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The microcirculation plays a crucial role in the distribution of perfusion to organs. Studies have shown that microcirculatory dysfunction is an independent predictor of morbidity and mortality. Hence, assessment of liver perfusion offers valuable information on the (patho)physiological state of the liver. The current review explores techniques in perfusion imaging that can be used intraoperatively. Available modalities include dynamic contrast-enhanced ultrasound, handheld vital microscopes, indocyanine green fluorescence angiography, and laser contrast speckle imaging. Dynamic contrast-enhanced ultrasound relays information on deep tissue perfusion and is a commonly used technique to assess tumor perfusion. Handheld vital microscopes provide direct visualization of the sinusoidal architectural structure of the liver, which is a unique feature of this technique. Intraoperative fluorescence imaging uses indocyanine green, a dye that is administered intravenously to visualize microvascular perfusion when excited using near-infrared light. Laser speckle contrast imaging produces non-contact large surface-based tissue perfusion imaging free from movement- or pressure-related artefacts. In this review, we discuss the intrinsic advantages and disadvantages of these techniques and their clinical and/or scientific applications. [ABSTRACT FROM AUTHOR]

Background/Aims: This study describes the peritoneal microcirculation, compares quantitative parameters and angioarchitecture to the standard of sublingual microcirculatory assessment, and determines the practical feasibility of this method. Methods: Incident dark field imaging was performed of the peritoneum and sublingually to determine angioarchitecture, total and perfused vessel density (TVD and PVD), the proportion of perfused vessels (PPV), the microvascular flow index (MFI) and image acquisition time. Results: Peritoneal angioarchitecture was characterized by a quadrangular network of longitudinally oriented capillaries, often flanked by fat cells. Differences between peritoneal and sublingual microcirculation were observed with regard to TVD (peritoneum 12 mm/mm2 [95% CI 10–14] vs. sublingual 23 mm/mm2 [95% CI 21–25]; p < 0.0001), PVD (peritoneum 11 mm/mm2 [95% CI 9–13] vs. sublingual 23 mm/mm2 [95% CI 21–25]; p < 0.0001), PPV (peritoneum 88% [95% CI 79–97] vs. sublingual 99% [95% CI 99–100]; p = 0.014), and MFI (peritoneum 3 [IQR 2.3–3.0] vs. sublingual 3 [IQR 3.0–3.0]; p = 0.012). There was no difference in image acquisition time (peritoneum 2: 34 min [95% CI 1: 49–3: 19] vs. sublingual 2: 38 [95% CI 1: 37–3: 32]; p = 0.916). Conclusion: The peritoneal microcirculation was characterized by a low capillary density and a distinctive angioarchitecture. The possibility of peri­toneal microcirculatory assessment offers promise for the study of peritoneal (patho-)physiology and (monitoring or detection of) associated diseases. [ABSTRACT FROM AUTHOR]

Artificially induced hypometabolism in nonhibernating mammals may have considerable clinical implications. Numerous studies in small rodent models have demonstrated that hydrogen sulfide (H2S) induces hypometabolism, supposedly as a result of histotoxic hypoxia. However, the induction of hypometabolism is absent in large animals following H2S administration. To determine the cause of this animal size-dependent discrepancy in H2S pharmacodynamics, the effects of sodium H2S (NaSH; 5 mg/kg/h, 4-hour intravenous administration) on systemic, pneumocardial, hematological, biochemical, microvascular (sublingual), and histological parameters were investigated in pigs. After 4 h, no differences were observed between the NaSH and control group with respect to systemic, pneumocardial, hematological, biochemical, and histological parameters. However, NaSH triggered significant hyperperfusion in the sublingual microcirculation, as evidenced by an increased blood vessel diameter (154 ± 16 and 85 ± 25% vs. baseline for NaSH and NaCl, respectively), total vessel density (139 ± 18 and 98 ± 13%, respectively), and perfused vessel density (139 ± 18 and 99 ± 13%, respectively). These phenomena are consistent with microvascular changes that occur during a panting response, an important heat loss mechanism (i.e., thermoregulatory effector) in pigs that is controlled by the thermoneutral zone (Ztn). On the basis of our findings and the literature, a mechanistic explanation is provided for the differential manifestation of hypometabolism between small and large animals. In large animals, H2S does not act via histotoxic hypoxia but likely triggers carotid bodies to transmit a hypoxic signal, which subsequently lowers the Ztn and activates heat loss mechanisms (e.g., panting) to align ATP consumption with ATP production through hypothermia. Since large animals have a small surface:size ratio, the cooling rate is too inefficient to accommodate hypothermia and subsequent hypometabolism. This is why large animals do not exhibit hypometabolism, despite the activation of thermoregulatory effectors. This is also a reason for the poor translatability of artificial hypometabolism to the clinical setting. © 2015 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]