1 Department of Kinesiology,
University of Colorado, Boulder, Colorado 80309;
2 Palo Alto Veterans Affairs
Health Care System, Palo Alto, California 94304; and
3 University of Colorado at
Denver, ...Health Sciences Center, Denver, Colorado, 80262
We have previously demonstrated that
acclimatization to high altitude elicits increased sympathetic nerve
activity in men. The purpose of this investigation was to
determine 1 ) whether women respond
in a similar manner as found previously in men and 2 ) the extent to which menstrual
cycle phase influences this response. Sixteen eumenorrheic women (age,
23.6 ± 1.2 yr; weight, 56.2 ± 4.3 kg) were studied at sea level
and during 12 days of high-altitude exposure (4,300 m) in either their
follicular (F; n = 11) or luteal (L;
n = 5) phase. Twenty-four-hour urine
samples were collected at sea level and during each day at altitude.
Catecholamines were determined by high-performance liquid
chromatography with electrochemical detection. Compared with sea-level
values, urinary norepinephrine excretion increased significantly during
altitude exposure, peaking on days
4-6 . Thereafter, levels remained constant
throughout the duration of altitude exposure. The magnitude of this
increase was similar between the F (138%) and L (93%)
phase. Urinary epinephrine levels were elevated on
day 2 of altitude exposure compared
with sea-level values for both F and L subjects (93%). Thereafter, urinary epinephrine excretion returned to sea-level values, and no
differences were found between F and L subjects. Plasma catecholamine content was consistent with urinary values and supports the concept of
an elevation in sympathetic activity over time at altitude. Mean and
diastolic blood pressure as well as heart rate adjustments to high
altitude correlated significantly with urinary norepinephrine excretion
rates. It was concluded that 1 )
urinary and plasma catecholamine responses to 12 days of high-altitude
exposure in women are similar to those previously documented to occur
for men; 2 ) whereas no differences
in catecholamine levels were observed between F- and L-phase
assignments, for a given urinary norepinephrine excretion rate, blood
pressure and heart rates were lower for F vs. L subjects; and
3 ) several cardiovascular
adaptations associated with high-altitude exposure correlated with 24-h
urinary norepinephrine excretion rates and thus sympathetic nerve
activity.
norepinephrine; epinephrine; urinary; plasma; hypoxia
Purpose: Currently, there are two types of treatment planning algorithms for intensity modulated radiation therapy (IMRT). The beamlet‐based algorithm generates fluence maps with high complexity, ...resulting in large numbers of segments in the delivery. The segment‐based direct aperture optimization (DAO) algorithm uses a small number of segments. However, the number of segments is typically pre‐fixed, and the optimization is computationally intensive. In this work, a regularization based algorithm is proposed to overcome the drawbacks of the DAO method. Method and Materials: Instead of smoothing the fluence maps, we include a total‐variation term in the optimization objective function to reduce the number of signal levels of the fluence maps and therefore the number of deliverable apertures. As compared to the DAO algorithm, our method has an efficient form of quadratic optimization, with an additional advantage of optimizing field specific numbers of segments based on the modulation complexity. Results: The proposed approach is evaluated using two clinical cases. Provided that the clinical acceptance criteria of the treatment plan are satisfied, for the prostate patient, the total number of segments is reduced from 61 using the Eclipse planning system to 35 using the proposed algorithm; for the head and neck patient, the total number of segments is reduced from 107 to 28. The head and neck result is also compared to that using an equal number of 4 segments for each field. The comparison shows that using field‐specific numbers of segments achieves a much improved dose distribution. Conclusion: A total‐variation based inverse planning method is proposed in this work. As compared to other existing methods, the proposed algorithm is derived using different principles and implemented efficiently. The patient studies show that the proposed algorithm significantly reduces the total number of segments used in the treatment without compromising the delivered dose distribution.
G. A. Brooks, G. E. Butterfield, R. R. Wolfe, B. M. Groves, R. S. Mazzeo, J. R. Sutton, E. E. Wolfel and J. T. Reeves
University of California, Berkeley 94720.
To evaluate the hypothesis that ...altitude exposure and acclimatization
result in increased dependency on blood glucose as a fuel, seven healthy
males (23 +/- 2 yr, 72.2 +/- 1.6 kg, mean +/- SE) on a controlled diet were
studied in the postabsorptive condition at sea level (SL), on acute
altitude exposure to 4,300 m (AA), and after 3 wk of chronic altitude
exposure to 4,300 m (CA). Subjects received a primed continuous infusion of
6,6-2Dglucose and rested for a minimum of 90 min, followed immediately by
45 min of exercise at 101 +/- 3 W, which elicited 51.1 +/- 1% of the SL
maximal O2 consumption (VO2 max; 65 +/- 2% of altitude VO2 max). At SL,
resting arterial glucose concentration was 82.4 +/- 3.2 mg/dl and rose
significantly to 91.2 +/- 3.2 mg/dl during exercise. Resting glucose
appearance rate (Ra) was 1.79 +/- 0.02 mg.kg-1.min-1; this increased
significantly during exercise at SL to 3.71 +/- 0.08 mg.kg-1.min-1. On AA,
resting arterial glucose concentration (85.8 +/- 4.1 mg/dl) was not
different from sea level, but Ra (2.11 +/- 0.14 mg.kg-1.min-1) rose
significantly. During exercise on AA, glucose concentration rose to levels
seen at SL (91.4 +/- 3.0 mg/dl), but Ra increased more than at SL (to 4.85
+/- 0.15 mg.kg-1.min-1; P less than 0.05). Resting arterial glucose was
significantly depressed with CA (70.8 +/- 3.8 mg/dl), but resting Ra
increased to 3.59 +/- 0.08 mg.kg-1.min-1, significantly exceeding SL and AA
values.
3 Department of Pediatrics, University of Colorado Health
Sciences Center, Denver 80262, 1 Department of Kinesiology,
University of Colorado at Boulder, Boulder, Colorado 80302; and
2 Exercise ...and Sport Research Institute, Arizona State
University, Tempe, Arizona 85287-0404
The purpose of the present study was to
determine whether fructose is the nutrient mediator of sucrose-induced
insulin resistance and glucose intolerance. Toward this end, male rats
were fed a purified starch diet (68% of total calories) for a 2-wk
baseline period. After this, rats either remained on the starch (ST)
diet or were switched to a sucrose (SU, 68% of total calories),
fructose/glucose (F/G, 34/34% of total calories), or fructose/starch
(F/ST, 34/34% of total calories) diet for 5 wk. Rats then underwent
either an intravenous glucose tolerance test ( n = 10/diet) or a euglycemic, hyperinsulinemic clamp ( n = 8 or 9/diet). Incremental glucose and insulin areas under the curve in
SU, F/G, and F/ST were on average 61 and 29% greater than ST,
respectively, but not significantly different from one another. During
clamps, glucose infusion rates (mg · kg 1 · min 1 ) required
to maintain euglycemia were significantly lower ( P < 0.05) in SU, F/G, and F/ST (13.4 ± 0.9, 9.5 ± 1.7, 11.3 ± 1.3, respectively) compared with ST (22.8 ± 1.1).
Insulin suppression of glucose appearance
(mg · kg 1 · min 1 ) was
significantly lower ( P < 0.05) in SU, F/G, and F/ST
(5.6 ± 0.5, 2.2 ± 1.2, and 6.6 ± 0.7, respectively)
compared with ST (9.6 ± 0.4). Insulin-stimulated glucose
disappearance
(mg · kg 1 · min 1 ) was
significantly lower ( P < 0.05) in SU, F/G, and F/ST
(17.9 ± 0.6, 16.2 ± 1.3, 15.3 ± 1.8, respectively)
compared with ST (24.7 ± 1.2). These data suggest that fructose
is the primary nutrient mediator of sucrose-induced insulin resistance
and glucose intolerance.
diet composition
Multi-matrix environmental monitoring was used to evaluate the influence of a municipal solid waste landfill (Ginestreto, Emilia Romagna, Italy) on the level and distribution of heavy elements in the ...surrounding environment (air, soil and soil biota). Concentrations of As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Sb, Tl and Zn were measured by inductively coupled plasma-mass spectrometry in transplanted lichens, topsoils and isopods. The highest accumulation levels found for Cd, Cr, Pb, Sb and Zn in lichens transplanted within the Ginestreto landfill. However, similar concentrations of these heavy elements were also found in lichens exposed in monitoring sites influenced by other man-made sources, such as vehicle traffic and truck movements. The fallout of heavy elements emitted by the landfill had low impact on their levels in topsoil: Cd, Cr, Pb, Sb and Zn showed higher contents in topsoil collected close to the landfill and a slight decrease in concentrations with increasing distance from the landfill. There was no variation in heavy element accumulation in isopods in relation to distance from the landfill. The results of this study indicate that the Ginestreto municipal solid waste landfill had limited impact on the environmental distribution of heavy elements, since accumulation and enrichment in lichens and topsoils were only detected close to the landfill, up to about 100 m from its border.
The purpose of this investigation was to examine the effects of dehydration on the lactate threshold and performance time to exhaustion in women.
Seven moderately trained women (age = 23.6 +/- 1.6 ...yr) performed two graded exercise tests on separate occasions, once in a normally hydrated state (HY) and once in a dehydrated state (DE). Dehydration was achieved by a 45-min submaximal exercise the evening before testing, followed by a 12-h period of fluid restriction. VO2, VCO2, V(E), R-values, blood lactate, and catecholamine concentrations were measured at baseline and during each workload. Plasma volume and plasma osmolality were also determined. Body weight dropped significantly for the dehydrated trial (2.6 +/- 0.7%).
There was a corresponding decrease in plasma volume measured (3.5 +/- 2.6%). The VO2max (3.1 +/- 0.3 L x min(-1) HY; 3.0 +/- 0.1 L x min(-1) DE) obtained was not significantly different between the hydration and dehydration trial. Plasma norepinephrine, epinephrine, and lactate concentrations were not significantly different at baseline or maximum intensity although epinephrine concentrations were higher for the dehydrated trial during submaximal workloads. Lactate concentrations were highly correlated with epinephrine (r = 0.95 HY; r = 0.97 DE). The lactate threshold occurred at a significantly lower relative percent of VO2max for the dehydrated trial (72.2 +/- 1.1% HY; 65.5 +/- 1.8% DE) as well as a lower absolute power output when compared with that in the hydrated trial. There was a significant decrease in time to exhaustion for the dehydrated trial (17.3 +/- 0.7 min HY; 16.3 + 0.7 min DE). Time to exhaustion for the dehydrated trial was correlated with the % VOmax at which the lactate threshold occurred (r = 0.74).
These data indicate that low levels of dehydration induced a shift in the lactate threshold, in part because of elevated epinephrine concentrations. This shift may have been one cause for the decrease in time to exhaustion for the dehydrated trial.
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