An appropriate inspiratory flow pattern can enhance CO2 exchange, facilitating protective ventilation of healthy lungs  L.W. Sturesson, G. Malmkvist, S. Allvin, M. Collryd, M. Bodelsson, B. Jonson  British Journal of Anaesthesia  Volume 117, Issue 2, Pages 243-249 (August 2016) DOI: 10.1093/bja/aew194 Copyright © 2016 The Author(s) Terms and Conditions

Fig 1 The 21 types of breath delivered, all having different inspiratory flow patterns but identical tidal volumes. In each panel, the light blue trace shows the pattern of ordinary breaths to which all other patterns were compared. (a) Breaths with ordinary insufflation at constant flow but with varying postinspiratory pause. (b) Breaths with varying inspiratory time, all with an ordinary pause. (c) Breaths with varying inspiratory time and pause time. (d) Breaths with varying inspiratory time and pause time, all with similar mean distribution time. (e) Breaths with constant, increasing, and decreasing flow profile, and also illustrating how end-inspiratory flow (EIF) was measured. British Journal of Anaesthesia 2016 117, 243-249DOI: (10.1093/bja/aew194) Copyright © 2016 The Author(s) Terms and Conditions

Fig 2 Flow rate (green line) and its integral, volume (blue line), against time. Initially, during inspiration, gas from the airway dead space returns to the alveolar zone. When a volume of gas equal to the airway dead space (VDaw, pink area) has been inhaled, the first portion of fresh gas reaches the respiratory zone of the lung. Later consecutive portions of fresh inspired gas (vertical lines) reach this zone. The first portion mixes by diffusion with resident alveolar gas during the distribution time DT1, and the last portion has the distribution time DT n. The volume-weighted mean for alveolar gas distribution of portions 1– n is the mean distribution time, MDT. Calculation of MDT ceases at the start of expiration because no further mixing between inspired and resident alveolar gas takes place thereafter. British Journal of Anaesthesia 2016 117, 243-249DOI: (10.1093/bja/aew194) Copyright © 2016 The Author(s) Terms and Conditions

Fig 3 The single breath test for CO2. The blue curve shows the fraction of CO2 at the Y-piece ( F C O 2 ) plotted against expired volume (VE). The descending limb of the loop reflects the next inspiration. The blue area represents the volume of CO2 eliminated during the ordinary breath ( V T C O 2 ). The green curve represents the expiratory limb of a breath with a prolonged pause. The Δ VDaw shows how airway dead space (VDaw) was reduced by a volume represented by the difference between the vertical dotted blue and green lines. The Δ F A C O 2 shows how the level of the alveolar plateau increased. The reverse-hatched area indicates how Δ V T C O 2 increased as a consequence of Δ VDaw and Δ F A C O 2 . British Journal of Anaesthesia 2016 117, 243-249DOI: (10.1093/bja/aew194) Copyright © 2016 The Author(s) Terms and Conditions