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Biomedical subjects

D Preiss

Publications and source records attributed to D Preiss.

14 recordsLinked to original sources
PubMed2005

Effects of maternal hyperoxia with and without normocapnia in uteroplacental and fetal Doppler studies.

OBJECTIVE: One hundred percent oxygen is given in pregnancy to improve fetal oxygenation, yet has been shown in both animal and human studies ex utero to increase cerebral vascular resistance. Adjusting end-tidal pCO2 (ET-pCO2) levels to normocapnic levels during hyperoxygenation offsets this effect in non-pregnant individuals. We aimed to evaluate the effect of maternal hyperoxygenation with and without maintaining normocapnia on the fetal and uteroplacental circulations in healthy near-term human pregnancies. METHODS: Eight healthy pregnant women, serving as their own controls, sequentially breathed room air, breathed 100% oxygen, and underwent normocapnic hyperoxygenation (NH) in a three-phase experiment involving a tight-fitting facemask. Each phase lasted 10-15 min. After steady state had been reached, peak velocities and pulsatility index (PI) values were obtained from the uterine, umbilical and fetal middle cerebral arteries (MCA) by color/pulsed Doppler. In addition, maternal ventilation and ET-pCO2 were monitored. RESULTS: One hundred percent oxygen induced maternal hyperventilation and hypocapnea. Uterine artery PI and peak systolic velocities were stable during 100% oxygen. In contrast, during NH uterine artery PI values decreased by 21% (P=0.04). Umbilical artery PI and peak velocities were stable during 100% oxygen; PI increased by 16% during NH (P=0.056), with no change in peak velocities. Peak MCA velocities decreased by 8% during 100% oxygen, and by 9.6% during NH, while MCA-PI decreased by 13% during 100% oxygen and by 21% during NH (P=0.06). CONCLUSIONS: Maternal and fetal circulations exhibit divergent responses to 100% oxygen and NH. While no change is observed in the uteroplacental circulation on 100% oxygen, decreased resistance and increased flow velocity are evident during NH. Increased umbilical artery PI during NH with no change in absolute velocities may suggest a reduction in fetoplacental blood flow. Maintaining normocapnia during hyperoxygenation does not appear to beneficially influence the circulation of the near-term human fetus as it does in non-pregnant individuals.

Adult↗
PubMed2005

Precise control of end-tidal carbon dioxide levels using sequential rebreathing circuits.

Anaesthesiologists have traditionally been consulted to help design breathing circuits to attain and maintain target end-tidal carbon dioxide (P(ET)CO2). The methodology has recently been simplified by breathing circuits that sequentially deliver fresh gas (not containing carbon dioxide (CO2)) and reserve gas (containing CO2). Our aim was to determine the roles of fresh gas flow, reserve gas PCO2 and minute ventilation in the determination of P(ET)CO2. We first used a computer model of a non-rebreathing sequential breathing circuit to determine these relationships. We then tested our model by monitoring P(ET)CO2 in human volunteers who increased their minute ventilation from resting to five times resting levels. The optimal settings to maintain P(ET)CO2 independently of minute ventilation are 1) fresh gas flow equal to minute ventilation minus anatomical deadspace ventilation, and 2) reserve gas PCO2 equal to alveolar PCO2. We provide an equation to assist in identifying gas settings to attain a target PCO2. The ability to precisely attain and maintain a target PCO2 (isocapnia) using a sequential gas delivery circuit has multiple therapeutic and scientific applications.

Anesthesia, Closed-Circuit↗
PubMed2003

Isocapnic hyperpnoea accelerates recovery from isoflurane anaesthesia.

BACKGROUND: Hyperventilation should speed up elimination of volatile anaesthetic agents from the body, but hyperventilation usually results in hypocapnia. We compared recovery from isoflurane anaesthesia in patients allowed to recover with assisted spontaneous ventilation (control) and those treated with isocapnic hyperpnoea. METHODS: Fourteen patients were studied after approximately 1 h of anaesthesia with isoflurane. Control patients were allowed to recover in the routine way. Isocapnic hyperpnoea patients received 2-3 times their intraoperative ventilation using a system to maintain end tidal PCO(2) at 45-50 mm Hg. We measured time to removal of the airway and rate of change of bispectral index (BIS) during recovery. RESULTS: With isocapnic hyperpnoea, the time to removal of the airway was markedly less (median and interquartile range values of 3.6 (2.7-3.7) vs 12.1 (6.8-17.2) min, P<0.001); mean (SD) BIS slopes during recovery were 11.8 (4.4) vs 4.3 (2.7) min(-1) (P<0.01) for isocapnic hyperpnoea and control groups, respectively. Isocapnic hyperpnoea was easily applied in the operating room. CONCLUSIONS: Isocapnic hyperpnoea at the end of surgery results in shorter and less variable time to removal of the airway after anaesthesia with isoflurane and nitrous oxide.

Adult↗
PubMed1988

[Improved diagnosis using deuterated radiopharmaceuticals?--A comparison of the brain affinity of amphetamine analogs].

Ruthenocene amphetamine analogues have the same brain uptake as iodo-labelled amphetamines. This paper compares the organ-distribution of 103Ru labelled ruthenocene- or ferrocene-amphetamine analogues in mice and rats with the same amphetamine in which H-atoms were partly substituted by D-atoms. The uptake in the brain is increased up to 180-200% for deuterium substituted compounds. The pattern of excreted metabolites leads to the conclusion that the deuterated amphetamines are more slowly metabolised than normal (H) compounds.

Amphetamine↗
PubMed1986

[Amphetamine analog of ruthenocene as a radiodiagnostic agent: brain affinity of ruthenocenoyl-isopropylamine].

N-alkyl derivatives of 1-ruthenocenoyl-2-aminopropane (Rc-amphetamine) were labelled with 103Ru and their organ distributions were measured in mice and rats. All Rc-amphetamines showed a high affinity for brain and lung. A concentration ratio brain/blood up to 17:1 and lung/blood up to 80:1 was measured. The advantages of 97Ru labelled Rc-amphetamine compared to 123I labelled amphetamine for measurement of regional cerebral blood flow are discussed.

Animals↗
PubMed1983

Dose-response studies on glycopyrrolate and atropine in conscious cardiac patients.

The dose-heart rate response relationship for the two anticholinergics, atropine and glycopyrrolate, were studied in non-anaesthetised patients about to undergo coronary artery surgery. Two methods were used, the administration of increasing doses to different groups of patients, and an incremental dose technique in the same patient. Both drugs increased heart rate in a dose-related manner with glycopyrrolate being approximately twice as potent as atropine. Glycopyrrolate is as effective as atropine in correcting bradycardia prior to open heart surgery.

Atropine↗
PubMed1978

[Successful therapy of a severe dextran incident using histamin H1- and H2-receptor blockaders].

A case of a severe systemic anaphylactoid reaction is reported in a patient treated with dextran 60 to prevent venous thrombosis. Significant improvement of clinical symptoms occurred after the usual treatment of such incidents with corticosteroids, histamine H1 receptor antagonists, and plasma substitutes was supplemented with a histamine H2 receptor antagonist. We would therefore like to recommend that for such cases a histamine H2 receptor antagonist should be given in addition to the usual medication with corticosteroids and histamine H1 receptor antagonists. However, the value of complete histamine antagonism in these rather rare occurrences, can only be determined after furtherexperience has been gained.

Adult↗
PubMed1975

The influence of non-cytotoxic concentrations of the herbicide 2,4-dichlorophenoxyacetic acid on the DNA synthesis in cultured vertebrate cells.

The influence of the herbicide 2,4-Dichlorophenoxyacetic acid on the growth of cultured chicken muscle cells was studied by observing morphological changes and by cytophotometric measurement of the DNA content of individual cells. DNA-synthesis curves were derived from the distribution of DNA values. No marked effects were observed at a concentration of 60 mug per liter. In contrast, doses of 600 mug per liter caused a loss in cell differentiation consisting of a partial lack of polar orientation, diminished formation of fibers, and an increase of the N/C ratio. The nuclear matrix of desoxyribonucleoprotein (DNP) changed to a more heteropycnotic structure. Isolated cell necroses were found after 44 hrs of exposure. When compared to the controls, the relative DNA synthesis time was found to be prolonged 1.5-fold. The number of cells in the G2 phase decreased during 44 hrs of exposure. It is concluded from these results that the dosedependent growth inhibition of 2,4-D on vertebrate cells in culture takes effect during DNA synthesis. The morphological changes of the nuclear structure suggests that 2,4-D directly affects the template activity of the DNP matrix.

2,4-Dichlorophenoxyacetic Acid↗