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Biomedical subjects

D Linnarsson

Publications and source records attributed to D Linnarsson.

At least 19 recordsLinked to original sources
PubMed1992

Effects of sulphur hexafluoride on psychomotor performance.

The narcotic influence of sulphur hexafluoride on mental and psychomotor performance has been studied in 9 subjects at normal atmospheric pressure. Control experiments were performed with air and with nitrous oxide. Psychomotor, perceptual and cognitive abilities were assessed using a computerized test battery. Subjects were exposed to air and six different normoxic gas mixtures: 13, 26, and 39% N2O, and 39, 59, and 79% SF6. Significant performance impairments were found with 13% N2O and gradual further impairment with 26, and 39% N2O. During exposure to 39, 59, and 79% SF6 over-all performance was impaired by 5, 10, and 18%, respectively. Impairment was significant with 59 and 79% SF6. The results indicate that the relative narcotic potency of SF6: N2O is about 1:4 in humans. It is concluded that a normoxic SF6-O2 mixture can be inhaled for lung function studies without any harmful effects and that the short-lasting narcotic effect, although detectable with a test battery, would not impair the ability of the subject to perform simple breathing procedures.

Adult↗
PubMed1991

Core temperature "null zone".

An experimental protocol was designed to investigate whether human core temperature is regulated at a "set point" or whether there is a neutral zone between the core thresholds for shivering thermogenesis and sweating. Nine male subjects exercised on an underwater cycle ergometer at a work rate equivalent to 50% of their maximum work rate. Throughout an initial 2-min rest period, the 20-min exercise protocol, and the 100-min recovery period, subjects remained immersed to the chin in water maintained at 28 degrees C. On completion of the exercise, the rate of forehead sweating (Esw) decayed from a mean peak value of 7.7 +/- 4.2 (SD) to 0.6 +/- 0.3 g.m-2.min-1, which corresponds to the rate of passive transpiration, at core temperatures of 37.42 +/- 0.29 and 37.39 +/- 0.48 degrees C, as measured in the esophagus (Tes) and rectum (Tre), respectively. Oxygen uptake (VO2) decreased rapidly from an exercising level of 2.11 +/- 0.25 to 0.46 +/- 0.09 l/min within 4 min of the recovery period. Thereafter, VO2 remained stable for approximately 20 min, eventually increased with progressive cooling of the core region, and was elevated above the median resting values determined between 15 and 20 min at Tes = 36.84 +/- 0.38 degrees C and Tre = 36.80 +/- 0.39 degrees C. These results indicate that the core temperatures at which sweating ceases and shivering commences are significantly different (P less than 0.001) regardless of whether core temperature is measured within the esophagus or rectum.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Changes in walking ability after knee replacement.

Walking ability has been assessed in 20 patients before and after knee replacement. In 8, who had severe osteoarthritis, a bicompartmental ICLH (Imperial College-London Hospital) prosthesis was used; in 12, with moderate arthritis, the medial side of the joint was replaced by a unicompartmental Brigham prosthesis. Knee function was assessed with the British Orthopaedic Association assessment chart, and walking capacity by the oxygen cost of level walking. Before operation, the function was the same in both groups, but patients with moderate osteoarthritis could walk faster with a lower energy cost than those with severe osteoarthritis. One year after operation, all the patients had improved clinically, alignment had been corrected, and the knees were stable with a satisfactory range of movement. Walking speed was improved; pain and perceived exertion were reduced. The oxygen cost of walking was decreased in patients with a unicompartmental arthroplasty, but not in patients with a total replacement. An uneconomic walking pattern, acquired before operation in those with severe osteoarthritis, was considered to be the reason why walking efficiency was not improved. The walking ability in patients with moderate osteoarthritis recovered to almost normal after unicompartmental replacement.

Aged↗
PubMed1990

Significance of airway resistance for the pattern of breathing and lung volumes in exercising humans.

The effects of increased airway resistance on lung volumes and pattern of breathing were studied in eight subjects performing leg exercise on a cycle ergometer. Airway resistance was changed 1) by increasing the density (D) of the respired gas by a factor of 4.2 and changing the inspired gas from O2 at 1.3 bar to air at 6 bar and 2) by increasing airway flow rates by exposing the subjects to incremental work loads of 0-200 W. Increased gas D caused a slower and deeper respiration at rest and during exercise and, at work loads greater than 120 W, depressed the responses of ventilation and mean inspiratory flow. Raised airway resistance induced by increases in D and/or airway flow rates altered respiratory timing by increasing the ratio of inspiratory time (TI) to total breath duration. Furthermore, analyses of the relationships between tidal volume and TI and between end-inspiratory volume and TI revealed elevation of Hering-Breuer inspiratory volume thresholds. We propose that this elevation, and hence exercise-induced increases of tidal volume, can largely be explained by previous observations that the threshold of the inspiratory off-switch mechanisms depends on central inspiratory activity (cf. C. von Euler, J. Appl. Physiol. 55: 1647-1659, 1983), which in turn increases with airway resistance (Acta Physiol. Scand. 120: 557-565, 1984).

Airway Resistance↗
PubMed1990

The body as a bioenergetic system--lessons from systems engineering and comparative physiology.

This introductory review considers some concepts of energy supply and demand from the perspective of a systems engineer looking at comparative physiology. The non-steady-state response of oxygen uptake shows major differences between animal species. Similarly, maximal oxygen uptake shows between-species differences. It is suggested that the systems engineering approach could help in understanding questions concerning the interrelationship of these observations.

Efficiency↗
PubMed1990

Walking efficiency after cemented and noncemented total hip arthroplasty.

Clinical evaluation using the Harris hip score has been supplemented with analysis of walking capacity before and after total hip arthroplasty (THA). Twenty patients were studied, ten of whom were treated with a cemented Charnley prosthesis and ten with a noncemented HP-Garches prosthesis. Tests were performed preoperatively and three, six, and 12 months postoperatively. Harris hip scores increased from a mean of 35 points preoperatively to 85 one year after surgery. Patients with a Charnley prosthesis had significantly higher scores than those with an HP-Garches prosthesis. The hip score did not differ between patients with uni- and bilateral disease. Mean maximum walking speed before surgery was 62 m/minute and increased to 80 m/minute one year after THA. The mean oxygen cost preoperatively was 0.267 ml/kg/m and decreased to 0.221 ml/kg/m one year after surgery. A weak correlation was found between differences in Harris hip scores and the corresponding oxygen cost. The onset of and the recovery from complications as well as differences between patients with uni- and bilateral diseases were reflected in changes in oxygen cost in contrast to clinical scores. The measurement of oxygen cost gave objective and valuable information about walking efficiency after THA.

Adult↗
PubMed1989

Determination of the oxygen cost of level walking.

We have developed devices and methods for the determination of the oxygen cost of level walking. Oxygen uptake is determined with an argon dilution method. The validity of this technique is demonstrated. Walking speed is recorded and controlled by means of a speedometer cart. The reproducibility of a convenient, self-selected walking speed and of a predetermined speed was studied. Coefficients of variation were below two per cent. Corresponding values of the oxygen cost of walking at a predetermined speed were three per cent or less up to an interval between tests of six months. We conclude that the proposed methods are suited for longitudinal studies of the oxygen cost of level walking, for example in patients with walking disorders.

Adult↗
PubMed1987

Measurement of lung volume by sulfur hexafluoride washout during spontaneous and controlled ventilation: further development of a method.

An open circuit tracer gas washout method for measurement of lung volume in patients during anesthesia and intensive care is described and tested. The method employs a device for dispensing the tracer gas, sulfur hexafluoride (SF6), a fast SF6 analyzer, a pneumotachograph, and a computer. The dispensing device delivers SF6 into the airway in proportion to instantaneous inspiratory flow so that inspiratory SF6 concentration is held constant, usually at about 0.5%, regardless of the inspiratory flow pattern. The amount of SF6 present in the lungs at the end of a washin is calculated during washout from signals representing expired SF6 concentration and expired flow. From this, lung volume is derived. Accurate and reproducible results were obtained in lung model tests during ventilation with air, N2O in O2, and halothane in O2. Functional residual capacity (FRC) was measured both with SF6 washout and nitrogen washout in five mechanically ventilated patients. This gave the regression equation: FRCSF6 = 10 ml + 1.04 x FRCN2, r = 0.99. A similar close agreement was observed for total lung capacity (TLC) and residual volume (RV) measurements in eight healthy, spontaneously breathing subjects: TLCSF6 = 91 ml + 1.01 x TLCN2, r = 0.99; RVSF6 = -32 ml + 0.97 x RVN2, r = 0.95. Comparison with body plethysmography in eight healthy, sitting subjects gave the regression equation: FRCSF6 = 180 ml + 0.96 x FRCbox, r = 0.99. The median (range) for the coefficient of variation at duplicate determinations in 10 anesthetized, paralyzed, and mechanically ventilated adults was 3.0% (0.2-6.6%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Perinatal origin of adult self-destructive behavior.

The study was undertaken to test whether obstetric procedures are of importance for eventual adult behavior of the newborn, as ecological data from the United States seem to indicate. Birth record data were gathered for 412 forensic victims comprising suicides, alcoholics and drug addicts born in Stockholm after 1940, and who died there in 1978-1984. The births of the victims were unevenly distributed among six hospitals. Comparison with 2,901 controls, and mutual comparison of categories, showed that suicides involving asphyxiation were closely associated with asphyxia at birth, suicides by violent mechanical means were associated with mechanical birth trauma and drug addiction was associated with opiate and/or barbiturate administration to mothers during labor. Irrespective of the mechanism transferring the birth trauma to adulthood--which might be analogous to imprinting--the results show that obstetric procedures should be carefully evaluated and possibly modified to prevent eventual self-destructive behavior.

Adult↗
PubMed1986

Ramp-function work test suitable for automatic computation.

Heart rate (HR) response to step-function and ramp-function (20 W/min) work tests was compared in 12 healthy subjects. For a given power output (P), HR was substantially lower in the ramp tests. The HR difference increased with power output and increasing difference in work time between the test types. The HR difference can be explained in terms of a drift component (which accounts for 1/3 of the difference) and a lag component (2/3). As a consequence of the HR differences, P for a given HR is higher in ramp tests. Work capacity expressed, for example as P170, can be determined in ramp tests, and the result can be translated to step-function P170. The precision in this translation is markedly improved if a steady-state period is incorporated into the ramp test.

Adolescent↗
PubMed1985

Pulmonary blood flow determination with selective rebreathing of CO2.

A new CO2-based non-invasive method for pulmonary blood flow has been developed. Selective rebreathing of CO2 was obtained in an open-circuit system by measuring the expired instantaneous CO2 flux in the expired air and by mixing pure CO2 into the inspired air. The time course of the inspired PCO2 was altered so that end-tidal PCO2 changed as a linear function of time (ramp). Pulmonary blood flow was computed as the ratio between the rate of change in net CO2 elimination (or uptake) and the concomitant rate of change of estimated arterial CO2 content. In comparison to simultaneously determined cardiac output by means of the O2 Fick method, the proposed CO2 ramp method underestimated cardiac output by some 20 per cent in 22 supine sedated patients with valvular heart disease. Differences in PCO2 between end-tidal gas and the gas in perfused alveoli are thought to be the main cause of this underestimation.

Adult↗