Chapter 2 6/min 10, 26. Paced breathing requires cooperation of the patient whereas spontaneous blood pressure variations can be recorded without specific instruc- tions. The same holds for squat-stand manoeuvres, although this seems a promis- ing addition 7. Another procedural aspect concerns possible circadian variations in dCA. Ainslie et al reported a significant lowering in ARI from evening to morning 3. Therefore, it might be necessary to standardise the time of day for dCA recording. For TFA different signal processing techniques can be applied and the most common will be evaluated in this study. First, before applying Fourier transform, offset and/or slow trends are removed either by subtracting the mean or by sophisticated detrending procedures to remove also very low frequencies. Sec- ond, for spectral estimation two approaches can be used: either the spectral averaging technique, also known as the Welch technique 32, in which spectra of subsequent epochs are averaged or spectral smoothing in which the spectra are smoothed with triangular smoothing windows 31. In this study the effect on reproducibility will be evaluated for the different TFA analysis options and for the MMPF method. A major question is whether results of MMPF compared to TFA analysis are more consistent and show less variabil- ity. To reveal effects of the measurement conditions also spontaneous vs. paced breathing and morning vs. afternoon recordings will be compared. Methods Subjects and measurements Nineteen healthy subjects (14M/5F) between 18 and 53 years old (mean 28) volun- tarily participated in the study. All were free of known cardiovascular, pulmo- nary and cerebrovascular disorders. Each subject was measured in supine posi- tion on two different days, one day in the morning at 10am and a different day one week apart in the afternoon at 2pm. The order of day was randomly as- signed. Each recording session lasted about one hour. A session consisted of three successive runs each consisting of 15 minutes of spontaneous breathing followed by 5 minutes of 6/min frequency paced breathing. A one channel electrocardiogram (ECG) was measured by an in-house made portable ECG-amplifier (IDEE Maastricht®, the Netherlands). Continuous arterial blood pressure (ABP) was measured using a non-invasive finger blood pressure monitor (Portapres®, TNO, Amsterdam, the Netherlands) commonly used in studies on dynamic cerebral autoregulation. The appropriate finger cuff (size: small, medium or large) was placed on the left hand middle finger. During 22
proefschrift gommer inhoud met kaft.indd
To see the actual publication please follow the link above