[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.
Facultad de Ciencias de la Educación Física y del Deporte (INEF), Universidad Politécnica de Madrid, Madrid, Spain. pedroj.benito@epm.es
P J
PJ
Benito
F J
FJ
Calderón
A
A
García-Zapico
J C
JC
Legido
J A
JA
Caballero
D000328:Adult; D015444:Exercise / Q000502:physiology*; D006801:Humans; D001239:Inhalation; D008297:Male; D013990:Tidal Volume; D013997:Time Factors