Possible incipient sympatric ecological speciation in blind mole rats (Spalax).

Sympatric speciation has been controversial since it was first proposed as a mode of speciation. Subterranean blind mole rats (Spalacidae) are considered to speciate allopatrically or peripatrically. Here, we report a possible incipient sympatric adaptive ecological speciation in Spalax galili (2n = 52). The study microsite (0.04 km(2)) is sharply subdivided geologically, edaphically, and ecologically into abutting barrier-free ecologies divergent in rock, soil, and vegetation types. The Pleistocene Alma basalt abuts the Cretaceous Senonian Kerem Ben Zimra chalk. Only 28% of 112 plant species were shared between the soils. We examined mitochondrial DNA in the control region and ATP6 in 28 mole rats from basalt and in 14 from chalk habitats. We also sequenced the complete mtDNA (16,423 bp) of four animals, two from each soil type. Remarkably, the frequency of all major haplotype clusters (HC) was highly soil-biased. HCI and HCII are chalk biased. HC-III was abundant in basalt (36%) but absent in chalk; HC-IV was prevalent in basalt (46.5%) but was low (20%) in chalk. Up to 40% of the mtDNA diversity was edaphically dependent, suggesting constrained gene flow. We identified a homologous recombinant mtDNA in the basalt/chalk studied area. Phenotypically significant divergences differentiate the two populations, inhabiting different soils, in adaptive oxygen consumption and in the amount of outside-nest activity. This identification of a possible incipient sympatric adaptive ecological speciation caused by natural selection indirectly refutes the allopatric alternative. Sympatric ecological speciation may be more prevalent in nature because of abundant and sharply abutting divergent ecologies.

Use of a fast transcutaneous CO2 detector to evaluate escape hoods: the "CAPS 2000" with the inlet valves removed from the nose-cup as a test case.

INTRODUCTION: The traditional method used to evaluate escape masks has been to examine the composition of the inspired gas, although arterial carbon dioxide (CO2) and oxygen (O2) would be more relevant physiological parameters. The recent development of reliable, fast-responding transcutaneous CO2 detectors makes it possible to evaluate arterial CO2 and O2 saturation. The CAPS 2000 escape mask was designed to protect the head and respiratory system from chemical or biological attack. The question arises of whether there might be a risk of dangerous hypoxia-hypercapnia in rebreathing from the mask because of leakage of the expired gas from the nose-cup into the hood, although theoretical considerations rule this out. We studied a worst case scenario. METHODS: Nine subjects wore the CAPS 2000 for 15 minutes after removal of the inspiratory valves. A mass spectrometer and transcutaneous sensor were used to measure O2 and CO2, arterial O2 saturation, and arterial partial pressure of CO2 (PCO2). RESULTS: Blood oxygen saturation decreased from an initial value of 98.4% to 96.2% at 2 minutes, subsequently rising and stabilizing at a level similar to control. Subcutaneous PCO2 rose from the control level of 36 to 43 torr after 5 minutes, then decreased to 42 torr and stabilized at that level. Inspired PO2 dropped from 21% to 16% at 3 to 4 minutes, rose to 17% at 8 minutes, and stabilized thereafter. Inspired PCO2 rose to 3% in the first minute and continued to rise to 3.5% at 3 minutes, after which it slowly decreased to 3% and stabilized at that level. DISCUSSION: The transcutaneous CO2 detector provided a true indication of the physiological state of the subject, and these parameters are sufficient on their own for the evaluation of breathing masks. CO2 and O2 did not reach dangerous levels with the inspiratory valves removed from the CAPS 2000 mask.

Flow resistance, work of breathing of humidifiers, and endotracheal tubes in the hyperbaric chamber.

Humidification of inspired gas is critical in ventilated patients, usually achieved by heat and moisture exchange devices (HMEs). HME and the endotracheal tube (ETT) add airflow resistance. Ventilated patients are sometimes treated in hyperbaric chambers. Increased gas density may increase total airway resistance, peak pressures (PPs), and mechanical work of breathing (WOB). We tested the added WOB imposed by HMEs and various sizes of ETT under hyperbaric conditions. We mechanically ventilated 4 types of HMEs and 3 ETTs at 6 minute ventilation volumes (7-19.5 L/min) in a hyperbaric chamber at pressures of 1 to 6 atmospheres absolute (ATA). Peak pressure increased with increasing chamber pressure with an HME alone, from 2 cm H2O at 1 ATA to 6 cm H(2)O at 6 ATA. Work of breathing was low at 1 ATA (0.2 J/L) and increased to 1.2 J/L at 6 ATA at minute ventilation = 19.5 L/min. Connecting the HME to an ETT increased PP as a function of peak flow and chamber pressure. Reduction of the ETT diameter (9 > 8 > 7.5 mm) and increase in chamber pressure increased the PP up to 27.7 cm H2O, resistance to 33.2 cmH2O*s/L, and WOB to 3.76 J/L at 6 ATA with a 7.5-mm EET. These are much greater than the usually accepted critical peak pressures of 25 cm H2O and WOB of 1.5 to 2.0 J/L. Endotracheal tubes less than 8 mm produce significant added WOB and airway pressure swings under hyperbaric conditions. The hyperbaric critical care clinician is advised to use the largest possible ETT. The tested HMEs add negligible resistance and WOB in the chamber.

Oxygen pretreatment as protection against decompression sickness in rats: pressure and time necessary for hypothesized denucleation and renucleation.

Pretreatment with HBO at 300-500 kPa for 20 min reduced the incidence of decompression sickness (DCS) in a rat model. We investigated whether this procedure would be effective with lower oxygen pressures and shorter exposure, and tried to determine how long the pretreatment would remain effective. Rats were pretreated with oxygen at 101 or 203 kPa for 20 min and 304 kPa for 5 or 10 min. After pretreatment, the animals were exposed to air at 1,013 kPa for 33 min followed by fast decompression. Pretreatment at 101 or 203 kPa for 20 min and 304 kPa for 10 min significantly reduced the number of rats with DCS to 45%, compared with 65% in the control group. However, after pretreatment at 304 kPa for 5 min, 65% of rats suffered DCS. When pretreatment at 304 kPa for 20 min was followed by 2 h in normobaric air before compression and decompression, the outcome was worse, with 70-90% of the animals suffering DCS. This is probably due to the activation of "dormant" micronuclei. The risk of DCS remained lower (43%) when pretreatment with 100% O(2) at normobaric pressure for 20 min was followed by a 2 h interval in normobaric air (but not 6 or 24 h) before the hyperbaric exposure. The loss of effectiveness after a 6 or 24 h interval in normobaric air is related to micronuclei rejuvenation. Although pretreatment with hyperbaric O(2) may have an advantage over normobaric hyperoxia, decompression should not intervene between pretreatment and the dive.

Endothelial Injury in Diving: Atomic Force-, Electronic-, and Light-Microscopy Study of the Ovine Decompressed Blood Vessels.

We suggested that the nanobubbles, which appear at the active hydrophobic spots (AHSs) at the luminal aspect of the blood vessels, are the gas micronuclei from which the decompression bubbles evolve and the endothelial injury during the decompression is due to the tearing off the cell membranes with the detaching bubbles. Ovine blood vessels were stretched over the polycarbonate plates or glass microscopic slides and were exposed under saline to the hyperbaric pressure (1,013 kPa, 19 h). Following decompression, the blood vessels were photographed for the identification (by bubble formation) of the AHS. Nanobubbles could not be demonstrated at the AHS by using the atomic force microscopy (AFM) because of the roughness of the surface, which disabled the close contact of the probe. In the electron microscopy, no endothelial cells were observed in the samples from the area near to the AHS, but the underlying elastin layer of the intima was observed adjacent to the media. Some intact endothelial cells were observed only in the locations far from an AHS. In the optical microscopy, no endothelial cells were observed in the blood vessels in close proximity to the AHS and in some sections, debris or a detached cluster of the endothelial cells were observed. Intact endothelial cells could be found at the sites distant from an AHS. This study supports the assumption, where the detached bubbles tear off the endothelial cells and cause the initial endothelial injury following the decompression.

Is the probable spillage of the lung surfactant dipalmitoylphosphatidylcholine the ultimate source of diabetes type 1?

The lung surfactant dipalmitoylphosphatidylcholine (DPPC) most probably leaks into the blood, settling on the luminal aspect of blood vessels to create active hydrophobic spots (AHS). Nanobubbles are formed at these spots from dissolved gas. We hypothesized that when a large molecule in the blood comes into contact with a nanobubble at the AHS, its tertiary structure is disrupted. An epitope not previously having undergone thymus education may then prompt an autoimmune response. There are thus two independent processes which may share the blame for autoimmune disease: spillage of large molecules into the blood, and the creation of AHS. DPPC was measured in 10 diabetes type 1 patients and 10 control subjects. DPPC in the diabetic group was 4.63 ± 0.68 µg/mL, non-significantly higher than in the control group (4.23 ± 0.94 µg/mL). However, in the diabetic group, DPPC was high when the samples were taken within 1.5 years of disease onset. This is closer to the time of AHS production, which takes place ahead of the disease. Further investigation, with sampling for DPPC as soon as possible after onset of the disease, may provide additional support for our hypothesis. If proved true, this may open up considerable therapeutic potential.

Energetic efficiency in trained and sedentary rats after exposure to normobaric and hyperbaric oxygen.

INTRODUCTION: Contradictory results have been obtained regarding the beneficial effect of hyperbaric oxygen (HBO) on exercise performance. The purpose of this study was to investigate the effect of different combinations of pressure and time in hyperoxia on the energetic efficiency of trained and sedentary rats. METHODS: At the end of the training period, rats were exposed to one of three protocols: 1) 100% normobaric oxygen for 24 h; 2) HBO at 2 ATA for 4 h; 3) HBO at 2.5 ATA for 6 h. After the hyperoxic exposures, V(O2max) was evaluated and compared with preexposure values. RESULTS: The slope of the linear section of the oxygen consumption-velocity curve in the trained rats was significantly steeper after exposure to either 100% normobaric oxygen for 24 h or HBO at 2 ATA for 4 h than before the exposure. The opposite was found for the sedentary rats. After exposure to HBO at 2.5 ATA for 6 h, the slope of the oxygen consumption-velocity curve in the trained rats did not differ from the pre-exposure slope. However, the highest velocity these rats reached was lower than their maximum velocity before this exposure. In the sedentary rats, the slope of the oxygen consumption-velocity curve was found to be steeper after the 2.5 ATA exposure compared with the preexposure slope. CONCLUSIONS: Our results suggest that exposure to 100% normobaric oxygen for 24 h and HBO at 2 ATA for 4 h induces a reduction in the energetic efficiency of trained rats, but improves energetic efficiency in sedentary rats.

Power Equation for Predicting the Risk of Central Nervous System Oxygen Toxicity at Rest.

Patients undergoing hyperbaric oxygen therapy and divers engaged in underwater activity are at risk of central nervous system oxygen toxicity. An algorithm for predicting CNS oxygen toxicity in active underwater diving has been published previously, but not for humans at rest. Using a procedure similar to that employed for the derivation of our active diving algorithm, we collected data for exposures at rest, in which subjects breathed hyperbaric oxygen while immersed in thermoneutral water at 33°C (n = 219) or in dry conditions (n = 507). The maximal likelihood method was employed to solve for the parameters of the power equation. For immersion, the CNS oxygen toxicity index is K I = t2 × PO2 10.93, where the calculated risk from the Standard Normal distribution is Z I = [ln(K I 0.5) - 8.99)]/0.81. For dry exposures this is K D = t2 × PO2 12.99, with risk Z D = [ln(K D 0.5) - 11.34)]/0.65. We propose a method for interpolating the parameters at metabolic rates between 1 and 4.4 MET. The risk of CNS oxygen toxicity at rest was found to be greater during immersion than in dry conditions. We discuss the prediction properties of the new algorithm in the clinical hyperbaric environment, and suggest it may be adopted for use in planning procedures for hyperbaric oxygen therapy and for rest periods during saturation diving.

Personal CO2 scrubbing device for use in a disabled submarine.

INTRODUCTION: In the sunken submarine, a breakdown in the power supply can disrupt the provision of fresh air and the absorption of CO2. A personal device based on a breathing mask and the soda lime canisters used in the submarine is proposed for CO2 absorption. METHODS: In an unmanned experiment, a breathing simulator provided a flow of air at 8.7 L x min(-1) and a carbon dioxide output of 20.9 L x h(-1), which passed through either one or two 3.8-kg canisters of soda lime. In the manned experiment, four subjects wore the breathing mask, which was connected to two 3.8-kg canisters of soda lime placed in a bag, and remained for 24 h in a sealed hyperbaric chamber. They inspired the chamber atmosphere and expired via the canisters. RESULTS: In the unmanned experiment, the concentration of CO2 when a single canister was used reached 1% after 8 h, 2% after 22 h, and 2.5% after 37 h. With two canisters connected in sequence, the concentration of CO2 reached 1% after 48 h, while the pressure at the entrance to the canisters did not exceed 0.7 cm H2O. In the manned experiment, the CO2 concentration decreased over the first 12 h from its initial value of 1.3%, stabilizing during sleep at 0.75%. DISCUSSION: The personal carbon dioxide absorption device lowered the ambient CO2 level over a period of 24 h, and could maintain this level for a further 24 h. Keeping CO2 at a low level has an advantage over the peaks of 3% obtained with absorbent LiOH curtains, where elevated pressure and increased P(CO2) may have an adverse effect on the survivors. Some of the crew can remain active without using the device, while the others do the job of clearing the carbon dioxide for the whole crew.

Taravana, vestibular decompression illness, and autochthonous distal arterial bubbles.

Decompression bubbles can develop only from pre-existing gas micronuclei. These are the nanobubbles which appear on active hydrophobic spots (AHS) found on the luminal aspect of all blood vessels. Following decompression, with the propagation of blood along the arterial tree, diffusion parameters cause increased transfer of nitrogen from the tissue into the artery, and more so if perfusion is low. Taravana is a neurological form of decompression illness (DCI) prevalent in repeated breath-hold diving. A nanobubble on an AHS in a distal artery of the brain may receive an influx of nitrogen after each dive until it occludes the arterial blood flow. The vestibular organ has very low perfusion compared with the brain and the cochlea of the inner ear. We suggest that a nanobbubble on an AHS in the distal artery of the vestibular organ will receive a high influx of nitrogen from the surrounding tissue after decompression due to the low nitrogen clearance, thus expanding to cause vestibular DCI.

In vitro evidence of decompression bubble dynamics and gas exchange on the luminal aspect of blood vessels: Implications for size distribution of venous bubbles.

We found that lung surfactant leaks into the bloodstream, settling on the luminal aspect of blood vessels to create active hydrophobic spots (AHS). Nanobubbles formed by dissolved gas at these AHS are most probably the precursors of gas micronuclei and decompression bubbles. Sheep blood vessels stretched on microscope slides, and exposed under saline to hyperbaric pressure, were photographed following decompression. Photographs of an AHS from a pulmonary vein, containing large numbers of bubbles, were selected in 1-min sequences over a period of 7 min, starting 18 min after decompression from 1,013 kPa. This showed bubble detachment, coalescence and expansion, as well as competition for dissolved gas between bubbles. There was greater expansion of peripheral than of central bubbles. We suggest that the dynamics of decompression bubbles on the surface of the blood vessel may be the closest approximation to true decompression physiology, and as such can be used to assess and calibrate models of decompression bubbles. We further discuss the implications for bubble size in the venous circulation.

Pulmonary oxygen toxicity in saturation dives with PO2 close to the lower end of the toxic range - A quantitative approach.

Pulmonary oxygen toxicity (POT) has been extensively described at partial pressures of oxygen (PO2) ≥ 1 bar, but much less so at lower PO2. We proposed the POT index [K = t2 × (PO2)4.57] as a means of evaluating the severity of POT, expressed either as reduced lung function or the incidence of POT in a group of divers. In the exponential recovery process (e - [- 0.42 + 0.384 × (PO2)ex] × tr), the time constant increases linearly from 0.0024 to 0.54 h-1 for a PO2 of 1.1 to 2.5 bar. A linear relationship was demonstrated between the incidence of POT and the POT index, given by the equation: POT incidence % = 1.85 + 0.171 × K. In saturation diving, PO2 is kept close to the lower end of the toxic limits for POT, which is approximately 0.5 bar. We suggested that at this low range of PO2, the two processes of cumulative toxicity and recovery operate simultaneously. For one example of saturation diving, we show that a recovery time constant of 0.0135 h-1 yields the measured incidence of POT. We therefore propose the formula K = t2 × PO24.57 × e-0.0135 × t for calculation of the POT index in further analyses of POT in saturation diving.

Calculated risk of pulmonary and central nervous system oxygen toxicity: a toxicity index derived from the power equation.

BACKGROUND: The risk of oxygen toxicity has become a prominent issue due to the increasingly widespread administration of hyperbaric oxygen (HBO) therapy, as well as the expansion of diving techniques to include oxygen-enriched gas mixtures and technical diving. However, current methods used to calculate the cumulative risk of oxygen toxicity during an HBO exposure i.e., the unit pulmonary toxic dose concept, and the safe boundaries for central nervous system oxygen toxicity (CNS-OT), are based on a simple linear relationship with an inspired partial pressure of oxygen (PO2) and are not supported by recent data. METHODS: The power equation: Toxicity Index = t2 × PO2c, where t represents time and c represents the power term, was derived from the chemical reactions producing reactive oxygen species or reactive nitrogen species. RESULTS: The toxicity index was shown to have a good predictive capability using PO2 with a power c of 6.8 for CNS-OT and 4.57 for pulmonary oxygen toxicity. The pulmonary oxygen toxicity index (PO2 in atmospheres absolute, time in h) should not exceed 250. The CNS-OT index (PO2 in atmospheres absolute, time in min) should not exceed 26,108 for a 1% risk. CONCLUSION: The limited use of this toxicity index in the diving community, after more than a decade since its publication in the literature, establishes the need for a handy, user-friendly implementation of the power equation.

Ovine plasma dipalmitoylphosphatidylcholine does not predict decompression bubbling.

Decompression illness (DCI) is the main risk associated with scuba diving. Some divers ("bubblers") are more sensitive to DCI than others ("non-bubblers"). We found that there are active hydrophobic spots (AHS) on the luminal aspect of ovine blood vessels, which contain the surfactant dipalmitoylphosphatidylcholine (DPPC). DPPC leaks from the lung into the plasma, settling on the blood vessel to create AHS. These are the main source of gas micronuclei from which bubbles develop after decompression. A correlation between bubbling ovine blood vessels and the animal's plasma DPPC might lead to the development of a blood test for vulnerability to DCI. Samples from ovine blood vessels were stretched on microscope slides, placed anaerobically in saline at the bottom of a Pyrex bowl, and exposed to high pressure. Automated photography was used after decompression to reveal AHS by visualising their bubble production. Phospholipids were extracted from the AHS and plasma for determination of DPPC. Bubbling was unrelated to the concentration of DPPC in the plasma (2.15 ±â€¯0.87 µg/ml). Bubble production from the AHS (n = 130) as a function of their DPPC content yielded two groups, one unrelated to DPPC and the other which demonstrated increased bubbling with elevation of DPPC. We suggest this may be related to alternate layering with hydrophobic and hydrophilic phospholipids. This study reinforces the connection between DPPC and DCI. However, a blood test for diver vulnerability to decompression stress is not recommended.

Acclimation to hypoxia does not improve hypoxic survival of the immature pig in confined atmosphere.

INTRODUCTION: Humans may be accidentally trapped in a confined atmosphere in which oxygen availability is limited. If acclimation would extend survival, hypoxic acclimation in confined spaces would be recommended. METHODS: After hypoxic acclimation, an immature pig was transferred into an experimental sealed chamber. The O2, CO2, chamber temperature, and pressure changes due to the animal's breathing were recorded. Six days acclimation (n = 3) and 3 weeks of acclimation (n = 3) were compared to control pigs (n = 3). RESULTS: No signs of acute mountain sickness were noted in the pigs acclimated for 6 days, but some acute symptoms (which were resolved on the following day) were observed during the 3-week acclimation. The terminal partial pressure of inspired oxygen (PIO2; 3.5-3.6 kPa) was not affected by hypoxic acclimation. Oxygen consumption and CO2 production were similar in the three experimental groups. CONCLUSIONS: Our hypothesis that hypoxia acclimation would produce improved survival in a confined space was not supported by the results. It is possible that at very low inspired oxygen of 3.6 kPa, the oxygen consumption of critical life-supporting tissue reached the limit of viable cells in mammals. If this is right, no further improvement could be expected after hypoxic acclimation.

Do skin rash and cutis marmorata stem from lamellar bodies within the skin?

Cutis marmorata (CM) manifests as bluish-red spots on the skin following decompression. These are often itchy or painful to touch, and appear half to one hour after surfacing. The pathogenesis of skin lesions in decompression illness (DCI) remains unresolved. The common belief has been that bubbles that shunted to the arterial circulation reached the skin and clogged blood vessels. An alternative explanation from studies in which air was injected into the internal carotid artery of swine is that arterial bubbles at the brain stem disturb the control of skin blood flow, causing CM. Other brain syndromes have also been seen to cause CM. It was suggested that bubbles affecting the brain stem result in the release of neuropeptides in the skin which control vasodilatation and vasoconstriction. However, this does not explain the inflammation in the skin lesions, with red blood cells, haemorrhage and neutrophil infiltrates. The percentage of right-to-left circulatory shunts in divers who suffered CM was 77% compared with 28% in divers with no record of CM, a finding which supports either of these explanations. Another study in swine concluded that there was "strong evidence to support autochthonous bubbles as the etiology of skin lesions". Lesions appeared without right-to-left shunting. Skin thickness from the squamous keratin to the dermis increased by 10% in the affected areas. The lesions showed congestion, haemorrhage and neutrophil infiltrates. Superficial counter-diffusion as a cause of CM, the increased risk of CM in a dry as opposed to a wet dive and the prevalence of CM in proximity to subcutaneous fat (which acts as a nitrogen reservoir), all support an autochthonous origin. Decompression bubbles can develop and expand only from pre-existing gas micronuclei. It is known that nanobubbles form spontaneously when a smooth hydrophobic surface is submerged in water containing dissolved gas. We have shown that these nanobubbles are the gas micronuclei underlying decompression bubbles and DCI. After decompression, bubbles evolved at definite hydrophobic sites composed of the lung surfactant dipalmitoylphosphatidylcholine. Nanobubbles are formed on the surface of these lamellar layers of phospholipids, and on decompression expand into venous and arterial bubbles. Lamellar bodies of phospholipids produced in the granular layer of the skin are used for the formation of a hydrophobic barrier at the cornified layer. We suggest that the hydrophobic layers in the skin may be the site at which bubbles develop from nanobubbles and cause CM, just as occurs at the active hydrophobic spots on the luminal aspect of a blood vessel. This is the reason no bubbles were observed in the skin microcirculation. Unlike bubbles on the inner wall of venous blood vessels, which are supplied with high quantities of nitrogen from the incoming venous blood, the expansion of skin bubbles will be limited due to a low supply of nitrogen (possibly from the nearby subcutaneous fat). Therefore, skin bubbles should be small and have a short life span, which may be why they have hitherto remained undetected. The sensitivity of some divers to CM and its localization to specific skin areas may be related to individual variability in the lamellar bodies and phospholipid skin barriers. Support for the present hypothesis may be found in the observation in some cases (though not all) of the movement of gas under the skin by means of echography (Balestra C, personal communication, 2018). CM is more frequent in female divers, and more so in subtropical than in cold European waters (van Ooij P-JAM, personal communication, 2018). This may be explained by women having more subcutaneous fat than men, coupled with the higher skin perfusion (and nitrogen loading) in warm water. This suggestion of possible autochthonous bubble formation in the skin does not exclude other causes, but may open a window for further investigation.