Fisiología respiratoria: relación ventilación/perfusión / Respiratory fisiology: ventilation/perfusion relationship

Las alteraciones de la relación entre la ventilación y el flujo sanguíneo (V/Q) en diversas regiones del pulmón alteran el aporte de oxígeno (O2) y remoción del dióxido de carbono (CO2) al organismo. Fisiológicamente existen diferencias regionales en la relación V/Q. Determinadas patologías pueden alterar esta relación, produciendo tres escenarios distintos: Cortocircuito (Shunt), Alteración V/Q y aumento del espacio muerto. Para evaluar estos escenarios y realizar una aproximación diagnostica son de utilidad el estudio de los gases arteriales y venosos, la diferencia alveolo arterial y la respuesta al suministrar O2

Alterations in the ventilation perfusion relationship (V/Q) in various lung regions alter the supply of oxygen (O2) and the removal of carbon dioxide (CO2) in the body. Physiologically, there are regional differences in the V/Q ratio. Certain pathologies can alter this relationship, producing three different scenarios: Shunt, V/Q mismach and dead space increased. To evaluate these scenarios and carry out a diagnostic approach, it is useful to study arterial and venous gasometry, the alveolar arterial difference and the response to oxygen supplying.

Fisiología respiratoria hipoxemia / Hypoxemia

La hipoxemia ocurre producto de una inadecuada captación de oxígeno a nivel pulmonar y se manifiesta como presión arterial de oxígeno menor a 60 mmHg o saturación arterial de oxígeno menor de 90%. Los mecanismos fisiopatológicos por los cuales se puede producir hipoxemia son hipoventilación, alteración del equilibrio ventilación perfusión, shunt cardiaco, alteración de la difusión y disminución de la presión inspirada de oxígeno. La comprensión de estos mecanismos es fundamental para entender su presentación clínica en distintas enfermedades.

Hypoxemia is the name given to inadequate uptake in the lung and is defined as an arterial oxygen pressure less than 60 mmHg or arterial oxygen saturation less than 90%. The pathophysiological mechanisms that can produce hypoxemia are: hypoventilation, ventilation perfusion mismatch, cardiac shunt, diffusion impairment and decreased inspired oxygen pressure. Full comprehension of these mechanism facilitates the understanding of hypoxemia among different diseases.

Guideline for Ventilation/Perfusion Scintigraphy

This paper is about the Guideline for Ventilation / Perfusion Scintigraphy. It has been developed by the Brazilian Society of Nuclear Medicine to be a best practices guide used in Nuclear Medicine. Its function is to be an educational tool to help the Nuclear Medicine Services in Brazil to guarantee a quality care to the patients

Efeitos da filtragem de leucócitos sobre a resposta inflamatória e a função pulmonar de pacientes submetidos à revascularização miocárdica com circulação extracorpórea / Effects of leukocyte filtering on the inflammatory response and pulmonary function in patients undergoing coronary artery bypass grafting with cardiopulmonary bypass

INTRODUÇÃO E OBJETIVOS: A Circulação extracorpórea (CEC) é associada a ativação leucocitária, resposta inflamatória e disfunção pulmonar. Objetivou-se avaliar os efeitos da filtragem leucocitária sobre a resposta inflamatória e a função pulmonar em indivíduos submetidos à revascularização do miocárdio (RM) com CEC. MÉTODO: Após aprovação pelo Comitê de Ética Institucional e obtenção do consentimento informado dos indivíduos, foi realizado estudo prospectivo randomizado, para comparar indivíduos adultos submetidos à RM com CEC, utilizando-se filtragem leucocitária (n=09) ou filtro standard (n=11) durante a CEC. Tomografia computadorizada (CT) de tórax, espirometria, análise da oxigenação e hemograma foram realizados antes da cirurgia. A anestesia foi induzida por via venosa com etomidato (0,3 mg.kg-1), sufentanil (0,3 ug.kg-1), pancurônio (0,08 mg.kg-1) e mantida com isoflurano (0,5 - 1,0 CAM) e sufentanil (0,5 ug.kg-1.h-1). A ventilação mecânica utilizou volume corrente de 8 mL.kg-1, com FiO2 de 0,6 e PEEP de 5 cm H2O, exceto durante a CEC. No grupo Filtragem, durante a CEC, foi inserido um filtro de leucócitos na linha arterial do circuito (LG-6, Pall Biomedical Products) e, no grupo Controle, foi utilizado o filtro Standard. Contagem leucocitária foi realizada após a indução, aos 5, 25 e 50 min de CEC, ao final da cirurgia, com 12 e 24 h PO. Dados hemodinâmicos, PaO2/FiO2, fração de Shunt, interleucinas, elastase e mieloperoxidase foram colhidos antes e após a CEC, no final da cirurgia, com 6,12 e 24 h PO. Trinta minutos depois da indução, e trinta após a CEC, três amostras sequenciais de ar exalado foram colhidas para análise de óxido nítrico (NO), por quimiluminescência. Espirometria e CT de tórax foram realizadas no primeiro dia pós-operatório. Os dados foram analisados por meio de ANOVA de duplo fator para medidas repetidas. RESULTADOS: O tempo de CEC foi similar entre os grupos controle e filtragem (86,78 ± 19,58 versus 104,64 ± 27,76 min, p=0,161)...

BACKGROUND AND OBJECTIVE: The Cardiopulmonary bypass (CPB) is related to leukocyte activation, inflammatory response and lung dysfunction. The aim of this study was to evaluate the effects of CPB-leukocyte filtration on the inflammatory response and lung function after coronary artery bypass grafting (CABG). METHODS: After approval by the institutional ethics committee and informed consent, a prospective randomized study was performed to compare CABG-patients undergoing CPB-leukocyte filtration (n=9) or standard CPB (n=11). Espirometry, chest computed tomography (CT), oxygenation analysis and leukocyte count were performed before surgery. Anesthesia induction was performed intravenously with etomidate (0,3 mg.kg-1), sufentanil (0,3 ug.kg-1), pancuronium bromide (0,08 mg.kg-1) e sustained with isoflurano (0,5 - 1,0 CAM) and sufentanil (0,5 ug.kg-1.h-1). The tidal volume used during mechanical ventilation was 8 mL.kg-1, the FiO2 0.6 and PEEP 5 cm H2O, except during CPB. In Filtered group, during CPB, was inserted a leukocyte filter in the arterial line of CPB circuit (LG-6, Pall Biomedical Products) and, in Control group, the Standard arterial line filter was utilized. Hemodynamic data, PaO2/FiO2, shunt fraction, interleukins, elastase and myeloperoxidase were evaluated before and after CPB, at the end of surgery, and 6, 12 and 24 h PO. Thirty minutes after induction, and Thirty after CPB, three sequential exhaled air samples were collected to perform analysis of nitric oxide (NO), by chemiluminescence technique. Espirometry and chest CT were performed on first PO. Data were analyzed using two-factor ANOVA for repeated measurements. RESULTS: Length of CPB was similar in the filtered and control groups (86.78 ± 19.58 versus 104.64 ± 27.76 min, p = 0.161). The filtered group showed lower neutrophil counts than the control group up to 50 minutes of CPB (3384 ± 2025 versus 6478 ± 3582 U/mm-3, p = 0.036), lower shunt fraction up to 6 hours after surgery (10 ± 2%)...

Análise da estabilidade de uma variável submáxima em teste cardiopulmonar de exercício: ponto ótimo cardiorrespiratório / Analysis of the stability of a submaximal variable in the cardiopulmonary exercise testing: Cardiopulmonary optimal point

O presente estudo teve por objetivo investigar a estabilidade do ponto ótimo cardiorrespiratório (POC) em dois testes cardiopulmonares de exercício máximos (TCPEs), realizados em cicloergômetro de membros inferiores. Para tanto, foram analisados retrospectivamente os dados de 1334 indivíduos avaliados por no mínimo duas vezes entre 1995 e 2013, sendo identificados, a partir de rígidos critérios de inclusão, 222 pacientes (159 homens) com a idade de 55±11,6 anos. Logo, foram verificados os dados do POC obtidos a partir da análise da ventilação e do consumo de oxigênio em cada minuto do TCPE, o VO2 máximo, e as curvas de eficiência do consumo de oxigênio (OUES) e do equivalente ventilatório de dióxido de carbono (VE/VCO2 slope), sendo a estabilidade avaliada pelos coeficientes de correlação intraclasse. A mediana do intervalo de tempo entre os dois TCPEs foi de 1,6 anos. Os valores de cada uma das variáveis obtidas nos dois TCPEs apresentaram altas e significativas associações (p <0,01), sendo: VO2max ri = 0,93 (IC95% = 0,91 a 0,94); POC ri = 0,87; (IC95% = 0,82 a 0,90); OUES ri = 0,90 (IC95% = 0,87 a 0,93) e VE/VCO2 slope ri = 0,74 (IC95% = 0,67 a 0,80). Concluímos que, em condições controladas, o POC é um índice ventilatório bastante estável em TCPEs realizadas em indivíduos adultos, com níveis de estabilidade similar ou superior de outras variáveis ou índices consagrados na literatura, corroborando, dessa forma, seu potencial de utilização em pesquisas fisiológicas e na prática clínica.

The present study aimed to assess the stability of the cardiorespiratory optimum point (COP) in two maximum cardiopulmonary exercise testing (CPET), performed in a lower limbs cycling ergometer. Therefore, we retrospectively analyzed data from 1334 subjects that were evaluated by at least twice between 1995 and 2013, and identified after rigid inclusion criteria, 222 subjects (159 men) aged 55 ± 11.6 years. COP results were obtained from the ventilation and oxygen consumption data averaged at each minute during CPET as well as maximum oxygen uptake, efficiency curves of oxygen consumption (OUES) and ventilatory equivalent for carbon dioxide (VE/VCO2 slope), and their stability assessed by intraclass correlation coefficients. The median time interval between two CPETs was 1.6 years. The values of the variables obtained in the two CPETs showed high and significant associations (p <0.01), being: VO2max ri = 0.93 (CI95% = 0.91 a 0.94); COP ri = 0.87; (CI95% = 0.82 a 0.90); OUES ri = 0.90 (CI95% = 0.87 a 0.93) and VE/VCO2 slope ri = 0.74 (CI95% = 0.67 a 0.80). We conclude that, under controlled conditions, COP is a very stable ventilatory index in CPET performed in adults, with stability levels similar or higher than other variables well-established in the literature, confirming thus its potential for use in physiological research and clinical practice.

Capnografía volumétrica: herramienta por excelencia para evaluar la ventilación alveolar en tiempo real / Volumetric capnography: an excellent tool to assess the alveolar ventilation in real time

La capnografía volumétrica es una herramienta de monitoreo que brinda información de la distribución del aire que ingresa al pulmón. Permite evaluar la relación ventilación/perfusión, siendo útil para la detección de colapso pulmonar y el establecimiento de un PEEP óptimo luego del reclutamiento pulmonar. Se presenta el caso de un paciente en shock séptico por carioamnionitis, que desarrolla síndrome de distrés respiratorio agudo en el postoperatorio inmediato de un parto por cesárea. En la unidad de cuidados intensivos, ante la no mejoría del cuadro respiratorio ni de los parámetros gasométricos, se inicia monitoreo con capnografía volumétrica, para medir el espacio muerto fisiológico y realizar un manejo óptimo de los parámetros ventilatorios. Por la inestabilidad hemodinámica y alteraciones de la coagulación, se instaura tratamiento vasopresor y se administran hemoderivados.

The volumetric capnography is a monitorina tool provides information about the distribution of air entering the lungs. Allow to assesses the ventilation/perfusion ratio, being useful for the detection of lung's collapse and establishing optimal PEEP after lung recruitment. We present a patient in septic shock by chorioamnionitis, which develops acute respiratory distresssyndrome in the immediate postoperative period of cesarean delivery. In the intensive care unit, considering that there was no respiratory symptoms improved neither the gasometric parameters, then the volumetric capnography monitoring was started, to measure the physiological dead space and making perform an optimal management of the ventilatory parameters. Due to hemodynamic instability and impaired coagulation, vasopressor therapy instituted and blood products administered.

[ effect of an eight-week aerobic exercise program on the homocysteine level and VO[2]max in young non-athlete men]

An elevated homocysteine level is a serious risk factor among the cardiovascular risk factors. The purpose of this study was to examine the effect of an eight-week aerobic exercise on the homocysteine level and VO[2]max and also to determine the correlation between the homocysteine level and VO[2]max. In this quasi-experimental study, 28 male students from Iran University of Science and Technology, who passed the primary physical training course, were randomly divided into the experimental and control groups [age= 19.14 +/- 1.24, weight= 70.13 +/- 11.76 kg, height= 175.42 +/- 5.86 cm, body fat percentage= 19.11 +/- 5.98]. Blood samples were taken from each participant in both groups and the experimental group performed the Bruce test [VO[2]max] and an eight-week aerobic exercise program three times a week with the intensity near 60-75 percent of maximum heart rate. Results of this study showed no significant difference between the experimental and control groups in the homocysteine level in posttest [P=0.75], but a significant difference was seen between the two groups in VO[2]max [P=0.0001]. However, no significant correlation was seen between the homocysteine level and VO[2]max [P=0.40, r=0.16]. Although an eight-week aerobic exercise program in young non-athlete men has no significant effect on the homocysteine level, it can increase the VO[2]max

Effect of hypercapnia on pleth variability index during stable propofol: Remifentanil anesthesia

The pleth variability index [PVI], which is calculated from respiratory variations in the perfusion index [PI], has been shown to predict fluid responsiveness in mechanically ventilated patients; however, vasomotor tone changes induced by hypercapnia can affect PI and hence may slim down the accuracy of PVI. This study was designed to find out the impact of mild hypercapnia on PVI. A total of 30 patients were randomized after induction of general anesthesia with target controlled infusion propofol and remifentanil to either hypercapnia, [etCO[2] =45 mmHg], [group 1, 15 patients] or normocapnia [etCO[2] =35 mmHg] [group 2, 15 patients]. After a stabilization period of 10 min, patients were crossed over to the other intentional level of etCO[2]. Heart rate [HR], mean arterial pressure [MAP], PI, PVI were collected at the end of each stabilization period. Patient characteristics and baseline values of HR, MAP, PI and PVI were comparable between the groups. Carryover effect was statistically excluded. Hypercapnia significantly increased PI and decreased PVI with significant negative correlation. Hypercapnia retracts back PVI values compared with normocapnia. Precise judgment of fluid responsiveness as indicated by PVI necessitates its comparison against similar etCO[2] levels

Combined radionuclide phlebography and V/Q scan in the assessment of iliac vein thrombosis and pulmonary embolism - a case report establishing a cause and effect relationship

Deep vein thrombosis [DVT] is an important life threatening condition that is difficult to diagnose, particularly in the early stages. Looking for DVT in lower limb can be considered ancillary in suspected cases of pulmonary embolism [PE] indirectly highlighting a cause and effect relationship of a single disease [i.e cause being DVT and effect is the assault on the lung vasculature]. Prompt and early identification of one or both of these pathologies calls for urgent intervention in the form of instituting anticoagulation therapy. Synthetic Tc-99m labeled peptides like apcitide, a glycoprotein [GP IIb/IIIa] receptor antagonist is increasingly used as a specific tracer in the detection of acute DVT. But due to its non availability in certain countries, one needs to resort to indirect evidence in the form of Tc-99m MAA to help in the identification of DVT. Radionuclide phlebography [RPh] combined with lung perfusion scintigraphy [LP] is a one stop shop for the rapid and noninvasive diagnostic assessment of PE due to DVT. The aim of this case report is to highlight the underutilization of nuclear techniques in the evaluation of DVT in routine clinical practice. We report a case of a young Indian male who presented with sudden onset dyspnoea. On scintigraphic evaluation by a simultaneous RPh and LP, the cause and effect of DVT could be easily established

Ponto ótimo cardiorrespiratório: uma variável submáxima do teste cardiopulmonar de exercício / Cardiorespiratory optimal point: a submaximal variable of the cardiopulmonary exercise testing

FUNDAMENTO: No Teste Cardiopulmonar de Exercício (TCPE) máximo são analisadas diversas variáveis ventilatórias, incluindo o equivalente ventilatório de oxigênio (VE/VO2). O valor mínimo do VE/VO2 reflete a melhor integração entre os sistemas respiratório e cardiovascular, podendo ser denominado Ponto Ótimo Cardiorrespiratório (POC). OBJETIVO: Determinar o comportamento do POC em função do gênero e da idade em adultos saudáveis e verificar a associação com outras variáveis do TCPE. MÉTODOS: De 2.237 indivíduos, foram selecionados 624 (62% homens e 48 ± 12 anos de idade), não atletas, saudáveis, submetidos ao TCPE máximo. O POC ou VE/VO2 mínimo foi obtido a partir da análise da ventilação e do consumo de oxigênio em cada minuto do TCPE. Foi verificada a relação entre idade e POC para os dois gêneros, assim como as associações com: VO2máx, VO2 no limiar anaeróbico (VO2LA), eficiência da inclinação de consumo de oxigênio (OUES) e com VE máxima. Comparou-se ainda a intensidade do esforço (MET) no POC, LA e VO2máx. RESULTADOS: O POC aumenta com a idade, sendo 23,2 ± 4,48 e 25,0 ± 5,14, respectivamente, em homens e mulheres (p < 0,001). Há associações moderadas e inversas com VO2máx (r = -0,47; p < 0,001), com VO2LA (r = -0,42; p < 0,001) e com o OUES (r = -0,34; p < 0,001). O POC ocorreu, em média, a (44% do VO2máx) e antes do LA (67% do VO2máx) (p < 0,001). CONCLUSÃO: POC, uma variável submáxima, aumenta com a idade e é discretamente mais alto em mulheres. Sendo modestamente associado a outras medidas ventilatórias, parece haver uma contribuição independente na interpretação da resposta cardiorrespiratória ao TCPE.

BACKGROUND: At the maximal Cardiopulmonary Exercise Testing (CPET), several ventilatory variables are analyzed, including the ventilatory equivalent for oxygen (VE/VO2). The minimum VE/VO2 value reflects the best integration between the respiratory and cardiovascular systems and may be called "Cardiorespiratory Optimal Point (COP)". OBJECTIVE: To determine the behavior of the COP according to gender and age in healthy adults and verify its association with other CPET variables. METHODS: Of 2,237 individuals, 624 were selected (62% men and 48 ± 12 years), non- athletes, healthy, who were submitted to maximal CPET. COP or minimum VE/VO2 was obtained from the analysis of ventilation and oxygen consumption in every minute of CPET. We investigated the association between age and COP for both genders, as well as associations with: VO2max, VO2 at anaerobic threshold (VO2AT), oxygen uptake efficiency slope (OUES) and with maximum VE. We also compared the intensity of exertion (MET) at the COP, AT and VO2max. RESULTS: COP increases with age, being 23.2 ± 4.48 and 25.0 ± 5.14, respectively, in men and women = (p < 0.001). There are moderate and inverse associations with VO2max (r = -0.47; p < 0.001), with VO2AT (r = -0.42; p < 0.001) and with OUES (r = -0.34; p < 0.001). COP occurred, on average, at 44% do VO2max and before AT (67% of VO2max) (p < 0.001). CONCLUSION: COP, a submaximal variable, increases with age and is slightly higher in women. Being modestly associated with other ventilation measures, there seems to be an independent contribution to the interpretation of the cardiorespiratory response to CPET.

Difference in the value of arterial and end-tidal carbon dioxide tension according to different surgical positions: Does it reliably reflect ventilation-perfusion mismatch? / 대한마취과학회지

BACKGROUND: Body posture, as a gravitational factor, has a clear impact on pulmonary ventilation and perfusion. In lung units with mismatched ventilation and perfusion, gas exchange and/or elimination of carbon dioxide can be impaired. In this situation, differences in the value of arterial and end-tidal carbon dioxide tension [Delta(PaCO2 - PETCO2)] are expected to increase. This study was conducted to observe how Delta(PaCO2 - PETCO2) changed according to the 3 different surgical positions, and to determine whether Delta(PaCO2 - PETCO2) is a reliable predictor of ventilation/perfusion mismatch when a patient is in different postural positions. METHODS: Fifty-nine patients were divided into either the chronic obstructive pulmonary disease (COPD) group (n = 29) or the non-COPD group (n = 30). PaCO2 and PETCO2 were measured during surgery in the supine, prone, and lateral decubitus positions after a 10 minute stabilization period. The Delta(PaCO2 - PETCO2) were calculated and compared among positions. RESULTS: The Delta(PaCO2 - PETCO2) decreased slightly in the prone position and increased significantly in the lateral decubitus position compared with the supine position in both groups. These patterns almost corresponded with the degree of ventilation/perfusion mismatch from the results of the radiological studies. The Delta(PaCO2 - PETCO2) in the COPD group was significantly greater than that in the non-COPD group at all surgical positions. CONCLUSIONS: Lateral decubitus position is associated with marked increase in Delta(PaCO2 - PETCO2), especially in patients with COPD. The Delta(PaCO2 - PETCO2) is a simple and reliable indicator to predict ventilation/perfusion mismatch at different surgical positions in patients with or without COPD.

Modelo experimental de perfusão pulmonar ex vivo em ratos: avaliação de desempenho de pulmões submetidos à administração de prostaciclina inalada versus parenteral / An experimental rat model of ex vivo lung perfusion for the assessment of lungs after prostacyclin administration: inhaled versus parenteral routes

OBJETIVO: Apresentar um modelo experimental de administração de prostaglandina I2 (PGI2) por via inalatória vs. parenteral e avaliar o desempenho funcional dos pulmões em um sistema de perfusão pulmonar ex vivo. MÉTODOS: Quarenta ratos Wistar foram anestesiados, ventilados, submetidos a laparotomia com ressecção do esterno e anticoagulados. O tronco da artéria pulmonar foi canulado. Todos os animais foram submetidos a ventilação mecânica. Os animais foram randomizados em quatro grupos (10 ratos/grupo): salina nebulizada (SN); salina parenteral (SP); PGI2 nebulizada (PGI2N); e PGI2 parenteral (PGI2P). A dose de PGI2 nos grupos PGI2N e PGI2P foi de 20 e 10 µg/kg, respectivamente. Os blocos cardiopulmonares foram submetidos in situ a perfusão anterógrada com solução de baixo potássio e dextrana a 4ºC via artéria pulmonar, extraídos em bloco e armazenados a 4ºC por 6 h. Os blocos foram ventilados e perfundidos em um sistema ex vivo por 50 min, sendo obtidas medidas de mecânica ventilatória, hemodinâmica e trocas gasosas. RESULTADOS: Houve redução da pressão arterial pulmonar média após a nebulização em todos os grupos (p < 0,001), sem diferença entre os grupos. Na perfusão ex vivo, a mecânica ventilatória não diferiu entre os grupos. Houve redução da capacidade relativa de oxigenação ao longo da perfusão nos grupos SN e SP (p = 0,04), e houve aumento significativo da pressão arterial pulmonar no grupo SN. CONCLUSÕES: O modelo experimental de administração de PGI2 na extração pulmonar é exequível e confiável. Na reperfusão, os resultados de hemodinâmica e de trocas gasosas demonstraram tendência a um melhor desempenho com o uso de PGI2 do que com solução salina.

OBJECTIVE:To present a model of prostaglandin I2 (PGI2) administration (inhaled vs. parenteral) and to assess the functional performance of the lungs in an ex vivo lung perfusion system. METHODS: Forty Wistar rats were anesthetized and placed on mechanical ventilation followed by median sterno-laparotomy and anticoagulation. The main pulmonary artery was cannulated. All animals were maintained on mechanical ventilation and were randomized into four groups (10 rats/group): inhaled saline (IS); parenteral saline (PS); inhaled PGI2 (IPGI2); and parenteral PGI2 (PPGI2). The dose of PGI2 used in the IPGI2 and PPGI2 groups was 20 and 10 µg/kg, respectively. The heart-lung blocks were submitted to antegrade perfusion with a low potassium and dextran solution via the pulmonary artery, followed by en bloc extraction and storage at 4ºC for 6 h. The heart-lung blocks were then ventilated and perfused in an ex vivo lung perfusion system for 50 min. Respiratory mechanics, hemodynamics, and gas exchange were assessed. RESULTS: Mean pulmonary artery pressure following nebulization decreased in all groups (p < 0.001), with no significant differences among the groups. During the ex vivo perfusion, respiratory mechanics did not differ among the groups, although relative oxygenation capacity decreased significantly in the IS and PS groups (p = 0.04), whereas mean pulmonary artery pressure increased significantly in the IS group. CONCLUSIONS: The experimental model of inhaled PGI2 administration during lung extraction is feasible and reliable. During reperfusion, hemodynamics and gas exchange trended toward better performance with the use of PGI2 than that with the use of saline.

Estudo dos efeitos da posição prona na distribuição regional da aeração e da perfusão pulmonar através da tomografia de impedância elétrica e da tomografia computadorizada multislice / Effects of prone position on regional distribution of lung aeration and perfusion. Analysis by electrical impedance tomography and computer tomography

Introdução: A utilização da posição prona melhora significativamente a oxigenação de pacientes com síndrome do desconforto respiratório agudo (SDRA). Estudos prévios sugerem que o recrutamento das regiões pulmonares colapsadas e pobremente aeradas é um dos possíveis mecanismos responsáveis pela melhora da oxigenação, no entanto, os mesmos ainda não foram comprovados. Objetivos: Quantificar a distribuição regional da aeração e da perfusão pulmonar, em ambas as posições prona e supina, através da tomografia de impedância elétrica (TIE) e da tomografia computadorizada multislice (TC), correlacionando-as com as respectivas trocas gasosas. Métodos: Foram estudados 21 suínos, da raça Ladrasse anestesiados e em ventilação mecânica controlada. Os animais foram divididos em dois grupos, de acordo com o método de imagem. 13 animais foram estudados com a TIE (grupo TIE) e 8 animais foram estudados com a TC (grupo TC). Após a indução do modelo de lesão pulmonar (infusão intermitente de solução salina e ventilação lesiva por 3 horas), os animais foram submetidos a uma manobra de recrutamento alveolar máxima (MR) seguida por uma manobra de titulação da PEEP (MTP), realizada em passos decrementais de 2 em 2 cmH2O PEEP. Onze animais (7 no grupo TIE e 4 no grupo TC) foram randomizados para iniciar o estudo na posição supina, seguida de uma segunda MR e MTP na posição prona. Dez animais (6 no grupo TIE e 4 no grupo TC) receberam as manobras na ordem inversa. Para o estudo da perfusão foram adicionados mais sete animais (2 no grupo TIE e 5 no grupo TC) que foram submetidos à injeção rápida de solução salina hipertônica e/ou de contraste iodado respectivamente. Resultados: Não foram encontradas diferenças significativas na quantidade de tecido pulmonar colapsado e hiperdistendido, entre as posições estudadas em ambos os grupos TIE e TC (p= 0.06). Entretanto, as trocas gasosas foram consistentemente melhores durante a posição prona (p<0.05), com shunt pulmonar significativamente...

Introduction: Prone position has been shown to consistently improve oxygenation in patients with acute respiratory distress syndrome (ARDS). Previous studies suggested some improvement in lung recruitment or a better ventilation of poorly aerated areas as possible mechanisms for such oxygenation benefits. Objective: To quantify the regional distribution of aeration (collapse and hyperdistend lung tissue) and lung perfusion by Computer Tomography (CT) and electrical impedance tomography in supine and prone positions and to correlate them with pulmonary gas exchange. Methods: We studied 21 anesthetized Landrace pigs under controlled mechanical ventilation. These animals were divided in two groups: Thirteen (13) animals in the EIT group and eight (8) in the CT group. After lung injury (saline lavage + VILI during 3 hours), animals were recruited and submitted to two sequential PEEP trials, both consisting of decremental PEEP steps (2 cmH2O steps). Seven (n=7) animals in the EIT group and four (4) in the CT group were allocated to a PEEP trial under supine position, followed by a second PEEP trial in prone. Six (6) animals in the EIT group and four (4) in the CT group received PEEP trials in reverse order. Seven (7) additional animals were studied for lung perfusion distribution, by analyzing the first pass kinetics of hypertonic solution (2 animals - EIT group) and iodine contrast (5 animals - CT group). Results: No differences in the amount of collapsed and hyperdistended lung tissue were found between both postures (p= 0.12 vs. p = 0.41 respectively) in both the EIT and CT groups. However, the gas exchange was consistently better (p <0.05), with much lower (55% lower) pulmonary shunt during prone position (p=0.001), at equivalent PEEP levels in both groups. The perfusion studies confirmed a higher perfusion ( 2 times increment in specific perfusion) of the atelectatic lung tissue in supine position, without majors gravitational effects between both...

Malformaciones pulmonares: enfisema lobar congénito / Lung malformations: lobar congenital emphysema

Congenital lobar emphysema (CLE) is a rare congenital lung anomaly. Clinical presentation varies from acute neonatal respiratory failure to recurrent episodes of tachypnea or infections. Chest x-ray is often enough to make the diagnosis in newborn, but a normal chest x-ray does not exclude the diagnosis and a CT scan must be done when there is a lung malformation suspect. The better antenatal ultrasound diagnosis has led to detection CLE in asymptomatic and mildly symptomatic infants, and involution of CLE has been demonstrated in some cases. Lobectomy is the treatment of choice for very symptomatic children, but could be expectant in the less symptomatic ones.

El enfisema lobar congénito (ELC), es una malformación pulmonar poco frecuente. Su presentación clínica varía desde la falla respiratoria en el recién nacido (RN) hasta episodios recurrentes de taquipnea o infecciones. La radiografía de tórax, muchas veces es suficiente para realizar el diagnóstico en el RN, pero ante una radiografía normal se debe realizar TAC de tórax si se sospecha malformación pulmonar. El aumento del diagnóstico por ecografía prenatal ha llevado a la pesquisa del ELC en lactantes asintomáticos o levemente sintomáticos, algunos de los cuales se ha demostrado involución de la malformación. El tratamiento de elección en niños francamente sintomáticos es la lobectomía, pudiendo ser conservador en el resto de los pacientes.

Análise regional da dinâmica ventilatória em transplante pulmonar com tomografia de impedância elétrica / Assessment of regional ventilatory dynamics in lung transplantation, using electrical impedance tomography

A monitorização da ventilação em transplante pulmonar depende de medidas estáticas e globais a partir de testes de função pulmonar e tomografia computadorizada, o que não é suficiente para detectar alterações regionais no parênquima pulmonar, que podem ser relevantes na avaliação de diferentes causas de comprometimento funcional. Tomografia de Impedância Elétrica (TIE) é uma técnica não-invasiva e livre de radiação com base na medição do potencial elétrico na superfície da parede torácica. O comportamento dinâmico e as informações quantitativas extraídas de imagens da TIE tornam possível avaliar as diferenças regionais na ventilação pulmonar. Objetivos: Avaliar a ventilação regional com a TIE, em pacientes submetidos a transplante pulmonar unilateral ou bilateral e avaliar as variações ventilatórias em várias posições diferentes. Métodos: A TIE foi realizada em 18 pacientes transplantados de pulmão (7 pacientes com transplante de pulmão bilateral, 6 pacientes com transplante unilateral por enfisema e 5 pacientes com transplante unilateral por fibrose), nas posições: sentada, supina, prona e decúbitos lateral direito e esquerdo. Os pacientes foram orientados a realizar 30 ciclos de ventilação espontânea e, em seguida, uma manobra de capacidade vital lenta. Resultados: A comparação entre os grupos mostrou que houve diferença entre porcentagem de ventilação referente ao melhor pulmão (nos unilaterais o melhor pulmão era o transplantado e nos bilaterais o pulmão com maior ventilação na posição sentada). Na ventilação espontânea os transplantes unilaterais por enfisema e fibrose tinham 79% e 83% da ventilação gerada pelo pulmão transplantado, enquanto para os bilaterais o melhor pulmão contribuía com 57% da ventilação. Houve redução significativa na desproporção da ventilação quando comparada a ventilação espontânea com a capacidade vital (p = 0,001). Na ventilação espontânea houve variação da ventilação...

Ventilation monitoring in lung transplantation is still depending on static and global measurements from lung function testing and computed tomography, what is not enough to detect regional changes in lung parenchyma, which may be relevant in evaluating different causes of functional impairment. Electrical Impedance Tomography (EIT) is a noninvasive and radiation-free technique based on the measurement of electric potentials at the chest wall surface. The dynamic behavior and the quantitative information extracted from EIT images make it possible to assess regional differences in lung ventilation. Objectives: To assess regional ventilation with EIT, in patients who underwent single or bilateral lung transplantation and to evaluate ventilatory variations in several different body positions. Methods: We performed the EIT in 18 lung transplanted patients (7 bilateral lung transplantation patients, 6 single lung transplantation patients with emphysema and 5 single lung transplantation patients with fibrosis), in seated, supine, right, left and ventral positions. Patients were asked to perform 30 cycles of spontaneous ventilation and then a slow vital capacity maneuver. Results: The comparison between groups showed that there was difference between the percentage of ventilation related to the best lung (the best lung in single lung patients was the transplanted lung and in the bilateral patients was the lung with best ventilation in the sitting position). The ventilation generated by the transplanted lung on spontaneous ventilation in single lung patients for emphysema and fibrosis were 79% and 83% respectively, whereas for the bilateral group better lung contributed with 57% of ventilation. Significant reduction in the disparity of ventilation occurred comparing the spontaneous ventilation and the vital capacity maneuver (p = 0.001). Ventilation changed in accordance...

Pulmonary embolism in soldiers serving at high altitude

To determine the frequency of different risk factors for pulmonary embolism with particular reference to high altitude as one of the factors. Cross sectional, analytical study. Department of Pulmonology, Military Hospital Rawalpindi, from December 2006 to December 2007. A total of 50 serving soldiers suspected of pulmonary embolism were enrolled. A detailed history and physical examination was carried out to ascertain the risk factors of the disease. Screening profile was performed for connective tissue and infectious diseases, thrombophilic disorders and plasma homocystein levels. If soldiers were evacuated from high altitude, their approximate height from sea level was noted. Pulmonary embolism was confirmed on spiral CT scan of chest and/or ventilation-perfusion lung scan. Results were analyzed by SPSS version 11. About 86% of patients were between 20-40 years of age. Dyspnea was the commonest symptom [40%] while tachypnea was the commonest clinical finding in these soldiers. D-dimer value was<250 in only 10% of patients. Pleural effusion was the commonest radiological abnormality[40%] while non-specific T-wave inversions were noted as the most frequent ECG change[44%]. Ventilation-perfusion [V/Q] scan was confirmatory in 80% of patients and spiral CT chest in 56%. When the frequency of risk factors of pulmonary embolism were analyzed, 50% of patients had high altitude as the only risk factor. Hereditary thrombophilic disorder was found in 14%, connective tissue disorder/infections in 20% and miscellaneous others in 16%. Pulmonary embolism occurs at an increased frequency in soldiers working at high altitude, without any other co-existent risk factor

Generación de imágenes planares a partir del estudio de SPECT pulmonar de ventilación y perfusión / Generation of planar images from a Lung ventilation/perfusion SPECT study

Dado que los estudios de pulmón utilizando la técnica de tomografía computada de emisión de fotón único (SPECT) han demostrado tener un mejor desempeño diagnóstico frente a la técnica planar para el diagnóstico de tromboembolismo pulmonar (TEP), existe un aumento de interés en la utilización de la primera metodología. Sin embargo, a menudo se requiere de cierto grado de entrenamiento por parte del médico nuclear para sentirse seguro al interpretar las imágenes tomográficas. El propósito de este trabajo fue aplicar un método para obtener imágenes planares a partir de los datos reconstruidos de SPECT, con el propósito de evitar la realización de ambos estudios lo que llevaría a tiempos de adquisición demasiados largos. Adicionalmente, se estaría contribuyendo con el período de entrenamiento necesario para el pasaje de una técnica a la otra. Fueron estudiados 50 pacientes referidos para diagnóstico de TEP a los cuales se les realizaron estudios de ventilación y de perfusión planares y SPECT. Las imágenes reconstruidas de SPECT fueron reproyectadas para obtener imágenes planares. La calidad de las imágenes así como el potencial diagnóstico de las mismas fue comparada con el protocolo planar convencional concluyéndose que las imágenes generadas brindan información clínica comparable a las verdaderas planares, teniendo además mejor relación señal:ruido.

Since lung studies using SPECT technique have shown better diagnostic performance compared to the planar technique for the evaluation of pulmonary embolism, there is an increasing interest in the use of this technology. However, there is more clinical experience in reporting planar images; hence some training is usually required in order to get confident in the interpretation of SPECT data. The aim of this study was to apply a method to obtain planar-like images from SPECT reconstructed data avoiding the extra time required for separate planar acquisition, which would drive to longer scan time. We studied 50 pts referred for the diagnosis of PE. Ventilation and perfusion scans were performed in planar and SPECT modalities. The reconstructed SPECT data was reprojected in order to obtain planar-like images. The image quality as well as the diagnostic potential was compared with the conventional planar protocol. It was concluded that the generated ‘planar-like’ images give clinical information equivalent to the true planar showing also better signal:noise properties. The method can facilitate with the necessary training needed to move from planar to SPECT techniques.

Value of radionuclide lung scintigraphy in the diagnosis and quantitative analysis of chronic thromboembolic pulmonary hypertension / 中华心血管病杂志

<p><b>OBJECTIVE</b>This study was to assess the reliability of perfusion/ventilation (Q/V) lung scintigraphy in the diagnosis and quantitative analysis of chronic thromboembolic pulmonary hypertension (CTEPH).</p><p><b>METHODS</b>A total of 78 in-patients with pulmonary hypertension who had no history of congenital heart disease, valvular disease and acute pulmonary embolism were included in this study. All patients underwent Q/V scintigraphy for detecting CTEPH. The sensitivity, specificity and accuracy of Q/V scintigraphy were defined by comparing with the results of pulmonary angiography. Percentage of Perfusion Defect score (PPDs%) was calculated in patients with CTEPH confirmed by pulmonary angiography. The correlations between PPDs% and mPAP, PPDs% and SPAP were analyzed.</p><p><b>RESULTS</b>The sensitivity, specificity and accuracy of a high-probability Q/V scintigraphy interpretation were 96.0%, 81.1% and 86.9%, respectively, compared with 100%, 69.8% and 79.5% for the combination of high- and intermediate- probability Q/V scintigraphy interpretation. PPDs% was significantly correlated with mPAP and SPAP (r = 0.538 for mPAP, P < 0.01 and r = 0.456 for SPAP, P < 0.05).</p><p><b>CONCLUSION</b>Perfusion/ventilation lung scintigraphy is a valuable technique for diagnosis and quantitative analysis of CTEPH.</p>

Estudio de las oscilaciones cardiogénicas en pacientes ventilados artificialmente / Study of cardiogenic oscillations in artificially ventilated patients

Antecedentes: Las oscilaciones cardiogénicas (OC) son perturbaciones en las señales de presión (OCpresión), flujo (OCflujo) y CO2(OCco2) de la vía aérea producidas por el latido cardíaco. Su análisis brinda información sobre la distribución de la ventilación y/o perfusión pulmonar de manera no invasiva. El estudio de las OC se limita a voluntarios y pacientes ventilando espontáneamente, mientras que en pacientes sometidos a ventilación mecánica el rol de las OC está subvalorado. Objetivos: Este trabajo analiza tres maniobras ventilatorias que tienen como objetivo resaltar las OCpresión, OCflujo y OCco2 para facilitar su estudio. Lugar de aplicación: Hospital de comunidad. Diseño: Estudio prospectivo observacional. Población: Se estudiaron 20 pacientes adultos sometidos a anestesia general con ventilación mecánica. Métodos: En cada paciente se realizaron tres maniobras ventilatorias: 1) test de respiración única (inspiración profunda + pausa inspiratoria + espiración lenta); 2) pausa inspiratoria (15 segundos) y espiratoria (15 segundos) y 3) desconexión entre tubo endotraqueal y el circular de anestesia (15 segundos). Resultados: Las tres maniobras propuestas mostraron las OC en la vía aérea. El test de respiración única presentó OCpresión de mayor amplitud (0.94 ± 0.08 cmH2O) comparada con las otras maniobras (vs pausas 0.78 ± 0.10 cmH2O y vs desconexión 0.21 ± 0.09 cmH2O; p < 0.05). Las OCflujo fueron más marcadas en la desconexión (5.09 ± 0.4 I/min) que en las pausas (2.18 ± 0.4 I/min; p < 0.05) y en el test de respiración única (1.75 ± 0.3 I/min; p < 0.05). No hubo diferencias significativas en la amplitud de las OCco2 entre las maniobras estudiadas. Conclusiones: Las tres maniobras estudiadas lograron resaltar las OC en las señales de presión, flujo y CO2 en pacientes ventilados artificialmente. La amplitud de las OC depende, en parte, del tipo de maniobra aplicada, por lo cual es necesario definir en los protocolos cuál maniobra será usada para posterio...