There is no evidence that carbon dioxide-enriched oxygen before apnea affects the time to arterial desaturation, but it might improve cerebral oxygenation in anesthetized obese patients: a single-blinded randomized crossover trial.

PURPOSE: Carbon dioxide (CO2) increases cerebral perfusion. The effect of CO2 on apnea tolerance, such as after anesthesia induction, is unknown. This study aimed to assess if cerebral apnea tolerance can be improved in obese patients under general anesthesia when comparing O2/Air (95%O2) to O2/CO2 (95%O2/5%CO2). METHODS: In this single-center, single-blinded, randomized crossover trial, 30 patients 18-65 years, with body mass index > 35 kg/m2, requiring general anesthesia for bariatric surgery, underwent two apneas that were preceded by ventilation with either O2/Air or O2/CO2 in random order. After anesthesia induction, intubation, and ventilation with O2/Air or O2/CO2 for 10 min, apnea was performed until the cerebral tissue oxygenation index (TOI) dropped by a relative 20% from baseline (primary endpoint) or oxygen saturation (SpO2) reached 80% (safety abortion criterion). The intervention was then repeated with the second substance. RESULTS: The safety criterion was reached in all patients before cerebral TOI decreased by 20%. The time until SpO2 dropped to 80% was similar in the two groups (+ 6 s with O2/CO2, 95%CI -7 to 19 s, p = 0.37). Cerebral TOI and PaO2 were higher after O2/CO2 (+ 1.5%; 95%CI: from 0.3 to 2.6; p = 0.02 and + 0.6 kPa; 95%CI: 0.1 to 1.1; p = 0.02). CONCLUSION: O2/CO2 improves cerebral TOI and PaO2 in anesthetized bariatric patients. Better apnea tolerance could not be confirmed.

Reduction of the vertical vestibular-ocular reflex in military aircraft pilots exposed to tactical, high-performance flight.

Background: Exposure to high-performance flight stresses the vestibular system and may lead to adaptive changes in the vestibular responses of pilots. We investigated the vestibular-ocular reflex of pilots with different histories of flight exposure both with respect to hours of flight and flight conditions (tactical, high-performance vs. non-high-performance) to evaluate if and how adaptative changes are observable. Methods: We evaluated the vestibular-ocular reflex of aircraft pilots using the video Head Impulse Test. In study 1, we assessed three groups of military pilots: Group 1 had 68 pilots with few hours of flight experience (<300 h) in non-high-performance flight conditions; Group 2 had 15 pilots with many hours of flight (>3,000 h) and regularly flying tactical, high-performance flight conditions; Group 3 had eight pilots with many hours of flight (>3,000 h) but not exposed to tactical, high-performance flight conditions. In study 2, four trainee pilots were followed up and tested three times over a 4-year period: (1) <300 h of flight on civil aircraft; (2) shortly after exposure to aerobatic training and with <2,000 h of overall flight; and (3) after training on tactical, high-performance aircraft (F/A 18) and for more than 2,000 h of flight. Results: Study 1: Pilots of tactical, high-performance aircrafts (Group 2) had significantly lower gain values (p < 0.05) as compared to Groups 1 and 3, selectively for the vertical semicircular canals. They also had a statistically (p = 0.022) higher proportion (0.53) of pathological values in at least one vertical semicircular canal as compared to the other groups. Study 2: A statistically significant (p < 0.05) decrease in the rVOR gains of all vertical semicircular canals, but not of the horizontal canals, was observed. Two pilots had a pathological value in at least one vertical semicircular canal in the third test. Discussion: The results evidence a decrease in the gain of the vestibular-ocular reflex as measured with the video head impulse test for the vertical canals. This decrease appears to be associated with the exposure to tactical, high-performance flight rather than with the overall flight experience.

Specific effect of hypobaria on cerebrovascular hypercapnic responses in hypoxia.

It remains unknown whether hypobaria plays a role on cerebrovascular reactivity to CO2 (CVR). The present study evaluated the putative effect of hypobaria on CVR and its influence on cerebral oxygen delivery (cDO2 ) in five randomized conditions (i.e., normobaric normoxia, NN, altitude level of 440 m; hypobaric hypoxia, HH at altitude levels of 3,000 m and 5,500 m; normobaric hypoxia, NH, altitude simulation of 5,500 m; and hypobaric normoxia, HN). CVR was assessed in nine healthy participants (either students in aviation or pilots) during a hypercapnic test (i.e., 5% CO2 ). We obtained CVR by plotting middle cerebral artery velocity versus end-tidal CO2 pressure (PET CO2 ) using a sigmoid model. Hypobaria induced an increased slope in HH (0.66 ± 0.33) compared to NH (0.35 ± 0.19) with a trend in HN (0.46 ± 0.12) compared to NN (0.23 ± 0.12, p = .069). PET CO2 was decreased (22.3 ± 2.4 vs. 34.5 ± 2.8 mmHg and 19.9 ± 1.3 vs. 30.8 ± 2.2 mmHg, for HN vs. NN and HH vs. NH, respectively, p < .05) in hypobaric conditions when compared to normobaric conditions with comparable inspired oxygen pressure (141 ± 1 vs. 133 ± 3 mmHg and 74 ± 1 vs. 70 ± 2 mmHg, for NN vs. HN and NH vs. HH, respectively) During hypercapnia, cDO2 was decreased in 5,500 m HH (p = .046), but maintained in NH when compared to NN. To conclude, CVR seems more sensitive (i.e., slope increase) in hypobaric than in normobaric conditions. Moreover, hypobaria potentially affected vasodilation reserve (i.e., MCAv autoregulation) and brain oxygen delivery during hypercapnia. These results are relevant for populations (i.e., aviation pilots; high-altitude residents as miners; mountaineers) occasionally exposed to hypobaric normoxia.

Protocol for a prospective, controlled, observational study to evaluate the influence of hypoxia on healthy volunteers and patients with inflammatory bowel disease: the Altitude IBD Study.

INTRODUCTION: Inflammatory bowel disease (IBD) is a chronic intestinal disorder, often leading to an impaired quality of life in affected patients. The importance of environmental factors in the pathogenesis of IBD, including their disease-modifying potential, is increasingly recognised. Hypoxia seems to be an important driver of inflammation, as has been reported by our group and others. The aim of the study is to evaluate if hypoxia can alter disease activity of IBD measured by Harvey-Bradshaw Activity Index in Crohn's disease (increase to ≥5 points) and the partial Mayo Score for ulcerative colitis (increase to ≥2 points). To test the effects of hypoxia under standardised conditions, we designed a prospective and controlled investigation in healthy controls and patients with IBD in stable remission. METHODS AND ANALYSIS: This is a prospective, controlled and observational study. Participants undergo a 3-hour exposure to hypoxic conditions simulating an altitude of 4000 metres above sea level (m.a.s.l.) in a hypobaric pressure chamber. Clinical parameters, as well as blood and stool samples and biopsies from the sigmoid colon are collected at subsequent time points. ETHICS AND DISSEMINATION: The study protocol was approved by the Ethics Committee of the Kanton Zurich (reference KEK-ZH-number 2013-0284). The results will be published in a peer-reviewed journal and shared with the worldwide medical community. TRIALS REGISTRATION NUMBER: NCT02849821; Pre-results.

Ankylosing spondylitis and heart abnormalities: do cardiac conduction disorders, valve regurgitation and diastolic dysfunction occur more often in male patients with diagnosed ankylosing spondylitis for over 15 years than in the normal population?

The objective of this study was to determine the rate of selected cardiac pathologies (conduction disorders, valve regurgitation and diastolic dysfunction) in patients with long-standing ankylosing spondylitis (AS) and compare the results with the prevalence in the normal population. A rheumatologic (structured questionnaire interview) and cardiac evaluation (resting electrocardiography and echocardiography) was performed in 100 male subjects with AS and a disease duration of more than 15 years. The rates for conduction disorders, aortic and mitral valve regurgitation and diastolic dysfunction were compared with the corresponding results in the literature among the normal population. In patients with long-standing AS there was no increased rate for valve regurgitation (mitral and aortic valve) and for arrhythmia. Diastolic dysfunction occurred more often in patients with long-standing AS. However, this might be caused by the presence of other cardiovascular risk factors such as age and hypertension. According to these results, a cardiologic evaluation with echocardiography should not be recommended routinely in patients with long-standing AS. To confirm these results, a large prospective study with patients with long-standing AS and with a matched control group should be performed in the future.

Airplane transport isolators may loose leak tightness after rapid cabin decompression.

Air medical transport of patients suffering of highly infectious diseases is typically performed employing portable isolation chambers. Although the likelihood of decompression flight emergencies is low, sustainability of the devices used is crucial. When a standard isolation unit was subjected to an explosive cabin decompression of 493 hPa, simulating a 32808 ft flight level accident, leak tightness of the unit was lost due to rupture of the bag caused by over expansion. When the pressure chamber experiment was repeated with a modified unit, distension was minimized by an additional compensation air bag, thus ensuring leak tightness.