there are symptoms common to both chronic heart failure ( chf ) and pulmonary arterial hypertension ( pah ) . pulmonary abnormalities play an important role in the evaluation and prognosis of chf and pah . the differences of pulmonary function in chronic left heart failure and chronic right heart failure are not fully understood . cardiopulmonary exercise testing ( cpx ) is considered the criterion standard for studying cardiovascular , pulmonary , and metabolic adaptations to exercise in heart disease . pulmonary abnormalities occur in both chf and chronic right heart failure secondary to pah [ 19 ] . left heart failure with cardiac enlargement causes restrictive lung disease , interstitial edema , alveolar - capillary hydrostatic injury , and fatigue of respiratory muscles , which contributes to pulmonary abnormalities . pah can cause ventilation / perfusion ( v / q ) inequality secondary to pulmonary vascular bed damage . we hypothesized that pulmonary function is different in patients with left heart failure and right heart failure secondary to pah . this study may help understand relationships between pulmonary abnormalities and different types of heart failure . a single cardiologist evaluated 120 patients with clinically stable chf , including 60 patients with chronic left heart failure and 60 patients with chronic right heart failure . left heart failure was diagnosed using the american college of cardiology foundation ( accf)/american heart association ( aha ) guidelines for heart failure . pah was defined as who group1 ph according to the accf / aha expert consensus document on pulmonary hypertension . we excluded patients with group 2 , 3 , 4 , or 5 , associated with congenital heart disease , portal hypertension , significant venous or capillary involvement , or persistent pulmonary hypertension of the newborn . right heart failure was defined as pah and cardiac index ( ci ) < 2.2 l/(minm ) as measured by right heart catheterization . all patients had a forced expiratory volume in 1 s / forced vital capacity ( fev1/fvc ) ratio > 65% at rest . the document was approved and recorded by the institutional ethics committee of fuwai hospital , china . pulmonary function testing at rest was performed using a closed - circuit spirometer ( cosmed , italy ) according to the american thoracic society ( ats ) recommendations . dead space volume / tidal volume ( vd / vt)=(paco2  peco2 mean)/paco2  [ vd ( machine)/vt ] where paco2 = arterial co2 tension , peco2 = the partial pressure of expired co2 . minute ventilation / co2 production ( ve / vco2 ) ratio was defined as ve / vco2 = 863/[paco2  ( 1-vd / vt ) ] . physician - supervised cpx was performed on a bicycle ergometer with a breath - by - breath system ( cosmed , italy ) according to the ats / american college of chest physicians ( accp ) statement on cpx . exercise - induced right - to - left shunt ( eis ) was performed according to criteria described by sun . breathing reserve ( br ) was defined as : br = ( mvv - peak ve)/mvv 100% where mvv = maximal voluntary ventilation . change in cpx parameter from rest to peak exercise was defined as :  measure = ( peak measure - rest measure)/rest measure 100% . two - dimensional echocardiography and doppler ultrasound ( philips ie33 , netherlands ) examinations were performed on the same day before cpx . left ventricular ejection fraction ( lvef ) was determined according to the recommendations of the european association of echocardiography . pulmonary capillary wedge pressure ( pcwp ) and mean pulmonary artery pressure ( mpap ) were determined with balloon flotation catheter ( edwards lifesciences , usa ) . multivariate linear regression was used to determine pulmonary function differences and the changes in cpx parameters between the 2 groups . to correct for demographic differences between the 2 groups of patients , variables that were either biologically plausible and/or significantly different between groups in univariate analysis a single cardiologist evaluated 120 patients with clinically stable chf , including 60 patients with chronic left heart failure and 60 patients with chronic right heart failure . left heart failure was diagnosed using the american college of cardiology foundation ( accf)/american heart association ( aha ) guidelines for heart failure . pah was defined as who group1 ph according to the accf / aha expert consensus document on pulmonary hypertension . we excluded patients with group 2 , 3 , 4 , or 5 , associated with congenital heart disease , portal hypertension , significant venous or capillary involvement , or persistent pulmonary hypertension of the newborn . right heart failure was defined as pah and cardiac index ( ci ) < 2.2 l/(minm ) as measured by right heart catheterization . all patients had a forced expiratory volume in 1 s / forced vital capacity ( fev1/fvc ) ratio > 65% at rest . the document was approved and recorded by the institutional ethics committee of fuwai hospital , china . pulmonary function testing at rest was performed using a closed - circuit spirometer ( cosmed , italy ) according to the american thoracic society ( ats ) recommendations . peco2 mean)/paco2  [ vd ( machine)/vt ] where paco2 = arterial co2 tension , peco2 = the partial pressure of expired co2 . minute ventilation / co2 production ( ve / vco2 ) ratio was defined as ve / vco2 = 863/[paco2  ( 1-vd / vt ) ] . physician - supervised cpx was performed on a bicycle ergometer with a breath - by - breath system ( cosmed , italy ) according to the ats / american college of chest physicians ( accp ) statement on cpx . exercise - induced right - to - left shunt ( eis ) was performed according to criteria described by sun . breathing reserve ( br ) was defined as : br = ( mvv - peak ve)/mvv 100% where mvv = maximal voluntary ventilation . change in cpx parameter from rest to peak exercise was defined as :  measure = ( peak measure - rest measure)/rest measure 100% . two - dimensional echocardiography and doppler ultrasound ( philips ie33 , netherlands ) examinations were performed on the same day before cpx . left ventricular ejection fraction ( lvef ) was determined according to the recommendations of the european association of echocardiography . pulmonary capillary wedge pressure ( pcwp ) and mean pulmonary artery pressure ( mpap ) were determined with balloon flotation catheter ( edwards lifesciences , usa ) . multivariate linear regression was used to determine pulmonary function differences and the changes in cpx parameters between the 2 groups . to correct for demographic differences between the 2 groups of patients , variables that were either biologically plausible and/or significantly different between groups in univariate analysis patients with left heart failure were older , had a higher proportion of men and smokers , and had a higher bmi . the anaerobic threshold ( at ) was detectable in all patients . among the patients with right heart failure , 21 showed eis . patients with right heart failure had lower oxygen uptake ( vo2 ) , vt , fev1 , fvc , mvv , and petco2 , and higher end - tidal partial pressure of o2 ( peto2 ) and ve / vco2 at rest . right heart failure patients had lower peak vo2 , peak ve , peak vt , and peak petco2 , and had higher peak vd / vt , peak peto2 , peak ve / vco2 , and ve / vco2 slope during exercise . right heart failure patients had lower vo2 , ve , petco2 , and ve / vco2 , from rest to exercise . patients with right heart failure had lower petco2 , and higher peto2 and ve / vco2 at rest . right heart failure patients had a lower peak petco2 , and higher peak vd / vt , peak peto2 , peak ve / vco2 , and ve / vco2 slope during exercise . right heart failure patients had lower petco2 and ve / vco2 , from rest to exercise . figure 1a shows the result of vd / vt ratio versus ve / vco2 at rest . the curves show patients with right heart failure had higher ve / vco2 and lower petco2 at any given vd / vt ratio at rest . the abrupt curve of right heart failure was suggestive of eis in the right heart failure patients during exercise . most right heart failure patients had higher ve / vco2 slope and peak vd / vt at any given peak petco2 . figure 1c shows the result of peak vd / vt ratio versus ve / vco2 slope . the curves show that most right heart failure patients had a lower petco2 and higher vd / vt ratio at any given . patients with right heart failure had lower petco2 , and higher peto2 and ve / vco2 at rest . patients with right heart failure showed a higher peak vd / vt , peak peto2 , peak ve / vco2 , and ve / vco2 slope , and a lower petco2 during exercise . patients with right heart failure had more changes in petco2 and ve / vco2 from rest to exercise . these results show that patients with right heart failure had worse pulmonary function at rest and exercise . pulmonary function changes compatible with restrictive lung disease are observed in most patients with severe chf , and findings compatible with airway obstruction are common in patients with right heart failure caused by idiopathic pulmonary arterial hypertension ( ipah ) . right heart failure patients had a lower petco2 ( table 3 , figure 1a ) . figure 1a shows that right heart failure patients had a lower petco2 at any given vd / vt . these results demonstrate that patients with right heart failure had more ventilation at given co2 discharge . considering there was no difference in respiratory frequency or ve , the lower petco2 was due to hyperventilation in alveolus with well - perfusion and hypoperfusion of well ventilated alveolus in patients with right heart failure . the lower petco2 could explain the higher ve / vco2 in patients with right heart failure . the higher ve / vco2 showed that right heart failure patients had lower ventilation efficiency . this result means that there was no difference in v / q mismatching at rest in the 2 groups . petco2 was lower in both chf and pah , reflecting the ventilation impairment [ 3,8,2025 ] . we found that right heart failure patients had a lower petco2 during exercise ( table 3 ) . the reason for the lower peak petco2 during exercise in patients with right heart failure was similar to the reason for lower petco2 at rest . sun et al .   found that patients with pah had an eis resulting in abrupt decreased petco2 , had increased peto2 , and increased ve / vco2 ratio during exercise . the abrupt curve of right heart failure demonstrated that patients with right heart failure had eis ( figure 1b ) . we found that patients with right heart failure had significantly higher peak vd / vt ratio ( table 3 ) . figure 1c shows that most patients with right heart failure had a lower peak petco2 and a higher ve / vco2 slope . these results demonstrate that patients with right heart failure had severe v / q mismatching at peak exercise . this means that primary pulmonary vesicular damage played a greater role in v / q mismatching during exercise than did pulmonary congestion . moreover , the eis was involved in the higher vd / vt in patients with right heart failure . ve / vco2 and ve / vco2 slope are important to reflect disease severity and prognosis in chf and pah , and reflect v / q mismatching in pah . we found that peak ve / vco2 and ve / vco2 slope were higher in patients with right heart failure . these results demonstrate that patients with right heart failure had more severe ventilation inefficiency and gas exchange abnormality compared to patients with left heart failure . these results were due to lower peak petco2 and higher peak vd / vt in right heart failure patients . we found that patients with right heart failure had higher absolute values of petco2 and ve / vco2 from rest to peak exercise ( table 2 and 3 ) . these results show that right heart failure patients had larger changes of pulmonary function from rest to exercise . the larger change of petco2 demonstrates that patients with right heart failure had more severe hyperventilation from rest to exercise . this should be attributed to more complex ventilation drive in pah , including exercise - induced hypoxia and eis . we found that patients with right heart failure had worse ventilation efficiency , severe v / q mismatching , and gas exchange abnormality , even without differences in peak vo2 . it was a single - center study and demographic differences were detected between the 2 groups . the etiology of heart failure in the 2 groups resulted in differences of sex and age . because there was no control group , we could not confirm a normal breathing pattern at rest . we could not perform invasive hemodynamic testing in all patients , which influenced our evaluation of left heart failure . we merged the 4 disease classes into 2 groups because there were not enough patients with class iv nyha right heart failure . pulmonary function changes compatible with restrictive lung disease are observed in most patients with severe chf , and findings compatible with airway obstruction are common in patients with right heart failure caused by idiopathic pulmonary arterial hypertension ( ipah ) . right heart failure patients had a lower petco2 ( table 3 , figure 1a ) . figure 1a shows that right heart failure patients had a lower petco2 at any given vd / vt . these results demonstrate that patients with right heart failure had more ventilation at given co2 discharge . considering there was no difference in respiratory frequency or ve , the lower petco2 was due to hyperventilation in alveolus with well - perfusion and hypoperfusion of well ventilated alveolus in patients with right heart failure . the lower petco2 could explain the higher ve / vco2 in patients with right heart failure . the higher ve / vco2 showed that right heart failure patients had lower ventilation efficiency . this result means that there was no difference in v / q mismatching at rest in the 2 groups . petco2 was lower in both chf and pah , reflecting the ventilation impairment [ 3,8,2025 ] . we found that right heart failure patients had a lower petco2 during exercise ( table 3 ) . the reason for the lower peak petco2 during exercise in patients with right heart failure was similar to the reason for lower petco2 at rest . sun et al .   found that patients with pah had an eis resulting in abrupt decreased petco2 , had increased peto2 , and increased ve / vco2 ratio during exercise . the abrupt curve of right heart failure demonstrated that patients with right heart failure had eis ( figure 1b ) . we found that patients with right heart failure had significantly higher peak vd / vt ratio ( table 3 ) . figure 1c shows that most patients with right heart failure had a lower peak petco2 and a higher ve / vco2 slope . these results demonstrate that patients with right heart failure had severe v / q mismatching at peak exercise . this means that primary pulmonary vesicular damage played a greater role in v / q mismatching during exercise than did pulmonary congestion . moreover , the eis was involved in the higher vd / vt in patients with right heart failure . ve / vco2 and ve / vco2 slope are important to reflect disease severity and prognosis in chf and pah , and reflect v / q mismatching in pah . we found that peak ve / vco2 and ve / vco2 slope were higher in patients with right heart failure . these results demonstrate that patients with right heart failure had more severe ventilation inefficiency and gas exchange abnormality compared to patients with left heart failure . these results were due to lower peak petco2 and higher peak vd / vt in right heart failure patients . we found that patients with right heart failure had higher absolute values of petco2 and ve / vco2 from rest to peak exercise ( table 2 and 3 ) . these results show that right heart failure patients had larger changes of pulmonary function from rest to exercise . the larger change of petco2 demonstrates that patients with right heart failure had more severe hyperventilation from rest to exercise . this should be attributed to more complex ventilation drive in pah , including exercise - induced hypoxia and eis . we found that patients with right heart failure had worse ventilation efficiency , severe v / q mismatching , and gas exchange abnormality , even without differences in peak vo2 . it was a single - center study and demographic differences were detected between the 2 groups . the etiology of heart failure in the 2 groups resulted in differences of sex and age . because there was no control group , we could not confirm a normal breathing pattern at rest . we could not perform invasive hemodynamic testing in all patients , which influenced our evaluation of left heart failure . we merged the 4 disease classes into 2 groups because there were not enough patients with class iv nyha right heart failure . the differences in pulmonary function at rest were due to different breathing patterns and worse gas exchange in patients with right heart failure . the differences during exercise were due to severe v / q mismatching , eis , alveolar ventilation disorder , and oxygenation dysfunction secondary to pulmonary vascular damage in patients with right heart failure .