Interactive physiology

Organ Crosstalk

The heart, lungs, liver and kidneys share one circulation, one oxygen supply, one volume-regulating hormone system and one inflammatory milieu. Failure in one is transmitted to the others, often in loops that feed back on the first.

The four-organ network

systemic hit:cytokines,vasodilation,capillary leak bar = stress, schematic 0–100
Arrows take the colour of the organ they leave. In a cascade, numbered badges give the order and dashed moving arrows mark a vicious loop. The bar under each organ is a schematic stress gauge from 0 to 100, not a measured value.
Network Four organs, twelve arrows

Each pair of organs is joined by two arrows, one for each direction. The heart failure cascade starts in a moment. Pick another cascade, or switch to Explore and tap an organ.

Matrix

Effect of each on the others

Rows are the organ that fails, columns the organ that suffers. Tap a cell for the mechanism, the named syndrome with its key criteria, a bedside clue and the main lever.

The coloured bar on each cell is the source organ, as on the arrows above.

Shared channels

What carries the crosstalk

The organs talk through pressure, oxygen delivery, the volume hormones, inflammation, and the acid–base and clearance load. The first two are worked through here.

Pressure: back-pressure steals perfusion

An organ is perfused by the pressure gradient across it. A rise in venous or abdominal pressure subtracts from that gradient as surely as a fall in MAP.

RPP=MAP 65 − max(CVP 15, IAP 8)=50 mmHg
APP=MAP 65 − IAP 8=57 mmHg
MAP 65 MAP 65 CVP 15 hepaticveins renalvein IVC Liver Kidney abdominal wall · IAP 8

65 mmHg
15 mmHg
8 mmHg

Renal perfusion pressure takes the higher of CVP and IAP as the outflow pressure; it is often written MAP − CVP. Normal IAP in critically ill adults is about 5–7 mmHg. WSACS 2013: intra-abdominal hypertension (IAH) when IAP ≥12 mmHg, grade I 12–15, II 16–20, III 21–25, IV >25; abdominal compartment syndrome is sustained IAP >20 mmHg with new organ dysfunction. Target APP ≥60 mmHg.

Oxygen delivery: three organs in one product

Every organ's oxygen supply depends on the others. The heart sets flow, the lungs load haemoglobin, the kidneys keep haemoglobin up through erythropoietin, and liver disease and bleeding pull it down.

CaO₂=1.34 × Hb 15.0 × SaO₂ 0.98 + 0.003 × PaO₂ 100=20.0 mL/dL
DO₂=CO 5.0 × CaO₂ 20.0 × 10=1000 mL/min
VO₂ ≈ 250 normal ≈ 1000

5.0 L/min
98%
100 mmHg
15.0 g/dL

PaO₂ in mmHg (kPa × 7.5). SaO₂ and PaO₂ move independently here; in a patient the dissociation curve links them. Resting DO₂ is about 1000 mL/min (indexed, about 500–600 mL/min/m²); resting consumption about 250 mL/min.

Volume and sodium

When the arterial circulation is underfilled, RAAS, the sympathetic system and ADH retain sodium and water, and natriuretic peptides push the other way. Heart failure, cirrhosis and CKD converge on this pathway, which is why oedema, ascites and hyponatraemia recur in all three. See the sodium and water page.

Inflammation

Sepsis, AKI and ventilator injury release cytokines into the shared circulation. They injure endothelium and epithelium in distant organs, so injury in one organ primes the next.

Acid–base and clearance

The lungs clear CO₂, the kidneys excrete H⁺ and regenerate HCO₃⁻, and the liver clears lactate and makes urea and albumin. When one fails the load shifts to the others. See the acid–base page.

Bedside

Crosstalk syndromes

Five checklists for the named syndromes. Each works through the criteria in order and says which one fails. Values accept a comma as the decimal mark.

Hepatorenal syndrome (HRS-AKI)

Illustrative values, not real patients. International Club of Ascites (ICA) 2015 criteria with the 2019 and 2024 updates; all must be met. Baseline is the last creatinine within 3 months. The albumin challenge is 2 consecutive days off diuretics with albumin 1 g/kg/day. Nephrotoxins: NSAIDs, aminoglycosides, iodinated contrast.

mmol/L

    Reference

    All twelve interactions

    One row per arrow, in short phrases.

    From → toMain mechanismSyndromeBedside clueLever