A. Jarrell Raper

Detailed Description of a Cranial Window Technique for Acute and Chronic Experiments

Methods for implantation of cranial windows for the direct observation of the pial microcirculation in experimental animals are described in detail. These techniques are suitable for both acute experiments in anesthetized animals and chronic implantation permitting several months of observation in awake animals. Experience over several years shows that these techniques have an acceptably low rate of failure, are low in cost and can easily be mastered in most laboratories. They make possible observation of the microcirculation and accurate measurement of the diameter of pial vessels, and permit study of the effects on the microcirculation of a variety of maneuvers and vasoactive agents which can be studied by direct application as well as by intravascular administration. Because they preserve the integrity of the skull, the techniques permit study of the cerebral microcirculation under conditions closely approximating the normal environment of these vessels.

Determinants of Response of Pial Arteries to Norepinephrine and Sympathetic Nerve Stimulation

Feline pial arteries larger than 100 μ in diameter constricted in response to cervical sympathetic nerve stimulation or in response to topical application of norepinephrine. Smaller pial arteries were unresponsive to norepinephrine. This unresponsiveness persisted when norepinephrine was dissolved in CSF with high calcium ion concentration, or in CSF with both high calcium ion and zero magnesium ion concentration, or when it was dissolved in the acid fluid used by Wahl et al. and applied by constant infusion or by intermittent application. Comparison of the responses of the larger pial vessels to norepinephrine and to sympathetic nerve stimulation suggests that maximal activation of sympathetic nerves achieves a concentration of released norepinephrine equal to 5.9 × 10-4 M. The constriction of the larger pial vessels in response to sympathetic nerve stimulation could account for modest reductions in cerebral blood flow.

Modification by Beta-Adrenergic Blockade of the Circulatory Responses to Acute Hypoxia in Man*

In 17 healthy men, beta-adrenergic blockade reduced significantly the tachycardia and the elevation of cardiac output associated with inhalation of 7.5% oxygen for 7 to 10 minutes. Hypoxia did not increase plasma concentrations of epinephrine or norepinephrine in six subjects. Furthermore, blockade of alpha and beta receptors in the forearm did not modify the vasodilation in the forearm induced by hypoxia, providing pharmacologic evidence that hypoxia of the degree and duration used was not associated with an increase in the concentrations of circulating catecholamines in man. Part of the increase in cardiac output and heart rate during acute hypoxia in man is produced by stimulation of beta-adrenergic receptors, probably by cardiac sympathetic nerves. The mechanism of the vasodilation in the forearm during hypoxia remains uncertain.

Unresponsiveness of Pial Precapillary Vessels to Catecholamines and Sympathetic Nerve Stimulation

A systematic analysis of the possible existence of neurogenic control of precapillary pial vessels was made in three species (cat, dog, and rabbit). In all of these animals, pial vessels failed to respond to externally applied isoproterenol or norepinephrine in high concentrations (up to 100 μg/ml), although the vessels did dilate in response to externally applied histamine. Adrenergic nerve endings on the pial vessels were demonstrated by fluorescent histochemical techniques specific for catecholamines. However, in the absence of changes in arterial blood pressure and arterial blood carbon dioxide tension, pial precapillary vessels showed no change in caliber in response to stimulation of the ipsilateral superior cervical ganglion. These results show that pial precapillary vessels are not subject to vasoconstriction probably because they lack sufficient receptors for the catecholamine neurotransmitter.

Pheochromocytoma of the urinary bladder: A broad clinical spectrum

A case of pheochromocytoma of the urinary bladder is reported, and 35 perviously reported cases are analyzed. This interesting entity can present with symptoms of catecholamine excess and severe hypertensive spells (often micturition-induced) or as asymptomatic hematuria without hypertension. The present case represents the severest end of the clinical spectrum, with advancing acute retinopathy and visual loss, very high blood pressure and greatly increased catecholamine excretion. Several special precautions were utilized during diagnostic studies and surgery. On the whole, prognosis is excellent in nonmalignant cases properly handled, and the location of the tumor provides opportunity for early case finding and complete cure.

Five Unusual Cases of Ventricular Aneurysm

Abstract Five patients with ventricular aneurysm exhibiting unusual etiological or anatomical features are presented. Resection of large portions of the ventricular myocardium, which may at times include the papillary muscle, is compatible with an excellent recovery despite diminution in the size of the left ventricular cavity and concomitant mitral valve replacement. Intentional fibrillation of the heart is recommended after the institution of bypass and prior to manipulation of the aneurysm in order to minimize the risk of intraoperative thromboembolism.