***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 
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    ***EXAMPLES*** 
    Input: A multicenter , double-blind , r and omized study was conducted to assess the effect of caffeine on regadenoson stress myocardial perfusion imaging ( MPI ) . Subjects with a high likelihood of coronary artery disease underwent a rest single-photon emission computed tomography MPI on day 1 ( MPI-1 ) and a stress MPI with regadenoson on day 3 ( MPI-2 ) . Individuals with ≥1 segment with a reversible defect received double-blind caffeine tablets ( 200 or 400 mg ) or placebo 90 min before a repeat regadenoson stress MPI ( MPI-3 ) on day 5 . Overall , 207 subjects completed the study  ( caffeine 200 mg , n = 70 ; caffeine 400 mg , n = 71 ; placebo , n = 66 ) . The mean number of segments with reversible defects decreased from MPI-2 to MPI-3 in the caffeine 200 and 400 mg groups versus no significant change in the placebo group [ mean ± st and ard deviation : −0.61 ± 1.097 , −0.62 ± 1.367 , and 0.12 ± 0.981 , respectively ( overall treatment effect , P < 0.001 ) ] . The majority of subjects who received caffeine shifted to a lower ischemia size category from MPI-2 to MPI-3 , with no clear pattern observed in subjects who received placebo . For caffeine exposed patients with ≥3 segments with reversible defects at MPI-2 , 21/23 had fewer detected at MPI-3 . Both the 200 and 400 mg doses of caffeine significantly reduced the number of segments with reversible defects detected by regadenoson stress MPI Objectives This prospect i ve study investigated the effects of caffeine ingestion on the extent of adenosine-induced perfusion abnormalities during myocardial perfusion imaging ( MPI ) . Methods Thirty patients with inducible perfusion abnormalities on st and ard ( caffeine-abstinent ) adenosine MPI  underwent repeat testing with supplementary coffee intake . Baseline and test MPIs were assessed for stress percent defect , rest percent defect , and percent defect reversibility . Plasma levels of caffeine and metabolites were assessed on both occasions and correlated with MPI findings . Results Despite significant increases in caffeine [ mean difference 3,106 μg/L ( 95 % CI 2,460 to 3,752 μg/L ; P < .001 ) ] and metabolite concentrations over a wide range , there was no statistically significant change in stress percent defect and percent defect reversibility between the baseline and test scans . The increase in caffeine concentration between the baseline and the test phases did not affect percent defect reversibility ( average change −0.003 for every 100 μg/L increase ; 95 % CI −0.17 to 0.16 ; P = .97 ) . Conclusion There was no significant relationship between the extent of adenosine-induced coronary flow heterogeneity and the serum concentration of caffeine or its principal metabolites . Hence , the stringent requirements for prolonged abstinence from caffeine before adenosine MPI — based on limited studies —appear ill-founded We investigated the effects of caffeine intake on fractional flow reserve ( FFR ) values measured using intravenous adenosine triphosphate ( ATP ) before cardiac catheterization . Caffeine is a competitive antagonist for adenosine receptors ; however , it is unclear whether this antagonism affects FFR values . Patients were evenly r and omized into 2 groups preceding the FFR study . In the caffeine group ( n = 15 ) , participants were given coffee containing 222 mg of caffeine 2 h before the catheterization . In the non-caffeine group ( n = 15 ) , participants were instructed not to take any caffeine-containing drinks or foods for at least 12 h before the catheterization . FFR was performed in patients with more than intermediate coronary stenosis using the intravenous infusion of ATP at 140 μg/kg/min ( normal dose ) and 170 μg/kg/min ( high dose ) , and the intracoronary infusion of papaverine . FFR was followed for 30 s after maximal hyperemia . In the non-caffeine group , the FFR values measured with ATP infusion were not significantly different from those measured with papaverine infusion . However , in the caffeine group , the FFR values were significantly higher after ATP infusion than after papaverine infusion ( P = 0.002 and P = 0.007 , at normal and high dose ATP vs. papaverine , respectively ) . FFR values with ATP infusion were significantly increased 30 s after maximal hyperemia ( P = 0.001 and P < 0.001 for normal and high dose ATP , respectively ) . The stability of the FFR values using papaverine showed no significant difference between the 2 groups . Caffeine intake before the FFR study affected FFR values and their stability . These effects could not be reversed by an increased ATP dose It is believed that caffeine attenuates the coronary hyperemic response to adenosine by blocking the A2a receptors . We studied the effect of caffeine on adenosine-induced myocardial hyperemia measured by fractional flow reserve after intracoronary adenosine administration . Fractional flow reserve was not affected by intravenous caffeine infusion at a dose that was comparable to oral consumption Adenosine is widely used as a vasodilator agent in myocardial perfusion imaging . Caffeine inhibits the effect , but the time of caffeine abstinence needed is under discussion and varies from 12 to 24 h. Therefore , our aim was to examine whether the time of caffeine abstinence affects the hyperaemic response using quantification of coronary sinus flow ( CSF ) with cardiac magnetic resonance ( CMR ) during adenosine infusion Background Adenosine stress cardiovascular magnetic resonance ( CMR ) can detect significant coronary artery stenoses with high diagnostic accuracy . Caffeine is a nonselective competitive inhibitor of adenosine2A-receptors , which might hamper the vasodilator effect of adenosine stress , potentially yielding false-negative results . Much controversy exists about the influence of caffeine on adenosine myocardial perfusion imaging . Our study sought to investigate the effects of caffeine on ischemia detection in patients with suspected or known coronary artery disease ( CAD ) undergoing adenosine stress CMR . Methods Thirty patients with evidence of myocardial ischemia on caffeine-naïve adenosine stress CMR were prospect ively enrolled and underwent repeat adenosine stress CMR after intake of 200 mg caffeine . Both CMR exams were then compared for evaluation of ischemic burden . Results Despite intake of caffeine , no conversion of a positive to a negative stress study occurred on a per patient basis . Although we found significant lower ischemic burden in CMR exams with caffeine compared to caffeine-naïve CMR exams , absolute differences varied only slightly ( 1 segment based on a 16-segment model , 3 segments on a 60-segment model , and 1 ml in total ischemic myocardial volume , p < 0.001 each ) . Moreover , no relevant ischemia ( ≥2 segments in a 16-segment model ) was missed by prior ingestion of caffeine . Conclusions Although differences were small and no relevant myocardial ischemia had been missed , prior consumption of caffeine led to significant reduction of ischemic burden , and might lower the high diagnostic and prognostic value of adenosine stress CMR . Therefore , we suggest that patients should still refrain from caffeine prior adenosine stress CMR tests Purpose To examine factors associated with false‐negative cardiovascular magnetic resonance ( MR ) perfusion studies within the large prospect i ve Clinical Evaluation of MR imaging in Coronary artery disease ( CE‐MARC ) study population . Myocardial perfusion MR has excellent diagnostic accuracy to detect coronary heart disease ( CHD ) . However , causes of false‐negative MR perfusion studies are not well understood . Material s and Methods CE‐MARC prospect ively recruited patients with suspected CHD and m and ated MR , myocardial perfusion scintigraphy , and invasive angiography .  This sub analysis identified all patients with significant coronary stenosis by quantitative coronary angiography ( QCA ) and MR perfusion ( 1.5 T , T 1‐weighted gradient echo ) , using the original blinded image read . We explored patient and imaging characteristics related to false‐negative or true‐positive MR perfusion results , with reference to QCA . Multivariate regression analysis assessed the likelihood of false‐negative MR perfusion according to four characteristics : poor image quality , triple‐vessel disease , inadequate hemodynamic response to adenosine , and Duke jeopardy score ( angiographic myocardium‐at‐risk score ) . Results In all , 265 ( 39 % ) patients had significant angiographic disease ( mean age 62 , 79 % male ) . Thirty‐five ( 5 % ) had false‐negative and 230 ( 34 % ) true‐positive MR perfusion . Poor MR perfusion image quality , triple‐vessel disease , and inadequate hemodynamic response were similar between false‐negative and true‐positive groups ( odds ratio , OR [ 95 % confidence interval , CI ] : 4.1 ( 0.82–21.0 ) , P = 0.09 ; 1.2 ( 0.20–7.1 ) , P = 0.85 , and 1.6 ( 0.65–3.8 ) , P = 0.31 , respectively ) . Mean Duke jeopardy score was significantly lower in the false‐negative group ( 2.6 ± 1.7 vs. 5.4 ± 3.0 , OR 0.34 ( 0.21–0.53 ) , P < 0.0001 ) . Conclusion False‐negative cardiovascular MR perfusion studies are uncommon , and more common in patients with lower angiographic myocardium‐at‐risk . In CE‐MARC , poor image quality , triple‐vessel disease , and inadequate hemodynamic response were not significantly associated with false‐negative MR perfusion . J. MAGN . RESON . IMAGING 2016;43:566–573 The coronary vasodilatory effect of dipyridamole is competitively blocked by caffeine . The purpose s of this study were to ( 1 ) assess the incidence of having detectable serum caffeine and ( 2 ) evaluate whether an intensive caffeine history screening strategy was superior to routine history screening before dipyridamole myocardial perfusion imaging . One hundred ninety-four patients who were r and omized to an intensive or a routine screening history strategy were prospect ively evaluated .  Serum caffeine levels were determined in all patients . Outcomes data , including death , nonfatal myocardial infa rct ion , and history of revascularization , were obtained at 24 months . Nearly 1 in 5 patients ( 19 % ) who screened negative by history had detectable serum caffeine . In patients who screened negative by history , there was no statistically significant difference in the percentage of caffeine seropositivity between the intensive and routine arms ( 16 % vs 22 % , respectively , p = 0.31 ) . The incidence of combined end points of death , myocardial infa rct ion , or revascularization was 22.9 % and 7.3 % in patients with and without detectable serum caffeine , respectively ( p = 0.01 ) . In conclusion , despite initial negative results on screening by history , a considerably high percentage of patients had positive  serum caffeine levels . These results do not support the use of an intensive screening strategy . Detectable serum caffeine was associated with a higher incidence of adverse outcomes Background . Patients with reactive airways are at risk for adenosine-induced bronchoconstriction , mediated via A2B and /or A3 adenosine receptors . Methods and Results . In this r and omized , double-blind , placebo-controlled crossover trial , we examined the safety of regadenoson , a selective adenosine A2A receptor agonist , in patients with moderate chronic obstructive pulmonary disease ( COPD ) ( n=38 ) and patients with severe COPD ( n=11 ) with a baseline mean forced expiratory volume in 1 second ( FEV1 ) of 1.74±0.50 L and 1.0±0.35 L , respectively , 37 % of whom had dyspnea during activities of daily living . Patients receiving glucocorticoids or oxygen and those with pretreatment wheezing were included . Short-acting bronchodilators were withheld for at least 8 hours before treatment . No differences emerged between regadenoson and placebo on multiple lung function parameters , including repeated FEV1 and forced vital capacity , respiratory rate , pulmonary examinations , and oxygen saturation . The mean maximum decline in FEV1 was 0.11±0.02 L and 0.12±0.02 L ( P=.55 ) in patients after regadenoson and placebo , respectively , and new-onset wheezing was observed in 6 % and 12 % , respectively ( P=.33 ) . No patient required acute treatment with bronchodilators or oxygen . Conclusions . This pilot study showed the overall safety of regadenoson in 49 compromised out patients with clinical 
    Output:
    
The available data indicate a significant influence of recent caffeine intake on cardiac perfusion measurements during adenosine and dipyridamole induced hyperemia .