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1 Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, Canada
2 Division of Cardiology, University of Alberta, Edmonton, Canada
3 Edmonton, Canada; Division of Cardiology, University of Alberta, Edmonton, Canada
4 Experimental Medicine, University of British Columbia, Vancouver, Canada
5 Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, Alberta, Canada
* To whom correspondence should be addressed. E-mail: mark.haykowsky{at}ualberta.ca.
We examined peak and reserve cardiovascular function and skeletal muscle oxygenation during unilateral knee extension (ULKE) exercise in 5 heart transplant recipients (HTR, mean ± SEM; age: 53 ± 3 years; years post-transplant: 6 ± 4) and 5 age and body mass matched healthy controls (CON). Pulmonary oxygen uptake (VO2p), heart rate (HR), stroke volume (SV), cardiac output (Q), and skeletal muscle deoxygenation (HHb) kinetics were assessed during moderate intensity ULKE exercise. Peak exercise and reserve VO2p, Q, and systemic arterial-venous oxygen difference (a-vO2diff) were 23-52% lower (p < 0.05) in HTR. The reduced Q and a-vO2diff reserve was associated with a lower HR and HHb reserve, respectively. The phase II VO2p time delay was greater (HTR: 38 ± 2 vs. CON: 25 ± 1 seconds, p < 0.05), while time constants for phase II VO2p (HTR: 54 ± 8 vs. CON: 31 ± 3 seconds), Q (HTR: 66 ± 8 vs. CON: 28 ± 4 seconds) and HHb (HTR: 27 ± 5 vs. CON: 13 ± 3 seconds) were significantly slower in HTR. The HR half-time was slower in HTR (113 ± 21 seconds) versus CON (21 ± 2 seconds, p < 0.05); however, no significant difference was found between groups for SV kinetics (HTR: 39 ± 8 seconds vs. CON 31 ± 6 seconds). The lower peak VO2p and prolonged VO2p kinetics in HTR was secondary to both impairments in cardiovascular and skeletal muscle function that result in reduced oxygen delivery and utilization by the active muscles.
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