VASOMOTION IN RAT DIAPHRAGM MICROCIRCULATION AT REST AND DURING STEPWISE ARTERIAL-PRESSURE REDUCTION

The effect of haemorrhagic hypotension on the incidence, frequency and relative amplitude of vasomotion in rat diaphragm microcirculation wa s assessed by laser Doppler flowmetry (LDF). Graded bleeding to four h ypotension levels (80, 60, 40 and 30% of the control state) were perfo rmed in 24 Sprague-Dawley rats, The incidence of vasomotion was 83% in the control stale, 96% ar the 80% level, 100% at the 60% level, 96% a t the 40% level, ind 46% at the 30% level, The median fundamental freq uency of vasomotion determined manually during the control state and a l the hypotension levels (in descending order) was 4.11 (range, 3.29-5 .58) cycles min(-1) (cpm), 4.48 (3.21-5.92) cpm, 4.20 (3.5-5.56) cpm. 4.01 (3.33-5.36) cpm, 3.71 (3.25-4.49) cpm (P < 0.01 from the fundamen tal frequency at 80 and 60% hypotension levels). The median relative a mplitudes determined manually during the control state and descending hypotension levels were 44.5% (range, 24.9-135.9%), 69.4% (26.6-147.2% ), 84.0% (40.3-177.1%) (P < 0.01 from resting and last stage of bleedi ng), 90.40% (26.2-189.6%) (P < 0.01 from resting and last stage of ble eding), 69.2% (35.6-93.2%). We concluded first that during the resting condition, vasomotion was frequently present in diaphragm microcircul ation, which is distinct from other vascular beds of skeletal muscles. Second. the relative amplitude of vasomotion during haemorrhagic hypo tension plotted against decreasing blood pressure exhibited a reverse U-shaped curve with a maximum al 40-60% of the control blood pressure, while the frequency of vasomotion remained relatively constant until the last stage of haemorrhage and centred around 3-5 cpm.