ABC | Volume 113, Nº6, December 2019

Original Article Elias Neto et al. Great arteries behavior during orthostasis Arq Bras Cardiol. 2019; 113(6):1072-1081 Once again, multiple linear regression defined age and SBP as the major independent predictive factors of PWV obtained during the tilt test, accounting together for 49% of the variations in PWV during that test (r 2  = 0.490). Association between PWV during the recovery phase and the anthropometric and hemodynamic characteristics of the participants The correlation of variables obtained when the individuals returned to the supine position 20 minutes after the tilt test (recovery phase) was assessed. This final phase of the study represents an immediate response (0–2 min) of the hemodynamic parameters and their correlation with PWV during the recovery phase (PWVrec). A significant correlation was observed between PWVrec and most variables assessed in this phase of the protocol. Once again, the variable age had the greatest positive correlation (r = 0.533, p < 0.001) with PWVrec. A positive correlation was also observed between PWVrec and the following parameters: BMI (r = 0.26, p < 0.05); SBP (r = 0.39, p < 0.001); DBP (r = 0.49, p < 0.001); and MBP (r = 0.457, p < 0.001). In the recovery phase, a negative correlation between HR (r = 0.055, NS) and PWVrec was no longer observed. As occurred in the 2 preceding phases, multiple linear regression in the recovery phase showed that SBP (p < 0.001) and age (p < 0.001) were independent predictors of variations in PWVrec. Together, these variables accounted for approximately 40% of the variations in PWVrec. Analysis of the effects of distensibility pressure on aortic stiffness in the baseline supine position, orthostatic position and after the tilt test Variation in the carotid-femoral PWV, as an index of aortic stiffness, was assessed with regard to the SBP values, aiming at comparing the effects of distensibility pressure on the mechanical properties of the great arteries in the population (Figure 2B). The analysis of SBP in the passive orthostatic position showed that SBP accounted for approximately 21% (r 2  = 0.214, p < 0001) of the variations observed in PWV. After adjusting SBP for age, SBP proved to play an even more significant role in the PWVp behavior pattern (r 2  = 0.38, p < 0.001). Finally, in the statistical analysis performed in the recovery phase, SBP continued to play a significant role in the PWVrec variations (r 2  = 0.15, p < 0.001). The same was observed for SBP adjusted for age (r 2  = 0.23, p < 0.001). Analysis of the effect of aging on aortic stiffness in the baseline supine position, orthostatic position and after the tilt test To assess the effects of aging on arterial stiffness, the correlation curve (Figure 2C) was performed with regard to age. In all phases of the protocol, PWV significantly increased with age (r 2  = 0.351, p < 0.001; r 2  = 0.4066, p < 0.001; r 2  = 0.283, p < 0.001). Assessment of the effect of heart rate on PWV measured in the different phases of the protocol The influence of heart rate behavior on arterial distensibility was assessed. As previously reported, no correlation was observed between HR and PWV assessed in the baseline and recovery phases. On the other hand, during the tilt test, a negative correlation was observed between PWVp and HR (Figura 2D). Heart rate accounted for approximately 13% of the variation in PWV during the tilt test (r 2  = 0.136, p < 0.001), and this influence continued to be observed even after PWV was adjusted for age (r 2  = 0.154, p < 0.001). The heart rate decrease in orthostatic position was significantly conditioned to age increase in the participants (r 2  = 0.27, p < 0.001). Finally, the correlation between the HR behavior in orthostatic position and the hemodynamic parameters at baseline was assessed. A negative correlation with baseline PWV measurement was observed (r = -0.30, p < 0.01). Discussion The main new finding of this study was the instant and significant increase in PWV in orthostatic position (Table 3). This pattern of vascular functional behavior was present in all individuals studied regardless of age, resulting in PWV levels in young individuals during the tilt test similar to those of elderly individuals in the supine position. As observed in this study, although SBP is one of the most important variables accounting for a direct increase in PWV, both at baseline and in orthostatic position (Table 4), no additional increase in SBP was detected during the tilt test compared with its baseline levels (baseline SBP: 130 ± 18 mmHg, SBPp: 128 ± 15 mmHg, NS). Indeed, a decreasing trend was observed in orthostatic position. This finding is in accordance with literature data, which also evidenced lack of a statistically significant increase or even a decreasing trend in SBP in orthostatic position. 14 Another important aspect is that although this study did not directly assess vasomotor activity, the fact that it found an increase in MAP (baseline MBP: 99 ± 15, MBPp: 103 ± 11, p < 0.05) means that there was probably an increase in peripheral vascular resistance due to reflex sympathetic activation induced by the fall in pulse pressure while standing. Thus, although a variable PWV may be strongly influenced by the MBP, the increased PWV can be attributed to both secondary circulatory disorders due to gravitational stress and increased peripheral vascular resistance, rather than to the effect of high MBP. Transmission of pulse wave is known to be primarily dependent on arterial elasticity or stiffness coefficient. However, several other factors should be considered. Some of these factors are related to cardiovascular physiology, while others result from specific pathophysiological conditions. 15 Analyzing the correlation between baseline PWV and PWVp, a direct influence of the baseline pattern of arterial compliance was observed on the response of the great arteries to orthostatic position (Figura 2). 1076