The cardiovascular consequences of fatiguing expiratory muscle work in otherwise resting healthy humans

In 11 healthy adults (25 ± 4 years; 2 females), we investigated the effect of expiratory resisted loaded breathing [65% maximal expiratory mouth pressure (MEP), 15 breaths·min−1, duty cycle 0.5; ERLPm] on mean arterial pressure (MAP), leg vascular resistance (LVR), and leg blood flow (Q̇L). On a separate day, a subset of 5 males performed ERL targeting 65% of maximal expiratory gastric pressure (ERLPga). ERL-induced expiratory muscle fatigue was confirmed by a 17 ± 5% reduction in MEP (P < 0.05) and a 16 ± 12% reduction in the gastric twitch pressure response to magnetic nerve stimulation (P = 0.09) from before to after ERLPm and ERLPga, respectively. From rest to task failure in ERLPm and ERLPga, MAP increased (ERLPm = 31 ± 10 mmHg, ERLPga = 18 ± 9 mmHg, both P < 0.05), but group mean LVR and Q̇L were unchanged (ERLPm: LVR = 0.78 ± 0.21 vs. 0.97 ± 0.36 mmHg·ml−1·min−1, Q̇L = 133 ± 34 vs. 152 ± 74 ml·min−1; ERLPga: LVR = 0.70 ± 0.21 vs. 0.84 ± 0.33 mmHg·ml−1·min−1, Q̇L = 160 ± 48 vs. 179 ± 110 ml·min−1) (all P ≥ 0.05). Interestingly, Q̇L during ERLPga oscillated within each breath, increasing (~66%) and decreasing (~50%) relative to resting values during resisted expirations and un-resisted inspirations, respectively. In conclusion, fatiguing expiratory muscle work did not affect group mean LVR or Q̇L in otherwise resting humans. We speculate that any sympathetically-mediated peripheral vasoconstriction was counteracted by transient mechanical effects of high intra-abdominal pressures during ERL.

Effect of expiratory loaded breathing during moderate exercise on intercostal muscle oxygenation

Background: In patients with obstructive lung disease, maintaining adequate ventilation during exercise may require greater contraction of the respiratory muscles, which may lead to a compression of muscle capillaries. Furthermore, dynamic hyperinflation (DH) is frequent during exercise in these patients, as it allows to reach higher expiratory flows and to satisfy respiratory demand. However, in such situation, intercostal muscles are likely to be stretched, which could affect the diameter of their capillaries. Thus, in a context of high level of expiratory resistance, intercostal muscle oxygenation may be disturbed during exercise, especially if DH occurs.Methods: Twelve participants (22±2 years) performed two sessions of moderate exercise (20 min) by breathing freely with and without a 20-cmH2O expiratory threshold load (ETL). Tissue saturation index (TSI) and concentration changes from rest (∆) in oxygenated ([O2Hb]) and total haemoglobin ([tHb]) were measured in the seventh intercostal space using near-infrared spectroscopy. Respiratory, metabolic and cardiac variables were likewise recorded.Results: Throughout exercise, dyspnea was higher and TSI was lower in ETL condition than in control (p<0.01). After a few minutes of exercise, ∆ [O2Hb] was also lower in ETL condition, as well as ∆ [tHb], when inspiratory capacity started to be reduced (p<0.05). Changes in [O2Hb] and dyspnea were correlated with changes in expiratory flow rate (Vt/Te) (r = -0.66 and 0.66. respectively; p<0.05).Conclusion: During exercise with ETL, impaired muscle oxygenation could be due to a limited increase in blood volume resulting from strong muscle contraction and/or occurrence of DH.

Experimental dyspnoea interferes with locomotion and cognition: a randomised trial

BackgroundChronic respiratory diseases are associated with cognitive dysfunction, but whether dyspnoea by itself negatively impacts on cognition has not been demonstrated. Cortical networks engaged in subjects experiencing dyspnoea are also activated during other tasks that require cognitive input and this may provoke a negative impact through interference with each other.MethodsThis randomised, crossover trial investigated whether experimentally-induced dyspnoea would negatively impact on locomotion and cognitive function among 40 healthy adults. Crossover conditions were unloaded breathing or loaded breathing using an inspiratory threshold load. To evaluate locomotion, participants were assessed by the Timed Up and Go (TUG) test. Cognitive function was assessed by categorical and phonemic verbal fluency tests, the Trail Making Tests (TMTs) A and B (executive function), the CODE test from the Wechsler Adult Intelligence Scale (WAIS)-IV (processing speed) and by direct and indirect digit span (working memory).ResultsThe mean time difference to perform the TUG test between unloaded and loaded breathing was −0.752 s (95% CI −1.012 to −0.492 s) (p<0.001). Executive function, processing speed and working memory performed better during unloaded breathing, particularly for subjects starting first with the loaded breathing condition.ConclusionOur data suggest that respiratory threshold loading to elicit dyspnoea had a major impact on locomotion and cognitive function in healthy adults.