Can a change in health be detected before the crisis itself?

Abstract and scientific scope

Physiological PSI investigates whether recovery dynamics after perturbations and changes in coupling between physiological signals can complement conventional descriptions of their absolute values. This website presents a methodological framework; clinical predictive utility must be validated for a specific population, event and dataset.

Information also lies in the way a system recovers

Heart rate, blood pressure or respiratory activity may remain within an acceptable range while whole-system dynamics change. A physiological system can be described not only by its values, but also by how quickly it recovers after a disturbance, how its subsystems interact and how changes persist over time. The Physiological Stability Index (PSI) is a research concept for investigating these relationships.

From time series to a dynamical model

The methodological question is whether concurrent time series can provide stability features that add information beyond simple threshold alarms. Relevant methods include defining time windows, preprocessing missing data and artefacts, estimating relaxation behaviour and measuring coupling between variables. To avoid analytical artefacts, feature selection, the endpoint and validation rules must be specified before testing.

Measuring usefulness

A single favourable example is insufficient to evaluate early warning. Assessment must consider sensitivity, specificity, AUROC or AUPRC in relation to event prevalence, false-alarm counts and actual warning lead time. Clinical populations can have different baseline characteristics. External testing on independent datasets and assessment of operational usefulness are therefore essential.

The limits of the current claim

PSI is a research concept, not an approved medical device or clinically validated diagnostic method. The available materials do not establish improved patient care or reliable prediction of a particular complication. Any clinical programme would need to prespecify its output, test robustness to missing data, and independently evaluate the impact of false-positive and false-negative alerts.

A distinct role in neurorehabilitation

PSI also has a theoretical role in NeuroCodec, which examines the stability of a new motor loop. This differs from predicting deterioration in hospitalised patients. The applications involve different data, outputs, risks and validation requirements.

Publication status

This website describes physiological PSI as a research framework for dynamic instability in physiological time series. The same abbreviation also appears in separate work on financial markets (Perturbation Susceptibility Index) and geophysics (Planetary Stability Interface). These are not a single metric automatically validated across all fields. Each application requires its own validation protocol and independent data.

Valid-transition methodology →

The opening graphic is a conceptual thematic illustration, not an experimental record.

Interdisciplinary connections and distinct PSI models

The PSI label also appears in the author's separate applications to financial markets and volcanic systems. These are differently defined indicators, rather than a direct transfer of a clinically validated physiological index. The separate studies provide the details: PSI and financial markets → and PSI and volcanic systems →. Each field requires assessment of its own data, measurement assumptions and independent-validation requirements.