Design of a randomised, double-blind, crossover, placebo-controlled trial of effects of sildenafil on cerebrovascular function in small vessel disease: Oxford haemodynamic adaptation to reduce pulsatility trial (OxHARP) - Webb, A; Werring, D; Dawson, J; Rothman, A; Lawson, A; Wartolowska, K (European Stroke Journal, 2021)