Exercise-induced ventilatory abnormalities in orthotopic heart transplant patients.
OBJECTIVE
The purpose of this investigation was to compare multiple ventilatory responses of heart transplant patients (HTP) with normal subjects (NL) at rest, at absolute and relative submaximal exercise levels, and at peak exercise.


METHODS
Ten male HTP and 10 matched NL were tested under similar conditions on a treadmill with the use of an incremental protocol to symptom-limited maximal levels while breath-by-breath measurements of gas exchange and ventilation were obtained.


RESULTS
At an absolute carbon dioxide (VCO2) level of 1 L.min-1, minute ventilation (VE) was significantly higher in HTP compared with NL (38.4 +/- 1.9 versus 29.3 +/- 0.9 L.min-1). However, when compared at similar relative levels (i.e., 40% and 60% of the peak oxygen consumption [VO2 peak]), VE was found to be significantly higher in NL compared with HTP (25.5 +/- 1.4 versus 21.2 +/- 1.0 L.min-1 at 40%; 39.9 +/- 3.1 versus 32.1 +/- 2.0 L.min-1 at 60%, respectively). The reduced VE was the result of a significantly lower tidal volume (VT) in HTP compared with NL at 40% (1.14 +/- 0.08 versus 1.33 +/- 0.05 L) and 60% (1.40 +/- 0.10 versus 1.85 +/- 0.06 L) of VO2 peak, since breathing frequency (BF) was not different between the groups at these levels.


CONCLUSIONS
These data demonstrate that HTP have abnormal ventilatory responses to incremental exercise that are largely explained by a diminished VT response. While mechanical factors known to affect VT cannot be ignored, it is likely that the abnormal VT response of HTP during exercise is secondary to respiratory muscle weakness and may be due to hypoperfusion, long-term deconditioning, and/or the long-term use of corticosteriods.
Brubaker
P H
PH
Department of Medicine, Wake Forest University, Winston-Salem, N.C. 27109, USA.
Brozena
S C
SC
Morley
D L
DL
Walter
J D
JD
Berry
M J
MJ
D000328:Adult; D001794:Blood Pressure; D002245:Carbon Dioxide / Q000378:metabolism; D016022:Case-Control Studies; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology; D005221:Fatigue / Q000503:physiopathology; D005938:Glucocorticoids / Q000627:therapeutic use; D006339:Heart Rate; D016027:Heart Transplantation / Q000502:physiology*; D006801:Humans; D008297:Male; D018908:Muscle Weakness / Q000503:physiopathology; D010101:Oxygen Consumption / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology; D011241:Prednisone / Q000627:therapeutic use; D011659:Pulmonary Gas Exchange / Q000502:physiology; D012123:Pulmonary Ventilation / Q000502:physiology; D012119:Respiration / Q000502:physiology*; D012132:Respiratory Muscles / Q000502:physiology; D012146:Rest / Q000502:physiology; D013990:Tidal Volume / Q000502:physiology
D005938:Glucocorticoids; D002245:Carbon Dioxide; D011241:Prednisone