title: Recovery mismatch between myocardial blood flow and cardiac workload after physical exercise: a positron emission tomography study.
abstract: OBJECTIVE
  We studied the interrelation between oxygen consumption and myocardial blood flow (MBF) during recovery. MBF is directly dependent on oxygen consumption. The latter is linearly related to the heart rate-blood pressure product (RPP, bpm × mmHg), an index reflecting external cardiac work. In the immediate post-exercise period, cardiac output decreases considerably. This is expected to be paralleled by a rapid fall in oxygen demand, rendering ischaemia unlikely. Thus, the phenomenon of ST-segment depression during recovery remains unexplained.
  
  
  RESULTS
  (15)O-labelled water and positron emission tomography were used to measure MBF in 14 young healthy volunteers (mean age 27 ± 3 years) during the following study conditions: (i) at rest, (ii) during a steady submaximal supine bicycle exercise stress within the scanner, and (iii) during recovery immediately after cessation of exercise. During recovery, RPP decreased by 43% (18 768 ± 1337 vs. 11 652 ± 3224, P < 0.001). In contrast, the associated decrease in MBF (2.52 ± 0.52 vs. 1.93 ± 0.50 mL/min/g, P < 0.001) and perfusion reserve (2.68 ± 0.51 vs. 2.03 ± 0.42, P < 0.001) was significantly less pronounced (-24%, P < 0.01), indicating a relative delay in MBF recovery compared with cardiac work load.
  
  
  CONCLUSIONS
  The mismatch between a rapid decrease in cardiac workload but preserved hyperaemic response early after cessation of physical exercise suggests an uncoupling of cardiac work and MBF during recovery.
authors.affiliation: Nuclear Medicine, University Hospital Zurich, Ramistrasse 100, CH-8091 Zurich, Switzerland.
authors.forename: Patrick T
authors.initials: PT
authors.lastname: Siegrist
authors.affiliation: Nuclear Medicine, University Hospital Zurich, Ramistrasse 100, CH-8091 Zurich, Switzerland.
authors.forename: Pascal
authors.initials: P
authors.lastname: Koepfli
authors.affiliation: Nuclear Medicine, University Hospital Zurich, Ramistrasse 100, CH-8091 Zurich, Switzerland.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Namdar
authors.affiliation: Nuclear Medicine, University Hospital Zurich, Ramistrasse 100, CH-8091 Zurich, Switzerland.
authors.forename: Aju P
authors.initials: AP
authors.lastname: Pazhenkottil
authors.affiliation: Nuclear Medicine, University Hospital Zurich, Ramistrasse 100, CH-8091 Zurich, Switzerland.
authors.forename: Rene
authors.initials: R
authors.lastname: Nkoulou
authors.affiliation: Cardiology, University Hospital Zurich, Ramistrasse 100, CH-8091 Zurich, Switzerland.
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Lüscher
authors.affiliation: Nuclear Medicine, University Hospital Zurich, Ramistrasse 100, CH-8091 Zurich, Switzerland pak@usz.ch.
authors.forename: Philipp A
authors.initials: PA
authors.lastname: Kaufmann
mesh_terms: D000328:Adult; D002302:Cardiac Output; D003326:Coronary Circulation; D005080:Exercise Test; D005260:Female; D005500:Follow-Up Studies; D064368:Healthy Volunteers; D006321:Heart / Q000000981:diagnostic imaging*; D006339:Heart Rate; D006801:Humans; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D010101:Oxygen Consumption; D049268:Positron-Emission Tomography / Q000379:methods*; D011237:Predictive Value of Tests; D020127:Recovery of Function; D012016:Reference Values; D012146:Rest; D012680:Sensitivity and Specificity
keywords: Myocardial blood flow; PET; Physical exercise; Recovery