Cardiovascular response during head-up tilt in chronic fatigue syndrome

This study examined the cardiovascular response to orthostatic challenge, and incidence and mechanisms of neurally mediated hypotension in chronic fatigue syndrome (CFS) during a head-up tilt test. Stoke volume was obtained by a thoracic impedance cardiograph, and continuous heart rate and blood pressure were recorded during a 45-min 70° head-up tilt test. Thirty-nine CFS patients and 31 healthy physically inactive control subjects were studied. A positive tilt, i.e. a drop in systolic blood pressure openface> 25 mmHg, no concurrent increase in heart rate and/or development of presyncopal symptoms, was seen in 11 CFS patients and 12 control subjects (P>0·05). During baseline and the first 5 min of head-up tilt, CFS patients had higher heart rate and smaller pulsatile-systolic area than control subjects (P<0·05). Among subjects who completed the test, those with CFS had higher heart rate and smaller stroke volume (P<0·05) than corresponding control subjects. When comparing those who had a positive test outcome in each group, CFS patients had higher heart rates and lower pulse pressure and pulsatile-systolic areas during the last 4 min before being returned to supine (P<0·05). These data show that there are baseline differences in the cardiovascular profiles of CFS patients when compared with control subjects and that this profile is maintained during head-up tilt. However, the frequency of positive tilts and the haemodynamic adjustments made to this orthostatic challenge are not different between groups.     

Phenylephrine increases near-infrared spectroscopy determined muscle oxygenation during head-up tilt in men

Abstract

Phenylephrine is an α-adrenergic agent and yet seems to increase near-infrared spectroscopy determined muscle oxygenation (S_mO₂) that reflects the ratio between oxygenated (O₂Hb) and deoxygenated (Hb) haemoglobin/myoglobin. We examined whether the increase in S_mO₂ by phenylephrine reflects veno-constriction and to secure filling of the veins, subjects were exposed to head-up tilt (HUT). Phenylephrine (0.2?mg) was administered to 10 healthy males (24?years (22–27; median with interquartile range)) during 40° HUT with S_mO₂, O₂Hb and Hb determined for the biceps brachii and vastus lateralis muscles. Changes in red cell volume within the thorax and thigh were evaluated by electrical admittance and brachial vein diameter determined by ultrasound. HUT accumulated blood in arms and legs as indicated by reduced thoracic and conversely enhanced thigh electrical admittance. Both over the arm and leg, HUT reduced S_mO₂ as a consequence of reduced O₂Hb and increased Hb (p?mO₂ increased due to a decrease in Hb and an increase in O₂Hb. The results confirm that S_mO₂ decreases during HUT and demonstrate venous filling in the limbs. Furthermore, vasoconstriction during HUT is indicated by a decrease in O₂Hb. Conversely, phenylephrine increased S_mO₂ likely illustrating increased muscle blood flow and venoconstriction as O₂Hb increased while Hb was reduced.     

Cardiovascular response to spinal anaesthesia in elderly men: effects of head-up tilt and dihydroergotamine administration

Summary. In nine elderly men (mean age 60, range 42–74 years) cardiovascular pressures and cardiac output have been measured by catheterization of the pulmonary and brachial artery during spinal anaesthesia without and with dihydroergotamine (DHE) and during an added slight head-up tilt (10–15^o). Spinal anaesthesia lowered arterial pressure and also stroke volume. After DHE arterial pressures as well as stroke volume were normalized. Tilting before spinal anaesthesia lowered stroke volume but arterial pressures were maintained. During spinal anaesthesia, tilting lowered arterial pressures as well as filling pressures of the heart. After administration of DHE during spinal anaesthesia the pressures were unaffected by tilting. It is concluded that in elderly men, unlike the young men previously studied, spinal anaesthesia decreases arterial blood pressures by a combination of reduced peripheral resistance and decreased stroke volume. The decreases in stroke volume and cardiac output were most pronounced in those patients with a reduced blood volume. DHE also prevents arterial pressure fall with head-up tilt during spinal anaesthesia.     

Intravenous nitrates for pharmacological stimulation during head-up tilt testing in patients with suspected vasovagal syncope and healthy controls

Nitrates may be used for pharmacological stimulation during tilt testing for the diagnosis of vasovagal syncope. In this study we assessed the diagnostic value of intravenous nitrates during tilt testing in patients with a typical history of vasovagal syncope. Twenty patients and 23 controls were tilted at 700 for a maximum duration of 30 minutes. After a 10-minute baseline supine phase, the test started with a continuous nitrate infusion at 1 microg/kg/min and increased every 5 minutes by 1 microg/kg/min, to a maximum of 6 microg/kg/min at the end of the test. The test was ended if the subjects developed a positive response (syncope or presyncope). Nineteen patients (95%) and 17 (74%) of the controls had a positive response. At test end sensitivity was 95%, but specificity was 26% and accuracy was 58%. Receiver operator characteristics (ROC) analysis revealed a maximum accuracy of 79% at 18 minutes, with a sensitivity of 80% and a specificity of 78%. Intravenous nitrates during tilt testing in patients with typical clinical criteria of vasovagal syncope is highly effective in provoking vasovagal syncope. Based on the ROC analysis, a maximum accuracy of 79% was attained at 18 minutes (at a dose of 4 microg/kg/min), suggesting a good diagnostic performance when tilt duration is limited to this point. A positive result requiring more than 18 minutes of stimulated tilting should be interpreted with caution, due to the accompanying considerable decrease of specificity.     

Altered autonomic regulation of cardiac function during head-up tilt after 28-day head-down bed-rest with counter-measures

Summary. The effects of 28 days continuous 6° head-down tilt bed-rest on heart rate variability and the slope of the spontaneous arterial baroreflex were evaluated during supine rest and the first 10 min of 60° head-up tilt. Twelve healthy men were assigned to either a no counter-measure (No-CM), or a counter-measure (CM) group so that there was no difference in maximal oxygen uptake. Counter-measures consisted of short-term, high resistance exercise for 6 days per week from days 7–28, and lower body negative pressure (-28 mmHg) for 15 min on days 16, 18, 20 and 22–28. In spite of balanced between-group fitness, mean RR-interval was different between the No-CM and the CM group prior to bed-rest, but neither this nor any other variables showed significant counter-measure by bed-rest interaction effects. Therefore, all data presented are from the main effects of bed-rest or tilt from the analysis of variance. RR-interval was reduced significantly by bed-rest and by tilt (P<0–0001). Indicators from spectral analysis of heart-rate variability suggested reduced parasympathetic nervous system activity with bed-rest (P<0–01) and head-up tilt (P<0–05), and increased sympathetic nervous system activity after bed-rest (P<0–01). An indicator of complexity of cardiovascular control mechanisms, taken from the slope (β) of log spectral power vs. log frequency relationship, suggested reduced complexity with bed-rest (P<0–05) and head-up tilt (P<0–01). The spontaneous baroreflex slope was reduced significantly by bed-rest (P<0–03) and by head-up tilt (P<0–04). Taken together, these data support the concept of altered autonomic nervous system function in the aetiology of cardiovascular deconditioning with bed-rest or space travel; and it would appear that no benefit is derived from these specific counter-measures.     

Blood volume distribution during head-up tilt induced central hypovolaemia in man

Summary. We evaluated regional electrical impedance (Z°) at 2.5 and 100 kHz to separate intra- and extracellular fluid changes and correlated Z° over the thorax (TI) to relative changes in the central blood volume (CBV) induced by head-up tilt. In nine experiments head-up tilt resulted in normotensive central hypovolaemia associated with a 3·7 & 0·4 Ohm (mean f SE) increase in TI_{100 kHz} after 60 min. In 24 experiments presyncopal symptoms were induced after 43±2 min, when TI_100kHz had increased 4·2 ± 0·2 Ohm. Head-up tilt instantly decreased the activity of technetium labelled erythrocytes (⁹⁹Tc^m) over the thorax by 24 ± 2%, and increased ⁹⁹Tc^m over the thigh by 68±10% (P< 0·01, n = 8) with no further changes during the sustained tilt. Haematocrite increased during head-up tilt from 43·1 ± 0·3 to 47·9 ± 0·6% (P<0·01, n= 8). Accordingly, the increase in TI (6·3 ± 0·6 vs. 4·5 0·4 Ohm, n= 6) and the decrease in Z° through one leg (7·2 ± 1·2 vs. 2·8 ± 0·5 Ohm, n= 6) at 2·5 kHz was more pronounced than at 100 kHz. Also the changes in TI were correlated to CBV as calculated from ⁹⁹T_c^m and haematocrite (r = 0.90, P < 0·01). The results suggest that: (1) Hypovolaemic shock is associated with a faster increase of TI than normotensive head-up tilt. (2) Head-up tilt is characterized by an initial decrease in CBV followed by a further decrease in plasma volume, which eventually leads to hypovolaemic shock. (3) Blood volume changes during head-up tilt are reflected in regional Z°.     

Middle cerebral artery velocity during head-up tilt induced hypovolemic shock in humans

Summary. Middle cerebral artery mean velocity (V_mean) and pulsatility index (PI) were followed during head-up tilt induced hypovolaemic shock in nine subjects. Mean arterial pressure (MAP), heart rate (HR), central venous pressure (CVP) and thoracic (TI) electrical impedance were also recorded. V_mean, PI, and CVP did not change during head-up tilt to 50°, while MAP increased from 92 (81–106) (median and range) to 100 (97–112) mmHg, HR from 63 (53–74) to 84 (68–89) beats min^-1 and Tl_100kHz from 30 (27–36) to 32 (30–39) Ohm (P < 0.01) (n= 8). During maintained tilt, V_mean decreased from 52 (32–72) to 34 (16–59) cms^-1, whereas HR increased to 87 (52–108) beats min^-1 and Tl_100kHz to 33 (31–39) Ohm (P < 0.01). Presyncopal symptoms appeared after 33 (3–46) min and were associated with a MAP of 65 (32–84) mmHg (P < 0.01) and a HR of 58 (52–71) beats min^-1 (P < 0.05).V_mean decreased to 25 (16–36) cms^-1, and cerebral conductance index (V_mean/MAP_brain) and PI increased (P < 0.01). Arterial collapse was observed (diastolic velocity of zero) in one subject at a brain (diastolic) blood pressure of 21 mmHg and he developed tachycardia (131 beats min^-1) during presyncope. P_aCO₂ did not change. Maintained tilt resulted in central volume depletion reflected by changes in MAP, HR, and thoracic electrical impedance but not in CVP. Transcranial Doppler derived indices of cerebral perfusion demonstrated critically low values despite marked increase in conductance index.     

An association between anxiety and neurocardiogenic syncope during head-up tilt table testing

To study the association between anxiety and neurocardiogenic syncope as determined by head-up tilt table testing (HUT) in men and women with presyncope or syncope, patients with unexplained syncope or presyncope undergoing HUT were asked to complete the Burns Anxiety Inventory (BAI), a validated inventory of 33 questions with responses graded from 0 to 3. HUT consisted of a 30-minute tilt to 60 degrees, which if negative, was repeated with an isoproterenol infusion. A positive HUT was defined as symptomatic hypotension and/or bradycardia. Of the 66 patients who completed the BAI and underwent HUT, 33 were men and 33 were women. The mean age was 57 +/- 18 years (17-91 years). Patients with a positive HUT had a higher BAI score than those with a negative HUT (22 +/- 12 vs 14 +/- 13, P = 0.017). This association was stronger in women with a BAI score of 24 +/- 11 in those with a positive HUT versus 13 +/- 8 in those with a negative HUT (P = 0.005). In contrast, the mean BAI score for men with a positive HUT was 19 +/- 13, as compared to 15 +/- 16 for a negative HUT (P = 0.5). In conclusion, the present study demonstrates a statistical association between anxiety (as determined by BAI) and HUT result. Gender-based analysis revealed a more statistically significant relationship between anxiety and HUT outcome for women as compared to men.     

Changes in the transthoracic impedance signal predict the outcome of a 70 degrees head-up tilt test

We determined whether early changes in central haemodynamics, as determined by transthoracic impedance, induced by a 70 degrees head-up tilt (HUT) test could predict syncope. Heart rate, arterial blood pressure and central haemodynamics [pre-ejection period and rapid left ventricular ejection time ( T (1)), slow ejection time ( T (2)) and d Z /d t (max) (where Z is thoracic impedance), assessed by the transthoracic impedance technique], were recorded during supine rest and during a 45 min 70 degrees HUT test in 68 patients (40+/-2 years) with a history of unexplained recurrent syncope. We found that 38 patients (42+/-3 years) had a symptomatic outcome to 70 degrees HUT (fainters) and 30 (39+/-2 years) had a negative outcome (non-fainters). When measured between 5 and 10 min of 70 degrees HUT, T (2) had increased significantly only in the fainters, and a change in T (2) of >40 ms from baseline predicted a positive outcome with a sensitivity of 68% and a specificity of 70%. During supine rest prior to 70 degrees HUT, the fainters exhibited a shorter T (2) than non-fainters (183+/-10 compared with 233+/-14 ms; P <0.01), and a T (2) of <199 ms predicted a positive outcome to 70 degrees HUT with a sensitivity of 68% and a specificity of 63%. Incorporation of the changes that occurred from rest to 70 degrees HUT in other haemodynamic variables (heart rate >11 beats/min, systolic pressure <2 mmHg, diastolic pressure <7 mmHg and pulse pressure <-3 mmHg) increased the specificity to 97% and the positive predictive value to 93%. Thus transthoracic impedance could detect differences in central haemodynamics between fainters and non-fainters during supine rest and during the initial period of 70 degrees HUT with a consistent sensitivity and specificity when combined with peripheral haemodynamic variables.     

Automated sphygmomanometer in spinal cord injured patients during head-up tilt: an evaluation

Fifteen patients with spinal cord injury above T6 who were complete or had sensory sparing only were monitored during head-up tilt to evaluate the clinical application of an indirect blood pressure monitoring device, Vital Signs Measurement System. Comparisons of the machine's auscultatory and oscillometric modes were made to simultaneously auscultated blood pressures obtained by a physician. Mean differences and standard deviations were calculated. The comparison between automatic auscultatory and manual pressures yielded a mean difference and standard deviation of 1.8 mmHg and 4.2 mmHg for systolic, and -0.8 mmHg and 4.9 mmHg for diastolic pressures. The comparison between automatic oscillometric and manual pressures yielded a mean difference and standard deviation of 2.2 mmHg and 7.1 mmHg for systolic, and -12.7 mmHg and 7.5 mmHg for diastolic. All automatically obtained values except oscillometric diastolic pressure indicate machine accuracy suitable for clinical testing when compared to standards set by the Association for the Advancement of Medical Instrumentation for ideal test conditions. Uncontrolled patient or tubing movement, room noise, and the small subject population may have contributed to the less favorable values. This study suggests that the automatic sphygmomanometer tested is capable of clinically acceptable accuracy in a very dynamic setting.     

Cerebral oxygenation monitor during head-up and -down tilt using near-infrared spatially resolved spectroscopy

Reflectance near-infrared spectroscopy (NIRS) has become a suitable and easily manageable method to monitor cerebral oxygenation changes in presyncopal and syncopal symptoms caused by postural changing or standing. A new clinical tissue oxygenation monitor has been recently developed which measures absolute tissue haemoglobin saturation (Tissue Oxygenation Index, TOI) utilizing spatially resolved spectroscopy (SRS). The present study examined the effects of postural changes on cerebral oxygenation as reflected in SRS-NIRS findings. Cerebral oxyhaemoglobin (O2Hb), deoxyhaemoglobin (HHb), and the TOI were recorded from both sides of the forehead in five healthy male subjects (age range, 28-40 years) during 90 degrees head-up tilt (HUT) and -6 degrees head-down tilt (HDT). Three series of measurements were carried out on separate days. O2Hb was decreased during HUT. TOI was significantly lower in HUT than in the supine position (SUP). There was no significant change in TOI during HDT. A significant session effect was observed in the left forehead TOI during SUP, but not in the right. SRS-NIRS measurements confirmed sub-clinical alterations of cortical oxygenation during HUT. NIRS data from the left side of the forehead, which may vary with cognitive or emotional activation, were more variable than those from the right side.     

Interrelationships among body mass, thyrotropin, thyroid hormones, and thyroid-hormone binding proteins in healthy 70-year-old men

In a previous study of a representative population of 460 men of age 70, we found that the free thyroxin (free T4) concentration was negatively correlated to body mass. In the present study we analyzed other indicators of thyroid function in relation to body mass and body mass index in 181 individuals without any disease or medication influencing thyroidal homeostasis or body mass. There was a significant negative relationship between body mass and body mass index and free T4, total T4, and 3,3',5'-triiodothyronine (rT3). Thus, individuals with high body mass normally had lower circulating concentrations of these hormones than lean individuals, whereas there was no such relationship for thyrotropin or 3,5,3'-triiodothyronine (T3). The thyroid-hormone binding proteins (thyroxin-binding globulin, prealbumin, and albumin) did not correlate with body mass or body mass index. As expected, thyroxin-binding globulin correlated with T4, T3, and rT3, but not with free T4 or thyrotropin. Concentrations of serum albumin correlated with T3 and rT3 concentrations but not with free T4, T4, or thyrotropin concentrations. Thyrotropin concentrations correlated negatively with free T4, T4, and rT3, but not with T3, indicating that circulating T4 plays the dominant role in feedback regulation of thyrotropin in healthy individuals.     

Isometric and isokinetic knee extension and flexion torque in men and women aged 20-70

An investigation was made of the influence of age and sex on peak muscle torque in knee extension and flexion during maximal isokinetic and isometric contraction. The study was performed on both legs of 139 clinically healthy men and 141 clinically healthy women aged 20, 30, 40, 50, 60 or 70 years. Maximum knee extension and flexion muscle torque (Newtonmetre, Nm) was measured isokinetically at various angles of velocity (12, 90 and 150 degrees/s) and isometrically under standardized conditions (Cybex II). No significant differences were found between the right and the left leg in the whole material. Muscle torque was higher in men than in women in all age groups (p less than 0.001). Both isokinetic and isometric torque decreased with age in both sexes. Isokinetic torque decreased significantly (p less than 0.05) between 20 and 30 years of age in men and between 40 and 50 years of age in women (at all velocities studied; p less than 0.05). A significant decrease (p less than 0.05) was found between the ages of 60 and 70 years in both sexes. Maximum isometric torque showed a significant decrease (p less than 0.05) between 60 and 70 years in men and women. There were no significant differences in isokinetic or isometric torque between moderately active and inactive men or women. Significant correlations were found between muscle torque and body weight, height and body surface area.     

Common carotid and common femoral arterial dynamics during head-up tilt in persons with spinal cord injury

We examined the effect of the level and completeness of spinal cord injury (SCI), tetraplegia and paraplegia, on common carotid arterial (CCA) and common femoral arterial (CFA) functions supine and during head-up tilt (HUT), compared with able-bodied controls. Subjects (tetraplegia [n = 7], paraplegia [n = 8], and controls [n = 8]) were healthy males between the ages of 19 and 60 years. We used Doppler ultrasound to determine vessel diastolic diameters and flow velocities while supine and at 45 HUT. The results indicated that supine CCA diameter and flow were augmented in the tetraplegia group compared with the paraplegia group (p < 0.05); no other group differences were noted. However, CCA(flow) was significantly reduced from supine to 45 HUT in the tetraplegia group (p < 0.01). CFA diameter and flow were significantly reduced in the SCI groups compared with the control group, and CFA(flow) was reduced from supine to 45 HUT in the tetraplegia group. These results demonstrate that individuals with tetraplegia have increased resting CCA diameters and flows compared with individuals with paraplegia, an adaptation which may contribute to orthostatic tolerance. The significant reduction in CFA(flow) from supine to 45 HUT in the tetraplegia group may be related to the completeness of lesion rather than the level of lesion.     

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

AIMS: 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). METHODS AND RESULTS: 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). CONCLUSION: 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.     

Renal haemodynamic and sympathetic responses to head-up tilt in essential hypertension

Nine mild-to-moderate hypertensive patients (HT), aged 41 +/- 0.6 years (mean +/- SEM) and nine age-matched normotensive control subjects (NT) were tilted to 60 degrees for 10 min. During tilt, both systolic (S) blood pressure (BP) (p less than 0.01) and diastolic (D) BP (p less than 0.05) increased in HT, but not in NT. At supine rest renal blood flow was higher in HT than in NT and increased by 17% in HT during tilt, while a decrease of 13% was observed in NT (p less than 0.05). Renal vascular resistance was unchanged in HT during tilt, while a significant increase (p less than 0.01) was observed in NT. Arterial plasma noradrenaline increased in both groups (p less than 0.05) during tilt, significantly more in HT than in NT (p less than 0.05). No statistically significant difference was observed between the groups in renal catecholamine uptake or release. Our data indicate enhanced general sympathetic and circulatory responses to tilt in subjects with mild-to-moderate essential hypertension. However, the enhanced haemodynamic and sympathetic responses were not shared by hypertensive kidneys and renovascular resistance remained unaffected by tilt.     

Increased dispersion of ventricular repolarization during head-up tilt test late after orthotopic heart transplantation in humans

Sympathetic reinnervation after heart transplantation may be regionally heterogeneous. It remains undetermined if such heterogeneous reinnervation will result in increased ventricular repolarization dispersion. To determine the changes of ventricular repolarization after transplantation, a 15-minute, 80-degree head-up tilt test was prospectively performed with isoproterenol provocation in 30 patients who were studied within 5 months after transplantation (early group) and 30 patients who were studied > or =12 months (late group). Holter monitor was initiated to evaluate heart rate variability, which was a surrogate of cardiac reinnervation. JT dispersion was defined as the difference between maximal and minimal JT interval measurements occurring among any of the 12 leads on a standard electrocardiogram. No subject had fewer than nine measurable leads. Compared with patients in the early group, the patients in the late group had higher low frequency activity, indicating partial sympathetic reinnervation. Analysis of the electrocardiogram showed that there were significant differences in the corrected JT dispersion in the late group compared with the early group and controls (74+/-18 vs 56+/-15 and 55+/-14 ms, both P <0.05) during isoproterenol infusion. Head-up tilt test is a useful tool to unmask the increased dispersion of ventricular repolarization, particularly during states of isoproterenol infusion. Early after cardiac transplantation, neither postural changes nor isoproterenol infusion caused a significant increase of corrected JT dispersion. Late after transplantation, heterogeneous sympathetic reinnervation may result in increased corrected JT dispersion. However, whether increased dispersion of ventricular repolarization is related to cardiac death late after operation warrants further investigation in a large and long-term trial.     

Dynamic changes of P-wave duration and P-wave axis during head-up tilt test in patients with vasovagal syncope

BACKGROUND: 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. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.     

Frequency-domain analysis of heart rate variability during positive and negative head-up tilt test: importance of age

The study of autonomic behavior during a head-up tilt test (HUT) has been deemed important to understand the loss of consciousness mechanism. Though HRV in patients with HUT(+) and HUT(-) has been compared, few trials emphasized the importance of age. HRV in frequency domain was analyzed based on 5-minute samples in the supine position, and between 5 and 10 minutes during early tilt test (R1) in 102 patients with one or more episodes of syncope (mean age 44.3 +/- 20.8, range 15-85 years, 55 women). Two subgroups were selected afterwards: (1) young patients between 15 and 35 years of age (41 patients) and (2) elderly patients aged 60 or more (36 patients). The following parameters were taken into account: the sum of low (LF) and high frequency (HF) (LF and HF in absolute values and in normalized units), the LF/HF ratio (L/H ratio), and the percentage of change between baseline and R1 values. The HRV behavior in young and elderly patients with positive and negative HUT was established. We then analyzed the correlation between HRV and age and HUT outcome. A multiple regression analysis encompassing age, HUT outcome, gender, and number of syncope episodes was performed. In young patients, the LF and HF areas and the L/H ratio changed significantly between baseline and R1. The L/H ratio increases from baseline to R1. Conversely, these differences were not significant in the elderly. No differences between HUT(+) and HUT(-) within the same age group were observed. Age related significantly to practically all HRV parameters analyzed, whereas the tilt test outcome correlates poorly with HF normalized units and LF normalized units during R1, and the L/H ratio changes between baseline and R1. By means of a multivariate analysis, only age shows a significant correlation with the HRV values. Despite an all age triggering of vasovagal syncope during HUT, the young and elderly patients' autonomic behavior differs. The young considerably increase their sympathovagal balance during HUT, whereas the elderly have a mitigated autonomic response. No significant differences were observed during the first minutes of the test between those with a HUT(+) and those with a HUT(-) within the same age group. Age, and not the HUT response, is the major determinant of the autonomic behavior during early HUT.