Sympathovagal balance: how should we measure it? (1/148)

There are complex interactions between the sympathetic and parasympathetic nervous system inputs to the sinus node. The concept of "sympathovagal balance" reflects the autonomic state resulting from the sympathetic and parasympathetic influences. Despite widespread usage of a variety of heart rate (HR) variability parameters as indexes of sympathovagal balance, no index has been validated as a measure of sympathovagal balance. This study evaluated the utility of HR, HR variability, and a new parameter termed the vagal-sympathetic effect (VSE) as indexes of sympathovagal balance. The ideal parameter had to satisfy the following criteria: 1) the index should vary similarly among subjects in response to different autonomic conditions; 2) the variability in the index among subjects exposed to the same autonomic conditions should be small; and 3) the response of the index to various autonomic conditions should reflect the underlying changes in physiological state and have a meaningful interpretation. Volunteers [8 men, 6 women; mean age 28.5 +/- 4.8 (SD) yr] were evaluated for the effects of sympathetic and parasympathetic stimulation and blockade on HR and HR variability. VSE was defined as the ratio of the R-R interval to the intrinsic R-R interval. VSE and R-R interval consistently changed in the expected directions with parasympathetic and sympathetic stimulation and blockade. A general linearized model was used to evaluate the response of each parameter. VSE and R-R interval had r2 values of 0.847 and 0.852, respectively. Natural logarithm of the low-frequency power had an r2 value of 0.781 with lower r2 values for all the other HR variability parameters. The coefficient of variation was also lowest for each condition tested for the VSE and the R-R interval. VSE and R-R interval best satisfy the criteria for the ideal index of sympathovagal balance. Because it is impractical under most conditions to measure the VSE as the index of sympathovagal balance, the most suitable index is the R-R interval.  (+info)

Lumbar sympathetic blocks speed early and second stage induced labor in nulliparous women. (2/148)

BACKGROUND: Rapid cervical dilation reportedly accompanies lumbar sympathetic blockade, whereas epidural analgesia is associated with slow labor. The authors compared the effects of initial lumbar sympathetic block with those of epidural analgesia on labor speed and delivery mode in this pilot study. METHODS: At a hospital not practicing active labor management, full-term nulliparous patients whose labors were induced randomly received initial lumbar sympathetic block or epidural analgesia. The latter patients received 10 ml bupivacaine, 0.125%; 50 microg fentanyl; and 100 microg epinephrine epidurally and sham lumbar sympathetic blocks. Patients to have lumbar sympathetic blocks received 10 ml bupivacaine, 0.5%; 25 microg fentanyl; and 50 microg epinephrine bilaterally and epidural catheters. Subsequently, all patients received epidural analgesia. RESULTS: Cervical dilation occurred more quickly (57 vs. 120 min/cm cervical dilation; P = 0.05) during the first 2 h of analgesia in patients having lumbar sympathetic blocks (n = 17) than in patients having epidurals (n = 19). The second stage of labor was briefer in patients having lumbar sympathetic blocks than in those having epidurals (105 vs. 270 min; P < 0.05). Nine patients having lumbar sympathetic block and seven having epidurals delivered spontaneously, whereas seven patients having lumbar sympathetic block and seven having epidurals had instrument-assisted vaginal deliveries. Cesarean delivery for fetal bradycardia occurred in one patient having lumbar sympathetic block. Cesarean delivery for dystocia occurred in five patients having epidurals compared with no patient having lumbar sympathetic block (P = not significant). Visual analog pain scores differed only at 60 min after block. CONCLUSIONS: Nulliparous parturients having induced labor and receiving initial lumbar sympathetic blocks had faster cervical dilation during the first 2 h of analgesia, shorter second-stage labors, and a trend toward a lower dystocia cesarean delivery rate than did patients having epidural analgesia. The effects of lumbar sympathetic block on labor need to be determined in other patient groups. These results may help define the tocodynamic effects of regional labor analgesia.  (+info)

Autonomic control of skeletal muscle blood flow at the onset of exercise. (3/148)

The purpose of this study was to determine whether the autonomic nervous system is involved in skeletal muscle vasodilation at the onset of exercise. Mongrel dogs (n = 7) were instrumented with flow probes on both external iliac arteries. Before treadmill exercise at 3 miles/h, 0% grade, hexamethonium (10 mg/kg) and atropine (0.2 mg/kg) or saline was infused intravenously. Ganglionic blockade increased resting heart rate from 87 +/- 5 to 145 +/- 8 beats/min (P < 0.01) and reduced mean arterial pressure from 100 +/- 4 to 88 +/- 5 mmHg (P < 0.01). During steady-state exercise, heart rate was unaffected by ganglionic blockade (from 145 +/- 8 to 152 +/- 5 beats/min), whereas mean arterial pressure was reduced (from 115 +/- 4 to 72 +/- 4 mmHg; P < 0.01). Immediate and rapid increases in iliac blood flow and conductance occurred with initiation of exercise with or without ganglionic blockade. Statistical analyses of hindlimb conductance at 5-s intervals over the first 30 s of exercise revealed a statistically significant difference between the control and ganglionic blockade conditions at 20, 25, and 30 s (P < 0.01) but not at 5, 10, and 15 s of exercise. Hindlimb conductance at 1 min of exercise was 9.21 +/- 0.68 and 11.82 +/- 1.32 ml. min(-1). mmHg(-1) for the control and ganglionic blockade conditions, respectively. Because ganglionic blockade did not affect the initial rise in iliac conductance, we concluded that the autonomic nervous system is not essential for the rapid vasodilation in active skeletal muscle at the onset of exercise in dogs. Autonomic control of skeletal muscle blood flow during exercise is manifested through vasoconstriction and not vasodilation.  (+info)

Effects of unilateral stellate ganglion block on the spectral characteristics of heart rate variability. (4/148)

The effect of unilateral stellate ganglion block on cardiovascular regulation remains controversial, so the present study used power spectral analysis of heart rate variability to investigate its effect on the autonomic neural control of the heart. In 20 young healthy volunteers (mean age: 25 years), heart rate variability was determined before and after unilateral stellate ganglion block (right side 11, left side 9) using 8 ml of 1% mepivacaine during supine rest. Using autoregressive spectrum analysis, power spectra were quantified by measuring the area in 3 frequency bands: high-frequency power (lnHF, parasympathetic influence) from 0.15 to 0.40 Hz, low-frequency power (lnLF, predominantly sympathetic influence) from 0.04 to 0.15 Hz, and total-frequency power (lnTF) less than 0.40 Hz. Right stellate ganglion block decreased not only the lnLF component from 6.55+/-0.84 to 5.77+/-0.47 but also the lnHF component from 4.40+/-0.95 to 3.42+/-1.12 (p<0.05). In contrast, left stellate ganglion block changed neither the lnLF nor the lnHF component. The lnTF component was also decreased significantly by right stellate ganglion block from 7.80+/-0.95 to 7.01+/-0.36 (p<0.05), but was unchanged following left stellate ganglion block. Neither right nor left stellate ganglion block induced any significant change in both the RR and corrected QT intervals. However, changes in the RR interval induced by right stellate ganglion block showed significant positive correlation with changes in lnHF (p<0.005) and lnTF (p<0.05). These results suggest that (1) autonomic innervation to the sinus node is mainly through the right-sided stellate ganglion, (2) pharmacological right-sided stellate ganglion block may attenuate not only sympathetic but also parasympathetic activity and (3) following right stellate ganglion block the decrease in both the sympathetic and parasympathetic influence on the sinus node may inconsistently counterbalance and change the RR interval.  (+info)

Hepatic and central nervous system cytochrome P450 are down-regulated during lipopolysaccharide-evoked localized inflammation in brain. (5/148)

The effect of central nervous system inflammation on the levels and activity of hepatic and brain cytochrome P450 were examined in the rat. Brain ethoxyresorufin dealkylkase (EROD) was depressed during localized inflammatory responses evoked by lipopolysaccharide (LPS) injected into the lateral ventricle. This loss was accompanied by a concomitant loss of EROD activity and cytochrome P450 in liver. Similar losses in hepatic enzyme were observed for benzyloxy-resorufin and pentoxy-resorufin dealkylase (CYP2B) and chlorzoxazone hydroxylation (CYP2E). Protein levels of CYP2D and CYP2E1 but not CYP1A also were depressed. Similar i.p. doses of LPS had no effect on hepatic cytochrome P450, indicating that the hepatic effect was not caused by LPS leakage from the central nervous system. Also in support of this contention is that heat shock protein 27 was expressed throughout the brain by LPS given i.c. v. but was undetectable in the liver. Tumor necrosis factor-alpha given i.c.v. depressed EROD activity in the brain but this was not accompanied by a concomitant loss in the liver. Hepatic EROD did respond to the i.p. injection of tumor necrosis factor-alpha. The LPS-evoked loss in hepatic cytochrome P450 could not be prevented by blocking beta-receptor-mediated sympathetic nerve activity. This study demonstrates that localized inflammatory responses in the brain cause a concomitant down-regulation of cytochrome P450 and drug-metabolizing activity in the liver and the brain. The effect on brain cytochrome P450 may be regulated via cytokine-mediated pathways but signaling to the liver does not involve a cytokine-mediated pathway nor a beta-receptor-mediated sympathetic nerve pathway.  (+info)

Treating electrical storm : sympathetic blockade versus advanced cardiac life support-guided therapy. (6/148)

BACKGROUND: Electrical storm (ES), defined as recurrent multiple ventricular fibrillation (VF) episodes, often occurs in patients with recent myocardial infarction. Because treating ES according to the Advanced Cardiac Life Support (ACLS) guidelines yields a poor outcome, we evaluated the efficacy of sympathetic blockade in treating ES patients and compared their outcome with that of patients treated according to the ACLS guidelines. METHODS AND RESULTS: Forty-nine patients (36 men, 13 women, mean age 57+/-10 years) who had ES associated with a recent myocardial infarction were separated into 2 groups. Patients in group 1 (n=27) received sympathetic blockade treatment: 6 left stellate ganglionic blockade, 7 esmolol, and 14 propranolol. Patients in group 2 (n=22) received antiarrhythmic medication as recommended by the ACLS guidelines. Patient characteristics were similar in the 2 groups. The 1-week mortality rate was higher in group 2: 18 (82%) of the 22 patients died, all of refractory VF; 6 (22%) of the 27 group 1 patients died, 3 of refractory VF (P<0.0001). Patients who survived the initial ES event did well over the 1-year follow-up period: Overall survival in group 1 was 67%, compared with 5% in group 2 (P<0.0001). CONCLUSIONS: Sympathetic blockade is superior to the antiarrhythmic therapy recommended by the ACLS guidelines in treating ES patients. Our study emphasizes the role of increased sympathetic activity in the genesis of ES. Sympathetic blockade-not class 1 antiarrhythmic drugs-should be the treatment of choice for ES.  (+info)

Periischemic cerebral blood flow (CBF) does not explain beneficial effects of isoflurane on outcome from near-complete forebrain ischemia in rats. (7/148)

BACKGROUND: Isoflurane improves outcome from near-complete forebrain ischemia in rats compared with fentanyl-nitrous oxide (N2O). Sympathetic ganglionic blockade with trimethaphan abolishes this beneficial effect. To evaluate whether anesthesia-related differences in cerebral blood flow (CBF) may explain these findings, this study compared regional CBF before, during, and after near-complete forebrain ischemia in rats anesthetized with either isoflurane (with and without trimethaphan) or fentanyl-nitrous oxide. METHODS: Fasted, normothermic isoflurane anesthetized Sprague-Dawley rats were prepared for near-complete forebrain ischemia (10 min of bilateral carotid occlusion and mean arterial pressure = 30 mmHg). After surgery, rats were anesthetized with either 1.4% isoflurane (with or without 2.5 mg of trimethaphan intravenously at onset of ischemia) or fentanyl-nitrous oxide (25 microgram. kg-1. h-1. 70% N2O-1). Regional CBF was determined (14C-iodoantipyrine autoradiography) before ischemia, 8 min after onset of ischemia, and 30 min after onset of reperfusion. RESULTS: Regional CBF did not differ significantly among groups at any measurement interval. Ischemia caused a marked flow reduction to 5% or less of baseline (P < 0.001) in selectively vulnerable regions, such as the cortex, caudoputamen and hippocampus, whereas flow in the brain stem and cerebellum was preserved. Reperfusion at 30 min was associated with partial restoration of flow to 35-50% of baseline values in ischemic structures. CONCLUSIONS: The results indicate that improved histologic-behavioral outcome provided by isoflurane anesthesia cannot be explained by differential vasodilative effects of the anesthetic states before, during, or after severe forebrain ischemia. This study also shows severe postischemic delayed hypoperfusion that was not affected by choice of anesthetic or the presence of trimethaphan. Mechanisms other than effects on periischemic CBF must be responsible for beneficial effects of isoflurane in this model.  (+info)

Capsaicin increases modulation of sympathetic nerve activity in rats: measurement using power spectral analysis of heart rate fluctuations. (8/148)

We assessed the sympatho-vagal activities of the heart after administration of capsaicin by measuring the power spectral analysis in rats. There were major two frequency components of heart rate variability, which we defined as high (1.0 Hz <, HF) and low (LF, < 1.0 Hz) frequency components. Vagal blockade by atropine abolished the high frequency component, and lowered the amplitude of the low frequency component. On the other hand, under conditions of sympathetic blockade by propranolol, the low frequency component was reduced. Combined vagal and sympathetic blockade abolished all heart rate fluctuations. We analyzed the low and high frequency components by integrating the spectrum for the respective band width. The rats administered capsaicin had a higher heart rate and sympathetic nervous system index (LF/HF) than the control group of rats. These results suggest that power spectral analysis is an effective and noninvasive method for detecting subtle changes in autonomic activity in response to the intake of foods or drugs.  (+info)