An evaluation of bone growth into porous high density polyethylene.

The purpose of this investigation was to study bone growth into porous polyethylene rods as a function of time and pore structure. Previous studies have indicated the biocompatibility of solid polyethylene materials which are currently being used clinically. Porous polyethylene rods were implanted in the femurs of mongrel dogs which are sacrificed four, eight, and 16 weeks postoperatively. The implants were then sectioned and examined histologically and microadiographically. Quantitative techniques were employed to determine the amount of bone ingrowth as a function of time and pore size. The pore structures of the materials were evaluated using optical microscopy and mercury intrusion porosimetry. The results of this investigation have demonstrated that porous polyethylene is capable of accepting bone growth into pores as small as 40 mum. The optimum rate of bone ingrowth was observed in pore sizes of approximately 100 to 135 mum, with no increase in the rate of bone ingrowth observed in samples possessing larger pore sizes. No adverse tissue response was found at implant times up to 16 weeks in pore sizes of 100 mum or larger.     

Thrombin contraction of vascular smooth muscle: implications for vasospasm

Thrombin contributes to hemostasis by activating platelets, the formation of fibrin, and contraction of the injured vessel. These effects are mediated through the proteolytic activity of thrombin. We hypothesized that thrombin may have a role in vasospasm after arterial injury and examined the physiologic and cellular signaling events of thrombin in intact vascular smooth muscles. Thrombin stimulation of strips of bovine carotid artery smooth muscle led to contractions which relaxed with the addition of the nitric oxide donor, sodium nitroprusside. However, washout of the thrombin and SNP resulted in the re-generation of force. This was not observed with other agonists such as endothelin, thromboxane analogues, or serotonin. Using two-dimensional immunoblotting we demonstrate that thrombin stimulation leads to increases in the tyrosine phosphorylation of 4 proteins, three different isoforms of P44 mitogen activated protein kinase (MAPK) and one isoform of P38 stress activated protein kinase (SAPK). Activation of P38 SAPK leads to activation of MAPKAP kinase-2 and a major substrate protein of MAPKAP kinase-2 is the small heat shock protein, HSP27. HSP27 has been implicated in mediating smooth muscle contraction. These data suggest that in the setting of arterial injury, thrombin-induced contraction may supercede over short acting vasorelaxants such as NO resulting in vasospasm. In addition to stress, physiologic substances such as thrombin, activate SAPKs leading to increases in the phosphorylation of HSP27. Thus, thrombin may play a central role in hemostasis after vascular injury and in the pathologic responses to plaque rupture and thrombosis in atherosclerosis.     

The relation between aerobic fitness and serum cholesterol levels in a large employed population

BACKGROUND. The purpose of this epidemiologic study was to determine the extent to which aerobic fitness was associated with total cholesterol/HDL-C ratios greater than 5.0 in 10,455 adults. The confounding effects of age, gender, income, body fat, smoking, and alcohol use were also examined. METHODS. A step test was used to estimate aerobic fitness, and serum cholesterol was measured in a certified lab. Lifestyle information was gathered using written questionnaires, and body fat was assessed using skinfold measurements. RESULTS. High fitness levels were associated with low prevalence of elevated total/HDL-C ratios. After controlling for the potential confounders, adults classified as having excellent, very good, good, or fair aerobic fitness levels were .46, .64, .61, and .85 times as likely to have elevated ratios compared to poorly fit adults, respectively. High-level fitness was also related to high HDL-C levels and low total cholesterol levels. DISCUSSION. Cause-and-effect conclusions are not warranted; however, poorly fit adults appear to be at increased risk of elevated levels of serum cholesterol.     

Vascular smooth muscle mechanics in isolated perfused segments of carotid arteries

BACKGROUND: We hypothesized that smooth muscle contraction and relaxation responses in a muscle bath (isometric tension) would be different than responses of intact vessels (isotonic tension). METHODS: Bovine carotid artery contractile responses to the catecholamine, norepinephrine, and smooth muscle relaxant, 3-isobutyl-1-methylxanthine, were examined in strips of vessels in a muscle bath and in intact whole vessels in an isolated perfused whole-vessel perfusion apparatus. RESULTS: The maximal tension in the muscle bath depended on the length of the strip. The responses of whole vessels to increasing pressure was curvilinear. The maximal decrease in vessel diameter in intact vessels in response to the catecholamine and norepinephrine occurred at low intraluminal pressures. The dose-response curve to norepinephrine was shifted to the left in intact vessels compared with strips of vessels in the muscle bath, which suggests that whole vessels were more sensitive to norepinephrine. The maximal increase in diameter to increasing intraluminal pressure occurred in the presence of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, which suggests that there was significant intrinsic tone in the vascular smooth muscle. CONCLUSIONS: These results suggest that there are differences in the contractile properties of the vascular smooth muscle that are related to the ex vivo system used to examine smooth muscle responses. Responses obtained in isolated perfused whole vessels may more closely approximate in vivo responses.     

African American women's preventative care usage: the role of social support and racial experiences and attitudes

Research suggests that African Americans are less likely to utilise preventative care services than Americans of European descent, and that these patterns may contribute to racial health disparities in the United States. Despite the persistence of inequalities in preventative care utilisation, culturally relevant factors influencing the use of these gateway health services have been understudied among marginalised groups. Using a stratified sample of 205 low‐income African American women, this research examines the predictors of receiving a physical exam, with a particular emphasis on how differing levels of social support from friend and family networks and experiences of racial discrimination and cultural mistrust shape utilisation. The findings underscore the importance of traditional predictors of utilisation, including insurance status and having a usual physician. However, they also indicate that supportive ties to friendship networks are associated with higher predicted rates of having an annual physical exam, while social support from family and sentiments of cultural mistrust are associated with lower rates of utilisation. Broadly, the findings indicate that even as traditional predictors of help‐seeking become less relevant, it will be critical to explore how variations in discrimination experiences and social relationships across marginalised groups drive patterns of preventative care utilisation.     

Pediatric dermatology workforce in the United States

Studies have suggested there is a shortage of pediatric dermatologists in the United States, but the workforce has not been well defined. The Society for Pediatric Dermatology (SPD) Workforce Committee sought to characterize the US pediatric dermatology workforce with a nine‐question survey, sent to all 484 US SPD members in December 2016. The response rate was 30%. Most pediatric dermatologists were practicing in major metropolitan markets, seeing an average of 80 patients a week with an average 6‐week wait time. These findings indicate that geographic maldistribution and long wait times for new patient appointments remain substantial hurdles for adequate access to subspecialty pediatric dermatology care.