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Biomedical subjects

R H Cox

Publications and source records attributed to R H Cox.

At least 145 records · Page 8Linked to original sources
PubMed1978

Comparison of carotid artery mechanics in the rat, rabbit, and dog.

Cylindrical segments of carotid arteries from rat, rabbit, and dog were studied in vitro in order to compare active and passive mechanical properties, with gross morphology and composition. Pressure-diameter relations were determined under active (norepinephrine) and passive (2 mM EGTA) conditions, and were used to compute values of tangential wall stress, incremental elastic moduli, characteristic impedance, and active smooth muscle responses. The water and connective tissue contents of these segments were also determined. Significant differences were found in the passive mechanical properties of these arteries, with those of the rat being most compliant and those of the dog being the stiffest. These differences were consistent with the connective tissue content of these arteries. The ratio of collagen to elastin was smallest in the rat and largest in the canine carotids. Differences were also demonstrated in the responses to smooth muscle activation. The maximum value of active stress response was essentially the same in the canine and rabbit arteries, both of which were larger than that of the rat carotids. On the other hand, the rabbit vessels produced a larger maximum diameter response than either of the other arteries. Values of incremental elastic modulus were largest at specific values of transmural pressure for the rabbit vessels. This latter fact may make the contractile system more effective in reducing wall diameter in the rabbit arteries in spite of the fact that they did not have the capacity to generate a larger active stress response.

Animals↗
PubMed1978

Regional variation of series elasticity in canine arterial smooth muscles.

Segments of carotid, iliac, renal, mesenteric, coronary, and internal thoracic arteries were studied in vitro to correlate the mechanical properties of series (SE) and parallel (PE) elastic elements with connective tissue (CT) composition and with active responses to potassium activation. The PE properties were determined using pressure-diameter data with passive smooth muscle (SM). SE properties were determined from periodic incremental releases imposed during isometric responses to [K+]O at a diameter corresponding to Lmax, the optimum muscle length. Active stress responses and diameter responses were determined using pressure-diameter data for active and passive conditions. Collagen and elastin contents were determined for each sample. No correlation was found between CT content and PE or SE properties for the various sites. A close correlation was found to exist between SE and PE properties at each site, i.e., the sites with the stiffest PE also had the stiffest SE. SM, with stiffer SE, had a larger diameter response with the same active stress response and the same diameter response with a smaller active stress response, compared to SM with more compliant SE. This suggests that passive properties of SM can have a significant influence on the external manifestations of contractile element properties.

Animals↗
PubMed1977

Photochemical transformation of the DDT and methoxychlor degradation products, DDE and DMDE, by sunlight.

DDE and DMDE, degradation products of the pesticides DDT and methoxychlor, rapidly undergo an unusual photoisomerization in solution when exposed to sunlight. The isomerization involves the exchange of a vinyl chlorine and an ortho aromatic hydrogen. Other photoproducts identified were corresponding benzophenones and 1,1-diaryl-2-chloroethylenes. Quantum yields for the reactions were measured and then used to compute sunlight photolysis half-lives for DMDE and DDE. Although both compounds absorb only the short-wavelength ultraviolet component of sunlight, their photolysis was found to be surprisingly rapid. During summer at latitude 40 degrees N, the photolysis half-lives near the surface of a water body are one hour and one day for dissolved DMDE and DDE, respectively. Photolysis of the DDE photoisomers is about an order of magnitude slower than that of DDE, suggesting that they may accumulate under environmental conditions. The DDE photoisomers photocyclize to form chlorinated dibenzofulvene and dichlorofluorenone. Neither DDE nor its photoisomers photoreact in solution to form PCB's. The environmental significance of these results is discussed, and its is suggested that the persistence of DDE in inland surface waters may be related to its tendency to sorb onto sediments and biota where not light is present.

Dichlorodiphenyl Dichloroethylene↗
PubMed1977

Baroreceptor control of regional haemodynamics during halothane anaesthesia in the dog.

Regional haemodynamic control by the cardiovascular baroreceptors was examined in dogs anaesthetized with 1 + MAC halothane in oxygen (1%). The open-loop relationships between carotid sinus pressure (CSP) and regional haemodynamics in the iliac, renal, mesenteric, aortic and coeliac beds were examined before vagotomy, following vagotomy and following thoracotomy. Around the carotid sinus reflex set point, the ratio of the reflex decrease in systemic arterial pressure to an increase in CSP (reflex gain) was -0.744+/-0.089 (mean+/-SEM): the latter increased to -1.275+/-0.093 following vagotomy. Reflex resistance changes were greatest in the renal bed and least in the coeliac bed, reflecting blood flow homeostasis which was well preserved in the renal bed but minimal in the coeliac bed. Thoracotomy in the dogs in which vagotomy had been performed resulted in no significant changes in the dependent variables studied. It is concluded that, in these dogs anaesthetized with 1 + MAC of halothane, baroreceptor control of regional pressure flow relationships is well preserved.

Anesthesia, Inhalation↗
PubMed1977

Sodium nitroprusside and regional arterial haemodynamics in the dog.

Blood flow to functionally different vascular beds was examined during a sodium nitroprusside infusion in 10 dogs anaesthetized with halothane (1 MAC) in oxygen. Blood flows were measured in the ascending aorta, and the coeliac, superior mesenteric, renal and iliac arteries. In two dogs, regional vascular impedance and related power were calculated. Regional pressure-flow relationships were measured at systemic pressure reductions of approximately 15, 35 and 55% of control. At pressure reductions of 15-35%, coeliac, mesenteric and aortic blood flow exceeded control values (P less than 0.025); renal and iliac blood flows were reduced, but not significantly. At pressure reductions of 55% a more significant reduction of iliac, renal and aortic blood flow occurred (P less than 0.05). All vascular resistances showed significant monotonic reductions (P less than 0.01) over the entire range of pressure reduction. Total power dissipation was reduced in all beds with a reduction of characteristic impedance in the coeliac, renal and iliac beds; aortic oscillatory pressure power increased.

Anesthesia, Inhalation↗
PubMed1977

Mycotoxins produced by Aspergillus fumigatus isolated from silage.

Results are presented which show that Aspergillus fumigatus was one of the predominant fungi contaminating moldy silage. Growth of A. fumigatus on silage appeared to depend on a preliminary aerobic fermentation by other natural microflora in silage. The clavine alkaloid, fumigaclavine A, and a new clavine alkaloid designated fumigaclavine C were produced by A. fumigatus. The LD50 of fumigaclavine C was approximately 150 mg/kg oral dose in day-old cockerels.

Animal Feed↗