Closing Capacity and Gas Exchange in Chronic Heart Failure: Research

Closing Capacity and Gas Exchange in Chronic Heart Failure: ResearchResting ventilation and P01 were higher in CHF patients than in control subjects (Table 4), with the increase of minute ventilation (Ve) resulting from increased respiratory frequency (fR). While the tidal volume (VT)/inspiratory time (Ti) ratio was significantly higher in CHF patients (reflecting the higher P01), Tl/total breathing cycle time (Ttot) ratio was the same in CHF patients and control subjects. The P01/Plmax ratio (percentage) was, on average, more than twice as large in CHF patients as in control subjects, reflecting in part the increased P0.1 and in part the decreased Plmax. As a result of the increased VE, the PaC02 was lower in CHF patients than in control subjects.

The Pa02 was also significantly lower in CHF patients than in control subjects, while the P(A-a)O2 was increased, reflecting the fact that in most of our CHF patients (13 of 20) the CC was higher than the FRC. This implies opening and closing of peripheral airway closure during tidal breathing with maldistribution of ventilation and impaired gas exchange, as reflected by the increased P(A-a)O2. In control subjects, P(A-a)O2 correlated best with age (r = 0.65; p < 0.002), while in CHF patients it did not correlate with age but with sPAP (r = 0.49; p < 0.03). read

Significant correlations were found for MRC score with Plmax, P01/Plmax ratio, fR, and PaC02. However, according to stepwise multivariate regression analysis, the only significant independent predictors of MRC score were fR (in breaths/min) and P01/ Plmax ratio (percentage): MRC = 0.08 + 0.08fR + 0.14 Pa1/Pimax where r = 0.78, r2 = 0.61, and p < 0.001. The new findings of this study are that in CHF patients at rest (mostly in Weber class B and C), the following conditions prevail: (1) CC is not increased; (2) as a result of decreased FRC, however, airway closure with compromised pulmonary gas exchange is present during tidal breathing; (3) tidal FL is absent; (4) ventilation is increased as a result of increased fR with a concurrent decrease in PaC02; and (5) Plmax is decreased. Together with the concurrent increase in P0.1, this implies a proportionately greater inspiratory effort per breath (P01/ Plmax ratio). These, together with the increased fR, are the only significant contributors to the MRC dyspnea score.

Table 4—Control of Breathing Data and Blood Gases in CHF Patients and Control Subjects

Variables CHF Patients Control Subjects p Value
Ve, L/min 12.9 ± 5.0 10.2 ± 2.7 < 0.005
Vt, L 0.72 ± 0.23 0.72 ± 0.18 NS
/r min 17.9 ± 5.1 14.2 ± 4.0 < 0.02
Vt/Ti ratio, L/s 0.55 ± 0.17 0.40 ± 0.13 < 0.003
Ti/Ttot ratio 0.41 ± 0.04 0.41 ± 0.04 NS
Plmax
cm H2O 69 ± 30 87 ± 23 < 0.05
% predicted 65 ± 28 80 ± 17 < 0.05
P0.1, cm H2O 2.8 ± 1.1 2.0 ± 0.4 < 0.005
P0.1/Pimax ratio, % 5.3 ± 4.2 2.5 ± 0.9 < 0.01
Pao2, kPa 10.7 ± 1.4 12.0 ± 0.4 < 0.001
Paco2, kPa 4.9 ± 0.4 5.2 ± 0.3 < 0.03
P(A-a2)O2, kPa 4.3 ± 1.2 2.7 ± 0.5 < 0.001
pH 7.44 ± 0.03 7.40 ± 0.03 < 0.001
Borg score 0.5 ± 0.7 0
FL/NFL ratio 0/20 0/20
CC > FRC 13/20 0/20
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