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R E McKlveen

Publications and source records attributed to R E McKlveen.

8 recordsLinked to original sources
PubMed1992

Halothane relaxes preconstricted small and medium isolated porcine coronary artery segments more than isoflurane.

To compare the putative vasodilatory effects of isoflurane versus halothane on porcine coronary arteries, we studied the capacity of isoflurane and halothane to relax K(+)-constricted (30 mM) small (0.5-1.0 mm outside diameter [OD]) and medium (1.0-1.5 mm OD) porcine coronary arteries with use of in vitro tension recording. We also examined the effect of the dihydropyridine calcium channel agonist BAY K8644 on previously constricted epicardial porcine coronary artery segments in the presence of halothane or isoflurane. Our purpose was to determine (a) whether anesthetic effect on coronary arteries varied with arterial diameter, and (b) whether halothane and isoflurane inhibited BAY K8644-induced contraction of coronary vessels. Small and medium porcine coronary artery segments were constricted with K+ (30 mM) and the resulting contraction was allowed to stabilize. This was followed by exposure to 0.5%, 1.0%, 2.0%, and 3.0% isoflurane or halothane and the resultant tension was again measured. Potassium-induced contractions were significantly relaxed by halothane in small coronary artery segments at 0.5%, 1.0%, 2.0%, and 3.0% and in medium coronary artery segments at 1.0%, 2.0%, and 3.0%. Potassium-induced contractions were significantly reduced by isoflurane only at 3.0% in both small and medium coronary artery segments. Halothane caused significantly more relaxation of both small and medium porcine coronary arteries previously constricted with K+ (30 mM) than did isoflurane. There were no significant differences in coronary artery response to isoflurane or halothane with respect to coronary artery diameter. These experiments indicate that in porcine coronary arteries greater than 0.5 mm OD, studied in vitro after K(+)-induced contraction, isoflurane was not a potent coronary vasodilator.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1992

Halothane relaxes previously constricted human epicardial coronary artery segments more than isoflurane.

To compare the vasodilatory effects of isoflurane versus halothane on coronary arteries in vitro, we studied the capacity of isoflurane and halothane to relax resting and previously constricted human coronary artery segments with use of in vitro tension recording. Human epicardial coronary artery segments (1.5-2.0 mm outside diameter) were obtained from hearts excised from recipient patients at time of heart transplantation. The effects of 0.5%, 1.0%, 2.0%, and 3.0% isoflurane or halothane on resting coronary artery segments stretched to their optimal resting tension were determined. Next, after removal of anesthetic from the bathing solution, the segments were constricted with K+ (60 mM), and this contraction was allowed to plateau. The arteries were then again exposed to isoflurane or halothane at 0.5%, 1.0%, 2.0%, and 3.0% concentrations. Isoflurane and halothane had no effect on noncontracted coronary artery segments stretched to their optimal resting tension. Halothane caused significant relaxation of K(+)-induced (60 mM) contractions at 2.0% and 3.0% but not at lower concentrations. Isoflurane did not cause significant relaxation of K(+)-induced (60 mM) contractions at any concentration studied. Our studies indicate that under the conditions studied, isoflurane at clinically relevant concentrations is not a significant coronary dilator.

Coronary Vessels↗
PubMed1988

Diffusion hypoxia: a reappraisal using pulse oximetry.

Sixty healthy surgical patients were monitored during surgery with a pulse oximeter. At the completion of the operation, nitrous oxide and oxygen were discontinued abruptly in 50 of these patients. During air breathing, a small drop in arterial hemoglobin oxygen saturation (SaO2), to about 4% below preoperative values, was observed in all patients. In 10 patients, only oxygen was given before removal of the mask. There was no sudden drop in SaO2 in these patients, but by 5 minutes after discontinuation there was no difference between the two groups of patients--SaO2 was reduced 2 to 3% below preoperative values in both groups. For patients without cardiopulmonary disease, the phenomenon of "diffusion hypoxia" is a mild and transient event. Clinically significant hypoxemia (SaO2 less than 90%) after removal of nitrous oxide/oxygen at the completion of the anesthetic occurred in 3 patients (6%) and was associated with airway obstruction in each case.

Adolescent↗
PubMed1987

Resuscitation of the newborn.

The simple mnemonic ABCDE summarizes the five key principles of neonatal resuscitation: 1. Airway 2. Breathing 3. Circulation 4. Drugs 5. Evaluation of concurrent and causative problems and maintenance of a neutral thermal Environment.

Anesthetics↗
PubMed1982

Dark pulses affect the circadian rhythm of activity in hamsters kept in constant light.

We compared the effects of light pulses in constant darkness (DD) and dark pulses in constant light (LL) on the free-running rhythm of locomotor activity in male golden hamsters. Light pulses yielded advances, delays, or no change in the rhythm of activity. These data conform to a typical phase-response curve; this curve was unaffected by pinealectomy. Dark pulses occurring either late in the subjective night or early in the subjective day had little effect. In contrast, dark pulses occurring either late in the subjective day or early in the subjective night altered the rhythm in one of three ways: advance of the rhythm; splitting into two components; or induction of a new component, in phase with the pulse. Because dark pulses in LL perturb the circadian system in a different manner than do light pulses in DD, they may have value in identifying heretofore unknown aspects of circadian systems. As such, the use of dark pulses to perturb circadian rhythmicity will be a useful tool in examining the formal properties of circadian systems.

Animals↗