Age-Related Impairment in Choroidal Blood Flow Compensation for Arterial Blood Pressure Fluctuation in Pigeons

Reiner, Anton, et al. "Age-related impairment in choroidal blood flow compensation for arterial blood pressure fluctuation in pigeons." Investigative ophthalmology & visual science 52.10 (2011): 7238-7247. It is well known in our area of research that increased sympathetic nerve activity is a risk factor for many cardiovascular disease states. Well we mainly focus on peripheral vascular consequences associated with cardiovascular disease states, there is also end organ damage that can have other damaging affects. This study in particular is examining changes in the regulation of choroidal blood flow (ChBF) with age. Similarly to the kidneys, the choroid will regulate blood flow by changing vascular resistance in correlation with blood pressure. In healthy individuals, an increase in blood pressure will cause an increase in vascular resistance and the maintenance of blood flow. Vice versa, if blood pressure decreases the choroid will vasodialate as much as possible to compensate and maintain blood flow. Using Doppler flowmetry to measure ChBF and telemetry in pigeons ranging from .5 to 17 years, Fitzgerald's laboratory was able to longitudinally charaterize ChBF regulation with age. They found that between a arterial blood pressures (ABP) of approximately 55mmHg-135mmHg pigeons younger than 8 years of age were able to properly maintain ChBF with changes in vascular resistance. However, in pigeons older than 8 years of age this baroreflex was impaired. Specifically, above 90mmHg and below 60mmHg these pigeons had a positive correlation between changes in ABP and changes in ChBF. It was also found that between 60mmHg-90mmHg older pigeons were only able to maintain ChBF between 60 and 70% of basal level. Where as, in young pigeons ChBF was maintained at 100% between 55mmHg-135mmHg. To support both sets of data, a positive correlation between changes in vascular resistance and ABP existed in the younger cohort of pigeons, but not the older cohort. These data suggest that regulation in ChBF is effected with age, and Reiner suggest two possible mechanisms. Either changes in neurogenic baroreflex regulation or myogenic regulation at the level of the vasculature. However, more studies need to be done in order to determine which and or if both are playing a role. Conclusively, the study determined this loss of ChBF regulation may in part be responsible for onset ocular disease states, and that these disease states may be perpetuated by risk factors that alter sympathetic nerve activity such as hypertension or age. ~JI