1126 
MONITORING 
Figure 1. — An inBtrumented dog running behind the mobile recording unit at a speed of 22 mph. Signals con- 
taining the flow/pressure measurements are telemetered from the apparatus carried by the dog in saddlebags. 
The FM signal is received by the antenna on the van and is coupled to the recording instruments inside. 
(Reproduced with permission from J. Clin. Invest. 50:1950, 1971). 
mm Hg ^ and to quadruple coronary blood flow.^^ 
Although resistance increased substantially in 
the mesenteric and renal beds during exercise, 
both mesenteric and renal flows remained es- 
sentially constant^ (Figure 1). Thus, even near 
maximal exercise was not sufficient to invoke 
the circulatory control mechanism of reduction 
and diversion of visceral flow. 
Even though diversion of visceral flow dur- 
ing exercise could not be demonstrated in nor- 
mal dogs, it was considered possible that this 
compensatory mechanism is utilized when the 
normal primary adjustments to exercise are 
impaired. We evaluated this hypothesis sys- 
tematically by examining the response to severe 
exercise in dogs with induced pathological im- 
pairments limiting either increases in heart 
rate or stroke volume or the oxygen-carrying 
capacity of the blood. Changes in heart rate 
were limited in a series of dogs by surgical in- 
duction of chronic complete heart block.'^ Stroke 
volume was limited by induction of chronic ex- 
perimental heart failure (tricuspid avulsion 
and progressive pulmonary stenosis) in another 
