Differentiation between arterial and venous vessel occlusion by simultaneous measurement with laser Doppler flowmetry and photoplethysmography.

In abdominal cutaneous island flaps of rats (n = 16), either the artery or the vein was clamped, while flap perfusion was simultaneously monitored with laser Doppler flowmetry (LDF) and photoplethysmography (PPG) to identify the occluded vessel responsible for insufficient perfusion. The LDF signal decreased promptly after arterial clamping. After venous clamping, only a slow decrease was noted. The LDF amplitude differed statistically significantly between arterial and venous clamping only up to 90 sec after onset but not thereafter, allowing no further distinction between the two types of vessel occlusion. Power spectral analysis of the LDF signal did not show clear differences in frequency ranges between arterial and venous occlusion. In contrast, PPG measurements demonstrated significant differences between both perfusion disorders throughout the entire observation period. These results suggest that dependable differentiation between prolonged arterial and venous vessel occlusion is not possible based on the amplitude or power spectral analysis of the LDF signal alone. PPG may be reliably used to differentiate between arterial and venous perfusion disorders.

Countinuous Laser-Doppler free-flap monitoring via the telephone line. Preliminary experiences.

It is possible to link a Laser-Doppler to a DOS-compatible personal computer in order to monitor microcirculation of the free flap after plastic surgery. We connected such a system to a second computer by telephone modems, in order to control the Laser-Doppler via the telephone line from a distant location using only commercially available hardware and software. The aim was to develop a low-cost system which would not require the purchase or construction of any specialised equipment. Using this system, it was possible to show the Laser-Doppler waveforms to colleagues who were not at the patient site, for their (more experienced) opinions without any further delays. Preliminary tests on five cases showed that it was indeed possible to transfer recorded information about the blood flow rate of free skin flaps from one computer to a remote one, without any loss of information. In these cases, the measured blood flow and clinical surveillance of the blood supply were adequate, thus making revision of the tissues not necessary. This preliminary study suggests that standard 'off-the-shelf' personal computer tools may be useful in improving the monitoring of microcirculation after plastic surgery.

[In-house radio-assisted emergency call system in continuous monitoring of microcirculation using laser doppler flowmetry]. / Dienstfunkergestütztes Notrufsystem bei kontinuierlicher Mikrozirkulationsüberwachung mit Hilfe der Laser-Doppler-Flowmetry.

Instrumental monitoring is being increasingly employed in the postoperative phase after microsurgery. For this purpose, laser Doppler flowmetry has proven to be very useful. Monitoring of the perfusion of tissue with blood is mainly by clinical examination, which, however, requires the physical presence of the observer, and this is generally not possible on a continuous basis. By connecting up a laser Doppler unit with a computer and telephone modem and making use of the in-house radio system, it proved possible to produce an automatic emergency call system that responds to a worsening of perfusion and alerts the responsible doctor. For this purpose, the software program "call-doc" was developed, which provides the necessary monitoring and control functions. A general perfusion-independent emergency call can also be triggered at the touch of a button.