSD were significantly increased during descent and at depth with OC, not with CCR. Mean RR interval was longer at depth with OC, but only during ascent and after the dive with CCR. HF power was higher than baseline during the descent both with OC and CCR and remained elevated at depth for OC. The LF/HF ratio was significantly lower than baseline for descent and at depth with both OC and CCR. After 30 min of recovery, the LF/HF ratio was higher than baseline with both OC and CCR. Nonlinear analysis detected differences at depth for OC and CCR. Discussion: Increased parasympathetic tone was present during diving. RR duration, SDNN; rMSSD, HF spectral power all increased during the dive above pre-dive levels. Conversely, HF power decreased (and the LF/HF increased) 30 min after the dive. Using FrD, a difference was detected between OC and CCR, which may be related to differences in partial pressure of oxygen breathed during the dive.

Decompression illness medically reported by hyperbaric treatment facilities: cluster analysis of 1929 cases.

INTRODUCTION: The term decompression illness (DCI) describes maladies resulting from inadequate decompression, but there is little consensus concerning clinically useful DCI subclasses. Our aim was to explore an objective DCI classification using multivariate statistics to assess naturally associated clusters of DCI manifestations. We also evaluated their mapping onto other DCI classifications and investigated the association with therapeutic outcome. METHODS: We defined the optimal number of clusters using "two-step" cluster analysis and Bayesian information criterion with confirmation by hierarchical clustering with squared Euclidian distances and Ward's method. The data were 1929 DCI cases reported by hyperbaric chambers to the Divers Alert Network (DAN America) from 1999-2003. RESULTS: Four robust and highly significant clusters of DCI manifestations were demonstrated containing 300, 741, 333, and 555 patients. Each cluster had characteristic manifestations. Cluster 1 was effectively pain only. For Cluster 2, characteristic manifestations included numbness, paresthesia, and decreased skin sensitivity; for Cluster 3, malaise, paralysis, muscular weakness, and bladder-bowel dysfunction; and for Cluster 4, hearing loss, localized skin swelling, tinnitus, skin rash and mottling, confusion, dyspnea/chokes, muscular problems, vision problems, altered consciousness, headache, vertigo, nausea, fatigue, dizziness, and abnormal sensations. DISCUSSION: Internal reliability was confirmed by arbitrarily dividing the dataset into two parts and repeating the analysis. The clusters mapped poorly onto traditional DCI categories (AGE, Type I DCS, Type II DCS), but more specifically onto the Perceived Severity Index (PSI). All three classification methods (DCI, Cluster, PSI) predicted complete relief of manifestations equally well. We conclude that cluster analysis is an objective method for classifying DCI manifestations independent of clinical judgment.

Endothelial function may be enhanced in the cutaneous microcirculation after a single air dive.

INTRODUCTION: The effects of scuba diving on the vessel wall have been studied mainly at the level of large conduit arteries. Data regarding the microcirculation are scarce and indicate that these two vascular beds are affected differently by diving. METHODS: We assessed the changes in cutaneous microcirculation before an air scuba dive, then 30 min and 24 h after surfacing. Endothelium-dependent and independent vasomotion were successively elicited by iontophoretic administration of acetylcholine and sodium nitroprusside respectively, and cutaneous blood flux was monitored by laser Doppler flowmetry. RESULTS: The response to sodium nitroprusside was significantly lower 30 min after surfacing than before diving (50 (SEM 6)% of the pre-dive values, P = 0.0003) and returned to normal values 24 h post-dive (102 (29)% of the pre-dive values, P = 0.113). When compared to pre-dive values, acetylcholine elicited a hyperaemia which was not statistically different 30 min after surfacing (123 (17)% of the pre-dive values, P = 0.230), but significantly increased 24 h post-dive (148 (10)% of the pre-dive values, P = 0.005). CONCLUSION: Microvascular smooth muscle function is transiently impaired after diving. On the contrary, microvascular endothelial function is enhanced for up to 24 h after diving. This further suggests that the microcirculation reacts differently than large conduit arteries to scuba diving. The impact of modifications occurring in the microvascular bed on the physiological effects of diving merits further study.

Association Between Heart Rate Variability and Decompression-Induced Physiological Stress.

The purpose of this study was to analyze the correlation between decompression-related physiological stress markers, given by inflammatory processes and immune system activation and changes in Heart Rate Variability, evaluating whether Heart Rate Variability can be used to estimate the physiological stress caused by the exposure to hyperbaric environments and subsequent decompression. A total of 28 volunteers participated in the experimental protocol. Electrocardiograms were performed; blood samples were obtained for the quantification of red cells, hemoglobin, hematocrit, neutrophils, lymphocytes, platelets, aspartate transaminase (AST), alanine aminotransferase (ALT), and for immunophenotyping and microparticles (MP) research through Flow Cytometry, before and after each experimental protocol from each volunteer. Also, myeloperoxidase (MPO) expression and microparticles (MPs) deriving from platelets, neutrophils and endothelial cells were quantified. Negative associations between the standard deviation of normal-to-normal intervals (SDNN) in the time domain, the High Frequency in the frequency domain and the total number of circulating microparticles was observed (p-value = 0.03 and p-value = 0.02, respectively). The pre and post exposure ratio of variation in the number of circulating microparticles was negatively correlated with SDNN (p-value = 0.01). Additionally, a model based on the utilization of Radial Basis Function Neural Networks (RBF-NN) was created and was able to predict the SDNN ratio of variation based on the variation of specific inflammatory markers (RMSE = 0.06).

Nitric Oxide and Oxidative Stress Changes at Depth in Breath-Hold Diving.

BACKGROUND: Several mechanisms allow humans to resist the extreme conditions encountered during breath-hold diving. Available nitric oxide (NO) is one of the major contributors to such complex adaptations at depth and oxidative stress is one of the major collateral effects of diving. Due to technical difficulties, these biomarkers have not so far been studied in vivo while at depth. The aim of this study is to investigate nitrate and nitrite (NOx) concentration, total antioxidant capacity (TAC) and lipid peroxidation (TBARS) before, during, and after repetitive breath-hold dives in healthy volunteers. MATERIALS AND METHODS: Blood plasma, obtained from 14 expert breath-hold divers, was tested for differences in NOx, TAC, and TBARS between pre-dive, bottom, surface, 30 and 60 min post-dive samples. RESULTS: We observed a statistically significant increase of NOx plasma concentration in the "bottom blood draw" as compared to the pre-dive condition while we did not find any difference in the following samples We found a statistically significant decrease in TAC at the bottom but the value returned to normality immediately after reaching the surface. We did not find any statistically significant difference in TBARS. DISCUSSION: The increased plasma NOx values found at the bottom were not observed at surface and post dive sampling (T0, T30, T60), showing a very rapid return to the pre-dive values. Also TAC values returned to pre- diving levels immediately after the end of hyperbaric exposure, probably as a consequence of the activation of endogenous antioxidant defenses. TBARS did not show any difference during the protocol.