Justin R. Geijer

Comparison of Intima-Media Thickness of the Carotid Artery and Cardiovascular Disease Risk Factors in Adults With Versus Without the Down Syndrome

Adults with Down syndrome (DS) residing in large institutional settings possess low levels of atherosclerosis. The purpose of this study was to determine whether community-residing adults with DS possess less atherosclerosis than adults without DS. The second purpose was to examine the relation between cardiovascular disease risk factors and intima-media thickness (IMT), a measure of atherosclerosis, in patients with DS. B-mode images of the left common carotid artery were collected to assess IMT in 52 adults with DS and age-, gender-, and race-matched adults without DS (27 women, 25 men; mean age 42 ± 5 years). Total body fat, blood pressure, fasting lipid profiles, insulin, glucose, C-reactive protein, homocysteine, physical activity, and dietary intake were also assessed. Adults with DS possessed lower IMT (0.43 ± 0.07 vs 0.48 ± 0.09 mm, p <0.001), systolic blood pressure (116 ± 15 vs 125 ± 17 mm Hg, p <0.011), and diastolic blood pressure (59 ± 10 vs 73 ± 9 mm Hg, p <0.001) and higher C-reactive protein (0.58 ± 0.55 vs 0.30 ± 0.42 mg/dl, p <0.003), triglycerides (126.5 ± 55.2 vs 103.8 ± 53.2 mg/dl, p <0.048), and total body fat (37.8 ± 10.2% vs 32.4 ± 11.2%, p <0.002) than controls. Male gender (p <0.001) and physical activity (p = 0.020) were identified as predictors of IMT for adults with DS and fasting insulin (p <0.001), age (p <0.001), gender (p <0.001), fruit and vegetable intake (p = 0.001), low-density lipoprotein cholesterol (p = 0.004), and smoking (p = 0.023) for controls. In conclusion, community residing adults with DS may be protected against atherosclerosis despite elevated total body fat and elevated cardiovascular disease risk factors. Predictors of IMT differed for patients with DS compared to controls, which indicates that patients with DS possess a unique model of atherogenesis.

Bone Mineral Density in Adults With Down Syndrome, Intellectual Disability, and Nondisabled Adults

Individuals with intellectual disability (ID) or Down syndrome (DS) may be at greater risk of osteoporosis. The purpose of this study was to compare bone mineral density (BMD) of DS, ID, and non-intellectually disabled (NID) populations. In each group, 33 participants between the ages of 28 and 60 years were compared. BMD was measured with dual-energy x-ray absorptiometry (DXA) scans. BMD (p < .0001) between all groups was significantly different. Participants with DS had significantly lower BMD compared to NID participants. Individuals with ID had significantly lower BMD compared to NID subjects. Participants with DS had the lowest BMD of all groups. DS subjects display a greater risk for osteoporosis than ID subjects or control populations.

Reproducibility of blood oxygen level‐dependent signal changes with end‐tidal carbon dioxide alterations

Hypercapnia has been utilized as a stimulus to elicit changes in cerebral blood flow (CBF). However, in many instances it has been delivered in a non‐controlled method that is often difficult to reproduce. The purpose of this study was to examine the within‐ and between‐visit reproducibility of blood oxygen level‐dependent (BOLD) signal changes to an iso‐oxic square wave alteration in end‐tidal carbon dioxide partial pressure (PetCO2). Two 3‐Tesla (3T) MRI scans were performed on the same visit, with two square wave alterations administered per scan. The protocol was repeated on a separate visit with minimum of 3 days between scanning sessions. PetCO2 was altered to stimulate changes in cerebral vascular reactivity (CVR), while PetO2 was held constant. Eleven subjects (six females; mean age 26·5 ± 5·7 years) completed the full testing protocol. Excellent within‐visit square wave reproducibility (ICC > 0·75) was observed. Similarly, square waves were reproducible between scanning sessions (ICC > 0·7). This study demonstrates BOLD signal changes in response to alterations in PetCO2 are reproducible both within‐ and between‐visit MRI scans.

Comparison of brachial dilatory responses to hypercapnia and reactive hyperemia.

Flow-mediated dilation (FMD) relies on reactive hyperemia to stimulate the endothelium to release nitric oxide, causing smooth muscle relaxation. Hypercapnia also produces vasodilation, which is thought to be nitric oxide-independent. The purpose of this study was to compare and contrast the effects of hypercapnia and reactive hyperemia as stimuli for brachial artery dilation. On separate days, twenty-five participants underwent vasodilation studies via reactive hyperemia or hypercapnia (i.e. 10 mmHg increase in end-tidal carbon dioxide [PetCO2)]). During both studies changes in brachial artery diameter were recorded using continuous ultrasound imaging. Heart rate (HR) was measured throughout both tests. Resting HR (63  ±  11 versus 68  ±  14 beats min(-1), p  =  0.0027) and baseline brachial artery diameter measurements (4.57  ±  1.51 versus 5.28  ±  1.86 mm, p  =  0.022) were significantly different between reactive hyperemia and hypercapnia, respectively. HR at peak dilation (65  ±  11 versus 76  ±  14 beats min(-1), p  <  0.0001), peak vessel dilation (8.68  ±  4.50 versus 5.28  ±  1.86%, p  =  0.002), and time to peak dilation (90.8  ±  120.1 versus 658.3  ±  226.6 s, p  <  0.0001) were also significantly different between reactive hyperemia and hypercapnia. The dynamics by which reactive hyperemia and hypercapnia stimulate vasodilation appear to differ. Hypercapnia produces a smaller and slower vasodilatory effect than reactive hyperemia. Further research is necessary to better understand the mechanisms of vasodilation under hypercapnic conditions.