Non-invasive assessment of the sensitivity of cardiac baroreflex was performed by recording each RR-interval and each blood pressure cycle (Finapres®). In sequences of at least three cardiac cycles in which systolic blood pressure and RR-interval had changed in the same direction, the slope of linear regression of RR duration as a function of the change in systolic arterial pressure was taken for estimating the sensitivity of the spontaneous cardiac baroreflex. This technique was used in healthy humans to examine how a postural change from supine to upright by either active standing up or 60° head-up tilting modified the sensitivity of the spontaneous baroreflex. We observed that the slope of the spontaneous baroreflex averaged 14.6 ±2 ms.mm Hg_1 during rest in the supine position, and decreased to 7.8 ± 1.2 ms.mm Hg"1 (p<0.05) after active standing, while the number of sequences was significantly increased in the upright as compared to the supine position. Head-up tilting by 60° led to values similar to those following active standing. The adjustment of baroreflex slope to either postural change occurred in a few seconds, so that posture-characteristic values were obtained from five-minute records. We conclude that non- invasive recording of spontaneous sequences of related changes in blood pressure and RR-interval during several minutes provides reproducible values of the slope of cardiac baroreflex in the supine and upright position. This easy and reliable determination of the sensitivity of the cardiac baroreflex might prove to be useful when assessment of baroreflex function is needed.
The aims were to explore the effect of head-up tilt (HUT) to 30 and 60 degrees on hemodynamics and tissue oxygenation in anesthetized healthy swine. The data serve as a reference for a study of resuscitation efficacy at HUT such as during transport. Nine healthy swine (49±4 kg) were anesthetized and multiple sensors including myocardial pressure-volume loops catheter, carotid flow probe, blood pressure catheters, near infrared spectroscopy (NIRS) tissue oximetry and mixed venous oximetry (SVO2) catheter were introduced and parameters continuously recorded. Experimental protocol consisted of baseline in supine position (15 min), 30 degrees HUT (15 min), recovery at supine position (15 min) and 60 degrees HUT (5 min). Vacuum mattress was used for body fixation during tilts. We found that 30 and 60 degrees inclination led to significant immediate reduction in hemodynamic and oximetry parameters. Mean arterial pressure (mm Hg) decreased from 98 at baseline to 53 and 39, respectively. Carotid blood flow dropped to 47 % and 22 % of baseline values, end diastolic volume to 49 % and 53 % and stroke volume to 47 % and 45 % of baseline. SVO2 and tissue oximetry decreased by 17 and 21 percentage points. The values are means. In conclusions, within minutes, both 30 and 60 degrees head-up tilting is poorly tolerated in anesthetized swine. Significant differences among individual animals exist., M. Mlcek, J. Belohlavek, M. Huptych, T. Boucek, T. Belza, S. Lacko, P. Krupickova, M. Hrachovina, M. Popkova, P. Neuzil, O. Kittnar., and Obsahuje bibliografii
Previously, increased diameter and enhanced myogenic tone were seen after 2-week 45º head-up (HUT2) in the rat. We studied the reversibility and the effect of extended tilt on this phenomenon using two experimental groups: HUT2 plus 2-week horizontal (HUT2HOR2), and 4-week tilting (HUT4). 4-weeks in normal cages (NC4) served as control. Diameter of saphenous vein (SV) in 2-20 mm Hg pressure range, wall and media thickness, endothelial and smooth muscle cell densities, and cell proliferation were measured. The diameter of SV from HUT4 was significantly larger compared with HUT2HOR2 or NC4 within the whole pressure range both in Krebs-Ringer (870.4±21.3 vs. 778.2±24.9 and 771.6±28.1 μm at 10 mm Hg, respectively) and in Ca2+-free solution. Myogenic and norepinephrine-induced vascular tone, wall and media thickness did not differ among the three groups. Endothelial cell density decreased in HUT4 (10.7±1.2) vs. HUT2HOR2 (15.1±1.0) and NC4 (15.3±0.6), while that of smooth muscle was unchanged. No cell proliferation marker was seen. In conclusion, both increased diameter and enhanced myogenic tone of SV seen in HUT2 proved to be reversible. HUT4 resulted in increased SV diameter, similarly to HUT2, however, vascular tone was not amplified. This suggests that a prolonged orthostatic load may readjust the function of smooth muscle., G. Raffai, C. Lódi, G. Illyés, G. Nádasy, E. Monos., and Obsahuje bibliografii a bibliografické odkazy
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
Arterial compliance (C) is a complex parameter influencing ventricular-arterial coupling depending on structural (arterial wall remodeling) and functional (blood pressure, smooth muscles tone) changes. Based on Windkessel model, C can be calculated as the ratio of a time constant Tau characterizing diastolic blood pressure decay and total peripheral resistance (TPR). The aim of this study was to assess changes of C in the context of systolic arterial pressure (SAP) perturbations during four physiological states (supine rest, head-up tilt, supine recovery, mental arithmetic). In order to compare pressure independent changes of C a new index of C120 was proposed predicting C value at 120 mm Hg of SAP. Eighty-one healthy young subjects (48 f, average age 18.6 years) were examined. Hemodynamic parameters were measured beat-to-beat using volume-clamp photoplethysmographic method and impedance cardiography. We observed that C was strongly related to SAP values on the beat-to-beat time scale. Interestingly, C120 decreased significantly during stress phases. In conclusion, potential changes of SAP should be considered when measuring C. Arterial compliance changes in the opposite direction to TPR pointing towards influence of vascular tone changes on its value.