Megan J Wallace

• PhD, BSc(Hons)
• Director of Medical Student Research Faculty of Medicine & Head, Lung Development Research Group at Monash University (Australia)

In this investigation, we applied a single-projection dark-field imaging technique to gain statistical information on the smallest airway structures within the lung$\unicode{x2014}$the alveoli$\unicode{x2014}$focusing on their size and number as key indicators of lung health. The algorithm employed here retrieves the projected thickness of the samp...

The mechanisms linking maternal asthma (MA) exposure in utero and subsequent risk of asthma in childhood are not fully understood. Pathological airway remodelling, including reticular basement membrane thickening, has been reported in infants and children who go on to develop asthma later in childhood. This suggests altered airway development befor...

Background Very preterm infants often require respiratory support after birth with current recommendations suggesting the use of continuous positive airway pressure (CPAP) of 4–8 cmH 2 O and an initial fraction of inspired oxygen (FiO 2 ) of 0.21–0.3. We have examined the interaction of high and low CPAP and FiO 2 levels on breathing rates and lung...

Introduction As airway liquid is cleared into lung interstitial tissue after birth, the chest wall must expand to accommodate this liquid and the incoming air. We examined the effect of applying external positive and negative pressures to the chest wall on lung aeration in near-term rabbit kittens at risk of developing respiratory distress. Method...

Maternal asthma is associated with increased rates of neonatal lung disease, and fetuses from asthmatic ewes have fewer surfactant‐producing cells and lower surfactant‐protein B gene (SFTPB) expression than controls. Antenatal betamethasone increases lung surfactant production in preterm babies, and we therefore tested this therapy in experimental...

Background: As very preterm infants have surfactant-deficient and highly incompliant lungs, slowing lung deflation during expiration might help preserve functional residual capacity(FRC) during lung aeration. In this study, we investigated the effect of expiratory resistance(Re) on lung aeration during positive pressure ventilation in preterm rabb...

Introduction: Much has been written about the need for medical students to have research skills. Increasing numbers of medical schools are incorporating compulsory research experiences to increase research literacy. However, little is known about the student perceptions of, and outcomes from, those programs. We aimed to examine medical students' pe...

Background: Manual tactile stimulation is used to counteract apnea in preterm infants, but it is unknown when this intervention should be applied. We compared an anticipatory to a reactive approach using vibrotactile stimulation to prevent hypoxia induced apneas. Methods: Preterm rabbit kittens were prematurely delivered and randomized to either...

Background: Infants with a congenital diaphragmatic hernia (DH) have underdeveloped lungs and require mechanical ventilation after birth, but the optimal approach is unknown. We hypothesised that sustained inflation (SI) increases lung aeration in newborn kittens with a DH. Methods: In pregnant New Zealand white rabbits, a left-sided DH was indu...

Disclosure: R.S. Dhavan: None. K.L. Short: None. J. Ng: None. M.J. Wallace: None. P. Monaghan-Nichols: None. D. DeFranco: None. T.J. Cole: None. Glucocorticoid (GC) signaling is essential for normal fetal organ development. During late gestation a surge of endogenous GCs contributes to organ maturation, particularly important for the lung where thi...

X-ray imaging is a fast, precise and non-invasive method of imaging which, combined with computed tomography, provides detailed 3D rendering of samples. Incorporating propagation-based phase contrast can vastly improve data quality for weakly attenuating samples via material-specific phase retrieval filters, allowing radiation exposure to be reduce...

Congenital diaphragmatic hernia (CDH) is a major cause of severe lung hypoplasia and pulmonary hypertension in the newborn. While the pulmonary hypertension is thought to result from abnormal vascular development and arterial vasoreactivity, the anatomical changes in vascular development are unclear. We have examined the 3D structure of the pulmona...

Simple Summary Bacille-Calmette Guérin (BCG), the vaccine against tuberculosis, is the most widely used vaccine in the world, given to almost two-thirds of newborns. BCG also has non-specific effects, which affect immune responses more broadly and impact mortality from unrelated infections. It is also important to understand the effects of BCG on o...

Objective . To develop a robust technique for calculating regional volume changes within the lung from X-ray radiograph sequences captured during ventilation, without the use of computed tomography (CT). Approach . This technique is based on the change in transmitted X-ray intensity that occurs for each lung region as air displaces the attenuating...

We present a robust technique for calculating regional volume changes within the lung from X-ray image sequences captured during ventilation without the use of computed tomography (CT). This technique is based on the change in transmitted X-ray intensity that occurs in each lung region as air displaces the attenuating lung tissue. Lung air volumes...

Approximately 53% of near-term newborns admitted into intensive care, experience respiratory distress. These newborns are commonly delivered by caesarean section and have elevated airway liquid volumes at birth, which can cause respiratory morbidity. We investigated the effect of providing respiratory support with a positive end expiratory pressure...

Background and aims: Preterm birth is associated with increased risk of cardiovascular disease (CVD). This may reflect a legacy of inflammatory exposures such as chorioamnionitis which complicate pregnancies delivering preterm, or recurrent early-life infections, which are common in preterm infants. We previously reported that experimental chorioam...

Preterm infants are commonly supported with 4–8 cm H2O continuous positive airway pressures (CPAP), although higher CPAP levels may improve functional residual capacity (FRC). Preterm rabbits delivered at 29/32 days (~26–28 weeks human) gestation received 0, 5, 8, 12, 15 cm H2O of CPAP or variable CPAP of 15 to 5 or 15 to 8 cm H2O (decreasing ~2 cm...

Background Research engagement plays an integral role in developing clinicians that practice effective, evidence-based medicine. Research participation by clinicians, however, is declining. Given the link between research during medical school and future research output, promotion of medical student research is one avenue by which this shortage can...

Background and aims Preterm birth is associated with increased risk of cardiovascular disease (CVD). This may reflect a legacy of inflammatory exposures such as chorioamnionitis, that complicate pregnancies delivering preterm, or recurrent early-life infections, common in preterm infants. We previously reported that experimental chorioamnionitis fo...

Maternal asthma is known to impact intrauterine growth outcomes, whic*h may be mediated, in part, by altered androgen signalling. Our aim was to explore whether the sheep placenta expresses androgen receptor (AR) isoforms and determine if the differential expression of AR protein isoforms is altered by maternal asthma. Four known AR isoforms were d...

Context: Scholarly experiences have been increasingly employed to support the development of scholarly skills for medical students. How the characteristics of the various scholarly experiences contributes to scholarly outcomes or the complexities of how the experiences build skills, warrants further exploration. Objective: To identify how medica...

Preterm newborns commonly receive intermittent positive pressure ventilation (iPPV) at birth, but the optimal approach that facilitates uniform lung aeration is unknown, particularly in a partially aerated lung. As both inflation time and exogenous surfactant facilitate uniform lung aeration, we investigated whether they can improve lung aeration a...

Glucocorticoid (GC) signalling via the glucocorticoid receptor (GR) is essential for lung maturation in mammals. Previous studies using global or conditional mouse model knockouts of the GR gene have established that GR-mediated signalling in the interstitial mesenchyme of the fetal lung is critical for normal lung development. Screens for downstre...

Background: Spontaneous breathing is essential for successful non-invasive respiratory support delivered by a facemask at birth. As hypoxia is a potent inhibitor of spontaneous breathing, initiating respiratory support with a high fraction of inspired O2 may reduce the risk of hypoxia and increase respiratory effort at birth. Methods: Preterm rabbi...

Key points Experimental maternal allergic asthma in sheep provides an experimental model in which to test impacts on progeny. Fetuses from allergic asthmatic ewes had fewer surfactant‐producing cells in lungs. A greater proportion of lymphocytes from thymus were CD44 positive in fetuses from allergic asthmatic ewes than in controls. These changes t...

Maternal asthma increases the risk of adverse pregnancy outcomes and may affect fetal growth and placental function by differential effects on the expression of glucocorticoid receptor (GR) isoforms, leading to altered glucocorticoid signalling. Our aim was to examine the effect of maternal asthma on placental GR profiles using a pregnant sheep mod...

Preterm birth is characterized by severe lung immaturity that is frequently treated antenatally or postnatally by the synthetic steroid betamethasone. The underlying cellular targets and pathways stimulated by betamethasone in the fetal lung are poorly defined. In this study betamethasone was compared to corticosterone in steroid treated primary cu...

Atherosclerosis is a chronic inflammatory disease that has its origins in early life. Postnatal inflammation exacerbates atherosclerosis, but the possible effect of intrauterine inflammation is largely unexplored. Exposure to inflammation in utero is common, especially in infants born preterm, who have increased cardiovascular risk in adulthood. We...

Background: Prenatal glucocorticoid treatment decreases alveolar tissue volumes and facilitates fetal lung maturation, however the mechanisms responsible are largely unknown. This study examines whether changes in versican levels or sulphation patterns of chondroitin sulphate (CS) side chains, are associated with glucocorticoid-induced reductions...

Imaging the Brain In Situ with Phase Contrast CT - Volume 24 Supplement - Linda Croton, Kaye Morgan, David Paganin, Lauren Kerr, Megan Wallace, Kelly Crossley, Gary Ruben, Suzanne Miller, Naoto Yagi, Kentaro Uesugi, Stuart Hooper, Marcus Kitchen

Phase contrast X-ray imaging (PCXI) is an emerging imaging modality that has the potential to greatly improve radiography for medical imaging and materials analysis. PCXI makes it possible to visualise soft-tissue structures that are otherwise unresolved with conventional CT by rendering phase gradients in the X-ray wavefield visible. This can impr...

Intrauterine growth restriction (IUGR) can lead to adverse neurodevelopmental sequelae in postnatal life. However, the effects of IUGR on the cerebellum are still to be fully elucidated. A major determinant of growth and development of the cerebellum is proliferation and subsequent migration of cerebellar granule cells. Our objective was to determi...

Phase contrast X-ray imaging (PCXI) is an emerging imaging modality that has the potential to greatly improve radiography for medical imaging and materials analysis. PCXI makes it possible to visualise soft-tissue structures that are otherwise unresolved with conventional CT by rendering phase gradients in the X-ray wavefield visible. This can impr...

Phase-contrast X-ray imaging can improve the visibility of weakly absorbing objects (e.g. soft tissues) by an order of magnitude or more compared to conventional radiographs. Combining phase retrieval with computed tomography (CT) can increase the signal-to-noise ratio (SNR) by up to two orders of magnitude over conventional CT at the same radiatio...

Background Non-invasive ventilation is sometimes unable to provide the respiratory needs of very premature infants in the delivery room. While airway obstruction is thought to be the main problem, the site of obstruction is unknown. We investigated whether closure of the larynx and epiglottis is a major site of airway obstruction. Methods We used...

Excessive liquid in airways and/or in distal lung tissue may underpin the respiratory morbidity associated with transient tachypnea of the newborn (TTN). However, its effects on lung aeration and respiratory function following birth are unknown. We investigated the effect of elevated airway liquid volumes on newborn respiratory function. Near term...

Intrauterine growth restriction (IUGR) is a major cause of antenatal brain injury. We aimed to characterize cerebellar deficits following IUGR and to investigate the potential underlying cellular and molecular mechanisms. At embryonic day 18, pregnant rats underwent either sham surgery (controls; n = 23) or bilateral uterine vessel ligation to rest...

Background: A congenital diaphragmatic hernia can result in severe lung hypoplasia that increases the risk of morbidity and mortality after birth, but little is known about the cardiorespiratory transition at birth. Methods: Using phase contrast X-ray imaging and angiography, we examined the cardiorespiratory transition at birth in rabbit kitten...

Key points: Lung aeration at birth significantly increases pulmonary blood flow, which is unrelated to increased oxygenation or other spatial relationships that match ventilation to perfusion. Using simultaneous X-ray imaging and angiography in near-term rabbits, we investigated the relative contributions of the vagus nerve and oxygenation to the...

Antenatal glucocorticoids, exogenous surfactant and positive end-expiratory pressure (PEEP) ventilation are commonly provided to preterm infants to enhance respiratory function after birth. It is unclear how these treatments interact to improve the transition to air-breathing at birth. We investigated the relative contribution of antenatal betameth...

BackgroundA sustained inflation (SI) facilitates lung aeration, but the most effective pressure and duration are unknown. We investigated the effect of gestational age and airway liquid volume on the required inflation pressure and SI duration.Methods Rabbit kittens were delivered at 27, 29 and 30 days gestation, intubated and airway liquid was asp...

Cardiovascular disease continues to be the leading cause of global morbidity and mortality. Traditional risk factors account for only part of the attributable risk. The origins of atherosclerosis are in early life, a potential albeit largely unrecognized window of opportunity for early detection and treatment of subclinical cardiovascular disease....

Respiratory health is directly linked to the structural and mechanical properties of the airways of the lungs. For studying respiratory development and pathology, the ability to quantitatively measure airway dimensions and changes in their size during respiration is highly desirable. Real-time imaging of the terminal airways with sufficient contras...

Lung aeration stimulates the increase in pulmonary blood flow (PBF) at birth, but spatial relationships between PBF and lung aeration and the role of increased oxygenation remains unclear. Using simultaneous phase-contrast X-ray imaging and angiography, we have investigated the separate roles of lung aeration and increased oxygenation in PBF change...

Maternal asthma during pregnancy adversely affects pregnancy outcomes but identification of the cause/s, and the ability to evaluate interventions, is limited by the lack of an appropriate animal model. We therefore aimed to characterise maternal lung and cardiovascular responses and fetal-placental growth and lung surfactant levels in a sheep mode...

For some lung diseases, assessment of alveolar dimension could add critical information to inform patient care and disease progression. However, current clinical imaging techniques, such as computed tomography, lack the resolution required to measure these small structures in patients. While the gold standard imaging modality for measuring alveoli...

Background: Trop2 was first discovered as a biomarker of invasive trophoblast cells. Since then most research has focused on its role in tumourigenesis because it is highly expressed in the vast majority of human tumours and animal models of cancer. It is also highly expressed in stem cells and in many organs during development. Results: We revi...

Herein a propagation-based phase contrast x-ray imaging technique for measuring particle size and number is presented. This is achieved with an algorithm that utilizes the Fourier space signature of the speckle pattern associated with the images of particles. We validate this algorithm using soda-lime glass particles, demonstrating its effectivenes...

Background: At birth, the transition to newborn life is triggered by lung aeration, which stimulates a large increase in pulmonary blood flow (PBF). Current theories predict that the increase in PBF is spatially related to ventilated lung regions as they aerate after birth. Using simultaneous phase contrast X-ray imaging and angiography we investig...

Atherosclerosis is a chronic condition that may begin prior to birth, particularly in the presence of factors that act through inflammatory pathways. Inflammation may alter epigenetic marks, and changes in methylation are observed in atherosclerotic lesions. We hypothesised that intrauterine inflammation (chorioamnionitis, which complicates 1-4% of...

Current recommendations suggest the use of positive end-expiratory pressures (PEEP) to assist very preterm infants to develop a functional residual capacity (FRC) and establish gas exchange at birth. However, maintaining a consistent PEEP is difficult and so the lungs are exposed to changing distending pressures after birth, which can affect respir...

Key points Erythropoietin (EPO) has been suggested as a potential treatment for bronchopulmonary dysplasia (BPD) in preterm infants. Ventilation‐induced lung injury (VILI) is a major cause of BPD in preterm neonates. We investigated whether early high‐dose EPO ( i.v. 5000 IU kg ⁻¹ ) administration can reduce lung inflammation and injury resultant f...

The interrelationship between the role of surfactant and a sustained inflation to aid ex-utero transition of the preterm lung is unknown. We compared the effect of surfactant administered before and after an initial sustained inflation on gas exchange, lung mechanics, spatial distribution of ventilation and lung injury in preterm lambs. 127d gestat...

Background: Sustained inflation (SI) at birth facilitates establishment of functional residual capacity (FRC) in the preterm lung, but the ideal lung recruitment strategy is unclear. We have compared the effect of SI and a stepwise positive end-expiratory pressure (PEEP; SEP) strategy in a preterm model. Methods: 127 d gestation lambs received e...

As neonatal resuscitation critically depends upon lung aeration at birth, knowledge of the progression of this process is required to guide ongoing care. We investigated whether expired CO2 (ECO2) levels indicate the degree of lung aeration immediately after birth in two animal models and in preterm infants. Lambs were delivered by caesarean sectio...

[This corrects the article DOI: 10.1371/journal.pone.0070895.].

Phase contrast X-ray movie of the increase in lung aeration in a newborn rabbit kitten (28 days of gestation). The appearance of gas in the distal gas exchange units of the lung coincided with the increase in ECO2 (see Figure 4). (MP4)

Phase contrast X-ray movie of a newborn rabbit kitten (28 days of gestation) demonstrating the changes in lung aeration when ventilation parameters are altered. The changes in ventilation parameters are demonstrated in Figure 6, Kitten 4. (MP4)

Proliferation and migration of fibroblasts are vital for fetal lung development. However the regulatory mechanisms are poorly understood. We have previously shown that TROP2 gene expression is closely associated with fetal lung cell proliferation in vivo and that TROP2 knock-down decreases proliferation of fetal lung fibroblasts in culture. We hypo...

Extremely preterm infants often receive mechanical ventilation (MV), which can contribute to bronchopulmonary dysplasia (BPD). However, the effects of MV alone on the extremely preterm lung and the lung's capacity for repair are poorly understood. To characterise lung injury induced by MV alone, and mechanisms of injury and repair, in extremely pre...

Purpose: Described herein is a new technique for measuring regional lung air volumes from two-dimensional propagation-based phase contrast x-ray (PBI) images at very high spatial and temporal resolution. Phase contrast dramatically increases lung visibility and the outlined volumetric reconstruction technique quantifies dynamic changes in respirat...

Background We investigatedthe effects of positive end expiratory pressure (PEEP) and tidal volume (VT) on lung aeration, pulmonary mechanics, and the distribution of ventilation immediately after birth using a preterm rabbit model.Methods Sixty preterm rabbits (27d) received volume-targeted positive pressure ventilation from birth, with one of 12 c...

Background Mice harbouring gene mutations that cause phenotypic abnormalities during organogenesis are invaluable tools for linking gene function to normal development and human disorders. To generate mouse models harbouring novel alleles that are involved in organogenesis we conducted a phenotype-driven, genome-wide mutagenesis screen in mice usin...

Amplifluor Genotyping Primers. (DOC)

ENU Organogenesis Screening Protocol. (DOC)

Background: Mice harbouring gene mutations that cause phenotypic abnormalities during organogenesis are invaluable tools for linking gene function to normal development and human disorders. To generate mouse models harbouring novel alleles that are involved in organogenesis we conducted a phenotype-driven, genome-wide mutagenesis screen in mice usi...

Key points Intrauterine inflammation is associated with preterm birth and poor long‐term cardiopulmonary and neurological outcomes. The effect of intrauterine inflammation on the cardiopulmonary and cerebral haemodynamic transition after preterm birth is poorly understood. We demonstrated that intrauterine inflammation increased pulmonary vascular...

Background: Recent phase-contrast X-ray imaging studies suggest that inspiration primarily drives lung aeration and airway liquid clearance at birth, which questions the role of adrenaline-induced activation of epithelial sodium channels (ENaCs). We hypothesized that pressures generated by inspiration have a greater role in airway liquid clearance...

Although high frequency ventilation (HFV) is an effective mode of ventilation, there is limited information available in regard to lung dynamics during HFV. To improve the knowledge of lung function during HFV we have developed a novel lung imaging and analysis technique. The technique can determine complex lung motion information in vivo with a te...

Lung motion during ventilation at 10 Hz. Phase contrast X-ray video showing the motion of the lung tissue as a result of the high frequency mechanical ventilation. Each frame contains 1016×1016 pixels and was recorded at 300 fps with a 2 ms exposure time. (MP4)

Lung motion during 1 Hz and 10 Hz ventilation. Phase contrast X-ray video showing a rabbit pup being ventilated at 1 Hz (left; 30 fps) and the same rabbit pup being ventilated at 10 Hz (right; 300 fps; video playback slowed down to 30 fps for comparison purposes). It can be seen that while there is less lung motion during high frequency ventilation...

In many animals, including humans, the lungs encase the majority of the heart thus the motion of each organ affects the other. The effects of the motion of the heart on the lungs potentially provides information with regards to both lung and heart health. We present a novel technique that is capable of measuring the effect of the heart on the surro...

Mechanical ventilation of preterm babies increases survival but can also cause ventilator-induced lung injury (VILI), leading to the development of bronchopulmonary dysplasia (BPD). It is not known whether shear stress injury from gases flowing into the preterm lung during ventilation contributes to VILI. Preterm lambs of 131 days' gestation (term ...

Background Although lung aeration increases pulmonary blood flow (PBF) at birth, the regional relationships between lung aeration and the increase PBF are unknown. We investigated the effect of partial ventilation on pulmonary vessels immediately after birth using simultaneous phase contrast X-ray imaging and angiography. Method Newborn rabbits wer...

Intra-amniotic (IA) lipopolysaccharide (LPS) induces intrauterine and fetal lung inflammation and increases lung surfactant and compliance in preterm sheep; however, the mechanisms are unknown. Prostaglandins (PGs) are inflammatory mediators, and PGE(2) has established roles in fetal lung surfactant production. The aim of our first study was to det...

Since lung diseases adversely affect airflow during breathing, they must also alter normal lung motion, which can be exploited to detect these diseases. However, standard imaging techniques such as CT and MRI imaging during breath-holds provide little or no information on lung motion and cannot detect diseases that cause subtle changes in lung stru...

Background: Positive end-expiratory pressure (PEEP) helps very preterm newborns develop functional residual capacity (FRC) and establish adequate gas exchange at birth. In the immediate newborn period, lungs commonly experience changes in PEEP, particularly when the face mask is removed and replaced. This study aimed to determine the distribution o...

Mechanical ventilation (MV) of very premature infants contributes to lung injury and bronchopulmonary dysplasia (BPD), the effects of which can be long-lasting. Little is currently known about the ability of the very immature lung to recover from ventilator-induced lung injury. Our objective was to determine the ability of the injured very immature...

The factors regulating growth of the developing lung are poorly understood, although the degree of fetal lung expansion is critical. The oncogene Trop2 (trophoblast antigen 2) is upregulated during accelerated fetal lung growth, and we hypothesized that it may regulate normal fetal lung growth. We investigated Trop2 expression in the fetal and neon...

Respiratory diseases are one of the greatest causes of morbidity and mortality in humans, affecting people at all stages of their lives. Indeed, respiratory failure is a major cause of morbidity and mortality in newborn infants, asthma is a common disease in children, and pulmonary fibrosis, emphysema, and asthma are all major health issues in adul...

Surfactant deficiency is a major cause of respiratory failure in newborns. We have investigated the roles of surfactant and positive end-expiratory pressure (PEEP) in the development of a functional residual capacity (FRC) and the distribution of ventilation at birth. Preterm rabbit pups (28 d GA) were delivered and received either saline or surfac...

Although bronchopulmonary dysplasia is closely associated with an arrest of alveolar development and pulmonary capillary dysplasia, it is unknown whether these two features are causally related. To investigate the relationship between pulmonary capillaries and alveolar formation, we partially embolized the pulmonary capillary bed. Partial pulmonary...

We have developed a custom-designed ventilator to deliver a stable pressure to the lungs of small animals for use in imaging experiments. Our ventilator was designed with indepen-dent pressure vessels to separately control the Peak Inspiratory Pressure (PIP) and Positive End Expiratory Pressure (PEEP) to minimise pressure fluctuations during the ve...