Ventilation Demand Research Articles

Therapeutic effect of insulin in reducing critical illness; polyneuropathy and myopathy in the pediatric intensive care unit.

Hyperglycemia may occur in the patients affected by any kind of critical illness. This complication makes an adverse effect on the clinical outcome of these patients by causing polyneuropathy and myopathy. It has been recently shown that treatment of hyperglycemia with insulin administration significantly reduces the prevalence of critical illness polyneuropathy and myopathy (CIPNM) and on the other hand reduces the demand for long-term mechanical ventilation in the patients admitted to the ICU for more than 1 week. The aim of this study was to determine the therapeutic effect of insulin in reducing the incidence of CIPNM in the pediatric intensive care unit (PICU). In this study, we recruited 30 patients admitted to the PICU of Tabriz Pediatric Hospital. The incidence of CIPNM following hyperglycemia was evaluated in these patients. The patients were categorized into two groups. In the case group, blood sugar was controlled in the range of 140-180mg/dl by administration of 0.05 unit per kilogram body weight of insulin as drip protocol in an hour and in the control group, placebo was used. Consequently, the incidence of CIPNM, duration of PICU and duration of mechanical ventilation were compared between the two groups. The incidence of CIPNM and duration of PICU stay and mechanical ventilation were significantly reduced in the patients treated with insulin compared to the control group. This study shows that blood sugar control decreases the incidence of CIPNM.

Retrograde Orotracheal Intubation with a Double-Lumen Tube

Difficult airway management in thoracic surgeries is a peculiar subject due to the demands of monopulmonary ventilation with double-lumen tubes. Flexible bronchoscopy guidance is extremely important, but it is not always available. The objective of this report was to describe a case of retrograde selective orotracheal intubation in the absence of specific endoscopy equipment for the procedure. This is a patient with a history of retosigmoidectomy, admitted for a right thoracotomy for a lung lesion. Preoperative anesthetic evaluation did not reveal any clinical and physical exam particularities. After anesthetic induction and ventilation with face mask, two attempts of orotracheal intubation under direct laryngoscopy were ineffective due to difficult visualization of the vocal folds (Cormack-Lehane grade III). Due to the unavailability of specific material for selective endoscopic intubation it was decided to use the retrograde technique using the double-lumen tube. The patient was extubated in the operating room shortly after the end of the surgery without complications secondary to the alternative technique. Retrograde selective orotracheal intubation is a minimally invasive technique, low cost, safe, and extremely useful whenever flexible bronchoscopy is not available.

Harmonizing Ventilation Requirements for Indoor Lighter-Than-Air Hazardous Atmospheres

This paper compares the major concepts in ventilation requirements contained in American Petroleum Institute (API) RP 500/505 and International Electrotechnical Commission (IEC) 60079-10, specific to indoor lighter-than-air natural gas hazardous atmospheres. Engineering professionals rely on API 505 as the basis for area classifications. Previously, IEC and North American standards have been successfully adopted in the body of API 500/505 (79-10 Mod). However, the informative appendixes of both standards covering ventilation calculations are not entirely consistent. This paper presents case studies for ventilation/classification, and an attempt is made to harmonize ventilation calculations to offer further uniformity in global standards. This will be of interest to those involved with area classification activities, as the result may offer reduced mechanical ventilation demands, while maintaining equivalent levels of safety and reliability.

Free-running temperature and potential for free cooling by ventilation: A case study

Free-cooling by ventilation is one of the most energy efficient techniques for cooling. When ventilation is used for cooling, variable airflow rates should to be used in order to achieve comfortable room temperatures and to minimize the energy demand for mechanical ventilation. Thus, free-cooling, requires, obviously, the existence of a potential for cooling and needs control mechanisms for the airflow. In this study, the free cooling potential by ventilation for office buildings is evaluated by the free-running temperature. The free-running temperature approach is based on the energy balance of heat gains and losses. It is adapted to evaluate the potential for free cooling by ventilation of office buildings for which the gains through the walls are negligible as compared to the internal and solar gains. The free-running temperature of each office room considers solar and internal heat gains, outdoor temperature, indoor temperatures and ventilation air flow rates. The approach is applied to 14 office rooms in a passively cooled office building in Germany and is used to estimate the potential and to evaluate the total energy saving by free cooling by ventilation. The good fit between monitoring data and calculation procedure proves that the free cooling potential can be accurately estimated by using the difference between the comfort limits, i.e. the target value of the indoor temperature, and the free-running temperature.

Effects of rotor structure on performance of small size axial flow fans

Small size axial flow fans are used as a cooling component for computers, electronic equipment and other electronic components. With the increasing power of electrical equipment, the demand for lower noise and higher ventilation of cooling fan is also increasing. Traditional methods of improving ventilation by raising the fan’s rotation speed causes a decrease in efficiency and an increase in noise. In this paper, different structures of fans were simulated, and as a result, the counter-rotating fan can achieve higher pressure, efficiency and facilitate ventilation in a smaller space. Furthermore, some other conclusions are as follows: (1) Higher pressure rise can be obtained by a counter-rotating fan than by the two-stage rotor fan in the same axial length. Meanwhile, the counter-rotating fan has a broader work scope. (2) The main noise type of the counter-rotating fan is rotating noise; the small peak pulse caused by vortex noise mainly due to the eddy current produced by small eddies. (3) When the distance of counter-rotating fans is smaller than 2 times the chord, the greater distance the greater total pressure of the circum-averages and along the axial direction, the total pressure begin to decline until the distance is three times the chord, so there is an optimal distance between rotors.

(A176) Mechanical Ventilation in Disasters: “To Intubate or Not to Intubate – That is the Question!”

The provision of mechanical ventilatory support for large numbers of casualties in disasters is a complex, controversial issue. Some experts consider this modality unsuitable for large disasters and a waste of resources better devoted to eminently salvageable victims. However, the reality has usually been that rescue teams bring with them some ventilatory capability, even if only for perioperative support. Also, there are many instances when the environment, the existing and potential capacities, allow for significant numbers of victims to be saved by providing artificial ventilation, that would otherwise have likely died. It is therefore important to discuss the issue, with all its complexity, so that the disaster preparedness and relief community fully understands its implications and makes informed, locally relevant decisions before and after disasters strike. The purpose of this presentation is to describe the ethical dilemmas, the technical and clinical considerations for such an endeavor. Ethical considerations: providing the most care to the most victims is the dictum of disaster medical management. Lowered standards of care are accepted and often the norm. However, in many moderate and even major disasters, the ability exists to save lives that will certainly be lost otherwise, by providing intensive care including mechanical ventilatory support, or may be provided if the managers so determine. Is it then ethical, to allow certain victims to die when such support may be available? What is the cost-benefit ratio of such a decision? Who should receive this limited resource? The young and healthy? The very sick? The salvageable? The postoperative? For how long? Until the international team leaves? Types of ventilator-dependency in disasters: (1) Primary ventilatory failure, normal lungs, prolonged ventilator dependency, e.g. botulinum toxin; (2) Combined ventilatory and hypoxemic failure, short to medium-term ventilator dependency, e.g. Sarin gas intoxication; (3) Primary hypoxemic failure, parenchymal lung injury, prolonged ventilator dependency, e.g. Anthrax, mustard gas, ricin; (4) Perioperative and prophylactic ventilatory support, short term but unpredictable. Ventilator supply versus demand: (1) Insufficient ventilators for first few hours only, then supplies come in; (2) Insufficient ventilators for days, then national or international relief expected; (3) Insufficient ventilators and no expected supplies. Care environment: (1) ICU, minority of casualties; (2) General floors: inexperienced nursing, medical staff; (3) Insufficient monitoring devices; (4) Insufficient numbers and quality of respiratory therapists; (5) Commercial companies normally providing technical support understaffed. Basic requirements from the ventilators: allows spontaneous ventilation, incorporates some alarms (ideally disconnect and minute volume), made by a reputable and stable company (will be there when the disaster strikes), low cost, user friendly, long shelf life, quick activation from storage, low weight and volume, few spares, few or generic disposables, little and simple maintenance, independent of compressed oxygen (i.e. electric, multiple voltages, long-life battery). The system: Mechanical ventilation is a complete patient care unit comprising: Bed and space, Oxygen supply, Vacuum, Cardiorespiratory monitor, Mechanical ventilator, Nursing staff, Medical staff, Expert consultatory staff, Logistic and technical support staff. Potential mechanical ventilators: (1) BVM or bag-valve-tube; (2) Transport-type, pneumatic or electrical ventilators; (3) Intermediate capability pneumatic, electrical or electronic ventilators; (4) Full capability intensive care ventilators; (5) Single patient use ventilators.

Patient-Ventilator Interaction During Acute Lung Injury, and the Role of Spontaneous Breathing: Part 2: Airway Pressure Release Ventilation

Airway pressure release ventilation (APRV) and bi-level positive airway pressure (BIPAP) are proposed to reduce patient work of breathing (WOB) sufficiently and to obviate issues related to patient-ventilator synchrony, so that spontaneous breathing can be maintained throughout the course of acute lung injury (ALI). Thus, APRV/BIPAP should reduce requirements for sedation and muscle paralysis, and thereby reduce the duration of mechanical ventilation. Only 17 human, animal, or lung-model studies have examined these claims, either directly or indirectly. Most did not target patients with ALI. Studies on sedation use have serious methodological limitations. Other studies found that APRV/BIPAP either increased WOB and asynchrony, or had no effect on energy expenditure. To supplement the discussion of patient WOB during APRV/BIPAP in ALI, 4 clinical examples showed marked elevation and wide variation in patient WOB. One plausible explanation is that spontaneous breathing is superimposed upon the mechanical ventilation pattern. Thus a variety of "breathing environments" exist during APRV/BIPAP that affect patient WOB and respiratory drive differently and perhaps unpredictably. This characteristic of APRV/BIPAP makes WOB comparisons with traditional modes problematic. Furthermore, the theoretical benefits of APRV, in terms of controlling patient WOB, appear particularly limited when lung-protective ventilation is used for ALI patients with high minute ventilation demand. Future research should focus on issues of WOB and synchrony, so that reasonable ventilation protocols can be devised to test clinical outcomes against traditional modes. To date, low-level evidence suggests that promoting spontaneous breathing with APRV/BIPAP may not be appropriate in patients with relatively severe ALI/ARDS.

Life cycle assessment of building materials: Comparative analysis of energy and environmental impacts and evaluation of the eco-efficiency improvement potential

The building industry uses great quantities of raw materials that also involve high energy consumption. Choosing materials with high content in embodied energy entails an initial high level of energy consumption in the building production stage but also determines future energy consumption in order to fulfil heating, ventilation and air conditioning demands. This paper presents the results of an LCA study comparing the most commonly used building materials with some eco-materials using three different impact categories. The aim is to deepen the knowledge of energy and environmental specifications of building materials, analysing their possibilities for improvement and providing guidelines for materials selection in the eco-design of new buildings and rehabilitation of existing buildings. The study proves that the impact of construction products can be significantly reduced by promoting the use of the best techniques available and eco-innovation in production plants, substituting the use of finite natural resources for waste generated in other production processes, preferably available locally. This would stimulate competition between manufacturers to launch more eco-efficient products and encourage the use of the Environmental Product Declarations. This paper has been developed within the framework of the “LoRe-LCA Project” co-financed by the European Commission’s Intelligent Energy for Europe Program and the “PSE CICLOPE Project” co-financed by the Spanish Ministry of Science and Technology and the European Regional Development Fund.

A low oxygen consumption pneumatic ventilator for emergency construction during a respiratory failure pandemic*

SummaryThe UK influenza pandemic plan predicts up to 750 000 additional deaths with hospitals prioritising patients against inadequate resources. We investigated three prototype low‐cost, gas‐efficient, pneumatic ventilators in a test lung model at different compliance and rate settings. Mean (SD) oxygen consumption was 0.913 (0.198) and 1.119 (0.267) l.min−1 at tidal volumes of 500 ml and 700 ml respectively. Values of F I o 2 increased marginally as lung compliance reduced, reflecting the increased ventilator workload and consequent increased enrichment of breathing gas by waste oxygen from the pneumatic mechanism. We also demonstrated that a stable nitric oxide concentration could be delivered by this design following volumetric principles. It is possible to make a gas‐efficient ventilator costing less than £200 from industrial components for use where oxygen is available at 2‐4 bar, with no pressurised air or electrical requirements. Such a device could be mass‐produced for crises characterised by an overwhelming demand for mechanical ventilation and a limited oxygen supply.

Elderly patients undergoing mechanical ventilation in and out of intensive care units: a comparative, prospective study of 579 ventilations

IntroductionMany mechanically ventilated elderly patients in Israel are treated outside of intensive care units (ICUs). The decision as to whether these patients should be treated in ICUs is reached without clear guidelines. We therefore conducted a study with the aim of identifying triage criteria and factors associated with in-hospital mortality in this population.MethodsAll mechanically invasive ventilated elderly (65+) medical patients in the hospital were included in a prospective, non-interventional, observational study.ResultsOf the 579 ventilations, 283 (48.9%) were done in ICUs compared with 296 (51.1%) in non-ICU wards. The percentage of ICU ventilations in the 65 to 74, 75 to 84, and 85+ age groups was 62%, 45%, and 23%, respectively. The decision to ventilate in ICUs was significantly and independently influenced by age (Odds Ratio (OR) = 0.945, P < 0.001), and pre-hospitalization functional status by functional independence measure (FIM) scale (OR = 1.054, P < 0.001). In-hospital mortality was 53.0% in ICUs compared with 68.2% in non-ICU wards (P < 0.001), but the rate was not independently and significantly affected by hospitalization in ICUs.ConclusionsIn Israel, most elderly patients are ventilated outside ICUs and the percentage of ICU ventilations decreases as age increases. In our study groups, the lower mortality among elderly patients ventilated in ICUs is related to patient characteristics and not to their treatment in ICUs per se. Although the milieu in which this study was conducted is uncommon today in the western world, its findings point to possible means of managing future situations in which the demand for mechanical ventilation of elderly patients exceeds the supply of intensive care beds. Moreover, the findings of this study can contribute to the search for ways to reduce costs without having a negative effect on outcome in ventilated elderly patients.

Gill morphometrics in relation to gas transfer and ram ventilation in high‐energy demand teleosts: Scombrids and billfishes

This comparative study of the gill morphometrics in scombrids (tunas, bonitos, and mackerels) and billfishes (marlins, swordfish) examines features of gill design related to high rates of gas transfer and the high-pressure branchial flow associated with fast, continuous swimming. Tunas have the largest relative gill surface areas of any fish group, and although the gill areas of non-tuna scombrids and billfishes are smaller than those of tunas, they are also disproportionally larger than those of most other teleosts. The morphometric features contributing to the large gill surface areas of these high-energy demand teleosts include: 1) a relative increase in the number and length of gill filaments that have, 2) a high lamellar frequency (i.e., the number of lamellae per length of filament), and 3) lamellae that are long and low in profile (height), which allows a greater number of filaments to be tightly packed into the branchial cavity. Augmentation of gill area through these morphometric changes represents a departure from the general mechanism of area enhancement utilized by most teleosts, which lengthen filaments and increase the size of the lamellae. The gill design of scombrids and billfishes reflects the combined requirements for ram ventilation and elevated energetic demands. The high lamellar frequencies and long lamellae increase branchial resistance to water flow which slows and streamlines the ram ventilatory stream. In general, scombrid and billfish gill surface areas correlate with metabolic requirements and this character may serve to predict the energetic demands of fish species for which direct measurement is not possible. The branching of the gill filaments documented for the swordfish in this study appears to increase its gill surface area above that of other billfishes and may allow it to penetrate oxygen-poor waters at depth.

Formaldehyde exposure risk in air-conditioned offices of Hong Kong

Formaldehyde (HCHO) is a carcinogenic toxicant commonly present in an air-conditioned office environment. This study examines the lifetime exposure risk of HCHO in air-conditioned offices of Hong Kong under various indoor environmental conditions. Using the regional indoor air quality assessment results of 511 Hong Kong offices recorded from 1996 to 2005, together with the mathematical correlations among HCHO exposure concentration, ventilation and thermal environment verified at 43 other local air-conditioned offices, the exposure risk in terms of loss of life expectancy (USEPA standard) was predicted for an office environment preset at certain air temperature and atmospheric carbon dioxide (CO 2) level. It was reported that the average increment of HCHO exposure risk was 2% for every 1°C increment in the air temperature range of 22.5—25.5°C, or 2.5% for every 10 ppm increment in the CO2 concentration range of 800—1000 ppm. This study presents useful information on HCHO exposure risk evaluation for air-conditioned offices associated with various policies on indoor air temperature and ventilation demands. Practical applications: This study outlines an approach to lifetime exposure risk assessment for HCHO inhaled in air-conditioned offices of Hong Kong under various indoor environmental conditions. In a typical office environment, the findings demonstrated that the average increment of HCHO exposure risk was 2% for every 1°C increment in air temperature or 2.5% for every 10 ppm increment in CO 2 concentration.

An Expiratory Assist During Spontaneous Breathing Can Compensate for Endotracheal Tube Resistance

Although inspiratory assist of spontaneous breathing in intubated patients is common, expiratory assist functions have rarely been reported. Effective expiratory support (ES) could be used to compensate for endotracheal tube (ETT) resistance during spontaneous breathing. In this study, we examined the performance of a new system designed to provide both inspiratory support (IS) and ES during spontaneous breathing with the goal of reducing the effective resistance of the ETT. The ES system consisted of a ventilator demand valve and a computer-controlled piston cylinder, which aspirated gas from the respiratory circuit during the expiratory phase. The movement of the piston was synchronized with spontaneous breathing. We compared the pressures at the tip of the ETT and in the breathing circuit during spontaneous breathing through an ETT of internal diameter (ID) 5 mm with that of an ETT with ID 8 mm in nine healthy adult male volunteers. The ventilatory mode was set to maintain a continuous airway pressure of 0 cm H(2)O. Three ventilator settings (no support, IS only, and IS plus ES) were compared using ID 5 mm ETT. We monitored pressure in the breathing circuit (P(aw)), ETT tip pressure (P(tip)), and respiratory flow. The P(tip) of the ID 5 mm ETT showed a large negative deflection during inspiration and a positive deflection during expiration without support. IS alone did not improve the respiratory pattern through the small ETT. However, IS plus ES resulted in negative P(aw) during expiration in addition to positive deflection of P(aw) during inspiration, making the pressure characteristics of P(tip) similar to those of ID 8 mm ETT. Moreover, IS plus ES produced a respiratory pattern through the ID 5 mm ETT that was similar to that through the ID 8 mm ETT. In this study of healthy volunteers, IS plus ES compensated for the airway resistance imposed by a ID 5.0 mm ETT to create pressure changes at the tip of the ETT similar to those of an ID 8.0 mm ETT.

Potential Intensive Care unit Ventilator Demand/Capacity Mismatch due to Novel Swine‐Origin H1N1 in Canada

To investigate the ability of Canadian intensive care units (ICUs) and ventilators to handle widespread re-emergence of the swine-origin H1N1 virus in the context of an aggressive strategy of vaccination. Data collected during the first wave in Winnipeg, Manitoba, were applied to a variety of second wave pandemic models to determine potential ICU and ventilator demand. For attack rates greater than 20% to 25%, significant shortages in ventilators may be expected across Canada regardless of the duration of the pandemic if vaccination is not considered. The shortfall arises largely due to the extended durations that patients must remain on ventilation. From the Winnipeg study, 50% of patients required ventilation for more than two weeks. For larger attack rates of 35%, ventilator demand may exceed capacity for over five weeks, with a peak shortfall of 700 ventilators. Vaccination can significantly reduce the attack rates, and is expected to reduce ventilator demand to manageable levels Canada's health care system must be prepared for the possibility of a significant influx of ICU patients during the second wave of swine-origin H1N1. Efficient vaccination and other disease prevention measures can reduce the attack rate to manageable levels.

Swine flu: provision of ventilation in a worst-case scenario

As a busy intensive care unit in a district general hospital in the UK, we are intrigued by the worst-case scenario plans for swine flu in our region and the ubiquitous algorithms that form part of this planning. A Department of Health document suggests for the purposes of planning that, during a first major UK pandemic wave, the peak clinical attack rate per week would be 8% [1]. Of these patients, the hospitalization rate would be 2% - and 25% of these would require intensive care if the capacity exists. Our hospital serves a population of 220,000. In our region, these estimates suggest that 352 patients will require hospital admission each week during the peak. Using these calculations, we could expect 88 patients per week to require intensive care unit support. In this hospital, there is the capacity to provide mechanical ventilation to 25 patients (utilizing all ventilators and anaesthetic machines). Clearly, as this is primarily a disease affecting the respiratory system, demand for mechanical ventilation could vastly outstrip supply. This lack of equipment will mean either severe rationing of treatment or obtaining more ventilators from an external source. At a time of heightened national demand, the latter is unlikely to be achieved. In the polio epidemic of the 1950s, patients were manually ventilated by medical students and anyone else on hand as the small number of cuirass ventilators was rapidly overwhelmed by clinical cases [2]. When we receive our 26th mechanically ventilated patient, rather than being unable to provide positive pressure ventilation, we propose - in a worst-case scenario - a return to basics. Our solution to this problem is to order 200 disposable bag-valve masks with adjustable positive end-expiratory pressure valves. This solution is conveniently a cost-neutral approach to the single organ support as we already use disposable bag-valve masks throughout the trust. Clinical staff are fully trained in their use, and support staff and relatives could be utilized. Any excess stock could be used as part of normal resource turnover. A similar issue might occur with the requirement for renal replacement therapy in large numbers of patients. In this scenario, perhaps a similar solution would be a return to continuous arteriovenous haemodiafiltration - which requires only a simple disposable item rather than the complex and limited resource of haemofiltration machines.

INNOVATION IN PLANT-GREENHOUSE INTERACTIONS AND CROP MANAGEMENT

(Semi)-closed greenhouses allow for better control of climate conditions compared to conventional greenhouses. To make the high investments for such greenhouses economically feasible, substantial yield increases are necessary. In north-Europe supplementary assimilation light in greenhouse horticulture is increasingly used to improve yield and product quality to meet market demands for year-round production and to obtain a more regular labor demand throughout the year. Using inter-lighting instead of lights only on top of the crop, and Light Emitting Diodes (LEDs), could increase substantially light and energy efficiency. As soon as LEDs will reach high enough efficiency and feasible price, they are expected to replace high pressure sodium lamps in greenhouse horticulture. Another important issue is the choice of the greenhouse cover which should be optimized from the crop point of view. A cover with high transmission of light, but low transmission of NIR, results in a better climate during the warm season (reduced temperatures, less crop transpiration, higher CO2-concentration possible because of reduced ventilation demand). Increasing the diffusive power of the cover material could result in a better distribution of the radiation over the crop canopy, therefore leading to substantial increase in absorbed radiation (up to 20% for highly diffusive covers) and improving radiation use efficiency and yield. Under these new conditions (high CO2 and high light levels) other genotypes than the present cultivars may be superior. However, the possible effect of breeding especially for these new conditions is still little investigated. Under improved crop management, maintaining leaf area index high enough and controlling source-sink balance is discussed. In conclusion, there are a lot of possibilities to further improve yield and quality of greenhouse produce, and meanwhile reduce the input of fossil fuel energy.

Lung and chest wall mechanics during exercise: Effects of expiratory flow limitation

This short review summarizes how lung and chest wall mechanics can be modelled and which are the mechanical constraints imposed on the ventilatory system and its components during exercise. In healthy humans the structural and functional characteristics of the ventilator pump are able to meet the increased demands of ventilation during exercise and it is rare that arterial blood gas is significantly altered up to maximal exercise. In contrast, exercise is frequently limited by the ventilator system in disease, especially when altered mechanical properties of the airway and lung make expiratory flow limitation (EFL) a common feature. EFL is a phenomenon that can be understood in terms of the viscous effects of gas flowing from the alveoli to the airway opening along a collapsible airway which leads during exercise to dynamic hyperflation and several abnormalities of the ventilatory pump. These, in turn, determine a series of secondary manifestations, namely dyspnoea, exercise limitation and hypercapnia that can cause serious morbidity.

Image-based monitoring of one-lung ventilation

With the increasing demand for one-lung ventilation in both thoracic surgery and other procedures, identifying the correct placement becomes increasingly important. Currently, endobronchial intubation is suspected based on a combination of auscultation and physiological findings. We investigated the ability of the visual display of airflow-induced vibrations to detect single-lung ventilation with a double-lumen endotracheal tube. Double-lumen tubes were placed prior to surgery. Tracheal and endobronchial lumens were alternately clamped to produce unilateral lung ventilation of right and left lung. Vibration response imaging, which detects vibrations transmitted to the surface of the thorax, was performed during both right- and left-lung ventilation. Geographical area of vibration response image as well as amount and distribution of lung sounds were assessed. During single-lung ventilation, the image and video obtained from the vibration response imaging identifies the ventilated lung with a larger and darker image on the ventilated side. During single-lung ventilation, 87.2 +/- 5.7% of the measured vibrations was detected over the ventilated lung and 12.8 +/- 5.7% over the non-ventilated lung (P < 0.0001). It was also noted that during single-lung ventilation, the vibration distribution in the non-ventilated lung had a majority of vibration detected by the medial sensors closest to the midline (P < 0.05) as opposed to the midclavicular sensors when the lung is ventilated. During single-lung ventilation, vibration response imaging clearly showed increased vibration in the lung that is being ventilated. Distribution of residual vibration differed in the non-ventilated lung in a manner that suggests transmission of vibrations across the mediastinum from the ventilated lung. The lung image and video obtained from vibration response imaging may provide useful and immediate information to help one-lung ventilation assessment.

An energy impact assessment of indoor air quality acceptance for air-conditioned offices

Treatment of fresh air in ventilation systems for the air-conditioning consumes a considerable amount of energy and affects the indoor air quality (IAQ). The ventilation demand is primarily related to the occupant load. In this study, the ventilation demands due to occupant load variations and occupant acceptability were examined against certain IAQ objectives using the mass balance of carbon dioxide (CO 2) concentrations in an air-conditioned office. In particular, this study proposed a ventilation model for the consideration of the occupant load variations and occupant acceptability based on the regional survey of typical offices (422 samples) in Hong Kong. The model was applied to evaluate the relative energy performance of different IAQ objectives in ventilation systems for typical office buildings in Hong Kong. The results showed that the energy consumption of a ventilation system would be correlated with the occupant load and acceptability in the air-conditioned office. Indicative CO 2 levels of 800 ppmv, 1000 ppmv and 1200 ppmv corresponding to 83%, 97% and 99.7% survey samples were shown, corresponding to the thermal energy consumptions of 1500 MJ m −2 yr −1, 960 MJ m −2 yr −1and 670 MJ m −2 yr −1, respectively. In regards to the monetary issue, an annual value of HK$ 762 million per year in electrical consumption could be saved in all office buildings in Hong Kong when the indoor target CO 2 concentration is increased from 1000 ppmv to 1200 ppmv. To achieve an excellent IAQ following the existing design standard, i.e. to decrease the CO 2 level from 1000 ppmv to 800 ppmv, 56% additional energy would be consumed, corresponding to an annual value of HK$ 1,419 million, even though the occupant acceptability is only improved from 81% to 86%. The development of the models in this study would be useful for the energy performance evaluation of ventilation systems in air-conditioned offices.

A transient ventilation demand model for air-conditioned offices

Ventilation to supply fresh air in an air-conditioned office consumes a considerable portion of energy in an air-conditioning system and affects the indoor-air quality (IAQ). The ventilation demand is primarily related to the occupant load. In this study, the ventilation demands due to occupant load variations were examined against certain IAQ objectives using the mass balance of carbon dioxide (CO 2) volume fractions in an air-conditioned office. In particular, this study proposed a transient ventilation demand model for occupant load, with the parameters determined from a year-round occupant load survey in Hong Kong. This model was applied to evaluate the performance of energy saving in different operating schedules of ventilation systems for typical office buildings in Hong Kong. The results showed that the energy consumption of a ventilation system would be correlated with the transient occupant load and its variations in the air-conditioned office. The ventilation system, with schedules taking account of the transient occupant loads, would offer a reduction in energy consumption up to 19% as compared with an operating schedule that assumed a steady occupant-load in the office during working hours. In both cases, the same IAQ objective was achieved.