Assessment of arterial compliance by carotid midwall strain-stress relation in normotensive adults

Examining left ventricular midwall as opposed to endocardial mechanics enhances understanding of left ventricular function in individuals with abnormal cardiac geometry. Accordingly, we used carotid ultrasound and applanation tonometry of arterial pressure to derive carotid midwall strain and its relation to carotid peak-systolic and end-diastolic stresses in 82 apparently normal, employed subjects (56 men, 26 women; median age, 47 years; 70% white; 21% overweight) with no evidence of coronary or valvular heart disease. Regression equations relating carotid luminal and midwall strain to the increment in carotid stress during systole (Delta carotid stress) were used to predict strain for the observed Delta stress. Observed/predicted carotid luminal or midwall strain was calculated as a measure of carotid luminal or midwall strain for imposed stress, termed stress-corrected strain. Midwall carotid strain was similar in women and men but was negatively related to older age (r=-0.35, P=0.001) and higher body mass index (r-=-0.31, P=0.005) and brachial and carotid blood pressure (r=-0.30 to -0.45, all P<0.01). The pulsatile change in arterial load, measured by Delta carotid stress, was positively related to midwall strain (r=0.44, P<0.001) more closely than was carotid luminal strain. Regression analyses revealed that carotid midwall strain was positively related to Delta stress, with additional negative relations to age and carotid diastolic diameter tall P<0.001). Stress-corrected carotid midwall strain was strongly and negatively correlated with midwall elastic modulus and Young's modulus (both r=-0.77, P<0.001), followed by elastic modulus (r=-0.74, P<0.001), midwall Young's modulus (r=-0.73, P<0.001), midwall stiffness index (r=-0.70, P<0.001), and stiffness index (r=-0.66, P<0.001). Thus, in normal adults, carotid midwall strain is unrelated to gender, is positively related to pulsatile carotid load as measured by Delta carotid stress, and is negatively related to age, overweight, and standard measures of arterial stiffness.