Monday, January 22, 2018

Refined Study Design with Spirometry

Spirometry is a widely known clinical pulmonary test measuring volumes and flows expired by patients that is used to confirm a diagnostic of respiratory disease or follow treatment. SCIREQ’s flexiVent’s offers an analogous test for preclinical research with its Negative Pressure Forced Expiration (NPFE) extension. By exposing the subject’s airway opening to a negative pressure to rapidly draw out air from the lungs, the system can generate flow-volume loops or volume-time plots, from which the flexiWare software can then extract clinically relevant volume and flow parameters (e.g. FEVx, FEFx, FVC, PEF).

A recent publication by Devos et al.1 characterized forced expiration measurements in some well-established mouse models of lung diseases, which specific phenotypes were confirmed by a concomitant respiratory mechanics assessment. The researchers observed that disease-induced changes in forced expiration-related charts and parameters were generally similar to what was observed in the clinic. For example, when compared to a control group of healthy mice.

  • Mice with fibrosis exhibited a typical restrictive profile, with a reduced PEF & FVC and a normal FEV0.1/FVC ratio. 
  • Mice with emphysema displayed a decrease in PEF characteristic of an obstructive phenotype.
  • Mice presenting an acute lung injury had significantly reduced PEF.
  • Mice with features of asthma showed a decrease in FEV0.1 following methacholine challenges.

SCIREQ’s flexiVent is the first platform that allows forced expiratory manoeuvres to be performed side-by-side with respiratory mechanics, pressure-volume loops, or lung volume measurements in mice and rats. This unique feature enables a refined study design with outcomes susceptible to translate between preclinical research and clinical settings. 

Read more
1Devos, FC et al. 2017. Forced expiration measurements in mouse models of obstructive and restrictive lung diseases. Respiratory Research 18: 123.

Leaving Nothing Out

The functional residual capacity (FRC) plays an important role in maintaining optimal ventilation.  FRC is a subdivision of the total lung capacity (TLC) and represents the volume of air left in the lungs at the end of an expiration.  It is involved in keeping the small airways open for an efficient gas transfer between the air and the blood.  Variations in that volume can be seen under several physiological or pathophysiological conditions and can be associated with clinical symptoms like dyspnea. 

FRC is a clinically important parameter which is determined, along with other lung volumes/capacities, when performing a full lung function assessment.  It is inversely related to airway resistance, such that a reduction in FRC will increase the level of opposition to airflow.  At the preclinical level, while measurements of airway resistance are routinely performed in many research laboratories, the determination of FRC is rarely reported as it can prove to be technically challenging, especially in subjects as small as mice.  

It is possible to obtain FRC from a full-range pressure-volume (PV) curve.  This was done until now in mice by determining the volume at a conventionally or arbitrarily defined equilibrium pressure (e.g. 0 cmH20), since FRC represents the volume at rest.  In a recent report1, FRC was estimated by a novel approach in rodents, following the automation of the full-range PV curve technique with SCIREQ’s flexiVent system.  It was estimated by volume subtraction and took advantage of the access to varied, precisely controlled, automated maneuvers within a single device.  In comparison to the previously established methodology, this novel approach demonstrated a more accurate estimation of FRC, particularly in diseased subjects.

The estimation of FRC by volume subtraction can be performed in rats and mice along with the determination of other lung volumes/capacities, measurements of respiratory mechanics, or partial PV curves.  The authors showed that the FRC estimate more than tripled in a mouse model of emphysema, representing the most important change in a panel of lung volumes/capacities.  Including measurements of FRC and other lung volumes/capacities in the characterization of respiratory models or novel therapeutic strategies can contribute to generate comprehensive and robust functional assessments. 

No model fully recapitulates human respiratory diseases.  Let’s reconsider the endpoints typically reported so that nothing that matters gets ignored.

Read more
1Robichaud, A et al. 2017. Automated full-range pressure-volume curves in mice and rats. Journal of Applied Physiology 123: 746-756.

Monday, January 8, 2018

Empower yourself

Attending a training such as the Phenotyping Mice Models of Human Lung Disease organized by the Jackson Laboratory is a great way to advance skillsets or simply get started in the field of respiratory research. It represents a wonderful opportunity for researchers of all stages to learn and network in a structured yet informal environment. The uniqueness of the event lies in the roundness of the approach, which combines theoretical sessions and practical experience in all topics.

SCIREQ has been a partner in this event for years now and has contributed with providing hands-on experience to participants with lung function measurements using the flexiVent alongside authorities in the field. Practical exercises are designed to demonstrate a response to a particular intervention, highlight unique measurements (including partitioning the lungs between airway and tissue effects), and analyze outcomes with respect to their physiological implications.

JAX Experiments
As an example, participants were guided during the last workshop to utilize pressure-volume loops to confirm the effects of an intervention with implications on lung surfactant and atelectasis.  
Figure 1: Pressure-volume loops from a subject before (left) and after (right) a lung lavage. The red line represents the Salazar-Knowles equation fit to the deflation limb of the pressure-volume curve.
They were also invited to examine the effect of increasing the positive end expiratory pressure (PEEP) during ventilation and lung function measurements while exploring the impact on detailed respiratory mechanics parameters before and after the intervention.

Airway responsiveness to a specific bronchoconstrictor agent before and after a therapeutic treatment or an assessment of various lung volumes are also typically part of the repertoire of techniques taught.  

Figure 2: Single (left) and broadband (right) forced oscillation outcomes prior to and following increasing doses of nebulised methacholine in presence or absence of a bronchodilator treatment.

Looking forward
The event runs every second year in Bar Harbor, Maine, and accepts a limited number of participants. Plan ahead to take part in the workshop, which we highly recommend to both senior researchers and students alike.