IMPORTANCE: Cardiorespiratory fitness is reduced after stroke due to inactivity which may cause structural and functional changes to blood vessels in the extremities. Identifying clinical factors contributing to vascular function may be important for tailoring rehabilitation programs that reduce secondary disease risk and adverse events. OBJECTIVE: The study objective was to compare measures of arterial and intramuscular blood flow between the paretic and nonparetic upper limbs of individuals with stroke and healthy comparators. Associations between these parameters and stroke-related impairment were also examined. DESIGN: This was a cross-sectional study. SETTING: The setting was a university laboratory. PARTICIPANTS: Participants were individuals with stroke (n = 64
mean age = 60.8 [SD = 7.7] years) and matched controls (n = 64
mean age = 59.4 [SD = 7.8] years). MAIN OUTCOMES/MEASURES: Brachial artery blood flow volume (Vflow) and arterial diameter (AD) were measured using Doppler ultrasound. Intramuscular blood perfusion of the biceps brachii was estimated using the vascularity index (VI). Motor recovery and perceived use of paretic upper limbs were assessed with the Fugl-Meyer Assessment (FMA) and Motor Activity Log (MAL), respectively. RESULTS: Side × group interactions were observed for AD (F = 22.6) and VI (F = 4.00). Post hoc analyses showed lower AD and VI for paretic sides (stroke group), greater Vflow for dominant sides (comparators), and greater percent side-to-side differences (%SSDs) in AD and VI for the stroke group than for comparators. %SSDs in Vflow, AD, and VI demonstrated weak correlations with impairment (MAL, FMA) (ρ = 0.253 to 0.347). MAL was an independent predictor of %SSD in Vflow (β = -0.286), and FMA was an independent predictor of %SSDs in AD (β = -0.307) and VI (β = 0.371). CONCLUSIONS/RELEVANCE: Relative to the nonparetic and bilateral limbs of comparators, arterial size and intramuscular blood flow in the paretic upper limbs of individuals with stroke were significantly reduced. Motor impairment and disuse emerged as independent predictors of all vascular outcomes and may be potential intervention targets for reducing cardiovascular disease risk after stroke.