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Biomedical subjects

W N van Asten

Publications and source records attributed to W N van Asten.

50 records · Page 3Linked to original sources
PubMed1991

Assessment of aortoiliac obstructive disease by Doppler spectrum analysis of blood flow velocities in the common femoral artery at rest and during reactive hyperemia.

Aortoiliac obstructive disease was assessed by Doppler spectrum analysis of blood flow velocities in the common femoral artery measured both at rest and during reactive hyperemia. The intraarterial femoral artery pressure measured at rest and during reactive hyperemia served as the "gold standard" for the definition of a hemodynamically significant aortoiliac stenosis. Our results, obtained from 93 patients (136 limbs), showed that differences between Doppler spectra obtained from limbs with a hemodynamically significant aortoiliac stenosis and those from limbs without were more pronounced during reactive hyperemia than at rest. The best assessment of aortoiliac obstructive disease could be obtained with a combination of parameters derived from Doppler spectra measured at rest and during reactive hyperemia. With these parameters, obtained by multivariate analysis, 85% of the limbs were diagnosed correctly compared with the gold standard. If angiographic data were added to the gold standard, even 91% of the limbs were diagnosed correctly. We conclude that analysis of Doppler spectra-obtained noninvasively from the common femoral artery at rest and during reactive hyperemia provides an accurate hemodynamic assessment of the aortoiliac segment.

Aortic Diseases↗
PubMed1990

Postural responses to simulated moving environments are not invariant for the direction of gaze.

Postural responses were measured for observers instructed to maintain an erect position when viewing a visual scene, which stimulated motion of the observer relative to a corridor with texture on the walls. Both the direction and amplitude of the postural responses appeared to depend on the fixation direction of the observer. This result indicates that postural responses are not invariant with respect to fixation direction. Our results suggest that not one of the frequently suggested features in the optical flow in particular is used to maintain posture but rather that a combination of several optical flow components, that have been suggested in the literature, is relevant.

Fixation, Ocular↗
PubMed1990

Detrimental sequelae on the hemodynamics of the upper left limb after subclavian flap angioplasty in infancy.

The long-term effect of two surgical techniques for repair of coarctation of the aorta in infancy, namely, resection and end-to-end anastomosis (RETE) and subclavian flap angioplasty (SFA) on the blood supply of the upper left limb, was quantified by Doppler spectrum analysis of blood flow velocities in the left brachial artery at rest and during postocclusive reactive hyperemia. Twenty-three patients participated in this study: nine patients after SFA (median age, 8 years), 14 patients after RETE (median age, 8 years), and 10 control subjects (median age, 9.5 years). At rest, a highly significant decrease of blood flow velocities in the left brachial artery was measured in all patients of the SFA group compared with those of the RETE and control groups, as documented by various Doppler spectrum parameters: maximal frequency of advancing curve (p = 0.0001), pulsatility index (p = 0.0005), and resistance index (p = 0.039). During reactive hyperemia, a moderate capacity of physiologic augmentation of blood flow velocities was observed in five patients of the SFA group. This capacity was marginal in two patients with complaints of claudication in the left upper limb during strenuous exercise, which can be related to the number of branches of the left subclavian artery ligated during operation. This study indicates that SFA in infancy may lead to compromised hemodynamics of the upper left limb with potential for symptoms of ischemia during exercise.

Anastomosis, Surgical↗
PubMed1990

A comparison of coarctation resection and subclavian flap angioplasty using ultrasonographically monitored postocclusive reactive hyperemia.

The reported relatively high incidence of early restenosis at the coarctation repair site with subclavian flap angioplasty, especially in infants less than 3 months of age, prompted a physiologically oriented analysis of relief of obstruction from coarctation after subclavian flap angioplasty versus resection and end-to-end anastomosis in infancy. Twenty-one patients who had undergone repair of coarctation in infancy by either subclavian flap angioplasty (nine patients) (median age 8 years) or resection and end-to-end anastomosis (12 patients) (median age 8 years) were evaluated by Doppler spectrum analysis of the blood flow velocities in the femoral artery at rest and during reactive hyperemia. The median resting right upper to lower limb systolic pressure difference (with interquartile range) was similar in the angioplasty, resection and anastomosis, and control groups: -5 mm Hg (18 mm Hg), 0 mm Hg (12 mm Hg), and -2.5 mm Hg (10 mm Hg), respectively. Also, similar resting values for the maximum frequency of the advancing curve and the pulsatility and resistance indices were measured in the three groups. During reactive hyperemia of the leg, however, a significant hemodynamic obstruction across the repair site became clinically manifest in the angioplasty group only, as documented by a lower pulsatility index in comparison with the control group (p = 0.01, Mann-Whitney U test). Comparison of the hemodynamic results between the angioplasty and resection and anastomosis groups in subdivisions of infants operated on at an age of less or greater than 3 months, both at rest and during reactive hyperemia, showed, already at rest, a significantly lower value for the pulsatility index in the former angioplasty subdivision (p = 0.05, Student's t test), indicating a significant resistance at the coarctation repair site in the angioplasty patients operated on before the third month of life. A disadvantage of angioplasty (compared with resection and anastomosis) was noted when angioplasty was performed before the third month of life, and an unequivocal lack of advantage was noted when performed beyond that period regarding relief of obstruction from coarctation. In addition, a definite potential for adverse long-term effects on the hemodynamics of the left upper limb after subclavian flap angioplasty in infancy has been documented. For these reasons we prefer to perform resection and end-to-end anastomosis for repair of coarctation in infancy.

Adolescent↗
PubMed1989

Evaluation of renal allograft function by Doppler spectrum analysis. A preliminary study.

A decreased renal function is rather common after renal transplantation. The causes of this decreased function are diverse and difficult to differentiate. Yet, duplex examination, and especially quantitative Doppler spectrum analysis of the blood velocities in the renal artery, may be an effective method for differentiating between some of these causes. Forty-five renal transplant recipients were included in this preliminary study. Doppler spectra were recorded from the renal artery to the allograft. Parameters were derived from every Doppler spectrum in order to characterize each spectrum. Renal allograft function was evaluated on the basis of a number of clinical parameters. A significant correlation was found between the clinical parameters and the Doppler spectrum parameters indicative for changes in the peripheral resistance. Patients with a normal renal allograft function showed Doppler spectra with a high diastolic flow, typical of a vascular bed with a low peripheral resistance. Patients with a decreased renal allograft function caused by a stenosis in the renal artery could be distinguished by a low peak velocity and a low pulsatility index. A decreased allograft function caused by allograft rejection or cyclosporin nephrotoxicity also led to characteristic arterial flow disturbances. In these cases, the peripheral resistance was increased, and this was primarily reflected in a decrease in the diastolic blood velocity. We conclude that quantitative analysis of the blood velocities in the renal artery by Doppler spectrum analysis seems to be a useful, noninvasive diagnostic tool that discriminates between some of the causes of a decreased renal allograft function.

Adolescent↗
PubMed1989

How accurate are high thigh narrow cuff pressure measurements in the assessment of aorto-iliac obstructive disease?

Thigh cuff pressure measurements are commonly used as a diagnostic method in the assessment of the aorto-iliac (AI) segment of patients with arterial obstructive disease. For a reliable assessment of the AI segment the use of a narrow cuff placed high on the thigh has been advocated. Although this method is commonly used, opinions on its diagnostic value are very divergent. To investigate its diagnostic value the pressure measured with a high thigh narrow cuff was compared with the intra-arterial pressure of the common femoral artery measured at rest and during reactive hyperaemia. Furthermore, the accuracy of these thigh pressures for detecting haemodynamically significant (HDS) AI stenoses was examined. The influence of an occlusion of the superficial femoral artery (SFA) on the pressure measurements was also studied. A correlation coefficient of 0.64 (P less than 0.05) was found between the femoro-brachial index (FBI) at rest and the thigh-brachial index (TBI). Using the TBI as a criterion for detecting a HDS AI stenosis, an accuracy of 73% could be obtained. Furthermore, it appeared that an occluded SFA could influence the pressure measurements dramatically. For clinical practice a TBI less than 0.90, in the presence of a patent SFA, ensures the presence of an HDS AI stenosis. A TBI greater than 1.35 suggests that the AI tract is normal, irrespective of the condition of the SFA. All other values of TBI should be interpreted with caution and only used as a decisive diagnostic method for the assessment of the haemodynamics of the AI segment in combination with other tests.

Adult↗
PubMed1988

Postural adjustments induced by simulated motion of differently structured environments.

We have investigated how visual information of a scene, moving along the line of sight of a subject, affects postural readjustments made by a subject when instructed to maintain an upright posture. Two different types of stimulus patterns were presented each inducing a different optic flow field. In one case an optic flow field was induced by simulating motion of a subject relative to a wall and in the second case by stimulating motion of a subject through a tunnel. In both cases clear effects on postural balance were observed. It suggests that postural responses are invariant for the structure of the moving environment. The amplitude of the postural responses did not depend on the velocity of the simulated motion, and therefore did not depend on the absolute magnitude of the optic flow components. The amount of texture in the moving scene proved to be an important factor. In addition, it was found that the control of postural balance is not exclusively dominated by information provided by the peripheral part of the subject's visual field. Moreover, the results indicate that the divergence component in the optic-flow field alone is not sufficient to control posture in forward/backward direction.

Humans↗
PubMed1988

The effect of isoluminant and isochromatic stimuli on latency and amplitude of saccades.

When two stimuli are presented in different positions successively at short time intervals saccadic eye movements are usually directed at intermediate positions. This phenomenon of "averaging" of saccadic eye movements has been studied in responses to double-step target displacements in different stimulus conditions. In these conditions isoluminant and isochromatic stimuli were used with variable contrast and at different background luminances. Although the critical duration of temporal summation differed considerably in these stimulus conditions the duration of the phenomenon of "averaging" remained the same in all conditions. This indicates that temporal properties of the sensory system are not the prime cause of "averaging". Moreover, the onset time of "averaging" relative to the second target displacement turned out to be highly correlated with the mean latency of saccades in the different conditions. The implications of the results for models of oculomotor control are discussed.

Color↗
PubMed1988

Postural movements induced by rotations of visual scenes.

The effect of visual information processing of a rotating visual scene on postural responses of a standing subject was studied. Rotation of a scene induced postural sway movements involving rotations in the ankle joint. For modulation frequencies of rotation below 0.3 Hz, a clear correlation was found between the visual stimulus and the postural movements in the lateral direction. The amplitude of postural movements appeared to be independent of the angular velocity of the rotation of the scene if the angular velocity exceeded 5 deg/sec for sinusoidally modulated rotations or 10 deg/sec (rms values) for randomly modulated rotations. To facilitate distinction between the contributions from visual information processing of the incoming visual stimuli and from the motor system, a model is presented that explains some aspects of visuo-motor interaction.

Adult↗
PubMedDate not supplied

Iliac artery stenosis after kidney transplantation.

In human kidney transplantation hypertension and renal dysfunction are common complications. Diagnosis of vascular involvement may frequently be necessary. Although iliac artery stenosis is a rare complication after renal transplantation, it can be the cause of hypertension and renal dysfunction. Because colour duplex scanning is a repeatable non-invasive technique, it may provide a useful tool in establishing a diagnosis of iliac artery stenosis in patients with hypertension and/or renal dysfunction. We present four cases of iliac artery stenosis in kidney allograft recipients. Colour duplex scanning was used in these patients to detect and localize the stenosis. Quantitative analysis of Doppler spectra was used to compare the Doppler spectrum waveforms obtained from both femoral arteries and from the kidney allograft arteries of these patients with the normal range. This normal range was determined from Doppler spectra obtained in a control group of 21 kidney allograft recipients. Clinical data, arterial DSA, and the outcome of treatment were used to validate colour duplex findings in the patients with iliac artery stenosis. Quantitative analysis of Doppler spectra showed differences between the femoral artery on the affected side and the contralateral side outside the normal range. In three patients the iliac artery stenosis was located proximal from the anastomosis with the kidney allograft artery and in these three patients Doppler parameters obtained from the allograft artery were also outside the normal range. In one patient the stenosis was located distally from the anastomosis with the kidney allograft artery. In this case Doppler spectra from the kidney allograft artery were within the normal range.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗