1502 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



sponses to exercise than the normal subject. A degree 

 of exercise (recumbent) on a bicyle ergometer which 

 had no influence on normal subjects (70 kg-m min) 

 had the effects shown in table 13 on cardiac patients 

 [Werko et al. (336)]. Patients were grouped into cate- 

 gories based on heart size [Group A, 512 ml m- BSA; 

 Group B, 796 ml/m 2 (no right heart failure) ; Group 

 C, 807 ml per m 2 (with right heart failure)]. Note 

 particularly reduction in RBF, percentage of cardiac 

 output, and increase in renal vascular resistance. The 

 work of others is in support of this (94, 155, 203). 

 Evidently heart failure lays additional stress on com- 

 pensatory mechanisms. When exercise is added, more 

 intense neurogenic and hormoral influences serve in 

 shunting blood away from the kidney. 



The kidney may not suffer as much as might be 

 anticipated during the curtailment of flow in exer- 

 cise, at least in heart disease, in view of the findings 

 of Bishop et al. (21). They have discovered that the 

 A-V oxygen difference of the kidney of the cardiac pa- 

 tient may increase, during exercise, in apparent con- 

 tradiction to the generally accepted "flow-limited" 

 characteristic of its circulation. The renal A-V oxygen 

 in 12 cardiac patients (mostly rheumatic heart disease 

 but none in congestive heart failure), averaged 2.03 

 vol per cent; this increased to a mean of 3.31 vol per 

 cent during exercise. In one, an increase to 12.40 vol 

 per cent was recorded. 



Posture and Orthostatic Hypotension 



In normal young males, C PA h in the sitting position 

 is 0.91 ± .04 of that recorded with the subject supine; 

 in the erect position, it is 0.85 ±0.14 (242). Tilting of 

 the subject from the horizontal similarly produces re- 

 duction in glomerular filtration rate, e.g., 127-120 



to 98-93 ml per min (6o° tilt), recovering to 126, 1 1 7, 

 and 1 12 ml per min (39). 



Motionless standing, or tilting of the subject lying 

 quietly on a tilt-table, leads to progressive venous 

 stagnation, reduced cardiac output, and neurogenic 

 vasoconstriction until the cerebral circulation becomes 

 inadequate, at which point syncope occurs. 



When tilting is done in increments from horizontal 

 to 60 °, RPF and C,„ progressively decrease; this is 

 more marked when reflex compensatory mechanisms 

 are good, as manifested by well-sustained blood 

 pressure, than when blood pressure is not sustained 

 and fainting is imminent (36, 60, 72, 286, 334). Pa- 

 tients prone to orthostatic hypotension in particular 

 manifest the latter responses (36). £ PAH usually is not 

 altered (36, 334). Filtration fraction tends to increase, 

 suggesting predominantlv efferent arteriolar constric- 

 tion (60, 287). 



Two different types of responses are shown in table 

 14. In table 14 A, compensation was good, and arterial 

 blood pressure was well maintained. In B, in a patient 

 subject to orthostatic hypotension, renal blood flow 

 "opened up" as syncope ensued. 



The type of response seen in table 14 B was also 

 shown during fainting produced by cuffing the lower 

 appendages, plus venisection (up to 500 ml) (72). In 

 all cases, when blood pressure fell, C PA h decreased 

 but the calculated renal vascular resistance decreased. 

 Thus, the kidney participates in the more widespread 

 splanchnic vasodilatation which occurs during syncope 



(14)- 



It is of interest that the medullary flow increases in 

 the subject (table 14 B) during the failure of vascular 

 compensation. Although this type of calculation of 

 medullary flow must be accepted with some reserva- 

 tion, the data suggest that vascular resistance de- 

 creases more markedlv in the medullary circulation, 



table 1 3. Effect of Exercise on Renal Hemodynamics in Cardiac Patients 



[After Werko et al. (336). 



