Ambient Barometric Pressure Research Articles

Barometric Pressure at High Altitude: Revisiting West's Prediction Equation, and More.

Apte, Chandrashekhar V. Barometric pressure at high altitude: revisiting West's prediction equation, and more. High Alt Med Biol. 24:85-93, 2023. Introduction: Since an earlier prediction equation to calculate barometric pressure at a given altitude had been tested against limited barometric pressure observations, its accuracy needed to be re-validated against additional pressure observations. Methods: Five-year (2016-2020) barometric pressure and altitude data were downloaded from an open-source website for 25 select locations. The calculated predicted pressure was compared with mean 5-year, mean monthly, and mean daily pressures. Percent prediction error and root mean square errors were used to assess accuracy of the prediction equation. Results: The original prediction equation was accurate to within 1% for locations only within 22° latitude. It was increasingly inaccurate at higher latitudes and also for means based on shorter time spans (e.g., mean monthly and daily pressures). A new prediction equation was proposed by developing a model using downloaded data. The new equation resulted in more accurate predictions for all latitudes and all time spans. The new equation also performed well when tested at seven new locations. Conclusions: Ideally, medical professionals at high altitude should rely on actual barometric pressure observations to assess hypoxic risk. In the absence of actual measurements, the suggested new prediction equation may be used to estimate, with some limitations, the ambient barometric pressure at latitudes below 47° and altitudes up to about 4,700 m.

Radon concentrations in the Sudwala cave, South Africa

There has been a growing interest in the effect of radon gas on humans visiting caves. A radon survey was consequently done in the Sudwala tourist cave close to Nelspruit in the eastern part of South Africa to determine the radon exposure of tourists and guides. The Sudwala cave, which evolved in karst geology, is a popular tourist destination. Twenty-eight electret ion chambers were placed in various locations throughout the cave for a period of 24 h. Radon concentrations varied between a minimum of 255 Bq/m3 and a maximum of 1822 Bq/m3 with a geometric mean of 750 Bq/m3. The radon levels were found to be relatively stable up to 600 m from the entrance, after which they sharply increased. This suggests that different processes disperse radon in the initial and deeper parts of the cave. It was concluded that this is the result of natural cave ventilation which is caused by changes in ambient barometric pressure. Despite the measured level being higher than the World Health Organization (WHO)’s mitigation level of 200 Bq/m3, the occupational exposure is quite low due to the frequency and duration of a typical cave tour and therefore poses no risk to the tourists and tour guides.

The Influence of CO2 Injection into Manure as a Pretreatment Method for Increased Biogas Production

Manure is considered a by-product or organic waste in cattle, pig, chicken or other animal breeding farms, which can be a valuable product as compost or feedstock for biogas production. The production of biomethane from biogas always copes with the formation of carbon dioxide (CO2) as a by-product. This CO2 may be recycled through the feedstock as a pretreatment to maximize homogeneity, and improve biogas yield and biogas quality. The CO2-pretreatment process of cow manure (CoM), chicken manure (ChM) and pig manure (PM) was performed in the continuously fed agitated reactor at 25 °C temperature and ambient barometric pressure. Biogas yield and composition exploration were performed in an anaerobic continuous feeding digester with controlled mesophilic (37 °C) environmental conditions. The CO2 pretreated PM, CoM and ChM yielded 234.62 ± 10.93 L/kgVS, 82.01 ± 3.19 L/kgVS and 374.53 ± 9.27 L/kgVS biomethane from feedstock volatile solids, respectively. The biomethane yield from CO2 pretreated CoM, ChM and PM achieved was higher over untreated manure by +33.78%, +28.76% and +21.78%, respectively. The anaerobic digestion process of tested feedstocks was stable, and the pH of the substrate was kept steady at a pH of CoM 7.77 ± 0.02, PM 8.07 ± 0.02 and ChM 8.09 ± 0.02 during all the experiment. The oxidation-reduction potential after pretreatment was within the optimal range (−255 ± 39.0 to −391 ± 16.8 mV) for anaerobic digestion. This process also had a positive effect on the energy generated from the feedstock, with ChM showing the greatest increase, from 2.38 MJ/kg to 3.06 MJ/kg.

A Practical Hybrid Height Estimation Algorithm Based on FM-Aided Motion Mode Recognition

Height estimation is critical for precise indoor localization in multistorey buildings. Traditionally, it is achieved by the barometric altimetry (BA)-based method, whose accuracy suffers from ambient barometric pressure fluctuations. Zero-velocity-update (ZUPT)-aided acceleration integration is another applicable approach, where zero velocity moments are introduced as calibration reference to limit error accumulation. However, zero velocity moments are derived from foot-mounted sensors in the stairs-climbing scenario, making it unavailable for other sensor locations and scenarios such as elevators. In this article, we propose a hybrid height estimation algorithm with both high accuracy and improved practicability. With the assistance of motion mode recognition (MMR), we apply a constraint on height estimations from both the BA-based method and the integration-based method, and then produce our height estimation by fusing the constraint heights. First, four typical motion modes comprising standing still, plane walking, climbing stairs, and taking elevator are recognized with features from acceleration, barometric pressure, and frequency-modulated (FM) signal. Second, we constrain the height estimations based on MMR results. To improve the BA-based method, a reference pressure update strategy is proposed to make the method applicable in an environment without reference barometers. Besides, the step-based integration strategy and the reverse compensation strategy are designed to optimize integration-based heights in stairs and elevators scenarios, respectively. Finally, the height estimations from these two sources are fused adaptively. Experiment results show that the accuracy of the proposed hybrid method outperforms that of the BA-based method. Moreover, the introduction of FM signal features effectively improves the performance of MMR and, thus, height estimation.

Influence of environmental parameter variations on X-ray beam intensities: a time-dependent absorption correction

Essential to the quality of X-ray analysis in crystallography, such as diffractometry and spectrometry, is a stable and reproducible X-ray source. Commonly, different optical elements are utilized to provide a dedicated X-ray beam. The stable alignment of all these components is a prerequisite in order to reduce aberrations and to achieve high signal-to-noise ratios. Besides such aberrations and electronically induced variations of the X-ray primary beam intensity, the environmental conditions are of particular importance, most prominently the barometric pressure, humidity and temperature. In a qualitative as well as quantitative study, the influence of the environmental conditions on the primary beam intensity of a sealed tube with a Cu anode and their correlations are determined. For a common setup, utilizing a scintillation counter, laboratory as well as external conditions are monitored simultaneously for 28 d. Their individual influence on the X-ray intensity and their correlations are evaluated by statistical analysis including time lag. By this comprehensive study, experimental intensity variations of up to ΔI/I= 1.153 ± 0.001% are determined during density of air changes of Δρ/ρ = 3.7 ± 0.6%. This is interpreted in terms of air transmission variations of up toTX-ray= 1.137 ± 0.001% for a typical X-ray analysis setup due to ambient barometric pressure, temperature and humidity changes for natural mid- and long-term variations. Significant correlations with respect to daily and weekly cycles and in particular with ambient conditions are determined. These results are used for a time-dependent absorption correction of the measured intensity, which reduces the standard error by about 25%.

Effect of ambient pressure variation on closed loop gas system for India based Neutrino Observatory (INO)

Pilot unit of a closed loop gas mixing and distribution system for the INO project was designed and is being operated with 1.8meters × 1.9meters RPCs for about two years. A number of studies on controlling the flow and optimisation of the gas mixture through the RPC stack were carried out during this period. The gas system essentially measures and attempts to maintain absolute pressure inside the RPC gas volume. During typical Mumbai monsoon seasons, the barometric pressure changes rather rapidly, due to which the gas system fails to maintain the set differential pressure between the ambience and the RPC gas volume. As the safety bubblers on the RPC gas input lines are set to work on fixed pressure differentials, the ambient pressure changes lead to either venting out and thus wasting gas through safety bubblers or over pressuring the RPCs gas volume and thus degrading its performance. The above problem also leads to gas mixture contamination through minute leaks in gas gap.The problem stated above was solved by including the ambient barometric pressure as an input parameter in the closed loop. Using this, it is now possible to maintain any set differential pressure between the ambience and RPC gas volumes between 0 to 20mm of water column, thus always ensuring a positive pressure inside the RPC gas volume with respect to the ambience. This has resulted in improved performance of the gas system by maintaining the constant gas flow and reducing the gas toping up frequency.In this paper, we will highlight the design features and improvements of the closed loop gas system. We will present some of the performance studies and considerations for scaling up the system to be used with the engineering module and then followed by Iron Calorimeter detector (ICAL), which is designed to deploy about 30,000 RPCs of 1.8meters × 1.9 meters in area.

Air Travel and Pneumothorax

The number of medical emergencies onboard aircraft is increasing as commercial air traffic increases and the general population ages, becomes more mobile, and includes individuals with serious medical conditions. Travelers with respiratory diseases are at particular risk for in-flight events because exposure to lower atmospheric pressure in a pressurized cabin at cruising altitude may result in not only hypoxemia but also pneumothorax due to gas expansion within enclosed pulmonary parenchymal spaces based on Boyle's law. Risks of pneumothorax during air travel pertain particularly to those patients with cystic lung diseases, recent pneumothorax or thoracic surgery, and chronic pneumothorax. Currently available guidelines are admittedly based on sparse data and include recommendations to delay air travel for 1 to 3 weeks after thoracic surgery or resolution of the pneumothorax. One of these guidelines declares existing pneumothorax to be an absolute contraindication to air travel although there are reports of uneventful air travel for those with chronic stable pneumothorax. In this article, we review the available data regarding pneumothorax and air travel that consist mostly of case reports and retrospective surveys. There is clearly a need for additional data that will inform decisions regarding air travel for patients at risk for pneumothorax, including those with recent thoracic surgery and transthoracic needle biopsy.

Efficient Fluorescence “Turn-On” Sensing of Dissolved Oxygen by Electrochemical Switching

We report on a novel method for sensing oxygen that is based on the use of a perylene diimide dye (1) which is electrochemically reduced to its nonfluorescent dianion form (1(2-)). In the presence of oxygen, the dianion is oxidized to its initial form via an electron-transfer reaction with oxygen upon which fluorescence is recovered. As a result, the fluorescence intensity of the dianion solution increases upon the addition of oxygen gas. Results demonstrate that high sensitivity is obtained, and the emission intensity shows a linear correlation with oxygen content (0.0-4.0% v/v) at ambient barometric pressure. In addition, using electrochemical reduction, oxygen determination becomes regenerative, and no significant degradation is observed over several turnovers. The limit of detection is 0.4% oxygen in argon gas.

Control of breathing and blood pressure by parafacial neurons in conscious rats

The retrotrapezoid nucleus (RTN), located in the parafacial region, contains glutamatergic neurons that express the transcriptor factor Phox2b and that are suggested to be central respiratory chemoreceptors. Studies in anaesthetized animals or in vitro have suggested that RTN neurons are important in the control of breathing by influencing respiratory rate, inspiratory amplitude and active expiration. However, the contribution of these neurons to cardiorespiratory control in conscious rats is not clear. Male Holtzman rats (280-300 g, n = 6-8) with bilateral stainless-steel cannulae implanted into the RTN were used. In conscious rats, the microinjection of the ionotropic glutamatergic agonist NMDA (5 pmol in 50 nl) into the RTN increased respiratory frequency (by 42%), tidal volume (by 21%), ventilation (by 68%), peak expiratory flow (by 24%) and mean arterial pressure (MAP, increased by 16 ± 4, versus saline, 3 ± 2 mmHg). Bilateral inhibition of the RTN neurons with the GABA(A) agonist muscimol (100 pmol in 50 nl) reduced resting ventilation (52 ± 34, versus saline, 250 ± 56 ml min(-1) kg(-1) with absolute values) and attenuated the respiratory response to hypercapnia and hypoxia. Muscimol injected into the RTN slightly reduced resting MAP (decreased by 13 ± 7, versus saline, increased by 3 ± 2 mmHg), without changing the effects of hypercapnia or hypoxia on MAP and heart rate. The results suggest that RTN neurons activate facilitatory mechanisms important to the control of ventilation in resting, hypoxic or hypercapnic conditions in conscious rats.

An Automated Data Logger for Simultaneously Recording Amphibian Vocalizations with Weather Variables

Understanding the environmental triggers for the calling behaviour of fauna is an important element of biological and ecological knowledge necessary for devising better monitoring and management strategies for wildlife. Amphibians calling is seasonal and in Australia, mostly limited to Spring-Summer (October-March). An investigation was instigated following numerous records of the Sphagnum Frog Philoria sphagnicola calling during periods outside (July) of the standard survey season (August-December). In response to this observation, a data logger was designed and programmed to detect only the calls of P. sphagnicola. At hourly intervals, the data logger recorded the number of frog calls, mean ambient temperature, relative humidity, rainfall, water temperature and barometric pressure. This device differs from data loggers used in other anuran studies in its capacity to record only those calls of the species that it is programmed to detect. Furthermore, the data logger simultaneously records vital environmental variables that are important in trying to decipher the single or multiple factors that may stimulate calling behaviour.

Response to Hemmingsson, Horn and Linnarsson article “Measuring Exhaled Nitric Oxide at High Altitude” Resp. Physiol. Neurobiol. 167(3), 292–298

The Hemmingsson, Horn and Linnarsson article (Hemmingsson et al., 2009) Measuring Exhaled Nitric Oxide at High Altitude highlights methodological and technical considerations for data collection and interpretation of exhaled nitric oxide (NO) (ATS/ERS, 2005) at high altitude. The discussion centers on technical issues with analyzers used to measure NO using the online technique for FeNO (fraction of exhaled nitric oxide) and comparing FeNO at sea level to results obtained at various altitudes. The data suggest that Aerocrine NO analyzers performance characteristics vary from sea level to high altitude (ambient barometric pressure was varied using a hyperbaric chamber) as a result of the change in barometric pressure and this in turn affects the internal mass flow controller accuracy in adapting to the pressure changes (Hemmingsson et al., 2009). Hemmingsson et al. discuss our published measures of NO at altitude in the context of correct and incorrect methodology. However, the technical issues addressed in the Hemmingsson article do not pertain to: (i) The GE Analytical Instruments Sievers NOA 280 (Boulder, CO) that was used in our studies and which was available years prior to the Aerocrine system (Duplain et al., 2000) or; (ii) the technique that we used for measurement of exhaled NO (Beall et al., 2001; Dweik et al., 2001; Brown et al., 2006). Since the development and FDA-approval of the Aerocrine device for clinical use, it has become readily available for research. Hemmingsson et al. raise valid cautionary points regarding the Aerocrine system; however our findings using the GE NO analyzer at altitude are not impacted by their findings (Duplain et al., 2000).

Physiology and pathophysiology at high altitude: considerations for the anesthesiologist

Millions of people live in, work in, and travel to areas of high altitude (HA). Skiers, trekkers, and mountaineers reach altitudes of 2500 m to more than 8000 m for recreation, and sudden ascents to high altitude without the benefits of acclimatization are increasingly common. HA significantly affects the human body, especially the cardiovascular and pulmonary systems, because of oxygen deprivation due to decreased ambient barometric pressure. Rapid ascents may lead to high-altitude diseases that sometimes have fatal consequences. Other factors, such as severe cold, dehydration, high winds, and intense solar radiation, increase the morbidity of patients at HA. Anesthesiologists working in or visiting areas of higher elevations should become familiar with the human physiology, altered pharmacology, and disease pattern of HA.

Obesity Exacerbates the Development of Hypoxia‐induced Pulmonary Hypertension

Obesity is a known risk factor for cardiovascular disease, insulin resistance and premature death. Recent observations from examining past medical records suggest that obesity may be a risk factor for the development of severe pulmonary hypertension. Therefore, we hypothesized that hypoxic pulmonary hypertension (PH) would be exacerbated in the Zucker obese vs. the Zucker lean rats. Methods: Male, age matched (8–10 wk) obese (547 ± 17 g) and lean (345 ± 11g) Zucker rats were exposed to either chronic hypoxia (3 wk; 18,000 ft; PB ~ 379 mm Hg;) or remained at ambient barometric pressure (5,280 ft; PB ~ 620 mm Hg). After wards, cardiac output (CO), mean pulmonary artery (Pa) and mean systemic pressures (MAP) and hemotocrit (Hct) were recorded. Following hemodynamic measurements, rats were euthanized, the lungs perfused with paraformaldehyde (PFA), dissected free of the heart and embedded in paraffin for histological analyses. The heart was removed, the right ventricle (RV) was dissected free from the left ventricle + septum (LV+S) and RV/LV+S ratio was determined as a further indication of the severity of PH. Results: Chronic hypoxia exposure increased Pa pressure, RV/ LV+S and Hct in all rats (P<0.001; P<0.01 and <0.001 vs. normoxia respectively). The Pa pressure, RV/LV+S were 37 ± 10%, 30 ± 12% and 18 ± 3% greater in the Zucker obese rats vs. Zucker lean cohorts (P=0.023; P=0.026 and P<0.01 respectively). Histological analyses revealed increased pulmonary remodeling in the obese vs. lean hypoxic rats. Conclusion: We conclude that obesity exacerbates hypoxia-induced mean Pa pressure, right ventricular hypertrophy and pulmonary vascular remodeling.

Renin Enhancer Is Critical for Control of Renin Gene Expression and Cardiovascular Function

Renin Enhancer Is Critical for Control of Renin Gene Expression and Cardiovascular Function

Variation in barometric pressure in Melbourne does not significantly affect the BTPS correction factor.

The conventional BTPS (body temperature and pressure, saturated with water vapour) correction factor varies with ambient barometric pressure (P(B)) and many lung function laboratories measure P(B) daily. The aim was to investigate whether a fixed value for P(B) could replace daily measurements. P(B) was measured daily over a 12-month period. The highest and lowest values in Melbourne in the last century were also recorded from data published by the Bureau of Meteorology. Using these P(B) values, the BTPS factor was determined for a range of spirometer temperatures and compared to the BTPS factors obtained using a fixed ambient pressure of 101.3 kPa. The mean (SD) P(B) measured over the 12-month period was 102.2 kPa (0.64) with a range of 99.9-103.6 kPa. The level of disagreement between the BTPS factor calculated using a P(B) of 101.3 kPa instead of the measured value was greater at lower temperatures. Over the extremes of P(B) during the last century (98.0-104.3 kPa) the use of a standard pressure (101.3 kPa) produced an error in the BTPS factor of </= 0.16%. Daily variations in P(B) do not significantly affect the magnitude of the conventional BTPS correction factor and a fixed value, such as 101.3 kPa at sea level, can be used with little error.

Parameters affecting maximum fluid transport in large aperture fractures

We present results of laboratory experiments to study the behavior of liquids moving in unsaturated wide-aperture fractures. A 5-mm-thick glass plate cut with a ∼1.7-mm aperture was used as a fractured rock analog to study behavior of film and capillary droplet flow modes. Flow rates ranged between 0.6 and 6.0 ml/min. Variability in the ambient barometric pressure, resulting from weather conditions, seemed to play a role in the natural selection of flow mode. For droplet mode, constant input conditions resulted in highly variable transport properties within the fracture. The advancing meniscus exhibited a dynamic contact angle that was a function of the droplet speed and much larger than the static contact angle. Flow rate was reduced due to the larger contact angle. Analytical expressions for droplet velocity and flow capacity are presented as a function of the dynamic rather than the static contact angle.

Lack of Effect of Rhodiola or Oxygenated Water Supplementation on Hypoxemia and Oxidative Stress

This study investigated the effects of 2 potentially "oxygen promoting" dietary supplements on hypoxia and oxidative stress at a simulated altitude of 4600 m. Fifteen volunteers (ages 20-33) received 3 separate 60-minute hypoxic exposures by breathing 13.6% oxygen at an ambient barometric pressure of 633 mm Hg (simulating the partial pressure of oxygen at 4600 m elevation). Each subject received, in random order, treatments of a 7-day supply of placebo, Rhodiola rosea, and an acute dose of stabilized oxygen dissolved in water. Arterialized capillary blood oxygen samples (PcO2) were measured at baseline and at 30 and 60 minutes of exposure. Pulse oximeter oxyhemoglobin saturation (SaO2) was measured at baseline and at every 10 minutes of hypoxic exposure. Oxidative stress markers measured included baseline and 60-minute exposure serum lipid peroxides (LPO) and urine malondialdehyde (MDA). For each treatment group, PcO2 decreased by approximately 38% from baseline to 60-minute hypoxic exposure. Similarly, SaO2 also decreased among groups from approximately 97 to 81%. Serum lipid peroxides increased significantly in the placebo group and decreased significantly from baseline in response to the stabilized oxygen treatment (P = .02); there was a trend for decreased LPO with the Rhodiola treatment (P = .10). There were no significant changes for MDA among groups. The 2 dietary supplements investigated did not have a significant effect on blood oxygenation after 60 minutes of sedentary hypoxic exposure. Hypoxia-induced oxidative stress was observed in the control group only. Both supplements appeared not to increase oxidative stress and may decrease free radical formation after hypoxic exposure compared with the control.

Daytime blood pressure elevation after nocturnal hypoxia.

The purpose of this study was to investigate whether nocturnal hypoxia causes daytime blood pressure (BP) elevation. We hypothesized that overnight exposure to hypoxia leads the next morning to elevation in BP that outlasts the hypoxia stimulus. We studied the effect on BP of two consecutive night exposures to hypobaric hypoxia in 10 healthy normotensive subjects. During the hypoxia nights, subjects slept for 8 h in a hypobaric chamber at a simulated altitude of 4,000 m (barometric pressure = 462 mmHg). Arterial O(2) saturation and electrocardiogram were monitored throughout the night. For 30 min before the nocturnal simulated ascent and for 4 h after return to baseline altitude the next morning, BP was measured every 5 min while the subject was awake. The same measurements were made before and after 2 normoxic nights of sleep in the hypobaric chamber at ambient barometric pressure (745 mmHg). Principal components analysis was applied to evaluate patterns of BP response after the second night of hypoxia and normoxia. A distinct pattern of diastolic BP (DBP) elevation was observed after the hypoxia night in 9 of the 10 subjects but in none after the normoxia night. This pattern showed a mean increase of 4 mmHg in DBP compared with the presleep-awake baseline in the first 60 min and a return to baseline by 90 min. We conclude that nocturnal hypoxia leads to a carryover elevation of daytime DBP.

This Month in the Journal

This Month in the Journal

Exercise training mode affects the hemodynamic responses to lower body negative pressure in women.

To determine if different exercise modes used to improve cardiovascular fitness result in differing cardiovascular responses to lower body negative pressure (LBNP) in exercise-trained women, seven chronically exercising female runners (RUN) and 11 swimmers (SWIM) of similar fitness levels maximal oxygen uptake, [VO(2max), mean (SEM) = 50 (2) and 45 (2) ml*kg(-1)*min(-1), respectively; P > 0.05] underwent serial exposures to LBNP at pressures of 0, -1.3, -2.7 and -5.3 kPa (referenced to ambient barometric pressure). Forearm vascular resistance (venous occlusion plethysmography) increased with LBNP but did not differ between groups at any level of LBNP. At 0 and - 1.3 kPa, the total peripheral resistance index (TPRI; impedance cardiography) was significantly (P <0.05) higher in RUN than SWIM [1.118(0.028) vs 0.787 (0.040) at 0 kPa and 1.245 (0.100) vs 0.840 (0.040) 2 kPa*l* min(-1)*m(-2) at -1.3kPa]. At an LBNP of -2.7kPa, stroke index (SI) was significantly higher in SWIM than RUN [57.8(4.6) vs 41.9 (4.0) ml*beat(-1)*m(-2)] while TPRI remained greater in RUN than SWIM. At -5.3 kPa, SWIM exhibited a higher cardiac index [3.232 (0.209) vs 2.447 (0.189) l*min(-1)*m(-2)] and SI [49.4 (4.4) vs 31.0 (4.5) ml *beat(-1)*m(-2)] but reduced heart rate [71(3) vs 83(5) beats . min(-1)] and TPRI [0.968 (0.043) vs 1.655 (0.128) kPa*1*min(-1)* m(-2)]. Mean arterial pressure declined significantly at an LBNP of -5.3 kPa in both groups; pulse pressure was lower (P <0.05) in RUN than SWIM at LBNP values of -2.7 and -5.3 kPa. These data suggest that: (1) female runners experience a greater increase in systemic vasoconstriction even though female swimmers can better maintain their cardiac index at high levels of LBNP, and (2) training mode appears to affect the pulse pressure responses to LBNP in exercise-trained women.