Molecular mechanisms and targets of right ventricular fibrosis in pulmonary hypertension

Right ventricular fibrosis is a stress response, predominantly mediated by cardiac fibroblasts. This cell population is sensitive to increased levels of pro-inflammatory cytokines, pro-fibrotic growth factors and mechanical stimulation. Activation of fibroblasts results in the induction of various molecular signaling pathways, most notably the mitogen-activated protein kinase cassettes, leading to increased synthesis and remodeling of the extracellular matrix. While fibrosis confers structural protection in response to damage induced by ischemia or (pressure and volume) overload, it simultaneously contributes to increased myocardial stiffness and right ventricular dysfunction. Here, we review state-of-the-art knowledge of the development of right ventricular fibrosis in response to pressure overload and provide an overview of all published preclinical and clinical studies in which right ventricular fibrosis was targeted to improve cardiac function.

Real-world characteristics and outcomes of patients with intermediate high risk acute pulmonary embolism

BACKGROUND

Exact benefits of currently recommended close monitoring in intermediate high risk acute pulmonary embolism (PE) patients are unknown.

METHODS

This prospective observational cohort study determined clinical characteristics, and disease course of intermediate high risk acute PE patients in an academic hospital setting . Frequency of hemodynamic deterioration, use of rescue reperfusion therapy and PE related mortality, were outcomes of interest.

RESULTS

Of 98 intermediate high risk PE patients included for analysis, 81 patients (83%) were closely monitored. Two deteriorated hemodynamically and were treated with rescue reperfusion therapy. One patient survived after this.

CONCLUSIONS

In these 98 intermediate high risk PE patients, hemodynamic deterioration occurred in three patients and rescue reperfusion therapy of two closely monitored patients led to survival of one. Underlining the need for better recognition of patients benefitting from and research in the optimal way of close monitoring.

Safety and efficacy of balloon pulmonary angioplasty in chronic thromboembolic pulmonary hypertension in the Netherlands

Background

Balloon pulmonary angioplasty (BPA) is an emerging treatment in patients with chronic thromboembolic pulmonary hypertension (CTEPH) and chronic thromboembolic disease (CTED). We describe the first safety and efficacy results of BPA in the Netherlands.

Methods

We selected all consecutive patients with inoperable CTEPH and CTED accepted for BPA treatment who had a six-month follow-up in the St. Antonius Hospital in Nieuwegein and the Amsterdam University Medical Center (UMC) in Amsterdam. Functional class (FC), N‑terminal pro-brain natriuretic peptide (NT-proBNP), 6‑minute walking test distance (6MWD) and right-sided heart catheterisation were performed at baseline and six months after last BPA. Complications for each BPA procedure were noted.

Results

A hundred and seventy-two BPA procedures were performed in 38 patients (61% female, mean age 65 ± 15 years). Significant improvements six months after BPA treatment were observed for functional class (63% FC I/II to 90% FC I/II, p = 0.014), mean pulmonary artery pressure (−8.9 mm Hg, p = 0.0001), pulmonary vascular resistance (−2.8 Woods Units (WU), p = 0.0001), right atrial pressure (−2.0 mm Hg, p = 0.006), stroke volume index (+5.7 ml/m², p = 0.009) and 6MWD (+48m, p = 0.007). Non-severe complications occurred in 20 (12%) procedures.

Conclusions

BPA performed in a CTEPH expert centre is an effective and safe treatment in patients with inoperable CTEPH.

Healthcare utilization in chronic thromboembolic pulmonary hypertension after acute pulmonary embolism

Essentials Diagnostic delay of chronic thromboembolic pulmonary hypertension (CTEPH) is long. We explored healthcare utilisation of patients diagnosed with CTEPH after pulmonary embolism. A large number of physicians were consulted and test results were not always interpreted correctly. Better education and higher awareness of CTEPH may lead to faster diagnosis. SUMMARY: Background The median diagnostic delay of chronic thromboembolic pulmonary hypertension (CTEPH) is 14 months, which may affect prognosis. We aimed to explore the healthcare utilization of patients diagnosed with CTEPH after acute pulmonary embolism (PE), and to identify the causes of diagnostic delay. Methods We collected all data on patient symptoms, medical specialist referrals and ordered diagnostic tests to reconstruct the clinical pathways of 40 patients referred to the VU University Medical Center Amsterdam (VUMC, the Netherlands) for CTEPH treatment. Diagnostic delay was defined as the time between first symptom onset and referral to the VUMC. Correlations of patient-specific characteristics and diagnostic delay were evaluated. Results Patients consulted four (median) different physicians for a median of 13 (interquartile range [IQR] 10-18) consultations before the correct diagnosis was made. The median diagnostic delay was 21 months (IQR 12-49 months). Echocardiographic results suggestive of CTEPH were not always followed by an adequate work-up; most patients were not subjected to ventilation/perfusion scanning. Prior cardiopulmonary comorbidity and recurrent venous thromboembolism were predictors of a longer delay. Conclusion Healthcare utilization in patients before their final CTEPH diagnosis was far from optimal, contributing to a considerable diagnostic delay. Better education and higher awareness of CTEPH among PE caretakers may lead to faster diagnosis.

Chronic thromboembolic pulmonary hypertension from the perspective of patients with pulmonary embolism

Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare but feared long-term complication of acute pulmonary embolism (PE), although CTEPH may occur in patients with no history of symptomatic venous thromboembolism. It represents the most severe presentation of the so-called 'post-PE syndrome', a phenomenon of permanent functional limitations after PE caused by deconditioning after PE or ventilatory or circulatory impairment as a result of unresolved pulmonary artery thrombi. Because the post-PE syndrome may occur in up to 50% of PE survivors, and CTEPH tends to have an insidious and non-specific clinical presentation, CTEPH is often not diagnosed or diagnosed after a very long delay. Once the diagnosis is confirmed, the treatment of choice is pulmonary endarterectomy which effectively lowers the pulmonary vascular resistance and normalizes resting pulmonary artery pressures, leading to recovery of the right ventricle. When pulmonary endarterectomy is not technically feasible, balloon pulmonary angioplasty may be a potential acceptable alternative. Also, medical treatment may help to improve patient's symptoms and hemodynamics. Current studies are focusing on strategies for earlier CTEPH diagnosis after acute PE, as well as the most optimal treatment of inoperable patients. This review will focus on the epidemiology, risk factors, diagnosis and treatment of CTEPH from the perspective of the PE patient.

Diagnostic workup, etiologies and management of acute right ventricle failure : A state-of-the-art paper

INTRODUCTION

This is a state-of-the-art article of the diagnostic process, etiologies and management of acute right ventricular (RV) failure in critically ill patients. It is based on a large review of previously published articles in the field, as well as the expertise of the authors.

RESULTS

The authors propose the ten key points and directions for future research in the field. RV failure (RVF) is frequent in the ICU, magnified by the frequent need for positive pressure ventilation. While no universal definition of RVF is accepted, we propose that RVF may be defined as a state in which the right ventricle is unable to meet the demands for blood flow without excessive use of the Frank-Starling mechanism (i.e. increase in stroke volume associated with increased preload). Both echocardiography and hemodynamic monitoring play a central role in the evaluation of RVF in the ICU. Management of RVF includes treatment of the causes, respiratory optimization and hemodynamic support. The administration of fluids is potentially deleterious and unlikely to lead to improvement in cardiac output in the majority of cases. Vasopressors are needed in the setting of shock to restore the systemic pressure and avoid RV ischemia; inotropic drug or inodilator therapies may also be needed. In the most severe cases, recent mechanical circulatory support devices are proposed to unload the RV and improve organ perfusion CONCLUSION: RV function evaluation is key in the critically-ill patients for hemodynamic management, as fluid optimization, vasopressor strategy and respiratory support. RV failure may be diagnosed by the association of different devices and parameters, while echocardiography is crucial.

[Chronic thromboembolic pulmonary hypertension: recognition, diagnosis and treatment]

- Chronic thromboembolic pulmonary hypertension (CTEPH), characterised by pulmonary hypertension and persistent perfusion defects despite adequate anticoagulation, causes significant morbidity and mortality.- Persistent dyspnoea after acute pulmonary embolism is frequent and an indication for additional diagnostics. Only a minority of these patients develop CTEPH.- Echocardiography and perfusion scintigraphy are the cornerstone of diagnostics when suspecting CTEPH. Right-heart catheterisation and pulmonary angiography should confirm the diagnosis.- The diagnostic phase is preferably carried out in an expert centre in order to optimise the diagnosis and choose the optimal treatment for each individual patient.- Treatment of patients with CTEPH is a multidisciplinary team effort.- Pulmonary endarterectomy is the only potentially curative treatment; perioperative mortality is less than 5% in experienced centres. Inoperable patients can be treated with medication that specifically targets pulmonary arterial hypertension, but a survival benefit has not yet been shown for this medication.- Balloon pulmonary angioplasty has recently become available in the Netherlands as a treatment option, but the exact role of this new technique in the treatment of patients with CTEPH still needs to be investigated.

Pneumonectomy combined with SU5416 induces severe pulmonary hypertension in rats

The SU5416 + hypoxia (SuHx) rat model is a commonly used model of severe pulmonary arterial hypertension. While it is known that exposure to hypoxia can be replaced by another type of hit (e.g., ovalbumin sensitization) it is unknown whether abnormal pulmonary blood flow (PBF), which has long been known to invoke pathological changes in the pulmonary vasculature, can replace the hypoxic exposure. Here we studied if a combination of SU5416 administration combined with pneumonectomy (PNx), to induce abnormal PBF in the contralateral lung, is sufficient to induce severe pulmonary arterial hypertension (PAH) in rats. Sprague Dawley rats were subjected to SuPNx protocol (SU5416 + combined with left pneumonectomy) or standard SuHx protocol, and comparisons between models were made at week 2 and 6 postinitiation. Both SuHx and SuPNx models displayed extensive obliterative vascular remodeling leading to an increased right ventricular systolic pressure at week 6 Similar inflammatory response in the lung vasculature of both models was observed alongside increased endothelial cell proliferation and apoptosis. This study describes the SuPNx model, which features severe PAH at 6 wk and could serve as an alternative to the SuHx model. Our study, together with previous studies on experimental models of pulmonary hypertension, shows that the typical histopathological findings of PAH, including obliterative lesions, inflammation, increased cell turnover, and ongoing apoptosis, represent a final common pathway of a disease that can evolve as a consequence of a variety of insults to the lung vasculature.

Serial assessment of right ventricular systolic function in patients with precapillary pulmonary hypertension using simple echocardiographic parameters: A comparison with cardiac magnetic resonance imaging

BACKGROUND

Although cardiac magnetic resonance imaging (CMRI) is the gold standard for the (serial) assessment of right ventricular (RV) function, the technique has several drawbacks: CMRI is relatively expensive, has a limited availability, and the analyses are time consuming. Echocardiography (echo) can overcome several of these issues. The aim of this study was to compare simple echo-derived parameters of RV systolic function with CMRI-derived RV ejection fraction (RVEF) in patients with precapillary pulmonary hypertension (PH) and to determine which echo parameters best followed the change in CMRI-derived-RVEF during follow-up.

METHODS

CMRI and echo were performed in 96 precapillary PH patients. In 38 patients a second set of a CMRI and echo were available. Retrospectively, echo-derived right ventricular fractional area change (RVFAC), tricuspid annulus plane systolic excursion (TAPSE), fractional transversal (FTWM), and longitudinal wall motion (FLWM) were assessed and compared with CMRI-derived-RVEF. Furthermore, the changes in RVFAC, TAPSE, FTWM, and FLWM during follow-up were compared with the change in CMRI-derived-RVEF.

RESULTS

All four echo parameters were significantly correlated to CMRI-derived-RVEF. The strongest relationship was seen between CMRI-derived-RVEF and RVFAC (r²=0.567). However, sensitivity for predicting a deterioration in CMRI-derived RVEF was poor for all four echo-derived parameters (ranging from 33% to 56%).

CONCLUSIONS

Although RVFAC, TAPSE, FTWM, and FLWM were significantly correlated to CMRI-derived-RVEF, all four echo parameters showed a low sensitivity for predicting a deterioration in CMRI-derived RVEF during follow-up. Therefore, RVFAC, TAPSE, FTWM, and FLWM are not suitable parameters for the serial assessment of RV systolic function in patients with precapillary PH.

[Balloon pulmonary angioplasty for chronic thromboembolic pulmonary hypertension]

Chronic thromboembolic pulmonary hypertension (CTEPH) is characterised by an elevated average blood pressure in the pulmonary artery (≥ 25 mmHg). This increase is secondary to fibrous organization of thromboembolic obstructions in the pulmonary arteries. CTEPH is associated with significant morbidity and mortality due to right-sided heart failure and ventilation-perfusion discrepancy. Therapy is aimed at normalising pulmonary artery pressure, and pulmonary endarterectomy is usually the treatment of first choice. When surgery is not possible because of peripheral disease localisation or comorbidity, percutaneous balloon pulmonary angioplasty (BPA) can be used. BPA is associated with improvements in functional status and haemodynamic profile. Initially procedural complications often occurred, but improvements in procedural technique have ensured that BPA is used increasingly worldwide. In this article, we discuss the history, procedural aspects and outcomes of BPA, and present our first experiences with BPA in a patient with CTEPH.

Hypoxia inducible factor-1α in human emphysema lung tissue

The pathobiology of chronic obstructive pulmonary disease (COPD) is not completely understood. The aim of this study was to assess the expression of hypoxia inducible factor (HIF)-1α in lung tissue from patients with COPD/emphysema. Lung tissue samples from 26 patients were included in this study. Seven samples were obtained from patients with normal lung function, the remainder of the samples were taken from patients with moderate COPD (n = 6; stage I and II Global Initiative for Chronic Obstructive Lung Disease classification) and severe COPD (n = 13; stage III and IV). We analysed mRNA and protein expression in the lung tissue samples and found that: 1) HIF-1α and histone deacetylase 2 proteins were significantly decreased and were correlated; 2) HIF-1α and vascular endothelial growth factor (VEGF) proteins, and forced expiratory volume in 1 s % predicted were correlated in all patients; 3) the changes in VEGF and HIF-1α protein levels in all patients were not age-related and not related to the pack-yr smoking history; and 4) the reduced HIF-1α protein expression was seen in lung endothelial cells and alveolar septal cells by immunohistochemistry. In conclusion, reduced expression of HIF-1α protein in severe COPD is consistent with the concept of a lung structure maintenance programme which is impaired on a molecular level.

Pleural thickening in a construction worker: it is not always mesothelioma

We describe the case of a 45-year-old man presenting with chest pain and pleural effusions. These symptoms were progressive over a period of three years, with pericardial involvement and respiratory insufficiency finally resulting in death. Despite repeated diagnostic procedures, a final diagnosis could only be made at autopsy. Multisystem foamy histiocyte infiltration suggested the diagnosis of Erdheim-Chester disease.

[Cutaneous nocardiosis as an opportunistic infection]

A 46-year-old man who had been treated with azathioprine and budesonide for Crohn's disease for the past eight years developed a purulent skin condition on the right ring finger. Despite surgical drainage and treatment with amoxicillin and flucloxacillin, the condition spread itself over the hand and lower arm, partly per continuum and partly in jumps. The patient did not feel ill and there were no systemic symptoms. Ultimately, Nocardia asteroides was cultured from the wound and complete cure was achieved after 8 months' treatment with co-trimoxazole. Infections with Nocardia spp. are rare but may occur more often and run a more fulminant course in patients under treatment with immunosuppressants. Cutaneous nocardiosis generally has a characteristic lymphogenous spreading pattern, but an atypical picture with pustules, pyoderma, cellulitis or abscess formation is also possible. In non-cutaneous nocardiosis there is usually pneumonia or lung abscess, possibly with secondary haematogenous spread to the central nervous system or skin. Culturing Nocardia requires more time than usual but can be promoted by special culture media. Treatment of the infection with co-trimoxazole is the method of choice and is almost always successful in cases of cutaneous nocardiosis.

Prediction of peak oxygen uptake in men using pulmonary and hemodynamic variables during exercise

PURPOSE

Many attempts have been made to predict peak VO2 from data obtained at rest or submaximal exercise. Predictive submaximal tests using the heart rate (HR) response have limited accuracy. Some tests incorporate submaximal gas exchange data, but a predictive test without gas exchange measurements would be of benefit. Addition of stroke volume and pulmonary function (PF) measurements might increase the predictability of a submaximal exercise test.

METHODS

In this study, an incremental exercise test (10 W x min(-1)) was performed in 30 healthy men of various habitual activity levels. Step-wise multiple regression analysis was used to isolate the most important predictor variables of peak VO2 from a set of measurements of PF: lung volumes, diffusion capacity, airway resistance, and maximum inspiratory and expiratory pressures; gas exchange; minute ventilation (V(E)), tidal volume (V(T)), respiratory exchange ratio (RER = carbon dioxide output divided by VO2); and hemodynamics (HR, stroke index (SI) = stroke volume/body surface area, and mean arterial pressure). These measurements were made at rest and during submaximal exercise.

RESULTS

Using the set of PF variables (expressed as percentages of predicted), FEV1 explained 30% of the variance of peak VO2. No other PF variables were predictive. After addition of resting hemodynamic data, SI was included in the prediction equation, raising the predictability to 40%. At the 60-W exercise level, 48% of the variance in peak VO2 could be explained by SI and FEV1. At 150 W, the prediction increased to 81%. At this level VCO2/O2 (RER) also entered the prediction equation of peak VO2: 6.44 x FEV1(%) + 13.0 x SI - 1921 x RER + 2380 (SE = 142 mL x min(-1) x m(-2), P < 0.0001). Leaving out the gas exchange variable RER, maximally 64% of the variance in peak VO2 could be explained.

CONCLUSION

In conclusion, inclusion of pulmonary function and hemodynamic measurements could improve the prediction accuracy of a submaximal exercise test. The submaximal exercise test should be performed until a level of 150 W is reached. Noninvasive stroke volume measurements by means of EIC have additional value to measurement of HR alone. Finally, measurement of gas exchange significantly improves the predictability of peak VO2.

The haemodynamic response to exercise in chronic obstructive pulmonary disease: assessment by impedance cardiography

This study aimed to determine the differences in haemodynamic responses to a standard incremental exercise test between outpatients with chronic obstructive pulmonary disease (COPD) and age-matched controls and to discover the relationship between severity of airflow obstruction and exercise haemodynamics in COPD. Twenty-two male patients with COPD (forced expiratory volume in one second (FEV1)/vital capacity (VC))<80% predicted) and 20 age-matched male controls performed an incremental exercise test (10 W x min(-1)) with ventilatory function and changes in stroke volume (deltaSV) and cardiac output (deltaCO) measured by means of electrical impedance cardiography (EIC). Submaximal deltaSV and deltaCO were lower in COPD patients. Peak exercise deltaSV were equal in patients and controls (128+/-33 versus 129+/-29%, p=0.98), whereas peak deltaCO was lower in patients (COPD versus controls: 232+/-71 versus 289+/-54%, p<0.005). In COPD patients, FEV1 (% pred) was significantly correlated to deltaSV at all submaximal exercise intensities, to peak exercise deltaSV and to peak exercise deltaCO. FEV1/VC (% pred) was significantly correlated to deltaSV at 30 and 60 W. In conclusion, in chronic obstructive pulmonary disease an aberrant haemodynamic response to exercise was found, especially in patients with severe airflow obstruction. This aberrant response is related to the degree of airflow obstruction and may limit exercise performance in patients with severe chronic obstructive pulmonary disease.

Non-invasive assessment of cardiac output during exercise in chronic obstructive pulmonary disease: comparison of the CO2-rebreathing method and electrical impedance cardiography

In exercise testing of patients with chronic obstructive pulmonary disease (COPD), non-invasive assessment of stroke volume (SV) and cardiac output (CO) would be valuable. Electrical impedance cardiography (EIC) has proved to be a valid and reliable instrument in healthy subjects. In this study it is investigated whether this also applies to patients with COPD. In 19 COPD patients simultaneous SV measurements were performed during steady-state exercise using the CO2-rebreathing method and EIC (using a fixed blood resistivity value (rho = 135 or 150 omega cm: EIC-135 and EIC-150) or a haematocrit based rho (EIC-ht)). Although close correlations were found (overall correlation between CO2-rebreathing and EIC-ht: R = 0.92 for CO, R = 0.79 for SV), SV and CO measured by means of EIC were significantly higher at low-intensity exercise and lower at high-intensity exercise. The mean differences between the CO2-rebreathing method and EIC-ht were 0.55 ml for SV and 0.01 l min-1 for CO (overall exercise data). The limits of agreement (2SD of the mean difference) were 24.7 ml for SV and 2.56 l min-1 for CO. These figures are comparable to what is found when healthy subjects are studied. CO was closely correlated to oxygen uptake using the CO2-rebreathing as well as the EIC method; the slope of the regression line was closer to what has been reported in the literature with EIC. Results were better with the EIC-ht than with the EIC-135 and EIC-150 methods. It is concluded that EIC is a reliable and valid method for measurements of SV and CO in COPD during exercise.

Prediction of pulmonary capillary wedge pressure and assessment of stroke volume by noninvasive impedance cardiography

Early recognition of heart failure is important because early treatment reduces mortality and hospitalization rates. In screening for this disease, there is a need for a simple, safe, and cost-effective method to obtain cardiovascular variables. Therefore we developed a noninvasive impedance cardiographic method to predict the pulmonary capillary wedge pressure (PCWP) from the impedance cardiogram. The impedance cardiographic technique, though, was originally designed for stroke volume (SV) determination. The objectives of this study were to validate both variables by comparison with the paired, invasively obtained equivalents. PCWP, measured with a pulmonary artery catheter, was related to the O/C ratio from the impedance cardiogram. The O/C ratio was calculated as the amplitude of the impedance cardiogram during diastole (O) divided by the maximum height during systole (C). Stroke volume was also calculated from the impedance cardiogram according to the equation of Kubicek (SVIC) and compared with thermodilution (SVTD). Data analysis was performed in 24 stable patients who underwent diagnostic heart catheterization. Linear regression analysis showed that the O/C ratio was strongly related to the invasively measured PCWP over a range of 3 to 30 mm Hg (r = 0.92, standard error of the estimate, 3.2 mm Hg). Between SVIC and SVTD a moderate correlation was established (r = 0.69), but after exclusion of the data from patients with an aortic valve disorder (n = 5), the correlation increased considerably (r = 0.87). No significant differences between SVIC and SVTD were found (mean difference +/- 2 SD = 1.8 +/- 28.8 ml). These preliminary observations suggest that impedance cardiography can predict PCWP and measure SV over a wide range of clinically relevant values. The combined measurement of SV and PCWP by impedance cardiography might be a clinical useful tool in screening for heart failure.

Assessment of the haemodynamic response to exercise by means of electrical impedance cardiography: method, validation and clinical applications

Over the past three decades, the technique of electrical impedance cardiography (EIC) has developed into a valid and reliable instrument for the assessment of stroke volume. Recent developments have made EIC suitable for routine use during exercise testing, too. However, standardization of electrode positioning, stroke volume calculation, and data processing is lacking. In our opinion the most reliable options are, respectively, a modified semicircular electrode array, the Kubicek equation including a haematocrit-based resistivity value, and computerized signal averaging. Although EIC derived stroke volume calculation is based on several debated assumptions, numerous validation studies have shown good accuracy and reproducibility, also during exercise. Addition of EIC measurements during standard clinical exercise testing might be of benefit in occupational medicine, cardiology and pulmonary medicine. Although in the latter setting no validation studies have been performed, major methodological problems are not expected.

Haemodynamic response to exercise in healthy young and elderly subjects

Whereas with advancing age, peak heart rate (HR) and cardiac index (CI) are clearly reduced, peak stroke index (SI) may decrease, remain constant or even increase. The aim of this study was to describe the patterns of HR, SI, CI, arteriovenous difference in oxygen concentration (Ca-vO2), mean arterial pressure (MAP), systemic vascular resistance index (SVRI), stroke work index (SWI) and mean systolic ejection rate index (MSERI) in two age groups (A: 20-30 years, n = 20; B: 50-60 years n = 20). After determination of pulmonary function, an incremental bicycle exercise test was performed, with standard, gas-exchange measurements and SI assessment using electrical impedance cardiography. The following age-related changes were found: similar submaximal HR response to exercise in both groups and a higher peak HR in A than in B[185 (SD 9) vs 167 (SD 14) beats.min-1, P < 0.0005]; increase in SI with exercise up to 60-90 W and subsequent stabilization in both groups. As SI decreased towards the end of exercise in B, a higher peak SI was found in A [57.5 (SD 14.0) vs 43.6 (SD 7.7) ml.m-2, P < 0.0005]; similar submaximal CI response-to exercise, higher peak CI in A [10.6 (SD 2.5) vs 7.2 (SD 1.3) 1.min-1.m-2, P < 0.0005]; no differences in Ca-vO2 during exercise; higher MAP at all levels of exercise in B; higher SVRI at all levels of exercise in B; lower SWI in B after recovery; higher MSERI at all levels of exercise in A. The decrease in SI with advancing age would seem to be related to a decrease in myocardial contractility, which can no longer be compensated for by an increase in preload (as during submaximal exercise). Increases in systemic blood pressure may also compromise ventricular function but would seem to be of minor importance.

Standardization of non-invasive impedance cardiography for assessment of stroke volume: comparison with thermodilution

Since its introduction by Kubicek and colleagues, impedance cardiography has been suggested as a non-invasive, simple, safe and cost-effective method of measuring stroke volume. Several controversial reports on its validity have been published. Pitfalls of this method included the nature of the electrode system and the validity of the equations. Therefore, the purpose of this study was to compare two different spot electrode arrays and the two most frequently used stroke volume equations with each other and with thermodilution. In 37 patients, 24-36 h after cardiac surgery, we performed simultaneous measurements of stroke volume with impedance cardiography (SVIC) and with thermodilution (SVTD). SVIC was obtained using the lateral spot (LS) electrode array, according to Bernstein, and a newly proposed modified semi-circular (MSC) spot electrode array. The equations of Kubicek and Sramek-Bernstein were used to calculate SVIC. The Sramek-Bernstein equation was valid only when the LS array was used; the Kubicek equation determined SVTD correctly only when the MSC array was used. However, a considerably better correlation and agreement (mean difference (2 SD)) was found between SVIC and SVTD for the latter (r = 0.90, 0.5 (17.1) ml vs r = 0.64, -4.9 (31.8) ml for the Sramek-Bernstein equation). We conclude that the most valid measurement of stroke volume using impedance cardiography was obtained when the MSC array was used together with Kubicek's equation.

The intra- and interobserver variability of impedance cardiography in patients at rest and during exercise

We studied the intra- and interobserver variability in the calculation of stroke volume by the impedance technique, using the recently proposed refinements in the electrode configuration and signal processing. Three groups of patients were included in this study: ten stable cardiac patients who underwent a diagnostic heart catheterization, ten patients 24-26 h after coronary artery bypass surgery and ten patients with severe chronic obstructive pulmonary disease (COPD). The first two groups were studied at rest and the COPD group during submaximal exercise. The intra-observer variability was 4.2%, 3.9-4.0% and 6.0-6.9% for the catheterized, surgical and COPD groups, respectively. The interobserver variability was 4.3%, 2.6% and 2.4%, respectively. It is concluded that highly reproducible data can be obtained with the newly proposed impedance technique in patients at rest and exercise which may be comparable or superior to other techniques used in clinical settings.

The influence of weight on stroke volume determination by means of impedance cardiography in cardiac surgery patients

OBJECTIVES

Obesity is thought to be one of the conditions in which the impedance cardiographic method is less reliable for estimating stroke volume (SV). This led to the introduction of a weight correction factor, sigma, into the equation according to Sramek and Bernstein. However, no scientific evidence has been published to support the use of this factor. The objectives of the present study are to evaluate the influence of body weight on the accuracy of impedance cardiography and to validate Bernstein's weight correction factor by comparison with thermodilution in patients after coronary bypass surgery.

DESIGN

Prospective clinical study.

SETTING

A surgical intensive care unit in a university hospital.

PATIENTS

37 consecutive patients 24-36 h after coronary bypass surgery, sub-divided into a normal-weight group (n = 24), patients whose weight deviated less than 15% from their ideal weight, and an obese group (n = 13), patients whose weight deviated more than 15% from their ideal weight.

MEASUREMENTS

Kubicek's impedance cardiographic method and Sramek and Bernstein's method to assess SV are applied and compared to thermodilution. In order to study the validity of sigma, the results are compared between 24 patients with normal weight and 13 obese patients.

RESULTS

A significant correlation between miscalculation of SV by impedance cardiography and the degree of obesity for Sramek and Bernstein's method is found when sigma is not included in the equation (r = -0.55, p < 0.05). This relation, however, remained significant when sigma was included in the equation (r = -0.40, p < 0.05). Kubicek's method shows no significant correlation for this relation (r = -0.30). Besides this, Sramek and Bernstein's method underestimates SV significantly in the obese group, independent of the use of sigma in the equation. These results are explained as being intrinsic to the equation, according to Sramek and Bernstein. In the whole group the impedance-derived SV did not significantly differ from SV as measured by means of thermodilution, independent of the method used to calculate SV. However, a considerably better correlation and agreement (mean difference +/- 2 standard deviations is found when Kubicek's method is applied (r = 0.90, 0.5 +/- 17.1 ml vs 0.64, -4.9 +/- 31.8 ml for Sramek and Bernstein's method).

CONCLUSIONS

Weight significantly influences Sramek and Bernstein's method of impedance cardiography, whereas Kubicek's method is not biased by this factor.

Comparison of the respiratory and hemodynamic responses of healthy subjects to exercise in three different protocols

Although the importance of exercise testing has been well established, standardization of protocols is lacking. In the current study three protocols were compared with respect to respiratory and hemodynamic variables at submaximal and peak exercise. Fifteen healthy young men underwent three maximal exercise tests using the following protocols: (I) an increase of 30 Watt, every three minutes; (II) an increase of 10 Watt, every minute; (III) a continuous load increase of 10 Watt/min. Respiratory measurements were made of oxygen uptake (VO2), carbon dioxide output (VCO2), minute ventilation (VE) and tidal volume (VT). Hemodynamic measurements were made of ECG, heart rate (HR), blood pressure and stroke volume (SV). The latter variable was measured by means of electrical impedence cardiography (EIC). There were no differences in mean maximum load or peak-VO2 between protocols I, II and III. The course of SV was similar in all protocols, i.e. an increase of about 30% until 100 Watt, with a subsequent stabilization until maximum load. All other hemodynamic measurements were similar in both protocols, too. Significant differences were found in submaximal values of VO2 and VCO2. There were no differences in other gas-exchange variables at any moment during exercise. With respect to the VO2max or the hemodynamic response to exercise, any protocol can be used. For the evaluation of submaximal exercise, the protocol that has been used has to be taken into account. Differences at these levels are not related to differences in hemodynamic responses.

The adjustment of post dialytic dry weight based on non-invasive measurement of extracellular fluid and blood volumes

One of the major problems in the clinical practice of hemodialysis is an incorrect estimation of post dialytic (PD) dry weight. Underestimation of dry weight leads to hypovolemia induced hypotension, and overestimation to hypertension, pulmonary edema, and left ventricular hypertrophy. Because of the insensitivity of clinical variables to estimate dry weight, a more accurate technique is warranted. For this purpose and for the continuous surveillance of changes in blood volume (BV) during hemodialysis, two non-invasive techniques were applied. Based on post dialytically obtained extracellular fluid volume (EFV) values, measured by means of a conductivity method, 30 stable hemodialysis patients were divided into three groups for further analysis: de- (n = 9), normo- (n = 15), and overhydrated (n = 6). Using an on-line optical reflection method, changes in BV were measured continuously during therapy. Mean BV decrease, corrected for UF, differed slightly between the three groups (0 = 1.84 +/- 2.06, N = 3.20 +/- 1.80, D = 4.20 +/- 1.60 %/L). However, eight hypotensive episodes occurred in group D versus none in groups N and O. These hypotensive episodes were characterized by a greater reduction of BV--corrected for ultrafiltration--from the start of treatment until the moment of hypotension (6.96 +/- 2.21 %/L), compared with the 22 non hypotensive controls (2.16 +/- 2.01 %/L, p < 0.001). Based on the PD EFV dry weight of the overhydrated and dehydrated patients was decreased and increased, respectively, by 500 g after each session, until PD EFV was within normal bounds.(ABSTRACT TRUNCATED AT 250 WORDS)