Acute L-Citrulline Supplementation Increases Nitric Oxide Bioavailability but Not Inspiratory Muscle Oxygenation and Respiratory Performance

The present study aimed to investigate whether acute L-citrulline supplementation would affect inspiratory muscle oxygenation and respiratory performance. Twelve healthy males received 6 g of L-citrulline or placebo in a double-blind crossover design. Pulmonary function (i.e., forced expired volume in 1 s, forced vital capacity and their ratio), maximal inspiratory pressure (MIP), fractional exhaled nitric oxide (NO•), and sternocleidomastoid muscle oxygenation were measured at baseline, one hour post supplementation, and after an incremental resistive breathing protocol to task failure of the respiratory muscles. The resistive breathing task consisted of 30 inspirations at 70% and 80% of MIP followed by continuous inspirations at 90% of MIP until task failure. Sternocleidomastoid muscle oxygenation was assessed using near-infrared spectroscopy. One-hour post-L-citrulline supplementation, exhaled NO• was significantly increased (19.2%; p < 0.05), and this increase was preserved until the end of the resistive breathing (16.4%; p < 0.05). In contrast, no difference was observed in the placebo condition. Pulmonary function and MIP were not affected by the L-citrulline supplementation. During resistive breathing, sternocleidomastoid muscle oxygenation was significantly reduced, with no difference noted between the two supplementation conditions. In conclusion, a single ingestion of 6 g L-citrulline increased NO• bioavailability but not the respiratory performance and inspiratory muscle oxygenation.

Pathophysiological mechanisms of resistive breathing

AIM: This study aimed to explore the pathophysiological mechanisms of resistive breathing by using a model of a conditioned respiratory reflex to external resistance to breathing. MATERIALS AND METHODS: Inspiratory resistive loads were used 11, 28, 54, and 78 cmAq/l/s to model a conditioned respiratory reflex. External respiration was parametrized on the basis of the analysis of motor and ventilatory outputs. Conditioned signals were pure sounds exceeding the threshold of perception by 10 db at 2000 Hz frequency. All the test persons were divided into two groups (large and small groups) according to the initial reinforcement value. (1) In the large group (37 individuals), the conditioned reflex was formed from 11 cmAq/l/s that was subsequently increased stepwise in the load to 76 cmAq/l/s. (2) In the small group (18 individuals), the initial reinforcements were different gradations of resistive loads, with a stepwise transition to the other parameters of an unconditioned stimulus. The period of the isolated application of a conditioned signal (CS) was 20 s, the interval between signals was not fixed, varying from 2 min to 4 min. Six to eight combinations of the conditioned and unconditioned stimuli were used for 1 day of the experiment. RESULTS: The increase in the added respiratory resistance was associated with the pronounced reduction of pulmonary and alveolar ventilation, that is, with the hypoventilation type of resistive load realization. Changes in ventilation during the isolated application of a conditioned signal had an alternative character. In particular, as the reinforcement factor increased, a pronounced shift to hyperventilation was noted. CONCLUSION: The reinforcement value of the conditioned reflex changed stepwise, thereby significantly restructuring the proportion between the effectiveness of the adaptive activity in the realization of external resistance to inspiration (the time of stay under a certain load) and its physiological cost (totalities of the deviations of physiological and energy parameters).

Inspiratory flow-resistive breathing, respiratory muscle-induced systemic oxidative stress, and diaphragm fatigue in healthy humans

We examined whether the respiratory muscles of humans contribute to systemic oxidative stress following inspiratory flow-resistive breathing, whether the amount of oxidative stress is influenced by the level of resistive load, and whether the amount of oxidative stress is related to the degree of diaphragm fatigue incurred. It is only when sufficiently strenuous that inspiratory flow-resistive breathing elevates plasma F2-isoprostanes, and our novel data show that this is not related to a reduction in transdiaphragmatic twitch pressure.

IMPORTANCE OF MOTIVATION IN TOLERABILITY OF INCREASED BREATHING RESISTANCE

Cortical mechanisms play an important role in breathing control under increased breathing resistance (resistive loads). Cortical mechanisms determine the level of voluntary motivation, which significantly affects the tolerance of resistive breathing loads. The purpose of the paper is to determine the effect of voluntary motivation on the tolerance of additional breathing resistance. Materials and Methods. The authors formed procedural motivation by means of moral encouragement or financial rewards of the subjects. Simulation of increased breathing resistance was performed using in-creasing values of thresholdless inspiratory aerodynamic loads: 40, 60, 70, and 80 % from the maximum intraoral pressure. Results. The maximum level of tolerance of additional breathing resistance was observed in volunteers with a material and subsidiary procedural motivation of activity. Under respiratory loads, these subjects demonstrated the greatest deviations of the functional state indicators. Undefined motivation based on the mobilization of goal-oriented resources with moral stimulation showed less efficiency. Lack of specially formed procedural motivation led to minimal tolerance of resistive loads. Conclusion. Procedural motivation, aimed at overcoming additional breathing resistance, significantly increases the tolerance of individual protective means of respiratory organs, which maintains health of workers in a polluted technological environment. Keywords: motivation, tolerance, increased breathing resistance. Большую роль в регуляции дыхания при увеличенном сопротивлении дыханию (резистивных нагрузках) играют кортикальные механизмы. Корковые механизмы определяют уровень произвольной мотивации, которая существенно влияет на переносимость резистивных дыхательных нагрузок. Цель исследования – определение влияния произвольной мотивации на переносимость дополнительного респираторного сопротивления. Материалы и методы. Процессуальную мотивацию формировали методом морального или материального поощрения испытуемых. Моделирование увеличенного сопротивления дыханию проводили с помощью предъявления возрастающих значений беспороговых инспираторных аэродинамических нагрузок: 40, 60, 70 и 80 % от максимального внутриротового давления. Результаты. Максимальный уровень переносимости дополнительного респираторного сопротивления наблюдался у добровольцев, у которых была сформирована материально-субсидивная процессуальная мотивация деятельности; у этой категории испытуемых во время действия дыхательных нагрузок отмечались наибольшие отклонения показателей функционального состояния. Произвольная мотивация на основе мобилизации волевых ресурсов при моральном стимулировании характеризовалась меньшей эффективностью, а отсутствие специально сформированной процессуальной мотивации сопровождалось минимальной переносимостью резистивных нагрузок. Выводы. Процессуальная мотивация, сформированная для преодоления дополнительного респираторного сопротивления, существенно повышает переносимость средств индивидуальной защиты органов дыхания, что имеет большое значение для сохранения здоровья работающих в условиях загрязненной производственной среды. Ключевые слова: мотивация, переносимость, увеличенное сопротивление дыханию.