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Latham R. D.; Sipkema P.; Westerhof N.; Rubal B. J. 《Journal of applied physiology》1988,65(4):1604-1610
Aortic input impedance was calculated in seven subjects in the control state (normal reflection) and during the Mueller maneuver (increased reflection) to evaluate "effective arterial length" under altered physiological conditions. Regional foot-to-foot pulse wave velocities and pressure waveforms along the aorta were used to define an "apparent anatomic length" or distance to a dominant discrete site of reflection "seen" by the ejecting ventricle. Time of wave travel was taken to be one-half the interval from the foot of the incident wave to the midsystolic inflection point. Knowing the time of travel from the returning reflection and velocity, distances calculated to the "apparent anatomic length" were 35 +/- 2 and 34 +/- 2 during control and Mueller maneuver, respectively (P = NS). The frequency of the first minimum of the modulus (fmin) and the first zero crossing of the phase angle (f phi) were determined from the input impedance spectra. During baseline conditions, fmin (3.9 +/- 0.2 Hz) approximately equaled f phi (4.2 +/- 0.2 Hz), and the resulting "effective lengths" calculated using the quarter-wavelength formula were similar to the apparent anatomic length. These data suggested that the aortic region incorporating the renal arterial branches as a site of discrete reflection and that terminal load was not significantly frequency dependent. During Mueller maneuver, however, f min (3.3 +/- 0.2 Hz) and f phi (5.1 +/- 0.2 Hz) were significantly discordant, the terminal load became strongly frequency dependent, and effective length calculated from f min was dissimilar (P less than 0.05) from the unchanged apparent anatomic length.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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R. J. Collins P. J. Boyle A. E. Clague A. E. Barr S. C. Latham 《Biological trace element research》1991,30(3):233-244
Patients with phenylketonuria (PKU) are frequently deficient in the essential trace element selenium (Se), because of their very low protein diet. Using two approaches to investigate T-cell response to proliferative signaling, viz, mitogenesis caused by the monoclonal antibody OKT3 and the plant lectin phytohaemagglutinin (PHA), we demonstrated significantly reduced responses to optimal concentrations of OKT3 in a group of PKU patients with reduced serum Se compared with a normal group (p = 0.0005) and with a group of PKU patients whose serum Se was normal (p = 0.0023). The response of the Se-deficient group to optimal levels of PHA did not differ from that of the normal controls or from that of Se-normal PKU patients. A dose-dependent relationship between serum Se levels and mitogenic response was evident for OKT3 (r = 0.34, p = 0.0154), but not for PHA (r = -0.02, p = 0.9086). We suggest that the reduced response to OKT3 mitogenesis in Se-deficient PKU patients is possibly the consequence of impaired Se-dependent metabolic activity, which affects mitogenic signaling via the T cell antigen receptor (TCR/CD3) complex. 相似文献
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Using in vivo microscopy, we made direct measurements of pulmonary capillary transit time by determining the time required for fluorescent dye to pass from an arteriole to a venule on the dependent surface of the dog lung. Concurrently, in the same animals, pulmonary capillary transit time was measured indirectly in the entire lung using the diffusing capacity method (capillary blood volume divided by cardiac output). Transit times by each method were the same in a group of five dogs [direct: 1.75 +/- 0.27 (SE) s; indirect: 1.85 +/- 0.33 s; P = 0.7]. The similarity of these transit times is important, because the widely used indirect determinations based on diffusing capacity are now shown to coincide with direct measurements and also because it demonstrates that measurements of capillary transit times on the surface of the dependent lung bear a useful relationship to measurements on the capillaries in the rest of the lung. 相似文献
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Maintenance of the cellobiose utilization genes of Escherichia coli in a cryptic state 总被引:6,自引:1,他引:5
The genes for cellobiose utilization are normally cryptic in Escherichia
coli. The cellobiose system was used as a model to understand the process
by which silent genes are maintained in microbial populations. Previously
reported was (1) the isolation of a mutant strain that expresses the
cellobiose-utilization (Cel) genes and (2) that expression of those genes
allows utilization of three beta- glucoside sugars: cellobiose, arbutin,
and salicin. The Cel gene cluster has now been cloned from that mutant
strain. In the course of locating the Cel genes within the cloned DNA
segment, it was discovered that inactivation of the Cel-encoded hydrolase
rendered the host strain sensitive to all three beta-glucosides as potent
inhibitors. This sensitivity arises from the accumulation of the
phosphorylated beta- glucosides. Because even the fully active genes
conferred some degree of beta-glucoside sensitivity, the effects of
cellobiose on a series of five Cel+ mutants of independent origin were
investigated. Although each of those strains utilizes cellobiose as a sole
carbon and energy source, cellobiose also acts as a potent inhibitor that
reduces the growth rate on glycerol 2.5-16.5-fold. On the other hand,
wild-type strains that cannot utilize cellobiose are not inhibited. The
observation that the same compound can serve either as a nutrient or as an
inhibitor suggests that, under most conditions in which cellobiose will be
present together with other resources, there is a strong selective
advantage to having the cryptic (Cel0) allele. In those environments in
which cellobiose is the sole, or the best, resource, mutants that express
the genes (Cel+) will have a strong selective advantage. It is suggested
that temporal alternation between these two conditions is a major factor in
the maintenance of these genes in E. coli populations. This alternation of
environments and fitnesses was predicted by the model for cryptic-gene
maintenance that was previously published.
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Karemaker JM Stok WJ Latham RD 《Journal of gravitational physiology : a journal of the International Society for Gravitational Physiology》1994,1(1):P33-P34
In the present experiments it was decided to have each test-subject serve as his own control by fitting the test-subjects with a G-suit and comparing the condition of inflated G-suit to the normal situation. G-suit inflation was intended to only displace blood on the venous side of the circulation, not to increase total peripheral resistance. Therefore, a very modest inflation of 50 mmHg was applied. This was considered sufficient to expel most of the blood from the venous pool in abdomen and legs, even under the condition of increased G-loading in the pull-up phase. The parabolas were to be undergone in three body positions: standing upright, sitting and supine. The prediction of the experimental outcome was that we would find no difference between transients with and without G-suit inflation in the supine position, that an initial overshoot in pressure and stroke volume in the upright position would be very much damped by the G-suit, even more in the standing than in the sitting position. Studies were performed in 5 flights of NASA's KC-135, in January 1993. Per flight 40 parabolas were flown in an adapted 'roller coaster profile', i.e. 0-G phases were followed by a 2-G pull-out phase, after a very brief 1-G phase again followed by the next 2-G pull-up phase. This sequence was flown for 10 parabolas, then a 1-G horizontal flight period was inserted. The first 3 parabolas of each set of 10 the subjects were sitting upright, seat belt fastened. The next three they were standing, feet stuck under a load strap on the floor, stabilizing themselves by a grip on the ceiling. Then three parabolas were flown with the test-subject supine, loosely attached to the floor by a load strap and further aided by a grip to another strap on the floor. The last parabola of a set was used as 'spare' to repeat any failed maneuver. 相似文献
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