Biomedical subjects
W Wieling
Publications and source records attributed to W Wieling.
Differences in circulatory control in normal subjects who faint and who do not faint during orthostatic stress.
We have determined if there are differences in normal subjects who fainted and those who did not faint during prolonged standing. We studied the short-term orthostatic responses in relation to heart rate, blood pressure measured by Finapres, left ventricular stroke volume analysed by pulse contour method, cardiac output and systemic vascular resistance, and also postural blood pressure and heart rate variability as assessed by spectral analysis. Thirteen healthy males without a history of syncope were studied. Three fainted after 10-13 min standing; the ten non-fainters remained upright for 20 min. The initial (first 30 s) postural circulatory adjustment was comparable for blood pressure but the rebound bradycardia was smaller in the fainters (heart rate at 22 s amounted to +13 +/- 10 beats/min above control vs. +1 +/- 5 beats/min in the non-fainters). Upright heart rate at 2 min standing was higher in the fainters (+31 +/- 2 beats/min vs. +20 +/- 5 beats/min), and blood pressure at 7 min standing was lower (-2/+5/+8 +/- 5/5/5 mmHg vs. +11/+13/+16 +/- 10/6/5 mmHg). The responses of stroke volume and cardiac output were comparable but systemic vascular resistance gradually decreased in the fainters from 5 min standing to the onset of fainting (+4 +/- 13% vs. +33 +/- 19% at 7 min standing). In fainters, the variability in upright blood pressure around 0.1 Hz was larger (8.8 mmHg2/Hz for diastolic blood pressure vs. 5.7 +/- 1.5 mmHg2/Hz in non-fainters).(ABSTRACT TRUNCATED AT 250 WORDS)
Physical manoeuvres that reduce postural hypotension in autonomic failure.
A young female with autonomic failure is described. She successfully reduced the symptoms of orthostatic hypotension by application of physical manoeuvres like leg-crossing, bending forward and placing a foot on a chair. The beneficial effects of these manoeuvres can be explained by a small (10-15 mmHg) increase in mean arterial pressure to a level just sufficient to maintain adequate cerebral blood flow. The underlying common mechanism appears to be an increase of thoracic blood volume by translocation of blood from the vascular beds below the diaphragm to the chest. Instruction in these physical manoeuvres should be part of the management programme to reduce the disabilities arising from postural hypotension in patients with autonomic failure.
Increased muscle perfusion reduces muscle sympathetic nerve activity during handgripping.
This study sought to determine whether increasing blood flow to active muscles can blunt the normal rise in muscle sympathetic nerve activity (MSNA) during heavy rhythmic forearm exercise in humans. Subjects performed 5- to 6-min exercise bouts of handgripping (30/min) at 40-50% of maximum voluntary contraction (MVC). Blood flow was increased by application of suction (50 mmHg) around the forearm. Suction increased deep venous oxygen saturation in blood draining the forearm from 34 +/- 4 to 45 +/- 4%, indicating that muscle blood flow had risen by approximately 20%. Suction had no impact on the heart rate, perceived exertion, or electromyographic responses to the handgripping. During 6 min of exercise at 50% of MVC, MSNA rose from 376 +/- 67 to 970 +/- 125 units during the control trial vs. 396 +/- 69 to 729 +/- 94 units during the suction trial, and the difference was maintained during 2 min of postexercise ischemia (P < 0.05; suction < control). Mean arterial pressure (MAP) rose from 99 +/- 4 to 129 +/- 6 mmHg during control vs. 99 +/- 4 to 126 +/- 6 mmHg during the suction trial, and these responses were only different (P < 0.05; suction < control) during the final minute of the exercise bouts. During postexercise ichemia, MAP was 122 +/- 6 mmHg after the control trial but was only 112 +/- 4 mmHg after the suction trial. These results indicate that forearm suction augmented muscle blood flow, limited the activation of chemosensitive muscle afferents, and blunted the rise in MSNA during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)
Feasibility of ambulatory, continuous 24-hour finger arterial pressure recording.
We tested Portapres, an innovative portable, battery-operated device for the continuous, noninvasive, 24-hour ambulatory measurement of blood pressure in the finger. Portapres is based on Finapres, a stationary device for the measurement of finger arterial pressure. Systems were added to record signals on tape, to alternate measurements between fingers automatically each 30 minutes, and to correct for the hydrostatic height of the hand. We compared the pressure as measured by Portapres with contralateral intrabrachial pressure measured with an Oxford device. Results were obtained in eight volunteers and 16 hypertensive patients. Time lost due to artifact was about 10% for each device. In two patients a full 24-hour Oxford profile was not obtained. In the remaining 22 subjects finger systolic, diastolic, and mean pressures differed +1 (SD 9), -8 (6), and -10 (6) mm Hg, respectively, from intrabrachial pressure. These diastolic and mean pressure underestimations are similar to what was found earlier for Finapres, are typical for the technique, and are systematic. Avoiding brisk hand movements resulted in fewer waveform artifacts. The hand had to be kept covered to continue recording at low outside temperatures. Sleep was not disturbed by Portapres, and arterial pressure showed a marked fall during siesta and nighttime. There were no major limitations in behavior, and no discomfort that originated from continuous monitoring was reported. Measurements continued normally during physical exercise. Portapres provides for the first time continuous 24-hour, noninvasive ambulatory blood pressure waveform monitoring and offers real and obvious advantages over current noninvasive and invasive devices.
Investigation and treatment of autonomic circulatory failure.
Investigation and treatment of patients suffering from autonomic circulatory failure should be based on the application of knowledge of basic physiology to the problem of a particular patient. For an overall evaluation of cardiovascular autonomic dysfunction, an analysis of the heart rate and blood pressure responses to standing usually is sufficient. Instruction in physical maneuvers such as squatting and leg crossing should be part of the treatment programs to reduce disabilities from orthostatic hypotension in patients with circulatory autonomic failure.
Physical manoeuvres for combating orthostatic dizziness in autonomic failure.
Some patients with orthostatic hypotension combat orthostatic dizziness by leg-crossing and squatting. Changes in blood pressure with these manoeuvres were studied in 7 patients with hypoadrenergic orthostatic hypotension and in 6 healthy subjects. Without leg-crossing, 5 of the patients reported dizziness within 10 min of standing up. Crossing of the legs allowed all to stand for 10 min or more, and there was an associated increase in mean blood pressure of 13 (SD 6) mm Hg compared with 1 (4) in healthy controls; the corresponding figures for squatting were 44 (18) and 8 (6) mm Hg. Patients with orthostatic intolerance should be told about these blood-pressure-raising manoeuvres.
Disparities in circulatory adjustment to standing between young and elderly subjects explained by pulse contour analysis.
1. The circulatory adjustment to standing was investigated in two age groups. Young subjects consisted of 20 healthy 10-14-year-old girls and boys. Elderly subjects consisted of 40 70-86-year-old healthy and active females and males. Continuous responses of blood pressure and heart rate were recorded by Finapres. A pulse contour algorithm applied to the finger arterial pressure waveform was used to assess stroke volume responses. 2. During the first 30s (initial phase), an almost identical drop in mean blood pressure was found in both age groups (young, 16 +/- 10 mmHg; old, 17 +/- 10 mmHg), but the initial heart rate increase was attenuated in the elderly subjects (young, 29 +/- 7 beats/min; old, 17 +/- 7 beats/min). 3. During the period from 30 s to 10 min of standing, mean blood pressure increased from 96 +/- 12 to 106 +/- 12 mmHg in the elderly subjects compared with almost no change in the young subjects (from 82 +/- 8 to 84 +/- 7 mmHg). In the elderly subjects a progressive increase in total peripheral resistance (from 114 +/- 14% to 146 +/- 29%) was found, compared with an initial rapid increase in total peripheral resistance (126 +/- 18% after 30 s) with no further change during prolonged standing (124 +/- 17% after 10 min) in the young subjects. In this age group the decrease in stroke volume and the increase in heart rate after 10 min of standing were large (young, -37 +/- 11% and 27 +/- 11 beats/min; old, -31 +/- 9% and 7 +/- 6 beats/min, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)
Treatment of orthostatic hypotension with sleeping in the head-up tilt position, alone and in combination with fludrocortisone.
We studied the effect of sleeping in the head-up tilt (HUT) position, alone and in combination with fludrocortisone, on orthostatic tolerance and blood pressure (BP) in six patients with hypoadrenergic orthostatic hypotension. A high salt diet of 150-200 mmol Na+ d-1 was also administered. Combined treatment reduced orthostatic dizziness in all patients (P less than 0.001), and increased the maximal standing period to at least 10 min. HUT alone (n = 4) reduced the BP decrease after 1 min of standing from -64/-42/-25 +/- 29/21/17 mmHg to -53/-37/-23 +/- 31/24/20 mmHg (P less than 0.01 for systolic BP). Addition of fludrocortisone to HUT (HUT/fludro) (n = 5) further reduced the BP decrease after 1 min of standing from -63/-40/-24 +/- 20/12/11 mmHg to -21/-19/-8 +/- 12/10/5 mmHg (P less than 0.05 for systolic, mean and diastolic BP, respectively). BP at maximal standing time increased from 58/47/42 +/- 9/8/7 mmHg initially to 95/69/57 +/- 27/22/20 mmHg during combined treatment (P less than 0.05 for systolic and mean BP), and remained unchanged during the 14-month (range 8-70 month) follow-up period. Nocturnal sodium excretion decreased from 8.0 +/- 2.3 mmol h-1 to 5.9 +/- 1.9 mmol h-1 with combined treatment; body weight increased by 1.6 kg on average (range 0.5-2.4 kg) (P less than 0.01). We conclude that the combination of HUT and fludrocortisone effectively minimizes orthostatic symptoms and increases orthostatic BP in patients with hypo-adrenergic orthostatic hypotension.
The clinical importance of routine measurement of liver enzymes, total protein and albumin in a general medicine outpatient clinic: a prospective study.
UNLABELLED: The objective was to study the usefulness of routine measurement of liver enzymes (ASAT, ALAT, alkaline phosphatase, gamma-GT), and total protein (TP) and albumin (Alb) in a general medicine outpatient clinic. A prospective study was made of consecutive patients who were classified according to whether or not an indication for the tests was present. All six tests were measured in all patients. Physicians were kept unaware of the results of tests in patients with no indication for ordering the test. The setting was a general internal medicine outpatient clinic in a 850-bed teaching hospital which serves as a referral clinic for general practitioners. There were 615 consecutive patients who were all new referrals to the outpatient clinic. The results of all patients with no indication for the test but who had abnormal results were presented to a panel of three experienced internists who decided whether the results had any clinical importance. Repeat measurements of the tests or follow-up results were obtained in all these patients. Seventy-eight of 320 patients in whom no indication for the test for liver enzymes existed had abnormal results. In only six of these (1.9%) were the abnormalities of clinical significance. In 56 of 449 patients in whom no indications were present for TP and Alb measurement the results were abnormal. In only 2 (0.4%) was this clinically important. CONCLUSION: the routine measurement of these six tests in general medicine outpatient clinics should be abandoned because of the low yield.
[The spectrum of clinical scientific research].
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Postural dizziness and transient hypotension in two healthy teenagers.
Neurocardiovascular control during postural change was investigated in two teenage females with complaints of dizziness almost immediately on standing up. Blood pressure and heart rate were monitored continuously with a Finapres device. On standing there was a brief but marked fall in blood pressure between 5-10 s after the onset of the manoeuvre. The maximum fall in systolic and diastolic blood pressure was 65 mmHg and 40 mmHg respectively in the first subject, and 58 mmHg and 29 mmHg respectively in the second subject. In both, postural tachycardia was present after 1-2 min of standing with heart rate increasing by up to 39 beats/min in the first subject and 60 beats/min in the second subject. On a follow-up examination 3 years later these changes had disappeared in the first subject while they persisted in the second subject, when she was studied two years later. We conclude that in these patients initial postural dizziness is related to an excessive fall in blood pressure upon standing.
Circulatory autonomic failure 50 years after acute poliomyelitis.
A 59-year old woman who presented with postural dizziness 50 years after an acute episode of poliomyelitis is described. There were no new neurological signs and no evidence of motor neuron disease. She had postural hypotension with an abnormal Valsalva. Investigations led to a diagnosis of hypo-adrenergic orthostatic hypotension, with a predominantly preganglionic sympathetic lesion and intact vagal baroreflex pathways. Although pure autonomic failure and multiple system atrophy are possible causes of circulatory autonomic failure, no other new neurological or autonomic features have developed during a 2 year follow-up. We propose that hypo-adrenergic orthostatic hypotension may be a late complication of poliomyelitis. Deterioration in ambulatory ability in a patient with previous poliomyelitis should additionally include assessment of cardiovascular autonomic function.
Cardiovascular instability and baroreflex activity in a patient with tetanus.
In a patient with tetanus we tested the hypothesis that the hyperadrenergic cardiovascular instability might be due to impairment of the baroreceptor reflex by the tetanus toxin. Baroreflex sensitivity assessed with the phenylephrine method was found to be normal. Changes in arterial pressure correlated inversely with relative changes in plasma volume but not with plasma catecholamine levels. There were both extreme hypo- and hyper-adrenergic episodes. We conclude that sympathetic overactivity in tetanus temporarily overrules a functionally intact baroreflex leading to severe blood pressure instability with episodes of hypertension.
Continuous finger arterial pressure: utility in the cardiovascular laboratory.
The clinical utility for autonomic research purposes of the Finapres, a device for measuring finger arterial pressure continuously and noninvasively, was assessed by estimating its accuracy, precision and within-subject variability in 48 subjects, aged 18-65 years, in comparison with intraarterial brachial blood pressure. At differences of -3.5 +/- 12, -8.0 +/- 8 and -4.4 +/- 8 mmHg from simultaneous intrabrachial systolic, mean and diastolic pressure, the Finapres meets the Association for the Advancement of Medical Instruments (AAMI) accuracy requirements for systolic and diastolic, but not for mean pressure. The precision requirements were nearly met for mean and diastolic, but not for systolic pressure. These results compare to those of others under widely varying circumstances in anaesthetized and awake subjects, and are comparable to those published for the auscultatory technique. The within-subject precision of Finapres is high; the 95% confidence intervals are 3.4-4.5 mmHg for systolic, 1.5-2.0 mmHg for mean and 1.7-2.2 mmHg for diastolic. This makes the Finapres suitable for tracking changes in blood pressure. Four case studies are provided as examples of the value of the Finapres in the clinical laboratory.
Circulatory adaptation to orthostatic stress in healthy 10-14-year-old children investigated in a general practice.
1. The magnitude and time course of circulatory adaptation to active standing were investigated in healthy premenarchic girls and boys (n = 24; 10-14 years old) by non-invasive measurement of heart rate and continuous finger blood pressure (Finapres). 2. Four subjects (two girls, two boys) showed presyncopal symptoms after 4-9 min of free standing. 3. In the 20 non-fainting subjects, changes in blood pressure and heart rate upon standing did not differ between girls (n = 10) and boys (n = 10). In the initial phase of standing (first 30 s) systolic and diastolic blood pressures dropped by 22 +/- 14 (mean +/- SD) and 16 +/- 7 mmHg, respectively, at 8 +/- 2 s. Blood pressure subsequently recovered and showed an overshoot in all subjects. The transient drop in blood pressure was accompanied by an increase in heart rate of 40 +/- 7 beats/min. These characteristic transient changes were not observed with passive head-up tilt. During the early steady-state phase (2 min), systolic blood pressure was similar to the supine value and diastolic blood pressure rose by 11 +/- 5 mmHg. Heart rate increased by 25 +/- 11 beats/min. In six of the subjects (three girls, three boys) the increase in heart rate exceeded 30 beats/min (postural tachycardia). Little further changes were observed during prolonged (10 min) standing.(ABSTRACT TRUNCATED AT 250 WORDS)
Spectrum of orthostatic disorders: classification based on an analysis of the short-term circulatory response upon standing.
1. In 31 consecutively referred patients (20 females, 11 males) with overt or suspected orthostatic disorders, the changes in blood pressure and heart rate that occur in the first 2 min of standing were analysed. 2. Blood pressure was measured continuously by Finapres. The blood pressure and heart rate responses after 1-2 min of standing (early steady-state response) were used to classify the patients as follows: group I (n = 17, age 42 +/- 17 years), normal early steady-state blood pressure and heart rate responses; group II (n = 5, age 40 +/- 14 years), combination of normal early steady-state blood pressure and postural tachycardia; group III (n = 9, age 51 +/- 14 years), hypotensive orthostatic response with (4/9) or without (5/9) postural tachycardia. We examined whether additional information could be obtained by beat-to-beat analysis of the initial circulatory response (first 30 s). It was quantified by identifying the blood pressure trough and overshoot and the maximum heart rate and relative bradycardia. 3. The initial drop in systolic and diastolic blood pressures did not differ between the three groups. A recovery of blood pressure with a systolic and/or diastolic blood pressure overshoot was present in all group I and II patients, but was absent in all except two patients in group III. The initial maximum heart rate increase did not differ between the three groups. The relative bradycardia was less in groups II and III than in group I. 4. We conclude that analysis of the beat-to-beat blood pressure changes in the first 30 s after the onset of standing provides almost all the information that is necessary to determine abnormalities in orthostatic circulatory control.
The vasovagal response.
The vasovagal response is the development of inappropriate cardiac slowing and arteriolar dilatation. Vasovagal responses reflect autonomic neural changes: bradycardia results from sudden augmentation of efferent vagal activity, and hypotension results from sudden reduction or cessation of sympathetic activity and relaxation of arterial resistance vessels. Two different neural pathways are thought to be involved, one originating in the hypothalamus, the other in the heart. Direct hypothalamic activation of the medullary cardiovascular centres triggered by emotional stress or pain causes a vasovagal response (central type). The combination of a reduced central blood volume secondary to venous pooling or blood loss, and an increased inotropic state of the heart, may stimulate ventricular mechanoreceptors and provoke vasodilatation and bradycardia (peripheral type). Cardiovascular afferents originating from stretch receptors in various parts of the vascular tree sometimes induce opposite reflexes when compared with those from ventricular afferents. The depressor reflex involved in the peripheral type of vasovagal response originates in the heart itself and overrides normal baroreflex circulatory control; an antagonism between the control of volume and pressure on the filling side of the heart and the control system of arterial pressure becomes apparent. Vasovagal responses are not necessarily abnormal; the neural pathways involved in the vasovagal response are probably present in all healthy subjects who individually mainly differ in susceptibility.