Changes in cMRI parameters following a switch to riociguat from phosphodiesterase type 5 inhibitors (PDE5i) in patients with pulmonary arterial hypertension: a REPLACE substudy

Background

The REPLACE study investigated the effect of switching to riociguat (RIO) in patients with pulmonary arterial hypertension receiving PDE5i but still at intermediate risk. The centrally adjudicated composite primary endpoint was clinical improvement in the absence of clinical worsening, where clinical improvement was defined as meeting at least two of the following criteria: 6-minute walk distance (6MWD), increase by ≥10% or ≥30 m from baseline (BL) to Wk 24; World Health Organization functional class (WHO FC) I or II at Wk 24; or N-terminal prohormone of brain natriuretic peptide reduction of ≥30% from BL to Wk 24. Twice as many patients switching to RIO (45/111, 41%) met the primary endpoint compared with those remaining on PDE5i (23/113, 20%); odds ratio (OR): 2.78 (95% confidence interval [CI] 1.53–5.06); p=0.0007.

Purpose

Assess changes in right and left ventricular (RV; LV) function using cardiac magnetic resonance imaging (cMRI) in a subgroup of patients participating in REPLACE.

Methods

REPLACE was a randomised, open-label, 24-week, Phase 4 study (NCT02891850). Patients in WHO FC III, with 6MWD 165–440 m, were randomised to switch to RIO 2.5 mg–max tid or remain on PDE5i. Background endothelin receptor antagonist therapy was permitted in both arms.

cMRI was performed on a subset of patients from the full analysis set as an exploratory substudy. The following parameters were measured at BL and Wk 24: RV and LV end-diastolic and end-systolic volumes (RVEDV; RVESV; LVEDV; LVESV), RV stroke volume and stroke volume index (RVSV; RVSVI), LV stroke volume (LVSV), RV ejection fraction (RVEF), and pericardial effusion.

Results

Twenty-seven patients participated in the cMRI substudy. This comprised 11/111 (10%) patients in the RIO arm (mean [standard deviation {SD}] 40.0 [12.4] years), and 16/113 (14%) patients (mean 44.5 [17.6] years) in the PDE5i arm. Like the main population, the treatment response in the cMRI subpopulation favoured RIO versus PDE5i (OR: 6.11 [95% CI 0.90–41.60]). From BL to Wk 24, RVEDV and RVESV decreased in the RIO treatment arm but increased in the PDE5i treatment arm (Table 1). Similar, but less pronounced, changes were observed for the left ventricle (LVESV, LVEDV). RVSV and RVEF levels were close to normal at BL and did not increase in either arm at Wk 24 (Table 1). Pericardial effusion, which was present in 5 patients in each group at BL, decreased in 1 patient in the RIO arm and no patients in the PDE5i arm.

Conclusions

Decreases in RVEDV and RVESV suggest improvements in cardiac function in the RIO arm compared with the PDE5i arm. Values for RVEF and RVSVI were close to normal at BL and did not change at Wk 24. Improvements in cMRI parameters were in line with the clinical improvement observed in patients switching to RIO in the overall population.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): The REPLACE study was co-funded by Bayer AG (Berlin, Germany) and Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc. (Kenilworth, NJ, USA)

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.

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.

Granulomatous lung disease in a patient with a family history of hematological disorders

A 29-year old patient presented with granulomatous lung disease and a family history of myelodysplastic syndrome/acute myeloid leukemia. She appeared to be a carrier of a mutation in the transcription factor GATA2. The case adds to the recent described heterogeneous clinical manifestations and syndromes in which, against a background of hematologic disorders, GATA2 mutations have been demonstrated, such as the Monomac and Emberger syndromes. In patients with a granulomatous disease and a history of (familial) hematologic disorders, the occurence of GATA2 mutations should be considered, as to gain further insight in the occurrence of granulomatous disease in a possible distinct phenotype among GATA2 mutation carriers.

Diaphragm muscle fiber function and structure in humans with hemidiaphragm paralysis

Recent studies proposed that mechanical inactivity of the human diaphragm during mechanical ventilation rapidly causes diaphragm atrophy and weakness. However, conclusive evidence for the notion that diaphragm weakness is a direct consequence of mechanical inactivity is lacking. To study the effect of hemidiaphragm paralysis on diaphragm muscle fiber function and structure in humans, biopsies were obtained from the paralyzed hemidiaphragm in eight patients with hemidiaphragm paralysis. All patients had unilateral paralysis of known duration, caused by en bloc resection of the phrenic nerve with a tumor. Furthermore, diaphragm biopsies were obtained from three control subjects. The contractile performance of demembranated muscle fibers was determined, as well as fiber ultrastructure and morphology. Finally, expression of E3 ligases and proteasome activity was determined to evaluate activation of the ubiquitin-proteasome pathway. The force-generating capacity, as well as myofibrillar ultrastructure, of diaphragm muscle fibers was preserved up to 8 wk of paralysis. The cross-sectional area of slow fibers was reduced after 2 wk of paralysis; that of fast fibers was preserved up to 8 wk. The expression of the E3 ligases MAFbx and MuRF-1 and proteasome activity was not significantly upregulated in diaphragm fibers following paralysis, not even after 72 and 88 wk of paralysis, at which time marked atrophy of slow and fast diaphragm fibers had occurred. Diaphragm muscle fiber atrophy and weakness following hemidiaphragm paralysis develops slowly and takes months to occur.

Iron deficiency in pulmonary arterial hypertension: a potential therapeutic target

Iron deficiency is known to be common and detrimental in chronic left heart failure, where parenteral iron treatment has been shown to improve exercise capacity, New York Heart Association functional class and patient wellbeing. There is now increasing interest in the role of iron in the natural history of pulmonary arterial hypertension (PAH). Iron availability influences the pulmonary vasoconstrictor response to hypoxia and accumulating evidence indicates that iron deficiency is prevalent in idiopathic and heritable forms of PAH, iron status being related to exercise capacity, symptoms and poorer survival in patients with idiopathic PAH (IPAH). Potential mechanisms behind iron deficiency in IPAH include inhibition of dietary iron uptake by the master iron regulator hepcidin. High hepcidin levels underlie the anaemia of chronic disease. Possible stimuli of the observed high levels of hepcidin in IPAH include dysfunctional bone morphogenetic protein receptor type II signalling and inflammation. Iron status may influence outcomes through modulation of the pulmonary circulation as well as myocardial and skeletal muscle function. Two parallel studies, from our centre (Hammersmith Hospital, London, UK) and others in the UK and Amsterdam (the Netherlands), investigating the safety and potential benefit of iron supplementation in patients with PAH are currently under way.

The arterial load in pulmonary hypertension

The anatomical differences between the pulmonary and systemic arterial system are the main cause of the difference in distribution of compliance. In the pulmonary arterial system compliance is distributed over the entire arterial system, and stands at the basis of the constancy of the RC-time. This distribution depends on the number of peripheral vessels, which is ∼8-10 times more in the pulmonary system than the systemic tree. In the systemic arterial tree the compliance is mainly located in the aorta (80% of total compliance in thoracic-abdominal aorta). The constant RC-time in the pulmonary bed results in proportionality of systolic and diastolic pressure with mean pressure and, in turn, in the constant ratio of oscillatory and mean power.

Perspectives on novel therapeutic strategies for right heart failure in pulmonary arterial hypertension: lessons from the left heart

Right heart function is the main determinant of prognosis in pulmonary arterial hypertension (PAH). At present, no treatments are currently available that directly target the right ventricle, as we will demonstrate in this article. Meta-analysis of clinical trials in PAH revealed that current PAH medication seems to have limited cardiac-specific effects when analysed by the pump-function graph. Driven by the hypothesis that "left" and right heart failure might share important underlying pathophysiological mechanisms, we evaluated the clinical potential of left heart failure (LHF) therapies for PAH, based on currently available literature. As in LHF, the sympathetic nervous system and the renin-angiotension-aldosterone system are highly activated in PAH. From LHF we know that intervening in this process, e.g. by angiotensin-converting enzyme inhibition or β-blockade, is beneficial in the long run. Therefore, these medications could be also beneficial in PAH. Furthermore, the incidence of sudden cardiac death in PAH could be reduced by implantable cardioverter-defibrillators. Finally, pilot studies have demonstrated that interventricular dyssynchrony, present at end-stage PAH, responded favourably to cardiac resynchronisation therapy as well. In conclusion, therapies for LHF might be relevant for PAH. However, before they can be implemented in PAH management, safety and efficacy should be evaluated first in well-designed clinical trials.

Iron deficiency is common in idiopathic pulmonary arterial hypertension

The aims of this study were to assess the prevalence of iron deficiency in idiopathic pulmonary arterial hypertension (IPAH) and investigate whether oral iron supplementation has effects in iron-deficient patients. Iron parameters were measure for all IPAH patients attending our centre (VU University Medical Center, Amsterdam, the Netherlands) between May 2009 and February 2010. Iron data were related to clinical parameters, including 6-min walking distance (6MWD), and haemodynamic parameters measured during right heart catheterisation. In a subset of iron-deficient patients, the uptake of iron from the bowel was studied after administering oral iron for 4 weeks. Iron deficiency was found in 30 (43%) out of 70 patients. 6MWD was reduced in iron-deficient patients compared with iron-sufficient patients (mean±sd 390±138 versus 460±143 m; p<0.05) irrespective of the existence of anaemia. In a subset of 18 patients that received oral iron, ferritin levels were significantly increased, although eight patients only slightly increased their iron storage. This study shows that iron deficiency is frequently present in IPAH and is associated with a lower exercise capacity. The small response to oral iron in 44% of the treated patients suggests impaired iron absorption in these patients.

RC time constant of single lung equals that of both lungs together: a study in chronic thromboembolic pulmonary hypertension

The product of resistance, R, and compliance, C ( RC time), of the entire pulmonary circulation is constant. It is unknown if this constancy holds for individual lungs. We determined R and C in individual lungs in chronic thromboembolic pulmonary hypertension (CTEPH) patients where resistances differ between both lungs. Also, the contribution of the proximal pulmonary arteries (PA) to total lung compliance was assessed. Patients ( n = 23) were referred for the evaluation of CTEPH. Pressure was measured by right heart catheterization and flows in the main, left, and right PA by magnetic resonance imaging. Total, left, and right lung resistances were calculated as mean pressure divided by mean flow. Total, left, and right lung compliances were assessed by the pulse pressure method. Proximal compliances were derived from cross-sectional area change Δ A and systolic-diastolic pressure difference ΔP (Δ A/ΔP) in main, left, and right PA, multiplied by vessel length. The lung with the lowest blood flow was defined “low flow” (LF), the contralateral lung “high flow” (HF). Total resistance was 0.57 ± 0.28 mmHg·s−1·ml−1, and resistances of LF and HF lungs were 1.57 ± 0.2 vs. 1.00 ± 0.1 mmHg·s−1·ml−1, respectively, P < 0.0001. Total compliance was 1.22 ± 1.1 ml/mmHg, and compliances of LF and HF lung were 0.47 ± 0.11 and 0.62 ± 0.12 ml/mmHg, respectively, P = 0.01. Total RC time was 0.49 ± 0.2 s, and RC times for the LF and HF lung were 0.45 ± 0.2 and 0.45 ± 0.1 s, respectively, not different. Proximal arterial compliance, given by the sum of main, right, and left PA compliances, was only 19% of total lung compliance. The RC time of a single lung equals that of both lungs together, and pulmonary arterial compliance comes largely from the distal vasculature.

Opposite Effects of Training in Rats With Stable and Progressive Pulmonary Hypertension

Background— Exercise training in pulmonary arterial hypertension (PH) is a promising adjunct to medical treatment. However, it is still unclear whether training is beneficial for all PH patients. We hypothesized that right ventricular adaptation plays a pivotal role in the response to training.

Methods and Results— Two different dosages of monocrotaline were used in rats to model stable PH with preserved cardiac output and progressive PH developing right heart failure. Two weeks after injection, PH was confirmed by echocardiography, and treadmill training was initiated. Rats were trained for 4 weeks unless manifest right heart failure developed earlier. At the end of the study protocol, all rats were functionally assessed by endurance testing, echocardiography, and invasive pressure measurements. Lungs and hearts were further analyzed in quantitative histomorphologic analyses. In stable PH, exercise training was well tolerated and markedly increased exercise endurance (from 25±3.9 to 62±3.9 minutes; P <0.001). Moreover, capillary density increased significantly (from 1.21±0.12 to 1.51±0.07 capillaries per cardiomyocyte; P <0.05). However, in progressive PH, exercise training worsened survival (hazard ratio, 2.7; 95% confidence interval, 1.1 to 14.2) and increased pulmonary vascular remodeling. In addition, training induced widespread leukocyte infiltration into the right ventricle (from 135±14 to 276±18 leukocytes per 1 mm 2 ; P <0.001).

Conclusions— In our rat model, exercise training was found to be beneficial in stable PH but detrimental in progressive PH. Future studies are necessary to address the clinical implications of our findings.

Pulmonary arterial hypertension in limited cutaneous systemic sclerosis: a distinctive vasculopathy

Systemic sclerosis-associated pulmonary arterial hypertension (SScPAH) has a worse prognosis and response to pulmonary arterial hypertension (PAH) therapy than idiopathic PAH (IPAH). These differences have not yet been explained. Knowledge concerning histological pulmonary vasculopathy in SScPAH is limited in contrast to IPAH. Therefore, we explored patterns of vasculopathy in SScPAH compared with IPAH. Parameters of vasculopathy were assessed from lung tissue of eight PAH patients with limited cutaneous systemic sclerosis and 11 IPAH patients. Lung tissue was obtained at autopsy (n = 15), explantation (n = 3) and biopsy (n = 1). Pulmonary arterial/arteriolar intimal fibrosis was identified in all SScPAH patients and in three IPAH patients (p = 0.003). Fibrosis of pulmonary veins/venules was found in all SScPAH patients and in three IPAH patients (p = 0.003). In four SScPAH patients, fibrosis of veins/venules was focal and associated with capillary congestion as in pulmonary veno-occlusive disease (PVOD). Of the IPAH patients, 10 had unequivocal evidence of plexogenic arteriopathy compared with none of the SScPAH patients (p = 0.001). SScPAH is characterised by small vessel intimal fibrosis, which is associated with a PVOD-like pattern in some cases. This might explain its different clinical behaviour from IPAH. Small vessel intimal fibrosis may provide clues to elucidation of differences in pathogenetic mechanisms between the groups.

Possible role of imatinib in clinical pulmonary veno-occlusive disease

The platelet-derived growth factor receptor inhibitor imatinib has demonstrated clinical and haemodynamical improvement in both animal models of pulmonary hypertension (PH) and patients with PH. It has been suggested that anti-proliferative effects on pulmonary vascular smooth muscle cells are responsible for these beneficial effects. The current study describes a patient with pulmonary arterial hypertension associated with a suspected pulmonary veno-occlusive disease. Treatment with imatinib resulted in rapid clinical improvement and decrease of ground-glass opacities and lobular septal thickening on high-resolution computed tomography. Based on these findings and on in vitro effects of imatinib on permeability of the endothelium, the authors hypothesise that the rapid clinical outcome is partly due to effects of imatinib on vascular integrity.

Right ventricular contractility in systemic sclerosis-associated and idiopathic pulmonary arterial hypertension

Since systemic sclerosis (SSc) also involves the heart, the aim of the present study was to evaluate possible differences in right ventricular (RV) pump function between SSc-associated pulmonary arterial hypertension (PAH; SScPAH) and idiopathic PAH (IPAH). In 13 limited cutaneous SScPAH and 17 IPAH patients, RV pump function was described using the pump function graph, which relates mean RV pressure ((RV)) and stroke volume index (SVI). Differences in pump function result in shift or rotation of the pump function graph. (RV) and SVI were measured using standard catheterisation. The hypothetical isovolumic (RV) ((RV,iso)) was estimated using a single-beat method. The pump function graph was approximated by a parabola: (RV) = (RV,iso)[1-(SVI/SVI(max))(2)], where SVI(max )is the hypothetical maximal SVI at zero (RV), enabling calculation of SVI(max). There were no differences in SVI and SVI(max). Both (RV) and (RV,iso) were significantly lower in SScPAH than in IPAH ((RV) 30.7+/-8.5 versus 41.2+/-9.4 mmHg; (RV,iso) 43.1+/-12.4 versus 53.5+/-10.0 mmHg). Since higher pressures were found at similar SVI, the difference in the pump function graph results from lower contractility in SScPAH than in IPAH. Right ventricular contractility is lower in systemic sclerosis-associated pulmonary arterial hypertension than in idiopathic pulmonary arterial hypertension.

A refined radio-telemetry technique to monitor right ventricle or pulmonary artery pressures in rats: a useful tool in pulmonary hypertension research

Implantable radio-telemetry methodology, allowing for continuous recording of pulmonary haemodynamics, has previously been used to assess effects of therapy on development and treatment of pulmonary hypertension. In the original procedure, rats were subjected to invasive thoracic surgery, which imposes significant stress that may disturb critical aspects of the cardiovascular system and delay recovery. In the present study, we describe and compare the original trans-thoracic approach with a new, simpler trans-diaphragm approach for catheter placement, which avoids the need for surgical invasion of the thorax. Satisfactory overall success rates up to 75% were achieved in both approaches, and right ventricular pressures and heart and respiratory rates normalised within 2 weeks. However, recovery was significantly faster in trans-diaphragm than in trans-thoracic operated animals (6.4 ± 0.5 vs 9.5 ± 1.1 days, respectively; p < 0.05). Stable right ventricular pressures were recorded for more than 4 months, and pressure changes, induced by monocrotaline or pulmonary embolisms, were readily detected. The data demonstrate that right ventricular telemetry is a practicable procedure and a useful tool in pulmonary hypertension research in rats, especially when used in combination with echocardiography. We conclude that the described trans-diaphragm approach should be considered as the method of choice, for it is less invasive and simpler to perform.

NT-proBNP reflects right ventricular structure and function in pulmonary hypertension

The aim of the current study was to investigate whether alterations in N-terminal pro brain natriuretic peptide (NT-proBNP) reflect changes in right ventricular structure and function in pulmonary hypertension patients during treatment. The study consisted of 30 pulmonary hypertension patients; 15 newly diagnosed and 15 on long-term treatment. NT-proBNP, right heart catheterisation and cardiac magnetic resonance imaging measurements were performed, at baseline and follow-up. There were no significant differences between newly diagnosed patients and those on treatment at baseline or follow-up with respect to NT-proBNP, haemodynamics and right ventricular parameters. Relative changes in NT-proBNP during treatment were correlated to the relative changes in right ventricular end-diastolic volume index (r = 0.59), right ventricular mass index (r = 0.62) and right ventricular ejection fraction (r = -0.81). N-terminal pro brain natriuretic peptide measurements reflect changes in magnetic resonance imaging-measured right ventricular structure and function in pulmonary hypertension patients. An increase in N-terminal pro brain natriuretic peptide over time reflects right ventricular dilatation concomitant to hypertrophy and deterioration of systolic function.

Noninvasive assessment and monitoring of the pulmonary circulation

In pulmonary vascular disease, changes in the pulmonary vascular bed will lead to altered pulmonary haemodynamics. This review describes the application of several physiological principles to measure these changes noninvasively by means of novel techniques. Flow characteristics of blood through the pulmonary vascular bed alter in pulmonary vascular disease. Recent developments in magnetic resonance imaging and computed tomography make it possible to visualise and quantify these abnormal flow patterns. Information regarding pulmonary perfusion can also be obtained by measuring the electrical impedance changes in the lung by electrical impedance tomography. A more indirect approach to measure the pulmonary blood flow is the measurement of the absorption of acetylene, a perfusion limited gas. Information on the pulmonary vascular bed can also be obtained by the measurement of exhaled products of the pulmonary vascular endothelium, such as nitric oxide. Although all the techniques described offer new ways to diagnose or monitor pulmonary vascular disease, clinical data on these techniques are limited. Further improvement and evaluation of the clinical value of these techniques are therefore obligatory before they can be used in clinical practice.

Tracheobronchial stenting in the terminal care of cancer patients with central airways obstruction

STUDY OBJECTIVES

To evaluate the palliative benefit of stent insertion in a group of patients with central airways obstruction due to terminal cancer.

DESIGN

Retrospective analysis of the symptomatic score of patients immediately after stent insertion, and questionnaires completed by the general practitioner (GP) after the patients died at home.

SETTING

Academic hospital, tertiary referral center for interventional bronchoscopy.

PATIENTS AND METHODS

Fourteen patients with imminent suffocation due to major obstruction of the central airways, caused by end-stage esophageal cancer (n = 5) and non-small cell lung cancer (n = 9), were referred for stent insertion. All prostheses were placed within 24 h after hospital admittance. Patients were then asked whether their symptoms had improved. After the patients died, a questionnaire was sent to each patient's GP.

RESULTS

All patients expressed immediate benefit after stenting. The average length of survival after stent insertion was 11 weeks (range, 0.5 to 34 weeks). Two patients died within 1 week in our hospital after stent placement. In the remaining 12 patients, the GP considered stent insertion in 7 patients to be worthwhile, no judgment was made in 4 patients, and stent insertion in 1 patient was regarded as futile.

CONCLUSION

Despite terminal disease and the fact that, in our country, patients may legally refuse any treatment and formally ask for euthanasia, the palliative benefit of stent placement should always be considered. All patients had immediate symptomatic relief afterwards. Retrospectively, the GPs responsible for terminal care at home still considered stent insertion worthwhile in 58% (7 of 12 patients) of cases. Stent placement should always be considered as part of the treatment of terminal cancer patients with imminent suffocation.

Sequential V(A)/Q distributions in the normal rabbit by micropore membrane inlet mass spectrometry

We developed micropore membrane inlet mass spectrometer (MMIMS) probes to rapidly measure inert-gas partial pressures in small blood samples. The mass spectrometer output was linearly related to inert-gas partial pressure (r(2) of 0.996-1.000) and was nearly independent of large variations in inert-gas solubility in liquid samples. We infused six inert gases into five pentobarbital-anesthetized New Zealand rabbits and used the MMIMS system to measure inert-gas partial pressures in systemic and pulmonary arterial blood and in mixed expired gas samples. The retention and excretion data were transformed into distributions of ventilation-to-perfusion ratios (V(A)/Q) with the use of linear regression techniques. Distributions of V(A)/Q were unimodal and broad, consistent with prior reports in the normal rabbit. Total blood sample volume for each VA/Q distribution was 4 ml, and analysis time was 8 min. MMIMS provides a convenient method to perform the multiple inert-gas elimination technique rapidly and with small blood sample volumes.

Determination of stroke volume by means of electrical impedance tomography

ECG-gated electrical impedance tomography (EIT) is a non-invasive imaging technique, developed to monitor blood volume changes. This study is the first in comparing this non-invasive technique in measuring stroke volume with established techniques. The objective of this study was to validate EIT variables derived from the EIT images with paired obtained stroke volume measurements by thermodilution and MRI. After right cardiac catheterization, EIT measurements were performed in 25 patients. Regression analysis was used to analyse the relation between the EIT results and stroke volume determined by thermodilution. From the regression line an equation was derived to estimate stroke volume (in ml) by EIT. A strong correlation was found between EIT and stroke volume measured by the thermodilution method (r = 0.86). In a group of 11 healthy subjects this equation was validated to MRI. The mean and standard deviation of the difference between EIT and MRI was 0.7 ml and 5.4 ml respectively. These data indicate that EIT is a valid and reproducible method for the assessment of stroke volume.