Criteria for diagnosis of exercise pulmonary hypertension

Effects of body position on exercise capacity and pulmonary vascular pressure-flow relationships

There has been revival of interest in exercise testing of the pulmonary circulation for the diagnosis of pulmonary vascular disease, but there still is uncertainty about body position and the most relevant measurements. Doppler echocardiography pulmonary hemodynamic measurements were performed at progressively increased workloads in 26 healthy adult volunteers in supine, semirecumbent, and upright positions that were randomly assigned at 24-h intervals. Mean pulmonary artery pressure (mPAP) was estimated from the maximum tricuspid regurgitation jet velocity. Cardiac output was calculated from the left ventricular outflow velocity-time integral. Pulmonary vascular distensibility α-index, the percent change of vessel diameter per millimeter mercury of mPAP, was calculated from multipoint mPAP-cardiac output plots. Body position did not affect maximum oxygen uptake (Vo2max), maximum respiratory exchange ratio, ventilatory equivalent for carbon dioxide, or slope of mPAP-cardiac output relationships, which was on average of 1.5 ± 0.4 mmHg·l−1·min−1. Maximum mPAP, cardiac output, and total pulmonary vascular resistance were, respectively, 34 ± 4 mmHg, 18 ± 3 l/min, and 1.9 ± 0.3 Wood units. However, the semirecumbent position was associated with a 10% decrease in maximum workload. Furthermore, cardiac output-workload or cardiac output-Vo2 relationships were nonlinear and variable. These results suggest that body position does not affect maximum exercise testing of the pulmonary circulation when results are expressed as mPAP-cardiac output or maximum total pulmonary vascular resistance. Maximum workload is decreased in semirecumbent compared with upright exercise. Workload or Vo2 cannot reliably be used as surrogates for cardiac output.

Exercise pulmonary haemodynamics predict outcome in patients with systemic sclerosis

The aim of the present study was to investigate the prognostic value of exercise haemodynamics measured during right heart catheterisation (RHC) in patients with systemic sclerosis (SSc) referred for evaluation of pulmonary hypertension.

SSc patients undergoing RHC at rest and during maximal supine incremental cycle exercise were grouped into resting precapillary pulmonary hypertension (PHrest) (mean pulmonary artery pressure (mPAP) ≥25 mmHg, pulmonary artery wedge pressure <15 mmHg), exercise-induced pulmonary hypertension (PHex) (mPAP ≥30 mmHg and mPAP/cardiac output >3 mmHg·L−1·min−1 at maximal exercise), and without pulmonary hypertension (PHnone). Patients' characteristics, haemodynamics and follow up data were compared between groups.

72 SSc patients were followed for median (interquartile range) 33 (15–55) months. Mean (95% CI) survival without transplantation estimated by Kaplan-Meyer analysis was 4.4 (0.8–2.9) years in PHrest (n=17), 5.2 (4.4–6.1) years in PHex (n=28) and 9.5(8.4–10.6) years in PHnone (n=27; p<0.05 versus others). In Cox regression models, the exercise-induced increase in mPAP (hazard ratio (HR) 1.097, 95% CI 1.002–1.200) and the coefficient of pulmonary vascular distensibility alpha (HR 0.100, 95% CI 0.012–0.871) controlled for age, but not resting haemodynamics predicted transplant-free survival.

Among SSc patients with normal mPAP at rest, an excessive increase in mPAP during exercise and an impaired vascular distensibility may indicate an early stage of pulmonary vasculopathy, associated with reduced survival similar to resting pulmonary hypertension patients.

Exercise echocardiography for the assessment of pulmonary hypertension in systemic sclerosis: a systematic review

BACKGROUND

Pulmonary arterial hypertension (PAH) complicates the course of systemic sclerosis (SSc) and is associated with poor prognosis. The elevation of systolic pulmonary arterial pressure (sPAP) during exercise in patients with SSc with normal resting haemodynamics may anticipate the development of PAH. Exercise echocardiography (ExEcho) has been proposed as a useful technique to identify exercise-induced increases in sPAP, but it is unclear how to clinically interpret these findings. In this systematic review, we summarize the available evidence on the role of exercise echocardiography to estimate exercise-induced elevations in pulmonary and left heart filling pressures in patients with systemic sclerosis.

METHODS

We conducted a systematic review of the literature using MEDLINE, Cochrane Library and Web of Knowledge, using the vocabulary terms: ('systemic sclerosis' OR 'scleroderma') AND ('exercise echocardiography') AND ('pulmonary hypertension'). Studies including patients with SSc without a prior diagnosis of PAH, and subjected to exercise echocardiography were included. All searches were limited to English and were augmented by review of bibliographic references from the included studies. The quality of evidence was assessed by the Effective Public Health Practice Project system.

RESULTS

We identified 15 studies enrolling 1242 patients, who were mostly middle-aged and female. Several exercise methods were used (cycloergometer, treadmill and Master's two step), with different protocols and positions (supine, semi-supine, upright); definition of a positive test also varied widely. Resting estimated sPAP levels varied from 18 to 35 mm Hg, all in the normal range. The weighted means for estimated sPAP were 22.2 ± 2.9 mmHg at rest and 43.0 ± 4.3 mmHg on exercise; more than half of the studies reported mean exercise sPAP ≥40 mmHg. The assessment of left ventricular diastolic function on peak exercise was reported in a minority of studies; however, when assessed, surrogate variables of left ventricular (LV) diastolic dysfunction were associated with higher sPAP on exercise.

CONCLUSIONS

We found very high heterogeneity in the methods, the protocols and the estimated sPAP response to exercise. LV diastolic dysfunction was common and was associated with greater elevation of sPAP on exercise.

Right ventricular and pulmonary vascular reserve in asymptomatic BMPR2 mutation carriers

BACKGROUND

Non-invasive estimates have suggested that asymptomatic BMPR2 mutation carriers may have an abnormal pulmonary vascular response to exercise and hypoxia. However, this has not been assessed with "gold standard" invasive measures.

METHODS

Eight controls and 8 asymptomatic BMPR2 mutation carriers underwent cardiac magnetic resonance imaging with simultaneous invasive pressure recording during bicycle exercise in normoxia, hypoxia and after sildenafil administration. Abnormal pulmonary vascular reserve was defined as an increase in mean pulmonary artery pressure relative to cardiac output (P/Q slope) >3 mm Hg/liter/min.

RESULTS

During normoxic exercise, BMPR2 mutation carriers had a similar P/Q slope when compared with healthy subjects. Only 1 of 8 BMPR2 mutation carriers had a P/Q slope >3 mm Hg/liter/min. During exercise in hypoxia, 3 of 8 BMPR2 mutation carriers had P/Q slopes >3 mm Hg/liter/min compared with none of the controls. Sildenafil decreased the P/Q slope both in controls and BMPR2 mutation carriers. The exercise-induced increase in right ventricular ejection fraction was similar between groups. None of the BMPR2 mutation carriers developed pulmonary arterial hypertension within 2 (range 1.3 to 2.8) years.

CONCLUSIONS

The presence of a BMPR2 mutation, per se, is not associated with an abnormal pulmonary vascular and right ventricular functional response to exercise in asymptomatic individuals. Longer follow-up will be required to determine whether a P/Q slope of >3 mm Hg/liter/min during exercise in normoxia or hypoxia is a sign of pre-clinical disease expression.

Exercise intolerance in pulmonary hypertension: mechanism, evaluation and clinical implications

INTRODUCTION

Exercise intolerance in pulmonary hypertension (PH) is a major factor affecting activities of daily living and quality of life. Evaluation strategies (i.e., non-invasive and invasive tests) are integral to providing a comprehensive assessment of clinical and functional status. Despite a growing body of literature on the clinical consequences of PH, there are limited studies discussing the contribution of various physiological systems to exercise intolerance in this patient population.

AREAS COVERED

This review, through a search of various databases, describes the physiological basis for exercise intolerance across the various PH etiologies, highlights the various exercise evaluation methods and discusses the rationale for exercise training amongst those diagnosed with PH. Expert commentary: With the growing importance of evaluating exercise capacity in PH (class 1, Level C recommendation), understanding why exercise performance is altered in PH is crucial. Thus, the further study is required for better quality evidence in this area.

Hemodynamic and ventilatory responses during exercise in chronic thromboembolic disease

BACKGROUND

Patients with chronic thromboembolic disease (CTED) may suffer from exercise intolerance without pulmonary hypertension at rest. Pulmonary endarterectomy (PEA) for symptomatic CTED results in improvement of symptoms and quality of life. Neither the pathophysiology of the exercise limitation nor the underlying mechanisms of the PEA-induced improvement have been studied previously.

OBJECTIVES

We studied hemodynamic and ventilatory responses upon exercise in 14 patients with CTED. After 1 year, we studied the underlying physiologic mechanisms of the PEA-induced symptomatic improvement.

METHODS

Cardiopulmonary exercise testing (CPET) was performed during right heart catheterization, and noninvasive CPET was performed 1 year postoperatively.

RESULTS

During exercise, we observed abnormal pulmonary vascular responses, that is, a steep mean pulmonary artery pressure/cardiac output (2.7 ± 1.2 mm Hg·min·L(-1)), and low pulmonary vascular compliance (2.8 ± 1.1 mL·mm Hg(-1)); mean pulmonary artery pressure/cardiac output slope correlated with dead-space ventilation (r = 0.586; P = .028) and ventilatory equivalents for carbon dioxide slope (r = .580; P = .030). Postoperatively, the improvement observed in exercise capacity was related to improvements in CPET-derived parameters pointing to restoration of right ventricle stroke volume response (oxygen pulse: 11.7 ± 3.1 to 13.3 ± 3.3; P = .027; heart rate response: 80.9 ± 12.4 to 72.0 ± 5.7; P = .003); and, indicating improved ventilatory efficiency, the ventilatory equivalents for carbon dioxide slope decreased from 38.2 ± 3.6 to 32.8 ± 7.0 (P = .014).

CONCLUSIONS

Patients with CTED showed an abnormal pulmonary vascular response to exercise and a decreased ventilatory efficiency. Responses after PEA point to restoration of right ventricle stroke volume response and ventilatory efficiency.

Connective tissue disease-related pulmonary arterial hypertension

Over the past two decades, there have been several advances in the assessment and management of connective tissue disease-related pulmonary arterial hypertension (CTD-PAH) that improved outcomes of the treatment of this lethal disease, and this will be the focus of this study. Systemic sclerosis is the leading cause of CTD-PAH, followed by systemic lupus erythematosus, mixed connective tissue disease, idiopathic inflammatory myositis, rheumatoid arthritis, and Sjogren's syndrome. Clinical registries have been invaluable in informing about the burden of disease, risk and prognostic factors, and temporal trends with respect to treatment and outcome in CTD-PAH. The major advances have centered on improved disease classification and diagnostic criteria, screening and early diagnosis, the emergence of evidence-based therapies including combination goal-orientated treatment strategies, and the establishment of centers with expertise in PAH.

The Diagnostic Challenge of Group 2 Pulmonary Hypertension

Pulmonary hypertension (PH) secondary to left heart diseases associated with an increased pulmonary venous pressure is the second of a total of five groups recognized in the classification of PH. Group 2 PH is the commonest form of PH, and is associated with high morbidity and mortality. The diagnosis of group 2 PH relies on a clinical probability assessment in which echocardiography plays a major role, eventually followed by the invasive measurements of a mean pulmonary artery pressure (mPAP) ≥25mmHg and a wedged PAP (PAWP) >15mmHg. This combination of mPAP and PAWP defines "post-capillary PH" (pcPH). Post-capillary PH is most often associated with a diastolic pressure gradient (DPG) or gradient between diastolic PAP and PAWP <7mmHg and/or a pulmonary vascular resistance (PVR) ≤3Wood units (WU), and is called isolated pcPH (IpcPH). Postcapillary PH with a DPG ≥7mmHg and/or a PVR >3WU is then combined pre- and postcapillary PH (CpcPH). Post-capillary PH is associated with a decreased survival in proportion to increased PAP and decreased right ventricular (RV) ejection fraction. CpcPH occurs in 12-13% of patients with pcPH. CpcPH is associated with pulmonary vascular remodeling and altered RV-arterial coupling. The prognosis of CpcPH is poor.

The Pulmonary Hypertension Consult: Clinical and Coding Considerations

Pulmonary hypertension (PH) is an increasingly recognized cause of morbidity and mortality, and in the past 20 years, there has been a rapid expansion in research and available therapies. Although it is defined quite simply as a mean pulmonary arterial pressure of ≥ 25 mm Hg, PH encompasses a heterogeneous group of disease processes. In the past, PH was classified as primary or secondary, but as understanding of the various contributing diseases has increased, classification systems have attempted to group these diseases by clinical features and disease mechanism. The evaluation of patients with suspected PH can be cumbersome, and a careful and methodical approach is needed to ensure timely and accurate diagnosis, correct physiological classification, and appropriate treatment. In this review, we discuss the classification and diagnostic evaluation of PH in adults as well as some of the billing and coding considerations involved in this evaluation.

The Evolving Landscape of Exercise-Induced Pulmonary Hypertension

OPINION STATEMENT

Normal pulmonary artery pressures at rest, with an exaggerated rise during exercise, characterize exercise-induced pulmonary hypertension. Exercise itself as it relates to this condition is not deleterious, nor does it cause or induce disease. However much like any classical stress test, it is a physiologic probe that aids in disease unmasking. Although more work is required to establish criteria for defining this clinical entity, the phenomenon is real. It remains unknown whether it represents a nascent form of cardiopulmonary disease and whether its genesis predicts fulminant cardiopulmonary disease. Incremental cardiopulmonary exercise testing and the construction of pressure-flow plots to describe the pulmonary vascular response to exercise will be essential in defining this disease. The critical first step remains a consensus definition that will allow for further prospective study focused by a common language.

Pulmonary endarterectomy for the treatment of chronic thromboembolic pulmonary hypertension

Pulmonary endarterectomy is a curative treatment option for patients with chronic thromboembolic pulmonary hypertension (CTEPH). There is a growing body of evidence suggesting that not only patients with CTEPH but also patients with pulmonary arterial obstructions and mean pulmonary artery pressures < 25 mmHg should be offered surgery. In this review, the recent literature regarding pathophysiology, diagnostic methods, decision making by an expert CTEPH team, and surgical techniques will be summarized. Novel alternative treatment options for inoperable CTEPH patients will be discussed, i.e. targeted medical therapy and balloon pulmonary angioplasty. For the future the major task will be to define a clear selection process for the optimal treatment of the individual CTEPH patient.

Pulmonary haemodynamics during recovery from maximum incremental cycling exercise

Assessment of cardiac function during exercise can be technically demanding, making the recovery period a potentially attractive diagnostic window. However, the validity of this approach for exercise pulmonary haemodynamics has not been validated.The present study, therefore, evaluated directly measured pulmonary haemodynamics during 2-min recovery after maximum invasive cardiopulmonary exercise testing in patients evaluated for unexplained exertional intolerance. Based on peak exercise criteria, patients with exercise pulmonary hypertension (ePH; n=36), exercise pulmonary venous hypertension (ePVH; n=28) and age-matched controls (n=31) were analysed.By 2-min recovery, 83% (n=30) of ePH patients had a mean pulmonary artery pressure (mPAP) <30 mmHg and 96% (n=27) of ePVH patients had a pulmonary arterial wedge pressure (PAWP) <20 mmHg. Sensitivity of pulmonary hypertension-related haemodynamic measurements during recovery for ePH and ePVH diagnosis was ≤25%. In ePVH, pulmonary vascular compliance (PVC) returned to its resting value by 1-min recovery, while in ePH, elevated pulmonary vascular resistance (PVR) and decreased PVC persisted throughout recovery.In conclusion, we observed that mPAP and PAWP decay quickly during recovery in ePH and ePVH, compromising the sensitivity of recovery haemodynamic measurements in diagnosing pulmonary hypertension. ePH and ePVH had different PVR and PVC recovery patterns, suggesting differences in the underlying pulmonary hypertension pathophysiology.

Pulmonary hypertension in the elderly: a different disease?

Pulmonary hypertension (PH) is a haemodynamic syndrome defined by a mean pulmonary arterial pressure (mPAP) >25 mmHg determined by right heart catheterisation (RHC) [1, 2]. A lot of ­diseases fulfil this definition, but they differ widely between each other in respect to their pathophysiology, their haemodynamic characteristics, their clinical presentation, their natural prognosis and their potential therapeutic strategies. The current guidelines on PH diagnosis and management make the distinction between five groups of more than 200 causes of PH [2], but these diseases are very different from one another. In the current classification, the first group (group 1) represents a progressive vasculopathy leading to pre-capillary PH called pulmonary arterial hypertension (PAH), characterised by a characteristic small-calibre pulmonary artery remodelling, as a result of proliferation of endothelial and smooth muscle cells as well as medial hypertrophy. So, if we compare PAH (for example idiopathic PAH) from PH due to valvular disease like mitral insufficiency (group 2.3) it is easy to understand that apart from the fact that mean pulmonary arterial pressure (mPAP) exceeds 25 mmHg in both cases, these two entities have very different pathophysiological pathways. In the first case, there is a true pulmonary vasculopathy. In the second, PH is mainly related to the consequences of an increased hydrostatic pressure in the left atrium ­transmitted to the venous compartment of the pulmonary circulation and then back through the capillary bed. If the pathophysiology of these entities is different, the targets of their treatments are too. The main goal of PAH treatment consists in reducing pulmonary vascular resistance (PVR) with specific medication and, when appropriate, with specific treatment of the underlying disease as it is the case for associated-PAH (group 1.4). Alternatively, the management of PH related to a mitral regurgitation would be to improve the ventricular preload, diminish the ventricular afterload and, if necessary, to correct the anatomical anomaly.

The distinction between PH in the elderly and normal ageing might make diagnosis difficulthttp://ow.ly/YYF1Q

Resting pulmonary artery pressure of 21–24 mmHg predicts abnormal exercise haemodynamics

A resting mean pulmonary artery pressure (mPAP) of 21–24 mmHg is above the upper limit of normal but does not reach criteria for the diagnosis of pulmonary hypertension (PH). We sought to determine whether an mPAP of 21–24 mmHg is associated with an increased risk of developing an abnormal pulmonary vascular response during exercise.

Consecutive patients (n=290) with resting mPAP <25 mmHg who underwent invasive exercise haemodynamics were analysed. Risk factors for pulmonary vascular disease or left heart disease were present in 63.4% and 43.8% of subjects. An abnormal pulmonary vascular response (or exercise PH) was defined by mPAP >30 mmHg and total pulmonary vascular resistance >3 WU at maximal exercise.

Exercise PH occurred in 74 (86.0%) out of 86 versus 96 (47.1%) out of 204 in the mPAP of 21–24 mmHg and mPAP <21 mmHg groups, respectively (OR 6.9, 95% CI: 3.6–13.6; p<0.0001). Patients with mPAP of 21–24 mmHg had lower 6-min walk distance (p=0.002) and higher New York Heart Association functional class status (p=0.03). Decreasing levels of mPAP were associated with a lower prevalence of exercise PH, which occurred in 60.3%, 38.7% and 7.7% of patients with mPAP of 17–20, 13–16 and <13 mmHg, respectively.

In an at-risk population, a resting mPAP between 21–24 mmHg is closely associated with exercise PH together with worse functional capacity.

Pressure-Flow During Exercise Catheterization Predicts Survival in Pulmonary Hypertension

BACKGROUND

Pulmonary hypertension manifests with impaired exercise capacity. Our aim was to investigate whether the mean pulmonary arterial pressure to cardiac output relationship (mPAP/CO) predicts transplant-free survival in patients with pulmonary arterial hypertension (PAH) and inoperable chronic thromboembolic pulmonary hypertension (CTEPH).

METHODS

Hemodynamic data according to right heart catheterization in patients with PAH and CTEPH at rest and during supine incremental cycle exercise were analyzed. Transplant-free survival and predictive value of hemodynamics were assessed by using Kaplan-Meier and Cox regression analyses.

RESULTS

Seventy patients (43 female; 54 with PAH, 16 with CTEPH; median (quartiles) age, 65 [50; 73] years; mPAP, 34 [29; 44] mm Hg; cardiac index, 2.8 [2.3; 3.5] [L/min]/m(2)) were followed up for 610 (251; 1256) days. Survival at 1, 3, 5, and 7 years was 89%, 81%, 71%, and 59%. Age, World Health Organization-functional class, 6-min walk test, and mixed-venous oxygen saturation (but not resting hemodynamics) predicted transplant-free survival. Maximal workload (hazard ratio [HR], 0.94 [95% CI, 0.89-0.99]; P = .027), peak cardiac index (HR, 0.51 [95% CI, 0.27-0.95]; P = .034), change in cardiac index, 0.25 [95% CI, 0.06-0.94]; P = .040), and mPAP/CO (HR, 1.02 [95% CI, 1.01-1.03]; P = .003) during exercise predicted survival. Values for mPAP/CO predicted 3-year transplant-free survival with an area under the curve of 0.802 (95% CI, 0.66-0.95; P = .004).

CONCLUSIONS

In this collective of patients with PAH or CTEPH, the pressure-flow relationship during exercise predicted transplant-free survival and correlated with established markers of disease severity and outcome. Right heart catheterization during exercise may provide important complementary prognostic information in the management of pulmonary hypertension.

Age-related upper limits of normal for maximum upright exercise pulmonary haemodynamics

The exercise definition of pulmonary hypertension was eliminated from the pulmonary hypertension guidelines in part due to uncertainty of the upper limits of normal (ULNs) for exercise haemodynamics in subjects >50 years old.The present study, therefore, evaluated the pulmonary haemodynamic responses to maximum upright incremental cycling exercise in consecutive subjects who underwent an invasive cardiopulmonary exercise testing for unexplained exertional intolerance, deemed normal based on preserved exercise capacity and normal resting supine haemodynamics. Subjects aged >50 years old (n=41) were compared with subjects ≤50 years old (n=25). ULNs were calculated as mean + 2 sdPeak exercise mean pulmonary arterial pressure was not different for subjects >50 and ≤50 years old (23 ± 5 versus 22 ± 4 mmHg, p=0.22), with ULN of 33 and 30 mmHg, respectively. Peak cardiac output was lower in older subjects (median (interquartile range): 12.1 (9.4-14.2)versus16.2 (13.8-19.2) L·min(-1), p<0.001). Peak pulmonary vascular resistance was higher in older subjects compared with younger subjects (mean ± sd: 1.20 ± 0.45 versus 0.82 ± 0.26 Wood units, p<0.001), with ULN of 2.10 and 1.34 Wood units, respectively.We observed that subjects >50 and ≤ 50 years old have different pulmonary vascular responses to exercise. Older subjects have higher pulmonary vascular resistance at peak exercise, resulting in different exercise haemodynamics ULNs compared with the younger population.

2015 ESC/ERS Guidelines for the diagnosis and treatment of pulmonary hypertension

Guidelines summarize and evaluate all available evidence on a particular issue at the time of the writing process, with the aim of assisting health professionals in selecting the best management strategies for an individual patient with a given condition, taking into account the impact on outcome, as well as the risk–benefit ratio of particular diagnostic or therapeutic means. Guidelines and recommendations should help health professionals to make decisions in their daily practice. However, the final decisions concerning an individual patient must be made by the responsible health professional(s) in consultation with the patient and caregiver as appropriate.

Non-Invasive Determination of Cardiac Output in Pre-Capillary Pulmonary Hypertension

Background

Cardiac output (CO) is a major diagnostic and prognostic factor in pre-capillary pulmonary hypertension (PH). Reference methods for CO determination, like thermodilution (TD), require invasive procedures and allow only steady-state measurements. The Modelflow (MF) method is an appealing technique for this purpose as it allows non-invasive and beat-by-beat determination of CO.

Methods

We aimed to compare CO values obtained simultaneously from non-invasive pulse wave analysis by MF (CO_MF) and by TD (CO_TD) to determine its precision and accuracy in pre-capillary PH. The study was performed on 50 patients with pulmonary arterial hypertension (PAH) or chronic thrombo-embolic PH (CTEPH). CO was determined at rest in all patients (n = 50) and during nitric oxide vasoreactivity test, fluid challenge or exercise (n = 48).

Results

Baseline CO_MF and CO_TD were 6.18 ± 1.95 and 5.46 ± 1.95 L·min^-1, respectively. Accuracy and precision were 0.72 and 1.04 L·min^-1, respectively. Limits of agreement (LoA) ranged from -1.32 to 2.76 L·min^-1. Percentage error (PE) was ±35.7%. Overall sensitivity and specificity of CO_MF for directional change were 95.2% and 82.4%, (n = 48) and 93.3% and 100% for directional changes during exercise (n = 16), respectively. After application of a correction factor (1.17 ± 0.25), neither proportional nor fixed bias was found for subsequent CO determination (n = 48). Accuracy was -0.03 L·min−1 and precision 0.61 L·min⁻¹. LoA ranged from -1.23 to 1.17 L·min⁻¹ and PE was ±19.8%.

Conclusions

After correction against a reference method, MF is precise and accurate enough to determine absolute values and beat-by-beat relative changes of CO in pre-capillary PH.