Variability of cardiovascular responses to hypercapnia in Man

Abstract

Abstract: This study was conducted to assess the significance of the difference between forearm and finger blood flow responses to hypercapnia in man.  Forearm and finger blood flows, arterial blood pressure and pulse were recorded in ten normal subjects, ages 19-22 years, while inhaling air and 8% CO2 in air containing 20% 02.  Flow in the forearm decreased by 14.99 to 35.15% in three (3/10) subjects and increased by 5.15 to 25.50% in seven (7/10) subjects.  In the finger, it decreased by 2.22 to 80.61% in six (6/10) subjects and increased by 1.63 to 27.86% in four (4/10) subjects.  The overall test mean forearm blood flow (4.53 +0.52m1/100m1) differed from the overall control mean forearm blood flow (4.32+0.4 ml/100m1) only slightly (Mean difference 0.209,  P > 0.50). On  the  other  hand,  the  overall  test  mean  finger  blood  flow (28.15 +5.24m1/100/min)  differed  from  the  overall  control  mean  finger  blood  flow (33.08 +2.83m1/100/min) relatively more considerably (mean difference = -4.934, P.>0.05).  The individual variations are marked and equivocal in the forearm and less so in the finger thus showing that forearm blood flow response to hypercapnia is obscured by cholinergic activation of vasodilator nerves found in the forearm and not in the fingers.  Any difference of response in the two vascular beds may probably be more evident in subjects who are more apprehensive and have muscular forearm.  Unlike forearm blood flow, arterial blood pressure and pulse rate increased significantly and unequivocally in response to hypercapnia (P<0.05-0.001).  This probably reflects an increased release of catecholamines and sympathetic activation with a respiratory "pacemaker"involvement. [Ethiop. J. Health Dev. 2000; 14 (2): 135 -141]