Correlation Between the Intra-Thoracic Pressure and Choroidal Blood Flow

Abstract

Abstract: : Purpose:The Valsalva maneuver (VM) is a forced expiration against a closed glottis that raises the intra-thoracic pressure to ∼40 mmHg. Since VM typically raises the intraocular pressure (IOP) and the systemic blood pressure (BP) it may be useful for studying ocular hemodynamics. In this study we explored this potential by examining the changes in the choroidal blood flow (ChBF) over a broad range of intra-thoracic pressures. Methods:6 healthy volunteers between 20-52 years of age blew into a pressure gauge to raise the intra-thoracic pressure for 10-15 sec in 20 mmHg steps. Simultaneously, the systemic BP was measured with a Colin 7000 noninvasive system, heart rate with an ear pulse transducer and the sub-foveal choroidal blood flow (ChBF) by confocal laser Doppler flowmetry (LDF). The IOP was measured in separate test sessions. Results:Continuous measurements of the mean arterial blood pressure (MABP) during forced expirations yielded MABP signatures with 4 phases unique to the VM. Phase I (onset of increased MABP) and Phase III (abrupt decrease in the MABP) of the Valsalva BP recording changed at an average rate of ∼0.57mmHg/mmHg expiration. Expiration < 40-50 mmHg had little effect on the ChBF, but expiration ≷ 60 mmHg typically increased the choroidal flow, and flow volume, but decreased the flow velocity. The VM induced changes in the MABP occurred immediately after any recorded changes in the ChBF. At the end of expiration, all ChBF parameters quickly returned to resting levels. The IOP increased 16-40% in proportion to the maximum expiration level achieved. With each increment in expiration, both systolic and diastolic BPs increased, but the systolic BP peaked at ∼40-50 mmHg. In contrast, the diastolic BP continued to increase, thereby creating a transient vascular stasis. The heart rate varied up to +/- 25% about the resting value during the VM. Conclusion:An increase in the intra-thoracic pressure ≷60mmHg increases the ChBF and volume through an increased diastolic BP. Presumably, the increase in IOP was due to an increase in the choroidal blood volume.

Keywords: 345 choroid • 331 blood supply • 444 intraocular pressure