Magnesium-induced vasodilation in the dorsal hand vein

OBJECTIVE: Magnesium affects blood pressure by modulating vascular tone and reactivity. In obstetric patients, magnesium is administered to prevent eclamptic seizures and as a tocolytic to treat preterm labour. Prior to studying vascular sensitivity in women with pre-eclampsia, we sought to determine the effect of magnesium on venous tone in healthy women of childbearing age. DESIGN: Dose-response study. SETTING: Columbia-Presbyterian Medical Center, New York. POPULATION: Ten healthy non-pregnant women (age range 21-47 years). METHODS: Vascular response to magnesium sulphate (MgSO4) was measured in a dorsal hand vein using the linear variable differential transformer (LVDT) technique. Complete dose-response curves to MgSO4 (0.0000275-0.088 mmol/min) were determined after 50% preconstriction of the vein with phenylephrine. MAIN OUTCOME MEASURES: The ED50 of MgSO4 (dose resulting in 50% of maximal effect, Emax) was determined. Blood samples from the contralateral upper extremity were obtained to assess total plasma magnesium levels at baseline and at the highest infused dose of magnesium. ED50 results are expressed as geometric mean (95% confidence interval, CI). Emax results and magnesium plasma concentrations are expressed as mean [SD]. RESULTS: The ED50 of MgSO4 was 0.000307 mmol/min (95% CI 0.138, 0.666) and Emax was 102% [20%]. CONCLUSION: Magnesium induces dose-dependent venodilation in healthy women in the absence of systemic haemodynamic effects. The dose resulting in vasodilation using the LVDT/hand vein model is two to three orders of magnitude less than the therapeutic doses of magnesium used for tocolysis or seizure prophylaxis. Studies of the effect of systemically administered therapeutic doses of magnesium on vascular reactivity in pre-eclampsia will be of interest.     

Alpha 1A-adrenergic receptor polymorphism and vascular response

OBJECTIVE: The alpha(1A)-adrenergic receptor is highly expressed in human vasculature including resistance arteries and veins, and its stimulation is primarily responsible for adrenergically mediated smooth muscle contraction. Variability in sensitivity to phenylephrine, an alpha(1A) adrenergic agonist, has a large genetic component. We examined the hypothesis that a common polymorphism of alpha(1A)-adrenergic receptor (Arg347Cys) affects in vivo response. METHODS: We measured vascular sensitivity to phenylephrine using the dorsal hand vein linear variable differential transformer technique and determined alpha(1A)-adrenergic receptor genotype in 74 healthy, nonsmoking adults (28 Arg/Arg, 30 Arg/Cys, and 16 Cys/Cys). RESULTS: Sensitivity to phenylephrine, expressed as the dose of phenylephrine resulting in 50% venoconstriction (Phe(50)), was not significantly different in subjects with the 3 alpha(1A) adrenergic receptor genotypes: Phe(50) geometric mean (95% confidence interval) was 513 ng/min (287-918 ng/min) for Arg/Arg, 431 ng/min (274-680 ng/min) for Arg/Cys, and 471 ng/min (197-1124 ng/min) for Cys/Cys (P =.90). CONCLUSION: We conclude that the Arg347Cys receptor polymorphism does not alter agonist-mediated venoconstriction in vivo.     

Comparison of Primary-Care Practitioners and Sleep Specialists in the Treatment of Obstructive Sleep Apnea

We wished to determine if being treated for sleep apnea by a sleep specialist increased patient awareness or long-term continuous positive airway pressure (CPAP) compliance. We performed a retrospective telephone survey and laboratory chart review in patients with a diagnosis of sleep apnea evaluated either at a laboratory in which only sleep specialists can order polysomnography (University Specialty Hospital, noted as USH) or at a laboratory serving the medical community at large (Kernan Hospital, noted as K). Both laboratories are under the same medical director, use the same policies and procedures, equipment, and technician pool. One hundred three patients participated in the survey (approximately 37% of those contacted), 59 from USH and 44 from K. The groups were comparable in terms of demographics, presenting complaints, and apnea severity. In patients treated by sleep specialists, awareness of the disease process was greater and the evaluation was timelier than in patients treated by generalists. However, there was no difference between the groups long-term self-reported CPAP acceptance or compliance. The most robust predictor of continued CPAP use was the patients self-report of feeling better.     

Normalisation of ocular pulse amplitude after embolisation of dural cavernous sinus arteriovenous fistula

BACKGROUND: The difference in the ocular pulse amplitude between an individual's eyes may reflect abnormalities of the cerebrovascular circulation and has been shown to be helpful in assessing patients with cavernous sinus arteriovenous fistulas. HISTORY AND SIGNS: A 71-year-old woman presented with episcleral injection, proptosis, bruit and retro-orbital pain on the left side. Ocular pulse amplitude as measured by dynamic contour tonometry was 4.38 +/- 1.23 mm Hg in the right and 9.57 +/- 2.71 mm Hg in the left eye. Angiography revealed the haemodynamics of a dural left cavernous sinus arteriovenous fistula. THERAPY AND OUTCOME: Successful occlusion of the fistula was performed by transvenous embolisation. After embolisation, ocular pulse amplitude was 2.84 +/- 0.60 mm Hg in the right and 1.88 +/- 0.29 mm Hg in the left eye. Conclusion: In this case of a dural arteriovenous fistula the ocular pulse amplitude as measured by dynamic contour tonometry parallels closely both clinical findings and neuroimaging.     

Breast feeding and respiratory morbidity in infancy: a birth cohort study

Aim: To examine the relation between the duration of breast feeding and morbidity as a result of respiratory illness and infection in the first year of life. Methods: Prospective birth cohort study of 2602 live born children ascertained through antenatal clinics at the major tertiary obstetric hospital in Perth, Western Australia. Main outcome measures were hospital, doctor, or clinic visits, and hospital admissions for respiratory illness and infection in the first year of life. Main exposure measures were the duration of predominant breast feeding (defined as the age other milk was introduced) and partial (any) breast feeding (defined as the age breast feeding was stopped). Main confounders were gender, gestational age less than 37 weeks, smoking in pregnancy, older siblings, maternal education, and maternal age. Results: Hospital, doctor, or clinic visits for four or more upper respiratory tract infections were significantly greater if predominant breast feeding was stopped before 2 months or partial breast feeding was stopped before 6 months. Predominant breast feeding for less than six months was associated with an increased risk for two or more hospital, doctor, or clinic visits and hospital admission for wheezing lower respiratory illness. Breast feeding for less than eight months was associated with a significantly increased risk for two or more hospital, doctor, or clinic visits or hospital admissions because of wheezing lower respiratory illnesses. Conclusions: Predominant breast feeding for at least six months and partial breast feeding for up to one year may reduce the prevalence and subsequent morbidity of respiratory illness and infection in infancy.     

Expandable Bioresorbable Endovascular Stent. I. Fabrication and Properties

A bioresorbable, expandable poly(L-lactic acid) stent has been designed, based on a linear, continuous coil array principle, by which multiple furled lobes convert to a single lobe upon balloon expansion, without heating. Stent strength and compliance are sufficient to permit deployment by a conventional balloon angioplasty catheter. Several multiple lobe configurations were investigated, with expansion ratios ranging from 1.4 to 1.9 and expanded diameters ranging from 2.3 to 4.7 mm. Compression resistance of the expanded stent is dependent on fiber coil density and fiber ply. A range sufficient for endovascular service was obtained, with less than 4% elastic recoil in six day saline incubation studies. Surface plasma treatment with di(ethylene glycol) vinyl ether significantly reduced platelet adhesion in a 1 h porcine arteriovenous shunt model. Patency was maintained in one week implant studies in the porcine common femoral artery. However, a strong inflammatory response, and significant reduction of the vascular lumen were observed following two weeks implantation. The design principles and fabrication techniques for this bioresorbable stent are sufficiently versatile that a broad range of applications can be addressed. Much work remains to be done, including long-term evaluation of the inflammatory response, and of polymer degradation. The results of this study demonstrate the feasibility of expandable biodegradable stent design and deployment by conventional means. © 2003 Biomedical Engineering Society. PAC2003: 8768+z, 8719Uv     

Elevated maternal mid-trimester chorionic gonadotropin > or =4 MoM is associated with fetal cerebral blood flow redistribution

BACKGROUND: Elevated mid-trimester human chorionic gonadotropin (hCG) is associated with adverse maternal and perinatal outcome. The aims of the study were to evaluate the association between elevated hCG, fetal pathological arterial waveforms and maternal and perinatal complications. METHODS: Pulsatility indices (PI) of middle cerebral artery (MCA) and umbilical artery (UA) were determined prospectively in 121 consecutive patients with abnormal maternal serum hCG (> 2.5 MoM). Each patient had four US scans during pregnancy. Patients with known structural or chromosomal anomalies were excluded. RESULTS: Of 121 women with hCG > 2.5 MoM, 36/121(29.6%) had hCG between 2.5 and 3.0 MoM, 35/121(28.9%) had hCG between 3.0 and 3.5 MoM, 21/121(17.3%) had hCG of 3.5-4.0 MoM, 17/121(14.1%) had hCG levels between 4.0 and 4.5 MoM, and 12/121(9.9%) had hCG > 4.5 MoM. Middle cerebral artery PI was significantly lower in women with hCG > 4.0 MoM between 28 and 36 weeks' gestation, but not between 18 and 27 weeks' gestation. No differences of MCA PI were found when the cut-off point of hCG was 3.5. Women with hCG levels > 4.0 MoM had a significantly higher rate of preterm deliveries, cesarean sections, higher rate of Apgar scores < 7 and a significantly lower mean birth weight in comparison with women with hCG < 4.0 MoM. The prevalence of PIH and preeclampsia and perinatal death were found to be higher among patients with hCG levels > 4.0 MoM, although not significantly. No differences were found at hCG levels less than 4.0 MoM. CONCLUSIONS: In pregnancies with mid-trimester hCG > 4.0 MoM, redistribution of cerebral blood flow is expressed after 28 weeks' gestation. These pregnancies have higher rates of maternal and neonatal complications as compared to pregnancies with lower hCG levels.