Effect of combined recompression and air, oxygen, or heliox breathing on air bubbles in rat tissues.

The fate of bubbles formed in tissues during the ascent from a real or simulated air dive and subjected to therapeutic recompression has only been indirectly inferred from theoretical modeling and clinical observations. We visually followed the resolution of micro air bubbles injected into adipose tissue, spinal white matter, muscle, and tendon of anesthetized rats recompressed to and held at 284 kPa while rats breathed air, oxygen, heliox 80:20, or heliox 50:50. The rats underwent a prolonged hyperbaric air exposure before bubble injection and recompression. In all tissues, bubbles disappeared faster during breathing of oxygen or heliox mixtures than during air breathing. In some of the experiments, oxygen breathing caused a transient growth of the bubbles. In spinal white matter, heliox 50:50 or oxygen breathing resulted in significantly faster bubble resolution than did heliox 80:20 breathing. In conclusion, air bubbles in lipid and aqueous tissues shrink and disappear faster during recompression during breathing of heliox mixtures or oxygen compared with air breathing. The clinical implication of these findings might be that heliox 50:50 is the mixture of choice for the treatment of decompression sickness.     

Effect of hypobaric air, oxygen, heliox (50:50), or heliox (80:20) breathing on air bubbles in adipose tissue.

The fate of bubbles formed in tissues during decompression to altitude after diving or due to accidental loss of cabin pressure during flight has only been indirectly inferred from theoretical modeling and clinical observations with noninvasive bubble-measuring techniques of intravascular bubbles. In this report we visually followed the in vivo resolution of micro-air bubbles injected into adipose tissue of anesthetized rats decompressed from 101.3 kPa to and held at 71 kPa corresponding to approximately 2.750 m above sea level, while the rats breathed air, oxygen, heliox (50:50), or heliox (80:20). During air breathing, bubbles initially grew for 30-80 min, after which they remained stable or began to shrink slowly. Oxygen breathing caused an initial growth of all bubbles for 15-85 min, after which they shrank until they disappeared from view. Bubble growth was significantly greater during breathing of oxygen compared with air and heliox breathing mixtures. During heliox (50:50) breathing, bubbles initially grew for 5-30 min, from which point they shrank until they disappeared from view. After a shift to heliox (80:20) breathing, some bubbles grew slightly for 20-30 min, then shrank until they disappeared from view. Bubble disappearance was significantly faster during breathing of oxygen and heliox mixtures compared with air. In conclusion, the present results show that oxygen breathing at 71 kPa promotes bubble growth in lipid tissue, and it is possible that breathing of heliox may be beneficial in treating decompression sickness during flight.     

Computerised therapy for depression with clinician vs. Assistant and brief vs. Extended phone support: study protocol for a randomised controlled trial

ABSTRACT: BACKGROUND: Computerised cognitive behaviour therapy (cCBT) involves standardised, automated, interactive self-help programmes delivered via a computer. Randomised controlled trials (RCTs) and observational studies have shown than cCBT reduces depressive symptoms as much as face-to-face therapy and more than waiting lists or treatment as usual. cCBT's efficacy and acceptability may be influenced by the "human" support offered as an adjunct to it, which can vary in duration and can be offered by people with different levels of training and expertise.Methods/designThis is a two-by-two factorial RCT investigating the effectiveness, cost-effectiveness and acceptability of cCBT supplemented with 12 weekly phone support sessions are either brief (5--10 min) or extended (20--30 min) and are offered by either an expert clinician or an assistant with no clinical training. Adults with non-suicidal depression in primary care can self-refer into the study by completing and posting to the research team a standardised questionnaire. Following an assessment interview, eligible referrals have access to an 8-session cCBT programme called Beating the Blues and are randomised to one of four types of support: brief-assistant, extended-assistant, brief-clinician or extended-clinician.A sample size of 35 per group (total 140) is sufficient to detect a moderate effect size with 90% power on our primary outcome measure (Work and Social Adjustment Scale); assuming a 30% attrition rate, 200 patients will be randomised. Secondary outcome measures include the Beck Depression and Anxiety Inventories and the PHQ-9 and GAD-7. Data on clinical outcomes, treatment usage and patient experiences are collected in three ways: by post via self-report questionnaires at week 0 (randomisation) and at weeks 12 and 24 post-randomisation; electronically by the cCBT system every time patients log-in; by phone during assessments, support sessions and exit interviews. DISCUSSION: The study's factorial design increases its efficiency by allowing the concurrent investigation of two types of adjunct support for cCBT with a single sample of participants. Difficulties in recruitment, uptake and retention of participants are anticipated because of the nature of the targeted clinical problem (depression impairs motivation) and of the studied interventions (lack of face-to-face contact because referrals, assessments, interventions and data collection are completed by phone, computer or post).Trial registrationCurrent Controlled Trials ISRCTN98677176.     

Probing the impact of axial diffusion on nitric oxide exchange dynamics with heliox.

Exhaled nitric oxide (NO) is a potential noninvasive index of lung inflammation and is thought to arise from the alveolar and airway regions of the lungs. A two-compartment model has been used to describe NO exchange; however, the model neglects axial diffusion of NO in the gas phase, and recent theoretical studies suggest that this may introduce significant error. We used heliox (80% helium, 20% oxygen) as the insufflating gas to probe the impact of axial diffusion (molecular diffusivity of NO is increased 2.3-fold relative to air) in healthy adults (21-38 yr old, n = 9). Heliox decreased the plateau concentration of exhaled NO by 45% (exhalation flow rate of 50 ml/s). In addition, the total mass of NO exhaled in phase I and II after a 20-s breath hold was reduced by 36%. A single-path trumpet model that considers axial diffusion predicts a 50% increase in the maximum airway flux of NO and a near-zero alveolar concentration (Ca(NO)) and source. Furthermore, when NO elimination is plotted vs. constant exhalation flow rate (range 50-500 ml/s), the slope has been previously interpreted as a nonzero Ca(NO) (range 1-5 ppb); however, the trumpet model predicts a positive slope of 0.4-2.1 ppb despite a zero Ca(NO) because of a diminishing impact of axial diffusion as flow rate increases. We conclude that axial diffusion leads to a significant backdiffusion of NO from the airways to the alveolar region that significantly impacts the partitioning of airway and alveolar contributions to exhaled NO.     

A comparison of the oxygen drift in downhill vs. level running.

This investigation explored the recent theory that muscle damage causes the drift in oxygen consumption (VO2) during low-intensity downhill running. Seven subjects participated in a maximal VO2 (VO2max) test and three submaximal bouts [one level (Level) and two downhill runs (Down 1, Down 2) at 40% peak VO2]. Two downhill runs (30 min at -10% grade) were performed to vary the extent of muscle damage. Creatine kinase (CK) increased more after Down 1 (61%) than after Down 2 (11%), as did soreness ratings, indicating reduced muscle damage during Down 2. Significantly greater increases in VO2 over time were noted for Down 1 (15.6%) and Down 2 (14.7%) than for Level (1.2%). Heart rate increased 8 beats/min for Level but 29 and 25 beats/min for Down 1 and Down 2, respectively. Expired ventilation increased more for Down 1 (20.5%) and Down 2 (24%) than for Level (3.5%). Rectal temperature increased approximately 0.8 degree C for all bouts. Because the magnitude of the drift was similar in the two downhill bouts, the findings suggest that muscle damage does not cause the drift in VO2 during low-intensity downhill running.     

Single vs. repeated microwave exposure: effects on benzodiazepine receptors in the brain of the rat.

We studied the effects of single (45 min) and repeated (ten daily 45-min sessions) microwave exposures (2450-MHz, 1 mW/cm2, average whole-body SAR of 0.6 W/kg, pulsed at 500 pps with pulse width of 2 microseconds) on the concentration and affinity of benzodiazepine receptors in the cerebral cortex, hippocampus, and cerebellum of the rat. We used a receptor-binding assay with 3H-flunitrazepam as ligand. Immediately after a single exposure, an increase in the concentration of receptor was observed in the cerebral cortex, but no significant effect was observed in the hippocampus or cerebellum. No significant change in binding affinity of the receptors was observed in any of the brain-regions studied. In rats subjected to repeated exposures, no significant change in receptor concentration was found in the cerebral cortex immediately after the last exposure, which may indicate an adaptation to repeated exposures. Our data also show that handling and exposure procedures in our experiments did not significantly affect benzodiazepine receptors in the brain. Because benzodiazepine receptors in the brain are responsive to anxiety and stress, our data support the hypothesis that low-intensity microwave irradiation can be a source of stress.     

急性减压病大鼠肺组织粘附分子的变化

目的:探讨急性减压病大鼠肺组织中内粘附分子的改变。方法:雄性SD大鼠置于加压舱内,压缩空气在3 min内匀速加压至0.7 MPa,停留60 min后,3 min内快速减压出舱。观察减压后生存率、减压病症状。在减压后30 min、6 h、24 h取大鼠脑、肺及肝脏组织,甲醛溶液固定、切片、HE染色观测病理改变。免疫组化测定肺组织中细胞间粘附分子-1(ICAM-1)、E-选择素(E-selectin)、主要组织相容性复合体-Ⅱ(MHC-Ⅱ)的表达变化。在减压后6h、24 h前30 min,大鼠尾静脉注射2%evans blue溶液。30 min后行生理盐水灌注,收集肺组织,观测肺组织蓝染程度,酶标仪测定血浆中evans blue含量。结果:肺、肝及脑组织在减压后30 min出现水肿、淤血等病理表现。和正常组比较,肺组织中ICAM-1、E-selectin、MHC-Ⅱ在减压后明显上升,并呈现动态变化。相对于正常组,减压后6 h、24h肺组织血浆中evans blue含量明显增加。结论:气泡导致的,粘附分子介导的血管内皮受损是减压病的发病机制之一。     

Seasonal changes in the oxygen storage capacity and aerobic dive limits of the muskrat (Ondatra zibethicus)

Summary The oxygen storage capacity and partitioning of body oxygen reserves were compared in summer-and winter-acclimatized muskrats (Ondatra zibethicus). Blood volume, blood oxygen capacity, and skeletal muscle myoglobin content were higher in December than in July (P<0.02). Total lung capacity increased only slightly in winter (P>0.05). The oxygen storage capacity of a diving muskrat was calculated at 25.2 ml O₂ STPD · kg^-1 in July, compared to 35.7 ml O₂ STPD · kg^-1 in December. Blood comprised the major storage compartment in both seasons, accounting for 57% and 65% of the total oxygen stores in summer and winter, respectively. Based on available oxygen stores and previous estimates of the cost of diving, the aerobic dive limit (ADL) increased from 40.9 s in July to 57.9 s in December. Concurrent behavioral studies suggested that most voluntary diving by muskrats is aerobic. However, the proportion of dives exceeding the calculated ADL of these animals was shown to vary with the context of the dive. Only 3.5% of all dives initiated by muskrats floating in the water exceeded their estimated ADL. Provision of a dry resting site and access to a submerged food source increased this proportion to 18–61%, depending on the underwater distance that foraging muskrats were required to swim. Serial dives exceeding the estimated ADL were not accompanied by extended postdive recovery periods.Abbreviations ADL acrobic dive limit - Hb hemoglobin - Hct hematocrit - Mb myoglobin - PaO₂ arterial O₂ tension - STPD standard temperature and pressure, dry     

Surfacers change their dive tactics depending on the aim of the dive: evidence from simultaneous measurements of breaths and energy expenditure

Air-breathing divers are assumed to have evolved to apportion their time between surface and underwater periods to maximize the benefit gained from diving activities. However, whether they change their time allocation depending on the aim of the dive is still unknown. This may be particularly crucial for ‘surfacers’ because they dive for various purposes in addition to foraging. In this study, we counted breath events at the surface and estimated oxygen consumption during resting, foraging and other dives in 11 green turtles (Chelonia mydas) in the wild. Breath events were counted by a head-mounted acceleration logger or direct observation based on an animal-borne video logger, and oxygen consumption was estimated by measuring overall dynamic body acceleration. Our results indicate that green turtles maximized their submerged time, following this with five to seven breaths to replenish oxygen for resting dives. However, they changed their dive tactic during foraging and other dives; they surfaced without depleting their estimated stores of oxygen, followed by only a few breaths for effective foraging and locomotion. These dichotomous surfacing tactics would be the result of behavioural modifications by turtles depending on the aim of each dive.     

Dosimetry in photodynamic therapy: oxygen and the critical importance of capillary density.

Recently published results of tumor response to various photoradiation protocols in photodynamic therapy appear to contradict accepted definitions of photodynamic dose. In this report, the failure of standard dosimetry models to predict therapeutic outcome is interpreted on the basis of PDT-induced oxygen consumption in tumors with relatively low capillary densities. Calculated estimates of oxygen consumption in photodynamic therapy are combined with the Krogh cylinder model of oxygen diffusion. It is shown that, for tissue volumes in which the intercapillary spacing is less than a specific critical distance, oxygen may be considered constant and unaffected by the therapy. Under these conditions, the 1O2 delivered to a given volume of tissue is spatially uniform and proportional to the number of photons absorbed by the sensitizer. When the intercapillary spacing exceeds the critical distance, the dose of 1O2 varies with radial distance from the capillary wall. In this situation, dose may no longer be considered simply in terms of the product of the photon fluence and the sensitizer absorption coefficient. Since fractionation will increase the 1O2 dose only to cells relatively remote from the capillary wall, the analysis further suggests that fractionating the radiation dose should result in an improved therapeutic ratio for photodynamic therapy.     

High-flow nasal cannula oxygen therapy versus conventional oxygen therapy in patients with acute respiratory failure: a systematic review and meta-analysis of randomized controlled trials

Background

Acute respiratory failure (ARF) is a common and life-threatening medical emergency in patients admitted to the hospital. Currently, there is a lack of large-scale evidence on the use of high-flow nasal cannulas (HFNC) in patients with ARF. In this systematic review and meta-analysis, we evaluated whether there were differences between HFNC therapy and conventional oxygen therapy (COT) for treating patients with ARF.

Methods

The EMBASE, Medline, and Wanfang databases and the Cochrane Library were searched. Two investigators independently collected the data and assessed the quality of each study. Randomized controlled trials that compared HFNC therapy with COT in patients with ARF were included. RevMan 5.3 was used to conduct the meta-analysis.

Results

Four studies that involved 703 patients with ARF were included, with 371 patients in the HFNC group and 332 patients in the COT group. In the overall estimates, there were no significant differences between the HFNC and COT groups in the rates of escalation of respiratory support (RR, 0.68; 95% CI, 0.37, 1.27; z?=?1.20, P?=?0.23), intubation (RR, 0.74; 95% CI, 0.55, 1.00; z?=?1.95, P?=?0.05), mortality (RR, 0.82; 95% CI, 0.36, 1.88; z?=?0.47, P?=?0.64), or ICU transfer (RR, 1.09; 95% CI, 0.57, 2.09; z?=?0.26, P?=?0.79) during ARF treatment. However, the subgroup analysis showed that HFNC therapy may decrease the rate of escalation of respiratory support (RR, 0.71; 95% CI, 0.53, 0.97; z?=?2.15, P?=?0.03) and the intubation rate (RR, 0.71; 95% CI, 0.53, 0.97; z?=?2.15, P?=?0.03) when ARF patients were treated with HFNC therapy for ≥24 h compared with COT.

Conclusions

HFNC therapy was similar to COT in ARF patients. The subgroup analysis showed that HFNC therapy may decrease the rate of escalation of respiratory support and the intubation rate when ARF patients were treated with HFNC for ≥24 h compared with COT. Further high-quality, large-scale studies are needed to confirm our results.

     

Short oxygen prebreathing and intravenous perfluorocarbon emulsion reduces morbidity and mortality in a swine saturation model of decompression sickness.

Disabled submarine (DISSUB) survivors will achieve inert gas tissue saturation within 24 h. Direct ascent to the surface when saturated carries a high risk of decompression sickness (DCS) and death, yet may be necessary during rescue or escape. O(2) has demonstrated benefits in decreasing morbidity and mortality resulting from DCS by enhancing inert gas elimination. Perfluorocarbons (PFCs) also mitigate the effects of DCS by decreasing bubble formation and increasing O(2) delivery. Our hypothesis is that combining O(2) prebreathing (OPB) and PFC administration will reduce the incidence of DCS and death following saturation in an established 20-kg swine model. Yorkshire swine (20 +/- 6.5 kg) were compressed to 5 atmospheres (ATA) in a dry chamber for 22 h before randomization into one of four groups: 1) air and saline, 2) OPB and saline, 3) OPB with PFC given at depth, 4) OPB with PFC given after surfacing. OPB animals received >90% O(2) for 9 min at depth. All animals were returned to the surface (1 ATA) without decompression stops. The incidence of severe DCS < 2 h after surfacing was 96%, 63%, 82%, and 29% for groups 1, 2, 3, and 4, respectively. The incidence of death was 88%, 41%, 54%, and 5% for groups 1, 2, 3, and 4, respectively. OPB combined with PFC administration after surfacing provided the greatest reduction in DCS morbidity and mortality in a saturation swine model. O(2)-related seizure activity before reaching surface did not negatively affect outcome, but further safety studies are warranted.     

Hyperbaric oxygen therapy in plastic surgery: a review article

The most important effects of hyperbaric oxygen (HBO), for the surgeon, are the stimulation of leukocyte microbial killing, the enhancement of fibroblast replication, and increased collagen formation and neovascularization of ischemic tissue. Preoperative hyperbaric oxygen induces neovascularization in tissue with radionecrosis. Refractory osteomyelitis and necrotizing fasciitis appear to respond to adjunctive hyperbaric oxygen. Crush injury and compartment syndrome appear to benefit through preservation of ATP in cell membranes, which limits edema. Hyperbaric oxygen in burn injury permits shorter hospital stays, a reduced number of surgeries, and less fluid replacement. Skin grafts and flaps are reported to take more completely and more rapidly. The same mechanisms may apply in ischemic problem wounds such as infected diabetic extremities. Contraindications and side effects are described. Hyperbaric oxygen will not heal normal wounds more rapidly but may, under certain circumstances, induce problem wounds to heal more like normal ones.