Impaired pulmonary oxygen uptake kinetics and reduced peak aerobic power during small muscle mass exercise in heart transplant recipients

Abstract

We examined peak and reserve cardiovascular function and skeletal muscle oxygenation during unilateral knee extension (ULKE) exercise in five heart transplant recipients (HTR, mean ± SE; age: 53 ± 3 years; years posttransplant: 6 ± 4) and five age- and body mass-matched healthy controls (CON). Pulmonary oxygen uptake (V̇o2p), heart rate (HR), stroke volume (SV), cardiac output (Q̇), and skeletal muscle deoxygenation (HHb) kinetics were assessed during moderate-intensity ULKE exercise. Peak exercise and reserve V̇o2p, Q̇, and systemic arterial-venous oxygen difference (a-vO2diff) were 23–52% lower ( P < 0.05) in HTR. The reduced Q̇ and a-vO2diff reserves were associated with lower HR and HHb reserves, respectively. The phase II V̇o2p time delay was greater (HTR: 38 ± 2 vs. CON: 25 ± 1 s, P < 0.05), while time constants for phase II V̇o2p (HTR: 54 ± 8 vs. CON: 31 ± 3 s), Q̇ (HTR: 66 ± 8 vs. CON: 28 ± 4 s), and HHb (HTR: 27 ± 5 vs. CON: 13 ± 3 s) were significantly slower in HTR. The HR half-time was slower in HTR (113 ± 21 s) vs. CON (21 ± 2 s, P < 0.05); however, no significant difference was found between groups for SV kinetics (HTR: 39 ± 8 s vs. CON 31 ± 6 s). The lower peak V̇o2p and prolonged V̇o2p kinetics in HTR were secondary to impairments in both cardiovascular and skeletal muscle function that result in reduced oxygen delivery and utilization by the active muscles.

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

“…We have recently extended these findings and demonstrated that pretransplantation heart failure etiology is also associated with prolonged V O 2p kinetics after heart transplantation in patients with antecedent ischemic compared to nonischemic heart failure (29). Finally, we have also recently demonstrated that prolonged V O 2p kinetics in heart transplant recipients are secondary to both impairments in cardiac output and skeletal muscle deoxygenation kinetics, despite engaging our heart transplant group in only small muscle mass (single limb) exercise (30). In the current investigation, we further extend these previous findings (21,(27)(28)(29)(30) by revealing that exercise intolerance in organ transplant recipients, which is likely mediated in part by the pretransplant disease and associated deconditioning, may be mitigated by physical activity levels posttransplantation.…”

“…Finally, we have also recently demonstrated that prolonged V O 2p kinetics in heart transplant recipients are secondary to both impairments in cardiac output and skeletal muscle deoxygenation kinetics, despite engaging our heart transplant group in only small muscle mass (single limb) exercise (30). In the current investigation, we further extend these previous findings (21,(27)(28)(29)(30) by revealing that exercise intolerance in organ transplant recipients, which is likely mediated in part by the pretransplant disease and associated deconditioning, may be mitigated by physical activity levels posttransplantation. The role that regular exercise training and higher levels of aerobic fitness have on skeletal muscle morphology and function has not been well studied in organ transplant recipients.…”

Exercise training improves aerobic capacity, muscle strength, and quality of life in renal transplant recipients

“…After 2 min of rest, the workload was set at 15 W and increased by 15 W every 2 min until volitional fatigue. Stroke volume (SV) was measured using impedance cardiography (Minnesota Impedance Cardiograph, model 304B; Surcom Inc., Minneapolis, Minn., USA) in conjunction with a phonocardiogram (Hewlett Packard, model 21050A) (Jendzjowsky et al 2007). Stroke volume was calculated during 20-s sampling periods at the end of each 2-min exercise stage using Bernstein's equation (Bernstein 1986).…”

Reliability of peak O2 uptake and O2 uptake kinetics in step exercise tests in healthy subjects

“…However, it has been underutilized and there is a major gap in its applicability due to the lack of well-defined protocols and scarce knowledge about ST reproducibility for measuring aerobic power (Petrella et al, 2001), includingV O 2 kinetics. Such analysis is important in order to determine the effects of training and rehabilitation (Jones and Burnley, 2009), heart transplantation (Jendzjowsky et al, 2007) and pharmacological effects (Berton et al, 2010), for example.…”