Alcohol potentiates orthostatic hypotension : implications for alcohol-related syncope.

BACKGROUND: Alcohol consumption may be linked to syncopal events. The mechanisms by which alcohol may induce syncope are unknown. Impairment of the response to orthostatic stress may be involved. Using a double-blind, randomized, placebo-controlled study, we tested the hypothesis that short-term alcohol intake causes orthostatic hypotension because of an impairment in the vasoconstrictor response to orthostatic stress. METHODS AND RESULTS: We examined the effects of alcohol on blood pressure, heart rate, and forearm vascular resistance (FVR) during orthostatic stress achieved by stepwise increases in lower-body negative pressure (LBNP) in 14 healthy young volunteers. During the placebo session, blood pressure did not change significantly during LBNP at -5, -10, and -20 mm Hg. A significant decrease in blood pressure was evident only at -40 mm Hg. In contrast, blood pressure fell significantly at all levels of LBNP during the alcohol session. Compared with placebo, alcohol potentiated the hypotensive responses to LBNP, particularly at -40 mm Hg, when the decrease in systolic blood pressure after alcohol intake (-14 mm Hg) was double that after placebo intake (-7 mm Hg). FVR increased with LBNP after placebo. However, after alcohol intake, FVR did not increase during LBNP despite the potentiated decrease in blood pressure. FVR responses during LBNP were reduced during alcohol compared with placebo consumption (P=0.04). CONCLUSIONS: Short-term alcohol consumption elicits hypotension during orthostatic stress because of impairment of vasoconstriction. These findings have implications for the understanding of the hemodynamic effects of alcohol and, in particular, for understanding syncopal events that occur in association with alcohol intake.

Sympathetic activity in obese subjects with and without obstructive sleep apnea.

BACKGROUND: Obese humans are reported to have increased muscle sympathetic nerve activity (MSNA). Obstructive sleep apnea (OSA) may also be accompanied by increased MSNA. Because there is a high prevalence of OSA in obese humans, it is possible that high MSNA reported in obese subjects may in fact reflect the presence of OSA in these subjects. We tested the hypothesis that obesity, per se, in the absence of OSA, is not accompanied by increased MSNA. METHODS AND RESULTS: We measured MSNA in 25 healthy normal-weight subjects and 30 healthy sedentary obese subjects. All subjects were screened by history and examination to exclude subjects with OSA or hypertension. OSA was further excluded by overnight polysomnographic studies. Despite careful screening, polysomnography revealed that 1 of 25 normal-weight subjects and 9 of 30 obese subjects had occult OSA (P=0.015). MSNA was similar in normal-weight subjects (41+/-3 bursts per 100 heartbeats) and obese subjects without sleep apnea (42+/-3 bursts per 100 heartbeats, P=0.99). MSNA in the 9 obese subjects with occult OSA was 61+/-8 bursts per 100 heartbeats, which was higher than MSNA in normal-weight subjects without sleep apnea (P=0.02) and higher than MSNA in obese subjects without sleep apnea (P=0.02). CONCLUSIONS: Obesity alone, in the absence of OSA, is not accompanied by increased sympathetic activity to muscle blood vessels.

Cigarette smoking increases sympathetic outflow in humans.

BACKGROUND: It is generally accepted that smoking increases blood pressure and inhibits muscle sympathetic nerve activity (SNA). The decrease in muscle SNA with cigarette smoking might be secondary to baroreflex responses to the pressor effect of smoking, thus obscuring a sympathetic excitatory effect of smoking. We tested the hypothesis that smoking increases sympathetic outflow. METHODS AND RESULTS: We examined the effects of sham smoking, cigarette smoking, and cigarette smoking in combination with nitroprusside on muscle (baroreflex-dependent) SNA in 10 healthy habitual smokers. The 3 sessions were performed in random order, each study on a separate day. In an additional study, we also investigated the effects of sham smoking and cigarette smoking on skin (baroreflex-independent) SNA in 9 subjects. Compared with sham smoking, cigarette smoking alone increased blood pressure and decreased muscle SNA. When the blood pressure increase in response to smoking was blunted by nitroprusside infusion, there was a striking increase in muscle SNA. Muscle SNA increased up to 3-fold the levels seen before smoking (P<0.001), accompanied by an increase in heart rate of up to 37+/-4 bpm. Cigarette smoking also induced a 102+/-22% increase in skin SNA (P=0.03). CONCLUSIONS: These data provide the first direct evidence that cigarette smoking increases sympathetic outflow.

Evidence for a central origin of the low-frequency oscillation in RR-interval variability.

BACKGROUND: Short-term variability of RR interval and blood pressure occurs predominantly at low frequency (LF; approximately 0.1 Hz) and high frequency (approximately 0.25 Hz). The arterial baroreflex is thought to be the predominant determinant of the LF component of RR variability. Patients with severe congestive heart failure (CHF) have an attenuated or absent LF oscillation in RR variability. The left ventricular assist device (LVAD) offers a unique possibility for analysis of spectral oscillations in RR interval independent of any effects of blood pressure that influence these oscillations via the baroreflex. METHODS AND RESULTS: We performed spectral analysis of RR, blood pressure, and respiration in 2 patients with CHF before and after LVAD implantation. LF components of the RR-interval and blood pressure variability were absent in both CHF patients before LVAD implantation. After LVAD implantation, spectral analysis of the RR interval showed restoration of a clear and predominant LF oscillation in the native hearts of both patients, with no such oscillation evident in the blood pressure profile. CONCLUSIONS: During total circulatory support with the LVAD, the LF oscillation in RR interval of the native heart, absent in CHF, is restored. This LF oscillation in RR interval occurs in the absence of LF oscillations in blood pressure and thus is unlikely to be explained by baroreflex mechanisms. Hence, the absence of LF oscillation in the RR interval in CHF is functional and is reversible by LVAD circulation. The presence of a predominant LF oscillation in RR interval independent of any oscillation in blood pressure suggests that the LF oscillation is a fundamental property of central autonomic outflow.

Effect of thermocycling times on dentin bond strength.

Thermocycling is widely used in the evaluation of dentin bonding agents. The purpose of this study was to determine the effect of increasing thermocycling times on the shear bond strength of composite resin to dentin using a NTG-GMA/BPDM-type bonding agent. Fifty human molar teeth were ground flat on the buccal surface into dentin (600 grit). Ten specimens were prepared for each thermocycling group of 100, 500, 1000, 2000, and 4000 cycles. The adhesive agent was applied to the dentin according to the manufacturer's instructions. A cyclindrical-shaped matrix was used to form the composite resin that was light cured to the treated dentin surface for 60 seconds. Thermocycling was started after 24 hours of storage in deionized water at 37 degrees C. Shear bond strengths were determined with an Instron universal testing machine at a cross-head speed of 0.5 mm per minute. The bond strengths in megapascals (MPa) were : 100 cycles 18.1 (+/- 5.2) MPa, 500 cycles 19.4 (+/- 4.0)MPa, 1000 cycles 16.5 (+/- 2.9), 2000 cycles 14.6 (+/- 5.1), and 4000 cycles 19.9 (+/- 3.2)MPa. When this data was subjected to an ANOVA, no significant difference was found between the groups.

Shear bond strengths of resin adhesive cements to dentin and Ni-Cr-Be alloy.

Two adhesives, Super Bond and Panavia, were evaluated for shear bond strength to dentin. Twenty human teeth were used for each adhesive. Bonding sites were prepared in dentin (600 grit) and the adhesives applied according to the manufacturers' instructions. Bond strengths were determined with an Instron testing machine at 24 hours. Super Bond developed the strongest bond of 21.59 +/- 3.91 MPa. Panavia produced a lower bond strength of 2.68 +/- 1.45 MPa. Statistically, Super Bond was found to have a stronger bond than Panavia. The same two adhesives were applied to Ni-Cr-Be specimens and compared to Comspan. Twenty Rexillium III specimens were used for each adhesive at 24 hours and 20 for thermocycling. The metal specimens were ground flat (600 grit) and then air abraded with 50-micron aluminous oxide. The adhesives were applied to the metal surface in accordance with the manufacturers' instructions. One group was tested at 24 hours while the second group was tested after thermocycling (2,500 cycles at 6 degrees C to 60 degrees C). At 24 hours, Super Bond had a significantly stronger bond than the other materials. Comparison of the 24-hour to thermocycled bond strengths found Comspan had a significant increase in bond strength, Panavia had no significant change and Super Bond had a significant decrease in bond strength. After 2,500 thermocycles, Comspan, Panavia, and Super Bond were not significantly different in bond strength.

Porcelain to dentin bond strength with a dentin adhesive.

Adhesion of porcelain to dentin may be important in those cases with little remaining enamel. The purpose of this study was to determine the bond strength of porcelain to dentin using a dentin adhesive (All-Bond) and compare it to the enamel bond strength. Sixty human molar teeth had either a dentin or enamel bonding site prepared by flat grinding to a 600 grit. The teeth were divided into three groups of 20 each. Sixty porcelain cylinders were prepared, hydrofluoric acid etched on one end and silane treated. Twenty of the cylinders were bonded to enamel, 20 bonded to dentin with a dentin adhesive to be tested at 48 hours, and 20 bonded to dentin with a dentin adhesive to be tested after 24 hours of thermocycling (800 cycles at 6 degrees C to 60 degrees C). The specimens were tested in an Instron at a crosshead speed of 0.5 mm/minute. The following bond strengths were found: enamel (19.0 +/- 2.9 MPa), dentin at 48 hours (14.4 +/- 5.4 MPa), and dentin after thermocycling (10.1 +/- 3.8 MPa). When this data was subjected to statistical analysis (ANOVA), there was a significant difference between the groups. A Scheffe's test found that the dentin-porcelain bond at 48 hours was stronger than the thermocycled group, and that the enamel bond was significantly stronger than the two dentin bonds.

Laboratory evaluation of adhesive systems.

Adhesive bonding of resin materials to acid-conditioned enamel is a clinically proven technique in preventative, restorative, and orthodontic procedures. Laboratory evaluations of etched-enamel resin bonding have shown excellent bond strengths and the virtual elimination of marginal microleakage. Adhesion to dentin has been more of a challenge. Earlier-generation dentin bonding systems did not yield high bond strengths in the laboratory or prevent marginal microleakage. Newer-generation adhesive systems generally use a dentin conditioner to modify or remove the smear layer and a subsequent application of an adhesive resin bonding agent. Laboratory evaluations of newer systems have shown bond strengths that approach or actually exceed that of etched enamel resin bonding. Bond strengths have improved with the evolution of dentin bonding systems, and microleakage from the cementum/dentin margin has been significantly reduced or prevented with the newer systems. Although laboratory testing of adhesive systems provides a mechanism to screen and compare newly developed systems, clinical trials are essential to document long-term clinical performance.

Dentinal bond strengths and microleakage of a 4-META adhesive to amalgam and composite resin.

A 4-META-containing adhesive was evaluated for its ability to bond a composite resin and two types of amalgam to dentin. One group of composite resin was tested after 24 hours and another group after 24 hours of thermocycling. Shear bond strengths were: composite resin at 24 hours = 22.38 MPa; thermocycled composite resin = 20.86 MPa; spherical alloy = 3.38 MPa; admixed alloy = 3.84 MPa. Microleakage was evaluated after the 4-META adhesive was applied to cavity preparations and compared to that of a group treated with a cavity varnish. There was statistically significantly less microleakage in the 4-META group at both the occlusal and gingival margins.

Comparison of manually and mechanically mixed glass ionomers.

Two mechanically mixed glass ionomer restorative materials (Ketac-Fil and Fuji Cap II) were compared with two manually mixed products (Chelon-Fil and Fuji Type II). One manually mixed material was substantially weaker than the others in bond strength tests. No significant differences in microleakage were found among the materials.

Fluoride-releasing retainers.

A method for fabrication of a fluoride-releasing retainer is described. The insert releases low levels of fluoride, which should promote remineralization and reduce caries potential. Previous research on the amount of fluoride release is also discussed.

Bond strength of light-cure fluoride-releasing base-liners as orthodontic bracket adhesives.

Fluoride-releasing bracket adhesives are desirable for their ability to minimize the potential for subsurface enamel demineralization adjacent to a bonded bracket. Self-applications with topical fluoride rinses, pastes, and gels have been documented to minimize and eliminate subsurface caries adjacent to bonded brackets. However, the success of these mediums are limited by patient compliance. A urethane with fluoride (TimeLine) and a glass ionomer with methyl methacrylate (Vitrabond), both of which are light cured and exhibit sustained fluoride ion release, were compared with a non-fluoride-releasing light-cured bracket adhesive (Transbond). Premolar brackets with mesh pads (A-Company) were positioned on the buccal surface of the premolars and placed in a PVC ring with polymethyl methacrylate. Two groups of 10 samples each of the tested material were prepared and immersed in distilled water immediately after in vitro bonding. Samples of each material were evaluated for enamel shear strength (Instron) at 24 hours and at 30 days. Bond strengths to enamel at 24 hours measured in megapascals (MPa) were 5.98 for TimeLine, 11.58 for Vitrabond, and 11.35 for Transbond. Bond strength to enamel at 30 days was found to be significantly less for TimeLine and Vitrabond: 3.05 for TimeLine, 5.39 for Vitrabond, and 10.80 for Transbond. The two fluoride-releasing, light-cured materials tested have low bond strengths after 30 days and are not acceptable as orthodontic bracket bonding agents. However, for patients with high caries risk, these materials may be placed around already bonded brackets.

Shear bond strength to dentin and Ni-Cr-Be alloy with the All-Bond universal adhesive system.

The shear bond strength of the All-Bond system to dentin and a nonprecious alloy was evaluated. Eighty human molar teeth (10 per group) were used in the dentin bonding phase of the study. A bond site was prepared in dentin, and both the succinic anhydride modified HEMA and 10 percent phosphoric acid dentin conditioning techniques were evaluated under both wet and dry conditions. Eighty Rexillium III specimens were used in the metal bonding phase of the study. All-Bond primer and opaquer were applied to the metal surface, followed by a visible light-cured composite restorative material. Dentin bond strengths were determined at 24 hours, while metal bond strengths were evaluated both at 24 hours and after thermocycling (2,500 cycles). Separate groups were established for adhesion to both dentin and metal with the composite placed in a plastic matrix or a gelatin capsule. The highest mean shear bond values to dentin were obtained in the groups with the gelatin capsule bonding procedure, where the dentin was treated with 10 percent phosphoric acid and then blotted dry (wet technique) before the bonding procedure (39.99 MPa). These values were higher than the succinic anhydride modified HEMA-treated group with gentle air drying (wet technique-29.56 MPa). There was essentially no difference in mean shear bond strengths to dentin when a succinic anhydride modified HEMA dentin conditioner was used with aggressive (dry technique) or gentle air drying (wet technique) [29.56 versus 29.08 MPa]. High bond strengths to Rexillium III were obtained when the All-Bond adhesive system was used in combination with a dual-care opaquer and a composite restorative material.(ABSTRACT TRUNCATED AT 250 WORDS)

Dentinal shear bond strength, microleakage, and contraction gap of visible light-polymerized liners/bases.

The bond strength and microleakage patterns of three light-curing glass-ionomer cement liners/bases (Vitrebond, XR Ionomer, and Zionomer) were evaluated and compared to a fluoride-releasing resin (TimeLine) designed for the same use. Bond strength tests were performed at 24 hours and 7 days. At 24 hours Vitrebond, Time-Line, and Zionomer had statistically significantly greater bond strengths than XR Ionomer. At 7 days, Vitrebond had a statistically significantly stronger bond than the others. Microleakage was evaluated after 24 hours of thermocycling. Vitrebond and XR Ionomer had statistically significantly less leakage than the others, while TimeLine had significantly more leakage than the others. Polymerization contraction gaps between the liners/bases and dentin were examined with scanning electron microscopy. Contraction gaps were approximately 10 microns with Vitrebond and XR Ionomer and 5 microns with TimeLine. A contraction gap generally was not observed with Zionomer.

Fluoride-releasing removable appliances.

A method was developed to give removable appliances a fluoride-releasing capability. Visible light-cured glass-ionomer cement inserts were made, placed in resins commonly used for removable appliances, and evaluated for fluoride release over a 2-month period. Fluoride release was measured daily for 7 days, weekly for 4 weeks, and monthly for 1 month. All specimens released fluoride at every time period. There was a "burst effect" in which more fluoride was released the first day, but the amount released decreased significantly on the second day. The amount of fluoride released decreased at each of the daily and weekly measurements, but became relatively stable after 7 days. All specimens were still releasing fluoride at the end of the 2-month test period.

Retention of pins in amalgam.

The Max 021 titanium alloy self-threading retentive pin was evaluated for retention in amalgam and compared to the Link Plus titanium alloy self-threading pin. Fifteen specimens in which amalgam was condensed around the retentive pins were prepared. The specimens were mounted in a specially constructed test apparatus in an Instron Testing Machine and placed under a continuous tensile force (1 mm/min) until failure occurred. The mean force required to induce failure in the Max pin specimens was 87.6 (+/- 37.4) Newtons while the mean for the Link Plus pins was 180.4 (+/- 39.8) Newtons. The failure of the specimens using the Max pins was primarily a result of fracture of the amalgam with removal of the pin intact. The failure site of the Link Plus pin was primarily fracture of the pin itself. Statistically, a significantly greater force was required to induce failure in the Link Plus pins.

Comparison of wet and dry finishing of resin composites with aluminum oxide discs.

Samples of four composites (Herculite, Visio-Dispers, Silux, and Prisma-Fil) were finished with aluminum-oxide discs either wet or dry so that the effects of these two finishing procedures could be compared. The samples were evaluated for surface smoothness, color stability, and surface hardness. Surface smoothness was determined immediately after a sample was finished with a profilometer. Knoop hardness values were determined for each sample immediately after being finished and once a week for five weeks. Color stability was evaluated with a tristimulus colorimeter by the color of each sample being finished and once a week for five weeks. When surface smoothness was compared between the wet- and dry-finished samples, there was no significant difference between Prisma-Fil, Silux, or Herculite; however, the wet-finished Visio-Dispers was significantly rougher than the dry-finished. When surface hardness was compared, there was no significant difference in hardness values between the wet and dry samples when compared over time. When changes in color were evaluated, only Visio-Dispers had no significant change in color for both the wet- and dry-finished samples over the five-week evaluation period. Dry finishing of only one composite (Silux) produced a significant change in color. Dry finishing of composites was superior or equal to wet finishing in all tests except for the color change in Silux.

Evaluation of a 4-META porcelain repair system.

A recently introduced porcelain repair system utilizing 4-META (Etch-Free Primer with C & B-Metabond) was evaluated for bond strength to porcelain. This system purportedly eliminates hydrofluoric acid-etching and silane pretreatment. Forty porcelain specimens were prepared and treated with the 4-META repair system. A resin cylinder was bonded to the treated porcelain surface. Twenty of the specimens were tested after 24 hours while the other 20 were tested after thermocycling (800 cycles at 6 degrees C to 60 degrees C). The mean bond strengths were: 24 hours 17.4 MPa (+/- 4.8), thermocycled 19.1 MPa (+/- 7). Cohesive failure of the porcelain occurred in all of the specimens, both the 24 hour and the thermocycled. These bond strengths compare favorably with or exceed those of other porcelain repair systems tested in other studies.

Evaluation of a 4-META adhesive cement.

This study investigated the shear bond strength of a new 4-META adhesive cement (C & B-Metabond) to dentin and Ni-Cr-Be alloy (Rexillium III). Fifteen human molar teeth had dentin bonding sites prepared by grinding away the enamel on a water-cooled abrasive wheel to a 600 grit. Fifteen metal alloy specimens were cast, ground to a 600 grit, and air abraded with 50 micron alumina. The 4-META cement was applied to the dentin and metal in accordance with the manufacturer's instructions. After 24 hours in water at 37 degrees C, the shear bond strengths were recorded. The mean bond strength to dentin and the metal alloy was 20.1 megapascals.

Evaluation of a phosphonate BIS-GMA resin as a bracket adhesive.

Panavia is a modified phosphate ester of dimethacrylate that purportedly forms a strong bond to tooth structure and to metals. The ability of this adhesive to bond orthodontic brackets to enamel was compared to the bond strengths of a no-mix bracket adhesive and a paste/paste autopolymerizing composite resin. Panavia did not form a bond as strong as that achieved by the bracket adhesive but was stronger than the composite resin.