Reduced systemic vascular resistance is the underlying hemodynamic mechanism in nitrate-stimulated vasovagal syncope during head-up tilt-table test

AbstractBackgroundNitroglycerin (NTG) challenge during head-up tilt-table testing (HUTT) is often utilized to determine the etiology of unexplained vascular syncope. However, conflicting results concerning nitrate-induced hemodynamic changes during HUTT have been reported. The purpose of this study was to assess the determinants of presyncopal symptoms during NTG-stimulated HUTT.MethodsWe evaluated 40 patients with suspected vasovagal syncope. Beat-to-beat changes in blood pressure, heart rate (HR), cardiac index (CI), and systemic vascular resistance (SVR) during HUTT were measured with thoracic impedance cardiography and a plethysmographic finger arterial pressure monitoring device.ResultsNone of the 40 patients complained of presyncopal symptoms during passive HUTT. However, after the administration of NTG 28 patients showed presyncopal symptoms (NTG+ group) and the remaining 12 patients did not (NTG– group). HR, CI, and the stroke index did not significantly differ between the two groups, whereas mean arterial pressure and SVR were significantly lower in the NTG+ group.ConclusionsPresyncopal symptoms during NTG-stimulated HUTT are SVR mediated, not cardiac output mediated. This study challenges the conventional idea of a decrease in cardiac output mediated by NTG as the overriding cause of presyncopal symptoms during HUTT

Reduced Sympathetic Response to Head-Up Tilt in Subjects with Mild Cognitive Impairment or Mild Alzheimer's Dementia

Background: Hemodynamic control was compared in patients with mild cognitive impairment (MCI) or mild Alzheimer's dementia (AD) as well as in healthy elderly subjects. Methods: Noninvasive, continuous hemodynamic recordings were obtained from 14 patients and 48 controls during supine rest (tilt of 30 and 70°). Cardiac output, end-diastolic volume, total peripheral resistance, heart rate variability (HRV), systolic blood pressure variability (SBPV), and baroreceptor sensitivity were calculated. Results: At 70° tilt, the HRV indices differed significantly, with higher high-frequency (HF) variability as well as lower low-frequency (LF) variability and LF/HF ratios in the patients. The patients had significantly lower SBPV in the LF range at 30° tilt. Conclusions: The results indicate a poorer sympathetic response to orthostatic stress in MCI and mild AD

Adolescent chronic fatigue syndrome; a follow-up study displays concurrent improvement of circulatory abnormalities and clinical symptoms

<p>Abstract</p> <p>Background</p> <p>The pathophysiology of chronic fatigue syndrome (CFS) in adolescents is unknown, and the clinical course and prognosis is still questioned. Recent research indicates that abnormalities of autonomic cardiovascular control may play an important role. The aim of this research project was to perform a follow-up study of adolescents with chronic fatigue syndrome, focusing on clinical symptoms and autonomic cardiovascular control.</p> <p>Methods</p> <p>47 adolescents (12-18 years old) with CFS were recruited from the outpatient clinic at the Department of Pediatrics, Oslo University Hospital. In a primary visit and a follow-up visit (3-17 months later), we evaluated: a) a wide range of complaints and symptoms and b) cardiovascular variables at baseline and during a 20° head-up tilt-test (HUT).</p> <p>Results</p> <p>At the second visit, patients reported significant improvement regarding functional impairments, fatigue severity, muscular pain, concentration problems, post-exertional malaise and the problem of non-relieving rest. Also, at the second visit, baseline heart rate (HR), blood pressure, total peripheral resistance index (TPRI) and LF/HF (low-frequency:high-frequency heart rate variability ratio, an index of sinus node sympathovagal balance derived from spectral analyses of heart rate) were significant lower, and the increases in HR, mean blood pressure (MBP), diastolic blood pressure (DBP) and TPRI during tilt were significantly less pronounced as compared to the first visit. There was a significant correlation between changes in autonomic symptom score, fatigue severity score and functional impairment score from the first to the second visit.</p> <p>Conclusions</p> <p>The majority of adolescents with CFS experienced an improvement over time in functional impairment, self-reported fatigue and additional symptoms, and a concurrent improvement of autonomic cardiovascular control. A possible connection between clinical symptoms and abnormal autonomic control in CFS might represent a focus for further research.</p

Cardiovascular responses to a glucose drink in young male individuals with overweight/obesity and mild alterations in glucose metabolism, but without impaired glucose tolerance

Little is known about whether mild aberrations in glucose metabolism, which are seen in overweight/obese subjects (OW/OB) without impaired glucose tolerance, affect regulator control elements for blood pressure homeostasis. Methods Hence, we measured in age-matched male subjects with normal weight (n = 16; BMI = 22.4 kg m−2) and OW/OB (n = 11; BMI = 28.6 kg m−2) continuous beat-to-beat blood pressure, heart rate, stroke volume, myocardial contractility and baroreflex sensitivity during a 30 min baseline and for 120 min after the ingestion of 75 g glucose dissolved in 300 mL tap water (OGTT). Blood samples for the assessment of plasma glucose and insulin were collected at baseline and every 30 min after the drink and homeostatic model assessment of insulin resistance (HOMA-IR) was calculated. Results At baseline, glucose (5.3 ± 0.4 SD vs 5.0 ± 0.4 mmol L−1; p = 0.01), insulin (7.4 ± 0.4 vs 3.7 ± 2.7 mU L−1; p = 0.02) and HOMA-IR (1.8 ± 1.3 vs 0.8 ± 0.6; p = 0.01) were significantly higher in subjects with OW/OB, but none classified as having impaired glucose tolerance (plasma glucose levels  7.8 mmol L−1 at 120 min post- OGTT) or hypertension (all  130/80 mmHg at baseline). In response to the glucose drink, and in comparison to subjects with normal weight, we observed in subjects with OW/OB a trend towards increased plasma insulin levels (+7445 ± 4858 vs. +4968 ±  1924 mU h L−1; p = 0.08), which was not seen for blood glucose (p = 0.59). Moreover, subjects with OW/OB showed impaired peripheral vasodilation, diminished heart rate and myocardial contractility responses but increased peripheral pulse pressure (all p   0.05). Conclusions Young male subjects with OW/OB, but without glucose intolerance or hypertension, showed attenuated peripheral vasodilation and diminished cardiac responses to a glucose drink

Relationship between changes in pulmonary V˙O2 kinetics and autonomic regulation of blood flow

Various regulatory mechanisms of pulmonary oxygen uptake () kinetics have been postulated. The purpose of this study was to investigate the relationship between vagal withdrawal, measured using RMSSDRR, the root mean square of successive differences in cardiac interval (RR) kinetics, a mediator of oxygen delivery, and kinetics. Forty-nine healthy adults (23 ± 3 years; 72 ± 13 kg; 1.80 ± 0.08 m) performed multiple repeat transitions to moderate- and heavy-intensity exercise. Electrocardiography, impedance cardiography, and pulmonary gas exchange parameters were measured throughout; time domain measures of heart rate variability were subsequently derived. The parameters describing the dynamic response of , cardiac output () and RMSSDRR were determined using a mono-exponential model. During heavy-intensity exercise, the phase II τ of was significantly correlated with the τ of RR (r = 0.36, P < 0.05), Q (r = 0.67, P < 0.05), and RMSSDRR (r = 0.38, P < 0.05). The τ describing the rise in Q explained 47% of the variation in τ, with 30% of the rate of this rise in Q explained by the τ of RR and RMSSDRR. No relationship was evident between kinetics and those of Q, RR, or RMSSDRR during moderate exercise. Vagal withdrawal kinetics support the concept of a centrally mediated oxygen delivery limitation partly regulating kinetics during heavy-, but not moderate-, intensity exercise