Abstract
Normal in utero lung development and growth rely upon the expansion of airspaces and the controlled efflux of lung liquid into the amniotic space. Infants with congenital diaphragmatic hernia (CDH) also have lung hypoplasia due to occupation of the chest cavity by the stomach and bowel and, in the most severe cases, the liver. Balloon tracheal occlusion reduces the severity of lung hypoplasia in fetuses with CDH but increases the risk of premature birth. Understanding the optimal occlusion pressure and duration required to improve lung hypoplasia with tracheal occlusion is essential to improving in utero corrective treatments for CDH. The study reports a new method for continuous measurement of the intratracheal and amniotic pressures in an unoccluded and occluded fetal lamb surgical model of CDH. Time-pregnant Merino ewes underwent two recovery hysterotomies: the first at ~80 days of gestation to create the CDH, and the second at ~101 days of gestation to occlude the fetal trachea and implant an intratracheal and amniotic pressure measurement device. Lambs were delivered at ~142 days, and the pressure measurement device was removed and cleaned. The data were downloaded and filtered using a 6 h window. Transrespiratory pressure was calculated.
Introduction
Normal lung development and growth rely upon the expansion of the potential airspaces with fetal lung liquid and the controlled efflux of the lung liquid into the amniotic space1,2,3,4,5. Fetal lung liquid production and the resistance of the upper airways create an in utero intrathoracic pressure1. Historically, in utero measurements of fetal airway pressures were obtained using external pressure sensors via catheters tunneled through the abdominal wall to the fetal trachea5,6,7,8,9,10,11,12,13. The use of these catheters and external sensors (distal to the measurement site) may dampen the pressure signal and necessitate restricted movement of the ewe for continuous measurement or measurements obtained at intervals across gestation. This study aimed to develop a method that allows continuous monitoring of fetal intratracheal and amniotic pressure in unrestrained pregnant animals. The continuous measurements of fetal intratracheal and amniotic pressure will provide a complete understanding of how these pressures change throughout the day over the course of gestation.
Human fetuses with congenital diaphragmatic hernia (CDH) have lung hypoplasia due to herniation of the stomach, the bowel, and the liver (in the most severe cases) into the chest cavity. Lung hyperplasia in infants with tracheal atresia (narrowing of the trachea) highlighted the potential of therapeutic tracheal occlusion for antenatal treatment of CDH14. Tracheal occlusion using an intra-tracheal balloon reduces the severity of lung hypoplasia in fetuses with CDH but at the cost of an increased risk of premature birth15,16,17. An additional risk of aspiration or suffocation exists if the balloon is not removed before birth. Consequently, current tracheal occlusion protocols require a second fetal procedure to remove the balloon occlusion before birth17. The optimal occlusion pressure and duration required to improve lung hypoplasia with tracheal occlusion is unknown, but this knowledge is vital for the optimization of in utero corrective treatments for CDH.
We tested the method using fetal lambs with a surgically created diaphragmatic hernia with and without an occluded trachea.
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Protocol
The protocol adhered to the Australian National Health and Medical Research Council Australian code for the care and use of animals for scientific purposes18. The University of Western Australia Animal Ethics Committee prospectively approved the protocol (RA3/100/1596). Sheep were sourced from the University of Western Australia (UWA) Ridgefield farm (2018-2020). The sheep were introduced to the AAALAC-accredited UWA Large Animal Facility 2-3 weeks prior to surgical intervention. Sheep were initially housed indoors in shared raised floor pens, with single pens used in the peri-operative period. Sheep were fed pellets, oaten chaff, and lupins with a mineral mix calculated on body weight. Rooms were controlled for temperature (20.5-21.5 °C) and maintained on a 12:12 h light: dark cycle. Pain and well-being were evaluated in the postoperative period twice daily for 7 days, then daily until study completion. Monitored postoperative parameters included signs of pain, orbital tightening, respiratory effort, temperature, heart rate, the surgical site, appetite and water intake, activity, lameness, coat condition, fecal consistency, preterm labor, demeanor, and signs of pregnancy toxemia. The scores attributed to each parameter triggered an intervention where necessary.
NOTE: Two recovery surgical procedures were required: ewe preparation, surgical approach and closure, and ewe recovery are the same for both surgical procedures. The first procedure is the surgical creation of the diaphragmatic hernia in the fetal lamb. The second procedure is for placement of the fetal intervention and pressure monitoring device.
1. Surgical creation of the diaphragmatic hernia in the fetal lamb
- Ewe preparation
- At ~80 days gestation, premedicate the ewe with an intramuscular injection of acepromazine (0.04 mg/Kg) and morphine (0.3 mg/Kg).
- Induce anesthesia intravenously with ketamine (5 mg/Kg) and midazolam (0.25 mg/Kg).
- Intubate the ewe trachea with an endotracheal tube (8 mm inner diameter [ID]). Maintain anesthesia with isoflurane (1%-3% in oxygen) delivered by positive pressure ventilation (10-12 breaths/min, tidal volume 8-10 mL/kg).
- Establish ewe monitoring with an electrocardiogram (ECG), invasive arterial blood pressure, expired CO2, peripheral oxygen saturation, and temperature during surgery.
- Place the ewe supine on the gurney. Loop ropes around the ewe's legs and gently secure to the table.
- Shear wool from the ewe's abdomen and flank and then clip it close to the skin.
- Remove dirt and lanolin from the ewe's abdomen, flank, and groin with soap and water.
- Give cefazolin (20 mg/Kg) intravenously every 90 min during surgery.
- Transfer the ewe to the surgical theatre on a gurney.
- Move the ewe from the transport gurney to the surgical table.
- Place ewe in dorsal recumbency position on the surgical table.
- Secure all limbs to the surgical table with soft rope ties.
- Aseptic preparation of the exposed abdomen: Wash 3 times with 4% chlorhexidine surgical scrub, removing contaminated solution between each wash with 70% alcohol.
- Complete sterile preparation by lightly spraying 10% iodine solution on the abdomen, flank, and groins.
- Cover the ewe with a sterile fenestrated surgical drape so that only the abdominal incision site is exposed. Ensure that all surgical instruments, catheters, syringes, and solutions used during surgery are sterile.
- Surgical approach
- Establish line-block local anesthesia by local subcutaneous and muscular infiltration of bupivacaine (5%; 9.5 mL) with a 10 mL syringe and 22 G needle.
- Expose the uterus by a para-midline abdominal incision (8-11 cm) through the ewe's skin, subcutaneous tissue, and linea alba made with a size 10 surgical blade with cautery as required to minimize incisional bleeding.
- Diaphragmatic hernia creation
- Locate the fetal head/thorax via palpation.
- Cover the uterus with sterile plastic wrap.
- Use surgical scissors to make a window (6 cm x 4 cm) in the plastic wrap.
- Make a 5-7 cm uterine incision through the uterus and amniotic sac with cautery cutting, avoiding uterine blood vessels and placental cotyledons.
- Exteriorize the fetal head and forelimbs.
- Use Babcock uterine clamps to seal the uterine incision edges and sterile plastic wrap tightly around the fetal abdomen to prevent amniotic fluid loss.
- Position the fetus on its right side and secure a second sterile plastic wrap over the exteriorized fetus to reduce loss of heat and moisture. Identify the intercostal space between the 9th and 10th ribs on the left and cut a hole in the plastic wrap with surgical scissors to access the intended fetal incision site.
- Establish line-block local anesthesia in the fetus by local subcutaneous and muscular infiltration of bupivacaine (5%; 0.25 mL diluted to 0.5 mL with sterile saline; 1 mL sterile syringe and 27 G needle) in the 9th intercostal space immediately adjacent to the upper border of the 10th rib to avoid subcostal vessels.
- Use a 60 mL sterile syringe to bathe the exposed fetal skin with warm Hartmann's solution (5-10 mL every 5-10 min) to keep the fetal skin moist throughout subsequent steps.
- Create a left posterolateral thoracotomy by making a 2-4 cm skin incision with a size 15 surgical blade in the 9th intercostal space immediately adjacent to the cranial border of the 10th rib. Use cautery as required to minimize incisional bleeding.
- Use mosquito hemostats to bluntly dissect the subcutaneous tissue, intercostal muscles, and pleural membrane to access the diaphragm.
- Use two small mosquito hemostats to pick up the diaphragm at each end of the intended 1 cm long hernia site and cranially elevate the diaphragm to keep it away from the underlying stomach, liver, and spleen.
- Make a 1 cm incision between the two hemostats using small angled scissors.
- Release the hemostats holding the diaphragm.
- Use atraumatic Potts forceps to pull the stomach superiorly through the hole in the diaphragm.
- Use a single tie of absorbable 5-0 polydioxanone monofilament (RB-1 taper point needle) to carefully envelop the 9th and 10th ribs to oppose the fetal ribs, avoiding the underlying lung.
- Close thoracotomy incision with a mattress suture (absorbable 5-0 polydioxanone monofilament).
- Surgical closure
- Return the fetus to the amniotic sac.
- Administer intra-operative meloxicam (0.25 mg/Kg; subcutaneously) to the ewe for postoperative analgesia.
- Replace lost amniotic fluid using warmed Hartmann's solution (~50 mL) along with intra-amniotic Piperacillin/Tazobactam (1000 mg/125 mg).
- Appose the opposing surfaces of the chorioamnion and adjacent uterine walls and use an absorbable polyglactin 910 braided 2-0 suture with an inverted mattress suture to close the uterus and amniotic sac together.
- Close the ewe's linea alba, subcutaneous tissue, and skin (absorbable polydioxanone monofilament 1, absorbable poliglecaprone 25 monofilament 3-0, and nonabsorbable polypropylene monofilament 2-0 respectively).
- Ewe recovery and monitoring
- Spray the abdominal wound post-operatively with waterproof dressing retention tape and cover it with a dressing to reduce the risk of postoperative wound infection.
- Apply a transdermal fentanyl patch (100 µg/h) to the groin for additional postoperative analgesia.
- Recover the ewe and extubate when breathing spontaneously, then allow it to wake.
- Monitor ewes daily until delivery for fetal intervention surgery.
- Remove sutures after 14 days.
2. Placement of the fetal intervention and pressure monitoring device
- Ewe preparation for fetal intervention surgery at 101 days of gestation
- Inject medroxyprogesterone (1 mL) intramuscularly at ~85 days of gestation (term ~147 days) to reduce the risk of preterm birth.
- Use the same anesthetic and surgical preparation procedure used for the initial diaphragm creation surgery.
- Follow the surgical approach in steps 2.1.2.2 and 2.1.2.3, similar to steps 1.2.1-1.2.2.
- Establish line-block local anesthesia by local subcutaneous and muscular infiltration of bupivacaine (5 %; 9.5 mL) with a 10 mL syringe and 22 G needle.
- With a para-midline abdominal incision (8 - 11 cm) adjacent to the abdominal incision site used for the diaphragm creation surgery, expose the uterus with a through the ewe's skin, subcutaneous tissue, and linea alba made with a size 10 surgical blade with cautery as required to minimize incisional bleeding.
- Additionally, administer oxytetracycline (20 mg/Kg) intramuscularly to the ewe to provide fetal antimicrobial protection against the chronically implanted monitoring device.
- Device activation
- Activate pressure measurement device19.
- Clamp pressure measurement tubing with hemostats.
- Place the entire device into a sterile bowl containing a mixture of 0.08% peracetic acid and 1% hydrogen peroxide for at least 1 h, ensuring the entire device is covered.
- Using a sterile clamp, move the device to a sterile bowl containing sterile water for at least 10 min prior to fetal implantation. Ensure the entire device is covered with sterile water.
- Surgical approach and fetal intervention
- Exteriorize the fetal head by hysterotomy using the same surgical approach used for the initial surgery but with adjacent uterine incisions (steps 1.1-2.2).
- Keep the exteriorized fetal head and neck wrapped in the sterile plastic drape to minimize loss of temperature and fluid.
- Instrument the trachea with a catheter for pressure measurements (Figure 1).
- For unoccluded trachea, follow steps 2.3.3.2-2.3.3.3.
- Intubate the fetal lamb with a 5 French (1.67 mm ID) suction catheter with the suction connector removed to a depth of 14 cm at the corner of the lamb's mouth.
- Connect the external end of the catheter with a 1.59 mm (outside diameter, OD) to 3.18 mm (OD) connector to 30 cm long 3.18 mm (ID) silicone tubing.
- For cccluded trachea, follow steps 2.3.3.5-2.3.3.6.
- Intubate the fetal lamb with a 3.0 microcuff endotracheal tube with the connector removed to a depth of 14 cm to a corner of the lamb's mouth.
- Connect the external end of the catheter with a 3.18 mm (OD) to 3.18 mm (OD) connector to 30 cm long 3.18 mm (ID) silicone tubing.
- Connect the other end of the 30 cm long 3.18 mm (ID) silicone tubing to the pressure measurement device by a 3.18 mm (OD) to 1.59 mm (OD) connector on the pressure measurement device.
- Suture the catheter at the corner of the lamb's mouth and neck (nonabsorbable nylon monofilament 4-0).
- Secure the pressure measurement device to the lamb's skin on the chest (nonabsorbable nylon monofilament 4-0) (Figure 2).
- Close the fetal and ewe surgical incisions as per initial diaphragmatic hernia creation surgery (steps 1.4- 1.5).
- Test device
- Test if the device is transmitting signal19.
- Ewe recovery and monitoring
- Recover the ewe as per the initial surgery.
- Monitor ewes daily until delivery.
- Give a second dose of medroxyprogesterone (0.5 mL) intramuscularly at ~120 days of gestation.
- Give betamethasone (5.7 mg) intramuscularly 48 h and 24 h before cesarean delivery to promote fetal maturation for postnatal care.
- Lamb delivery
- At ~142 days of gestation (term ~147-150 days), pre-medicate ewe by intramuscular injection of acepromazine (0.03 mg/Kg) and morphine (0.3 mg/Kg).
- Induce anesthesia intravenously with thiopental (10-15 mg/Kg), intubate the ewe with an endotracheal tube (size 8.5 mm), and maintain anesthesia by isofluorane with appropriate monitoring per earlier anesthetics.
- Proceed with surgical delivery of the fetus via hysterotomy as per previous surgeries, with ewe in dorsal recumbency (steps 1.1 - 2.2).
- Remove the monitoring device. Clean the device with water and 70% ethanol.
- Data
- Download data to a laptop and analyze19. Filter the pressure data using a 6-h window. Compute the difference in pressure between amniotic and tracheal pressures.
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Representative Results
Congenital diaphragmatic hernia creation and pressure measurement device insertion were performed in 28 fetal lambs (14 unoccluded and 14 balloon occluded). Fifteen fetal lambs (6 unoccluded and 9 balloon occluded) survived to near term (142 days gestation; term ~147 days gestation). Pressure measurement recordings of 14 days were successful in 8 fetal lambs (4 unoccluded and 4 balloon occluded).
Pressure measurements were analyzed from the two groups of fetal lambs following the completion of the surgical protocol. The two pressure sensors in the device allow continuous and simultaneous sampling of the amniotic and fetal intratracheal pressures. Measurement of both amniotic and intra-tracheal pressures allows compensation for changes in fetal lung pressure due to ewe movement and abdominal/uterine pressure. The difference between the fetal intratracheal and amniotic pressures is the transrespiratory pressure. Occluding the fetal trachea led to higher transrespiratory pressure compared to the unoccluded trachea animal (Figure 3).
Figure 1: Device setup. (A) Setup for the balloon unoccluded fetal lamb. (B) Setup for the occluded fetal lamb. Please click here to view a larger version of this figure.
Figure 2: Device after insertion of pressure measurement catheter. Please click here to view a larger version of this figure.
Figure 3: Representative fetal in utero pressure measurements over 18 days of gestation. Transrespiratory pressure represents the actual intraluminal pressure of the fetal lung. Pressure in the balloon-occluded lamb (grey line) is greater than that of the unoccluded (black line) lamb. Please click here to view a larger version of this figure.
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Discussion
Fetal lung liquid fills the potential airspaces during gestation and is vital for normal lung development1. Altering the normal lung liquid amount and pressure affects fetal lung growth: narrowing or constriction of the fetal trachea leads to lung hyperplasia; conversely, oligohydramnios and chronic drainage of lung fluid cause lung hypoplasia20,21,22,23. Tracheal occlusion is effective in improving lung hypoplasia15,16,17 Animal and human studies suggest that occluding the trachea earlier in gestation is of greater benefit due to the longer period of expansion and higher chest wall compliance of a younger fetus17,24,25,26. However, the timing of placement and duration of the tracheal occlusion needs further refinement. Additionally, understanding the pressure changes generated by tracheal occlusion over time is essential for improving in utero treatments.
Early methods for in utero intrathoracic pressure measurements used tracheotomy and externalized tracheal loops with periodic measurements1,2,4,5,6,7. While reporting increased lung pressure with occlusion, these early methods ligated the trachea. Occlusion of an intact trachea and measurement of intra-tracheal pressure with a Swan-Ganz catheter increased pulmonary pressure27. Previous studies measuring pressure with a Swan-Ganz catheter obtained measurements weekly. Telemetric measurement of tracheal pressure with a modified urinary catheter has collected data over 2 min three times a day28.
The innovative telemetric approach advances previous methods used to monitor fetal tracheal pressures. Firstly, no externalized catheters were used: internal catheters provide the opportunity to measure pressures without restricting the movements of the ewe, while externalized catheters are a potential source of infection and can dampen the pressure signal. Secondly, the approach facilitated continuous measurement of tracheal pressure regardless of ewe position and sleep/wake cycle. Fetal breathing and associated pressure fluctuation are essential in normal lung development, and the effect of tracheal occlusion on these pressures can be understood better by measuring pressures continuously.
The protocol has three limitations. Firstly, the lamb quadruples in size from fetal intervention to delivery, so securing the device is challenging. Initially, the device was attached to the fetus using elastic band netting. However, the mesh caused thickened and reduced amniotic fluid. Creating several attachment points on the device and suturing the fetal skin with extra sutures reduced the risk of detachment without causing an inflammatory response. Secondly, the battery life of the device limited the duration of measurement recordings. Thirdly, the fluid-filled amniotic sac environment presented challenges for maintaining the device's impermeability to water and maintaining the integrity of the device's electronics.
In conclusion, the innovative telemetric measurement protocol allows continuous monitoring of fetal intratracheal and amniotic pressure in unrestrained pregnant animals. Additionally, with improved device battery life, the continuous measurement of fetal intratracheal and amniotic pressure will provide a complete understanding of how these pressures change throughout gestation.
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Disclosures
The authors declare that no conflicts of interest exist.
Acknowledgments
The authors acknowledge the surgical assistance of Jane Choi (University of Western Australia), Ellen Williams (University of Western Australia), and Veena Kurup (University of Western Australia), as well as the husbandry care of the Animal Care Services staff at the University of Western Australia. This study was supported by the Telethon Perth Children's Research Fund, National Health and Medical Research Council RF 1077691 (JJP), Metropolitan Health and Medical Research Infrastructure Fund (West Australian Government), and Australian International Research Training Program (MD).
Materials
| Name | Company | Catalog Number | Comments |
| 1.59 mm (outside diameter, OD) to 3.18 mm (OD) connector | Qosina | 11913 | |
| 3.18 mm (OD) to 3.18 mm (OD) connector | Qosina | 11684 | |
| 70 % Alcohol | Henry Schein | 1127067 | |
| Absorbable poliglecaprone 25 monofilament 3-0 | Riverpoint Medical | Q316 | |
| Absorbable polydioxanone monofilament 1 | Riverpoint Medical | D879 | |
| Absorbable polyglactin 910 braided 2-0 | Riverpoint Medical | V317 | |
| Absorbable polydioxanone monofilament 5-0 | Riverpoint Medical | D303 | |
| Acepromazine | Ceva Animal Health | APVMA No: 36680 | |
| Babcock, uterine forceps 6.25 inch | Roboz | RS-8022 | |
| Betamethasone | Merck Sharp & Dohme | Aust R 18777 | |
| Blade, size 10 | Becton Dickinson | 371110 | |
| Blade, size 15 | Becton Dickinson | 371115 | |
| Bupivacaine | Pfizer Australia Pty Ltd | AUST R 11312 | |
| Cefazolin | AFT pharmaceuticals | AUST R 171582 | |
| Chlorhexidine | Henry Schein | 0404-0175-02 | |
| Endotracheal tube (size 8.0) | Jorgen Kruuse | 272411 | |
| Forceps, Potts-Smith | Roboz | RS-5314 | |
| Iodine solution (10 %) | Henry Schein | 6907281 | |
| Isoflurane | Piramal Critical Care | APVMA No: 53120/112272 M. L. No.:220/AP/MD/96/B&F/R |
|
| Ketamine | Ceva Animal Health | APVMA 37711/58317 KETALAB04 |
|
| Hartmanns Solution | Baxter | AUST R 48510 | |
| Hemostats, Mosquito forceps curved delicate | Roboz | RS-7271 | |
| Medroxyprogesterone acetate | Pfizer Australia Pty Ltd | AUST R 12300 | |
| Meloxicam | Ilium | APVMA Approval No.: 62535/127884 LI0119V1 |
|
| Methocel | Colorcon | ID34435 | |
| Microcuff endotracheal tube (3.0) | Halyard | 35111 | |
| Midazolam | Mylan | AUST R 160205 | |
| Morphine | Pfizer Australia Pty Ltd | AUST R 101240 | |
| Needle, 22 G | Becton Dickinson | 305155 | |
| Needle, 27 G | Becton Dickinson | 305109 | |
| Nonabsorbable nylon monofilament 4-0 | Riverpoint Medical | 662BL | |
| Nonabsorbable polypropylene monofilament 2-0 | Riverpoint Medical | P8411 | |
| OpSite Transparent Film | Smith and Nephew | 66000040 | |
| Oxytetracycline | Norbrook | APVMA Approval No: 53087/49616 | |
| Peracetic acid/hydrogen peroxide | Medivators Inc | ref: 78401-649 | |
| Piperacillin/Tazobactam | Sandoz Pty Ltd | AUST R 140840 | |
| Scissors, Metzenbaum Surgical 7 inch straight | Roboz | RS-6955SC | |
| Scissors, Vannas 0.15 mm tip width | Roboz | RS-5618 | |
| Silicone tubing (1.59 mm inside diameter) | Qosina | T2013 | |
| Suction catheter (5 French) | Covidien | 30500 | |
| Syringe, 1 mL | Becton Dickinson | 309659 | |
| Syringe, 10 mL | Becton Dickinson | 309604 | |
| Syringe, 60 mL | Becton Dickinson | 309654 | |
| Thiopentone sodium | Jurox Pty Ltd | APVMA No. 51520/5g/0809 | |
| Transdermal fentanyl patch | Janssen-Cilag Pty Ltd | AUST R 112371 |
References
- Harding, R., Hooper, S. B. Regulation of lung expansion and lung growth before birth. J Appl Physiol (1985). 81 (1), 209-224 (1996).
- Olver, R. E., Strang, L. B. Ion fluxes across the pulmonary epithelium and the secretion of lung liquid in the foetal lamb. J Physiol. 241 (2), 327-357 (1974).
- Schittny, J. C. Development of the lung. Cell Tissue Res. 367 (3), 427-444 (2017).
- Vilos, G. A., Liggins, G. C. Intrathoracic pressures in fetal sheep. J Dev Physiol. 4 (4), 247-256 (1982).
- Dawes, G. S., Fox, H. E., Leduc, B. M., Liggins, G. C., Richards, R. T. Respiratory movements and rapid eye movement sleep in the foetal lamb. J Physiol. 220 (1), 119-143 (1972).
- Bowes, G., et al. Development of patterns of respiratory activity in unanesthetized fetal sheep in utero. J Appl Physiol Respir Environ Exerc Physiol. 50 (4), 693-700 (1981).
- Clewlow, F., Dawes, G., Johnston, B., Walker, D. Changes in breathing, electrocortical and muscle activity in unanaesthetized fetal lambs with age. J Physiol. 341, 463-476 (1983).
- Chapman, R. L., Dawes, G. S., Rurak, D. W., Wilds, P. L. Breathing movements in fetal lambs and the effect of hypercapnia. J Physiol. 302, 19-29 (1980).
- Badalian, S. S., Fox, H. E., Chao, C. R., Timor-Tritsch, I. E., Stolar, C. J. Fetal breathing characteristics and postnatal outcome in cases of congenital diaphragmatic hernia. Am J Obstet Gynecol. 171, 970-976 (1994).
- Badalian, S. S., Fox, H. E., Zimmer, E. Z., Fifer, W. P., Stark, R. I. Patterns of perinasal fluid flow and contractions of the diaphragm in the human fetus. Ultrasound Obstet Gynecol. 8 (2), 109-113 (1996).
- Fox, H. E., Moessinger, A. C. Fetal breathing movements and lung hypoplasia: preliminary human observations. Am J Obstet Gynecol. 151 (4), 531-533 (1985).
- Fox, H. E., Badalian, S. S. Ultrasound prediction of fetal pulmonary hypoplasia in pregnancies complicated by oligohydramnios and in cases of congenital diaphragmatic hernia: A review. Am J Perinatol. 11 (2), 104-108 (1994).
- Fox, H. E., Badalian, S. S., Fifer, W. P. Patterns of fetal perinasal fluid flow in cases of congenital diaphragmatic hernia. Am J Obstet Gynecol. 176 (4), 807-813 (1997).
- Carmel, J. A., Friedman, F., Adams, F. H. Fetal tracheal ligation and lung development. Am J Dis Child. 109, 452-456 (1965).
- Deprest, J. A., et al. Randomized trial of fetal surgery for moderate left diaphragmatic hernia. N Engl J Med. 385 (2), 119-129 (2021).
- Deprest, J. A., et al. Randomized trial of fetal surgery for severe left diaphragmatic hernia. N Engl J Med. 385 (2), 107-118 (2021).
- Van Calster, B., et al. The randomized TOTAL-trials on fetal surgery for congenital diaphragmatic hernia: re-analysis using pooled data. Am J Obstet Gynecol. 226 (4), 560.e1-560.e24 (2021).
- NHMRC. National Health and Medical Research Council (2013) Australian Code for the Care and Use of Animals for Scientific Purposes. , 8th edition, National Health and Medical Research Council. Canberra. (2021).
- Robbiani, S., et al. An implantable electronic device for monitoring fetal lung pressure in a lamb model of Congenital Diaphragmatic Hernia. IEEE Transactions on Instrumentation and Measurement. 71, 1-10 (2022).
- Moessinger, A. C., Harding, R., Adamson, T. M., Singh, M., Kiu, G. T. Role of lung fluid volume in growth and maturation of the fetal sheep lung. J Clin Invest. 86 (4), 1270-1277 (1990).
- Dickson, K. A., Harding, R. Fetal breathing and pressures in the trachea and amniotic sac during oligohydramnios in sheep. J Appl Physiol (1985). 70 (1), 293-299 (1991).
- Alcorn, D., et al. Morphological effects of chronic tracheal ligation and drainage in the fetal lamb lung. J Anatomy. 123 (3), 649-660 (1977).
- Wigglesworth, J. S., Desai, R., Hislop, A. A. Fetal lung growth in congenital laryngeal atresia. Pediatr Pathol. 7 (5-6), 515-525 (1987).
- Khan, P. A., Cloutier, M., Piedboeuf, B. Tracheal occlusion: a review of obstructing fetal lungs to make them grow and mature. Am J Med Genet C Semin Med Genet. 145C (2), 125-138 (2007).
- De Paepe, M. E., Johnson, B. D., Papadakis, K., Luks, F. I. Lung growth response after tracheal occlusion in fetal rabbits is gestational age-dependent. Am J Respir Cell Mol Biol. 21 (1), 65-76 (1999).
- Probyn, M. E., Wallace, M. J., Hooper, S. B. Effect of increased lung expansion on lung growth and development near midgestation in fetal sheep. Pediatr Res. 47 (6), 806-812 (2000).
- Hashim, E., Laberge, J. M., Chen, M. F., Quillen, E. W. Jr Reversible tracheal obstruction in the fetal sheep: effects on tracheal fluid pressure and lung growth. J Pediatr Surg. 30 (8), 1172-1177 (1995).
- Hellmeyer, L., et al. Telemetric monitoring of tracheal pressure after tracheal occlusion for treatment of severe congenital diaphragmatic hernia. Arch Gynecol Obstet. 275 (4), 245-248 (2007).
