FLOW OF BLOOD THROUGH BONES AND JOINTS 



'659 



erally be no farther than 100 n from a nutrient vessel. 

 Actually few quantitative measurements of the oxy- 

 gen content of the blood circulating through bone 

 have been made, and these have been concerned with 

 the blood taken from marrow. Thus, Grant & Root 

 (51) punctured the humerus of unanesthetized dogs 

 and determined the oxygen saturation and tension in 

 the first 0.15 ml of blood removed. The oxygen satu- 

 ration of bone marrow blood is similar to that of blood 

 drawn from the jugular vein. The oxygen contents 

 and capacities, and the hematocrit values decrease to 

 about the same extent in jugular and bone marrow 

 blood after a 30 per cent hemorrhage, and recovery 

 takes place at the same rate. Similar studies have been 

 carried out on normal man and patients suffering 

 from anemia and polycythemia vera (5, 102), and pa- 

 tients with primary and secondary polycythemia 

 (59). The oxygen saturation of marrow blood was 

 found to be similar to that of normal man; that of 

 polycythemic individuals appears to be greater than 

 normal. 



The factors controlling the oxygen tension and 

 oxygen supply to "erythrogenic nests" are not well 

 understood. It is likely that the oxygen consumption 

 of these growing cells is one consideration, and that 

 the quantity and partial pressure of oxygen in the 

 blood perfusing the area constitutes another factor. 

 The bulk of marrow blood appears from histological 

 evidence to be contained in the venous sinusoids. It 

 seems reasonable to think that most of the mature 

 erythrocytes found in the sample obtained by needle 

 puncture are derived from the sinusoids. Presumably 

 the erythrogenic nests are in diffusion equilibrium 

 with the blood in the sinusoids even though the 

 growing erythroid cells may be sealed off from the 

 sinusoids as proposed by Doan (37, 38). 



Intramedullary Pressure 



The pressure within the medullary canal has been 

 measured in various bones in different animals by a 

 number of investigators. In animals, such as the dog 

 and cat, it varies between 20 and 1 15, averaging some 

 50 mm Hg (8, 60, 74, 82). According to Petrakis (95), 

 the pressures in the marrow of patients without 

 marrow disease are uniformly low. Thus, in the 

 sternum the pressures were approximately atmos- 

 pheric, ranging from 2/0 to 17/15 mm Hg. Tocantins 

 & O'Neill (106) report intramedullary pressures of 

 50 to 120 mm H 2 (3.7-8.9 mm Hg) in the human 

 sternum. Petrakis (95) notes that human marrow 

 pressures are lower than those seen in lower animals, 

 and suggests that the difference may be attributed to 

 the effects of anesthesia. The pressures measured in 

 the region of the diaphysis are said to be definitely 

 higher than those found near the epiphyses (fig. 5) 

 (103). 



Marrow pressure records show a definite, but small, 

 pulse pressure (60, 74, 82, 103). This observation may 

 be of practical importance, for Miles (90) reports 

 that the absence of such fluctuations in pressure in the 

 femoral head of patients indicates necrosis of this 

 structure. 



In addition to changes in pulse pressure, records of 

 marrow pressure show rhythmic fluctuations corre- 

 sponding to respiration (fig. 5) (60, 103). Also, slower 

 rhythmic variations in pressure, presumably Traube- 

 Hering waves, are sometimes seen (8). 



Rasgone, Vater, and Marbarger (see 74) concluded 

 that the marrow behaves as a semiclosed cavity and 

 that changes in intramedullary pressure are dependent 

 upon the volume of blood within the marrow cavitv. 

 When the venous return is obstructed, the mean 

 pressure of the marrow increases and the pulse pres- 



100 







x 



5 



50 



RESP 



DIAPHYSIS EPIPHYSIS 



FEMUR 



fig. 5. Bone marrow pres- 

 sure in diaphysis and epiphysis, 

 and respiration rate recorded 

 simultaneously in the dog. [From 

 Stein (103).] 



