1208 



HANDBOOK OF PH^'SIOLOfJ V 



NEUROPHYSIOLOGY II 



similar device vvliich requires only an infinitesimal 

 movement of fluid from the bladder. The recording 

 being isometric, the activity of the bladder is mani- 

 fested as pressure whereas, in other devices, the 

 volume of the bladder actually decreases in varying 

 degrees and the contraction is manifested in the 

 movement of fluid as well as in pressure. The muscle 

 progressively contracts at a shorter length of fiber, 

 a condition which in skeletal muscle decreases the 

 tension produced. No thoroughgoing comparisons 

 of isoinetric and isotonic recording of bladder con- 

 traction have been pui)lished. 



Cystometry 



The variety of cystometers is bewildering. .AH 

 'short-circuit" the sphincters by the urethral catheter 

 so that only detrusor activity is studied. This situation 

 has analytical value but dictates caution in reasoning 

 from cystometrograms to normal micturition. All 

 cystometrograms relate intravesical volume to pres- 

 sure, the latter by convenience and convention being 

 graphed on the ordi nates. In some critical details, 

 cystometers vary considerably. Most are isotonic but 

 some are isometric. .Second, in some, the fluid flows 

 into the bladder continuously; in others by equal 

 sudden increments, spaced equally in time. How- 

 ever, provided certain strictures on the two methods 

 are observed, there is no demonstrated significant 

 difference in the resulting pressure-\olume curve. 



A continuous flow should be delivered at a pres- 

 sure which results in equal increments per unit time 

 and requires volume monitoring. This method is 

 defended as more natural although, at best, the flow 

 exceeds the rate of urine formation. The resistance of 

 the catheter orifice is a major factor unless the filling 

 is exceedingly slow, in which case deterioration of 

 an animal preparation, limitation of the number of 

 determinations and time consumption enter the pic- 

 ture. A double-lumen catheter is necessary for re- 

 cording true intravesical pressure, and this necessity 

 aggravates the proljlem of catheterizing small ani- 

 mals such as the cat. 



In the discontinuous increment method, the 

 instantaneous rate of fluid input is higher, and the 

 record is more influenced by a) the viscous properties 

 of the bladder wall and h) errors related to the re- 

 cording of pressures during fluid movement. The 

 position of the manometer is irrelevant. The abrupt 

 rise of recorded pressure with each increment is an 

 orifice-viscosity factor and should be regarded as a 



convenient signal, marking the time of the increment. 

 \ double-lumen catheter eliminates the orifice factor 

 but is not needed if the intravesical pressure is read 

 at the end of the interval between increments when 

 the pressure curve is asymptotic and no fluid is flow- 

 ing. 



The cystometer yields, in addition to the pressure- 

 volume cur\ e, a measure of the micturition threshold, 

 i.e. the volume (or pressure) which precipitates the 

 vigorous, sustained, easily recognizable, micturition 

 contraction of the detrusor. If tiie record is isometric, 

 or to a lesser extent, if it is semi-isotonic, the rate, 

 strength and duration of detrusor activity are also 

 measured. Both the threshold volume and the mic- 

 turition-reflex record are measures of the excitability 

 of the reflex arc, a state which is determined by 

 facilitation and inhibition from the iirain. 



Micturition Threshold Determinations in Intact Animal 



The volume of a "spontaneous" micturition (i.e. 

 that occurring when the bladder of an unanesthe- 

 tized uncatheterized animal is filled by urine secre- 

 tion) is, by definition, a measure of the micturition 

 threshold, suijject to correction by the amount of 

 residual urine (36). Unlike cystometry, "spontaneous' 

 micturition volume determinations assay the func- 

 tioning of the whole urinary tract and the sum of the 

 neural influences from supraspinal levels, acting on 

 the sphincters as well as on the detrusor. The method 

 is comparable to the 'times and volume" observation 

 of a clinical patient. The technique involves an 

 efficient metabolism cage pan connected with a 

 volume recorder. Induction of diuresis permits more 

 micturition volumes to be measured in a unit time. 



Other Methods 



Electrodes may i)e applied to the bladder wall or 

 to the afferent or efferent neurons innervating the 

 bladder. Fluoroscopic, roentgenographic and cine- 

 fluorographic techniques have also have been used, 

 and various arrangements of pressure recorders have 

 been utilized to obser\'e sphincter activity separately 

 or simultaneouslv with detrusor activity. 



CENTR.'KL CONTROL OF BL.\DDER TONUS 



Few words are as loosely defined and have so many 

 vague connotations as 'tone' or 'tonus.' It seems best 

 to use these words in a generic sense to mean a kind 



