Nonlinearity and load sensitivity of end-systolic pressure-volume relation of canine left ventricle in vivo.

The effects of mechanical changes in loading conditions on the left ventricular end-systolic pressure-volume relation (ESPVR) were studied in nine open-chest dogs, including three dogs studied before and after beta-adrenergic blockade. Left ventricular pressure was measured with a micromanometer, and left ventricular volume was measured with a conductance catheter. ESPVRs were obtained by increasing left atrial inflow over wide volume ranges (as much as threefold) under three different conditions: control or high or low aortic impedance. High impedance was obtained by occlusion of the descending aorta, and low impedance was obtained by a shunt between the subclavian artery and the left atrium. In the unblocked animals in 21 of 28 runs, a second-order polynomial equation gave a better fit for the ESPVR than a linear relation. To quantify the effects of the changes in aortic impedance on the ESPVR, we calculated from the quadratic equation its volume intercept (V18) and its local slope (E18) at an end-systolic pressure (Pes) of 18 kPa. In the unblocked animals, a statistically significant difference was found in V18 between low impedance (21.50 +/- 6.27 ml) and high impedance (14.10 +/- 8.98 ml; p less than 0.005) and between control (19.14 +/- 9.58 ml) and high impedance (p less than 0.05). In most dogs, E18 was increased at high and decreased at low impedance, but not significantly. In the additional experiments with beta-blockade, the nonlinearity diminished somewhat, but the load dependency of the ESPVR remained present after beta-blockade because the same leftward shift of the ESPVR with high aortic impedance was found. Two other relations, namely, of dP/dtmax and of stroke work versus end-diastolic volume, were also investigated, which on the whole showed the same behavior as the ESPVR. These results indicate that the ESPVR and dP/dtmax-Ved and stroke work-end-diastolic volume relations, when studied over a wide volume range, are nonlinear and that changes in loading conditions influence indexes of contractility derived from these relations, especially the volume intercepts, in such a way that an increase in aortic impedance may be interpreted as an increase in contractility. Blocking the beta-adrenergic receptors did not influence the load dependency of the ESPVR but, in some cases, tended to decrease the nonlinearity in concordance with the relation between contractility and nonlinearity in isolated hearts.

Neonatal pneumothorax drainage systems: in vitro evaluation.

We studied, in vitro, different commercially available components for pneumothorax drainage, i.e. drainage tubes, Heimlich flutter valve and vacuum control units. The drainage of a pneumothorax by a drainage tube was, as expected, directly dependent on Poiseuille's law and was influenced more by diameter than length. Of practical importance, a size 6 French gauge tube, used for the very small newborn, may not efficiently evacuate a pneumothorax due to a large air leak. The Heimlich flutter valve, though useful clinically, adds to the resistance of the system especially if fluids accumulate in the valve. All vacuum control units, adaptations of the basic three- or four-bottle pleural drainage system, functioned adequately but simple changes in construction may increase the safety of some of these systems.

Increased frequency of spontaneous and X-ray-induced chromosomal aberrations in lymphocytes from neonates and the influence of caffeine--an in vitro study.

We have examined lymphocytes from human preterm (PT) and fullterm (FT) babies for an effect of gestational age (GA) on chromosomal aberrations either occurring spontaneously or induced by treatment with X-rays (1 Gy) alone; or with caffeine (1,3,7-trimethylxanthine) supplementation (5 X 10(-4) M), in comparison to the lymphocytes of healthy adults (AD). Percent of abnormal cells (%Abn) was used as an indicator of chromosome sensitivity to the different treatments. PT babies had significantly higher spontaneous and X-ray-induced %Abn values than AD, but were comparable to FT. After X-irradiation + caffeine the yield of aberrations in any 2 groups was not significantly different. Chromosomal sensitivity may result from factors other than GA. This in vitro model may permit study of the mechanisms of chromosomal damage repair and prevention of free radical damage of DNA during the perinatal period.

The effect of a manometer on the mean airway pressure during hand ventilation, an in vitro study.

The effect of an on-line manometer on the variables of ventilation i.e. peak inspiratory pressure (PIP), mean airway pressure (MAP), positive end expiratory pressure (PEEP), and inspiratory to expiratory time ratio (I:E) was studied in vitro. Analysis of PIP, MAP, PEEP, and I:E was made during hand ventilation of a resuscitation mannequin at the preselected PIP of 15 and 25 cm water with and without a manometer. Use of the manometer decreased the range of variation in PIP, but the MAP was higher. This was due to an increased I:E while PEEP remained unchanged. An on-line manometer during hand ventilation prevents excessive PIP but may increase the MAP and therefore may not prevent development of a pneumothorax.

Plastic blankets and heat shields decrease transmission of phototherapy light.

An in vitro study showed that the use of transparent plastic insulation to decrease heat loss from newborn infants substantially decreases the transmission of phototherapy light. The decrease is proportional to the number of plastic layers between the light source and the baby because of reflection from the surface of the plastic. This increases if the surface is irregular. Thickness and the type of plastic used had no effect.