Hydrodynamic principles in hydrocephalus: the engineer's perspective.

There have been significant improvements in the prognosis for patients suffering from hydrocephalus stemming from the introduction of the cerebrospinal fluid (CSF) shunt some 40 years ago. Currently, one of the major obstacles to effective shunt treatment is the mismatch between the physiology of the patient and the hydraulics of the shunt system. In order to maintain the proper relationship between CSF and cerebrovascular pressures, the implanted shunt needs to establish normal CSF outflow (absorption) and storage (compliance). Many of today's shunts establish a limited range of normal CSF outflow (absorption) and storage (compliance) once implanted, but a mismatch between CSF and cerebrovascular pressures may exist when the patient changes body position during daily activities. An uncoupling of these pressures creates mechanical strains within cerebral tissues, which are implicated in pathologies related to shunt malfunction. We suggest that re-establishment of normal CSF outflow resistance, which by definition is an indicator of both absorption and compliance, is a fundamental requirement for shunt treatment under most conditions.

Urinary flow velocity as an index of male voiding function.

Urinary velocity and urinary peak flow rate developed by 463 male patients were measured before and after treatment for prostatic obstruction, stricture or prostatitis and compared to 121 documented normal males. It was shown that peak flow rate does discriminate partially between the normal and non-normal populations, but that many subjects who presented with ostensibly normal flow rates were actually obstructed when measured by peak urinary velocity. Velocity is shown to be a valuable secondary measurement in the clinic, and the flow velocity vs. flow rate diagram is demonstrated to be a good tool for classifying patients urodynamically.

Selectivity of peak versus average male urinary flow rates.

Multiple peak and average urinary flow rates were measured in 34 normal men. In addition, this population was compared to 114 patients with prostatic obstruction. No matter which flow rate measurement is used some overlap is present between the 2 populations. The sensitivity of the flow rate test was defined for the 90 or 95 per cent limit of each normal and abnormal population. The specificity of both tests also was statistically determined. The ability to separate abnormal from normal voiding is enhanced significantly if peak flow rate is the measurement made. The loss of specificity for average flow rate is owing to a greater percentage of both populations, normal or abnormal, within the overlap region between the 2.

Male peak urinary flow rate: relationships to volume voided and age.

We performed 126 studies of replicate voiding in 7 individuals and 552 observations in normal, abnormal or treated male populations with a disposable device that measures peak flow and volume voided. These observations have led us to suggest that a voided volume of 150 ml. be used as the minimum acceptable volume for studies of male subjects in which peak flow is used to define normal versus abnormal voiding. At volumes greater than 150 ml. a straight line describes the relationship between volume voided and peak flow as accurately as the previously suggested hyperbolic curve. Increasing age of men again reveals progressive decrease in peak flow rate no matter what volume is voided. Comparison of peak flow rate, volume voided and age by 3-dimensional graphing was attempted but was found unsuccessful for clinical use. However, 3 biaxial linear graphs may be used to chart effectively the 3 parameters (age, volume and peak flow) and thereby judge normality or abnormality of peak flow rate for any age and volume voided.