Right Ventricular Physiology and Ventricular Interdependence

The right ventricle moves blood through the lungs so that it can reach the left heart. When right ventricular output falls, blood accumulates in the systemic veins while less blood reaches the left ventricle. Systemic congestion and low cardiac output can therefore develop together, even when left ventricular contraction appears preserved.

11.1 A Ventricle Built for a Different Task

The right ventricle normally ejects into a low-pressure pulmonary circulation. It has a thinner free wall than the left ventricle and a more complex shape. In cross-section, it partly wraps around the left ventricle. Its geometry and muscle arrangement suit the relatively low pressure needed to move blood through healthy lungs.

Several movements contribute to ejection. The tricuspid annulus moves toward the apex, shortening the chamber along its length. The free wall moves inward toward the septum. Septal contraction and the mechanical action of the left ventricle also help empty the right ventricle. Longitudinal shortening is important, but observing that movement alone does not show how much blood the chamber ejects.

Without a significant shunt, the two ventricles deliver essentially the same effective flow over time. Otherwise, blood would continue accumulating in one circulation. Their pressure requirements differ. The right ventricle usually moves that flow at a much lower pressure, so it performs less pressure–volume work per beat.

Its normal pressure–volume loop also differs from the conventional left ventricular rectangle described in Chapter 10. Right ventricular ejection can continue as ventricular pressure falls. The periods with almost no volume change are less distinct. Redington and colleagues demonstrated these features using simultaneous pressure recordings and biplane angiography in ten adults with normal hemodynamic function. 1

These adaptations work well while pulmonary load remains low. A sudden increase in the pressure required for ejection demands much more force from a relatively thin wall. If the ventricle cannot increase contraction enough, it ejects less blood and begins to dilate.

Assess right ventricular performance against this changing load. Size shows how much the chamber has enlarged. Motion measures describe particular components of contraction. Pressure and forward flow show what the ventricle achieves against its current circulation. These observations need to be interpreted together.

11.2 Pulmonary Load Is More Than Pulmonary Artery Pressure

Right ventricular afterload is the load that opposes ejection. Part of it comes from resistance to steady flow through the lungs. Another part comes from the pulsatile circulation: blood accelerates with each beat, pulmonary arteries expand, and pressure waves travel and return. Left atrial pressure sets an important downstream pressure.

Pulmonary vascular resistance, or PVR, describes the steady pressure difference across the pulmonary circulation relative to flow:

Mean pulmonary artery pressure is the average pressure entering that circulation. Pulmonary artery occlusion pressure estimates left atrial pressure when the measurement is valid. Subtracting the latter from the former estimates the pressure drop across the pulmonary vessels. Dividing by cardiac output relates that pressure drop to the flow passing through them.

For an illustrative calculation, let mean pulmonary artery pressure be 30 mm Hg, occlusion pressure 10 mm Hg, and cardiac output 5 L/min. First calculate the pressure difference:

30 − 10 = 20 mm Hg

Then divide by flow:

20 ÷ 5 = 4 Wood units

One Wood unit is 1 mm Hg·min/L. These numbers explain the calculation; they are not treatment targets. The result depends on reliable pressure and flow measurements and on occlusion pressure representing the relevant downstream pressure.

PVR does not describe the whole load. Pulmonary arterial compliance determines how much the arteries expand as blood enters during systole. Less compliant arteries accommodate a given ejected volume with a larger pressure rise. Wave reflections can also change pressure during ejection. Pulmonary valve or outflow obstruction adds a load that the usual PVR calculation does not include.

A pressure change must therefore be interpreted with a flow change. A severely failing right ventricle may eject too little blood to generate a very high pulmonary artery pressure. As output collapses, pulmonary pressure can fall even though the pulmonary vascular disease remains severe. Lower pressure with lower output may indicate deterioration.

High left atrial pressure can also raise pulmonary artery pressure. This differs from a primary increase in pulmonary arteriolar resistance. If pulmonary vasodilation increases flow into a poorly accommodating left heart, left atrial pressure and pulmonary congestion may rise. Establish the mechanism before interpreting a pressure reduction as successful unloading.

11.3 Acute Pressure Overload and Chronic Adaptation

An abrupt increase in pulmonary vascular load reduces ejection when the right ventricle cannot generate enough additional force. More blood remains at end systole. Continuing venous return then increases the volume present before the next contraction. The chamber enlarges, and its wall must sustain greater tension to generate pressure.

Dilation can initially recruit a Frank–Starling response, but it cannot compensate indefinitely for severe afterload. As the chamber enlarges, wall stress rises and tricuspid valve closure may deteriorate. More myocardial effort may then produce little additional forward flow.

Chronic pressure loading allows time for a different response. The wall can hypertrophy and increase its pressure-generating capacity. A patient with established pulmonary hypertension may therefore sustain pressures that would overwhelm a previously normal right ventricle during an acute pulmonary embolism. The same measured pressure can represent very different challenges in those two patients.

Hypertrophy does not guarantee adequate reserve. More muscle requires perfusion, and remodeling can impair diastolic filling. Collagen accumulation and changes within cardiomyocytes can make the chamber stiffer. When compliance falls, an additional volume of blood causes a larger increase in diastolic pressure.

Rain and colleagues examined right ventricular pressure–volume behavior and myocardial tissue in pulmonary arterial hypertension. They found increased diastolic stiffness, with contributions from collagen accumulation and greater passive tension in cardiomyocytes. Chronic pressure loading therefore changes filling properties as well as systolic performance. 2

Acute illness can overwhelm the remaining reserve of a chronically remodeled ventricle. Infection, hypoxemia, arrhythmia, pulmonary embolism, or a ventilator change may increase demand or reduce the ventricle's ability to meet it. Prior imaging, wall thickness, earlier hemodynamics, and the clinical time course help distinguish acute loading from chronic disease or an acute deterioration on chronic disease.

11.4 Coronary Perfusion and the Failure Cycle

The right ventricular free wall usually receives much of its blood supply from the right coronary artery, although anatomy varies. With normal right ventricular pressure, myocardial compression is relatively limited. Coronary flow can occur during both systole and diastole.

As right ventricular pressure and wall tension rise, contracting muscle compresses vessels within the wall more strongly. Blood then has greater difficulty reaching vulnerable inner layers during systole. At the same time, generating the higher pressure increases myocardial oxygen requirements. Pressure overload can therefore increase demand while restricting supply.

Gold and Bache tested this mechanism during acute pulmonary artery constriction in awake dogs. Increased right ventricular systolic pressure impeded systolic perfusion of the subendocardium under the experimental conditions. This animal study demonstrates a mechanism of impaired blood supply; it does not define a clinical pressure threshold for ischemia. 3

Systemic hypotension reduces the arterial pressure available to drive coronary flow. Tachycardia shortens the time available for diastolic perfusion and increases the number of oxygen-consuming contractions each minute. These changes are particularly harmful when systolic perfusion is already restricted.

The failure cycle then becomes easier to understand. Poor ejection causes dilation. Dilation raises wall stress and can worsen functional tricuspid regurgitation. More blood is ejected backward into the right atrium instead of forward through the lungs. Reduced coronary supply impairs contraction further. Left ventricular filling falls, systemic pressure falls, and coronary perfusion becomes still less favorable.

Support must address several links in this cycle. Restoring adequate systemic pressure can support coronary perfusion, but output and pulmonary load must also be reassessed. Inotropic stimulation may improve ejection while increasing oxygen use. Treating the cause of the overload remains essential because neither pressure support nor stronger contraction removes the underlying obstruction or pulmonary vascular problem.

11.5 Ventricular Interdependence

The ventricles interact through the flow between them and through the structures they share. These are separate mechanisms, and both can reduce left ventricular filling during right ventricular failure.

First, the ventricles are connected in series. Right ventricular output crosses the lungs and becomes left ventricular inflow. When right ventricular output falls, less blood reaches the left heart over subsequent beats. Preserved left ventricular contractility cannot maintain output if too little blood arrives for ejection.

Second, the ventricles share the interventricular septum, myocardial fibers, and the space enclosed by the pericardium. An enlarging right ventricle can flatten and displace the septum toward the left ventricle. This changes left ventricular shape and reduces the space available for filling.

Pericardial constraint adds another effect. Once the pericardium limits further expansion, increasing right ventricular volume can raise the pressure surrounding the left ventricle. Measured left ventricular diastolic pressure may rise even while left ventricular volume falls. The pressure inside the chamber is then partly supporting the pressure outside it, rather than simply distending the wall.

The relevant distinction is transmural pressure: intracavitary pressure minus surrounding pressure. A high filling pressure measured relative to atmosphere does not necessarily mean that the left ventricle has a large volume or a large distending pressure. This helps explain how systemic congestion can coexist with a small left ventricular cavity.

Brinker and colleagues used forced inspiration against a closed airway to acutely increase right ventricular loading in healthy volunteers. Echocardiography showed leftward septal displacement and altered left ventricular shape. The study provides direct human evidence of mechanical interaction between the ventricles. 4

The timing of septal flattening helps interpret the load. Predominantly systolic flattening commonly accompanies pressure overload. Diastolic flattening can accompany volume overload. Severe or mixed loading can affect both phases. These patterns support a physiological interpretation but do not identify a specific cause, such as pulmonary embolism, by themselves.

A small left ventricle beside a markedly enlarged right ventricle therefore requires more explanation than a diagnosis of volume depletion. Fluid may enlarge the right ventricle further, displace the septum, and raise pericardial pressure. Left ventricular filling can worsen despite adding blood to the circulation.

11.6 Preload: Enough Filling Without Excess Distension

The right ventricle needs enough venous return to support ejection. If filling is genuinely insufficient, increasing it may raise stroke volume through the Frank–Starling mechanism. The clinical question is whether additional filling produces useful forward flow under the current conditions.

When severe afterload or myocardial dysfunction prevents effective ejection, added blood may mainly enlarge the chamber and raise right atrial pressure. More filling then produces little additional pulmonary flow. The rise in pressure is evidence of an upstream consequence, not proof that cardiac output has improved.

Further dilation can worsen tricuspid regurgitation, wall stress, and ventricular interdependence. An attempt to increase left ventricular preload by giving fluid can therefore have the opposite effect. The right ventricle becomes larger while less blood reaches or fits within the left ventricle.

Belenkie and colleagues examined volume loading during experimental pulmonary embolism in dogs. Before embolism, volume loading increased an index of left ventricular stroke work. After repeated embolizations, further loading enlarged the right ventricle, reduced an index of left ventricular filling volume, and reduced stroke work. These findings demonstrate a mechanism of harm under severe loading conditions. They do not establish one fluid strategy for every patient with pulmonary embolism. 5

A reversible filling test, such as passive leg raising when technically appropriate, temporarily increases venous return. Measure its effect on stroke volume or cardiac output. A rise in venous pressure without a convincing increase in forward flow does not establish fluid responsiveness. The test must also be technically adequate, and the measured flow change must exceed the method's uncertainty.

Fluid responsiveness and fluid tolerance answer different questions. Responsiveness asks whether additional filling increases flow. Tolerance asks whether that additional filling causes unacceptable congestion or other harm. A modest flow increase may be outweighed by increasing venous pressure, worsening right ventricular dilation, or pulmonary edema.

11.7 Ventilation and the Pulmonary Vascular Environment

Positive-pressure ventilation changes right ventricular loading in two main ways. It raises surrounding intrathoracic pressure, which can reduce the pressure gradient driving systemic venous return. It also changes lung volume and the pressures acting on pulmonary vessels, which can alter right ventricular afterload.

Different vessels respond differently to lung inflation. Extra-alveolar vessels are held open partly by traction from the surrounding lung. At low lung volumes, reduced traction and regional collapse can narrow these vessels. Hypoxia in poorly ventilated regions can also cause pulmonary vasoconstriction.

At high lung volumes, expanding alveoli can compress vessels within alveolar walls. Overdistension can therefore increase the resistance opposing pulmonary flow. Recruitment of collapsed lung and overdistension of already open lung can have opposite effects, even though both follow an increase in airway pressure.

The effect of PEEP depends on which process predominates. Recruitment may reopen useful lung and reduce hypoxic vasoconstriction. Excess inflation may compress alveolar vessels and make ejection more difficult. Changes in venous return occur at the same time, so the net response must be assessed from flow, right ventricular findings, respiratory mechanics, and gas exchange.

Airway pressure does not equal the pressure across every alveolar wall or the pressure transmitted to the heart. Lung and chest wall mechanics affect that transmission. The same PEEP can therefore have different circulatory effects in different patients.

Hypoxemia, hypercapnia, and acidemia can further increase pulmonary vascular tone. Their effects depend on severity and the underlying disease. Correcting one blood gas value may require a ventilator change that introduces another problem, such as greater overdistension. Balance oxygenation, carbon dioxide clearance, lung protection, and circulation together.

In a prospective study of 752 patients with moderate-to-severe ARDS receiving protective ventilation, Mekontso Dessap and colleagues found acute cor pulmonale in 22%. It was defined by right ventricular dilation with septal dyskinesia. Protective ventilation therefore did not eliminate important right ventricular loading. 6

Prone positioning can improve lung inflation and ventilation distribution, potentially reducing pulmonary vascular load. In a physiological study of severe ARDS, Vieillard-Baron and colleagues observed reduced right ventricular enlargement and septal abnormality after prone ventilation in patients with acute cor pulmonale. This supports a mechanism of right ventricular unloading. The study itself was not a randomized survival trial. 7

11.8 Congestion Is Part of the Hemodynamic Problem

When the right ventricle cannot handle incoming blood effectively, right atrial and systemic venous pressures can rise. The consequences extend beyond visible edema. Organs need an adequate pressure difference between arterial inflow and venous drainage to sustain blood flow.

If arterial pressure stays the same while venous pressure rises, that pressure difference becomes smaller. Increased venous and capillary hydrostatic pressures also favor fluid movement into the interstitium. Tissue pressure may then rise and compress vessels, adding another limitation to perfusion.

The kidney illustrates why hypotension and oliguria do not automatically call for fluid. Urine output may fall because arterial inflow is inadequate, renal venous pressure is high, intrinsic injury is present, or several mechanisms coexist. If congestion is an important cause, adding fluid can raise venous pressure further without restoring filtration.

Mullens and colleagues found that greater venous congestion was associated with worsening renal function in advanced decompensated heart failure. This observational study supports the clinical relevance of downstream pressure. It does not prove that lowering central venous pressure to one specified value prevents renal injury across all ICU populations. 8

Central venous pressure, or CVP, still requires a reliable tracing and an explanation. Intrathoracic pressure can raise the measured value without an equivalent increase in transmural right atrial pressure. Severe tricuspid regurgitation can create large systolic waves. Catheter position, the reference level, and respiratory timing also affect interpretation.

A distended inferior vena cava provides information about venous size under those conditions. Its caliber and respiratory changes depend on right heart function, respiration, and abdominal pressure. It does not independently measure total blood volume or establish fluid responsiveness.

Combine the pressure tracing with organ findings, echocardiography, and forward flow. A patient can have low arterial pressure and high venous pressure at the same time. That combination may reflect inadequate pumping through the right heart and can make additional fluid poorly tolerated.

11.9 What Echocardiography Can and Cannot Establish

Echocardiography shows right ventricular size, septal shape, valve disease, and pericardial abnormalities. It also provides several measurements of systolic motion. Because the right ventricle is a complex three-dimensional chamber, a single motion measurement cannot describe its entire performance.

Tricuspid annular plane systolic excursion, or TAPSE, measures how far the lateral tricuspid annulus moves toward the apex during systole. Tissue Doppler S′ measures the velocity of systolic annular movement. Both mainly describe longitudinal motion. Their values depend on loading, image alignment, and the pattern of contraction.

Fractional area change measures how much right ventricular area decreases between end diastole and end systole in an appropriate view. Subtract end-systolic area from end-diastolic area, then divide by end-diastolic area and express the result as a percentage. This describes chamber emptying in the selected plane. Image quality and border definition affect the result, and the view does not capture the whole ventricle.

In 282 mechanically ventilated patients with septic shock, Vieillard-Baron and colleagues found that 42% met their research definition of right ventricular failure: dilation combined with elevated CVP. Many had a TAPSE within the study's normal range. Greater dilation was associated with a lower likelihood of a flow response to passive leg raising for a given pulse-pressure variation. 9

The size and pressure criteria were study definitions, not universal diagnostic boundaries. The finding explains why preserved annular movement cannot exclude failure of the right-heart circulation. The chamber may retain longitudinal motion while its overall interaction with load produces congestion and an inadequate response to additional filling.

Doppler estimates of pulmonary pressure require separate care. Tricuspid regurgitant velocity is used to estimate the systolic pressure difference between the right ventricle and right atrium. Adding an estimated right atrial pressure gives an estimate of right ventricular systolic pressure. This approximates pulmonary artery systolic pressure only when there is no important pulmonary valve or right ventricular outflow obstruction.

An adequate Doppler envelope and a reasonable right atrial pressure estimate are essential. An absent or poor regurgitant signal does not establish normal pulmonary pressure. A severely failing ventricle may also generate only a modest pressure. Integrate the estimate with size, septal motion, valve findings, and measured forward flow. 11

11.10 Matching Support to the Limiting Mechanism

Identify the cause of right ventricular dysfunction while supporting perfusion. Pulmonary embolism, right ventricular infarction, pulmonary vascular disease, ARDS, severe left-sided disease, and external cardiac compression require different definitive treatments. Hemodynamic support allows time for those treatments to work.

Adjust filling according to measured response and congestion. An underfilled circulation may benefit from additional volume. If the ventricle is markedly distended and venous pressure rises without a useful flow increase, further filling may worsen the problem. Neither approach removes a fixed obstruction or restores an ischemic coronary territory.

Support systemic pressure with attention to coronary and organ perfusion. Also assess rhythm. Loss of coordinated atrial contraction can impair ventricular filling, especially in a stiff chamber. Excessive tachycardia shortens filling and coronary perfusion time while raising oxygen requirements. Correcting the relevant rhythm disturbance may improve output without adding fluid.

Reducing pulmonary load can allow the right ventricle to eject more effectively. The intervention may be correction of a respiratory disturbance, a ventilator adjustment, or selected pulmonary vasodilator support. Check whether forward flow and perfusion improve. A lower pulmonary artery pressure alone does not establish benefit, particularly if output has also fallen.

The left heart must be able to accept any increase in pulmonary flow. If left atrial pressure rises markedly, an intervention that unloads the right ventricle may worsen pulmonary congestion. Systemic hypotension is another possible limitation of vasodilator treatment. Follow both circulations after the intervention.

Short-term physiological improvement and patient outcome benefit are different endpoints. Taylor and colleagues randomized patients with acute lung injury to low-dose inhaled nitric oxide or placebo. Oxygenation improved transiently, but ventilator-free days and mortality did not improve significantly. The trial excluded sepsis-related lung injury and significant nonpulmonary organ dysfunction. It therefore does not settle every rescue situation involving severe right ventricular failure. 10

Inotropic or mechanical circulatory support may be needed when output remains inadequate despite treatment of loading conditions and reversible causes. Selection depends on the diagnosis, oxygenation needs, left ventricular involvement, and available expertise. Each intervention must be reassessed against the problem it was intended to correct.

11.11 An Integrated Bedside Example

Consider an illustrative patient with ARDS who develops hypotension after a ventilator change. CVP rises, the right ventricle enlarges, and the septum flattens. The left ventricular cavity is small, but left ventricular systolic shortening appears preserved.

This combination suggests that the right heart may be limiting forward flow. Reduced right ventricular ejection supplies less blood to the left heart. Septal displacement and pericardial constraint may further reduce the space available for left ventricular filling. Preserved left ventricular shortening does not resolve either problem.

Review what changed in ventilation. Examine airway and plateau pressures where interpretable, respiratory mechanics, gas exchange, and the hemodynamic waveforms. Also assess other causes of acute deterioration, including pneumothorax, pulmonary embolism, ischemia, arrhythmia, and pericardial compression. A close temporal relationship does not by itself prove that PEEP caused the event.

Suppose a technically adequate reversible filling test raises CVP from 14 to 18 mm Hg. Stroke volume remains near 45 mL per beat. The added venous return has raised upstream pressure by 4 mm Hg without a convincing increase in the volume ejected with each beat.

That is the basic meaning of the result. Next consider measurement reliability. If the small observed stroke-volume change lies within the method's variability, it cannot establish a flow response. Under the tested conditions, the result provides little support for giving fluid to increase output. The CVP rise also requires interpretation in relation to respiratory pressure and the rest of the tracing.

The next intervention addresses the demonstrated cause while preserving oxygenation and systemic perfusion. If overdistension has increased pulmonary load, a suitable ventilator adjustment may improve ejection. If an obstructive or ischemic process is responsible, that process needs definitive treatment. Reassess both ventricles, forward flow, congestion, and gas exchange after the change.

A useful response means that more blood reaches the systemic circulation with adequate perfusion pressure and acceptable gas exchange. Less right ventricular distension or a lower CVP may support that interpretation. Neither observation alone proves that perfusion has improved.

References

1. Redington AN, Gray HH, Hodson ME, Rigby ML, Oldershaw PJ. Characterisation of the normal right ventricular pressure-volume relation by biplane angiography and simultaneous micromanometer pressure measurements. Br Heart J. 1988;59(1):23–30. doi:10.1136/hrt.59.1.23.

2. Rain S, Handoko ML, Trip P, et al. Right ventricular diastolic impairment in patients with pulmonary arterial hypertension. Circulation. 2013;128(18):2016–2025. doi:10.1161/CIRCULATIONAHA.113.001873.

3. Gold FL, Bache RJ. Influence of systolic intracavity pressure on right ventricular perfusion in the awake dog. Cardiovasc Res. 1982;16(8):467–472. doi:10.1093/cvr/16.8.467.

4. Brinker JA, Weiss JL, Lappé DL, et al. Leftward septal displacement during right ventricular loading in man. Circulation. 1980;61(3):626–633. doi:10.1161/01.CIR.61.3.626.

5. Belenkie I, Dani R, Smith ER, Tyberg JV. Effects of volume loading during experimental acute pulmonary embolism. Circulation. 1989;80(1):178–188. doi:10.1161/01.CIR.80.1.178.

6. Mekontso Dessap A, Boissier F, Charron C, et al. Acute cor pulmonale during protective ventilation for acute respiratory distress syndrome: prevalence, predictors, and clinical impact. Intensive Care Med. 2016;42(5):862–870. doi:10.1007/s00134-015-4141-2.

7. Vieillard-Baron A, Charron C, Caille V, Belliard G, Page B, Jardin F. Prone positioning unloads the right ventricle in severe ARDS. Chest. 2007;132(5):1440–1446. doi:10.1378/chest.07-1013.

8. Mullens W, Abrahams Z, Francis GS, et al. Importance of venous congestion for worsening of renal function in advanced decompensated heart failure. J Am Coll Cardiol. 2009;53(7):589–596. doi:10.1016/j.jacc.2008.05.068.

9. Vieillard-Baron A, Prigent A, Repessé X, et al. Right ventricular failure in septic shock: characterization, incidence and impact on fluid responsiveness. Crit Care. 2020;24:630. doi:10.1186/s13054-020-03345-z.

10. Taylor RW, Zimmerman JL, Dellinger RP, et al.; Inhaled Nitric Oxide in ARDS Study Group. Low-dose inhaled nitric oxide in patients with acute lung injury: a randomized controlled trial. JAMA. 2004;291(13):1603–1609. doi:10.1001/jama.291.13.1603.

11. Mukherjee M, Rudski LG, Addetia K, et al. Guidelines for the Echocardiographic Assessment of the Right Heart in Adults and Special Considerations in Pulmonary Hypertension: Recommendations from the American Society of Echocardiography. J Am Soc Echocardiogr. 2025;38(3):141–186. doi:10.1016/j.echo.2025.01.006.