Respiratory Determinants of Exercise Limitation: Focus on Phrenic Afferents and the Lung Vasculature

Inspiratory muscles pre-activation in young swimmers submitted to a tethered swimming test: effects on mechanical, physiological, and skin temperature parameters

Inspiratory muscles pre-activation (IMPA) has been studied to improve subsequent performance in swimming. However, the effects of IMPA on various parameters in swimmers are still unknown. Therefore, this study aimed to investigate the effects of IMPA on the mechanical parameters, physiological responses, and their possible correlations with swimming performance. A total of 14 young swimmers (aged 16 ± 0 years) underwent a 30-s all-out tethered swimming test, preceded or not by IMPA, a load of 40% of the maximal inspiratory pressure (MIP), and with a volume of 2 sets of 15 repetitions. The mechanical (strength, impulse, and fatigue index) and physiological parameters (skin temperature and lactatemia) and the assessment of perceived exertion and dyspnea were monitored in both protocols. The IMPA used did not increase the swimming force, and skin temperature, decrease blood lactate concentration, or subjective perception of exertion and dyspnea after the high-intensity tethered swimming exercises. Positive correlations were found between mean force and blood lactate (without IMPA: r = 0.62, P = 0.02; with IMPA: r = 0.65, P = 0.01). The impulse was positively correlated with blood lactate (without IMPA: r = 0.71, P < 0.01; with IMPA: r = 0.56, P = 0.03). Our results suggest that new IMPA protocols, possibly with increased volume, should be developed in order to improve the performance of young swimmers.

Motor Dysfunctions in Fibromyalgia Patients: The Importance of Breathing

The classification of fibromyalgia (FM) is not always immediate and simple, with the time from the first diagnosis, compared to the onset of symptoms, of a few years. Currently, we do not have instrumental or biochemical tests considered as gold standards; the clinician will make a diagnosis of FM based on the patient's medical history and subjective assessment. The symptoms can involve physical, cognitive and psychological disorders, with the presence of pain of different origins and classifications: nociplastic, nociceptive and neuropathic pain. Among the symptoms highlighted, postural disorders and neuromotor uncoordination emerge, whose functional dysfunctions can increase the mortality and morbidity rate. An alteration of the diaphragm muscle could generate such functional motor problems. Considering that the current literature underestimates the importance of breathing in FM, the article aims to highlight the relationship between motor and diaphragmatic difficulties in the patient, soliciting new points of view for the clinical and therapeutic framework.

Systemic Determinants of Exercise Intolerance in Patients With Fibrotic Interstitial Lung Disease and Severely Impaired DLCO

BACKGROUND

The precise mechanisms driving poor exercise tolerance in patients with fibrotic interstitial lung diseases (fibrotic ILDs) showing a severe impairment in single-breath lung diffusing capacity for carbon monoxide (DLCO < 40% predicted) are not fully understood. Rather than only reflecting impaired O2 transfer, a severely impaired DLCO may signal deranged integrative physiologic adjustments to exercise that jointly increase the burden of exertional symptoms in fibrotic ILD.

METHODS

Sixty-seven subjects (46 with idiopathic pulmonary fibrosis, 24 showing DLCO < 40%) and 22 controls underwent pulmonary function tests and an incremental cardiopulmonary exercise test with serial measurements of operating lung volumes and 0-10 Borg dyspnea and leg discomfort scores.

RESULTS

Subjects from the DLCO < 40% group showed lower spirometric values, more severe restriction, and lower alveolar volume and transfer coefficient compared to controls and participants with less impaired DLCO (P < .05). Peak work rate was ∼45% (vs controls) and ∼20% (vs DLCO > 40%) lower in the former group, being associated with lower (and flatter) O2 pulse, an earlier lactate (anaerobic) threshold, heightened submaximal ventilation, and lower SpO2 . Moreover, critically high inspiratory constrains were reached at lower exercise intensities in the DLCO < 40% group (P < .05). In association with the greatest leg discomfort scores, they reported the highest dyspnea scores at a given work rate. Between-group differences lessened or disappeared when dyspnea intensity was related to indexes of increased demand-capacity imbalance, that is, decreasing submaximal, dynamic ventilatory reserve, and inspiratory reserve volume/total lung capacity (P > .05).

CONCLUSIONS

A severely reduced DLCO in fibrotic ILD signals multiple interconnected derangements (cardiovascular impairment, an early shift to anaerobic metabolism, excess ventilation, inspiratory constraints, and hypoxemia) that ultimately lead to limiting respiratory (dyspnea) and peripheral (leg discomfort) symptoms. DLCO < 40%, therefore, might help in clinical decision-making to indicate the patient with fibrotic ILD who might derive particular benefit from pharmacologic and non-pharmacologic interventions aimed at lessening these systemic abnormalities.

Cardiopulmonary exercise testing applied to respiratory medicine: Myths and facts

Cardiopulmonary exercise testing (CPET) remains poorly understood and, consequently, largely underused in respiratory medicine. In addition to a widespread lack of knowledge of integrative physiology, several tenets of CPET interpretation have relevant controversies and limitations which should be appropriately recognized. With the intent to provide a roadmap for the pulmonologist to realistically calibrate their expectations towards CPET, a collection of deeply entrenched beliefs is critically discussed. They include a) the actual role of CPET in uncovering the cause(s) of dyspnoea of unknown origin, b) peak O₂ uptake as the key metric of cardiorespiratory capacity, c) the value of low lactate ("anaerobic") threshold to differentiate cardiocirculatory from respiratory causes of exercise limitation, d) the challenges of interpreting heart rate-based indexes of cardiovascular performance, e) the meaning of peak breathing reserve in dyspnoeic patients, f) the merits and drawbacks of measuring operating lung volumes during exercise, g) how best interpret the metrics of gas exchange inefficiency such as the ventilation-CO₂ output relationship, h) when (and why) measurements of arterial blood gases are required, and i) the advantages of recording submaximal dyspnoea "quantity" and "quality". Based on a conceptual framework that links exertional dyspnoea to "excessive" and/or "restrained" breathing, I outline the approaches to CPET performance and interpretation that proved clinically more helpful in each of these scenarios. CPET to answer clinically relevant questions in pulmonology is a largely uncharted research field: I, therefore, finalize by highlighting some lines of inquiry to improve its diagnostic and prognostic yield.

The Importance of the Diaphragm in Neuromotor Function in the Patient with Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a constant and chronic narrowing of the respiratory airways, with numerous associated symptoms, not always related to the pathological adaptation of the lungs. Statistical projections show that COPD could become the third leading cause of death globally by 2030, with a significant increase in deaths by 2060. Skeletal muscle dysfunction, including the diaphragm, is one of the causes linked to the increase in mortality and hospitalization. Little emphasis is given by the scientific literature to the importance of the diaphragm towards functional neuromotor pathological expressions. The article reviews the adaptation of the skeletal muscles, with greater attention to the adaptations of the diaphragm, thereby highlighting the non-physiological variations that the main respiratory muscle undergoes and the neuromotor impairment found in COPD. The text could be an important reflection from a clinical and rehabilitation point of view, to direct greater attention to the function and adaptation of the diaphragm muscle.

Regulation of the microvasculature during small muscle mass exercise in chronic obstructive pulmonary disease vs. chronic heart failure

Aim: Skeletal muscle convective and diffusive oxygen (O₂) transport are peripheral determinants of exercise capacity in both patients with chronic obstructive pulmonary disease (COPD) and chronic heart failure (CHF). We hypothesised that differences in these peripheral determinants of performance between COPD and CHF patients are revealed during small muscle mass exercise, where the cardiorespiratory limitations to exercise are diminished.

Methods: Eight patients with moderate to severe COPD, eight patients with CHF (NYHA II), and eight age- and sex-matched controls were studied. We measured leg blood flow (Q̇_leg) by Doppler ultrasound during submaximal one-legged knee-extensor exercise (KEE), while sampling arterio-venous variables across the leg. The capillary oxyhaemoglobin dissociation curve was reconstructed from paired femoral arterial-venous oxygen tensions and saturations, which enabled the estimation of O₂ parameters at the microvascular level within skeletal muscle, so that skeletal muscle oxygen conductance (D_SMO₂) could be calculated and adjusted for flow (D_SMO₂/Q̇_leg) to distinguish convective from diffusive oxygen transport.

Results: During KEE, Q̇_leg increased to a similar extent in CHF (2.0 (0.4) L/min) and controls (2.3 (0.3) L/min), but less in COPD patients (1.8 (0.3) L/min) (p <0.03). There was no difference in resting D_SMO₂ between COPD and CHF and when adjusting for flow, the D_SMO₂ was higher in both groups compared to controls (COPD: 0.97 (0.23) vs. controls 0.63 (0.24) mM/kPa, p= 0.02; CHF 0.98 (0.11) mM/kPa vs. controls, p= 0.001). The Q̇-adjusted D_SMO₂ was not different in COPD and CHF during KEE (COPD: 1.19 (0.11) vs. CHF: 1.00 (0.18) mM/kPa; p= 0.24) but higher in COPD vs. controls: 0.87 (0.28) mM/kPa (p= 0.02), and only CHF did not increase Q̇-adjusted D_SMO₂ from rest (p= 0.2).

Conclusion: Disease-specific factors may play a role in peripheral exercise limitation in patients with COPD compared with CHF. Thus, low convective O₂ transport to contracting muscle seemed to predominate in COPD, whereas muscle diffusive O₂ transport was unresponsive in CHF.

Effects of different inspiratory muscle warm-up loads on mechanical, physiological and muscle oxygenation responses during high-intensity running and recovery

Inspiratory muscle warm-up (IMW) has been used as a resource to enhance exercises and sports performance. However, there is a lack of studies in the literature addressing the effects of different IMW loads (especially in combination with a shorter and applicable protocol) on high-intensity running and recovery phase. Thus, this study aimed to investigate the effects of three different IMW loads using a shorter protocol on mechanical, physiological and muscle oxygenation responses during and after high-intensity running exercise. Sixteen physically active men, randomly performed four trials 30 s all-out run, preceded by the shorter IMW protocol (2 × 15 breaths with a 1-min rest interval between sets, accomplished 2 min before the 30 s all-out run). Here, three IMW load conditions were used: 15%, 40%, and 60% of maximal inspiratory pressure (MIP), plus a control session (CON) without the IMW. The force, velocity and running power were measured (1000 Hz). Two near-infrared spectroscopy (NIRS) devices measured (10 Hz) the muscle’s oxygenation responses in biceps brachii (BB) and vastus lateralis (VL). Additionally, heart rate (HR) and blood lactate ([Lac]) were also monitored. IMW loads applied with a shorter protocol promoted a significant increase in mean and minimum running power as well as in peak and minimum force compared to CON. In addition, specific IMW loads led to higher values of peak power, mean velocity (60% of MIP) and mean force (40 and 60% of MIP) in relation to CON. Physiological responses (HR and muscles oxygenation) were not modified by any IMW during exercise, as well as HR and [Lac] in the recovery phase. On the other hand, 40% of MIP presented a higher tissue saturation index (TSI) for BB during recovery phase. In conclusion, the use of different loads of IMW may improve the performance of a physically active individual in a 30 s all-out run, as verified by the increased peak, mean and minimum mechanical values, but not in performance assessed second by second. In addition, 40% of the MIP improves TSI of the BB during the recovery phase, which can indicate greater availability of O₂ for lactate clearance.

Caffeine alters the breathing pattern during high-intensity whole-body exercise in healthy men

PURPOSE

The current study investigated the effect of caffeine on the breathing pattern during a high-intensity whole-body exercise.

METHODS

Using a randomized, crossover, counterbalanced, and double-blind design, twelve healthy men ingested either 5 mg.kg^-1 of caffeine or cellulose (placebo) one hour before performing a high-intensity whole-body exercise (i.e., work rate corresponding to 80% of the difference between the gas exchange threshold and maximal oxygen uptake) until the limit of tolerance. Ventilatory and metabolic responses were recorded throughout the trial and at task failure.

RESULTS

Caffeine ingestion increased time to task failure in relation to the placebo (368.1 ± 49.6 s vs. 328.5 ± 56.6 s, p = 0.005). Caffeine also increased tidal volume and inspiratory time throughout the exercise (p < 0.05). Compared to task failure with placebo, task failure with caffeine intake was marked by higher (p < 0.05) minute ventilation (134.8 ± 16.4 vs. 147.6 ± 18.2 L.min^-1), the ventilatory equivalent of oxygen consumption (37.8 ± 4.2 vs. 41.7 ± 5.5 units), and respiratory exchange ratio (1.12 ± 0.10 vs. 1.19 ± 0.11 units).

CONCLUSION

In conclusion, ingestion of caffeine alters the breathing pattern by increasing tidal volume and lengthening the inspiratory phase of the respiratory cycle. These findings suggest that caffeine affects the ventilatory system, which may account, in part, for its ergogenic effects during high-intensity whole-body exercises.

Lung mitochondria adaptation to endurance training in rats

We elucidated the impact of eight weeks of endurance training on the oxidative metabolism of rat lungs. Adult 3.5-month-old male rats were randomly allocated to a treadmill training group or a sedentary group as control. In the lungs, endurance training raised the expression level of the oxygen sensors hypoxia inducible factor 1α (HIF1α) and lysine-specific demethylase 6A (KDM6A) as well as stimulated mitochondrial oxidative capacity and mitochondrial biogenesis, while lactate dehydrogenase activity was reduced. Endurance training enhanced antioxidant systems (the coenzyme Q content and superoxide dismutase) in lung tissue but decreased them (and uncoupling protein 2) in lung mitochondria. In the lung mitochondria of trained rats, the decreased Q content and Complex I (CI) activity and the enhanced cytochrome pathway activity (CIII + CIV) may account for the diminished Q reduction level, resulting in a general decrease in H₂O₂ formation by mitochondria. Endurance training enhanced oxidation of glutamate and fatty acids and caused opposite effects in functional mitochondrial properties during malate and succinate oxidation, which were related to reduced activity of CI and increased activity of CII, respectively. In addition, endurance training downregulated CI in supercomplexes and upregulated CIII in the CIII₂+CIV supercomplex in the oxidative phosphorylation system. We concluded that the adaptive lung responses observed could be due to hypoxia and oxidative stress induced by strenuous endurance training.