Effects of Interval Physical Training on Expiratory Flow Limitation in Recent Myocardial Infarction

Introduction: Expiratory flow limitation (EFL) and ventilatory inefficiency during dynamic exercise have been identified in patients with recent myocardial infarction (RMI) with preserved ventricular and pulmonary function. However, it is not known what is the prevalence of EFL in this population and what are the effects of physical and respiratory training on this limitation.

Objectives: To evaluate the prevalence of EFL and ventilatory inefficiency during dynamic exercise in individuals with uncomplicated RMI, and to evaluate the effects of interval physical training (IT) in addition to inspiratory muscle training (IMT), exclusive IT and absence of cardiopulmonary rehabilitation (CR) on EFL and ventilatory efficiency.

Methods: 54 patients will be included, divided into three groups with 18 participants each. All will be submitted to evaluations of heart rate variability, hematological and biochemical profile, erythrocytes membrane deformability and stability, inflammatory markers, respiratory pressures, plethysmography, spirometry, carbon monoxide diffusion capacity, ankle brachial index, electrical bioimpedance, echocardiogram, quality of life questionnaires, cardiopulmonary exercise testing and constant load tests. Then, groups 1 (IT) and group 2 (IT + IMT) will participate in a physical training program for 12 weeks and will be re-evaluated after this period. In addition, they will be monitored for a 6 month period after discharge, with returns every two months to measure the energy expenditure through an accelerometer, and at the end of this period they will repeat all the tests again. Group 3 (absence of CR), will consist of patients who do not live in the city or those who can not participate in the CR program for any other reason, and will only participate in the evaluations.

Patients with coronary artery disease (CAD) attended by the Sistema Unico de Saude (SUS) in the city of Uberlandia and region are routinely referred to Hospital de Clinicas - Federal University of Uberlandia after acute myocardial infarction (AMI) for coronary angiography and other exams, receiving appropriate clinical or surgical follow-up. After the resolution of the clinical condition, the patient is released from the hospital with a medical referral to the Cardiorespiratory Rehabilitation Program offered by the institution.

These patients are contacted by telephone by the team of the rehabilitation sector, and invited to attend for a pre-entry evaluation for inclusion in treatment. In this telephone contact the secretary of the sector clarifies that the hospital does not have transportation services for the patients who accept to be part of the program, and afterwards the evaluation is scheduled. The initial anamnesis will be performed by a multidisciplinary team. In this screening are collected complaints, past and current history of possible diseases, personal and family history, life habits, medications in use, exams performed pre-hospital discharge and physical examination, collected from an individual anamnesis form. At the end of the evaluation the patient receives a card with the scheduling of training days that occur three times a week and dressing and feeding instructions prior to training.

All volunteers who fit the study criteria will be invited to participate in the study, being informed about the experimental procedures to which they would be submitted. They will also be clarified that all the information collected during the accomplishment of the work will be kept confidential, protecting their identities. Individuals who agree to participate in the study will sign an informed consent according to National Health Council (466/12) guidelines, and a next return will be scheduled to begin physical testing and blood collection. At that moment, the Research Participant Identification Card will be filled in, which will be kept in a confidential place separated from the other evaluations, with restricted access to the researcher, and a code will be given to the participant. In case of refusal to participate in the study, the participant will receive the same care offered to other patients routinely referred to the rehabilitation sector, being included into the conventional rehabilitation program that also lasts for 12 weeks.

Considering that the patients enrolled in the research will have to attend for evaluation and monitoring related to the study, all the displacements related to these additional activities will be refunded to the participants during the entire period of the study.

The evaluation procedures that will be performed in 2 days will consist of: Step 1 - ankle brachial index, heart rate variability at rest, respiratory pressures (maximal inspiratory and expiratory pressures), cardiopulmonary exercise test (incremental and constant load tests), spirometry and quality of life questionnaires (SF-36 and MacNew QLMI); Step 2 - blood collection (hematological and biochemical profile, erythrocytes membrane deformability and stability, inflammatory markers), plethysmography, carbon monoxide diffusion capacity and echocardiography.

After these exams the participant will be randomized to a training group: Group 1 - interval training (IT) or group 2 - IT + inspiratory muscle training (IMT), and will participate in the cardiorespiratory rehabilitation program for a period of 12 weeks, three times a week. Group 3 will consist of those participants who for any reason do not agree to participate in the rehabilitation program, such as those who do not live in the city, and will remain without intervention.

During the 6 months of discharge, participants will be monitored monthly, by telephone contact to verify possible changes in medications in use and general health status.

At the end of the 2nd, 4th and 6th month of discharge, in the last week of each period, the patient will be invited to return to the rehabilitation sector for placement of an accelerometer, a monitor that quantifies free activities and sedentary lifestyle. The selected equipment (activPAL3 ™ micro, PAL Technologies Ltd, Scotland, UK) makes use of algorithms properties to quantify periods of sitting, orthostatism and walking. This information will be used to estimate the daily energy expenditure in the period and will store information of seven consecutive days during the selected weeks.

The re-evaluations will consist of all the exams mentioned above (steps 1 and 2), and will be performed at the beginning and at the end of the training period and after 6 months of the program's discharge.

Eligibility Criteria:
Inclusion Criteria:

* Men
* Aged 35 to 80 years
* Recent myocardial infarction (RMI), between 15 and 45 days post-event, being the 1st MI event
* Left ventricular ejection fraction (LVEF) ≥ 50%
* Preserved respiratory muscle strength (Maximal Inspiratory Pressure \> 60% predicted)
* Whether or not submitted to Percutaneous Transluminal Coronary Angioplasty (PTCA)
* Presence of expiratory flow limitation by incremental cardiopulmonary test
* Agreement to participate in the study after reading and signing the informed consent

Non-inclusion Criteria:

* Body Mass Index (BMI) ≥ 35 kg / m2
* Previous diagnosis of any musculoskeletal, neurological, respiratory or vascular diseases
* Ankle Brachial Index (ABI) \< 0.90 and \> 1.4
* Diabetes mellitus
* Active or smoking cessation for less than six months
* Chronic organic dysfunction such as renal or hepatic impairment
* Patients submitted to Coronary Artery Bypass Graft Surgery (CABG)
* Inadequate response of systemic or electrocardiographic blood pressure during the cardiopulmonary exercise test (CPET)
* Presence of Chronic Obstructive Pulmonary Disease (COPD) or Interstitial Lung Diseases
* Presence of valvulopathies or Chagas disease
* Participants with pacemaker (PM) or implantable cardioverter defibrillator (ICD)

Exclusion Criteria:

* Refusal to participate in the study
* Participants who do not complete all the steps proposed in the research
* Participants who request their exclusion at any time during the study, will be excluded