Priming the cardiodynamic phase of pulmonary oxygen uptake through voluntary modulations of the respiratory pump at the onset of exercise

Locomotor-Respiratory Entrainment upon Phonated Compared to Spontaneous Breathing during Submaximal Exercise

Recently, increased attention to breathing techniques during exercise has addressed the need for more in-depth study of the ergogenic effects of breathing manipulation. The physiological effects of phonation, as a potential breathing tool, have not yet been studied. Thus, the aim of this study was to investigate the respiratory, metabolic and hemodynamic responses of phonated exhalation and its impact on locomotor-respiratory entrainment in young healthy adults during moderate exercise. Twenty-six young, healthy participants were subjected to peak expiratory flow (PEF) measurements and a moderate steady cycling protocol based on three different breathing patterns (BrP): spontaneous breathing (BrP1), phonated breathing pronouncing "h" (BrP2) and phonated breathing pronouncing "ss" (BrP3). The heart rate, arterial blood pressure, oxygen consumption, CO2 production, respiratory rate (RR), tidal volume (VT), respiratory exchange ratio and ventilatory equivalents for both important respiratory gasses (eqO2 and eqCO2) were measured (Cosmed, Italy) simultaneously during a short period of moderate stationary cycling at a predefined cadence. To evaluate the psychological outcomes, the rate of perceived exertion (RPE) was recorded after each cycling protocol. The locomotor-respiratory frequency coupling was calculated at each BrP, and dominant coupling was determined. Phonation gradually decreased the PEF (388 ± 54 L/min at BrP2 and 234 ± 54 L/min at BrP3 compared to 455 ± 42 L/min upon spontaneous breathing) and affected the RR (18.8 ± 5.0 min-1 at BrP2 compared to 22.6 ± 5.5 min-1 at BrP1 and 21.3 ± 7.2 min-1 at BrP3), VT (2.33 ± 0.53 L at BrP2 compared to 1.86 ± 0.46 L at BrP1 and 2.00 ± 0.45 L at BrP3), dominant locomotor-respiratory coupling (1:4 at BrP2 compared to 1:3 at BrP1 and BrP2) and RPE (10.27 ± 2.00 at BrP1 compared to 11.95 ± 1.79 at BrP1 and 11.95 ± 1.01 at BrP3) but not any other respiratory, metabolic or hemodynamic measures of the healthy adults during moderate cycling. The ventilatory efficiency was shown to improve upon dominant locomotor-respiratory coupling, regardless of BrP (eqO2 = 21.8 ± 2.2 and eqCO2 = 24.0 ± 1.9), compared to the other entrainment coupling regimes (25.3 ± 1.9, 27.3 ± 1.7) and no entrainment (24.8 ± 1.5, 26.5 ± 1.3), respectively. No interaction between phonated breathing and entrainment was observed during moderate cycling. We showed, for the first time, that phonation can be used as a simple tool to manipulate expiratory flow. Furthermore, our results indicated that in young healthy adults, entrainment, rather than expiratory resistance, preferentially affected ergogenic enhancement upon moderate stationary cycling. It can only be speculated that phonation would be a good strategy to increase exercise tolerance among COPD patients or to boost the respiratory efficiency of healthy people at higher exercise loads.

Blood shifts between body compartments during submaximal exercise with induced expiratory flow limitation in healthy humans

External expiratory flow limitation (EFLe) can be applied in healthy subjects to mimic the effects of chronic obstructive pulmonary disease during exercise. At maximal exercise intensity, EFLe leads to exercise intolerance owing to respiratory pump dysfunction limiting venous return. We quantified blood shifts between body compartments to determine whether such effects can be observed during submaximal exercise, when the load on the respiratory system is milder. Ten healthy men (25.2 ± 3.2 years of age, 177.3 ± 5.4 cm in height and weighing 67.4 ± 5.8 kg) exercised at 100 W (∼40% of maximal oxygen uptake) while breathing spontaneously (CTRL) or with EFLe. We measured respiratory dynamics with optoelectronic plethysmography, oesophageal (P_es ) and gastric (P_ga ) pressures with balloon catheters, and blood shifting between body compartments with double body plethysmography. During exercise, EFLe resulted in the following changes: (i) greater intrabreath blood shifts between the trunk and the extremities [518 ± 221 (EFLe) vs. 224 ± 60 ml (CTRL); P < 0.001] associated with lower P_es during inspiration (r = 0.53, P < 0.001) and higher P_ga during expiration (r = 0.29, P < 0.024); and (ii) a progressive pooling of blood in the trunk over time (∼700 ml after 3 min of exercise; P < 0.05), explained by a predominant effect of lower inspiratory P_es (r = 0.54, P < 0.001) over that of increased P_ga . It follows that during submaximal exercise, EFLe amplifies the respiratory pump mechanism, with a prevailing contribution from lower inspiratory P_es over increased expiratory P_ga , drawing blood into the trunk. Whether these results can be replicated in chronic obstructive pulmonary disease patients remains to be determined. KEY POINTS: External expiratory flow limitation (EFLe) can be applied in healthy subjects to mimic the effects of chronic obstructive pulmonary disease and safely study the mechanisms of exercise intolerance associated with the disease. At maximal exercise intensity with EFLe, exercise intolerance results from high expiratory pressures altering the respiratory pump mechanism and limiting venous return. We used double body plethysmography to quantify blood shifting between the trunk and the extremities and to examine whether the same effects occur with EFLe at submaximal exercise intensity, where the increase in expiratory pressures is milder. Our data show that during submaximal exercise, EFLe amplifies the respiratory pump mechanism, each breath producing greater blood displacements between the trunk and the extremities, with a prevailing effect from lower inspiratory intrathoracic pressure progressively drawing blood into the trunk. These results help us to understand the haemodynamic effects of respiratory pressures during submaximal exercise with expiratory flow restriction.

Priming Cardiac Function with Voluntary Respiratory Maneuvers and Effect on Early Exercise Oxygen Uptake

Oxygen uptake (V'O₂) at exercise onset is determined in part by acceleration of pulmonary blood flow (Q'p). Impairments in the Q'p response can decrease exercise tolerance. Prior research has shown that voluntary respiratory maneuvers can augment venous return, but the corollary impacts on cardiac function, Q'p and early-exercise V'O₂ remain uncertain. We examined a) the cardiovascular effects of 3 distinct respiratory maneuvers (abdominal, AB; rib cage, RC and deep breathing, DB) under resting conditions in healthy subjects (Protocol 1, n=13) and b) the impact of pre-exercise DB on pulmonary O₂ transfer during initiation of moderate intensity exercise (Protocol 2, n=8). In Protocol 1, echocardiographic analysis showed increased RV and LV cardiac output (RVCO and LVCO, respectively) following AB (by +23±13 and +18±15%, respectively, P<0.05), RC (+23±16; +14±15%, P<0.05) and DB (+27±21; +23±14%, P<0.05). In Protocol 2, DB performed for 12 breaths produced a pre-exercise increase in V'O₂ (+801±254 ml·min^-1 over ~ 6 s), presumably from increased Q'p followed by a reduction in pulmonary O₂ transfer during early phase exercise (first 20 s) compared to the control condition (149±51 vs 233±65 ml, P<0.05). We conclude that (1) respiratory maneuvers enhance RVCO and LVCO in healthy subjects under resting conditions, (2) AB, RC and DB have similar effects on RVCO and LVCO, and (3) DB can increase Q'p prior to exercise onset. These findings suggest that pre-exercise respiratory maneuvers may represent a promising strategy to prime V'O₂ kinetics and thereby to potentially improve exercise tolerance in patients with impaired cardiac function.

Influence of the fitting window on the O2 uptake kinetics at the onset of moderate intensity exercise

The O₂ uptake (V̇o₂) data at the onset of an exercise are usually fitted with a mono-exponential function, after removal of the data pertaining to a conventional initial time period (ΔTr) lasting ∼20 s. We performed a thorough quantitative analysis on the effects of removing data pertaining to different ΔTr, aiming at identifying an objective method to establish the appropriate ΔTr. Breath-by-breath O₂ uptake responses, acquired from 25 healthy adults performing a step moderate-intensity exercise, and 10⁴ simulated biexponential responses, were analyzed. For all the responses, the kinetic parameters of a mono-exponential function and the corresponding asymptotic standard errors (ASEs) were estimated by nonlinear regression, removing the data pertaining to progressively longer initial periods (1 s each) up to 60 s. Four methods to establish objectively ΔTr were compared. The minimum estimated τ was obtained for ΔTr ≅ 35 s in both the V̇o₂ and simulated data, that was about 30% lower compared with that obtained for ΔTr ≅ 0s. The average ASE values remained quite constant up to ΔTr ≅ 35 s, thereafter they increased remarkably. The τ used to generate the simulated response fell within the confidence intervals of the estimated τ in ∼85% of cases for ΔTr = 20 s ("20 s-w" method); this percentage increased to ∼92% of cases when ΔTr was established according to both the minimum τ and its narrowest confidence interval ("Mixed" method). In conclusion, the effects of removing V̇o₂ data pertaining to different ΔTr are remarkable. The "Mixed" method provided estimated parameters close to those used to generate the simulated responses and is thus endorsed.NEW & NOTEWORTHY We propose a method to objectively establish the initial time period to be removed from the fitting window when, using a mono-exponential model, the kinetics of the fundamental component is determined on breath-by-breath O₂ uptake data collected at the onset of a moderate-intensity exercise. Innovative statistical parameters ("Coverage" and "Concordance_5%," applicable on simulated responses) were used to compare its performance with that of other three methods. The proposed method yielded the best "Coverage" and "Concordance_5%."