Reviews in Cardiovascular Medicine  2020, Vol. 21 Issue (3): 353-363     DOI: 10.31083/j.rcm.2020.03.67
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Relationship between cardio-ankle vascular index and obstructive sleep apnea
Yasuhiro Tomita1, 2, 3, Takatoshi Kasai2, 3, 4, *()
1Cardiovascular Center, Toranomon Hospital, 2-2-2 Toranomon, Minato-ku, Tokyo 105-8470, Japan
2Sleep Center, Toranomon Hospital, 2-2-2 Toranomon, Minato-ku, Tokyo 105-8470, Japan
3Department of Cardiovascular Medicine, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyoku, Tokyo 113-8421, Japan
4Cardiovascular Respiratory Sleep Medicine, Juntendo University Graduate School of Medicine, 2-1-1 Hongo, Bunkyoku, Tokyo 113-8421, Japan
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Abstract:

Patients with obstructive sleep apnea (OSA) are susceptible to developing atherosclerosis. Consequently, such patients are at a high risk of developing cardiovascular diseases, leading to poor prognosis. Many physiological parameters have been previously used to predict the development of atherosclerosis. One such parameter, the cardio-ankle vascular index (CAVI), a measure of arterial stiffness, has garnered much attention as it can also predict the degree of atherosclerosis. The CAVI can be calculated based on noninvasive measurements, and is less susceptible to blood pressure variations at the time of measurement. Therefore, the CAVI can assess changes in arterial stiffness and the risk of developing atherosclerosis independent of blood pressure changes. Continuous positive airway pressure (CPAP) is a standard therapy for OSA and can suppress the issue significantly. Several studies have shown that CPAP treatment for OSA could also reduce the CAVI. In this review, we discuss the relationship between OSA and arterial stiffness, primarily focusing on the CAVI. Furthermore, we propose future perspectives for the CAVI and OSA.

Submitted:  22 April 2020      Revised:  22 July 2020      Accepted:  24 July 2020      Published:  30 September 2020
Fund: a JSPS KAKENHI Grant Number JP17K09527
*Corresponding Author(s):  Takatoshi Kasai     E-mail:  kasai-t@mx6.nisiq.net

Yasuhiro Tomita, Takatoshi Kasai. Relationship between cardio-ankle vascular index and obstructive sleep apnea. Reviews in Cardiovascular Medicine, 2020, 21(3): 353-363.

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Fig. 1.  Arterial pressure waveforms at each point are shown on the same timeline. Aortic pressure starts rising at the time of the first heart sound and has two peaks. The first peak is called augmenting pressure (AP), and the second peak is called pulse pressure (PP). The augmentation index (AIx) is calculated as AP divided by PP. Since the dicrotic notch in the aorta coincides with the second heart sound, the time between the dicrotic notch at the brachial artery and the second heart sound indicates the propagation time from the heart to the brachial artery. Pulse wave velocity (PWV) can be calculated using the propagation time between two points if the distance between them is known. Lf is the distance from the upper margin of the sternum to the navel, and from there to the groin. Lc is the distance from the upper margin of the sternum to the neck. La is the distance from the upper margin of the sternum to the navel, and from there to the ankle. Lb is the distance from the upper margin of the sternum to the elbow. The cardio-ankle vascular index (CAVI) is calculated using the heart-ankle PWV (haPWV). Ps and Pd are the systolic and diastolic blood pressure values, respectively, and $\rho{}$ is the blood density.

Fig. 2.  Using probes or a tonometer, the pulse wave velocity (PWV) can be measured between the carotid and femoral arteries (cfPWV) or brachial and ankle arteries (baPWV). The cardio-ankle vascular index (CAVI) can be obtained from blood pressure and heart-ankle PWV (haPWV) measurements. The carotid intima-media thickness (IMT) is measured using ultrasonography. The augmenting pressure (AP) and the augmentation index (AIx) are derived from the central arterial waveforms. The arterial stiffness parameter $\beta{}$ is calculated using systolic and diastolic pressure values and the variation in the aortic diameter. Flow-mediated vasodilation (FMD) is a technique that uses ultrasonography and plethysmography to analyze changes in the forearm blood flow. Coronary artery calcification is assessed by computed tomography (CT).

Fig. 3.  Patients were divided based on a cardio-ankle vascular index (CAVI) cut-off value of 7. In men, the apnea-hypopnea index (AHI) was similar in both groups (37.1 vs. 35.6, P = 0.483). In women, the AHI was higher in the CAVI $\geq{}$ 7 group (26.1 vs. 9.0, P = 0.001).

Table 1.  Change in the CAVI after intervention for sleep disordered breathing