Biomedical subjects
Publications and source records attributed to J Duffin.
This article describes the construction and operation of fluidic and pneumatic devices in current use, as well as the principles of their use in medical devices. The designs for an automatic blood pressure cuff inflator, a blood pump and a high performance ventilator are presented.
1. The incidence of entrainment of breathing frequency by the rhythm of exercise was detected by a cross-correlation of the two frequencies. 2. During moderate, steady-state exercise on a bicycle ergometer at 50 rev/min, eight of fifteen volunteers (53%) showed entrainment when pedalling speed was kept constant with a metronome, and three of fifteen volunteers (20%) showed entrainment when pedalling speed was kept constant with a speedometer. 3. At 70 rev/min, in a second group of fifteen volunteers, the results were nine of fifteen (60%) and five of fifteen (33%) respectively. 4. During moderate, steady state exercise on a treadmill, in a third group of fifteen volunteers, eight of 15 volunteers (53%) showed entrainment while walking, and twelve of fifteen volunteers (80%) showed entrainment while running. 5. It is concluded that the rhythm of exercise is likely to affect the rhythm of breathing and that this controlling factor must be considered during studies of breathing pattern in exercise.
Membrane oxygenators, now commercially available, are undergoing clinical trials as long-term (days) respiratory support devices for patients in potentially reversible respiratory failure. However, these devices must be used in an integrated system of controls, monitors and alarms if they are to be reliable and easy to operate in the clinical environment. This paper describes such a system. The tubing circuits for blood and for oxygen are described first. Next, details of the blood pump controls are presented. The system features servo control of pump speed to match blood inflow, and deactivation of the pump in the case of excessive output pressure. Gas circuit controls are described which allow the independent adjustment of both oxygen flow through the gas phase of the membrane lung and oxygen pressure developed at the inlet gas port. Audible alarms are provided for low blood inflow to the system, excessive blood outflow pressure, changes in oxygen flow and failure of the electric power supply to the system. In addition to pressure and flow monitors in the blood and gas circuits, blood oxygen saturation is continuously monitored at both input and output of the system. The membrane oxygenator system has proved to be reliable and easy to operate in both animal and human long-term perfusions.
The activity and responsiveness of the peripheral ventilatory chemoreflex were assessed by the transient depression of ventilation following two breaths of oxygen in air-breathing subjects, and the differing times of onset of the ventilatory response to i.v. sodium bicarbonate in subjects breathing either air or oxygen. In patients premedicated with pethidine, in whom anaesthesia was induced with thiopentone, it was found that halothane, in an inspired concentration of 0.7-0.8%, reduced the activity and responsiveness of the peripheral ventilatory chemoreflex markedly. When halothane was discontinued and anaesthesia was maintained wtih intermittent injections of thiopentone (0.2 mg/kg/min) evidence of peripheral chemoreceptor activity and responsiveness returned.
The i.v. administration of sodium bicarbonate was found to cause an increase in arterial pH, followed by an increase in PaCO2. This caused a large increase in lung ventilation in in PaO2. Oxygen administration in human subjects, and anatomical denervation of the chemoreceptors in dogs, caused a substantial delay in the ventilatory responses to sodium bicarbonate. It was concluded that the i.v. administration of sodium bicarbonate provides a method of testing the presence of peripheral chemoreflexes which has the advantage of being independent of alveolar ventilation.
A 24-year-old woman with chronic granulocytic leukemia and alveolar proteinosis required extracorporeal membrane oxygenator support for respiratory failure refractory to conventional therapy. During perfusion, each lung was lavaged with 10 L. of normal saline. The lavage led to marked clearing of the lungs and improvement in pulmonary function. Extracorporeal support was terminated successfully after 54 hours. The patient died 2 weeks later with bone marrow insufficiency and overwhelming sepsis. Pulmonary lavage is technically feasible during venovenous oxygenator bypass, and may be of value, since such lavage debrides alveoli as well as the bronchial tree. Because pulmonary lavage provides a possible means of improving pulmonary function, it seems worthy of consideration as an adjunct to membrane oxygenator support.
A 19-year-old woman developed cardiorespiratory failure from multiple, peripheral pulmonary emboli apparently developing over the preceding 3 weeks. She was not considered to be an operative candidate. However, when 3 days of intravenous heparin infusion and 30 hours of membrane oxygenator support failed to improve the pulmonary pathology, pulmonary embolectomy was performed. The membrane oxygenator support had to be continued for 34 hours following the operation before it was successfully discontinued. The patient made a complete recovery.
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Cold water is known to facilitate the drowning process. To gather information on the possible relationship between ventilation and cold stimuli, measurements of inspired and expired breath by breath ventilation and alveolar PCO2 were made on 8 male subjects suddenly immersed in both cold (11 degrees C) and warm water (28 degrees C). The mean ventilation for all subjects for the 1st three breaths following cold water immersion was 94.5, 71.3 and 94.6 L/min (BTPS) as compared to 60.0, 36.2 and 38.5 L/min (BTPS) for warm water immersion. Alveolar CO2 fell dramatically in cold water from a pre-immersion mean value of 36.4 torr to 23.9 torr, whereas there was only a change associated with the first few breaths following immersion in warm water. In prolonged cold exposure, ventilation was still markedly above that observed in warm water after 5 min. There was no relationship between skin fold thickness and ventilatory response over the period studied. A large increase in ventilations is likely to result in inefficient swim stroke mechanics. This, combined with a high probability of inspiration of water, may contribute to death as a consequence of cold water exposure.
In this report we shall describe a new route for perfusion during long-term support with the membrane oxygenator. The ascending aorta is cannulated so that blood from the oxygenator mixes with blood in the ascending aorta. Thus oxygenated blood is supplied to both the cerebral and coronary systems.
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