Passive Head-up Tilt Test Research Articles

Influence of Gravitational Unloading on the Dynamics of Blood Redistribution during Orthostasis: The Study by Near-Infrared Spectroscopy

We studied the effects of long-term anti-orthostatic hypokinesia (head-down bed rest—BR, a model of gravitational unloading) on the dynamics of orthostasis-induced changes in the content of total (THb), deoxygenated (HHb), and oxygenated (OHb) hemoglobin in the calf at the level of the gastrocnemius muscle medial head using near-infrared spectroscopy. In seven young men, 2–4 days before and on the 19th day of BR, a passive head-up tilt test was performed (15 min in the supine position, then 15 min at 65°). After BR, there was an increase in heart rate and a decrease in stroke volume in the supine position, as well as more pronounced changes in these parameters during orthostasis. Blood pressure in the supine position and orthostasis did not change after BR. THb content increased gradually during orthostasis and reached a plateau by the end of the test; after BR, an increase in the half-rise time and a twofold increase in the plateau level were observed. Tissue HHb content by the end of the tilt test also increased after BR. The dynamics of OHb before BR was more complicated: this indicator grew, reached a maximum during a minute, and then gradually decreased to half of the maximum by the end of the test. After BR, the dynamics of OHb changed drastically: the signal increased gradually and reached a level that was twice the peak value of OHb content before BR. The results allow us to conclude that exposure to BR weakens the compensatory constriction of calf vessels during tilt test; consequently, it is followed by higher blood accumulation in calf vascular bed, which, in turn, leads to smaller SV during orthostasis.

Influence of Gravitational Unloading on the Dynamics of Blood Redistribution During Orthostasis: The Study by Near-Infrared Spectroscopy

The effects of long-term anti-orthostatic hypokinesia (bed rest – BR, a model of gravitational unloading) on the dynamics of orthostasis-induced changes in the content of total (THb), deoxygenated (HHb), and oxygenated (OHb) hemoglobin in the calf at the level of the gastrocnemius muscle medial head were studied using the near-infrared spectroscopy. In seven young men, 2−4 days before and on the 19th day of BR, a passive head-up tilt test was performed (15 min in the supine position, then 15 min at 65°). After BR, there was an increase in heart rate and a decrease in stroke volume in the supine position, as well as more pronounced changes in these parameters during orthostasis. Blood pressure in the supine position and orthostasis did not change after BR. THb content increased gradually during orthostasis and reached a plateau by the end of the test; after BR, an increase in the half-rise time and a two-fold increase in the plateau level were observed. Tissue HHb content by the end of the tilt test also increased after BR. The dynamics of OHb before BR was more complicated: this indicator grew, reached a maximum during a minute, and then gradually decreased to half of the maximum by the end of the test. After BR, the dynamics of OHb changed drastically: the signal increased gradually and reached a level that was twice the peak value of OHb content before BR. The results allow us to conclude that exposure to BR weakens the compensatory constriction of calf vessels during tilt test; consequently, it is followed by higher blood filling of calf vascular bed, which, in turn, leads to smaller SV during orthostasis.

Cardiovascular autonomic responses during head-up tilt test in newly diagnosed type 2 diabetes.

Autonomic dysfunction is commonly observed in patients with long-standing type 2 diabetes. Previous studies have confirmed the value of both subjectively assessed symptoms and objective measurements of autonomic nervous system function in diagnosing cardiovascular autonomic neuropathy. However, the head-up tilt test (HUTT) has been rarely used to investigate cardiovascular autonomic responses in subjects with high risk ofnewly diagnosed type 2 diabetes (nT2D). To evaluate autonomic cardiovascular responses through passive orthostatic challenge along the diabetes continuum. The study population was stratified as normoglycemic (n = 16), prediabetes (n = 20), and nT2D (n = 20). The prevalence of orthostatic intolerance and autonomic cardiovascular responses was evaluated with the Task Force Monitor during a 30-min passive HUTT. Spectral indices of heart rate and blood pressure variability and baroreceptor effectiveness index (BEI) were calculated through the HUTT. BEI was obtained by the sequence method. There were no differences in the prevalence of orthostatic intolerance or in the indices of heart rate and blood pressure variability among the three groups of study. The BEI was attenuated in the nT2D group in supine rest and throughout HUTT compared with normoglycemic and prediabetes groups. The multivariable linear regression analysis showed that BEI was associated with fasting glucose (β = - 0.52, p <0.001) and HbA1c (β = - 0.57, p <0.001) independently of cardiovascular risk factors. Cardiovascular autonomic neuropathy, expressed as blunted BEI, is the only abnormal autonomic nervous test detected in nT2D, and it was independently associated with fasting glucose and HbA1c values.

Comparison of the Active Sitting Test and Head-Up Tilt Test for Diagnosis of Postural Tachycardia Syndrome in Children and Adolescents.

Objectives: We aimed to compare the hemodynamic responses to the active sitting test with the passive head-up tilt test (HUTT) in children and adolescents with postural tachycardia syndrome (POTS). We hypothesized that sitting tachycardia was also present in POTS patients during sitting.Materials and methods: We tested 30 POTS patients and 31 control subjects (mean age = 12 years, range = 9–16 years) who underwent both active sitting test and HUTT successively. We measured the heart rate (HR) and blood pressure (BP) during each test.Results: For both POTS patients and control subjects, the HUTT produced significantly larger HR and BP increases from 3 to 10 min of postural change than did the sitting test. Moreover, POTS patients with excessive orthostatic tachycardia during the HUTT also had significantly larger increases in HR at all test intervals during the sitting test than did the control subjects. A maximum increase in HR ≥ 22 bpm within 10 min of the sitting test was likely suggested to predict orthostatic tachycardia, yielding a sensitivity and specificity of 83.3 and 83.9%, respectively. Only six of 30 POTS patients (20%) reached the 40-bpm criterion during the sitting test, and no one complained of sitting intolerance symptoms.Conclusions: We have shown that POTS patients also have sitting tachycardia when changing from a supine position to a sitting position. We believe that the active sitting test is a reasonable alternative maneuver in assessing POTS in population groups that cannot tolerate the standing test or HUTT.

Mathematical modeling of the cardiovascular autonomic control in healthy subjects during a passive head-up tilt test

A mathematical model is proposed for the autonomic control of cardiovascular system, which takes into account two separated self-exciting sympathetic control loops of heart rate and peripheral vascular tone. The control loops are represented by self-exciting time-delay systems and their tone depends on activity of the aortic, carotid, and lower-body baroreceptors. The model is used to study the dynamics of the adaptive processes that manifest in a healthy cardiovascular system during the passive head-up tilt test. Computer simulation provides continuous observation of the dynamics of the indexes and variables that cannot be measured in the direct experiment, including the noradrenaline concentration in vessel wall and heart muscle, tone of the sympathetic and parasympathetic control, peripheral vascular resistance, and blood pressure. In the supine and upright positions, we estimated the spectral characteristics of the model variables, especially in the low-frequency band, and the original index of total percent of phase synchronization between the low-frequency oscillations in heart rate and blood pressure signals. The model demonstrates good quantitative agreement with the dynamics of the experimentally observed indexes of cardiovascular system that were averaged for 50 healthy subjects.

Transient Orthostatic Hypertension During Head-Up Tilt Test in Young Adults: A Phenotype of Blood Pressure Variability.

The mechanisms underlying orthostatic hypertension (OHT) remain poorly understood. The authors evaluated the cardiovascular, cerebrovascular dynamics, and autonomic response to head-up tilt test (HUTT) in young adults with symptoms of orthostatic intolerance and transient OHT. Forty-four female subjects were included (34 ± 13 years old) and categorized in three groups after a 30-minute 70° passive HUTT: symptomatic patients with OHT (surge of systolic blood pressure ≥20 mm Hg for at least 5 minutes at any given time during HUTT), orthostatic intolerance (symptomatic patients without orthostatic blood pressure changes), and healthy asymptomatic control subjects. At baseline, OHT patients had lower systolic blood pressure than orthostatic intolerance patients (103 ± 8 vs. 116 ± 10 mm Hg, p < 0.01) and lower baroreflex sensitivity than control subjects (15.8 ± 8.3 vs. 27.1 ± 11.7 ms/mm Hg, p = 0.01). On tilt, cardiac output decreased in OHT patients from 6.1 ± 1.4 L/minute during baseline to 5.2 ± 0.8 L/minute after 10 minutes of HUTT (p = 0.01). In OHT patients at 30 minutes of HUTT, sympathetic efferent heart activity was higher (77.4 ± 14.9 normalized units or nu) than orthostatic intolerant patients (63.5 ± 11.8 nu, p = 0.02) and control subjects (65.8 ± 11.2 nu, p = 0.05). Cerebrovascular resistance in OHT was higher than control subjects after 30 minutes (2.2 ± 0.8 vs. 1.6 ± 0.3 cm/second, respectively, p = 0.02). This study demonstrates that transient OHT can occur at any given time during HUTT. These patients exhibit a decrease in cardiac output and a hyperadrenergic response to tilt.

Syncope and an Intra-Hisian Atrioventricular Block After Radiation Therapy: Electrophysiologic Observations and Review of Literature

We present a case of a patient with recurrent syncope of sudden onset. She had a positive passive head-up tilt test for a mixed type of neurocardiogenic syncope. Additionally, she developed a narrow complex tachycardia on telemetry monitoring. Electrophysiology study revealed an intra-Hisian delay which upon provocation with programmed electrical stimulation, developed into a complete intra-Hisian atrioventricular block. Based on past medical history of radiation therapy for adenocarcinoma of the breast, the etiology of heart block was attributed to the remote effect of radiation-induced cardiac toxicity. Positive head-up tilt test for neurocardiogenic syncope and supraventricular tachycardia were incidental findings that could have confounding influence on management of such patients. J Med Cases. 2019;10(4):116-119 doi: https://doi.org/10.14740/jmc3233

Monitoring of cerebral oximetry during head-up tilt test in adults with history of syncope and orthostatic intolerance

We applied near-infrared-spectroscopy (NIRS) to measure absolute frontal cerebral tissue oxygen saturation (SctO2) during head-up tilt test (HUT) in patients investigated for unexplained syncope. Synchronized non-invasive beat-to-beat haemodynamic monitoring, ECG, SctO2 (NIRS; normal range: 60-80%), and peripheral oxygen saturation (left hand, SpO2) were applied during HUT in a random sample of patients with unexplained syncope. Tracings of 54 patients (mean-age: 55 ± 19 years, 39% male) with negative HUT, vasovagal syncope (VVS), or orthostatic hypotension (OH) were analysed. In 44 patients HUT was diagnostic, in 10 HUT was negative. Thirty-one experienced VVS. Of these, 6 had spontaneous and 25 nitroglycerin-induced syncope. Thirteen patients had orthostatic hypotension (OH). Although there was no significant change in mean-arterial pressure from baseline to 1 min before syncope or end of passive HUT phase (-1.4 ± 13.9 mmHg; P = 0.45), there was a significant fall in SctO2 during the same period (-3.2 ± 3.2%; P ≤ 0.001). Among patients who experienced syncope, a decrease in SctO2 from 71 ± 5% at baseline to 53 ± 9% (P < 0.001) at syncope was observed. During HUT, there was a significant difference in delta SctO2 between spontaneous VVS (-4.5 ± 3.0%) and negative HUT (-1.3 ± 1.9%; P = 0.021), but not between spontaneous VVS and OH (-5.4 ± 4.2%; P = 0.65). In spontaneous VVS, progressive decrease of SctO2 was independent of mean arterial pressure decrease (P = 0.22). Progressive decrease in cerebral tissue oxygenation independent of mean-arterial pressure may precede spontaneous vasovagal reflex during tilt. Patients experience syncope when SctO2 falls below 60%. These data confirm clinical utility of absolute cerebral oximetry monitoring for syncope investigation. We applied NIRS to measure frontal cerebral tissue oxygen saturation (SctO2) during head-up tilt test (HUT) in patients with unexplained syncope. In 44 of 54 patients, HUT was diagnostic. In patients with syncope, a significant SctO2-decrease was observed. Different patterns of SctO2 can be detected.

Physiological Mechanisms Mediating the Coupling between Heart Period and Arterial Pressure in Response to Postural Changes in Humans.

The upright posture strengthens the coupling between heart period (HP) and systolic arterial pressure (SAP) consistently with a greater contribution of the arterial baroreflex to cardiac control, while paradoxically decreasing cardiac baroreflex sensitivity (cBRS). To investigate the physiological mechanisms that mediate the coupling between HP and SAP in response to different postures, we analyzed the cross-correlation functions between low-frequency HP and SAP fluctuations and estimated cBRS with the sequence technique in healthy male subjects during passive head-up tilt test (HUTT, n = 58), during supine wakefulness, supine slow-wave sleep (SWS), and in the seated and active standing positions (n = 8), and during progressive loss of 1 L blood (n = 8) to decrease central venous pressure in the supine position. HUTT, SWS, the seated, and the standing positions, but not blood loss, entailed significant increases in the positive correlation between HP and the previous SAP values, which is the expected result of arterial baroreflex control, compared with baseline recordings in the supine position during wakefulness. These increases were mirrored by increases in the low-frequency variability of SAP in each condition but SWS. cBRS decreased significantly during HUTT, in the seated and standing positions, and after blood loss compared with baseline during wakefulness. These decreases were mirrored by decreases in the RMSSD index, which reflects cardiac vagal modulation. These results support the view that the cBRS decrease associated with the upright posture is a byproduct of decreased cardiac vagal modulation, triggered by the arterial baroreflex in response to central hypovolemia. Conversely, the greater baroreflex contribution to cardiac control associated with upright posture may be explained, at least in part, by enhanced fluctuations of SAP, which elicit a more effective entrainment of HP fluctuations by the arterial baroreflex. These SAP fluctuations may result from enhanced fluctuations of vascular resistance specific to the upright posture, and not be driven by the accompanying central hypovolemia.

Spontaneous vs nitroglycerin-induced vasovagal reflex on head-up tilt: Are there neuroendocrine differences?

Head-up tilt test (HUT) has been used for nearly 30 years for diagnosing vasovagal syncope (VVS) and was enhanced by sublingual nitroglycerin (glyceryl trinitrate [GTN]) challenge in the 1990s. The purpose of this study was to explore neuroendocrine differences between spontaneous and drug-induced HUT positivity. Two hundred eighty-eight patients (41.3% male, age 49 ± 21 years) with either positive passive (n = 60 [20.8%], age 38 ± 17 years) or GTN-enhanced HUT (n = 228, age 51 ± 21 years) were assessed. Beat-to-beat hemodynamic data, plasma epinephrine, plasma norepinephrine, plasma renin, C-terminal pro-arginine vasopressin (CT-proAVP), C-terminal endothelin-1, and mid-regional fragment of pro-atrial natriuretic peptide were measured resting supine and after 3 minutes of HUT. In multivariate-adjusted regression analyses controlling for age and gender, clinical, neuroendocrine, and hemodynamic parameters were compared between spontaneous and GTN-mediated positive tests. Patients with spontaneous VVS reported more syncope compared to those with GTN-mediated VVS (median interquartile range 6 [17] vs 4 [6], P = .002). There was no difference in resting concentrations of neurohormones between the 2 groups. However, after 3 minutes of HUT, those who later developed spontaneous VVS demonstrated higher levels of CT-proAVP (59.5 ± 137 vs 6.9 ± 4.6, P <0.001) and epinephrine (0.57 ± 1.43 vs 0.23 ± 0.19, P = .003), and lower blood pressure (119/73 vs 139/81 mm Hg, P <.001). Asystole during VVS was more common in the spontaneous VVS group (35% vs 17.5%, P = .016). Patients with spontaneous VVS on HUT reported more syncopal events than those with drug-potentiated positive HUT, but both groups shared similar supine neuroendocrine profiles. However, spontaneous VVS during HUT is characterized by lower blood pressure, pronounced increases in epinephrine and vasopressin during early HUT phase, and higher frequency of reflex asystole.

Sympathetic activity–associated periodic repolarization dynamics predict mortality following myocardial infarction

Enhanced sympathetic activity at the ventricular myocardium can destabilize repolarization, increasing the risk of death. Sympathetic activity is known to cluster in low-frequency bursts; therefore, we hypothesized that sympathetic activity induces periodic low-frequency changes of repolarization. We developed a technique to assess the sympathetic effect on repolarization and identified periodic components in the low-frequency spectral range (≤0.1 Hz), which we termed periodic repolarization dynamics (PRD). We investigated the physiological properties of PRD in multiple experimental studies, including a swine model of steady-state ventilation (n=7) and human studies involving fixed atrial pacing (n=10), passive head-up tilt testing (n=11), low-intensity exercise testing (n=11), and beta blockade (n=10). We tested the prognostic power of PRD in 908 survivors of acute myocardial infarction (MI). Finally, we tested the predictive values of PRD and T-wave alternans (TWA) in 2,965 patients undergoing clinically indicated exercise testing. PRD was not related to underlying respiratory activity (P<0.001) or heart-rate variability (P=0.002). Furthermore, PRD was enhanced by activation of the sympathetic nervous system, and pharmacological blockade of sympathetic nervous system activity suppressed PRD (P≤0.005 for both). Increased PRD was the strongest single risk predictor of 5-year total mortality (hazard ratio 4.75, 95% CI 2.94-7.66; P<0.001) after acute MI. In patients undergoing exercise testing, the predictive value of PRD was strong and complementary to that of TWA. We have described and identified low-frequency rhythmic modulations of repolarization that are associated with sympathetic activity. Increased PRD can be used as a predictor of mortality in survivors of acute MI and patients undergoing exercise testing. ClinicalTrials.gov NCT00196274. This study was funded by Angewandte Klinische Forschung, University of Tübingen (252-1-0).

Differences in autonomic balance in patients with cardioinhibitory and vasodepressor type of reflex syncope during head-up tilt test and active standing

Objective. To improve the pathophysiological understanding of cardioinhibitory and vasodepressor reflex syncope, by evaluating orthostatic effects on electrical and hemodynamic variables. To unravel the pathogeneses further, we studied these effects during both the passive head-up tilt test and the active standing test. Background. The current knowledge of the compromised autonomic balance in patients with reflex syncope is limited. The orthostatic responses to head-up tilt test in cardioinhibitory and vasodepressor patients differ, suggesting different pathogeneses; however, the more physiological active standing test represents daily life situations better. Methods. We included 74 patients; 36 cardioinhibitory and 38 vasodepressor. Patients were compared with respect to vascular hemodynamics and heart rate variability during the change from supine to upright position. Resting electrolytes, brain natriuretic peptide (BNP), pro-atrial natriuretic peptide (pro-ANP), and the C-terminal of pro-vasopressin, copeptin were measured. Results. Resting systolic blood pressure was higher in cardioinhibitory (117.8 ± 15.7 mmHg) than in vasodepressor patients (109.1 ± 15.3 mmHg, p < 0.001). Changes in heart rate tended to be smaller in cardioinhibitory patients (6.7 ± 9.8vs. 10.7 ± 8.9 bpm, p = 0.056). Heart rate variability was lower and changed less in cardioinhibitory patients (p < 0.05). Cardioinhibitory patients had higher pro-ANP levels (63.5 ± 18.8pM) compared to vasodepressor patients (54.2 ± 31.4 pM, p = 0.018). Responses during active standing were attenuated compared to head-up tilt in both groups. Conclusions. This study demonstrated that cardioinhibitory patients had higher blood pressure, attenuated hemodynamic responses, and reduced autonomic regulation compared to vasodepressor patients. Furthermore, cardioinhibitory patients showed a sympathetic predominance in their modulation of autonomic responses. Orthostatic responses induced by active standing were modest and did not sufficiently explain potential pathophysiological differences between cardioinhibitory and vasodepressor patients.

Differences in autonomic balance in patients with cardioinhibitory and vasodepressor type of reflex syncope during head-up tilt test and active standing

Objective. To improve the pathophysiological understanding of cardioinhibitory and vasodepressor reflex syncope, by evaluating orthostatic effects on electrical and hemodynamic variables. To unravel the pathogeneses further, we studied these effects during both the passive head-up tilt test and the active standing test. Background. The current knowledge of the compromised autonomic balance in patients with reflex syncope is limited. The orthostatic responses to head-up tilt test in cardioinhibitory and vasodepressor patients differ, suggesting different pathogeneses; however, the more physiological active standing test represents daily life situations better. Methods. We included 74 patients; 36 cardioinhibitory and 38 vasodepressor. Patients were compared with respect to vascular hemodynamics and heart rate variability during the change from supine to upright position. Resting electrolytes, brain natriuretic peptide (BNP), pro-atrial natriuretic peptide (pro-ANP), and the C-terminal of pro-vasopressin, c...

Impaired arterial baroreflex function before nitrate-induced vasovagal syncope during head-up tilt test

The aim of this study was to evaluate arterial baroreflex control of heart rate immediately before head-up tilt test (HUT)-induced vasovagal syncope (VVS). We enrolled 97 otherwise healthy subjects with recurrent unexplained syncope. After 10 min of rest in supine position, they underwent a passive HUT potentiated with nitroglycerin administration after 20 min. Beat-to-beat heart rate and systolic blood pressure were continuously recorded. Sequence method was used to measure two complementary parameters reflecting arterial baroreflex control of heart rate: the baroreflex sensitivity (BRS) and the baroreflex effectiveness index (BEI). Twenty-one patients fainted before nitrate administration (HUT+) and 37 after nitrate administration (NTG+). Immediately before syncope, the NTG+ patients showed significantly lower BRS values than those observed at the end of the test in the patients without syncope (5.5 +/- 2.8 vs. 7.7 +/- 3.4 ms/mmHg; P = 0.004) and a significantly lower BEI (30 +/- 20% vs. 53 +/- 24%; P < 0.001). The HUT+ patients did not show any significant differences in BRS and BEI before syncope from the values observed during the corresponding tilt period in the other groups. A significant depression in BRS and BEI occurs immediately before syncope in patients who faint after nitrate administration, thus suggesting that arterial baroreflex dysfunction plays a role in mediating nitrate-induced VVS.

Tilt testing potentiated with sublingual nitroglycerin in children with unexplained syncope

We read with great interest the article by Foglia-Manzillo et al. 1 on head-up tilt testing (HUT) with sublingual nitroglycerin in children with unexplained syncope. The authors concluded that nitroglycerin challenge greatly increased the positive rate of passive tilt with a small decrease in specificity. In our early studies with passive HUT, we observed …

Individual Differences in Blood Pressure Changes after Endurance and Resistance Training

PURPOSE: Large individual differences in the responsiveness of systolic blood pressure (SBP) to regular endurance training have been observed in healthy normotensive subjects. The training induced changes have ranged from a +20 increase to a −40 mmHg decrease. The individual effect of exercise training mode to decrease SBP among the healthy subjects is not well known. We tested the hypothesis that subjects with a poor responsiveness to endurance training might benefit from resistance training in terms of SBP. METHODS: The study population consisted of sedentary normotensive (SBP<150 mmHg) healthy male and female subjects (n=73, 42±5 year). The randomized crossover study design included a 2-week lab oratory-controlled endurance or resistance training period with a 2-month detraining period between the interventions. SBP was measured at resting condition and during a 5 min passive head-up tilt test. RESULTS: Large individual differences were observed in the changes of SBP (?SBP) after both the endurance (average −3±7 mmHg, P=0.001, range −20 to +13 mmHg) and resistance training (average −2±7 mmHg, P=0.034, range −31 to +16 mmHg) in resting condition. The average decrease in ?SBP between genders was similar after both the endurance and resistance training (P=ns between males and females). There was no linear relationship between the δSBP after each training intervention (r=−.06, P=ns). On the contrary, when the study group was divided into quartiles according to the endurance training response (+6±3, −1±2, −5±2, and −12±3 mmHg change in resting SBP, P<0.0001), the group with the increased SBP after endurance training (+6±3 mmHg, n=1 8) decreased SBP after the resistance training intervention (−2±3 mmHg, P<0.0001, compared with endurance training response). The same difference in ?SBP was also observed during a sympathetic stimulation caused by the head-up tilting (+4±8 mmHg vs. −1±5 mmHg, P=0.052, after endurance and resistance training, respectively). CONCLUSIONS: The individual responsiveness of SBP to exercise training is related to the mode of training. The healthy subjects whose SBP increase after endurance training intervention results in a decreased SBP after resistance training intervention. Supported by the Ministry of Education, Helsinki, Finland.

EFNS guidelines on the diagnosis and management of orthostatic hypotension

Orthostatic (postural) hypotension (OH) is a common, yet under diagnosed disorder. It may contribute to disability and even death. It can be the initial sign, and lead to incapacitating symptoms in primary and secondary autonomic disorders. These range from visual disturbances and dizziness to loss of consciousness (syncope) after postural change. Evidence based guidelines for the diagnostic workup and the therapeutic management (non-pharmacological and pharmacological) are provided based on the EFNS guidance regulations. The final literature research was performed in March 2005. For diagnosis of OH, a structured history taking and measurement of blood pressure (BP) and heart rate in supine and upright position are necessary. OH is defined as fall in systolic BP below 20 mmHg and diastolic BP below 10 mmHg of baseline within 3 min in upright position. Passive head-up tilt testing is recommended if the active standing test is negative, especially if the history is suggestive of OH, or in patients with motor impairment. The management initially consists of education, advice and training on various factors that influence blood pressure. Increased water and salt ingestion effectively improves OH. Physical measures include leg crossing, squatting, elastic abdominal binders and stockings, and careful exercise. Fludrocortisone is a valuable starter drug. Second line drugs include sympathomimetics, such as midodrine, ephedrine, or dihydroxyphenylserine. Supine hypertension has to be considered.

Dynamic Changes of P‐Wave Duration and P‐Wave Axis During Head‐Up Tilt Test in Patients with Vasovagal Syncope

The exact role of venous pooling in the pathogenesis of vasovagal syncope (VVS) is not fully elucidated. P-wave duration on an electrocardiogram can serve as a measure of atrial volume. Sixty-six patients (15 men, 51 women, mean age 32 years) with unexplained syncope were enrolled in the study.P-wave duration and the P-wave axis (PWA) were measured during passive head-up tilt test (HUT) in order to evaluate dynamic changes of atrial filling in patients with VVS. HUT was positive in 40 patients (6 men, 34 women, mean age 32 +/- 9 years) and negative in 26 patients (9 men, 17 women, mean age 33 +/- 8 years). The P-wave duration was significantly reduced in HUT-positive patients at the onset of symptoms as compared to 5 minutes (88.8 +/- 11.9 vs 96.2 +/- 12.0 ms, P = 0.008), and baseline (88.8 +/- 11.9 vs 96.8 +/- 13.8 ms, P = 0.005). The P-wave duration was significantly shorter at the onset of presyncope in HUT-positive patients as compared to HUT-negative patients (88.8 +/- 11.9 vs 100.3 +/- 11.2 ms, P = 0.0002). In HUT-positive patients, a significant increase in PWA was found at the onset of symptoms when compared to baseline (67.7 +/- 22.1 degrees vs 47.9 +/- 14.9 degrees, P < 0.0001) and 5 minutes of HUT (67.7 +/- 22.1 degrees vs 54.4 +/- 14.9 degrees, P = 0.005). At the time of syncope, PWA was more inferior in HUT-positive patients than in HUT-negative patients (67.7 +/- 22.1 degrees vs 51.8 +/- 13.8 degrees, P = 0.015). VVS is associated with the reduction in P-wave duration and the increase in PWA, which can be a result of exaggerated venous pooling and reduction in atrial volume.

Enhanced plasma catecholamine and cAMP response during the head-up tilt test in patients with vasovagal syncope

Vasovagal syncope appears related to transient changes in sympathetic neural outflow. Several studies have documented sympathetic inhibition at the time of syncope. However, data on the activity of the sympathetic nervous system a short time before the onset of syncope are controversial. The aim of the study was to examine sympathoadrenal activity by measuring levels of plasma catecholamines and plasma cAMP in patients with vasovagal syncope induced in the head-up tilt test (HUT). Sixty-one syncopal patients (age 35 +/- 15 years) underwent the passive HUT (60 degrees, 45 minutes). Blood samples for measurement of noradrenaline (NA), adrenaline (A) and dopamine (D) were obtained prior to tilt (0 minutes), at 5 minutes of tilt and at syncope or at the end of the HUT (45 minutes). Two samples were obtained for measurement of cAMP: at 0 minutes and at the end of the test. Plasma levels of NA, A and D were measured using high-performance liquid chromatography; plasma cAMP was measured using a radioimmunoassay technique. Thirty-three patients (15 men, age 35 +/- 16 years) developed vasovagal syncope during the test (HUT-positive); twenty-eight patients (15 men, age 34 +/- 14 years) completed the test without syncope (HUT-negative). No significant differences in NA, A and D were observed between the two groups at baseline or at 5 minutes of tilt. At the time of syncope, catecholamine levels in HUT-positive patients were higher than baseline levels (NA 428 vs. 209 pg/ml, A 90 vs. 55 pg/ml, D 297 vs. 142 pg/ml) and higher than in HUT-negative patients (NA 428 vs. 263 pg/ml, A 98 vs. 67 pg/ml, D 297 vs. 195 pg/ml). cAMP levels increased at syncope and were higher than in non-syncopal patients at the end of the HUT (607 +/- 460 vs. 328 +/- 297 nmol/ml). Vasovagal syncope induced by tilt testing is associated with increased levels of noradrenaline, adrenaline, dopamine and cAMP. These results suggest that sympathoadrenal activation antecedes development of vasovagal syncope and may play a role in its pathophysiology.

RELATIONSHIP BETWEEN TRAINING RESPONSE AND HEART RATE VARIABILITY IN ENDURANCE ATHLETES

The effects of long-term training period on cardiac autonomic function in athletes is not well known. PURPOSE This study was designed to assess the relationship between training response and cardiac autonomic function in endurance athletes over 5 months. METHODS Fifteen national level cross-country skiers (8 male 21±4 years; 7 female 17±1 years) and 7 sedentary control subjects were studied during the training season (Sep 2001) and during the competition season (Jan 2002). An incremental treadmill test was performed until exhaustion and the time to exhaustion used as maximal performance index. The R-R intervals were recorded at rest, during 80° passive head-up tilt test (5-min) and during each 3-min load of treadmill test. The vagally mediated beat-to-beat R-R interval fluctuation (SD1) was analyzed by two-dimensional vector analysis method from Poincaré plot at rest, during tilt test and during exercise. The relationship between individual changes in time to exhaustion and heart rate behaviour was analyzed. RESULTS The change in exhaustion time (+2.0±8.0 %, range from +14 to −13 %) correlated with the change in heart rate (r = 0.62, p = 0.012) and with the change in beat-to-beat heart rate variability (r = 0.60, p = 0.018) measured during passive head-up tilt test. The change in exhaustion time correlated strongly also with the change in heart rate and with the change in beat-to-beat heart rate variability measured during exercise, e.g. at the level of 55±9% of VO2max correlations were r = −0.68 (p = 0.005) and r = 0.81 (p = 0.001) respectively. The changes in heart rate behaviour at rest were not associated with changes in maximal performance. Changes in control group were not observed. CONCLUSION Increased vagal modulation of HR during passive head-up tilt test and during submaximal exercise is associated with improved performance after long-term training period in endurance athletes.