Plethysmographic estimation of thoracic gas volume in apneic mice

Abstract

Electrical stimulation of intercostal muscles was employed to measure thoracic gas volume (TGV) during airway occlusion in the absence of respiratory effort at different levels of lung inflation. In 15 tracheostomized and mechanically ventilated CBA/Ca mice, the value of TGV obtained from the spontaneous breathing effort available in the early phase of the experiments (TGVsp) was compared with those resulting from muscle stimulation (TGVst) at transrespiratory pressures of 0, 10, and 20 cmH2O. A very strong correlation (r2= 0.97) was found, although with a systematically (approximately 16%) higher estimation of TGVst relative to TGVsp, attributable to the different durations of the stimulated (approximately 50 ms) and spontaneous (approximately 200 ms) contractions. Measurements of TGVst before and after injections of 0.2, 0.4, and 0.6 ml of nitrogen into the lungs in six mice resulted in good agreement between the change in TGVst and the injected volume (r2= 0.98). In four mice, TGVsp and TGVst were compared at end expiration with air or a helium-oxygen mixture to confirm the validity of isothermal compression in the alveolar gas. The TGVst values measured at zero transrespiratory pressure in all CBA/Ca mice [0.29 +/- 0.05 (SD) ml] and in C57BL/6 (N = 6; 0.34 +/- 0.08 ml) and BALB/c (N = 6; 0.28 +/- 0.06 ml) mice were in agreement with functional residual capacity values from previous studies in which different techniques were used. This method is particularly useful when TGV is to be determined in the absence of breathing activity, when it must be known at any level of lung inflation or under non-steady-state conditions, such as during pharmaceutical interventions.

Altered Upper Airway and Soft Tissue Structures in the New Zealand Obese Mouse

“…In humans, reductions in functional residual capacity result in narrowing of the upper airway due to reduction in tracheal tug on the upper airway (53). We did not measure functional residual capacity in our studies, although this measurement can be obtained noninvasively using sophisticated micro-CT methods (54) or complex plethysmography (55). As Tankersley and colleagues have shown (56), differences in lung mechanics are found in different mouse strains.…”

Acute diesel exhaust particle exposure increases viral titre and inflammation associated with existing influenza infection, but does not exacerbate deficits in lung function

“…Thoracic gas volume (TGV) was measured using plethysmography as described previously 40 . This technique involves using electrodes to electrically stimulate the intercostal muscles during a pause in ventilation.…”

“…Twelve inspiratory efforts were created per mouse by stimulation with individual electrical impulses ∼20 V in amplitude, ∼1–2 ms in duration and 0·8 s apart (model S44; Grass Instruments, Quincy, MA, USA). Boyle’s law was applied to the relationship between tracheal pressure and plethysmograph pressure after correcting for the impedance and thermal characteristics of the chamber to calculate TGV 40 . Measurements were averaged to provide a single TGV measure for each individual.…”

Crackle sounds and lung recruitment

“…The TGV at end expiration at zero transrespiratory pressure (FRC) was measured with the plethysmographic technique [61], modified recently for the measurement of TGV in anaesthetized mice that have a weak or no respiratory effort [62]. P box and tracheal pressure (P tr ) were measured with miniature pressure transducers (model 8507C-2, Endevco, San Juan Capistrano, CA) during stimulation of the intercostal muscles.…”

“…P box and tracheal pressure (P tr ) were measured with miniature pressure transducers (model 8507C-2, Endevco, San Juan Capistrano, CA) during stimulation of the intercostal muscles. The FRC was estimated from the P box vs P tr relationship on the basis of Boyle's principle, as detailed previously [62].…”