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1.
EBioMedicine ; 76: 103868, 2022 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-35172957

RESUMO

BACKGROUND: The manufacturing of any standard mechanical ventilator cannot rapidly be upscaled to several thousand units per week, largely due to supply chain limitations. The aim of this study was to design, verify and perform a pre-clinical evaluation of a mechanical ventilator based on components not required for standard ventilators, and that met the specifications provided by the Medicines and Healthcare Products Regulatory Agency (MHRA) for rapidly-manufactured ventilator systems (RMVS). METHODS: The design utilises closed-loop negative feedback control, with real-time monitoring and alarms. Using a standard test lung, we determined the difference between delivered and target tidal volume (VT) at respiratory rates between 20 and 29 breaths per minute, and the ventilator's ability to deliver consistent VT during continuous operation for >14 days (RMVS specification). Additionally, four anaesthetised domestic pigs (3 male-1 female) were studied before and after lung injury to provide evidence of the ventilator's functionality, and ability to support spontaneous breathing. FINDINGS: Continuous operation lasted 23 days, when the greatest difference between delivered and target VT was 10% at inspiratory flow rates >825 mL/s. In the pre-clinical evaluation, the VT difference was -1 (-90 to 88) mL [mean (LoA)], and positive end-expiratory pressure (PEEP) difference was -2 (-8 to 4) cmH2O. VT delivery being triggered by pressures below PEEP demonstrated spontaneous ventilation support. INTERPRETATION: The mechanical ventilator presented meets the MHRA therapy standards for RMVS and, being based on largely available components, can be manufactured at scale. FUNDING: Work supported by Wellcome/EPSRC Centre for Medical Engineering,King's Together Fund and Oxford University.


Assuntos
Desenho de Equipamento , Respiração Artificial/instrumentação , Animais , COVID-19/patologia , COVID-19/prevenção & controle , COVID-19/virologia , Feminino , Masculino , Taxa Respiratória , SARS-CoV-2/isolamento & purificação , Suínos , Volume de Ventilação Pulmonar
2.
Artigo em Inglês | MEDLINE | ID: mdl-34891243

RESUMO

Patients undergoing mechanical lung ventilation are at risk of lung injury. A noninvasive bedside lung monitor may benefit these patients. The Inspired Sinewave Test (IST) can measure cardio-pulmonary parameters noninvasively. We propose a lung simulation to improve the measurement of pulmonary blood flow using IST. The new method was applied to 12 pigs' data before lung injury (control) and after lung injury (ARDS model). Results using the lung simulation shown improvements in correlation in both simulated data (R2 increased from 0.98 to 1) and pigs' data (R2 increased from <0.001 to 0.26). Paired blood flow measurements were performed by both the IST (noninvasive) and thermodilution (invasive). In the control group, the bias of the two methods was negligible (0.02L/min), and the limit of agreement was from -1.20 to 1.18 L/min. The bias was -0.68 L/min in the ARDS group and with a broader limit of agreement (-2.49 to 1.13 L/min).Clinical Relevance- the inspired sinewave test can be used to measure cardiac output noninvasively in mechanically ventilated subjects with and without acute respiratory distress syndrome.


Assuntos
Circulação Pulmonar , Síndrome do Desconforto Respiratório , Animais , Humanos , Pulmão , Síndrome do Desconforto Respiratório/diagnóstico , Testes de Função Respiratória , Suínos , Termodiluição
3.
Artigo em Inglês | MEDLINE | ID: mdl-33654391

RESUMO

BACKGROUND: There is marked variability in the symptoms and outcomes of patients with chronic obstructive pulmonary disease (COPD) which are poorly predicted by spirometry/FEV1%pred. Furthermore, as spirometry requires the performance of potentially distressing respiratory manoeuvres which are to some extent user-effort dependent, there is need for non-invasive and simple-to-perform techniques to identify subtypes of COPD which are more closely related to clinically relevant outcomes. MATERIALS AND METHODS: The inspired sinewave test (IST) sinusoidally modulates the inspired concentration of a tracer gas (N2O) over successive tidal breaths. A single-compartment tidal-ventilation lung model processes the amplitude/phase of the expired N2O sinewave and estimates cardiopulmonary variables including: effective lung volume and indices of ventilatory heterogeneity (VH; ELV180/FRCpleth and ELV180/ELVpred). 83 COPD patients and 53 healthy controls performed the IST test, standard pulmonary function tests (Spirometry, body plethysmography and the single breath test of carbon monoxide uptake), and symptom severity questionnaires (COPD assessment test, CAT; mMRC dyspnoea-scale, mMRC-DS; Cough+Mucus score; C+M score). RESULTS: ELV180/FRCpleth and ELV180/ELVpred were significantly lower in patients with COPD vs healthy participants (0.34±0.11 vs 0.68±0.14 and 0.7±0.27 vs 0.98±0.15, respectively; P<0.05). Multivariable regression analysis demonstrated that ELV180/FRCpleth was a stronger and independent predictor of CAT, mMRC-DS and C+M score vs FEV1%pred. ELV180/ELVpred was a stronger and independent and better predictor of C+M score vs FEV1%pred. Phenotyping patients, based upon ELV180/ELVpred and FRC%pred, uncovered significant symptomatic differences between groups. CONCLUSION: The IST indices of VH were superior and independent predictors of symptom severity vs FEV1%pred and has potential as a non-invasive and simple-to-perform method to stratify patients into subgroups related to clinically relevant features of COPD.


Assuntos
Doença Pulmonar Obstrutiva Crônica , Dispneia , Volume Expiratório Forçado , Humanos , Pulmão , Doença Pulmonar Obstrutiva Crônica/diagnóstico , Testes de Função Respiratória , Espirometria
4.
Intensive Care Med Exp ; 9(1): 3, 2021 Jan 11.
Artigo em Inglês | MEDLINE | ID: mdl-33496887

RESUMO

BACKGROUND: Bedside measurement of lung volume may provide guidance in the personalised setting of respiratory support, especially in patients with the acute respiratory distress syndrome at risk of ventilator-induced lung injury. We propose here a novel operator-independent technique, enabled by a fibre optic oxygen sensor, to quantify the lung volume available for gas exchange. We hypothesised that the continuous measurement of arterial partial pressure of oxygen (PaO2) decline during a breath-holding manoeuvre could be used to estimate lung volume in a single-compartment physiological model of the respiratory system. METHODS: Thirteen pigs with a saline lavage lung injury model and six control pigs were studied under general anaesthesia during mechanical ventilation. Lung volumes were measured by simultaneous PaO2 rate of decline (VPaO2) and whole-lung computed tomography scan (VCT) during apnoea at different positive end-expiratory and end-inspiratory pressures. RESULTS: A total of 146 volume measurements was completed (range 134 to 1869 mL). A linear correlation between VCT and VPaO2 was found both in control (slope = 0.9, R2 = 0.88) and in saline-lavaged pigs (slope = 0.64, R2 = 0.70). The bias from Bland-Altman analysis for the agreement between the VCT and VPaO2 was - 84 mL (limits of agreement ± 301 mL) in control and + 2 mL (LoA ± 406 mL) in saline-lavaged pigs. The concordance for changes in lung volume, quantified with polar plot analysis, was - 4º (LoA ± 19°) in control and - 9° (LoA ± 33°) in saline-lavaged pigs. CONCLUSION: Bedside measurement of PaO2 rate of decline during apnoea is a potential approach for estimation of lung volume changes associated with different levels of airway pressure.

5.
Physiol Meas ; 41(11)2020 12 09.
Artigo em Inglês | MEDLINE | ID: mdl-33049721

RESUMO

Acute respiratory distress syndrome (ARDS) is associated with a high rate of morbidity and mortality, as patients undergoing mechanical ventilation are at risk of ventilator-induced lung injuries.Objective: To measure the lung heterogeneity and deadspace volume to find safer ventilator strategies. The ventilator settings could then offer homogeneous ventilation and theoretically equalize and reduce tidal strain/stress in the lung parenchyma.Approach: The inspired sinewave test (IST) is a non-invasive lung measurement tool which does not require cooperation from the patient. The IST can measure the effective lung volume, pulmonary blood flow and deadspace volume. We developed a computational simulation of the cardiopulmonary system to allow lung heterogeneity to be quantified using data solely derived from the IST. Then, the method to quantify lung heterogeneity using two IST tracer gas frequencies (180 and 60 s) was introduced and used in lung simulations and animal models. Thirteen anaesthetized pigs were studied with the IST both before and after experimental lung injury (saline-lavage ARDS model). The deadspace volume was compared between the IST and the SF6washout method.Main results: The IST could measure lung heterogeneity using two tracer gas frequencies. Furthermore, the value of IST ventilation heterogeneity in ARDS lungs was higher than in control lungs at a positive end-expiratory pressure of 10 cmH2O (area under the curve = 0.85,p<0.001). Values for the deadspace volume measured by the IST have a strong relationship with the measured values of SF6(9 ml bias and limits of agreement from -79 to 57 ml in control animals).Significance: The IST technique has the potential for use in the identification of ventilation and perfusion heterogeneity during ventilator support.


Assuntos
Síndrome do Desconforto Respiratório , Animais , Humanos , Pulmão , Medidas de Volume Pulmonar , Respiração com Pressão Positiva , Respiração Artificial , Síndrome do Desconforto Respiratório/diagnóstico , Síndrome do Desconforto Respiratório/terapia , Testes de Função Respiratória , Suínos , Volume de Ventilação Pulmonar
6.
Annu Int Conf IEEE Eng Med Biol Soc ; 2020: 2438-2441, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-33018499

RESUMO

We have created a lung simulation to quantify lung heterogeneity from the results of the inspired sinewave test (IST). The IST is a lung function test that is non-invasive, non-ionising and does not require patients' cooperation. A tidal lung simulation is developed to assess this test and also a method is proposed to calculate lung heterogeneity from IST results. A sensitivity analysis based on the Morris method and linear regression were applied to verify and to validate the simulation. Additionally, simulated emphysema and pulmonary embolism conditions were created using the simulation to assess the ability of the IST to identify these conditions. Experimental data from five pigs (pre-injured vs injured) were used for validation. This paper contributes to the development of the IST. Firstly, our sensitivity analysis reveals that the IST is highly accurate with an underestimation of about 5% of the simulated values. Sensitivity analysis suggested that both instability in tidal volume and extreme expiratory flow coefficients during the test cause random errors in the IST results. Secondly, the ratios of IST results obtained at two tracer gas oscillation frequencies can identify lung heterogeneity (ELV60/ELV180 and Qp60/Qp180). There was dissimilarity between simulated emphysema and pulmonary embolism (p < 0.0001). In the animal model, the control group had ELV60/ELV180 = 0.58 compared with 0.39 in injured animals (p < 0.0001).


Assuntos
Pulmão , Animais , Humanos , Testes de Função Respiratória , Suínos , Volume de Ventilação Pulmonar
7.
ACS Nano ; 14(10): 12313-12340, 2020 10 27.
Artigo em Inglês | MEDLINE | ID: mdl-32866368

RESUMO

Personal protective equipment (PPE) is critical to protect healthcare workers (HCWs) from highly infectious diseases such as COVID-19. However, hospitals have been at risk of running out of the safe and effective PPE including personal protective clothing needed to treat patients with COVID-19, due to unprecedented global demand. In addition, there are only limited manufacturing facilities of such clothing available worldwide, due to a lack of available knowledge about relevant technologies, ineffective supply chains, and stringent regulatory requirements. Therefore, there remains a clear unmet need for coordinating the actions and efforts from scientists, engineers, manufacturers, suppliers, and regulatory bodies to develop and produce safe and effective protective clothing using the technologies that are locally available around the world. In this review, we discuss currently used PPE, their quality, and the associated regulatory standards. We survey the current state-of-the-art antimicrobial functional finishes on fabrics to protect the wearer against viruses and bacteria and provide an overview of protective medical fabric manufacturing techniques, their supply chains, and the environmental impacts of current single-use synthetic fiber-based protective clothing. Finally, we discuss future research directions, which include increasing efficiency, safety, and availability of personal protective clothing worldwide without conferring environmental problems.


Assuntos
Transmissão de Doença Infecciosa/prevenção & controle , Pessoal de Saúde , Equipamento de Proteção Individual/normas , Humanos , Equipamento de Proteção Individual/classificação , Equipamento de Proteção Individual/virologia , Guias de Prática Clínica como Assunto , Têxteis/normas
8.
Br J Anaesth ; 124(3): 345-353, 2020 03.
Artigo em Inglês | MEDLINE | ID: mdl-31952649

RESUMO

BACKGROUND: Bedside lung volume measurement could personalise ventilation and reduce driving pressure in patients with acute respiratory distress syndrome (ARDS). We investigated a modified gas-dilution method, the inspired sinewave technique (IST), to measure the effective lung volume (ELV) in pigs with uninjured lungs and in an ARDS model. METHODS: Anaesthetised mechanically ventilated pigs were studied before and after surfactant depletion by saline lavage. Changes in PEEP were used to change ELV. Paired measurements of absolute ELV were taken with IST (ELVIST) and compared with gold-standard measures (sulphur hexafluoride wash in/washout [ELVSF6] and computed tomography (CT) [ELVCT]). Measured volumes were used to calculate changes in ELV (ΔELV) between PEEP levels for each method (ΔELVIST, ΔELVSF6, and ΔELVCT). RESULTS: The coefficient of variation was <5% for repeated ELVIST measurements (n=13 pigs). There was a strong linear relationship between ELVIST and ELVSF6 in uninjured lungs (r2=0.97), and with both ELVSF6 and ELVCT in the ARDS model (r2=0.87 and 0.92, respectively). ELVIST had a mean bias of -12 to 13% (95% limits=±17 - 25%) compared with ELVSF6 and ELVCT. ΔELVIST was concordant with ΔELVSF6 and ΔELVCT in 98-100% of measurements, and had a mean bias of -73 to -77 ml (95% limits=±128 - 186 ml) compared with ΔELVSF6 and -1 ml (95% limits ±333 ml) compared with ΔELVCT. CONCLUSIONS: IST provides a repeatable measure of absolute ELV and shows minimal bias when tracking PEEP-induced changes in lung volume compared with CT in a saline-lavage model of ARDS.


Assuntos
Respiração com Pressão Positiva/métodos , Síndrome do Desconforto Respiratório/terapia , Animais , Modelos Animais de Doenças , Medidas de Volume Pulmonar/métodos , Testes Imediatos , Reprodutibilidade dos Testes , Síndrome do Desconforto Respiratório/diagnóstico por imagem , Síndrome do Desconforto Respiratório/etiologia , Síndrome do Desconforto Respiratório/fisiopatologia , Solução Salina , Sus scrofa , Tomografia Computadorizada por Raios X
9.
Crit Care Med ; 48(3): e200-e208, 2020 03.
Artigo em Inglês | MEDLINE | ID: mdl-31809278

RESUMO

OBJECTIVES: Determine the intra-tidal regional gas and blood volume distributions at different levels of atelectasis in experimental lung injury. Test the hypotheses that pulmonary aeration and blood volume matching is reduced during inspiration in the setting of minimal tidal recruitment/derecruitment and that this mismatching is an important determinant of hypoxemia. DESIGN: Preclinical study. SETTING: Research laboratory. SUBJECTS: Seven anesthetized pigs 28.7 kg (SD, 2.1 kg). INTERVENTIONS: All animals received a saline-lavage surfactant depletion lung injury model. Positive end-expiratory pressure was varied between 0 and 20 cm H2O to induce different levels of atelectasis. MEASUREMENTS AND MAIN RESULTS: Dynamic dual-energy CT images of a juxtadiaphragmatic slice were obtained, gas and blood volume fractions within three gravitational regions calculated and normalized to lung tissue mass (normalized gas volume and normalized blood volume, respectively). Ventilatory conditions were grouped based upon the fractional atelectatic mass in expiration (< 20%, 20-40%, and ≥ 40%). Tidal recruitment/derecruitment with fractional atelectatic mass in expiration greater than or equal to 40% was less than 7% of lung mass. In this group, inspiration-related increase in normalized gas volume was greater in the nondependent (818 µL/g [95% CI, 729-908 µL/g]) than the dependent region (149 µL/g [120-178 µL/g]). Normalized blood volume decreased in inspiration in the nondependent region (29 µL/g [12-46 µL/g]) and increased in the dependent region (39 µL/g [30-48 µL/g]). Inspiration-related changes in normalized gas volume and normalized blood volume were negatively correlated in fractional atelectatic mass in expiration greater than or equal to 40% and 20-40% groups (r = 0.56 and 0.40), but not in fractional atelectatic mass in expiration less than 20% group (r = 0.01). Both the increase in normalized blood volume in the dependent region and fractional atelectatic mass in expiration negatively correlated with PaO2/FIO2 ratio (ρ = -0.77 and -0.93, respectively). CONCLUSIONS: In experimental atelectasis with minimal tidal recruitment/derecruitment, mechanical inspiratory breaths redistributed blood volume away from well-ventilated areas, worsening PaO2/FIO2.


Assuntos
Lesão Pulmonar/terapia , Respiração com Pressão Positiva/efeitos adversos , Atelectasia Pulmonar/terapia , Circulação Pulmonar/fisiologia , Respiração Artificial/métodos , Algoritmos , Animais , Modelos Animais de Doenças , Mecânica Respiratória , Suínos , Volume de Ventilação Pulmonar
10.
Intensive Care Med Exp ; 7(1): 59, 2019 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-31676929

RESUMO

BACKGROUND: Dynamic single-slice CT (dCT) is increasingly used to examine the intra-tidal, physiological variation in aeration and lung density in experimental lung injury. The ability of dCT to predict whole-lung values is unclear, especially for dual-energy CT (DECT) variables. Additionally, the effect of inspiration-related lung movement on CT variables has not yet been quantified. METHODS: Eight domestic pigs were studied under general anaesthesia, including four following saline-lavage surfactant depletion (lung injury model). DECT, dCT and whole-lung images were collected at 12 ventilatory settings. Whole-lung single energy scans images were collected during expiratory and inspiratory apnoeas at positive end-expiratory pressures from 0 to 20 cmH2O. Means and distributions of CT variables were calculated for both dCT and whole-lung images. The cranio-caudal displacement of the anatomical slice was measured from whole-lung images. RESULTS: Mean CT density and volume fractions of soft tissue, gas, iodinated blood, atelectasis, poor aeration, normal aeration and overdistension correlated between dCT and the whole lung (r2 0.75-0.94) with agreement between CT density distributions (r 0.89-0.97). Inspiration increased the matching between dCT and whole-lung values and was associated with a movement of 32% (SD 15%) of the imaged slice out of the scanner field-of-view. This effect introduced an artefactual increase in dCT mean CT density during inspiration, opposite to that caused by the underlying physiology. CONCLUSIONS: Overall, dCT closely approximates whole-lung aeration and density. This approximation is improved by inspiration where a decrease in CT density and atelectasis can be interpreted as physiological rather than artefactual.

11.
Br J Anaesth ; 123(2): 126-134, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-30954237

RESUMO

BACKGROUND: Cardiac output (Q˙) monitoring can support the management of high-risk surgical patients, but the pulmonary artery catheterisation required by the current 'gold standard'-bolus thermodilution (Q˙T)-has the potential to cause life-threatening complications. We present a novel noninvasive and fully automated method that uses the inspired sinewave technique to continuously monitor cardiac output (Q˙IST). METHODS: Over successive breaths the inspired nitrous oxide (N2O) concentration was forced to oscillate sinusoidally with a fixed mean (4%), amplitude (3%), and period (60 s). Q˙IST was determined in a single-compartment tidal ventilation lung model that used the resulting amplitude/phase of the expired N2O sinewave. The agreement and trending ability of Q˙IST were compared with Q˙T during pharmacologically induced haemodynamic changes, before and after repeated lung lavages, in eight anaesthetised pigs. RESULTS: Before lung lavage, changes in Q˙IST and Q˙T from baseline had a mean bias of -0.52 L min-1 (95% confidence interval [CI], -0.41 to -0.63). The concordance between Q˙IST and Q˙T was 92.5% as assessed by four-quadrant analysis, and polar plot analysis revealed a mean angular bias of 5.98° (95% CI, -24.4°-36.3°). After lung lavage, concordance was slightly reduced (89.4%), and the mean angular bias widened to 21.8° (-4.2°, 47.6°). Impaired trending ability correlated with shunt fraction (r=0.79, P<0.05). CONCLUSIONS: The inspired sinewave technique provides continuous and noninvasive monitoring of cardiac output, with a 'marginal-good' trending ability compared with cardiac output based on thermodilution. However, the trending ability can be reduced with increasing shunt fraction, such as in acute lung injury.


Assuntos
Débito Cardíaco , Monitorização Fisiológica/métodos , Animais , Modelos Animais , Óxido Nitroso , Suínos , Termodiluição/métodos
12.
Exp Physiol ; 103(5): 738-747, 2018 05 01.
Artigo em Inglês | MEDLINE | ID: mdl-29460470

RESUMO

NEW FINDINGS: What is the central question of this study? We present a new non-invasive medical technology, the inspired sine-wave technique, which involves inhalation of sinusoidally fluctuating concentrations of a tracer gas. The technique requires only passive patient cooperation and can monitor different cardiorespiratory variables, such as end-expired lung volume, ventilatory heterogeneity and pulmonary blood flow. What is the main finding and its importance? In this article, we demonstrate that the measurements of end-expired lung volume are repeatable and accurate, in comparison to whole-body plethysmography, and the technique is sensitive to the changes in ventilatory heterogeneity associated with advancing age. As such, it has the potential to provide clinically valuable information. ABSTRACT: The inspired sine-wave technique (IST) is a new method that can provide simple, non-invasive cardiopulmonary measurements. Over successive tidal breaths, the concentration of a tracer gas (i.e. nitrous oxide, N2 O) is sinusoidally modulated in inspired air. Using a single-compartment tidal-ventilation lung model, the resulting amplitude/phase of the expired sine wave allows estimation of end-expired lung volume (ELV), pulmonary blood flow and three indices for ventilatory heterogeneity (VH; ELV180 /FRCpleth , ELV180 /FRCpred and ELV60 /ELV180 ). This investigation aimed to determine the repeatability and agreement of ELV with FRCpleth and, as normal ageing results in well-established changes in pulmonary structure and function, whether the IST estimates of ELV and VH are age dependent. Forty-eight healthy never-smoker participants (20-86 years) underwent traditional pulmonary function testing (e.g. spirometry, body plethysmography) and the IST test, which consisted of 4 min of quiet breathing through a face mask while inspired N2 O concentrations were oscillated in a sine-wave pattern with a fixed mean (4%) and amplitude (3%) and a period of either 180 or 60 s. The ELV180 /FRCpleth and ELV180 /FRCpred were age dependent (average decreases of 0.58 and 0.48% year-1 ), suggesting an increase in VH with advancing age. The ELV showed a mean bias of -1.09 litres versus FRCpleth , but when normalized for the effects of age this bias reduced to -0.35 litres. The IST test has potential to provide clinically useful information necessitating further study (e.g. for mechanically ventilated or obstructive lung disease patients), but these findings suggest that the increases in VH with healthy ageing must be taken into account in clinical investigations.


Assuntos
Pulmão/fisiologia , Volume de Ventilação Pulmonar/fisiologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Envelhecimento/fisiologia , Feminino , Humanos , Medidas de Volume Pulmonar/métodos , Masculino , Pessoa de Meia-Idade , Alvéolos Pulmonares/fisiologia , Fluxo Sanguíneo Regional/fisiologia , Respiração , Testes de Função Respiratória/métodos , Espirometria , Adulto Jovem
13.
IEEE J Transl Eng Health Med ; 5: 2700209, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-29282434

RESUMO

The inspired sinewave technique is a noninvasive method to measure airway dead space, functional residual capacity, pulmonary blood flow, and lung inhomogeneity simultaneously. The purpose of this paper was to assess the repeatability and accuracy of the current device prototype in measuring functional residual capacity, and also participant comfort when using such a device. To assess within-session repeatability, six sinewave measurements were taken over two-hour period in 17 healthy volunteers. To assess day-to-day repeatability, measurements were taken over 16 days in 3 volunteers. To assess accuracy, sinewave measurements were compared to body plethysmography in 44 healthy volunteers. Finally, 18 volunteers who experienced the inspired sinewave device, body plethysmography and spirometry were asked to rate the comfort of each technique on a scale of 1-10. The repeatability coefficients for dead space, functional residual capacity, and blood flow were 48.7 ml, 0.48L, and 2.4L/min respectively. Bland-Altman analyses showed a mean BIAS(SD) of -0.68(0.42)L for functional residual capacity when compared with body plethysmography. 14 out of 18 volunteers rated the inspired sinewave device as their preferred technique. The repeatability and accuracy of functional residual capacity measurements were found to be as good as other techniques in the literature. The high level of comfort and the non-requirement of patient effort meant that, if further refined, the inspired sinewave technique could be an attractive solution for difficult patient groups such as very young children, elderly, and ventilated patients.

14.
Sci Rep ; 7(1): 7499, 2017 09 06.
Artigo em Inglês | MEDLINE | ID: mdl-28878215

RESUMO

Arterial oxygen partial pressure can increase during inspiration and decrease during expiration in the presence of a variable shunt fraction, such as with cyclical atelectasis, but it is generally presumed to remain constant within a respiratory cycle in the healthy lung. We measured arterial oxygen partial pressure continuously with a fast intra-vascular sensor in the carotid artery of anaesthetized, mechanically ventilated pigs, without lung injury. Here we demonstrate that arterial oxygen partial pressure shows respiratory oscillations in the uninjured pig lung, in the absence of cyclical atelectasis (as determined with dynamic computed tomography), with oscillation amplitudes that exceeded 50 mmHg, depending on the conditions of mechanical ventilation. These arterial oxygen partial pressure respiratory oscillations can be modelled from a single alveolar compartment and a constant oxygen uptake, without the requirement for an increased shunt fraction during expiration. Our results are likely to contribute to the interpretation of arterial oxygen respiratory oscillations observed during mechanical ventilation in the acute respiratory distress syndrome.


Assuntos
Artérias Carótidas/metabolismo , Pulmão/fisiologia , Oxigênio/análise , Animais , Pressão Arterial , Pulmão/irrigação sanguínea , Respiração Artificial , Suínos
15.
Respir Physiol Neurobiol ; 242: 12-18, 2017 08.
Artigo em Inglês | MEDLINE | ID: mdl-28323205

RESUMO

Routine estimation of functional residual capacity (FRC) in ventilated patients has been a long held goal, with many methods previously proposed, but none have been used in routine clinical practice. This paper proposes three models for determining FRC using the nitrous oxide concentration from the entire expired breath in order to improve the precision of the estimate. Of the three models proposed, a dead space with two mixing compartments provided the best results, reducing the mean limits of agreement with the FRC measured by whole body plethysmography by up to 41%. This moves away from traditional lung models, which do not account for mixing within the dead space. Compared to literature values for FRC, the results are similar to those obtained using helium dilution and better than the LUFU device (Dräger Medical, Lubeck, Germany), with significantly better limits of agreement compared to plethysmography.


Assuntos
Capacidade Residual Funcional , Pulmão/fisiologia , Modelos Biológicos , Espaço Morto Respiratório , Testes Respiratórios/instrumentação , Testes Respiratórios/métodos , Simulação por Computador , Feminino , Capacidade Residual Funcional/fisiologia , Hélio , Humanos , Análise dos Mínimos Quadrados , Pulmão/anatomia & histologia , Masculino , Óxido Nitroso/análise , Pletismografia Total , Análise de Regressão , Respiração , Adulto Jovem
16.
J Psychopharmacol ; 28(6): 536-44, 2014 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-24699062

RESUMO

BACKGROUND: Ketamine has a rapid antidepressant effect in treatment-resistant depression (TRD). The effects on cognitive function of multiple ketamine infusions and of concurrent antidepressant medication on response rate and duration are not known. METHOD: Twenty-eight patients with uni- or bipolar TRD were treated over three weeks with either three or six ketamine infusions (0.5 mg/kg over 40 minutes) in the recovery room of a routine ECT clinic. Post-treatment memory assessments were conducted on day 21 (4-7 days after the final infusion). Patients were followed up for six months where possible, with severity of depression and side effects monitored throughout. RESULTS: Eight (29%) patients responded of whom four remitted. Only three (11%) patients had responded within six hours after a single infusion, but in all responders, the response had developed before the third infusion. The duration of response from the final infusion was variable (median 70, range 25-168 days). Discontinuations included two (7%) because of acute adverse reactions during the infusion and five (18%) because of failure to benefit and increasing anxiety. Ketamine was not associated with memory impairment. The ECT clinic was rated suitable by patients and offered appropriate levels of monitoring. CONCLUSION: This small, open label naturalistic study shows that up to six low dose ketamine infusions can safely be given within an existing NHS clinical structure to patients who continue their antidepressants. The response rate was comparable to that found in RCTs of single doses of ketamine in antidepressant-free patients but took slightly longer to develop.


Assuntos
Afeto/efeitos dos fármacos , Antidepressivos/administração & dosagem , Encéfalo/efeitos dos fármacos , Transtorno Depressivo Resistente a Tratamento/tratamento farmacológico , Eletroconvulsoterapia , Ketamina/administração & dosagem , Ambulatório Hospitalar , Adulto , Antidepressivos/efeitos adversos , Encéfalo/fisiopatologia , Transtorno Depressivo Resistente a Tratamento/diagnóstico , Transtorno Depressivo Resistente a Tratamento/fisiopatologia , Transtorno Depressivo Resistente a Tratamento/psicologia , Esquema de Medicação , Feminino , Humanos , Infusões Intravenosas , Ketamina/efeitos adversos , Masculino , Memória/efeitos dos fármacos , Pessoa de Meia-Idade , Fatores de Tempo , Resultado do Tratamento
18.
Respir Physiol Neurobiol ; 191: 1-8, 2014 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-24184746

RESUMO

Two challenges in the management of Acute Respiratory Distress Syndrome are the difficulty in diagnosing cyclical atelectasis, and in individualising mechanical ventilation therapy in real-time. Commercial optical oxygen sensors can detect [Formula: see text] oscillations associated with cyclical atelectasis, but are not accurate at saturation levels below 90%, and contain a toxic fluorophore. We present a computer-controlled test rig, together with an in-house constructed ultra-rapid sensor to test the limitations of these sensors when exposed to rapidly changing [Formula: see text] in blood in vitro. We tested the sensors' responses to simulated respiratory rates between 10 and 60 breaths per minute. Our sensor was able to detect the whole amplitude of the imposed [Formula: see text] oscillations, even at the highest respiratory rate. We also examined our sensor's resistance to clot formation by continuous in vivo deployment in non-heparinised flowing animal blood for 24h, after which no adsorption of organic material on the sensor's surface was detectable by scanning electron microscopy.


Assuntos
Simulação por Computador , Tecnologia de Fibra Óptica , Oxigênio/sangue , Atelectasia Pulmonar/sangue , Análise de Variância , Animais , Relógios Biológicos , Coagulação Sanguínea/fisiologia , Pressão Sanguínea/fisiologia , Técnicas In Vitro , Microscopia Eletrônica de Varredura , Pressão Parcial
19.
Physiol Meas ; 34(9): N71-81, 2013 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-23954921

RESUMO

The development and construction of a tapered-tip fibre-optic fluorescence based oxygen sensor is described. The sensor is suitable for fast and real-time monitoring of human breathing. The sensitivity and response time of the oxygen sensor were evaluated in vitro with a gas pressure chamber system, where oxygen partial pressure was rapidly changed between 5 and 15 kPa, and then in vivo in five healthy adult participants who synchronized their breathing to a metronome set at 10, 20, 30, 40, 50, and 60 breaths min(-1). A Datex Ultima medical gas analyser was used to monitor breathing rate as a comparator. The sensor's response time in vitro was less than 150 ms, which allows accurate continuous measurement of inspired and expired oxygen pressure. Measurements of breathing rate by means of our oxygen sensor and of the Datex Ultima were in strong agreement. The results demonstrate that the device can reliably resolve breathing rates up to 60 breaths min(-1), and that it is a suitable cost-effective alternative for monitoring breathing rates and end-tidal oxygen partial pressure in the clinical setting. The rapid response time of the sensor may allow its use for monitoring rapid breathing rates as occur in children and the newborn.


Assuntos
Monitorização Fisiológica/instrumentação , Fibras Ópticas , Oxigênio/metabolismo , Respiração , Adulto , Humanos , Medições Luminescentes , Temperatura , Fatores de Tempo
20.
Respir Physiol Neurobiol ; 189(1): 174-82, 2013 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-23702307

RESUMO

Conventional methods for monitoring lung function can require complex, or special, gas analysers, and may therefore not be practical in clinical areas such as the intensive care unit (ICU) or operating theatre. The system proposed in this article is a compact and non-invasive system for the measurement and monitoring of lung variables, such as alveolar volume, airway dead space, and pulmonary blood flow. In contrast with conventional methods, the compact apparatus and non-invasive nature of the proposed method could eventually allow it to be used in the ICU, as well as in general clinical settings. We also propose a novel tidal ventilation model using a non-invasive oscillating gas-forcing technique, where both nitrous oxide and oxygen are used as indicator gases. Experimental results are obtained from healthy volunteers, and are compared with those obtained using a conventional continuous ventilation model. Our findings show that the proposed technique can be used to assess lung function, and has several advantages over conventional methods such as compact and portable apparatus, easy usage, and quick estimation of cardiopulmonary variables.


Assuntos
Modelos Biológicos , Testes de Função Respiratória/métodos , Adulto , Voluntários Saudáveis , Humanos , Troca Gasosa Pulmonar/fisiologia
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