96 research outputs found

    Chemoreceptor responsiveness at sea level does not predict the pulmonary pressure response to high altitude

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    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

    H. R. Gallman

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    "Pvte H. R. Gallman 27th AustInfBtn (AIF) Winnellie + 49 1/2 Mile Site Dec 1941 - Mar 1943"Private H. R. Gallman. 27th Australian Infantry Battalion (Australian Imperial Forces) Winnellie + 49 1/2 Mile Site. December 1941 - March 1943

    Effects of Two DOF Lining Tolerances on Modeled Inlet Acoustic Attenuation

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    The effect of manufacturing tolerances on realized attenuation for two degree of freedom linings is investigated with the use of lining models and finite element duct propagation codes. Acoustic linings are created for a small turbofan engine that optimizes attenuation at takeoff/sideline and approach conditions. Lining physical and geometric parameters are set which best meet the optimum impedance requirements at two target frequencies. Variations of these parameters representing realistic manufacturing tolerances are used to systematically examine the effect on installed impedance and predicted attenuation. Attenuation at sideline and approach conditions is found to sensitive to manufacturing tolerances around optimum conditions. It is found that local lining impedance variation due to local Sound Pressure Level also has a significant effect on realized attenuation in the sideline case. The results of the study are case dependent; however the analysis scheme presented provides a method for cost-benefit analysis of maintaining tight tolerances on manufacturing processes
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