Search PubMed⌕ Search

Biomedical subjects

R W Millard

Publications and source records attributed to R W Millard.

At least 91 records · Page 5Linked to original sources
PubMed1976

Effects of isoproterenol on regional myocardial function, electrogram, and blood flow in conscious dogs with myocardial ischemia.

The effects of coronary occlusion and of subsequent isoproterenol infusion were examined in conscious dogs. Left ventricular (LV) function was assessed by measurements of LV diameter, pressure, velocity and dP/dt/P, and regional myocardial function was assessed by measurements of segment length (SL) and velocity of SL shortening in normal, border, and ischemic zones. Regional myocardial function was measured from the same sites, along with intramyocardial electrograms and regional myocardial blood flow as determined by radioactive microspheres. Coronary occlusion resulted in graded loss of function from the normal to severely ischemic zones with graded flow reductions and graded increases in ST segment elevation. Isoproterenol improved overall LV function, and function in the normal zone. Isoproterenol also improved function in 19 of 21 border-zone segments and in all moderately ischemic segments, while elevating further the ST segments. These changes were accompanied by increases in myocardial blood flow. In contrast, in severely ischemic segments, isoproterenol resulted in a deterioration of function, in that paradoxical motion occurred in segments previously akinetic during systole, while paradoxical motion was intensified in those segments in which it was already present. These changes were accompanied by further ST segment elevation but not by concurrent increases in blood flow. In addition, in 2 of 21 border zone segments, myocardial blood flow fell and these segments responded to isoproterenol with complete loss of function; paradoxical motion developed. Thus, in the conscious dog, a strong inotropic agent can improve function, even in the ischemic myocardium, as long as the required additional blood flow can be provided wither through primary or collateral channels.

Animals↗
PubMed1975

Peripheral vascular response to norepinephrine at temperatures from 2 to 40 degrees C.

The response to norepinephrine (NE) was studied in the perfused whole vascular bed and perfused arteries in situ and on helical strips of arteries and veins from the isolated duck leg. NE consistently produced vasoconstriction but the sensitivity was 3-50 times greater in the whole vascular bed than in artery segments. The drug effect was maximal at temperatures near 25 degrees C and diminished considerably at low temperatures (2-5 degrees C). Isolated helical strips of arteries and veins, when exposed to NE, showed maximal developed force at 25-30 degrees C. Tibial vessels developed only slight force at 5 degrees C while the tarsal-metatarsal and digital vessels responded even at 2 degrees C. The sensitivity to NE of both vessel types from the same region was similar. Flow in whole vascular bed perfused at constant pressure (40 cmH2O) was maximum at 30-35 degrees C. At both higher and lower temperatures flow declined and was about the same at 2 degrees C as at 40 degrees C. Our findings indicate that the vasoconstrictor effect of NE is exerted on both large and small veins and arteries; yet peripheral vessels respond more than do proximal segments at low temperatures. These findings suggest that peripheral vascular compartments may be capable of regulating regional blood flow at temperatures approaching freezing.

Animals↗
PubMed1975

Regional myocardial functional and electrophysiological alterations after brief coronary artery occlusion in conscious dogs.

The time relationship for recovery of mechanical function, the intramyocardial electrogram and coronary flow after brief periods of regional myocardial ischemia, was studied in conscious dogs. Total left vemtricular (LV) function was assessed with measurements of LV systolic and diastolic pressures, rate of change of LV pressure (dP/dt), and dP/dt/P. Regional LV function was assessed with measurements of regional segment length and velocity of shortening. An implanted hydraulic occluder on either the left anterior descending or circumflex coronary artery was inflated for 5- and 15-min periods on separate days. A 5-min occlusion depressed overall LV function transiently, but just before release of occlusion overall function had nearly returned to control. At this time regional function in the ischemic zone was still depressed to the point of absent shorteining or paradoxical motion during systole and was associated with marked ST segment elevation (+ 10 +/- 2.2 mV) at the site where function was measured. With release of occlusion and reperfusion the intramyocardial electrogram returned to normal within 1 min, and reactive hyperemia subsided by 5-10 min. In contrast to the rapid return to preocclusion levels for coronary flow and the electrogram, regional mechanical function remained depressed for over 3 h. A 15-min coronary occlusion resulted in an even more prolonged (greater than 6 h) derangement of function in the ischemic zone. Thus, brief periods of coronary occlusion result in prolonged impairement of regional myocardial function which could not have been predicted from the rapid return of the electrogram and coronary flow. These observations indicate that brief interruptions of coronary flow result either in a prolonged period of local ischemia or that alterations of mechanical induced by ischemia far outlast the repayment of the oxygen debt.

Animals↗
PubMedDate not supplied

Nursing assessment of positive adjustment for individuals with multiple sclerosis.

The chronic, progressive nature of multiple sclerosis (MS) often interferes with effective psychosocial adjustment. When presented with physical limitations and/or cognitive impairment, the client with MS may experience problems such as depression, family dissolution, and loss of important roles. However, some persons are able to adjust positively and enjoy life. This article explains a model for assessing psychosocial adjustment of those with MS and describes its practical application for the rehabilitation nurse.

Adaptation, Psychological↗
PubMedDate not supplied

Evaluation of the influence of the aqueous phase bioconstituent environment on the F-19 T1 of perfluorocarbon blood substitute emulsions.

Oxygen-sensitive F-19 magnetic resonance imaging of perfluorocarbon compounds requires that fluorocarbon T1 changes correlate with the local PO2 and not with the composition of the surrounding aqueous phase. The influence of various bioconstituents and paramagnetic ions within the aqueous phase on the F-19 fluorocarbon phase T1 for PFC emulsions was evaluated at 0.14 and 0.66 T. T1 was measured for FC-43, perflubron, and a fluorinated surfactant. Controlled variables introduced in the aqueous phase included annex solution constituents, blood, pH changes, and Gd-DTPA. For a constant PO2, the F-19 T1s were independent of the emulsion constituents, blood concentration, and pH. For FC-43 and perflubron, F-19 T1 was independent of the Gd-DTPA concentration, while the aqueous phase T1 decreased by more than an order of magnitude. XMO-10 (smallest emulsion particle size) showed a slight decrease in F-19 T1 with increasing Gd-DTPA concentration at 0.66 T.

Animals↗