Relationship between anal pressure and anodermal blood flow

PURPOSE: The aim of this study was to investigate the relationship between anal pressure and anodermal blood flow. METHODS: We performed Doppler laser flowmetry of the anoderm combined with anorectal manometry in 178 subjects (87 males and 91 females; median age, 55 (range, 17-87) years). This group consisted of 31 healthy volunteers, 23 patients with fecal incontinence, 17 patients with hemorrhoids, and 9 patients with anal fissure. The remaining 98 patients had other colorectal disorders. In 16 controls we examined anodermal blood flow in the four quadrants of the anal canal. RESULTS: Perfusion of the anoderm at the posterior midline was significantly lower than in the other three segments of the anal canal (posterior midline: 0.74 +/- 0.26 V; left lateral side: 1.68 +/- 0.81 V; right lateral side: 1.57 +/- 0.52 V; anterior midline: 1.48 +/- 0.69 V, P < 0.001). In the overall group, we found a significant correlation between maximum and resting pressure and anodermal blood flow at the posterior midline (r = -0.616, P < 0.001). In the nine patients with chronic anal fissure, the mean maximum anal resting pressure was 125 +/- 26 mmHg, which was significantly higher than in patients with hemorrhoids (82 +/- 15 mmHg), controls (66 +/- 19 mmHg), and patients with fecal incontinence (42 +/- 14 mmHg, P < 0.001), whereas the blood flow at the base of the fissure was significantly lower (0.43 +/- 0.10 V vs. 0.57 +/- 0.19 V vs. 0.75 +/- 0.26 vs. 1.03 +/- 0.34 V). In ten patients we also studied the influence of anesthesia on both anal pressure and anodermal blood flow. During the administration of anesthesia, anal pressure dropped from 63 +/- 21 mmHg to 32 +/- 15 mmHg (P < 0.001), whereas anodermal blood flow at the posterior midline increased from 0.79 +/- 0.22 V to 1.31 +/- 0.35 V (P < 0.001). CONCLUSION: Anodermal blood flow at the posterior midline is less than in the other segments of the anal canal. The perfusion of the anoderm at the posterior commissure is strongly related to anal pressure. The higher the pressure, the lower the flow. Our findings support the hypothesis that anal fissures are ischemic ulcers.