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Biomedical subjects

W Wieling

Publications and source records attributed to W Wieling.

At least 91 records · Page 5Linked to original sources
PubMed1991

Prediction of tonic parasympathetic cardiac control using respiratory sinus arrhythmia: the need for respiratory control.

Respiratory sinus arrhythmia (RSA) has received much attention in recent years due to the large body of evidence indicating that variations in this phenomenon represent alterations in parasympathetic cardiac control. Although it appears that respiratory sinus arrhythmia is mediated by vagal mechanisms, the extent to which the well-known respiratory influences (i.e., rate and tidal volume) on respiratory sinus arrhythmia (in altering its magnitude) may moderate the relationship between RSA and cardiac vagal tone has never been systematically studied. We addressed this issue by examining intraindividual relationships among RSA magnitude, respiration (rate and tidal volume), and heart period among six healthy male adults after intravenous administration of 10 mg propranolol, a beta-adrenergic blocker. Subjects were exposed to various behavioral tasks which altered all physiological variables measured. Variations in heart period after beta blockade were assumed to be predominantly vagally mediated. Within-subject regression analyses consistently showed that respiratory parameters influenced RSA magnitude, but not tonic variations in beta-blocked heart period, suggesting that respiratory-mediated RSA alterations are not associated with changes in cardiac vagal tone. Only when respiratory variables were statistically controlled was there evidence of a reasonable correspondence between beta-blocked heart period and RSA amplitude, providing support for the idea that respiratory parameters need to be controlled when using RSA amplitude as an index of cardiac vagal tone. Repeated-measures analyses of variance of mean levels of heart period and respiratory sinus arrhythmia across subjects supplemented and supported the intraindividual results. These findings point to the importance of controlling for respiratory parameters when using respiratory sinus arrhythmia as a cardiac vagal index.

Adult↗
PubMed1991

Initial circulatory responses to changes in posture: influence of the angle and speed of tilt.

To assess if changes in the angle or speed of tilt could account for the differences between the initial (first 30 s) circulatory responses induced by active and passive changes in posture, as found in previous studies, we investigated the initial heart rate and blood pressure responses induced by stand up from supine and various head-up tilt manoeuvres in 12 healthy, male subjects. Comparison was made between 70 degrees head-up tilt in 3 s, 90 degrees head-up tilt also in 3 s and 70 degrees head-up tilt in 1.5 s, using an automatic pneumatic-driven tilt table with foot support. It was found that the initial heart rate and blood pressure responses induced by the three tilt manoeuvres were almost identical in time course and amplitude, but significantly different from those induced by stand up. The results of this study prove that regardless of the angle and speed of tilt, the initial circulatory responses induced by passive changes in posture are essentially different from the responses induced by active changes in posture.

Adult↗
PubMed1991

Circulatory responses to stand up: discrimination between the effects of respiration, orthostasis and exercise.

The initial circulatory responses to an active change in posture (stand up from supine) were compared with the responses induced by a passive change in posture (head-up tilt) and a burst of muscular exercise on a bicycle ergometer (upright cycling) in order to differentiate between exercise- and orthostasis-induced effects. In eight subjects heart rate responses and in four subjects intra-arterial pressure transients were measured. In addition the effects of respiration on heart rate responses to the three manoeuvres were assessed. Both stand up and cycling induced almost superimposable and pronounced heart rate responses lasting for about 30 s. This contrasts with the more gradual increases following head-up tilt. Changing the respiratory phase during the performance of the manoeuvres exerted its effect on heart rate responses in the first 5 s only. Like stand up, cycling induced a transient blood pressure fall lasting for 30 s on average. As both manoeuvres were performed during inspiration the transients observed are not caused by involuntary Valsalva straining. In conclusion, the maximum and duration of the heart rate responses induced by stand up, cycling and head-up tilt are not influenced by respiratory activity. The initial fall in blood pressure following stand up is probably the result of the muscular effort of the manoeuvre and not due to the effects of orthostasis or Valsalva straining.

Adult↗
PubMed1991

Initial blood pressure fall on stand up and exercise explained by changes in total peripheral resistance.

To elucidate the underlying mechanisms of the initial fall in blood pressure on standing upright from the supine position, we measured the beat-to-beat changes in intra-arterial pressure in eight healthy male subjects in response to standing. Changes in stroke volume, cardiac output, and total peripheral resistance were computed from the pressure waveform using a pulse contour method. To determine possible mechanisms for the changes observed on standing, similar measures were made on passive tilting and a brief (3-s) bout of cycle exercise. Standing elicited a transient 25% (23-mmHg) fall in mean blood pressure as a result of a 36% fall in total peripheral resistance. Head-up tilt elicited a gradual change in haemodynamic parameters, which reached plateau levels in 20-30 s. Cycling elicited a transient 17% (18-mmHg) fall in blood pressure and a 41% fall in total peripheral resistance. In addition, we measured right atrial and esophageal pressures in two subjects on standing and cycling and found a 10- to 15-mmHg rise in right atrial pressure without a corresponding change in esophageal pressure. This points to the cardiopulmonary reflex as the primary effector of peripheral vasodilation, but we cannot exclude the possibility that 1) local metabolic vasodilation and 2) central command-mediated cholinergic vasodilation contributed to the fall in vascular resistance.

Adult↗
PubMed1991

Contrasting effects of acute and chronic volume expansion on orthostatic blood pressure control in a patient with autonomic circulatory failure.

We studied the effects of acute and chronic volume expansion on orthostatic blood pressure control in a 22-year-old female with hypoadrenergic orthostatic hypotension. Acute volume expansion on two occasions had unexpected effects: a decrease respectively no change in orthostatic tolerance and no change in upright blood pressure immediately after volume expansion followed by a marked improvement 8 h thereafter. The time course of changes in haematocrit and serum protein indicated an initial extravasation of plasma followed by a subsequent larger fluid shift back to the intravascular space. These effects had vanished after 3 days. Chronic volume expansion by head-up tilt at night and fludrocortisone resulted in a marked improvement in orthostatic blood pressure control at a comparable increment in body weight and sodium balance for the next 7 years until now. The circadian circulatory variation with orthostatic blood pressure lowest in the morning remained present after chronic volume expansion. We conclude in this patient that the effects of acute volume expansion on orthostatic blood pressure in autonomic failure are complex and not predictive for the beneficial effects of chronic volume expansion.

Adult↗
PubMed1991

Singing-induced hypotension: a complication of a high spinal cord lesion.

Cardiovascular autonomic control was studied in a patient with an incomplete high spinal cord lesion who presented with the symptoms of severe dizziness during debating and singing but not during orthostasis. The marked falls in blood pressure upon singing and orthostasis (45 degrees passive head-up tilt) were comparable in magnitude but different in time course. The fall in blood pressure upon graded Valsalva manoeuvres, however, was comparable to singing in magnitude and time course; similarly, 20 and 30 mmHg strain evoked complaints of dizziness. These differential circulatory responses upon orthostasis versus singing and Valsalva in tetraplegic patients have not been described before. We suggest that rapidly developing hypotension such as that induced by a moderate Valsalva strain represents the instantaneous mechanical effects of a raised intrathoracic pressure with lack of abdominal compression on the cardiovascular system when baroreflex vasomotor modulation is disrupted.

Adult↗
PubMed1990

Relaxation therapy and continuous ambulatory blood pressure in mild hypertension: a controlled study.

OBJECTIVE: To determine the long term effects of relaxation therapy on 24 hour ambulatory intra-arterial blood pressure in patients with mild untreated and uncomplicated hypertension. DESIGN: Four week screening period followed by randomisation to receive either relaxation therapy or non-specific counselling for one year. Ambulatory intra-arterial blood pressure was measured before and after treatment. SETTING: Outpatient clinic in Amsterdam's university hospital. SUBJECTS: 35 Subjects aged 20-60 who were being treated by general practitioners for hypertension but were referred to take part in the study. At three consecutive screening visits all subjects had a diastolic blood pressure without treatment of 95-110 mm Hg. Subjects were excluded if they had damaged target organs, secondary hypertension, diabetes mellitus, a cholesterol concentration greater than 8 mmol/l, or a history of malignant hypertension. INTERVENTIONS: The group allocated to relaxation therapy was trained for eight weeks (one hour a week) in muscle relaxation, yoga exercises, and stress management and continued exercising twice daily for one year with monthly visits to the clinic. The control group had the same attendance schedule but had no training and were requested just to sit and relax twice a day. All subjects were asked not to change their diet or physical activity. MAIN OUTCOME MEASURE: Changes in ambulatory intra-arterial blood pressure after one year of relaxation therapy or non-specific counselling. RESULTS: Mean urinary sodium excretion, serum concentration of cholesterol, and body weight did not change in either group. Diastolic pressures measured by sphygmomanometry were 2 and 3 mm Hg lower in subjects in the relaxation group and control group respectively at the one year follow up compared with initial readings. The mean diastolic ambulatory intra-arterial pressure during the daytime had not changed after one year in either group, but small treatment effects could not be excluded: the mean change for the relaxation group was -1 mm Hg (95% confidence interval -6 to 3.9 mm Hg) and for the control group -0.4 mm Hg (-5.3 to 4.6 mm Hg). Mean ambulatory pressure in the evening also had not changed over the year, and in both groups nighttime pressure was 5 mm Hg higher. The variability in blood pressure was the same at both measurements. CONCLUSIONS: Relaxation therapy was an ineffective method of lowering 24 hour blood pressure, being no more beneficial than non-specific advice, support, and reassurance--themselves ineffective as a treatment for hypertension.

Adult↗
PubMed1990

Effects of cuff inflation on self-recorded blood pressure.

Changes in continuously recorded 'Finapres' finger blood pressure in ten normotensive and seven hypertensive subjects induced by self-inflation of the cuff or just wearing the inflated cuff were studied. Inflating the cuff caused an instantaneous rise in systolic blood pressure of 13 and 12 mm Hg (hypertensive and normotensive subjects, respectively). Wearing the inflated cuff did not change blood pressure. Thus the rise in pressure was related to the muscular activity required for cuff inflation. Systolic blood pressure took on average 7 s and at most 21 s to return to baseline level after stopping cuff inflation. Since first Korotkoff sounds may already be heard after 10-15 s when following recommended procedures, self-recorded systolic blood pressure may be recorded as too high when subjects inflate their cuff at too low a pressure or deflate it too fast.

Adult↗
PubMed1990

Orthostatic circulatory control in the elderly evaluated by non-invasive continuous blood pressure measurement.

1. Continuous orthostatic responses of blood pressure and heart rate were measured in 40 healthy and active elderly subjects over 70 years of age in order to assess the time course and rapidity of orthostatic cardiovascular adaptation in old age. 2. During the first 30 s (initial phase) the effects of active standing and passive head-up tilt closely resembled those observed earlier in younger age groups. Standing up was accompanied by a drop (mean +/- SD) in systolic and diastolic blood pressures of 26 +/- 13 mmHg and 12 +/- 18 mmHg, respectively, at around 10 s, and a subsequent rise up to 11 +/- 17 mmHg and 8 +/- 6 mmHg above supine values at around 20 s. The drop in blood pressure upon standing was accompanied by a transient increase in heart rate with a maximum of 13 beats/min, followed by a gradual decrease to 7 beats/min above supine levels. These characteristic transient changes were absent upon a passive head-up tilt. 3. After 1-2 min of standing (early steady-state phase) diastolic blood pressure and heart rate increased significantly after active and passive postural changes. On average, for all subjects systolic blood pressure tended to increase from control during 5-10 min standing, reaching a significant difference at 10 min. During standing, the largest increases in systolic blood pressure were found in subjects with the lowest supine blood pressures. 4. In conclusion, for the investigation of orthostatic circulatory responses in elderly subjects the following factors have to be taken into account: active versus passive changes in posture, the timing of the blood pressure reading, and the level of supine blood pressure.

Aged↗
PubMed1990

Non-invasive continuous finger blood pressure measurement during orthostatic stress compared to intra-arterial pressure.

STUDY OBJECTIVE: The aim of the study was to evaluate whether invasive blood pressure responses to orthostatic stress can be replaced by non-invasive continuous finger blood pressure responses. DESIGN - Intrabrachial and Finapres blood pressures were simultaneously measured during passive head up tilt and during active standing from the supine or sitting position in healthy volunteers. SUBJECTS: Subjects (n = 11) were healthy males aged 22-40 years, mean age 30 years. MEASUREMENTS AND MAIN RESULTS: Beat to beat values of systolic, diastolic, and mean arterial pressures were calculated for both methods of measurement and the differences compared during a 30 s control period before, and during the first 120 s after, the change of posture. In the control period the difference between finger pressure and intra-arterial pressure was +2 (SD11) mm Hg for systolic, -4(8) mm Hg for mean, and -3(7) mm Hg for diastolic pressure. Compared to these control differences, the average finger minus intra-arterial pressure differences for mean and diastolic pressures during the three orthostatic manoeuvres were always within the range -6 to +6 mm Hg. The average systolic deviations were larger, ranging from -10 to +11 mm Hg. Despite these differences the characteristic changes in intra-arterial pressure during the initial phase (first 30 s after change of posture), as well as during the early steady state phase (1-2 min after the change of posture) were well reflected by finger pressure measurements in all subjects. CONCLUSIONS: For the assessment of the continuous blood pressure responses to orthostatic stress similar information can be obtained with non-invasive Finapres blood pressure recordings as with invasive recordings.

Adult↗
PubMed1990

Assessment of cardiovascular reflexes: influence of posture and period of preceding rest.

The aim of the present study was to investigate the effects of a pretest redistribution of blood volume and of a change in the neurohumoral condition on the blood pressure (BP) and heart rate (HR) responses to three commonly used cardiovascular reflex tests: standing up, forced breathing, and the Valsalva maneuver in 10 healthy male subjects. Base-line conditions were altered by changing posture and the duration of rest preceding the test stimulus. A continuous recording of finger BP was obtained noninvasively by a Finapres. The main observations from this study are with respect to standing up: lengthening the period of preceding rest from 1 to 20 min enlarges the initial BP (systolic/diastolic) decrease (from 8 +/- 10/9 +/- 4 to 27 +/- 8/19 +/- 4 mmHg, P less than 0.01) and the subsequent BP overshoot (from 17 +/- 10/12 +/- 7 to 31 +/- 10/18 +/- 7 mmHg, P less than 0.05); to forced breathing: inspiratory-expiratory changes in BP but not in HR are larger in the upright posture (P less than 0.05); and to the Valsalva maneuver: change in posture from supine to standing increases the phase II BP decrease (from 18 +/- 12/8 +/- 6 to 45 +/- 16/21 +/- 9 mmHg), phase IV systolic BP overshoot (from 26 +/- 16 to 71 +/- 17 mmHg), delta HRmax (from 30 +/- 10 to 47 +/- 12 beats/min), and the Valsalva ratio (HRmax/HRmin), from 2.0 +/- 0.3 to 2.6 +/- 0.7, all significant at P less than 0.01.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Orthostatic hypotension caused by sympathectomies performed for hyperhidrosis.

We studied sympathetic cardiovascular control in a patient after sympathectomies and found severe hypoadrenergic orthostatic hypotension before and after, but not during upright exercise. This report is the first to correlate in man anatomical sympathetic lesions with autonomic function test results and to document that in a sequence of sympathectomies orthostatic hypotension does not develop until the major part of splanchnic sympathetic outflow is destroyed.

Adult↗
PubMed1989

Pitfalls in the assessment of cardiovascular reflexes in patients with sympathetic failure but intact vagal control.

1. Two patients are described who presented with orthostatic hypotension as the main symptom. The diagnosis was sympathetic failure with intact vagal control. 2. Unusual test results were obtained. Assessment of the integrity of the total baroreflex arc by the Valsalva manoeuvre measuring only heart rate changes proved impossible, since the magnitude and time course of the heart rate response were normal notwithstanding the presence of a blood pressure response typical of sympathetic failure. 3. Sustained handgrip, cold pressor test and mental stress test all could induce a rise in blood pressure, despite the presence of sympathetic vasomotor lesions, but only when accompanied by a rise in heart rate. Efferent parasympathetic blockade by atropine, resulting in an increase in heart rate, was also accompanied by a substantial rise in blood pressure. These findings seem to result from a heart rate rise dependent increase in cardiac output unopposed by reflex vasodilatation. 4. In these patients the only baroreflex way to control blood pressure is by varying heart rate. This condition can be evaluated only if blood pressure and heart rate are measured on a beat-by-beat basis.

Adult↗
PubMed1989

Cardiovascular response to coughing: its value in the assessment of autonomic nervous control.

1. The relationship between blood pressure and heart rate responses to coughing was investigated in 10 healthy subjects in three body positions and compared with the circulatory responses to commonly used autonomic function tests: forced breathing, standing up and the Valsalva manoeuvre. 2. We observed a concomitant intra-cough increase in supine heart rate and blood pressure and a sustained post-cough elevation of heart rate in the absence of arterial hypotension. These findings indicate that the sustained increase in heart rate in response to coughing is not caused by arterial hypotension and that these heart rate changes are not under arterial baroreflex control. 3. The maximal change in heart rate in response to coughing (28 +/- 8 beats/min) was comparable with the response to forced breathing (29 +/- 9 beats/min, P greater than 0.4), with a reasonable correlation (r = 0.67, P less than 0.05), and smaller than the change in response to standing up (41 +/- 9 beats/min, P less than 0.01) and to the Valsalva manoeuvre (39 +/- 13 beats/min, P less than 0.01). 4. Quantifying the initial heart rate response to coughing offers no advantage in measuring cardiac acceleratory capacity; standing up and the Valsalva manoeuvre are superior to coughing in evaluating arterial baroreflex cardiovascular function.

Adult↗