Continuous infusion indicator dilution measurement of limb blood flow and vascular response to magnesium sulfate in normotensive and hypertensive men

Abstract

A B S T R A C T A constant infusion, indicator dilutiontechnique for blood flow measurements in the forearm and hand of man was tested and validated in vitro and in vivo. This technique employs jet injection to improve mixing of indicator with arterial blood. The mixing characteristics of the jet injection system were studied in vitro in tubing simulating the brachial artery of man. In addition, actual blood flows in the isolated pumpperfused forelimbs of five dogs were compared with constant infusion, indicator dilution calculated flows. Measurements were also made of mixing and of blood flow in the forearm and hand of man. The technique was used to compare forearm and hand vascular responses with constant intrabrachial arterial infusions of magnesium sulfate in 13 normotensive and 13 essential hypertensive men.In vitro and in vivo the jet injection system significantly improved mixing of indicator with blood, as compared with mixing produced by standard infusion techniques, without causing hemolysis. In 30 measurements in isolated, perfused dog forelimbs the correlation coefficient between actual and calculated blood flow was 0.992. Resting limb vascular resistance in the hypertensive group was significantly higher than in the normotensive group. Limb vascular resistance in all 26 men decreased in response to intrabrachial-arterial infusion of 0.25% magnesium sulfate (8 ml/min). Rate of infusion of Mg`+ was 0.162 mEq/min. There was a significant positive linear correlation between level of This work appeared in part as abstracts in Clin. Res. 13: 95, 1965, and Physiologist. 8: 247, 1965, and 9: 258, 1966 Dr. Overbeck's present address is Department of Physiology, Michigan State University, East Lansing, Mich. 48823.

Response of the Limb Vascular Bed in Man to Intrabrachial Arterial Infusions of Hypertonic Dextrose or Hypertonic Sodium Chloride Solutions

“…All venous and arteiial punctures were performed under local procaine (Procaine HC1, Cutter Laboratories) anesthesia. To improve mixing of infusate with brachial arteiial blood a jet-injector needle (Kimray, Inc., Oklahoma City, Oklahoma)' previously described (14) was used for the intraarterial infusions. Infusion rate was 8.2 ml/min.…”

“…Infusion rate was 8.2 ml/min. This jet-injection system improves mixing of infused substances with brachial arterial blood at infusate kinetic energies too low to cause significant hemolysis (14). The jet needle was introduced into the brachial artery through the Riley needle, an adapter on the jet needle hub locking into the hub of the Riley needle.…”

“…Increases in plasma osmolarity were produced by intrabrachial arterial infusions of hypertonic dextrose or sodium chloride solutions. Limb blood flow responses were measured by an indicator-dilution technique (14,15).…”

Attenuated Vasodilator Responses to K+ in Essential Hypertensive Men

“…We reached this conclusion by interpreting our data in terms of the highly significant positive relationship in both normotensives and hvpertensives between magnitude of response to K+ (AR) and the level of IR. Considering this relationship, one would expect that hvpertensives, with higher limb resistances than normotensives, would have greater vasodilator responses to K+, as they (1o to other vasodilator agents (9,12 (Fig. 1), one-third of the hypertensive subjects actually appear to have markedly attenuated responses to the highest dose level of K+.…”

“…The procedures employed for infusions and measurement of limb intravascular pressures and calculation of blood flows by indicator-dilution have been described in detail (12,13). Briefly, we used a jet injection system to infuse solutions intrabrachial arterially at 8.2 ml/min and at 37°C.…”