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R F Bellamy

Publications and source records attributed to R F Bellamy.

66 records · Page 4Linked to original sources
PubMed1981

Effect of atrial systole on canine and porcine coronary blood flow.

A feature of phasic coronary flow patterns recorded in conscious chronically instrumented dogs is the atrial cove--a transient depression of arterial flow that occurs during atrial systole. The association between the hemodynamic effects of atrial systole and the atrial cove was studied in anesthetized dogs and pigs with complete heart block. Many atrial coves are available for study in these preparations because atrial activity continues unabated during the diastolic ventricular arrest that follows cessation of electrical pacing. The effect of atrial systole is to translate the pressure-flow relation found during diastole to a higher intercept pressure without change in slope. The increase in the intercept pressure equals the increase in intramyocardial pressure measured with microtransducers embedded in the left ventricular wall. The decrement in flow during the atrial cove is a direct function of the change in intramyocardial pressure and an inverse function of coronary vascular resistance. Each atrial systole is associated with a forward flow transient in the coronary veins, the peak of which occurs at the same instant as does the nadir of atrial flow. These data suggest that the coronary vessels are acting as collapsible tubes and that the waterfall model of the coronary circulation is applicable. The following sequence is proposed to account for the atrial cove. Atrial systole ejects a bolus of blood into the left ventricle increasing both ventricular cavity and intramyocardial pressures. The increase in intramyocardial pressure raises the back pressure opposing coronary flow, reducing the arterial perfusion pressure gradient and causing flow to fall.

Animals↗
PubMed1980

Calculation of coronary vascular resistance.

A conscious, chronically instrumented canine model was used to investigate resistance changes in the distribution of the circumflex coronary artery as the artery was constricted. Several discrete constrictions were studied at two different levels of flow: resting and peak flow reactive hyperaemia. The resistance of the bed downstream from the constriction was calculated by formulae which defined the coronary back pressure as either venous pressure (Pv) or the arterial pressure at which coronary flow ceased (Pc). When Pv was taken as the back pressure, the resistance of the coronary bed during reactive hyperaemia progressively increased as the upstream artery was constricted. When Pc was taken as the back pressure, calculated coronary resistance for reactive hyperaemia showed little change. It is not known if elastic recoil of coronary resistance vessels, consequent to low poststenotic pressure, could occur to the extent required to be the physical basis for the calculated increase in resistance when Pv is taken to be the back pressure. Use of Pc as the back pressure implies that the coronary circulation contains a segment having the hydraulic characteristics of a collapsible tube.

Animals↗
PubMed1980

Effect of systole on coronary pressure-flow relations in the right ventricle of the dog.

Downey and Kirk's hypothesis that ventricular systole inhibits coronary blood flow by forming vascular waterfalls was examined in conscious chronically instrumented dogs by studying the effect of right ventricular systole on right coronary blood flow. Diastolic and systolic pressure-flow relations were constructed at resting-level flow and peak flow reactive hyperemia from phasic pressure and flow tracings recorded in nine dogs with right ventricular pressures ranging between 14 and 154 mmHg. Linear relations were found between aortic pressure and right coronary flow during diastolic and during systole when peak ventricular pressure was less than systemic. At resting-level flow and when peak ventricular pressure was less than one-half systemic, systole translated the diastolic relation to a higher zero-flow-intercept pressure and did not alter the slope of the relation. We interpret the data as showing that ventricular systole inhibits coronary blood flow by augmenting a vascular waterfall mechanism that exists during diastole.

Animals↗
PubMed1980

Effect of coronary sinus occlusion on coronary pressure-flow relations.

We studied the effect of transient occlusion of the coronary sinus on the relationship between aortic pressure and circumflex coronary blood flow in open-chest anesthetized dog preparations during artificially prolonged diastoles. The coronary pressure-flow relation was linear, and flow stopped at an arterial pressure (Pf = 0) that always exceeded coronary venous pressure (Pcv). During reactive hyperemia, Pf = 0 was 31 mmHg when Pcv was 5 mmHg and increased to 52 mmHg when the coronary sinus was occluded (Pcv, 38 mmHg). Elevation of Pcv translated the coronary pressure-flow relation to a higher Pf = 0 without altering the slope of the relation. Pf = 0 increased by about two-thirds of the increase in Pcv. We found no evidence that there existed a level of Pcv below which changes in Pcv had no effect on the coronary pressure-flow relation. These data are not compatible with the existence of a vascular waterfall mechanism in the coronary circulation unless it is assumed that Pcv is one of the determinants of Pf = 0.

Animals↗
PubMed1979

Factors determining delayed peak flow in canine myocardial reactive hyperaemia.

It has been suggested that delayed restoration of flow to the deeper layers of the myocardium is responsible for the gradual rise to peak flow rate characteristic of myocardial hyperaemia (RH). The distribution of coronary flow during RH was studied by injecting radiomicrospheres into the left atrium open chest dog preparations just prior to the end of a 15 s occlusion of the left circumflex branch. The artery was then reoccluded after 1, 2, or 4 s of RH. Myocardium perfused by the left anterior decending branch served as a control; the ratio of endocardial to epicardial (end/epi) perfusion in this bed averaged 1.14. During coronary occlusion and during the first second of RH the end/epi ratio in the hyperaemic zone averaged 50% of control, but rose progressively to equal control at the time of peak flow. Although evanescent subendocardial ischaemia may contribute to the gradual rise to peak flow rate it cannot by itself account for the time course of this response.

Animals↗
PubMed1979

Blood viscosity.

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Blood Viscosity↗
PubMed1978

Diastolic coronary artery pressure-flow relations in the dog.

Conscious dogs were used to investigate the relations between aortic (Pa) pressure and coronary flow (F) during individual diastoles. When the dogs were in a semibasal state, coronary pressure-flow relations were described by a family of lines, and diastolic flow was a linear function of aortic pressure. For a given perfusion pressure, higher flows were associated with lines of progressively greater slope and lower zero flow pressure intercept (Pf=0). Zero flow pressure intercepts were estimated by extrapolation and found to vary between 20 and 50 mm Hg, depending on the magnitude of flow. The zero flow pressure may represent the height of a vascular waterfall caused by vasomotor tone with the resistance-controlling coronary flow being (P-Pf=0).F-1. Interventions that decrease vasomotor tone increase coronary flow by both decreasing vascular resistance and increasing the perfusion pressure gradient. The gradient increases because the effective coronary back pressure is the height of the vascular waterfall and the latter is reduced when vasomotor tone falls. Passive changes in vessel dimensions, arterial recruitment, and autoregulation appear to be of little importance during individual diastoles.

Animals↗
PubMedDate not supplied

The medical effects of conventional weapons.

The medical effects of weapons used in modern conventional warfare are, overwhelmingly, penetrating. Fragments from explosive munitions such as shells, rockets, and grenades are the predominate source of missiles, especially in high-intensity war. Bullets from assault rifles and machine guns cause fewer casualties, except in counterinsurgency operations. The threat from penetrating missiles depends upon the part of the body that is struck and, to a lesser extent, upon the physical characteristics of the missile. The missile's mass and velocity determine its potential to do physical damage, but the extent to which this potential is realized depends upon diverse factors such as shape, construction, and stability. The American experience in the wars of this century indicate that approximately 20%-25% of all casualties died on the battlefield and are therefore classified as killed in action. Approximately 3%-5% die while receiving care, and thus are classified as died of wounds. Wounds of the brain or heart and great vessels are the most common causes of death. Prevention of sepsis in soft-tissue and orthopedic wounds is the major medical treatment problem in survivors. Since it determines the quality and quantity of combat casualty care, the single most important factor determining mortality or morbidity for combat casualties is the tactical situation.

Firearms↗