title: Prolonged mean VO2 response time in systolic heart failure: an indicator of impaired right ventricular-pulmonary vascular function.
abstract: BACKGROUND
  In patients with left ventricular systolic dysfunction (LVSD), the rate at which oxygen uptake (VO2) increases on initiation of exercise is inadequate to match metabolic demands. To gain mechanistic insights into delayed VO2 kinetics in LVSD, we simultaneously assessed hemodynamic measurements, ventilatory parameters, and peripheral oxygen usage during exercise.
  
  
  RESULTS
  Forty-two patients with symptomatic LVSD (age, 59±2 years [mean±SEM]; LV ejection fraction, 30±1%) and 17 controls (LV ejection fraction, 68±1%) underwent maximum upright cycle ergometry cardiopulmonary exercise testing. Hemodynamic monitoring and first-pass radionuclide ventriculography were performed at rest and during exercise. VO2 kinetics were quantified by mean response time (MRT), which was significantly longer in patients with LVSD compared with controls (64±3 versus 45±5 s; P=0.004). In LVSD patients, MRT was associated with higher biventricular filling pressures and reduced cardiac output during early exercise. LVSD patients with MRT ≥60 s, compared with LVSD subjects with MRT <60 s, demonstrated greater impairment in right ventricular-pulmonary vascular function during exercise as evidenced by lower right ventricular ejection fraction (35±2 versus 45±2%; P=0.03), steeper increment in transpulmonary gradient relative to cardiac output (3.7 versus 2.2 mm Hg/L; P<0.001), and increased ventilatory dead-space fraction (17±1 versus 12±2%; P=0.03). In contrast, MRT was not associated with LV ejection fraction (rest, exercise), PaO2, hemoglobin, or resting pulmonary function test results.
  
  
  CONCLUSIONS
  Delayed oxygen uptake on initiation of exercise (ie, MRT ≥60 s) in LVSD is closely related to impaired right ventricular-pulmonary vascular function and may represent an important surrogate for inability to augment RV performance during physical activity in patients with heart failure.
authors.affiliation: Cardiology Division, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
authors.forename: Neal A
authors.initials: NA
authors.lastname: Chatterjee
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Murphy
authors.forename: Rajeev
authors.initials: R
authors.lastname: Malhotra
authors.forename: Bishnu P
authors.initials: BP
authors.lastname: Dhakal
authors.forename: Aaron L
authors.initials: AL
authors.lastname: Baggish
authors.forename: Paul P
authors.initials: PP
authors.lastname: Pappagianopoulos
authors.forename: Stacyann S
authors.initials: SS
authors.lastname: Hough
authors.forename: Marc J
authors.initials: MJ
authors.lastname: Semigran
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Lewis
mesh_terms: D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D054143:Heart Failure, Systolic / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology; D010101:Oxygen Consumption / Q000502:physiology*; D011652:Pulmonary Circulation / Q000502:physiology*; D013997:Time Factors; D018487:Ventricular Dysfunction, Left / Q000503:physiopathology*; D018497:Ventricular Dysfunction, Right / Q000503:physiopathology*; D015646:Ventriculography, First-Pass
keywords: exercise physiology; exercise testing; heart failure