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UBC Theses and Dissertations

Cerebral blood flow in heart transplant recipients at rest and during incremental exercise Smirl, Jonathan David


Pathological impairments to cardiac output may impact cerebral blood flow (CBF). Prior studies on heart transplant recipients (HTR) have reported increases of 25-53% in CBF, 1-6 months following transplant. It is currently unknown if CBF is chronically altered in the years following transplant or during progressive exercise stress, when compared with aged-matched controls (AM). Donor population controls (DC) were included to determine if the responses observed in HTR are related to the age of the donor rather than the individual. The aim of this thesis was to examine the influence of long-term heart transplantation on the regulation of CBF velocity (CBFv) at rest and during incremental exercise. Two hypotheses were tested: 1) CBFv would be similar in HTR when compared to AM, but lower than DC; 2) that during incremental exercise, the HTR would have reduced elevations in CBFv compared with AM and DC. To address these hypotheses, HTR were tested who have a reported inability to acutely increase cardiac output during exercise. Seven male clinically stable HTR (62 ± 9 yrs of age, 9 ± 7 yrs post-transplant), seven male AM (62 ± 7 yrs), and seven male DC (22 ± 3 yrs) were recruited for this study. Bilateral middle cerebral arteries were insonated using transcranial Doppler ultrasound to obtain an index of CBFv. Data were obtained while seated and during an incremental cycling test to volitional exhaustion. A repeated measures ANOVA was applied to identify differences across exercise intensity. Comparisons between groups were performed with Fisher's LSD post hoc test. The main findings were: 1) Rest: CBFv was comparable between HTR and AM (40 vs. 41 cm/s), as expected, CBFv was 68% higher in the DC compared with the HTR and AM groups (P<0.05). 2) Incremental exercise: mean CBFv was not significantly different between the HTR and AM groups across any of the exercise intensities. In conclusion, the CBFv of long-term HTR are comparable to AM both at rest and during incremental exercise that despite a suppressed VO₂ Peak (and likely Q) CBFv is well maintained during incremental exercise in long – term HTR.

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