Low-intensity resistance training with moderate blood flow restriction appears safe and increases skeletal muscle strength and size in cardiovascular surgery patients: a pilot study

INTERVENTION: Cardiac patients are randomised using the envelope method to the control group (n=10) and the KAATSU resistance training group. All patients receive a standard aerobic cardiac rehabilitation program. The KAATSU resistance training group additionally execute low‐intensity leg extension and leg press exercises with moderate blood flow restriction twice a week for 3 months. CONDITION: Cardiac open surgery ; Circulatory System PRIMARY OUTCOME: ; 1. Muscle volume measured using a multi‐frequency bioelectrical impedance analyzer (BIA) at baseline, 5‐7 days after cardiac surgery, and after 3 months; 2. The anterior thigh muscle thickness measured using ultrasound at baseline, 5‐7 days after cardiac surgery, and after 3 months; 3. Handgrip strength during maximal voluntary isometric contraction measured using a handgrip dynamometer at baseline, 5‐7 days after cardiac surgery, and after 3 months; 4. Knee extensor strength during maximal voluntary isometric contraction measured using a digital handheld dynamometer at baseline, 5‐7 days after cardiac surgery, and after 3 months; 5. Walking speed computed as the time needed to walk 4 m at a habitual pace at baseline, 5‐7 days after cardiac surgery, and after 3 months; SECONDARY OUTCOME: ; 1. Left ventricular ejection fraction calculated using the Simpson method based on two‐dimensional images measured using cardiovascular ultrasound at baseline; 2. Hemoglobin A1, albumin, brain natriuretic peptide, creatinine, creatine phosphokinase, high‐sensitivity C‐reactive protein, prothrombin time‐international normalized ratio, and D‐dimer (only for KAATSU resistance training group) obtained from routine biochemical analysis performed in the hospital’s clinical laboratory at baseline and after 3 months; 3. Body composition including body fat volume, % body fat, extracellular water, and total body water, measured using BIA at baseline, 5‐7 days after cardiac surgery, and after 3 months; 4. Circulatory hemodynamics monitored using a hemodynamics analyzer during hospitalization; 5. Adverse side events including dizziness, subcutaneous hemorrhage, petechial hemorrhage, drowsiness, numbness, nausea, itchiness, and new deep vein thrombosis monitored by medical staff during KAATSU resistance training; INCLUSION CRITERIA: Of the inpatients receiving cardiac open surgery between April 2017 and June 2020, a total of 25 patients, who met the following criteria, were recruited to participate in the study: 1. Able to perform the preoperative evaluation of leg extension strength 2. Able to perform postoperative cardiac rehabilitation program consisting of aerobic exercise 3. Able to provide written informed consent