title: Atrial aspiration from pulmonary and caval veins is caused by ventricular contraction and secures 70% of the total stroke volume independent of resting heart rate and heart size.
abstract: BACKGROUND
  Whereas ventricular filling has been extensively studied and debated, atrial filling is less well characterized. Therefore, the aim of this study was to quantify atrial filling secured during ventricular diastole and systole, and to investigate whether atrial filling depends on heart rate (HR) and total heart volume (THV).
  
  
  METHODS
  Thirty-two athletes (16 women) and 32 normal subjects (16 women) underwent cardiac magnetic resonance imaging. Cardiac volumes and atrioventricular plane displacement (AVPD) were determined. Longitudinal and radial contribution to stroke volume was calculated using planimetry and used to determine diastolic and systolic atrial filling.
  
  
  RESULTS
  Atrial filling during ventricular diastole was 29 ± 10% of the total stroke volume, and during ventricular systole atrial filling was 68 ± 8% of the total stroke volume. There were no differences between groups of different HR (P = 0·70 and P = 0·41 for diastolic and systolic filling, respectively) or THV (P = 0·44 and P = 0·46 for diastolic and systolic filling, respectively). Systolic atrial filling was strongly correlated to longitudinal ventricular pumping (R = 0·76, P<0·001).
  
  
  CONCLUSIONS
  This study demonstrated that in healthy humans at rest, approximately 30% of the total stroke volume enters the atria during ventricular diastole and approximately 70% during systole, independent of heart rate (HR) or heart size. The atria are filled through suction driven by ventricular longitudinal contraction which aspirates blood from the pulmonary and caval veins. As 70% of the atrial filling occurs during ventricular emptying, the heart volume remains relatively constant over the cardiac cycle, which minimizes pulling on surrounding tissues and therefore optimizes energy expenditure.
authors.affiliation: Department of Clinical Physiology, Lund University, Skåne University Hospital Lund, Lund, Sweden.
authors.forename: K
authors.initials: K
authors.lastname: Steding-Ehrenborg
authors.forename: M
authors.initials: M
authors.lastname: Carlsson
authors.forename: S
authors.initials: S
authors.lastname: Stephensen
authors.forename: H
authors.initials: H
authors.lastname: Arheden
mesh_terms: D000328:Adult; D016275:Atrial Function; D016279:Atrial Function, Left; D016280:Atrial Function, Right; D059267:Cardiomegaly, Exercise-Induced; D004734:Energy Metabolism; D005080:Exercise Test; D005260:Female; D006339:Heart Rate; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009200:Myocardial Contraction; D015588:Observer Variation; D011237:Predictive Value of Tests; D011667:Pulmonary Veins / Q000502:physiology*; D015203:Reproducibility of Results; D013318:Stroke Volume; D014682:Vena Cava, Inferior / Q000502:physiology*; D014683:Vena Cava, Superior / Q000502:physiology*; D016276:Ventricular Function; D016277:Ventricular Function, Left; D016278:Ventricular Function, Right; D055815:Young Adult