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Biomedical subjects

M K Sykes

Publications and source records attributed to M K Sykes.

At least 55 records · Page 3Linked to original sources
PubMed1987

High PEEP decreases hyaline membrane formation in surfactant deficient lungs.

Lung lavage was performed in 16 anaesthetized rabbits to produce surfactant-deficient lungs. This resulted in alveolar collapse, an arterial PO2 of less than 15 kPa on 100% oxygen and an inflection point on the inspiratory limb of the pressure-volume curve at an airway pressure of 8-10 mm Hg. One group of eight animals was then ventilated with a positive end-expiratory pressure (PEEP) equal to the pressure at the inflection point, whilst the second group of eight was ventilated with a PEEP 5 mm Hg less than the inflection point. Animals in the high PEEP group had a significantly greater arterial PO2 than those in the low PEEP group, but the mean survival time for each group was similar. However, there was a significantly greater incidence of hyaline membranes in the low PEEP group. Various mechanisms to explain these findings are discussed.

Animals↗
PubMed1987

Estimation of arterial PCO2 during high frequency jet ventilation. Studies in the dog.

The arterial to end-tidal PCO2 difference (PaCO2-PE'CO2) was measured in five anaesthetized dogs during controlled ventilation at 0.25 Hz (15 b.p.m.) and during high frequency jet ventilation at 1, 3 and 5 Hz. Because of the slow response of the infra-red carbon dioxide analyser, satisfactory recordings of end-tidal carbon dioxide could not be obtained at frequencies greater than 1 Hz. The interruption of high frequency jet ventilation by conventional ventilation resulted in approximately equal arterial and end-tidal PCO2 values during the first breath, and restoration of the normal arterial to end-tidal PCO2 difference by the third breath. It is concluded that, when high frequency jet ventilation at 1, 3 or 5 Hz is interrupted with normal tidal volumes at low frequencies, the arterial PCO2 can be estimated from recordings of the end-tidal PCO2.

Animals↗
PubMed1986

Extracorporeal oxygen and CO2 transfer of a polypropylene dimpled membrane lung with variable secondary flows: partial bypass in the dog.

In vivo gas transfer performance, during veno-venous bypass, is presented for one form of the Oxford membrane lung in which vortex mixing is induced in blood flow across a dimpled polypropylene membrane. Good agreement has been found with in vitro data presented in an earlier paper. Two experiments were extended to attain total extracorporeal CO2 removal with apnoeic diffusion oxygenation to motionless lungs. Measurements of arterial oxygen partial pressure during apnoea suggest that the time-constant for equilibration of alveolar nitrogen partial pressure with that on the gas side of the membrane lung is of the order of 100 min.

Animals↗
PubMed1986

Carbon dioxide clearance and deadspace during high frequency jet ventilation. Investigations in the dog.

The effects of frequency, tidal volume and added deadspace on carbon dioxide clearance were measured during high frequency jet ventilation at 1, 3 and 5 Hz in dogs. With a short, small volume deadspace, carbon dioxide clearance increased with minute volume at each frequency, but for a given minute volume the clearance decreased with increase in frequency. At 5 Hz, carbon dioxide clearance was less than carbon dioxide production. At 1 Hz, an increase in the volume of added deadspace decreased carbon dioxide clearance, but changes in the length of the deadspace, without change in volume, had no effect. At 5 Hz, an increased volume of added deadspace had little effect on carbon dioxide clearance, but increased length, without change in volume, decreased clearance. Carbon dioxide clearance was increased by placing the jet at the lung end of the tracheostomy tube. It is concluded that at 1 Hz, carbon dioxide elimination is governed by bulk flow, but at 5 Hz other mechanisms are important.

Animals↗
PubMed1986

A ventilator for use in nuclear magnetic resonance studies.

The problem of ventilating small animals during nuclear magnetic resonance studies has been solved by using a T-piece system with a remotely controlled non-magnetic expiratory valve. This system does not affect the NMR signal, has minimal internal compliance and expiratory resistance, permits accurate control of peak airway pressure, and may be of use when animals have to be ventilated in hazardous surroundings.

Animals↗
PubMed1986

Carbon dioxide clearance during high frequency jet ventilation. Effect of deadspace in a lung model.

The effects of the volume and length of deadspace on the clearance of carbon dioxide from a lung model have been investigated during high frequency jet ventilation (HFJV) at 1, 3 and 5 Hz. At 1 Hz, increasing the volume of the deadspace without changing the length caused a reduction in the clearance of carbon dioxide. At 5 Hz, an increase in the length of deadspace decreased carbon dioxide clearance, whilst an increase in volume had no effect. Since the delivered tidal volume was less than the volume of the morphological deadspace at this frequency, the elimination of carbon dioxide must have been accomplished by mechanisms which are not considered important at normal tidal volumes and frequencies. Furthermore, the clearance of carbon dioxide at 5 Hz was very inefficient compared with that at 1 Hz. It is concluded that, during HFJV, carbon dioxide is cleared most efficiently when the frequency is low enough for the delivered tidal volume to be greater than the volume of the morphological deadspace.

Carbon Dioxide↗
PubMed1986

Effect of lignocaine and nitrous oxide on hypoxic pulmonary vasoconstriction in the dog constant-flow perfused left lower lobe preparation.

The effects of lignocaine hydrochloride on hypoxic pulmonary vasoconstriction in the presence and absence of nitrous oxide were examined during constant-flow perfusion of the left lower lobe. Lignocaine had no effect on lobar pulmonary vascular resistance during lobar ventilation with oxygen or 7% oxygen in nitrogen. The substitution of nitrous oxide for nitrogen diminished the hypoxic vasoconstrictor response, whilst the subsequent infusion of lignocaine during 7% oxygen in nitrous oxide increased the response to a value which was not significantly different from that produced by 7% oxygen in nitrogen alone.

Animals↗
PubMed1986

Reversal of nitrous oxide-induced depression of hypoxic pulmonary vasoconstriction by lignocaine hydrochloride during collapse and ventilation hypoxia of the left lower lobe.

The blood flow to the left lower lobe (QL), and total (QT) pulmonary blood flow, were measured in 10 open-chest dogs using electromagnetic flowmeters. Ventilation of the left lower lobe with 7% oxygen in nitrogen produced a greater reduction in QL/QT (41%) than lobar ventilation with 7% oxygen in nitrous oxide (33%). Lobar collapse reduced QL/QT by 65%, but there was no change in QL/QT when 50% nitrous oxide was administered to the right lung. The i.v. infusion of lignocaine hydrochloride during ventilation of the lobe with 7% oxygen in nitrogen produced no change in QL/QT. However, lignocaine infusion during lobar ventilation with 7% oxygen in nitrous oxide produced a further reduction in QL/QT to a value which was not significantly different from that observed during ventilation with 7% oxygen in nitrogen. Lignocaine had no effect on QL/QT during lobar collapse whether the right lung was ventilated with 50% oxygen in nitrogen or 50% oxygen in nitrous oxide. It is concluded that lignocaine reverses the depression of hypoxic pulmonary vasoconstriction produced by lobar ventilation with nitrous oxide.

Animals↗
PubMed1986

Mechanisms by which dopamine alters blood flow distribution during lobar collapse in dogs.

Dopamine increases blood flow to a hypoxic left lower lobe in dogs. To elucidate possible mechanisms, left lower lobe collapse was induced in anesthetized dogs, and lobar (QLLL) and total (QT) pulmonary blood flow was measured by electromagnetic flow probes. Dopamine infusion increased mean pulmonary arterial pressure (Ppa), QT, and QLLL. However, the increase in QLLL was double that produced by a similar increase in Ppa without increase in QT (inflation of a Swan-Ganz balloon in right pulmonary artery) or by a similar increase in QT with smaller increase in Ppa (opening of arteriovenous fistulas). QLLL/QT was not changed by opening arteriovenous fistulas, but was increased by Swan-Ganz balloon inflation, and by infusion of dopamine. It is concluded that the increase in QLLL/QT produced by dopamine was due to a decrease in hypoxic vasoconstriction in the lobe secondary to an increase in mixed venous PO2 and to vasoconstriction in the oxygenated lung.

Animals↗
PubMed1985

Oxygen and CO2 transfer of a polypropylene dimpled membrane lung with variable secondary flows.

Gas transfer performance is presented for one form of the Oxford membrane lung in which vortex mixing is induced in blood flow across a dimpled polypropylene membrane. Dimensional analysis has been used to define the parameters characterizing mass transfer in the device, and of three fluid mechanical parameters: Reynolds number based on peak pulsation velocity, Strouhal number, and ratio of mean to oscillatory flows, only the first has been found to affect mass transfer significantly in the ranges studied. For oxygenation, rated flows in excess of 5 l min-1 m-2 are measured. A new definition is presented for a rated flow for extracorporeal CO2 removal and values in excess of 1.2 l min-1 m-2 are obtained.

Animals↗
PubMed1985

Pulmonary lobe blood flow during ventilation hypoxia and lobar collapse in the dog.

The aim of the present study was to determine whether the diversion of blood flow away from a collapsed pulmonary lobe is due to hypoxic pulmonary vasoconstriction alone, or whether hypercapnia and mechanical factors also contribute. Hypoxic pulmonary vasoconstriction was tested in a canine pulmonary left lower lobe. Alveolar hypoxia was produced by absorption collapse or by ventilation with 7% oxygen, which has previously been shown to produce an end-pulmonary capillary pO2 similar to mixed venous pO2. The proportion of the cardiac output flowing to the lobe was reduced in both hypoxic states but was significantly lower during collapse than during ventilation hypoxia. The beta 1-adrenergic agonist dobutamine hydrochloride (30 micrograms X kg-1 X min-1 iv) produced a significant increase in the proportion of the cardiac output flowing to the lobe during collapse but no significant change during ventilation hypoxia. It is concluded that changes in local pCO2 during collapse may account for the greater diversion of blood flow from the lobe when compared with ventilation hypoxia.

Animals↗
PubMed1985

Effects of dopamine and dobutamine on the distribution of pulmonary blood flow during lobar ventilation hypoxia and lobar collapse in dogs.

Hypoxic pulmonary vasoconstriction was induced in the left lower lobe of fifteen dogs by ventilating the lobe with 7% O2 or by absorption collapse, and the distribution of flow between the lobe and the remainder of the lung was measured with electromagnetic flow probes. The lobar to total blood flow ratio was reduced by lobar ventilation hypoxia and decreased further during lobar collapse. In seven dogs, an infusion of 20 micrograms kg-1 min-1 of dopamine produced an increase in total blood flow, an increase in pulmonary artery pressure (P less than 0.01), and an increase in lobar to total flow ratio (P less than 0.05) during both hypoxic states. There was a significant fall in arterial PO2 (P less than 0.01) during ventilation hypoxia. Similar changes in total and lobar to total flow ratio (P less than 0.01) were observed in eight dogs given 20 micrograms kg-1 min-1 of dobutamine, but there were no changes in pulmonary artery pressure. The greater increase in total flow (+ 111%) resulted in a marked increase in mixed venous PO2 and no significant changes in arterial PO2 in this group of dogs. It is concluded that both drugs produce an increase in lobar to total blood flow ratio and shunt fraction, but that the mechanisms causing the redistribution of flow may differ.

Animals↗
PubMed1984

Inverse ratio ventilation compared with PEEP in adult respiratory failure.

We have compared the cardiorespiratory effects of an inspiratory: expiratory (I:E) ratio of 4:1 with a ratio of 1:2 in 10 adult patients requiring intermittent positive pressure ventilation (IPPV) for acute respiratory insufficiency. Further comparisons were made with IPPV with positive end-expiratory pressure (PEEP) which was adjusted to achieve an equal external end-expiratory volume (EEEV) to that produced by the 4:1 ratio, as determined by respiratory inductive plethysmography, and with an I:E ratio that only changed the EEEV minimally (IRV-min). Percentage pulmonary shunt (Qs/Qt) was reduced equally with PEEP and with the 4:1 I:E ratio but both patterns reduced cardiac output and oxygen delivery. IRV-min also reduced Qs/Qt significantly but had no effect on cardiac output so that oxygen delivery was increased. The dead space to tidal volume ratio (VD/VT) during IPPV-4:1 and IRV-min was reduced significantly when compared with that during IPPV-1:2. The clinical implications of the findings suggest that for some ITU patients, a modest increase in I:E ratio to between 1.1:1 and 1.7:1 may produce better gas exchange without significantly effecting the cardiac output.

Adult↗
PubMed1984

Failure of large tidal volumes to improve oxygen availability during anaesthesia.

Eight patients undergoing peripheral vascular surgery were ventilated with small (5.3 ml/kg) and large (16.3 ml/kg) tidal volumes at a constant respiratory rate. Carbon dioxide was added to the inspired gases to maintain normal end-tidal levels. The use of large tidal volumes resulted in a significant increase in arterial oxygen tension and content, but, due to a reduction in cardiac output, failed to improve oxygen availability.

Aged↗
PubMed1984

CO2 and mechanical factors reduce blood flow in a collapsed lung lobe.

Left lower lobe-to-total blood flow ratio (Ql/QT) was measured with electromagnetic flow probes in anesthetized open-chest dogs. There was a 66% reduction in Ql/QT during lobar collapse, a 53% reduction during lobar ventilation hypoxia with pulmonary venous PO2 and PCO2 equal to mixed venous tensions, and a 45% reduction during a similar degree of ventilation hypoxia but with normal end-tidal PCO2. We concluded that the reduction in blood flow during lobar collapse is due predominantly to hypoxic vasoconstriction, but that this mechanism is augmented by the raised PCO2 and mechanical factors present during collapse.

Animals↗