Volume rather than flow incentive spirometry is effective in improving chest wall expansion and abdominal displacement using optoelectronic plethysmography

Background: Incentive spirometers (IS) are widely used in clinical practice and classified as flow-oriented (FIS) and volumetric (VIS). Until recently, the respiratory inductive plethysmography used to evaluate the effects of IS on chest wall mechanics presented limitations, which may explain why the impact of VIS and FIS remains poorly known.

Objective: We compared the effects of the VIS and FIS on thoracoabdominal mechanics and respiratory muscular activity in healthy volunteers.

Methods: This cross-sectional trial assessed 20 subjects, 60% female, aged between 20 and 40 years and with a body mass index (BMI) between 20 and 30 kg/m². All participants performed 8 quiet and 8 deep breaths using both FIS and VIS in a randomized order. The outcomes measured were the thoracoabdominal kinematics (i.e., chest wall, upper and lower ribcage and abdominal volumes), assessed using Optoelectronic Plethysmography, and the muscular activity of the sternocleidomastoid and superior and inferior intercostal muscles, assessed using electromyography. The statistical analysis was performed with one-way repeated measures ANOVA, and the significance level was set to 5%.

Results: VIS increased 17 the chest wall volume to a greater extent than the FIS (p=0.007) and induced a larger increase in the upper and lower ribcages and abdomen (respectively, 156%, 91% and 151% p<0.001). By contrast, the FIS induced more activity in the accessory muscles of respiration compared to VIS (p<0.001).

Conclusion: Our results demonstrate that the VIS promotes a greater increase in the chest wall volume with a larger abdominal contribution and lower respiratory muscular activity than the FIS in healthy adults.