Blanche Willis Howard Correspondence

Entries include brief biographies and a personal letter about Howard

Bulk Cutting of Carbon Nanotubes Using Electron Beam Irradiation

According to some embodiments, the present invention provides a method for attaining short carbon nanotubes utilizing electron beam irradiation, for example, of a carbon nanotube sample. The sample may be pretreated, for example by oxonation. The pretreatment may introduce defects to the sidewalls of the nanotubes. The method is shown to produces nanotubes with a distribution of lengths, with the majority of lengths shorter than 100 tun. Further, the median length of the nanotubes is between about 20 nm and about 100 nm

Optical coherence tomography in the assessment of acute changes in cutaneous vascular diameter induced by heat stress.

There are limited imaging technologies available that can accurately assess or provide surrogate markers of the in vivo cutaneous microvessel network in humans. In this study, we establish the use of optical coherence tomography (OCT) as a novel imaging technique to assess acute changes in cutaneous microvessel area density and diameter in humans. OCT speckle decorrelation images of the skin on the ventral side of the forearm up to a depth of 500 μm were obtained prior to and following 20-25 mins of lower limb heating in eight healthy males (30.3±7.6 yrs). Skin red blood cell flux was also collected using laser Doppler flowmetry probes immediately adjacent to the OCT skin sites, along with skin temperature. OCT speckle decorrelation images were obtained at both baseline and heating time points. Forearm skin flux increased significantly (0.20±0.15 to 1.75±0.38 CVC, P<0.01), along with forearm skin temperature (32.0±1.2 to 34.3±1.0°C, P<0.01). Quantitative differences in the automated calculation of vascular area densities (26±9 to 49±19%, P<0.01) and individual microvessel diameters (68±17 to 105±25 μm, P<0.01) were evident following the heating session. This is the first in vivo within-subject assessment of acute changes in the cutaneous microvasculature in response to heating in humans and highlights the use of OCT as an exciting new imaging approach for skin physiology and clinical research

UBC-Nepal expedition: The use of oral antioxidants does not alter cerebrovascular function at sea-level or high-altitude

Hypoxia is associated with an increased systemic and cerebral formation of free radicals and associated reactants that may be linked to impaired cerebral vascular function a neurological sequela. To what extent oral antioxidants prophylaxis impacts cerebrovascular function in humans throughout the course of acclimatization to the hypoxia of terrestrial high-altitude has not been examined. Thus, the purpose of the current study was to examine the influence of orally ingested antioxidants at clinically relevant doses (vitamin C, E, and alpha-lipoic acid) on cerebrovascular regulation at sea-level (344 m; n = 12; female n = 2 participants), and at high altitude (5050 m; n = 9; female n = 2), in a randomized, placebo-controlled, and double-blinded crossover design. Hypercapnic and hypoxic cerebrovascular reactivity tests of the internal carotid (ICA)] were conducted at sea-level, while global and regional cerebral blood flow [i.e. ICA and vertebral artery (VA)] were assessed after 10–12 days following arrival at 5050 m. At sea-level, acute administration of antioxidants did not alter cerebral hypoxic cerebrovascular reactivity (pre vs. post: 1.5 ± 0.7 vs. 1.2 ± 0.8 %∆CBF/-%∆SpO2; P = 0.96), or cerebral hypercapnic cerebrovascular reactivity (pre vs. post: 5.7 ± 2.0 vs. 5.8 ± 1.9 %∆CBF/∆mmHg; P = 0.33). Furthermore, global cerebral blood flow (P = 0.43), as well as cerebral vascular conductance (ICA P = 0.08; VA P = 0.32), were unaltered at 5050 m following antioxidant administration. In conclusion, these data show that an oral antioxidant cocktail known to attenuate systemic oxidative stress failed to alter cerebrovascular function at sea-level and cerebral blood flow during acclimatization to high-altitude

Shear-Mediated Dilation of the Internal Carotid Artery Occurs Independent of Hypercapnia.

Evidence for shear stress as a regulator of carotid artery dilation in response to increased arterial carbon dioxide was recently demonstrated in humans during sustained elevations in CO2 (hypercapnia); however, the relative contributions of CO2 and shear stress to this response remains unclear. We examined the hypothesis that, following a 30-second transient increase in arterial CO2 tension and consequent increase in internal carotid artery shear stress, internal carotid artery diameter would increase, indicating shear-mediated dilation, in the absence of concurrent hypercapnia. In 27 healthy participants the partial pressures of end-tidal O2 and CO2, ventilation (pneumotachography), blood pressure (finger-photoplethysmography), heart-rate (electrocardiogram), internal carotid artery flow, diameter and shear stress (high resolution duplex ultrasound) and middle cerebral artery blood velocity (transcranial Doppler) were measured during 4-minute steady state and transient 30-second hypercapnic tests (both +9mmHg CO2). Internal carotid artery dilation was lower in the transient, compared to the steady state hypercapnia (3.3±1.9% vs. 5.3±2.9%, respectively; P<0.03). Increases in internal carotid artery shear stress preceded increases in diameter in both the transient (time: 16.8±13.2s vs. 59.4±60.3s; P<0.01) and steady state (time: 18.2±14.2s vs. 110.3±79.6s; P<0.01) tests. Internal carotid artery dilation was positively correlated with shear rate area under the curve in the transient (r(2)=0.44; P<0.01), but not steady state (r(2)=0.02; P=0.53) trial. Collectively, these results suggest that hypercapnia induces shear-mediated dilation of the internal carotid artery in humans. This study further promotes the application and development of hypercapnia as a clinical strategy for the assessment of cerebrovascular vasodilatory function and health in humans

Distinct Effects of Blood Flow and Temperature on Cutaneous Microvascular Adaptation

Aims: We performed two experiments to determine whether cutaneous microvascular adaptations in response to repeated core temperature elevation are mediated by increases in skin temperature, and/or, skin blood flow. Methods: Healthy subjects participated for 8-weeks in thrice-weekly bouts of 30mins lower limb heating (40°C). In Study 1, both forearms were “clamped” at basal skin temperature throughout each heating bout (n=9). Study 2 involved identical lower limb heating, with the forearms under ambient conditions (unclamped, n=10). In both studies, a cuff was inflated around one forearm during the heating bouts to assess the contribution of skin blood flow and temperature responses. We assessed forearm skin blood flow responses to both lower limb (systemic reflex) heating, and to local heating of the forearm skin, pre and post intervention. Results: Acutely, lower limb heating increased core temperature (Study 1: +0.63±0.15°C, Study 2: +0.69±0.19°C, P<0.001) and forearm skin blood flow (Study 1: 10±3 vs 125±44, Study 2: 16±9 vs 136±41 PU, P<0.001), with skin responses significantly attenuated in the cuffed forearm (P<0.01). Skin blood flow responses to local heating decreased in Study 1 (clamped forearms, week 0vs8: 1.46±0.52 vs 0.99±0.44 CVC, P<0.05), whereas increases occurred in Study 2 (unclamped; week 0vs8: 1.89±0.57 vs 2.27±0.52 CVC, P<0.05). Cuff placement abolished local adaptations in both studies. Conclusion: Our results indicate that repeated increases in skin blood flow and skin temperature result in increased skin flux responses to local heating, whereas repeated increases in skin blood flow in the absence of change in skin temperature induced the opposite response. Repeated increases in core temperature induce intrinsic microvascular changes, the nature of which are dependent upon both skin blood flow and skin temperature

Validation of Kepler's Multiple Planet Candidates. III: Light Curve Analysis & Announcement of Hundreds of New Multi-planet Systems

The Kepler mission has discovered over 2500 exoplanet candidates in the first two years of spacecraft data, with approximately 40% of them in candidate multi-planet systems. The high rate of multiplicity combined with the low rate of identified false-positives indicates that the multiplanet systems contain very few false-positive signals due to other systems not gravitationally bound to the target star (Lissauer, J. J., et al., 2012, ApJ 750, 131). False positives in the multi- planet systems are identified and removed, leaving behind a residual population of candidate multi-planet transiting systems expected to have a false-positive rate less than 1%. We present a sample of 340 planetary systems that contain 851 planets that are validated to substantially better than the 99% confidence level; the vast majority of these have not been previously verified as planets. We expect ~2 unidentified false-positives making our sample of planet very reliable. We present fundamental planetary properties of our sample based on a comprehensive analysis of Kepler light curves and ground-based spectroscopy and high-resolution imaging. Since we do not require spectroscopy or high-resolution imaging for validation, some of our derived parameters for a planetary system may be systematically incorrect due to dilution from light due to additional stars in the photometric aperture. None the less, our result nearly doubles the number of verified exoplanets.Comment: 138 pages, 8 Figures, 5 Tables. Accepted for publications in the Astrophysical Journa

Resistance, but not endurance exercise training, induces changes in cerebrovascular function in healthy young subjects

It is generally considered that regular exercise maintains brain health and reduces the risk of cerebrovascular diseases such as stroke and dementia. Since the benefits of different “types” of exercise are unclear, we sought to compare the impacts of endurance and resistance training on cerebrovascular function. In a randomized and crossover design, 68 young healthy adults were recruited to participate in 3 mo of resistance and endurance training. Cerebral hemodynamics through the internal carotid, vertebral, middle and posterior cerebral arteries were measured using Duplex ultrasound and transcranial Doppler at rest and during acute exercise, dynamic autoregulation, and cerebrovascular reactivity (to hypercapnia). Following resistance, but not endurance training, middle cerebral artery velocity and pulsatility index significantly decreased (P < 0.01 and P = 0.02, respectively), whereas mean arterial pressure and indices of cerebrovascular resistance in the middle, posterior, and internal carotid arteries all increased (P < 0.05). Cerebrovascular resistance indices in response to acute exercise and hypercapnia also significantly increased following resistance (P = 0.02), but not endurance training. Our findings, which were consistent across multiple domains of cerebrovascular function, suggest that episodic increases in arterial pressure associated with resistance training may increase cerebrovascular resistance. The implications of long-term resistance training on brain health require future study, especially in populations with pre-existing cerebral hypoperfusion and/or hypotension. NEW & NOTEWORTHY Three months of endurance exercise did not elicit adaptation in any domain of cerebrovascular function in young healthy inactive volunteers. However, resistance training induced decreased pulsatility in the extracranial arteries and increased indices of cerebrovascular resistance in cerebral arteries. This increase in cerebrovascular resistance, apparent at baseline and in response to both hypercapnia and acute exercise, may reflect a protective response in the face of changes in arterial pressure during resistance exercise. Listen to this article’s corresponding podcast at https://ajpheart.podbean.com/e/exercise-and-cerebrovascular-function/

The Effect of Water Immersion during Exercise on Cerebral Blood Flow

Introduction: Regular exercise induces recurrent increases in cerebrovascular perfusion. In peripheral arteries, such episodic increases in perfusion are responsible for improvement in arterial function and health. We examined the hypothesis that exercise during immersion augments cerebral blood flow velocity compared with intensity-matched land-based exercise. Methods: Fifteen normotensive participants were recruited (26 ± 4 yr, 24.3 ± 1.9 kg·m−2). We continuously assessed mean arterial blood pressure, HR, stroke volume, oxygen consumption, and blood flow velocities through the middle and posterior cerebral arteries before, during, and after 20-min bouts of water- and land-based stepping exercise of matched intensity. The order in which the exercise conditions were performed was randomized between subjects. Water-based exercise was performed in 30°C water to the level of the right atrium. Results: The water- and land-based exercise bouts were closely matched for oxygen consumption (13.3 mL·kg−1·min−1 (95% confidence interval (CI), 12.2–14.6) vs 13.5 mL·kg−1·min−1 (95% CI, 12.1–14.8), P = 0.89) and HR (95 bpm (95% CI, 90–101) vs 96 bpm (95% CI, 91–102), P = 0.65). Compared with land-based exercise, water-based exercise induced an increase in middle cerebral artery blood flow velocity (74 cm·s−1 (95% CI, 66–81) vs 67 cm·s−1 (95% CI, 60–74) P < 0.001), posterior cerebral artery blood flow velocity (47 cm·s−1 (95% CI, 40–53) vs 43 cm·s−1 (95% CI, 37–49), P < 0.001), mean arterial blood pressure (106 mm Hg (95% CI, 100–111) vs 101 mm Hg (95% CI, 95–106), P < 0.001), and partial pressure of expired CO2 (P ≤ 0.001). Conclusions: Our findings suggest that water-based exercise augments cerebral blood flow, relative to land-based exercise of similar intensity, in healthy humans