ABC | Volume 110, Nº1, January 2018

Original Article Liporaci et al Effects of tilt test in healthy subjects Arq Bras Cardiol. 2018; 110(1):74-83 Methods Sample The study protocol was approved by the Ethics Committee of the General Hospital of Ribeirao Preto Medical School, University of Sao Paulo. All subjects signed the informed consent form before participating in the study. A convenience sample of 23 healthy female volunteers aged from 18 to 30 years (mean of 23.4 years), mean height 1.62m and mean weight 56.2 Kg, with no history of syncope was selected. Recruitment was performed by the same cardiologist and all subjects underwent clinical examination and electrocardiography to rule out the possibility of cardiovascular changes. Then, functional assessment of the lower limbs was carried out by a physiotherapist to exclude musculoskeletal disorders that could affect the results. All volunteers underwent both AS and HUT, and the order of the tests was randomized by drawing (cross-over design): HUT was first conducted in 13 patients (HUT-AS, n = 13), and the AS was first conducted in 10 patients (AS-HUT, n = 10). All volunteers were instructed to refrain from consuming caffeine or other stimulating agents on the day before the test, and not to undergo the tests in fasting conditions. Data collection HUT test For HR and EMG activity analyses during the HUT, each volunteer was positioned supine on the tilt table for 15 minutes at rest. On the fifteenth minute, the volunteer was tilted to 70 degrees for 15 minutes or until the initial signs and symptoms of syncope or orthostatic intolerance. Participants were monitored by electrocardiography and muscle activity was recorded using the Myosystem Br-1P84 (DATA-HOMINIS‑BR) EMG system with electrodes placed bilaterally over the medial gastrocnemius (MG), the tibialis anterior (TA), the rectus abdominis (RA) and the erector spinae (ES) muscles. Positioning of the electrodes followed the SENIAM (Surface ElectroMyoGraphy for the Non-Invasive Assessment of Muscles - www.seniam.org ) guidelines and recorded using the Myosystem I software, version 3.5 (DATA-HOMINIS-BR) for further calculation of the root mean square (RMS) and amplitude of the EMG signal (mV). The mean RMS for each minute of the test was recorded. The EMG data were normalized to the maximal isometric effort of each volunteer. AS test For analyses of HR, EMG activity and postural oscillation on the force platform during the AS test, each volunteer was positioned supine for 15 minutes on the tilt table strategically placed beside the force platform (Figure 1). The subject was then instructed to stand up from the supine position and stay in standing position on the center of the platform, with legs 20 cm apart, for another 15minutes. Data of postural oscillation on the force platform (AMTI - OR6-7-1000, MA - USA) were analyzed using the ByoDinamics software in the LabVIEW environment (DATA-HOMINIS, MG - Brazil). Total displacement (TD) and total mean velocity (TMV) of the COP per minute of the orthostatic test (CP) were analyzed. TD and TMV values in each minute of the AS test were compared with the values of the minute before. After the fifth minute in standing position in both HUT and AS, patients were instructed to perform three VMs every three minutes (on the 6 th , 9 th and 12 th minute), and the test was finished on the 15 th minute. The aneroid manometer was connected to a mouthpiece by a 1.5 m connector. The mouthpiece used for application of the expiratory effort was held by a stand and placed in front of the patient, who did not need to touch it. The same procedure was performed for the VMs during the HUT. Statistical analysis Continuous variables with normal distribution was analyzed by within-test (minute-by-minute) and between‑test analyzes. Also, these variables were grouped into three periods – pre-VM, during the VM and post-VM and presented as mean and standard deviation. Continuous variables with non-normal distribution were presented as median and interquartile range. Analyses of HR response to the tests and EMG data were performed by linear mixed-effects models (random and fixed effects). These data analysis models are used in case the responses of the same individual are grouped and the assumption of independence between observations within the same group is not adequate. EMG signal was analyzed in time domain by RMS. Normality of the signal amplitude was tested using the by Kolmogorov-Smirnov test and according to the results obtained, non-parametric statistics was used for the analysis. In the mixed model used for data analysis, subjects were considered as random effect and the orthostatic tests and time points as well as the interaction between them were considered as fixed effects. The analysis of variance (ANOVA) was used for analyses of the data obtained during the active postural maneuver on the force platform. This analysis was performed using the PROC GLM in the SAS® 9.2 software. Orthogonal contrasts based on t distribution for ANOVA with repeated measures were used for comparisons. Statistical significance was set at 5%. Data were normalized to the maximum values of each variable. Results Significant differences in the minute-by-minute HR between AS and HUT were observed during the first VM (minute 6), minute 7 and minute 8, with higher values during the AS than the HUT (Figure 1). TMV and TD on the force platform during the AS Mean values of TMV over time are depicted in Figure 2, with statistically relevant values during the first VM (minute 6) and second VM (minute 9) as compared with minute 1. This was also observed during the second VM in comparison with minutes 2-8, and the values measured from minute 10 to 14 in relation to the second VM. 75