Phenylephrine-induced anterior chamber hypoxia

The effect of topical phenylephrine 10% solution on anterior chamber oxygen tension (PO2) was studied in cats using an oxygen-sensitive electrode inserted into the midanterior chamber. A decrease in anterior chamber PO2 was usually observed within eight to 25 minutes and declined steadily thereafter. Within two hours, the drug caused a dramatic 60% reduction in anterior chamber oxygen tension (P less than or equal to .0005). We suggest that the mechanism for this phenylephrine-induced anterior chamber hypoxia is reduced blood flow, mediated by the direct vasoconstrictive effect of the drug and compression of the iris vasculature (induced by dilatation). The resulting decrease in the caliber of the iris arteries produced a parallel decrease in blood volume and flow which resulted in diminished PO2. Phenylephrine 10% may contribute to hypoxia and exacerbate the underlying pathology in those disorders where hypoxia plays an important causal role.     

Assessment of cutaneous sensory and autonomic axon reflexes in rheumatoid arthritis.

OBJECTIVE--To assess sensory function in skin overlying the joints of patients with rheumatoid arthritis, in relation to the pain and tenderness which commonly arises in structures not directly involved in the inflammatory process. METHODS--An intradermal injection of capsaicin 0.05 microgram in 10 microliters was made over the wrists and forearms of 40 patients with rheumatoid arthritis and 46 control subjects. Axon reflex vasodilatation was measured using laser Doppler flowmetry. Cholinergic sympathetic function was assessed by measuring axon reflex sweating induced by a single intradermal injection of nicotine 0.5 microgram in 0.1 ml. RESULTS--Capsaicin induced axon reflex vasodilation over the wrists was found to decrease with age in normal subjects (r = -0.62, p < 0.001). In patients with rheumatoid arthritis, capsaicin induced axon reflex vasodilatation was significantly greater over the wrists, but not the forearms, when compared with age matched normal controls (p < 0.01). A minimal correlation between axon reflex vasodilatation and visual analogue pain score was apparent in the rheumatoid group (r = -0.37, p < 0.05). Nicotine induced sweating responses were similar in the rheumatoid and normal groups, and both showed a linear age related decline. CONCLUSIONS--The results show a selective increase of capsaicin induced vasodilatation in skin overlying joints in patients with rheumatoid arthritis. This suggests that the activity of a sub-population of periarticular small sensory fibres is altered, which may explain, at least in part, some of the clinical findings in this disorder.     

Pathogenesis and changes in the aetiology of arterio-venous fistulae

There has been a marked shift in the causes of arterio-venous fistulae. Gunshot and stab wounds used to be the most frequent cause but iatrogenic fistulae, especially those arising as a result of reconstructive skeletal operations or following diagnostic and therapeutic procedures, are now becoming increasingly common. If morphological vascular changes have not yet occurred and cardiac volume overloading has not led to permanent damage, a recently established arterio-venous fistula can be easily corrected by resection and oversewing of the artery and vein. The special cases of arterio-venous fistulae arising as a result of catheter procedures in the groin have to be identified in terms of cause and morphology in order to facilitate early surgical correction.     

Initial experience with Tc-99m-HM-PAO in the study of brain tumors

A preliminary study of the distribution of the 99mTc complex of hexamethylpropylene amine oxime (HM-PAO) in 12 patients with brain neoplasms before, during, and after radiotherapy has been performed. Untreated brain tumors were found to exhibit a range of 99mTc-HM-PAO uptake, varying from areas of markedly increased isotope activity to photopenic areas, when compared to normal brain tissue. A ratio of 99mTc-HM-PAO tumor uptake to contralateral normal tissue uptake was calculated prior to and during radiotherapy. This ratio tended to return towards unity in lesions responding to therapy. A predictable alteration in whole brain 99mTc-HM-PAO uptake during radiotherapy was not demonstrated. Unlike the radiolabeled amines, 99mTc-HM-PAO localizes in primary tumors, probably indicating that its uptake mechanism is independent of non specific amine receptors. 99mTc-HM-PAO may be useful in the study of brain tumor physiology and response to therapy.