Elevated pulmonary arterial pressure in high-altitude residents may be a maladaptive response to chronic hypoxia. If so, well-adapted populations would be expected to have pulmonary arterial pressures that are similar to sea-level values. Five normal male 22-yr-old lifelong residents of > or = 3,600 m who were of Tibetan descent were studied in Lhasa (3,658 m) at rest and during near-maximal upright ergometer exercise. We found that resting mean pulmonary arterial pressure [15 +/- 1 (SE) mmHg] and pulmonary vascular resistance (1.8 +/- 0.2 Wood units) were within sea-level norms and were little changed while subjects breathed a hypoxic gas mixture [arterial O2 pressure (PaO2) = 36 +/- 2 Torr]. Near-maximal exercise [87 +/- 13% maximal O2 uptake (VO2max)] increased cardiac output more than threefold to values of 18.3 +/- 1.2 l/min but did not elevate pulmonary vascular resistance. Breathing 100% O2 during near-maximal exercise did not reduce pulmonary arterial pressure or vascular resistance. We concluded that this small sample of healthy Tibetans with lifelong residence > or = 3,658 m had resting pulmonary arterial pressures that were normal by sea-level standards and exhibited minimal hypoxic pulmonary vasoconstriction, both at rest and during exercise. These findings are consistent with remarkable cardiac performance and high-altitude adaptation.
Lifelong high-altitude residents of North and South America acquire blunted hypoxic ventilatory responses and exhibit decreased ventilation compared with acclimatized newcomers. The ventilatory characteristics of Himalayan high-altitude residents are of interest in the light of their reportedly lower hemoglobin levels and legendary exercise performance. Until recently, Sherpas have been the only Himalayan population available for study. To determine whether Tibetans exhibited levels of ventilation and hypoxic ventilatory drives that were as great as acclimatized newcomers, we compared 27 lifelong Tibetan residents of Lhasa, Tibet, China (3,658 m) with 30 acclimatized Han ("Chinese") newcomers matched for age, body size, and extent of exercise training. During room air breathing, minute ventilation was greater in the Tibetan than in the Han young men because of an increased respiratory frequency, but arterial O2 saturation and end-tidal PCO2 did not differ, indicating similar levels of effective alveolar ventilation. The Tibetan subjects had higher hypoxic ventilatory response shape parameter A values and hypercapnic ventilatory responsiveness than the Han subjects. Among the Han subjects, duration of high-altitude residence correlated with the degree of blunting of the hypoxic ventilatory drive. Paradoxically, hyperoxia (inspired O2 fraction 0.70) increased minute ventilation and decreased end-tidal PCO2 in the Tibetan but not in the Han men. We concluded that lifelong Tibetan residents of high altitude neither hypoventilated nor exhibited blunted hypoxic ventilatory responses compared with acclimatized Han newcomers, suggesting that the effects of lifelong high-altitude residence on ventilation and ventilatory response to hypoxia differ in Tibetan compared with other high-altitude populations.
This study, using an information processing model of memory, made a detailed examination of the possible locus (loci) of any memory change in gravid and postpartum women using a battery of seven objective memory tests: implicit, incidental, explicit, semantic, short-term, working, and prospective memory. In addition, links were sought both between (a) self-reported data on sleep, health, and memory performance, and (b) these variables and objective memory performance. Five groups of women were tested (n = 22/23 per group), (1) primigravid, (2) multigravid, (3) postpartum, (4) non-pregnant parents with children, and (5) never been pregnant, on self-report and objective memory tests. The gravid and postpartum groups reported significantly more everyday forgetting than the non-pregnant groups but on the objective tests performed no differently from the non-pregnant groups on all tests. Sleep loss was a significant predictor of reported memory change, but not of any memory test performance, and may contribute to a perceived memory change. Pregnant women and new mothers generally should be confident of performing to their normal cognitive capabilities, but may be more affected than usual by a high cognitive load.
This study investigated the belief held by over 50% of parous women that they are more forgetful during pregnancy and postpartum relative to other times. Comparisons were made between both the reported and objective memory performances of three groups of women (n = 20 per group), (1) primigravid, (2) primiparous (baby younger than 12 months), and (3) never been pregnant, matched on age and education levels. Participants completed a questionnaire on demographic, health, and sleep details, the Inventory of Memory Experiences, and tests of implicit, explicit, and working memory. The groups did not differ on self-rated levels of physical or emotional health, or anxiety level. The primigravid and primiparous groups reported overall poorer memory performance since pregnancy relative to controls. The primigravid group also reported significantly more sleep disruption, with this being a significant predictor of reported memory change. On the objective tests, there were no differences between groups on the implicit and explicit memory tests, but the primigravid and primiparous groups scored significantly lower on a test of working memory. Self-reports of memory change during pregnancy and postpartum may be related to life changes, such as sleep change, and may reflect changed perceptions rather than objective changes.
Tailoring support to better meet individual degree groups' preferences can maximize resources and may encourage preceptor retention. Special attention to physicians' needs may be warranted to avoid decreased preceptor numbers in this at-risk group. Future studies are needed to determine whether these findings are unique to North Carolina, which has a strong infrastructure to support preceptors.
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