Tibetans exhibit lower hemoglobin concentration and decreased heart response to hypoxia during poikilocapnia at intermediate altitude relative to Han Chinese.

Background: High-altitude populations exhibit distinct cellular, respiratory, and cardiovascular phenotypes, some of which provide adaptive advantages to hypoxic conditions compared to populations with sea-level ancestry. Studies performed in populations with a history of high-altitude residence, such as Tibetans, support the idea that many of these phenotypes may be shaped by genomic features that have been positively selected for throughout generations. We hypothesize that such traits observed in Tibetans at high altitude also occur in Tibetans living at intermediate altitude, even in the absence of severe sustained hypoxia. Methodology: We studied individuals of high-altitude ancestry (Tibetans, n = 17 females; n = 12 males) and sea-level ancestry (Han Chinese, n = 6 females; n = 10 males), both who had been living at ∼1300 m (∼4327 ft) for at least 18 months. We measured hemoglobin concentration ([Hb]), hypoxic ventilatory response (HVR), and hypoxic heart rate response (HHRR) with end-tidal CO2 (PetCO2) held constant (isocapnia) or allowed to decrease with hypoxic hyperventilation (poikilocapnia). We also quantified the contribution of CO2 on ventilation and heart rate by calculating the differences of isocapnic versus poikilocapnic hypoxic conditions (Δ V˙I/ΔPetCO2 and ΔHR/ΔPetCO2, respectively). Results: Male Tibetans had lower [Hb] compared to Han Chinese males (p < 0.05), consistent with reports for individuals from these populations living at high altitude and sea level. Measurements of ventilation (resting ventilation, HVR, and PetCO2) were similar for both groups. Heart rate responses to hypoxia were similar in both groups during isocapnia; however, HHRR in poikilocapnia was reduced in the Tibetan group (p < 0.03), and the heart rate response to CO2 in hypoxia was lower in Tibetans relative to Han Chinese (p < 0.01). Conclusion: These results suggest that Tibetans living at intermediate altitude have blunted cardiac responses in the context of hypoxia. Hence, only some of the phenotypes observed in Tibetans living at high altitude are observed in Tibetans living at intermediate altitude. Whereas blunted cardiac responses to hypoxia is revealed at intermediate altitudes, manifestation of other physiological adaptations to high altitude may require exposure to more severe levels of hypoxia.

Estimates of the prevalence of acute stroke impairments and disability in a multiethnic population.

BACKGROUND AND PURPOSE: The goals of the present study were to estimate the prevalence of acute impairments and disability in a multiethnic population of first-ever stroke and to identify differences in impairment and early disability between pathological and Bamford subtypes. Associations between impairments and death and disability at 3 months were identified. METHODS: Impairments that occur at the time of maximum neurological deficit were recorded, and disability according to the Barthel Index (BI) was assessed 1 week and 3 months after stroke in patients in the South London Stroke Register: RESULTS: Of 1259 registered patients, 6% had 1 or 2, 31.1% had 3 to 5, 50.6% had 6 to 10, and 10.6% had >10 impairments. Common impairments were weakness (upper limb, 77.4%), urinary incontinence (48.2%), impaired consciousness (44.7%), dysphagia (44.7%), and impaired cognition (43.9%). Patients with total anterior circulation infarcts had the highest age-adjusted prevalence of weakness, dysphagia, urinary incontinence, cognitive impairment, and disability. Patients with subarachnoid hemorrhage had the highest rates of coma. Patients with lacunar stroke had the high prevalence of weakness but were least affected by disability, incontinence, and cognitive dysfunction. Blacks had higher age- and sex-adjusted rates of disability in ischemic stroke (BI <20, odds ratio 2.76, 95% CI 1.47 to 5.21, P=0.002; BI <15, odds ratio 1.8, 95% CI 1.45 to 2.81, P=0.01) but impairment rates similar to those of whites. On multivariable analysis, incontinence, coma, dysphagia, cognitive impairment, and gaze paresis were independently associated with severe disability (BI <10) and death at 3 months. CONCLUSIONS: The extent of these findings indicates that an acute assessment of impairments and disability is necessary to determine the appropriate nursing and rehabilitation needs of patients with stroke.