Orthostatic vasoconstrictor response in patients with occlusive arterial disease assessed by laser Doppler flux and transcutaneous oximetry

Posturally induced microvascular constriction normally causes a decrease of transcutaneous oxygen pressure (tcPO(2)) and laser Doppler flux (LDF) measured on the forefoot at 37 degrees C. The authors used both methods to assess the vasoconstrictor response (VCR) in 31 patients with various degrees of peripheral arterial occlusive disease (PAOD) and analyzed factors that could have influenced the response. Disturbed VCR was indicated by a signal increase following leg dependency, which occurred significantly more often in tcPO(2) than in LDF measurements (69% vs 32%, P < 0.001). Correspondingly the median sitting/supine ratio was 2.4 for tcPO(2) and 0.7 for LDF (P < 0.0001). Age and clinical stage had no influence on the VCR. With ankle artery pressures below 50 mmHg an increase of LDF was more probable. TcPO2 predominantly increased with ankle artery pressures up to 100 mmHg, though the sitting/supine ratio of tcPO(2) was correlated with ankle artery pressure. In nondiabetics the response of tCPO(2) but not of LDF was influenced by the values at rest. Differences between the two methods may be explained in part by their different sample volumes. The authors assume that tcPO(2) is predominantly monitoring a local myogenic response while LDF is reflecting venoarteriolar response.