Passive Orthostasis Research Articles

Cardiorhythm in postural changes depending on the autonomic centers reactivity

Postural changes are accompanied by the formation of an adaptive response of the cardiovascular system. This is manifested by a change in heart rate variability. The features of the reaction largely depend on the excitability (reactivity) of the vegetative centers. The aim of the study was to identify individual features of heart rate regulation in postural changes depending on the reactivity of sympathetic and parasympathetic autonomic centers in students. Material and Methods. In 50 men, temporal, frequency, geometric and calculated indicators of heart rate variability were determined in a horizontal position, with active orthostasis, passive orthostasis and passive antiorthostasis. The reactivity of the sympathetic system was assessed by the change of heart rate in active orthostasis. The reactivity of the parasympathetic system was determined by K30:15. Results and Discussion. With normal and high sympathetic reactivity, active orthostasis causes an increase in the low-frequency power of the spectrum, stress index, heart rate, a decrease in the high-frequency component and the duration of cardiac intervals. The changes are more pronounced with high sympathetic reactivity. In passive orthostasis, high sympathetic reactivity is manifested by a large increase in heart rate, shortening of cardiac intervals and a decrease in the proportion of the spectrogram high-frequency component. Passive antiorthostasis with normal sympathetic reactivity causes a decrease in the adequacy of the regulation processes and an expansion of the scatterogram. In subjects with high parasympathetic reactivity with active orthostasis, the increase in the stress index is less than with normal and low reactivity. With low parasympathetic reactivity, the indicator of the adequacy of the regulation processes is greater than with normal and high reactivity, and the increase in heart rate and shortening of the minimum cardiac interval is greater than with normal. In passive orthostasis, the proportion of the high-frequency component decreases, the proportion of the ultra-low-frequency component increases, the modal cardiointerval shortens, which is more pronounced with low parasympathetic reactivity than with normal. In passive antiorthostasis, the ultra-low frequency component decreases in individuals with normal reactivity. With high reactivity, the maximum value of the high-frequency component increases and the adequacy of the regulation processes decreases. Conclusion. Active and passive orthostasis is accompanied by activation of sympathetic centers. It is more pronounced with high reactivity of the sympathetic department and low reactivity of the parasympathetic. Passive antiorthostasis stimulates the activity of parasympathetic cardiac centers in subjects with normal, high parasympathetic reactivity and normal sympathetic reactivity.

Approaches to antihypertensive therapy in patients predisposed to symptomatic hypotension and syncope

The management of a hypertensive patient with a history of syncope is aimed at maintaining a balance between cardiovascular and hypotensive (syncope) risks. The article presents an analysis of the literature data regarding the relationship between these clinical problems, and also draws practical conclusions that allow to ensure the optimal reduction in blood pressure in the interests of preventing cardiovascular diseases without the threat of drug-related hypotension (fainting). Variants of syncope in patients with arterial hypertension are summarized, depending on the association with antihypertensive therapy. There presented an expert opinion on the recommended target level of systolic blood pressure (120 mm Hg) in hypertensive patients under 70 years of age with a low syncope but high cardiovascular risk, as well as the target level of systolic blood pressure (140 mm Hg) in patients with high syncope and low cardiovascular risk or in elderly and / or frail individuals with hypertension. There noted the admissibility of bringing the systolic blood pressure to the target value up to 160 mm Hg in persons with severe frailty or disability. Examples of normal and pathological (hypotensive) patterns of hemodynamic response in persons with hypertension to long-term passive orthostasis obtained during the tilt test and influencing the decision-making on the activity of antihypertensive therapy are given. The importance of an interdisciplinary team approach with the participation of experts in regulatory circulatory disorders and geriatrics, which can significantly improve the quality of management of patients with a combination of hypertension and syncope, is stated.

Blunted autonomic response to standing up and head-up tilt in individuals with intellectual disabilities.

Previous research suggests individuals with intellectual disabilities (ID) may experience autonomic dysfunction, however, this has not been thoroughly investigated. The aim of this study was to compare the autonomic response to standing up (active orthostasis) and head-up tilt (passive orthostasis) in individuals with ID to a control group without ID. Eighteen individuals with and 18 individuals without ID were instrumented with an ECG-lead and finger-photoplethysmography for continuous heart rate and blood pressure recordings. The active and passive orthostasis protocol consisted of 10-min supine rest, 10-min standing, 10-min supine recovery, 5-min head-up tilt at 70°, followed by 10-min supine recovery. The last 5 min of each position was used to calculate hemodynamic and autonomic function (time- and frequency-domain heart rate and blood pressure variability measures and baroreflex sensitivity). Individuals with ID had higher heart rate during baseline and recovery (P < 0.05), and an attenuated hemodynamic (stroke volume, heart rate) and heart rate variability response to active and passive orthostasis (interaction effect P < 0.05) compared with individuals without ID. Mean arterial pressure (MAP) was higher in individuals with ID at all timepoints. Individuals with ID demonstrated altered hemodynamic and autonomic regulation compared with a sex- and age-matched control group, evidenced by a higher mean arterial pressure and a reduced response in parasympathetic modulation to active and passive orthostasis.NEW & NOTEWORTHY Individuals with ID demonstrated altered hemodynamic and autonomic regulation to the clinical autonomic function tasks standing up and head-up tilt (active and passive orthostasis). Higher resting heart rate and higher MAP throughout the protocol suggest a higher arousal level, and individuals with ID showed a blunted response in parasympathetic modulation. Further research should investigate the relationship of these findings with clinical outcomes.

Baroreflex circulation regulation during tilt test in young males with a history of vasovagal syncopes

Background. Vasovagal syncopes (VVS) are relatively often recorded in the population of young people. Objective. To establish the changes in the baroreflex function during the tilt test in healthy young males with the history of VVS. Design and methods. A total of 102 people aged 18–30 years were examined and divided into 4 groups, taking into account the specific features of fainting history and response to the tilt test. Subjects of the group 1 (n = 14) had a history of VVS and a positive response to the tilt test (syncope). Subjects of the group 2 (n = 14) had a history of VVS and a pattern of postural tachycardia without fainting verified during the tilt test. Subjects of the group 3 (n = 42) had a history of VVS and a negative response to the tilt test. Subjects of the group 4 (n = 32) did not have a history of VVS and showed a negative response to the tilt test. During the tilt test, we studied the dynamics of the baroreflex functional parameters (the number of baroreflex reactions (NBR), the baroreflex effectiveness index (BEI), the baroreflex sensitivity (BRS)). Results. In the individuals of each group, in the initial horizontal phase, values of NBR, BEI, BRS were within normal range and did not show significant intergroup differences (p &gt; 0,05). The passive orthostasis was associated with the increase in NBR (in each group beside control group), a decrease in BEI and BRS. The increase in NBR in the vertical phase of the tilt test (relative to the initial horizontal phase) was 87 %, 6 %, 16 % in the groups 1, 2, 3 and 4, respectively. The tilt-induced decrease in NBR comprised 8 % in the group 4. The decrease in the BEI in the vertical phase of the tilt test (relative to the initial horizontal phase) consisted: 22 %, 19 %, 12 %, 10 % in subjects of the 1, 2, 3, 4 groups, respectively. During the passive orthostasis we observed a decrease in BRS: by 65 %, 69 %, 64 %, 57 % in individuals of the groups 1, 2, 3 and 4, respectively. Returning from a vertical to a horizontal position in all groups led to a pronounced decrease in NBR and an increase in the BEI to values lower than in baseline horizontal tilt test phase; to an excessive increase in the BRS exceeding the pre-test values in each study group. Conclusions. In prolonged passive orthostasis, healthy young males, regardless of the fainting history, demonstrate a decrease in the baroreflex regulation. Among those with the history of VVS, tilt-positive subjects are characterized by a more pronounced orthostasis-induced drop in the baroreflex sensitivity and the baroreflex effectiveness index and a slow recovery of the baroreflex regulatory function compared to the tilt-negative subjects and to those who demonstrated postural tachycardia pattern without syncope.

DIFFERENCES IN THE LOW FREQUENCY VARIABILITY OF DIASTOLIC BLOOD PRESSURE INTERVAL IN PATIENTS WITH TYPE 1 AND TYPE 2 DIABETES

Objective: Dysfunction of the autonomic nervous system can be diagnosed by spectral analysis of variability of cardiac frequencies of consecutive RR interval using TASK FORCE monitor. Design and method: Study was done using TASK FORCE monitor and software analysis of HRV, Fourier transform algorithm. Testing at rest (20 min) and passive orthostasis (tilt table 90 for 6 minutes). Parameters analyzed: baroreceptor sensitivity (BRS), of this spectrum variability of RR-interval of high frequencies of (HF-RRI which is linked to the parasympathetic), part of the spectrum of low frequency variability of diastolic blood pressure interval (LF-DBP, partly linked to effects of sympathicus), LF / HF-RRI (sympathovagal balance of RR interval). Diagnostic procedures were done in 45 patients, of which 20 treated for type 1 diabetes, average age 37 years, of which 12 men and 8 women. The second group contained 25 patients with type 2 diabetes, average age 62 years of which 18 men and 7 women. Results: In groups with type 1 diabetes LF / HF at rest X 1.745 ± 0.91 SD; LF / HF orthostasis X 3.08 ± 2.65 SD; LF-DBP at rest 44.79SD ± 16:52; LF-DBP orthostasis X 51.91SD ± 11:41; HF-RRI at rest 36.01SD ± 14.65; HF-RRI orthostasis X 25.98 SD ± 8.2; BRS at rest 10.1; ± SD 6.18. In the group with type 2 diabetes LF / HF at rest X 4.01 The SD ± 7.02; LF / HF orthostasis X SD 4.7 ± 8.9; LF-DBP at rest SD 37.17 ± 14.85; LF-DBP orthostasis X SD 37.32 ± 10.89; HF-RRI at rest 43.51; SD ± 17:48; HF-RRI orthostasis X 43.51 ± 23:30; BRS at rest SD 9.78 ± 6.50. Correlation between the groups showed highly significant difference for LF-DBP in orthostasis (p < 0.00067). Conclusions: Significantly lower values of LF-DBP were registered in the group with type 2 diabetes, which represents the failure of sympathetic in orthostasis. It is common that patients with diabetes have a dominant parasympathetic dysfunction. Analyses revealed sympathetic dysfunction in patients with type 2 diabetes but not in subjects with type 1 diabetes.

Intermittent calf compression reverses lower limb pooling and improves cardiovascular control during passive orthostasis.

When upright, venous pooling and capillary filtration reduce the effective circulating volume and are key contributors to susceptibility to syncope (fainting). Recurrent syncope has a devastating impact on quality of life. Static calf compression garments are frequently prescribed for patients with syncope, but have questionable efficacy. Intermittent calf compression, which mimics the skeletal muscle pump to minimize pooling and filtration, is a potential alternative that holds promise for the management of syncope. We aimed to evaluate use of intermittent calf compression compared to commonly prescribed compression stockings, and determine the optimal intermittent calf compression paradigm, for improvement of orthostatic fluid shifts and cardiovascular control. We evaluated heart rate, blood pressure, stroke volume, cardiac output and peripheral resistance (finger plethysmography with Modelflow™) and calf pooling and filtration (calf circumference; strain gauge plethysmography) during a series of 10-min head-upright tilts. We first compared (protocol one) low (ICLF; 4 s on, 11 s off) and high (ICHF; 4 s on, 6 s off) frequency 0-100 mm Hg intermittent calf compression with static elastic and inelastic compression stockings and a placebo condition (n = 19, 5 males, aged 23.5 ± 0.1 years). We then compared (protocol two) ICLF applied at 0-40 mm Hg, 0-60 mm Hg, 0-80 mm Hg and 0-100 mm Hg as well as a placebo condition (n = 15, 5 males, aged 22.7 ± 0.5 years). The intervention order was randomized. In protocol one, all compression conditions significantly reduced calf circumference (p < 0.001) compared to placebo after 10-min upright; however, this reduction was greater in ICLF (-0.88 ± 0.18%) and ICHF (-1.14 ± 0.21%) conditions than both elastic (+0.49 ± 0.17%) and inelastic (-0.01 ± 0.19%) compression (p < 0.001). ICLF and ICHF, but not elastic or inelastic compression, were associated with improved stroke volume (p ≤ 0.001), allowing cardiac output to be maintained at a reduced heart rate (p < 0.001) without increases in vascular resistance responses, increasing hemodynamic reserve. ICHF showed no significant benefit over ICLF, evidenced by the lack of significant difference between ICLF and ICHF in any parameter measured. In protocol two, 0-60 mm Hg ICLF was considered the optimal intermittent compression because it was the lowest pressure that abolished the increase in calf circumference during orthostasis, while improving SV (p = 0.002), and reducing HR (p < 0.001) throughout tilt. Intermittent calf compression from 0 to 60 mm Hg ICLF is the optimal intermittent compression paradigm to ameliorate orthostatic fluid shifts and improve hemodynamic control. Commonly prescribed static calf compression garments do not improve orthostatic cardiovascular responses.

Effects of a Mononitrate, a β1-Blocker and a Dihydropyridine Calcium Channel Blocker on Cardiovascular Responsiveness to Passive Orthostasis

The aim of this study was to compare the influences of antianginal drugs such as mononitrate, beta-blocker and calcium channel blocker on cardiovascular responsiveness to orthostasis. The responses to passive orthostasis (tilt provocation at 60 degrees for 3 min) were measured in normotensive healthy volunteers with whole-body impedance cardiography and finger blood-pressure monitoring after a single moderate oral dose of isosorbide-5-mononitrate (CAS 16051-77-7, 10 mg), the beta1-blocker bisoprolol fumarate (CAS 104344-23-2, 5 mg), the dihydropyridine calcium channel blocker nisoldipine (CAS 63675-72-9, 5 mg), and placebo in a randomised, double-blind fashion. In supine position, none of the drugs altered pre-tilt arterial pressure or heart rate (HR) when compared to placebo. Nisoldipine decreased systemic vascular resistance index (SVRI) when compared to either placebo or bisoprolol, and increased the cardiac index (CI) when compared to placebo. During the passive orthostasis, the mononitrate decreased SVRI when compared to placebo or bisoprolol. The mononitrate increased HR and pulse wave velocity (PWV) when compared to the other study groups, and decreased the stroke index when compared to placebo. In the bisoprolol group, the tilt responses of diastolic arterial pressure, HR, CI, left cardiac work index, and PWV decreased significantly compared to those in the placebo group. Nisoldipine did not alter the responses to orthostasis when compared to placebo. When compared to the mononitrate, both nisoldipine and bisoprolol decreased CI response to orthostasis. The mononitrate adversely affects the cardiovascular responsiveness to orthostasis. The beta-blocker reduces the responses and thus probably oxygen demand during orthostasis. The dihydropyridine calcium blocker seems to influence the responsiveness less than the mononitrate or beta-blocker.

Effects of Adrenoceptor Blocking Drugs on Cardiovascular Responsiveness to Passive Orthostasis

To compare the acute effects of the beta-blocker propranolol (CAS 525-66-6), beta + alpha1-blocker carvedilol (CAS 72956-09-3) and alpha1-blocker tamsulosin (CAS 106463-17-6) on the cardiovascular responses to passive orthostasis. The responses to passive orthostasis (tilt provocation at 60 degress for 8 min) were measured in normotensive healthy volunteers with finger-blood-pressure and whole-body impedance cardiography prior to drugs and three days after beginning the medications. The treatments were moderate oral doses of the beta-blocker propranolol HCl (40 mg twice daily, n = 7), (beta + alpha1-blocker carvedilol (12.5 mg once daily for two days and thereafter 25 mg daily, n = 7), alpha1-blocker tamsulosin HCl (0.4 mg once daily, n = 6), or placebo. The drugs were distributed in a randomised, double-blind fashion. When measured prior to the head-up tilt test, propranolol and carvedilol had decreased supine systolic arterial pressure (SAP) more than placebo, and heart rate (HR) more than placebo and tamsulosin. Propranolol had decreased also pulse wave velocity more than placebo. The cardiac index (CI), stroke index (SI) and systemic vascular resistance index (SVRI) were not changed with any drugs. During the head-up tilt, tamsulosin decreased SAP and SVRI and augmented CI but not SI. The SVRI response curve with tamsulosin differed from that with propranolol or carvedilol. Also, tamsulosin increased HR compared to the beta-blocking drugs. The propranolol and carvedilol groups did not differ from each other in terms of any parameter. Tamsulosin significantly decreases SAP in the passive head-up tilt, indicating that it is not purely uroselective alpha1-blocker. The responses with tamsulosin clearly differ from those with propranolol and carvedilol, the responses with the latter two being practically equal.

Baroreceptor reflex and arterial rigidity in adolescents

The heart rate (HR) variability and pulse wave delay (PWD) in the major arteries of schoolchildren were studied. The function of ordinary coherence of the HR and PWD was used, which reflects the linear relationship between the two processes in the heart and vessels. The high tone of the sympathetic part of the autonomic nervous system (ANS) in schoolchildren causes an increase in heart performance and decreases the shift in the phase of association between HR and PWD, which leads to the appearance of a new characteristic of the system, arterial rigidity. The results of the physiological activation of the sympathetic part of ANS during passive orthostasis and pharmacological trials with blockers of ANS receptors in schoolchildren with heart arrhythmia at rest are presented.

Studies on the systemic features of autonomic diabetic neuropathy

Thirty diabetics with peripheral neuropathy underwent complex assessment of autonomic nervous disorders of seven different organ systems. Functional analysis was done of the cardiovascular system (respiratory arrhythmia at rest and during regulated breathing, 3rd order waves of cardiac frequency and of arterial mean pressure, active and passive orthostasis), pupillary regulation (infra-red pupillography), peripheral vasomotor regulation (skin temperature) and sudomotorics (psychogalvanic skin reflex). Involvement of the genitourinary system, of stomach and intestine was evaluated by clinical criteria. Twelve diabetics showed signs of autonomic neuropathy in four to six, eight patients in three organ systems. The amplitudes of respiratory arrhythmia during regulated breathing, spectral analytic evaluation of cardiac frequency waves of 3rd order and cardiac frequency immediate reaction during orthostasis were particularly indicative. The demonstrated disturbance of conduction of centrally generated cardiac frequency waves of 3rd order and the diminished amplitudes of the spontaneous rhythms of acral skin temperatures complement the previously known symptomatology of autonomic diabetic neuropathy. The systemic character of autonomic diabetic neuropathy objectivated by the investigations indicates a metabolic pathogenesis.

The Effects of Tamsulosin and Sildenafil in Separate and Combined Regimens on Detailed Hemodynamics in Patients With Benign Prostatic Enlargement

We measured the detailed hemodynamic effects of tamsulosin and sildenafil separately and together in patients with benign prostatic enlargement. The supine effects of and responses to passive orthostasis (60 degrees for 8 minutes) were measured in 16 patients with benign prostatic enlargement with the finger blood pressure method and whole-body impedance cardiography. The medications, 100 mg sildenafil (single doses) and 0.4 mg tamsulosin (once daily for up to 14 days), were administered in a randomized, double-blind, crossover fashion. Supine systolic arterial pressure decreased with sildenafil (mean +/- SEM -11 +/- 2 mm Hg) and sildenafil plus tamsulosin (-14 +/- 2 mm Hg) more than with placebo (-2 +/- 4 mm Hg, p <0.05). In comparison to placebo sildenafil plus tamsulosin decreased the systemic vascular resistance index (328 +/- 129 vs -241 +/- 134 dyn.sec/cm.m, p = 0.01). Tamsulosin alone did not cause any significant changes in comparison to placebo. Heart rate, diastolic arterial pressure, stroke index, cardiac index and arterial pulse wave velocity were not affected to a statistically significant degree by any of the treatments compared to placebo. Upon head-up tilt the drugs caused only 1 significant change in that diastolic arterial pressure was significantly higher (-2.7 vs -8.0 mm Hg, p = 0.04) in the placebo group than in the tamsulosin plus sildenafil group. Tamsulosin does not disturb hemodynamics in patients with benign prostatic enlargement. Sildenafil decreases blood pressure with the patient supine but not during head-up tilt. The combination treatment also decreases the systemic vascular resistance index in the supine position.

The Vasodilatory Effect of Alfuzosin and Tamsulosin in Passive Orthostasis: A Randomised, Double-Blind, Placebo-Controlled Study

Objective: To compare in details the effects of urologically used α 1-blockers alfuzosin and tamsulosin on the cardiovascular responses to passive orthostasis. Methods: The responses to passive orthostasis (tilt provocation at 60° for 8 min) were measured in normotensive healthy volunteers with finger blood pressure method and whole-body impedance cardiography prior to the administration of the drugs as well as three days after the beginning of the randomised, double-blind medications. The parallel treatments were standard clinically used doses of α 1-blockers alfuzosin (5 mg twice daily, n = 10), tamsulosin (0.4 mg once daily, n = 10), or placebo ( n = 11). Results: When measured prior to the head-up tilt test in supine position, neither alfuzosin nor tamsulosin significantly changed any of the cardiovascular variables. During the passive orthostasis, however, both tamsulosin and alfuzosin reduced systemic vascular resistance index compared to pre-drug responses (−540 and −462 dyn s/cm 5 m 2, respectively, p < 0.05). Both drugs also augmented orthostatic responses of heart rate (11 and 9 bpm, respectively, p < 0.05) and cardiac index (0.50 and 0.40 l/min/m 2, respectively, p < 0.05) but not those of stroke index when compared to the responses during placebo or before the administration of the drugs. The alfuzosin and tamsulosin groups did not significantly differ from each other in terms of any parameter. Conclusions: Both alfuzosin and tamsulosin have clear cardiovascular effects, which are most strikingly evident in the influences on systemic vascular resistance and cardiac output.

Cardiovascular and Hormonal Changes with Different Angles of Head-up Tilt in Men

The purpose of this study was to assess the endocrine status, thoracic impedance, blood concentration, and hemodynamic dose-responses using different angles of passive head-up tilt (HUT) ranging from 12° to 70° in the same subjects. Measurements were performed during 20 min supine position (pre-HUT), 30 min upright (HUT12, HUT30, HUT53, or HUT70), and 20 min supine (post-HUT); subjects 70 min in the supine position only (HUT0) served as resting controls. Norepinephrine increased above resting control values by 19, 44, 80, and 102 %; epinephrine by 30, 41, 64, and 68 %; aldosterone by 29, 62, 139, and 165 %; plasma renin activity n. s., 41, 91, and 89 %; vasopressin n.s., 27, 47, and 59 %; thoracic bioimpedance n. s., 8, 13, and 16 %; heart rate n. s., 5, 26, and 45 %, and mean arterial pressure n. s., 5, 7, and 10 %; at min 27 of HUT12, HUT30, HUT53, and HUT70, respectively. Pulse pressure decreased with HUT53 and HUT70 by 4 and 10 %. Hematocrit increased by 0.2, 1.7, 6.3, and 7.2 %, respectively. Blood density increased by 2.3 and 3.0 g/l, plasma density by 1.7 and 1.8 g/l with HUT53 and HUT70. After finishing HUT, heart rate fell to values which stayed below pre-HUT, and also below resting control levels for ł 5 min ("post-orthostatic bradycardia") even after the lowest orthostatic load (HUT12). Thoracic impedance and arterial pressure remained increased after terminating HUT30, HUT53, and HUT70. In conclusion, passive orthostatic loading of different extent produces specific dose-responses of different magnitude in the endocrine system, blood composition, thoracic impedance, and hemodynamic variables. The heart rate is depressed even after HUT12, while arterial blood pressure and thoracic impedance exceed pre-stimulus levels after greater head-up tilt, indicating altered cardiovascular response after passive orthostasis.

Pulsometric study of the functional state of cardiovascular system under conditions provoking neurogenic syncopes.

The effects of passive and active orthostatic loads on the amplitude and temporal parameters of pulse waves were studied using an original computer assisted method of differential sphygmomanometry. Changes in the cardiac rhythm reflecting impairment of the autonomic regulation of the circulatory system and preceding neurogenic cardiovascular syncope were revealed and evaluated. Comparative analysis revealed similarity between these changes under conditions of both passive and active orthostasis, which confirmed the diagnostic value of differential sphygmomanometry.

Are heart rate responses reproducible in the tilt-table test?

Measurement of blood pressure and heart rate in active orthostasis has proven to be effective in the diagnosis of autonomic regulatory dysfunctions. The following study was carried out in order to clarify to what extent reproducible heart rate reactions also occur in passive orthostasis. 61 people with normal results in five standardized tests were examined. All 61 test persons had individually differing courses of heart rate. After an initial increase of frequency an almost straight line results from a superimposed projection of the graphs. In 20 of these cases the tilt-table test was repeated in order to detect intra-individual regularities. Even when the test was repeated, no reproducible intraindividual heart rate reactions occurred. And here as well, projection of the graphs produced an almost straight line. We could not find any quotient, such as the 30/15 ratio in active orthostasis, during our tests with the tilt-table.

Time-frequency dynamics in neurally mediated syncope

In this study, the responses during syncope were determined by noninvasive beat-to-beat analysis during passive orthostasis. Twenty patients with recurrent unexplained syncope (13 men and seven women) and ten healthy aged-matched control subjects were studied during 80 degrees head-up tilt for 25 min. Time-frequency mapping of R-R intervals, systolic and diastolic pressures and respiration was used to determine the responses to tilt. The spectral estimation was based on a modified Wigner distribution and the frequency content was evaluated on a beat-to-beat basis. Ten patients developed syncope (tilt-positive group) during tilt, while the remaining ten were asymptomatic (tilt-negative group). Control subjects reacted to tilt by the immediate shortening of R-R intervals to a plateau with an accompanying moderate increase in diastolic pressure. In the tilt-negative group the responses to tilt were similar, but of greater amplitude. In contrast, in the tilt-positive group, R-R intervals gradually and continuously decreased with tilt while systolic and diastolic pressures increased until shortly before syncope, when an abrupt fall in blood pressure followed by R-R intervals lengthening occurred. Furthermore, the R-R intervals fluctuations at both respiratory and nonrespiratory frequencies were the highest at rest as well as during tilt in the tilt-positive group. Nonrespiratory fluctuations in blood pressure increased more during tilt in both tilt-positive and negative groups compared to the control group. The nonrespiratory fluctuations in R-R intervals and blood pressure reached a maximum at syncope, simultaneously with hypotension and bradycardia. Time-frequency mapping has demonstrated that an elevated parasympathetic tone at rest which persists during orthostasis identifies patients prone to vasodepressor syncope. The counteracting sympathetic activation is not sustained and results in hypotension followed by cardioinhibition and loss of consciousness.

The Valsalva maneuver in vasodepressor syncope.

In this work the authors propose the Valsalva maneuver as a diagnostic test in a group of patients shown, by anamnestic, physical, and instrumental criteria, to be affected by vasodepressor syncope. They studied the response of heart rate and baseline arterial pressure to the maneuver performed in passive orthostasis in 7 healthy volunteers and 24 patients. These patients showed a hypotensive response and a time of recovery to the initial values that was significantly longer than in the control group (p less than 0.01). The authors conclude that studying the response to the Valsalva maneuver can be useful in the diagnosis of vasodepressor syncope.