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We aim to provide reference values for military aircrews participating in hypoxia awareness training (HAT). We describe several parameters with potential biomedical interest based on selected segments and slopes of the changes in oxygen saturation (SatO2) during a standard HAT. A retrospective analysis of 2298 records of the SatO2 curve was performed, including 1526 military men aged 30.48 ± 6.47 years during HAT in a hypobaric chamber. HAT consisted of pre-oxygenation at 100% and an ascent to 7620 m, followed by O2 disconnection starting the phase of descent of SatO2 until reaching the time of useful consciousness (TUC), and finally reconnection to 100% O2 in the recovery phase. Using an ad hoc computational procedure, the time taken to reach several defined critical values was computed. These key parameters were the time until desaturation of 97% and 90% (hypoxia) after oxygen mask disconnection (D97/D90) and reconnection (R97/R90) phases, the time of desaturation (TUC-D97) and hypoxia (TUC-D90) during disconnection, the total time in desaturation (L97) or hypoxia (L90), and the slopes of SatO2 drop (SDSAT97 and SDSAT90) and recovery (SRSAT97). The mean of the quartiles according to TUC were compared by ANOVA. The correlations between the different parameters were studied using Pearson's test and the effect size was estimated with ω2. Potentially useful parameters for the HAT study were those with statistical significance (p < 0.05) and a large effect size. D97, D90, R97, and R90 showed significant differences with small effect sizes, while TUC-D97, TUC-D90, L97, L90, and SDSAT97 showed significant differences and large effect sizes. SDSAT97 correlated with TUC (R = 0.79), TUC-D97 (R = 0.81), and TUC-D90 (R = 0.81). In conclusion, several parameters of the SatO2 curve are useful for the study and monitoring of HAT. The SDSAT97 measured during the test can estimate the TUC and thus contribute to taking measures to characterize and protect the aircrew members.

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OBJECTIVE: To define percentile charts for arterial oxygen saturation (SpO2), heart rate (HR), and cerebral oxygen saturation (crSO2) during the first 15 minutes after birth in neonates born very or extremely preterm and with favorable outcome. STUDY DESIGN: We conducted a secondary-outcome analysis of neonates born preterm included in the Cerebral regional tissue Oxygen Saturation to Guide Oxygen Delivery in preterm neonates during immediate transition after birth III (COSGOD III) trial with visible cerebral oximetry measurements and with favorable outcome, defined as survival without cerebral injuries until term age. We excluded infants with inflammatory morbidities within the first week after birth. SpO2 was obtained by pulse oximetry, and electrocardiogram or pulse oximetry were used for measurement of HR. crSO2 was assessed with near-infrared spectroscopy. Measurements were performed during the first 15 minutes after birth. Percentile charts (10th to 90th centile) were defined for each minute. RESULTS: A total of 207 neonates born preterm with a gestational age of 29.7 (23.9-31.9) weeks and a birth weight of 1200 (378-2320) g were eligible for analyses. The 10th percentile of SpO2 at minute 2, 5, 10, and 15 was 32%, 52%, 83%, and 85%, respectively. The 10th percentile of HR at minute 2, 5, 10, and 15 was 70, 109, 126, and 134 beats/min, respectively. The 10th percentile of crSO2 at minute 2, 5, 20, and 15 was 15%, 27%, 59%, and 63%, respectively. CONCLUSIONS: This study provides new centile charts for SpO2, HR, and crSO2 for neonates born extremely or very preterm with favorable outcome. Implementing these centiles in guiding interventions during the stabilization process after birth might help to more accurately target oxygenation during postnatal transition period.

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RESUMEN La afinidad de la hemoglobina (Hb) por oxigeno (O2) es un factor importante que influye en el transporte de este gas, especialmente en hipoxia y en diferentes enfermedades como anemia o fibrosis quística. En la medición de la afinidad se usa la determinación de la curva de disociación Hb:O2. El método presentado para establecer la curva de disociación Hb:O2 (CDO) simplifica los protocolos normalmente utilizados, ya que elimina el requerimiento del equipo específico para equilibrar la sangre con oxígeno en niveles fijos de presión parcial (PO2). Mediante el uso de ecuaciones matemáticas es posible establecer la cinética de saturación de la hemoglobina (SO2) a valores crecientes de PO2. De igual forma, mediante el método se determinan aspectos típicos de la unión Hb: O2 como la dependencia del pH (coeficiente de Bohr) y el tipo de asociación de la proteína con su ligando mediante el diagrama de Hill. En virtud de la simplificación realizada, el método es aplicable en prácticas de laboratorio en población humana y animal, así como en la investigación de diferentes condiciones experimentales.

ABSTRACT The affinity of hemoglobin (Hb) for oxygen (O2) is an important factor influencing the transport of this gas especially in hypoxia and in different diseases such as anemia or cystic fibrosis. By the affinity measurement, the determination of the Hb: O2 dissociation curve is used. The presented method to establish the Hb: O2 oxygen dissociation curve (CDO) simplifies the protocols normally used, since it eliminates the requirement of specific equipment to equilibrate blood with oxygen at fixed levels of oxygen pressure (PO2). By using mathematical equations, it is possible to establish the saturation change of hemoglobin (SO2) at increasing oxygen partial pressure. Similarly, the method determines typical aspects of the Hb: O2 binding as the pH dependence (Bohr coefficient) and the association type of protein with its ligand by the Hill diagram. By this simplification, the method is applicable in laboratory practices in human and animal population, as well as in the investigation of different experimental conditions.

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Moraga, Fernando A., Jorge Osorio, Rodrigo Calderón-Jofré, and Andrés Pedreros. Hemoconcentration during maximum exercise in miners with chronic intermittent exposure to hypobaric hypoxia (3800 m). High Alt Med Biol. 19:15-20, 2018. OBJECTIVE: To evaluate the effect of maximum exercise on hemoconcentration in miners with chronic intermittent hypobaric hypoxia (CIHH) at 3800 m. MATERIALS AND METHODS: Sixteen miners with CIHH at high altitude (3800 m) were subjected to maximum exercise levels on a cycle ergometer, increasing exercise load by 50 W every 3 minutes at sea level and high altitude (3800 m). During exercise, arterial oxygen saturation and heart rate were measured. Blood samples were taken at each step to measure hemoglobin concentration and hematocrit. Arterial blood oxygen content was also calculated. RESULTS: At sea level, a decrease in arterial oxygen saturation to 92.1% ± 2.5% was observed at 150 W and the hematocrit, hemoglobin concentration and oxygen content were not altered. At high altitude, arterial oxygen saturation decreased, reaching 88.2% ± 4.9% at 50 W and remained constant during the entire exercise protocol. Hemoglobin concentration and hematocrit increased reaching 16.4 ± 0.9 g/dL and 48.8% ± 1.6%, respectively, at 100 W and were maintained until recovery. Arterial oxygen content was constant during exercise and increased in the recovery period. CONCLUSION: An increase in hemoglobin concentration during exercise compensates for the decline in arterial oxygen saturation, meanwhile arterial oxygen content remains constant.

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Resumen Introducción: la validez de la relación saturación arterial de oxígeno y fracción inspiratória de oxígeno (SaO2/FiO2), calculada por oximetría de pulso y por gases arteriales en pacientes con exacerbación de la enfermedad pulmonar obstructiva crónica (E-EPOC) a la altitud de Bogotá no son conocidos, los pacientes con EPOC pueden presentar alteraciones en el intercambio de gases que pueden empeorar con los episodios de broncoespasmo, obtener valores de la SaO2 por oximetría y FiO2 puede brindar información valiosa sobre el curso de la exacerbación. Objetivo: determinar la validez de la relación SaO2/FiO2 calculada por oximetría de pulso y por gases arteriales con relación a los desenlaces de ventilación mecánica (VM) y mortalidad a siete y 30 días. Métodos: se realizó un estudio de cohorte prospectivo con análisis de prueba diagnóstica calculando los puntajes DECAF, BAP-65, CURB-65, gases arteriales y oximetría de pulso al ingreso de pacientes con E-EPOC, se evaluó el desenlace de mortalidad a los siete y 30 días de ingreso y el requerimiento de VM durante su hospitalización, se calculó la relación SaO2/FiO2 utilizando la SaO2 obtenida en los gases arteriales y de manera independiente la relación SaO2/FiO2 con la SaO2 obtenida por oximetría de pulso, con los datos obtenidos se calculó los valores de sensibilidad (S), especificidad (E), valor predictivo positivo (VPP), valor predictivo negativo (VPN), razón de verosimilitud positiva (LR+), razón de verosimilitud negativa (LR-) y área bajo la curva de características operativas del receptor (ACOR). Resultados: se analizaron 462 E-EPOC, el requerimiento de VM fue de 14.3% y mortalidad a 30 días de 5.71%, la sensibilidad de la relación SaO2/FiO2 calculada por oximetría de pulso para desenlace de VM fue de 84.6% (IC95%:75-94.2), especificidad 42% (IC95%:37- 47), VPP: 19.6% (IC95%:14.8-24.4), VPN: 94.3% (IC95%:90.5-98), LR+: 1.46 (IC95%:1.28-1.67), LR: 0.37(IC95%:0.20-1.67), ACOR: 0.779% (IC95%:0.711-0.847) p<0.0001, la sensibilidad de relación SaO2/FiO2 por gases arteriales para VM fue de 83% (IC95%:73.2-92.9), especificidad 57% (IC95%:51.9-62.2), VPP: 24.8% (IC95%:18.8-30.7), VPN: 95.2% (IC95%:92.2-98.2), LR+: 1.94 (IC95%:1.65-2.27), LR-: 0.30 (IC95%:0.17-0.51), ACOR: 0.799% (IC95%:0.737-0.861) p<0.0001, la sensibilidad de la relación SaO2/FiO2 por oximetría para desenlace de mortalidad tiene una sensibilidad del 76.8% (IC95%:58.8-95), especificidad de 39.2% (IC95%:34.4-43.9), VPP: 7.1% (IC95%:3.9-10.3), VPN: 96.5% (IC95%:93.5-99.5), LR+: 1.26 (IC95%:1.01-1.58), LR-: 0.59 (IC95%:0.29-1.20), ACOR: 0.689% (IC95%:0.568-0.810) p<0.0001, la sensibilidad de la relación SaO2/FiO2 por gases arteriales para mortalidad fue de 80.8% (IC95%:63.7-97.8), especificidad 53.2% (IC95%:48.3-58), VPP: 9.6% (IC95%:5.5-13.8), VPN: 97.8% (IC95%:95.7-99.9), LR+: 1.73 (IC95%:1.39-2.14), LR-: 0.36 (IC95%:0.16-0.80), ACOR: 0.732% (IC95%:0.617-0.846) p<0.0001. Conclusión: los valores de SaO2/FiO2 calculados por oximetría y por gases arteriales pueden ser útiles para predecir desenlaces de VM y mortalidad en pacientes con exacerbación de la EPOC. (Acta Med Colomb 2017; 42: 215-223).

Abstract Introduction: the validity of the ratio arterial oxygen saturation and inspiratory oxygen fraction (SaO /FiO2), calculated by pulse oximetry and by arterial gases in patients with exacerbation of chronic obstructive pulmonary disease (E-COPD) at the altitude of Bogotá are not known. Patients with COPD can present alterations in gas exchange that can worsen with bronchospasm episodes. Obtaining values of SaO2 by oximetry and FiO2 can provide valuable information on the course of the exacerbation. Objective: to determine the validity of the SaO2/ iO2 ratio calculated by pulse oximetry and by arterial gases in relation to mechanical ventilation (VM) outcomes and mortality at seven and 30 days. Methods: a prospective cohort study with diagnostic test analysis was performed, calculating DECAF, BAP-65, CURB-65, arterial blood gas and pulse oximetry scores on admission of patients with E-COPD, and the outcome of mortality was evaluated at seven and 30 days of admission and the MV requirement during hospitalization; the SaO2/FiO2 ratio was calculated using the SaO2 obtained in the arterial gases and independently the SaO2/FiO2 ratio with the SaO2 obtained by pulse oximetry. With the data obtained, the values of sensitivity (S), specificity (E), positive predictive value (VPP), negative predictive value (NPV), positive likelihood ratio (LR +), negative likelihood ratio (LR-) and low area the operating characteristics curve of the receiver (ACOR) were calculated. Results: 462 E-COPD were analyzed; the MV requirement was 14.3% and 30-day mortality of 5.71%, the sensitivity of the SaO2/FiO2 ratio calculated by pulse oximetry for MV outcome was 84.6% (95% CI : 75-94.2), specificity 42% (95% CI: 37-47), PPV: 19.6% (95% CI: 14.8-24.4), NPV: 94.3% (95% CI: 90.5-98), LR +: 1.46 (95% CI : 1.28-1.67), LR: 0.37 (95% CI: 0.20-1.67), ACOR: 0.779% (95% CI: 0.711-0.847) p <0.0001, sensitivity of SaO2/FiO2 ratio for arterial blood gases for MV was 83% (95% CI: 73.2-92.9), specificity 57% (95% CI: 51.9-62.2), PPV: 24.8% (95% CI: 18.8-30.7), NPV: 95.2% (95% CI: 92.2-98.2), LR +: 1.94 (IC95%: 1.65-2.27), LR-: 0.30 (IC95%: 0.17-0.51), ACOR: 0.799% (IC95%: 0.737-0.861) p <0.0001, the sensitivity of the SaO2/FiO2 ratio by oximetry for outcome of mortality has a sensitivity of 76.8% (95% CI: 58.895), specificity of 39.2% (95% CI: 34.4-43.9), PPV: 7.1% (95% CI: 3.9-10.3), NPV: 96.5% (95% CI : 93.5-99.5), LR +: 1.26 (IC95%: 1.01-1.58), LR-: 0.59 (CI 95%: 0.29-1.20), ACOR: 0.689% (IC95%: 0.568-0.810) p <0.0001, the sensitivity of the SaO2/FiO2 ratio for arterial blood gases was 80.8% (95% CI: 63.7-97.8), specificity 53.2% (95% CI: 48.3-58), PPV: 9.6% (95% CI: 5.5-13.8), NPV: 97.8% (95% CI: 95.7-99.9), LR +: 1.73 (95% CI: 1.39-2.14), LR-: 0.36 (IC95%: 0.16-0.80), ACOR: 0.732% (IC95%: 0.617-0.846) p <0.0001. Conclusion: SaO2/FiO2 values calculated by oximetry and arterial blood gases can be useful to predict MV outcomes and mortality in patients with exacerbation of COPD. (Acta Med Colomb 2017; 42: 215-223).

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Introducción: En cardiología, la aplicación de teorías, como la de los sistemas dinámicos y la geometría fractal, han generado nuevos diagnósticos matemáticos que diferencian, de manera geométrica y cuantitativa, el comportamiento normal del enfermo a partir de la ocupación del atractor caótico cardíaco. El objetivo de este estudio fue desarrollar, en el contexto de la teoría de los sistemas dinámicos, una metodología de evaluación de la saturación arterial de oxígeno para pacientes en la Unidad de Cuidados Intensivos. Materiales y Métodos: Se seleccionaron 10 pacientes con diferentes enfermedades, provenientes de la Unidad de Cuidados Intensivos, a los cuales se les registró la saturación arterial de oxígeno durante su estancia en la Unidad, y se construyeron atractores caóticos en el mapa de retardo. Posteriormente, se establecieron cuantificaciones de los valores mínimos y máximos del atractor. Resultados: Los valores máximos y mínimos de los atractores de la saturación de oxígeno variaron entre el 100% y el 70%, para los pacientes que fallecieron, mientras que para aquellos que vivieron, se mantuvo entre el 99% y el 85%. Conclusiones: Se observó un comportamiento caótico asociado a la saturación arterial de oxígeno, cuantificable a partir de los valores máximos y mínimos hallados de la totalidad del atractor, estableciendo una nueva medida matemática y física del paciente crítico en la Unidad de Cuidados Intensivo (AU)

Introduction: In cardiology, the application of theories, such as dynamical systems and fractal geometry, has generated new mathematical diagnoses that differentiate geometrically and quantitatively the normal from the diseased behavior through the occupation of the cardiac chaotic attractor. The objective of this study was to develop, in the context of the dynamical systems theory, a methodology for the evaluation of arterial oxygen saturation in patients of the Intensive Care Unit. Materials and Methods: Ten patients with different pathologies from the Intensive Care Unit were selected. The arterial oxygen saturation was recorded during their stay in the Intensive Care Unit and chaotic attractors were built in the delay map. Subsequently, quantifications of the minimum and maximum values of the attractor were established. Results: The maximum and minimum values of the oxygen saturation attractors varied between 100% and 70% for patients who died, whereas for those who lived, saturation values between 99% and 85% were maintained. Conclusions: A chaotic behavior associated with arterial oxygen saturation, quantifiable through the maximum and minimum values found in the entire attractor, was observed, establishing a new mathematical and physical measurement of the critical patient in the Intensive Care Unit.(AU)

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OBJECTIVE: To investigate whether changes in cardiac function and cerebral blood flow (CBF) precede the occurrence of peri/intraventricular hemorrhage (P/IVH) in extremely preterm infants. STUDY DESIGN: In this prospective observational study, 22 preterm infants (gestational age 25.9 ± 1.2 weeks; range 23-27 weeks) were monitored between 4 and 76 hours after birth. Cardiac function and changes in CBF and P/IVH were assessed by ultrasound every 12 hours. Changes in CBF were also followed by continuous monitoring of cerebral regional oxygen saturation (rSO2) and by calculating cerebral fractional oxygen extraction. RESULTS: Five patients developed P/IVH (1 patient grade II and 4 patients grade IV). Whereas measures of cardiac function and CBF remained unchanged in neonates without P/IVH, patients with P/IVH tended to have lower left ventricular output and had lower left ventricle stroke volume and cerebral rSO2 and higher cerebral fractional oxygen extraction during the first 12 hours of the study. By 28 hours, these variables were similar in the 2 groups and myocardial performance index was lower and middle cerebral artery mean flow velocity higher in the P/IVH group. P/IVH was detected after these changes occurred. CONCLUSIONS: Cardiac function and CBF remain stable in very preterm neonates who do not develop P/IVH during the first 3 postnatal days. In very preterm neonates developing P/IVH during this period, lower systemic perfusion and CBF followed by an increase in these variables precede the development of P/IVH. Monitoring cardiac function and cerebral rSO2 may identify infants at higher risk for developing P/IVH before the bleeding occurs.

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OBJECTIVE: To define reference ranges for regional cerebral tissue oxygen saturation (crSO2) and regional cerebral fractional tissue oxygen extraction (cFTOE) during the first 15 minutes after birth in neonates requiring no medical support. STUDY DESIGN: The crSO2 was measured using near infrared spectroscopy (Invos 5100 cerebral/somatic oximeter monitor; Somanetics Corp, Troy, Michigan) during the first 15 minutes after birth for term and preterm neonates. The near infrared spectroscopy sensor was placed on the left forehead. Peripheral oxygen saturation and heart rate were continuously measured by pulse oximetry, and cFTOE was calculated. Neonates were excluded if they required any medical support. RESULTS: A total of 381 neonates were included: 82 term neonates after vaginal delivery, 272 term neonates after cesarean delivery, and 27 preterm neonates after cesarean delivery. In all neonates, median (10th-90th percentiles) crSO2 was 41% (23-64) at 2 minutes, 68% (45-85) at 5 minutes, 79% (65-90) at 10 minutes, and 77% (63-89) at 15 minutes of age. In all neonates, median (10th-90th percentiles) cFTOE was 33% (11-70) at 2 minutes, 21% (6-45) at 5 minutes, 15% (5-31) at 10 minutes, and 18% (7-34) at 15 minutes of age. CONCLUSION: We report reference ranges of crSO2 and cFTOE in neonates requiring no medical support during transition immediately after birth. The use of cerebral oxygenation monitoring and use of these reference ranges in neonates during transition may help to guide oxygen delivery and avoid cerebral hypo-oxygenation and hyperoxygenation.

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