Dean L. Franklin

Blood Flow Measured by Doppler Frequency Shift of Back-Scattered Ultrasound

The Doppler shift of ultrasound, scattered from moving elements within a stream of blood, is related to the velocity of blood flow. A flowmeter based on this principle has been constructed and was used to record blood flow through intact vessels in dogs.

Mechanisms of Cardiac Control in Exercise

Left ventricular performance during spontaneous exercise has been continuously analyzed in terms of direct recordings of diameter, effective pressure and other parameters derived by electronic computors. The changes in left ventricular performance during treadmill exercise have been compared with a number of experimentally induced responses in the same intact unanesthetized dog on the same day. These direct comparisons revealed that experimentally-induced increased venous return, reduced peripheral resistance, or administration of autonomic hormones do not reproduce the spontaneous exercise response. Better reproductions of the exercise response could be achieved by careful administration of isopropyl arterenol (Isuprel), by combined administration of epinephrine or norepinephrine) and experimental tachycardia or by stimulating sympathetic nerves to the heart. Stimulation of discrete areas in the diencephalon reproduced the exercise response with remarkable accuracy without movement or evidence of distress.

Cardiovascular Performance of Alaska Sled Dogs during Exercise

Radiotelemetry was used to study regional blood flow distribution in Alaska sled dogs during cross-country runs. Doppler ultrasonic flowmeter transducers were chronically implanted on the coronary, renal, and mesenteric arteries, terminal abdominal aorta, and ascending aorta or pulmonary artery, and a miniature blood pressure gauge was installed in the aorta or carotid artery. Flow and pressure data telemetered from dogs running on the trail were received and recorded remotely. The heart rate, 40 to 60/min in sleeping dogs, increased to 80 to 100/min when the dogs were ambulatory and to 100 to 150/min when the dogs were excited before a race. Heart rate accelerated to 300/min at the start of exercise and commonly remained at that level throughout prolonged runs. Aortic blood pressure averaged 130/90 mm Hg at rest, but the systolic pressure often exceeded 300 mm Hg when the dogs were running. A transient drop in mean pressure occurred at the onset of running, but mean pressure during sustained exercise was practically identical to that at rest. Flow in the terminal aorta increased 9 to 12 times and coronary flow 5 to 6 times, but mesenteric and renal flows were unchanged during violent, prolonged exercise. These findings contrast with diminished visceral flows recorded in exercising humans and suggest that compensatory redistribution of flow is not a significant reserve mechanism in these animals during exercise.

Balance Between Right and Left Ventricular Output

The right ventricular ejection pattern is characterized by early onset, gradual rise to peak flow velocities in midsystole and gradual return to baseline. Left ventricular ejection begins very shortly after right ventricular systole, abruptly reaches peak flow, and diminishes during the remainder of the systolic interval, terminating with a brief, sharp, retrograde surge as the aortic valves close. The duration of ejection is shorter in the left ventricle than in the right. In healthy dogs, respiratory activity produces very slight fluctuations in right and left ventricular output that are almost in phase. In dogs with hydrothorax and pulmonary atelectasis, the right and left ventricular outputs fluctuate in greatly exaggerated fashion with each forced respiratory effort. Under such conditions, the changes in right and left ventricular stroke volume are nearly 180 Degrees out of phase. Pulmonary outflow resistance is increased and the right ventricular ejection pattern closely resembles those generally characteristic of the left ventricle. Assume that the erect posture causes cardio-acceleration and large changes in right and left ventricular stroke volume. which are essentially synchronous. Treadmill exercise with sudden and unexpected onset produces changes in the outputs of the right and left ventricles without obvious lead or lag of one ventricle over the other. These experiments do not support the concept that changes in “venous return” are dominant mechanisms inducing alterations in cardiac output.

A Pulsed Ultrasonic Flowmeter

A pulsed ultransonic flowmeter has been developed specifically for the simultaneous measurement of blood flow through various major blood vessels in the intact unanesthetized animal. The flow section is a small (1-3 cm) lucite cylinder which is clamped about the blood vessel. Piezoelectric crystals are mounted on the flow section so that bursts of 3-mc sound may be transmitted alternately upstream and downstream. The flowmeter develops a voltage which is proportional to the difference in the upstream and downstream transit times of the sound. This voltage is recorded continuously and calibrated in terms of flow. Under optimal conditions, the output voltage is a linear and accurate representation of volume flow within ±5 per cent, independent of the velocity profile. The flowmeter responds to a step variation in flow within 0.01 second. The maximum noise and baseline drift is equivalent to a flow velocity variation of less than 1 cm/second measured over a 4-hour period.

Blood flow and pressure in the giraffe carotid artery

1. n1. Carotid artery blood pressure and blood flow were measured and telemetered from wild giraffes ranging freely on the African plains. n n2. n2. The blood pressure ranged between 260/160 mm Hg when the animal was lying flat, and 120/75 mm Hg when it was standing upright; dp/dt at the onset of systole was 1500 mm/sec. n n3. n3. Peak systolic blood velocity measured at the same site was 60 cm/sec; during diastole velocity remained above 40 cm/sec. Calculated blood flow in the carotid artery ranged between 50 cm3/sec in the prone animal, and 35 cm3/sec in the standing. n n4. n4. XY plots of flow and pressure produced open clockwise loops which varied in shape with activity and posture; such phase differences probably reflect mechanical properties peculiar to the giraffes arterial system.

Aortic blood flow in free-swimming elasmobranchs☆

Abstract 1. 1. Ventral aortic blood velocity and pressure in free-swimming elasmobranchs were recorded with the Doppler ultrasonic telemetry blood flowmeter. 2. 2. Ejection time from the heart varied with the heart rate. Peak injection velocities ranged from 12–14 cm/sec in Horn sharks, 12–20 cm/sec in skates and 8–15 cm/sec in dogfish. Acceleration of the blood lasted from 120 msec in the Horn shark (T = 24°C) to 450 msec in the skates (T = 9°C). Deceleration of flows was slow in all species. Oscillations from bulbus cordis contraction and respiratory movements were superimposed on the basic wavefrom. Participation of the bulbar contraction in the cardiac sequence varied widely. 3. 3. Heart rates increased during short-lasting exercise. Peak velocity and flow were largeley unchanged. Peak velocity and flow frequently increased in the post-exercise period. 4. 4. The hemodynamic effects of atropine, acetylcholine and adrenaline are discussed in relation to the fact that the fish heart receives parasympathetic but not, apparently, sympathetic innervation.

Role of Autonomic Hormones on Left Ventricular Performance Continuously Analyzed by Electronic Computers

Ventricular responses during spontaneous activity by intact dogs have been studied by using electronic computors to continuously analyze ventricular function in terms of various parameters, including effective ventricular pressure, changes in left ventricular circumference or diameter, rate of change in ventricular dimensions, myocardial “power,” myocardial “stroke work,” “eumulative work” per unit time and heart rate. Simultaneous recordings of these various factors permit characterization and direct comparison of the nature and sequence of left ventricular responses during infusion of autonomic hormones, spontaneous activity or exercise. Intravenous infusion of catechol amines in “physiologic doses’ produces changes in ventricular performance which differ significantly from those observed during exercise, particularly with reference to heart rate. The left ventricle appears to be directly influenced by neural reflexes, some of which are probably initiated by higher centers of the nervous system.

Length-Circumference Relations of the Left Ventricle

Changes in length and circumference of the left ventricle were recorded simultaneously by variable resistance gages on its external surface in intact dogs. The absolute changes in circumference were considerably greater than the changes in length, but the relative changes in these dimensions were similar (averaging around 2 to 3 per cent). Under most circumstances, the length and circumference vary in the same direction but occasionally inexplicable differences in response were observed.

Some Axioms, Popular Notions, and Misconceptions Regarding Cardiovascular Control

The present status and future prospects of cardiovascular research have been evaluated in terms of a series of axioms that may serve to summarize this report and to guide our efforts in the future.Axiom I. An important objective of cardiovascular physiology is elucidation of the mechanisms of function and control in animals and human subjects under normal conditions.Axiom II. The use of ambiguous and poorly defined terms tends to obscure ignorance and impede progress.Axiom III. Ideally, investigation of physiologic mechanisms should be conducted with minimal disturbances of either the organ system or its controls.Axiom IV. Experimental data are applicable without reservation only to the specific conditions under which they were collected.Axiom V. Extrapolation in the applicationof experimental data to species or to conditions of function different from those in which the information was collected should be based on knowledge of the kind and extent of deviation of the experimental from the normal.Axiom VI. The circulation of anesthetized animals must be regarded as experimental models of normal cardiovascular function.Axiom VII. Experimental models are frequently desirable and useful, but their validation requires quantitative comparison of the specific model with the physiologic mechanism or condition it is designed to represent.Axiom VIII. With the development of technics for comprehensive analysis of cardiovascular function in alert, active animals, general anesthesia, thoracotomy, and heart-lung preparations should be less frequently employed for studies of cardiovascular responses.Axiom IX. The use of general anesthesia to perform on animals the same procedures that are routinely accomplished on human subjects with nothing more than topical anesthesia (venipunctures, catheterization, etc.) may complicate interpretation of experimental observations without contributing significantly to the humane treatment of animals.Axiom X. Before extrapolating from one species to another, an investigator has a responsibility to determine to the best of his ability the extent to which appropriate correspondences have been established for the functions or control mechanisms under study.Axiom XI. A scientific term is most useful when it has a unique definition that immediately indicates what characteristics or properties must be quantitatively measured to determine its existence or change in its status.Axiom XII. Changes in function induced by an investigator during physiologic experiments indicate potential rather than actual mechanisms. The responses to artificially induced loads indicate what can happen rather than what does happen during normal spontaneous reactions.Axiom XIII. Although newly discovered natural laws may frequently bring order and clarity out of chaos, simplicity is not a reliable criterion for the validity of postulates regarding physiologic function or control mechanisms.