obesity is a condition that causes damage to the various body functions , such as cardiovascular , musculoskeletal , and metabolic functions amongst others . the respiratory function is also affected by obesity , as excess fat deposited on the chest wall and the abdominal cavity affects the chest mechanics . this results in increased work of breathing , reduced lung volumes , dysfunction of the respiratory muscle , impairment in gas exchange , and reduced exercise tolerance [ 29 ] . a few studies have demonstrated that weight loss due to bariatric surgery has resulted in a huge improvement in some functions , such as decrease in hemoglobin and hematocrit , decreased heart rate and oxygen consumption , and reduction of insulin resistance . in addition , especially improved lung function with increased forced vital capacity ( fvc ) [ 3 , 12 , 13 ] and forced expiratory volume in one second ( fev1 ) , improved alveolar - capillary diffusion capacity   and improvement in gas exchange [ 12 , 13 ] have also been observed . there is strong evidence supporting the increase in fvc and erv ( expiratory reserve volume ) after weight loss [ 3 , 12 , 13 ] . however , controversy still persists regarding the behavior of the respiratory muscle strength and irv ( inspiratory reserve volume ) after weight loss caused by the roux - en - y gastric bypass surgery . the objective of the present study was to evaluate the effect of weight loss , after 1 year of the roux - en - y gastric bypass surgery ( rygb ) , on the lung volumes and the respiratory muscle strength in obese women . were recruited 24 obese women candidates for rygb at the meridional hospital . patients with body mass index ( bmi ) 3550  kg / m were included if they met the minimal criteria for bariatric surgery proposed by the world health organization ( who ) report of 2000 . the following were not included in the study : patients suffering from pulmonary diseases or those unable to carry out the pulmonary function tests adequately , smokers , patients who did not attend the reevaluation 1 year after surgery , and patients refusing to sign the informed consent term . the present study was approved by the meridional hospital ethics committee ( protocol number 01/07 ) . the evaluation of the pulmonary function was carried out by conventional spirometry using a personal computer version of the ndd easyone spirometer model 2001 ( medizintechnik ag , zurich , switzerland ) . parameters , such as volume , capacity , and flow of the lungs , were directly evaluated by using the slow vital capacity ( svc ) , the forced vital capacity ( fvc ) , and the maximum voluntary ventilation ( mvv ) tests , with volunteers in a sitting position and a minimum of three repetitions , as recommended by the american thoracic society ( ats ) and the european respiratory society ( ers ) . the obtained results were expressed in absolute values and as percentages of the predicted reference values for the brazilian population . the svc test produced the following variables : vital capacity ( vc ) , tidal volume ( vt ) , inspiratory reserve volume ( irv ) , and expiratory reserve volume ( erv ) . the fvc test allowed the determination of the forced expiratory volume in 1  s ( fev1 ) and the fev1/fvc ratio . the mvv , a variable that evaluates the respiratory endurance , was expressed in liters per minute and as a percentage of the predicted reference value for the brazilian population . the respiratory muscle strength was determined through the maximal static respiratory pressures measured during forced inspiration and expiration  maximal inspiratory pressure ( mip ) and maximal expiratory pressure ( mep ) . the measurement was carried out using an aneroid manometer ( wika , iper , sp , brazil ) , calibrated in centimeter h2o ( 300  cm h2o ) , and equipped with a 2  mm hole to relieve the oral pressure . mip and mep were determined using the residual volume and the total lung capacity , respectively , with the subjects in a sitting position . patients carried out at least three acceptable inspirations / expirations wearing a nose clip for determining the two reproducible inspirations / expirations . the mip and mep values were also expressed as percentages of the predicted values , according to the equation proposed by neder et al . . the patients were evaluated in the preoperative period , and one year after surgery , they were asked to return for a reevaluation of the pulmonary function tests , by the spirometry and respiratory muscle strength . the data collected were expressed as mean  standard deviation and analyzed by the shapiro - wilk test . after verifying the normal distribution of the variables , the paired t - test was used to compare the preoperative and 1-year postoperative results . the pearson correlation was used to correlate these variables : w / h ratio and erv ; irv and mip . the sample size had an 80% power at the 5% level of significance with mep as the main variable . the characteristics of the patients , such as age , bmi , weight , and w / h ratio , are shown in table 1 . there was a significant reduction in the values of weight , bmi , and w / h ratio 1 year after the surgery . the bmi value returned to normal in 11 patients ; in the other 11 patients , it lowered to the range of overweight ( 2530  kg / m ) , and only 2 patients remained obese , despite significant reduction in the bmi one year after surgery . before surgery , 12 patients had hypertension , 7 had dyslipidemia , and 8 had diabetes . one year after the surgery , 6 patients continued with hypertension and 2 with dyslipidemia . on analyzing the variables that measure lung volumes , it was observed that there was a significant increase in the vc , fvc , and fev1 . however , when examining the components of the vc separately , an increase in erv and reduction of irv , keeping the vt unchanged 1 year after surgery , was observed . furthermore , respiratory endurance assessed by mvv also increased after weight loss ( table 2 ) . moreover , in assessing respiratory muscle strength , a reduction statistically significant in the values of mip and mep was recorded ( table 3 ) . there was a significant negative correlation between w / h ratio and erv ( r = 0.37 ; p = 0.01 ) ( figure 1 ) and a significant positive correlation between mip and irv ( r = 0.41 ; p = 0.004 ) ( figure 2 ) . based on the obtained results , it was established that 1 year after the rygb surgery , the patients showed a significant reduction in the measures of weight , bmi , and w / h ratio , especially changes in the lung function tests , such as spirometry and respiratory muscle strength . studies by some authors [ 9 , 12 , 18 ] have shown an improved lung function in patients evaluated after 1 year following weight loss induced by bariatric surgery , and others have attributed this improvement mainly to the reduction in the w / h ratio . ( 2005 )   found that the patients showed an improvement in dyspnea and a reduction in the respiratory drive after weight loss induced by bariatric surgery . in the present study , one year after surgery , the patients showed increased lung volumes and decreased the respiratory muscle strength . with respect to the volumes , an increase in vc , fvc , and fev1 could be observed after weight loss . other authors have also found similar results in previous studies [ 9 , 12 , 18 , 2022 ] . however , in this study , a finding still not published and discussed in the literature was noted : the irv reducing associated with an increase of erv after weight loss . the reduction of erv is a major known change in the respiratory function caused by obesity . according to koenig ( 2001 ) , this is because the diaphragm is pressed upwards due to the expanded abdominal volume and w / h ratio of the obese individuals , which is a mechanical disadvantage for this muscle . besides these detrimental mechanics aspects to the pulmonary function of obese individuals , young et al . 2003   also suggested that the reduction of the erv could lead to an increase in areas of atelectasis . as a result , the ventilation / perfusion mismatch could be harmed , thereby leading to arterial hypoxemia in those individuals . the reduction of w / h ratio after weight loss may have contributed to improvement in chest mechanics and consequent increase in erv , as demonstrated by the significant correlation between these variables ( r = 0.37 ; p = 0.01 ) ( figure 1 ) . ( 2008 )   compared the pulmonary function in the obese and nonobese subjects , and the authors found a higher irv and lower erv in the first and the opposite in the other one , with no significant changes in the vc values between the groups observed . according to the authors , this is due to the problems in the chest mechanics of obese individuals , which could have resulted in a compensatory increase in irv by reducing the erv caused by obesity , while retaining an unchanged cv . thus , in the present study there was a tendency to return to the patterns of distribution of the lung volumes of the non - obese individuals in studied patients . therefore , the obtained results suggested that the weight loss induced by bariatric surgery altered the chest mechanics , by a rearrangement of the volumetric lung compartments inside the rib cage , especially for abdominal decompression after weight loss of these obese patients . el - gamal et al . ( 2005 )   evaluated obese patients in the preoperative and 1 year after bariatric surgery and found that the low value of erv is related to increased of respiratory drive and dyspnea , with improvement in these parameters after weight loss . these results help to consolidate the hypothesis that obesity , by reducing erv , leads to a respiratory overload ( inspiratory mainly ) , verified by the increase in dyspnea and respiratory drive , leading to increased of irv . and finally , after weight loss these changes are reversed . besides these changes of the chest mechanics due to weight loss , the reduction of inspiratory muscle strength ( mip ) may also have contributed to the reduction of irv , since the inspiratory muscles are responsible for expanding the rib cage and promote entry of air into the lungs . this finding can be confirmed by the significant and positive correlation between these variables  mip and irv ( r = 0.41 ; p = 0.004 ) ( figure 2 ) . the respiratory muscle strength is also an important variable that influences the lung function , and the available data in the literature are still few and controversial about this variable after weight loss . ( 1998 )   also measured mip and mep after bariatric surgery and found an increase in these variables . ( 1991 )   found a reduction in the respiratory muscle strength after weight loss induced by bariatric surgery , in agreement with the results of the present study . one explanation for this finding could be the loss of lean body mass after bariatric surgery , as described by some authors [ 2528 ] . the average weight loss with rygb is 30% , which is similar to the results of the present study . however , this loss is not only fat of mass but also lean body mass . stegen et al .   found a reduction in the lean body mass associated with a reduction of static and dynamic muscle strength , whereby the authors suggested that physical activity prevents the reduction of muscle strength after bariatric surgery . however , one limitation of the present study was that it did not evaluate the lean body mass of the patients . another hypothesis is that the reduced work of breathing in the obese individuals achieved with weight loss , no longer exerted  training  on the respiratory muscles of these individuals , thereby reducing the values of the respiratory muscle strength . despite a trend to decrease the maximal static respiratory pressures mip and mep , there was an increase in mvv ( a variable that evaluates the respiratory endurance ) . this fact can be justified as the weight loss promotes an improvement of the chest mechanics , increases the lung volumes [ 9 , 22 ] , and reduces the work of breathing . based on the obtained findings , it was concluded that weight loss induced by bariatric surgery provides an improvement in the ventilatory mechanics , as evidenced by the increase in lung volumes ( erv , vc , fvc , and fev1 ) and respiratory endurance ( mvv ) of obese women . furthermore , the reduction in irv appears to show a trend distribution of static lung volumes in the pattern as seen in the nonobese patients . additionally , there was also a reduction in the respiratory muscle strength , which could be caused by a loss of lean body mass and a reduction in the work of breathing after weight loss .
introduction . 
 obesity is a condition that causes damage to the respiratory function . 
 however , studies have demonstrated that weight loss due to bariatric surgery has resulted in a huge improvement on some lung volumes , but controversy still persists regarding the behavior of the respiratory muscle strength and irv ( inspiratory reserve volume ) . objective . to evaluate the effect of weight loss , after 1 year of the roux - en - y gastric bypass surgery ( rygb ) , on the lung volumes and the respiratory muscle strength in obese women . methods . 
 24 obese women candidates were recruited for rygb . 
 lung volumes ( spirometry ) and respiratory muscle strength were evaluated in preoperative period and one year after surgery . 
 results . 
 there was a significant increase in some lung volumes . 
 however , when examining the components of the vc ( vital capacity ) separately , an increase in erv ( expiratory reserve volume ) and reduction of irv were observed . 
 moreover , a statistically significant reduction in the values of respiratory muscle strength was recorded : mip ( maximal inspiratory pressure ) and mep ( maximal expiratory pressure ) . conclusion . 
 weight loss induced by bariatric surgery provides an increase in some lung volumes of obese women , but reduction in irv . 
 additionally , there was also a reduction in the respiratory muscle strength .