Measurement of the Pressure-volume Curve in Mouse Lungs

Summary

Here we present a protocol to simply and reliably measure the lung pressure-volume curve in mice, showing that it is sufficiently sensitive to detect phenotypic parenchymal changes in two common lung pathologies, pulmonary fibrosis and emphysema. This metric provides a means to quantify the lung’s structural changes with developing pathology.

Abstract

In recent decades the mouse has become the primary animal model of a variety of lung diseases. In models of emphysema or fibrosis, the essential phenotypic changes are best assessed by measurement of the changes in lung elasticity. To best understand specific mechanisms underlying such pathologies in mice, it is essential to make functional measurements that can reflect the developing pathology. Although there are many ways to measure elasticity, the classical method is that of the total lung pressure-volume (PV) curve done over the whole range of lung volumes. This measurement has been made on adult lungs from nearly all mammalian species dating back almost 100 years, and such PV curves also played a major role in the discovery and understanding of the function of pulmonary surfactant in fetal lung development. Unfortunately, such total PV curves have not been widely reported in the mouse, despite the fact that they can provide useful information on the macroscopic effects of structural changes in the lung. Although partial PV curves measuring just the changes in lung volume are sometimes reported, without a measure of absolute volume, the nonlinear nature of the total PV curve makes these partial ones very difficult to interpret. In the present study, we describe a standardized way to measure the total PV curve. We have then tested the ability of these curves to detect changes in mouse lung structure in two common lung pathologies, emphysema and fibrosis. Results showed significant changes in several variables consistent with expected structural changes with these pathologies. This measurement of the lung PV curve in mice thus provides a straightforward means to monitor the progression of the pathophysiologic changes over time and the potential effect of therapeutic procedures.

Introduction

The mouse is now the primary animal model of a variety of lung diseases. In models of emphysema or fibrosis, the essential phenotypic changes are best assessed by measuring the changes in lung elasticity. Although there are many ways to measure elasticity, the classical method is that of the total pressure-volume (PV) curve measured from residual volume (RV) to total lung capacity (TLC). This measurement has been made on adult lungs from nearly all mammalian species dating back almost 100 years^1-3. Such PV curves also played a major role in the discovery and understanding of the function of pulmonary surfactant in fetal lung development^4-7. Despi....

Protocol

The Johns Hopkins University Animal Care and Use Committee approved all animal protocols.

1. Equipment

The composite system set up, ready to measure the PV curve is shown in Figure 1.

1. Volume measurement:
   1. Generate a constant rate of inflation and deflation by using a syringe pump with a switch that allows the user to quickly reverse the pump after reaching the pressure limits. For mouse PV curves, use a very lightly greased 5 ml glass syringe with the initial volume (prior to inflation) set at 3 ml of air. 3 ml is sufficiently large to measure volumes in nearly all mouse PV....

Results

Although the procedure for the PV curves is demonstrated in the video only for control healthy mice, we examined the ability of the PV curve to detect functional and pathologic changes in mice with two different common pathologies, emphysema and fibrosis. Details of these traditional models described elsewhere^12,13. Very briefly, after anesthesia with 3% isoflurane the emphysema was caused by 3 or 6 U porcine pancreatic elastase instilled into the trachea and studied 3 weeks later, and the fibrosis was caused .......

Discussion

In this paper a straightforward reproducible method has been described to measure in mice a classical method of phenotyping lung elasticity, the total lung PV curve. Such curves were instrumental in the discovery of pulmonary surfactant and its importance in providing lung stability. Here it is shown how the PV curve is also useful in providing a means to measure several variables related to lung elasticity in adult mouse lungs. There were highly significant changes in all variables in two commonly used mouse models to g.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Syringe pump	Harvard Apparatus	55-2226	Infuse/withdraw syringe pump
Pump 22 reversing switch	Harvard Apparatus	552217	Included with pump
Linear displacement transformer	Trans-Tek, Inc.	0244-0000
5 ml glass syringe	Becton Dickenson		Several other possible vendors
Digital recorder	ADInstruments	PL3504	Several other possible vendors
Bridge amp signal conditioner	ADInstruments	FE221
Gas tank, 100% oxygen	Airgas, Inc		Any supplier or hospital source will work
Pressure transducer: 0 - 1 psi mV output	Omega Engineering	PX-137	Range ≈ 0 - 60 cm H2O