Analysis of Blood Flow in the Long Posterior Ciliary Artery of the Cat

PURPOSE. Experiments were undertaken to use a new technique for direct on-line measurement of blood flow in the long posterior ciliary artery (LPCA) in cats and to evaluate possible physiological mechanisms controlling blood flow in the vascular beds perfused by this artery. METHODS. Blood flow in the temporal LPCA was measured on a continuous basis using ultrasonic flowmetry in anesthetized cats. Effects of acute sectioning of the sympathetic nerve and changes in LPCA and cerebral blood flows in response to altered levels of inspired CO 2 and O 2 were tested in some animals. In others, the presence of vascular autoregulatory mechanisms in response to stepwise elevations of intraocular pressure was studied. RESULTS. Blood flow in the temporal LPCA averaged 0.58 ± 0.03 ml/min in 45 cats anesthetized with pentobarbital. Basal LPCA blood flow was not altered by acute sectioning of the sympathetic nerve or by changes in low levels of inspired CO 2 and O 2 , although 10% CO 2 caused a modest increase. Step wise elevations of intraocular pressure resulted in comparable stepwise decreases of LPCA blood flow, with perfusion pressure declining in a linear manner throughout the perfusion-pressure range. CONCLUSIONS. Ultrasonic flowmetry seems to be a useful tool for continuous on-line measurement of LPCA blood flow in the cat eye. Blood flow to vascular beds perfused by this artery does not seem to be under sympathetic neural control and is refractory to modest alterations of blood gas levels of CO 2 and O 2 . Blood vessels perfused by the LPCA show no clear autoregulatory mechanisms. (Invest Ophthalmol Vis Sci. 1999;40:800-804) M any techniques have been used for measurement of uveal blood flow, including direct cannulation of venous outflow channels, measurement of temperature changes in specific ocular regions, and determination of changes of oxygen tension by placement of oxygen-sensitive electrodes in the eye. 1 ' 2 Quantitative blood flow determinations have been accomplished using tissue clearance of inert gases. 3 Drawbacks of these techniques include the need to enter the globe for regional measurements and the limited number of data points that can be determined in a given time. In the most common noninvasive method for ocular blood flow determinations, radioactively labeled microspheres are injected and become trapped in proportion to blood flow in the capillary beds. In this study, an attempt was made to measure LPCA blood flow directly in a continuous manner in the cat eye in vivo, by using ultrasonic flowmetry and miniature flow probes specifically designed for flow measurements in very small-diameter arteries. Cats were chosen because the anatomy and perfusion region of the two LPCAs in this species are more similar to those of humans than are those of other nonprimate experimental animals. Experiments were performed to determine the underlying physiological mechanisms controlling flow in the blood vessels supplied by this artery, including the role of sympathetic innervation, responsiveness to alterations of blood gases, and presence of autoregulatory mechanisms in response to stepwise decreases of perfusion pressure. MATERIALS AND METHODS General Adult cats of either sex were anesthetized with 36 mg/kg pentobarbital injected intraperitoneally. The trachea was intubated for positive-pressure artificial ventilation. A femoral artery and vein were cannulated with a pressure transducer for measurement of systemic arterial blood pressure (model P23; Statham, Hato Roy, Puerto Rico) and for intravenous drug administration, respectively. The animals were positioned in a stereotaxic device (David Kopf, Tujunga, CA) to immobilize the head and were placed on positive artificial ventilation with room air using a respirator (Harvard Apparatus, South Natick, MA). Neuromuscular relaxation was achieved with 4 mg/kg intravenous gallamine triethiodide. End-expiratory CO 2 levels were maintained between 35% and 4% by a capnometer (model 2200; Traverse Medical Monitors, San Luis Obispo, CA) by adjustments of rate and depth of respiration. Determinations of arterial pH and blood gas levels were measured (model 1304; Instrumentation Laboratory, Lexington, MA). Heart rate was derived from the femoral arterial pulse wave. Rectal temperature was maintained at approximately 37°C with a heating pad and infrared lamp. All physiological responses were recorded on a polygraph (model 7; Grass, Quincy, MA). The animals were treated in accordance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. Blood Flow Measurements Blood flow in the temporal LPCA was measured by ultrasonic flowmetry using a transit time ultrasonic flowmeter (model T106; Transonic, Ithaca, NY) coupled with a 0.5-mm miniature flow probe (7.2 mHz). With this technique, after extensive surgery on the lateral orbit, the vessel is exposed and placed within the window of the probe, which houses two ultrasonic transducers and a fixed acoustic reflector. Electrical excitation causes the transducer to emit ultrasound waves, which interDownloaded from iovs.arvojournals.org on 07/01/201

Extended X-ray emission in the IC 2497 - Hanny's Voorwerp system: energy injection in the gas around a fading AGN

We present deep Chandra X-ray observations of the core of IC 2497, the galaxy associated with Hanny's Voorwerp and hosting a fading AGN. We find extended soft X-ray emission from hot gas around the low intrinsic luminosity (unobscured) AGN ($L_{\rm bol} \sim 10^{42}-10^{44}$ erg s$^{-1}$). The temperature structure in the hot gas suggests the presence of a bubble or cavity around the fading AGN (\mbox{E_{\rm bub}} \sim 10^{54} - 10^{55} erg). A possible scenario is that this bubble is inflated by the fading AGN, which after changing accretion state is now in a kinetic mode. Other possibilities are that the bubble has been inflated by the past luminous quasar ($L_{\rm bol} \sim 10^{46}$ erg s$^{-1}$), or that the temperature gradient is an indication of a shock front from a superwind driven by the AGN. We discuss the possible scenarios and the implications for the AGN-host galaxy interaction, as well as an analogy between AGN and X-ray binaries lifecycles. We conclude that the AGN could inject mechanical energy into the host galaxy at the end of its lifecycle, and thus provide a source for mechanical feedback, in a similar way as observed for X-ray binaries.Comment: 9 pages, 5 figures, accepted for publication in MNRA

Compton-thick accretion in the local universe

Heavily obscured accretion is believed to represent an important stage in the growth of supermassive black holes and to play an important role in shaping the observed spectrum of the cosmic X-ray background. Hard X-ray (E > 10 keV) selected samples are less affected by absorption than samples selected at lower energies, and are therefore one of the best ways to detect and identify Compton-thick (CT, log NH ≥ 24) active galactic nuclei (AGNs). In this letter we present the first results of the largest broadband (0.3–150 keV) X-ray spectral study of hard X-ray selected AGNs to date, focusing on the properties of heavily obscured sources. Our sample includes the 834 AGNs (728 non-blazar, average redshift z sime 0.055) reported in the 70-month catalog of the all-sky hard X-ray Swift/Burst Alert Monitor survey. We find 55 CT AGNs, which represent 7.6-2.1+1.1 % of our non-blazar sample. Of these, 26 are reported as candidate CT AGNs for the first time. We correct for selection bias and derive the intrinsic column density distribution of AGNs in the local universe in two different luminosity ranges. We find a significant decrease in the fraction of obscured Compton-thin AGNs for increasing luminosity, from 46 ± 3% (for log L14-195 = 40–43.7) to 39 ± 3% (for log L14-195 = 43.7–46). A similar trend is also found for CT AGNs. The intrinsic fraction of CT AGNs with log NH = 24–25 normalized to unity in the NH = 20–25 range is 27 ± 4%, and is consistent with the observed value obtained for AGNs located within 20 Mpc