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Biomedical subjects

J Christensen

Publications and source records attributed to J Christensen.

At least 181 records · Page 10Linked to original sources
PubMed1987

Cerebral blood flow in patients with normal-pressure hydrocephalus before and after shunting.

Cerebral blood flow (CBF) was measured by xenon-133 inhalation and single photon emission tomography in 17 demented patients with normal-pressure hydrocephalus before and after shunt treatment. All patients had a decreased conductance to outflow (C out) of cerebrospinal fluid as measured by lumboventricular perfusion (C out less than 0.12 ml X mm Hg-1 X min-1). Computerized tomography (CT) scanning, clinical assessment, and neuropsychological grading were performed pre- and postoperatively. The preoperative CBF studies revealed abnormal flow patterns in all patients. Fourteen patients showed moderate-sized, large, or very large central low-flow areas, and four patients had reduced flow bilaterally in the occipital and contiguous temporoparietal regions. After shunting, six patients had a significant reduction in the size of the central low-flow area on the CBF map, agreeing well with the changes of ventricular size on the CT scan. All six patients showed an improvement in either clinical or neuropsychological grading. In 10 of the remaining 11 patients flow patterns were essentially unchanged; one patient deteriorated further. Four of these 11 patients improved on postoperative clinical or neuropsychological testing. Thus, a positive correlation was found between the changes in CBF and the reduction of the ventricular size on the CT scan, but changes in CBF as measured by the present technique did not accompany improvement in the functional state in all patients.

Adult↗
PubMed1987

Comparison of various anesthetic regimens in the domestic fowl.

Three anesthetic agents (equithesin, metomidate, and ketamine) combined with diazepam were tested in the domestic fowl. Laparotomy and thoractomy were possible with the equithesin/diazepam combination, but only laparotomy was possible with the metomidate/diazepam combination. The combination of ketamine/diazepam did not result in the depth of anesthesia required for surgical procedures. Repeated blood pressure and heart rate measurements were recorded by use of a modified noninvasive Doppler technique. Equithesin/diazepam was our combination of choice for long-duration surgical anesthesia. The depth of anesthesia could be modulated by increasing the dose of diazepam. Metomidate/diazepam was useful when short-term anesthesia was required. In contrast to equithesin/diazepam, the metomidate/diazepam combination provided unstable anesthesia of varying depth and duration. Adverse reactions with metomidate indicated caution when using this drug in chickens; the drug also caused marked bradycardia. Ketamine/diazepam combination cannot be recommended as an anesthetic agent for use in chickens. The combination may be useful for minor surgical procedures or treatment, but not for experimental procedures that involve major surgery. Diazepam alone had a slight tranquilizing effect.

Anesthesia, General↗
PubMed1986

Substrate dependence and oxygen sensitivity of tone and of spontaneous and evoked contractions of the distal colonic muscularis mucosae of opossum.

The muscularis mucosae of the opossum distal colon fails to maintain tone and to generate spontaneous contractions in an anaerobic environment in vitro. To investigate this phenomenon further, dose-response curves to agonists under different oxygen concentrations were examined. In other experiments the tissue was actively exhausted (i.e., repeatedly stimulated in a substrate-free environment until no response to K+, acetylcholine, or histamine could be observed) and then equilibrated with an alternative substrate for 3 h, when the ability of the tissue to contract to agonists was reevaluated. Reducing the available oxygen abolished tone and caused a graded loss of responses to histamine; in contrast, at 0% oxygen maximum responses to acetylcholine were reduced by only 75%. Abolition of tone by the addition of cyanide to the bathing medium did not affect the amplitude of responses to histamine and acetylcholine. The tissue was able to use all the chosen alternative substrates to different degrees for acetylcholine-induced contraction; similarly, with the exception of beta-hydroxybutyrate it could use all substrates to some degree to support responses to histamine. The evidence suggests that the source of energy required to maintain tone is different from the source required to sustain K+ or agonist-induced contractions, and that the dependence of isotonic contractions on exogenous substrates varies with the pharmacologic stimulus.

Acetylcholine↗
PubMed1986

Characteristics of speech production after tracheoesophageal puncture: voice onset time and vowel duration.

Voice onset time (VOT) and vowel duration characteristics of speakers following the Singer-Blom technique of tracheoesophageal puncture (1980) were compared to those of traditional esophageal and laryngeal speakers. Fifteen subjects in each of the three speaker groups produced the words /pik/, /kap/, /kup/ in a carrier phrase while audio recordings were obtained. Broadband spectrograms were made of the consonant-vowel-consonant (CVC) utterances and vowel duration and VOT were measured. Analysis of variance (ANOVA) procedures revealed that the tracheoesophageal speakers produced significantly shorter VOTs and longer vowel durations than the laryngeal speakers. However, the longer vowel durations for the tracheoesophageal speakers were not completely accounted for by the shorter VOTs found for that group. Spectrographic examination suggests that delayed voice offset time for the tracheoesophageal speakers also contributes to their longer vowel durations. Overall findings indicate that the physical characteristics and motor control properties of the neoglottis, even when driven by pulmonary air as in tracheoesophageal speakers, exert a major influence on alaryngeal voice production.

Aged↗
PubMed1986

Insect allergy. Predictive value of diagnostic tests: a three-year follow-up study.

One hundred and six adults with various reactions to yellow jacket (YJ), honey bee (HB) or unidentified insects (UI) were tested for allergy to insect venoms. For various reasons none received immunotherapy. Individuals completed questionnaires annually for three consecutive years and described sting reactions within the previous season. Ninety subjects completed all the questionnaires and 77 of these were re-tested at the end of the period. Nine out of 25 patients reacted with a systemic reaction when re-stung. High IgE and low IgG venom-specific antibody levels indicated an unfavourable prognosis, since eight of 11 individuals who initially presented venom-specific IgE greater than RAST class 2 and venom-specific IgG below detection limit had systemic reactions at re-sting. No such reactions occurred in subjects with no specific IgE and only one out of six with specific IgE as well as IgG reacted systematically. Skin prick tests (SPT) of less than 3mm with YJ venom 1,000 micrograms/ml excluded later systemic symptoms to stings, whereas larger skin reactions gave an equal chance of systemic or local reactions at re-sting. In individuals not stung by UI, YJ and/or HB the decline in venom-specific IgG and IgE was significant, median values ranging from 41% to 75% over the 3-year period. The decline was unaffected by the type of sting reaction prior to the initial test. SPT results did not change significantly. The findings are relevant when testing patients several years after their last insect sting and the results might indicate that the antibody decline is accompanied by a decrease in clinical sensitivity.

Adult↗
PubMed1986

Pharmacological characterization of opossum distal colonic muscularis mucosae in vitro.

In muscularis mucosae from the opossum distal colon, both tone and spontaneous contractions were highly dependent on the available oxygen. Acetylcholine and histamine caused, respectively, atropine- and pyrilamine-sensitive contractions. Norepinephrine relaxed the tissue, an effect abolished by propranolol. Under these conditions norepinephrine failed to elicit contractions and at higher concentrations again caused relaxations. The tissue gave concentration-dependent relaxations to ATP but not to ADP, AMP, or adenosine. Electrical field stimulation (20-30 Hz, 1-2 ms, 120 mA) revealed a cholinergic excitatory innervation and a nonadrenergic, noncholinergic neural inhibition. Cholecystokinin, gastrin, substance P, and vasoactive intestinal polypeptide were without effect on this tissue. In these respects, colonic muscularis mucosae differs considerably from that of other gastrointestinal viscera.

Acetylcholine↗