Cerebral hemodynamics in patients with heart failure associated and hypertension and the response to treatment

Cerebral blood flow and metabolism in hypertensive patients with cerebral infarction

The authors investigated, by positron emission tomography, the effect of long-standing hypertension on cerebral blood flow (CBF) and oxygen metabolism in patients with chronic atherothrombotic brain infarction. In the nonbrain infarct (non-BI) group (n = 13, mean age: sixty-two years), the regional CBF (rCBF) was decreased significantly with a rise in the mean arterial blood pressure (MABP) in the cerebral cortexes (r = -0.575) and the deep gray matter (r = -0.451), whereas the regional cerebral metabolic rate for oxygen (rCMRO2) remained unchanged. In the brain infarct (BI) group (n = 22, mean age: fifty-eight years), however, the rCBF as well as the rCMRO2 were reduced even in the normotensive patients and thus did not correlate with the MABP. These results suggest that long-standing hypertension per se causes a reduction in the rCBF but not in the oxygen metabolism with a compensatory increase in the oxygen extraction fraction. On the other hand, patients with brain infarction, even normotensives, show a diffuse decrease in cerebral circulation and metabolism, which is probably due to the more severe sclerotic changes that take place in the cerebral vessels.

A comparison between regional cerebral blood flow measurements obtained in human subjects using 11C-methylalbumin microspheres, the C15O2 steady-state method, and positron emission tomography

Regional cerebral blood flow (rCBF) values were measured in nine normotensive subjects with known previous myocardial infarctions using 15 mu 11C-methylalbumin microspheres and positron emission tomography (PET). Microspheres were injected directly into the left ventricle of each subject during routine cardiac angiography and blood flow calibrated using the reference sample technique. rCBF values were compared with those obtained for a group of fifteen age-matched normal controls using the C15O2 steady-state inhalation technique. Using 1 cm radius circular regions of interest, the 11C-microspheres approach yielded mean blood flow values of 51 ml/100 ml/min and 48 ml/100 ml/min for regions of interest dominated by temporal and frontal cortical grey matter respectively. An rCBF value of 32 ml/100 ml/min was obtained for regions of interest dominated by frontal white matter. Mean rCBF values obtained for these regions using the C15O2 method were not significantly different (52 ml/100 ml/min, 44 ml/100 ml/min, and 28 ml/100 ml/min respectively), but the C15O2 approach gave a significantly lower rCBF value than the 11C-microspheresfor regions of interest dominated by occipital grey matter. Although the two groups of subjects studied were not strictly equivalent, the good agreement between blood flow values obtained using the 11C-microspheres and the C15O2 techniques is of interest, and suggests that the assumptions of the C15O2 steady-state approach do not lead to large errors in practice.

Critical assessment of use of central venous oxygen saturation as a mirror of mixed venous oxygen in severely ill cardiac patients

Bedside catheterization of the right heart with a percutaneously introduced flowdirected catheter was carried out in 24 critically ill patients; 71 determinations of mixed venous oxygen saturation (MVo 2 ) were obtained. A second catheter was inserted either into a central intrathoracic vein or the right atrium for simultaneous sampling of central venous (CVo 2 ) or right atrial (RAo 2 ) oxygen saturation.

For the group as a whole, mean CVo 2 (57.9% ± 15.25) was significantly greater than mean MVo 2 (53.3% ± 14.84) ( P <0.001), but there was no significant difference and correlation was good between changes in central venous compared to changes in mixed venous oxygen saturation. On the other hand, there was no significant mean difference as well as an excellent correlation between individual values of RAo 2 and MVo 2 (r=+0.95).

Patients with heart failure or shock showed poor correlation between CVo 2 and simultaneously determined MVo 2 . Furthermore, subjects with shock showed a mean CVo 2 (58.0%±13.05) that was significantly greater than mean MVo 2 (47.5% ± 15.11). In contrast, there was no significant difference between mean RAo 2 and mean MVo 2 and excellent correlation of individual values in patients with either heart failure or shock. Although CVo 2 is a poor reflection of MVo 2 in subjects with severe heart failure or shock, there was a better correlation between changes in CVo 2 with corresponding changes in MVo 2 . In addition, RAo 2 correlated closely with corresponding values of MVo 2 . The reversal of the normal relationship between CVo 2 and MVo 2 under these circumstances is compatible with the thesis that low output states are attended by redistribution of blood flow away from femoral, splanchnic, and renal circulation with preferential preservation of cerebral blood flow.