Biomedical subjects

F Mast

Publications and source records attributed to F Mast.

At least 19 recordsLinked to original sources

PubMed2001

Methods for determining the refractory period and excitable gap during persistent atrial fibrillation in the goat.

BACKGROUND: Recently, the temporal excitable gap during atrial fibrillation (AF) has been identified as a vulnerable parameter for cardioversion of AF. In this study, we evaluated 5 methods to measure the refractory period (RP(AF)) and the excitable period (EP(AF)) during persistent AF. METHODS AND RESULTS: In 11 goats instrumented with 83 epicardial atrial electrodes, persistent AF (43+/-34 days) was induced with a median AF cycle length (CL) of 98+/-14 ms. To measure RP(AF), premature stimuli were applied to the center of the electrode array on the right or left atrium. The RP(AF) measured by mapping of premature stimuli was 70+/-12 ms ("gold standard"). The RP(AF) determined during entrainment of AF was 77+/-17 ms (R(2)=0.88, P<0.01). Statistical analysis of the effects of synchronized stimuli (each coupling interval x100) on the AFCL histogram yielded an RP(AF) of 70+/-13 ms (R(2)=0.94, P<0.01). A further simplification was to apply slow fixed-rate pacing (1 Hz) during AF. For each stimulus (n=250 to 500), the paced AFCL was plotted against its coupling interval, and capture was determined by statistical shortening of the AFCL (RP(AF) 71+/-17 ms, R(2)=0.84, P<0.01). The 5th percentile of the AFCL histogram as an index of RP(AF) was 77+/-12 ms (R(2)=0.90, P<0.01). CONCLUSIONS: During persistent AF with an AFCL of 98+/-14 ms, the RP(AF) determined by mapping of synchronized premature stimuli (gold standard) was 70+/-12 ms, with an excitable period of 28+/-8 ms. Although the indirect methods to measure RP(AF) all correlated well with the gold standard, slow fixed-rate pacing seems to be the most attractive technique because of the ease of acquiring the data and the clear graphic result.

Animals↗

PubMed2001

Time course of atrial fibrillation-induced cellular structural remodeling in atria of the goat.

BACKGROUND: Previously we documented cellular structural changes of a non-degenerative nature in atrial myocytes after atrial fibrillation (AF) in the goat. The time course of these changes was not studied. METHODS AND RESULTS: Cellular structural changes were studied by light- and electron microscopy and immunohistochemistry in goat atria after 0-16 weeks AF. The first sign of cellular structural remodeling was a more homogeneous chromatin distribution, at 1 week of AF. Sub-structural changes in mitochondria and sarcoplasmic reticulum occurred gradually. Cellular degeneration was absent. The degree of myolysis and glycogen accumulation increased till 8 weeks of AF and did not increase further from thereon. After 16 weeks of AF, 42% of the myocytes in the right atrial free wall were affected by myolysis. The diameter of the atrial myocytes increased. Dedifferentiation of the atrial myocytes was suggested by altered expression patterns of structural proteins, such as the disappearance of cardiotin (1 week), the A-I junctional part of titin (4 weeks), desmin at the intercalated disk (ID) (8 weeks) and a gradual re-expression of alpha-smooth muscle actin. CONCLUSION: Remodeling of the cellular ultrastructure in atrial myocardium of the goat develops progressively during AF. Re-expression of fetal proteins indicate dedifferentiation of atrial myocytes, analogous to observations in hibernating myocardium of the ventricle.

Actinin↗

PubMed2000

Widening of the excitable gap during pharmacological cardioversion of atrial fibrillation in the goat: effects of cibenzoline, hydroquinidine, flecainide, and d-sotalol.

BACKGROUND: Previous studies suggest that the antifibrillatory action of class I and III drugs is due to prolongation of the atrial wavelength. The aim of the present study was to directly evaluate the electrophysiological action of antifibrillatory drugs in a goat model of chronic atrial fibrillation (AF). METHODS AND RESULTS: Six goats were instrumented with multiple atrial electrodes, and sustained AF was induced by electrical remodeling. During sustained AF, the effects of intravenous infusion of cibenzoline, hydroquinidine, flecainide, and d-sotalol on AF cycle length (AFCL), refractory period (RP(AF)), conduction velocity (CV(AF)), pathlength (PL(AF)), wavelength (WL(AF)), temporal (AFCL-RP(AF)), and spatial (PL(AF)-WL(AF)) excitable gap were studied. The RP(AF) was measured by determining the earliest moment at which single stimuli could capture the fibrillating atria. CV(AF) was measured during regional entrainment of AF. Contrary to our expectation, cardioversion of AF could not be attributed to prolongation of WL(AF). Hydroquinidine and d-sotalol did not affect WL(AF) significantly, whereas cibenzoline and flecainide even shortened WL(AF) by 18% and 36%, respectively. PL(AF) was increased by hydroquinidine and d-sotalol by 30%, whereas cibenzoline and flecainide did not prolong PL(AF). The only parameter that correlated consistently with cardioversion of AF was a widening of the temporal excitable gap (cibenzoline 176%, hydroquinidine 105%, flecainide 86%, d-sotalol 88%). CONCLUSIONS: Pharmacological cardioversion of AF cannot be explained by prolongation of WL(AF). An alternative explanation for the antifibrillatory effect of class I and III drugs may be a widening of the temporal excitable gap.

Action Potentials↗

PubMed2000

Preferential depression of conduction around a pivot point in rabbit ventricular myocardium by potassium and flecainide.

INTRODUCTION: During reentrant arrhythmias, the circulating wavefront often makes a sharp turn around a functional or anatomic barrier. We tested the hypothesis that lowering the safety factor for conduction by high K+ or flecainide preferentially depresses conduction of sharply turning wavefronts. METHODS AND RESULTS: In 16 Langendorff-perfused rabbit hearts, a thin layer of anisotropic ventricular myocardium was made using a cryoprocedure. In this layer, a linear radiofrequency lesion was made parallel to the fiber orientation. The tip of the lesion was extended by a short incision. U-turning wavefronts were initiated by pacing at one side of the lesion. A mapping electrode (240 electrodes, resolution 350 to 700 microm) was used to measure conduction times and velocity of planar waves (longitudinal and transverse) and U-turning wavefronts. The safety factor for conduction was lowered by high potassium (8, 10, and 12 mmol/L) and flecainide (1 and 2 mg/L). On average, high potassium and flecainide increased the conduction times of U-turning wavefronts 1.6 times more than longitudinal or transverse planar wavefronts (P < 0.01). At a critical lowering of the excitatory current, functional conduction block occurred at the pivot point, which forced the wavefront to make a longer U-turn. In these cases, the total U-turn conduction time increased from 27+/-9 msec to 75+/-37 msec. About 40% of this delay was caused by a shift of the pivot point and consequent lengthening of the returning pathway. CONCLUSION: Lowering the amount of excitatory current by potassium or flecainide preferentially impairs U-turn conduction. The occurrence of long delays and conduction block at pivot points may explain the mode of action of Class I drugs.

Animals↗

PubMed1999

Visual mental imagery interferes with allocentric orientation judgements.

The subjective visual vertical is determined when a subject judges the orientation of an indicator (e.g. a short line segment) as apparently vertical. The mechanisms that underlie this perceptual performance are usually assumed to be based predominantly on bottom-up processing of primarily vestibular and visual information. However, it is also possible that top-down processes play a role in such abilities. We used an interference paradigm in order to investigate the effects of mental images on the perception of the visual vertical. The results demonstrate for the first time that visual mental imagery can exert the same directional influence on the subjective visual vertical as a perception of the corresponding stimulus.

Adolescent↗

PubMed1999

Assessing otolith function by the subjective visual vertical.

The effects of peripheral vestibular diseases on the subjective visual vertical (SVV) are resumed and provide the basis for some insights into the otolith pathophysiology. With a normal range of 0 +/- 2 deg (when measured in an upright body position), the SVV was shifted by 11 +/- 6 deg toward the ipsilateral ear in 40 patients following an acute unilateral vestibular deafferentiation (UVD), but in the opposite direction in 9 of 52 patients after stapes surgery. These opposite effects suggest a push-pull mechanism of the pairs of otolith organs with respect to the SVV. The dissociation between the SVV and the perception of body position indicates influences by unconscious reflexive mechanisms such as ocular cyclotorsion on the SVV. In chronic UVD patients, lateral shifts of the subjects during constant angular velocity rotation into various eccentric positions (+/- 16 cm) revealed a shift of the "center of graviception" close to the remaining intact contralateral inner ear. To date, this seems to be the most consistent test for clinical identification of a chronic compensated unilateral loss of otolith function. The findings regarding asymmetries in otolithic sensitivity to medially and laterally directed roll-tilts remain controversial, probably mainly because of influences of extravestibular cues.

Afferent Pathways↗

PubMed1999

Repetitive electrical remodeling by paroxysms of atrial fibrillation in the goat: no cumulative effect on inducibility or stability of atrial fibrillation.

INTRODUCTION: Episodes of atrial fibrillation (AF) are known to cause both a rapid reduction in atrial refractoriness (atrial electrical remodeling) and a more delayed increase in AF stability in the chronic goat model. The aims of this study were to examine (1) the hypothesis that an AF-induced increase in AF stability might be due to a mechanism with a longer onset and offset than that of changes in refractoriness and (2) the possibility that repeated paroxysms of maintained AF might cause a cumulative increase in AF stability independent of changes in atrial refractoriness. METHODS AND RESULTS: AF was maintained by rapid atrial pacing in seven goats for three consecutive 5-day periods, each separated from each other by 48 hours of sinus rhythm. Assessments of atrial refractory periods, conduction velocity, AF inducibility, and duration of individual episodes of AF were attempted at intervals throughout the protocol. Forty-eight hours of sinus rhythm was just sufficient for refractoriness changes to fully reverse in all goats, with no evidence of any "residual" increase in AF inducibility. There was no significant difference among any of the three periods of pacing-maintained AF with regard to time to develop episodes of AF of 60-second duration (22.1+/-13, 23.8+/-16, and 30.3+/-29 hours), 1-hour duration (56.6+/-28, 61.3+/-31, and 60.1+/-32 hours), or 24-hour duration (84.0+/-31, 87.0+/-33, and 83.5+/-32 hours). CONCLUSION: There is no evidence for a cumulative effect of AF paroxysms on AF inducibility or stability independent of changes in refractoriness. These findings highlight the importance of atrial refractoriness as a potential target for antiarrhythmic strategies aimed at inhibiting the self-perpetuation of AF.

Action Potentials↗

PubMed1999

Chronic unilateral loss of otolith function revealed by the subjective visual vertical during off center yaw rotation.

Assessing the subjective visual vertical, SVV, in a static upright position is an easy clinical test in which a deviation of some 10 degrees from true vertical indicates an acute loss of unilateral (otolithic) vestibular function on the side to which the SVV is tilted. Because this deviation of the SVV is compensated during the following months, patients with chronic unilateral vestibular loss do no longer differ from normal subjects. This study presents an experimental set-up that allows for clear detection of compensated chronic loss of unilateral otolithic function by testing the SVV. 21 normals and 17 unilaterally vestibular deafferentiated (UVD) patients (vestibular neurectomies) were first rotated on a human centrifuge about an earth vertical yaw axis through the midsagittal plane of the head (240 degrees/s). This induced tilts of the gravito-inertial force (GIF) vectors, which differed at the two inner ears by 8 degrees. During constant velocity rotation, the subjects were moved in pseudo-randomized steps laterally up to 16 cm apart from the rotation axis, inducing roll tilts of the GIF vectors up to 16 degrees. Normal subjects set their SVV to pre-centrifugation values at positions with the midsagittal plane of their head close to the rotation axis, while chronic UVD patients indicated pre-centrifugation values during positions with the rotation axis 5.9 +/- 2.5 cm paramedian on the side of the intact ear. Tilts of the GIF vectors shifted the SVV with a gain of 0.70 in normals and only 0.32 in UVD patients. Roll gains for laterally directed GIF vectors relative to the intact inner ear did not differ from medially directed roll gains in the UVD patients. The roll gains observed in this experimental set-up were lower than those observed with static body tilts or during eccentric rotation with a larger radius, which might be at least partially due to conflicting stimulation between otolithic and extra-vestibular cues.

Adult↗

PubMed1997

Mitochondrial function is not decreased in stunned papillary muscle at 20 degrees C.

It is unclear to what extent mitochondrial function in vivo is changed after brief anoxia. Heat measurements allow evaluation of mitochondrial function within intact cardiac muscle. Heat production was determined using fast metal-film thermopiles, during contraction and post-contractile recovery in control and stunned superfused rabbit papillary muscles at 20 degrees C. Heat rate was measured for a train of ten twitches (0.2 Hz) before anoxia and after 40 min anoxia followed by 2 h of normoxic recovery. During anoxia muscles were stimulated at 0.2 Hz (group A) or at 1.0 Hz (group B). A normoxic control group C was stimulated at 0.2 Hz. After 2 h recovery, tension was 77 +/- 5% (S.E.M.), 72 +/- 7% and 94 +/- 3% of initial values, for group A, B and C respectively, indicating stunning by anoxia. The economy of contraction or the ratio of recovery heat to initial heat did not change significantly in groups A and B when compared with control, indicating that stunning with this protocol is not associated with mitochondrial uncoupling. Post-contractile recovery heat initially decayed exponentially with time constant 24.9 +/- 2.2 s for all groups and with 22.7 +/- 1.1, 22.0 +/- 0.8 and 41.7 +/- 4.4 s at the end for group A, B and C respectively. The cause of the remarkable slowing of the recovery rate over time in controls is unknown, but is mimicked by blocking fatty acid utilization. No slowing of metabolic recovery is observed in the stunned papillary muscles. We conclude that stunning is not associated with a decrease in mitochondrial function or oxidative capacity in cardiac muscle.

Analysis of Variance↗

PubMed1997

Effects of lidocaine, ajmaline, and diltiazem on ventricular defibrillation energy requirements in isolated rabbit heart.

The majority of patients with implanted cardioverter defibrillators (ICD) require antiarrhythmic (AR) drugs. ARs may increase defibrillation energy requirements. This study investigated the effects of lidocaine, ajmaline, and diltiazem on ventricular defibrillation energy needs. In 24 isolated rabbit hearts, the 50 and 80% successful defibrillation energy (ED50, ED80) was calculated in four phases: predrug baseline condition (phase 1), and phases 2, 3, and 4 with increasing concentrations of lidocaine, ajmaline, diltiazem (n = 18). Control experiments (n = 6) with only Tyrode's solution infusion indicated that the preparation was stable over time. Defibrillation energy requirements significantly (p < 0.05) increased with all ARs. Low, medium, and high lidocaine concentrations increased ED50 and ED80 to 146, 223, and 312% and 139, 207, and 285%, respectively. Ajmaline increased ED50 and ED80 to 133, 175, and 251% and 135, 208, and 285%, respectively. Diltiazem increased ED50 and ED80 by 175, 236, and 334% and 158, 212, and 286%, respectively. The results of this study demonstrate a dose-dependent increase in defibrillation energy requirements by using lidocaine, diltiazem, and ajmaline. In patients with ICDs, administration of these drugs might cause a critical increase in defibrillation energy requirements, resulting in device failure.

Ajmaline↗

PubMed1997

[Resident-oriented nursing care in nursing homes. Testing of a measuring tool].

The findings of an investigation of a patient oriented nursing system in nursing homes are reported in this article. The direct translation of the Dutch word for this type of nursing system is 'Integrated Nursing'. Central to this study are the two premises of Integrated Nursing, namely patient allocation and working in a systemical manner, which is similar to the nursing process. The aim of this study was to determine the validity and reliability of an instrument which was developed to measure the degree of Integrated Nursing in nursing homes. For this purpose, an existing instrument designed for use in general hospitals was modified for use with nursing homes. The modified instrument was tested in two nursing homes: one with a task-oriented nursing system and the other with Integrated Nursing. The instrument was used in the form of both questions and observations. It was concluded that the modified instrument which consists of a Patient Allocation SubScale and a Nursing Process SubScale was reliable and valid.

Aged↗

PubMed1996

Perceived body position and the visual horizontal.

This contribution examines the relation between the subjective visual vertical, the subjective visual horizontal, and the perceived body position of human subjects. Firmly fixed on a tiltable chair with head and torso restrained, 11 healthy subjects were rolled sideways and indicated their subjective horizontal body position. In these positions the subjects were also asked to adjust a luminous line alternately to the vertical and to the horizontal. The adjustments of the subjective horizontal body position cluster around a mean of 96.3 degrees with a remarkably broad range (SD: 19.7 degrees). In the subjective horizontal body position, the luminous line does not appear horizontal when in line with one's own spinal axis. It is set further down by 27.4 degrees on average and, therefore, perpendicular to the subjective visual vertical. This finding supports the idea that the judgement of the own body position and the judgement of the orientation of a seen object respective to gravity are based on different references. Contradictory to other investigations [23,24], is the empirical fact that the individual subjects were not able to adjust the horizontal body position with the reported accuracy (range of mean adjustments 77.5 to 117.6 degrees).

Adult↗

PubMed1996

Can a unilateral loss of otolithic function be clinically detected by assessment of the subjective visual vertical?

Asymmetries in the settings of the subjective visual vertical after unilateral vestibular neurectomy during eccentric centrifugation [3] might provide a clinical test for unilateral otolithic function. This study investigates whether these asymmetries can also be revealed by a technically much easier practicable roll tilt of the subject relative to gravity instead of a roll tilt of the gravitational force on a human centrifuge. Twenty-seven normal subjects and 13 patients before surgery indicated verticality very accurately in the upright position. In 26 degrees roll positions (subjects seated on a slanted chair), they were only slightly more variable with no asymmetries larger than 5.3 and 7.8 degrees in normals and preoperative patients, respectively, between the roll positions toward the healthy and toward the affected ear. One week after surgical unilateral vestibular deafferentation, there was a consistent shift (mean 11.9 degrees) of the subjective vertical toward the affected ear in all patients and in all body positions. When the settings in the two roll tilt positions were referred to the setting in upright position, the group means of the patients were symmetrical although single subjects revealed asymmetries up to 22.4 degrees. Only one of four patients who were tested also during eccentric rotation revealed an important asymmetry with decreased sensitivity for tilts of the gravitational vector toward the affected ear. Measuring the subjective visual vertical assesses only asymmetrical tonic otolithic input, while a simple clinical test for unilateral otolithic sensitivity still has to be found.

Adolescent↗

PubMed1995

Hemodynamic changes in HH stage 34 chick embryos after treatment with all-trans-retinoic acid.

To obtain insight into the hemodynamics of abnormal cardiac development, a chick embryo model was recently developed in which a spectrum of double outlet right ventricle was induced with all-trans-retinoic acid. In Hamburger and Hamilton (HH) stage 34 white Leghorn chick embryos, we simultaneously measured dorsal aortic flow velocities with a 20 MHz pulsed Doppler velocity meter and vitelline artery blood pressures with a servonull system. These measurements were performed in embryos treated at HH stage 15 with 1 microgram of all-trans-retinoic acid (n = 47), or with the solvent DMSO (n = 15), and in control embryos (n = 21). After the wave form recordings were collected, all embryos were examined histologically. Embryos treated with all-trans-retinoic acid showed in 15 cases hearts with a rightward positioned aorta with an additional subaortic ventricular septal defect and 32 cases without septation abnormalities of the heart. The hemodynamic data were correlated with the morphology. Statistical comparison was performed between control and experimental values. There was no significant discrepancy in hemodynamics of sham-operated and control embryos. Heart rate, peak systolic and mean velocities, peak systolic and mean blood flows, and peak acceleration and stroke volume were reduced in embryos treated with all-trans-retinoic acid (p < 0.01). Furthermore, in the presence of a subaortic ventricular septal defect the diameter of the dorsal aorta was reduced. Pressure readings were not statistically significant. Our findings suggest that the hemodynamic changes are the result of a decrease in cardiac contraction force.

Animals↗

PubMed1993

Geometrical reconstruction of images obtained with electronic endoscopy.

We use an electronic video endoscope (Fujinon EG7-HR2) to image the mitral valve in situ in an isolated pig heart preparation. From video recordings, images are digitized and analysed with a computer. A complication encountered during the study concerned the geometric wide angle distortion caused by the device. The present paper describes a method developed to reconstruct the image, and to correct for this distortion. In order to quantify the relation between object and image, model equations were formulated based on mild assumptions. Points in object space are transformed through a non-linear relation to corresponding points in image space. Furthermore, an oblique camera view, and an aspect ratio correction factor, are accounted for. As a test object, a regular grid of points was recorded at several distances from the camera. The images of the grid points were digitized, and the model equations were fitted to these data. From test measurements, carried out in air as well as in water, it was concluded that the distortion could be quantified by three parameters. Application of the straightforward correction procedure enables us to obtain quantitative information from endoscopic images.

Animals↗

PubMed1993

Hemodynamic parameters of stage 20 to stage 35 chick embryo.

Hemodynamic parameters of the chick embryo from stage 20 (3 d of a 21-d incubation) up to stage 35 (8 d) are described. Normal values of dorsal aortic flow velocity wave forms were measured with a 20-MHz directional-pulsed Doppler velocity meter that was validated to be accurate above 5 mm/s. An analysis of variance was carried out for each of the flow velocity parameters. The correlation coefficient that represents the reproducibility was satisfactory (r > 0.90). There was a 17-fold rise in mean dorsal aortic blood flow (mm3/s). Heart rate doubled from 123 +/- 12 to 239 +/- 8 bpm, and stroke volume increased from 0.14 +/- 0.08 to 1.28 +/- 0.55 mm3. A stage-related rise was seen in peak systolic and mean velocities and peak acceleration. These data may serve as a basis for flow velocity wave form investigation and interpretation in developmental stages of cardiac malformations.

Animals↗

PubMed1992

An analysis of ocular counterrolling in response to body positions in three-dimensional space.

Four normal subjects underwent ocular counterrolling testing in a tiltable chair. Measurements were taken in 62 different body positions in steps of 30 degrees varied rolls and pitches. In each body position the eyes were recorded on video and their roll angle was determined automatically by computer analysis. The ocular counterrolling profile showed a periodic characteristic with maximal amplitude at roll tilts of 60 degrees. In this study we can clearly show that the eyes' rolling response is not systematically affected when lateral body tilts are combined with any tilts in the pitch direction. This undoubtedly implies that the ocular counterrolling was mainly stimulated by the subject's roll angle. As an empirical contribution, this study provides new data specially to be used in modelling and simulating the function of otolith organs.

Adult↗

PubMed1990

Myocardial force production and energy turnover in anoxia.

ATP turnover of isolated rabbit papillary muscles, contracting isometrically at 20 degrees C, was determined in oxygen and during 40 min of exposure to nitrogen (anoxia). Stimulus frequency was 0.2 hertz (Hz) in oxygen and 0.2 or 1.0 Hz in nitrogen. In oxygen, ATP turnover was determined from oxygen consumption using a P/O2 ratio of 6.3. The time-dependent rate of ATP turnover in nitrogen was found from the production of lactate, and the changes in adenine nucleotides and phosphocreatine, measured in rapidly frozen preparations at different time-points during the anoxic period. A P/lactate ratio of 1.5 was used. In muscles stimulated at 0.2 Hz, twitch force dropped during the anoxic period to 33% while force production of muscles stimulated at 1.0 Hz stopped completely. However, in the latter muscles, resting force rose to 19% of the twitch force in oxygen. The rate of ATP hydrolysis in anoxia depended strongly on stimulus frequency, indicating that it is not solely determined by the glycolytic capacity. In the 0.2 Hz-stimulated muscles the decrease in energy turnover occurred in parallel with the drop in force. However, the rise in resting force in muscles stimulated at 1.0 Hz occurred when ATP turnover was close to zero. It was concluded that anoxia hardly affects the energy required for twitch force production, but that the rise of resting force measured when twitch force had disappeared occurred when the rates of cross-bridge cycling and calcium turnover were very low.

Adenine Nucleotides↗