Biomedical subjects

T J Faes

Publications and source records attributed to T J Faes.

34 records · Page 2Linked to original sources

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↗

PubMed1995

Skin temperature response to a pressure load: studies in subjects before and during spinal anesthesia.

The Pressure-Temperature-Time method (PTT-method) is a method to investigate skin temperature changes in response to a pressure load. This method was used to investigate the effect of an acute nerve conduction block on the skin temperature increase of the trochanter major, after the pressure load was removed. The PTT-method was used in a group of 30 subjects, undergoing minor surgical procedures, before and during an anesthetic nerve conduction block at L2-L3. In comparison with the results before spinal anesthesia, the skin temperature responses were significantly delayed (p < .01) and slower (p < .001) after the spinal blockade. We concluded, therefore, that the nervous system has an important effect on the recovery of skin temperature after a pressure load.

Adult↗

PubMed1995

On the quantification of heart rate changes in autonomic function tests: relations between measures in beats per minute, seconds and dimensionless ratios.

1. Disorders of the autonomic nervous system are frequently diagnosed by measuring heart rate changes in response to deep-breathing and lying-to-standing manoeuvres. The heart rate changes in these manoeuvres are quantified in measures using various units, like beats per minute, seconds and dimensionless ratios. 2. In the present study we mathematically derived relationships between the measures which quantify heart rate changes in beats per minute, seconds and dimensionless ratios. The theoretical outcomes were experimentally confirmed by the results of the deep-breathing and the lying-to-standing test in 525 healthy and diabetic subjects. The measures were found to be non-equivalent, because the mean RR interval duration influenced the measures in different ways. 3. It is argued that measures in seconds are preferable to measures in beats per minute or ratios, because the physiological interpretation of this measure is easier, and the sensitivity of measures in seconds is expected to be greater. 4. Finally, we recommend that measures of heart rate variation in the deep-breathing and lying-to-standing manoeuvre are accompanied by information on the mean RR interval duration or mean heart rate to allow correct interpretation of the measures.

Autonomic Nervous System↗

PubMed1994

Spectra of data sampled at frequency-modulated rates in application to cardiovascular signals: Part 2. Evaluation of Fourier transform algorithms.

For three direct Fourier transform algorithms we quantified the influence of pulse frequency modulation (PFM) on the spectral estimation of pulse amplitude modulation (PAM). The simulation study is based on sinusoid functions sampled according to a pulse sequence which is the output of an integral pulse frequency modulator (IPFM). One algorithm exactly reproduces the theoretical spectrum derived in Part 1. The other two, including the classical FFT, scale all PFM-induced components in a different way, and in addition, generate higher modulating frequency harmonics. For a PFM depth below 30%, the sum of spurious PFM components is almost linearly dependent on this modulation depth, for all three algorithms. Dividing the effect of PFM in a 'harmonic' and 'aliasing' distortion, we found that the FFT has a relatively high harmonic distortion, compared to an algorithm that takes into account the non-uniform character of the data. In the cardiovascular (worst) case of 30% modulation in heart rate (PFM) at a frequency of 0.1 Hz, the FFT spectrum of beat-to-beat systolic blood pressure variations contains approximately 20% of spurious components caused solely by the modulation in time occurrences of the blood pressure samples. The 'non-uniform' algorithm performs twice as well in this case.

Algorithms↗

PubMed1994

Frequency synthesis of digital filters based on repeatedly applied unweighed moving average operations.

Simple formulae are presented for designing filters based on repeatedly applied moving average operations with unit coefficients. Design formulae are derived to synthesise the filter in a way that satisfies specified passband and stopband specifications. These filters are attractive because of the reasonable frequency characteristics, the computational efficiency of the design and filter algorithms, and the uncomplicated implementation in software.

Algorithms↗

PubMed1993

Treatment of diabetic autonomic neuropathy with an aldose reductase inhibitor.

To evaluate the effects of the aldose reductase inhibitor Ponalrestat (Statil) on diabetic autonomic neuropathy, a double-blind placebo controlled trial was carried out on a group of 34 diabetic patients with documented cardiac autonomic neuropathy. After a 4-week, placebo run-in period, patients were randomised for treatment with 600 mg Statil or placebo for another 24 weeks. Moreover, the reliability of the autonomic nerve function tests was investigated by comparing the results at onset and at week 4. Fifteen patients treated with Statil and 12 with placebo completed the study. Neither symptom scores nor cardiovascular reflexes, pupil reflexes and skin vasomotor reflexes improved after Statil therapy, which led us to conclude that Statil is not effective in the treatment of diabetic autonomic neuropathy. Reliability coefficients for cardiovascular reflexes and pupil reflex showed high values, ranging from 60% to 80%. Therefore these methods are recommended in future therapy trials.

Aldehyde Reductase↗

PubMed1993

The validity and reproducibility of the skin vasomotor test--studies in normal subjects, after spinal anaesthesia, and in diabetes mellitus.

Skin sympathetic vasomotor control can be examined in the extremities by the skin vasomotor test. In this test the change in skin blood flow and skin temperature in the hand and foot in response to a cold stimulus is utilized as an index of distal sympathetic nerve fibre integrity. This is of importance in conditions such as diabetes mellitus as peripheral autonomic neuropathy is associated with orthostatic hypotension and diabetic foot complications. The validity and reproducibility of the test as a marker of distal sympathetic nerve function has been studied. The test was performed in nine healthy control subjects and in nine subjects (undergoing minor surgery) after a sympathetic nerve conduction block (L2-L3) was achieved in the lower extremities by spinal analgesia. Changes in skin temperature (p < 0.001) and skin blood flow (p < 0.005) in responses to cooling were significantly larger in the control group than in the group with spinal analgesia. Repeated skin temperature measurements on 42 occasions (test-retest period of 4 weeks) in eight healthy and 34 diabetic subjects indicated a reliability coefficient of 80%. We conclude, therefore, that the skin vasomotor test provides a valid and reproducible quantitative assessment of skin sympathetic nerve function in upper and lower extremities.

Adult↗

PubMed1991

The cause of increased pupillary light reflex latencies in diabetic patients: the relationship between pupillary light reflex and visual evoked potential latencies.

In 42 diabetic patients the relationship between the latency of the pupillary light reflex and the pattern reversal visual evoked potential (P100) was examined. Fifty-five percent of diabetic patients had pupillary light reflex latencies above the normal range. In 19% the visual evoked potentials were prolonged when compared to the normal range. Latencies of pupillary light reflexes and VEPs showed no correlation. There was a minimal correlation between the presence of retinopathy and prolongation of both the pupillary light reflex and the visual evoked response latency (kappa coefficients respectively: 0.31, P less than 0.01 and 0.36, P less than 0.02). The presence of an increased pupillary light reflex latency was positively correlated with a reduced respiratory sinus arrhythmia (kappa coefficient: 0.58, P less than 0.0001). Increased VEP latencies showed no correlation with signs of cardiovascular autonomic neuropathy. We conclude that the afferent optic pathway can be affected in diabetic patients. However, prolongation of pupillary light reflex latency in diabetic patients is primarily due to an efferent pupillary defect and represents parasympathetic dysfunction.

Adult↗

PubMed1991

Cardiovascular autonomic function in multiple sclerosis.

In this study blood pressure (BP) and heart rate (HR) responses to standing and HR responses to deep breathing were assessed in 34 patients with clinically definite multiple sclerosis (MS) and 63 healthy subjects. Normal ranges, which were clearly age related for both HR responses, were obtained. The BP response to standing was abnormal in 13% of the MS patients, these patients demonstrating significant postural hypotension. The HR response to standing was abnormal in 28% of the MS patients, with a normal initial increase in heart rate and a significantly reduced reflex bradycardia. On deep breathing 36% of MS patients showed abnormal HR changes. The resting HR did not differ between both groups. Abnormalities of one or more tests were found in 53% of the MS patients. No relationship was found between abnormal cardiovascular autonomic responses and the symptoms, duration, severity and progression of the disease. Based on clinical and magnetic resonance imaging findings no indications were found for localisation of the autonomic disturbances in the brainstem. It is suggested that at least a part of the cardiovascular autonomic lesions in MS is located outside the brainstem, i.e. in supramedullary reflex pathways or in the spinal cord.

Adult↗

PubMed1990

Quantitation of skin vasomotor control in normal subjects and in diabetic patients with autonomic neuropathy.

Peripheral autonomic neuropathy in diabetes has been difficult to evaluate. We have developed a test to quantitate sympathetic skin vasomotor function in the extremities. Skin vasomotor reflexes were investigated after warming and cooling the left arm and recording changes in skin temperature as a measure of skin blood flow in the right hand and both feet. Twenty-three diabetic patients with cardiac autonomic neuropathy and 28 healthy control subjects were examined. In contrast to the healthy subjects, the diabetic patients showed reduced or even absent responses in skin temperature to both warming and cooling. The rate of skin temperature decrease for the hand and feet during cooling, which was used as the actual parameter to quantitate skin vasomotor control, was significantly reduced in the diabetic group as compared with the healthy control subjects. We conclude that this technique provides a simple non-invasive method for quantitating skin vasomotor function in the extremities of diabetic patients.

Adult↗

PubMed1989

[A patient with botulism caused by Clostridium botulinum type B].

A case of botulism type B acquired in The Netherlands is presented. The diagnosis was made on clinical grounds and positive mouse bio-assay. The patient was a man aged 37 years. Additional evidence was obtained by electromyography, single fibre electromyography and autonomic function tests. Antitoxin was administered without side effects. The clinical outcome was good.

Adult↗

PubMed1989

Autonomic and somatic peripheral nerve function and the correlation with neuropathic pain in diabetic patients.

Pupillary and cardiovascular autonomic functions were examined in 25 diabetic patients with and 25 diabetic patients without painful neuropathy. There were no significant differences between the groups with regard to age, duration of diabetes or glycaemic control. Vibratory perception, reflecting peripheral large fibre function, was more severely disturbed in the symptomatic group (P = 0.003). Thermal discrimination thresholds (TDTs), reflecting somatic small fibre function, were abnormal in all symptomatic patients and the difference between patients with and without symptoms was more pronounced (P less than 0.0001), than for large fibre function. The latency of the constriction reaction of the pupil (parasympathetic function) was prolonged in 17 symptomatic patients and in 6 patients without pain; it proved to be significantly more prolonged in the group with painful neuropathy (P = 0.001). Cardiovascular autonomic neuropathy was present in 29 patients, especially in patients with painful neuropathy (22 in the group with painful neuropathy, 7 in the group without pain). There was a significant correlation between results of TDT and respectively pupillary and cardiovascular autonomic function tests (kappa coeëfficient: 0.63 and 0.56, respectively, P less than 0.0001). We conclude that autonomic dysfunction is often present in patients with painful neuropathy. However, thermal sensory dysfunction is better correlated with the presence of symptoms than cardiovascular and pupillary autonomic dysfunction.

Adult↗

PubMedDate not supplied

Spectral analysis of spontaneous heart rate variation in diabetic patients.

In 28 diabetic patients and 62 control subjects spectral analysis of spontaneous beat-to-beat RR interval variations was performed. The spectral analysis focused on the dominant frequency of the mid-frequency band (0.04-0.12 Hz) or baro-oscillatory phenomenon (BOP). Compared with control subjects the dominant frequency of the BOP (BOP frequency) in the diabetic patients was lower (p less than 0.001), and the difference increased with age. The shift of the BOP frequency was positively correlated with the reduced variation in heart rate during deep breathing (r = 0.80, p less than 0.001) in the diabetic patients. These findings indicate that determination of the BOP frequency is a useful method for assessing cardiovascular autonomic function, supplementary to the known cardiovascular reflex tests. Measurement of the BOP frequency has the advantage that no active patient co-operation is required.

Adolescent↗

PubMedDate not supplied

Quantitative measurement of vibratory sense and temperature sense in patients with multiple sclerosis.

In this study the vibratory perception threshold (VPT) and the thermal discrimination threshold (TDT) were measured in 33 patients with clinically definite multiple sclerosis (MS). VPT values were abnormal in a majority of MS patients (68%). There was no relation between VPT and the severity of the disease. TDT values were elevated less frequently (30%); abnormal TDTs were found only in patients with severe disease. It is suggested that this can be explained by MS-plaques having predilection sites within the central nervous system and by differences in functional and morphological properties of sensory pathways. Quantitative measurements of VPT and TDT seem to be suitable techniques for the detection of minor sensory signs of central origin.

Adult↗