Chronic coronary artery stenosis and the coronary microcirculation239Oxygen sensing in microvascular network adaptation: interaction of tissue, vessel wall and RBC signalling

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Metabolic stimuli are needed to generate and maintain functionally adequate microvascular networks. The vessel wall may play a central role as an oxygen sensor in structural diameter adaptation in steady state, as we reported recently. However, experimental studies have shown that oxygen dependent signals from the tissue or RBC can also modify vessel diameter. Here, a previously developed model simulation was used to investigate possible interaction of these signalling modes in structural diameter adaptation. In the simulation model, all vessels of a rat mesentery microvascular network (576 vessels) change their diameter in response to wall shear stress, transmural pressure and local Po2. Decreasing levels of local Po2 evoke increasing signalling by tissue cells (‘Tissue’), vessel wall (‘Wall’) and RBCs (‘RBC’). (A) Singular signalling of modes assuming whole range Po2 sensitivity. (B) Combined signalling assuming whole range Po2 sensitivity, while systematically changing relative strength of modes. (C) Singular signalling assuming Po2 sensitivity only above a threshold Po2 which was changed systematically. (D) Combined signalling of two modes assuming split range Po2 sensitivity while systematically changing the split Po2. For all conditions tested, model parameters were optimized to achieve lowest deviation between predicted and measured flow velocities (velocity error VErr). (A) VErr was ∼ 0.59 for ‘Wall’, ∼ 0.72 for ‘Tissue’ and ∼ 0.83 for ‘RBC’. (B) ‘Wall’ ≥ 80% led to the lowest VErr (∼ 0.59). Adding to ‘Wall’ an increasing component of ‘Tissue’ resulted in a linear increase of VErr. For all combinations of ‘Wall’ and ‘RBC’, the addition of 10% ‘Tissue’ consistently reduced VErr. For combined action of ‘Wall’ and ‘Tissue’, the addition of ‘RBC’ components of 60% relevantly increased VErr. (C) ‘Wall’ for all threshold Po2 values up to 80 mmHg resulted in the lowest Verr (∼ 0.59). (D) Whole range Po2 sensitivity of ‘Wall’ led to the lowest VErr (∼ 0.59). ‘RBC’ Po2 sensitivity in low Po2 ranges ( < 50 mmHg) scarcely changed Verr determined for singular ‘Wall’ and ‘Tissue’ signalling. The present results suggest the following conclusions: 1. Exclusive or predominant signalling by the vessel wall to local oxygenation is suited best to guide structural diameter adaptation. Wall oxygen sensitivity needed may be limited to high Po2 levels. 2. A contribution of 10% tissue signalling may exist. 3. RBC signalling of up to 60% of total signalling and singular RBC signalling below 50 mmHg scarcely changed the results, and thus cannot be ruled out. RBC signalling is not possible above these ranges.

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