Muscle sympathetic nerve activity is higher in intensively versus conventionally treated IDDM subjects

OBJECTIVE

To determine whether poor long-term glycemic control may play a role in the lower muscle sympathetic nerve activity (MSNA) levels in insulin-dependent diabetes mellitus (IDDM).

RESEARCH DESIGN AND METHODS

Intraneural electrodes were used to record MSNA from the peroneal nerve at baseline and during euglycemic insulin infusion (120 mU.m-2.min-1) in 16 IDDM subjects enrolled in the Diabetes Control and Complications Trial (DCCT), 8 intensively treated (HbA1c 7.1 +/- 1.2%) and 8 conventionally treated (HbA1c 9.0 +/- 1.5%; P < 0.05).

RESULTS

Fasting plasma glucose levels tended to be higher at baseline in the conventionally treated group (11.3 +/- 1.7 mmol/l) than in the intensively treated group (7.4 +/- 1.1 mmol/l, P < 0.1), but did not differ during insulin infusion (conventional, 5.0 +/- 0.3 mmol/l; intensive, 5.1 +/- 0.4 mmol/l). Plasma free insulin levels did not differ between groups either before or during insulin infusion. The intensively treated group had significantly high MSNA levels than the conventionally treated group both in the fasting state (16.2 +/-2.7 vs 10.5 +/- 4.4 bursts/min, P < 0.05 and during insulin infusion with euglycemia (27.8 +/- 2.1 vs 17.5 +/- 5.2 bursts/min.

CONCLUSIONS

MSNA levels in intensively treated IDDM subject are higher than in conventionally treated subjects. These results suggest that improved long-term glycemic control is associated with increased sympathetic neural outflow to muscle. The mechanism for this effect remains unclear.

Mechanisms of insulin action on sympathetic nerve activity

Insulin resistance and hyperinsulinemia may contribute to the development of arterial hypertension. Although insulin may elevate arterial pressure, in part, through activation of the sympathetic nervous system, the sites and mechanisms of insulin-induced sympathetic excitation remain uncertain. While sympathoexcitation during insulin may be mediated by the baroreflex, or by modulation of norepinephrine release from sympathetic nerve endings, it has been shown repeatedly that insulin increases sympathetic outflow by actions on the central nervous system. Previous studies employing norepinephrine turnover have suggested that insulin causes sympathoexcitation by acting in the hypothalamus. Recent experiments from our laboratory involving direct measurements of regional sympathetic nerve activity have provided further evidence that insulin acts in the central nervous system. For example, administration of insulin into the third cerebralventricle increased lumbar but not renal or adrenal sympathetic nerve activity in normotensive rats. Interestingly, this pattern of regional sympathetic nerve responses to central neural administration of insulin is similar to that seen with systemic administration of insulin. Further, lesions of the anteroventral third ventricle hypothalamic (AV3V) region abolished increases in sympathetic activity to systemic administration of insulin with euglycemic clamp, suggesting that AV3V-related structures are critical for insulin-induced elevations in sympathetic outflow.

Measuring service quality at a university health clinic

Describes research undertaken to assess the quality of service provided by a public university health clinic. The SERVQUAL instrument was administered to patients of the University of Houston Health Center in order to evaluate customer perceptions of service quality. The results of this study are currently being incorporated into the clinic's strategic planning process, specifically with respect to future resource allocation towards quality improvement projects.

Three-state thermodynamic analysis of the denaturation of staphylococcal nuclease mutants

Using microcalorimetry, we found an equilibrium intermediate state during the denaturation of the wild-type and five mutant staphylococcal nuclease proteins: V66L, V66W, G88V, D77A, and E75V. The presence of two distinct heat absorption peaks allowed direct measurement of the enthalpy differences between the native, intermediate, and denatured states. Conditions of low pH and high NaCl concentration facilitated observation of the intermediate, or I-state. We propose to consider the nuclease protein as composed of two subdomains, divided along the active-site cleft. The structure of the I-state apparently consists mainly of the folded beta-barrel subdomain, as does that of a nuclease fragment protein [Shortle, D., & Abeygunawardana, C. (1993) Structure 1, 121-134]. The cooperativity of folding of the subdomains is maintained by electrostatic bonds across the active-site cleft. Removal of these bonds by the mutation D77A or E75V results in decooperation of the protein's structure and a three-state mechanism of denaturation at pH 7.0. The origins of differences in the enthalpy change of denaturation and in the m value of guanidinium chloride-induced denaturation with mutant nucleases are discussed in terms of this three-state mechanism.

Hypoglycemia increases muscle sympathetic nerve activity in IDDM and control subjects

OBJECTIVE

The relationship between the increase in adrenomedullary catecholamine secretion and the sympathetic response to hypoglycemia is not well understood in humans. To explore this relationship more closely, we directly muscle sympathetic nerve activity (MSNA) in control subjects and in insulin-dependent diabetes mellitus (IDDM) subjects without clinically evident diabetic complications.

RESEARCH DESIGN AND METHODS

Twelve IDDM subjects (22.5 +/- 3.9 years of age, diabetes duration of 9.8 +/- 8.3 years) and 12 age-matched control subjects were studied. MSNA was measured during insulin infusion (720 pM.m-2.min-1) with 30-min periods of 1) euglycemia, 2) hypoglycemia (target plasma glucose, 2.8 mM), and 3) recovery. The effect of increased insulin dose (1,440 pM.m-2.min-1) was studied in six subjects in each group, and the effect of prolonged hypoglycemia (1 h) was studied in five IDDM subjects and four control subjects.

RESULTS

MSNA levels increased in IDDM and control subjects, 31 +/- 8 and 29 +/- 6%, respectively, above euglycemia during hypoglycemia and returned to euglycemic levels during recovery. MSNA levels during hypoglycemia were lower in IDDM subjects than in control subjects (26 +/- 3 vs. 35 +/- 2 bursts/min, P < 0.01). Importantly, no relationships were found between the MSNA and epinephrine responses to hypoglycemia in either group. Increasing the insulin infusion rate did not alter the MSNA response to hypoglycemia. During prolonged hypoglycemia, MSNA remained elevated above euglycemic levels throughout hypoglycemia.

CONCLUSIONS

These results demonstrate that insulin-induced hypoglycemia increases muscle sympathetic neural outflow in IDDM and control subjects. The lack of correlation between the MSNA and epinephrine responses to hypoglycemia indicates that the adrenomedullary and peripheral sympathetic responses to hypoglycemia are independently mediated.

Recruitment of family physicians in rural practice

We report the results of a study to find out how rural family physicians choose their practice location--information that could allow physicians and practices to be more appropriately and easily matched. We interviewed rural family physicians who completed a Minnesota residency in 1990 or 1991 to determine what factors influenced their final practice selection. The survey revealed that partners in practice are physicians' greatest concern, followed by geographic location, recreational activities, call schedule, and opportunities for spouse and children. Despite numerous available practice options, it was difficult for physicians to find practices and communities that met the majority of their personal, professional, and familial needs. This study suggests a need for a physician placement network that would increase retention and help ease the current health care provider shortage in rural Minnesota.

Thermodynamics of staphylococcal nuclease denaturation. I. The acid-denatured state

Using high-sensitivity differential scanning calorimetry, we reexamined the thermodynamics of denaturation of staphylococcal nuclease. The denaturational changes in enthalpy and heat capacity were found to be functions of both temperature and pH. The denatured state of staphylococcal nuclease at pH 8.0 and high temperature has a heat capacity consistent with a fully unfolded protein completely exposed to solvent. At lower pH values, however, the heat capacity of the denatured state is lower, resulting in a lower delta Cp and delta H for the denaturation reaction. The acid-denatured protein can thus be distinguished from a completely unfolded protein by a defined difference in enthalpy and heat capacity. Comparison of circular dichroism spectra suggests that the low heat capacity of the acid-denatured protein does not result from residual helical secondary structure. The enthalpy and heat capacity changes of denaturation of a less stable mutant nuclease support the observed dependence of delta H on pH.

Thermodynamics of staphylococcal nuclease denaturation. II. The A-state

Staphylococcal nuclease, at low pH and in the presence of high salt concentrations, has previously been proposed to exist in a partially folded or molten globule form called the "A-state" (Fink et al., 1993, Protein Sci 2:1155-1160). We have found that the A-state of nuclease at pH 2.1 in the presence of moderate to high salt concentrations and at low temperature exists in a substantially folded form structurally more similar to a native state. The A-state has the far-UV circular dichroism spectra characteristic of the native protein, which indicates that it has a large degree of secondary structure. Upon heating, the A-state denatures with a sigmoidal change in far-UV ellipticity and an observable peak in a differential scanning calorimeter trace, indicating that it is thermodynamically distinct from the denatured state. Three different mutations in a residue normally buried in the protein's core stabilize or destabilize the A-state in the same way as they affect the denaturation of the native state. The A-state must, therefore, contain at least some tertiary packing of side chains. Unlike the native state, which shows cold denaturation at low temperatures, the A-state is most stable at temperatures below 0 degrees C.

Muscle sympathetic nerve activity in response to glucose ingestion. Impact of plasma insulin and body fat

Carbohydrate intake stimulates sympathetic nervous system activity in lean subjects, whereas in obese subjects, the results have been inconsistent. The aim of this study was to directly measure sympathetic neural outflow to skeletal muscle in response to a 75-g oral glucose tolerance test (OGTT) in 15 Pima Indian and 16 Caucasian men, matched for body fat and age, but covering a large range of body weight (57-113 kg) and body fat (4-41%). Fasting muscle sympathetic nerve activity (MSNA) correlated positively with body fat (r = 0.73; P = 0.001) in Caucasians but not in Pima Indians, whereas the increase in MSNA during the OGTT correlated negatively with the percentage of body fat (r = -0.38, P = 0.03) independently of race. In each subject, the increase in MSNA over time correlated positively with the increase in plasma insulin levels, but the slopes of these relationships were inversely related to the percentage of body fat (r = -0.52, P = 0.003) independently of race. In conclusion, obesity is associated with a higher fasting sympathetic neural outflow to muscle but a blunted increase in response to an oral glucose load despite a larger increase in plasma insulin levels. This blunted response may represent another feature of the obesity/insulin resistance syndrome.

Effects of fludrocortisone on sympathetic nerve activity in humans

Fludrocortisone reduces plasma norepinephrine in healthy humans, but forearm vascular and pressor responses to norepinephrine are potentiated. The effects of fludrocortisone on sympathetic nerve activity in healthy humans are not known. To investigate these effects we evaluated muscle sympathetic nerve activity, heart rate, and arterial pressure in 11 healthy volunteers during three protocols: (1) before and on day 7 of fludrocortisone (0.4 mg/d) treatment with ad libitum diet (n = 6); (2) before and on day 7 of fludrocortisone (0.4 mg/d) or placebo with a 150 mmol/24 h (mEq/24 h) sodium diet (n = 7); and (3) before and on day 2 of fludrocortisone (0.4 mg/d) or placebo with a 150 mmol/24 h (mEq/24 h) sodium diet (n = 4). Placebo did not alter any parameter.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced sympathetic nervous activity. A potential mechanism predisposing to body weight gain

The sympathetic nervous system is recognized to play a role in the etiology of animal and possibly human obesity through its impact on energy expenditure and/or food intake. We, therefore, measured fasting muscle sympathetic nerve activity (MSNA) in the peroneal nerve and its relationship with energy expenditure and body composition in 25 relatively lean Pima Indian males (means +/- SD; 26 +/- 6 yr, 82 +/- 19 kg, 28 +/- 10% body fat) and 19 Caucasian males (29 +/- 5 yr, 81 +/- 13 kg, 24 +/- 9% body fat). 24-h energy expenditure, sleeping metabolic rate, and resting metabolic rate were measured in a respiratory chamber, whereas body composition was estimated by hydrodensitometry. Pima Indians had lower MSNA than Caucasians (23 +/- 6 vs 33 +/- 10 bursts/min, P = 0.0007). MSNA was significantly related to percent body fat in Caucasians (r = 0.55, P = 0.01) but not in Pimas. MSNA also correlated with energy expenditure adjusted for fat-free mass, fat mass, and age in Caucasians (r = 0.51, P = 0.03; r = 0.54, P = 0.02; and r = 0.53, P = 0.02 for adjusted 24-h energy expenditure, sleeping metabolic rate, and resting metabolic rate, respectively) but not in Pima Indians. In conclusion, the activity of the sympathetic nervous system is a determinant of energy expenditure in Caucasians. Individuals with low resting MSNA may be at risk for body weight gain resulting from a lower metabolic rate. A low resting MSNA and the lack of impact of MSNA on metabolic rate might play a role in the etiology of obesity in Pima Indians.

Muscle sympathetic nerve activity is reduced in IDDM before overt autonomic neuropathy

Studies of heart-rate variability have demonstrated that abnormal cardiac parasympathetic activity in individuals with IDDM precedes the development of other signs or symptoms of diabetic autonomic neuropathy. To determine whether IDDM patients have impaired sympathetic activity compared with normal control subjects before the onset of overt neuropathy, we directly recorded MSNA. We also examined the effects of changes in plasma glucose and insulin on sympathetic function in each group. MSNA was recorded by using microneurographic techniques in 10 IDDM patients without clinically evident diabetic complications and 10 control subjects. MSNA was compared during a 15-min fasting baseline period and during insulin infusion (120 mU.m-2.min-1) with 30 min of euglycemia. A cold pressor test was performed at the end of euglycemia. Power spectral analysis of 24-h RR variability was used to assess cardiac autonomic function. IDDM patients had lower MSNA than control subjects at baseline (8 +/- 1 vs. 18 +/- 3 burst/min, P < 0.02). MSNA increased in both groups with insulin infusion (P < 0.01) but remained lower in IDDM patients (20 +/- 3 vs. 28 +/- 3 burst/min, P < 0.01). In the IDDM group, we found no relationships between MSNA and plasma glucose, insulin, or HbA1c concentrations. BP levels did not differ at rest or during insulin. Heart-rate variability and the MSNA response to cold pressor testing in IDDM patients did not differ from those in healthy control subjects. IDDM patients had reduced MSNA at rest and in response to insulin. The lower MSNA is not attributable to differences in plasma glucose or insulin, but, rather, is most likely an early manifestation of diabetic autonomic neuropathy that precedes impaired cardiac parasympathetic control.

Sympathetic neural mechanisms in human hypertension

This review discusses the role of the sympathetic nervous system in the pathogenesis and maintenance of human hypertension. Three points are emphasized: first, there are mechanisms by which the sympathetic nervous system can contribute to the long-term regulation of vascular resistance and arterial pressure in addition to the moment-to-moment regulation of arterial pressure; second, the microneurographic method for direct intraneural recording of sympathetic nerve activity in humans has provided mounting evidence for increased sympathetic neural activity in human essential and renovascular hypertension; and third, there are both peripheral reflex and humoral mechanisms that may contribute to sympathetic overactivity in human hypertension.

A signal-averaging technique for the analysis of human muscle sympathetic nerve activity

We present a signal-averaging technique for analysis of human muscle sympathetic nerve activity (SNA). Nerve traffic was averaged by coupling signal acquisition to electrocardiographic R waves. The amplitude of the averaged waveform was multiplied by the number of R waves sampled to provide a measure of SNA in arbitrary units. This was compared with SNA measured by manual digitization of hard-copy records. In nine volunteers, SNA was increased or decreased with stepwise infusions of nitroprusside or phenylephrine: there were 10 5-min periods of data in each subject. Across all subjects, the correlation between manual and signal-averaged measures of SNA was excellent during both nitroprusside (r = 0.98) and phenylephrine infusions (r = 0.91) and the slopes of the regression lines were near unity. In three periods of data collection, electrical artifacts were added randomly at frequencies of 0.5 and 0.07 Hz during playback of the signal into the computer. Signal-averaged estimates of SNA were unaffected by artifacts. This technique provides reliable observer-independent measures of SNA.

Insulin increases sympathetic activity but not blood pressure in borderline hypertensive humans

We have previously demonstrated that physiological hyperinsulinemia in normotensive humans increases sympathetic nerve activity but not arterial pressure since it also causes skeletal muscle vasodilation. However, in the presence of insulin resistance and/or hypertension, insulin may cause exaggerated sympathetic activation or impaired vasodilation and thus elevate arterial pressure. This study sought to determine if insulin causes a pressor response in borderline hypertensive humans by producing exaggerated increases in sympathetic neural outflow or impaired vasodilation. We recorded muscle sympathetic nerve activity (microneurography, peroneal nerve), forearm blood flow, heart rate, and blood pressure in 13 borderline hypertensive subjects during a 1-hour insulin infusion (38 microunits/m2/min) while holding blood glucose constant. Plasma insulin rose from 12 +/- 3 microunits/ml (mean +/- SEM) during control to 73 +/- 7 microunits/ml during insulin infusion and fell to 9 +/- 2 microunits/ml 2 hours after insulin infusion was stopped. Muscle sympathetic nerve activity, which averaged 25 +/- 2 bursts per minute in control, increased significantly during insulin infusion (+9 bursts per minute) and remained elevated 1.5 hours into recovery (+7 bursts per minute, p less than 0.001). Despite increased muscle sympathetic nerve activity, there were significant (p less than 0.001) increases in forearm blood flow and decreases in forearm vascular resistance during insulin infusion. Further, systolic and diastolic pressures fell approximately 3 and 6 mm Hg, respectively, during insulin infusion (p less than 0.01). This study suggests that acute physiological increases in plasma insulin elevate sympathetic neural outflow in borderline hypertensive humans but produce vasodilation and do not elevate arterial pressure.

Correlation of endomyocardial biopsy findings with autopsy findings in human cardiac allografts

To determine the reliability of endomyocardial biopsies in the detection of rejection, we took biopsy specimens from 22 autopsied human cardiac allografts by direct visualization. Five specimens were taken from each of four sites: left ventricular free wall, left ventricular septum, right ventricular free wall, and right ventricular septum. The findings in individual biopsy specimens and the summed diagnosis in the five biopsy specimens from each site were graded for rejection by a grading system similar to the Billingham criteria. Grading of the five specimens from each site also was done using criteria recommended by the International Society for Heart and Lung Transplantation. These findings were compared with the rejection grade determined by examination of large tissue sections from the autopsied hearts, used as the standard. Overall, X-Y correlation for single-specimen grading had an r value of 0.792. Grading based on five biopsy specimens from all sites using the modified Billingham criteria grading scheme had an r value of 0.845; the r value was 0.857 for the new grading system. Specificity of findings was high for all grades. Sensitivity of findings, however, was dramatically less for grades 1, 2, and 3. Predictive values for these grades also were less for grades 1, 2, and 3, but to a lesser degree than sensitivity. No difference in detection of rejection was found from specimens taken from different areas of the heart. We conclude that a significant number of hearts with middle grades of rejection may be underestimated by routine biopsies. The criteria for grading of the International Society for Heart and Lung Transplantation had a slight advantage over a more traditional grading system.

Hyperinsulinemia produces both sympathetic neural activation and vasodilation in normal humans

Hyperinsulinemia may contribute to hypertension by increasing sympathetic activity and vascular resistance. We sought to determine if insulin increases central sympathetic neural outflow and vascular resistance in humans. We recorded muscle sympathetic nerve activity (MSNA; microneurography, peroneal nerve), forearm blood flow (plethysmography), heart rate, and blood pressure in 14 normotensive males during 1-h infusions of low (38 mU/m2/min) and high (76 mU/m2/min) doses of insulin while holding blood glucose constant. Plasma insulin rose from 8 +/- 1 microU/ml during control, to 72 +/- 8 and 144 +/- 13 microU/ml during the low and high insulin doses, respectively, and fell to 15 +/- 6 microU/ml 1 h after insulin infusion was stopped. MSNA, which averaged 21.5 +/- 1.5 bursts/min in control, increased significantly (P less than 0.001) during both the low and high doses of insulin (+/- 5.4 and +/- 9.3 bursts/min, respectively) and further increased during 1-h recovery (+15.2 bursts/min). Plasma norepinephrine levels (119 +/- 19 pg/ml during control) rose during both low (258 +/- 25; P less than 0.02) and high (285 +/- 95; P less than 0.01) doses of insulin and recovery (316 +/- 23; P less than 0.01). Plasma epinephrine levels did not change during insulin infusion. Despite the increased MSNA and plasma norepinephrine, there were significant (P less than 0.001) increases in forearm blood flow and decreases in forearm vascular resistance during both doses of insulin. Systolic pressure did not change significantly during infusion of insulin and diastolic pressure fell approximately 4-5 mmHg (P less than 0.01). This study suggests that acute increases in plasma insulin within the physiological range elevate sympathetic neural outflow but produce forearm vasodilation and do not elevate arterial pressure in normal humans.

Mental stress increases sympathetic nerve activity during sustained baroreceptor stimulation in humans

Muscle sympathetic nerve activity (MSNA) in humans is regulated in part by arterial baroreceptors. However, although mental stress increases blood pressure, it also increases MSNA. This suggests that baroreceptor control of MSNA is altered during mental stress. In nine healthy men (age range, 20-26 years), we recorded heart rate, blood pressure, and efferent MSNA (peroneal nerve, microneurography) during a 4-minute mental arithmetic task performed both before and during infusion of phenylephrine sufficient to markedly suppress resting MSNA. Before phenylephrine, mental stress significantly increased mean blood pressure (p less than 0.01), heart rate (p less than 0.01), and MSNA (from 18.5 +/- 3.2 to 24.8 +/- 3.5 bursts/min, p less than 0.001). Phenylephrine infusion increased resting mean blood pressure (from 84.0 +/- 2.6 to 90.0 +/- 2.7 mm Hg, p less than 0.01) and decreased resting heart rate (from 65.6 +/- 1.7 to 55.6 +/- 2.0 beats/min, p less than 0.01). Resting MSNA decreased dramatically during phenylephrine (from 18.5 +/- 3.2 to 3.3 +/- 1.3 bursts/min, p less than 0.01). During phenylephrine, mental stress again significantly (p less than 0.01) increased mean blood pressure, heart rate, and MSNA (from 3.1 +/- 1.4 to 10.9 +/- 1.8 bursts/min). The magnitude of stress-induced increases in MSNA and heart rate were comparable before and during phenylephrine infusion despite the greater elevation in diastolic pressure during stress plus phenylephrine. The present study demonstrates that mental stress produces sympathoexcitatory and pressor responses even during sustained stimulation of arterial baroreceptors.

Effect of dietary potassium on blood pressure, renal function, muscle sympathetic nerve activity, and forearm vascular resistance and flow in normotensive and borderline hypertensive humans

We evaluated the effect of a low potassium diet on blood pressure in normotensive (NT) and in borderline hypertensive subjects (BHT). There were 11 BHT men (age, 24.6 +/- 1.2 years) and 10 NT men (age, 23.5 +/- 1.0 years). Subjects were studied while on both low potassium, high sodium (30 meq/day, 400 meq/day) diets and high potassium, high sodium (100 meq/day, 400 meq/day) diets, each taken for 6 days. During the low potassium diet, daytime ambulatory systolic blood pressure increased in both NT (123 +/- 5 mm Hg, low potassium, vs. 116 +/- 4 mm Hg, high potassium, p less than 0.01) and BHT groups (134 +/- 3, low potassium, vs. 124 +/- 3, high potassium, p less than 0.001). Mean blood pressure was not different in NT during the two diets but was significantly higher during the low potassium diet in BHT subjects (97 +/- 2 mm Hg low potassium, vs. 92 +/- 1 mm Hg, high potassium, p less than 0.05) without change in heart rate in BHT subjects during the two diets. Low potassium diet increased the postural rise in diastolic blood pressure when subjects changed from the supine position to quiet standing (standing diastolic blood pressure for NT: low potassium, 79 +/- 2 mm Hg vs. high potassium, 72 +/- 2 mm Hg; for BHT: low potassium, 89 +/- 2 mm Hg vs. high potassium diet, 83 +/- 2 mm Hg, p less than 0.01). The effects of low potassium diet on blood pressure were not related to marked changes in renal hemodynamics, in plasma renin activity, in aldosterone, or in norepinephrine, nor to increases in forearm vascular resistance or in muscle sympathetic nerve activity. In fact, muscle sympathetic nerve activity decreased in the BHT group during low potassium compared with high potassium diets (p less than 0.001) and did not change in the NT group. Sympathetic nerve activity was also higher in BHT compared with the NT group during high potassium and low potassium diets, p less than 0.001. In the NT group, the low potassium diet was associated with lower hematocrit levels, weight gain, and increased 24 hour urinary calcium levels. After the low potassium diet, serum potassium fell in both groups, and serum phosphorus fell significantly in the BHT group.(ABSTRACT TRUNCATED AT 400 WORDS)

Muscle relaxants change myocardial metabolism in patients with ischemic heart disease during high-dose fentanyl anesthesia

Although not unanimously accepted, high-dose fentanyl anesthesia has been associated with hemodynamic stability and little derangement of myocardial oxygen balance. This apparent inconsistency inspired us to investigate the effects on cardiac function and myocardial metabolism of stepwise increasing doses of fentanyl, accumulating to 15, 30, and 50 micrograms.kg-1, with the least possible interference from other drugs. Subjects were unpremedicated patients with ischemic cardiac disease scheduled for coronary artery bypass grafting or major vascular surgery. In an initial study employing succinylcholine for muscle relaxation, we found that heart rate (HR), coronary sinus blood flow (CSF) and coronary vascular resistance (CVR) remained unchanged, while systemic arterial pressure (SBP), rate-pressure product (RPP), coronary perfusion pressure (CPP) and left ventricular work (LVW) decreased. Myocardial uptake of oxygen (MVO2) and free fatty acids (FFA) both decreased in a dose-dependent manner. Arterial lactate concentration and myocardial lactate uptake both increased. These findings opposed the postinduction myocardial ischemia noted by some other investigators. In most of these studies pancuronium bromide had been used for muscle relaxation. Since the latter agent has been claimed to increase cardiac work, a second group of correspondingly diseased patients was studied in which succinylcholine was replaced by pancuronium bromide. In this group HR, RPP, CSF and MVO2 all increased at the lowest dose of fentanyl and HR additionally also at 30 micrograms.kg-1. The cardiac index was higher in the pancuronium group at the lowest and middle dose steps of fentanyl. Lactate uptake decreased with higher doses of fentanyl and relative myocardial lactate extraction declined.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevated sympathetic nerve activity in borderline hypertensive humans. Evidence from direct intraneural recordings

Reports of elevated plasma catecholamine levels and augmented responses to autonomic blockade suggest increased sympathetic tone in borderline hypertension. It is not known if this reflects greater sympathetic neural outflow. We directly recorded muscle sympathetic nerve activity (microneurography) in 15 normotensive and 12 borderline hypertensive age-matched men to determine whether borderline hypertensive individuals have elevated sympathetic nerve activity. Supine heart rate, blood pressure, plasma norepinephrine, and efferent muscle sympathetic nerve activity (peroneal nerve) were measured after 6 days of both low and high dietary sodium intake (10 and 400 meq sodium/24 hr). Sympathetic nerve activity was elevated significantly in borderline hypertensive individuals on both low (37 +/- 1 in borderline hypertensive individuals vs. 29 +/- 1 bursts/min in normotensive individuals; p less than 0.01) and high (25 + 1 in borderline hypertensive individuals vs. 16 +/- 1 bursts/min in normotensive individuals; p less than 0.01) sodium diets. The borderline hypertensive group had higher systolic (p less than 0.01) and diastolic (p less than 0.05) blood pressures independent of sodium intake. Across both groups, high sodium intake reduced muscle sympathetic nerve activity (p less than 0.001), plasma norepinephrine (p less than 0.001), diastolic blood pressure (p less than 0.02), heart rate (p less than 0.002), and increased weight (p less than 0.005). A significant (p less than 0.05) group-by-diet interaction was observed for plasma norepinephrine levels. Specifically, compared with the normotensive group, plasma norepinephrine levels in the borderline hypertensive group tended to be higher on low sodium diet (p = 0.08) and lower on high sodium diet (p = 0.23).(ABSTRACT TRUNCATED AT 250 WORDS)

Flow-mediated and reflex changes in large peripheral artery tone in humans

Studies of peripheral blood vessels in humans have focused primarily on regulation of blood flow and vascular resistance, which are thought to reflect small vessel caliber. Recent studies in animals have identified flow-mediated and neurogenic changes in large artery diameter. This study tested for flow-mediated dilatation and reflex constriction of the brachial artery in humans. A dual-crystal pulsed Doppler system was used to measure brachial artery diameter and blood flow proximal to the antecubital fossa. To test for flow-mediated dilatation, flow through the brachial artery was altered by an occluding cuff placed on the forearm distal to the site of brachial artery flow and diameter measurement. Control blood flow was 123 +/- 20 ml/min, and brachial artery diameter was 4.74 +/- 0.17 mm (mean +/- SEM). By inflating the distal occluding cuff (distal circulatory arrest), flow was reduced through the brachial artery to 21 +/- 5 ml/min (p less than 0.005), and brachial artery diameter was reduced to 4.35 +/- 0.20 mm (p less than 0.001). By deflating the distal occluding cuff after 10 minutes (reactive hyperemia), brachial artery flow was increased to 358 +/- 55 ml/min (p less than 0.001), and diameter was increased to 5.6 +/- 0.19 mm (p less than 0.001). These interventions did not change systemic arterial pressure and, as measured in three subjects, caused only small changes in local brachial artery distending pressure. Thus, both increased and decreased brachial artery blood flow produced significant changes in brachial artery diameter without altering arterial distending pressure. These data provide evidence for flow-mediated dilatation in humans.(ABSTRACT TRUNCATED AT 250 WORDS)