chronic kidney disease ( ckd ) is an irreversible and progressive disorder characterized by loss of kidney function . esrd patients eventually need renal replacement therapy via dialysis ( subdivided into hemodialysis and peritoneal dialysis ) or kidney transplantation in order to survive . as the life expectancy of esrd patients has increased with improvements in dialysis technology , systemic complications of kidney disease are likely to become increasingly important . ckd , in fact , is not only a localized disease , but also affects virtually all organ systems , especially at the late stage of disease . among these , a variety of pulmonary abnormalities , including pulmonary edema , pleural effusion , acute respiratory distress syndrome , pulmonary fibrosis and calcification , pulmonary hypertension , hemosiderosis , pleural fibrosis , and sleep apnea syndrome , have been documented in these patient cohorts [ 35 ] . impaired pulmonary function may be the direct result of circulating uremic toxins or may indirectly result from fluid overload , anemia , immune suppression , extraosseous calcification , malnutrition , electrolyte disorders , and/or acid - base imbalances , which are common issues in esrd patients . it is known that fluid overload is a common and serious problem that leads to severe complications in hd patients . in the interdialytic period , weight fluctuations are commonly seen in patients with esrd on regular hemodialysis program due to body fluid overload . fluid overload , together with a potential increase in pulmonary capillary permeability , can result in pulmonary edema and pleural effusion , abnormalities that could explain , at least in part , the decrease in pulmonary function . since hemodialysis removes excess body fluid , it can also lead to improvement in pulmonary functions by reducing water content of the lungs . relatively few studies have investigated the alterations of pulmonary function in esrd patients undergoing hemodialysis treatment , and conflicting results have been reported . therefore , we designed this study to investigate the acute effects of hemodialysis treatment on spirometry parameters . we particularly focussed on the relationship between pulmonary function and fluid status in esrd patients on regular hemodialysis , using a novel bioelectrical impedance analysis device to measure the fluid status . the study design included 54 patients with esrd receiving chronic hd therapy 3 times per week in dicle university hospital s dialysis unit . this cross - sectional study was conducted at a tertiary care university hospital and among patients diagnosed with esrd . the local human research ethics committee approved the study protocol , and informed consent was obtained from all patients at the time of study enrollment . all patients were dialyzed with using 1.6 m surface area high - flux polysulphone dialyzers ( fresenius , bad homberg , germany ) with bicarbonate - based dialysate ( glucose 1 mmol / l , na 140 meq / l , hco332 the prescribed duration was 5 h with a blood flow rate of 250350 ml / min and dialysate flow rate of 500 ml / min . the exclusion criteria were : ( 1 ) hemodynamically unstable patients ; ( 2 ) patients with lung disease , such as chronic obstructive pulmonary disease , asthma , or pleural disease ; ( 3 ) known cardiovascular disease ; ( 4 ) patients who had limb amputation , pacemakers , metallic intravascular devices , any malignant disease , or pregnancy ; and ( 5 ) patients who have been receiving diuretic treatment . all patients demographics and baseline clinical characteristics were obtained from patient registries and the patients themselves . body mass index ( bmi ) was calculated as the ratio weight / height ( kg / m ) . standard spirometric pulmonary function tests ( easy - on pc , true flow by ndd , medizintechnik ag ch-8005 zurich , switzerland ) were performed immediately before and after the midweek hemodialysis session . all patients were able to perform acceptable and re - producible forced expiratory maneuvers with the same physician . the patients were studied in sitting posture while wearing a nose clip using standard methodology . forced vital capacity ( fvc ) , forced expiratory volume in the first second ( fev1 ) , peak expiratory flow rate ( pefr ) , mean forced expiratory flow between 25% and 75% of the fvc ( fef2575 ) , and the fev1/fvc ratio were measured and calculated as%predicted using normal values determined on the basis of age , race , height , and sex ( fvc% , fev1% , pefr% , and fef 2575% ) . in recent years , multifrequency bioelectrical impedance analysis ( bia ) , which is a simple , safe , novel , rapid , noninvasive , and promising method , has been used to determine fluid status in patients on dialysis therapy . a multi - frequency bia device ( body composition monitor , bcm , fresenius medical care d gmbh ) , which measures 50 different frequencies from 5 to 1000khz , bia was performed just before ( pre - hd ) and 30 min after ( post - hd ) the midweek dialysis session . the following parameters were obtained : overhydration ( oh ) , extracellular water ( ecw ) , and oh / ecw% ratio . fluid overload was defined as a oh / ecw 7% , corresponding to the value of the 90th percentile for the reference cohort . data analyses were performed using the statistical package for social sciences ( spss ) , version 18.0 for windows ( spss inc . , the variables were investigated using visual ( histograms and probability plots ) and analytical ( kolmogorov - smirnov test ) methods whether or not they were normally distributed . normally distributed variables are presented as means and standard deviations , and non - normally distributed variables are presented as median and range ( maximum and minimum ) . the paired student s t - test was used to compare the pre - hd and post - hd measurements . the study design included 54 patients with esrd receiving chronic hd therapy 3 times per week in dicle university hospital s dialysis unit . this cross - sectional study was conducted at a tertiary care university hospital and among patients diagnosed with esrd . the local human research ethics committee approved the study protocol , and informed consent was obtained from all patients at the time of study enrollment . all patients were dialyzed with using 1.6 m surface area high - flux polysulphone dialyzers ( fresenius , bad homberg , germany ) with bicarbonate - based dialysate ( glucose 1 mmol / l , na 140 meq / l , hco332 the prescribed duration was 5 h with a blood flow rate of 250350 ml / min and dialysate flow rate of 500 ml / min . the exclusion criteria were : ( 1 ) hemodynamically unstable patients ; ( 2 ) patients with lung disease , such as chronic obstructive pulmonary disease , asthma , or pleural disease ; ( 3 ) known cardiovascular disease ; ( 4 ) patients who had limb amputation , pacemakers , metallic intravascular devices , any malignant disease , or pregnancy ; and ( 5 ) patients who have been receiving diuretic treatment . all patients demographics and baseline clinical characteristics were obtained from patient registries and the patients themselves . body mass index ( bmi ) standard spirometric pulmonary function tests ( easy - on pc , true flow by ndd , medizintechnik ag ch-8005 zurich , switzerland ) were performed immediately before and after the midweek hemodialysis session . all patients were able to perform acceptable and re - producible forced expiratory maneuvers with the same physician . the patients were studied in sitting posture while wearing a nose clip using standard methodology . forced vital capacity ( fvc ) , forced expiratory volume in the first second ( fev1 ) , peak expiratory flow rate ( pefr ) , mean forced expiratory flow between 25% and 75% of the fvc ( fef2575 ) , and the fev1/fvc ratio were measured and calculated as%predicted using normal values determined on the basis of age , race , height , and sex ( fvc% , fev1% , pefr% , and fef 2575% ) . in recent years , multifrequency bioelectrical impedance analysis ( bia ) , which is a simple , safe , novel , rapid , noninvasive , and promising method , has been used to determine fluid status in patients on dialysis therapy . a multi - frequency bia device ( body composition monitor , bcm , fresenius medical care d gmbh ) , which measures 50 different frequencies from 5 to 1000khz , bia was performed just before ( pre - hd ) and 30 min after ( post - hd ) the midweek dialysis session . the following parameters were obtained : overhydration ( oh ) , extracellular water ( ecw ) , and oh / ecw% ratio . fluid overload was defined as a oh / ecw 7% , corresponding to the value of the 90th percentile for the reference cohort . data analyses were performed using the statistical package for social sciences ( spss ) , version 18.0 for windows ( spss inc . , chicago , il ) . the variables were investigated using visual ( histograms and probability plots ) and analytical ( kolmogorov - smirnov test ) methods whether or not they were normally distributed . normally distributed variables are presented as means and standard deviations , and non - normally distributed variables are presented as median and range ( maximum and minimum ) . the paired student s t - test was used to compare the pre - hd and post - hd measurements . the mean age of the study population ( n=54 ) was 49.5115.08 years and 51.8% were male . the baseline demographic and clinical characteristics and relevant laboratory parameters of the patients are presented in table 1 . fvc , fvc% , and fev1 levels were significantly increased after the hemodialysis session ( p<0.05 ) . as regards the bia parameters , oh / ecw% were significantly lower in post - hd patients compared to pre - hd patients ( p<0.05 ) . table 2 depicts comparison of pulmonary function tests and bia characteristics in pre - dialysis and post - dialysis patients . fvc , fvc% , fev1 , fev1% , fef2575 , fef2575% , pefr , and pefr% were significantly lower in patients with fluid overload than in those without fluid overload ( p<0.05 ) . there were significant negative correlations between oh / ecw and fvc , fvc% , fev1 , fev1% , fef2575 , fef2575% , pefr , and pefr% ( table 4 ) . further , we modelled a stepwise multiple regression analysis to define the independent determinants of post - hemodialysis fvc . sex , age , oh / ecw% ratio , and ultrafiltration volume were included into the model . male sex and increased ultrafiltration volume were independently associated with higher fvc , whereas increased age and oh / ecw% ratio were independently associated with lower fvc ( r=0.569 , p<0.001 , table 5 ) . ckd , which can lead to esrd , is a worldwide public health problem and is associated with increased morbidity , mortality , and diminished quality of life . unfortunately , the prevalence of esrd is increasing with the rise in diabetes , hypertension , obesity , and the aging population . almost all systems of the body are adversely affected as the patient approaches esrd ; therefore , these patients suffer from serious respiratory , cardiovascular , and metabolic complications . the respiratory system is especially affected due to the pulmonary complications commonly encountered in esrd patients receiving hemodialysis treatment . the pathogenesis of impaired pulmonary functions has not been completely elucidated in hd patients , perhaps partly due to the small number of studies . to the best of our knowledge , this is the first study to investigate the relationship between fluid overload based on oh / ecw ratio measured by using bia and pulmonary function in patients receiving regular hd . several alterations in pulmonary functions , including restriction , obstruction , and impaired diffusion capacity , have been reported in ckd patients . despite some conflicting results , improvement of spirometry parameters after demonstrated that spirometry parameters ( fvc , fev1 , fef75 , 50 , 25,% of predicted ) significantly improved at 1 h after a hemodialysis session . in a study by alves et al . , including in 61 hemodialysis patients , spirometry parameters were examined before and after hemodialysis ; they found a significant correlation between the improvement of pulmonary functions ( fev1 and fvc ) and weight reduction after dialysis . they also suggested that correction of volume overload after hemodialysis seems to be an important factor in the spirometric improvement . moreover , a study by kovelis et al . conducted in a relatively small number of patients ( 17 hd patients ) showed an improvement in fvc after a hemodialysis session , and they also concluded that the pronounced weight gain in the interdialytic period is associated with worsening of pulmonary function , which is almost fully reversible by hemodialysis . on the contrary , myers et al . reported that the accumulation of body water between dialysis sessions did not significantly influence pulmonary function . in a similar study , lang et al . found no significant difference in pre- and post - dialysis values of vc ( % ) , fev1/vc ( % ) , and correlation between lung function parameters and interdialytic changes in body weight in 14 patients receiving hd . in the present study , we demonstrated that spirometry parameters ( fvc , fvc% , and fev1 ) were significantly improved after hemodialysis . another finding of the present study is that pulmonary functions tests ( fvc , fvc% , fev1 , fev1% , fef2575 , fef2575% , pefr , and pefr% ) were significantly lower in patients with volume overload . also , oh / ecw , which was used to assess volume overload , was negatively correlated with fvc , fvc% , fev1 , fev1% , fef2575 , fef2575% , pefr , and pefr% . importantly , this study showed that volume overload , determined by oh / ecw ratio and ultrafiltration volume , is an independent predictor of fvc after hd . our study results support previous studies by demonstrating the improvement of spirometry parameters , which are mainly related to reduction of excess lung water , after a hemodialysis session . in addition , the findings of the present study demonstrated that volume overload is closely associated with restrictive and obstructive respiratory abnormalities . although excess fluid is removed by ultrafiltration during a dialysis session , patients still can be overhydrated . on the other hand , many hemodialysis patients also return to the pre - dialysis period with overhydration as a consequence of water overload . one major consequence is the accumulation of fluid during the interdialytic period , which has a propensity to collect in the lungs and lead to progressive pulmonary congestion . pulmonary congestion is highly prevalent among patients with esrd treated with hemodialysis and is associated with a mixed restrictive - obstructive pattern on pulmonary function tests . hemodialysis can lead to improvement in lung restriction , due to decreasing interstitial edema and bronchial wall decongestion . hemodialysis can remove the excess fluid from the body in overhydrated patients , which in turn reduces water content of the lungs and thus decreases the pressure on airways , and reduces obstruction . a major limitation of the present study is the lack of a long - term follow - up . remeasurement of pulmonary function tests after achievement of euvolemia in overhydrated patients is needed in a future prospective study . the present study indicates that fluid overload is closely associated with restrictive and obstructive respiratory abnormalities in patients with end - stage renal disease on maintenance hemodialysis treatment . in addition , hemodialysis has a beneficial effect on pulmonary function tests , which can attributed to reduction of volume overload . we suggest that intervention to reduce excess volume in hemodialysis patients with volume overload could result in better pulmonary functions .
backgroundrespiratory system disorders are one of the most prevalent complications in end - stage renal disease patients on hemodialysis . 
 however , the pathogenesis of impaired pulmonary functions has not been completely elucidated in these patients . 
 we designed a study to investigate acute effects of hemodialysis treatment on spirometry parameters , focusing on the relationship between pulmonary function and fluid status in hemodialysis patients.material/methodswe enrolled 54 hemodialysis patients in this study . 
 multifrequency bioimpedance analysis ( bia ) was used to assess fluid status before and 30 min after the midweek of hemodialysis ( hd ) . 
 overhydration ( oh)/extracellular water ( ecw)% ratio was used as an indicator of fluid status . 
 fluid overload was defined as oh / ecw 7% . 
 spirometry was performed before and after hemodialysis.resultsforced vital capacity ( fvc ) , fvc% , and forced expiratory volume in the first second ( fev1 ) levels were significantly increased after hemodialysis . 
 fvc , fvc% , fev1 , fev1% , mean forced expiratory flow between 25% and 75% of the fvc ( fef2575 ) , fef2575% , peak expiratory flow rate ( pefr ) , and pefr% were significantly lower in patients with fluid overload than in those without . 
 oh / ecw ratio was negatively correlated with fvc , fvc% , fev1 , fev1% , fef2575 , fef2575% , pefr , and pefr% . 
 stepwise multiple regression analysis revealed that male sex and increased ultrafiltration volume were independently associated with higher fvc , whereas increased age and oh / ecw ratio were independently associated with lower fvc.conclusionsfluid overload is closely associated with restrictive and obstructive respiratory abnormalities in hd patients . 
 in addition , hemodialysis has a beneficial effect on pulmonary function tests , which may be due to reduction of volume overload .