Sarah Witkowski

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We measured blood erythropoietin (EPO) concentration, arterial O(2) saturation (Sa(O(2))), and urine PO(2) in 48 subjects (32 men and 16 women) at sea level and after 6 and 24 h at simulated altitudes of 1,780, 2,085, 2,454, and 2,800 m. Renal blood flow (Doppler) and Hb were determined at sea level and after 6 h at each altitude (n = 24) to calculate renal(More)
BACKGROUND We tested the hypothesis that individual variability in orthostatic tolerance is dependent on the degree of neural and vasomotor reserve available for vasoconstriction. METHODS AND RESULTS Muscle sympathetic nerve activity (MSNA) and hemodynamics were measured in 12 healthy young volunteers during 60 degrees head-up tilt (HUT), followed by a(More)
Performance on the Sternberg working memory task, and MEG cortical response on a variation of the Sternberg task were examined in middle-aged carriers and non-carriers of the APOE epsilon4 allele. Physical activity was also assessed to examine whether exercise level modifies the relationship between APOE genotype and neurocognitive function. Regression(More)
Orthostatic tolerance is reduced in the heat-stressed human. The purpose of this project was to identify whether skin-surface cooling improves orthostatic tolerance. Nine subjects were exposed to 10 min of 60 degrees head-up tilting in each of four conditions: normothermia (NT-tilt), heat stress (HT-tilt), normothermia plus skin-surface cooling 1 min before(More)
We tested the hypothesis that women have blunted sympathetic neural responses to orthostatic stress compared with men, which may be elicited under hypovolemic conditions. Muscle sympathetic nerve activity (MSNA) and hemodynamics were measured in eight healthy young women and seven men in supine position and during 6 min of 60 degrees head-up tilt (HUT)(More)
PURPOSE The purpose of this study was to examine the relationship of exercise energy expenditure (EEE) with both telomere length and telomerase activity in addition to accounting for hTERT C-1327T promoter genotype. METHODS Sixty-nine (n = 34 males; n = 35 females) participants 50-70 yr were assessed for weekly EEE level using the Yale Physical Activity(More)
Clinical transcranial Doppler assessment of cerebral vasomotor reactivity (CVMR) uses linear regression of cerebral blood flow velocity (CBFV) vs. end-tidal CO(2) (Pet(CO(2))) under steady-state conditions. However, the cerebral blood flow (CBF)-Pet(CO(2)) relationship is nonlinear, even for moderate changes in CO(2). Moreover, CBF is increased by increases(More)
Chronic living at altitudes of ∼2,500 m causes consistent hematological acclimatization in most, but not all, groups of athletes; however, responses of erythropoietin (EPO) and red cell mass to a given altitude show substantial individual variability. We hypothesized that athletes living at higher altitudes would experience greater improvements in sea level(More)
We evaluated the impact of long-term exercise on telomere dynamics in wild-derived short telomere mice (CAST/Ei) over 1 year. We observed significant telomere shortening in liver and cardiac tissues in sedentary 1-year-old mice compared with young (8 weeks) baseline mice that were attenuated in exercised 1-year-old animals. In contrast, skeletal muscle(More)
The aim of this study was to determine whether inhibition of nitric oxide synthase (NOS) alters dynamic cerebral autoregulation in humans. Beat-to-beat blood pressure (BP) and cerebral blood flow (CBF) velocity (transcranial Doppler) were measured in eight healthy subjects in the supine position and during 60 degrees head-up tilt (HUT). NOS was inhibited by(More)