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Biomedical subjects

L C Johnson

Publications and source records attributed to L C Johnson.

At least 55 records · Page 3Linked to original sources
PubMed1987

Measuring problems in estimating the exposure to passive smoking using the excretion of cotinine.

Quality control studies on cotinine measurements following low level environmental tobacco smoke (ETS) exposure are rare. The exposure to ETS was controlled and systematically changed in a series of experiments in a climatic chamber. Healthy nonsmoking volunteers were exposed to ETS simultaneously. The duration and level of exposure varied using high (8, 17 and 25 ppm CO), and low (2 and 5 ppm CO) exposure levels. The variation between radioimmunoassay (RIA) and gas chromatography (GC) was high as was the variation between the results of RIA laboratories. There was also a high within-laboratory-variation. A 1:10 dilution seems to be preferable over a 1:3 dilution. Freezing the urine samples immediately after collection led to the detection of higher cotinine values than freezing the samples 24 h after collection. Highly reliable data for cotinine were obtained when the urine samples were kept frozen immediately after collection and fractionated sampling over 48-72 h was used. Our data show that estimating low-level ETS exposure by measuring urinary cotinine is highly susceptible to uncontrolled variation and errors. Sufficiently reliable estimates of low-level ETS exposure can be made only when fractionated sampling over 48-72 h is used and when the urine samples are kept frozen just after collection.

Chromatography, Gas↗
PubMed1986

Influence of PaO2 on cerebral macro- and microcirculation as observed by light reflection: time course of changes.

A silicon intensified target camera was used to study cerebral cortical vessels of the cat through a skull window implant, and red cell content changes were measured by light reflectance. Red cell content changes were observed in cerebral arterioles, capillaries, and venules when the PaO2 was decreased by lowering the PiO2. The time course of change in the diameter of the arterioles and venules was measured by selecting a cross section of the vessel plus some surrounding tissue. From the averaged cross-sectional reflectance signal, the change in vessel diameter was followed as a function of time following the PiO2 change. All vessels of greater than 10 microns were observed in focus. Substantial areas where no vessels could be discriminated would contain only capillaries, and changes in light reflectance from such areas would indicate changes in capillary red cell content. The time course of these changes following a step decrease in PiO2 was recorded. Results show that the sequence of red cell content increase in cerebral microcirculation during hypoxia is capillary before venule and arteriole. The times of initial red cell content increase are 37.9 +/- 7 s, 59.7 +/- 7.9 s, and 60.8 +/- 9.1 s, respectively. These results suggest an increase in the capillary bed red cell content as the initial response to hypoxia, but venules and arterioles change only on longer exposure to hypoxia. The sequence of the increase in red cell content suggests the capillaries rather than the arterioles are the vessels which respond to the oxygen autoregulation signal.

Animals↗
PubMed1985

Passive smoking under controlled conditions.

Ten healthy subjects were exposed to passive smoking at a high level corresponding to 25-30 ppm CO in the ambient air for 3 h. All subjects were exposed at the same time in a climatic chamber especially designed for exposure experiments. Despite an identical exposure rate considerable interindividual variability of subsequent nicotine and cotinine levels in saliva, plasma and 24-h urine were observed. This variability was more prominent in nicotine than in cotinine levels. The kinetic pattern as reflected by saliva levels for up to 24 h was consistent with previous data found in active smokers. Nicotine levels found in saliva were markedly influenced by repeated sampling. This was not the case for cotinine levels. With regard to laboratory techniques RIA seems to be more sensitive than gas chromatography (GC). The results of this study suggest that measuring cotinine levels in 24-h urine with RIA is presently the most sensitive and reliable criterion for estimating exposure to passive smoking and for validating questionnaires or interviews about short-term exposure to passive smoking.

Adolescent↗
PubMed1985

Disqualified and qualified poor sleepers: subjective and objective variables.

Sleep laboratory studies of patients complaining of insomnia have demonstrated discrepancies between subjective reports and electroencephalograph (EEG)-recorded measures. In our research studies on sleeping aids, 60% of the self-described poor sleepers who reported usual sleep latencies of at least 45 min did not meet the laboratory qualification criterion of a 30-min or longer sleep latency. To learn to predict who would qualify for our studies, we compared 30 laboratory-qualified poor sleepers (QPS) with 30 laboratory-disqualified poor sleepers (DPSs) on subjective report, mood, and all-night sleep laboratory variables. QPSs had significantly lower sleep efficiency and total sleep time in the laboratory, but these differences were due to the longer sleep latencies (50.7 +/- 27.8 min vs. 15.2 +/- 6.1 min) of the QPS group. QPSs and DPSs differed significantly in their morning estimates of their laboratory sleep latencies; as a group, QPSs gave an accurate estimate (51.6 +/- 27.8 min), but DPSs were significantly more likely to exaggerate their sleep latencies. Although we did not identify ways of predicting which poor sleepers would show sleep-onset insomnia in the sleep laboratory, we did find that, in this young, healthy population, there are poor sleepers who give an accurate report of a rather severe sleep-onset insomnia.

Adult↗
PubMed1984

Measuring passive smoking: methods, problems, and perspectives.

The definition of passive smoking used by T. Hirayama [Brit. Med. J. 282, 183-185 (1981)] and other authors has at least three major shortcomings: it is only applicable to a highly selective sub-population; varying lifestyle patterns cannot be taken into account; and exposure outside the home is neglected. To overcome these shortcomings, a preliminary qualitative and classificatory definition of passive smoking that includes the total population as well as any smoke exposure, regardless of its location, was developed. This definition does not include the quantity of exposure or changes over time. Based on a representative survey, 17.8% of the population over 35 years are potential passive smokers according to this definition. The questionnaire developed by E.L. Wynder and associates (American Health Foundation, New York) presents difficulties in scoring the results for different lifestyles. Therefore a quantitative concept was developed for estimating exposure over any period of time as a generalized assessment instrument. The concept of maximum exposed M-time for an individual (TMI) as well as for a group (TMG) is introduced. The results are presented graphically by a cumulative standardized exposed M-time diagram. Results obtained so far lean toward plausibility and stability of the data and the concept. The interview form has still to be validated.

Classification↗
PubMed1984

The extent of passive smoking in the Federal Republic of Germany.

A representative survey of 1,670 persons between 14 and 65 years of age was conducted in order to obtain current data on active and passive smoking in the Federal Republic of Germany. Overall, 36.7% were smokers, 21.3% were former smokers, and 42.0% were nonsmokers. These rates vary for sociodemographic subgroups and for states, cities, and rural areas. The time pattern during the 24 hr preceding the interview is identical in shape for active as well as passive smoking. The exposed maximum time for passive smoking varies with age and sex. It lies somewhere between 2 and 15% of the observed 24 hr; the best estimates seem to be 5% for nonsmoking men and 3-4% for nonsmoking women. It consistently compares with our preliminary definition of passive smoking. A reconstruction of Hirayama's definition reveals parallel results in terms of maximum exposure time when compared with our preliminary definition. A direct comparison between both definitions showed inconsistencies to an extent that could jeopardize the results of a case-control study. Data demonstrate a massive effect of measuring techniques on study results with regard to the frequency and extent of passive smoking. They also show the vulnerability of the calculation of equivalence of actively smoked cigarettes.

Adolescent↗
PubMed1983

Sleep spindle and delta changes during chronic use of a short-acting and a long-acting benzodiazepine hypnotic.

Twenty-one medically screened insomniacs were studied over 59 nights in a double-blind, parallel groups design study. The 7 patients receiving a short-acting (triazolam) and the 7 receiving a long-acting (flurazepam) benzodiazepine hypnotic showed a similar pattern and magnitude of sleep EEG changes, especially during the latter part of the 37-night treatment period. Both groups significantly increased sleep spindle rate and decreased delta count per minute. The patterns of withdrawal were also similar. Plasma levels of N-desalkylflurazepam were not significantly related to the magnitude of EEG changes.

Adult↗
PubMed1983

REM-NREM cycle in the cat may be sleep-dependent.

The periodicity of the rapid eye movement-nonrapid eye movement (REM-NREM) cycle in real time versus compressed sleep was determined by autocorrelation, computed on the sequence of sleep stages in recordings from spontaneously sleeping cats. The resulting autocorrelation function was correlated to damped cosine waves, and the highest squared correlation coefficient (r2) was taken as indicating the most likely periodicity in the data entered for each animal. The periodicity of REM sleep was stronger (significantly higher r2) in the compressed sleep data than in the real-time data, indicating sleep dependency of the REM-NREM cycle. The REM-NREM cycle lengths determined by the autocorrelation technique were not significantly different for the real-time and compressed sleep data. The REM sleep episode interval, defined as the average interval between the start of successive REM sleep episodes, was significantly shorter for real-time sustained sleep than the cycle lengths as determined by the autocorrelation technique. A model is proposed which explains this phenomenon as due to fragmentation of REM sleep within the time periods with high probability for REM sleep. When such fragmentation occurs, the average REM sleep episode interval will not reflect an ultradian REM sleep periodicity.

Animals↗
PubMed1982

Effects of triazolam (0.5 mg) on sleep, performance, memory, and arousal threshold.

The effects of a short-acting benzodiazepine hypnotic, triazolam (0.5 mg), on sleep, performance, and arousal threshold were assessed in 20 male poor sleepers (age 21 +/- 2.37 years). Following in a laboratory screening night, all subjects received placebo for 3 nights (single-blind), ten received triazolam and ten placebo for 6 nights (double-blind), and all received placebo on 2 withdrawal nights (single-blind). All effects described below were statistically significant. Triazolam reduced sleep latency and increased total sleep time and sleep efficiency. Percent Stage 2 was increased and percent Stage 4 was reduced during treatment. Morning performance, measured 8.25 h post-drug, showed no decrements. Acute effects were assessed on treatment night 6 during arousals from sleep at 1.5, 3, and 5 h post-administration: performance was impaired in triazolam subjects on the Wilkinson 4-Choice Reaction Time Test, Digit Symbol Substitution Test, Williams Word Memory Test, and Card Sorting Task. In the morning following treatment night 6, long-term memory was tested using a recognition task requiring subjects to identify words presented during night-time test batteries: triazolam subjects correctly identified fewer target words. Triazolam administration produced anterograde amnesic effects. However, in a Paired Associates Test learned prior to drug ingestion on the previous evening, triazolam did not impair morning recall of word pairs. Threshold for arousal from slow wave sleep was elevated during treatment, and triazolam subjects did not show increased sensitivity to the arousing tone over nights as did placebo subjects.

Adult↗
PubMed1982

Sedative-hypnotics and human performance.

In 52 studies, performance data were obtained the next day following bedtime ingestion of a sedative-hypnotic or a placebo. Only eight of these studies used insomniac patients. Most studies used young adult males. Benzodiazepine hypnotics were most frequently administered and psychomotor performance was most often measured. Little consistent data are available on cognitive functioning and more complex behavior. Drug-related improvement in performance was not found, and, in comparing active drug to placebo, it is clear that all hypnotics, at some doses, produce decrements in performance the next day. Higher doses consistently showed a decrement, and this decrement was usually persistent over the entire day. Although long-acting drugs generally showed more performance decrement, half-life data were not consistent.

Adolescent↗
PubMed1982

Benzodiazepine hypnotics increase heart rate during sleep.

The cardiovascular effects of benzodiazepines administered intravenously as preoperative sedatives have received considerable study, but sleep laboratory research on benzodiazepines administered orally as hypnotics has not focused on assessment of cardiovascular changes. Analysis of heart rate (HR) data collected in sleep laboratory studies on the effects of 0.5 mg of triazolam (Halcion) and 30 mg of flurazepam (Dalmane) demonstrated that both benzodiazepine hypnotics produced a significant HR elevation that was present for up to 4 h during sleep. By the 3rd night of bedtime administration of triazolam, the HR increase was no longer statistically significant, but on the 5th night of flurazepam administration, HR was still significantly elevated over baseline levels. The HR elevation does not appear to be of clinical significance for most patients. However, this finding indicates that benzodiazepines administered at hypnotic-dose levels have peripheral as well as central effects.

Administration, Oral↗
PubMed1981

Effect of a short-acting benzodiazepine on brain electrical activity during sleep.

The effects of the short-acting benzodiazepine, triazolam, on EEG activity during sleep were assessed in poor sleepers. Twenty male subjects, mean age 21 +/- 2.37 years, participated. A screening night preceded 3 placebo nights, 6 treatment nights, and 2 placebo-withdrawal nights. During treatment, 10 subjects received triazolam (0.5 mg) and 10 received placebo. The treatment condition was double-blind. In addition to rate/min spindle count and number of delta half-waves/min, the auditory evoked response (AEP) was obtained on the last placebo baseline and the fifth drug night. Subjects receiving triazolam showed a significant increase in sleep spindles and a significant decrease in delta count during drug administration. Both values returned to baseline on the first withdrawal night. The AEP peak-to-trough amplitude was also significantly reduced during sleep by triazolam, but, as the time since drug ingestion increased, the amplitude of the AEP also increased. There was no difference in AEP amplitude between the two groups 5 h post-drug ingestion.

Adult↗
PubMed1980

The REM cycle is a sleep-dependent rhythm.

Two studies, using data from fragmented sleep studies from three sleep laboratories, are reviewed. These studies indicate that the REM cycle is primarily governed by a sleep-dependent oscillator. These data, however, do not rule out the potential influence of endogenous or environmental variables as factors influencing the REM cycle. Further, acceptance of the REM cycle as a sleep-dependent rhythm does not lead to the denial of the basic rest-activity cycle (BRAC) proposed by Kleitman. It is questioned, however, whether the BRAC measured during waking is an extension of the REM cycle recorded during sleep.

Adolescent↗