Browsing by Author "Andrade, A."
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- On the influence of time-series length in EMD to extract frequency content : simulations and models in biomedical signalsPublication . Fonseca-Pinto, Rui; Ducla-Soares, J. L.; Araújo, F.; Aguiar, P.; Andrade, A.In this paper, fractional Gaussian noise (fGn) was used to simulate a homogeneously spreading broadband signal without any dominant frequency band, and to perform a simulation study about the influence of time-series length in the number of intrinsic mode functions (IMFs) obtained after empirical mode decomposition (EMD). In this context three models are presented. The first two models depend on the Hurst exponent H, and the last one is designed for small data lengths, in which the number of IMFs after EMD is obtained based on the regularity of the signal, and depends on an index measure of regularity. These models contribute to a better understanding of the EMD decomposition through the evaluation of its performance in fGn signals. Since an analytical formulation to evaluate the EMD performance is not available, using well-known signals allows for a better insight into the process. The last model presented is meant for application to real data. Its purpose is to predict, in function of the regularity signal, the time-series length that should be used when one wants to divide the spectrum into a pre-determined number of modes, corresponding to different frequency bands, using EMD. This is the case, e.g., in heart rate and blood pressure signals, used to assess sympathovagal balance in the central nervous system.
- Preference for and tolerance of the intensity of exercise questionnaire (PRETIE-Q): validity, reliability and gender invariance in Portuguese health club exercisersPublication . Teixeira, D. S.; Ekkekakis, Panteleimon; Andrade, A.; Rodrigues, F.; Evmenenko, Anastasiia; Faria, J.; Marques, P.; Cid, Luis; Monteiro, DiogoThe aim of the present study was to translate and adapt the Preference for and Tolerance of the Intensity of Exercise Questionnaire to Portuguese (PRETIE-Q-PT), and to analyze its psychometric properties (factorial validity with gender invariance analyses, reliability, temporal stability, and construct validity). The sample was composed of 445 Portuguese participants (55.9%women), with a mean age of 29.6 years (SD = 8.2). To verify the psychometric properties of the scale, structural equation modeling procedures were used. Results showed that an abbreviated 10-item scale presented good fit, reliability, and convergent validity. Latent mean analysis between samples, sex, and time points showed no differences. Construct validity tested with self-reported exercise frequency, vitality, well-being, and habit supported the use of the PRETIE-Q-PT in exercise settings, highlighting the need for exercise professionals to consider these intensity-related trait variables in the promotion of a pleasant exercise experience. As a general conclusion, the PRETIE-Q-PT seems to be a valid scale that can be used to assess intensity-trait characteristics in health club exercisers, and may allow professionals to better adjust exercise prescription to subjective needs aiming to achieve theoretically suggested promotion of pleasurable exercise experiences.
- Screening of obstructive sleep apnea using Hilbert–Huang decomposition of oronasal airway pressure recordingsPublication . Caseiro, P.; Fonseca-Pinto, Rui; Andrade, A.Polysomnographic signals are usually recorded from patients exhibiting symptoms related to sleep disorders such as obstructive sleep apnea (OSA). Analysis of polysomnographic data allows for the determination of the type and severity of sleep apnea or other sleep-related disorders by a specialist or technician. The usual procedure entails an overnight recording several hours long. This paper presents a methodology to help with the screening of OSA using a 5-min oronasal airway pressure signal emanating from a polysomnographic recording during the awake period, eschewing the need for an overnight recording. The clinical sample consisted of a total of 41 subjects, 20 non-OSA individuals and 21 individuals with OSA. A signal analysis technique based on the Hilbert-Huang transform was used to extract intrinsic oscillatory modes from the signals. The frequency distribution of both the first mode and second mode and their sum were shown to differ significantly between non-OSA subjects and OSA patients. An index measure based on the distribution frequencies of the oscillatory modes yielded a sensitivity of 81.0% (for 95% specificity) for the detection of OSA. Two other index measures based on the relation between the area and the maximum of the 1st and 2nd halves of the frequency histogram both yielded a sensitivity of 76.2% (for 95% specificity). Although further tests will be needed to test the reproducibility of these results, the proposed measures seem to provide a fast method to screen OSA patients, thus reducing the costs and the waiting time for diagnosis.