Critical Assessment of the Xenon Washout Technic for Measurement of Placental Blood Flow

Abstract

The xenon washout technic has been assessed as a method for measuring placental blood flow in humans. In the first group of 20 patients, the ¹³³Xe injection was made blindly into the placenta; in the second group of 20 patients, a new technic was employed to ensure injection into the vascular (intervillous) space. The results have been calculated as clearance half-times, in seconds. Both groups gave widely differing results. After comparing the clearance half-times for ¹³³Xe with those for ^99mTc-albumin, it was concluded that with intervillous ¹³³Xe injections, a true xenon washout effect does not occur. Thus, calculations for blood flow in ml/g tissue/unit time are not considered valid. Further, the method cannot be recommended as a test for the action of drugs on placental blood flow. Firstly, under the influence of spontaneous placental pressure variations, single measurements are of limited value. Secondly, as blood examinations have shown the needle puncture itself may damage fetal vessels, permitting possibly dangerous fetomaternal transfusion.

A method for the assessment of placental blood perfusion using99mTc pertechnetate

“…The so calculated perfusion rate values vary between 0.40 and 2.77 ml/min for 24Na [2], and between 0.16 and 1.54 ml/min/ml for l a a x e [9], which are in a good agreement with our study. If we suppose that the partition coefficient (A) is 1 mi/ml for placental tissue, we can express the half-times by perfusion units using the equation F/V = iln2/T+.…”

“…Obviously, this is due to the complexity of the physiological system and the lack of any established atraumatic technique for determining the blood flow of the placenta in vivo. The disadvantages of the above methods are connected with the traumatic injection techniques and the uncertainty of the localization of the injection site [9]. Localization of the placenta with radioactive isotopes has become widely employed.…”

Exercise and Pregnancy: A Review

“…Exercise-related increases in mean blood pressure may compensate for increases in uterine artery vascular resistance during moderate-and high-intensity, short-duration physical activities in humans. Confirmatory evidence comes from a study in which radioactive xenon133 was injected directly into the intervillous space (124); however, the reliability of this technique is questioned (125). blood flow in animals, compensatory mechanisms occur similar to those at rest, including relative sparing of the placental circulation (116) and increased fetal oxygen extraction (75).…”

Utero-placental blood flow index. Its relationship with the placental histology and fetal hypoxia

“…However puncturing the intervillous space has several drawbacks äs indicated for instance by LIPPERT et al [15]. To avoid them several ingenious techniques have been proposed in which the 133 Xe reaches the intervillous space indirectly, either by maternal Inhalation [12,25] or by injection into a branchial vein [19]; the measurement of clearance of the labelled gas from the intervillous space is the basis of these techniques.…”