Diamond-winged variants of the Müller-Lyer figure: a test of Virsu's (1971) centroid theory.

Diamond-winged variants of the Müller-Lyer figure were used to test predictions of Virsu's (1971) theory of the Müller-Lyer illusion based on efferent readiness for eye movements toward the figure's center of gravity. A Müller-Lyer figure with diamond-shaped wings resulted in a greater center-of-gravity distance than the corresponding, conventional Müller-Lyer figure, but fin length and the rest of the figure remained constant; in Virus's study, fin length and center-of-gravity distance covaried. Results were consistent with Virus's data when we used the stimulus conditions that he reported. Results from a wide range of stimuli challenge Virsu's theory, and thus are consistent with the conclusions of Brigell, Uhlarik, and Goldhorn (1977).

The hemodynamic effects of intubation during nitroglycerin infusion in severe preeclampsia.

The effectiveness of intravenous nitroglycerin infusion in lowering maternal blood pressure and in blunting the hemodynamic responses to endotracheal intubation was evaluated in six primigravid women with severe preeclampsia. Monitoring consisted of continuous electrocardiogram monitoring, arterial cannulation, and flow-directed pulmonary arterial catheterization in each patient. All patients underwent oxytocin induction of labor and crystalloid and/or colloid expansion to produce a pulmonary capillary wedge pressure of 10 to 15 mm Hg and a colloid osmotic pressure of greater than 17 mm Hg. Intravenous nitroglycerin was administered before induction of general anesthesia. The hemodynamic effects associated with endotracheal intubation revealed a change in the heart rate from 104 +/- 10 to 133 +/- 17 beats/min, an increase in mean arterial pressure from 134 +/- 12 to 164 +/- 32 mm Hg, and an increase in systemic vascular resistance from 1262 +/- 342 to 1351 +/- 259 dynes-sec-cm-5 that was accompanied by a small change in the cardiac index from 4.5 +/- 1.2 to 4.5 +/- 0.9 L.min-1.m-2.

Post-caesarean section analgesia: a comparison of epidural butorphanol and morphine.

Epidural butorphanol 1, 2 and 4 mg were compared with morphine, 5 mg, for postoperative analgesia in 92 consenting, healthy, term parturients who had undergone Caesarean section under epidural lidocaine anaesthesia in a randomized double-blind study. Postoperative pain was assessed using a visual analogue scale and recorded with heart rate, blood pressure and respiratory rate. The demographic characteristics, and the incidences of primary and repeat Caesarean sections, were not different among the four treatment groups. At 15, 30, 45 and 60 min after treatment the median pain scores following butorphanol were similar and lower than those following morphine (P less than 0.05). Calculated median percentage pain relief values for butorphanol were higher than morphine at each of these times (P less than 0.05). At 90 min and 2 hr the pain scores and pain relief values were similar. Beyond 45 min the number of patients requesting supplemental medication and dropping out of the study increased progressively in both the butorphanol and morphine treated patients. The attrition profiles for butorphanol were different from morphine (P less than 0.01). The median time in the study was greater than 24 hr for morphine, and 3, 2.5 and 4 hr for butorphanol, 1, 2 or 4 mg, respectively. No patient developed a clinically important change in heart rate or blood pressure, and none experienced a decrease in respiratory rate below 12 breaths.min-1. One of 69 patients (1.4 per cent) who received butorphanol developed pruritus compared with ten (43 per cent) of 23 patients who received morphine. The global assessments of the adequacy of analgesia were indistinguishable between morphine and butorphanol. Epidural butorphanol provides safe, effective postoperative analgesia, has a prompt onset, and a limited duration.

Alfentanil for urgent caesarean section in a patient with severe mitral stenosis and pulmonary hypertension.

We present the case of a parturient with severe mitral stenosis and pulmonary hypertension who received general anaesthesia using alfentanil for urgent Caesarean section. Alfentanil promoted haemodynamic stability and allowed immediate postoperative extubation. Epidural morphine provided postoperative analgesia. This combination permitted early ambulation and prevention of thromboembolism. A disadvantage of this technique, neonatal respiratory depression, was promptly reversed with a single dose of naloxone. The anaesthetic management of mitral stenosis in pregnancy is discussed and the neonatal pharmacokinetics of maternally administered alfentanil are presented.

Role of volume expansion in severe pre-eclampsia.

Fifteen primigravid patients with severe pregnancy-induced hypertension were studied by catheterization of the right side of the heart. A hemodynamic protocol was implemented that required maintaining colloid osmotic pressure above 17 millimeters of mercury, pulmonary capillary wedge pressure below 15 millimeters of mercury and the mean arterial pressure in a very narrow range throughout labor and delivery and for 48 hours postpartum. The initial colloid osmotic pressures and pulmonary capillary wedge pressures were 18.0 +/- 2.6 and 10.5 +/- 4.0 millimeters of mercury, respectively, and remained essentially unchanged throughout the post partum period. The only benefit derived from volume expansion in these patients appeared to be the absence of acute fetal distress after the initiation of antihypertensive therapy. Six of 15 patients had late fetal stress develop during labor, suggesting that aggressive volume repletion and colloid osmotic pressure correction in pregnancy-induced hypertension does not effect the over-all incidence of fetal distress. We recommend that correction of colloid osmotic pressure be restricted to instances in which extremely low values (less than 12 millimeters of mercury) or a prolonged negative colloid osmotic pressure to pulmonary capillary wedge pressure gradient are identified. Finally, the benefit of volume expansion in pregnancy-induced hypertension appears to be the prevention of sudden and profound drops in blood pressure with antihypertensive therapy--not the prevention of fetal distress during labor.

Influence of crystalloid versus colloid infusion on peripartum colloid osmotic pressure changes.

Plasma colloid osmotic pressure acts to retain fluid in the intravascular space. Intravenous crystalloids have been identified as one of the major factors contributing to the consistent peripartum decline in colloid osmotic pressure. This study was undertaken to compare the effect of two crystalloid infusions (1000 and 2000 mL Plasma-Lyte A) and a colloid infusion (1000 mL 5% albumin) on the peripartum colloid osmotic pressure. Before elective cesarean section, 45 parturients received one of the three infusions. The lowest mean maternal colloid osmotic pressure (16.6 +/- 1.1 mmHg, P less than .05 compared with baseline) occurred in the 2000-mL crystalloid infusion group eight to 16 hours postpartum. Although the colloid osmotic pressure fell in all groups postpartum, this reduction was significantly (P less than .05) less during the first 24 hours in the colloid infusion group. Minimizing this disruption of the colloid osmotic pressure to pulmonary capillary wedge pressure gradient may be clinically important in selected patients.

Cardiovascular alterations in severe pregnancy-induced hypertension: effects of intravenous nitroglycerin coupled with blood volume expansion.

Control of blood pressure in severe pregnancy-induced hypertension has often relied on agents with an unpredictable onset and duration of action. Because intravenous nitroglycerin is a potent, rapidly acting agent with a hemodynamic half-life measured in minutes, we evaluated its cardiovascular effects with and without volume expansion in six patients with severe pregnancy-induced hypertension. Nitroglycerin alone reduced mean arterial pressure by 27.5% without any significant changes in heart rate, central venous pressure, or stroke volume. The pulmonary capillary wedge pressure fell from 9 +/- 3 to 4 +/- 2 mm Hg (p less than 0.05) while the cardiac index decreased from 3.51 +/- 0.67 to 2.87 +/- 0.76 L/min X m2. Oxygen delivery fell significantly (p less than 0.05), from 617 +/- 78 to 491 +/- 106 ml/min X m2. While volume expansion alone had no effect on mean arterial pressure, the combination of blood volume expansion and nitroglycerin resulted in a marked resistance to the hypotensive effect of nitroglycerin. Cardiac index, pulmonary capillary wedge pressure, and oxygen utilization were not significantly different from baseline values when volume expansion preceded nitroglycerin. We conclude that the ease with which nitroglycerin reduces blood pressure is dependent on the individual patient's volume status. Although volume expansion allows one to maintain cardiac index, pulmonary capillary wedge pressure, and oxygen utilization when used in combination with nitroglycerin, this benefit may be offset by a concomitant reduction in hypotensive capability.

Role of intravenous nitroglycerin in the treatment of severe pregnancy-induced hypertension complicated by pulmonary edema.

Intravenous nitroglycerin would appear to be an ideal agent for the treatment of severe pregnancy-induced hypertension complicated by cardiogenic pulmonary edema. Nitroglycerin infusion effectively reduces preload by venous dilatation and, at higher doses, results in arterial vasodilatation. Because of these pharmacologic properties, the effects of intravenous nitroglycerin were studied in three patients with severe pregnancy-induced hypertension complicated by pulmonary edema. The major cardiovascular effects of nitroglycerin were to reduce the mean pulmonary capillary wedge pressure from 27 +/- 4 to 14 +/- 6 mm Hg, which result in a change in the colloid osmotic pressure to pulmonary capillary wedge pressure gradient from -10 to 2 mm Hg. No significant changes occurred in heart rate, central venous pressure, or cardiac index. Analysis of oxygen-related parameters revealed a significant (p less than 0.05) increase in oxygen delivery and extraction accompanied by a 53% increase in oxygen consumption. The changes in oxygen-related variables appeared to be secondary to a fall in mixed venous oxygen tension from 39 +/- 4 to 33 +/- 1 torr. These changes occurred without any significant improvement in arterial oxygen tension. We conclude that while intravenous nitroglycerin expeditiously corrects the hydrostatic derangements of pulmonary edema seen in pregnancy-induced hypertension, a rapid improvement in arterial oxygenation does not occur.