Physiology as Topology: Intervenable Organ Graphs for Longitudinal Patient Forecasting

Do language models forecast patient trajectories by reasoning through physiology, or by fitting surface statistics? We introduce PhysioCircuit, a multi-agent agent system that represents each organ as an agent and each physiological relation as an editable mechanism card with direction, lag, and evidence. Its expert-defined graph is frozen at inference, enabling controlled edge interventions. We also introduce PhysioCircuit-Bench, a mechanism-controlled benchmark spanning three organ systems, treatment events, and real ICU admissions. We evaluate intervention-direction agreement (IDAR), which requires the affected organ to change in the expected direction within the expected lag window. The expert graph substantially outperforms all topology controls on edge-IDAR, including fully connected, random, and reversed graphs. Independent clinician adjudication supports the counterfactual results. PhysioCircuit transfers to new organ systems by configuration alone, without retraining, while preserving inspectable and editable relations.