Despite being a prognostic predictor, cardiac autonomic dysfunction (AD) has not been well investigated in chronic obstructive pulmonary disease (COPD). We aimed to characterise computed tomography ...(CT), spirometry, and cardiopulmonary exercise test (CPET) features of COPD patients with cardiac AD and the association of AD with CT-derived vascular and CPET-derived ventilatory efficiency metrics.
This observational cohort study included stable, non-severe COPD patients. They underwent clinical evaluation, spirometry, CPET, and CT. Cardiac AD was determined based on abnormal heart rate responses to exercise, including chronotropic incompetence (CI) or delayed heart rate recovery (HRR) during CPET.
We included 49 patients with FEV1 of 1.2-5.0 L (51.1-129.7%), 24 (49%) had CI, and 15 (31%) had delayed HRR. According to multivariate analyses, CI was independently related to reduced vascular volume (VV; VV ≤ median; OR 95% CI, 7.26 1.56-33.91) and low ventilatory efficiency (nadir VE/VCO2 ≥ median; OR 95% CI, 10.67 2.23-51.05). Similar results were observed for delayed HRR (VV ≤ median; OR 95% CI, 11.46 2.03-64.89, nadir VE/VCO2 ≥ median; OR 95% CI, 6.36 1.18-34.42).
Cardiac AD is associated with impaired pulmonary vascular volume and ventilatory efficiency. This suggests that lung blood perfusion abnormalities may occur in these patients. Further confirmation is required in a large population-based cohort.
This open access book systematically summarizes the current research progress of attachment ventilation, covering vertical wall attachment, column attachment, and adaptive attachment ventilation. ...Attachment ventilation is a high-performance ventilation mode that was first proposed by the author, Prof. Angui Li 20 years ago. Now it has been widely used in office spaces, subway stations, high-speed railway stations, international airport terminals, and other large spaces. This book introduces attachment ventilation in detail to eliminate the cooling/heating load of the occupied zone and provide an expected environment for the air-conditioned zone. Attachment ventilation combines the advantages of traditional mixed ventilation and displacement ventilation. This book consists of six chapters, covering a series of airflow patterns, mechanisms, parameter correlations, and attachment ventilation design methods. It is helpful for HVAC engineers to design attachment ventilation effectively.
The mechanism of structure formation of non-uniform pollutant concentration distributions in indoor environments have been investigated over the past several decades to determine effective ...ventilation designs. In this study, numerical analyses of local pollutant concentration distributions in indoor environments are performed based on computational fluid dynamics techniques. In particular, the influence of gas phase chemical reactions and turbulent diffusion on the formation of the local pollutant concentration is parametrically analyzed, and the structures are quantitatively investigated using the index for ventilation efficiency, namely the net escape velocity (NEV) concept. The NEV concept represents the substantive velocity scale, combining advection and diffusion velocity of pollutant at a point, and functions as an index to determine the pollutant concentration at that point. Sensitivity analyses as functions of the first Damköhler number (Da) and the turbulent Schmidt number (Sct) were performed, and the influence of Sct on pollutant concentration distributions was more significant compared with that of Da. When Sct was changed from 0.5 to 1.0, the significant NEV increase, especially that in the stagnant flow region, could be attributed to the enhanced pollutant discharge efficiency due to turbulent diffusion in addition to convective flow. Thus, NEV could be used to quantitatively assess the changes in pollutant concentrations accompanying the change in Da or Sct.
•The definition of net escape velocity has been extended to incorporate chemical reaction terms.•Net escape velocity at a point was changed up to 32% when the turbulent Shumidt number varied from 0.5 to 1.0.•Net escape velocity demonstrated no sensitivity about the change in Damköhler number from 1×10-5 to 1×10-2.•Turbulent diffusion has a significant impact on the local pollutant concentration in contrast to gas-phase chemical reactions.
This book contains twenty-one original papers and one review paper published by internationally recognized experts in the Atmosphere Special Issue "Recent Advances in Urban Ventilation Assessment and ...Flow Modelling", years 2017–2019. The Special Issue includes contributions on recent experimental and modelling works, techniques, and developments mainly tailored to the assessment of urban ventilation on flow and pollutant dispersion in cities. The study of ventilation is of critical importance, as it addresses the capacity with which a built urban structure is capable of replacing the polluted air with ambient fresh air. Here, ventilation is recognized as a transport process that improves local microclimate and air quality and closely relates to the term “breathability”. The efficiency with which street canyon ventilation occurs depends on the complex interaction between the atmospheric boundary layer flow and the local urban morphology.The individual contributions to this Issue are summarized and categorized into four broad topics: (1) outdoor ventilation efficiency and application/development of ventilation indices, (2) relationship between indoor and outdoor ventilation, (3) effects of urban morphology and obstacles to ventilation, and (4) ventilation modelling in realistic urban districts. The results and approaches presented and proposed will be of great interest to experimentalists and modelers, and may constitute a starting point for the improvement of numerical simulations of flow and pollutant dispersion in the urban environment, for the development of simulation tools, and for the implementation of mitigation strategies.
Wind corridors are expected to be effective in alleviating the canopy urban heat island effect and air pollution. However, investigations on airflow characteristics within wind corridors, especially ...the influences of structural factors, are still limited. This current work performed numerical simulations on a group of idealised wind corridor models with different aspect ratios (ARs) and varying heights and/or widths along the corridors. Simulations revealed that the AR value had a vital influence on the wind speed, and an AR value of 0.1 facilitated the best ventilation conditions within the wind corridor. Structural variations along the corridor have a critical influence on ventilation, where the width contraction (contraction structure) and high-rise buildings (protrusion structure) would considerably weaken the wind speed within the corridors. The results suggested that wider and step-up structural design along the corridor should be encouraged in urban wind corridor planning, which would be helpful in promoting ventilation efficiency; but contraction structures should be prevented for primary wind corridor design.
In this study, confluent jets ventilation (CJV) supply devices with three different nozzle arrays (1 × 19, 2 × 19, 3 × 19) were investigated both numerically and experimentally at two different ...airflow and supply air temperature set-ups. The performance of the CJV supply devices was investigated concerning thermal comfort, indoor air quality (IAQ), and heat removal effectiveness in a conference room environment. A comparison between the experimental and numerical results showed that the ϑ2¯−f model had the best agreement out of the investigated turbulence models. The numerical results showed that the size of the array had a great impact both on near-field development and on the conditions in the occupied zone. A larger array with multiple rows and a lower momentum conserved the inlet temperature and the mean age of the air better than a single-row array with a higher momentum. A larger array with multiple rows had a higher IAQ and a greater heat removal effectiveness in the occupied zone because the larger array conserved the mean age of air better and the buoyancy driven flow was slightly better at removing the heat. Because of the lower inlet velocities, they also had lower velocities at ankle level, which decreased the risk of draft and thermal discomfort.
The aim of this study was to compare ventilation performance of four different air supply devices in an office environment with respect to thermal comfort, ventilation efficiency and energy-saving ...potential, by performing numerical simulations. The devices have the acronyms: Mixing supply device (MSD), Wall confluent jets supply device (WCJSD), Impinging jet supply device (IJSD) and Displacement supply device (DSD). Comparisons were made under identical set-up conditions, as well as at the same occupied zone temperature of about 24.2 °C achieved by adding different heat loads and using different air-flow rates. Energy-saving potential was addressed based on the air-flow rate and the related fan power required for obtaining a similar occupied zone temperature for each device.
Results showed that the WCJSD and IJSD could provide an acceptable thermal environment while removing excess heat more efficiently than the MSD, as it combined the positive effects of both mixing and stratification principles. This benefit also meant that this devices required less fan power than the MSD for obtaining equivalent occupant zone temperature. The DSD showed a superior performance on heat removal, air exchange efficiency and energy saving to all other devices, but it had difficulties in providing acceptable vertical temperature gradient between the ankle and neck levels for a standing person.
•Ventilation performance of four different air supply devices in an office environment is studied.•The wall confluent jets and impinging jet supply devices behave like a combined mixing and displacement system.•The wall confluent jets and impinging jet supply devices provide a good indoor environment and save energy.•The displacement supply device provides the highest ventilation efficiency but have problems with local discomfort.
This paper aims to numerically evaluate the effects of building arrangements on average ventilation efficiency in newly-built residential areas at pedestrian level. It proposes a practical design ...parameter as a practical guide for urban ventilation design. A reference urban model was designed according to a typical residential area in Shanghai. Other urban models with constant floor area ratio and various urban building arrangements with various building coverage ratios, passage widths, building arrays and building height variations were considered. The ventilation efficiency was evaluated by spatially-averaged wind speed ratio, spatially-averaged normalized concentration, and visitation frequency. Flow flux analysis was conducted to explain the ventilation mechanism and the relationships among ventilation efficiency indices. The results showed that small building coverage ratios and large passage widths resulted in higher ventilation efficiency in most cases. The staggered array showed better ventilation efficiency than the aligned array when the wind direction was 0° and 45° and the advantage of building height variation was distinct in the densest case for 90°. A general relationship was found among the three indices: a large spatially-averaged wind speed ratio and a low visitation frequency resulted in a low spatially-averaged normalized concentration, although there were a few exceptions. A practical design parameter (passage ratio) for urban ventilation was proposed based on the calculation results.
► Keeping total residential capacity constant, newly-built urban models are designed. ► Urban parameters (BCR, passage width, building array and height variation) are varied. ► Ventilation efficiency reflected by ventilation indices are evaluated by CFD analysis. ► Relationships among ventilation indices are studied and C* is found to be core index. ► Passage ratio was proposed as a parameter for practical ventilation design.
To examine the correlation DCO
2
/PaCO
2
on high-frequency oscillatory ventilation (HFOV) combined with volume guarantee (VG) throughout increasing frequencies in two different respiratory ...conditions, physiological and low compliance. Neonatal animal model was used, before and after a bronchoalveolar lavage (BAL). HFOV combined with VG was used. The frequency was increased from 10 to 20 Hz, and high-frequency tidal volume (VThf) was gradually decreased maintaining a constant DCO
2
. Arterial partial pressure of carbon dioxide (PaCO
2
) was evaluated after each frequency and VThf change. Six 2-day-old piglets were studied. A linear decrease in PaCO
2
was observed throughout increasing frequencies in both respiratory conditions while maintaining a constant DCO
2
, showing a significant difference between the initial PaCO
2
(at 10 Hz) and the PaCO
2
obtained at 18 and 20 Hz. A new DCO
2
equation (corrected DCO
2
) was calculated in order to better define the correlation between DCO
2
and the observed PaCO
2
.
Conclusion
: The correlation DCO
2
/PaCO
2
throughout increasing frequencies is not linear, showing a greater CO
2
elimination efficiency at higher frequencies, in spite of maintaining a constant DCO
2
. So, using frequencies close to the resonant frequency of the respiratory system on HFOV combined with VG, optimizes the efficiency of gas exchange.
What is Known:
•
The efficacy of CO
2
removal during high-frequency oscillatory ventilation (HFOV), described as the diffusion coefficient of CO
2
(DCO
2
) is related to the square of the high-frequency tidal volume (VThf) and the frequency (f), expressed as DCO
2
= VThf
2
× f.
What is New:
•
The correlation between DCO
2
and PaCO
2
throughout increasing frequencies is not linear, showing a greater CO
2
elimination efficiency at higher frequencies. So, using very high frequencies on HFOV combined with volume guarantee optimizes the efficiency of gas exchange allowing to minimize lung injury.
Purpose
Ventilation of indoor spaces is required for the delivery of fresh air rich in oxygen and the removal of carbon dioxide, pollutants and other hazardous substances. The COVID-19 pandemic ...brought the topic of ventilating crowded indoors to the front line of health concerns. This study developed a new biologically inspired concept of biomimetic active ventilation (BAV) for interior environments that mimics the mechanism of human lung ventilation, where internal air is continuously refreshed with the external environment. The purpose of this study is to provide a detailed proof-of-concept of the new BAV paradigm using computational models.
Design/methodology/approach
This study developed computational fluid dynamic models of unoccupied rooms with two window openings on one wall and two BAV modules that periodically translate perpendicular to or rotate about the window openings. This study also developed a time-evolving spatial ventilation efficiency metric for exploring the accumulated refreshment of the interior space. The authors conducted two-dimensional (2D) simulations of various BAV configurations to determine the trends in how the working parameters affect the ventilation and to generate initial estimates for the more comprehensive three-dimensional (3D) model.
Findings
Simulations of 2D and 3D models of BAV for modules of different shapes and working parameters demonstrated air movements in most of the room with good air exchange between the indoor and outdoor air. This new BAV concept seems to be very efficient and should be further developed.
Originality/value
The concept of ventilating interior spaces with periodically moving rigid modules with respect to the window openings is a new BAV paradigm that mimics human respiration. The computational results demonstrated that this new paradigm for interior ventilation is efficient while air velocities are within comfortable limits.
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