Splenic contraction during breath-hold diving in the Korean ama

Major increases of hemoglobin concentration and hematocrit, possibly secondary to splenic contraction, have been noted during diving in the Weddell seal. We sought to learn whether this component of the diving response could be present in professional human breath-hold divers. Splenic size was measured ultrasonically before and after repetitive breath-hold dives to approximately 6-m depth in ten Korean ama (diving women) and in three Japanese male divers who did not routinely practice breath-hold diving. Venous hemoglobin concentration and hematocrit were measured in nine of the ama and all Japanese divers. In the ama, splenic length and width were reduced after diving (P = 0.0007 and 0.0005, respectively) and calculated splenic volume decreased 19.5 +/- 8.7% (mean +/- SD, P = 0.0002). Hemoglobin concentration and hematocrit increased 9.5 +/- 5.9% (P = 0.0009) and 10.5 +/- 4% (P = 0.0001), respectively. In Japanese male divers, splenic size and hematocrit were unaffected by repetitive breath-hold diving and hemoglobin concentration increased only slightly over baseline (3.0 +/- 0.6%, P = 0.0198). Splenic contraction and increased hematocrit occur during breath-hold diving in the Korean ama.     

Ascent rate, age, maximal oxygen uptake, adiposity, and circulating venous bubbles after diving.

Decompression sickness in diving is recognized as a multifactorial phenomenon, depending on several factors, such as decompression rate and individual susceptibility. The Doppler ultrasonic detection of circulating venous bubbles after diving is considered a useful index for the safety of decompression because of the relationship between bubbles and decompression sickness risk. The aim of this study was to assess the effects of ascent rate, age, maximal oxygen uptake (VO(2 max)), and percent body fat on the production of bubbles after diving. Fifty male recreational divers performed two dives at 35 m during 25 min and then ascended in one case at 9 m/min and in the other case at 17 m/min. They performed the same decompression stops in the two cases. Twenty-eight divers were Doppler monitored at 10-min intervals, until 60 min after surfacing, and the data were analyzed by Wilcoxon signed-rank test to compare the effect of ascent rate on the kinetics of bubbles. Twenty-two divers were monitored 60 min after surfacing. The effect on bubble production 60 min after surfacing of the four variables was studied in 47 divers. The data were analyzed by multinomial log-linear model. The analysis showed that the 17 m/min ascent produced more elevated grades of bubbles than the 9 m/min ascent (P < 0.05), except at the 40-min interval, and showed relationships between grades of bubbles and ascent rate and age and interaction terms between VO(2 max) and age, as well as VO(2 max) and percent body fat. Younger, slimmer, or aerobically fitter divers produced fewer bubbles compared with older, fatter, or poorly physically fit divers. These findings and the conclusions of previous studies performed on animals and humans led us to support that ascent rate, age, aerobic fitness, and adiposity are factors of susceptibility for bubble formation after diving.     

Separation of Forearm Hemodynamics Into Skin and Muscle Components by Means of I-Epinephrine Iontophoresis

By a combination of iontophoresis of I-epinephrine into the skin of one arm and simultaneous venous occlusion plethysmography in both treated (muscle only) and untreated forearms (muscle plus skin), we examined in 16 normal volunteers forearm blood flow, capillary filtration coefficient and venous capacity at cuff pressure of 40 mm of mercury (VC₄₀) at rest, during tonic finger exercise and after interrupted repetitive finger exercise. Blood pressure did not change during the testing procedure. Forearm muscle conductance was about 60% to 70% of total conductance and was positively correlated with total conductance during rest and exercise. With standard exercises muscle conductance rises to 1½ to 2½ times resting level, and skin conductance rises to 2½ to 4½ times resting level. The capillary filtration coefficient is almost entirely in the muscle. It doubles in value with tonic exercise but decreases to half its resting value after interrupted repetitive exercise despite greatly increased conductance. Therefore, repetitive exercise-induced dissociation between conductance and filtration surface occurs in striated muscle. The mechanism is yet unknown. VC₄₀ in muscle is about 84% of total forearm VC₄₀. During tonic exercise muscle VC₄₀ was reduced, and during interrupted repetitive exercise the values for muscle and skin returned to resting values. A high correlation between muscle only and muscle-plus-skin for forearm blood flow and the identify between arms for measuring capillary filtration coefficient makes iontophoresis unnecessary for determining these values in forearm striated muscle under these experimental conditions.     

Specifics of Gas Bubble Formation and Growth in Tissues during Decompression after Saturation Dives

It is shown that the decompression schedules after saturation diving to the depth of 30 m designed to hold the nitrogen supersaturation for the most “slow” tissues at the acceptable levels is significantly shorter than the decompression schedules with zero supersaturation of these tissues with nitrogen and all dissolved gases. Equality of the risk for decompression sickness (DCS) onset during this decompression schedule to the risk of DCS onset under non-stop ascent to the surface after saturation diving to the depth of 6.1 m indicates that the effect of the high ambient pressure decreases the density of gas bubble seeds in tissues and the growth rate of their total volume. The DCS symptoms in the experienced divers under dangerous decompression profiles not appear due to the lower density of gas bubble seeds in their tissues relatively to the average level inherent to the many of humans.     

Research on nitrogen-oxygen saturation diving with repetitive excursions

For some tasks of underwater operation the need for longer dive duration and more working divers necessitates the use of saturation diving techniques with excursions. Saturation diving with excursion has high working efficiency. A collaborative experiment with Chinese Underwater Technology Institute, American National Office of Research Undersea Program and Hamilton Research Ltd. was conducted at our Institute in Shanghai. The main experiment objectives were to assess the longer, deeper repetitive excursions during nitrogen-oxygen saturation situation, oxygen exposure management, nitrox saturation decompression after excursions and performance aspects. Four Chinese professional experienced divers were saturated at 25 msw for 5 days at the hyperbaric facility, where they did 15 air excursions to depths between 50 and 75 msw, for duration up to 240 min. Decompression from excursions to the storage were mostly no-stops, but 5 required stops for 3 to 116 min. Saturation decompression began with the "precursory" ascent following a brief return to 25 msw. Doppler bubble detection showed some bubbles of Spencer Grade II and occasionally III, following excursions and during saturation decompression, especially after muscle flexing. No symptoms of decompression sickness were reported: one diver was more of fatigued on one occasion than other times. Oxygen exposure reached its peak of 3103 Oxygen Toxicity Units on Day 6. The only subjective symptom of oxygen toxicity was mild and transient numb fingertips. No significant change was seen in vital capacity.     

Simulated high altitude diving experiment for the underwater construction operation

The simulated dive experiments were conducted at the high altitude of 4500 meters and 5000 meters, for the requirement of diving operation in the lakes at the altitude of 4442 meters for the construction of large-scale hydroelectric power station. The high & low pressure chamber-complex was used, and 15 professional divers participated in the experiment. The divers were stayed at the altitude of 4500 and 5000 meters for 7-9 days. Totally 85 persons-times of dives to the depths of 30-50 meters were operated; they stayed under the water for 30-90 minutes while processing physical activities. During the experiment, we studied the pressurization procedure, decompression table, and physiological functions of the divers. The results indicate that, although the relative pressure differences between the surface and underwater was larger at high altitude than at sea level, the appropriate prolongation of the compression time was able to prevent the difficulty in pressure regulation for the divers to avoid the injury of middle ear. Four tables of the decompression A, B, C and D was calculated with Haldane's theory, and the speed of decompression increased in the order from A to D. The safest procedure was C, and there was no decompression sickness and bubbles in body of the divers. The methods of decompression included underwater stage decompression, surface decompression, oxygen-breathing decompression, and repetitive diving decompression. The surface decompression was the most suitable method for the high altitude, as it could greatly decrease the time in the cold water for the divers. The power spectrum analysis of EEG (electroencephalogram) indicated that, when the divers were exposed to the altitude of 5000 meters, the delta activity in EEG increased, alpha and beta activity decreased. And the delta activity decreased, the alpha and beta activity increased while diving during a dry condition. According to the diving and decompression procedure studied under simulated conditions, 272 person-times of diving training and underwater operations were processed in a high altitude hydroelectric power station at the altitude of 4442 meters, including photographing, video-recording, measuring, and drilling. There were no signs and symptoms of decompression sickness and bubbles.     

Norwegian deep diving trials

In 1983 NUTEC, together with two diving companies, completed two dives with 12 divers (6 in each dive) to pressures equivalent to 350 m s.w., one dive lasted for 17 d, and the other, 24 d. The purpose of the dives was to demonstrate that the diving companies were prepared for diving to 300 m depth in the North Sea. No major medical or physiological problems arose during the dives, although all divers had minor symptoms of high pressure nervous syndrome during compressions. During decompression three decompression sickness incidents occurred, which involved pain only, and all were successfully treated. All divers went through comprehensive medical physiological examinations before and after the dives. No significant changes from values measured before diving have been found in the six divers who have so far been examined after diving, except that five of them were considerably more sensitive to CO2 after the dive than before. Several problems arose in connection with the divers' breathing equipment, thermal protection and communication, which need to be improved.     

Exercise-induced intrapulmonary shunting of venous gas emboli does not occur after open-sea diving.

Paradoxical arterializations of venous gas emboli can lead to neurological damage after diving with compressed air. Recently, significant exercise-induced intrapulmonary anatomical shunts have been reported in healthy humans that result in widening of alveolar-to-arterial oxygen gradient. The aim of this study was to examine whether intrapulmonary shunts can be found following strenuous exercise after diving and, if so, whether exercise should be avoided during that period. Eleven healthy, military male divers performed an open-sea dive to 30 m breathing air, remaining at pressure for 30 min. During the bottom phase of the dive, subjects performed mild exercise at approximately 30% of their maximal oxygen uptake. The ascent rate was 9 m/min. Each diver performed graded upright cycle ergometry up to 80% of the maximal oxygen uptake 40 min after the dive. Monitoring of venous gas emboli was performed in both the right and left heart with an ultrasonic scanner every 20 min for 60 min after reaching the surface pressure during supine rest and following two coughs. The diving profile used in this study produced significant amounts of venous bubbles. No evidence of intrapulmonary shunting was found in any subject during either supine resting posture or any exercise grade. Also, short strenuous exercise after the dive did not result in delayed-onset decompression sickness in any subject, but studies with a greater number of participants are needed to confirm whether divers should be allowed to exercise after diving.     

Effect of N2-He-O2 on decompression outcome in rats after variable time-at-depth dives

No study of decompression sickness has examined both variable gas mixtures and variable time at depth to the point of statistical significance. This investigation examined the effect of N2-He-O2 on decompression outcome in rats after variable time-at-depth dives. Unanesthetized male albino rats were subjected to one of two series of simulated dives: 1) N2-He-O2 dives (20.9% O2) at 175 feet of seawater fsw) and 2) N2-O2 dives (variable percentage of O2; depths from 141 to 207 fsw). Time at depth ranged from 10 to 120 min; rats were then decompressed within 10 s to surface pressure. The probability of decompression sickness (severe bends symptoms or death) was analyzed with a Hill equation model, with parameters for gas potency and equilibrium time for the three gases and weight of the animal. Relative potencies for the three gases were of similar magnitude for bends and statistically different for death in ascending order: O2 less than He less than N2. Estimated gas uptake rates were different. N2 took three to four times as long as He to reach full effect; the rate of O2 appeared to be considerably shorter than that of N2 or He. The large influence of O2 on decompression outcome questions the simplistic view that O2 cannot contribute to the decompression requirement.     

Biophysical basis for inner ear decompression sickness.

Isolated inner ear decompression sickness (DCS) is recognized in deep diving involving breathing of helium-oxygen mixtures, particularly when breathing gas is switched to a nitrogen-rich mixture during decompression. The biophysical basis for this selective vulnerability of the inner ear to DCS has not been established. A compartmental model of inert gas kinetics in the human inner ear was constructed from anatomical and physiological parameters described in the literature and used to simulate inert gas tensions in the inner ear during deep dives and breathing-gas substitutions that have been reported to cause inner ear DCS. The model predicts considerable supersaturation, and therefore possible bubble formation, during the initial phase of a conventional decompression. Counterdiffusion of helium and nitrogen from the perilymph may produce supersaturation in the membranous labyrinth and endolymph after switching to a nitrogen-rich breathing mixture even without decompression. Conventional decompression algorithms may result in inadequate decompression for the inner ear for deep dives. Breathing-gas switches should be scheduled deep or shallow to avoid the period of maximum supersaturation resulting from decompression.     

Cerebral gas embolism absorption during hyperbaric therapy: theory.

Cerebral gas embolism is a serious consequence of diving. It is associated with decompression sickness and is assumed to cause severe neurological dysfunction. A mathematical model previously developed to calculate embolism absorption time based on in vivo bubble geometry is used in which various conditions of hyperbaric therapy are considered. Effects of varying external pressure and inert gas concentrations in the breathing mixtures, according to US Navy and Royal Navy diving treatment tables, are predicted. Recompression alone is calculated to reduce absorption times of a 50-nl bubble by up to 98% over the untreated case. Lowering the inhaled inert gas concentration from 67.5% to 50% reduces absorption time by 37% at a given pressure. Bubbles formed after diving and decompression with He are calculated to absorb up to 73% faster than bubbles created after diving and decompression with air, regardless of the recompression gas breathed. This model is a useful alternative to impractical clinical trials in assessing which initial step in hyperbaric therapy is most effective in eliminating cerebral gas embolisms should they occur.     

Simulated breath-hold diving to 20 meters: cardiac performance in humans

Cardiac performance was assessed in six subjects breath-hold diving to 20 m in a hyperbaric chamber, while nonsubmersed or submersed in a thermoneutral environment. Cardiac index and systolic time intervals were obtained with impedance cardiography and intrathoracic pressure with an esophageal balloon. Breath holding at large lung volume (80% vital capacity) decreased cardiac index, probably by increasing intrathoracic pressure and thereby impeding venous return. During diving, cardiac index increased (compared with breath holding at the surface) by 35.1% in the nonsubmersed and by 29.5% in the submersed condition. This increase was attributed to a fall in intrathoracic pressure. Combination of the opposite effects of breath holding and diving to 20 m left cardiac performance unchanged during the dives (relative to the surface control). A larger intrathoracic blood redistribution probably explains a smaller reduction in intrathoracic pressure observed during submersed compared with nonsubmersed diving. Submersed breath-hold diving may entail a smaller risk of thoracic squeeze (lesser intrathoracic pressure drop) but a greater risk of overloading the central circulation (larger intrathoracic blood pooling) than simulated nonsubmersed diving.     

REPETITIVE SHALLOW DIVES POSE DECOMPRESSION RISK IN DEEP-DIVING BEAKED WHALES

The impact of naval sonar on beaked whales is of increasing concern. In recent years the presence of gas and fat embolism consistent with decompression sickness (DCS) has been reported through postmortem analyses on beaked whales that stranded in connection with naval sonar exercises. In the present study, we use basic principles of diving physiology to model nitrogen tension and bubble growth in several tissue compartments during normal diving behavior and for several hypothetical dive profiles to assess the risk of DCS. Assuming that normal diving does not cause nitrogen tensions in excess of those shown to be safe for odontocetes, the modeling indicates that repetitive shallow dives, perhaps as a consequence of an extended avoidance reaction to sonar sound, can indeed pose a risk for DCS and that this risk should increase with the duration of the response. If the model is correct, then limiting the duration of sonar exposure to minimize the duration of any avoidance reaction therefore has the potential to reduce the risk of DCS.     

Time course of deacclimatization to cold water immersion in Korean women divers

Seasonal basal metabolic rates (BMR), critical water temperature (Tcw), maximal body insulations (Imax), and finger blood flow during hand immersion in 6 degrees C water (Q finger) were measured periodically during the course of a 3-yr longitudinal study (1980-1982) of modern Korean diving women (ama), who have been wearing wet suits since 1977 to avoid cold stress during work. Methods and protocols were identical to previous studies of cotton-suited ama from 1961-1974. The BMR of modern ama did not undergo seasonal fluctuation (1980-1981) and was within the DuBois standard and comparable to nondivers year around Tcw of ama was still reduced by 2-3 degrees C in 1980 but increased progressively to equal that of nondivers in 1982, when compared at comparable subcutaneous fat thickness (SFT). Since modern ama and nondivers have 2.4 times thicker SFT (i.e., 4-13 mm) than in 1962 the absolute Tcw is significantly reduced. Q finger of ama was also significantly lower than controls in 1980 but in 1981-1982 was identical to controls. Imax of modern ama was identical to controls of comparable SFT in 1980-1982. The time course of cold deacclimatization thus was BMR, 3 yr; Imax, 3 yr; Q finger, 4 yr; and Tcw, 5 yr. This longitudinal study provides further evidence that acclimatization to cold did at one time exist in these diving women.     

Change in plasma amino acid concentrations during breath-hold diving at high altitude

We studied the plasma concentration of various amino acids in 6 Italian sport divers in Italy and at approximately 4,500 m altitude in Peru; 6 Peruvian inhabitants were examined for comparison. We attempted to create a situation of pronounced hypoxia in muscles by breath-hold diving at altitude. The diving reflex diverts blood away from muscles while diving increases central oxygen tension and prevents loss of consciousness. Differences in certain amino acids, probably related to diet, were noted between Italy and Peru. Increases in concentration of plasma alanine and some branched-chain amino acids occurred after breath-hold diving. These changes were similar to those seen after prolonged hard exercise, even though physical work was low. Hypoxia in muscles, common during hard work and during breath-hold diving at altitude, might thus be the stimulus for amino acid release from working muscles.     

Lung collapse in the diving sea lion: hold the nitrogen and save the oxygen

Lung collapse is considered the primary mechanism that limits nitrogen absorption and decreases the risk of decompression sickness in deep-diving marine mammals. Continuous arterial partial pressure of oxygen profiles in a free-diving female California sea lion (Zalophus californianus) revealed that (i) depth of lung collapse was near 225 m as evidenced by abrupt changes in during descent and ascent, (ii) depth of lung collapse was positively related to maximum dive depth, suggesting that the sea lion increased inhaled air volume in deeper dives and (iii) lung collapse at depth preserved a pulmonary oxygen reservoir that supplemented blood oxygen during ascent so that mean end-of-dive arterial was 74 ± 17 mmHg (greater than 85% haemoglobin saturation). Such information is critical to the understanding and the modelling of both nitrogen and oxygen transport in diving marine mammals.     

Near infrared monitoring of human skeletal muscle oxygenation during forearm ischemia

Changes in tissue oxygenation of forearm muscles were measured by near infrared (NIR) spectrophotometry in 10 healthy adults during tourniquet ischemia and venous outflow restriction. Muscle O2 stores were depleted rapidly by forearm ischemia manifest by a progressive decrease in tissue oxyhemoglobin and oxymyoglobin over 4-5 min. Muscle ischemia significantly decreased the oxidation level of cytochrome aa3, to below resting base line after only 1.5 min, and the enzyme became fully reduced after 6.5 min. After 8 min of ischemia, tourniquet release was accompanied by a transient increase in muscle blood volume due to influx of oxyhemoglobin. The cytochrome aa3 oxidation level increased above resting base line within 1 min after tourniquet release. Transcutaneous PO2 measurements recorded simultaneously from the same forearm correlated poorly with the kinetics of O2 availability and cytochrome oxidation in the underlying muscle tissue; this was not unexpected because overlying skin did not contribute significantly to NIR muscle signals. Venous outflow restriction without inflow obstruction increased muscle deoxyhemoglobin and tissue blood volume but did not change muscle O2 stores or cytochrome aa3 oxidation level. The ability of the NIR technique to detect dynamic trends in tissue oxygenation reveals that muscle O2 is rapidly consumed during tourniquet ischemia and rapidly restored by hyperemic responses after brief ischemia.     

Limb congestion enhances the synchronization of sympathetic outflow with muscle contraction

In this report, we examined if the synchronization of muscle sympathetic nerve activity (MSNA) with muscle contraction is enhanced by limb congestion. To explore this relationship, we applied signal-averaging techniques to the MSNA signal obtained during short bouts of forearm contraction (2-s contraction/3-s rest cycle) at 40% maximal voluntary contraction for 5 min. We performed this analysis before and after forearm venous congestion; an intervention that augments the autonomic response to sustained static muscle contractions via a local effect on muscle afferents. There was an increased percentage of the MSNA noted during second 2 of the 5-s contraction/rest cycles. The percentage of total MSNA seen during this particular second increased from minute 1 to 5 of contraction and was increased further by limb congestion (control minute 1 = 25.6 +/- 2.0%, minute 5 = 32.8 +/- 2.2%; limb congestion minute 1 = 29.3 +/- 2.1%, minute 5 = 37.8 +/- 3.9%; exercise main effect <0.005; limb congestion main effect P = 0.054). These changes in the distribution of signal-averaged MSNA were seen despite the fact that the mean number of sympathetic discharges did not increase over baseline. We conclude that synchronization of contraction and MSNA is seen during short repetitive bouts of handgrip. The sensitizing effect of contraction time and limb congestion are apparently due to feedback from muscle afferents within the exercising muscle.     

Enriched Air Nitrox Breathing Reduces Venous Gas Bubbles after Simulated SCUBA Diving: A Double-Blind Cross-Over Randomized Trial

ObjectiveTo test the hypothesis whether enriched air nitrox (EAN) breathing during simulated diving reduces decompression stress when compared to compressed air breathing as assessed by intravascular bubble formation after decompression.MethodsHuman volunteers underwent a first simulated dive breathing compressed air to include subjects prone to post-decompression venous gas bubbling. Twelve subjects prone to bubbling underwent a double-blind, randomized, cross-over trial including one simulated dive breathing compressed air, and one dive breathing EAN (36% O₂) in a hyperbaric chamber, with identical diving profiles (28 msw for 55 minutes). Intravascular bubble formation was assessed after decompression using pulmonary artery pulsed Doppler.ResultsTwelve subjects showing high bubble production were included for the cross-over trial, and all completed the experimental protocol. In the randomized protocol, EAN significantly reduced the bubble score at all time points (cumulative bubble scores: 1 [0–3.5] vs. 8 [4.5–10]; P < 0.001). Three decompression incidents, all presenting as cutaneous itching, occurred in the air versus zero in the EAN group (P = 0.217). Weak correlations were observed between bubble scores and age or body mass index, respectively.ConclusionEAN breathing markedly reduces venous gas bubble emboli after decompression in volunteers selected for susceptibility for intravascular bubble formation. When using similar diving profiles and avoiding oxygen toxicity limits, EAN increases safety of diving as compared to compressed air breathing.

Trial Registration

ISRCTN 31681480     

The human spleen as an erythrocyte reservoir in diving-related interventions.

Twelve subjects without and ten subjects with diving experience performed short diving-related interventions. After labeling of erythrocytes, scintigraphic measurements were continuously performed during these interventions. All interventions elicited a graduated and reproducible splenic contraction, depending on the type, severity, and duration of the interventions. The splenic contraction varied between approximately 10% for "apnea" (breath holding for 30 s) and "cold clothes" (cold and wet clothes applied on the face with no breath holding for 30 s) and approximately 30-40% for "simulated diving" (simulated breath-hold diving for 30 s), "maximal apnea" (breath holding for maximal duration), and "maximal simulated diving" (simulated breath-hold diving for maximal duration). The strongest interventions (simulated diving, maximal apnea, and maximal simulated diving) elicited modest but significant increases in hemoglobin concentration (0.1-0.3 mmol/l) and hematocrit (0.3-1%). By an indirect method, the splenic venous hematocrit was calculated to 79%. No major differences were observed between the two groups. The splenic contraction should, therefore, be included in the diving response on equal terms with bradycardia, decreased peripheral blood flow, and increased blood pressure.