Cardiac responses and adaptations to blood flow restriction exercise.

BFR exercise increased arterial elastance compared with rest and unoccluded exercise conditions.

• Arterial elastance values: rest 1.07 ± 0.32 mmHg/mL, BFR 1.32 ± 0.33 mmHg/mL, work-match 0.93 ± 0.25 mmHg/mL, HR-match 0.97 ± 0.25 mmHg/mL.
• All pairwise comparisons with BFR were statistically significant (all P < 0.01).
• Assessed in 16 athletes (11 M/5 F) using echocardiography during semirecumbent cycling.
• Indicates increased afterload as a distinctive hemodynamic feature of BFR exercise.

BFR exercise altered left ventricular diastolic filling, with a greater proportion of filling achieved through atrial contraction.

• Proportion of LV filling from atrial contraction: rest 45 ± 8%, BFR 56 ± 8%, work-match 49 ± 6%, HR-match 46 ± 7%.
• All comparisons between BFR and other conditions were statistically significant (all P < 0.05).
• End-diastolic volume was maintained across conditions (rest: 163 ± 40 mL, BFR: 163 ± 40 mL, work-match: 167 ± 37 mL, HR-match: 168 ± 38 mL; P = 0.5).
• The shift toward atrial-dependent filling appears to be a compensatory mechanism to maintain end-diastolic volume under increased afterload.

BFR exercise reduced stroke volume compared with unoccluded exercise conditions.

• Stroke volume values: rest 99 ± 26 mL, BFR 95 ± 23 mL, work-match 109 ± 27 mL, HR-match 110 ± 25 mL (P < 0.05).
• BFR stroke volume was lower than both work-matched and HR-matched unoccluded exercise.
• Despite reduced stroke volume, cardiac output was maintained during BFR (BFR: 7.5 ± 1.0 L/min vs. rest: 5.1 ± 1.2 L/min; P < 0.0001).

Heart rate was elevated during BFR exercise compared with work-matched unoccluded exercise, serving as a compensatory mechanism for reduced stroke volume.

• Heart rate values: rest 54 ± 10 beats/min, BFR and HR-match 87 ± 13 beats/min, work-match 74 ± 11 beats/min (P < 0.01).
• BFR heart rate was significantly higher than work-matched unoccluded exercise.
• Cardiac output during BFR (7.5 ± 1.0 L/min) was lower than HR-matched unoccluded exercise (9.1 ± 1.7 L/min; P < 0.0001), indicating the HR compensation was only partial.

Six weeks of low-intensity BFR walking training increased stroke volume during BFR exercise but did not affect resting LV mass index or LV function during unoccluded exercise.

• This was an exploratory analysis in a subset of 7 athletes (5 M/2 F) who completed 6 weeks of BFR walking three times per week.
• Stroke volume during BFR exercise increased from pre- to post-training (Pre: 101 ± 25 mL, Post: 113 ± 23 mL; P = 0.03).
• LV mass index was unchanged after training (Pre: 121 ± 18 g/m², Post: 123 ± 11 g/m²; P = 0.5).
• LV function at rest and during unoccluded exercise was not affected by training.
• The cardiac adaptation was specific to BFR exercise conditions and did not generalize to free-flow low-intensity exercise.