Canine Hindlimb Research Articles

Oxygen indicator dilution curves of the canine cerebral circulation.

Indicator-dilution methodology is a useful tool in studies of transcapillary exchange (6,10), but oxygen isotopes have seldom been used in such studies, because they require non-standard laboratory techniques. Of the two isotopes of oxygen currently used in physiological research, positron-emitting oxygen-15 is not suitable for the indicator-dilution technique, because one cannot distinguish between signal originating from unmetabolized 15O2, and that from metabolically-formed H2 15O molecules (28). The other is the stable isotope oxygen-18, which can be detected by mass spectrometric techniques. Tb our knowledge, there are only two preliminary reports of stable oxygen tracer dilution curves. Chinard et al, (8) published a 18O2 dilution curve of kidney, with 51Crlabelled red blood cells (Cr-rbc) as the reference indicator. In that experiment, the labelled oxygen curve preceeded the reference curve, which was attributed to the existence of a diffusional shunt in kidney. Forster et al, (13) obtained 18O2 dilution curves of skinned canine hind limb, with indocyanine green as the reference tracer. In these experiments, labelled oxygen curves lagged behind the reference.KeywordsCerebral Blood VolumeReference CurveDilution CurveOxygen DistributionReference IndicatorThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

A comparison of the effects of verapamil and cinnarizine upon responses elicited by selective α1-and α2-adrenoceptor agonists in the autoperfused canine hindlimb

In an attempt to extend the hypothesis that activation of vascular postsynaptic α 2-adrenoceptors requires an influx of Ca 2+ ions, the effects of 2 calcium entry blocking drugs verapmil and cinnarizine have been examined as inhibitors of the pressor responses to methoxamine and B-HT 920 in autoperfused dog hindlimb preparations. Verapamil (0.1–1 mg i.a) selectively responses to B-HT 920 and had little or no effet upon responses to methoxamine, thus supporting this hypothesis. However cinnarizine, over the dose range studied (0.1–1 mg/kg i.a.) produced quantitatively similar inhibitions of the hindlimb responses to B-HT 920 and methoxamine. These results suggest that cinnarizine may have a different site of action to verapamil in resistance vessels of the dog hindlimb.

Reflex control of canine hindlimb resistance under different modes of perfusion.

The carotid sinus control of hindlimb hemodynamics was determined in halothane-anesthetized vagotomized dogs. The carotid sinuses were bilaterally isolated and perfused under controlled conditions. The hindlimb was perfused under conditions of 1) physiological inflow, 2) constant pressure, and 3) constant flow. The variation of hindlimb resistance with mean carotid sinus perfusion pressure was largest under conditions of constant-pressure perfusion and smallest with physiological inflow. Values for constant-flow perfusion were intermediate. The effects of different values of constant-flow perfusion on the carotid sinus control of hindlimb hemodynamics was also determined. Values of hindlimb resistance increased with decreasing flow rate as did the variation with carotid sinus perfusion pressure. No evidence of a contribution of local control mechanisms related to changes in perfusion pressure or bed inflow could be demonstrated. The differences in the variation of hindlimb resistance with carotid sinus pressure under the various perfusion conditions can be explained on the basis of the mechanics of vascular smooth muscle. The amount of lumen constriction associated with changes in degree of activation depends on the conditions under which shortening occurs as well as upon the initial muscle length. It appears that local factors do not contribute to the control of hindlimb hemodynamics under the conditions in which these studies were performed.

Defects in peripheral oxygen utilization following trauma and shock.

Following shock and trauma, there may be capillary block or stasis that sets up a neurohumoral response, causing further capillary constriction and ischemia. This ischemia may not result in tissue hypoxia, as functioning capillaries may still exist near the damaged areas. Following resuscitation, however, a reperfusion syndrome causing massive tissue edema, endothelial swelling, and further capillary blocking may lead to tissue hypoxia. We used isolated canine hind limb as a model of the peripheral circulation in a series of experiments that showed that interstitial edema alone did not reproduce the defect in peripheral oxygen utilization. On the other hand, both reperfusion syndrome and microembolization were able to reproduce this response. Hypertonic mannitol and imidazole reversed this defect following either reperfusion syndrome or microembolization, respectively. These data suggest that resuscitated posttrauma patients suffering from defects in peripheral oxygen utilization probably owing to microembolization, reperfusion and tissue edema, which may be treated by specific therapy.

Effects of hypertonic mannitol on oxygen utilization in canine hind limbs following shock

Abnormalities in peripheral oxygen utilization persist in fully resuscitated trauma patients. We studied the effects of hypoperfusion, reperfusion, and mannitol on peripheral oxygen utilization in a regional shock model. Vascular isolation was accomplished in 10 anesthetized (sodium pentobarbitol 30 mg/kg) adult mongrel dogs by ligating all arterial branches between the renal and the profunda femoris artery to one limb (RL). RL was hypoperfused by lowering the blood pressure (BP) to 50 Torr for 90 min. The other limb served as control (CL). Limb blood flow ( Q ̇ ), BP, and limb oxygen delivery and consumption ( V ̇ O 2 ) were measured at control, at 5 and 90 min during hypoperfusion, and at 5, 60, and 120 min following reperfusion. Immediately before reperfusion 6 of the 10 dogs received bolus injection of 25% mannitol (12 g) followed by 10 g of 20% mannitol/hr. At baseline, there were no differences in Q ̇ , oxygen delivery (O 2del), V ̇ O 2 , femoral venous PO 2( P vO 2), oxygen diffusing capacity ( DO 2T) and vascular resistance (VR) between the CL and RL or between the untreated and mannitol-treated dogs. During reperfusion Q ̇ , O 2del, V ̇ O 2 and DO 2T decreased and VR increased significantly in RL of untreated dogs ( P < .05) but did not change in RL of mannitol-treated dogs. P vO 2 did not change. Those parameters in CL did not change. Thus, reperfusion of hypoperfused canine limb was associated with a defect in oxygen utilization which may be due to tissue edema. Hypertonic mannitol restored the defects in the peripheral oxygen utilization during reperfusion syndrome of canine hind limb.

Dissociation of glucagon's central and peripheral hemodynamic effects: Mechanisms of reduction and redistribution of canine hindlimb blood flow

Effects of parenterally administered pharmacologic doses of glucagon on canine hindlimb blood flow were studied. Cardiac output (CO), mean arterial pressure (MAP), total peripheral resistance (TPR), common femoral artery flow (CFAQ), common femoral artery resistance (CFAR), percentage shunt in the hindlimb (AVA%) determined by 99 mTc microsphere technique, the volume of hindlimb shunt flow (AVAQ), and the volume of hindlimb nutrient capillary flow (NCQ) were determined at baseline and at 10, 20, and 30 min during continuous intravenous infusion of 1 μg/kg/min glucagon ( n = 8). Blood glucagon and glucose levels were measured at all time periods. Glucagon infusion significantly increased CO throughout the infusion, while reducing MAP and TPR. Unexpectedly, CFAQ decreased significantly despite the increase in CO. CFAR increased despite the reduction of TPR during glucagon infusion. The reduction of CFAQ was associated with diminished nonshunt hindlimb NCQ and increased AVA%. Changes in CFAQ, AVA%, AVAQ, and NCQ did not correlate in a linear fashion with the changes in either blood glucose or glucagon levels by linear regression analysis. Glucagon appeared to cause a major redistribution of peripheral blood flow. Hindlimb arteriolar dilatation was not an effect of this hormone in this experimental model. Glucagon appeared to have a salutary central hemodynamic effect, but was detrimental to canine extremity perfusion.

Effects of transient ischemia on nutrient flow and arteriovenous shunting in canine hindlimb.

A canine model was developed to simulate use of a pneumatic tourniquet in the clinical setting in order to study the acute and delayed effects of transient ischemia on limb and tissue blood flow, using radioactive microspheres and electromagnetic flow probes. Experimental femoral artery flow rose markedly after tourniquet ischemia, and remained significantly elevated for 24 hours (p less than 0.01). Blood flow to the rectus femoris and anterior tibial muscles rose significantly (p less than 0.05) immediately after tourniquet ischemia, and the latter remained significantly elevated at 24 hours (p less than 0.05). Blood flow to the skin of the experimental limbs was elevated significantly (p less than 0.05), immediately ater tourniquet ischemia, and at no other time. Blood flow to the nerves did not increase to its maximum until 15 minutes after tourniquet deflation, and by 24 hours was normal. Tibial and femoral marrow blood flow remained significantly lower in the experimental limb throughout the 24-hour period. Ater tourniquet ischemia (300 mmhg; 2 hours), greatly increased femoral artery flow was related to reactive hyperemia in skin, muscle, and nerve. Twenty-four hours after tourniquet deflation, there was a significant increase in femoral artery and anterior tibial muscle blood flow, and significant arteriovenous shunting from the experimental limb. These data suggest that the hemodynamic response to a transient ischemic injury is more prolonged and of greater magnitude than previously believed.

An approach to the pathogenesis of "white finger" induced by vibratory stimulation: acute but sustained changes in vascular responsiveness of canine hindlimb to noradrenaline.

A fixed vibratory stimulation (60 Hz in frequency, 3 g in acceleration, and 2.2 mm in amplitude) was applied to a hindlimb (test limb) of dogs anaesthetised with sodium pentobarbital. Peripheral vascular resistance in the test limb was calculated as the ratio of mean pressure difference between the femoral artery and the femoral vein to the rate of femoral arterial blood flow. By means of a highly sensitive clinical thermometer, interdigital temperature was recorded not only from the test limb but also from a forelimb (control limb). The vibratory stimulation significantly reduced the peripheral resistance in the test limb. The increase in peripheral resistance induced by noradrenaline administration was suppressed during, and enhanced 1 h after, the stimulation. With the start of the vibratory stimulation, interdigital temperature in the test limb rose gradually and reached a constant level. The temperature first went below, and then returned to, the initial level after interruption of the stimulation. No change in the temperature was produced in the control limb. The decrease of temperature induced by noradrenaline administration was suppressed during, and enhanced 1 h after, the stimulation. These results indicate that, even in the living body, the conclusion of our previously report is valid: ie the responsiveness of arterial smooth muscle to noradrenaline decreases during, and increases soon after, vibratory stimulation. Assuming that our results obtained from acute experiments can be applicable to human digital arteries, the occurrence of "white fingers" on vibration disease may be understood in terms of vibration-induced hyperresponsiveness following stimulation.

Effect of endotoxin on oxygen consumption by a flow-controlled canine hind-limb preparation.

The effect of endotoxin upon oxygen consumption in a peripheral vascular bed was assessed in a canine hind-limb preparation. The left iliac vessels in 12 adult male mongrel dogs were isolated, the artery cannulated proximally and distally such that arterial inflow could be routed through a roller pump, and a nonocclusive catheter placed in the vein. Oxygen consumption was then calculated as the product of flow rate and and arteriovenous oxygen content difference at a series of flow rates before and after the systemic administration of endotoxin (3 mg/kg) or saline solution. At each flow rate, oxygen consumption by the extremities of endotoxic animals was significantly greater (P < 0.01) than that measured in control animals. This finding mitigates the hypothesis that endotoxin has a direct effect on cells reducing tissue oxygen consumption.

Responses to arachidonic acid and other dilator agonists and their modification by inhibition of prostaglandin synthesis in the canine hindlimb.

The influence of indomethacin, in doses that completely inhibit the response to arachidonic acid, has been examined on canine hindlimb vascular responses to intra-arterial administration of bradykinin, histamine, nitroglycerin, isoprenaline and papaverine. The hindlimb was perfused at constant flow. Dose-response curves to intra-arterial administration of arachidonic acid (12 to 200 microgram kg-1), bradykinin (0.4 to 100 ng kg-1), histamine (1.8 to 120 ng kg-1), nitroglycerin (15 to 100 ng kg-1), isoprenaline (12 to 100 ng kg-1) and papaverine (1.2 to 160 microgram kg-1) (all n = 4) were compared before and 30 min after indomethacin (5 mg kg-1 i.v.). All the drugs produced dose-related decreases in hindlimb perfusion pressure. After indomethacin, responses for all dilator agonists except arachidonic acid, were significantly greater than control (P less than 0.05), both in terms of absolute (mmHg) or percent change. Dose-response curves after indomethacin had a left upward shift compared with control. Arachidonic acid responses were completely blocked by indomethacin. These findings suggest that indomethacin produces a non-specific increase in responsiveness of the hindlimb vascular bed to dilator substances, except arachidonic acid. The data presented do not support the hypothesis that the peripheral vasodilatation produced by bradykinin, nitroglycerin and histamine could be mediated by endogenous prostaglandin release.

Reversal of bradykinin action: Possible involvement of prostaglandins or dual receptors

The vascular effects of synthetic bradykinin were studied in perfused isolated canine hind limb preparations. Repeated low doses of bradykinin or high doses administered at sufficiently long time intervals elicited dose-related hypotensive responses. In contrast, administration of increasing doses of bradykinin at short time intervals led first to diminishing hypotensive responses followed by frank increases in perfusion pressure. This autoreversal of bradykinin might be explainable either on the basis of known effects of bradykinin on prostaglandin synthesis with specific reference to PGF 2α, or the existence of two types of bradykinin receptors.

O2 extraction by canine hindlimb during alpha-adrenergic blockade and hypoxic hypoxia.

Hindlimb and total blood flow and O2 uptake were measured in anesthetized paralyzed dogs in which venous outflow from the left hindlimb (less paw) was directed through the femoral vein. After ventilation on room air, 10 dogs were given 3 mg/kg phenoxybenzamine + 10 ml/kg dextran and 10 other dogs were isovolemically exchanged with 10 ml/kg dextran without alpha-block while continuing to be ventilated on room air. All animals were then ventilated with 9.1% O2 in N2, followed by a recovery period on room air. Total and limb peripheral resistances were lowered by alpha-block, but total and limb blood flow changed little from control levels. Both total and limb O2 uptake were decreased below control values during hypoxia. Cardiac output and limb blood flow increased during hypoxia in both groups. Although alpha-block caused O2 extraction by the whole body to be less during hypoxia than in unblocked dogs, the hindlimb in both groups extracted O2 equally well. We concluded that skeletal muscle was not overperfused relative to O2 demand when alpha-blocked during hypoxia.

β-adrenoceptor and cardiovascular effects of MJ 13105 (Bucindolol) in anesthetized dogs and rats

This report describes the β-adrenoceptor blocking and cardiovascular activity of MJ 13105 (Bucindolol), an indolyl-tert-butyl substituted phenoxypropanolamine. Increases in heart rate elicited by (a) isoproterenol, (b) stellate ganglion stimulation, and (c) bilateral carotid occlusion were antagonized to the same extent (80%) by a dose as low as 30 μg/kg, i.v. MJ 13105 blocked isoproterenol-induced vasodilator responses in the canine hindlimb. Intra-arterial infusions of MJ 13105 effected dose-dependent decreases in perfusion pressure, which persisted even in the presence of prior β-adrenoceptor blockade. Intravenous administration of MJ 13105 lowered mean arterial blood pressure and total peripheral resistance, and increased heart rate and right ventricular contractile force in the open chest, anesthetized dog. The vasodilator response to MJ 13105 persisted and may have been enhanced following propranolol. In vivo, MJ 13105 demonstrated weak α-adrenoceptor blocking activity in both rat and dog. Inhibition of the α-mediated vasoconstriction was more apparent if phenylephrine, rather than norepinephrine was the agonist. MJ 13105 exhibited intrinsic sympathomimetic activity at β 1-receptors, although its maximum capacity to increase heart rate was less than that of pindolol. Plasma renin activity of anesthetized dogs was elevated following administration of MJ 13105, an effect that was attenuated by propranolol. Oral administration lowered blood pressure of SHR and DOCA-salt hypertensive rats and renal hypertensive dogs, with a concomitant decrease in heart rate of rats and an increase in heart rate of dogs.

Experimental end-to-end anastomosis of lymphatic trunks in the canine hind limb

Experimental end-to-end anastomoses were carried out between the femoral lymphatic trunks in the dog. They measured between 0.2 to 0.6 mm. A new triple cut technique is described. The long-term patency rates were, for the no-tension group 25%, for the normal tension group 22%. Result control was performed by re-exploration of each anastomosis.

Revascularization of the ischemic canine hindlimb by arteriovenous reversal.

Arteriovenous reversal (AVR) for revascularization of ischemic tissues has previously failed to meet theoretical, experimental, and clinical expectations despite recurrent trials. The efficacy of a new staged approach to AVR was tested against a canine ischemic limb preparation in which global ligation of ipsilateral collaterals inevitably led to limb gangrene. In 12 animals the complications of direct, single-stage end-to-end femoral AVR, inevitably accompanied by the development of extreme edema, were demonstrated. However, when the ischemic preparation was accompanied by a staged AVR, in which an initial end-artery-to-side-vein arteriovenous fistula was converted 1 week later to AVR by ligation of the central venous limb, 20 of 20 animals survived, and 19 of 20 were ambulatory long-term survivors with only mild edema. Serial angiograms at 1 week, 1 month, and 4 months demonstrated patency rates of 100, 84, and 63%, respectively. Histologic examination of animals electively killed from 4 to 24 months showed normal skeletal muscle histology, venous intimal thickening, and mild edema. In the acutely ischemic canine hind limb, a staged AVR can provide both viability and function with only mild edema formation.

Oxygen extraction by canine hindlimb during hypoxic hypoxia

Regional and total blood flow and O2 uptake (VO2) were measured in 10 anesthetized paralyzed dogs in which venous outflow from the left hindlimb (less paw) was directed through the femoral vein. After being ventilated on room air during a 40-min control period, they were ventilated on 12.0% O2 for 40 min, 9.2% O2 for 40 min, and again on room air for 40 min. A second group of 10 was treated the same after they were given 1.0 mg/kg propranolol to block beta-adrenergic receptors. Neither limb blood flow nor cardiac output changed significantly during moderate hypoxia in either group; both increased in severe hypoxia but only in the no-beta-block group. Limb VO2 was not decreased significantly in either group during moderate hypoxia but total VO2 was decreased in the beta-block group. Total VO2 was decreased in both groups during severe hypoxia but limb VO2 was maintained in the beta-block group. beta-Block prevented the fall in total and limb peripheral resistance seen in severe hypoxia but did not alter the consistently more efficient utilization of total O2 delivery shown by the limb in comparison to the whole body by higher O2 extraction ratios and lower venous O2 pressure. beta-Vasodilator receptors evidently played an active part in the vasodilatation seen during severe hypoxia.

Role of Inorganic Phosphate in Active Hyperemia in Skeletal Muscle

SummaryThe purpose of this study was to determine the extent of involvement of the inorganic phosphate ion (Pi) in exercise hyperemia. Lymph and venous plasma from resting and contracting muscles of the canine and feline hindlimbs were analyzed for Pi. The vasoactivity of exogenous inorganic phosphate was assessed by close intra-arterial infusion of the sodium monobasic phosphate while blood flow and lymph and venous plasma Pi concentrations were determined. The results showed that there was no increase in venous plasma Pi with muscle contraction, only a small increase in lymph Pi, and that the phosphate ion is very vasoinactive. We therefore conclude that the inorganic phosphate ion may play only a minor role, if any, in active hyperemia in skeletal muscle.

Effect of changing metabolic rate on local blood flow control in the canine hindlimb.

This study examined the effect of changing hindlimb metabolic rate on hindlimb blood flow control in anesthetized dogs. The hyperemias induced by graded levels of arterial hypoxia and the degree of steady state autoregulation evoked by changes in blood pressure were measured. Metabolic rate was increased above the resting value by direct electrical stimulation of hindlimb muscles at rates from 0.5 to 1.5 pulses/second, and in three dogs was reduced by cooling. In response to 6 minutes of arterial hypoxia, hindlimb blood flow steadily increased. At rest, and at each level of muscle stimulation, the steepness of the response increased as arterial oxygen saturation (SAO2) decreased. At all levels of SAO2, the response was steeper at increasing stimulation rates. For SAO2 greater than 50%, the relationship between the percentage increase in blood flow from control and SAO2, however, was unaffected by the degree of muscle activity, suggesting that during mild to moderate hypoxia the dynamics of the response were similar whether the muscles were at rest or exercising. The responses to severe hypoxia (SAO2 less than 50%) during stimulation were significantly enhanced compared with those at rest. Autoregulation of blood flow was measured in the steady state by comparing the relative change in blood flow from control with the relative change in blood pressure that produced it. Steady state autoregulation was weak at rest, but improved markedly with increasing muscle stimulation. Conversely, cooling the hindlimb depressed the resting steady state autoregulation. A close correlation was found between the degree of autoregulation and the hindlimb metabolic rate. The results suggest that tissue metabolic rate determines the precision of local blood flow control.

Oxygen uptake of canine whole body and hind limb with hypocapnic alkalosis.

The effect of hypocapnic alkalosis induced by hyperventilation on whole-body and hind-limb oxygen uptake (VO2) was studied in dogs anesthetized with pentobarbital. In the intact dog with a self-perfused hind limb, increasing pHa from 7.41 to 7.58 increased whole-body VO2 8% and decreased hind-limb VO2 6%. Isolated hind limbs perfused with heparinized whole blood had similar decreases in VO2 with increases in arterial blood pH (pHa). However, isolated hind limbs perfused with whole blood containing citrate, phosphate, and dextrose (CPD) showed muscle twitches, had larger VO2 values at identical pHa's, and had an increase in VO2 with increase in pHa. These changes with a CPD perfusate were associated with low levels of ionized calcium (less than 0.5 mEq/1), disappeared when calcium ion spontaneously increased to 1.0 mEq/1, and could be prevented or abolished by the addition of calcium chloride, dantrolene, d-tubocurarine, or succinylcholine. These results are in accord with the findings of others regarding an increase in whole-body VO2 with hypocapnic alkalosis, but do not support a contributory role of skeletal muscle to the overall increase.

Tissue hydrogen ion concentration in ischemic muscle: Effects of gradual and acute arterial occlusion, with and without acute venous hypertension

Accurate assessment of extremity &hernia is often a prerequisite to the successful completion of complex arterial reconstructions. Muscle surface pH, reflecting the status of local tissue metabolism, offers a means for continuously monitoring limb perfusion. The present investigation was designed to evaluate muscle surface pH measurements in ischemic canine hindlimbs. These measurements, subjected to careful statistical analysis, were related to extremity blood flow, perfusion pressure, effluent blood pH, and arteriovenous oxygen differences.