Peak expiratory flow values are higher in older and taller healthy male children: An observational study

Purpose: Peak expiratory flow (PEF) was measured in healthy children aged five to ten years in order to provide baseline values and to determine correlations between PEF and factors such as gender, age and type of school. Methods: After the Ethical Committee of Research in Human of the School of Medicine of ABC - FMABC approval, PEF and height were measured in 1942 children between five and ten years old from nine public schools and nine private schools throughout Sao Bernardo do Campo City. PEF was measured using the Mini-Wright Peak Flow Meter (Clement Clarke International Ltd.) and. height was measured using a Sanny professional stadiometer. Results: Significant differences were found in values for PEF: higher values were seen in older students in comparison with younger students, in males in comparison with females and in students from private schools in comparison with public schools, with average values ranging from 206 L/min to 248 L/min,. Linear correlations were seen for PEF values with both height and age (Spearman Coefficient). Conclusions: Differences were seen for PEF between genders and between types of school, and a linear correlation was seen for PEF with both age and height in healthy children from five to ten years old.

Changes in peak expiratory flow and respiratory strength during the menstrual cycle

This study evaluated the spirometry and respiratory static pressures in 17 young women, twice a week for three successive ovulatory menstrual cycles to determine if such variables changed across the menstrual, follicular, periovulatory, early-tomid luteal and late luteal phases. The factors phases of menstrual cycle and individual cycles had no significant effect on the spirometry variables except for peak expiratory flow (PEF) and respiratory static pressures. Significant weak positive correlations were found between the progesterone:estradiol ratio and PEF and between estrogen and tidal volume (r = 0.37), inspiratory time (r = 0.22), expiratory time (r = 0.19), maximal inspiratory pressure (r = 0.25) and maximal expiratory pressure (r = 0.20) and for progesterone and maximal inspiratory pressure (r = 0.32) during the early-to-mid luteal phase. Although most parameters of the spirometry results did not change during the menstrual cycle, the correlations observed between sexual hormones and respiratory control variables suggest a positive influence of sexual female hormones controlling the thoracic pump muscles in the luteal phase

Observational study on efficacy of negative expiratory pressure test proposed as screening for obstructive sleep apnea syndrome among commercial interstate bus drivers - protocol study

Background: Obstructive sleep apnea (OSA) is a respiratory disease characterized by the collapse of the extrathoracic airway and has important social implications related to accidents and cardiovascular risk. The main objective of the present study was to investigate whether the drop in expiratory flow and the volume expired in 0.2 s during the application of negative expiratory pressure (NEP) are associated with the presence and severity of OSA in a population of professional interstate bus drivers who travel medium and long distances.Methods/Design: An observational, analytic study will be carried out involving adult male subjects of an interstate bus company. Those who agree to participate will undergo a detailed patient history, physical examination involving determination of blood pressure, anthropometric data, circumference measurements (hips, waist and neck), tonsils and Mallampati index. Moreover, specific questionnaires addressing sleep apnea and excessive daytime sleepiness will be administered. Data acquisition will be completely anonymous. Following the medical examination, the participants will perform a spirometry, NEP test and standard overnight polysomnography. The NEP test is performed through the administration of negative pressure at the mouth during expiration. This is a practical test performed while awake and requires little cooperation from the subject. In the absence of expiratory flow limitation, the increase in the pressure gradient between the alveoli and open upper airway caused by NEP results in an increase in expiratory flow.Discussion: Despite the abundance of scientific evidence, OSA is still underdiagnosed in the general population. In addition, diagnostic procedures are expensive, and predictive criteria are still unsatisfactory. Because increased upper airway collapsibility is one of the main determinants of OSA, the response to the application of NEP could be a predictor of this disorder. With the enrollment of this study protocol, the expectation is to encounter predictive NEP values for different degrees of OSA in order to contribute toward an early diagnosis of this condition and reduce its impact and complications among commercial interstate bus drivers.

Variations in peak expiratory flow measurements associated to air pollution and allergic sensitization in children in Sao Paulo, Brazil

Background In the last 20 years, there has been an increase in the incidence of allergic respiratory diseases worldwide and exposure to air pollution has been discussed as one of the factors associated with this increase. The objective of this study was to investigate the effects of air pollution on peak expiratory flow (PEF) and FEV1 in children with and without allergic sensitization. Methods Ninety-six children were followed from April to July, 2004 with spirometry measurements. They were tested for allergic sensitization (IgE, skin prick test, eosinophilia) and asked about allergic symptoms. Air pollution, temperature, and relative humidity data were available. Results Decrements in PEF were observed with previous 24-hr average exposure to air pollution, as well as with 310-day average exposure and were associated mainly with PM10, NO2, and O3 in all three categories of allergic sensitization. Even though allergic sensitized children tended to present larger decrements in the PEF measurements they were not statistically different from the non-allergic sensitized. Decrements in FEV1 were observed mainly with previous 24-hr average exposure and 3-day moving average. Conclusions Decrements in PEF associated with air pollution were observed in children independent from their allergic sensitization status. Their daily exposure to air pollution can be responsible for a chronic inflammatory process that might impair their lung growth and later their lung function in adulthood. Am. J. Ind. Med. 55:10871098, 2012. (c) 2012 Wiley Periodicals, Inc.

Observational study on efficacy of negative expiratory pressure test proposed as screening for obstructive sleep apnea syndrome among commercial interstate bus drivers - protocol study

Abstract Background Obstructive sleep apnea (OSA) is a respiratory disease characterized by the collapse of the extrathoracic airway and has important social implications related to accidents and cardiovascular risk. The main objective of the present study was to investigate whether the drop in expiratory flow and the volume expired in 0.2 s during the application of negative expiratory pressure (NEP) are associated with the presence and severity of OSA in a population of professional interstate bus drivers who travel medium and long distances. Methods/Design An observational, analytic study will be carried out involving adult male subjects of an interstate bus company. Those who agree to participate will undergo a detailed patient history, physical examination involving determination of blood pressure, anthropometric data, circumference measurements (hips, waist and neck), tonsils and Mallampati index. Moreover, specific questionnaires addressing sleep apnea and excessive daytime sleepiness will be administered. Data acquisition will be completely anonymous. Following the medical examination, the participants will perform a spirometry, NEP test and standard overnight polysomnography. The NEP test is performed through the administration of negative pressure at the mouth during expiration. This is a practical test performed while awake and requires little cooperation from the subject. In the absence of expiratory flow limitation, the increase in the pressure gradient between the alveoli and open upper airway caused by NEP results in an increase in expiratory flow. Discussion Despite the abundance of scientific evidence, OSA is still underdiagnosed in the general population. In addition, diagnostic procedures are expensive, and predictive criteria are still unsatisfactory. Because increased upper airway collapsibility is one of the main determinants of OSA, the response to the application of NEP could be a predictor of this disorder. With the enrollment of this study protocol, the expectation is to encounter predictive NEP values for different degrees of OSA in order to contribute toward an early diagnosis of this condition and reduce its impact and complications among commercial interstate bus drivers.

(Table 1) Characteristics of South Pole personnel according to forced expiratory flow (FEF25-75) response to altitude

The impact of acute altitude exposure on pulmonary function is variable. A large inter-individual variability in the changes in forced expiratory flows (FEFs) is reported with acute exposure to altitude, which is suggested to represent an interaction between several factors influencing bronchial tone such as changes in gas density, catecholamine stimulation, and mild interstitial edema. This study examined the association between FEF variability, acute mountain sickness (AMS) and various blood markers affecting bronchial tone (endothelin-1, vascular endothelial growth factor (VEGF), catecholamines, angiotensin II) in 102 individuals rapidly transported to the South Pole (2835 m). The mean FEF between 25 and 75% (FEF25-75) and blood markers were recorded at sea level and after the second night at altitude. AMS was assessed using Lake Louise questionnaires. FEF25-75 increased by an average of 12% with changes ranging from -26 to +59% from sea level to altitude. On the second day, AMS incidence was 36% and was higher in individuals with increases in FEF25-75 (41 vs. 22%, P = 0.05). Ascent to altitude induced an increase in endothelin-1 levels, with greater levels observed in individuals with decreased FEF25-75. Epinephrine levels increased with ascent to altitude and the response was six times larger in individuals with decreased FEF25-75. Greater levels of endothelin-1 in individuals with decreased FEF25-75 suggest a response consistent with pulmonary hypertension and/or mild interstitial edema, while epinephrine may be upregulated in these individuals to clear lung fluid through stimulation of beta2-adrenergic receptors.

The effect of positive end-expiratory pressure level on peak expiratory flow during manual hyperinflation

Including positive end-expiratory pressure (PEEP) in the manual resuscitation bag (MRB) may render manual hyperinflation (MHI) ineffective as a secretion maneuver technique in mechanically ventilated patients. In this study we aimed to determine the effect of increased PEEP or decreased compliance on peak expiratory flow rate (PEF) during MHI. A blinded, randomized study was performed on a lung simulator by 10 physiotherapists experienced in MHI and intensive care practice. PEEP levels of 0-15 cm H2O, compliance levels of 0.05 and 0.02 L/cm H2O, and MRB type were randomized. The Mapleson-C MRB generated significantly higher PEF (P < 0.01, d = 2.72) when compared with the Laerdal MRB for all levels of PEEP. In normal compliance (0.05 L/cm H2O) there was a significant decrease in PEF (P < 0.01, d = 1.45) for a PEEP more than 10 cm H2O in the Mapleson-C circuit. The Laerdal MRB at PEEP levels of more than 10 cm H2O did not generate a PEF that is theoretically capable of producing two-phase gas-liquid flow and, consequently, mobilizing pulmonary secretions. If MHI is indicated as a result of mucous plugging, the Mapleson-C MRB may be the most effective method of secretion mobilization.

Changes in peak expiratory flow and respiratory strength during the menstrual cycle

This study evaluated the spirometry and respiratory static pressures in 17 young women, twice a week for three successive ovulatory menstrual cycles to determine if such variables changed across the menstrual, follicular, periovulatory, early-tomid luteal and late luteal phases. The factors phases of menstrual cycle and individual cycles had no significant effect on the spirometry variables except for peak expiratory flow (PEF) and respiratory static pressures. Significant weak positive correlations were found between the progesterone:estradiol ratio and PEF and between estrogen and tidal volume (r = 0.37), inspiratory time (r = 0.22), expiratory time (r = 0.19), maximal inspiratory pressure (r = 0.25) and maximal expiratory pressure (r = 0.20) and for progesterone and maximal inspiratory pressure (r = 0.32) during the early-to-mid luteal phase. Although most parameters of the spirometry results did not change during the menstrual cycle, the correlations observed between sexual hormones and respiratory control variables suggest a positive influence of sexual female hormones controlling the thoracic pump muscles in the luteal phase

Changes in peak expiratory flow and respiratory strength during the menstrual cycle

This study evaluated the spirometry and respiratory static pressures in 17 young women, twice a week for three successive ovulatory menstrual cycles to determine if such variables changed across the menstrual, follicular, periovulatory, early-tomid luteal and late luteal phases. The factors phases of menstrual cycle and individual cycles had no significant effect on the spirometry variables except for peak expiratory flow (PEF) and respiratory static pressures. Significant weak positive correlations were found between the progesterone:estradiol ratio and PEF and between estrogen and tidal volume (r = 0.37), inspiratory time (r = 0.22), expiratory time (r = 0.19), maximal inspiratory pressure (r = 0.25) and maximal expiratory pressure (r = 0.20) and for progesterone and maximal inspiratory pressure (r = 0.32) during the early-to-mid luteal phase. Although most parameters of the spirometry results did not change during the menstrual cycle, the correlations observed between sexual hormones and respiratory control variables suggest a positive influence of sexual female hormones controlling the thoracic pump muscles in the luteal phase

Análise do efeito do envelhecimento e da doença pulmonar obstrutiva crônica sobre a limitação ao fluxo expiratório por meio da técnica de pressão expiratória negativa

O termo limitação ao fluxo expiratório (LFE) refere-se a uma condição na qual o fluxo expiratório máximo obtido durante um ciclo da respiração espontânea é menor que o previsto e permanece constante apesar do aumento do gradiente pressórico. A LFE pode estar presente durante o envelhecimento pulmonar fisiológico, e em afecções pulmonares obstrutivas, como na doença pulmonar obstrutiva crônica (DPOC). A aferição direta para determinar a LFE requer a mensuração do volume pela relação entre o fluxo e a pressão transpulmonar, porém é um método invasivo. Os testes usualmente empregados estão baseados na comparação da curva fluxo-volume expiratório máximo e corrente, porém estas técnicas requerem alto grau de colaboração do indivíduo e podem gerar alteração do tônus muscular brônquico. Estudos sugerem que a Técnica de Pressão Expiratória Negativa (NEP) pode ser aplicada para detecção da LFE, sendo um método simples, não invasivo e que não requer esforço dos voluntários. Contudo, índices quantitativos para a avaliação deste fenômeno ainda não foram definidos, assim como também não foram estudadas a LFE no processo de envelhecimento e nos diversos estágios de obstrução das vias aéreas na DPOC. Neste contexto, os objetivos deste estudo foram: (1) avaliar o comportamento da LFE durante o processo de envelhecimento e (2) estudar a LFE presente nos portadores de DPOC. Trata-se de um estudo transversal controlado com avaliação de casos prevalentes, tendo como unidade de avaliação o indivíduo. Os exames realizados incluíram medidas de espirometria e NEP. Foram selecionados indivíduos saudáveis para o grupo envelhecimento separados em três grupos: grupo jovem (GJ), n=17; grupo meia idade (GMI), n=17 e grupo idoso (GI), n=17. No grupo DPOC foram selecionados indivíduos tabagistas e com doença obstrutiva, sendo classificados de acordo com o nível de obstrução sugerido pela espirometria. Essa classificação resultou em cinco categorias: indivíduos normais ao exame espirométrico (NE, n= 18); com distúrbio ventilatório obstrutivo leve (DVOL, n=15); distúrbio ventilatório obstrutivo moderado (DVOM, n= 18); distúrbio ventilatório obstrutivo acentuado (DVOA, n= 18) e distúrbio ventilatório obstrutivo muito acentuado (DVOMA, n= 18). Todos os indivíduos realizaram os exames de NEP e posteriormente foram submetidos à espirometria. No estudo sobre envelhecimento o parâmetro LFE% foi o que melhor caracterizou a LFE, apresentando uma correlação moderada com a idade. Os parâmetros ∆EF0-50% e ∆EF25-75% apresentaram uma correlação razoável com o progredir da idade, possivelmente devido a LFE no idoso apresentar componentes relacionadas às vias aéreas superiores. No grupo DPOC a NEP caracterizou adequadamente a LFE, sendo o melhor parâmetro a LFE%. Alterações significativas também foram encontradas com os parâmetros ∆EF0-50% e ∆EF25-75%. Avaliando-se a influência da idade neste grupo, pode-se observar que a idade é um fator de contribui para a LFE, no entanto, o efeito preponderante foi a gravidade da doença. Pode-se concluir que: (1) a NEP é útil no estudo da LFE em idosos saudáveis; (2) nestes indivíduos a LFE ocorre principalmente nas vias aéreas extratorácicas; (3) que a NEP é útil na avaliação de pacientes com DPOC, e: (4) que os efeitos da DPOC se sobrepõe ao efeito do envelhecimento.

Pulmonary function in obese vs non-obese cats

Obesity is a risk factor in the development of several respiratory diseases. Lung volumes tend to be decreased, especially expiratory reserve volume, increasing expiratory flow limitation during tidal breathing. Barometric whole-body plethysmography is a non-invasive pulmonary function test that allows a dynamic study of breathing patterns. The objective of this study was to compare pulmonary function variables between obese and non-obese cats through the use of barometric whole-body plethysmography. Nine normal-weight and six obese cats were placed in the plethysmograph chamber, and different respiratory variables were measured. There was a significant decrease in tidal volume per kilogram (P=0.003), minute volume per kilogram (P=0.001) and peak inspiratory and expiratory flows per kilogram (P=0.001) in obese cats compared with non-obese cats. Obesity failed to demonstrate a significant increase in bronchoconstriction index variable enhanced pause (Penh), as previously reported in humans and dogs. The results show that feline obesity impairs pulmonary function in cats, although a significant increase in bronchoconstriction indexes was not observed. Non-invasive barometric whole-body plethysmography can help characterise mechanical dysfunction of the airways in obese cats.

Simulation using novel equipment designed to explain spirometric abnormalities in respiratory disease enhances learning in higher cognitive domains

Simulation of disorders of respiratory mechanics shown by spirometry provides insight into the pathophysiology of disease but some clinically important disorders have not been simulated and none have been formally evaluated for education. We have designed simple mechanical devices which, along with existing simulators, enable all the main dysfunctions which have diagnostic value in spirometry to be simulated and clearly explained with visual and haptic feedback. We modelled the airways as Starling resistors by a clearly visible mechanical action to simulate intra- and extra-thoracic obstruction. A narrow tube was used to simulate fixed large airway obstruction and inelastic bands to simulate restriction. We hypothesized that using simulators whose action explains disease promotes learning especially in higher domain educational objectives. The main features of obstruction and restriction were correctly simulated. Simulation of variable extra-thoracic obstruction caused blunting and plateauing of inspiratory flow, and simulation of intra-thoracic obstruction caused limitation of expiratory flow with marked dynamic compression. Multiple choice tests were created with questions allocated to lower (remember and understand) or higher cognitive domains (apply, analyse and evaluate). In a cross-over design, overall mean scores increased after 1½ h simulation spirometry (43-68 %, effect size 1.06, P < 0.0001). In higher cognitive domains the mean score was lower before and increased further than lower domains (Δ 30 vs 20 %, higher vs lower effect size 0.22, P < 0.05). In conclusion, the devices successfully simulate various patterns of obstruction and restriction. Using these devices medical students achieved marked enhancement of learning especially in higher cognitive domains.

Avaliação do débito máximo da tosse (peak cough flow) na doença pulmonar obstrutiva crónica

Resumo Objectivos: Avaliação da Tosse em doentes com Doença Pulmonar Obstrutiva Crónica (DPOC). Identificar e determinar a relação dos factores preditivos que contribuem para a deterioração da capacidade de tosse nestes indivíduos. Tipo de estudo: Estudo observacional descritivo de natureza transversal. Definição dos casos: Os critérios de diagnóstico da DPOC são o quadro clínico e o Gold standard para diagnóstico da DPOC – a espirometria. População-alvo: Todos os utentes com patologia primária de DPOC diagnosticada que se desloquem ao serviço de função respiratória do Hospital de Viseu, para realizar provas. Método de Amostragem: Foi utilizada uma amostra aleatória constituída por todos os indivíduos, que cumpriram os critérios de inclusão, conscientes e colaborantes, que aceitaram participar neste estudo. Dimensão da amostra: Uma amostra de 55 indivíduos que se deslocaram ao serviço de função respiratória, entre Janeiro e Junho de 2009, para realizar provas de função respiratória. Condução do estudo: Os utentes que aceitaram participar neste estudo foram sujeitos a um questionário de dados clínicos e realizaram 5 testes: índice de massa corporal (IMC), estudo funcional respiratório e gasometria arterial, avaliação da força dos músculos respiratórios (PImax e PEmax) e avaliação do débito máximo da tosse (Peak Cough Flow). Análise estatística: Foram obtidos dados caracterizadores da amostra em estudo, sendo posteriormente correlacionado o valor de débito máximo da tosse (Peak Cough Flow) com os resultados obtidos para as avaliações do IMC, estudo funcional respiratório, PImax e PEmax, gasometria, avaliação da capacidade de Tosse e número de internamentos no último ano por agudização da DPOC. Tendo sido encontrados os valores de correlação entre o Peak Cough Flow e os restantes parâmetros. Resultados: Após análise dos resultados, foram obtidos os valores de Peak Cough Flow para a população com DPOC e verificou-se valores diminuídos em comparação com os valores normais da população, tendo-se verificado maiores valores de PCF em indivíduos do sexo masculino, em comparação aos valores do sexo feminino. Foi analisada a relação entre o PCF e a idade, peso, altura e IMC, não tendo sido encontrada relação, dado que a tosse não apresenta uma variação segundo os valores antropométricos, tal como a relação com os valores espirométricos. Quanto aos parâmetros funcionais respiratórios foram analisadas as relações com o PCF. Verificou-se relações significativas entre o PCF e o FEV1, a FVC, o PEF, apresentando uma relação positiva, onde maiores valores destes parâmetros estão correlacionados com maiores picos de tosse. Quanto a RAW e RV, o PCF apresenta uma relação negativa, onde uma maior resistência da via aérea ou doentes mais hiperinsuflados leva a menores valores de PCF. Por outro lado não foi encontrada relação entre o PCF e a FRC e o TLC. Quanto à força dos músculos respiratórios, verificou-se relação significativa com o PImax e a PEmax em que a fraqueza ao nível dos músculos respiratórios contribuem para um menor valor de PCF. Relativamente aos valores da gasometria arterial, verificou-se relação entre o PCF e a PaO2 de forma positiva, em que doentes hipoxémicos apresentam menores valores de tosse, e a PaCO2, de forma negativa, em que os doentes hipercápnicos apresentam menores valores de PCF tendo sido verificada relação entre o PCF e o pH e sO2. Quanto à relação entre o número de internamentos por agudização da DPOC no último ano e o PCF verificou-se uma relação significativa, onde um menor valor de PCF contribui para uma maior taxa de internamento por agudização da DPOC. Conclusão: Este conjunto de conclusões corrobora a hipótese inicialmente formulada, de que o Peak Cough Flow se encontra diminuído nos indivíduos com Doença Pulmonar Obstrutiva Crónica onde a variação do PCF se encontra directamente relacionada com os parâmetros funcionais respiratórios, com a força dos músculos respiratórios e com os valores de gasometria arterial. ABSTRACT: Aims: Cough evaluation in Chronic Obstructive Pulmonary Disease (COPD) patients. Identify and determine the relation of the predictive factors that contribute to the cough capacity degradation in this type of patients. Type of study: Descriptive observational study of transversal nature. Case definition: The COPD diagnosis criteria are the clinical presentation and the gold standard to the COPD diagnosis- the Spirometry. Target Population: Every patients, with primary pathology of COPD diagnosed, who went to the respiratory function service of Viseu hospital to perform tests. Sampling Method: It was used a random sample constituted by all the, conscious and cooperating individuals, who complied with the inclusion criteria and who accepted to make part of this study. Sample size: A sample of 55 individuals that went to the respiratory function service between January and June 2009 to perform respiratory function tests. Study: The patients who accepted to make part of this study were submitted to a clinical data questionary and performed 5 tests: body mass index (BMI), respiratory functional study, arterial blood gas level, evaluation of respiratory muscles strength (maximal inspiratory pressure (MIP) and maximum expiratory pressure (MEP)), and Peak Cough Flow evaluation. Statistic Analysis: Were obtained characterizing data of the sample in study, and later correlated the value of the Peak Cough Flow with the results from the evaluation of the body mass index (BMI), the respiratory functional study the MIP and MEP, the arterial blood gas level and also with the ability to cough evaluation and the number of hospitalizations in the last year for COPD exacerbations. The values of correlation between the Peak Cough Flow and the other parameters were found. Results: After analyzing the results, were obtained the values of Peak Cough Flow for the population with COPD. There were decreased values compared with the population normal values, having been found higher values of PCF in males compared to female values. It was analyzed the relation between the PCF and the age, weight, height and BMI but no relation was found on account of the fact that the cough does not show a variation according to anthropometric parameters, such as the relation with spirometric values. As for the respiratory functional parameters were analyzed relations with the PCF. There were significant relations between the PCF and FEV1, the FVC, the PEF, presenting a positive relation, where higher values of these parameters are correlated with higher incidence of cough. Concerning the RAW and RV, the PCF has a negative relation, in which a higher airway resistance or in more hyperinflated patients, leads to lower values of PCF. On the other hand no correlation was found between the PCF and the FRC and TLC. Regarding the respiratory muscle strength, there was a significant relation with the MIP and MEP, in which the weakness at the level of respiratory muscles contribute to a lower value of PCF. For values of arterial blood gas level, there was no relation between the PCF and PaO2, in a positive way, in which patients with hypoxemia present lower values of cough, and PaCO2, in a negative way in which hypercapnic patients had lower values of PCF, having being founded a relation between the PCF and the pH and sO2. As for the relation between the number of hospitalizations for COPD exacerbation in the last year and the PCF was found a significant relation, in which a smaller value of PCF contributes to a higher rate of hospitalization for COPD exacerbation. Conclusion: This set of findings supports the hypothesis first formulated that Peak Cough Flow is decreased in individuals with Chronic Obstructive Pulmonary Disease, in which the variation of the PCF is directly related to the respiratory function parameters, the strength of respiratory muscles and the values of arterial blood gases.

A lung computed tomographic assessment of positive end-expiratory pressure-induced lung overdistension

The aim of this study was to assess positive end-expiratory pressure (PEEP)-induced lung overdistension and alveolar recruitment in six patients with acute lung injury (ALI) using a computed tomographic (CT) scan method. Lung overdistension was first determined in six healthy volunteers in whom CT sections were obtained at FRC and at TLC with a positive airway pressure of 30 cm H2O. In patients, lung volumes were quantified by the analysis of the frequency distribution of CT numbers on the entire lung at zero end-expiratory pressure (ZEEP) and PEEP. In healthy volunteers at FRC, the distribution of the density histograms was monophasic with a peak at -791 ± 12 Hounsfield units (HU). The lowest CT number observed was -912 HU. At TLC, lung volume increased by 79 ± 35% and the peak CT number decreased to -886 ± 26 HU. More than 70% of the increase in lung volume was located below -900 HU, suggesting that this value can be considered as the threshold separating normal aeration from overdistension. In patients with ALI, at ZEEP the distribution of density histograms was either monophasic (n = 3) or biphasic (n = 3). The mean CT number was -319 ± 34 HU. At PEEP 13 ± 3 cm H2O, lung volume increased by 47 ± 19% whereas mean CT number decreased to -538 ± 171 HU. PEEP induced a mean alveolar recruitment of 320 ± 160 ml and a mean lung overdistension of 238 ± 320 ml. In conclusion, overdistended lung parenchyma of healthy volunteers is characterized by a CT number below -900 HU. This threshold can be used in patients with ALI for differentiating PEEP-induced alveolar recruitment from lung overdistension.