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1.
J Thorac Dis ; 10(6): 3689-3700, 2018 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30069367

RESUMO

BACKGROUND: Air leak post-lobectomy continues to remain a significant clinical problem, with upper lobectomy associated with higher air leak rates. This paper investigated the pathophysiological role of pleural stress in the development of post-lobectomy air leak. METHODS: Preoperative characteristics and postoperative data from 367 consecutive video assisted thoracic surgery (VATS) lobectomy resections from one centre were collected prospectively between January 2014 and March 2017. Computer modelling of a lung model using finite element analysis (FEA) was used to calculate pleural stress in differing areas of the lung. RESULTS: Air leak following upper lobectomy was significantly higher than after middle or lower lobectomy (6.3% versus 2.5%, P=0.044), resulting in a significant six-day increase in mean hospital stay, P=0.004. The computer simulation model of the lung showed that an apical bullet shape was subject to eightyfold higher stress than the base of the lung model. CONCLUSIONS: After upper lobectomy, the bullet shape of the apex of the exposed lower lobe was associated with high pleural stress, and a reduction in mechanical support by the chest wall to the visceral pleura due to initial post-op lack of chest wall confluence. It is suggested that such higher stress in the lower lobe apex explains the higher parenchymal air leak post-upper lobectomy. The pleural stress model also accounts for the higher incidence of right-sided prolonged air leak post-resection.

2.
J Thorac Dis ; 9(10): 3793-3801, 2017 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-29268387

RESUMO

BACKGROUND: The adherence of the heart to physical laws, such as Laplace's Law, may act as a measure of the organ's relative efficiency. Allometric relationships were investigated to assess the heart's efficiency concerning end-diastolic and end-systolic volumes, cardiac pressurization energy, cardiac output and mass. METHODS: Data to generate allometric relationships was obtained using a literature search, identifying heart and lung data across different mammalian and bird species. Statistical analysis was carried out using ordinary least squares (OLS) estimation. RESULTS: Near isometric relationships exist between body mass and seven parameters indicating no "efficiency of size" with scaling of the heart, and size-matching of the heart to the lungs and whole body. Even though there was equal efficiency in pressurization energy generation, cardiac output was maximally efficient in small mammals <10 kg and birds; the human heart reached only 71% efficiency. This loss in cardiac efficiency with increasing body mass can be explained by the aortic cross-section that scales following the three-quarter allometry law, compared to end-systolic and end-diastolic volumes that scale isometrically. The heart is therefore throttled by a relatively small aorta at large body size. CONCLUSIONS: Mammalian and avian hearts operate at similar efficiencies, demonstrating a high degree of symmorphosis, however cardiac output efficiency decreases in larger animals due to a relatively negative aortic cross-section allometry. This work has a myriad of potential applications including explaining cardiac dysfunction in athletes, patient-prosthesis mismatch in aortic valve replacement and why heavy exercise is associated with a worse prognosis than mild or moderate exercise.

3.
J Thorac Dis ; 9(4): 979-989, 2017 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-28523153

RESUMO

BACKGROUND: Theories elucidating pleural pressures should explain all observations including the equal and opposite recoil of the chest wall and lungs, the less than expected pleural hydrostatic gradient and its variation at lobar margins, why pleural pressures are negative and how pleural fluid circulation functions. METHODS: A theoretical model describing equilibrium between buoyancy, hydrostatic forces, and capillary forces is proposed. The capillary equilibrium model described depends on control of pleural fluid volume and protein content, powered by an active pleural pump. RESULTS: The interaction between buoyancy forces, hydrostatic pressure and capillary pressure was calculated, and values for pleural thickness and pressure were determined using values for surface tension, contact angle, pleural fluid and lung densities found in the literature. Modelling can explain the issue of the differing hydrostatic vertical pleural pressure gradient at the lobar margins for buoyancy forces between the pleural fluid and the lung floating in the pleural fluid according to Archimedes' hydrostatic paradox. The capillary equilibrium model satisfies all salient requirements for a pleural pressure model, with negative pressures maximal at the apex, equal and opposite forces in the lung and chest wall, and circulatory pump action. CONCLUSIONS: This model predicts that pleural effusions cannot occur in emphysema unless concomitant heart failure increases lung density. This model also explains how the non-confluence of the lung with the chest wall (e.g., lobar margins) makes the pleural pressure more negative, and why pleural pressures would be higher after an upper lobectomy compared to a lower lobectomy. Pathological changes in pleural fluid composition and lung density alter the equilibrium between capillarity and buoyancy hydrostatic pressure to promote pleural effusion formation.

4.
Ann Thorac Surg ; 103(3): e299-e300, 2017 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-28219577

RESUMO

Patients with Marfan syndrome and presenting with acute aortic dissection have fragile aorta, causing bleeding problems in the anastomosis between the graft and the aorta. Hemostatic impairment following circulatory arrest and prolonged cardiopulmonary bypass contribute to these problems. We describe a technique to control persistent bleeding from the anastomosis in the aortopulmonary recess using two kissing inflated balloons at the tip of two Foley catheters to tamponade the bleeding sites.


Assuntos
Aneurisma Aórtico/cirurgia , Dissecção Aórtica/cirurgia , Hemostasia Cirúrgica/métodos , Dissecção Aórtica/etiologia , Aneurisma Aórtico/etiologia , Humanos , Síndrome de Marfan/complicações
6.
Med Hypotheses ; 92: 88-93, 2016 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-27241265

RESUMO

OBJECTIVE: A hypothesis is presented suggesting that the pathogenesis of apical lung disease is due to progression of subclinical congenital apical bullae in people with low Body Mass Index (BMI), a combination present in 15% of the population, due to high pleural stress levels present in the antero-posteriorly flattened chests of these individuals. DESIGN: The hypothesis was tested for validity in two apical lung pathologies with widespread epidemiological literature, namely tuberculosis (TB) and primary spontaneous pneumothorax (PSP), assessing whether the hypothesis could identify high-risk populations, explain exceptional cases like apical lower lobe disease and confirm predictions. RESULTS: The biomechanical hypothesis can explain the high-risk factors of apical location, age, gender and low-BMI build, as well as the occurrence of disease in the apex of the lower lobe, in both TB and PSP patients. A predicted common pathogenesis for apical lung disease was confirmed by the higher-than-expected incidence of concomitant TB and PSP. CONCLUSION: Pleural stress levels depend on chest wall shape, but are highest in the apex of young males with low BMI, leading to growth of congenital bullae that can eventually limit clearance inhaled material, superinfect or burst. This hypothesis suggests that low-dose computerized tomography may be used to screen for TB eradication. This paper is the first to propose a biomechanical mechanism for all apical lung disease pathophysiology.


Assuntos
Pneumopatias/fisiopatologia , Pleura/fisiopatologia , Adolescente , Adulto , Fenômenos Biomecânicos , Índice de Massa Corporal , Criança , Pré-Escolar , Estudos de Coortes , Progressão da Doença , Feminino , Humanos , Lactente , Recém-Nascido , Pulmão/fisiologia , Masculino , Pessoa de Meia-Idade , Pneumotórax/fisiopatologia , Risco , Fatores Sexuais , Tórax/anatomia & histologia , Tuberculose/fisiopatologia , Adulto Jovem
7.
Clin Anat ; 28(8): 1008-16, 2015 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-26297570

RESUMO

The human rib cage resembles a masonry dome in shape. Masonry domes have a particular construction that mimics stress distribution. Rib cortical thickness and bone density were analyzed to determine whether the morphology of the rib cage is sufficiently similar to a shell dome for internal rib structure to be predicted mathematically. A finite element analysis (FEA) simulation was used to measure stresses on the internal and external surfaces of a chest-shaped dome. Inner and outer rib cortical thickness and bone density were measured in the mid-axillary lines of seven cadaveric rib cages using computerized tomography scanning. Paired t tests and Pearson correlation were used to relate cortical thickness and bone density to stress. FEA modeling showed that the stress was 82% higher on the internal than the external surface, with a gradual decrease in internal and external wall stresses from the base to the apex. The inner cortex was more radio-dense, P < 0.001, and thicker, P < 0.001, than the outer cortex. Inner cortical thickness was related to internal stress, r = 0.94, P < 0.001, inner cortical bone density to internal stress, r = 0.87, P = 0.003, and outer cortical thickness to external stress, r = 0.65, P = 0.035. Mathematical models were developed relating internal and external cortical thicknesses and bone densities to rib level. The internal anatomical features of ribs, including the inner and outer cortical thicknesses and bone densities, are similar to the stress distribution in dome-shaped structures modeled using FEA computer simulations of a thick-walled dome pressure vessel. Fixation of rib fractures should include the stronger internal cortex.


Assuntos
Modelos Teóricos , Costelas/anatomia & histologia , Parede Torácica/anatomia & histologia , Densidade Óssea , Cadáver , Análise de Elementos Finitos , Humanos , Fraturas das Costelas/patologia , Costelas/diagnóstico por imagem , Estresse Mecânico , Parede Torácica/diagnóstico por imagem , Tomografia por Raios X
8.
Clin Anat ; 28(5): 614-20, 2015 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-25851916

RESUMO

This study was aimed at determining the cause for the high incidence of tuberculosis (TB) reactivation occurring in males with a low body mass index (BMI). Current thinking about pulmonary TB describes infection in the lung apex resulting in cavitation after reactivation. A different hypothesis is put forward for TB infection, suggesting that this occurs in subclinical apical cavities caused by increased pleural stress due to a low BMI body habitus. A finite element analysis (FEA) model of a lung was constructed including indentations for the first rib guided by paramedian sagittal CT reconstructions, and simulations were conducted with varying antero-posterior (AP) diameters to mimic chests with a different thoracic index (ratio of AP to the transverse chest diameters). A Pubmed search was conducted about gender and thoracic index, and the effects of BMI on TB. FEA modeling revealed a tenfold increase in stress levels at the lung apex in low BMI chests, and a four-fold increase with a low thoracic index, r(2) = 0.9748 P < 0.001. Low thoracic index was related to BMI, P = 0.001. The mean thoracic index was statistically significantly lower in males, P = 0.001, and increased with age in both genders. This article is the first to suggest a possible mechanism linking pulmonary TB reactivation to low BMI due to the flattened thoracic wall shape of young male adults. The low thoracic index in young males may promote TB reactivation due to tissue destruction in the lung apex from high pleural stress levels.


Assuntos
Parede Torácica/anatomia & histologia , Tuberculose Pulmonar/epidemiologia , Índice de Massa Corporal , Feminino , Análise de Elementos Finitos , Humanos , Incidência , Masculino , Modelos Anatômicos , Radiografia Torácica/métodos , Recidiva , Fatores Sexuais , Parede Torácica/diagnóstico por imagem , Tomografia Computadorizada por Raios X , Adulto Jovem
9.
BMJ Case Rep ; 20152015 Apr 16.
Artigo em Inglês | MEDLINE | ID: mdl-25883250

RESUMO

The incidence of pulmonary arteriovenous malformations (PAVMs) is 2.5 in 100,000. 80% are associated with Osler-Weber-Rendu syndrome or hereditary haemorrhagic telangiectasia. We report the case of a 70-year-old man with a 6 cm spherical mass incidentally found on chest X-ray. There was a localised systolic bruit over the right lower zone posteriorly; however, he was asymptomatic. He had suffered a stroke, affecting his right hand and his speech, from which he recovered. He experienced regular transient ischaemic attacks, on an average of every 2 months. He underwent a right lower lobectomy and on ligating the right lower lobe pulmonary artery the saturations of oxygen rose from 92% to 97%, demonstrating a significant right to left extracardiac shunt. Postoperative recovery was excellent and 1 year later the patient reports no further neurological symptoms. 40% of such lesions exhibit symptoms, however, only one-third are neurological. Treatment should be by percutaneous embolisation.


Assuntos
Malformações Arteriovenosas/complicações , Acidente Vascular Cerebral/etiologia , Receptores de Activinas Tipo II/genética , Receptores de Activinas Tipo II/metabolismo , Idoso , Fístula Arteriovenosa/complicações , Fístula Arteriovenosa/diagnóstico , Malformações Arteriovenosas/cirurgia , Humanos , Masculino , Artéria Pulmonar/anormalidades , Veias Pulmonares/anormalidades , Doenças Raras/diagnóstico , Doenças Raras/etiologia , Acidente Vascular Cerebral/diagnóstico , Resultado do Tratamento
10.
Clin Anat ; 28(4): 512-9, 2015 May.
Artigo em Inglês | MEDLINE | ID: mdl-25716367

RESUMO

As ribs adapt to stress like all bones, and the chest behaves as a pressure vessel, the effect of stress on the ribs can be determined by measuring rib height and thickness. Rib height and thickness (depth) were measured using CT scans of seven rib cages from anonymized cadavers. A Finite Element Analysis (FEA) model of a rib cage was constructed using a validated approach and used to calculate intramuscular forces as the vectors of both circumferential and axial chest wall forces at right angles to the ribs. Nonlinear quadratic models were used to relate rib height and rib thickness to rib level, and intercostal muscle force to vector stress. Intercostal muscle force was also related to vector stress using Pearson correlation. For comparison, rib height and thickness were measured on CT scans of children. Rib height increased with rib level, increasing by 13% between the 3rd and 7th rib levels, where the 7th/8th rib was the widest part or "equator" of the rib cage, P < 0.001 (t-test). Rib thickness showed a statistically significant 23% increase between the 3rd and 7th ribs, P = 0.004 (t-test). Intercostal muscle force was significantly related to vector stress, Pearson correlation r = 0.944, P = 0.005. The three nonlinear quadratic models developed all had statistically significant parameter estimates with P < 0.03. External rib morphology, in particular rib height and thickness, can be predicted using statistical mathematical models. Rib height is significantly related to the calculated intercostal muscle force, showing that environmental factors affect external rib morphology.


Assuntos
Músculos Intercostais/fisiologia , Modelos Biológicos , Costelas/anatomia & histologia , Costelas/fisiologia , Análise de Elementos Finitos , Humanos , Imageamento Tridimensional , Radiografia , Fraturas das Costelas/etiologia , Costelas/diagnóstico por imagem , Estresse Mecânico
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