Instant of vascular occlusion defined with laser-Doppler flowmetry

Derivation of capillary pressure from tracings postarterial (AO) or -venous (VO) occlusion requires back extrapolation to an instant near the time of occlusion. This instant is difficult to identify because of pressure artifacts created by the occlusion maneuver. Theoretically, when the flow in the main artery (or veins) is stopped instantaneously, the flow in the arterioles (or venule) will stop after a short time delay (perhaps less than 100 ms). When flow had stopped in the main artery and in the arteriole, the pressure in the main artery at that instant would equal the pressure in the arterioles. We sought to identify the instant when flow stops in the arterioles and venules after AO and VO, respectively. In an isolated perfused dog left lower lobe preparation flow in the main vessels were monitored with inline flow probes, whereas flow in the microcirculation was monitored with laser-Doppler flow (LDF) probe placed on the lung surface. A sudden decline in arterial flow was detected by the LDF probe after 54 ms, while a sudden decline in venous flow was detected in the venules after 35 ms. These time delays were used as wave transmission time across the arterial and venous trees. Consequently, it was concluded that after AO, flow in the arterioles would stop 54 ms after it had become zero in the main artery, while after VO flow in the venules would stop 35 ms after it had become zero in the main vein. The pressure post-AO and post-VO was read at these instants (54 and 35 ms after flow in the main vessel reached zero).(ABSTRACT TRUNCATED AT 250 WORDS)