Hold Duration Research Articles

Frictional dynamics of viscoelastic solids driven on a rough surface.

We study the effect of viscoelastic dynamics on the frictional properties of a (mean-field) spring-block system pulled on a rough surface by an external drive. When the drive moves at constant velocity V, two dynamical regimes are observed: at fast driving, above a critical threshold V(c), the system slides at the drive velocity and displays a friction force with velocity weakening. Below V(c) the steady sliding becomes unstable and a stick-slip regime sets in. In the slide-hold-slide driving protocol, a peak of the friction force appears after the hold time and its amplitude increases with the hold duration. These observations are consistent with the frictional force encoded phenomenologically in the rate-and-state equations. Our model gives a microscopical basis for such macroscopic description.

SU-E-J-62: Breath Hold for Left-Sided Breast Cancer: Visually Monitored Deep Inspiration Breath Hold Amplitude Evaluated Using Real-Time Position Management

Purpose: We used Real-Time Position Management (RPM) to evaluate breath hold amplitude and variability when gating with a visually monitored deep inspiration breath hold technique (VM-DIBH) with retrospective cine image chest wall position verification. Methods: Ten patients with left-sided breast cancer were treated using VM-DIBH. Respiratory motion was passively collected once weekly using RPM with the marker block positioned at the xiphoid process. Cine images on the tangent medial field were acquired on fractions with RPM monitoring for retrospective verification of chest wall position during breath hold. The amplitude and duration of all breath holds on which treatment beams were delivered were extracted from the RPM traces. Breath hold position coverage was evaluated for symmetric RPM gating windows from ± 1 to 5 mm centered on the average breath hold amplitude of the first measured fraction as a baseline. Results: The average (range) breath hold amplitude and duration was 18 mm (3–36 mm) and 19 s (7–34 s). The average (range) of amplitude standard deviation per patient over all breath holds was 2.7 mm (1.2–5.7 mm). With the largest allowable RPM gating window (± 5 mm), 4 of 10 VM-DIBH patients would have had ≥ 10% of their breath hold positions excluded by RPM. Cine verification of the chest wall position during the medial tangent field showed that the chest wall was greater than 5 mm from the baseline in only 1 out of 4 excluded patients. Cine images verify the chest wall/breast position only, whether this variation is acceptable in terms of heart sparing is a subject of future investigation. Conclusion: VM-DIBH allows for greater breath hold amplitude variability than using a 5 mm gating window with RPM, while maintaining chest wall positioning accuracy within 5 mm for the majority of patients.

Acoustic modeling of the perception of place information in incomplete stops

Previous research on stop consonant production found that less than 60% of the stops sampled from a connected speech corpus contained a clearly defined hold duration followed by a plosive release [Crystal & House, JASA 1988]. How listeners perceive the remaining portion of incomplete stop consonants is not well understood. The purpose of the current study was to investigate whether relative formant deflection patterns, a potential model of acoustic invariance proposed by Story and Bunton (2010), is capable of predicting listeners’ perceptions of acoustically continuous, voiced stop consonants lacking a canonical hold duration. Listeners were randomly presented a total of 60 voiced stop-consonant VCV stimuli, each 100 ms in duration, synthesized using a computational model of speech production. Stimuli were created using a continuum of 20 equal step constrictions along the length of the vocal tract in three vowel-to-vowel contexts [see Story & Bunton, JSLHR 2010]. Participants listened to the stimuli and performed a forced choice test (i.e., /b-d-g/). The phonetic boundaries predicted by the relative formant deflection patterns and phonetic boundaries obtained by the forced choice test were compared to determine the ability of the acoustic model to predict participants’ perceptions. The acoustic and perceptual results are reported. [Work supported by NIH R01-DC011275.]

Ascorbic acid attenuates the pressor response to voluntary apnea in postmenopausal women

We recently demonstrated that postmenopausal women have an augmented blood pressure response to voluntary apnea compared to premenopausal women. Both obstructive sleep apnea (OSA) and healthy aging are associated with increased oxidative stress, which may impair cardiovascular function. Restoring physiological responses could have clinical relevance since transient surges in blood pressure are thought to be an important stimulus for end-organ damage in aging and disease. We tested the hypothesis that acute antioxidant infusion improves physiological responses to voluntary apnea in healthy postmenopausal women (n = 8, 64 ± 2 year). We measured beat-by-beat mean arterial pressure (MAP), heart rate (HR), and brachial artery blood flow velocity (BBFV, Doppler ultrasound) following intravenous infusion of normal saline and ascorbic acid (∼3500 mg). Subjects performed maximal voluntary end-expiratory apneas and changes (Δ) from baseline were compared between infusions. The breath hold duration and oxygen saturation nadir were similar between saline (29 ± 6 sec, 94 ± 1%) and ascorbic acid (29 ± 5 sec, 94 ± 1%). Ascorbic acid attenuated the pressor response to voluntary apnea (ΔMAP: 6 ± 2 mmHg) as compared to saline (ΔMAP: 12 ± 2 mmHg, P = 0.034) and also attenuated forearm vasoconstriction (ΔBBFV: 4 ± 9 vs. −12 ± 7%, P = 0.049) but did not affect ΔHR. We conclude that ascorbic acid lowers the blood pressure response to voluntary apnea in postmenopausal women by inhibiting vasoconstriction in the limb vasculature. Whether ascorbic acid has similar effects in OSA patients remains to be prospectively tested.

Development and Characterisation of a Smoking Behaviour Measurement System

Summary Respiratory deposition from smoking articles is influenced by particle or droplet properties (such as diameter), puffing parameters (such as draw effort or pressure drop, flow rate, duration), mouth losses, and post-puff inhalation dynamics (determined by inhalation depth, volume and breath hold duration). The Smoking Behaviour System (SBS) described herein is a novel system with regard to its capability to measure flow and duration characteristics of typical smoking cycles, which may consist of puffing, mouth hold, post-puff inhalation, breath hold and exhalation. It combines two analysers: the first measures the puffing topography and optical obscuration from puffed aerosol, while the second measures the respiratory topography and optical obscuration from exhaled aerosol. The puffing and respiratory analysers were calibrated and operated between flow rates of 0-7 L.min-1 and 0-50 L.min-1, respectively, as typically encountered during the human smoking cycle. The volumes measured by the puffing and respiratory analysers met the design specification and tolerance limits of ± 2% and ± 5%, respectively. The optical obscuration measurements showed no statistical difference among the three units tested or in day-to-day variation, verifying the robustness of the SBS for use in optical measurements of smoke when combined with topography measurements. In conclusion, the SBS is a validated technology that provides a means to measure the real-time flow and duration profile of puffing, mouth hold, post-puff inhalation, breath hold

The influence of pause, attack, and decay duration of the ongoing envelope on sound lateralization.

Klein-Hennig et al. [J. Acoust. Soc. Am. 129, 3856-3872 (2011)] introduced a class of high-frequency stimuli for which the envelope shape can be altered by independently varying the attack, hold, decay, and pause durations. These stimuli, originally employed for testing the shape dependence of human listeners' sensitivity to interaural temporal differences (ITDs) in the ongoing envelope, were used to measure the lateralization produced by fixed interaural disparities. Consistent with the threshold ITD data, a steep attack and a non-zero pause facilitate strong ITD-based lateralization. In contrast, those conditions resulted in the smallest interaural level-based lateralization.

Viral Inactivation: Low pH and Detergent.

Studies presented at the 2011 Viral Clearance Symposium served to further understand the critical process parameters (CPPs) involved in effective low-pH viral inactivation, and to define worst-case conditions regarding pH, temperature, hold duration, and ionic strength ([1][1]). One of the outcomes

Air evacuation during vacuum bag only prepreg processing of honeycomb sandwich structures: In-plane air extraction prior to cure

Out-of-autoclave (OoA) prepregs offer good in-plane air permeability that enable efficient in-plane air-extraction. In this paper, OoA prepregs skins were applied to honeycomb sandwich structures, to act as in-plane air extraction media during the vacuum hold prior to cure. An in-plane extraction model was developed to predict the pressure drop in a honeycomb sandwich structure. The model was experimentally validated by measuring the local pressure in a 1m long sandwich structure. The model provides design guidelines vacuum hold duration to achieve a given final pressure in the part prior to cure. Finally, the in-plane and transverse extraction strategies were compared for large parts. The in-plane extraction was faster for parts smaller than 0.4m.

Sex differences in forearm vasoconstrictor response to voluntary apnea (1171.1)

Clinical evidence indicates that obstructive sleep apnea is more common and more severe in men compared to women. Sex differences in the vasoconstrictor response to hypoxemia‐induced sympathetic activation might contribute to this clinical observation. In the current laboratory study, we determined sex differences in the acute physiological responses to maximal voluntary end‐expiratory apnea (MVEEA) during wakefulness in healthy young subjects (ten women, nine men, 26 ± 1 yrs). In addition, we studied eight postmenopausal women (62 ± 2 yrs) to determine the effect of menopause status. Mean arterial pressure (MAP), heart rate (HR), brachial artery blood flow velocity (BBFV, Doppler ultrasound) and cutaneous vascular conductance (CVC, laser Doppler flowmetry) were measured and changes in physiological parameters from baseline were compared between groups. The breath hold duration and oxygen saturation nadir were similar between groups. In response to MVEEA, young women had significantly less forearm vasoconstriction compared to young men (ΔBBFV: 2 ± 7 versus ‐25 ± 6% and ΔCVC: ‐5 ± 4 versus ‐31 ± 4 %) whereas ΔMAP (12 ± 2 versus 16 ± 3 mmHg) and ΔHR (4 ± 2 versus 6 ± 3 bpm) were comparable between groups. The attenuated forearm vasoconstriction in young women was not observed in postmenopausal women (ΔBBFV ‐21 ± 5%). We conclude that young women have blunted forearm vasoconstriction in response to MVEEA compared to young men and this effect is not evident in older postmenopausal women. These data suggest that female sex hormones dampen neurogenic vasoconstriction in response to apnea‐induced hypoxemia.Grant Funding Source: Supported by NIH P01 HL096570 and UL1 TR000127

The Effect of Climbing Mount Everest on Spleen Contraction and Increase in Hemoglobin Concentration During Breath Holding and Exercise

Release of stored red blood cells resulting from spleen contraction improves human performance in various hypoxic situations. This study determined spleen volume resulting from two contraction-evoking stimuli: breath holding and exercise before and after altitude acclimatization during a Mount Everest ascent (8848 m). Eight climbers performed the following protocol before and after the climb: 5 min ambient air respiration at 1370 m during rest, 20 min oxygen respiration, 20 min ambient air respiration at 1370 m, three maximal-effort breath holds spaced by 2 min, 10 min ambient air respiration, 5 min of cycling at 100 W, and finally 10 min ambient air respiration. We measured spleen volume by ultrasound and capillary hemoglobin (HB) concentration after each exposure, and heart rate (HR) and arterial oxygen saturation (Sao2) continuously. Mean (SD) baseline spleen volume was unchanged at 213 (101) mL before and 206 (52) mL after the climb. Before the climb, spleen volume was reduced to 184 (83) mL after three breath holds, and after the climb three breath holds resulted in a spleen volume of 132 (26) mL (p=0.032). After exercise, the preclimb spleen volume was 186 (89) mL vs. 112 (389) mL) after the climb (p=0.003). Breath hold duration and cardiovascular responses were unchanged after the climb. We concluded that spleen contraction may be enhanced by altitude acclimatization, probably reflecting both the acclimatization to chronic hypoxic exposure and acute hypoxia during physical work.

Velocity encoding with the slice select refocusing gradient for faster imaging and reduced chemical shift‐induced phase errors

To investigate a novel phase-contrast MRI velocity-encoding technique for faster imaging and reduced chemical shift-induced phase errors. Velocity encoding with the slice select refocusing gradient achieves the target gradient moment by time shifting the refocusing gradient, which enables the use of the minimum in-phase echo time (TE) for faster imaging and reduced chemical shift-induced phase errors. Net forward flow was compared in 10 healthy subjects (N = 10) within the ascending aorta (aAo), main pulmonary artery (PA), and right/left pulmonary arteries (RPA/LPA) using conventional flow compensated and flow encoded (401 Hz/px and TE = 3.08 ms) and slice select refocused gradient velocity encoding (814 Hz/px and TE = 2.46 ms) at 3 T. Improved net forward flow agreement was measured across all vessels for slice select refocused gradient compared to flow compensated and flow encoded: aAo vs. PA (1.7% ± 1.9% vs. 5.8% ± 2.8%, P = 0.002), aAo vs. RPA + LPA (2.1% ± 1.7% vs. 6.0% ± 4.3%, P = 0.03), and PA vs. RPA + LPA (2.9% ± 2.1% vs. 6.1% ± 6.3%, P = 0.04), while increasing temporal resolution (35%) and signal-to-noise ratio (33%). Slice select refocused gradient phase-contrast MRI with a high receiver bandwidth and minimum in-phase TE provides more accurate and less variable flow measurements through the reduction of chemical shift-induced phase errors and a reduced TE/repetition time, which can be used to increase the temporal/spatial resolution and/or reduce breath hold durations.

Skill learning involves optimizing the linking of action phases

Many manual tasks involve object manipulation and are achieved by an evolving series of actions, or action phases, recruited to achieve task subgoals. The ability to effectively link action phases is an important component of manual dexterity. However, our understanding of how the effective linking of sequential action phases develops with skill learning is limited. Here, we addressed this issue using a task in which participants applied forces to a handle to move a cursor on a computer screen to successively acquire visual targets. Target acquisition required actively holding the cursor within the target zone (hold phase) for a required duration before moving to the next target (transport phase). If the transport phase was initiated prematurely, before the end of the required hold duration, participants had to return to the target to acquire it. The goal was to acquire targets as quickly as possible. Distinct visual and auditory sensory events marked goal completion of each action phase. During initial task performance, the transport phase was reactively triggered by sensory events signaling hold phase completion. However, with practice, participants learned to initiate the transport phase based on a prediction of the time of hold phase completion. Simulations revealed that participants learned to near-optimally compensate for temporal uncertainty, presumably related to estimation of time intervals and execution of motor commands, so as to reduce the average latency between the end of the required hold phase duration and the start of the transport phase, while avoiding an excess of premature exits.

SU‐C‐134‐06: Guidance for CT Departments Desiring to Optimize Protocols for: Multiple Scanner Architectures

Purpose: Clinical protocol development must consider a CT scanners architecture both in hardware and software. Differences in tube output, beam collimation, availability of iterative reconstruction, etc., may only allow some protocols to be properly performed on higher end scanners due to clinical constraints like breath hold duration and contrast dynamics. This study presents an overview of techniques for translating and optimizing a protocol from one scanner to another. Cases in which protocols are not compatible with a given scanner architecture are also discussed. Methods: At our institution, intensive protocol optimization is performed for each protocol using a single scanner architecture. Once a protocol is optimized in both technical and clinical parameters, the protocol can be translated to other scanner architectures (both older and newer). Essential restraints on the translation process include the maximum clinically allowable scan time and the maximum tube output of the scanner. Successful translation can be done if scan parameters can be modified within these essential constraints. If this is not possible then compromises have to be made that can affect clinical performance. Mathematical relationships related to tube output and clinical considerations will be discussed that guide the transformation and any needed compromises. Results: Several test cases are presented providing details of translating optimized protocols to an older and newer CT scanner architecture. Cases in which older scanners cannot provide the required performance are common for angiography exams that require high spatial resolution, thin reconstructed slice thickness, low noise, and fast scan times due to breath hold and contrast dynamic constraints. Conclusion: Understanding the limitations of older generation CT scanners and the benefits of newer CT architectures is critical for maintaining a uniquely optimized set of CT protocols across a wide range of CT architectures. Equipment grant from GE healthcare.

Characterization of the Evolution and Properties of Silicon Carbide Derived From a Preceramic Polymer Precursor

This study reports on the fabrication and characterization of polymer‐derived amorphous and nano‐grained SiC, by controlled pyrolysis of allylhydridopolycarbosilane (AHPCS) under inert atmosphere. Processing temperatures and hold times at final temperatures are varied to study the influence of processing parameters on the structure and resulting properties. Chemical changes, phase transformations, and microstructural changes occurring during the pyrolysis process are studied. Polymer cross‐linking and polymer to ceramic conversion is studied using infrared spectroscopy (FTIR). Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) are performed to monitor the mass loss and phase change as a function of temperature. X‐ray diffraction studies are performed to study the intermediate phases and microstructural changes. Hardness and modulus measurements are carried out using instrumented nanoindentation to establish processing‐property‐structure relationship for SiC derived from the polymer precursor. It is seen that the presence of nanocrystalline domains in amorphous SiC significantly influences the modulus and hardness. A nonlinear relationship is observed in these properties with optimal mechanical properties observed for SiC processed to 1150°C for 1 h hold duration, having average grain size of 3 nm. In addition, bulk mechanical characterization, in terms of biaxial flexure strength, is done for SiC–SiC particulate composites purely derived from the polymer precursor.

Nitric oxide in the breath of bottlenose dolphins: Effects of breath hold duration, feeding, and lung disease

AbstractBreath analysis, including measurement of nitric oxide (NO), is a noninvasive diagnostic tool that may help evaluate cetacean health. This is the first report on the effects of breath hold duration, feeding, and lung disease on NO in dolphin exhaled breath. Three healthy dolphins were trained to hold their breath for 30, 60, 90, and 120 s and then exhale into an underwater funnel. Exhaled NO values from 157 breath samples were compared among three healthy dolphins by breath hold time and after fasting and feeding. Exhaled NO values were also measured in two dolphins with pulmonary disease. NO in dolphin breath was higher compared to ambient air; healthy dolphins had higher NO concentrations in their breath after feeding compared to after overnight fasting; and there were no significant differences in exhaled NO levels by breath hold duration. A dolphin with Mycoplasma‐associated pneumonia and chronic gastrointestinal disease had higher postprandial exhaled NO levels compared to healthy controls. This study demonstrates, contrary to previous publications, that dolphins exhale NO. Given the high standard deviations present in exhaled breath NO values, future studies are needed to further standardize collection methods or identify more reliable samples (e.g., blood).

Breath Holding Duration and Self-Reported Smoking Abstinence Intolerance as Predictors of Smoking Lapse Behavior in a Laboratory Analog Task

Distress intolerance (DI) is elevated in smokers and confers increased risk for relapse following a quit attempt. Intolerance of respiratory distress and of nicotine withdrawal may be particularly relevant predictors of smoking cessation outcomes. However, no studies to date have examined the association between smoking relevant DI and smoking lapse behavior in a laboratory setting. The current study examined whether DI was associated with the risk of initiating smoking in a laboratory-based lapse analog task. This study is a secondary data analysis from a study of the impact of alcohol administration on smoking behavior. Ninety-six cigarette smokers completed measures of DI and a smoking lapse analog task. Breath holding (BH) duration and self-reported intolerance of smoking abstinence were analyzed as predictors of smoking initiation in a survival analysis model. Shorter BH duration was associated with greater risk of smoking initiation, controlling for nicotine dependence, nicotine withdrawal symptoms, and demographics. Self-report measures of smoking abstinence DI were not associated with BH duration or time to smoking initiation when controlling for nicotine dependence severity. BH captures a domain of DI that is specifically associated with a higher risk of initiating smoking in this analog of smoking lapse. The prediction of smoking in an analog lapse task adds to the extant literature identifying an association between DI and smoking lapse and may enable further research to understand and address the mechanism through which BH affects smoking lapse risk.

The development of microstructural damage during high temperature creep–fatigue of a nickel alloy

Alloy 617 is the leading candidate material for an Intermediate Heat Exchanger (IHX) of the Very High Temperature Reactor (VHTR). To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests that include hold times up to 9000s at maximum tensile strain were conducted at 950°C. The fatigue resistance decreased when a hold time was added at peak tensile strain, owing to the mechanisms resulting in a change in fracture mode from transgranular in pure fatigue to intergranular in creep–fatigue. Increases in the tensile hold duration beyond an initial value were not detrimental to the creep–fatigue resistance. An analysis of the evolving failure modes was facilitated by interrupting tests during cycling for ex situ microstructural investigation.

K-t-GRAPPA accelerated flow measurements

Background Parallel imaging can reduce scan time with typical reduction factors of ~2, often not sufficient to reduce scan time to breath hold duration. Spatiotemporal parallel imaging such as k-t-GRAPPA allows for a significantly higher speed-up in data acquisition, but previous studies mostly acquired full k-space data while removing data retrospectively. Here, aortic flow scans were acquired during breath-hold using kt-GRAPPA based reconstruction [1,2] and compared to conventional protocols using GRAPPA and navigator respiration gating.

Improving the mechanical reliability of cryomilled Al–Mg alloy using a two-stage spark plasma sintering cycle

Dense bimodal-grained aluminum magnesium alloys were produced by spark plasma sintering of cryomilled powders. The use of a two-stage sintering cycle did not induce grain growth or influence the hardness and flexural strength, but doubled the fracture strength distribution statistic (Weibull modulus) from 13 to 25. The increased duration of the second hold (from 5 to 20 min) marginally increased the Weibull Modulus, from 23 to 25.

The influence of different segments of the ongoing envelope on sensitivity to interaural time delays

The auditory system is sensitive to interaural timing disparities in the fine structure and the envelope of sounds, each contributing important cues for lateralization. In this study, psychophysical measurements were conducted with customized envelope waveforms in order to investigate the isolated effect of different segments of a periodic, ongoing envelope on lateralization. One envelope cycle was composed of the four segments attack flank, hold duration, decay flank, and pause duration, which were independently varied to customize the envelope waveform. The envelope waveforms were applied to a 4-kHz sinusoidal carrier, and just noticeable envelope interaural time differences were measured in six normal hearing subjects. The results indicate that attack durations and pause durations prior to the attack are the most important stimulus characteristics for processing envelope timing disparities. The results were compared to predictions of three binaural lateralization models based on the normalized cross correlation coefficient. Two of the models included an additional stage to mimic neural adaptation prior to binaural interaction, involving either a single short time constant (5 ms) or a combination of five time constants up to 500 ms. It was shown that the model with the single short time constant accounted best for the data.