Pulse/Breathing Rate Ratio (PBR)

A pre-intervention PBR retains predictive value for downstream outcomes regardless of whether vital signs normalise after treatment. PBR is calculated by dividing pulse rate by breathing rate. The ancient Chinese text Pulse Classic described a ratio-based pulse-breath framework that anticipates modern PBR norms, including recognising 1–2 beats per breath as signalling critical illness. The relationship between PBR and each adverse outcome follows a statistically significant U-shaped nonlinear curve, with risk lowest at intermediate values. PBR uses pulse rate rather than heart rate as the numerator because pulse rate represents effective cardiac output reaching the distal limbs, not merely the electrical impulse. PBR simultaneously reflects cardiopulmonary function, blood perfusion, and autonomic nervous system regulation, acting as a composite indicator of heart-lung-brain coordination.