Medical and biological engineering

, Volume 8, Issue 2, pp 111–128 | Cite as

Continuous measurement of blood gasesin vivo by mass spectrography

  • A. Wald
  • W. K. Hass
  • F. P. Siew
  • D. H. Wood
Article

Abstract

The application of the mass spectrometer to the continuous monitoring of blood gases in humans is described. At the heart of the system is an intravascular catheter consisting of a cannula impermeable to gas tipped with a membrane whose special gas permeability characteristics permits accurate calibration. Expressions are presented which describe gas flow through the membrane in response to a step increase in gas concentration; characterize thermal effects on gas diffusion and illustrate the effect of the cannula and carrier tubing on steady state gas flow. The system has been successfully employed in the study of arterial nitrogen washout and the determination of human cerebral blood flow by the nitrous oxide technique.

Keywords

Cerebral Blood Flow Nitrous Oxide Jugular Bulb Mass Spectrography Carrier Tubing 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notation

A

area (cm2)

Am

membrane surface area

Aw

effective water surface area

a

parameter characteristic of cross-section (cm)

a′

dummy constant (torr)

b

dummy constant (torr)

D

diffusivity (cm2/sec/torr)

D

modified diffusivity

Dm

membrane diffusivity

Do

reference diffusivity

Dw

diffusivity in water

d

differential

Ep

activation energy (cal/mole)

F

conductance (cm3/sec)

Fmem

membrane conductance

L

length (membrane thickness) (cm)

Lm

membrane thickness

Lp

mean free path

Lw

effective water path length

M

molecular weight (amu)

n

number (units, base 10)

P

gas pressure (torr)

Pa

average pressure

Patm

atmospheric pressure

Po

total pressure

Pw

gas pressure in water

P1

pressure on inner surface of membrane

P2

ion pump pressure

P33

steady state pressure

Pt

transient pressure

R

radius (cm)

Ro

universal gas constant (2 cal/mole/°K)

S

ion pump speed (cm3/sec)

T

temperature (°K)

t

time (sec)

V

gas flow (cm3/sec)

x

distance (cm)

α′

solubility coefficient (cm3/cm3)

α

membrane type

η

viscosity (P)

λ

dummy constant (1/cm)

π

numeric (3·14159)

Σ

summation

infinity

τ

time constant (sec)

Sommaire

L'article décrit une application de la spectrométrie de masse pour la surveillance continue des gaz sanguins chez l'homme. Le coeur du système est un catheter intravasculaire fait d'une canule imperméable aux gaz et munie à une extrémité d'une membrane dont la perméabilité particulière permet des calibrations précises. Des résultats fournissent les débits de gaz à travers la membrane en réponse à des échelons de concentration; ces résultats caractérisent les effets thermiques sur la diffusion gazeuse et illustrent les effets de la canule et des conduits de gaz sur les débits de gaz à l'état stable.

Le système a été utilisé avec succès pour l'étude de la technique de “washout” artériel à l'azote, ainsi que pour l'étude de la circulation cérébrale par la technique de l'oxyde nitreux.

Zusammenfassung

Die Anwendung des Massenspektrometers zur kontinuierlichen Messung der Blutgase des Menschen wird beschrieben. Ein intravaskulärer Katheter ist der Kern des Systems. Er besteht aus einer für Gase impermeablen Kanüle mit einer Membranspitze, deren spezielle Gaspermeabilitätseigenschaften eine genaue Eichung erlauben. Die Beziehungen zwischen dem Gasfluß durch die Membran und einer stufenweisen Erhöhung der Gaskonzentration werden mitgeteilt. Die Temperaturabhängigkeit der Gasdiffusion und der Effekt der Kanüle und der Trägergasschläuche auf den Gasfluß im Steady State wird ebenfalls beschrieben.

Das System wurde in Untersuchungen über das arterielle Auswaschen von Stickstoff und bei der Bestimmung der Hirndurchblutung beim Menschen mit der Stickoxydtechnik erfolgreich angewendet.

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Copyright information

© International Federation for Medical and Biological Engineering 1970

Authors and Affiliations

  • A. Wald
    • 1
  • W. K. Hass
    • 2
  • F. P. Siew
    • 3
  • D. H. Wood
    • 2
  1. 1.Department of NeurosurgeryNew York University Medical CentreNew YorkU.S.A.
  2. 2.Department of NeurologyNew York University Medical CentreNew YorkU.S.A.
  3. 3.Department of RadiologyNew York University Medical CentreNew YorkU.S.A.

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