The contribution of chemoreflex drives to resting breathing in man

Citation
S. Mahamed et al., The contribution of chemoreflex drives to resting breathing in man, EXP PHYSIOL, 86(1), 2001, pp. 109-116
Citations number
23
Categorie Soggetti
Physiology
Journal title
EXPERIMENTAL PHYSIOLOGY
ISSN journal
09580670 → ACNP
Volume
86
Issue
1
Year of publication
2001
Pages
109 - 116
Database
ISI
SICI code
0958-0670(200101)86:1<109:TCOCDT>2.0.ZU;2-4
Abstract
The contribution of automatic drives to breathing at rest, relative to beha vioural drives such as 'wakefulness', has been a subject of debate. We meas ured the combined central and peripheral chemoreflex contribution to restin g ventilation using a modified rebreathing method that included a prior hyp erventilation and addition of oxygen to maintain isoxia at a P-ET,P-O2 (end -tidal partial pressure of oxygen) of 100 mmHg. During rebreathing, ventila tion was unrelated to P-ET,P-CO2 (end-tidal partial pressure of carbon diox ide) in the hypocapnic range, but after a threshold P-ET,P-CO2 was exceeded , ventilation increased linearly with P-ET,P-CO2. We considered the sub-thr eshold ventilation to be an estimate of the behavioural drives to breathe ( mean +/- S.E.M. = 3.1 +/- 0.5 1 min(-1)), and compared it to ventilation at rest (mean +/- S.E.M. = 9.1 +/- 0.7 1 min(-1)). The difference was signifi cant (Student's paired t test, P < 0.001). We also considered the threshold P-CO2 observed during rebreathing to be an estimate of the chemoreflex thr eshold at rest (mean +/- S.E.M. = 42.0 +/- 0.5 mmHg), However, P-ET,P-CO2 d uring rebreathing estimates mixed venous or tissue P-CO2, whereas the resti ng P-ET,P-CO2 during resting breathing estimates P-a,P-CO2 (arterial partia l pressure of carbon dioxide). The chemoreflex threshold measured during re breathing was therefore reduced by the difference in P-ET,P-CO2 at rest and at the start of rebreathing (the plateau estimates the mixed venous P-CO2 at rest) in order to make comparisons. The corrected chemoreflex thresholds (mean +/- S.E.M. = 26.0 +/- 0.9 mmHg) were significantly less (paired Stud ent's t test, P < 0.001) than the resting P-ET,P-CO2 values (mean +/- S.E.M . = 34.3 +/- 0.5 mmHg). We conclude that both the behavioural and chemorefl ex drives contribute to resting ventilation.