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J T Marcus

Publications and source records attributed to J T Marcus.

32 records · Page 2Linked to original sources
PubMed1998

Pulmonary perfusion measured by means of electrical impedance tomography.

Electrical impedance tomography (EIT) is a recent imaging technique based on electrical impedance, offering the possibility of measuring pulmonary perfusion. In the present study the influence of several pulmonary haemodynamical parameters on the EIT signal were investigated. First, the influence on the systolic wave of the EIT signal (delta Zsys) of stroke volume, large pulmonary artery distensibility (both assessed by means of MRI) and the extent of the pulmonary peripheral vascular bed in 11 emphysematous patients (reduced peripheral vascular bed) and 9 controls (normal peripheral vascular bed) was investigated. Second, the influence of hypoxic pulmonary vasoconstriction on delta Zsys was examined in 14 healthy subjects. Finally, the origin of the diastolic wave was examined in three patients with atrioventricular dissociation. Multiple regression analysis showed that delta Zsys was only dependent on the variable emphysema (p < 0.02), but not dependent on stroke volume (p < 0.3) or pulmonary artery distensibility (p > 0.9). The mean value of delta Zsys for emphysematous patients (131 +/- 32 arbitrary units (AU)) was significantly lower (p < 0.001) than in the control group (200 +/- 39). In the group of healthy subjects delta Zsys decreased significantly (p < 0.001) during hypoxia (193 +/- 38 AU) compared with rest measurements (260 +/- 62 AU). The absence of the diastolic wave in the cardiological patients suggests the influence of reverse venous blood flow on the EIT signal. It is concluded that volume changes in the small pulmonary vessels contribute significantly to the EIT signal. Moreover, the hypoxia induced decrease in delta Zsys indicates the potential of EIT for measuring pulmonary vascular responses to external stimuli.

Aged↗
PubMed1997

Myocardial function in infarcted and remote regions early after infarction in man: assessment by magnetic resonance tagging and strain analysis.

Early after infarction in the perfusion bed of the left anterior descending coronary artery, cine MRI with spatial modulation of magnetization (SPAMM) tagging (7-mm grid) was used for short- and long-axis cardiac imaging. Two-dimensional strain analysis of triangular finite elements was performed between end-diastole and end-systole. Patients (n = 10) were compared with age-matched healthy subjects (n = 8). The anteroseptal region at midventricular level was considered representative for "infarcted" and the posterolateral region at basal level was considered "remote". The left ventricular end-diastolic volume index was larger in the patients (69 +/- 15 ml/m2 versus 56 +/- 4 ml/m2, P < 0.05). Short-axis images showed in the infarcted region a decrease of first principal strain (greatest systolic lengthening: 1.10 +/- .06 versus 1.27 +/- 0.04, P < 0.0001), and in the remote region an increase (1.48 +/- 0.11 versus 1.36 +/- 0.07, P < 0.025). The lateral and inferior ventricular regions at mid- and basal levels were found to function normally. Long-axis images yielded similar results. Early after infarction, regions with dysfunction, normal function, and hyperfunction can be delineated with MR tagging. The compensatory increased contraction in the remote region is possibly triggered by the Frank-Starling mechanism.

Case-Control Studies↗
PubMed1997

Noninvasive assessment of right ventricular diastolic function by electrical impedance tomography.

STUDY OBJECTIVES: Electrical impedance tomography (EIT) offers the possibility to study blood volume changes within the right atrium during the cardiac cycle. The aim of this study was to determine the applicability of EIT in the assessment of right ventricular diastolic function in COPD. DESIGN: By means of region of interest analysis, impedance changes within the right atrium during the cardiac cycle were plotted as a function of time. As a diastolic index of the right ventricle, the right atrium emptying volume (RAEV), defined as the ratio between the volume change during the rapid filling phase relative to the total ventricular filling volume, was calculated. In a first study, the validity of the EIT method was assessed by comparison of the RAEV measured by EIT and MRI in a group of eight patients with severe COPD and seven control subjects. A second study was undertaken to assess the relation between RAEV and pulmonary artery pressure in a group of 27 patients measured by right-sided heart catheterization. RESULTS: The correlation coefficient between RAEV measured with MRI and EIT was 0.78. The difference between RAEV measured by MRI and EIT was 8.3 +/- 15.7% (mean +/- SD) for the control subjects and 3.5 +/- 10.9% for the COPD patients. RAEV values measured by EIT and MRI were larger in the control group (47.1 +/- 7.6%) compared with the patient group (38.1 +/- 10.4%). There was a clear nonlinear relationship between RAEV and the pulmonary artery pressure (y = 315 x-0.64, r = 0.83, p < 0.001). CONCLUSION: Our results indicate that RAEV measured by EIT is a useful noninvasive and inexpensive method for assessing right ventricular diastolic function in COPD patients.

Blood Pressure↗
PubMed1997

The effect of right ventricular hypertrophy on left ventricular ejection fraction in pulmonary emphysema.

STUDY OBJECTIVE: The development of right ventricular (RV) hypertrophy in emphysema is accompanied by involvement of the left ventricle (LV) and its systolic function. Our objective was to study the relation between RV hypertrophy and LV ejection fraction in emphysema by means of MRI. PATIENTS: Ten emphysematous patients (FEV1, 0.99+/-0.32 L; FEV1/vital capacity (VC), 0.32+/-0.11 [mean+/-SD]) and 10 age-matched control subjects were included. Exclusion criteria were any history of systemic hypertension, ischemic or valvular heart disease, or episodes of right- and/or left-sided cardiac failure. MEASUREMENTS AND RESULTS: Rapid scout imaging was used to measure RV and LV wall mass, wall thickness, and end-diastolic volume. Stroke volume was derived from the main pulmonary artery flow. RV wall volume, RV wall thickness, and the ratio of RV to LV wall thickness were significantly larger in the patient group than in the control group (p<0.01). Furthermore, patients had significantly lower values of LV ejection fraction (p<0.01) than the control subjects. A flattening or leftward displacement of the ventricular septum during systole was observed. In addition, our study showed an increase of LV ejection fraction proportional with the RV wall thickness (r=0.78, p<0.01) in severely emphysematous patients. CONCLUSION: These data are in support of the hypothesis that flattening of the interventricular septum explains the relatively normal LV ejection fraction in emphysematous patients with severe RV hypertrophy.

Aged↗
PubMed1996

Improvement of cardiac imaging in electrical impedance tomography by means of a new electrode configuration.

Until now, electrical impedance tomography (EIT) has been used for cardiac imaging with the electrodes attached transversally at the level of the fourth intercostal space at the anterior side. However, the results obtained with this electrode configuration have been disappointing. The aim of the present study was to improve the measurement design of EIT for cardiac imaging. Therefore, magnetic resonance imaging (MRI) scans were analysed in two healthy subjects to determine the optimum anatomical plane in which atria and ventricles are clearly visually separated. From these findings, we proposed a new oblique plane at the level of the ictus cordis anteriorly and 10 cm higher posteriorly. EIT pictures obtained in the oblique plane revealed a better visual separation between the ventricles and atria than with the electrodes attached in the transverse plane. Comparison between volume changes measured by means of MRI and impedance changes in different regions of interest measured with EIT were performed with the electrodes in the proposed oblique plane. Ventricular and atrial volume changes measured by MRI show the same pattern as do impedance changes measured by EIT. Furthermore, we assessed the reproducibility and validity of the oblique electrode configuration in ten healthy mate volunteers during rest and during exercise compared with the currently used transverse electrode configuration. The reproducibility coefficient assessed from repeated measurements with the electrodes attached in the oblique plane was 0.98 at rest and 0.85 during exercise. For the transverse plane the reproducibility coefficient was 0.96 at rest and 0.66 during exercise. The well-known increase in stroke volume during exercise is 40% in healthy subjects. The increase in impedance change during exercise compared with rest was 34 +/- 13% (20-59%) for the oblique plane and 68 +/- 57% (13-140%) for the transverse plane. From these results we infer that the stroke volume is assessed more accurately by using the oblique plane. From these findings, we conclude that the oblique plane improved the cardiac measurements, because (i) a better spatial separation of the heart compartments is obtained, (ii) the results are more reliable and (iii) measurements during exercise are more accurate with the electrodes attached in an oblique plane.

Cardiography, Impedance↗
PubMed1993

Otolith responses in man during parabolic flight.

The influence of the varying gravito-inertial (Gz) force during parabolic flight on human otolith function was investigated experimentally. It was hypothesised that a varying Gz force profile initiates an otolith-ocular response that manifests itself in modulation of optokinetic nystagmus slow-phase eye velocity (OKN-SPV). Six subjects were seated in the ESA-Caravelle, facing perpendicular to the aircraft's longitudinal axis. The Gz profile was subsequently 1.8 Gz pull-up, 0 Gz microgravity, and 1.8 Gz recovery, each phase lasting about 20 s. Vertical eye movements were recorded with electro-nystagmography throughout the parabolic manoeuvre. Conditions were: (1) visual fixation, (2) darkness and (3) optokinetic stimulation of 50 deg/s in an upward or downward direction, projected on a cylindrical screen at 0.6 m viewing distance. No consistent nystagmus or gaze shift was measured in darkness. With optokinetic stimulation, however, ANOVA revealed downward enhancement of OKNSPV by 5 degrees/s in 1.8 Gz hypergravity, as compared with the 0 Gz condition and the 1 Gz condition. It is concluded that an otolith-ocular pathway modulates optokinetic eye movements in parabolic flight.

Adult↗
PubMed1991

Spatiotemporal representation of moving luminance edges in human vision.

The edges of straight bars in a square-wave luminance grating appear undulating to an observer when the retinal image of this pattern is in motion. The amplitude of the perceived undulations increases linearly with retinal image speed with an average slope of 30 +/- 4 ms. The period of the motion-induced bulges is 2.5 +/- 0.5 degree and shows no consistent variation with the retinal image velocity of the pattern. The close quantitative agreement between the spatiotemporal extent of this effect and recent estimates of the spatiotemporal parameters of human motion-sensitive mechanisms suggests the existence of motion-sensitive cells in the central nervous system that have a fixed time constant but change the shape and size of their retinal support with retinal image velocity.

Humans↗
PubMed1990

Vestibulo-ocular responses in man to +Gz hypergravity.

The influence of high +Gz gravito-inertial force on the vestibular system in man was investigated in a 4-m centrifuge with a freely swinging gondola. The Gz profile was: acceleration +0.2 Gz/s, +3 Gz sustained for 3 min, deceleration -0.2 Gz/s. The subject was exposed to this profile under two conditions in randomized order: facing forward and facing backward. Under these conditions, the effective angular velocity in the plane of the vertical semicircular canals is opposed. Adding the slow phase velocity responses from these conditions yields the Gz effect only; subtracting yields the angular velocity effect only. Vertical vestibular nystagmus was analysed in five subjects. Results indicate that +3 Gz induced a subject-dependent vertical nystagmus with slow phase downwards. The average amplitude of this nystagmus reached a maximum of 27 degrees/s at 16 s from G onset, and was 11 degrees/s after 3 min of sustained +3 Gz. The vestibular stimulation by +Gz could result in false subjective perception of attitude, and play a major role in spatial disorientation in flight.

Acceleration↗
PubMed1989

Influence of gravitoinertial force on vestibular nystagmus in man observed in a centrifuge.

The influence of gravity load on the vestibular system in man was investigated in a centrifuge operating on the free swing principle. The vertical vestibular nystagmus induced by acceleration to 3G was analyzed and compared with reference measurements during 1G. Our data indicate that the effects of increased gravity load include a prolonged decay time constant of upbeat nystagmus and a subject-dependent persisting upbeat nystagmus. In an attempt to explain these findings, an extension of the velocity storage model is proposed, with gravity as a second stimulus function in addition to angular acceleration.

Acceleration↗
PubMed1989

The pupillary light reflex in diabetes mellitus: evaluation of a newly developed infrared light reflection method.

Pupillary light reflexes were measured in 18 diabetic patients without clinical signs of neuropathy and in 18 control subjects, using a newly developed infrared light reflection technique called IRIS. This method has some important advantages. Apart from being non traumatic, it enables the recording of dynamic pupillary light reflexes simultaneously in both eyes. Furthermore, it has a large amplitude and time resolution (1 ms), permitting accurate determination of latency values. It was found that 78% of the diabetic patients show a significantly prolonged latency of the constriction reaction, while 39% of the diabetic patients show an abnormally prolonged dilatation latency. All patients with an abnormally prolonged dilatation latency also show a prolonged constriction latency. This finding suggests that in diabetes mellitus the parasympathetic system is affected before abnormalities of the sympathetic nervous system can be demonstrated. Assessment of the pupillary light reflex, using the sensitive IRIS method, is an easily applicable and reliable method for detection of subclinical autonomic nervous system dysfunction associated with diabetes mellitus. The method may also provide an objective tool for the assessment of therapy results in diabetic neuropathy.

Adult↗
PubMedDate not supplied

MRI evaluation of right ventricular pressure overload in chronic obstructive pulmonary disease.

In chronic obstructive pulmonary disease (COPD), the development of pulmonary hypertension is common. This study was performed to assess the signs of right ventricular (RV) pressure overload and RV failure in COPD. In 8 COPD patients without primary cardiac disease, RV wall thickness, mass, and end-diastolic volume were measured by cardiac-triggered cine MRI. MR phase-contrast velocity quantification was used to measure stroke volume and the patterns of flow into and out of the RV. Data of patients were tested versus those of a control group matched for age (n = 8). Results showed that the RV wall thickness was increased (.6 +/- 0.1 vs 0.4 +/- 0.1 cm, P < .001). RV mass was increased (67 +/- 11 vs 57 +/- 5 g, P < .005). RV stroke volume was decreased (57 +/- 13 vs 71 +/- 13 ml, P < .01), but RV ejection fraction was not different. In the main pulmonary artery flow, the quotient of acceleration time divided by ejection time was decreased (33 +/- 5% vs 38 +/- 4%, P < .05), which is indicative of pulmonary hypertension. In conclusion, this MRI protocol provides a tool to assess the effects of RV pressure overload in COPD before heart failure has become manifest.

Aged↗
PubMedDate not supplied

Flow profiles in the left anterior descending and the right coronary artery assessed by MR velocity quantification: effects of through-plane and in-plane motion of the heart.

PURPOSE: The purpose of this work was to compare the temporal profiles of volume flow in the left anterior descending artery (LAD) and the right coronary artery (RCA) and to assess the effect of through-plane and in-plane myocardial motion. METHOD: In eight healthy volunteers, MR phase-difference velocity quantification was applied with prospective ECG triggering, pixel size of 1.16 x 0.98 mm2 (LAD) or 1.25 x 0.98 mm2 (RCA), velocity sensitivity of 40 cm/s, and data acquisition time window of 64 ms for LAD (3 ky lines per heartbeat) and 24 ms for RCA. In-plane motion was measured from the magnitude images. RESULTS: In the LAD, systolic peak and mean flow values were 0.94+/-0.28 and 0.30 +/-0.22 ml/s, respectively. Diastolic peak and mean flows were 2.42+/-0.56 and 1.38+/-0.43 ml/s. The systolic to diastolic ratio was 0.37+/-0.12 for peak flow and 0.22+/-0.15 for mean flow. Mean flow through the cardiac cycle was 59.1+/-15.0 ml/min. In the RCA, systolic peak and mean flow values were 1.96+/-0.69 and 0.74+/-0.31 ml/s, respectively. Diastolic peak and mean flows were 1.80+/-0.53 and 0.83+/-0.20 ml/s. The systolic to diastolic ratio was 0.97+/-0.58 for peak flow and 0.85+/-0.39 for mean flow. Mean flow through the cardiac cycle was 38.4+/-10.8 ml/min. The in-plane velocity of the coronary artery cross-section was 6.4+/-1.8 cm/s for the LAD and 14.9 +/-4.0 cm/s for the RCA (given by peak values in diastole). CONCLUSION: It is confirmed noninvasively with MR that the LAD shows a predominantly diastolic flow, whereas the RCA shows about equal flow values in systole and diastole. Through-plane motion correction is required for assessing the true flow patterns. The in-plane velocities of the coronary artery cross-sections imply a maximum data acquisition time window, estimated at 58 ms for the LAD and at 23 ms for the RCA.

Adult↗