Effects of Unsupervised Inspiratory Muscle Training on Ventilation Variability in Post-covid-19 Patients.

Dysfunctional breathing and persistent hypocapnia can be associated with many of the symptoms experienced by patients such as dyspnea, fatigue, chest pain and palpitations. The identification of dysfunctional breathing and hypocapnia in these patients is important as it may represent a target for treatment.

In many of these patients, tachypnea at low levels of exertion suggests increased respiratory muscle activity, which can lead to the sensation of dyspnea. Sympathetic hyperactivity leads to excessive and irregular ventilation during exercise. In this way, inspiratory muscle training can improve symptoms (dysfunctional breathing), possibly by attenuating the metaboreflex (vagal modulation-attenuation of the sympathetic response) of the inspiratory muscle in post-covid-19 subjects, reducing ventilatory variability.

Primary objective To evaluate the effects of an unsupervised inspiratory muscle training (IMT) protocol on the behavior of ventilatory variability.

Secondary objective Evaluate the effects of IMT on, respiratory muscle strength, pulmonary function, quality of life, peripheral muscle strength, functional capacity and adverse effects and adherence.

Material and methods Type of study and location of research This randomized, controlled, double-blind, parallel, two arm clinical trial will be conducted at the Laboratory of Health Assessment Measures (LABMAS), Department of Physiotherapy of the Federal University of Rio Grande do Norte (UFRN).

I The subjects included in the research will undergo three assessment stages: pre-training (Initial), post-training (6 weeks). Assessments in the pre-training period will be carried out in 1 day. After recruitment, participants will be invited to attend the UFRN Physiotherapy Department to carry out the first day of assessment by a previously trained evaluator blind to the intervention allocation group and will include anamnesis and physical examination, with measurement of vital signs. , anthropometric measurements, spirometry, respiratory muscle strength (manovacuometry), functional capacity (6-minute step test) and analysis of ventilatory variability (portable ventilator), assessment of peripheral muscle strength (dynamometry), quality of life (SF-36) .

The sample will be automatically randomized through the website www.randomization.com and allocated into two distinct groups: Experimental Group (GE): inspiratory muscle training and Sham Group (G2): IMT without load. Three evaluators will participate in the research: researcher 1 will be responsible only for the evaluations, researcher 2 for respiratory muscle training with weekly load adjustment and researcher 3 for randomization. The study will be double-blind, as researcher 1 and participants will not be aware of the allocation of subjects into groups, nor of the effects of the intervention.

After the initial assessment, all volunteers will receive a POWERbreathe® classic light resistance device (POWERbreathe®, Nsc, Brazil), to carry out the training, and will be individually guided on how to use it and how to complete the protocol. They will perform a trial session to familiarize themselves with the device that will not be considered for analysis. Every week, volunteers will receive a telephone call from researcher 2, who will not participate in the evaluation, to confirm whether the exercise with the POWERbreathe® will be performed appropriately at the recommended frequency, intensity, and duration and whether there are any questions regarding the protocol. At the end of each week, participants will receive a video call from researcher 2 to adjust the device according to G1's weekly load progression.

Eligibility Criteria:
Inclusion Criteria:

* Subjects of both sexes will be included, with a diagnosis of COVID-19 confirmed by RT-PCR, aged over 18 years, without any underlying respiratory or cardiac disease and reduced respiratory muscle strength (≤100 cmH2O). Reduced inspiratory muscle strength will be defined using MIP.

Exclusion Criteria:

* Patients with conditions impairing assessments, health complications that justify interrupting data collection (e.g., syncope, intense chest pain, or cough with blood-tinged sputum), hospitalized due to exacerbation of clinical conditions, or requested to leave the study will be excluded.