***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: AIMS Exercise limitation is common post-Fontan . Hybrid X-ray and magnetic resonance imaging ( XMR ) catheterization allows haemodynamic assessment by means of measurement of ventricular volumes and flow in major vessels with simultaneous invasive pressures . We aim to assess haemodynamic response to stress in patients with hypoplastic left heart syndrome ( HLHS ) post-Fontan . METHODS AND RESULTS Prospect i ve study of 13 symptomatic children ( NHYA 2 ) with HLHS post-Fontan using XMR catheterization .  Three conditions were applied : baseline ( Stage 1 ) , dobutamine at 10 µg/kg/min ( Stage 2 ) , and dobutamine at 20 µg/kg/min ( Stage 3 ) . Seven consecutive patients received inhaled nitric oxide ( iNO ) at peak stress . Control MRI data were from normal healthy adults . In the HLHS  patients , baseline mean pulmonary vascular resistance ( PVR ) was 1.51 ± 0.59 WU m(2 ) and aortopulmonary collateral flow was 17.7 ± 13.6 % of systemic cardiac output . Mean right ventricular end-diastolic pressure was 6.7 ± 2.5 mmHg which did not rise with stress . Cardiac index ( CI ) increased at Stage 2 in HLHS ( 40 % ) and controls ( 61 % ) but continued to increase at Stage 3 only in controls ( 19 % ) but not in HLHS . The blunted rise in CI in HLHS was due to a continuing fall in end-diastolic volume throughout stress , with no significant change in PVR or CI at peak stress in response to iNO . CONCLUSION Cardiac output post-Fontan in HLHS at peak stress is blunted due to a limitation in preload which is not responsive to inhaled pulmonary vasodilators in the setting of normal PVR Introduction The aim of this multicenter , prospect i ve study was to evaluate the long-term prognostic value of low-dose dobutamine stress echocardiography ( LDDSE ) in patients with aortic stenosis ( AS ) and depressed left ventricular ( LV ) function . Material and methods The study group comprised 39 patients ( 34 male , mean age 59 ±13 years ) with AS ( peak gradient > 25 mm Hg ) , LV ejection fraction ( LVEF ) ≤ 45 % and low transaortic gradient ( peak gradient ≤ 45 mm Hg , mean gradient ≤ 35 mm Hg ) . The qualification for subsequent therapeutic procedures was based on generally accepted indications . All patients underwent LDDSE and coronary angiography . Twelve months after LDDSE patients underwent control resting echocardiography and clinical evaluation . Results Twenty-seven ( 69.2 % ) patients had preserved contractile reserve . In this subgroup , true-severe AS was diagnosed in 12 patients , whereas pseudo-severe AS was found in 15 patients . Nine patients with true-severe AS , 2 patients with pseudo-severe AS and 7 patients without contractile reserve were referred for surgical treatment . The independent risk factors of death during follow-up were : aortic valve area ( AVA ) at peak stress < 0.8 cm2 ( OR 1.4 ; p = 0.003 ) and LVEF at rest < 35 % ( OR 6.8 ; p = 0.05 ) . The independent risk factors of composite end-point ( death or myocardial infa rct ions or pulmonary edema ) were : AVA at stress < 0.8 cm2 ( OR 4.0 ; p = 0.03 ) , absence of AVA increase during LDDSE ( OR 5.7 ; p = 0.005 ) , absence of contractile reserve ( OR 4.5 ; p = 0.01 ) and presence of significant CAD ( OR 6.9 ; p = 0.02 ) . Conclusions In patients with AS and depressed LVEF  , LDDSE is a useful tool for long-term risk stratification Background The prognostic value of dobutamine stress hemodynamic data in the setting of low‐gradient aortic stenosis has been addressed in small , single‐center studies . Larger studies are needed to define the criteria for selecting the patients who will benefit from valve replacement . Methods and Results Six centers prospect ively enrolled 136 patients with aortic stenosis ( 96 men ; median age , 72 years [ range , 65 to 77 years ] ; median aortic valve area , 0.7 cm2 [ range , 0.6 to 0.8 ] ; mean transaortic gradient , 29 mm Hg [ range , 23 to 34 mm Hg ] ; cardiac index , 2.11 L min‐1 m‐2 [ range , 1.75 to 2.55 L min‐1 m‐2 ] ) . Left ventricular contractile reserve on the dobutamine stress Doppler study was present in 92 patients ( group I ) and absent in 44 patients ( group II ) . Operative mortality was 5 % ( 3 of 64 patients ) in group I compared with 32 % ( 10 of 31 patients ) in group II ( P=0.0002 ) . Predictors for operative mortality were the lack of contractile reserve ( odds ratio , 10.9 ; 95 % confidence interval [ CI ] , 2.6 to 43.4 ; P=0.001 ) and a mean transaortic gradient ≤20 mm Hg ( odds ratio , 4.7 ; 95 % CI , 1.1 to 21.0 ; P=0.04 ) . Predictors for long‐term survival were valve replacement ( hazard ratio , 0.30 ; 95 % CI , 0.17 to 0.53 ; P=0.001 ) and left ventricular contractile reserve ( hazard ratio , 0.40 ; 95 % CI , 0.23 to 0.69 ; P=0.001 ) . Conclusions In the setting of low‐gradient aortic stenosis , surgery seems beneficial for most of the patients with left ventricular contractile reserve . In contrast , the postoperative outcome of patients without reserve is compromised by a high operative mortality . Thus , dobutamine stress Doppler hemodynamics may be factored into the risk‐benefit analysis for each patient . ( Circulation . 2003;108:319‐324 . PURPOSE This study compared cardiac hemodynamics during supine cycle ergometry and dobutamine stress . METHODS Thirty-two healthy volunteers ( 19 female , 13 male , 23.5 + /- 3.5 yr old ) completed respective tests on separate days and in r and om order . Heart rate , blood pressure , and cardiac output were recorded at baseline and peak stress . Echocardiographic measures included left ventricular end-diastolic dimension , fractional shortening , heart rate corrected velocity of circumferential fiber shortening , end-systolic wall stress , and the difference between measured and predicted fiber shortening for measured wall stress . RESULTS Compared with peak exercise , dobutamine infusion result ed in lower cardiac output ( 12 + /- 2 vs 16 + /- 4 l x min(-1 ) , P < 0.0001 ) , heart rates ( 163 + /- 7 vs 175 + /- 12 beats x min(-1 ) , P < 0.0001 ) , and systolic blood pressure ( 160 + /- 22 vs 185 + /- 20 mm Hg , P < or = 0.0001 ) . Echocardiography demonstrated smaller left ventricular end-diastolic dimension ( 4.2 + /- 0.7 vs 4.5 + /- 0.7 cm , P = 0.013 ) , higher fractional shortening ( 0.55 + /- 0.07 vs 0.50 + /- 0.06 % , P < 0.001 ) , higher VCFc ( 2.07 + /- 0.36 vs 1.54 + /- 0.20 circs x s(-1 ) , P < 0.001 ) higher VCFdiff ( 0.94 + /- 0.35 vs 0.48 + /- 0.20 circs x s(-1 ) , P < 0.001 ) , and lower end-systolic wall stress ( 25 + /- 11 vs 42 + /- 16 g x cm(-2 ) , P < 0.001 ) . The stress-velocity relationship during dobutamine demonstrated higher y-intercept and steeper slope , indicating greater load-independent contractility . CONCLUSION The cardiovascular adaptation to exercise and dobutamine stress differ significantly . Cardiac output during peak exercise is greater than during peak dobutamine secondary to increased heart rate and stroke volume . Despite a greater increase in contractility and decrease in afterload , a smaller increase in cardiac output during dobutamine stress may be secondary to limited ventricular preload OBJECTIVE : To test the feasibility of creating a valid and reliable checklist with the following features : appropriate for assessing both r and omised and non-r and omised studies ; provision of both an overall score for study quality and a profile of scores not only for the quality of reporting , internal validity ( bias and confounding ) and power , but also for external validity . DESIGN : A pilot version was first developed , based on epidemiological principles , review s , and existing checklists for r and omised studies . Face and content validity were assessed by three experienced review ers and reliability was determined using two raters assessing 10 r and omised and 10 non-r and omised studies . Using different raters , the checklist was revised and tested for internal consistency ( Kuder-Richardson 20 ) , test-retest and inter-rater reliability ( Spearman correlation coefficient and sign rank test ; kappa statistics ) , criterion validity , and respondent burden . MAIN RESULTS : The performance of the checklist improved considerably after revision of a pilot version . The Quality Index had high internal consistency ( KR-20 : 0.89 ) as did the subscales apart from external validity ( KR-20 : 0.54 ) . Test-retest ( r 0.88 ) and inter-rater ( r 0.75 ) reliability of the Quality Index were good . Reliability of the subscales varied from good ( bias ) to poor ( external validity ) . The Quality Index correlated highly with an existing , established instrument for assessing r and omised studies ( r 0.90 ) . There was little difference between its performance with non-r and omised and with r and omised studies . Raters took about 20 minutes to assess each paper ( range 10 to 45 minutes ) . CONCLUSIONS : This study has shown that it is feasible to develop a checklist that can be used to assess the method ological quality not only of r and omised controlled trials but also non-r and omised studies . It has also shown that it is possible to produce a checklist that provides a profile of the paper , alerting review ers to its particular method ological strengths and weaknesses . Further work is required to improve the checklist and the training of raters in the assessment of external validity Exercise testing has an established role in the evaluation of patients with valvular heart disease and can aid clinical decision making . Because symptoms may develop slowly and indolently in chronic valve diseases and are often not recognized by patients and their physicians , the symptomatic , blood pressure , and electrocardiographic responses to exercise can help identify patients who would benefit from early valve repair or replacement . In addition , stress echocardiography has emerged as an important component of stress testing in patients with valvular heart disease , with relevant established and potential applications . Stress echocardiography has the advantages of its wide availability , low cost , and versatility for the assessment of disease severity . The versatile applications of stress echocardiography can be tailored to the individual patient with aortic or mitral valve disease , both before and after valve replacement or repair . Hence , exercise-induced changes in valve hemodynamics , ventricular function , and pulmonary artery pressure , together with exercise capacity and symptomatic responses to exercise , provide the clinician with diagnostic and prognostic information that can contribute to subsequent clinical decisions . Nevertheless , there is a lack of convincing evidence that the results of stress echocardiography lead to clinical decisions that result in better outcomes , and therefore large-scale prospect i ve r and omized studies focusing on patient outcomes are needed in the future To clarify the influence of body position on exercise prescription , 14 men ( mean age + /- st and ard deviation 60.0 + /- 6.1 years ) with coronary artery disease who underwent r and omized recumbent and upright cycle ergometer tests to volitional fatigue were studied . At 100 watts , heart rate ( HR ) , systolic blood pressure , oxygen consumption ( VO2 ) , rate pressure product and rating of perceived exertion were greater ( p less than 0.05 ) in the upright than in the recumbent position . At peak exercise , however , these variables were not significantly different . Regressions of relative HR versus VO2 for recumbent and upright cycle ergometry were comparable : y = 1.24x - 32.7 and y = 1.26x - 31.5 , respectively , where y = % maximal VO2 , and x = % maximal HR . These findings indicate that recumbent exercise prescriptions may be based on the peak HR and VO2 values obtained during upright cycle ergometry , and vice versa . However , differences in the cardiorespiratory responses at submaximal exercise preclude the interchangeability of upright and recumbent training work rates INTRODUCTION Despite high error ranges , age-predicted maximal heart rate ( APMHR ) is frequently used to gauge the achievement of adequate effort during an exercise test . The current analysis revisits this 
    Output:
    
HR increase and age were inversely correlated at high stress intensities .
Conclusion : This systematic review and meta- analysis presents pooled hemodynamic changes under light , moderate and high intensity exercise and pharmacological stress , while considering the potential influence of age .