Hyperbaric Oxygen Therapy for Decompression Accidents — Potential Applications to Space Station Operation

Although very comprehensive, the AAGBI safe vascular access guideline fails to mention the important role of hyperbaric oxygen therapy (HBOT) in the management of air embolism complicating vascular access 1. Depending on the speed and quantity of air/gas entrainment, cardiac arrest may be irreversible. Some patients are resuscitated successfully; others have insidious onset, presenting with air in the coronary or cerebral circulation. The latter present with varied neurological signs, but a ‘peri-procedural stroke’ should trigger suspicion of cerebral air embolism, a life-threatening emergency. Although there are case reports of these being aspirated percutaneously, the most effective treatment is urgent HBOT 2-4. The outcome is dependent on HBOT within 6–8 h, akin to early thrombolysis in thromboembolic stroke. Hyperbaric oxygen therapy beyond this ideal window should still be considered and discussed with experts in the field. Good outcomes from delayed HBOT may be more likely related to retrograde cerebral venous air embolism rather than cerebral arterial air embolism. Peripheral venous lines have been described many times as a source of cerebral gas embolism, and the absence of a central line should not exclude the diagnosis. The pathophysiology of gas bubbles in the cerebral vascular system and the mechanism of HBOT has been clearly described 5. The diagnosis may be difficult, and a high index of suspicion is required in case of a peri-procedural neurological event, including any form of vascular procedure. Sometimes the diagnosis is inevitably associated with delays, but once the diagnosis is made, every minute counts. For that reason, clear guidance is essential. The quoted incidence of 0.8% of all air embolism events translates into several dozen cases per year of significant cerebral gas embolism, which currently may be missed in the UK 1. The incidence may be higher 2-4. Vascular-related air embolism has recently been removed from the ‘Never Event’ list in the UK and it will be interesting to see if the rate of reporting will change. The British Hyperbaric Association has guidance on their website about how to access emergency HBOT in a suitable Category 1 unit (able to deal with critically ill patients) 6.

Limited evidence suggests that shorter recompression schedules may be as efficacious as the US Navy Treatment Table 6 (USN TT6) for treatment of milder presentations of decompression sickness (DCS). This study aimed to determine if divers with mild DCS could be effectively treated with a shorter chamber treatment table. All patients presenting to the Fremantle Hospital Hyperbaric Medicine Unit with suspected DCS were assessed for inclusion. Participants with mild DCS were randomly allocated to receive recompression in a monoplace chamber via either a modified USN TT6 (TT6m) or a shorter, custom treatment table (FH01). The primary outcome was the number of treatments required until resolution or no further improvement (plateau). Forty-one DCS cases were included, 21 TT6m and 20 FH01. Two patients allocated to FH01 were moved to TT6m mid-treatment due to failure to significantly improve (as per protocol), and two TT6m required extensions. The median total number of treatments till symptom resolution was 1 (IQR 1-1) for FH01 and 2 (IQR 1-2) for TT6m (P = 0.01). More patients in the FH01 arm (17/20, 85%) showed complete symptom resolution after the initial treatment, versus 8/21 (38%) for TT6m (P = 0.003). Both FH01 and TT6m had similar overall outcomes, with 19/20 and 20/21 respectively asymptomatic at the completion of their final treatment (P = 0.97). In all cases where two-week follow-up contact was made, (n = 14 FH01 and n = 12 TT6m), patients reported maintaining full symptom resolution. The median total number of treatments till symptom resolution was meaningfully fewer with FH01 and the shorter treatment more frequently resulted in complete symptom resolution after the initial treatment. There were similar patient outcomes at treatment completion, and at follow-up. We conclude that FH01 appears superior to TT6m for the treatment of mild decompression sickness.

Arterial cerebral air embolism (CAE) is an uncommon but potentially catastrophic event. Patients can present with focal neurologic deficits, seizures, or coma. They may be treated with hyperbaric oxygen therapy. We review the causes, radiographic and clinical characteristics, and outcomes of patients with CAE. We performed a retrospective chart review via an existing institutional database at Mayo Clinic to identify patients with arterial CAE. Demographic data, clinical characteristics, and diagnostic studies were extracted and classified on predefined criteria of diagnostic confidence, and descriptive and univariate analysis was completed. Fifteen patients met criteria for inclusion in our study. Most presented with focal deficits (80%) and/or coma (53%). Seven patients (47%) had seizures, including status epilepticus in one (7%). Five presented with increased muscle tone at the time of the event (33%). Computed tomography (CT) imaging was insensitive for the detection of CAE, only identifying free air in 4 of 13 who underwent this study. When obtained, magnetic resonance imaging typically showed multifocal areas of restricted diffusion. Six patients (40%) were treated with hyperbaric oxygen therapy. Age, Glasgow Coma Scale score at nadir, and use of hyperbaric oxygen therapy were not associated with functional outcome at 1year in our cohort. Twenty-six percent of patients had a modified Rankin scale score of 0 one year after the event, and functional improvement over time was common after discharge. A high index of clinical suspicion is needed to identify patients with CAE because of low sensitivity of free air on CT imaging and nonspecific clinical presentation. Acute alteration of consciousness, seizures, and focal signs occur frequently. Because improvement over time is possible even among patients with severe presentation, early prognostication should be approached with caution.

A 79-year-old gentleman developed a severe right hemispheric syndrome (NIH Stroke Scale [NIHSS] 20) within minutes of undergoing left atrial appendage occlusion (LAAO). Stroke protocol imaging showed air emboli in...

<div class="htmlview paragraph">This paper presents the basic test data obtained from tests of a cabin air distribution system in a simulated Space Station U.S. Lab-A module.</div> <div class="htmlview paragraph">The cabin air distribution system controls the flow of air in the open space of a Space Station module. In order to meet crew comfort criteria the local velocities for this cabin air are required to be distributed within a specified range with upper and lower limits. Achieving this desired velocity distribution is dependent upon the: (1.) design of the cabin air supply equipment and cabin air return equipment, (2.) total flowrate of air supplied to and subsequently returned from the cabin, and (3.) interactive effects of any other additional air flow streams which enter and exit the cabin.</div> <div class="htmlview paragraph">The basic Space Station design for the cabin air supply and air return equipment was used in this test program. Only directional adjustments to vanes in supply air diffusers were made during the test. This equipment is included in the Temperature and Humidity Control (THC) subsystem for the Space Station. Two other air streams, in addition to what is defined as THC cabin airflow, which were involved in the test program were:</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"> <span class="li-label">1.</span> <div class="htmlview paragraph">Standoff airflow – Standoffs are described in the paper. Briefly, they are enclosures within the cabin which formerly included ventilation fans. The consequent standoff airflow interacted with THC cabin airflow. The present baseline THC subsystem does not include the standoff fans.</div></li> <li class="list-item"> <span class="li-label">2.</span> <div class="htmlview paragraph">Intermodule Ventilation (IMV) Airflow – IMV assemblies are used to interchange airflow between Space Station modules. These modules include the U.S. Lab-A module, the nodes, and, later in the Space Station program, the international modules.</div></li></ol></div> <div class="htmlview paragraph">Test results from eight (8) of the test runs which demonstrate the ability for the air distribution system to meet its objectives are presented. These test run results are compared with each other with respect to their standing relative to meeting the test objectives.</div> <div class="htmlview paragraph">The test program investigated the effects of the variables noted above in meeting the test objectives. The basic variable in these test runs was the THC airflow. This airflow varied from 300 cfm to 500 cfm in the 8 test runs presented here. Some changes were made in supply air diffuser vane directional settings. Standoff airflow was used in one test run (number 4) and IMV airflow was used in test runs 5, 6, 7, and 8. Based on the test results, the desired velocity range and an engineering evaluation of the test results, a THC airflow rate for U.S. Lab-A is recommended.</div>

To assess the relationship between the time period before hyperbaric oxygenation therapy (HBO) and clinical outcome in patients with iatrogenic cerebral air embolism. Retrospective study in a hyperbaric chamber and medical intensive care unit of a university hospital. All patients with air embolism from 1980 to 1999. We retrieved the cases of 86 patients who benefited from an identical HBO and analyzed the relationship between the time period before HBO and clinical outcome. Patients treated with HBO less than 6 h had a better outcome than those treated later. In patients treated within this delay the cause was venous air embolism in 84% and arterial air embolism in only 16% of cases. After this delay the cause was venous air embolism (53%) and arterial air embolism (47%). Patients with venous air embolism and recovery had a shorter delay than patients with sequelae or death (2 h 15 min vs. 4 h). Patients with venous air embolism treated less than 6 h had a better outcome than those treated later. In patients with arterial air embolism the time period before HBO was longer than in venous air embolism (8 h vs. 3 h) and the outcome worse (recovery in 35% vs. 67%). In patients with arterial air embolism no difference in the time period was found between patients with recovery and sequelae or death. We stress the beneficial effect of an early HBO in air embolism, the importance of an increased awareness of physicians concerned with this severe complication, and the need to develop techniques to detect air emboli in the cerebral circulation.

Objective To investigate the mechanism of brain and spinal cord injury in experimental rabbits with decompression sickness (DCS) and the effect of hyperbaric oxygen (HBO).Methods Twentyeight adult male healthy New Zealand rabbits were randomly divided into 4 groups:the normal control group,the DCS group,the safe decompression group and the HBO group,each consisting of 7 animals.The rabbits in the DCS group were compressed with air in 5 minutes to a pressure 0.8 MPa and maintained at the said pressure for 60 min,and then were decompressed to normal pressure within 5 min.The animals in the HBO group underwent the same compression and decompression procedures,as the animals in the DCS group,but were immediately put into the hyperbaric chamber to receive HBO therapy.The safe decompression group was compressed and decompressed with the profile of the Chinese Navy Diving Decompression Tables.Changes in pathological morphology and apoptosis of brain and spinal cord tissue cells in the thoracic and lumbar segments were observed with light microscopy and terminal deoxynucleotidyl transferase-mediated DUTP nick end labeling (TUNEL) method.Results For the animals in the DCS group,cavity in the white matter of the spinal cord and proliferation of gliocytes around the damaged tissue could obviously be observed.TUNEL results showed that more positive apoptotic cells were detected in the DCS group (28.29 ± 2.56)/HP,as compared with those of the normal control group (0.57 ± 0.54)/HP,the safe decompression group (2.29 ± 1.11)/HP and the HBO group (3.71 ± 1.11)/HP,with statistical significance (P ＜ 0.05).More positive apoptotic cells were also seen in the HBO group (3.71 ± 1.1 1)/HP,as compared with those of the normal control group (P ＜0.05),but were significantly less,as compared with those of the DCS group (P ＜ 0.05),also with statistical significance (P ＜ 0.05).Slightly more positive apoptotic cells were detected in the animals of the HBO group,when compared with those of the safe decompression group,but without statistical significance (P ＜ 0.05).No significant apoptosis of cells could be seen in the brain tissue.Conclusions Spinal core was the main site involved in the central nervous system injury induced by rapid decompression.The spinal cord injury induced by rapid decompression was the result of the apoptosis of gliocytes,and gliocytes might play a key role in the recovery of spinal cord injury.HBO therapy could obviously inhibit the apoptosis of gliocytes,following spinal cord injury. Key words: Decompression sickness ; Spinal cord injury ; Brain injury ; Apoptosis ; Gliocyte ; Hyperbaric oxygen; Rabbit

<div class="htmlview paragraph">Future space stations and platforms will require a centralized thermal utility to provide temperature control of various heat sinks or sources. Its purpose is to transport large amounts of energy over long distances towards a heat rejection system, with very small temperature differences.</div> <div class="htmlview paragraph">The present paper deals with the heat rejection system. A concept of a multi-tubes condenser has been selected and designed, using ammonia as the working fluid. In order to support and confirm the modelization software, an experiment is set up with a one-tube condenser uniformly cooled, involving limited heat power, but representative of thermo-hydraulic conditions.</div> <div class="htmlview paragraph">This paper presents the test programme. Objectives are first to confirm the selected technology, and to assess internal operation from the measurements of the external temperature along the tube, and differential pressure drop. The experiment which is thought out from an industrial viewpoint also has for purpose to enable simplifications in the modelization, without going into the condensation phenomenon. A description of the test apparatus is also given.</div> <div class="htmlview paragraph">A second condenser tube with asymmetrical cooling, more representative of the space concept (Og), will be tested to quantify the influence of the cooling device on the condensation of the fluid, and adapt the modelization to the space case.</div>

High-altitude flight simulation familiarizes military trainees with the symptoms of hypoxia to prepare them for emergency situations. Decompression sickness (DCS) can occur as a result of these simulations. In cases when ground-level supplemental oxygen does not resolve symptoms, hyperbaric oxygen (HBO) therapy is indicated. Many military hyperbaric chambers have been closed because of cost reductions, necessitating partnerships with community hospitals to ensure access to treatment. This article describes the unique arrangement between a community hospital in Colorado and a military training site to treat DCS cases emergently. We gathered cost data from the community hospital to estimate and compare the cost of providing HBO therapy in the hospital versus a standalone chamber similar to the former military hyperbaric chamber. Since the closure of the military hyperbaric chamber, the community hospital treated an estimated 50 patients with DCS requiring HBO therapy attributed to high-altitude flight simulation between October 2003 and April 2015. Cost to the institution providing HBO treatment varies widely on the basis of patient volume. Assuming a volume of five treatments, per-treatment cost at a standalone center is $95,380. In contrast, per-treatment cost at the hospital assuming a volume of 1,000 treatments commensurate with the hospital's ability to bill for other services is $698 per treatment. The cost analysis demonstrates that the per-treatment cost of operating a standalone HBO therapy center may be greater than 100 times that of operating a center at a community hospital, suggesting the arrangement is beneficial to the military.

A Novel Treatment Modality for Myofascial Pain Syndrome: Hyperbaric Oxygen Therapy

To evaluate the effectiveness of hyperbaric oxygen therapy (HBOT) in the treatment of osteonecrosis of the femoral head (ONFH). Search for term systems related to ONFH and HBOT in PubMed, Cochrane Library, Embase and Web of Science databases. The risk ratio (RR) was used as the effective index for dichotomous variables while mean difference (MD) and 95% confidence interval (CI) were used as the effective index for continuous variables, with a two-sided P < 0.05 considered statistically significant. I2 statistic and Q test were used to evaluate the statistical heterogeneity of the included studies. Ten studies were included, involving 568 participants. Pre-post meta-analyses to show the visual analog scale after HBOT (MD = -2.94, 95% CI: -4.27, -1.60, P < 0.0001), short form 12 physical component summary scale (SF12 PCS) (MD = 17.28, 95% CI: 8.26, 26.31, P = 0.0002), short form 12 mental component summary scale (SF12 MCS) (MD = 4.26, 95% CI: 2.56, 5.95, P < 0.00001), Harris hip score (HHS) (MD = 26.91, 95% CI: 0.35, 53.46, P = 0.05), modified Harris hip score (mHHS) (MD = 44.31, 95% CI: 13.75, 74.87, P = 0.004) were significantly different from those before treatment. The results of SF12 PCS (MD = -0.39, 95% CI: -7.85, 7.06, P = 0.92) and SF12 MCS (MD = 0.76, 95% CI: -7.02, 8.52, P = 0.85), patients' improved events (RR = 1.83, 95% CI: 0.37, 9.09, P = 0.46) showed no significant difference between the HBO and non-HBO groups. The results of this study indicate that HBOT cannot be regarded as an effective measure for the treatment of early-stage necrosis of the femoral head and more large-scale randomized controlled trials are needed for further verification.

Hyperbaric oxygen treatment (HBOT) is a therapeutic modality that delivers 100% oxygen under supra-atmospheric pressure, which has been widely used in the clinical management of various diseases. The incidence of genitourinary fistulas is relatively low in developed countries, mainly presenting as complications of gynecological surgeries, while it remains high in developing nations due to factors such as prolonged labor and inadequate medical care. Among these, bladder fistula is the most common type of genitourinary fistula. This article presents the outcomes of 7 patients who received HBOT after bladder fistula repair surgery, including 6 cases of vesicovaginal fistula (VVF) and 1 case of colovesical fistula (CVF). HBOT was initiated on the first postoperative day, administered once daily for a total of 10 consecutive days, and no relevant adverse reactions occurred in any patient during the HBOT course. All patients achieved uneventful postoperative recovery and were discharged from the hospital, with no recurrence of symptoms observed during the 3–12 months of follow-up. As a novel adjunctive therapy for patients after bladder fistula surgery, HBOT exhibits satisfactory preliminary efficacy and favorable safety profile, yet further research with expanded sample size and in-depth investigation is warranted.

Delayed treatment of iatrogenic cerebral air embolism with hyperbaric oxygen

&lt;div class="htmlview paragraph"&gt;The Spacelab Life Sciences missions are intended to support Life Sciences experiments. The Spacelab Life Sciences 1 (SLS-1) mission originated with a call to the scientific community for experiments in 1978. Accepted experiments involved humans, primates, rodents, amphibians, and plants. The original payload configuration has been reduced to include human, passive rodent, and basic biology experiments and engineering evaluations.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;Human experiments will address effects of micro-gravity on various physiological parameters during and postflight. Investigations with nonhuman subjects will study microgravity effects on the cardiopulmonary, cardiovascular, and musculoskeletal systems, on the regulation of blood volume and erythropoiesis, and on calcium metabolism and gravity receptors.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;SLS-1 will serve as a stepping stone in establishing capabilities for flying nonhuman subjects and performing in-flight manipulations on these subjects without jeopardizing the crew environment. Fundamental technology incorporated in the animal holding facilities and laboratory work bench will be used in subsequent missions and in the future Space Station.&lt;/div&gt;

Although the advancements in craniomaxillofacial surgery have been significant, ischemic craniomaxillofacial diseases remain challenging to treat due to insufficient blood supply. Hyperbaric oxygen therapy (HBOT) has emerged as a promising adjunctive treatment, exhibiting the potential to promote angiogenesis, exert anti-inflammatory effects, enhance bone regeneration, and possess antibacterial properties. Numerous studies have demonstrated its efficacy in stimulating healing processes, particularly in cases such as medication-related osteonecrosis of the jaw, osteoradionecrosis, chronic jaw osteomyelitis, and refractory wounds. Hyperbaric oxygen therapy not only accelerates healing and shortens recovery times but also reduces postoperative complications, infection risks, and enhances patients' overall quality of life. This review aims to synthesize the research progress on the application of hyperbaric oxygen therapy in ischemic craniomaxillofacial diseases, providing a valuable reference for clinicians.