Search PubMed⌕ Search

Biomedical subjects

R E Barrow

Publications and source records attributed to R E Barrow.

At least 91 records · Page 5Linked to original sources
PubMed1986

Volume-pressure cycles from air and liquid-filled intact rabbit lungs.

Air-filled and liquid-filled VP loops cycled over 100-300% FRC were measured using rabbit lung preparations. Four different stages of lung confinement were used ranging from intact lungs with the rib cage immobilized (Stage I) to isolated lungs (Stage IV). Stage I preparations showed larger air-filled and liquid-filled hysteresis areas of 1338 +/- 214 units2(air) and 849 +/- 73 units2(liquid), respectively, compared to 797 +/- 210 units2(air) and 128 +/- 33 units2(liquid) for excised lungs. The average peak pressure for Stage I at 300% FRC was 27.3 +/- 3.5 cm H2O compared to 21.8 +/- 4.8 cm H2O for Stage IV. The tissue contribution of the total air-filled hysteresis area was 63.5% for the Stage I lung preparation and decreased to 23.7% for the Stage IV lung preparations. These observations suggest that the tissue contribution to VP hysteresis may be greater in the intact lung preparation than previously assumed based upon excised lung studies and that geometric irreversibility may be a contributing factor.

Air↗
PubMed1984

An 'engine' phenomenon displayed by monolayers of a pulmonary surfactant cycled to steady state.

Monolayers of dipalmitoyl phosphatidylcholine--the predominant lung surfactant--have been studied at the surface of buffered Ringer's solution at 37 degrees C using the Langmuir trough with surface tension measured by both the Wilhelmy and du Noüy methods. When the surface was loaded with surfactant in excess of that needed to give a condensed monolayer on compression, the films displayed the conventional loops of surface tension versus area, demonstrating large hysteresis. However, when this system was cycled several hundred times over a physiological (25%) area change, it reached a steady state in which the surface tension for compression now exceeded that for expansion at all areas. This inversion was also recorded after attaining steady state by two other approaches--low initial concentration and 'aging' for two hours--while the phenomenon was further displayed over a larger non-physiological (75%) area excursion after 90 cycles. Inversion of surface tension hysteresis under physiological conditions implies the conversion of some other form of energy into mechanical work which could aid respiration, i.e. an 'engine'. Calculations are included to show how it might make a contribution of the order of 23% to the energy needed to satisfy the work of breathing under resting conditions.

Biomechanical Phenomena↗
PubMed1983

Properties of four lung surfactants and their mixtures under physiological conditions.

Surface properties of four of the most prevalent surfactants found in the lung have been studied on the Langmuir trough under simultaneously simulated physiological conditions. Surfactants studied are dipalmitoyl lecithin (DPL), L-alpha-dipalmitoyl phosphatidyl D,L-glycerol (DPPG), dipalmitoyl phosphatidyl ethanolamine (DPPE) and sphingomyelin and various mixtures of these. Studies using both the Wilhelmy and Ring methods showed that only sphingomyelin displayed any appreciable hysteresis between surface tension and surface area. All surfactants and their various mixtures reached similar minimal surface tension values of about 24-26 dyne/cm for compression to 75% of initial area and they all showed more than twice the change in surface tension with area needed to impart alveolar stability. These surfactants and their mixtures (except sphingomyelin) displayed appreciable contact angles, reaching 53 degrees for DPPE and 55 degrees C for a 1 : 1 mixture of DPL and DPPG. These mild anti-wetting properties are discussed in relation to their implications to gas transfer and fluid distribution at the alveolar wall.

Chemical Phenomena↗
PubMed1982

Air embolism: possible role of surfactant on recompression.

The relationship between surface tension and surface area has been measured on each of three common pulmonary surfactants - dipalmitoyl lecithin (DPL), dipalmitoyl phosphatidylethanolamine, and sphyngomyelin-under simultaneously simulated physiological conditions. These are selected to simulate the state of any surfactant that has migrated onto the surface of venous bubbles filtered by the pulmonary vasculature. It is concluded that, in the absence of shunt vessels, only DPL could reduce surface tension enough to allow pulmonary gas emboli to escape into arterial blood and then only after compression. This finding is discussed in relation to the delay in any appearance of bubbles in arterial blood and the possible facilitation of the release of asymptomatic lung bubbles by recompression therapy. The suggestion is made to reconsider stopping recompression of a subject with peripheral decompression sickness (the bends) at the depth of relief rather than risk releasing pulmonary gas emboli by further recompression. It is also demonstrated how the introduction of 1-min stops into compression can avoid surface tension falling to the low values at which it is theoretically possible for venous bubbles to escape into arterial blood during pulmonary hypertension.

Decompression↗
PubMed1982

Boundary lubrication imparted by pleural surfactants and their identification.

Phospholipids have been identified in pleural washings from live dogs and were found to include phosphatidylethanolamines, sphingomyelin, and, predominantly, phosphatidylcholines. The extracts were highly surface active when studied on the Langmuir trough using a Wilhelmy balance and produced surface tension/area loops similar to those for synthetic phosphatidylcholines and phosphatidylethanolamines but differing from the pure dipalmitoyl derivative (DPL). The extracts, the synthetic surfactants and their mixtures, were all found to be good lubricants when tested by a standard method for evaluating textile "sizes." The results are consistent with the classical theory of "boundary" lubrication for which surfactant molecules would have an almost ideal molecular structure for adsorption, film cohesion, and mutual interaction of the hydrophobic ends. This concept is suggested as a mechanism that can explain some of the anomalies in the hydrodynamic theory of sliding of the pleurae and may possibly apply to other surfaces.

Animals↗
PubMed1981

Methods for liquid filling inflated lungs and measuring any retained gas.

A method is described for liquid filling lungs without collapse by ventilating them on CO2 and then absorbing this gas with isotonic Tris buffer solution. The gas retained in each of 16 liquid-filled lungs has been measured by their compression in a dilatometer and averages 0.13% of lung volume. The liquid filling method has the advantage that it can be used either for lungs in situ or excised; total elimination of any retained gas, if desired, can be ensured by subsequent compression to 8.3 ATA for 10 min.

Absorption↗
PubMed1979

The contact angle induced by DPL at pulmonary epithelial surfaces.

A contact angle has been measured at the surface of dog tracheal epithelium by means of two surface balances simultaneously monitoring the apparent surface tension of the same film in a Langmuir trough - one method dependent upon contact angle and the other independent of contact angle. This was confirmed by direct observation. The contact angle was absent for Ringer's solution alone but was induced by DPL deposited on the fluid surface in physiological concentrations. The contact angle varied from 9 degrees to 67 degrees for compression of the DPL film from 100% to 27.5% of its original area and displayed hysteresis with respect to area. These findings show that DPL has unusual surface properties in reducing surface tension yet decreasing wettability, i.e. acting as an anti-wetting agent. The physiological advantages of this unusual combination of properties are discussed in relation to maintaining pulmonary homeostasis and the forward propulsion of mucus which could be facilitated by the differential wettability of cilia induced by DPL. One possible disadvantage of DPL is indicated where fluid plugs might seal an airway - such as in the newborn.

Animals↗
PubMed1979

A critical assessment of the Wilhelmy method in studying lung surfactants.

1. The surface properties of over 250 films of diplamitoyl lecithin (DPL) and Tween 20 on distilled water have been investigated using two different surface balances simultaneously, the Wilhelmy balance, popular in physiological studies, and the Du Nuoy ring method whose readings are independent of contact angle. 2. Using concentrations of DPL ranging from 0.08 to 1.90 microgram cm-2 on a Langmuir trough where the pool area was cycled from 100 to 27.5% of maximum, the Wilhelmy balance registered virtually the same force per wetted perimeter as the ring method for both pure water and Tween 20, but appreciably lower values for DPL over the whole cycle. 3. The above differences can be explained on the basis of a significant (45-70 degrees) contact angle, a surface property also demonstrated photographically and by direct measurement. 4. Contact angle was shown to vary with pool area, a relationship exhibiting hysteresis. 5. This study indicates that the Wilhelmy balance has been an unfortunate choice of instrument for studying DPL films whose surface tensions are appreciably higher than previously estimated.

Methods↗
PubMed1979

Surface tension induced by dipalmitoyl lecithin in vitro under physiological conditions.

1. The surface tension of 161 films of DPL have been measured on a Langmuir trough using a Wilhelmy balance under conditions controlled to simulate the state of the alveolar lining in vivo.2. The parameters controlled were temperature (maintained at 37 degrees C), humidity (100% at 37 degrees C), surfactant concentrations (encompassing the best available estimates), area changes (consistent with normal respiration), frequency adaptation to continuous cycling and composition and pH of the aqueous hypophase.3. Simultaneously maintaining all of these parameters within the best estimates of physiological limits, the relationships between surface tension and surface area showed appreciable differences from previous studies, our results showing higher minimum values of surface tension, appreciably less change in surface tension with compression and far less hysteresis between surface tension and surface area.4. The higher minimum values are consistent with original estimates of alveolar surface tension made by von Neergaard, namely 35-41 dyne cm(-1).5. Although appreciably smaller than hitherto reported, the change in surface tension with change in area is still adequate to impart alveolar stability.6. The reversibility between surface tension and surface area under physiological conditions is discussed in connection with compliance hysteresis which is considered to be more dependent upon geometric irreversibility of the alveolar surface than upon any intrinsic property of the surfactant.

In Vitro Techniques↗
PubMed1979

Method for estimating absolute lung volumes at constant inflation pressure.

A method has been devised for measuring functional residual capacity in the intact killed animal or absolute lung volumes in any excised lung preparation without changing the inflation pressure. This is achieved by titrating the absolute pressure of a chamber in which the preparation is compressed until a known volume of air has entered the lungs. This technique was used to estimate the volumes of five intact rabbit lungs and five rigid containers of known dimensions by means of Boyle's law. Results were found to agree to within +/- 1% with values determined by alternative methods. In the discussion the advantage of determining absolute lung volumes at almost any stage in a study of lung mechanics without the determination itself changing inflation pressure and, hence, lung volume is emphasized.

Animals↗
PubMed1979

Pulmonary function studies of conjoined thoracopagus twins.

Lung functions were measured on 13-day-old conjoined thoracopagus twins. Mean values for tidal volume and minute ventilation were 14.8 ml and 1102 ml/min for twin A and 12.8 ml and 963 ml/min for twin B. Functional residual capacities (FRC) were 35 ml/kg and 39 ml/kg for twins A and B, respectively. Pulmonary compliance and flow resistance for twin A were 2.8 ml/cm H2O and 75 cm H2O/liter.sec-1 with 45% of the total work used to overcome elastic resistance. Although values for resistance and work of breathing are within the normal range for studies reported elsewhere, these results tend to be elevated and probably reflect an abnormal state.

Airway Resistance↗
PubMed1977

Atraumatic measuring of pulmonary capillary blood flow in dogs.

Pulmonary capillary blood flow (Qc) was measured by a nitrous oxide uptake technique using a capacitance-plethysmograph to measure pulmonary volume changes. One hundred and four paired Qc and total cardiac outputs (Qt) were measured in 13 normal mongrel dogs. The mean Qc was 0.101 +/- 0.020 1-min -1-kg-1 while the mean Qt, measured by dye dilution, was 0.117 +/- 0.025 1-min-1-kg-1. This technique minimizes subject trauma and provides a method for repeated pulmonary capillary blood flow determinations in acute or chronic studies.

Animals↗
PubMed1976

Nonrebreathing valve system for small animal respiratory measurements.

Flow resistence, frequency response, and backflow characteristics of a nonrebreathing valve system applicable to measuring small animal respiratory volumes are described. Unidirectional valves, molded from liquid resin, were fitted into a modified Y tube for direct use on an endotracheal tube or face mask. Valve size and dead space volume can be scaled to fit several small animal species. In this system, valve resistance was 2.0 and 5.6 mm of water for steady flow rates of 0.5 and 3.0 1/min, respectively.

Airway Resistance↗