CAPILLARY BLOOD PRESSURE IN MAN. DIRECT MEASUREMENTS IN THE DIGITS DURING INDUCED VASOCONSTRICTION 1

Abstract

Capillary blood pressure was detd. in the digits by the direct microinjection method. Following "neurogenic" vasoconstrictor stimuli, the pressure in normal-sized capillaries decreased by 5%-33%. The magnitude and duration of this decrease was the same in 4 hypertensive patients as in 3 normal subjects. Neither reflex vasodilatation nor the local hyperemia induced by histamine altered the response. Similar stimuli are known to induce much greater reductions in digital blood flow than the relatively small decreases in capillary blood pressure here observed. A further examination of the relationship between capillary blood pressure and digital vasoconstriction was made in the abnormally large capillaries of 7 patients with Raynaud''s disease and scleroderma. Digital vasoconstriction was measured by plethysmography. During intact digital innervation, the capillary blood pressure decreased when reductions in digital volume were induced by "neurogenic" vasoconstrictor stimuli and by epinephrine intravenously. Epinephrine induced changes of longer duration and greater magnitude than the neurogenic stimuli, which were followed by reductions similar to those observed in the normal-sized capillaries. Following interruption of the sympathetic innervation to the digits (para-vertebral block or preganglionic sympathectomy) the response to epinephrine remained unaltered, whereas neurogenic stimuli now failed to induce any change in either capillary blood pressure or digital volume. The data indicate that the fall in capillary blood pressure induced by neurogenic vasoconstrictor stimuli depends on mediation over the sympathetic nervous system, the fall induced by epinephrine does not; and that a homeostatic mechanism maintains the digital capillary blood pressure relatively constant during the wide fluctuations in digital blood flow produced by vasoconstrictor stimuli.