System for monitoring of fluidic pressures in cranial cavity uses a miniaturized pressure sensing transducer, combined with suitable amplification means, a meter with scale calibrated in terms of pressures between minus 100 and plus 900 millimeters of water, and a miniaturized chart recorder covering similar range of pressures

Fager, C. A., Jr.

Long, L. E.

Trent, R. L.

English

NASA Technical Reports Server

December 1970	 Brief 70-10436 
NASA TECH BRIEF	 lk 11  
-4r 
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application. Tech Briefs are available on a subscription basis from the National Technical Information Service, Springfield, 
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nology Utilization Division, NASA, Code UT, Washington, D.C. 20546. 
Post-Operative Cranial Pressure Monitoring System 
A system has been devised for post-operative 
monitoring of fluidic pressures within the cranial 
cavity at or near the site of neurosurgical operations. 
Provision is made for both meter-indication, and 
short-term chart recording of such pressures. High and 
low limits can be present, utilizing opto-electric limit-
detection devices, adjustable in accordance with the 
physicians's requirements; if these limits are exceeded, 
subsidiary alerting signals may be activated. 
During initial recovery periods following extensive 
neurosurgical operations, the body's normal recovery 
pattern results in increased cranial fluidic pressures 
at the site of the trauma. One of the major problems 
encountered in monitoring the patient's condition is 
the similarity of response of immediately available 
indicators, such as physical responses and body tem-
peratures, and their trends due to increased cranial 
pressures, the formation of haematorna, and/or infec-
tion. The actions required by the physician to enhance 
recovery differ widely, depending upon the causative 
factors involved. 
This monitoring system utilizes a miniaturized 
pressure-sensing transducer, combined with suitable 
stable amplification means, a meter provided with a 
scale calibrated in terms of pressures between - 100 
and +900 millimeters of water, and a miniaturized 
chart recorder covering a similar range of pressures. 
The transducer can be sterilized in accordance with 
normal operating room chemical procedures. 
This system could also be used in those cases involv-
ing reduction of aneurisms associated with major 
branches of either carotid artery, within the cranium. 
It is common practice, following such an operation, 
to temporarily clamp off the associated carotid artery 
to promote healing and reduce blood pressures at the
site of the operation. Arterial blood flow to that hemi-
sphere of the brain is maintained through the "circle 
of Willis", permitting the unclamped carotid artery 
as the prime source of blood supply. A commonly 
encountered problem is the sympathetic reduction of 
blood flow through this carotid artery which could 
result in dangerously low levels of blood flow to the 
brain. On the other hand, excessive blood pressures 
at the site of the operation frequently necessitate fur-
ther operative procedures. 
For this application, the pressure transducer could 
be sutured in the carotid artery, between the site of 
the operation and the arterial clamp, and the moni-
toring pressure range of the instrument changed to 
approximately - 10 to 300 millimeters of mercury. A 
range shifting switch, modifying the forward-current 
transfer ratio of the amplification means, is provided 
for this purpose. The low-pressure limiting feature 
would be employed to provide an alerting indication, 
and to automatically open up the arterial clamp. The 
high pressure limiting feature would be used to provide 
an alerting indication only. Since it is possible for a 
decrease in cranial blood pressure to lag blood flow 
loss to the brain by a period of time measurable in 
minutes, and considerable variation among patients 
exists in what might be considered normal, it may be 
desirable to use an additional monitoring transducer 
to reduce this time lag. The additional transducer 
could take the following forms: (I) a means of moni-
toring actual blood flow through the unclamped 
carotid artery: the transducer output reflecting 
volume flow; (2) a means of monitoring the blood 
pulse amplitude of the unclamped carotid artery: 
or (3) an EEG probe whose output provides an 
indication of brain activity in the region of the dcc-
(continued overleaf) 
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trode contacting area. If the peak EEG amplitude 
decreases by some appreciable proportion (10-20%), 
this information would serve as an energizing input. 
If either or any of the additional transducer outputs 
noted above were made available, a suitable logic-
combining OR function could be introduced at the 
input of the system to energize the low-limit feature. 
A modified carotid arterial clamp has been designed 
which provides fail-safe operation in the event of 
power failures. The clamp retains the pressure "re-
set" feature, and incorporates a quick-release solenoid 
normally held "ON" to apply pressure to the artery. 
If the power fails, or the low-level indication point is 
exceeded, the solenoid releases the clamp, without 
applying any torquing force. An auxiliary battery pro-
vides an audible alarm in the event of local or general 
power failures. 
For patient convenience, all hard-wired intercon-
nections between patient and monitoring equipment 
could be replaced by existing telemetry equipment and 
systems.
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Headquarters 
National Aeronautics 
and Space Administration 
Washington, D. C. 20546 
Reference: B70-10436 
Patent status: 
No patent action is contemplated by NASA. 
Source: R. L. Trent and L. E. Long 
Electronics Research Center 
and Dr. C. A. Fager, Jr. of 
Lahey Clinic 
under contract to 
Electronics Research Center 
(ERC-10336)
[-I: 
Brief 70-10436	 Category 05


Post-operative cranial pressure monitoring system

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