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Biomedical subjects

A D Greenfield

Publications and source records attributed to A D Greenfield.

13 recordsLinked to original sources
PubMed1978

On being a dean.

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College Admission Test↗
PubMed1967

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.

Journal Article↗
PubMed1966

Circulatory responses to simulated gravitational shifts of blood in man induced by exposure of the body below the iliac crests to sub-atmospheric pressure.

1. Exposure of the body from iliac crests to feet of a horizontal subject to a pressure 70 mm Hg below atmospheric causes a displacement of about 10 g of blood/kg total body weight from the upper to the lower part of the body. Much of this blood is returned very rapidly at the end of suction.2. During suction, the changes in the circulation resemble those during a foot-down tilt. After suction, the changes resemble to some extent those following the Valsalva manoeuvre.3. The overshoot of forearm blood flow following suction is caused by variations in the activity of adrenergic vasoconstrictor nerves. The receptors for this reflex have not been identified, but their stimulation depends upon a rapid and large return of blood to the central circulation.

Adrenal Glands↗
PubMed1966

The interrelation of thermoregulatory and baroreceptor reflexes in the control of the blood vessels in the human forearm.

1. The interrelation of thermoregulatory and baroreceptor reflexes in the control of the circulation through the forearm has been investigated in eight men.2. The results are compatible with the current hypotheses that thermoregulatory reflexes employ exclusively blood vessels in the skin, and that baroreceptor vasodilator reflexes excited by transfer of blood from the legs to the trunk employ exclusively blood vessels in the muscles. They are compatible with the hypothesis that baroreceptor vasoconstrictor reflexes excited by transfer of blood from the trunk to the legs employ blood vessels in muscles, but not with the hypothesis that they do so exclusively.3. The results indicate that when blood is transferred from the trunk to the legs, vasoconstriction over-rides thermoregulatory vasodilatation, presumably in the blood vessels of the skin.4. The circulation through the skin appears, therefore, to be under baroreceptor as well as thermoregulatory reflex control, and over the short period of time examined, namely 1 min, the baroreceptor control takes precedence.

Adolescent↗