Manifold-Informed Neural Networks for Low-Label ECG Electrolyte Inference
Organizations: Duke University, USA
Abstract
Physics-informed neural networks (PINNs) supervise on the residual of a known differential operator. Many high-stakes inference problems admit no such operator: clinical signals, behavioral measurements, materials properties. We introduce the Manifold-Informed Neural Network (MINN), a PINN-parallel paradigm that replaces the physics operator residual with a manifold operator residual: a discrete Poisson equation on a -nearest-neighbor graph in the learned latent space, with a learned, task-aware source. The construction is a structural parallel to PINNs (squared operator residual plus label data, in place of operator residual plus boundary data); the limit recovers the homogeneous Laplace equation (classical manifold regularization solves the same equation but minimizes the Dirichlet energy , a different penalty form). The source takes input features and auxiliary metadata directly, breaking the homogeneous smoothness prior that limits classical Laplacian penalties; gated Feature-wise Linear Modulation separately fuses metadata into the prediction branch. We evaluate MINN on three-class classification of potassium, calcium, and magnesium from 12-lead ECGs in MIMIC-IV-ECG, against twelve baselines spanning supervised and tabular methods, ECG foundation models, and manifold/graph approaches. MINN attains the highest K Macro-F1 of 0.61 (best baseline 0.55), with consistent gains on Ca and Mg and a 31% relative improvement at 1% labeled data. Six targeted ablations show that the inhomogeneous Poisson formulation, not graph smoothing alone, drives the gain.
Figures & tables
| K + | Ca 2+ | Mg 2+ | ||||
| Method | F1 ( ) | BAcc ( ) | F1 ( ) | BAcc ( ) | F1 ( ) | BAcc ( ) |
| Supervised & Tabular | ||||||
| ResNet-18 [ 36 ] | 0.48 | 0.55 | 0.40 | 0.46 | 0.32 | 0.39 |
| Logit Adj. [ 32 ] | 0.53 | 0.60 | 0.43 | 0.50 | 0.34 | 0.41 |
| TabPFN [ 34 ] | 0.47 | 0.54 | 0.43 | 0.50 | 0.36 | 0.43 |
| CatBoost [ 35 ] | 0.48 | 0.55 | 0.44 | 0.51 | 0.37 | 0.47 |
| Variant | K + ( ) | Ca 2+ ( ) | Mg 2+ ( ) |
|---|---|---|---|
| MINN (full) | 0.61 | 0.50 | 0.40 |
| Operator residual ( ) | 0.54 | 0.44 | 0.35 |
| Source ( ) | 0.56 | 0.46 | 0.36 |
| Poisson Classical reg. | 0.55 | 0.45 | 0.36 |
| Learned source Label-only | 0.57 | 0.45 | 0.36 |
| Latent Logit constraint | 0.56 | 0.46 | 0.37 |
Appendix figures & tables18 assets
Supplementary material from the paper’s appendix.
Appendix
| Symbol | Description |
|---|---|
| Input signal | |
| Auxiliary metadata vector | |
| Categorical label ( classes) | |
| Training samples, prediction tasks, embedding dimension | |
| Encoder network (parameters ) | |
| Latent embedding / metadata-fused embedding |
| Property | Manifold Reg. [ 9 ] | MINN |
|---|---|---|
| Penalty form | (Dirichlet) | (squared residual) |
| PDE analogy | Laplace ( ) | Poisson ( ) |
| Source term | None (zero RHS) | Learned |
| Task dependence | No | Yes (source encodes metadata) |
| Collocation analog | No | Yes (residual at all nodes) |
| Low-label stability | Degenerates [ 10 ] | Stable (non-trivial source) |
| Beats per window ( ) | K + Macro-F1 ( ) |
|---|---|
| (single beat) | 0.54 |
| 0.59 | |
| ( default ) | 0.61 |
| 0.60 | |
| 0.58 |
| sweep ( ) | sweep ( ) | ||||||
|---|---|---|---|---|---|---|---|
| 0.57 | 0.60 | 0.61 | 0.59 | 0.58 | 0.61 | 0.59 | 0.55 |
| Encoder | w/ MINN | w/o MINN | ( ) |
|---|---|---|---|
| ResNet-18 | 0.61 | 0.54 | +0.07 |
| 4-layer CNN | 0.55 | 0.48 | +0.07 |
| Electrolyte | Bin | Train | Val | Test |
|---|---|---|---|---|
| K + | Hypo | 2,187 (1,102) | 274 (138) | 273 (137) |
| Normal | 8,280 (4,172) | 1,035 (522) | 1,033 (521) | |
| Hyper | 1,123 (566) | 141 (71) | 139 (70) | |
| Ca 2+ | Hypo | 1,616 (814) | 202 (102) | 201 (101) |
| Normal | 7,465 (3,762) | 933 (470) | 932 (470) | |
| Hyper | 965 (486) | 121 (61) | 119 (60) |
| K + | Ca 2+ | Mg 2+ | ||||||||
| Stratum | MINN | RN+FiLM | best base | MINN | RN+FiLM | best base | MINN | RN+FiLM | best base | |
| Male | k | 0.61 | 0.56 | 0.55 | 0.50 | 0.46 | 0.45 | 0.40 | 0.37 | 0.36 |
| Female | k | 0.61 | 0.57 | 0.55 | 0.49 | 0.46 | 0.44 | 0.39 | 0.36 | 0.35 |
| Age | k | 0.62 | 0.58 | 0.55 | 0.51 | 0.47 | 0.45 | 0.41 | 0.38 | 0.36 |
| Age – | k | 0.61 | 0.56 | 0.55 | 0.50 | 0.46 | 0.45 | 0.40 | 0.36 | 0.36 |
| Age | k | 0.59 | 0.55 | 0.52 | 0.47 | 0.43 | 0.41 | 0.37 | 0.34 | 0.32 |
| Subgroup | ECGFounder | Logit Adj. | Manifold Mixup | ResNet+FiLM | Poisson Learn. | MINN | |
|---|---|---|---|---|---|---|---|
| K-sparing diuretics + ACEi | 142 | 0.40 | 0.46 | 0.43 | 0.49 | 0.47 | 0.53 |
| Age 85 + 8 medications | 238 | 0.45 | 0.46 | 0.45 | 0.47 | 0.46 | 0.50 |
| Dialysis patients | 487 | 0.38 | 0.42 | 0.41 | 0.46 | 0.44 | 0.51 |
| Heart failure + concurrent hypoK | 195 | 0.44 | 0.46 | 0.46 | 0.48 | 0.47 | 0.52 |
| Setting | Method | K + F1 ( ) | Ca 2+ F1 ( ) | Mg 2+ F1 ( ) |
|---|---|---|---|---|
| In-distribution | ECGFounder | 0.55 | 0.44 | 0.35 |
| MINN | 0.61 | 0.50 | 0.40 | |
| Temporal split (2008–2016 2017–2019) | ECGFounder | 0.51 | 0.39 | 0.30 |
| MINN | 0.59 | 0.48 | 0.39 | |
| Care-unit split (ICU ED) | ECGFounder | 0.47 | 0.34 | 0.27 |
| MINN | 0.57 | 0.46 | 0.37 |
| Component | Hyperparameter | Value |
| Encoder (ResNet-18) | Input channels | 12 |
| Embedding dim | 128 | |
| Dropout | 0.3 | |
| FiLM Fusion | Metadata dim | 40 |
| Output dim | 128 | |
| Source Network | Hidden layers | 3 |
| Method | K + ( ) | Ca 2+ ( ) | Mg 2+ ( ) |
|---|---|---|---|
| S4/S4D-ECG | 0.52 | 0.41 | 0.33 |
| LDAM+DRW | 0.53 | 0.43 | 0.34 |
| Focal Loss | 0.51 | 0.42 | 0.33 |
| SMOTE | 0.49 | 0.40 | 0.32 |
| Label Propagation | 0.46 | 0.37 | 0.30 |
| MINN | 0.61 | 0.50 | 0.40 |
| K + | Ca 2+ | Mg 2+ | ||||
|---|---|---|---|---|---|---|
| Method | Hypo ( ) | Hyper ( ) | Hypo ( ) | Hyper ( ) | Hypo ( ) | Hyper ( ) |
| ECGFounder | 0.38 | 0.34 | 0.28 | 0.22 | 0.20 | 0.18 |
| Poisson Learning | 0.37 | 0.33 | 0.27 | 0.21 | 0.19 | 0.17 |
| Logit Adj. | 0.36 | 0.31 | 0.26 | 0.20 | 0.18 | 0.16 |
| MINN | 0.45 | 0.40 | 0.35 | 0.28 | 0.26 | 0.22 |
| Method | ECE ( ) |
|---|---|
| ECGFounder | 0.124 |
| Poisson Learning | 0.116 |
| Logit Adj. | 0.105 |
| MINN | 0.083 |
| Labeled fraction | |||||||
|---|---|---|---|---|---|---|---|
| Electrolyte | Method | 1% | 5% | 10% | 25% | 50% | 100% |
| K + | ECGFounder | 0.29 | 0.37 | 0.43 | 0.49 | 0.53 | 0.55 |
| Poisson Learning | 0.27 | 0.35 | 0.40 | 0.44 | 0.47 | 0.49 | |
| Logit Adj. | 0.25 | 0.33 | 0.41 | 0.47 | 0.51 | 0.53 | |
| MINN | 0.38 | 0.47 | 0.52 | 0.56 | 0.59 | 0.61 | |
| Ca 2+ | ECGFounder | 0.28 | 0.33 | 0.36 | 0.40 | 0.42 | 0.44 |
| Comparison | Electrolyte | Mean F1 (MINN baseline) | Paired -test |
|---|---|---|---|
| MINN vs. ECGFounder | K + | ||
| MINN vs. ECGFounder | Ca 2+ | ||
| MINN vs. Logit Adj. | K + | ||
| MINN vs. Logit Adj. | Ca 2+ |
| Asset | Type | Version | License |
|---|---|---|---|
| MIMIC-IV [ 12 ] | Dataset | 2.2 | PhysioNet credentialed (DUA) |
| MIMIC-IV-ECG [ 38 ] | Dataset | 0.3 | PhysioNet credentialed (DUA) |
| ECGFounder [ 6 ] | Model weights | v1.0 | per upstream release |
| ECG-FM [ 7 ] | Model weights | v0.1 | per upstream release |
| TabPFN [ 34 ] | Library | 0.1.x | Apache-2.0 |
| CatBoost [ 35 ] | Library | 1.2 | Apache-2.0 |
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