Incidence of high altitude pulmonary edema in low-landers during re-exposure to high altitude after a sojourn in the plains.

BACKGROUND: There is uncertainty whether acclimatized low-landers who return to high altitude after a sojourn at low altitude have a higher incidence of pulmonary edema than during the first exposure to high altitude. METHODS: This was a prospective cohort study consisting of men ascending to 3400 m by road (N = 1003) or by air (N = 4178). The study compared the incidence of high altitude pulmonary edema during first exposure vs the incidence during re-exposure in each of these cohorts. RESULTS: Pulmonary edema occurred in 13 of the 4178 entries by air (Incidence: 0.31%, 95% CI: 0.18%-0.53%). The incidence during first exposure was 0.18% (0.05%-0.66%) and 0.36% (0.2%-0.64%) during re-exposure (Fisher Exact Test for differences in the incidence (two-tailed) p = 0.534). The relative risk for the re-exposure cohort was 1.95 (95% CI, 0.43%-8.80%). Pulmonary edema occurred in 3 of the 1003 road entrants (Incidence: 0.30%, 95% CI: 0.08%-0.95%). All three cases occurred in the re-exposure cohort. CONCLUSION: The large overlap of confidence intervals between incidence during first exposure and re-exposure; the nature of the confidence interval of the relative risk; and the result of the Fisher exact test, all suggest that this difference in incidence could have occurred purely by chance. We did not find evidence for a significantly higher incidence of HAPE during re-entry to HA after a sojourn in the plains.

Pulmonary artery pressure in Ladakhi men on exposure to acute hypoxia after a stay at sea level.

We had observed that very few Ladakhi soldiers (native highlanders: NHL) are hospitalized for high altitude pulmonary oedema. We hypothesized that this may happen because pulmonary artery pressures of NHLs do not increase even after exposure to acute hypoxia. The aim of this study was to test the above hypothesis by non-invasive echocardiographic assessment of pulmonary arterial pressure in freshly inducted Ladakhi soldiers and comparing it with that in freshly inducted lowlander soldiers (LL). The pre-ejection period and acceleration time ratio as measured from the pulmonary artery Doppler signal was used to compute mean pulmonary arterial pressure. In NHL this pressure on day 1 of induction was significantly lower at 25.8 +/- 6.5 mmHg as compared to 31.9 +/- 9.5 mmHg in LL (P = 0.0002). Another finding of interest was the very low Lake Louise acute mountain sickness score in the NHL (0.278 +/- 0.461 on day 2). This appears to be further evidence that the natives of Ladakh are adapted to hypoxia and not merely acclimatized.

Beta-adrenoreceptor blockade attenuates heat-induced tachycardia,but not the tolerance to the stress.

Ten healthy males (age 34 +/- 3 yr 9 SE) underwent 40 min of heat exposure (WD 39.7.C) after 2 hours of ingesting 120 mg of Propranolol (Inderal; ICI), or a placebo, in a random manner, the exposures being about a week apart. That there was no placebo effect was ensured by giving a control run (no medication). In the placebo trials, the end-experiment heart rate had increased by 52%, while after propranolol the increase was only 43%. Regression analysis showed that with the placebo, the HR increased by 22 beats/min/o rise in core (aural) temperature, while with propranolol, the rise (14 beats/min) was significantly lower (P < 0.02). The various heat strain indices viz the Craig's Index, the Body heat storage (Kilocals/m2/hr), and the effective heat storage were also similar for both the treatments. We conclude that beta-adrenoreceptor activity plays a significant role in producing tachycardia of heat exposure in humans, but blocking this activity with propranolol does not affect tolerance to heat stress.

An approach to expert control of interactive software systems.

Expert problem-solving strategies in many domains require the use of detailed mathematical techniques coupled with experiential knowledge about how and when to use the appropriate techniques. In many of these domains, such techniques are made available to experts in large software packages. In attempting to build expert systems for these domains, we wish to make use of these packages, and are therefore faced with an important problem: how to integrate the existing software, and knowledge about its use, into a practical expert system. The expert knowledge is used, in dynamic selection and interpretation of appropriate programs and parameters, to reach a successful goal in the problem solving. We describe the framework of a hybrid expert system for representing problem-solving knowledge in these domains. This hybrid system may be characterized as consisting of a production system and mathematical methods. The software package is reorganized as necessary to map it into the mathematical-method representation of a hybrid system. This approach has evolved out of an effort to build an expert system for performing well-log analysis, ELAS (expert log analysis system).