avaliar os efeitos da presso expiratria positiva ( pep ) na permeabilidade da membrana epitelial pulmonar em indivduos saudveis . foi avaliada uma coorte de 30 indivduos saudveis ( 15 homens e 15 mulheres ) , com mdia de idade de 28,3  5,4 anos , mdia da relao vef1/cvf de 0,89  0,14 e mdia os indivduos foram submetidos a cintilografia pulmonar por inalao de radioaerossol de cido dietilenotriaminopentactico marcado com tecncio-99 m tc - dtpa em ingls ) em dois estgios : durante respirao espontnea e durante respirao com uma mscara de pep de 10 cmh2o ( n = 10 ) , 15 cmh2o ( n = 10 ) ou 20 cmh2o ( n = 10 ) . o tc - dtpa foi nebulizado por 3 min , e sua depurao foi registrada por cintilografia por um perodo de 30 min durante respirao espontnea e por um perodo de 30 min durante a respirao com uma mscara de pep . a depurao pulmonar do tc - dtpa foi significativamente menor quando pep foi aplicada a 10 cmh2o ( p = 0,044 ) , 15 cmh2o ( p = 0,044 ) e 20 cmh2o ( p = 0,004 ) , em comparao com a observada durante a respirao espontnea . nossos achados indicam que o uso de pep nos nveis testados pode induzir um aumento na permeabilidade da membrana epitelial pulmonar e no volume pulmonar em indivduos saudveis . the alveolar - capillary barrier , also known as the blood - gas barrier , is excellent at maintaining the separation between alveolar air and pulmonary capillary blood , allowing rapid , efficient exchange of respiratory gases while preventing the diffusion of water - soluble particles suspended in alveolar air . the integrity of the blood - gas barrier is extremely important to the maintenance of pulmonary homeostasis . in 1953 , frank low published the first high - resolution electron micrographs of the human pulmonary blood - gas barrier , showing that a structure only 0.3 m thick separates capillary blood from alveolar gas , which suggested that the barrier might be vulnerable to mechanical failure if the capillary pressure increased 
  or in states of high lung inflation , in which the capillary wall is under tension because of longitudinal stress in the alveolar walls . technetium-99m - labeled diethylenetriaminepentaacetic acid tc - dtpa ) radioaerosol inhalation lung scintigraphy is a rapid , easily performed , extremely sensitive , noninvasive technique for assessing lung epithelial permeability . 


  when inhaled , tc - dtpa particles arrive at the alveolar epithelial surface and then diffuse from the air space into the vascular space . the clearance rate of tc - dtpa is a reliable index of alveolar epithelial permeability . therefore , tc - dtpa aerosol - inhaled scintigraphy has been used in numerous experiments and clinical investigations designed to assess the integrity of the respiratory epithelium . positive expiratory pressure ( pep ) therapy involves breathing with slightly active expiration against mild expiratory resistance ( typically 10 - 20 cmh2o ) . its application via a pep mask represents a reliable , safe , low - cost intervention that can increase lung volumes and intrathoracic pressure . it has been shown to improve lung volume , promote dilation of the airways , and decrease pulmonary resistance . the purpose of pep therapy is to increase the transpulmonary pressure gradient and improve pulmonary expansion , which consequently improves oxygenation and the response to inhaled bronchodilators . the effects of different intensities of pep on the pulmonary clearance of tc - dtpa in healthy subjects have been largely unexplored in the literature and require further elucidation . therefore , the aim of the present study was to evaluate the effects of pep on pulmonary epithelial membrane permeability in healthy subjects . subjects with cardiovascular or neuromuscular disease were excluded , as were those with a history of smoking or respiratory disease , as well as those who were pregnant . all participants were recruited from a tertiary care hospital in the city of porto alegre , brazil , and were evaluated between january and july of 2012 . the study was approved by the research ethics committee of the porto alegre hospital de clnicas ( protocol no . 04 - 418 ) , which is accredited by the brazilian national commission on research ethics , and all subjects gave written informed consent . pulmonary scintigraphy with tc - dtpa radioaerosol was conducted over two 30-min periods : during spontaneous breathing ; and while subjects were breathing via a pep mask ( vital signs / ge healthcare , totowa , nj , usa ) , which we adapted to fit each subject by using headgear , coupled to a pep therapy device ( resistex ; mercury medical , clearwater , fl , usa ) . using computer - generated randomization codes , we divided the subjects into three groups : those receiving pep at 10 cmh2o ( pep10 ) ; those receiving pep at 15 cmh2o ( pep15 ) ; and those receiving pep at 20 cmh2o ( pep20 ) . during data acquisition , the subjects were in a sitting position with their hands on their thighs and their arms held away from their body . a spirometer ( masterscreen v4.31 ; jaeger , wrzburg , germany ) was used in order to measure fev1 and fvc . the technical procedures , acceptability criteria , and reproducibility criteria , as well as standardization of measures , were in accordance with the guidelines established by the brazilian thoracic association . the spirometer was routinely calibrated ( on a daily basis ) with a 3-l syringe in order to compensate for ambient temperature conditions . a minimum of three and a maximum of eight tests were conducted with a 1-min interval between them . three reproducible maneuvers were performed , and the best curve was considered for the study . the tc - dtpa was chelated by adding tc - pertechnetate tc - o4 
 , ipen - tec ; institute for energy research and nuclear science , so paulo , brazil ) to 740 mbq ( 20 mci ) of dtpa ( institute for energy research and nuclear science ) in 5 ml of normal saline . using instant thin layer chromatography , we determined the labeling efficiency to be above 98% . the solution was placed in the reservoir of the nebulizer ( aerogama medical , porto alegre , brazil ) and was inhaled by the volunteer during 3 min of normal tidal breathing , with an oxygen flow rate of 9 l / min . during nebulization , the subjects remained under supervision , which allowed us to verify the appropriate performance of the inhalation maneuvers , as well as to correct any errors in inhalation techniques . the subjects were placed in a sitting position in front of a gamma camera ( starcam 4000i ; ge medical systems , milwaukee , wi , usa ) , and images were obtained every 20 s over a 30-min period . two regions of interest were defined - the left lung and the right lung - and were drawn manually , a time - activity curve being constructed by the same investigator . for each lung , we employed the negative slope of the curve to define clearance , using the minimum and maximum clearance values . the tc - dtpa clearance rate was expressed as its half - time ( t1/2)-i.e . , the time for its activity to decrease to 50% of the peak value . all statistical analyses were performed with the spss statistics software package , version 20.0 ( ibm corp . , armonk anthropometric variables and lung function parameters were compared among groups by one - way anova ( with the exception of gender , which was compared by the chi - square test ) . the difference in t1/2 among groups was determined with one - way analysis of covariance , with body weight , height , and body mass index ( bmi ) as the dependent variables . the influence of the pressure levels on t1/2 was compared among the groups by two - way anova . we evaluated 30 healthy subjects ( 15 males and 15 females ) , with a mean age of 28.26  5.40 years , a mean fev1/fvc ratio of 0.89  0.14 , and a mean fev1 of 98.5  13.1% of the predicted value . body weight , height , and bmi were higher in the pep20 group than in the pep15 group ( p = 0.038 , p = 0.027 , and p = 0.015 , respectively ) . the tc - dtpa pulmonary clearance rate was not found to correlate significantly with age ( r = 0.120 ; p = 0.951 ) , body weight ( r = 0.115 ; p = 0.545 ) , height ( r = 0.085 ; p = 0.655 ) , or bmi ( r = 0.120 ; p = 0.528 ) . in the analysis of the results related to the tc - dtpa pulmonary clearance rate , we considered the mean values for the left and right lungs together , given that the difference between the two lungs was not found to be statistically significant in the pep10 group ( p = 0.258 ) , the pep15 group ( p = 0.908 ) , or the pep20 group ( p = 0.570 ) . variablepep group p*pep10pep15pep20 
 ( n = 10)(n = 10)(n = 10)male gender , n ( % ) 6 ( 60)2 ( 20)7 ( 70)0.061age , years27.7  5.130.4  5.926.6  5.10.286weight , kg70.7  13.660.4 5.276.5  11.50.009height , cm173  7.7165.5  5.5176.1  8.50.017bmi , kg / m223.4  2.822.1  1.524.5  2.10.004fvc , % of predicted99.5  15.997.1  17.899.4 18.50.347 
 97.8  12.399.3  12.698.6  14.40.356avalues are expressed in mean  sd , except where otherwise indicated . pep : positive expiratory pressure ; pep10 : pep at 10 cmh2o for 30 min ; pep15 : pep at 15 cmh2o for 30 min ; pep20 : pep at 20 cmh2o for 30 min ; and bmi : body mass index . * between - group comparisons . significant difference between the pep15 group and the pep20 group ( p = 0.038 ) . significant difference between the pep15 group and the pep20 group ( p = 0.027 ) . significant difference between the pep15 group and the 
  values are expressed in mean  sd , except where otherwise indicated . pep : positive expiratory pressure ; pep10 : pep at 10 cmh2o for 30 min ; pep15 : pep at 15 cmh2o for 30 min ; pep20 : pep at 20 cmh2o for 30 min ; and bmi : body mass index . * between - group comparisons . significant difference between the pep15 group and the pep20 group ( p = 0.038 ) . significant difference between the pep15 group and the pep20 group ( p = 0.027 ) . significant difference between the pep15 group and the in comparison with the value obtained during spontaneous breathing , the mean t1/2 was significantly lower in the pep10 group-90.3  25.4 min versus 73.3  30.6 min ( p = 0.044 ) , as can be seen in figure 1 . that difference was also significant in the pep15 group-89.8  28.9 min versus 63.1  22.1 min ( p = 0.044)-and in the pep20 group-99.3  49.6 min versus 64.5  29.6 min ( p = 0.004 ) . regarding the delta variation in t1/2 values , no statistically significant difference was found among the groups ( p = 0.322 ) . figure 1effects of positive expiratory pressure ( pep ) on the pulmonary clearance of technetium-99m - labeled diethylenetriaminepentaacetic acid tc - dtpa ) . at all pep levels , there was a significant decrease in the tc - dtpa half - time ( the time for its activity to decrease to 50% of the peak value ) in comparison with the baseline ( spontaneous breathing ) values ( analysis of covariance , p < 0.05 for all ) . pep10 : pep at 10 cmh2o for 30 min ; pep15 : pep at 15 cmh2o for 30 min ; and pep20 : and pep at 20 cmh2o for 30 min . * to our knowledge , this was the first study to investigate the effects that different levels of pep ( 10 , 15 , and 20 cmh2o ) have on the rate of pulmonary clearance of tc - dtpa . we demonstrated that pep was able to induce increases in epithelial permeability , at all of the levels tested . another important finding is that no significant variation in pulmonary clearance rate was observed among the three groups under the effects of any of the three pep levels . the effect of positive end - expiratory pressure ( peep ) on solute clearance has been described as a sigmoidal dose - response relationship dependent on the pressure level applied ( 5 - 15 cmh2o ) ; in other words , the rate of pulmonary clearance of tc - dtpa accelerates exponentially due to the increase in lung volume caused by the administration of different peep levels . contrary to our hypothesis , we did not find any differences among the three levels of pep . in accordance with our results , the study conducted by bishai et al . 
  showed an increase in the pulmonary epithelial permeability in mice at a peep level of 10 cmh2o . this difference in pulmonary clearance might be because mice have smaller alveoli and are probably more sensitive to the distension of inter - epithelial junctions of the alveolar epithelium induced by the application of lower pressure levels . our findings differ from those reported by paiva et al . , 
  who assessed the permeability of the alveolar epithelial membrane in 36 healthy individuals submitted to 10 cmh2o and 20 cmh2o under continuous positive airway pressure ( cpap ) . the authors showed that 20 cmh2o of cpap induced an increase in epithelial permeability , whereas 10 cmh2o of cpap did not . previous studies in humans , 
  sheep , 


  and dogs 


  showed that the application of peep increases lung volume and accelerates the rate of pulmonary clearance of tc - dtpa . therefore , the increased end - expiratory lung volume produced by pep reduces airway resistance and promotes an increase in functional residual capacity . however , other factors , such as airway / alveolar distension , prevention of alveolar collapse during expiration , and recruitment of collapsed alveoli , can also increase functional residual capacity . 

  in keeping with the findings of the present study , suzuki et al . observed that , during the application of 20 cmh2o of peep , pulmonary clearance of tc - dtpa increased but returned to baseline values when peep was discontinued . that suggests that the increase in the tc - dtpa pulmonary clearance rate achieved through the application of peep is reversible after breathing returns to atmospheric pressure levels .   the mechanisms by which pulmonary insufflation accelerates the pulmonary clearance of tc - dtpa remain unclear . some authors attribute this effect to an increase in the alveolar surface area available for diffusion , 
  due to either the increase in epithelial permeability , 
  functional alterations in the surfactant layer , 
  or distension of the intercellular junctions of the alveolar epithelium . first , we evaluated subjects with healthy lungs . therefore , any conclusions drawn from this study can not be applied to patients with lung disease . this needs to be investigated in different , clearly specified disease groups , especially because pep is not usually applied in patients with healthy lungs . nevertheless , our findings offer new perspectives on the role of noninvasive ventilation , particularly in relation to pep and its influence on the alveolar epithelium . on the basis of the findings of the present study , we conclude that the application of 10 , 15 , or 20 cmh2o of pep for 30 min can induce an increase in epithelial permeability and lung volume in healthy subjects . given that the application of pep represents a reliable , safe , and low - cost intervention in a variety of clinical situations , future investigations should be conducted with a focus on expanding upon these findings .
abstractobjective : to evaluate the effects of positive expiratory pressure ( pep ) on pulmonary epithelial membrane permeability in healthy subjects . 
 methods : we evaluated a cohort of 30 healthy subjects ( 15 males and 15 females ) with a mean age of 28.3  5.4 years , a mean fev1/fvc ratio of 0.89  0.14 , and a mean fev1 of 98.5  13.1% of predicted . 
 subjects underwent technetium-99m - labeled diethylenetriaminepentaacetic acid ( 99mtc - dtpa ) radioaerosol inhalation lung scintigraphy in two stages : during spontaneous breathing ; and while breathing through a pep mask at one of three pep levels-10 cmh2o ( n = 10 ) , 15 cmh2o ( n = 10 ) , and 20 cmh2o ( n = 10 ) . 
 the 99mtc - dtpa was nebulized for 3 min , and its clearance was recorded by scintigraphy over a 30-min period during spontaneous breathing and over a 30-min period during breathing through a pep mask . 
 results : the pulmonary clearance of 99mtc - dtpa was significantly shorter when pep was applied - at 10 cmh2o ( p = 0.044 ) , 15 cmh2o ( p = 0.044 ) , and 20 cmh2o ( p = 0.004)-in comparison with that observed during spontaneous breathing . 
 conclusions : our findings indicate that pep , at the levels tested , is able to induce an increase in pulmonary epithelial membrane permeability and lung volume in healthy subjects .