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Biomedical subjects

J W Snellen

Publications and source records attributed to J W Snellen.

14 recordsLinked to original sources
PubMed1986

Increased metabolic heat production following chronic alpha-methyldopa therapy in hypertensives.

The objective of this study was to measure metabolic heat production in mild-moderate hypertensives when given chronic alpha-methyldopa for control of hypertension and to compare this with hydrochlorothiazide. Four men and one woman, age range 29-55 years, euthyroid, and not previously on alpha-methyldopa, had their drugs replaced by placebo for 4 weeks, and then alpha-methyldopa or hydrochlorothiazide was randomized single blindly to patients. The dose of each drug was increased until the ambulatory diastolic blood pressure was less than 95 mmHg (1 mmHg = 133.322 Pa), and then the dose was maintained for 20-24 weeks. The two active drugs were then crossed over, and each medication was again titrated to attain diastolic normotension (less than 95 mmHg). Maintenance was for a comparable 20-24 weeks. At week 4 (end of placebo period), weeks 20-24 (for hydrochlorothiazide or alpha-methyldopa monotherapy), and again at week 40-48 (end of cross-over period), metabolic heat production (watts), heart rate (beats per minute), and blood pressure (millimetres of Hg) were measured in a resting sitting position for 1 h in a whole body calorimeter (air temperature 28 degrees C and a dew point temperature less than 5 degrees C) for 15 experimental sessions. In four out of five patients, metabolic heat production was significantly (P less than 0.05) higher when patients were treated with alpha-methyldopa. We speculate from our data that alpha-methylnorepinephrine, the major metabolite of alpha-methyldopa, may be thermogenic and that this should be considered when the drug is prescribed.

Aged↗
PubMed1984

Calorimetrical comparison of insulative properties of metalized plastic, clear polyethylene, and polyester blanket.

The thermal insulation properties of metalized plastic sheeting (MPS), clear polyethylene sheeting (CPS) and 100 per cent polyester thermal bed blanket (TBB) were tested and compared quantitatively using direct calorimetry. The experiments were carried out on individual subjects sitting in a whole body calorimeter and covered first with a TBB bag up to the neck. Then the three materials were tested, one at a time, over the original TBB up to the neck. The temperature of the calorimeter was set at normal operating room temperature of 18 degrees C. MPS provided the greatest reduction in sensible heat loss (SHL) of all three materials tested. The total SHL saving provided by an MPS over TBB was 29.7 per cent and was statistically highly significantly different from that provided by a CPS or TBB over TBB (the difference is 9.6 and 9.9 per cent, respectively, p less than 0.001 for both). While the SHL saving provided by a CPS over TBB was 20.1 per cent, and a TBB over TBB was 19.8 percent, the difference of 0.3 per cent is statistically not significant (p greater than 0.5). An additional finding was that MPS is electrically conductive on one side. Precautions must be taken when it is used on patients connected to electrical devices. Also, insensible perspiration trapped inside the bag can be as much as 10 g X hour-1 and may become a problem when the patient is wrapped in MPS for an extended period of time.

Body Temperature Regulation↗
PubMed1984

Demonstration of a problem in estimating sensible heat loss from the respiratory tract by thermometry.

We have investigated sensible respiratory loss, which is usually taken as the product of expired volume and the temperature difference between inspired and expired air (VE X delta T). Air temperature was measured with a 0.122 mm copper-constantan thermocouple mounted in the mouthpiece of a T-piece breathing system, and expired volume with a pneumotachograph. Changing air temperature (delta T) at the mouth and expired air volume (VE) were recorded simultaneously while the subject voluntarily breathed at different tidal volumes and rates. Inspired temperatures were controlled at 12.05 degrees C, 21.80 degrees C and 25.74 degrees C at a low dewpoint temperature of 4-5 degrees C. Temperature volume "loops" were constructed using an x-y plotter. The areas of each "loop" and enclosing rectangle (VE X delta T) were measured. The difference was divided by the weight of the rectangle to give the percentage of overestimation of sensible heat loss, which ranged from 5.5 to 17.2 per cent. The error increased significantly with decreasing tidal volume and increasing respiratory rate.

Body Temperature Regulation↗
PubMed1982

Bioelectric activity in the rabbit ear regeneration.

A 1-cm-diameter hole was punched through rabbits' ears. The surface potentials during wound healing of regenerating (normal) and partially and nonregenerating (decartilaged) ears were measured. The time sequence of these surface potentials were similar to those reported to occur in regenerating amphibians forelimbs. A small positive potential was observed for about 1 week, and this was followed by a larger negative potential of up to 20 mV, with different durations. The duration of the positive potential was about the same as which was observed in amphibians. The duration and the amplitude of the negative potential were greatest for completely regenerating ears with overgrowth, smaller for partially regenerating ears, and smallest for the nonregenerating ears. The surface potential was localized. If a nipple-shaped outgrowth developed after the hole was closed, the surface potential was observed only on this outgrowth; immediately outside it, the potential was normal. We concluded that the negative bioelectric activity accompanies growth, and while growth continues, negative bioelectric potential continues.

Animals↗
PubMed1982

The use of sinusoidally changing workloads as an aid to identify dynamic properties of physiological systems.

The methodology of using frequency analysis in order to identify types of system(s) is discussed. A number of models with their characteristic Nyquist plots are presented graphically, to facilitate the identification of various types of systems by pattern recognition. A small series of measurements of oxygen consumption and heart rate has been carried out to illustrate the possibilities and limitations of the use of frequency analysis in exercise physiology. With a step function method one can only establish whether a system has multiple components in parallel or not, but with the frequency analysis method one can identify whether a system has multiple components in parallel or in series. It was found that under moderate exercise, the response of oxygen consumption to exercise is a system with multiple components in series, but the response of heart rate to exercise is a system with multiple components in parallel. The data that were obtained are in agreement with those produced by other authors, but the curves to fit the observed data were obtained using second order linear transfer functions.

Adult↗