No abstract

SUMMARY This investigation tests the hypothesis that the normal cerebral image obtained non-invasively during continuous inhalation of C"O, is related to cerebral blood flow. Trace amounts of CO, labeled with the positron-emitting radionuclide " 0 were administered to 4 normal subjects at normo-and hypocapnia and to 2 of these subjects at hypercapnia. Hypocapnia typically caused a marked decrease in cerebral " 0 activity, and hypercapnia a small increase in activity. The relative difference in the change in count rate in response to hypoand hypercapnia is what one would expect if the activity represented blood flow, according to a mathematical model which assumes the " 0 label enters the brain as water of perfusion. The findings in this study suggest that the normal cerebral image obtained during continuous inhalation of C"0 2 is related to cerebral blood flow, but in a non-linear fashion, and that the technique would be more sensitive to ischemic events than to hyperemic phenomena.Stroke 2 have suggested that because the l 5 0 label transfers to water in its passage through the lungs 3 it enters the brain as water of perfusion and distributes there in proportion to CBF. During continuous inhalation the short half-life of the label (T x h = 124 sec) facilitates rapid establishment of a dynamic equilibrium, at which time the amount of label entering the brain equals that leaving through physiologic wash-out and radioactive decay. Brain images obtained at equilibrium should provide qualitative measures of CBF, flow being proportional to the count rate and to the corresponding brightness of the cerebral image.The C 16 O 2 technique is attractive because it is noninvasive, potentially quantifiable, 4 and when paired with studies made during continuous inhalation of 15 O 2 theoretically can provide oxygen metabolism information.5 Before beginning patient trials with this technique, however, we wished to determine if changes in CBF in physiologic ranges could produce detectable changes in cerebral count rates and whether the identifiable alteration in activity might be appropriate for a flow index. We therefore applied the method in normal volunteers at rest and during marked changes in Paco 2 .This report discusses the effects of large alterations in Paco 2 on the brain images obtained in 4 normal subjects during continuous inhalation of trace No previous studies had been undertaken to show that changes in CBF within physiologic ranges might be identified with this technique. The results of this study served as the rationale for our subsequent patient investigations. Methods 15O is a cyclotron-produced positron-emitting radionuclide with a 2 minute half-life. Its distribution in brain can be imaged by detecting the photons released following positron emission. Positrons are positive electrons emitted in the decay of certain nuclei. Interaction of the positron with an electron leads to an annihilation process in which the masses of these particles are converted to two 511 KeV photons travelling in opposite directions....

No abstract

During routine cardiac catheterization of ten patients with ventricular septal defect, the hemodynamic parameters were measured in the resting state and during sodium nitroprusside infusion at an average rate of 8 micrograms/kg/min. Two distinct hemodynamic groups could be identified. Group I characterised by elevated left ventricular filling pressure showed a consistently favourable response to sodium nitroprusside infusion with a decrease in the left ventricular filling pressure, the pulmonary arterial pressures and the left to right shunt. The favourable effect was most pronounced in patients who had pulmonary arterial hypertension in addition to elevated left ventricular filling pressures. Group II patients characterised by normal left ventricular filling pressures showed a variable response to sodium nitroprusside administration. The left ventricular end-diastolic pressure fell or was unaltered. The pulmonary arterial pressures and pulmonary vascular resistance fell in those with pulmonary arterial hypertension. Patients without pulmonary arterial hypertension showed an increase in the magnitude of left to right shunt. On the basis of our data, we feel that vasodilator drugs have a specific role in the management of congestive heart failure secondary to large left to right shunts. The present study strongly indicates the need for further investigations utilizing orally effective vasodilators in patients with congestive heart failure due to left to right shunts.

No abstract