61 research outputs found
Chemoreceptor responsiveness at sea level does not predict the pulmonary pressure response to high altitude
The hypoxic ventilatory response (HVR) at sea level (SL) is moderately predictive of the
change in pulmonary artery systolic pressure (PASP) to acute normobaric hypoxia. However, because of
progressive changes in the chemoreflex control of breathing and acid-base balance at high altitude (HA),
HVR at SL may not predict PASP at HA. We hypothesized that resting peripheral oxyhemoglobin
saturation (SpO2) at HA would correlate better than HVR at SL to PASP at HA. In 20 participants at SL,
we measured normobaric, isocapnic HVR (L/min·-%SpO2
-1) and resting PASP using echocardiography.
Both resting SpO2 and PASP measures were repeated on day 2 (n=10), days 4-8 (n=12), and 2-3 weeks
(n=8) after arrival at 5050m. These data were also collected at 5050m on life-long HA residents (Sherpa;
n=21). Compared to SL, SpO2 decreased from 98.6 to 80.5% (P<0.001), while PASP increased from
21.7 to 34.0mmHg (P<0.001) after 2-3 weeks at 5050m. Isocapnic HVR at SL was not related to SpO2
or PASP at any time point at 5050m (all P>0.05). Sherpa had lower PASP (P<0.01) than lowlanders on
days 4-8 despite similar SpO2. Upon correction for hematocrit, Sherpa PASP was not different from
lowlanders at SL, but lower than lowlanders at all HA time points. At 5050m, whilst SpO2 was not
related to PASP in lowlanders at any point (all R2=0.50), there was a weak relationship in the
Sherpa (R2=0.16; P=0.07). We conclude that neither HVR at SL nor resting SpO2 at HA correlates with
elevations in PASP at HA
Technology, Productivity, and Profits: British-American Whaling Competition in the North Atlantic, 1816-1842.
In 1815, the North Atlantic whaling fleet was entirely British, but by 1842 almost every ve ssel was American. This paper analyzes the productivity and profitabi lity of the two fleets in an attempt to explain the near total Americ an victory in the competitive struggle off Greenland and in the Davis Straights. The analysis indicates that the American fleet was more p roductive and considerably more profitable, but that neither producti vity or profit differentials can completely explain the speed of the transition. A complete explanation must also include the effects of c hanges in British government policy. Copyright 1987 by Royal Economic Society.
Reduced Structural Modeling of Integrally-Strained Slender Wings
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77134/1/AIAA-2004-2038-697.pd
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