Cerebral hemodynamics and oxygenation in preterm infants after low-vs. high-dose surfactant replacement therapy

In thirteen preterm infants receiving surfactant (Curosurf) replacement therapy, changes in cerebral hemodynamics and oxygenation were investigated by near infrared spectroscopy. Surfactant instillation led to an instantaneous increase in cerebral blood volume (CBV) in all infants, which was primarily due to an increase in deoxygenated hemoglobin. Five infants received a low dose (100 mg/kg = 1.25 ml/kg) of surfactant and 8 a high dose (200 mg/kg = 2.50 ml/kg). A significantly larger increase in CBV was observed in the infants receiving a high dose compared to those receiving a low dose of surfactant. We conclude that cerebral perfusion is affected more after the instillation of a high dose compared to a low dose of surfactant.     

The four-electrode resistivity technique in anisotropic media:theoretical analysis and application on myocardial tissue in vivo

Several aspects of the 4-electrode resistivity technique were studied with special emphasis on the theoretical determination of penetration depth and sample volume in anisotropic media such as (cardiac) muscle. Moreover, the presence of a thin disturbing layer on top of the medium under study was analyzed. A 4-electrode sensor was developed for the measurement of local myocardial resistivity in 2 orthogonal directions. The sensor was applied to the epicardium of anesthetized open chest dogs and, as an example, results are given on the frequency dependence (5-60 kHz) and the changes during the cardiac cycle of longitudinal and transverse myocardial resistivity     

Effects of critical coronary stenosis on global systolic left ventricular function quantified by pressure-volume relations during dobutamine stress in the canine heart

OBJECTIVES: In this study we quantified the effects of a critical coronary stenosis on global systolic function using pressure-volume relations at baseline and during incremental dobutamine stress. BACKGROUND: The effects of coronary stenosis have previously been analyzed mainly in terms of regional (dys)function. Global hemodynamics are generally considered normal until coronary flow is substantially reduced. However, pressure-volume analysis might reveal mechanisms not fully exposed by potentially load-dependent single-beat parameters. Moreover, no systematic analysis by pressure-volume relations of the effects of dobutamine over a wide dose range has previously been presented. METHODS: In 14 dogs left ventricular volume and pressure were measured by conductance and micromanometer catheters, and left circumflex coronary flow by Doppler probes. Measurements in control and with left circumflex stenosis were performed at baseline and at five levels of dobutamine (2.5 to 20 microg/kg/min). The end-systolic pressure-volume relation (ESPVR) dP/dtMAX vs. end-diastolic volume (dP/dtMAX - V(ED)) and the relation between stroke work and end-diastolic volume (preload recruitable stroke work [PRSW]) were derived from data obtained during gradual caval occlusion. RESULTS: In control, dobutamine gradually increased heart rate up to 20 microg/kg/min, the inotropic effect blunted at 15 microg/kg/min. With stenosis, the chronotropic effect was similar, however, contractile state was optimal at approximately 10 microg/kg/min and tended to go down at higher levels. At baseline, the positions of ESPVR and PRSW, but not of dP/dtMAX - V(ED), showed a significant decrease in function with stenosis. No differences between control and stenosis were present at 2.5 microg/kg/min; the differences were largest at 15 microg/kg/min. CONCLUSIONS: Pressure-volume relations and incremental dobutamine may be used to quantify the effects of critical coronary stenosis. The positions of these relations are more consistent and more useful indices than the slopes. The positions of the ESPVR and PRSW show a reduced systolic function at baseline, normalization at 2.5 microg/kg/min and a consistent significant difference between control and stenosis at dobutamine levels of 5 microg/kg/min and higher.     

The trans-cardiac conductance method for on-line measurement of left ventricular volume: assessment of parallel conductance offset volume

The trans-cardiac conductance (TCC) method provides on-line left ventricular (LV) volume signals by determining the electrical conductance of blood in the LV by means of central venous and epithoracic electrodes. Conductive structures outside the LV blood pool cause a "parallel conductance" offset term (Vp) that can be determined by bolus injections of hypertonic saline in the pulmonary artery (Vp(saline)), which cause a transient increase in blood conductivity. This study in anesthetized sheep evaluates the accuracy of the saline calibration method and the variabilities of Vp between animals, between hemodynamic conditions and during the cardiac cycle. The conventional intra-cardiac conductance catheter method was used to obtain independent estimates of Vp by the zero-volume method (Vp(zero volume)). Mean baseline Vp(saline) and Vp(zerovolume) were 104 +/- 6 ml and 106 +/- 6 ml, respectively. Bland-Altman analysis showed a small nonsignificant bias (-2.5 ml) and narrow limits of agreement (4.6 ml). Vp was not significantly different between hemodynamic conditions (baseline, dobutamine, volume load, propranolol), but had a substantial interanimal variability (IAV) (38%). Average variations during the cardiac cycle were < 10% of mean Vp. We conclude that the saline method can be applied to determine Vp for TCC. IAV is substantial, so that Vp must be determined in each animal, but within-animal variability is relatively small.