Role of characteristic impedance in carotid stiffness and cognitive dysfunction: interaction with proximal aortic stiffness

Increased stiffness in the proximal aorta and carotid artery, both crucial for regulating blood pressure and flow pulsatility, may contribute to cerebral microcirculation damage and cognitive decline. While aortic stiffness measured by aortic characteristic impedance (Zc) has been linked to suspected mild cognitive impairment (MCI), the role of carotid stiffness remains unclear due to inconsistent findings using traditional distensibility measures. This study investigates the relationship between carotid characteristic impedance (CCI) and suspected MCI, and examines how CCI interacts with Zc in contributing to cognitive dysfunction. A total of 1423 healthy community residents (average age 59.8 ± 11.7 years; 46.9% male) underwent comprehensive hemodynamic evaluations and carotid ultrasonography. CCI and Zc were calculated in the time domain, and the characteristic impedance ratio (CIR), defined as CCI/Zc, was used to assess the influence of impedance mismatch. Suspected MCI was determined using education-adjusted Mini-Mental State Examination (MMSE) cut-offs. Among participants, 478 (33.6%) were identified with suspected MCI. These individuals showed significantly higher CCI, while other carotid distensibility parameters were not significantly different. CCI was the only carotid stiffness measure independently associated with suspected MCI (OR per SD: 1.18; 95% CI: 1.02-1.36). CIR was negatively associated with MCI (OR: 0.84; 95% CI: 0.73-0.95), suggesting that a mismatch in impedance contributes to cognitive decline. The combination of elevated Zc and CCI was the strongest predictor of suspected MCI (OR: 2.10; 95% CI: 1.47-2.98). These findings underscore CCI as a sensitive and valuable marker for assessing carotid stiffness in relation to cognitive dysfunction.