Growth of Oxide Compounds under Dynamic Atmosphere Composition

Commercially available gases contain residual impurities leading to a background oxygen partial pressure of typically several 10^{-6} bar, independent of temperature. This oxygen partial pressure is inappropriate for the growth of some single crystals where the desired oxidation state possesses a narrow stability field. Equilibrium thermodynamic calculations allow the determination of dynamic atmosphere compositions yielding such self adjusting and temperature dependent oxygen partial pressures, that crystals like ZnO, Ga2O3, or Fe{1-x}O can be grown from the melt.Comment: 4 pages, 3 figures, talk on CGCT-4 Sendai, May 21-24, 200

Heart rate variability in non-apneic snorers and controls before and after continuous positive airway pressure

BACKGROUND: We hypothesized that sympathetic nervous system activity (SNSA) is increased and parasympathetic nervous system activity (PNSA) is decreased during non-rapid eye movement (NREM) sleep in non-apneic, otherwise healthy, snoring individuals compared to control. Moreover, we hypothesized that these alterations in snoring individuals would be more evident during non-snoring than snoring when compared to control. METHODS: To test these hypotheses, heart rate variability was used to measure PNSA and SNSA in 11 normotensive non-apneic snorers and 12 control subjects before and 7-days after adapting to nasal continuous positive airway pressure (nCPAP). RESULTS: Our results showed that SNSA was increased and PNSA was decreased in non-apneic snorers during NREM compared to control. However, these changes were only evident during the study in which snoring was eliminated with nCPAP. Conversely, during periods of snoring SNSA and PNSA were similar to measures obtained from the control group. Additionally, within the control group, SNSA and PNSA did not vary before and after nCPAP application. CONCLUSION: Our findings suggest that long-lasting alterations in autonomic function may exist in snoring subjects that are otherwise healthy. Moreover, we speculate that because of competing inputs (i.e. inhibitory versus excitatory inputs) to the autonomic nervous system during snoring, the full impact of snoring on autonomic function is most evident during non-snoring periods

Ventilatory responses after major surgery and high dependency care

BACKGROUND: Disturbed breathing during sleep, with episodic upper airway obstruction, is frequent after major surgery. Ventilatory responses to hypercapnia and hypoxia during episodes of airway obstruction are difficult to investigate because the usual measure, that of ventilation, has been attenuated by the obstruction. We simulated the blood gas stimulus associated with obstruction to allow investigation of the responses. METHODS: To assess ventilatory responses, we studied 19 patients, mean age 59 (19–79), first at discharge from high dependency care after major abdominal surgery and then at surgical review, ∼6 weeks later. Exhaled gas was analysed and inspired gas adjusted to simulate changes that would occur during airway obstruction. Changes in ventilation were measured over the following 45–70 s. Studies were done from air breathing if possible, and also from an increased inspired oxygen concentration. RESULTS: During simulated obstruction, hypercapnia developed similarly in all the test conditions. Arterial oxygen saturation decreased significantly more rapidly when the test was started from air breathing. The mean ventilatory response was 5.8 litre min(−2) starting from air breathing and 4.5 litre min(−2) with oxygen breathing. The values 6 weeks later were 5.9 and 4.3 litre min(−2), respectively (P=0.05, analysis of variance). There was no statistical difference between the responses starting from air and those on oxygen. CONCLUSIONS: After major surgery, ventilatory responses to hypercapnia and hypoxaemia associated with airway obstruction are small and do not improve after 6 weeks. With air breathing, arterial oxygen desaturation during simulated rebreathing is substantial

Positive End-Expiratory Pressure may alter breathing cardiovascular variability and baroreflex gain in mechanically ventilated patients

<p>Abstract</p> <p>Background</p> <p>Baroreflex allows to reduce sudden rises or falls of arterial pressure through parallel RR interval fluctuations induced by autonomic nervous system. During spontaneous breathing, the application of positive end-expiratory pressure (PEEP) may affect the autonomic nervous system, as suggested by changes in baroreflex efficiency and RR variability. During mechanical ventilation, some patients have stable cardiorespiratory phase difference and high-frequency amplitude of RR variability (HF-RR amplitude) over time and others do not. Our first hypothesis was that a steady pattern could be associated with reduced baroreflex sensitivity and HF-RR amplitude, reflecting a blunted autonomic nervous function. Our second hypothesis was that PEEP, widely used in critical care patients, could affect their autonomic function, promoting both steady pattern and reduced baroreflex sensitivity.</p> <p>Methods</p> <p>We tested the effect of increasing PEEP from 5 to 10 cm H2O on the breathing variability of arterial pressure and RR intervals, and on the baroreflex. Invasive arterial pressure, ECG and ventilatory flow were recorded in 23 mechanically ventilated patients during 15 minutes for both PEEP levels. HF amplitude of RR and systolic blood pressure (SBP) time series and HF phase differences between RR, SBP and ventilatory signals were continuously computed by complex demodulation. Cross-spectral analysis was used to assess the coherence and gain functions between RR and SBP, yielding baroreflex-sensitivity indices.</p> <p>Results</p> <p>At PEEP 10, the 12 patients with a stable pattern had lower baroreflex gain and HF-RR amplitude of variability than the 11 other patients. Increasing PEEP was generally associated with a decreased baroreflex gain and a greater stability of HF-RR amplitude and cardiorespiratory phase difference. Four patients who exhibited a variable pattern at PEEP 5 became stable at PEEP 10. At PEEP 10, a stable pattern was associated with higher organ failure score and catecholamine dosage.</p> <p>Conclusions</p> <p>During mechanical ventilation, stable HF-RR amplitude and cardiorespiratory phase difference over time reflect a blunted autonomic nervous function which might worsen as PEEP increases.</p

Long-term facilitation of ventilation in humans with chronic spinal cord injury

RATIONALE: Intermittent stimulation of the respiratory system with hypoxia causes persistent increases in respiratory motor output (i.e., long-term facilitation) in animals with spinal cord injury. This paradigm, therefore, has been touted as a potential respiratory rehabilitation strategy. OBJECTIVES: To determine whether acute (daily) exposure to intermittent hypoxia can also evoke long-term facilitation of ventilation after chronic spinal cord injury in humans, and whether repeated daily exposure to intermittent hypoxia enhances the magnitude of this response. METHODS: Eight individuals with incomplete spinal cord injury (>1 yr; cervical [n = 6], thoracic [n = 2]) were exposed to intermittent hypoxia (eight 2-min intervals of 8% oxygen) for 10 days. During all exposures, end-tidal carbon dioxide levels were maintained, on average, 2 mm Hg above resting values. Minute ventilation, tidal volume, and breathing frequency were measured before (baseline), during, and 30 minutes after intermittent hypoxia. Sham protocols consisted of exposure to room air and were administered to a subset of the participants (n = 4). MEASUREMENTS AND MAIN RESULTS: Minute ventilation increased significantly for 30 minutes after acute exposure to intermittent hypoxia (P < 0.001), but not after sham exposure. However, the magnitude of ventilatory long-term facilitation was not enhanced over 10 days of intermittent hypoxia exposures. CONCLUSIONS: Ventilatory long-term facilitation can be evoked by brief periods of hypoxia in humans with chronic spinal cord injury. Thus, intermittent hypoxia may represent a strategy for inducing respiratory neuroplasticity after declines in respiratory function that are related to neurological impairment. Clinical trial registered with www.clinicaltrials.gov (NCT01272011)

Dielectric constants of YVO_4, Fe-, Ge-, and V-containing garnets, the polarizabilities of Fe_2O_3, GeO_2, and V_2O_5, and the oxide additivity rule

The dielectric constants and dissipation factors of Y_3Fe-5O_(12) , YVO_4 , NaCa_2Mg_2V_3O_(12), and a variety of Ge garnets were determined at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: Y_3Fe_5O_(12) K'=15.70 tan δ = 0.0009 Ca_3Ga_2Ge_3O_(12) K'=9.73 tan δ = 0.0007 Ca_(.90) Y_(1.88)Mg_(2.27)Ge_3O_(12) K'=10.35 tan δ = 0.0006 CaY_(1.96)Nd_(.04)Zn_2Ge_3O_(12) K'=11.32 tan δ = 0.0006 Nd_(2.95)Mg_(1.48)ln_(.68)Ga_(1.54)Ge_(1.32)O_(12) K'=11.86 tan δ = 0.0009 NaCa_2Mg_2V3O_(12) K'=10.32 tan δ = 0.0007 YVO_4 K_a'=9.68 tan δ_a = 0.0010 K_c' = 16.59 tan δ_c = 0.0278. The dielectric polarizabilities of Fe_2O_3, GeO_2, and V_2O_5 derived from the dielectric constants of the above compounds are 10.5, 5.5, and 15.8 Å^3, respectively. The agreement between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of oxide polarizabilities according to α_D(mineral) = Σα_D(oxides) for the above garnets is ~0.5%

Long-Term Facilitation of Ventilation in Humans with Chronic Spinal Cord Injury

RATIONALE: Intermittent stimulation of the respiratory system with hypoxia causes persistent increases in respiratory motor output (i.e., long-term facilitation) in animals with spinal cord injury. This paradigm, therefore, has been touted as a potential respiratory rehabilitation strategy. OBJECTIVES: To determine whether acute (daily) exposure to intermittent hypoxia can also evoke long-term facilitation of ventilation after chronic spinal cord injury in humans, and whether repeated daily exposure to intermittent hypoxia enhances the magnitude of this response. METHODS: Eight individuals with incomplete spinal cord injury (>1 yr; cervical [n = 6], thoracic [n = 2]) were exposed to intermittent hypoxia (eight 2-min intervals of 8% oxygen) for 10 days. During all exposures, end-tidal carbon dioxide levels were maintained, on average, 2 mm Hg above resting values. Minute ventilation, tidal volume, and breathing frequency were measured before (baseline), during, and 30 minutes after intermittent hypoxia. Sham protocols consisted of exposure to room air and were administered to a subset of the participants (n = 4). MEASUREMENTS AND MAIN RESULTS: Minute ventilation increased significantly for 30 minutes after acute exposure to intermittent hypoxia (P < 0.001), but not after sham exposure. However, the magnitude of ventilatory long-term facilitation was not enhanced over 10 days of intermittent hypoxia exposures. CONCLUSIONS: Ventilatory long-term facilitation can be evoked by brief periods of hypoxia in humans with chronic spinal cord injury. Thus, intermittent hypoxia may represent a strategy for inducing respiratory neuroplasticity after declines in respiratory function that are related to neurological impairment. Clinical trial registered with www.clinicaltrials.gov (NCT01272011)