LAUSR

Age-related changes in cerebral hemodynamics are controversial and discrepancies may be due to experimental techniques. As such, the purpose of this study was to compare cerebral hemodynamics measurements of the middle cerebral artery (MCA) between transcranial Doppler ultrasound (TCD) and four-dimensional flow MRI (4D flow MRI). Twenty young (25 ± 3 years) and 19 older (62 ± 6 years) participants underwent two randomized study visits to evaluate hemodynamics at baseline (normocapnia) and in response to stepped hypercapnia (4% CO2, and 6% CO2) using TCD and 4D flow MRI. Cerebral hemodynamics measures included MCA velocity, MCA flow, cerebral pulsatility index (PI) and cerebrovascular reactivity. Cerebrovascular reactivity was calculated as the linear relationship between cerebrovascular conductance (CVC using 4D flow MRI) or cerebrovascular conductance index (CVCi using TCD) and changes in ETCO2 at rest and during hypercapnia. MCA velocity between the methods was positively correlated across the conditions (r=0.262; p=0.004). Additionally, cerebral PI of the MCA was significantly correlated between TCD and 4D flow MRI across the conditions (r=0.236; p=0.010). However, there was no association between MCA velocity using TCD and MCA flow using 4D flow MRI across the conditions (r=0.079; p=0.397). When age-associated differences in cerebrovascular reactivity were compared using both methodologies, cerebrovascular reactivity was greater in young adults compared to older adults when using 4D flow MRI (2.11±1.68 ml/min/mmHg/mmHg vs. 0.78±1.68 ml/min/mmHg/mmHg; p=0.019), but not with TCD (0.88±1.01 cm/s/mmHg2 vs. 0.68±0.94 cm/s/mmHg2; p=0.513). In conclusion, our results demonstrated good agreement between the methods measuring MCA velocity at normocapnia and in response to hypercapnia, but MCA velocity with TCD and MCA flow with MRI were not related. In addition, measurements using 4D flow MRI revealed additional effects of aging on cerebral hemodynamics that were not apparent using TCD. This study was funded by the NIH grants (HL118154, NS117746), the NIH, Ruth L. Kirschstein National Research Service Award T32's from the National Institute on Aging to the University of Wisconsin-Madison Biology of Aging & Age-Related Diseases (AG000213) and the National Heart Lung and Blood Institute to the University of Wisconsin-Madison Cardiovascular Research Center (HL007936) as well as the Wisconsin Alumni Research Foundation. This study was also supported by Alzheimer's Association Research Fellowship (AARF-22-924325). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.