Clinical Significance of the Sympathetic Nervous System in the Development and Progression of Pulmonary Arterial Hypertension.

BACKGROUND: Pulmonary arterial hypertension (PAH) is defined as a complex disease of clinically characterized by elevated pulmonary pressure eventually resulting in right heart failure and premature death. To date, PAH still remains a life-threatening disease. Published evidence suggests that patients with PAH present profound sympathetic nervous system abnormalities and sympathetic activity has been shown to be increased. The mechanism of PAH is still complex and poorly understood. RESULTS: Some data have showed that adrenoceptors are involved in the process of the pathology and have different functions in the progression of PAH followed by heart failure. Alpha-adrenergic receptors mediate most excitatory effects and induce growth of smooth muscle cells and adventitial fibroblasts via complex cellular and molecular mechanisms. However, beta-adrenergic receptor mainly detected in endothelial layer commonly exerts relaxation effects on pulmonary artery. In addition, G protein-coupled receptor kinase 2, the primary G protein-coupled receptor kinase expressed in the heart, has been shown to be increased, resulting in the distinctive loss of inotropic reserve and functional capacity of the failing heart according to the activation of sympathetic nervous system. CONCLUSION: Here, we summarize the relevant available studies describing the roles of sympathetic nervous system in the progression of PAH.

Treatment of bilateral idiopathic trigeminal neuralgia by radiofrequency thermocoagulation at different temperatures.

Radiofrequency thermocoagulation (RFT) is an effective treatment for trigeminal neuralgia, but consensus regarding an optimal treatment temperature is lacking. While treatment temperatures ranging from 60°C to 95°C have been reported, RFT at too high a temperature is often followed by serious complications, and comparative evaluations of RFT at different temperatures in a single study are rare.This current prospective cohort study was to compare immediate and long-term outcomes of RFT at varying temperatures in patients with bilateral idiopathic trigeminal neuralgia (ITN) of maxillary division of trigeminal nerve (V2), mandibular division of trigeminal nerve (V3), and V2+V3, including pain relief, complications, recurrence rate, and patient satisfaction. From May 2011 to April 2016, 62 consecutive patients with bilateral ITN of V2, V3, and V2+V3 were enrolled in the study. These patients underwent bilateral RFT at 68°C and 75°C, respectively, using the same RF parameters. Side-to-side results, including pain relief, complications, and patient satisfaction, were compared during a 5-year follow-up period.Overall pain relief was satisfactory after RFT. The rate of pain relief after treatment at 75°C was slightly higher than at 68°C (P > 0.05). The pain-free rate was 95.1% at 75°C and 93.5% at 68°C at 1 year, 84.3% and 78.1% at 3 years, and 80.7% and 74.4% at 5 years. There were 10 and 13 cases of recurrence, respectively, and 6 cases of bilateral recurrence. The incidence and severity of complications were greater at 75°C (P < 0.05) than at 68°C, and therefore the patient satisfaction at the higher temperature was lower (P < 0.05).Patients with bilateral ITN who underwent RFT at different temperatures had consistent pain relief after RFT at both 75°C and 68°C, but there were fewer and less severe complications at 68°C, which was accompanied by greater patient satisfaction. This suggests that RFT at lower temperatures may be preferable, and that a temperature of 68°C can be recommended.

Effect of thigh cuffs on haemodynamic changes of the middle cerebral artery and on orthostatic intolerance induced by 10 days head-down bed rest.

Thigh cuffs are used by cosmonauts to limit fluid shift during space flight, but the appropriate level of cuff pressure and the duration of application to optimize their beneficial effects require further detailed investigations. In the present study, 10 days head-down tilt (HDT) bed rest was performed to assess the effects of thigh cuffs (40 mmHg, 10 h/day) on haemodynamic changes of the middle cerebral artery (MCA) and on orthostatic tolerance in six healthy male volunteers. Another six healthy male volunteers without thigh cuffs served as the control group. Haemodynamic parameters of the MCA were measured using transcranial Doppler. Orthostatic tolerance was assessed before and after HDT. After HDT, the mean upright time in the control and thigh cuff groups was 14.0 +/- 4.1 and 19.2 +/- 0.7 min, respectively. Compared with values before HDT, the percentage increase in heart rate from baseline in the upright position after HDT was significantly higher in the control group and the percentage change from baseline of mean diastolic arterial blood decreased more after HDT in this group. In the control group, systolic blood velocity (Vs) and mean blood velocity (Vm) of the right MCA decreased significantly during HDT. In the thigh cuffs group, the Vs of the right MCA decreased significantly on Days 3 and 7 of HDT and the Vm of the right MCA decreased significantly on Day 7 of HDT. The results indicate that daily use of thigh cuffs during 10 days of HDT does not completely prevent the decrease in haemodynamics of the right MCA, but is effective in preventing orthostatic intolerance.

Effect of lower-body negative pressure on cerebral blood flow velocity during 21 days head-down tilt bed rest.

BACKGROUND: The purpose of this study was to investigate cerebral blood flow (CBF) velocity in humans during 21 days of head-down tilt (HDT) bed rest with and without lower-body negative pressure (LBNP). MATERIAL/METHODS: Twelve healthy male volunteers were exposed to -6 degrees HDT bed rest for 21 days. Six subjects received -30 mmHg LBNP sessions for 1 h per day from the 1st to the 7th day and from the 15th to the 21st day of HDT, and six others served as controls. CBF velocity was measured by use of the transcranial Doppler technique in the right middle cerebral artery before and during HDT. RESULTS: In the control group, mean and systolic CBF velocities decreased on day 1 of HDT compared with the pre-HDT value, and dropped further on day 3 of HDT, then remained significantly below the pre-HDT baseline on days 7 and 10 of HDT, and reached a minimum value on day 21 of HDT. In the LBNP group, mean and systolic CBF velocities decreased significantly on day 1 of HDT compared with the pre-HDT value, and remained lowered throughout HDT. Diastolic CBF showed no significant change throughout HDT in both groups. There were no significant differences in these parameters between the two groups. CONCLUSIONS: The results of this study suggest that CBF velocity is reduced during 21 days of HDT, and brief daily LBNP sessions used in the first and last weeks of 21-day HDT bed rest does not improve CBF velocity.

Effect of lower body negative pressure on orthostatic tolerance and cardiac function during 21 days head-down tilt bed rest.

The purpose of the present study was to investigate the changes of orthostatic tolerance and cardiac function during 21 d head-down tilt (HDT) bed rest and effect of lower body negative pressure in the first and the last week in humans. Twelve healthy male volunteers were exposed to -6 degrees HDT bed rest for 21 d. Six subjects received -30 mmHg LBNP sessions for 1 h per day from the 1st to the 7th day and from the 15th to the 21st day of the HDT, and six others served as control. Orthostatic tolerance was assessed by means of standard tilt test. Stroke volume (SV), cardiac output (CO), preejection period (PEP) and left ventricular ejection time (LVET) were measured before and during HDT. Before HDT, all the subjects in the two groups completed the tilt tests. After 10 d and 21 d of HDT, all the subjects of the control group and one subject of the LBNP group could not complete the tilt test due to presyncopal or syncopal symptoms. The mean upright time in the control group (15.0 +/- 3.2 min) was significantly shorter than those in the LBNP group (19.7 +/- 0.9 min). SV and CO decreased significantly in the control group on days 3 and 10 of HDT, but remained unchanged throughout HDT in the LBNP group. A significant increase in PEP/LVET was observed on days 3 and 14 of HDT in both groups. The PEP/LVET in the LBNP group was significantly lower on day 3 of HDT, while LVET in the LBNP group was significantly higher on days 3, 7 and 14 of HDT than those in the control group. The results of this study suggest that brief daily LBNP sessions used in the first and the last weeks of 21 d HDT bed rest were effective in diminished the effect of head-down tilt on orthostatic tolerance, and LBNP might partially improve cardiac pumping function and cardiac systole function.

[Effects of simulated microgravity on cardiovascular function and counter effect of lower body negative pressure].

Studies on effect of simulated microgravity on cardiovascular function and counter effect of lower body negative pressure (LBNP) in recent years were summarized. The mechanism of simulated microgravity induced orthostatic intolerance may involve the reduction of cardiovascular function and cerebral blood flow, and endocrine changes. The significance of mathematical model in the study of mechanism of microgravity induced orthostatic intolerance was also discussed. The counter effect of LBNP was emphasized.

[Effects of 21 d -6 degrees bed rest on diastolic function of human left ventricle].

Objective. To investigate the effects of head down bed rest (HDBR), the simulated weightlessness, on the diastolic function of human left ventricle, and to discuss its role in cardiovascular deconditioning after space flight. Method. Six healthy young volunteers were subjected to -6 degrees HDBR for 21 d. Ultrasound Doppler technique was used to examine the changes of the diastolic function before, on the 10th, and 21st day during and 2nd day after HDBR. The orthostatic tolerance was also tested before and after HDBR. Result. Peak E-wave velocity (PEV) , peak A-wave velocity (PAV) , and velocity total integration of E-wave (VTI E), were significantly decreased (P<0.05) on the 10th and 21st day during and the 2nd day after HDBR, and velocity, total integration of A-wave (VTI A), ratio of E/A, and ratio of VTI E/A were also decreased, but did not reach the significant level (P>0.05). None of the six subjects passed the orthostatic tolerance test after HDBR. Conclusion. Simulated weightlessness can induce marked decline in diastolic function of human left ventricle.

[Effects of lower body negative pressure in the first and last week during 21 d head-down bed rest on orthostatic tolerance and cardiac function].

OBJECTIVE: To investigate the changes of orthostatic tolerance and cardiac function during 21 d head-down tilt (HDT) bed rest and effect of lower body negative pressure (LBNP) in the first and the last weeks in humans. METHOD: Twelve healthy male volunteers were exposed to -6 degrees HDT bed rest for 21 d. Six subjects received -30 mmHg LBNP sessions for 1 h/d from the 1st to the 7th day and from the 15th to the 21st day of the HDT, and the other six who did not receive LBNP served as control. Orthostatic tolerance was assessed by means of standard tilt test. The cardiac pumping function and cardiac systolic function were measured before and during HDT. RESULT: Before HDT, all the subjects in the two groups completed the tilt tests. After 10 d and 21 d of HDT, all the subjects of the control group and one subject of the LBNP group could not complete the tilt test due to presyncopal or syncopal symptoms. The mean time of upright standing in the control group (15.0 +/- 3.2 min) was significantly shorter than those in the LBNP group (19.7 +/- 0.9 min). The stroke volume and cardiac output decreased significantly in the control group on days 3 and 10 of HDT, but remained unchanged throughout HDT in the LBNP group. A significant increase in preejection period (PEP)/left ventricular ejection time (LVET) was observed on days 3 and 14 of HDT in both groups. The PEP/LVET in the LBNP group was significantly lower than those in the control group on days 3 of HDT, while LVET in LBNP group was significantly higher than those in the control group on days 3, 7 and 14 of HDT. CONCLUSION: It is suggested that the brief daily LBNP sessions in the first and the last weeks were effective in preventing orthostatic intolerance and the reduction of cardiac pumping function and cardiac systole function induced by 21 d HDT bed rest.

Effect of lower body negative pressure against orthostatic intolerance induced by 21 days head-down tilt bed rest.

BACKGROUND: Exposure to actual or simulated weightlessness is known to induce orthostatic intolerance in humans. Many different methods have been suggested to counteract orthostatic hypotension. The repetitive or prolonged application of lower body negative pressure (LBNP) has shown beneficial effects to counter orthostatic intolerance, but devoting so much time to countermeasures is not compatible with space mission objectives or costs. The purpose of the present study was to assess the effects of brief LBNP sessions against orthostatic intolerance during a 21-d head-down tilt (HDT) bed rest. METHODS: There were 12 healthy male volunteers who were exposed to -6 degrees HDT bed rest for 21 d. Six subjects received -30 mm Hg LBNP sessions for 1 h x d(-1) from day 15 to day 21 of the HDT, and six others served as control. Orthostatic tolerance was assessed by means of standard tilt test. RESULTS: Before HDT, all the subjects in the two groups completed the tilt tests. After 21 d of HDT, five subjects of the control group and one subject of the LBNP group could not complete the tilt test due to presyncopal or syncopal symptoms. The mean upright time in the control group 13.0 +/- 4.0 min) was significantly shorter (p < 0.05) than that in the LBNP group (19.0 +/- 2.2 min). Body weight decreased significantly in the control group during HDT, while increasing significantly on day 21 of HDT in the LBNP group. Urine volume increased on days 15-21 of HDT in the control group, but remained unchanged throughout HDT in the LBNP group. A significant decrease in cardiac output and cardiac index, and a significant increase in total peripheral resistance, pre-ejection period, plasma renin activity, aldosterone, and prostaglandin 12 were observed during HDT in both groups. There were no significant differences in these parameters between the two groups. CONCLUSIONS: Brief daily LBNP sessions were effective in preventing orthostatic intolerance induced by 21 d HDT bed rest. However, it did not improve cardiac pump and systolic functions and did not preserve volume regulating hormones.