title: The sensation of dyspnea during exercise is not determined by the work of breathing in patients with heart failure.
abstract: OBJECTIVE
  The present study sought to investigate whether the work of breathing was reduced after heart transplantation. Accordingly, the tension time index of the diaphragm was measured in patients with heart failure and in transplant recipients.
  
  
  BACKGROUND
  Patients with heart failure are frequently limited by exertional dyspnea that may be due to the increased work of breathing. After heart transplantation, exertional dyspnea is markedly diminished. Whether work of breathing is reduced in posttransplant recipients is unknown.
  
  
  METHODS
  Nine patients with heart failure, six normal subjects and six heart transplant recipients were studied. Transdiaphragmatic pressure was measured throughout exercise. Accessory respiratory muscle oxygenation was assessed using near-infrared spectroscopy. Peak oxygen consumption, time in inspiration, time per breath and maximal inspiratory and expiratory pressures were measured in all subjects.
  
  
  RESULTS
  The tension time index remained markedly abnormal after heart transplantation both at rest ([mean +/- SD] normal group 0.01 +/- 0.006, heart failure group 0.026 +/- 0.018, transplant group 0.058 +/- 0.015, p < 0.004) and at peak exercise (normal group 0.03 +/- 0.02, heart failure group 0.10 +/- 0.03, transplant group 0.10 +/- 0.04, p < 0.0001). Accessory respiratory muscle deoxygenation was present only in patients with heart failure (near-infrared absorbency changes [arbitrary units]: normal group -3 +/- 6, heart failure group 28 +/- 5, transplant group -3.5 +/- 4.4, p < 0.0001).
  
  
  CONCLUSIONS
  Although heart transplantation alleviates dyspnea in patients with heart failure, the work of breathing as assessed by the tension time index of the diaphragm is not decreased. Amelioration of exertional dyspnea is achieved by other mechanisms, such as improved respiratory muscle perfusion.
authors.affiliation: Division of Cardiology, Columbia Presbyterian Medical Center, New York 10032, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Mancini
authors.forename: J
authors.initials: J
authors.lastname: La Manca
authors.forename: L
authors.initials: L
authors.lastname: Donchez
authors.forename: D
authors.initials: D
authors.lastname: Henson
authors.forename: S
authors.initials: S
authors.lastname: Levine
mesh_terms: D016022:Case-Control Studies; D003964:Diaphragm / Q000503:physiopathology; D004417:Dyspnea / Q000503:physiopathology*; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006333:Heart Failure / Q000503:physiopathology*; D016027:Heart Transplantation / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D012132:Respiratory Muscles / Q000503:physiopathology; D014939:Work of Breathing / Q000502:physiology*