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PubMed1977

Stabilization of gas cavitation nuclei by surface-active compounds.

Gas bubbles are the primary agent in producing the pathogenic effects of decompression sickness. Numerous experiments indicate that bubbles originate in water, and probably also in man, as pre-existing gas nuclei. This is surprising considering that gas phases larger than 1 micron should rise to the surface of a standing liquid, whereas smaller ones should dissolve rapidly due to surface tension. Several stabilizing mechanisms have been suggested, and each has been refuted on experimental grounds. In this article, we propose a new model that arises out of a systematic study of the earlier theories. We review these theories and conclude that gas cavitation nuclei must be held intact by surface-active skins that are initially permeable. The first quantitative analysis of bubble formation data from supersaturated gelatin is summarized and leads to the further conclusion that skins can become impermeable if the ambient pressure is increased rapidly by a sufficient amount. Our model owes much to Sirotyuk, who "demonstrated experimentally that stabilization of gas bubbles acting as cavitation nuclei in water is always attributable to the presence of surface-active substances in the water".

Chemical Phenomena↗

PubMed1982

Evidence for subacute fat embolism as the cause of multiple sclerosis.

The neurological features of decompression sickness, which is thought to be due to gas embolism, are similar to those of multiple sclerosis (MS). This similarity suggested the re-examination of a concept, first proposed in 1882, that the demyelination in MS is due to venous thrombosis. Unfortunately, although the plaques of MS are often perivenular, thromboses are not always present. Nevertheless, vascular theories can explain the topography of the lesions in MS. Embolism is generally associated with arterial rather than venous damage, and with neuronal infarction rather than loss of myelin. However, the intra-arterial injection of a range of substances can cause venous damage and perivenous demyelination in the brain, although it does not exactly reproduce the plaques seen in man. There is also evidence in man that fat may lodge in the microcirculation of the nervous system and cause distal perivenous oedema with the loss of myelin from axons. Since acute fat embolism may produce lesions not only in the white matter of the brain, but also in the cord, the retina, the meninges, and the skin, and since all these have been described in MS, subacute fat embolism may be the cause of MS.

Animals↗

PubMed1993

Transcranial Doppler detection of circulating cerebral emboli. A review.

BACKGROUND: The identification of gaseous emboli using Doppler ultrasound was described as early as the 1960s. Recently it has been demonstrated that this method can also detect solid emboli such as thrombi and platelet aggregates. This may make this technology useful in a large number of patients with, or at risk of, embolic stroke. SUMMARY OF REVIEW: Emboli appear as short-duration, high-intensity signals in the Doppler spectrum. The intensity of the Doppler signal from an artery containing an embolus depends on the density difference between the embolic material and blood. This difference is greatest for gaseous emboli, which are therefore the most easy to detect. Gaseous emboli have been demonstrated during deep-sea diving, and their presence correlates with the occurrence of decompression sickness. Similar signals have been detected during cardiopulmonary bypass. A relation has been demonstrated between the number of emboli detected by transcranial Doppler and a decline in neuropsychological function after cardiopulmonary bypass. Solid emboli such as thrombi and platelet aggregates result in less intense signals than air emboli. Their detection, using Doppler ultrasound, has recently been described in patients with prosthetic heart valves, atrial fibrillation, and carotid artery disease. It may also help in the detection and localization of embolic sources in patients with stroke. Studies in in vitro and in vivo models demonstrate that this technique provides information on the size and type of emboli. Larger emboli produce signals of greater intensity and duration. Practical patient monitoring will require automatic emboli detectors incorporated into the Doppler machine; such programs are being developed. CONCLUSIONS: Detection of solid emboli using Doppler techniques offers an exciting new diagnostic tool. It has been demonstrated that the technique can detect solid emboli. The prognostic significance of such emboli remains to be determined. It is hoped that the technique will allow detection of patients at high risk of embolic stroke in whom appropriate prophylactic treatment can then be instituted.

Animals↗

PubMedDate not supplied

Interfacility transport of patients with decompression illness: literature review and consensus statement.

OBJECTIVE: Decompression illness (DCI) is a potentially lethal complication of diving and may occur far from hyperbaric facilities. The need for prompt transport to a hyperbaric facility often involves air medical transport, but this may exacerbate DCI. The authors reviewed available literature to establish evidence-based transport strategies utilizing safe altitudes for patients, with DCI. METHODS: MEDLINE, EMBASE, and materials from organizations with expertise in diving medicine were searched for the following terms: decompression sickness, caisson disease, hyperbaric oxygenation, depth intoxication, or diving. Two reviewers independently selected relevant citations involving patients with DCI and air medical transport for review and consensus statement development by an expert working group. RESULTS: A total of 341 citations were identified, and 53 unique citations were reviewed. Nine relevant citations were selected for consensus statement development. There were no clinical trials or prospective cohort studies. Only two retrospective case series, including nine patients, specifically examined the effect of altitude on patients with DCI during transport. No symptom recurrence occurred when the cabin altitude remained within 500 feet of ground level. Seven citations were either letters or statements of expert opinion, recommending a maximum cabin altitude of 500-1000 feet (152-305 meters). CONCLUSIONS: The working group identified the paucity of clinical studies and evidence-based recommendations for air medical transport of patients with DCI. Transport selection should be based on minimizing total transport time and, when transporting by air, ensuring that a cabin altitude of the transporting vehicle does not exceed 500 feet (152 meters) above the departure point.

Air Ambulances↗

PubMed2000

Test and evaluation of exercise-enhanced preoxygenation in U-2 operations.

BACKGROUND: Preoxygenation to prevent decompression sickness (DCS) during U-2 reconnaissance flights requires considerable time and occasionally does not provide adequate protection. Increasing preoxygenation within a practical period of time provides marginally increased protection and is not always operationally feasible. Including exercise during preoxygenation to increase muscle tissue perfusion, cardiac output, and ventilation can improve the quality of the denitrogenation. METHODS: A pilot, who reported two cases of DCS during his first 25 U-2 high flights involving cabin altitudes of 29,000-30,000 ft, volunteered to test exercise-enhanced preoxygenation. He performed 10 min of strenuous upper and lower body exercise at the beginning of preoxygenation prior to subsequent high flights without increasing total preoxygenation time. RESULTS: The exercise was performed at 75% of maximal oxygen uptake based on the estimated maximal oxygen uptake determined during an Air Force aerobic fitness test and heart rate. The pilot's next 36 high flights, using exercise-enhanced preoxygenation, were completed with no reports of DCS. CONCLUSIONS: This statistically significant operational test reinforced the laboratory studies. Implementation of this procedure for reducing DCS in susceptible U-2 pilots and collecting additional data from the U-2 pilot population is recommended.

Adult↗

PubMed1985

Statistical aspects of the design and testing of decompression tables.

Before a decompression procedure is recommended for general use it is subjected to a limited number of human trial dives. Based on the trial, one attempts to reject unsafe procedures but accept those with a low incidence of decompression sickness (DCS). Binomial confidence regions are often so broad that even after 40 dives it may be impossible to distinguish between the possibility that the table being tested has a 0.6% risk of DCS and the possibility that it has a 17% risk. Our proposed alternative is to select some rule (e.g., one or more cases of DCS in 10 dives) for rejecting tables and to calculate the probabilities of accepting tables as a function of the probability of DCS. With such calculations we conclude that (a) generally one cannot reduce the risk of adopting unsafe tables without increasing the risk of rejecting safe ones unless one chooses to increase the number of test dives; (b) truncated sequential designs could reduce the number of dives required for testing by 15 to 20%; and (c) rules similar to the ones tested will always have a zone of indifference. Tables with a probability of DCS in this zone will be accepted or rejected with nearly equal frequency even if tested with hundreds of dives. The use of models describing the probability of DCS as a function of dive parameters should allow us to combine information from dives previously analyzed separately and perhaps to improve our selection of new tables to be tested.

Atmospheric Pressure↗

PubMed1995

Texture analysis of divers' brains using 99Tcm-HMPAO SPET.

The potential use of regional cerebral blood flow (rCBF) single photon emission tomography (SPET) imaging with 99Tcm-hexamethylpropyleneamine oxime (HMPAO) in the management of divers who have undergone a form of decompression sickness (DCS) was investigated using texture analysis. We imaged 50 divers, 10 of whom had only experienced DCS which had been categorized as Type 1, 20 of whom had a history of DCS classified as Type 2 and 20 of whom had not suffered an episode of DCS. A number of divers who had experienced Type 2 DCS had also had incidents of Type 1. The reconstructed SPET images were pre-processed and analysed using a first-order texture analysis technique based on a grey level histogram. The results showed that there was a significant textural difference between the divers who had only suffered episodes of DCS Type 1 and the diving controls and a difference between the divers with a history of Type 2 and the diving controls. No differences were found between the two groups of divers who had a history of DCS. This result suggests that DCS produces a detectable change in 99Tcm-HMPAO SPET brain images. However, the segmentation between the groups investigated was not complete and so the usefulness of this approach appears limited in individual cases but may provide useful information about the effects of different diving practices.

Adult↗

PubMed2003

The effect of breathing hyperoxic gas during simulated submarine escape on venous gas emboli and decompression illness.

Raised internal pressure in a distressed submarine rapidly increases the risk of decompression sickness (DCS) following submarine escape. The hypothesis that breathing a hyperoxic gas during escape may reduce the risk of DCS was tested using goats. Shallow air saturation and simulated submarine escape dives were carried out either singularly or in combination (saturation, escape, or saturation followed by escape) using air or 60% / 40% oxygen (O2) / nitrogen (N2) mixture as breathing gas during the escapes. Post-surfacing, animals were observed for signs of DCI and O2 toxicity. Precordial Doppler ultrasound was used to score venous gas emboli (VGE) using the Kisman Masurel (KM) scale. Following escape from 2.5 MPa, the rate at which VGE disappeared in the hyperoxic group (n = 8) was significantly faster(p < 0.05) than the air group (n = 7). One case of pulmonary barotrauma with arterial gas embolism occurred in the air group, but no cases of DCS were observed. After saturation at 0.18 MPa followed by escape from 2.5 MPa, DCS occurred in four of 15 animals in the air group and in two of 16 animals in the hyperoxic group. The rate of disappearance of VGE was significantly faster (p < 0.01) in the hyperoxic group. O2 toxicity was not discernible in any of the animals.

Air↗

PubMed1975

[Para- and tetraplegia caused by decompression accident (deep sea diving). Study of 9 cases with more or less severe sequelae].

The authors report 9 cases of para and tetraplegia due to decompression sickness following deep sea diving. Poor technique was the cause of 8 of these cases, but one remained totally unexplained. The sequelae were serious; 3 dorsal paraplegias, which were functionally complete, 4 incomplete tetraplegias giving rise to permanent disability. In 2 cases there remained some spasticity of the lower limbs, in some cases associated with genito-urinary disorders. The authors review recent physiopathological theories. -- Blood disturbances may be due to the presence of gas bubbles which aggress the organism and give rise to coagulation disorders. -- The formation of the bubbles may be the cause of the spinal lesions, e.g. liberation in situ, gas embolism; the bubbles may form in various parts of the circulation and may cross the pulmonary barrage. Bubbles probably form in the lung itself, in the pulmonary veins and in the aorta, including the spinal capillaries. There is some slowing of the circulation, secondary to increased pressure, and pulmonary stasis may also play a harmful role. Finally, the dorsal spinal segments, which are the most poorly vascularised, are particularly exposed. This corresponds to the clinical findings. As far as treatment is concerned, the authors emphasize that recompression with hyperbaric equipment, should be carried out as an emergency, especially in unconsciuos subjects, together with other appropriate treatment. Such facts are important now that deep sea diving is becoming more and more commonly practised.

Adult↗

PubMed2001

The reduced oxygen breathing paradigm for hypoxia training: physiological, cognitive, and subjective effects.

UNLABELLED: The current training program for hypoxia familiarization requires a low-pressure chamber that places aviator trainees at risk for decompression sickness. A cost-effective reduced oxygen-breathing (ROB) paradigm that decreases oxygen (O2) concentration leading to normobaric hypoxia was assessed as an alternative to the hypobaric chamber. PURPOSE: To help establish the validity of the ROB paradigm, this report documents cognitive performance, cardiopulmonary and subjective changes during ROB exposure. METHODS: Performance on a two-dimensional tracking task, as well as BP, heart rate, end-tidal carbon dioxide (ETCO2), O2 saturation, and subjective reports of hypoxia symptoms were observed in 12 U.S. Navy divers during exposure to normoxic air followed by one of four experimental gas mixtures per session. All participants received all gas conditions that differed in their relative concentrations of O2 and nitrogen (6.20/93.80, 7.00/93.00, 7.85/92.15, and 20.85/79.15% O2/N2). RESULTS: ROB caused increases in tracking task error (p < 0.0001). ROB also increased heart rate (p < 0.001) and systolic BP (p = 0.004), and decreased ETCO2 and O2 saturation (p < 0.0001). Finally, subjects responded to ROB-induced hypoxia with higher subjective symptom ratings (p < 0.0001). CONCLUSIONS: These data are consistent with those expected from hypoxic states and support the validity of the ROB paradigm for hypoxia training. Future validation studies comparing a ROB device with hypobaric chambers are needed.

Adaptation, Physiological↗

PubMed1995

The feasibility of Doppler monitoring during EVA.

During extravehicular activities (EVA) outside the spacecraft, astronauts have to work under reduced pressure in a space suit. This pressure reduction induces the risk of decompression sickness (DCS) by the formation of gas bubbles from excess nitrogen dissolved in the organism by breathing air at normal pressure. Under laboratory conditions the gas bubbles moving in the blood stream can be detected by the non-invasive ultrasonic Doppler method. By early detection of excessive bubble formation the development of DCS symptoms may be prevented by early application of preventative measures. The method could also be useful when applied in the space suit in order to compare the results of laboratory tests with operational results, because there is a discrepancy according to the DCS risk of laboratory experiments and actual EVA missions, where no symptoms have been reported yet. A prototype Doppler sensor has been developed and implemented in the Russian Orlan suit. To investigate the feasibility of this method under simulated space conditions, the equipment has been used in a series of 12 thermovacuum chamber tests with suited subjects, where intravenous bubble formation was compared to unsuited control experiments. In more than 50% of the suited tests good Doppler recordings could be achieved. In some cases with unsatisfying results the signal could be improved by breathholding. Although the results do not yet allow any conclusion about a possible difference between suited and unsuited subjects due to the small number of tests performed, the method proved its feasibility for use in EVA suits and should be further developed to enhance the safety of EVA procedures.

Aerospace Medicine↗

PubMed2005

Bubble incidence after staged decompression from 50 or 60 msw: effect of adding deep stops.

OBJECTIVES: The French Navy uses the Marine Nationale 90 (MN90) decompression tables for air dives as deep as 60 msw. The resulting incidence of decompression sickness (DCS) for deep dives (45-60 msw) is one case per 3000 dives. METHODS: Three protocols with experimental ascent profiles (EAPs) were tested in the wet compartment of a hyperbaric chamber. For each protocol, eight subjects dove to 50 or 60 msw and ascended according to the standard MN90 table or an EAP. Precordial bubbles were monitored with Doppler sensors at 30-min intervals after surfacing. Protocol I went to 60 msw and used deep stops beginning at 27 msw. Protocol II was a repetitive dive to 50 msw with a 3-h surface interval; the EAP made the first deep stop at 18 msw. Protocol III again went to 60 msw, but the EAP used a single, shorter deep stop at 25 msw. RESULTS: For Protocol I, all divers developed bubbles at Spencer grade 2-3 and still had bubbles 120 min after surfacing; there was no statistical difference between bubbling for the MN90 and EAP, but one diver presented a case of DCS after the EAP. For Protocol II, the EAP produced severe bubbling for the eight divers. Those findings led to stopping the EAPs with the longer deep stops used in Protocols I and II. Protocol III again showed no difference between the standard and modified profiles. DISCUSSION: The addition of deep stops requires careful consideration. Two of our EAPs made no difference and one produced increased bubbling.

Adult↗

PubMed1976

Recovery from experimental paraplegia after levodopa administration.

In decompression sickness and during some surgical procedures, air emboli that form sometimes cause serious damage if the gas bubbles find their way to the vital organs. Paralysis of the spinal cord is one of the most serious manifestations induced by air emboli. Exposure to compression chambers is effective in air emboli treatment, but availability of chambers is inadequate and the treatment is lengthy. Until now there has been no fully effective injectable agent that can remedy the damage caused by air embolization. In this work levodopa was chosen as an injectable drug that might help to improve recovery from experimental paraplegia because of the reported effects of levodopa on muscle tone, spasticity and locomotion. To induce air emboli, the descending aorta of rats was chronically cannulated. Two weeks later, after full recovery from surgery, air was injected through the chronically implanted cannula into unanesthetized rats (0.35 ml of air per 100 g, during 4 sec). The paraplegia (paralysis of both hind legs) was manifested 2-10 minutes later. Only animals that had total paraplegia, without any sensation, were used in the experiments. Levodopa was administered 2 minutes after paraplegia was established. The levodopa treatment was repeated each day during one week. After six days, ten levodopa treated (intra-arterially) animals in a group of twelve and six levodopa treated (intraperitoneally) animals in a group of eight recovered completely from paraplegia. In control groups only three from thirteen (untreated), or two from twelve (solvent administration) animals recovered from paraplegia.

Animals↗

PubMed2006

Decision analysis in aerospace medicine: costs and benefits of a hyperbaric facility in space.

INTRODUCTION: Assembly and maintenance of the International Space Station (ISS) requires an unprecedented number of spacewalks, which expose astronauts to the risk of decompression sickness (DCS). We illustrate the use of decision analysis to compare a hyperbaric oxygen (HBO) chamber to currently available therapy for DCS treatment on the ISS. METHODS: A decision-analytic model that simulates events over the lifespan of the ISS was constructed. Inputs to the model for probabilities, costs, and measures of morbidity and mortality were derived from a variety of sources, including a systematic literature review and an iterative consultation process with personnel at the Canadian Space Agency and the National Aeronautics and Space Administration (NASA). The decision model was analyzed using the methods of Monte-Carlo simulation and expected value calculation. Main outcome measures included the present value of costs and quality adjusted life years (QALYs), and the cumulative probability of mission-related events over the life cycle of the ISS. Sensitivity analysis was performed. RESULTS: The HBO chamber strategy is associated with a mean cost of -12.5 million dollarsw (a net cost saving of 12.5 million dollars) with a 95% CI (-112.8 million dollars, 51.3 million dollars). An HBO chamber reduces the likelihood of a premature shuttle return and a premature Soyuz return by 8% and 3%, respectively. The result is sensitive to the lifespan of the ISS. CONCLUSIONS: At a 50 million dollars cost, an HBO chamber is likely, though not certain, to result in cost savings. Decision analysis is a useful tool for use in priority setting in aerospace medicine.

Cost-Benefit Analysis↗

PubMed1999

Mathematical models of diffusion-limited gas bubble dynamics in tissue.

Mathematical models of bubble evolution in tissue have recently been incorporated into risk functions for predicting the incidence of decompression sickness (DCS) in human subjects after diving and/or flying exposures. Bubble dynamics models suitable for these applications assume the bubble to be either contained in an unstirred tissue (two-region model) or surrounded by a boundary layer within a well-stirred tissue (three-region model). The contrasting premises regarding the bubble-tissue system lead to different expressions for bubble dynamics described in terms of ordinary differential equations. However, the expressions are shown to be structurally similar with differences only in the definitions of certain parameters that can be transformed to make the models equivalent at large tissue volumes. It is also shown that the two-region model is applicable only to bubble evolution in tissues of infinite extent and cannot be readily applied to bubble evolution in finite tissue volumes to simulate how such evolution is influenced by interactions among multiple bubbles in a given tissue. Two-region models that are incorrectly applied in such cases yield results that may be reinterpreted in terms of their three-region model equivalents but only if the parameters in the two-region model transform into consistent values in the three-region model. When such transforms yield inconsistent parameter values for the three-region model, results may be qualitatively correct but are in substantial quantitative error. Obviation of these errors through appropriate use of the different models may improve performance of probabilistic models of DCS occurrence that express DCS risk in terms of simulated in vivo gas and bubble dynamics.

Air Pressure↗

PubMed2002

The exercise and environmental physiology of extravehicular activity.

Extravehicular activity (EVA), i.e., exercise performed under unique environmental conditions, is indispensable for supporting daily living in weightlessness and for further space exploration. From 1965-1996 an average of 20 h x yr(-1) were spent performing EVA. International Space Station (ISS) assembly will require 135 h x yr(-1) of EVA, and 138 h x yr(-1) is planned for post-construction maintenance. The extravehicular mobility unit (EMU), used to protect astronauts during EVA, has a decreased pressure of 4.3 psi that could increase astronauts' risk of decompression sickness (DCS). Exercise in and repeated exposure to this hypobaria may increase the incidence of DCS, although weightlessness may attenuate this risk. Exercise thermoregulation within the EMU is poorly understood; the liquid cooling garment (LCG), worn next to the skin and designed to handle thermal stress, is manually controlled. Astronauts may become dehydrated (by up to 2.6% of body weight) during a 5-h EVA, further exacerbating the thermoregulatory challenge. The EVA is performed mainly with upper body muscles; but astronauts usually exercise at only 26-32% of their upper body maximal oxygen uptake (VO2max). For a given ground-based work task in air (as opposed to water), the submaximal VO2 is greater while VO2max and metabolic efficiency are lower during ground-based arm exercise as compared with leg exercise, and cardiovascular responses to exercise and training are also different for arms and legs. Preflight testing and training, whether conducted in air or water, must account for these differences if ground-based data are extrapolated for flight requirements. Astronauts experience deconditioning during microgravity resulting in a 10-20% loss in arm strength, a 20-30% loss in thigh strength, and decreased lower-body aerobic exercise capacity. Data from ground-based simulations of weightlessness such as bed rest induce a 6-8% decrease in upper-body strength, a 10-16% loss in thigh extensor strength, and a 15-20% decrease in lower-body aerobic exercise capacity. Changes in EVA support systems and training based on a greater understanding of the physiological aspects of exercise in the EVA environment will help to insure the health, safety, and efficiency of working astronauts.

Arm↗

PubMedDate not supplied

The relative safety of forward and reverse diving profiles.

A recent workshop found that with no-decompression dives, "reversed dive profiles" (RDP) did not increase the risk of decompression sickness (DCS). Thus in multi-level dives, the deeper part of a dive may be performed later in the dive, and repetitive dives may progress from shallow to deep. This contradicts the conventionally recommended forward dive profile (FDP) when the deeper dive, or deeper part of the dive, is performed first. The RDP Workshop recommendations were made despite the absence of adequate data. We performed two groups of experiments to test this hypothesis. We exposed two matched groups of 11 guinea pigs each to forward and reverse multi-level diving profiles to determine any substantial difference between FDPs and RDPs. There was no evidence of DCS in any of the FDP animals, while six (55%) of the RDP animals exhibited symptoms of severe DCS and died. This difference was statistically significant (P = 0.01). We then compressed two groups each of 11 guinea pigs to repetitive dives to determine any substantial difference in the risk of DCS when two equivalent sets of three dives were conducted from the deepest to most shallow on the one hand (FDP), and from the shallowest to the deepest on the other (RDP). Over two such series of dives (the second extended in time and depth to increase DCS risk), there was a significantly higher incidence of severe DCS in those animals in the RDP group. Seven of 21 exposures (33%) in the RDP group resulted in severe DCS versus none in the FDP group (P = 0.01). Our findings suggest that multi-level and repetitive dives performed in the established FDP manner are less hazardous than those performed in the reverse profile mode, at least for the exposures we chose. We believe the recommendations of the workshop should be re-examined.

Animals↗

PubMed2002

Clinical impact of patent foramen ovale diagnosis with transcranial Doppler.

The role of patent foramen ovale (PFO) in cryptogenic stroke is still debated, but from recent follow-up studies it seems that the amount of right-to-left shunt (RLS) and the association with atrial septal aneurysm (ASA) are major determinants of stroke recurrence. PFO and RLS through the atrial chambers have been recently studied in a number of conditions not or marginally related to cerebrovascular disease. Historically the first studies addressed the presence of RLS in scuba divers as a possible abnormality related to decompression sickness (DS) of unknown aetiology. Despite initial debate there is now robust evidence to claim that patency of foramen ovale increases the risk of developing DS by two and half to four times. Patients with PFO-related DS tend to have early occurrence of symptoms after surfacing and a clinical presentation that indicates brain or upper cervical spinal cord involvement. Recent reports suggest that divers with hemodynamically significant RLS may have an increased risk of developing clinically asymptomatic multiple brain lesions. PFO has been found in patients suffering from migraine with aura with approximately the same frequency as that encountered in cryptogenic stroke patients. This finding has prompted speculations on the possible role of RLS in increasing the stroke risk in migraineurs and in the pathophysiology of the aura. Recent reports showing that migraine with aura is dramatically improved after transcatheter closure of PFO suggest that migraine with aura may indeed be triggered by humoral factors that reach the brain by escaping the pulmonary filter. A RLS is involved in a rare condition known as platypnea-orthodeoxia and perhaps underlies an increased risk of cerebral complications after major orthopedic surgery. Valsalva-like activities often precede the occurrence of attacks of transient global amnesia (TGA) and abnormalities consistent with hypoperfusion of deep limbic structures have been reported during a typical TGA episode. This had raised the hypothesis that TGA may be triggered by paradoxical embolism of platelets aggregates in the posterior circulation, but the search for an increased frequency of PFO in TGA patients has yielded conflicting results. Conditions that determine an increase in pulmonary pressure may facilitate the opening of the virtual interatrial valve and thus promoting shunting of blood to the left heart chambers which in turn might contribute to further desaturation of arterial blood. It is therefore not surprising that RLS has been found in 70% of patients with chronic obstructive pulmonary disease and increased pulmonary pressure and in the same proportion of patients with obstructive sleep apnoea, a condition that ultimately may result in pulmonary hypertension. In conclusion, from the evidence gathered so far the picture is emerging of an important role of PFO in a number of non-stroke conditions, either as causative factor or as associated condition predisposing to complications. The availability of simple diagnostic techniques such as transcranial Doppler (TCD) to assess RLS will undoubtedly contribute a great deal of knowledge on the relevance in medicine of this hitherto neglected condition.

Decompression Sickness↗