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Biomedical subjects

H D Johnson

Publications and source records attributed to H D Johnson.

At least 145 records · Page 8Linked to original sources
PubMedDate not supplied

Fluid exchanges through capillary walls: a modification of the Starling hypothesis.

In textbooks of physiology it is usually stated that fluids are extravasated from the arterial ends of capillaries, because, there, the outward transmural pressure of the blood exceeds its net inward osmotic pressure. At the venous ends, however, the position is reversed. The fluids are, therefore, reabsorbed. Inthis paper it is argued that this is not a true picture of what must really happen. For, having once become equal there is no reason why the pressures should ever cease to be so. Instead, fluids are absorbed at exactly that rate which just keeps pace with falling hydraulic pressure, as the blood proceeds along the capillary loop. Moreover, the forces are indeed shown to be equal at the extreme venous ends of the capillaries. It is further argued that, though this mechanism might operate anywhere in the horizontal position, it could not possibly work in the feet of a standing man. For here the hydraulic blood pressure everywhere greatly exceeds the osmotic pressure of plasma proteins. An addition to Starling's hypothesis is therefore suggested to adapt it to dependent tissues. An experiment by which the validity of this addition might be tested is described.

Capillaries↗
PubMedDate not supplied

Basic pressure: an important feature of the vascular system.

Starling's concept, "mean systemic pressure", is considered and its implications discussed. It is argued that since cardiovascular capacity and blood volume must obviously always be identical, any addition to or loss from the blood must simply compel an identical change in vascular capacity, without necessarily being associated with any change in venous return. Reasons are given for a need to differentiate between pressure and compression, and for appreciating that though the two are usually equal to one another, the second is not the cause of the first (as it is often thought to be). Indeed, the origin of blood pressure is the net osmotic pressure of plasma. We have demonstrated experimentally that Starling's method of measuring "mean systemic pressure" did not correspond to mean vascular compression during life. Moreover, when we remeasured mean systemic pressure by a method not much different from Starling's own, we arrived at quite a different figure. This fact we have attempted to explain. Finally we have described an entity which we hold to be more closely representative of mean systemic compression during life, and have shown how to arrive at it.

Animals↗