Pressure-flow characteristics of horizontal lung preparations of minimal height

This study analyzes the pressure-flow characteristics during the peristaltic pumping of power law fluids in an axi-symmetric non-uniform distensible tube. The analyzed geometry is of a diverging shape that is common in several biological flow conduits, especially in mammals. Using the Fourier series, the dimensionless wall coordinates for sinusoidal, triangular, trapezoidal, and square wave forms are obtained to simulate wall movement. Equations expressing the pressure-flow rate relationship for different wall shapes are developed from the wave equation. Pressure-flow and velocity plots are obtained by solving the equations numerically. The results indicate that there is significant difference in pressure-flow relationship between Newtonian and non-Newtonian fluid. Also, the maximum flow rate can be achieved when the wall movement follows a square wave form.

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Collateral influence on pressure-flow characteristics of coronary circulation

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1989.257.3.h717 ◽

1989 ◽

Vol 257 (3) ◽

pp. H717-H725 ◽

Cited By ~ 6

Author(s):

K. W. Scheel ◽

H. Mass ◽

S. E. Williams

Keyword(s):

Coronary Circulation ◽

Perfusion Pressure ◽

Isolated Heart ◽

Flow Characteristics ◽

Positive Pressure ◽

Circumflex Artery ◽

Pressure Flow ◽

Coronary Pressure ◽

Heart Preparation ◽

Collateral Vessels

The purpose of this study was to determine the role of the coronary collateral circulation on the shape of the coronary pressure-flow (P-F) relationship and its effects on the pressure at zero flow (PZF) or pressure intercept. We investigated the P-F characteristics of the coronary circulation under two conditions. 1) To minimize the influence of collaterals, we measured coronary flow by timed collections of coronary sinus outflow in 15 dog hearts, as perfusion pressure to all vessels was varied; 2) to maximize the effect of collaterals, we measured circumflex artery flow in six dog hearts, as perfusion pressure to only the circumflex coronary artery was varied and the pressure in the remaining vessels was maintained constant. We used an isolated heart preparation in which ventricular chamber and venous outflow pressures equalled atmospheric pressure and the vessels were maximally dilated with adenosine. In the first condition, the P-F relationship was curvilinear with a PZF of 0 mmHg; in the second condition, the P-F relationship was curvilinear with a PZF of 16 +/- 2 mmHg, and flow was retrograde at pressures below PZF. We conclude that in both conditions the curvilinearity of the coronary P-F relationship was the result of nonlinear elastic properties of blood vessels, not requiring the “waterfall” concept to be invoked, and that in the second condition the influence of collateral vessels produced the positive pressure intercept.

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Pulmonary Vascular Pressure-Flow Characteristics: Effects of Dopamine before and after Pulmonary Embolism

American Review of Respiratory Disease ◽

10.1164/ajrccm/146.2.307 ◽

1992 ◽

Vol 146 (2) ◽

pp. 307-312 ◽

Cited By ~ 15

Author(s):

John Ducas ◽

Marshall Stitz ◽

Shian Gu ◽

Usha Schick ◽

Richard M. Prewitt

Keyword(s):

Pulmonary Embolism ◽

Flow Characteristics ◽

Pressure Flow ◽

Before And After

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Effect of tracheal smooth muscle tone on collapsibility of immature airways

Journal of Applied Physiology ◽

10.1152/jappl.1988.65.2.863 ◽

1988 ◽

Vol 65 (2) ◽

pp. 863-869 ◽

Cited By ~ 29

Author(s):

R. B. Penn ◽

M. R. Wolfson ◽

T. H. Shaffer

Keyword(s):

Smooth Muscle ◽

Muscle Tone ◽

Flow Characteristics ◽

Smooth Muscle Contraction ◽

Chamber Pressure ◽

Developmental Difference ◽

Pressure Flow ◽

Smooth Muscle Tone ◽

Airway Function ◽

Newborn Animals

To test the influence of smooth muscle tone on extremely immature airways, tracheal segments (n = 19) were excised from premature lambs at 114-121 days gestation and mounted in a chamber filled with Krebs solution. Inflation (Si) and collapsing (Sc) compliance were determined by altering transmural pressure from 30 to 0 Torr and -30 to 0 Torr, respectively, both during control (C) and after acetylcholine (ACh) administration (experimental, E). Flow (V = 2-15 l/min) was then introduced through the tracheal lumen while chamber pressure (Pc) was increased from 0 to 30 Torr and driving pressure (Pd) was recorded for both C and E conditions. Tracheae were found to be extremely compliant; both Si and Sc were significantly (P less than 0.005) lower after ACh administration. Resistance to airflow (R = Pd/V) was also significantly (P less than 0.05) lower after ACh administration at each compressive pressure and each flow value. These results suggest that the highly compliant preterm trachea exhibits pressure-flow characteristics similar to a Starling resistor, and the effects of compressive pressures may be attenuated by ACh-induced smooth muscle contraction. Comparison of these results with data from adult and newborn animals suggests a developmental difference in tracheal mechanics and pressure-flow relationships, as well as in the way airway function is altered by smooth muscle stimulation.

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Needle Tracheostomy: A Laboratory Study

Anaesthesia and Intensive Care ◽

10.1177/0310057x8000800112 ◽

1980 ◽

Vol 8 (1) ◽

pp. 72-80 ◽

Cited By ~ 2

Author(s):

T. L. Dobbinson ◽

J. Whalen ◽

D. A. Pelton ◽

H. I. A. Nisbet ◽

G. Volgyesi

Keyword(s):

Airway Obstruction ◽

Laboratory Study ◽

Artificial Ventilation ◽

Flow Characteristics ◽

Upper Airway ◽

Upper Airway Obstruction ◽

Spontaneous Respiration ◽

Pressure Flow ◽

Transtracheal Ventilation ◽

Tracheal Occlusion

Percutaneous needle tracheostomy and transtracheal ventilation continues to be advocated for the management of upper airway obstruction. Recent studies recommend the use of artificial ventilation. However, as apparatus for this is not always available and because there remains some doubt regarding conditions for successful use of needle tracheostomy during spontaneous respiration, we undertook such a study in dogs. Pressure-flow characteristics of short hollow needles 18–10 SWG were first determined. The smallest of these (14 SWG Bardic Intracath) that would deliver flow sufficient (by calculation) to meet the respiratory requirement of 10–13 kg laboratory dogs was selected for further study. Respiration was possible by spontaneous or artificial methods in the presence of complete tracheal occlusion. Little or no deterioration was noted in an hour of such breathing. Artificial ventilation by machine and by hand could considerably lower PaCO2. We conclude that the technique is possible provided appropriate needles are selected and care is given to their method of use.

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