Parenchymal Blood Volume Research Articles

Regional distribution of cerebral blood volume and cerebral blood flow in newborn piglets—effect of hypoxia/hypercapnia

The relationship between regional parenchymal cerebral blood volume (CBV), regional cerebral blood flow (CBF) and the calculated mean transit time (MTT) was investigated in 14 newborn piglets. The effects of combined hypoxic hypoxia ( p aO 2=32±5 mm Hg) and hypercapnia ( p aCO 2=68±5 mm Hg) were measured in seven animals. Remaining animals served as the control group. During baseline conditions the highest CBF and CVB values were found in the lower brainstem and cerebellum, whereas white matter exhibited the lowest values ( p<0.05). MTT was prolonged within the cerebral cortex (2.34±0.42 s −1) compared with the thalamic MTT (1.53±0.38 s −1) ( p<0.05). Under moderate hypoxia/hypercapnia, a CBF increase to the forebrain ( p<0.05) resulted in an elevated brain oxygen delivery ( p<0.05) and so CMRO 2 remained unchanged. Moreover, a moderate increase of CBV and a marked shortening of MTT occurred ( p<0.05). The CBV increase was higher in structures with lowest baseline values, i.e., thalamus (66% increase) and white matter (62% increase) ( p<0.05). MTT was between 22% of baseline in the lower brainstem and 49% in white matter ( p<0.05). We conclude that under normoxic and normocapnic conditions the newborn piglets exhibit a comparatively enlarged intraparenchymal CBV. Moderate hypoxia and hypercapnia induced a marked increase in cerebral blood flow which appears to be caused by an increased perfusion velocity, expressed by a strongly reduced mean transit time and by a concomitant CBV increase.

Late Effects of X Irradiation on Regulation of Cerebral Blood Flow after Whole-Brain Exposure in Rats

Hemodynamic parameters such as total cerebral blood volume (total CBV), cerebral parenchymal blood volume (CBV), cerebral blood flow (CBF) and cerebral blood velocity index were measured in rats 6, 12 and 18 months after single exposures of brain to 5, 10, 15 and 20 Gy X rays for total CBV, CBF and blood velocity index, and only 20 Gy for CBV. Total CBV and blood velocity index were determined by a noninvasive blood dilution method using [99mTc]pertechnetate and CBF by [131I]iodoantipyrine brain extraction. The CBV was obtained from both parenchymal plasma and erythrocyte volumes measured in isolated brain by 125I-labeled serum albumin and 51Cr-labeled erythrocytes, respectively. Neither the dose nor the time after irradiation influenced total CBV. Nevertheless, CBV decreased slightly while CBF decreased strongly at 12 and 18 months after 20 Gy. In contrast, the blood velocity index increased progressively at 12 and 18 months after 15 Gy and at all times after 20 Gy. According to the coexistence in irradiated brains of a remodeling with microvascular occlusions and dilated abnormal vessels, this lowered CBF can be explained by the smaller number of open capillaries and a "steal phenomenon" through low-resistance channels developed in the parenchymal and extraparenchymal vasculatures. Such a "steal phenomenon" is also supported by the response of the blood velocity index, which appears to be the earliest sensitive index for the detection of hemodynamic changes with respect to time (6 months) and dose of radiation (15 Gy).

A search for a pulsatile component in pulmonary capillary blood volume

An examination was made of externally detected radioactivity over the thorax of two human subjects after the infusion of red cells labeled with Cr51. An electronic gating technique was used which enabled the mean counting rate to be determined over various preselected time intervals within the cardiac cycle and a comparison made between the rates which obtained during each quarter of this. When counting over the heart the rates were 20—30% greater in diastole than in systole. When counting over rib 2 or rib 4 on the right side no significant variation in count rate could be detected. From this it was deduced that pulmonary parenchymal blood volume in these regions did not vary by more than ± 10% within the cardiac cycle. It was concluded that within the erect lung a proportion of closed capillaries exists in the upper zone, and that the distensibility of the small vessels is insufficient to explain the large vertical inequality of blood flow observed experimentally. pulmonary circulation; parenchymal blood volume; pulsations in volume; distensibility of small vessels Submitted on August 17, 1964