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A simple ventilator is described where a spring-loaded bellows is filled from a compressed gas supply. The outflow from the bellows to the subjects is controlled by solenoid valves. The device is a minute volume divider and the durations of inspiration and expiration are set by timers that operate the solenoid valves. The valves are positioned near the subject to minimize dead space and gas compression effects. Precise valve timing ensures separation of inspirate and expirate. The ventilator is suitable for respiratory gas studies on animals and may be modified for human use if required.

The Siemens-Elema Servo Ventilator 900 B is an electronically-controlled, volume-limited ventilator. To adapt this ventilator for use in newborns with respiratory failure, minute volume control, PEEP valves, air-oxygen blenders, and respiratory tubing circuits were modified. During a 22-month period, 161 newborn infants with severe respiratory distress syndrome (RDS) were managed with this ventilator. The overall survival rate was 66%; the incidence of barotrauma was 20%; the survival rate was 53%. Of the infants studied, 12% developed bronchopulmonary dysplasia, and 79% of these survived. Of the 19% of patients with a symptomatic intraventricular hemorrhage, 6% survived. The experience of the authors with this ventilator modified to manage newborn infants with severe RDS has been extremely encouraging. Furthermore, this ventilator is versatile because it can be readily recalibrated for use in older patients and can be easily adapted for patients requiring surgery. This ventilator has the extremely important advantage of being a volume ventilator which can effectively provide positive pressure ventilatory support to patients of all age and weight groups.

Megamed 05.2.2.D is a ventilation analyser. Pressure and flow is measured pneumotachographically; tidal volume, compliance, resistance, work and power are calculated. This values are given on a digital display, besides being printed continuously or in given intervals. Analog recording of graphics is possible as well as storing the values in a data processing system.

Studies of vocal cord function were undertaken in a quadriplegic patient requiring ventilatory assistance, and in 2 normal subjects during controlled ventilation in a tank-type respirator. When the patient and the normal subjects relaxed and made no conscious effort to assist the respirator, the vocal cords were observed to close during inspiration and a large pressure gradient (12 to 19 cm H2O) developed across the cords. When the subjects made a slight inspiratory effort ("assist" mode), the cords opened widely during inspiration. There were large increases in flow and tidal volume in the "assist" mode compared with passive ventilation. Measurements of transdiaphragmatic pressure and esophageal pressure showed that these variables did not increase with the slight assist. Thus, increase in ventilation during the "assist" mode appeared to be due to alleviation of inspiratory obstruction at the level of the vocal cords. The same phenomenon was observed in the patient during phrenic nerve pacing. A pacemaker was designed to be triggered by the electromyographic impulse from an accessory muscle of respiration. In this manner, vocal cord opening could be coordinated with the mechanical assist given by the phrenic nerve pacer.

A device is described that provides a reliable automatic deep breath to an animal being ventilated with a typical laboratory ventilator. The deep breath is provided by closing a solenoid valve in the expiratory tubing causing the animal to inspire two, three, or four consecutive tidal volumes without expiration. The interval between deep breaths is selected to be every 1, 2, 4, 6, 8, or 10 min. Control of this interval is provided by simple integrated circuits. Total parts cost of this device is approximately $90.

The occupational exposure of hospital staff to inhaled anaesthetics was investigated using a personal sampling device that provides a measure of the average concentrations breathed by a person over a period of time, as distinct from the spot sampling in the general environment. The anaesthetist's average exposure to nitrous oxide and halothane during complete operating sessions was twice that expected from simple dilution of the escaping gases by the operating room ventilation. The sampling technique was also used to evaluate the effect of (1) redirection of the waste gas outflow; (2) active scavenging connected to the piped vacuum system. Short-period studies under controlled conditions in the operating theatres and anaesthesia induction rooms showed that the anaesthetist's exposure could be reduced two- or fourfold by redirecting the outflow and another four- to sixfold by active scavenging. Exposures during complete operating sessions were reduced two- to seven-fold by scavenging.

We measured the "effective" dead space of five commonly used respiratory valves: Hans Rudolph valve, two-way J valve, triple-J valve, and modified Otis-McKerrow valves without and with vane. The dead space was measured using a technique that mimicked the operation of valves during ordinary laboratory procedures. The valves were ventilated with tidal volumes ranging from 0.35-3.00 liters and at different frequencies. With all valves, there was a marked tendency for "effective" dead space to be tidal volume dependent. The measured dead space approached the water-displacement volume of the common chamber of the valve only at tidal volumes in excess of 2.0 liters. The relation between valve dead space and tidal volume was independent of frequency.

An adaptor for the conversion of a standard bag mount for coaxial circuits is described.

In 30 patients ageing from 19-60 years dueing forced mask-ventilation, the pressures present in the epipharynx and the middle ear were measured. In 12 patients results raising pressure of the middle ear which has a corresponding level in the epipharynx accompanied by a time delay. It was possible to measure peaks in pressure of 100 cm H2O which however, by increased forced ventilation could produce higher results. Disturbances of the movable structures of the middle ear, due to increased forced ventilation appears probable.

A new range of ventilators which can be used during anaesthesia for infants, children and adults is described. The ventilators work on the moving-part fluid logic principle and are simple, inexpensive and robust; the patient valve can be autoclaved at standard temperatures (140 degrees C). There are facilities for providing PEEP, attachment of a scavenging system and for relief of over-pressure. The unit is 'fail-safe'. The ventilators, being constant flow generators, have a high specification and equal the performance of other machines which are five times the cost. The weight and size are such that servicing can be provided on a replacement exchange basis through the post.

The history of tank and cuirass respirators from the first known use of the intermittent negative pressure principle in 1832 to 1918, on the threshold of its extensive use in the treatment of respiratory paralysis, has been related. A second article will consider the period 1918 to the present day and suggest that negative pressure apparatus-particularly the cuirass respirator-still has its uses.

Transportation of patients requiring continuous ventilatory support and increased inspired oxygen concentrations may be troublesome for the physician and the nursing staff and dangerous for the patients. A new portable ventilator requiring oxygen of three atm. pressure as gas supply was tested for use during in-hospital transportation of more than 300 critically ill patients. Ventilator operation was simple, the machine was resistant to rude handling and the patients were ventilated reliably.

The inspiratory resistance, which a patient has to overcome while doing SIMV and CPAP with a Servoventilator 900 B, can be lowered by a simple modification of the ventilator. This modification is done by measuring the ventilation-pressure at the patients side of the humidifier. Measurements of pressure and flow demonstrated that, with a flow of 11 s-1 a 66%-reduction of the inspiratory resistance can be achieved.

A device is described with which the PEPP may be used with the Bird ventilator (mark 7 or 8) during assisted and/or controlled ventilation. Advantages over other currently available systems providing PEPP are discussed and these include ease of use, cheapness, versatility and safety.

To achieve synchronized differential pulmonary ventilation, an Ohio 560 ventilator was modified through separation of the outputs of the deep breath bellows and the tidal volume bellows and providing independent volume, flow rate, PEEP, oxygen-humidification, and alarm systems. The described ventilator modification is simple, inexpensive, and does not alter the performance characteristics of the original unmodified ventilator. Differential lung ventilation may be more easily achieved with this modified ventilator than with the simultaneous use of two ventilators or external electronic synchronizers.

The A4/6 is a newly developed ventilator, which may be used in the operating theatre or in the intensive care unit. The machine is electronically driven (microprocessor) and is characterised by a highly sensitive triggering mechanism. It is designed for the ventilation of the newborn (including premature infants) and children up to approximately 5 years. The significant and important features of its control design including its triggering mechanism will be described.

The Cape Bristol ventilator is a volume-preset machine which utilises oxygen from a flowmeter and air-entrainment attachment to provide a known inspired oxygen level. The level can be calculated from the oxygen flow rate and the patient's minute ventilation using a nomogram supplied by the manufacturers. Serious discrepancies between predicted and measured inspired oxygen levels delivered by these machines can occur and the advisability of using air entrainment devices in high oxygen dependent patients is questioned. Modification to the Cape Bristol ventilator to limit these errors are discussed and the more frequent use of oxygen monitors recommended.