Assessment of Respiratory Function in Conscious Mice by Double-chamber Plethysmography
Samuel Mailhot-LaroucheLouis DeschênesKatherine LortieMorgan GazzolaDavid MarsolaisDavid BrunetAnnette RobichaudYnuk Bossé
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Abstract:
Air volume changes created by a conscious subject breathing spontaneously within a body box are at the basis of plethysmography, a technique used to non-invasively assess some features of the respiratory function in humans as well as in laboratory animals. The present article focuses on the application of the double-chamber plethysmography (DCP) in small animals. It provides background information on the methodology as well as a detailed step-by-step procedure to successfully assess respiratory function in conscious, spontaneously breathing animals in a non-invasive manner. The DCP can be used to monitor the respiratory function of multiple animals in parallel, as well as to identify changes induced by aerosolized substances over a chosen time period and in a repeated manner. Experiments on control and allergic mice are used herein to demonstrate the utility of the technique, explain the associated outcome parameters, as well as to discuss the related advantages and shortcomings. Overall, the DCP provides valid and theoretically sound readouts that can be trusted to evaluate the respiratory function of conscious small animals both at baseline and after challenges with aerosolized substances.Keywords:
Plethysmograph
Respiratory physiology
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The rat lung undergoes rapid changes during the first several weeks of life. Respiratory function on neonatal rats was performed to determine if physiologic alterations coincides with classically described lung growth, and morphologic and morphometric changes. The authors examined respiratory mechanics during normal postnatal lung development in the rat utilizing both a forced oscillation technique, which partitions the mechanical properties of the lung tissue from the airways, as well as pressure-volume (PV) curves to assess lung elasticity. Respiratory function testing was performed on each postnatal days of life 10 to 20. The PV curves were characterized by a leftward shift over days 10 to 16, followed by a shift back to the right over days 17 to 20. Both tissue damping (G) and elastance (H) decreased from days of life 10 to 15, and then equilibrated from days 15 to 21. Hysteresivity (=G/H) at positive end-expiratory pressure (PEEP) = 1 and 3 cm H2O declined significantly with age. The effect of PEEP was significantly greater in the younger animals than in the older animals. The respiratory function assessments coincide well with the classically described periods of lung growth. These studies provide a normal baseline for correlating changes in structural with respiratory function.
Elastance
Respiratory physiology
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Assessing lung function in the newborn relates to the need for early markers of chronic respiratory diseases such as cystic fibrosis or asthma. Non-invasive respiratory measurements of forced oscillations mechanics are recently shown to be possible in unsedated babies. The bronchodilator effect of catecholamine release at birth, and the respiratory muscle contribution to respiratory mechanical impedance resulting in sometimes excessive variability suggest that measurements should be performed beyond the first 24 hr of life.
Respiratory physiology
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Respiratory Medicine
Respiratory physiology
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Respiratory physiology
Comparative physiology
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1. Mechanical behavior of the respiratory system and pulmonary histopathology were investigated in young (8 months) and old (18 months) adult Wistar rats. 2. Respiratory mechanics were studied under static conditions and during both relaxed and forced expiration. Morphological studies consisted of descriptive light microscopy analysis of intratracheally-fixed, paraffin-embedded pulmonary tissue. 3. Old animals exhibited morphological emphysema and chronic bronchitis, decreased respiratory system (2.40 vs 3.42 cm H2O/ml) and lung (1.32 vs 2.30 cm H2O/ml) elastances, forced vital capacity (13.00 vs 14.32 ml), forced expiratory mean flows between 50 and 75% (35.67 vs 60.50 ml/s) and 75 and 100% (6.67 vs 17.67 ml/s) of forced vital capacity, and an increased respiratory system time constant (0.114 vs 0.082 s) in relation to young rats. 4. These results indicate that old animals suffer from a chronic obstructive pulmonary disease that resembles human pulmonary emphysema.
Vital capacity
Chronic bronchitis
Respiratory physiology
Histopathology
Expiration
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Elastance
Respiratory physiology
Work of breathing
Pulmonary compliance
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Respiratory physiology
Pulmonary compliance
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The relationship between respiratory mechanics, changes in pulmonary blood flow (PBF), pulmonary arterial pressure, and left atrial pressure is unclear. Conventional methods for the measurement of respiratory mechanics model the respiratory system as a single compartment, which may not adequately represent the respiratory system in a diseased state. The interrupter technique models the respiratory system as two compartments, with the "flow resistance" of the conducting airways and chest wall (Raw) considered separately from Pdif, a measure of the viscoelastic properties of the lung and chest wall, together with any pendelluft present. The respiratory mechanics of 15 infants in the first year of life were studied during cardiac catheterization with the use of conventional methods and the interrupter technique. The infants had a PBF-to-systemic blood flow ratio ranging from 0.6 to 4.0:1. The specific dynamic compliance of the respiratory system was not related to the PBF; however, there was a significant relationship between PBF and the total resistance of the respiratory system (Rrs) [analysis of variance (ANOVA) F = 5.69, P < 0.05], Raw (ANOVA, F = 12.30, P < 0.01), and Pdif (ANOVA, F = 3.79, P < 0.05). Rrs increased significantly with an increase in mean left atrial pressure (ANOVA, F = 6.92, P < 0.05); however, dynamic compliance, Raw, and Pdif did not. These results suggest that the relationship between Rrs and PBF is due an increase in the resistive properties of the conducting airways and tissue components.
Interrupter
Respiratory physiology
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