Pulmonary Oxygen Uptake and Heart Rate Kinetics During the Six-Minute Walk Test in Transplant Recipients

Background. The effect of organ transplantation on arterial compliance, pulmonary oxygen uptake (VO 2p ) and heart rate kinetics during the 6-minute walk test (6-MWT) remains unknown. Methods. Twenty-two thoracic (heart and/or lung) organ transplant recipients (TOTR, 51±12 years) and 30 abdominal (kidney, kidney-pancreas, or liver) organ transplant recipients (AOTR, 46 ±11 years) from the 2006 Canadian Transplant Games, and 37 healthy controls (HC) completed a 6-MWT. VO 2p , heart rate kinetics, and arterial compliance were determined. Results. The 6-MWT distance and highest VO 2p were significantly lower in TOTR and AOTR versus HC. The highest 6-MWT heart rate was lower in TOTR (11%) and AOTR (13%) versus HC. VO 2p kinetics were slower in TOTR (52±11 sec, P≤0.001) and AOTR (45±24 sec, P≤0.001) versus HC (28±9 sec). Heart rate kinetics were slower in TOTR (100±49 sec) versus AOTR (41±21 sec, P≤0.001) and HC (34±21 sec, P≤0.001), but not between AOTR and HC. Small and large artery compliance were 26% (P=0.007) and 19% (P=0.004) lower, respectively, in TOTR versus HC. Large artery compliance was 14% lower in TOTR versus AOTR (P=0.017). 6-MWT distance was significantly related to VO 2p kinetics (r= -0.35) and the highest 6-MWT VO 2p (r=0.72). Conclusions. TOTR and AOTR have abnormal VO 2p kinetics, which is secondary to prolonged heart rate kinetics and impaired vascular function in TOTR, but not AOTR.