Ventilation related heart rate oscillations – respiratory sinus
arrhythmia (RSA) – originate in human from several mechanisms.
Two most important of them – the central mechanism (direct
communication between respiratory and cardiomotor centers),
and the peripheral mechanism (ventilation-associated blood
pressure changes transferred to heart rate via baroreflex) have
been described in previous studies. The major aim of this study
was to compare the importance of these mechanisms in the
generation of RSA non-invasively during various states by
quantifying the strength of the directed interactions between
heart rate, systolic blood pressure and respiratory volume
signals. Seventy-eight healthy volunteers (32 male, age range:
16.02-25.77 years, median age: 18.57 years) participated in this
study. The strength of mutual interconnections among the
spontaneous beat-to-beat oscillations of systolic blood pressure
(SBP), R-R interval (RR signal) and respiration (volume changes –
RESP signal) was quantified during supine rest, orthostatic
challenge (head-up tilt, HUT) and cognitive load (mental
arithmetics, MA) using bivariate and trivariate measures of
cardio-respiratory information transfer to separate baroreflex and
nonbaroreflex (central) mechanisms. Our results indicate that
both basic mechanisms take part in RSA generation in the intact
cardiorespiratory control of human subjects. During orthostatic
and mental challenges baroreflex based peripheral mechanism
becomes more important
n previous studies, one of the systolic time intervals - preejection period (PEP) - was used as an index of sympathetic activity reflecting the cardiac contractility. However, PEP could be also influenced by several other cardiovascular variables including preload, afterload and diastolic blood pressure (DBP). The aim of this study was to assess the behavior of the PEP together with other potentially confounding cardiovascular system characteristics in healthy humans during mental and orthostatic stress (head-up tilt test - HUT). Forty-nine healthy volunteers (28 females, 21 males, mean age 18.6 years (SD=1.8 years)) participated in the study. We recorded finger arterial blood pressure by volume-clamp method (Finome ter Pro, FMS, Netherlands), PEP, thoracic fluid content (TFC) - a measure of preload, and cardiac output (CO) by impedance cardiography (CardioScreen ®2000, Medis, Germany). Systemic vascular resistance (SVR) - a measure of afterload - was calculated as a ratio of mean arterial pressure and CO. We observed that during HUT, an expected decrease in TFC was accompanied by an increase of PEP, an increase of SVR and no significant change in DBP. During mental stress, we observed a decrease of PEP and an increase of TFC, SVR and DBP. Correlating a change in assessed measures (delta values) between mental stress and previous supinerest, we found that ΔPEP correlated negatively with ΔCO and positively with ΔSVR. In orthostasis, no significant correlation between ΔPEP and ΔDBP, ΔTFC, ΔCO, ΔMBP or ΔSVR was found. We conclude that despite an expected increase of sympathetic activity during both challenges, PEP behaved differently indicating an effect of other confounding factors. To interpret PEP values properly, we recommend simultaneously to measure other variables influencing this cardiovascular measure., J. Krohova, B. Czippelova, Z. Turianikova, Z. Lazarova, I. Tonhajzerova, M. Javorka., and Obsahuje bibliografii