Dog Foreleg Research Articles

Measurement and analysis of invivo bone strains on the canine radius and ulna

A strain gauge rosette was bonded in vivo to one of 5 locations on the radius or ulna of 7 mongrel dogs. The strain patterns during gait were recorded daily for each animal for at least 7 days following implantation. Strain and stress patterns in the principal material directions were calculated for typical gait cycles. Stress calculations were made using an anistropic analysis which assumes that the bone surface is an orthotropic lamina. The results showed that significant longitudinal and shear stresses were present in the midshaft of the radius and ulna. Tensile longitudinal stresses were present on convex surfaces, and compressive stresses were present on concave surfaces. The calculated shear stresses were consistent with torsional loading of the radius in the direction of external rotation of the proximal bone end. Significant transverse stresses were calculated for the rosette bonded to the caudal aspect of the distal radius. The results of this study suggest that the in vivo loading conditions in the dog foreleg are complex. The use of single gauges to estimate stresses in the canine foreleg is therefore of limited value.

The Z-plasty: Biomechanics and mathematics

Summary The following observations were made in experimental Z-plasties in dogs: 1.Z-plasties of different sizes: Single 8 cm. Z-plasties (60°-60°) neeed seven to ten times as much force for closure as 1 cm. and 2 cm. Z-plasties. Lengthening was almost directly proportional to the size of the Z-plasty. 2.Serial Z-plasties differing in number and size of flaps but equal in length: The fewer the flaps in the series, the greater was the lengthening effect. Corollary: The larger the flaps, the greater the lengthening effect. 3.Z-plasties with differing tip angles: A 90°-90° Z-plasty required about ten times as much tension for closure as a 30°-30° Z-plasty and lengthening ranged from 10 per cent for the 30°-30° Z-plasty to 75 per cent for a 90°-90° Z-plasty. 4.Asymmetrical Z-plasties: The flap always required less tension for closure than the flap, but was subjected to more distortion. Greater strain in the surrounding skin was associated with the flap. 5.Field strain: The surrounding skin stretched over a disproportionately larger area, the larger the Z-plasty or the wider the tip angles. 6.Distortion of tip angles and limb lenghts: After transposition, Z-plasties on flat surfaces showed an increase in the length of the post-operative central limbs (at right angles to the pre-operative central limbs), diminished length of the side limbs, and narrowing of the tip angles, which were unaccounted for by geometrical calculations. Biomechanical explanations were suggested and strain topography maps were devised. 7.Z-plasties on webs: A continuum of three-dimensional Z-Plasty forms was noted, beginning with the Z-plasty on a flat surface, progressing through the wide web, the tetrahedral, and the narrow forms. Increasing tension and lengthening were noted with widening of the peak angle beyond ideal. Increasing overhang of the flaps was noted in progressing from the tetrahedral through the narrow-web forms. 8.Single vs. serial Z-plasties on a web: A single 6 cm. Z-plasty proved more effective than a series of three 2 cm. Z-plasties in obliterating the axillary web of a dog's foreleg. 9.Measured lengthening vs. predicted lengthening: In each instance where lengthening was anticipated in the above studies, lengthening was always less than predicted by the usual geometrical calculations, although the values were almost always directly proportional to the geometrical predictions. 10.Tension related curves: Throughout the studies each tension related curve showed a more or less exponential rise as the size of the tip angles, peak angles, or limbs of the Z-plasties increased in size, reminiscent of the Gibson-Kenedi curve for load deformation of skin. 11.Z-plasty mathematics: An equation solving for lengthening in any Z-plasty, regardless of configuration, was derived, and a graph was assembled from which lengthening of any Z-plasty on a flat surface would be obtained.

VENOUS AND ARTERIAL RESPONSES TO STIMULATION OF BETA ADRENERGIC RECEPTORS.

The effects of intra-arterial injections of isoproterenol on small vessels, arteries, and veins were studied in the paw and muscle of the foreleg of dog. Total blood flow to the foreleg was held constant. Blood pressures were measured in large and small arteries and veins. In some experiments venous outflow from paw and muscle was measured. The small vessel segment was the site of major dilatation. Venodilator responses were small, but they were enhanced when isoproterenol was injected in the presence of venous constriction induced by intra-arterial infusions of norepinephrine. Dichloroisoproterenol and nethalide blocked the dilator responses to isoproterenol in all segments but they did not block the dilator responses to acetylcholine or glyceryl trinitrate. Isoproterenol did not change the distribution of blood flow within the foreleg; responses in muscle and paw were not significantly different. The results indicate that stimulation of beta receptors with isoproterenol causes much more dilatation in small vessels than in veins in the foreleg and that small vessels of both paw and muscle dilate equally.

VASCULAR RESISTANCE OF DOG FORELEG DURING HEMORRHAGIC SHOCK.

Anesthetized dogs were submitted to conventional bleeding and reinfusion procedures so as to be able to compare vascular pressure gradients in the forelimb during acute hemorrhage with those recorded subsequently during the development of normovolemic shock. In some animals venous outflow from the limb was recorded to permit calculation of vascular resistances. The results demonstrate a marked increase in arterial and small vessel resistance during shock as compared to the changes observed in acute hemorrhage. Venous resistance also was appreciably greater during shock than during acute hemorrhage, which would argue against the possibility that the hemodynamic failure in shock might relate to a generalized collapse of venomotor tone. The data also show a tendency toward elevation of large vein pressure in shock, interpreted as signifying some degree of cardiac failure.

Small-field x-irradiation. Description of a dog-holding, field-limiting unit and dosimetry.

The irradiation of very small fields in the foreleg of the dog presents two significant problems. The first is that of accurately collimating the beam and directing it at the suitably immobilized limb during an extended treatment time. The second is accurate dose determination. Consideration of these matters and their solutions will be presented. Dog-Holding, X-Ray Field-Limiting Unit A mechanical device to meet the above requirements must (a) hold the dog's leg immobile; (b) be adjustable, to accommodate dogs of different sizes; (c) permit easy adjustment to the irradiation fields of the desired size and shape; (d) permit treatment of the same area from opposite sides of the leg (for more homogeneous dosage). The irradiation studies were done in conjunction with the roentgenographic time-lapse method previously reported (1, 2). In this procedure Roger Anderson pins are inserted into the bone, and a special crossbar attached between the pins stabilizes the limb while multiple exactly positioned interval roentgenograms are made. It was a natural extension to use the same pin and crossbar system for immobilization during irradiation. As can be noted in Figures 1 to 3, considerable flexibility has been incorporated in the unit. The upper platform measures 18 × 34 inches. At one end is a 6 × 9 1/ 2-inch cutout in which the holding device for the crossbar is mounted. The cutout permits the dog's foreleg to be brought above the platform surface and the clamp can be adjusted vertically to accommodate different limb lengths and pin positions. Sturdy legs, 16 inches in length, support the platform. Holes drilled at 1 1/4-inch intervals in the platform legs permit variable insertion of pegs that support a sub-platform, on which the dog rests. The remainder of the unit is designed to facilitate positioning of the field-limiting lead squares (described below). The principal component is a hinged arm mounted on a base that permits precise vertical and horizontal adjustments. The handles attached to the screw threads which move this base are calibrated in thousandths of an inch and so permit predetermined changes to be made. The hinged mounting of this arm allows it to be \ldraised\rd over the dog's limb and placed on the other side by providing for lateral adjustment as well (Fig. 2, B). The end of the hinged arm contains a central ring that turns inside an incomplete outer ring (Fig. 3, A). The center ring has four pins which match holes in lead collimating devices. The angular position of the center disk may be measured on a calibrated dial. The x-ray field-limiting squares (Fig. 3, B) are made of 1/8-inch lead glued with Armstrong A-6 cement to 1/32-inch brass plates. The brass lends support and helps keep the lead from deforming. These squares measure 5 cm. on a side and have mounting holes in each corner. The lead has been precisely machined with either slits or round holes. The slit type has longitudinal openings varying in width from 2 to 12 mm.

Na, K, Ca, and Mg ion action on coronary vascular resistance in the dog heart.

Local effects of major cations on coronary vascular resistance were studied in the beating dog heart. This was accomplished by shunting the blood around the heart and lungs, clamping the arch of the aorta and perfusing arterial blood at a constant rate into the ascending aorta. Perfusion pressure was measured during intracoronary infusion of isotonic solutions of NaCl, KCl, CaCl2, MgCl2, and MgSO4 and hypertonic solutions of NaCl and KCl at rates which raised cation concentrations in coronary blood without significantly affecting concentrations generally within the body. Coronary vascular resistance decreased as a function of the infusion rate of isotonic solutions of KCl, MgCl2, and MgSO4 and increased as a function of the infusion rate of an isotonic solution of CaCl2. Isotonic NaCl had no effect. Resistance changes occurred before measurable change in the proportion of a minute spent in electrical systole by the ventricle. These findings, together with those previously reported for the dog foreleg, suggest that the coronary vascular bed is actively dilated by localized slight increase in plasma concentration of K or Mg and actively constricted by localized slight increase in plasma concentration of Ca.

Effect of histamine on small and large vessel pressures in the dog foreleg.

In order to determine how histamine raises small venous pressure in the dog foreleg, response of pressure during spontaneous blood flow was compared with that during constan blood flow. With spontaneous blood flow, small venous pressure rose in response to both slow and fast rates of infusion of histamine into the brachial artery. Rise of small venous pressure preceded rise of interstitial pressure. Edema appeared whenever small venous pressure exceeded 26 mm Hg for 7 minutes or more. With blood flow held constant, slow rates of infusion failed to either raise small venous pressure or produce edema. Pressure rose and edema appeared despite a constant blood flow rate when the rate of infusion was increased to values which lowered systemic arterial pressure. Pressure increase was unaffected by section of foreleg nerves but was partially abolished by adrenergic blockade. Rapid intravenous infusion during constant blood flow raised small venous pressure much less and this rise was completely abolished by adrenergic blockade. These studies indicate that low rates of infusion into the brachial artery raise small venous pressure by arteriolar dilatation whereas high rates raise this pressure both by arteriolar dilatation and venous constriction. Venous constriction probably results both from a direct action of histamine and indirectly through an adrenal discharge. The study also suggests that elevation of capillary hydrostatic pressure is an adequate explanation for histamine edema.

Local effects of sodium, calcium and magnesium upon small and large blood vessels of the dog forelimb.

Resistance to blood flow through the small vessels of the dog foreleg decreased following local elevation of serum sodium and magnesium concentrations. Small vessel resistance increased following elevation of calcium concentration. Associated with the former changes was decreased responsiveness to levarterenol and methacholine. These changes likely result from effects of the cations upon the smooth muscle cell of the arteriole.

Effect of potassium on small and large blood vessels of the dog forelimb.

Potassium salts were infused into the brachial artery while holding the rate of blood flow constant and measuring pressures at four sites along the length of the bed. Small vessel resistance progressively decreased as a function of infusion rate. Arterial resistance did not change and then increased as a function of infusion rate. The net effect was a decrease and then an increase in total resistance. The decrease was associated with lessened responses to norepinephrine and acetylbetamethylcholine, serum potassium concentrations in the leg up to about 8 mEq/l. and no change of serum concentration in the body as a whole. The increase in resistance was associated with serum concentrations in the leg in excess of 8 mEq/l. and slight elevation of concentrations in the body as a whole. The decrease of small vessel resistance was lessened but still present following denervation of the leg and adrenergic blockade. Arterial resistance did not increase following adrenergic blockade. Those findings indicate that potassium excess dilates arterioles in the dog foreleg by a direct action as well as by decreasing the sensitivity of the arteriole to natural pressor substances. The large arterial constriction may be related to an adrenal discharge.

Tissue pressure and critical closing pressure in the isolated denervated dog foreleg.

Experiments designed to obtain very low pressures and flows in the isolated leg were performed on the weighed, denervated dog foreleg perfused with homologous blood. Continuous strain gauge recordings of pressure decay curves and rates of weight loss (venous outflow) were obtained after arrest of the arterial inflow. In some instances tissue pressures were measured by a ‘null-point’ procedure. The results provide no evidence for a generalized critical closing pressure in the denervated, blood-perfused, nonedematous leg. After occlusion of arterial inflow the arteriovenous pressure difference fell to zero (0.0 mm Hg) as venous outflow approached zero. Evidence was obtained showing that if a pressure difference is found at zero flow in the isolated leg, it is produced by the existing tissue pressure. An elevated closing pressure is readily obtained in the dog foreleg when the tissue pressure is increased, and its magnitude is directly related to the extent of tissue edema.

The influence of tone upon responses of small and large vessels to serotonin.

In the dog foreleg, serotonin antagonizes extremes of vascular tone induced by neurogenic means. It produces net dilatation when the bed is constricted and net constriction when the bed is dilated. This bidirectional response derives ultimately from the facts that changes in nervous activity change calibers of small vessels without greatly altering calibers of large vessels, and that serotonin produces small vessel dilatation at the same time that it constricts large vessels. When small vessels are already neurogenically dilated, serotonin cannot dilate them further, but continues to constrict large vessels. Thus, the net effect is constriction. When small vessels are highly constricted, serotonin dilates small vessels more than it constricts large vessels. The net effect is dilatation. The study also indicates why it is more difficult to demonstrate a similar antagonism when tone is varied by humoral means.

Effect of pH change upon systemic large and small vessel resistance.

In the dog foreleg acute increase and decrease of hydrogen ion concentration is associated with active small vessel dilatation and constriction, respectively, through some direct effect upon vascular smooth muscle. These small vessel resistance changes do not affect total resistance in the intact leg because of directionally opposite active changes in artery resistance. The latter response appears to be related to central nervous connections and perhaps to circulating or locally released epinephrine, norepinephrine or unknown vasoactive substances.

Effect of epinephrine, norepinephrine and serotonin upon systemic small and large vessel resistance.

Locally injected epinephrine and norepinephrine elevate dog foreleg total vascular resistance primarily through small vessel constriction. Serotonin does not significantly change total resistance, constricts large arteries and veins and dilates small vessels.