title: Myocardial blood flow and its transit time, oxygen utilization, and efficiency of highly endurance-trained human heart.
abstract: Highly endurance-trained athlete's heart represents the most extreme form of cardiac adaptation to physical stress, but its circulatory alterations remain obscure. In the present study, myocardial blood flow (MBF), blood mean transit time (MTT), oxygen extraction fraction (OEF) and consumption (MVO2), and efficiency of cardiac work were quantified in highly trained male endurance athletes and control subjects at rest and during supine cycling exercise using [(15)O]-labeled radiotracers and positron emission tomography. Heart rate and MBF were lower in athletes both at rest and during exercise. OEF increased in response to exercise in both groups, but was higher in athletes (70 ± 21 vs. 63 ± 11 % at rest and 86 ± 13 vs. 73 ± 10 % during exercise). MTT was longer and vascular resistance higher in athletes both at rest and during exercise, but arterial content of 2,3-diphosphoglycerate (oxygen affinity) was unchanged. MVO2 per gram of myocardium trended (p = 0.08) lower in athletes both at rest and during exercise, while myocardial efficiency of work and MVO2 per beat were not different between groups. Arterial levels of free fatty acids were ~twofold higher in athletes likely leading to higher myocardial fatty acid oxidation and hence oxygen cost, which may have blunted the bradycardia-induced decrease in MVO2. Finally, the observed group differences in MBF, OEF, MTT and vascular resistance remained significant also after they were controlled for differences in MVO2. In conclusion, in highly endurance-trained human heart, increased myocardial blood transition time enables higher oxygen extraction levels with a lower myocardial blood flow and higher vascular resistance. These physiological adaptations to exercise training occur independently of the level of oxygen consumption and together with training-induced bradycardia may serve as mechanisms to increase functional reserve of the human heart.
authors.affiliation: Turku PET Centre, University of Turku and Turku University Hospital, PO Box 52, 20521, Turku, Finland, ilkka.heinonen@utu.fi.
authors.forename: Ilkka
authors.initials: I
authors.lastname: Heinonen
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Kudomi
authors.forename: Jukka
authors.initials: J
authors.lastname: Kemppainen
authors.forename: Antti
authors.initials: A
authors.lastname: Kiviniemi
authors.forename: Tommi
authors.initials: T
authors.lastname: Noponen
authors.forename: Matti
authors.initials: M
authors.lastname: Luotolahti
authors.forename: Pauliina
authors.initials: P
authors.lastname: Luoto
authors.forename: Vesa
authors.initials: V
authors.lastname: Oikonen
authors.forename: Hannu T
authors.initials: HT
authors.lastname: Sipilä
authors.forename: Jaakko
authors.initials: J
authors.lastname: Kopra
authors.forename: Ilkka
authors.initials: I
authors.lastname: Mononen
authors.forename: Dirk J
authors.initials: DJ
authors.lastname: Duncker
authors.forename: Juhani
authors.initials: J
authors.lastname: Knuuti
authors.forename: Kari K
authors.initials: KK
authors.lastname: Kalliokoski
mesh_terms: D019794:2,3-Diphosphoglycerate / Q000097:blood; D000222:Adaptation, Physiological; D000328:Adult; D001642:Bicycling; D015415:Biomarkers / Q000097:blood; D002302:Cardiac Output; D016022:Case-Control Studies; D003326:Coronary Circulation; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006339:Heart Rate; D006801:Humans; D008297:Male; D055414:Myocardial Perfusion Imaging / Q000379:methods; D009206:Myocardium / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D010807:Physical Endurance; D049268:Positron-Emission Tomography; D013997:Time Factors; D014655:Vascular Resistance; D016277:Ventricular Function, Left
chemical_list: D015415:Biomarkers; D005230:Fatty Acids, Nonesterified; D019794:2,3-Diphosphoglycerate; D010100:Oxygen