[Response of tidal volume to inspiratory time ratio during incremental exercise].
OBJECTIVE
There is some debate about the participation of the Hering-Breuer reflex during exercise in human beings. This study aimed to investigate breathing pattern response during an incremental exercise test with a cycle ergometer. Participation of the Hering-Breuer reflex in the control of breathing was to be indirectly investigated by analyzing the ratio of tidal volume (VT) to inspiratory time (tI).


METHODS
The 9 active subjects who participated the study followed an incremental protocol on a cycle ergometer until peak criteria were reached. During exercise, VT/ti can be described in 2 phases, separated by activation of the Hering-Breuer reflex (inspiratory off-switch threshold). In phase 1, ventilation increases because VT increases, resulting in a slight decrease in tI, whereas, in phase 2, increased ventilation is due to both an increase in VT and a decrease in tI.


RESULTS
The mean (SD) inspiratory off-switch threshold was 84.6% (6.3%) when expressed relative to peak VT (mean, 3065 [566.8] mL) and 48% (7.2%) relative to the forced vital capacity measured by resting spirometry. The inspiratory off-switch threshold correlated positively (r=0.93) with the second ventilatory threshold, or respiratory compensation point.


CONCLUSIONS
The inspiratory off-switch threshold and VT/ti are directly related to one another. The inspiratory off-switch threshold was related to the second ventilatory threshold, suggesting that the Hering-Breuer reflex participates in control of the breathing pattern during exercise. Activation of the reflex could contribute by signaling the respiratory centers to change the breathing pattern.
Benito
P J
PJ
Facultad de Ciencias de la Educación Física y del Deporte (INEF), Universidad Politécnica de Madrid, Madrid, Spain. pedroj.benito@epm.es
Calderón
F J
FJ
García-Zapico
A
A
Legido
J C
JC
Caballero
J A
JA
D000328:Adult; D015444:Exercise / Q000502:physiology*; D006801:Humans; D001239:Inhalation; D008297:Male; D013990:Tidal Volume; D013997:Time Factors