title: Carotid chemoreceptors and respiratory adaptations to dead space loading during incremental exercise.
abstract: Dead space (VD) loading has been shown to cause an increase in tidal volume and a decrease in respiratory frequency at moderate to high levels of ventilation (VI) during exercise (J. Appl. Physiol. 70: 55-62, 1991). This study examined the role of carotid chemoreceptors (CC) in the breathing pattern response to added VD during maximal incremental exercise; we used hyperoxia to silence the CC. Nine healthy subjects exercised on a bicycle ergometer on 4 different days while inspiring air with VD (AVD) and without VD [air control (AC)] and while inspiring 100% O2 with VD (O2VD) and without VD (O2C). Equipment resistance for VD and control studies was identical, and the exercise tests were done in a randomized order. At a matched level of VI equivalent to 75% VI at the end of the AC experiments (102 l/min), the breathing pattern in the AVD and O2VD tests was significantly deeper and slower (P < 0.05) than that in the AC and O2C tests. The difference in tidal volume between AVD and AC tests (delta = 0.26 +/- 0.16 liter) was not significantly different from that between O2VD and O2C tests (delta = 0.23 +/- 0.23 liter). The breathing pattern was the same in the AC and O2C tests. It is concluded that the altered breathing pattern with VD loading is not mediated by the CC.
authors.affiliation: Division of Respiratory Medicine, Royal University Hospital, Saskatoon, Saskatchewan, Canada.
authors.forename: N C
authors.initials: NC
authors.lastname: Syabbalo
authors.forename: T
authors.initials: T
authors.lastname: Zintel
authors.forename: R
authors.initials: R
authors.lastname: Watts
authors.forename: C G
authors.initials: CG
authors.lastname: Gallagher
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D002344:Carotid Body / Q000502:physiology*; D002628:Chemoreceptor Cells / Q000502:physiology*; D015444:Exercise; D006801:Humans; D008297:Male; D012119:Respiration / Q000502:physiology*; D012126:Respiratory Dead Space