Respiratory sinus arrhythmia: opposite effects on systolic and mean arterial pressure in supine humans

1.Are arterial blood pressure fluctuations buffered or reinforced by respir atory sinus arrhythmia (RSA)? There is still considerable debate about this simple question. Different results have been obtained, triggering a discus sion as to whether or not the baroreflexes are responsible for RSA. We susp ected that the measurement,; of different aspects of arterial pressure (mea n arterial pressure (MAP) and systolic pressure (SP)) can explain the confl icting results. 2. Simultaneous recordings of beat-to-beat MAP, SP, left cardiae stroke vol ume (SV, pulsed ultrasound Doppler), heart rate (HR) and respiration (RE) w ere obtained in 10 healthy young adults (luring spontaneous respiration. In order to eliminate HR variation at respiratory frequency we used propranol ol and atropine administration in the supine and tilted positions. Respirat ion-synchronous variation in the recorded variables was quantified by spect ral analysis of the recordings of each of these variables, and the phase re lations between them were determined by cross-spectral analysis. 3. MAP fluctuations increased after removing heart rate variations in both supine and tilted position, whereas SP fluctuations decreased in the supine position and increased in the head-up tilted position. 4. RSA buffers respiration-synchronous fluctuations in MAP in both position s. However, fluctuations in SP were reinforced by RSA in the supine and buf fered in the tilted position.