Influence of hypoxia on coordination between breathing and cycling rhythms in women

Abstract

To investigate interactions between neural (movement) and chemical (hypoxia) respiratory drives during exercise, we analyzed coordination between breathing and cycling rhythms in normoxia (N) and hypoxia (H, 14.5% O(2)). Twenty women [28 (1) years old] cycled for 6 min at three workloads (55%, 75%, and 95% peak oxygen consumption, VO(2peak); WL1, WL2, and WL3) in N and H. Leg movements, respiratory parameters, peripheral oxygen saturation, and heart rate were continuously recorded. The degree of coordination (%COORD) was quantified as the percentage of breaths starting during the same phase of leg movement. Ventilatory response to isocapnic hypoxia (VRH) was assessed at rest during an exposure to an end-tidal PO(2) of 50 mmHg. There were no differences in %COORD between N and H at any of the three workloads, but %COORD increased significantly from WL1 to WL3 in H. There was no correlation between VRH and %COORD. In conclusion, chemical and neural respiratory drives did not competitively interact: coordination between breathing and cycling rhythms was not reduced during H and did not depend on individual VRH.

Locomotor-respiratory coupling is maintained in simulated moderate altitude in trained distance runners

“…We believe our results mirror this conclusion, as the rowers completed the hypoxic tests at an elevation of 2,877 meters, only slightly higher than our FI O 2 equivalent. Seebauer et al (31) found comparable effects of hypoxia during cycling exercise, where no decrements in the degree of LRC were observed at any of three separate workloads. In fact, the degree of LRC was increased at a workload of 95% peak oxygen uptake.…”

Ventilation and Locomotion in Humans: Mechanisms, Implications, and Perturbations to the Coupling of These Two Rhythms

“…Second, the workloads used in the two studies were dissimilar: running at 40 % VO 2max vs. cycling at 55, 75, and 95 % VO 2max . As Seebauer et al [134] propose, at lower workloads, both ventilatory and locomotor rhythms have greater degrees of freedom and may be more susceptible to other central and/or peripheral inputs. Certainly, evidence exists to support increasing levels of coordination with higher workloads, and thus the more vigorous workloads in work by Seebauer et al [134] may have negated the impact of a hypoxic stimulus.…”

“…As Seebauer et al [134] propose, at lower workloads, both ventilatory and locomotor rhythms have greater degrees of freedom and may be more susceptible to other central and/or peripheral inputs. Certainly, evidence exists to support increasing levels of coordination with higher workloads, and thus the more vigorous workloads in work by Seebauer et al [134] may have negated the impact of a hypoxic stimulus. Finally, differences exist in hormonal levels/activity between men and women, resulting in well-defined disparities in physiological measures.…”

“…Additionally, there was no significant correlation between resting measures of hypoxic ventilatory responsiveness and LRC in normoxia, hypoxia, or the change from normoxia to hypoxia. At least three possibilities exist to at least partially explain the varying results of Paterson et al [121] and Seebauer et al [134]. First, the latter used cycling as the primary mode of exercise; however, LRC appears to be less prevalent during cycling as opposed to other modes of exercise, such as running.…”

“…Seebauer et al [134] also investigated entrainment in hypoxia, measuring coordination between breathing and cycling rhythms in 20 healthy women during moderate-tovigorous exercise in normoxia and hypoxia. The single level of hypoxia utilized (14.5 % O 2 ) corresponded closely to the intermediate level used in the previous study by [121].…”