Fall In Forearm Blood Flow Research Articles

Cardiovascular Effects of Asymmetric Dimethylarginine

To the Editor: Kielstein et al1 describe the effects of the endogenous nitric oxide synthase inhibitor, asymmetric dimethylarginine (ADMA), in humans in vivo but do not make reference to two previous human studies.2,3 In the original paper describing the presence of ADMA in human plasma and its accumulation in chronic renal failure, Vallance et al2 also described the effects of ADMA in isolated blood vessels, on blood pressure in the guinea pig, and on forearm blood flow in healthy human subjects. They described an 8.3% fall in forearm blood flow after an 8 μmol/min ADMA infusion.2 It was this finding that led …

43] Use of l-arginine and its analogs to study nitric oxide pathway in humans

This chapter discusses the use of L -arginine and its analogs to study nitric oxide (NO) pathway in humans. Three isoforms of nitric oxide synthase are identified in humans: an endothelial type (eNOS), a neuronal type (nNOS), and a macrophage type (mNOS). The most widely used inhibitor of NOS is N G -monomethyl- L -arginine ( L -NMMA). This guanidino-substituted arginine analog inhibit two steps in the synthetic process and is approximately equipotent against all three isoforms of NOS. Its inhibitory effects may be reversed by addition of excess L -arginine; however, under certain conditions irreversible inhibition of NOS can occur. L -NMMA causes endothelium-dependent contractions of human isolated resistance vessels, and inhibits the endothelium-dependent relaxation produced by acetylcholine or bradykinin in human arteries, arterioles, veins, and venules. L -NMMA also inhibits relaxation of human blood vessels caused by release of NO from nonadrenergic noncholinergic nerves. Local infusions of L -NMMA into the brachial artery cause a dosedependent fall in forearm blood flow. L -NMMA and other related methylarginines are naturally occurring amino acids that circulate in plasma, are excreted in urine, and are found in cells.

Effects of peptide YY on the human cardiovascular system: reversal of responses to vasoactive intestinal peptide.

Peptide YY (PYY) reverses the increased intestinal secretion stimulated by vasoactive intestinal peptide (VIP) in humans. VIP also dilates blood vessels, so we investigated the effect of PYY on the cardiovascular system. Six volunteers received PYY, 0.4 and 1.2 pmol.kg-1 x min-1 i.v. for 2 h, reproducing plasma levels seen postprandially and during a diarrheal illness, respectively. Cardiac function was assessed by echocardiography. PYY infused at 0.4 pmol.kg-1 x min-1 had no effect on cardiovascular parameters. PYY infused at 1.2 pmol.kg-1 x min-1 caused a fall in both stroke volume from 128 +/- 8 to 110 +/- 8 ml/beat (mean +/- 95 confidence interval, P < 0.01) and cardiac output from 7.2 +/- 0.4 to 6.1 +/- 0.4 l/min (P < 0.01). Effects of infusion of PYY into the brachial artery at doses of 0-16 pmol/min were assessed using venous occlusion plethysmography in six subjects. PYY infusion caused a dose-dependent fall in forearm blood flow. Six subjects received VIP, 5 pmol.kg-1 x min-1 i.v., causing a rise in heart rate from 55 +/- 3 to 70 +/- 3 beats/min and increased cardiac output from 7.3 +/- 1.1 to 13.1 +/- 1.1 l/min. The addition of PYY, 0.4 pmol.kg-1 x min-1 i.v., did not affect the heart rate significantly but decreased the cardiac output to 10.4 +/- 1.1 l/min (P < 0.01). Infusions of PYY into the brachial artery at 5 pmol/min decreased local vasodilation induced by VIP infused at 2 pmol/min at the same site by 40% (P < 0.01), even though this dose of PYY had no significant effect on local blood flow when given alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Independent stimulation of glucose metabolism and Na+-K+ exchange by insulin in the human forearm.

Insulin promotes potassium uptake into skeletal muscle by stimulating the activity of the Na+-K+ pump. To test whether insulin-induced glucose and potassium uptake are linked processes in vivo, we used the perfused forearm technique in healthy volunteers. Local hyperinsulinemia (125 +/- 11 microU/ml for 100 min) induced a net uptake of glucose and potassium (4.79 +/- 0.61 and 0.76 +/- 0.22 mumol.min-1.100 ml-1 of forearm volume, respectively). When an intra-arterial ouabain infusion (0.72 microgram.min-1.100 ml-1, producing local levels of approximately 0.5 mM) was superimposed on the insulin infusion, potassium uptake was blocked (0.026 +/- 0.190 ml.min-1.100 ml-1, P less than 0.02), and glucose uptake was decreased (to 3.31 +/- 0.34 mumol.min-1.100 ml-1, P less than 0.03). The latter change was explained by a 30% fall in forearm blood flow (from 2.95 +/- 0.10 to 2.01 +/- 0.18 ml.min-1.100 ml-1, P less than 0.001). To separate out the effect of blood flow, in another series of studies forearm blood flow was clamped by co-infusing propranolol and phentolamine (7 and 8 micrograms.min-1.100 ml-1, respectively). Under these conditions of fixed flow (7.0 +/- 0.8 ml.min-1.100 ml-1), ouabain still abolished the stimulatory effect of insulin on potassium uptake but had only a small (and statistically insignificant) effect on forearm glucose extraction (from 20 +/- 2 to 16 +/- 2%, P = N>). We conclude that in human forearm muscle ouabain inhibits Na+-K+ exchange and depresses insulin-induced glucose uptake via an adrenergic-mediated limitation of blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of heat stress on cutaneous vascular responses to the initiation of exercise.

To explore further the competition between vasoconstrictor and vasodilator reflexes in the regulation of skin blood flow, responses in forearm blood flow (FBF) to the initiation of supine leg exercise were measured by plethysmography against a background of rising internal temperature. In 17 studies involving six men, skin temperature (Tsk) was controlled with water-perfused suits first at normothermic levels, followed by a 40- to 50-min period during which Tsk was held at 38-38.5 degrees C. Supine leg exercise at a moderate intensity (100-150 W) was performed for 5-6 min of each 15 min throughout, yielding one period of exercise performed during normothermic conditions and three periods of exercise performed during the period of elevated Tsk. On the average, FBF fell significantly with the beginning of each period of exercise (P less than 0.05). Furthermore, the amount by which FBF fell tended to increase with increasing levels of preexercise FBF. Thus the average fall in FBF associated with the onset of the last period of exercise, 2.45 ml X 100 ml-1 X min-1, significantly exceeded the 1.12 ml X 100 ml-1 X min-1 fall in FBF seen with onset of work in normothermic conditions. These responses were not due to changes in internal temperature as reflected by esophageal temperatures. However, individual studies occasionally revealed a reduction or abolition of the vasoconstrictor response with the last period of exercise. These findings are in agreement with earlier studies showing a cutaneous participation in the vasoconstrictor responses to exercise but also indicate that sufficient hyperthermia can attenuate or even abolish this response.

PERIPHERAL VASCULAR EFFECTS OF PETHIDINE AND PENTAZOCINE DURING TRICHLOROETHYLENE ANAESTHESIA

SUMMARY Forearm blood flow was measured by strain gauge plethysmography and arterial pressure by the Riva-Rocci method in two groups of nine patients during tachypnoea accompanying trichloroethylene anaesthesia and 7-10 min after intravenous injection of pethidine or pentazocine in doses sufficient to control the tachypnoea. The mean doses of pethidine and pentazocine used were 34.4 mg and 37 mg. Pethidine caused a significant fall in forearm blood flow and rise in vascular resistance without change in the mean arterial pressure. These changes were absent in two patients after brachial plexus block. There was no rise in circulating catecholamine levels in three patients studied. It is suggested that the observed vasoconstriction is nervously mediated. Pentazocine caused only a significant rise in mean arterial pressure without change in forearm blood flow or vascular resistance. While the mild cardiac stimulant property of pentazocine may antagonize the depressant effect of trichloroethylene, the combined depressant effect of trichloroethylene and pethidine may be severe enough to cause reflex vasoconstriction.

Arterial blood gas changes and the diving response in man.

SummaryFace immersion breath‐holds were performed by five seated male subjects after normal breathing of room air, normal breathing of 100% oxygen for 15 minutes and hyperventilation of 100% oxygen for 15 minutes. Heart rate and forearm blood flow were determined in all three procedures and PO2,PCO2 and pH of brachial artery blood were measured in the oxygen breathing experiments.Simulated diving after breathing room air significantly reduced the heart rate and forearm blood flow. After normal breathing and hyperventilation of oxygen, PaO2 was elevated by three and five times, respectively. PaCO2 was unchanged by normal breathing but halved by hyperventilation. “Diving” after both oxygen breathing procedures still significantly reduced both heart rate and forearm blood flow below resting control levels and these responses were not significantly different from those after breathing room air.The fall in arterial oxygen tension during “diving” after hyperventilation of oxygen was inversely related to the fall in forearm blood flow (P &lt; 0.001) which fits the concept that the diving response may serve an oxygen conserving function in man. Despite arterial hyperoxia with or without hypocapnia, a significant diving response was still evoked by face immersion breath‐holding, showing that the response is basically independent of asphyxial blood gas changes.

Simultaneous calf and forearm blood flow during immersion in man.

SummaryForearm and calf blood flows were recorded simultaneously in eleven subjects in the horizontal plane during one minute breath‐holds in air, in water with the torso immersed but the face out. and with total body immersion. Brachial arterial pressure, electrocardiogram and respiratory excursions were also recorded continuously throughout the experiments.Breath‐holding witli total immersion caused a fall in forearm blood flow of 28 ± 17% and in calf flow of 47 ± 30%. Forearm vascular resistance increased by an average of 70% and calf resistance by 147%.Breath‐holding in air resulted in an increase in forearm blood flow and a decrease in calf flow in seven subjects. The average response of all subjects showed a significant vasoconstriction in the calf (average 72%) but no significant change in the forearm resistance.Breath‐holding with the torso immersed but the face out of water caused a response which was intermediate between that shown in air and that during total immersion. Thirty to sixty seconds after this manoeuvre there was a significant overshoot in both forearm and calf blood flow, unlike the former procedures.

Effects of Diazepam on Anxiety as Measured by Forearm Blood Flow

Intravenous diazepam has been shown to produce both a fall in forearm blood flow and coincidental diminution in subjective anxiety, as compared with the resting state and after injection of intravenous saline.

Circulatory responses of supine subjects to the exposure of parts of the body below the xiphisternum to subatmospheric pressure

1. Observations are reported on the effects of exposure of parts of the body below the level of the xiphisternum of supine subjects to a pressure 70 mm Hg below atmospheric for 1 min.2. The stress on the circulation was greater than when parts below the iliac crests were similarly exposed. Heart rate increased by 15-20 beats/min, there was a sustained fall in arterial blood pressure, and forearm blood flow fell profoundly and in some subjects was reduced to below 0.1 ml./100 ml. min.3. In arms that were sympathectomized, or had received an intraarterial infusion of an adrenergic blocking drug, the fall in forearm blood flow was much less and could be related to the fall in arterial pressure.4. When the suction was released there was a brief overshoot of arterial blood pressure and brief cardiac slowing. Forearm blood flow rose to reach a peak some 15 sec after the release.5. In the sympathectomized forearm on release of suction there was an immediate rise in blood flow which was proportionately much greater than the rise in arterial blood pressure.6. This rise was not due to circulating vasodilator substances or to the activity of cholinergic vasodilator nerves. The possibility that it was the result of a change in the tone of the resistance vessels occurring in response to the sudden change in transmural pressure is discussed.