Development of a dynamic pressure standard of low amplitudes and frequencies.

The height of the gravitational wave is an influential magnitude in the estimation of its energy content, a very important parameter in the design of maritime structures such as piers and breakwaters, however, there are reasonable doubts among researchers regarding the quality of its measurement. The objective of the present work was to demonstrate that a stationary calibrated pressure transmitter allows the indirect calculation of the wave height with satisfactory accuracy despite the fact that it is a dynamic event as long as its frequency range is low, as is the case with the gravitational waves of the Costa Rican Central Pacific Ocean: between 0.05 Hz and 0.39 Hz. In the absence of a primary pattern of periodic pressure disturbances, an alternate path was developed based on the characterization of the parameters of the differential equation characteristic of a pressure measurement system in a shock tube prototype from normal shock wave theory and subsequent verification in a periodic disturbance generator that its attenuation and delay are practically negligible at the frequency of 0,1 Hz. The effect of the different geometry of the chamber of the pressure measurement system used in the sea was evaluated pneumatically by comparison with the dynamic pressure standard in the prototype of the periodic disturbance generator, while the effect of the compressibility of the fluid was evaluated in water in the wave channel of the Laboratory of Maritime Engineering, Rivers and Estuaries of the University of Costa Rica. The results show that the pressure measured from the least-squared adjustment coefficients of an electric current transmitter obtained by stationary calibration is acceptable to estimate the climatology of the gravitational wave characteristic of the Costa Rican Central Pacific Ocean with maximum errors of 136 mm in waves of height up to 1,4 m.

Correlation Between Serum Total Bilirubin Levels and Blood Pressure Variability in Patients With Hypertension

Background To investigate the effect of serum total bilirubin levels on blood pressure and its variability in patients with hypertension. Methods This study was a retrospective observational study. A total of 189 subjects were recruited from September 2019 to March 2020. All hypertensive patients were scheduled for ambulatory blood pressure and a 24-hour dynamic electrocardiography. Standard deviations of 24-hour systolic and diastolic blood pressure were used as blood pressure variability indicators. A multiple linear regression was used to analyze the relationship between total bilirubin serum levels and blood pressure variability in hypertensive patients. Results All patients were divided into 3 groups according to tertile values of total bilirubin: low (≤12.2 µmol/l, n = 64), moderate (12.3–16.7 µmol/l, n = 64), and high (>16.8 µmol/l, n = 62) total bilirubin groups. Compared with low total bilirubin group, 24-hour mean systolic and diastolic blood pressure, 24-hour systolic blood pressure standard deviation, systolic blood pressure coefficient of variability, and 24-hour systolic blood pressure load were reduced in the moderate and high total bilirubin groups (all P < 0.05). Multiple linear regression analysis showed that female (B = −1.408, P = 0.013), age (B = 0.043, P = 0.035), diabetes (B = 2.624, P < 0.001), and moderate and high bilirubin grouping (B = −1.582, −3.079; both P < 0.05) were influencing factors of 24-hour systolic pressure standard deviation. Serum total bilirubin levels had no effect on the standard deviation of 24-hour diastolic blood pressure(P > 0.05). Conclusions In hypertensive patients, the total bilirubin serum level is an influencing factor for 24-hour systolic blood pressure variability.