DIMINISHED FOREARM VASOMOTOR RESPONSE TO CENTRAL HYPERVOLEMIC LOADINGIN AEROBICALLY FIT INDIVIDUALS

The aim of this study was to test the hypothesis that cardiopulmonary baroreflex control of forearm vascular resistance (FVR) during central hypervolemic loading was less sensitive in exercise trained high fit individuals (HF) compared to untrained average fit individuals (AF). E ight AF (age: 24 +/- 1 yr and weight: 78.9 +/- 1.7 kg) and eight HF (2 2 +/- 1 yr 79.5 +/- 2.4 kg) voluntarily participated in the investigat ion. Maximal aerobic power (determined on a treadmill), plasma volume and blood volume (Evans blue dilution method) were significantly great er in the HF than AF (60.8 +/- 0.7 vs. 41.2 +/- 1.9 ml . kg(-1). min(- 1), 3.96 +/- 0.17 vs 3.36 +/- 0.08 l, and 6.33 +/- 0.23 vs 5.25 +/- 0. 13 l). Baseline heart rate (HR). central venous pressure (CVP), mean a rterial pressure (MAP, measured by an intraradial catheter or a Finapr es finger cuff), forearm blood flow (FBF, plethysmography), and FVR, c alculated from the ratio (MAP-CVP)/FBF, were not different between the HF and the AF. Lower body negative pressure (LBNP, -5, -10, -15, and -20 torr) and passive leg elevation (LE, 50 cm) combined with lower bo dy positive pressure (LBPP, +5, + 10, and +20 torr) were utilized to e licit central hypovolemia and hypervolemia. respectively. Range of CVP (from LBNP to LE+LBPP) was similar in the AF (from -3.9 to + 1.9 mm H g) and HF (from -4.0 to +2.2 mm Hg). However, FVR/CVP was significantl y less in the HF (-1.8 +/- 0.1 unit . mm Hg-1) than AF (-3.4 +/- 0.1 u nit . mm Hg-1). The FVR decrease in response to increase in CVP was si gnificantly diminished in the HF (-1.46 +/- 0.45 unit . mm Hg-1) compa red to the AF (-4.40 +/- 0.97 unit . mm Hg-1), and during LBNP induced unloading the FVR/CVP of the HF (-2.01 +/- 0.49 unit . mm Hg-1) was l ess (P < 0.08) than the AF (-3.28 +/- 0.69 unit . mm Hg-1). We conclud ed that the cardiopulmonary baroreceptor mediated FVR reflex response was significantly less sensitive to changes in CVP in individuals who practice exercise training.