Aortic haemodynamics: the effects of habitual endurance exercise, age and muscle sympathetic vasomotor outflow in healthy men

Purpose We determined the effect of habitual endurance exercise and age on aortic pulse wave velocity (aPWV), augmentation pressure (AP) and systolic blood pressure (aSBP), with statistical adjustments of aPWV and AP for heart rate and aortic mean arterial pressure, when appropriate. Furthermore, we assessed whether muscle sympathetic nerve activity (MSNA) correlates with AP in young and middle-aged men. Methods Aortic PWV, AP, aortic blood pressure (applanation tonometry; SphygmoCor) and MSNA (peroneal microneurography) were recorded in 46 normotensive men who were either young or middle-aged and endurance-trained runners or recreationally active nonrunners (10 nonrunners and 13 runners within each age-group). Between-group differences and relationships between variables were assessed via ANOVA/ANCOVA and Pearson product-moment correlation coefficients, respectively. Results Adjusted aPWV and adjusted AP were similar between runners and nonrunners in both age groups (all, P > 0.05), but higher with age (all, P < 0.001), with a greater effect size for the age-related difference in AP in runners (Hedges’ g, 3.6 vs 2.6). aSBP was lower in young (P = 0.009; g = 2.6), but not middle-aged (P = 0.341; g = 1.1), runners compared to nonrunners. MSNA burst frequency did not correlate with AP in either age group (young: r = 0.00, P = 0.994; middle-aged: r = − 0.11, P = 0.604). Conclusion There is an age-dependent effect of habitual exercise on aortic haemodynamics, with lower aSBP in young runners compared to nonrunners only. Statistical adjustment of aPWV and AP markedly influenced the outcomes of this study, highlighting the importance of performing these analyses. Further, peripheral sympathetic vasomotor outflow and AP were not correlated in young or middle-aged normotensive men.

Imaging the Water Snowline around Protostars with Water and HCO+ Isotopologues

The water snowline location in protostellar envelopes provides crucial information about the thermal structure and the mass accretion process as it can inform about the occurrence of recent (≲1000 yr) accretion bursts. In addition, the ability to image water emission makes these sources excellent laboratories to test indirect snowline tracers such as H13CO+. We study the water snowline in five protostellar envelopes in Perseus using a suite of molecular-line observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA) at ∼0.″2−0.″7 (60–210 au) resolution. B1-c provides a textbook example of compact H 2 18 O (31,3−22,0) and HDO (31,2−22,1) emission surrounded by a ring of H13CO+ (J = 2−1) and HC18O+ (J = 3−2). Compact HDO surrounded by H13CO+ is also detected toward B1-bS. The optically thick main isotopologue HCO+ is not suited to trace the snowline, and HC18O+ is a better tracer than H13CO+ due to a lower contribution from the outer envelope. However, because a detailed analysis is needed to derive a snowline location from H13CO+ or HC18O+ emission, their true value as a snowline tracer will lie in the application in sources where water cannot be readily detected. For protostellar envelopes, the most straightforward way to locate the water snowline is through observations of H 2 18 O or HDO. Including all subarcsecond-resolution water observations from the literature, we derive an average burst interval of ∼10,000 yr, but high-resolution water observations of a larger number of protostars are required to better constrain the burst frequency.

MH370 Controlled Eastward Veering and Descent After the 6th Arc

Past expert analyses of communication signals from missing Malaysian Airlines MH370 reconciled Burst Frequency Offset (BFO) errors up to the 6th of 7 arcs for a southerly track. After the 6th arc, the Satellite Data Unit (SDU) power-up or reboot resulted in settling errors in the last two data points that were ignored (first search) and later bounded (second search). For the second search, investigators invoked a high-speed vertical descent to account for BFO errors for the south track fuel-starved scenario. Two searches disappointingly failed to find the implied violent-crash site. We report that interpretations were flawed in suggesting the plane dived vertically, as investigators did not recognize that BFO extrapolations implicitly implied mathematically that the plane was also cruising along the south track, but with no fuel. Our reanalysis used the “Penang Longitude” (PL) theory that predicted a similar southerly track to the 6th arc, and that MH370 subsequently veered eastwards and descended. Doppler Shifts from vertical motions were replaced with plausible horizontal veering and declination of a high-speed aircraft. Veering predicted by the PL theory plus controlled descent plausibly accounts for nominal 7th arc BFO discrepancies for the warm-reboot scenario. We conclude that the fuel-starvation scenario analyses wrongly implied a vertical high-speed crash that ignored the impossible implicit southerly cruise, with no fuel, assumption. Instead, MH370 was piloted to a precise glide landing under power, east of the 7th arc.

Dynamic Burst Actuation to Enhance the Flow Control Authority of Plasma Actuators

A computational study was conducted on flows over an NACA0015 airfoil with dielectric barrier discharge (DBD) plasma. The separated flows were controlled by a DBD plasma actuator installed at the 5% chord position from the leading edge, where operated AC voltage was modulated with the duty cycle not given a priori but dynamically changed based on the flow fluctuations over the airfoil surface. A single-point pressure sensor was installed at the 40% chord position of the airfoil surface and the DBD plasma actuator was activated and deactivated based on the strength of the measured pressure fluctuations. The Reynolds number was set to 63,000 and flows at angles of attack of 12 and 16 degrees were considered. The three-dimensional compressible Navier–Stokes equations including the DBD plasma actuator body force were solved using an implicit large-eddy simulation. Good flow control was observed, and the burst frequency proven to be effective in previous fixed burst frequency studies is automatically realized by this approach. The burst frequency is related to the characteristic pressure fluctuation; our approach was improved based on the findings. This improved approach realizes the effective burst frequency with a lower control cost and is robust to changing the angle of attack.

Low-Dose Fentanyl Reduces Pain Perception, Muscle Sympathetic Nerve Activity Responses, and Blood Pressure Responses During the Cold Pressor Test

Our knowledge about how low-dose (analgesic) fentanyl affects autonomic cardiovascular regulation is primarily limited to animal experiments. Notably, it is unknown if low-dose fentanyl influences human autonomic cardiovascular responses during painful stimuli in humans. Therefore, we tested the hypothesis that low-dose fentanyl reduces perceived pain and subsequent sympathetic and cardiovascular responses in humans during an experimental noxious stimulus. Twenty-three adults (10F/13M; 27±7 y; 26±3 kg•m-2, mean ± SD) completed this randomized, crossover, placebo-controlled trial during two laboratory visits. During each visit, participants completed a cold pressor test (CPT; hand in ~0.4 °C ice bath for two minutes) before and five minutes after drug/placebo administration (75 μg fentanyl or saline). We compared pain perception (100 mm visual analog scale), muscle sympathetic nerve activity (MSNA; microneurography, 11 paired recordings), and beat-to-beat blood pressure (BP; photoplethysmography) between trials (at both pre- and post-drug/placebo time points) using paired, two-tailed t-tests. Before drug/placebo administration, perceived pain (p=0.8287), Δ MSNA burst frequency (p=0.7587), and Δ mean BP (p=0.8649) during the CPT were not different between trials. After the drug/placebo administration, fentanyl attenuated perceived pain (36 vs. 66 mm, p<0.0001), Δ MSNA burst frequency (9 vs. 17 bursts/minute, p=0.0054), and Δ mean BP (7 vs. 13 mmHg, p=0.0174) during the CPT compared to placebo. Fentanyl-induced reductions in pain perception and Δ mean BP were moderately related (r=0.40, p=0.0641). These data provide valuable information regarding how low-dose fentanyl reduces autonomic cardiovascular responses during an experimental painful stimulus.

Phrenic afferent activation modulates cardiorespiratory output in the adult rat

Phrenic afferents project to brainstem areas responsible for cardiorespiratory control and the mid-cervical spinal cord containing the phrenic motor nucleus. Our purpose was to quantify the impact of small and large diameter phrenic afferent activation on phrenic motor output. Anesthetized and ventilated rats received unilateral phrenic nerve stimulation while contralateral phrenic motor output and blood pressure were recorded. Twelve currents of 40Hz inspiratory-triggered stimulation were delivered (20 seconds on, 5 minutes off) to establish current response curves. Stimulation pulse width was varied to preferentially activate large diameter phrenic afferents (narrow pulse width) and recruit small diameter fibers (wide pulse width). Contralateral phrenic amplitude was elevated immediately post-stimulation at currents above 35 µA for wide, and 70 µA for narrow pulse stimulation when compared to animals not receiving stimulation (time controls). Wide pulse width stimulation also increased phrenic burst frequency at currents ≥35 µA, caused a transient decrease in mean arterial blood pressure at currents ≥50 µA, and resulted in a small change in heart rate at 300 µA. Unilateral dorsal rhizotomy attenuated stimulation-induced cardiorespiratory responses, indicating phrenic afferent activation is required. Additional analyses compared phrenic motor amplitude to output before stimulation and showed that episodic activation of phrenic afferents with narrow pulse stimulation can induce short-term plasticity. We conclude that activation of phrenic afferents: 1) enhances contralateral phrenic motor amplitude when large diameter afferents are activated, and 2) when small diameter fibers are recruited the amplitude response is associated with changes in burst frequency and cardiovascular parameters.

An open-source application for the standardized burst identification from the integrated muscle sympathetic neurogram.

Muscle sympathetic nerve activity (MSNA) can be acquired from humans using the technique of microneurography. The resulting integrated neurogram displays pulse-synchronous bursts of sympathetic activity which undergoes processing for standard MSNA metrics including burst frequency, height, area, incidence, total activity and latency. The procedure for detecting bursts of MSNA and calculating burst metrics is tedious and differs widely amongst laboratories world-wide. We sought to develop an open-source, cross-platform web application that provides a standardized approach for burst identification and a tool to increase research reproducibility for those measuring MSNA. We compared the performance of this web application against a manual scoring approach under conditions of rest, chemoreflex activation (N = 9, 20 min isocapnic hypoxia), and metaboreflex activation (N = 13, 2 min isometric handgrip exercise and 4 min post exercise circulatory occlusion). The intraclass correlation coefficient (ICC) indicated good to strong agreement between scoring approaches for burst frequency (ICC = 0.92 - 0.99), incidence (ICC = 0.94 - 0.99), height (ICC = 0.76 - 0.88), total activity (ICC = 0.85 - 0.99), and latency (ICC = 0.97 - 0.99). Agreement with burst area was poor to moderate (ICC = 0.04 - 0.67) but changes in burst area were similar with chemoreflex and metaboreflex activation. Scoring using the web application was highly efficient and provided data visualization tools which expedited data processing and the analysis of MSNA. We recommend the open-source web application be adopted by the community for the analysis of MSNA.

MH370 Eastward Descent After the 6th Arc

Past analyses of satellite and phone signals from missing Malaysian Airlines MH370 reconciled Burst Frequency Offset (BFO) errors up to the 6th of 7 arcs for a southerly track. After the 6th arc, the Satellite Data Unit (SDU) power-up or reboot resulted in settling errors. Investigators bounded these but needed to invoke a high-speed descent for nominal errors that remained from assuming the southerly track continued to the 7th arc. However, the implied violent-crash site was not found nor supported by damage found on debris, which instead suggested a glided landing. In our reanalysis, we relaxed the south track assumption and used the “Penang Longitude” (PL) theory that predicted a similar southerly track to the 6th arc, and that MH370 subsequently veered eastwards and descended. In essence, we simply replaced the Doppler Shift from vertical motions with horizontal veering of a high-speed aircraft. Our results suggests that veering predicted by the PL theory plus controlled descent plausibly accounts for nominal 7th arc BFO discrepancies. Synergistic resolution of observation by this theory suggests that MH370 did not violently crash at the 7th arc. Instead MH370 headed east towards a glide landing, predicted by the PL theory to be where the longitude of Penang intersects the 33oS latitude at a deep hole. The main lesson to learn is that all plausible scenarios need to be considered for complex high-uncertainty problems.