Pulmonary oedema without critical increase in left atrial pressure in acute myocardial infarction.

Twelve patients with acute myocardial infarction and radiological evidence of pulmonary oedema were observed in whom the left atrial pressure, measured indirectly as pulmonary artery end-diastolic pressure, was not critically increased (range 5-12 mm Hg with reference to sternal angle). Eight of the patients had been treated with frusemide, but only six had responded: hence in at least half of the series diuresis could not account for the anomalous finding. Six patients with low cardiac output were given infusions to expand plasma volume. Appreciable increments in mean values for cardiac index (1.6 to 2.0 1/min/m2), stroke index (18 to 23 ml/beat/m2), mean arterial pressure (65 to 86 mm Hg), and pulmonary artery end-diastolic pressure (8 to 15 mm Hg) were recorded. This group, and the remaining six patients with higher cardiac output, survived to leave hospital. Delay in radiographic clearing after a fall of left atrial pressure was a possible explanation for the relatively low pulmonary artery end-diastolic pressures, especially in the patients treated successfully with diuretics. Other mechanisms, such as alterations in pulmonary vascular permeability, might also have contributed to the syndrome. Pulmonary oedema without a critical increase in the left atrial pressure is unusual in acute myocardial infarction but the therapeutic implications are important. Withdrawal;of diuretics may be indicated, and in some cases expansion of plasma volume may lead to striking clinical improvement.     

Spatial control of rhabdom shedding in the lateral eye of the American horseshoe crab, <Emphasis Type="Italic">Limulus polyphemus</Emphasis>

Membrane leaves the rhabdom of Limulusphotoreceptors either by transient shedding at dawn or throughout the day by light-driven shedding. We examined whether the light trigger for transient shedding and the light drive for light-driven shedding are localized properties of the illuminated photoreceptors or whether they are an array property of the retina. Four experiments were conducted during which the lateral eye was exposed to one of a variety of different illumination patterns for a day, fixed, dissected and cut into serial frozen sections. Immunocytochemistry with different antibodies to Limulus opsin and arrestin revealed the results of the two processes in a distinguishable way. Eyes stimulated with whole-eye illumination had both types of shedding or just light-driven shedding when transient shedding was blocked by cutting the optic nerve. Eyes exposed to whole-eye darkness had neither type of shedding. However, when only half of an eye was exposed to light, the dark half had the same kinds of shedding as the lighted half. We conclude that the signals to trigger or drive shedding must be communicated laterally from illuminated ommatidia to unilluminated ommatidia. Rhabdom shedding is an array property.     

Character phylogeny of the primate forelimb superficial venous system.

The ontogeny and comparative anatomy of the forelimb superficial veins were investigated in humans, non-human primates and other mammals. Adult humans and the orangutan (Pongo) possess two autonomous forelimb veins, one on the lateral (preaxial) margin of the limb, the other on the medial (postaxial) margin. All other adult primates and mammals examined possess a lateral vein alone. In African apes (Pan and Gorilla) and in 24% of human forelimbs the lateral vein is short, being essentially confined to the antebrachial region, whereas in other mammals and in 76% of human limbs the lateral vein runs from the carpus to the clavicular region. In humans the medial vein develops before the lateral vein, whereas in the rabbit and the pig the medial vein is present in early embryos but is subsequently lost. We propose that in humans, and probably also in the orangutan, the possession of a medial vein is a neotenic retention of a primitive tetrapod condition. These animals, which retain their medial vein, are united by losing a late stage in their ontogeny. Other animals subsequently pass through a stage in which the medial vein is lost, but Pongo and Homo retain this vein to adulthood. The loss of an ontogenetic stage can arise independently, and the presence of a medial vein therefore affords only weak evidence for a close phylogenetic relationship between humans and the orangutan. The polymorphic lateral vein of humans may be a character state that is intermediate between the derived (short) lateral vein of the African apes and the primitive long lateral vein of other non-human primates and mammals.