PubMed Health⌕ Search

Biomedical subjects

J Tim Marcus

Publications and source records attributed to J Tim Marcus.

At least 19 recordsLinked to original sources
PubMed2007

Reverse right ventricular remodeling after pulmonary endarterectomy in patients with chronic thromboembolic pulmonary hypertension: utility of magnetic resonance imaging to demonstrate restoration of the right ventricle.

OBJECTIVES: Pulmonary arterial hypertension causes right ventricular remodeling; that is, right ventricular dilatation, hypertrophy, and leftward ventricular septal bowing. We studied the effect of pulmonary endarterectomy on the restoration of right ventricular remodeling in patients with chronic thromboembolic pulmonary hypertension by magnetic resonance imaging. METHODS: In 17 patients with chronic thromboembolic pulmonary hypertension, before and at least 4 months after pulmonary endarterectomy, and in 12 healthy controls, right ventricular and left ventricular end-diastolic and end-systolic volumes (milliliters) and mass (grams per meter squared) and leftward ventricular septal bowing (1 divided by the radius of curvature in centimeters) were determined by magnetic resonance imaging. RESULTS: Before pulmonary endarterectomy, right ventricular volumes, left ventricular end-diastolic volume, right ventricular mass, and leftward ventricular septal bowing differed significantly between patients with chronic thromboembolic pulmonary hypertension and healthy control subjects. After pulmonary endarterectomy, pulmonary hemodynamics improved, and right and left ventricular volumes and leftward ventricular septal bowing normalized; right ventricular mass decreased significantly (46 +/- 14 to 31 +/- 9 g x m(-2), P< .0005), but did not completely normalize. The change in total pulmonary resistance correlated with the change in right ventricular ejection fraction (r = 0.50, P < .05), right ventricular mass (r = 0.63, P < .01), and leftward ventricular septal bowing (r = 0.50, P < .05). CONCLUSIONS: Right ventricular remodeling was observed in patients with chronic thromboembolic pulmonary hypertension and restored almost completely after a hemodynamically successful pulmonary endarterectomy. Magnetic resonance imaging is a valuable tool to evaluate cardiac remodeling and function in patients with chronic thromboembolic pulmonary hypertension, both before and after pulmonary endarterectomy.

Adult↗
PubMed2006

The effect of left bundle branch block on left ventricular remodeling, dyssynchrony and deformation of the mitral valve apparatus: an observational cardiovascular magnetic resonance imaging study.

BACKGROUND: The effect of a left bundle branch block (LBBB) on cardiac function and remodeling in patients at different stages of heart failure (HF) is unknown. We used cardiac magnetic resonance imaging (CMR) to evaluate the effect of LBBB on left ventricular (LV) remodeling, mechanical dyssynchrony, functional mitral regurgitation (FMR) and deformation of the mitral valve apparatus (MVA) in LBBB patients at different stages of HF. METHODS: In 12 LBBB patients with HF, 4 patients with isolated LBBB, and 4 controls, cine CMR was performed to measure LV remodeling, FMR grade and deformation of the MVA. CMR tagging was used to measure septal-to-lateral onset of shortening delay and coefficient of circumferential strain variation (CV) to quantify dyssynchrony. RESULTS: LV end-diastolic volume (LVEDV) and end-systolic volume (LVESV) were largest in LBBB patients with HF. Patients with isolated LBBB tended to have a larger LVESV and smaller LV ejection fraction compared to controls, (56 +/- 22 ml/m2 versus 45 +/- 9 ml/m2, P = ns, 42 +/- 9% versus 53 +/- 4 %, P = ns). QRS duration and septal-to-lateral-onset-of-shortening delay were comparable between LBBB patients with HF and isolated LBBB patients, CV was larger (98 +/- 45 versus 40 +/- 4, P < 0.05). MVA tenting and FMR were present both in LBBB patients with HF and patients with isolated LBBB and were not observed in controls. CONCLUSION: The presence of a LBBB in asymptomatic patients is related to mechanical dyssynchrony and deformation of the MVA and may be associated with LV remodeling. If confirmed, close monitoring or even timely initiation of therapy may be warranted in patients with isolated LBBB. This advocates to conduct a longitudinal CMR follow-up study on the clinical course in patients with isolated LBBB.

Action Potentials↗
PubMed2006

Stroke volume response during exercise measured by acetylene uptake and MRI.

The intra-breath technique to measure acetylene absorption offers the possibility to determine augmentation of the pulmonary blood flow per heart beat (Q(C)) as an estimate of the stroke volume response during exercise. However, this method has not been compared with a validated test until now. Therefore, the aim of this study was to compare Q(C) with stroke volume (SV(MRI)) determined by magnetic resonance imaging (MRI) at rest and during exercise in healthy subjects and patients. For this purpose, ten healthy subjects and ten patients with idiopathic pulmonary arterial hypertension (iPAH) with expected impaired stoke volume response during exercise were measured by both methods. Exercise-induced changes in Q(C) and SV(MRI) were correlated in healthy controls (r = 0.75, p < 0.05). Compared to healthy controls, Q(C) increased less during exercise in iPAH patients (11 +/- 17 ml versus 33 +/- 12 ml, p < 0.05). A similar difference in stroke volume response to exercise between the two groups was measured by MRI (-0.6 +/- 8 ml versus 23 +/- 12 ml, p < 0.05, respectively). Hence, intra-breath and MRI measurements showed similar differences in exercise-induced changes in stroke volume between controls and patients. From these results it can be concluded that the intra-breath measurement of acetylene absorption might be of value as a non-invasive tool to estimate stroke volume augmentation during exercise and can detect differences in stroke volume responses between iPAH patients and healthy subjects.

Acetylene↗
PubMed2006

Myocardial strain and torsion quantified by cardiovascular magnetic resonance tissue tagging: studies in normal and impaired left ventricular function.

Accurate quantification and timing of regional myocardial function allows early identification of dysfunction, and therefore becomes increasingly important for clinical risk assessment, patient management, and evaluation of therapeutic efficacy. For this purpose, the application of tissue Doppler echocardiography has rapidly increased. However, echocardiography has some major inherent limitations. Cardiovascular magnetic resonance imaging with tissue tagging provides highly reproducible data on myocardial function, not only in longitudinal and radial directions, but also in the circumferential direction. Because of the development of faster imaging protocols, improved temporal resolution, less time-consuming postprocessing procedures, and the potential of quantifying myocardial deformation in 3 dimensions at any point in the heart, this technique may serve as an alternative for tissue Doppler echocardiography and is now ready for more widespread clinical use. This review discusses the clinical use of cardiovascular magnetic resonance tissue tagging for quantitative assessment of regional myocardial function, thereby underlining the specific features and emerging role of this technique.

Heart↗
PubMed2006

Quantification of right ventricular afterload in patients with and without pulmonary hypertension.

Right ventricular (RV) afterload is commonly defined as pulmonary vascular resistance, but this does not reflect the afterload to pulsatile flow. The purpose of this study was to quantify RV afterload more completely in patients with and without pulmonary hypertension (PH) using a three-element windkessel model. The model consists of peripheral resistance (R), pulmonary arterial compliance (C), and characteristic impedance (Z). Using pulmonary artery pressure from right-heart catheterization and pulmonary artery flow from MRI velocity quantification, we estimated the windkessel parameters in patients with chronic thromboembolic PH (CTEPH; n = 10) and idiopathic pulmonary arterial hypertension (IPAH; n = 9). Patients suspected of PH but in whom PH was not found served as controls (NONPH; n = 10). R and Z were significantly lower and C significantly higher in the NONPH group than in both the CTEPH and IPAH groups (P < 0.001). R and Z were significantly lower in the CTEPH group than in the IPAH group (P < 0.05). The parameters R and C of all patients obeyed the relationship C = 0.75/R (R(2) = 0.77), equivalent to a similar RC time in all patients. Mean pulmonary artery pressure P and C fitted well to C = 69.7/P (i.e., similar pressure dependence in all patients). Our results show that differences in RV afterload among groups with different forms of PH can be quantified with a windkessel model. Furthermore, the data suggest that the RC time and the elastic properties of the large pulmonary arteries remain unchanged in PH.

Adult↗
PubMed2006

Extended harmonic phase tracking of myocardial motion: improved coverage of myocardium and its effect on strain results.

PURPOSE: To extend the harmonic phase (HARP) tracking method in order to track the myocardial tissue that appears near the epicardial contour during systole and reappears near the endocardial contour during diastole, due to the longitudinal motion and conical shape of the heart. MATERIALS AND METHODS: A mathematical model of myocardial deformation was used to quantify the accuracy of the extended HARP tracking and of the strain computation. For six healthy volunteers, the number of tracked points and the two-dimensional strain components were computed with the extended and with the original HARP tracking version. RESULTS: High accuracy was obtained for the circumferential strain (maximum error is 0.5% relative to analytical strain). The extended version tracked 22 +/- 7%, 51 +/- 19%, and 67 +/- 20% more points than the original version on the basal, mid, and apical slices, respectively (P < or = 0.001 for each slice), and yielded a decreased circumferential shortening (relative decrease: 2 +/- 4%, 9 +/- 4%, and 12 +/- 5% for the three slices; P < 0.005 for mid and apex), at end systole. These differences in circumferential strain were related to the more complete coverage of the myocardial wall with tracked points. CONCLUSION: The extended HARP tracking also provides strain values from myocardial regions that were not covered by the original HARP tracking.

Adult↗
PubMed2006

DENSE and HARP: two views on the same technique of phase-based strain imaging.

PURPOSE: To discuss differences between displacement encoding with stimulated echoes (DENSE) and the harmonic phase (HARP) in imaging and reconstruction strategies. MATERIALS AND METHODS: HARP and DENSE are presented in their historical context: while the HARP method was developed from the framework of myocardial tagging, DENSE arose from the framework of stimulated echo and displacement encoding using bipolar gradients. Both techniques have evolved since their introduction, thereby becoming more similar over time and losing their distinct features. Newly introduced improvements have successfully been applied in both methods. Differences between both methods are discussed point by point. RESULTS: From this discussion it follows that almost all apparent differences are in fact nonexistent. CONCLUSION: In the literature, both techniques are still regarded as distinctly different techniques, where a more general treatment of the technique is justified. Once it is realized that both frameworks are easily merged, the benefits are 1) less confusion about the (dis)advantages of either technique, and 2) understanding of phase-based strain imaging that is more general than HARP or DENSE alone.

Algorithms↗
PubMed2006

Regional heterogeneity of resting perfusion in hypertrophic cardiomyopathy is related to delayed contrast enhancement but not to systolic function: a PET and MRI study.

BACKGROUND: Regional differences in resting myocardial blood flow (MBF) have been observed in patients with hypertrophic cardiomyopathy (HCM), but their determinants are currently unknown. This study verifies whether MBF at rest in HCM is related to delayed contrast enhancement (DCE) or regional systolic function (or both) as determined by magnetic resonance imaging. METHODS AND RESULTS: Fourteen patients with HCM were studied. MBF was measured with positron emission tomography by use of oxygen 15-labeled water. DCE and tissue tagging, to calculate end-systolic circumferential shortening (Ecc), were obtained with magnetic resonance imaging. The mean resting MBF was 0.78 +/- 0.19 mL x min(-1) x mL(-1), and there was a trend toward reduced MBF in the septum (0.72 +/- 0.11 mL x min(-1) x mL(-1)) compared with that in the lateral wall (0.84 +/- 0.29 mL x min(-1) x mL(-1)) (P = .092). The distribution patterns of DCE and Ecc were both heterogeneous, displaying significantly increased enhancement and impaired regional systolic function in the hypertrophic septum compared with the lateral wall (both P < .001). Resting MBF was inversely related to the extent of DCE (r = -0.30, P < .001), whereas MBF was not significantly related to Ecc (r = -0.15, P = .072). CONCLUSIONS: Regional heterogeneity of resting perfusion in HCM is related to the extent of DCE but not to regional systolic function.

Adult↗
PubMed2006

Does myocardial fibrosis hinder contractile function and perfusion in idiopathic dilated cardiomyopathy? PET and MR imaging study.

PURPOSE: To prospectively evaluate, by using positron emission tomography (PET) and magnetic resonance (MR) imaging, the interrelationships between regional myocardial fibrosis, perfusion, and contractile function in patients with idiopathic dilated cardiomyopathy (DCM). MATERIALS AND METHODS: The study protocol was approved by the hospital ethics committee, and all subjects gave written informed consent. Sixteen patients with idiopathic DCM (mean age, 54 years +/- 11 [standard deviation]; nine men) and six healthy control subjects (mean age, 28 years +/- 2; five men) were examined with PET and MR tissue tagging. Oxygen 15-labeled water and carbon monoxide were used as tracers at PET to assess myocardial blood flow (MBF) and the perfusable tissue index (PTI), which is inversely related to fibrosis. MBF was determined at rest and during pharmacologically induced hyperemia. Maximum circumferential shortening (E(cc)) was determined with MR tissue tagging. Student t tests were performed for comparison of data sets, and linear regression was used to investigate the association between parameters. RESULTS: Mean global hyperemic MBF (2.23 mL/min/mL +/- 0.73), E(cc) (-10.5% +/- 2.9), and PTI (0.95 +/- 0.10) were lower in the patients with DCM than in the control subjects (4.33 mL/min/mL +/- 0.85, -17.4% +/- 0.6, and 1.09 +/- 0.12, respectively; P < .05 for all). In the patients with DCM, regional PTI was related to E(cc) (r = -0.21, P = .009) but not to resting or hyperemic MBF. Furthermore, regional E(cc) was correlated to both resting (r = -0.28, P = .004) and hyperemic MBF (r = -0.29, P < .001). In addition, the ratio of left ventricular end-diastolic volume to mass, as a reflection of wall stress, was related to global hyperemic MBF (r = -0.52, P = .047) and to global E(cc) (r = 0.69, P = .003). CONCLUSION: In idiopathic DCM, the extent of myocardial fibrosis is related to the impairment in contractile function, whereas fibrosis and perfusion do not seem to be interrelated. The degree of impairment of hyperemic myocardial perfusion is related to contractility and end-diastolic wall stress.

Adult↗
PubMed2005

Propagation of onset and peak time of myocardial shortening in time of myocardial shortening in ischemic versus nonischemic cardiomyopathy: assessment by magnetic resonance imaging myocardial tagging.

OBJECTIVES: We aimed to study the relation between onset and peak time of circumferential shortening and the direction of propagation of these parameters in both ischemic and nonischemic patients. BACKGROUND: Peak time is often used to select patients for cardiac resynchronization therapy, whereas pacing influences only the onset times directly. Furthermore, it is unclear whether there is a consistent direction of propagation delay and whether this depends on the etiology. METHODS: Magnetic resonance imaging myocardial tagging with high temporal resolution (14 ms) was applied to 29 patients (18 nonischemic, 11 ischemic) and 17 healthy control subjects. Time to onset (T(onset)), to first peak (T(peak,first)), and to maximum peak (T(peak,max)) of circumferential shortening were determined. Three-dimensional vectors were calculated to denote the main direction of asynchrony. RESULTS: In both patient groups, T(onset) showed a significant positive relation with both T(peak,first) and T(peak,max); however, T(peak,first) correlated considerably better with T(onset) than did T(peak,max) (p < 0.0001 for nonischemic, and p < 0.01 for ischemic patients). Moreover, the relations between T(peak) and T(onset) were stronger in the nonischemic patients than in the ischemic patients (p < 0.001). In nonischemic patients, the propagation of T(onset) was consistently from septum to lateral wall. In the ischemic patients, however, no consistent direction of propagation was found. For both groups, the longitudinal propagation delays (between apex and base) were negligible compared with the short-axis delays. CONCLUSIONS: The relation between peak time and onset time of shortening is strongest in nonischemic patients and is most consistent when time to first peak is used (instead of time to maximum peak).

Aged↗
PubMed2005

Impaired left ventricular filling due to right-to-left ventricular interaction in patients with pulmonary arterial hypertension.

The aim of this study was to investigate the contribution of direct right-to-left ventricular interaction to left ventricular filling and stroke volume in 46 patients with pulmonary arterial hypertension (PAH) and 18 control subjects. Stroke volume, right and left ventricular volumes, left ventricular filling rate, and interventricular septum curvature were measured by magnetic resonance imaging and left atrial filling by transesophageal echocardiography. Stroke volume, left ventricular end-diastolic volume, and left ventricular peak filling rate were decreased in PAH patients compared with control subjects: 28 +/- 13 vs. 41 +/- 10 ml/m(2) (P < 0.001), 46 +/- 14 vs. 61 +/- 14 ml/m(2) (P < 0.001), and 216 +/- 90 vs. 541 +/- 248 ml/s (P < 0.001), respectively. Among PAH patients, stroke volume did not correlate to right ventricular end-diastolic volume or mean pulmonary arterial pressure but did correlate to left ventricular end-diastolic volume (r = 0.62, P < 0.001). Leftward interventricular septum curvature was correlated to left ventricular filling rate (r = 0.64, P < 0.001) and left ventricular end-diastolic volume (r = 0.65, P < 0.001). In contrast, left atrial filling was normal and not correlated to left ventricular end-diastolic volume. In PAH patients, ventricular interaction mediated by the interventricular septum impairs left ventricular filling, contributing to decreased stroke volume.

Adult↗
PubMed2005

Interventricular septal configuration at mr imaging and pulmonary arterial pressure in pulmonary hypertension.

PURPOSE: To investigate whether a relationship exists between septum shape and systolic pulmonary arterial pressure (PAP) in patients with pulmonary hypertension. MATERIALS AND METHODS: Study protocol was approved by institutional ethics review committee; all patients gave informed consent. Right-sided heart catheterization with vasodilator testing was performed in 39 adult subjects suspected of having pulmonary hypertension. There were 11 men and 28 women, aged 21-75 years (mean, 46 years). Only two patients showed favorable response to vasodilators, defined by a decrease in PAP of more than 20%. Synchronous right- and left-ventricular pressure measurements and four-chamber magnetic resonance (MR) imaging were used to identify timing of maximal leftward ventricular septal bowing within cardiac cycle. Septal bowing was evaluated with MR, measured on short-axis cine heart images, and expressed as curvature (reciprocal of radius). Curvature was quantified on one image (the one that showed the most severe distortion of normal septal shape). The relationship between systolic PAP and septal curvature was tested with linear regression analysis. P <.05 was considered to indicate a statistically significant difference. RESULTS: Of 39 subjects, 37 had pulmonary hypertension. Maximal distortion of normal septal shape was found during right ventricular relaxation phase. Systolic PAP was proportional to septal curvature: r=0.77 (P < .001), slope=-114.7, and intercept=67.2. In the two vasodilator responsive subjects, a significant reduction of leftward ventricular septal bowing was observed in response to reduction of right ventricular pressure. CONCLUSION: In 37 patients with pulmonary hypertension, systolic PAP higher than 67 mm Hg may be expected when leftward curvature is observed.

Adult↗
PubMed2005

A comparison of noninvasive MRI-based methods of estimating pulmonary artery pressure in pulmonary hypertension.

PURPOSE: To assess the accuracy of several noninvasive MRI-based estimators of pulmonary artery pressure by comparing them with invasive pressure measurement. MATERIALS AND METHODS: We compared five MRI methods with invasive pressure measurement by catheterization, in one group of pulmonary hypertension (PH) patients. Doppler echocardiography was included as a reference method. Main inclusion criterion was a mean pulmonary artery pressure above 25 mmHg at catheterization. MRI velocity quantification was used to obtain pulmonary flow acceleration and ejection times, and pulse wave velocity. The ventricular mass index was also assessed on MRI. Two commercially available 1.5-T systems were used for this study. RESULTS: Data from 44 patients were analyzed. Correlation of acceleration time with mean pressure was: r = -0.21, P = 0.21, correlation of the acceleration/ejection time ratio with systolic pressure was: r = -0.26, P = 0.01. The ventricular mass index showed the best correlation with mean pressure, with r = 0.56, P < 0.001. Using the pulse wave velocity and the cross-sectional area of the pulmonary artery, the mean pressure could not be estimated accurately. CONCLUSION: Accurate estimation of pulmonary artery pressure in PH patients was not feasible by the MRI estimators studied. These noninvasive methods cannot replace right heart catheterization at this moment.

Blood Pressure↗
PubMed2005

Correction of phase offset errors in main pulmonary artery flow quantification.

PURPOSE: To investigate whether an existing method for correction of phase offset errors in phase-contrast velocity quantification is applicable for assessment of main pulmonary artery flow with an MR scanner equipped with a high-power gradient system. MATERIALS AND METHODS: The correction method consists of fitting a surface through the time average of stationary pixels of velocity-encoded phase images, and subtracting this surface from the velocity images. Pixels are regarded as stationary if their time standard deviation falls into the lowest percentile. Flow was measured in the main pulmonary artery of 15 subjects. Each measurement was repeated on a stationary phantom. The phase offset error in the phantom was used as a reference. Correction was applied with varying polynomial surface orders (0-5) and stationarity percentiles (5-50%). The optimal surface order and stationarity percentile were determined by comparing the fitted surface with the phantom. RESULTS: Using a first-order surface and a (noncritical) 25% percentile, the correction method significantly reduced the phase offset error from 1.1 to 0.35 cm/second (RMS), which is equivalent to a reduction from 11% to 3.3% of mean volume flow. Phase error correction strongly affected stroke volume (range -11 to 26%). CONCLUSION: The method significantly reduces phase offset errors in pulmonary artery flow.

Adult↗
PubMed2005

Impact of head movements on morphology and flow in the internal carotid artery after carotid angioplasty and stenting versus endarterectomy.

OBJECTIVE: Because stents can cause vessel angulation during movement, we hypothesized that internal carotid artery (ICA) stents might lead to alterations of cerebropetal blood flow. This study assessed three-dimensional anatomy and volumetric flow rate (VFR) in the ICA in various head positions by comparing patients treated with carotid angioplasty and stenting (CAS) with patients treated with carotid endarterectomy (CEA). METHODS: Three-dimensional time-of-flight magnetic resonance angiography and magnetic resonance flow quantification were performed on six subjects after CAS (median age, 70 years) and on six subjects after CEA (median age, 67 years). All investigations were performed in five head positions: neutral, bent forward, bent backward, and turned to the treated, ipsilateral side and to the contralateral side. Maximum-intensity projection reconstructions were obtained to measure maximal angulation of the ICA in the forward, backward, ipsilateral, and contralateral positions compared with neutral. Subsequently, the plane perpendicular to the ICA, 1 cm distal to the stent or 4 cm distal to the carotid bifurcation (CEA patients), was established. The VFR through this plane was measured for each position, and the forward, backward, ipsilateral, and contralateral positions were compared with neutral. RESULTS: In CAS patients, there was a median change in ICA angulation of +10.2 degrees (interquartile range, +7.3 degrees to +17.9 degrees ) in the forward position, compared with +0.2 degrees (-1.0 degrees to +2.4 degrees ) in CEA patients ( P = .016). In all other head positions, there was no statistically significant difference in angulation change. There was no statistically significant difference in VFR change between groups in any of the head positions tested. CONCLUSIONS: There was a significant increase in ICA angulation in CAS patients if the head was bent forward; this was not observed in CEA patients. This angulation change did not lead to significant acute changes in cerebropetal blood flow, but it might have chronic effects not yet tested.

Aged↗
PubMed2005

Early changes of cardiac structure and function in COPD patients with mild hypoxemia.

BACKGROUND: COPD is often associated with changes of the structure and the function of the heart. Although functional abnormalities of the right ventricle (RV) have been well described in COPD patients with severe hypoxemia, little is known about these changes in patients with normoxia and mild hypoxemia. STUDY OBJECTIVES: To assess the structural and functional cardiac changes in COPD patients with normal Pa(O2) and without signs of RV failure. METHODS: In 25 clinically stable COPD patients (FEV1, 1.23 +/- 0.51 L/s; Pa(O2), 82 +/- 10 mm Hg [mean +/- SD]) and 26 age-matched control subjects, the RV and left ventricular (LV) structure and function were measured by MRI. Pulmonary artery pressure (PAP) was estimated from right pulmonary artery distensibility. RESULTS: RV mass divided by RV end-diastolic volume as a measure of RV adaptation was 0.72 +/- 0.18 g/mL in the COPD group and 0.41 +/- 0.09 g/mL in the control group (p < 0.01). LV and RV ejection fractions were 62 +/- 14% and 53 +/- 12% in the COPD patients, and 68 +/- 11% and 53 +/- 7% in the control subjects, respectively. PAP estimated from right pulmonary artery distensibility was not elevated in the COPD group. CONCLUSION: From these results, we conclude that concentric RV hypertrophy is the earliest sign of RV pressure overload in patients with COPD. This structural adaptation of the heart does not alter RV and LV systolic function.

Aged↗
PubMed2004

Determinants of pulmonary perfusion measured by electrical impedance tomography.

Electrical impedance tomography (EIT) is a non-invasive imaging technique for detecting blood volume changes that can visualize pulmonary perfusion. The two studies reported here tested the hypothesis that the size of the pulmonary microvascular bed, rather than stroke volume (SV), determines the EIT signal. In the first study, the impedance changes relating to the maximal pulmonary pulsatile blood volume during systole (Delta Z(sys)) were measured in ten healthy subjects, ten patients diagnosed with chronic obstructive pulmonary disease, who were considered to have a reduced pulmonary vascular bed, and ten heart failure patients with an assumed low cardiac output but with a normal lung parenchyma. Mean Delta Z(sys) (SD) in these groups was 261 (34)x10(-5), 196 (39)x10(-5) ( P<0.001) and 233 (61)x10(-5) arbitrary units (AU) (P=NS), respectively. In the second study, including seven healthy volunteers, Delta Z(sys) was measured at rest and during exercise on a recumbent bicycle while SV was measured by means of magnetic resonance imaging. The Delta Z(sys) at rest was 352 (53)x10(-5 ) and 345 (112)x10(-5 )AU during exercise (P=NS), whereas SV increased from 83 (21) to 105 (34) ml (P<0.05). The EIT signal likely reflects the size of the pulmonary microvascular bed, since neither a low cardiac output nor a change in SV of the heart appear to influence EIT.

Aged↗