Effects of Controlled Breathing on Cardiorespiratory Variables in Multiple Myeloma

Inclusion Criteria:

* Age ≥ 18 years.
* Confirmed diagnosis of multiple myeloma, currently undergoing active treatment with daratumumab, and under clinical follow-up by the Hematology Department of HU12O.
* Explicit medical indication for supervised physical activity issued by the responsible hematologist and documented in the medical record.
* No scheduled hematopoietic stem cell transplantation within the 60 days following the planned start date of the intervention (verified through medical record review).
* Functional status of ECOG 0-2 (Eastern Cooperative Oncology Group), assessed by a healthcare professional from the Hematology Department, ensuring the ability to perform at least basic and light instrumental activities of daily living, including independent ambulation.
* Access to a smartphone with stable internet connection, required for monitoring and recording adherence to the intervention.
* Ability to provide written informed consent, demonstrating understanding of the study's nature, purpose, and procedures.

Exclusion Criteria:

* Medical risk contraindicating exercise or breathing techniques:

  * Clinically significant cardiovascular disease, including:decompensated heart failure, acute myocardial infarction within the past 3 months, clinically uncontrolled arrhythmias, unstable angina, acute-phase deep vein thrombosis or pulmonary embolism, pacemakers or cardiac devices whose monitoring parameters contraindicate supervised exercise according to cardiology.
  * Severe decompensated respiratory disease, such as acute exacerbation of COPD, severe respiratory insufficiency, or persistently low resting oxygen saturation \< 90% (not correctable).
* High musculoskeletal or bone risk:

  * Extensive lytic bone lesions, high risk of pathological fracture, or unstable vertebral fracture, documented by imaging or based on the assessment of the Hematology/Traumatology specialist.
  * Uncontrolled pain that prevents safe participation in an exercise program.
* Hematologic or systemic conditions contraindicating exercise:

  * Severe anemia: hemoglobin \< 9 g/dL in women or \< 8 g/dL in men (latest laboratory test ≤ 14 days).
  * Active systemic infection contraindicating exercise, fever ≥ 38 °C, or neutropenia \< 0.5 × 10⁹/L.
  * Severe cytopenias that, in the opinion of the hematologist, preclude moderate exercise.
* Functional or procedural limitations:

  * Inability to remain in the supine position for ≥ 5 minutes, required for part of the breathing intervention.
  * Confirmed pregnancy or reasonable suspicion of pregnancy.
  * Severe cognitive impairment, major psychiatric disorders, or neurological diseases that limit understanding of the procedures or safe participation.
  * Significant difficulty understanding the language (spoken or written) that prevents following essential instructions or completing validated questionnaires.