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INNOVATIVE METHODOLOGY

Breath-by-breath assessment of alveolar gas stores and exchange

¹Laboratorio di tecnologie Biomediche, Dipartimento di Bioingegneria, Politecnico di Milano, 20133 Milano, Italy; ²Faculty of Medicine, Université de Genève, CH1205 Switzerland; and ³Meakins-Christie Laboratories, Montreal Chest Institute, McGill University Health Center, H2X 2P4 Montreal, Canada

Submitted 10 November 2003 ; accepted in final form 24 November 2003

The volume of O₂ exchanged at the mouth during a breath (VO_2,m) is equal to that taken up by pulmonary capillaries (VO_2,A) only if lung O₂ stores are constant. The latter change if either end-expiratory lung volume (EELV), or alveolar O₂ fraction (FA_O2) change. Measuring this requires breath-by-breath (BbB) measurement of absolute EELV, for which we used optoelectronic plethysmography combined with measurement of O₂ fraction at the mouth to measure VO_2,A = VO_2,m - (EELV·FA_O2 + EELV·FA_O2), and divided by respiratory cycle time to obtain BbB O₂ consumption (O₂) in seven healthy men during incremental exercise and recovery. To synchronize O₂ and volume signals, we measured gas transit time from mouthpiece to O₂ meter and compared O₂ measured during steady-state exercise by using expired gas collection with the mean BbB measurement over the same time period. In one subject, we adjusted the instrumental response time by 20-ms increments to maximize the agreement between the two O₂ measurements. We then applied the same total time delay (transit time plus instrumental delay = 660 ms) to all other subjects. The comparison of pooled data from all subjects revealed r² = 0.990, percent error = 0.039 ± 1.61 SE, and slope = 1.02 ± 0.015 (SE). During recovery, increases in EELV introduced systematic errors in O₂ if measured without taking EELV·FA_O2+EELV·FA_O2 into account. We conclude that optoelectronic plethysmography can be used to measure BbB O₂ accurately when studying BbB gas exchange in conditions when EELV changes, as during on- and off-transients.

oxygen consumption; exercise; opto-electronic plethysmography; respiration

This article has been cited by other articles:

				P. T. Macklem Circulatory effects of expiratory flow-limited exercise, dynamic hyperinflation and expiratory muscle pressure Eur. Respir. Rev., December 1, 2006; 15(100): 80 - 84. [Abstract] [Full Text] [PDF]