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. Author manuscript; available in PMC: 2010 Sep 24.
Published in final edited form as: Eur Respir J. 2009 Jul 2;35(1):124–131. doi: 10.1183/09031936.00178408

Figure 3.

Figure 3

Panel A shows the VE- PETCO2 relation in 1999 (open squares) and 2006 (filled triangles). Each point represents data points obtained at rest, and in the steady state of breathing gas mixtures with 3, 5 and 7% inspired CO2 in all 14 subjects, as described in Methods. The slope of the relation was the same in 1999 and 2006 (1999, y=1.28 (x) − 35.6; 2006, y=1.31 (x) − 28.6, t= 0.08, P = 0.94), but the regression line obtained in 2006 was markedly left-shifted, as discussed in text. Panel B shows the relationship between tidal volume (VT) and PETCO2 in all subjects. As with VE, the slope of the relation was the same in 1999 and 2006 (1999, y=0.045 (x) − 1.1; 2006, y= 0.066 (x) − 1.45, t= 1.43, P = 0.16), but the curve in 2006 was markedly left-shifted. These data indicate that the left-shift in the ventilatory response to CO2 (panel A) was due to differences in the VT response, as the frequency response was unaltered (data not shown).