The impact of conjunctival flap method and drainage cannula diameter on bleb survival in the rabbit model

Purpose To examine the effect of cannula diameter and conjunctival flap method on bleb survival in rabbits undergoing cannula-based glaucoma filtration surgery (GFS). Methods Twelve New Zealand White rabbits underwent GFS in both eyes. The twenty-four eyes were divided into four groups. Two of the four groups (N = 12) received limbus-based con- junctival flaps (LBCF), and the other two (N = 12) received fornix-based conjunctival flaps (FBCF). Six FBCF rabbit eyes were implanted with 22-gauge drainage tubes, and the other six were implanted with 26-gauge tubes. Likewise, six LBCF rabbits received 22-gauge drainage tubes and six received 26-gauge tubes. Filtration blebs were evaluated every three days by a masked observer. Bleb failure was defined as the primary endpoint in this study and was recorded after two consecutive flat bleb evaluations. Results Group 1 (LBCF, 22- gauge cannula) had a mean bleb survival time (Mean ± SD) of 18.7 ± 2.9 days. Group 2 (LBCF, 26-gauge cannula) also had a mean bleb survival time of 18.7 ± 2.9 days. Group 3 (FBCF, 22-gauge cannula) had a mean bleb survival time of 19.2 ± 3.8 days. Group 4 (FBCF, 26-gauge cannula) had a mean bleb survival time of 19.7 ± 4.1 days. A 2-way analysis of variance showed that neither surgical approach nor cannula gauge made a statistically significant difference in bleb survival time (P = 0.634 and P = 0.874). Additionally, there was no significant interaction between cannula gauge and conjunctival flap approach (P = 0.874), suggesting that there was not a combination of drainage gauge and conjunctival flap method that produced superior bleb survival. Conclusion Limbus and fornix-based conjunctival flaps are equally effective in promoting bleb survival using both 22 and 26-gauge cannulas in the rabbit model. The 26-gauge drainage tube may be preferred because its smaller size facilitates the implantation process, reducing the risk of corneal contact

Dynamic assessment of cerebral metabolic rate of oxygen (CMRO 2) with magnetic resonance imaging

The brain is almost entirely dependent on oxidative metabolism to meet its energy requirements. As such, the cerebral metabolic rate of oxygen (CMRO2) is a direct measure of brain energy use. CMRO2 provides insight into brain functional architecture and has demonstrated potential as a clinical tool for assessing many common neurological disorders. Recent developments in magnetic resonance imaging (MRI)-based CMRO2 quantification have shown promise in spatially resolving CMRO2 in clinically feasible scan times. However, brain energy requirements are both spatially heterogeneous and temporally dynamic, responding to rapid changes in oxygen supply and demand in response to physiologic stimuli and neuronal activation. Methods for dynamic quantification of CMRO2 are lacking, and this dissertation aims to address this gap. Given the fundamental tradeoff between spatial and temporal resolution in MRI, we focus initially on the latter. Central to each proposed method is a model-based approach for deriving venous oxygen saturation (Yv) – the critical parameter for CMRO2 quantification – from MRI signal phase using susceptometry-based oximetry (SBO). First, a three-second-temporal-resolution technique for whole-brain quantification of Yv and CMRO2 is presented. This OxFlow method is applied to measure a small but highly significant increase in CMRO2 in response to volitional apnea. Next, OxFlow is combined with a competing approach for Yv quantification based on blood T2 relaxometry (TRUST). The resulting interleaved-TRUST (iTRUST) pulse sequence greatly improves T2-based CMRO2 quantification, while allowing direct, simultaneous comparison of SBO- and T2-based Yv. iTRUST is applied to assess the CMRO2 response to hypercapnia – a topic of great interest in functional neuroimaging – demonstrating significant biases between SBO- and T2-derived Yv and CMRO2. To address the need for dynamic and spatially resolved CMRO2 quantification, we explore blood-oxygen-level-dependent (BOLD) calibration, introducing a new calibration model and hybrid pulse sequence combining OxFlow with standard BOLD/CBF measurement. Preliminary results suggest Ox-BOLD provides improved calibration “M-maps” for converting BOLD signal to CMRO2. Finally, OxFlow is applied clinically to patients with obstructive sleep apnea (OSA). A small clinical pilot study demonstrates OSA-associated reductions in CMRO2 at baseline and in response to apnea, highlighting the potential utility of dynamic CMRO2 quantification in assessing neuropathology

Bleb survival of LBCF and FBCF rabbits using 22 and 26-gauge cannulas.

<p>Bleb survival of LBCF and FBCF rabbits using 22 and 26-gauge cannulas.</p

Experimental groups.

<p>Experimental groups.</p

Kaplan-Meier bleb survival plot of rabbits who received either limbus-based conjunctival flaps (LBCF) or fornix-based conjunctival flaps (FBCF), using either 22 or 26-gauge drainage cannulas.

<p>Bleb failure was declared after a masked evaluator deemed the bleb flat on two consecutive occasions.</p