Microvascular basis for growth of small infarcts following occlusion of single penetrating arterioles in mouse cortex.

Small cerebral infarcts, i.e. microinfarcts, are common in the aging brain and linked to vascular cognitive impairment. However, little is known about the acute growth of these minute lesions and their effect on blood flow in surrounding tissues. We modeled microinfarcts in the mouse cortex by inducing photothrombotic clots in single penetrating arterioles. The resultant hemodynamic changes in tissues surrounding the occluded vessel were then studied using in vivo two-photon microscopy. We were able to generate a spectrum of infarct volumes by occluding arterioles that carried a range of blood fluxes. Those resulting from occlusion of high-flux penetrating arterioles (flux of 2 nL/s or higher) exhibited a radial outgrowth that encompassed unusually large tissue volumes. The gradual expansion of these infarcts was propagated by an evolving insufficiency in capillary flow that encroached on territories of neighboring penetrating arterioles, leading to the stagnation and recruitment of their perfusion domains into the final infarct volume. Our results suggest that local collapse of microvascular function contributes to tissue damage incurred by single penetrating arteriole occlusions in mice, and that a similar mechanism may add to pathophysiology induced by microinfarcts of the human brain.

Estimation of unsteady aerodynamics in the wake of a freely flying European starling (Sturnus vulgaris).

Wing flapping is one of the most widespread propulsion methods found in nature; however, the current understanding of the aerodynamics in bird wakes is incomplete. The role of the unsteady motion in the flow and its contribution to the aerodynamics is still an open question. In the current study, the wake of a freely flying European starling has been investigated using long-duration high-speed Particle Image Velocimetry (PIV) in the near wake. Kinematic analysis of the wings and body of the bird has been performed using additional high-speed cameras that recorded the bird movement simultaneously with the PIV measurements. The wake evolution of four complete wingbeats has been characterized through reconstruction of the time-resolved data, and the aerodynamics in the wake have been analyzed in terms of the streamwise forces acting on the bird. The profile drag from classical aerodynamics was found to be positive during most of the wingbeat cycle, yet kinematic images show that the bird does not decelerate. It is shown that unsteady aerodynamics are necessary to satisfy the drag/thrust balance by approximating the unsteady drag term. These findings may shed light on the flight efficiency of birds by providing a partial answer to how they minimize drag during flapping flight.

Targeted Occlusion of Individual Pial Vessels of Mouse Cortex.

Targeted photothrombosis is a method to occlude individual arterioles and venules that lie on the surface of the cerebral cortex. It has been used to study collateral flow patterns within the pial vascular network following occlusion of single surface vessels (Schaffer et al., 2006; Blinder et al., 2010; Nguyen et al., 2011), as well as to generate localized ischemic strokes following occlusion of single penetrating vessels (Nishimura et al., 2007; Drew et al., 2010; Shih et al., 2013). The intravascular clot is formed by irradiation of a target vessel with a focused green laser after injection of a circulating photosensitizing agent, Rose Bengal (Watson et al., 1985). We briefly describe modifications of custom-designed and commercial two-photon imaging systems required to introduce a green laser for photothrombosis. We further provide instructions on how to occlude a single penetrating arteriole within the somatosensory cortex of an anesthetized mouse.

Heat Stress and Injury Prevention Practices During Summer High School Football Training in South Texas.

The purpose was to describe practice conditions influencing the risk of heat stress to athletes in summer football training in South Texas high schools, and to compare these conditions to ACSM recommendations for heat stress/injury risk reduction in this population. Thirty (N=30) high school summer football practices were observed. Wet bulb globe temperature (WBGT) was measured before/after practices and practices were observed for: duration/structure; athlete clothing; and rest break frequency/duration/content. Practices averaged 125±31 min and WBGT (pre- to post-practice) was 29.7±2.1°C to 31.2±2.2°C for morning, and 31.2±1.6°C to 28.9±1.2°C for evening practices. Most practices included contact (93%), and a majority were full-contact (53%). Most athletes wore full pads (83%) and medium/dark colored clothing (73%). Outside of scheduled breaks athletes removed helmets (63%), sat/knelt (63%), and had access to fluid (90%). Athletic trainers were present at 93% of the practices. A typical practice had 3 rest breaks, each lasting approximately 5 min. During breaks, athletes were provided fluid (93%), removed helmets (89%), and sat/knelt (76%), but were rarely provided shade (2%). While none of the practice sessions were conducted in conditions warranting the cancellation of outside activity (WBGT>33.1°C), the environmental data confirms that this region presents athletes with a very high risk of heat stress/injury. While a majority of the schools were taking many of the precautionary measures recommended by ACSM, many of the guidelines were not being followed. Governing bodies of high school athletics need to encourage compliance with recommendations for the reduction of heat stress/injury in this population.