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M Hennes

Publications and source records attributed to M Hennes.

5 recordsLinked to original sources
PubMed1994

Intra-arterial pressure wave parameters modeled using electrical analogs.

An Electrical Model was developed to help identify parameters obtained from dynamic pressure data on the in vitro rat aortic artery. The data was obtained using a Multifunction Pressure Generator (MPG) and recording MPG Input Pressure (Pi) and Intraarterial Pressure (Po). Transfer functions of the form Po/Pi = (A1S+Ao)/(B2S2 + B1S+Bo) were obtained and it is necessary to link A1, Ao, B2, B1 and Bo to the Biological Parameters of Inertance (M), Vascular Resistance (R) and Compliance (C). Using the Electrical Analogs to P, M, R and C which are Voltage (V), Inductance (L), Resistance (Re), and Capacitance (Ce), an Electrical Model was built. The Electrical Model has the form Vo/Vi = (Re1S + 1/Ce)/[LS2 + (Re1 + Re2)S + 1/Ce]. Since Ao = Bo = 1 from our experimental data we multiplied the denominator and numerator by Ce to obtain Vo/Vi = (CeRe1S + 1)/[CeLS2 + Ce(Re1 + Re2)S + 1]. We then transformed our Electrical Model to its Pressure Equivalent and obtained Po/Pi = (CR2S + 1)/[CMS2 + C(R1 + R2)S + 1]. Since R2 is less than R1 + R2 we theorize that total R is composed of two viscoelastic or resistive elements R1 and R2. Using measured values of compliance it should be possible to obtain reasonable values for R1, R2 and Inertance.

Animals↗
PubMed1993

Dynamic intra-vascular pressure harmonic analysis.

The postulate that dynamic intra vascular pressure is a function of positional wall properties has been difficult to verify due to non-linear viscoelastic influences in arteries. It was tested, in rabbit carotid artery in vitro segments using dynamic and static input. A Multifunction Pressure Generator (MPG, Millar Inc.) provide dynamic input of defined swept frequency (2-200 Hz) pressure superimposed on multiple levels of mean intraluminal pressure (IP). Bode plots were analyzed for natural frequency (omega n), gain (dB) and damping (zeta) of the IP/MPG transfer function. An increase in omega n (all zeta > 0.25) was found with increase in mean IP. An increase in segment Elastic modulus (Em) was found with increase in static force input. Relation between Em and omega n results was demonstrative of non-linear elasticity. Results supported the postulate and verified estimating vessel properties by harmonic analysis.

Animals↗
PubMed1993

Arterial elastic modulus for fixed and varied wall volume.

It is commonly assumed that a blood vessel maintains a constant wall volume over a wide range of intraluminal pressures. We have found that vessel wall volume decreases under increasing load. To determine the effect of decreasing wall volume on values of Elastic modulus (Em), two computer models were used. The first model held volume constant with measured values of rabbit carotid artery length and width while thickness was calculated. In the second model wall volume was allowed to vary with measured length, width and thickness. Em increased with increasing load in both models with higher values in the nonconstant volume model. Up to 30% loading, the difference was 11% or less; above 30% loading, the difference increased to over 100%.

Animals↗