Minimum Saturation Research Articles

Treatment of Central Sleep Apnea in US Veterans

There are no standard therapies for the management of central sleep apnea (CSA). Either positive pressure therapy (PAP) or supplemental oxygen (O(2)) may stabilize respiration in CSA by reducing ventilatory chemoresponsiveness. Additionally, increasing opioid use and the presence of comorbid conditions in US veterans necessitates investigations into alternative titration protocols to treat CSA. The goal was to report on the effectiveness of titration with PAP, used alone or in conjunction with O(2), for the management of CSA associated with varying comorbidities and opioid use. This was a retrospective chart review over 3 years, performed at a VA sleep disorders center. The effects of CPAP, CPAP+O(2), and BPAP+O(2), used in a step-wise titration protocol, on consecutive patients diagnosed with CSA were studied. CSA was diagnosed in 162 patients. The protocol was effective in eliminating CSA (CAI ≤ 5/h) in 84% of patients. CPAP was effective in 48%, while CPAP+O(2) combination was effective in an additional 25%, and BPAP+O(2) in 11%. The remaining 16% were non-responders. Forty-seven patients (29%) were on prescribed opioid therapy for chronic pain, in whom CPAP, CPAP+O(2), or BPAP+O(2) eliminated CSA in 54%, 28%, and 10% cases, respectively. CPAP, CPAP+O(2), and BPAP+O(2) each produced significant declines in the AHI, CAI, and arousal index, and an increase in the SpO(2). The data demonstrate that using a titration protocol with CPAP and then PAP with O(2) effectively eliminates CSA in individuals with underlying comorbid conditions and prescription opioid use. Comparative studies with other therapeutic modalities are required.

GEOCHEMICAL CONTROLS ON CARBONATE SHELL TAPHONOMY IN NORTHERN GULF OF MEXICO CONTINENTAL SHELF AND SLOPE SEDIMENTS

Abstract We examine the linkage between the sediment geochemical milieu and the process of carbonate degradation over a wide range of continental shelf and slope sediments using molluscan shells deployed for 13 years by the Shelf and Slope Experimental Taphonomy Initiative (SSETI). Geochemical characterization of the environment of preservation included the breadth of the pore-water carbonate undersaturation window, a depth-integrated carbonate dissolution index, the depth of minimum pore-water saturation, diffusive fluxes of oxygen and calcium, average sulfate and chloride concentration in the upper 5 cm, and the carbonate and organic carbon fractions in the same sedimentary horizon. Taphonomic indices included the maximum degree of dissolution; average dissolution; the incidences of chalkiness, pitting, deep dissolution, and a soft shell surface; the maximum degree of discoloration; the incidences of fading, gray-to-black discoloration, brown discoloration, and orange discoloration; the presence of pyri...

Development and Validation of a Cerebral Oximeter Capable of Absolute Accuracy

Cerebral oximetry may be a valuable monitor, but few validation data are available, and most report the change from baseline rather than absolute accuracy, which may be affected by individuals whose oximetric values are outside the expected range. The authors sought to develop and validate a cerebral oximeter capable of absolute accuracy. An in vivo research study. A university human physiology laboratory. Healthy human volunteers were enrolled in calibration and validation studies of 2 cerebral oximetric sensors, the Nonin 8000CA and 8004CA. The 8000CA validation study identified 5 individuals with atypical cerebral oxygenation values; their data were used to design the 8004CA sensor, which subsequently underwent calibration and validation. Volunteers were taken through a stepwise hypoxia protocol to a minimum saturation of peripheral oxygen. Arteriovenous saturation (70% jugular bulb venous saturation and 30% arterial saturation) at 6 hypoxic plateaus was used as the reference value for the cerebral oximeter. Absolute accuracy was defined using a combination of the bias and precision of the paired saturations (A(RMS)). In the validation study for the 8000CA sensor (n = 9, 106 plateaus), relative accuracy was an A(RMS) of 2.7, with an absolute accuracy of 8.1, meeting the criteria for a relative (trend) monitor, but not an absolute monitor. In the validation study for the 8004CA sensor (n = 11, 119 plateaus), the A(RMS) of the 8004CA was 4.1, meeting the prespecified success criterion of <5.0. The Nonin cerebral oximeter using the 8004CA sensor can provide absolute data on regional cerebral saturation compared with arteriovenous saturation, even in subjects previously shown to have values outside the normal population distribution curves.

Capillary trapping in sandstones and carbonates: Dependence on pore structure

Residual non‐wetting phase saturation and wetting‐phase permeability were measured in three limestones and four sandstones ranging in porosity from 0.13 to 0.28 and in absolute permeability from 2 × 10−15 to 3 × 10−12 m2. This paper focuses on the residual state established by waterflooding at low capillary number from minimum water saturation achieved using the porous plate technique, which yields the maximum residual under strongly water‐wet conditions. The pore coordination number and pore body‐throat aspect ratio of each rock were estimated using pore networks extracted from X‐ray microtomography images of the rocks. Residual saturation decreases with increasing porosity, with no apparent difference in magnitude between the limestones and sandstones at a given porosity. Thus intraparticle/intra‐aggregate microporosity does not significantly alter the efficiency of capillary trapping in the rocks considered presently. Residual saturation broadly decreases as conditions become less favorable for snap‐off, i.e., with decreasing pore aspect ratio and increasing coordination number. The measured residual saturations imply that capillary trapping may be an effective mechanism for storing carbon dioxide in both sandstones and carbonates provided that the systems are strongly water‐wet.

Clinical and polysomnographic findings of patients with large goiters

Goiters cause a series of compressive symptoms, including dyspnea and dysphagia. There have been reports of the coexistence of this syndrome with obstructive sleep apnea (OSA). The objective of this study was to evaluate the prevalence of OSA in a group of patients with goiters. Twenty-four patients with a mean age of 52.7 ± 12.7 years, including five males (20.8 %) and 19 (79.2 %) females, who were diagnosed with euthyroid goiters with volumes exceeding 100 ml were consecutively selected. The protocol consisted of sleep questionnaires, physical examinations, and baseline polysomnography measurements. Patients were divided into two groups, OSA and NOSA (no OSA), and all findings were compared between the two groups. Of the studied patients, 70.8 % had OSA (p = 0.004). Regarding clinical parameters, age (p = 0.001), Epworth Sleepiness Scale scores (p = 0.039) and complaints of habitual snoring (p < 0.001) had higher values in the OSA group. Regarding physical examination parameters, body mass index (p = 0.012), neck circumference (p = 0.009) and the presence of tracheal compression (p = 0.021) had higher values in the OSA group. The polysomnographic parameters that were significantly different between the two groups were the greater apnea and hypopnea index per hour of sleep (p < 0.001) and the lower minimum oxyhemoglobin saturation in the OSA group (p = 0.011). There is a high prevalence of OSA in patients with goiters. The main findings that were associated with the presence of OSA are known clinical predictors of OSA and the presence of tracheal compression.

Serum S100B protein: a useful marker in obstructive sleep apnea syndrome

Background and purposeWe aimed to underline the importance of serum S100B protein as a useful biochemical marker in patients with obstructive sleep apnea syndrome (OSAS). Material and methodsForty-three newly diagnosed patients with OSAS (median apnea-hypopnea index [AHI, events/hour]: 37.5 [range 11.3–137]) and 25 subjects with AHI < 5 (median AHI: 4.4 [range 0.7–4.8]) were included in the study. Serum S100B protein level was tested in serum samples taken after polysomnography in both groups and the difference between OSAS patients and the control group regarding that level was assessed. In addition, the association of S100B protein serum level with age, body mass index, AHI, mean O2 saturation percentage during sleep, minimum O2 saturation value (%) at the end of the apneas, and the time spent at an O2 saturation less than 90% were analyzed in the OSAS patient group. ResultsMedian serum S100B protein level was 133.7 pg/mL (range 20.97–230.70 pg/mL) in patients with OSAS and 16.1 pg/mL (range 10.1–22.9 pg/mL) in the control group (p < 0.005). Serum S100B protein level did not correlate with any studied variable (p > 0.05 for each correlation coefficient). ConclusionsSerum S100B protein level is increased in patients with OSAS and may be a useful biochemical marker in those patients.

Sleep-Disordered Breathing with Nighttime Hypocapnia Relates to Daytime Enhanced Ventilatory Response to Exercise in Patients with Heart Disease

Sleep-disordered breathing (SDB) induces nighttime disturbance of arterial gases, such as carbon dioxide. However, it is still unclear whether nighttime SDB-related gas abnormality is related to respiratory dysregulation in daytime. Therefore, we examined the relationship between the arterial partial pressure of carbon dioxide (PaCO(2)) at nighttime and the respiratory response to exercise in daytime. Eighteen men (age, mean ± SD; 55 ± 11 years) with heart disease underwent multichannel respiratory monitoring through the night with transdermal measurement of PaCO(2) (PtcCO(2)) reflecting PaCO(2) and a cardiopulmonary exercise test in daytime. The ventilatory equivalent (VE)/carbon dioxide production (VCO(2)) slope as an index of ventilatory response to exercise and peak oxygen consumption (VO(2)) were obtained with a cardiopulmonary exercise test. Of the 18 patients, 10 patients had obstructive SDB, 5 had central SDB, and 3 patients did not have SDB. The mean apnea-hypopnea index was 21 ± 17. Minimum nighttime saturation of O(2) was positively correlated with peak VO(2), but not with VE/VCO(2). Nighttime PtcCO(2) was not correlated with peak VO(2) but was negatively correlated with the VE/VCO(2) slope of the daytime cardiopulmonary exercise test (r=-0.53). Nighttime lowering of PaCO(2) in SDB is related to an abnormal ventilatory response to exercise testing in the daytime. This finding suggests that nighttime hyperventilation in SDB alters both nighttime and daytime pathophysiological conditions in patients with heart disease.

Evolution of petrophysical properties of oil shales during high-temperature compaction tests: Implications for petroleum expulsion

The transport properties of Permian to Miocene oil shales (Torbanite, Posidonia, Messel, Himmetoglu, and Condor) were studied using petrophysical and geochemical techniques. The aims of this study were to assess permeability of oil shales, evaluate the evolution of porosity, specific surface area and intergranular permeability during high temperature compaction tests and to verify the suitability of intergranular permeability for petroleum expulsion. Measured permeability coefficients for two samples were 0.72 × 10−21 m² for the Eocene Messel shale and 2.63 × 10−21 m² for the Lower Jurassic Posidonia shale from S. Germany, respectively. BET specific surface areas of the original samples ranged from 0.7 to 10.6 m²/g and decreased after compaction to values from 0.3 to 3.7 m²/g. Initial porosity values ranged from 7.6 to 20.1 % for pre-deformation and from 9.99 to 20.7 % for post-deformation samples. Porosity increased during the high-temperature compaction experiments due to petroleum generation and expulsion. Permeability coefficients estimated using the Kozeny–Carman equation varied from 6.97 × 10−24 m² to 5.22 × 10−21 m² for pre-deformation and from 0.2 × 10−21 m² to 4.8 × 10−21 m² for post-deformation samples reflecting the evolution of their porosity and BET specific surface areas. Measured and calculated permeability were similar for the Messel shale whereas calculated permeability was two orders of magnitude lower for the Posidonia shale from S. Germany. Petroleum expulsion efficiencies under the experimental conditions ranged from 38.6% for the Torbanite to 96.2% for the Posidonia shale from S. Germany. They showed strong positive correlation with the petroleum generation index (R² = 0.91) and poor correlations with porosity (R² = 0.46), average pore throat diameters (R² = 0.22), and compaction (R² = 0.02). Estimated minimum pore-system saturations for petroleum expulsion during the experiments were 12% for the Torbanite and 30% for the Posidonia shale from N. Germany. Pore-system saturation determines whether expulsion occurs mainly through matrix or fracture permeability. For samples with saturation levels above 20%, fracture permeability dominated during the experiments. Evidence based on the measured permeability coefficients, expulsion flow rates, consideration of capillary displacement during generation-related pore invasion and the existence of transport porosity suggests that fracture permeability is the principal avenue of petroleum expulsion from source rocks. This conclusion is supported by microscopic observations.

An Experimental Study of CO2 Exsolution and Relative Permeability Measurements During CO2 Saturated Water Depressurization

Dissolution of CO2 into brine is an important and favorable trapping mechanism for geologic storage of CO2. There are scenarios, however, where dissolved CO2 may migrate out of the storage reservoir. Under these conditions, CO2 will exsolve from solution during depressurization of the brine, leading to the formation of separate phase CO2. For example, a CO2 sequestration system with a brine-permeable caprock may be favored to allow for pressure relief in the sequestration reservoir. In this case, CO2-rich brine may be transported upwards along a pressure gradient caused by CO2 injection. Here we conduct an experimental study of CO2 exsolution to observe the behavior of exsolved gas under a wide range of depressurization. Exsolution experiments in highly permeable Berea sandstones and low permeability Mount Simon sandstones are presented. Using X-ray CT scanning, the evolution of gas phase CO2 and its spatial distribution is observed. In addition, we measure relative permeability for exsolved CO2 and water in sandstone rocks based on mass balances and continuous observation of the pressure drop across the core from 12.41 to 2.76 MPa. The results show that the minimum CO2 saturation at which the exsolved CO2 phase mobilization occurs is from 11.7 to 15.5%. Exsolved CO2 is distributed uniformly in homogeneous rock samples with no statistical correlation between porosity and CO2 saturation observed. No gravitational redistribution of exsolved CO2 was observed after depressurization, even in the high permeability core. Significant differences exist between the exsolved CO2 and water relative permeabilities, compared to relative permeabilities derived from steady-state drainage relative permeability measurements in the same cores. Specifically, very low CO2 and water relative permeabilities are measured in the exsolution experiments, even when the CO2 saturation is as high as 40%. The large relative permeability reduction in both the water and CO2 phases is hypothesized to result from the presence of disconnected gas bubbles in this two-phase flow system. This feature is also thought to be favorable for storage security after CO2 injection.

Impact of Obstructive Sleep Apnea Syndrome in P300 Latency

Objective: Evaluate the impact and linear correlation between Obstructive Sleep Apnea Syndrome (OSAS) and P300 latency. It also aimed to identify which variables of polysomnography and scales of excessive daytime sleepiness best correlate with the increase in P300 latency. Method: This is a survey study, conducted between March 2010 and January 2011, in which polysomnography, scales of sleepiness and P300 latency from 54 patients were analyzed. These results were evaluated in patients with different stages of OSAS, using as independent variables: sleep stages, arousals, apnea/hyponea index(AHI), oxyhemoglobin desaturation and limb movements (PLM). Results: All patients were male, mean age 41.3 ± 2.1 years, body mass index of 29.3 ± 1.2 kg/m2 and hearing threshold in17.1 ± 1.3 dB. According to the AHI, the patients were divided into normal (n = 15), mild (n = 14), moderate (n = 9), and severely increased (n = 16). It was found the following correlations with P300 latency: Epworth scale (r = 0.33; P = .2), Karolinska scale (r=-0.14; P = .55), Stanford scale (r=0.01; P = .29), sleep efficiency (r = 0.11; P = .83), percentage of N3(r = -0.48; P = .24) and REM (r = -0.18; P = .13), arousals index (r=0.74; P &lt; .05), AHI (r = 0.99; P &lt; .01), oxyhemoglobin desaturation index (r = 0.99; P &lt; .01), PLM (r=0.44; P &lt; .01), mean oxyhemoglobin saturation (r = -0.84; P &lt; .01) and minimum oxyhemoglobin desaturation (r = -0.85; P &lt; .01). Conclusion: The apnea/hypopnea index, arousals, oxyhemoglobin desaturation index and periodic limb movements were positively correlated with P300 latency ( P &lt; .05). The average and minimum oxyhemoglobin saturation exhibited negative correlation with P300 latency ( P &lt; .01). No statistically significant correlation was seen between P300 latency and sleepiness scales, as well as REM and N3 sleep stage percentage.

Effects of magnesia addition on structural, morphological and magnetic properties of nano-crystalline nickel ferrite system

Nano-crystalline magnesia doped nickel ferrite powders have been synthesized by the combustion route. The structural, morphological and magnetic properties of the products were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy and vibrating sample magnetometer (VSM). X-ray analysis showed that all samples were cubic spinel. The increase in magnesia concentration resulted in a decrease in the average crystallite size, lattice constant, unit cell volume, X-ray density, ionic radii, the distance between the magnetic ions and bond lengths on tetrahedral sites and octahedral sites of the as prepared ferrite. The combustion method led to formation of spongy and fragile network structure. Increasing amounts of magnesia brought about remarkable changes in the microstructure and porosity of nickel ferrite. Doping of nickel ferrite by magnesia led to a decrease in its saturation magnetization. The minimum saturation magnetization value of nickel ferrite due to the doping 1 wt.% MgO attained 44.18 emu/g.

Effect of hyoid suspension with uvulopalatopharyngoplasty in the treatment of obstructive sleep apnea hypopnea syndrome

To discuss the methodology and therapeutic effect of hyoid suspension in association with uvulopalatopharyngoplasty (UPPP) in the treatment of severe obstructive sleep apnea hypopnea syndrome (OSAHS). Sixty-nine patients with severe OSAHS (apnea hyponea index, AHI > 30) were treated with hyoid suspension and UPPP. Sixty-one patients were followed for 6 months (48 of them for 12 months). Polysomnogram (PSG) tests were performed and an Epworth sleepiness scale (ESS) was recorded preoperatively and postoperatively in these patients. After the surgery,the snoring of the patients disappeared or was alleviated to varing degrees. Eighteen patients underwent fiberoptic nasopharyngolaryngoscopic examination. Twelve of them showed palatopharyngeal and glossopharyngeal stenosis was improved 6 months after surgery. Six patients showed no change, but had no glossoptosis. Fourteen patients underwent fiberoptic nasopharyngolaryngoscopic examination 1 year after surgery, with no recurrence of the stenosis being found. A decrease of 50% in the AHI was considered effective, and in patients the effective rate was 78.7% (48/61) 6 months after the operation and 75.0% (36/48) 1 year after the operation. The average AHI decreased from 44.8 to 15.1 and 17.2, and the minimum arterial oxygen saturation average increased from 0.512 to 0.880 and 0.730. Matching t tests were utilized and the results of follow-up indicated that there was a significant improvement in the indexes in those cases which could be followed up (P < 0.01). The average of the ESS was 6.7 six months after operation and 7.2 one year after operation, with a significant decrease compared to the preoperative (16.6) data (P < 0.01). Modified hyoid suspension in association with UPPP has the advantage of a simple operation, short hospitalization and less expense, and the effect of the operation was significant. Patients with palatopharyngeal and glossopharyngeal stenosis should be chosen for this operation.

The influence of summertime convection over Southeast Asia on water vapor in the tropical stratosphere

The relative contributions of Southeast Asian convective source regions during boreal summer to water vapor in the tropical stratosphere are examined using Lagrangian trajectories. Convective sources are identified using global observations of infrared brightness temperature at high space and time resolution, and water vapor transport is simulated using advection-condensation. Trajectory simulations are driven by three different reanalysis data sets, GMAO MERRA, ERA-Interim, and NCEP/NCAR, to establish points of consistency and evaluate the sensitivity of the results to differences in the underlying meteorological fields. All ensembles indicate that Southeast Asia is a prominent boreal summer source of tropospheric air to the tropical stratosphere. Three convective source domains are identified within Southeast Asia: the Bay of Bengal and South Asian subcontinent (MON), the South China and Philippine Seas (SCS), and the Tibetan Plateau and South Slope of the Himalayas (TIB). Water vapor transport into the stratosphere from these three domains exhibits systematic differences that are related to differences in the bulk characteristics of transport. We find air emanating from SCS to be driest, from MON slightly moister, and from TIB moistest. Analysis of pathways shows that air detrained from convection over TIB is most likely to bypass the region of minimum absolute saturation mixing ratio over the equatorial western Pacific; however, the impact of this bypass mechanism on mean water vapor in the tropical stratosphere at 68 hPa is small 0.1 ppmv). This result contrasts with previously published hypotheses, and it highlights the challenge of properly quantifying fluxes of atmospheric humidity.

Optimization of pulse train presaturation for CEST imaging in clinical scanners

Chemical exchange saturation transfer (CEST) imaging depends on the performance of radiofrequency saturation during the experiment. Scanner specifications, in particular limited pulse width and duty-cycle, and specific absorption rate guidelines restrict the full exploitation of CEST effects in clinical MR systems. The purpose of this study was to optimize techniques for effective pulse train presaturation for CEST imaging in a whole-body MR scanner. Theoretical analysis and simulations of the spectral properties of radiofrequency pulse trains demonstrated the significance of pulse width τ(P) and interpulse delay τ(D) for effective and selective labeling of a chemically exchanging proton pool. CEST experiments with model solutions, e.g., creatine dissolved in water, showed best performance of pulse trains with τ(P) = τ(D) = 100 msec, regarding minimum direct water saturation in z-spectra and distinct magnetization transfer ratio asymmetry that can be determined quantitatively. Saturation efficiency of trains of Gaussian-shaped radiofrequency pulses using this timing was evaluated in MR imagers with field strengths of 1.5, 3, and 7 T. The proposed saturation pulse train does not require hardware modifications, offers low specific absorption rate, and can be used in a standard clinical setup.

Successful termination of recurrent ventricular arrhythmias by adaptive servo-ventilation in a patient with heart failure

A 60-year-old woman who underwent operation due to severe aortic stenosis with left ventricular dysfunction had frequent nonsustained ventricular tachycardia (NSVT) at night. She had an increased apnea-hypopnea index and a reduction in minimum O2 saturation during sleep, which was closely associated with the frequency of NSVT. Adaptive servo-ventilation (ASV) therapy improved sleep disorder breathing (SDB) and also reduced ventricular arrhythmias. These effects were associated with the attenuation of the sympathetic nerve activities by the analysis of heart rate variability. ASV is expected to be effective in the treatment of ventricular tachyarrhythmias in patients with heart failure and SDB.

Impact of sensor characteristics on source characterization for dispersion modeling

An accidental or intentional release of hazardous chemical, biological, radiological, or nuclear material into the atmosphere obligates responsible agencies to model its transport and dispersion in order to mitigate the effects. This modeling requires input parameters that may not be known and must therefore be estimated from sensor measurements of the resulting concentration field. The genetic algorithm (GA) method used here has been successful at back-calculating not only these source characteristics but also the meteorological parameters necessary to predict the contaminants subsequent transport and dispersion. This study assesses the impact of sensor thresholds, i.e. the sensor minimum detection limit and saturation level, on the ability of the algorithm to back-calculate modeling variables. The sensitivity of the back-calculation to these sensor constraints is analyzed in the context of an identical twin approach, where the data is simulated using the same Gaussian Puff model that is used in the back-calculation algorithm in order to analyze sensitivity in a controlled environment. The solution is optimized by the GA and further tuned with the Nelder–Mead downhill simplex algorithm. For this back-calculation to be successful, it is important that the sensor capture the maximum concentrations.

Simultaneous Increase in Gas and Liquid Relative Permeabilities and Reduction of High-Velocity Coefficient From Wettability Alteration

Summary The alteration of the wettability from liquid-wetting to intermediate gas-wetting results in improved liquid mobility, which has been demonstrated by a number of authors in recent years. In this work, we show that the gas-phase mobility may either increase or decrease in the state of intermediate gas-wetting. The increase or decrease in the gas-phase mobility is a function of the minimum liquid saturation. We also confirm that, as a result of the wettability alteration, there may be a substantial decrease in the two-phase high-velocity coefficient compared to the unaltered wettability state. The increase in the gas- and liquid-phase relative permeabilities and a decrease in the high-velocity coefficient of the two-phase flow from the wettability alteration contribute to improved gas well productivity.

Three-dimensional numerical simulation of fluid flow with phase change heat transfer in an asymmetrically heated porous channel

Fluid flow with phase change heat transfer in a three-dimensional porous channel with asymmetrically heating from one side is numerically studied in this paper. The “modified” Kirchhoff method is used to deal with the spatial discontinuity in the thermal diffusion coefficient in the energy equation. The velocity and temperature fields, as well as the liquid saturation field on the heated section of the wall with different Peclet and Rayleigh numbers are investigated. The results show that the liquid flow bypasses the two-phase zone, while the vapor flows primarily to the interface between the sub-cooled liquid zone and the two-phase zone. An increase in the Peclet number decreases the two-phase region while an increase in the Rayleigh number helps to spread the heat to a larger region of the domain. The distribution of the liquid saturation on the heated section of the wall indicates that the minimum liquid saturation increases with the increase of both the Peclet and Rayleigh numbers.

Transient behavior of fluid flow and heat transfer with phase change in vertical porous channels

The transient behavior of flow boiling in vertical porous channels is numerically studied in this paper. The velocity and temperature fields under different parameters for both aiding and opposing flows are investigated. Distinctly different flow and heat transfer features are observed in the comparison of aiding and opposing flows. An analysis of liquid saturation along the heated wall indicates that the minimum liquid saturation for aiding flow is located at the tail of the heated section, whereas for opposing flow, it is within the heated section and shifts upstream with the increase of Rayleigh number and decrease of Peclet number.

Variability of Pulse Signal Frequency Obtained Using Nocturnal Pulse Oximetry in Patients with Sleep Apnoea/Hypoapnoea Syndrome

IntroductionThe measurement of central tendency (MCT) is a non-linear analysis technique which applied to second order differences diagrams enables the degree of variability to be quantified in a data series. In the present study an attempt is made to quantify and characterise the changes in heart rate obtained by pulse oximetry in patients with a clinical suspicion of sleep apnoea/hypoapnoea syndrome (SAHS) using the MCT and to evaluate its diagnostic use. Patients and MethodsA total of 187 patients were included in the study, on whom a nocturnal polysomnographic and pulse oximetry study was performed. To evaluate the variability of the heart rate the MCT applied to graphs of second order differences obtained from the heart rate record. ResultPatients with SAHS had a higher heart rate variablity than patients without SAHS (0.449 vs 0.666, P<.001). In the multivariate analysis, the heart rate, the minimum saturation and the desaturation index of 4% were independently associated with the heart rate variability. As a diagnostic method, the MCT of the heart rate gives a sensitivity of 69.3%, a specificity of 77.6% and a diagnostic precision of 72.7%. ConclusionsPatients with SAHS have a greater variabilityin heart rate during the night, evaluated by applying the MCT of the heart rate to diagrams of second order differences. As a screening method, the MCT applied to the heart rate has a moderate sensitivity and specificity.