Right ventricular pressure-volume loop shape and systolic pressure change in pulmonary hypertension

Echocardiographic assessment of right ventricular performance in COVID-19 related acute respiratory distress syndrome: the importance of systo-diastolic interaction

BACKGROUND

The cardiac manifestations of COVID-19 have been described in patients with acute respiratory distress syndrome (ARDS) admitted to intensive care unit (ICU). The presence and impact of right ventricular (RV) diastolic function and performance has not been studied in this population yet. We describe the prevalence of RV diastolic dysfunction, assessed by the pulmonary valve pre-ejection A wave (PV A wave), and the RV systo-diastolic interaction, using the RV total isovolumic time (t-IVT), in COVID-19 ARDS.

RESULTS

Prospective observational study enrolling patients with moderate to severe COVID-19 ARDS admitted to ICU who underwent a transthoracic echocardiogram within 24 h of ICU admission and at least a second one during the ICU stay. Respiratory, hemodynamic and biochemistry parameters were collected. 163 patients (age 61.0 ± 9.3 years, 72% males) were enrolled. 36 patients (22.1%) had RV dysfunction, 45 (27.1%) LV systolic dysfunction. 73 patients (44.7%) had PV A wave. The RV t-IVT correlated with TAPSE at ICU admission (p < 0.002; r - 0.61), presence of PV A wave (p < 0.001; r 0.78), peak inspiratory pressure (PIP) (p < 0.001; r 0.42), PEEP (p < 0.001; r 0.68), dynamic driving pressure (DDP) (p < 0.001; r 0.58), and PaO2/FiO2 ratio (p < 0.01; r - 0.35). The presence of PV A wave was associated with higher PIP (p < 0.001; r 0.45), higher PEEP (p < 0.001; r 0.56), higher DDP (p < 0.01, r 0.51), and lower PaO2/FiO2 ratio (p < 0.001; r - 0.49).

CONCLUSIONS

RV t-IVT and the presence of PV A wave are non-invasive means to describe a significant RV diastolic dysfunction and may be consider descriptive signs of RV performance in COVID-19 ARDS.

Right ventricular performance during acute hypoxic exercise

Acute hypoxia increases pulmonary arterial (PA) pressures, though its effect on right ventricular (RV) function is controversial. The objective of this study was to characterize exertional RV performance during acute hypoxia. Ten healthy participants (34 ± 10 years, 7 males) completed three visits: visits 1 and 2 included non-invasive normoxic (fraction of inspired oxygen (F i O 2 ${F_{{\mathrm{i}}{{\mathrm{O}}_{\mathrm{2}}}}}$ ) = 0.21) and isobaric hypoxic (F i O 2 ${F_{{\mathrm{i}}{{\mathrm{O}}_{\mathrm{2}}}}}$  = 0.12) cardiopulmonary exercise testing (CPET) to determine normoxic/hypoxic maximal oxygen uptake (V ̇ O 2 max ${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ ). Visit 3 involved invasive haemodynamic assessments where participants were randomized 1:1 to either Swan-Ganz or conductance catheterization to quantify RV performance via pressure-volume analysis. Arterial oxygen saturation was determined by blood gas analysis from radial arterial catheterization. During visit 3, participants completed invasive submaximal CPET testing at 50% normoxicV ̇ O 2 max ${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ and again at 50% hypoxicV ̇ O 2 max ${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ (F i O 2 ${F_{{\mathrm{i}}{{\mathrm{O}}_{\mathrm{2}}}}}$  = 0.12). Median (interquartile range) values for non-invasiveV ̇ O 2 max ${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ values during normoxic and hypoxic testing were 2.98 (2.43, 3.66) l/min and 1.84 (1.62, 2.25) l/min, respectively (P < 0.0001). Mean PA pressure increased significantly when transitioning from rest to submaximal exercise during normoxic and hypoxic conditions (P = 0.0014). Metrics of RV contractility including preload recruitable stroke work, dP/dtmax , and end-systolic pressure increased significantly during the transition from rest to exercise under normoxic and hypoxic conditions. Ventricular-arterial coupling was maintained during normoxic exercise at 50%V ̇ O 2 max ${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ . During submaximal exercise at 50% of hypoxicV ̇ O 2 max ${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$ , ventricular-arterial coupling declined but remained within normal limits. In conclusion, resting and exertional RV functions are preserved in response to acute exposure to hypoxia at anF i O 2 ${F_{{\mathrm{i}}{{\mathrm{O}}_{\mathrm{2}}}}}$  = 0.12 and the associated increase in PA pressures. KEY POINTS: The healthy right ventricle augments contractility, lusitropy and energetics during periods of increased metabolic demand (e.g. exercise) in acute hypoxic conditions. During submaximal exercise, ventricular-arterial coupling decreases but remains within normal limits, ensuring that cardiac output and systemic perfusion are maintained. These data describe right ventricular physiological responses during submaximal exercise under conditions of acute hypoxia, such as occurs during exposure to high altitude and/or acute hypoxic respiratory failure.

Looking Back, Going Forward: Understanding Cardiac Pathophysiology from Pressure-Volume Loops

Knowing cardiac physiology is essential for health care professionals working in the cardiovascular field. Pressure-volume loops (PVLs) offer a unique understanding of the myocardial working and have become pivotal in complex pathophysiological scenarios, such as profound cardiogenic shock or when mechanical circulatory supports are implemented. This review provides a comprehensive summary of the left and right ventricle physiology, based on the PVL interpretation.

Right Ventricular-Vascular Uncoupling Predicts Pulmonary Hypertension in Clinically Diagnosed Heart Failure With Preserved Ejection Fraction

BACKGROUND

Pulmonary hypertension (PH) is highly prevalent in patients with heart failure with preserved ejection fraction (HFpEF), and it is a strong predictor of adverse outcomes. We aimed to determine possible echocardiographic parameters to predict the presence of PH in patients with HFpEF.

METHODS AND RESULTS

A total of 113 patients with HFpEF were prospectively enrolled from November 2017 to July 2022. The patients underwent invasive cardiac catheterization and simultaneous echocardiography at rest and during exercise. The parameters indicating right ventricle-pulmonary artery uncoupling, including tricuspid annular plane systolic excursion (TAPSE)/pulmonary artery systolic pressure (PASP) and tricuspid annular systolic velocity (TAS')/PASP were calculated. Receiver operating characteristic curve analysis was used to determine the optimal cut-off points of TAPSE/PASP and TAS'/PASP to differentiate patients with HFpEF with PH from those without PH. Sixty-eight patients with HFpEF with PH and 45 without PH were included. Those with PH had lower TAPSE/PASP and TAS'/PASP at rest and during exercise compared with those without PH. Both resting/stress TAPSE/PASP and TAS'/PASP were correlated with rest/exercise pulmonary capillary wedge pressure and mean pulmonary artery pressure. In multivariable regression analysis, TAPSE/PASP remained a significant predictor of exercise pulmonary capillary wedge pressure and mean pulmonary artery pressure. In receiver operating characteristic curve analysis, the optimal cut-off points of TAPSE/PASP and TAS'/PASP to differentiate patients with HFpEF with PH from those without PH were ≤0.62 and ≤0.47, respectively.

CONCLUSIONS

Right ventricle-pulmonary artery uncoupling is closely correlated with abnormal rest/exercise hemodynamics (pulmonary capillary wedge pressure and mean pulmonary artery pressure) in patients with HFpEF. TAPSE/PASP and TAS'/PASP can be useful parameters to detect PH in patients with HFpEF.

MRI pulmonary artery flow detects lung vascular pathology in preterms with lung disease

BACKGROUND

Pulmonary vascular disease (PVD) affects the majority of preterm neonates with bronchopulmonary dysplasia (BPD) and significantly determines long-term mortality through undetected progression into pulmonary hypertension. Our objectives were to associate characteristics of pulmonary artery (PA) flow and cardiac function with BPD-associated PVD near term using advanced magnetic resonance imaging (MRI) for improved risk stratification.

METHODS

Preterms <32 weeks postmenstrual age (PMA) with/without BPD were clinically monitored including standard echocardiography and prospectively enrolled for 3 T MRI in spontaneous sleep near term (AIRR (Attention to Infants at Respiratory Risks) study). Semi-manual PA flow quantification (phase-contrast MRI; no BPD n=28, mild BPD n=35 and moderate/severe BPD n=25) was complemented by cardiac function assessment (cine MRI).

RESULTS

We identified abnormalities in PA flow and cardiac function, i.e. increased net forward volume right/left ratio, decreased mean relative area change and pathological right end-diastolic volume, to sensitively detect BPD-associated PVD while correcting for PMA (leave-one-out area under the curve 0.88, sensitivity 0.80 and specificity 0.81). We linked these changes to increased right ventricular (RV) afterload (RV-arterial coupling (p=0.02), PA mid-systolic notching (t2; p=0.015) and cardiac index (p=1.67×10-8)) and correlated echocardiographic findings. Identified in moderate/severe BPD, we successfully applied the PA flow model in heterogeneous mild BPD cases, demonstrating strong correlation of PVD probability with indicators of BPD severity, i.e. duration of mechanical ventilation (rs=0.63, p=2.20×10-4) and oxygen supplementation (rs=0.60, p=6.00×10-4).

CONCLUSIONS

Abnormalities in MRI PA flow and cardiac function exhibit significant, synergistic potential to detect BPD-associated PVD, advancing the possibilities of risk-adapted monitoring.

Integrating Right Ventricular Pressure Waveform Analysis With Two-Point Volume Measurement for Quantification of Systolic and Diastolic Function: Experimental Validation and Clinical Application

OBJECTIVE

To define in an experimental model the variance, accuracy, precision, and concordance of single-beat measures of right ventricular (RV) contractility and diastolic capacitance relative to conventional reference standards, and apply the methods to a clinical data set.

DESIGN

A retrospective, observational analysis of recorded pressure waveforms and RV volume measurements.

SETTING

At a university laboratory.

PARTICIPANTS

Archived data from previous studies of anesthetized swine and awake patients undergoing clinically-indicated right-heart catheterization.

INTERVENTIONS

Recording of RV pressure with simultaneous measurement of RV volume by conductance (swine) or 3-dimensional (3D) echocardiography (humans) during changes in contractility and/or loading conditions.

MEASUREMENTS AND MAIN RESULTS

Using experimental data, single-beat measures of RV contractility quantified as end-systolic elastance, and diastolic capacitance quantified as the predicted volume at an end-diastolic pressure of 15 mmHg (V15), were compared to multi-beat, preload- variant, reference standards using correlation, Bland-Altman analysis, and 4-quadrant concordance testing. This analysis indicated that the methods were not directly interchangeable with reference standards, but were sufficiently robust to suggest potential clinical utility. Clinical application supported this potential by demonstrating enhanced assessment of the response to inhaled nitric oxide in patients undergoing diagnostic right-heart catheterization.

CONCLUSIONS

Study results supported the possibility of integrating automated RV pressure analysis with RV volume measured by 3D echocardiography to create a comprehensive assessment of RV systolic and diastolic function at the bedside.

Echocardiographic pressure-strain loop-derived stroke work of the right ventricle: validation against the gold standard

AIMS

Commercially available integrated software for echocardiographic measurement of stroke work (SW) is increasingly used for the right ventricle, despite a lack of validation. We sought to assess the validity of this method [echo-based myocardial work (MW) module] vs. gold-standard invasive right ventricular (RV) pressure-volume (PV) loops.

METHODS AND RESULTS

From the prospectively recruiting EXERTION study (NCT04663217), we included 42 patients [34 patients with pulmonary arterial hypertension (PAH) or chronic thromboembolic pulmonary hypertension (CTEPH) and 8 patients with absence of cardiopulmonary disease] with RV echocardiography and invasive PV catheterization. Echocardiographic SW was assessed as RV global work index (RVGWI) generated via the integrated pressure-strain MW software. Invasive SW was calculated as the area bounded by the PV loop. An additional parameter derived from the MW module, RV global wasted work (RVGWW), was correlated with PV loop measures. RVGWI significantly correlated with invasive PV loop-derived RV SW in the overall cohort [rho = 0.546 (P < 0.001)] and the PAH/CTEPH subgroup [rho = 0.568 (P < 0.001)]. Overall, RVGWW correlated with invasive measures of arterial elastance (Ea), the ratio of end-systolic elastance (Ees)/Ea, and end-diastolic elastance (Eed) significantly.

CONCLUSIONS

Integrated echo measurement of pressure-strain loop-derived SW correlates with PV loop-based assessment of RV SW. Wasted work correlates with invasive measures of load-independent RV function. Given the methodological and anatomical challenges of RV work assessment, evolution of this approach by incorporating more elaborated echo analysis data and an RV reference curve might improve its reliability to mirror invasively assessed RV SW.

Pulmonary Hypertension: A Contemporary Review

Major advances in pulmonary arterial hypertension, pulmonary hypertension (PH) associated with lung disease, and chronic thromboembolic PH cast new light on the pathogenetic mechanisms, epidemiology, diagnostic approach, and therapeutic armamentarium for pulmonary vascular disease. Here, we summarize key basic, translational, and clinical PH reports, emphasizing findings that build on current state-of-the-art research. This review includes cutting-edge progress in translational pulmonary vascular biology, with a guide to the diagnosis of patients in clinical practice, incorporating recent PH definition revisions that continue emphasis on early detection of disease. PH management is reviewed including an overview of the evolving considerations for the approach to treatment of PH in patients with cardiopulmonary comorbidities, as well as a discussion of the groundbreaking sotatercept data for the treatment of pulmonary arterial hypertension.

Combined use of right ventricular coupling and pulmonary arterial elastance as a comprehensive stratification approach for right ventricular function

Right ventricular (RV)-pulmonary arterial uncoupling is the consequence of increased afterload and/or decreased RV contractility. However, the combination of arterial elastance (Ea) and end-systolic elastance (Ees)/Ea ratio to assess RV function is unclear. We hypothesized that the combination of both could comprehensively assess RV function and refine risk stratification. The median Ees/Ea ratio (0.80) and Ea (0.59 mmHg/mL) were used to classify 124 patients with advanced heart failure into four groups. RV systolic pressure differential was defined as end-systolic pressure (ESP) minus beginning-systolic pressure (BSP). Patients among different subsets showed dissimilar New York Heart Association functional class (V = 0.303, p = 0.010), distinct tricuspid annular plane systolic excursion/ pulmonary artery systolic pressure (mm/mmHg; 0.65 vs. 0.44 vs. 0.32 vs. 0.26, p < 0.001), and diverse prevalence of pulmonary hypertension (33.3% vs. 35% vs. 90% vs. 97.6%, p < 0.001). By multivariate analysis, Ees/Ea ratio (hazard ratio [HR] 0.225, p = 0.004) and Ea (HR 2.194, p = 0.003) were independently associated with event-free survival. Patients with Ees/Ea ratio greater than or equal to 0.80 and Ea less than 0.59 mmHg/mL had better outcomes (p < 0.05). In patients with Ees/Ea ratio greater than or equal to 0.80, those with Ea greater than or equal to 0.59 mmHg/mL had a higher adverse outcome risk (p < 0.05). Ees/Ea ratio less than or equal to 0.80 was associated with adverse outcomes, even when Ea was less than 0.59 mmHg/mL (p < 0.05). Approximately 86% of patients with ESP-BSP greater than 5 mmHg had an Ees/Ea ratio less than or equal to 0.80 and/or an Ea greater than or equal to 0.59 mmHg/mL (V = 0.336, p = 0.001). Combined use of Ees/Ea ratio and Ea could be a comprehensive approach to assessing RV function and predicting outcomes. An exploratory analysis demonstrated that Ees/Ea ratio and Ea might be roughly estimated based on RV systolic pressure differential.

Pathophysiology of the right ventricle in health and disease: an update

The contribution of the right ventricle (RV) to cardiac output is negligible in normal resting conditions when pressures in the pulmonary circulation are low. However, the RV becomes relevant in healthy subjects during exercise and definitely so in patients with increased pulmonary artery pressures both at rest and during exercise. The adaptation of RV function to loading rests basically on an increased contractility. This is assessed by RV end-systolic elastance (Ees) to match afterload assessed by arterial elastance (Ea). The system has reserve as the Ees/Ea ratio or its imaging surrogate ejection fraction has to decrease by more than half, before the RV undergoes an increase in dimensions with eventual increase in filling pressures and systemic congestion. RV-arterial uncoupling is accompanied by an increase in diastolic elastance. Measurements of RV systolic function but also of diastolic function predict outcome in any cause pulmonary hypertension and heart failure with or without preserved left ventricular ejection fraction. Pathobiological changes in the overloaded RV include a combination of myocardial fibre hypertrophy, fibrosis and capillary rarefaction, a titin phosphorylation-related displacement of myofibril tension-length relationships to higher pressures, a metabolic shift from mitochondrial free fatty acid oxidation to cytoplasmic glycolysis, toxic lipid accumulation, and activation of apoptotic and inflammatory signalling pathways. Treatment of RV failure rests on the relief of excessive loading.

Evolution and optimization of clinical trial endpoints and design in pulmonary arterial hypertension

Selection of endpoints for clinical trials in pulmonary arterial hypertension (PAH) is challenging because of the small numbers of patients and the changing expectations of patients, clinicians, and regulators in this evolving therapy area. The most commonly used primary endpoint in PAH trials has been 6-min walk distance (6MWD), leading to the approval of several targeted therapies. However, single surrogate endpoints such as 6MWD or hemodynamic parameters may not correlate with clinical outcomes. Composite endpoints of clinical worsening have been developed to reflect patients' overall condition more accurately, although there is no standard definition of worsening. Recently there has been a shift to composite endpoints assessing clinical improvement, and risk scores developed from registry data are increasingly being used. Biomarkers are another area of interest, although brain natriuretic peptide and its N-terminal prohormone are the only markers used for risk assessment or as endpoints in PAH. A range of other genetic, metabolic, and immunologic markers is currently under investigation, along with conventional and novel imaging modalities. Patient-reported outcomes are an increasingly important part of evaluating new therapies, and several PAH-specific tools are now available. In the future, alternative statistical techniques and trial designs, such as patient enrichment strategies, will play a role in evaluating PAH-targeted therapies. In addition, modern sequencing techniques, imaging analyses, and high-dimensional statistical modeling/machine learning may reveal novel markers that can play a role in the diagnosis and monitoring of PAH.

Clinical Usefulness of Right Ventricle-Pulmonary Artery Coupling in Cardiovascular Disease

Right ventricular-pulmonary artery coupling (RV-PA coupling) refers to the relationship between RV contractility and RV afterload. Normal RV-PA coupling is maintained only when RV function and pulmonary vascular resistance are appropriately matched. RV-PA uncoupling occurs when RV contractility cannot increase to match RV afterload, resulting in RV dysfunction and right heart failure. RV-PA coupling plays an important role in the pathophysiology and progression of cardiovascular diseases. Therefore, early and accurate evaluation of RV-PA coupling is of great significance for a patient's condition assessment, clinical decision making, risk stratification, and prognosis judgment. RV-PA coupling can be assessed by using invasive or noninvasive approaches. The aim of this review was to summarize the pathological mechanism and evaluation methods of RV-PA coupling, the advantages and disadvantages of each method, and the application value of RV-PA coupling in various cardiovascular diseases.

A Comprehensive Assessment of Right Ventricular Function in Chronic Thromboembolic Pulmonary Hypertension

While chronic thromboembolic pulmonary hypertension (CTEPH) results from macroscopic and microscopic obstruction of the pulmonary vascular bed, the function of the right ventricle (RV) and increased RV afterload are the main determinants of its symptoms and prognosis. In this review, we assess RV function in patients diagnosed with CTEPH with a focus on the contributions of RV afterload and dysfunction to the pathogenesis of this disease. We will also discuss changes in RV function and geometry in response to treatment, including medical therapy, pulmonary endarterectomy, and balloon pulmonary angioplasty.

A standardized definition for right ventricular failure in cardiac surgery patients

Right ventricular failure (RVF) is a significant cause of mortality and morbidity after cardiac surgery. Despite its prognostic importance, RVF remains under investigated and without a universally accepted definition in the perioperative setting. We foresee that the provision of a standardized perioperative definition for RVF based on practical and objective criteria will help to improve quality of care through early detection and facilitate the generalization of RVF research to advance this field. This article provides an overview of RVF aetiology, pathophysiology, current diagnostic modalities, as well as a summary of existing RVF definitions. This is followed by our proposal for a standardized definition of perioperative RVF, one that captures RV structural and functional abnormalities through a multimodal approach based on anatomical, echocardiographic, and haemodynamic criteria that are readily available in the perioperative setting (Central Image).

Invasive Right Ventricular Pressure-Volume Analysis: Basic Principles, Clinical Applications, and Practical Recommendations

Right ventricular pressure-volume (PV) analysis characterizes ventricular systolic and diastolic properties independent of loading conditions like volume status and afterload. While long-considered the gold-standard method for quantifying myocardial chamber performance, it was traditionally only performed in highly specialized research settings. With recent advances in catheter technology and more sophisticated approaches to analyze PV data, it is now more commonly used in a variety of clinical and research settings. Herein, we review the basic techniques for PV loop measurement, analysis, and interpretation with the aim of providing readers with a deeper understanding of the strengths and limitations of PV analysis. In the second half of the review, we detail key scenarios in which right ventricular PV analysis has influenced our understanding of clinically relevant topics and where the technique can be applied to resolve additional areas of uncertainty. All told, PV analysis has an important role in advancing our understanding of right ventricular physiology and its contribution to cardiovascular function in health and disease.

Unmasking right ventricular-arterial uncoupling during fluid challenge in pulmonary hypertension

BACKGROUND

Patients with pulmonary hypertension (PH) frequently show preserved right ventricular (RV) function at rest. However, volume challenge may uncover pending RV dysfunction. We aimed to assess the physiological and prognostic impact of RV-pulmonary arterial (RV-PA) uncoupling during volume challenge in patients with precapillary PH.

METHODS

We prospectively assessed 32 patients with PH (pulmonary arterial hypertension, n = 27; inoperable chronic thromboembolic disease, n = 5) and 4 controls using invasive pressure-volume (PV) catheterization. PV loops were recorded during preload reduction (balloon occlusion of inferior vena cava; baseline) and acute volume loading (200 ml saline in 20 s). Contractility (multi-beat end-systolic elastance [Ees]), arterial elastance (Ea), and RV-PA coupling (Ees/Ea) were obtained at baseline and at maximum volume loading (MVL).

RESULTS

Median [interquartile range] time to MVL was 19 [18-22] s. Ees/Ea significantly declined from baseline (0.89 [0.69-1.23]) to MVL (0.16 [0.12-0.34]; p < 0.001) in patients with PH but remained stable in controls (baseline: 1.08 [0.94-1.80]; MVL: 1.01 [0.80-2.49]; p = 0.715). The same pattern was observed for Ees, while Ea remained unchanged. The percent decline of RV-PA coupling (ΔEes/Ea) during fluid challenge was significantly associated with pulmonary resting hemodynamics, RV ejection fraction (RVEF), and RV end-diastolic volume. Kaplan-Meier analysis revealed that patients with PH who had a smaller ΔEes/Ea (<-65%) had a significantly better prognosis (log-rank p = 0.0389). In multivariate Cox regression analysis, clinical worsening was predicted by ΔEes/Ea (hazard ratio: 0.96 [95% confidence interval: 0.93-1.00]) and RVEF (hazard ratio: 0.95 [95% confidence interval: 0.92-0.98]).

CONCLUSIONS

Assessment of PV loops during fluid challenge uncovers exhausted RV coupling reserve with severely reduced contractility in PH. RV-PA uncoupling during volume challenge can be predicted by pulmonary resting hemodynamics and RVEF. RV-PA uncoupling during fluid challenge and RVEF (as a noninvasive correlate) are predictors of clinical worsening.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT03403868 (January 19, 2018).

The physiologic basis of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare dyspnea-fatigue syndrome caused by a progressive increase in pulmonary vascular resistance (PVR) and eventual right ventricular (RV) failure. In spite of extensive pulmonary vascular remodeling, lung function in PAH is generally well preserved, with hyperventilation and increased physiologic dead space, but minimal changes in lung mechanics and only mild to moderate hypoxemia and hypocapnia. Hypoxemia is mainly caused by a low mixed venous PO₂ from a decreased cardiac output. Hypocapnia is mainly caused by an increased chemosensitivity. Exercise limitation in PAH is cardiovascular rather than ventilatory or muscular. The extent of pulmonary vascular disease in PAH is defined by multipoint pulmonary vascular pressure-flow relationships with a correction for hematocrit. Pulsatile pulmonary vascular pressure-flow relationships in PAH allow for the assessment of RV hydraulic load. This analysis is possible either in the frequency-domain or in the time-domain. The RV in PAH adapts to increased afterload by an increased contractility to preserve its coupling to the pulmonary circulation. When this homeometric mechanism is exhausted, the RV dilates to preserve flow output by an additional heterometric mechanism. Right heart failure is then diagnosed by imaging of increased right heart dimensions and clinical systemic congestion signs and symptoms. The coupling of the RV to the pulmonary circulation is assessed by the ratio of end-systolic to arterial elastances, but these measurements are difficult. Simplified estimates of RV-PA coupling can be obtained by magnetic resonance or echocardiographic imaging of ejection fraction.

Defining end-systolic pressure for single-beat estimation of right ventricle-pulmonary artery coupling: simple… but not really

Surrogates of right ventricle (RV) end-systolic pressure (ESP) used to determine RV-pulmonary artery coupling vary across studies. ESP using point of maximal time varying elastance provides most accurate estimate of actual ESP. https://bit.ly/3xuqX3B.