Role of tissue hypoxia in local regulation of cerebral microcirculation.

The mechanism of action of hypoxia on cerebral blood vessels and its role in the regulation of the cerebral circulation were investigated in anesthetized cats. Arterial hypoxia produced marked cerebral arteriolar vasodilation, which was partially reversed by perfusing the space under the cranial window with artificial cerebrospinal fluid (CSF) containing 6-94% oxygen. More marked increase in the local supply of oxygen, via perfusion of the space under the cranial window with fluorocarbon FC-80 equilibrated with 100% oxygen, completely eliminated the vasodilation induced by arterial hypoxia. Fluorocarbon equilibrated with 100% N2 had no effect on the vasodilation. The vasodilation associated with hypotension was completely reversed by perfusion with fluorocarbon equilibrated with 100% oxygen and was unaffected by perfusion with fluorocarbon or CSF equilibrated with gas not containing oxygen. The vasodilation associated with Metrazole-induced seizures was partially reversed by perfusion with fluorocarbon containing oxygen. The results show that hypoxia dilated cerebral blood vessels entirely via a local mechanism, that hypoxia is the dominant mechanism involved in the vasodilation associated with hypotension, and that it is, at least partially, responsible for the vasodilation associated with seizures.

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.

Paraganglioma of urinary bladder wall.

A classic case of pheochromocytoma of the urinary bladder is presented. The history of headaches and palpitations during micturition is the result of sudden release of catecholamines into the general circulation. The diagnosis using selective arteriography as well as the medical and surgical management are described.

Analysis of vasoactivity of local pH, PCO2 and bicarbonate on pial vessels.

The mechanism by which the local effect of CO2ON pial arterioles is exerted was examined in anesthetized cats equipped with a cranial window for the direct observation of the microcirculation of the parietal cortex. The dilation of pial arterioles in response to application of artificial cerebrospinal fluid with low pH was the same whether or not the PCO2 of the solution was maintained in the normal range or markedly increased. The constriction of pial arterioles in response to application of artificial cerebrospinal fluid with high pH was the same whether or not the PCO2 of the solution was maintained in the normal range or markedly decreased. Finally, pial arterioles did not change their caliber in response to application of cerebrospinal fluid with unchanged pH but markedly increased or decreased Pco, or bicarbonate ion concentration. These results show that the action of CO2 on cerebral vessels is exerted via changes in extracellular fluid pH and that molecular CO2 and bicarbonate ions do not have independent vasoactivity on these vessels.

Local mechanism of CO2 action of cat pial arterioles.

The effect of local hypercapnic acidosis or local hypocapnic alkalosis on pial arterioles were studied in anesthetized cats equipped with a cranial window for the direct observation of the pial microcirculation of the parietal cortex. Changes in PCO2 and pH of the extracellular fluid were induced by perfusing the space under the cranial window with artificial cerebrospinal fluid equilibrated with different concentrations of CO2, while PaCO2 was maintained constant. Hypercapnic acidosis dilated and hypocapnic alkalosis constricted pial arteioles markedly. The results indicate that a basis exists for considering CO2 as a mediator for local regulation of brain blood flow. The vasodilation associated with arterial hypercapnia was abolished by a reduction in CSF PCO2 equal in magnitude to the rise in arterial blood PCO2, suggesting that the action of CO2 is entirely local.

Hypertension screening among dental patients.

Between January 1974 and March 1975, blood pressures were taken on all 2,222 dental patients admitted for treatment at the Virginia Commonwealth University, Medical College of Virginia School of Dentistry. According to the criteria of an elevated diastolic blood pressure (above 95 mm Hg) at three successive readings not less than five days apart, 131 patients were referred to physicians as suspected hypertensives. One hundred and thirteen patients were deemed hypertensive by their physician. A positive family history of hypertension was noted for 54% of the 113 undetected hypertensives. Of the 113 hypertensives, 6% visited their dentist yearly but did not visit their physician during the same time. On this basis we conclude that about 6% of dental patients can be expected to be referred to physicians as a result of high blood pressure screening in a dentist's office.

A dental school hypertension screening program.

This paper has described a hypertension screening program at the Medical College of Virginia School of Dentistry. The program, which has been in operation for over two years, incorporates referral to a physician and a system of repeated follow-ups. The results indicate that the program has been successful in that 134 of a total of 141 patients with suspected hypertension have been successfully referred.

Determinants of response of pial arteries to norepinephrine and sympathetic nerve stimulation.

Feline pial arteries larger than 100 mu in diameter constricted in response to cervical sympathetic nerve stimulation suggests 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 that maximal activation of sympathetic nerves achieves a concentration of released norepinephrine equal to 5.9 x 10(-6) M. The constriction of the larger pial vessels in response to sympathetic nerve stimulation could account for modest reductions in cerebral blood flow.

Detailed description of a cranial window technique for acute and chronic experiments.

Methods for implatation of cranial windows for the direct observations 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 intergrity of the skull, the techniques permit study of the cerebral microcirculation under conditions closely approximating the normal environment of these vessels.