Acute cutaneous microvascular responses to local negative pressure in the human forearm.

Local negative pressure (LNP), the physical basis of cupping therapy, deforms the skin and alters the mechanical environment of the cutaneous microcirculation. Although previous studies have demonstrated increased local blood flow following LNP, it remains unclear whether the resulting physiological responses remain confined to the stimulated tissue or can also be detected at spatially separated cutaneous sites. Accordingly, this study investigated the spatial distribution of the acute microvascular and autonomic responses to LNP in the human upper limb. Sixteen healthy young adults (9 males, 7 females; 20.8 ± 1.6 years) underwent a 3-min application of -525 mmHg using a suction cup applied to the proximal forearm. Skin perfusion was assessed in both upper limbs using photoplethysmography (PPG) and videocapillaroscopy (VC), while electrodermal activity (EDA) was recorded continuously from the contralateral hand. LNP increased proximal forearm hemoglobin index (CHb) from 0.17 (0.11-0.24) to 0.25 (0.18-0.30) AU and PPG amplitude from 50.8 (13.0-81.2) to 166.5 (22.3-404.7) AU (both p = 0.001). In contrast, finger PPG amplitude decreased during LNP in the test limb from 138.3 (14.6-862.4) to 88.9 (12.6-730.0) AU (p = 0.017), whereas EDA increased from 6.1 (1.1-24.5) to 14.2 (5.4-24.6) μS (p = 0.004). These findings demonstrate spatially heterogeneous microvascular responses, characterized by increased local hemoglobin index and forearm perfusion together with reduced digital perfusion, occurring concurrently with increased electrodermal activity. The present design, however, does not establish whether autonomic mechanisms contributed to the distal perfusion response. Collectively, these findings extend current understanding of the acute physiological effects of LNP by demonstrating that its microvascular responses are spatially heterogeneous, thereby contributing to a more comprehensive understanding of the spatial organization of the human cutaneous microvascular response to local mechanical stimulation.