Effects of posture on regional pulmonary blood flow in rats as measured by PET

Abstract

Using small animal PET with 68 Ga-radiolabeled human albumin microspheres (Ga-68-microspheres), we investigated the effect of posture on regional pulmonary blood flow (PBF) in normal rats. This in vivo method is noninvasive and quantitative, and it allows for repeated longitudinal measurements. The purpose of the experiment was to quantify spatial differences in PBF in small animals in different postures. Two studies were performed in anesthetized, spontaneously breathing Wistar rats. Study 1 was designed to determine PBF in the prone and supine positions. Ga-68-microspheres were given to five prone and eight supine animals. We found that PBF increased in dorsal regions of supine animals (0.75) more than in prone animals (0.70; P ϭ 0.037), according to a steeper vertical gradient of flow in supine than in prone animals. No differences in spatial heterogeneity were detected. Study 2 was designed to determine the effects of tissue distribution on PBF measurements. Because microspheres remained fixed in the lung, PET was performed on animals in the position in which they received Ga-68-microsphere injections and thereafter in the opposite posture. The distribution of PBF showed a preference for dorsal regions in both positions, but the distribution was dependent on the position during administration of the microspheres. We conclude that PET using Ga-68-microspheres can detect and quantify regional PBF in animals as small as the rat. PBF distributions differed between the prone and supine postures and were influenced by the distribution of lung tissue within the thorax. pulmonary blood flow; positron emission tomography;68 Ga radiolabel; human serum albumin microspheres; prone position; supine position; small animal COLORED OR FLUORESCENT MICROSPHERES have primarily been used for blood flow measurements in small animals. Intravenously administered microspheres larger than 10 m are predicted to become trapped in the pulmonary capillaries. Their spatial distribution therefore reflects pulmonary blood flow (PBF; Refs. 11,13,14,20,32,38). Data analysis for colored or fluorescent microspheres requires lung excision and post mortem processing. In contrast, by using radiolabeled microspheres, data for the blood flow distribution could be achieved noninvasively and in vivo (22,35). A major advantage of positron emission tomography (PET) is its high sensitivity and the ability to quantify the concentration of radiotracers in the lung (24). The use of a dedicated small animal PET could allow this method to be translated to rodents. Therefore, we tested the feasibility of measuring PBF in rats using biodegradable, 68 Ga-radiolabeled human serum microspheres (Ga-68-microspheres) and micro-PET.Subsequently, and with a variety of radiotracers, positional changes in regional blood flow from upper to lower regions have been found in large animals and humans (4,15,23,25,33,36). However, to the best of our knowledge there are no data regarding the influence of posture (prone and supine) on regional pulmonary blood flow in small a...

In Vivo MR Imaging of Pulmonary Perfusion and Gas Exchange in Rats via Continuous Extracorporeal Infusion of Hyperpolarized 129Xe

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