Abstract / Summary
A hypothesis paper. No patient was studied, no data were collected, and nothing here is a treatment recommendation or a reason to withhold or delay analgesia. Version 2.0.0 is the version submitted to Medical Hypotheses. In the last days of life, opioid infusion is commonly titrated against observed signs of distress, but these signs may reflect nociception, autonomic arousal, delirium or opioid-related neurotoxicity. The paper proposes that part of terminal opioid escalation is driven by a self-reinforcing loop between autonomic arousal and perceived distress, and that the loop may be accessible through hearing. It separates what is established (brainstem auditory processing; the central autonomic network; tone-evoked auditory potentials persisting in actively dying patients) from what is hypothesised (that residual auditory processing can lower autonomic arousal in dying patients) and from what is untested (whether that changes opioid requirement). A minimal, fully specified model of the loop (equations, initial conditions and every parameter with its units given in the paper) indicates that damping arousal postpones rather than prevents accumulation-driven agitation: +6.2 hours at modest damping, a ceiling of 34.8 hours, and no damping strength prevents the crossing. A one-at-a-time sensitivity analysis over all eleven parameters (22 runs) moves the delay between 3.5 and 10.7 hours and the ceiling between 21.0 and 50.7 hours, and in no run does damping prevent the crossing. All parameters are illustrative. The paper gives five falsifiable predictions, a feasibility protocol for heart-rate-variability measurement in dying patients (arrhythmia, respiration, medication timing, signal quality, within-patient design), and an explicit account of how the proposal could cause harm. Changes from version 1.0.0: title ("modulating" rather than "limiting"); evidence hierarchy; reproducible model specification and sensitivity analysis; revised Figure 1 evidence coding; HRV feasibility protocol; references re-verified against their abstracts, replacing a withdrawn Cochrane review and a source too indirect for the claim it supported.