Passive Changes In Posture Research Articles

Venous dynamics in anesthetized sheep govern postural-induced changes in cerebrospinal fluid pressure comparable to those in humans.

Sheep are popular large animals in which to model human disorders and to study physiological processes such as cerebrospinal fluid dynamics. However, little is known about vascular compensatory mechanisms affecting cerebrospinal fluid pressures during acute postural changes in sheep. Six female white Alpine sheep were anesthetized to investigate the interactions of the vascular and cerebrospinal fluid system by acquiring measurements of intracranial pressure and central and jugular venous pressure during passive postural changes induced by a tilt table. The cross-sectional area of the common jugular vein and venous blood flow velocity was recorded. Anesthetized sheep showed bi-phasic effects of postural changes on intracranial pressure during tilting. A marked collapse of the jugular vein was observed during head-over-body tilting; this is in accordance with findings in humans. Active regulatory effects of the arterial system on maintaining cerebral perfusion pressure were observed independent of tilting direction. Conclusion: Anesthetized sheep show venous dynamics in response to posture-induced changes in intracranial pressure that are comparable with those in humans.

System dynamics of active and passive postural changes: Insights from principal dynamic modes analysis of baroreflex loop

The baroreflex being a key modulator of cardiovascular control ensures adequate blood pressure regulation under orthostatic stress which otherwise may cause severe hypotension. Contrary to conventional baroreflex sensitivity indices derived across a-priori traditional frequency bands, the present study is aimed at proposing new indices for the assessment of baroreflex drive which follows active (supine to stand-up) and passive (supine to head-up tilt) postural changes. To achieve this, a novel system identification approach of principal dynamic modes (PDM) was utilized to extract data-adaptive frequency components of closed-loop interactions between beat-to-beat interval and systolic blood pressure recorded from 10 healthy humans. We observed that the gain of low-pass global PDM of cardiac arm (:feedback reflex loop, mediated by pressure sensors to adjust heart rate in response to arterial blood pressure), and 0.2 Hz global PDM of mechanical arm (:feed-forward pathways, originating changes in arterial blood pressure in response to heart rate variations) may function as potential markers to distinguish active and passive orthostatic tests in healthy subjects.

Cardiovascular adjustments during anticipated postural changes.

It is well‐documented that feedforward cardiovascular responses occur at the onset of exercise, but it is unclear if such responses are associated with other types of movements. In this study, we tested the hypothesis that feedforward cardiovascular responses occur when a passive (imposed) 60° head‐up tilt is anticipated, such that changes in heart rate and carotid artery blood flow (CBF) commence prior to the onset of the rotation. A light cue preceded head‐up tilts by 10 sec, and heart rate and CBF were determined for 5‐sec time periods prior to and during tilts. Even after these stimuli were provided for thousands of trials spanning several months, no systematic changes in CBF and heart rate occurred prior to tilts, and variability in cardiovascular adjustments during tilt remained substantial over time. We also hypothesized that substitution of 20° for 60° tilts in a subset of trials would result in exaggerated cardiovascular responses (as animals expected 60° tilts), which were not observed. These data suggest that cardiovascular adjustments during passive changes in posture are mainly elicited by feedback mechanisms, and that anticipation of passive head‐up tilts does not diminish the likelihood that a decrease in carotid blood flow will occur during the movements.

Impact of Dynamic Transrectal Ultrasonography on Pelvic Organ Prolapse

We developed a new method to evaluate pelvic organ prolapse dynamically in patients in supine and standing positions using transrectal ultrasonography. We visualized the descent and prolapse of pelvic organs in real time using dynamic transrectal ultrasonography. The dynamic transrectal ultrasonography findings were compared with intraoperative findings. A prospective analysis was performed including 31 women with symptomatic pelvic organ prolapse. Before surgical repair for pelvic organ prolapse, transrectal ultrasonography was performed by an operator separate from the surgeon, and the transrectal ultrasonography findings were compared with the intraoperative findings, focused on the diagnosis of pelvic organ prolapse. The patients were put on the fluoroscopic tilting table for passive postural change from supine to standing position. After injection of sonographic jelly into the vaginal lumen, the ultrasound probe was inserted into the rectum. With passive postural change from supine to standing position using the fluoroscopic tilting table, descent and prolapse of pelvic organs were dynamically evaluated in real time. Cystocele, uterine prolapse and rectocele were dynamically observed in this procedure. Morphological details of pelvic organ prolapse such as movement, sliding, eversion, descent, and looseness of vaginal wall and bladder wall were successfully demonstrated in most cases. Dynamic transrectal ultrasonography demonstrated a high sensitivity (85.0%), specificity (81.1%), and positive (77.3%) and negative (87.8%) predictive value. We successfully demonstrated morphological conditions and dynamic changes of pelvic organs during passive postural change using dynamic transrectal ultrasonography in real time. Dynamic transrectal ultrasonography can be a useful modality to visualize pelvic organ prolapse preoperatively.

Intersystem Relationships of Respiration and Hemodynamics in the Initial Period of Postural Effects

We studied the dependence of parameters of lung volumes and the elastic properties of the lungs on changes in the central hemodynamics occurring in the initial period of passive postural changes in cats. It was found that transition from the horizontal to head-up and head-down tilting was accompanied by opposite hemodynamic changes in the cranial and caudal parts of the body. Changes in lung compliance and functional residual capacity of the lungs were opposite and linearly depended on the intensity of hemodynamic shifts, which indicates passive character of the primary disorders primarily determined by a physical factor, gravity-dependent redistribution of body fluids.

The consensus statement on the definition of orthostatic hypotension: a revisit after 13 years

The consensus statement on the definition of orthostatic hypotension: a revisit after 13 years

Evaluation of Carotid Atherosclerosis from the Perspective of Blood Flow Reflection

Detection and prevention of atherosclerosis at an early stage is important for its prevention. The aim of this study was to propose a valid and highly reliable index for the evaluation of carotid atherosclerosis or carotid function. Images of carotid Doppler wave profiles were processed using an image processing software, and the relative fluctuation in blood flow was calculated from the luminance in one cardiac cycle. Frequency analysis was performed and up to 10 time components of basic frequency (f1) were indicated. The evaluation functionαwas estimated by calculating the ratio of the sum of components f3–f10 against the f1 + f2 components. Blood pressure of the finger was continuously measured using Finapress during passive postural change from the supine to the standing position, the baroreceptor function was evaluated by the frequency method, and the plaque score was measured by ultrasound tomography. The influence of factors such as arterial compliance, blood vessel resistance, and heart rate on this index was studied using electric circuit model simulation. The subjects were 33 patients (18 men, 15 women) who had various types of atherosclerotic disease and hypertension. The average age was 67.3 + 12.2 years. The results showed that index α had a strong negative correlation with age and plaque score, and a weak positive correlation with baroreceptor function. Simulation results supported the clinical result. We proposed a new index to evaluate carotid atherosclerosis without blood pressure measurement using the carotid Doppler method. It is a potential index for detecting atherosclerosis of local arteries such as the carotid.

Clinical screening of autonomic dysfunction in multiple sclerosis

Multiple sclerosis (MS) can affect the autonomic nervous system. Although exercise may be beneficial for people with MS, those with autonomic dysfunction may have altered heart rate responses to exercise. We investigated the hypothesis that the pattern of increase in heart rate on commencement of a simple cycle test would be different in those participants with MS who had been shown to have autonomic dysfunction on laboratory testing compared with both control participants and MS participants not exhibiting autonomic involvement. A controlled cohort study with a volunteer sample of 31 adults with MS (26 women, 5 men) with a mean age of 46 +/- 8.00 years (32-60 years), a median Expanded Disability Severity Scale of 3 (1-6) and a mean duration since diagnosis of 10.3 years (0.1-39 years). Thirty-one age-matched, non-disabled, sedentary but healthy adults (26 women, 5 men) with a mean age of 45 +/- 9.5 years (24-57) comprised the control group. Autonomic function was evaluated using continuous heart rate and blood pressure responses to rhythmical deep breathing, the Valsalva manoeuvre, passive postural change and a simple cycle test. There were no significant differences in age, height or weight (p < 0.05) between the two groups or on any of the autonomic test results (p < 0.05). Five participants with MS (16%) had abnormal autonomic function on laboratory testing, two of whom demonstrated an abnormal heart rate response to the cycle test. It is suggested that physiotherapists monitor the heart rate response to a dynamic exercise test in people with MS prior to prescribing an exercise programme to ensure patients' safety. Should the response appear delayed or attenuated, referral for more formal autonomic laboratory testing is recommended.

Motor correlates of models of secondary bilateral synchrony and multiple epileptic foci

Bilateral synchronous epileptiform discharges registered in patients with partial epilepsies may be generated by different pathophysiological mechanisms. Differentiation between underlying mechanisms is often crucial for correct diagnosis and adequate treatment in clinical epileptology. The aim of this study was to model in rats two possible mechanisms--secondary bilateral sychrony and interaction between multiple epilepic foci. Furthermore, to describe in detail semiology, laterality and differences in motor phenomena. Secondary bilateral synchrony was modeled by unilateral topical application of bicuculline methiodide (BMI) over the sensorimotor cortex. Bilateral symmetric application of BMI was used as a model of multiple epileptic foci. Electrographic and behavioural phenomena were recorded for 1h following the application of BMI. Electroencephalogram in both groups was characterized by presence of bilateral synchronous discharges. Myoclonic and clonic seizures involving forelimb and head muscles represented the most common motor seizure pattern in both groups. Significant differences were found in the laterality of motor phenomena. Motor seizures in unilateral foci always started in the contralateral limbs whereas symmetrical foci exhibited bilateral independent onset of convulsions. Similar lateralization was observed in interictal motor phenomena (myoclonic jerks). An important influence of posture on epileptic motor phenomena was demonstrated. Active or passive changes in animal posture (verticalization to bipedal posture) caused conversion from unilateral myoclonic jerks or clonic seizures to bilaterally synchronous (generalized) motor phenomena in both groups.

Effects of age and hypertension on autonomic nervous regulation during passive head-up tilt.

To study the effects of age and hypertension on autonomic nervous function with passive postural change, we examined 31 normotensive subjects (25 to 85 years old) and 31 hypertensive patients (21 to 71 years old) without any cardiac disease, diabetes mellitus, or neurological disorders. Subjects were passively placed in a 60 degrees head-up tilting position after 15 minutes in the supine position. Autonomic nervous function was evaluated by frequency domain analysis of heart rate with the autoregressive method. Using low-frequency (0.1 Hz) and high-frequency (0.25 Hz) peaks, the ratio of low- to high-frequency power (L/H) was calculated as an index of sympathetic activity and the ratio of high to total power (%HF) as that of parasympathetic activity. With the patient in the supine position, total power spectral density declined logarithmically with age in normotensive subjects and hypertensive patients, but %HF and L/H showed no changes. In response to passive tilting, L/H was increased and %HF was decreased in the normotensive subjects, and these responses declined with age logarithmically. In contrast, hypertensive patients exhibited less autonomic response to postural change regardless of age. These results suggest that autonomic neural response to tilt is decreased with age; however, attenuation of the response by hypertension is not associated with an increase in age.

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.

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.

The Effect of Active and Passive Changes in Posture on Autonomic Function

The Effect of Active and Passive Changes in Posture on Autonomic Function

Properties of deep spinothalamic tract cells in the rat, with special reference to ventromedial zone of lumbar dorsal horn.

Spinothalamic tract cells lying at the base of the dorsal horn or in deeper areas were identified in the rat at the lumbar spinal cord level by injecting horseradish peroxidase or stimulating posterior thalamic areas. Two groups of neurons were delineated; each constituted a homogeneous population of cells in terms of electrophysiological properties. Ventromedial dorsal horn cells lay at the base of the dorsal horn in its most medial aspect. They constitute a densely packed formation, which in the rat's ascending pathway system is restricted to the spinothalamic tract. Their main characteristics were a) ongoing activity, which consisted of small groups of spikes occurring at regular intervals, with a maximal discharge during ankle extension; b) unilateral receptive fields, which were restricted to the distal parts of the limb and involved both proprioceptive (ankle, joint digits) and exteroceptive (foot skin) structures; c) input of innocuous origin (midrange articular movement, touch, pressure) that was excitatory and input of noxious cutaneous origin (radiant heat) that was inhibitory; the same areas of foot skin were thus potentially either excitatory or inhibitory, depending on the nature of the stimulus applied; d) ankle flexion could differentially modulate both ongoing activity and excitatory responses from distal parts of the limb, inhibiting the former and potentiating the latter. In consequence, the ability of these cells to be driven by both proprioceptive and cutaneous inputs from limb extremities as well as by interactions of these inputs would appear to be very favorable for informing the central nervous system about limb position in both passive postural changes and the step cycle. It is suggested that they supply the thalamus with integrated information about locomotion. Lamina VII cells also constituted a subpopulation of neurons with very homogeneous electrophysiological properties. They were characterized by widespread inhibitory receptive fields, possibly spanning both hindlimbs and the ipsilateral forelimb. Inhibition was most effective when the stimulus (pressure, pinch) was intense and applied to proximal parts of the hindlimb. Ongoing activity consisted of spikes set at regular intervals and sometimes related to midrange movements of the knee. Although the significance of the widespread inhibitory receptive fields remains unclear, it has been suggested that these neurons are involved in the transmission of proprioceptive information.(ABSTRACT TRUNCATED AT 400 WORDS)

Venous pressure-volume relation and calf blood flow determined by changes in posture

The volume capacity of the venous system in the calves of 70 normal subjects was determined by passive and active changes in posture, using mercury-in-rubber strain gauges. The mean volume capacity was 1.26% (SD 0.39%) at a venous pressure of 0 kPa (o mm Hg) and 2.05% (SD 0.70%) at 1.60 kPa (12 mm Hg). With this method the blood flow in the calves at rest was measured without venous occlusion: 2.84 ml-100 ml-1/min (SD 1.20). During interpolated venous occlusion the mean blood flow was 2.67 ml-100 ml-1/min (SD 1.21). The pressure-volume relation over the pressure range 0 to 9.31 kPa (0 to 70 mm Hg) was determined in seven normal subjects.

Fluctuations in O2 stores and gas exchange with passive changes in posture.

To clarify the role of O2 stores in the fluctuations in VO2 observed with changing posture, O2 intake (Veo2) and pulmonary capillary O2 transfer (Vpco2) were calculated breath by breath with a box-balloon sprometer and mass spectrometer. Changes in O2 stores of the lungs (O2L) and blood (O2b) were computed assuming metabolic rate (Vco2) constant (O2L = Veo2 - Vpco2; O2b = Vpco2 - Vco2). Measurements were made before, during, and after passive tilt to 60 degrees and on return to recumbency after 10 min erect. From supine to upright O2L increased rapidly and O2b dropped slowly, creating a net deficit in Veo2 of 130 ml in 10 min. Return to supine caused rapid loss in O2L and gain in O2b with a net Veo2 excess of 117 ml. Shifts in O2b were 2.5 times greater but opposite to shifts in O2L. Changes in O2b result from shifts in blood volume and flow more than from changes in cardiac output. Refilling of O2b, matching loss while upright, caused transient hypoxia with significant hyperpnea.

Hemodynamic Alterations Caused by Passive Changes in Body Position in Dogs with Chronic Atrial Septal Defects

The effects of passive tilting on the circulatory pressures and on the magnitude of shunts across chronic atrial septal defects were studied in 11 dogs with closed chests. These determinations were performed with the dogs in four positions: 45-degree head-up, 45-degree head-down, right lateral decubitus, and left lateral decubitus. Control values were obtained with the animals in the supine horizontal position. The 45-degree head-up tilt position was associated with an increase in the magnitude of the right-to-left shunt detected after injections of indicator into the inferior vena cava, while change from supine to the 45-degree head-down tilt resulted in a decrease or disappearance of a pre-existing right-to-left shunt detected after similar injections. These effects on the right-to-left shunt were not demonstrable after injections of indicator into the superior vena cava, either during the head-up or head-down tilt, in spite of identical alterations in circulatory pressures. A significant interanimal correlation between the magnitude of the changes in systemic or right atrial pressures and the magnitude of the changes in right-to-left shunts could not be demonstrated. Passive changes in posture from supine to 45-degree head-up or head-down positions were not associated with demonstrable systematic effects on the magnitude of the left-to-right shunts. It is postulated that the descent of the heart and diaphragm during the head-up tilt results in a closer anatomical relation between the ostium of the inferior vena cava and the defect in the atrial septum and consequently an increase in the preferential shunting of inferior caval blood through this defect. In these animals, changing the body position from the supine to the right lateral decubitus position was consistently associated with an increase in the magnitude of the left-to-right shunts across the atrial septal defect and an increase in pulmonary blood flow. Since these animals have preferential shunting of blood from the right lung in the left-to-right direction, it is believed that the increase in blood flow through the dependent right lung is responsible for the observed increase in the left-to-right shunt. The left lateral decubitus position was not associated with appreciable effects on pulmonary blood flow or left-to-right shunting of blood across the atrial septal defect.

Effect of tilting on RK time in normal subjects and in patients with heart disease

The time from onset of the R wave of the electrocardiogram to the registration of the arterial compression sound of Korotkoff at diastolic pressure level (RK D time) was measured before and after passive changes in posture. In normal subjects the RK D time was significantly prolonged after they assumed the upright position and shortened to control values when they returned to the horizontal position. These effects were diminished by compression of the calves, thighs, and abdomen of the subject with an antigravity suit. In patients with previous or present congestive heart failure the response of the RK D time to the changes in posture was significantly reduced or was opposite to that seen in normal subjects. These data may be interpreted to suggest that in normal subjects with a relatively constant level of diastolic pressure, RK D time varies inversely with the stroke volume. This relationship is eliminated in patients with congestive failure. The simplicity of the method permits the study of responses to experimental or therapeutic procedures.

Variations in Pulse and Blood Pressure With Interrupted Change of Posture*

Article1 February 1931Variations in Pulse and Blood Pressure With Interrupted Change of Posture*DAVID G. GHRIST, M.D.DAVID G. GHRIST, M.D.Search for more papers by this authorAuthor, Article, and Disclosure Informationhttps://doi.org/10.7326/0003-4819-4-8-945 SectionsAboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinkedInRedditEmail ExcerptCareful studies of the normal circulatory response to uninterrupted changes of posture from recumbency to standing have been previously reported4,5,6. Following Ghrist and Brown's report of a step-like fall of both systolic and diastolic blood pressure, with associated faintness or syncope on passive, interrupted change of posture from recumbency to standing in one case of postural hypotension with syncope and in one case of proved Addison's disease, it was deemed advisable to repeat these fractional postural studies on groups of normal subjects and of patients. The following study of pulse rate, blood pressure and resultant symptoms from passive postural change,...1 ADSON AW: Surgical relief of Raynaud's disease and other vascular disturbances by sympathetic ganglionectomy and perivascular neurectomy. Ann. Clin. Med., 5:161-167 (Aug.) 1926. Google Scholar2 GHRIST DG: The temperature of the upper and lower extremities in relation to the control exercised by the sympathetic nervous system. Proc. Staff Meetings of Mayo Clinic., 5:25-26 (Jan. 29) 1930. Google Scholar3 GHRISTBROWN DGGE: Postural hypotension with syncope; its successful treatment with ephedrine. Am. Jour. Med. Sc., 175:336-349 (March) 1928. CrossrefGoogle Scholar4 HILLBARNARD LH: The influence of the force of gravity on the circulation. Part II. Jour. Physiol., 21: 323-352 (May) 1897. CrossrefMedlineGoogle Scholar5 KERNOHANANDERSONKEITH JWEWNM: The arterioles in cases of hypertension. Arch. Int. Med., 44:395-423 (Sept.) 1929. CrossrefGoogle Scholar6 MORTENSEN MA: Blood-pressure reactions to passive postural changes: An index to myocardial efficiency. Am. Jour. Med. Sc., 165:667-675 (May) 1923. CrossrefGoogle Scholar7 SCHNEIDERTRUESDELL ECD: A statistical study of pulse rate and the arterial blood pressures in recumbency, standing, and after a standard exercise. Am. Jour. Physiol., 61:429-474 (Aug.) 1922. CrossrefGoogle Scholar This content is PDF only. To continue reading please click on the PDF icon. Author, Article, and Disclosure InformationAffiliations: The Mayo Foundation Rochester, Minnesota**Abridgement of thesis submitted to the Faculty of the Graduate School of the University of Minnesota in partial fulfillment of the requirements for the degree of Master of Science in Medicine, 1930.†Certain of these were studied before and after sympathetic ganglionectomy and trunk resection. PreviousarticleNextarticle Advertisement FiguresReferencesRelatedDetails Metrics Cited byTransmembrane gationic gradient and blood pressure regulationUntersuchungen zur Frage der Kreislaufregulation des Menschen beim Wechsel der KörperlageBlood pressure in the arm and thigh of manAbnormal brachial blood pressure response to postural change in patients suffering from psychoses of the senium. Control by thyroidThe Importance of Studying the Postural Responses of the Blood Pressure and the Heart Rate, with a Note on the Method of Taking the Blood Pressure in the Erect PostureThe effect of fever on postural changes in blood pressure and pulse rate 1 February 1931Volume 4, Issue 8Page: 945-958KeywordsBlood pressureFallsGraduate medical educationHeart rateHypotensionPostural controlSyncope Issue Published: 1 February 1931 PDF downloadLoading ...