Double-illumination photoacoustic microscopy of intestinal hemodynamics following massive small bowel resection

Massive small bowel resection (SBR) results in villus angiogenesis and intestinal adaptation. The exact mechanism that causes intestinal villus angiogenesis remains unknown. We hypothesize that hemodynamic changes within the remnant bowel after SBR will trigger intestinal angiogenesis. To validate this, we used photoacoustic microscopy (PAM) to image the microvascular system of the intestine in C57B6 mice and to measure blood flow and oxygen saturation (sO₂) of a supplying artery and vein. Baseline measurements were made 6 cm proximal to the ileal-cecal junction (ICJ) prior to resection. A 50% proximal bowel resection was then performed, and measurements were again recorded at the same location immediately, 1, 3 and 7 days following resection. The results show that arterial and venous sO₂ were similar prior to SBR. Immediately following SBR, the arterial and venous sO₂ decreased by 14.3 ± 2.7% and 32.7 ± 6.6%, respectively, while the arterial and venous flow speed decreased by 62.9 ± 17.3% and 60.0 ± 20.1%, respectively. Such significant decreases in sO₂ and blood flow indicate a hypoxic state after SBR. Within one week after SBR, both sO ₂ and blood flow speed had gradually recovered. By 7 days after SBR, arterial and venous sO₂ had increased to 101.0 ± 2.9% and 82.7 ± 7.3% of the baseline values, respectively, while arterial and venous flow speed had increased to 106.0 ± 21.4% and 150.0 ± 29.6% of the baseline values, respectively. Such increases in sO₂ and blood flow may result from angiogenesis following SBR.