British Journal of Anaesthesia 85 (6): 928±35 (2000)
HISTORY
The inventions of John Blease
A. G. McKenzie
Department of Anaesthetics, Royal In®rmary, Lauriston Place, Edinburgh EH3 9YW, UK
Though he had no formal training in engineering, John Blease of Merseyside invented numerous
devices that greatly bene®ted the practice of anaesthesia. Starting with the turning of
component parts for simple anaesthetic machines in the 1930s, he was introduced to clinical
anaesthesia and became skilled in the art of dental anaesthesia. In the early 1940s he developed
the all-purpose Alfo-Blease anaesthetic machine. In 1945 he designed an intermittent positive
pressure ventilator, which was used successfully around Liverpool. After World War II he
improved this into the Blease `Pulmo¯ator', which was the ®rst British positive-pressure ventilator in commercial production. From then until the early 1960s he patented many other inventions, duly utilized in the manufacture of anaesthetic equipment, in which industry the Blease
name survives in the company he founded.
Br J Anaesth, 2000; 85; 928±35
Keywords: history, anaesthesia; history, Blease, John Henry; equipment, anaesthesia
machines; equipment, ventilators
Accepted for publication: July 26, 2000
Between 1939 and 1960 John Henry Blease successfully
applied for no less than 19 patents for anaesthetic equipment
which he invented. Thereafter, he was involved in several
more patents for inventions by Roger Manley, who had
received his advice and support.
Early days
John Blease was born in 1906 in Bootle and grew up in
Moreton on the Wirral (Merseyside). Although he began
work as a butcher's boy at 14 yr of age, he had a
mechanical mind and was brilliant at repairing clocks.
Next he applied himself to tractor repairs, then became
a motorcycle enthusiast, and in his late teens set up a
car repair business jointly with a younger brother. In the
early 1930s he built his own 1000 cc motorcycle, which
he called the `Blease Special' (Fig. 1). With this he
entered races on sand against prestige machines and for
6 yr, beginning in 1933, he won every race in which he
competed at Wallasey and Southport (personal communication, Tony and Doreen Blease).
Anaesthetic machines
At this time John Blease befriended a neighbour, Dr Henry
Roberts, who was a general medical practitioner and
anaesthetist to the Liverpool Dental Hospital.1 At Roberts'
request, Blease made component parts from drawings of
American (Gwathmey and Heidbrink) anaesthetic machines. His work impressed a full-time anaesthetist, Dr
John Halton, with whom Blease also became friendly.
Through these two men, Blease became acquainted with
clinical anaesthesia. The improved Roberts dental anaesthetic machine (Fig. 2) became very popular and is said to
have been installed in the Cunard-White Star liner Queen
Mary. In 1937 Roberts died suddenly1 and his role as dental
anaesthetist was taken on by Blease(!), who became highly
skilled in the art. Furthermore, Blease established contact
with the Liverpool surgical instrument company, Alexander
and Fowler. In 1938, Blease and George Fowler applied for a
patent for improvements in anaesthetic apparatus2 making
use of manifold technology, valves and temperature compensation. They ®led a second patent application in 19403
for the addition of carbon dioxide absorption and one-way
valves. Utilization of these advances resulted in the AlfoBlease anaesthetic machine, which was described in R. J.
Minnitt's revision of the Handbook of Anaesthetics (5th
edition, 1940).4 Blease ®led two more patents for improvements in 19415 and 1942;6 the latter invention was a
¯owmeter with a by-pass: it avoided erratic readings and
allowed for a more open scale. Again these patents were
incorporated in an improved model of the Alfo-Blease
Ó The Board of Management and Trustees of the British Journal of Anaesthesia 2000
The inventions of John Blease
Fig 1 John Blease and the `Blease Special' (courtesy of Mr M. A.
Blease).
Fig 2 Roberts dental anaesthetic machine (courtesy of Mr M. A. Blease).
Fig 3 Alfo-Blease anaesthetic machine, circa 1948. Prior to this, the head bore the insignia `Alfo-Blease' (ã Thackray Medical Museum, 2000).
929
McKenzie
Intermittent positive pressure ventilators
Fig 4 Drawing of prototype of Blease `Pulmo¯ator', 1947 (modi®ed from
British Patent 625,284). Key: 1, glass cylinder; 2, rubber rebreathing bag;
3, corrugated tubing to anaesthetic apparatus; 4, in¯ation pressure gauge;
5, adjustable expiratory valve (semi-closed circuit); 6, hand bellows
(closed circuit); 7, compression chamber; 8, rotary pump with air inlet; 9,
belt gearing; 10, electric motor; 11, cam; 12, adjustable de¯ation valve
(cam operated); 13, manual valve to discontinue pressure; 14, branch for
introduction of oxygen, nitrous oxide; 15, in¯ation pressure gauge; 16,
inspiratory valve; 17, auxiliary inlet to enable introduction of oxygen or
carbon dioxide. Modus operandi The `bag in a bottle' is rhythmically
squeezed by the electric compressor through the cam and valve
mechanism.
machine (Fig. 3). This portable apparatus included a head
(rectangular metal box 6.5 in. deep 35 in. 3 4.5 in.), a sodalime cannister, a rebreathing bag and afferent and efferent
corrugated tubes attached to an `E' mount (with two nonreturn valves) for connection to the face-mask or tracheal
tube. The head had three rotameters calibrated for oxygen,
nitrous oxide and cyclopropane. Inside the box was an ether
vaporiser with a 3-way tap and control valve, enabling the
gases to either pass over or bubble through the ether.7 8 The
`all purpose Alfo-Blease' was well received and by 1944
Alexander and Fowler Ltd were producing 100 machines a
year (price £100 each).9
In the early 1940s, during the World War II bombing of
Liverpool, Blease was pressed into further anaesthetic
service and was appointed `Emergency Anaesthetist' at
Birkenhead General Hospital. He even anaesthetised
thoracic cases for Mr Hugh Morriston-Davies (pioneer of
thoracoplasty in the UK).10 This was an astonishing
achievement on two counts: ®rst, anaesthesia in Britain
was traditionally administered by physicians and, secondly,
Mr Morriston-Davies would not have tolerated a `second
best' anaesthetic. `Controlled ventilation' had been introduced into British anaesthesia in 194111 and thoracic
anaesthetists became `bag squeezers' when the chest was
opened. Blease had plenty of time to re¯ect on the drudgery
of manually controlled ventilation, and in 1945 he designed
a pulmonary ventilator, which, with the help of Dr J. Halton,
was tested successfully on patients.12 This apparatus was
much appreciated when the use of d-tubocurarine in
anaesthesia became more common and necessitated controlled ventilation throughout many surgical operations.13
In 1945, after World War II, Blease left the Wirral
(and Alexander and Fowler) to join Multitone Electric
Co Ltd, which made hearing aids, at 223±227 St John
Street, London (personal communication, Tony and
Doreen Blease). From this location Blease continued to
supply the `Alfo-Blease', imprinted with the name
`Blease Anaesthetic Equipment Co. Ltd'. From 1946
until his retirement he resided at Royston Park Road,
Hatch End, Middlesex where, in a large workshop, he
did most of his inventing. In 1946 he applied for a
patent for a portable mechanical ventilator,14 shown
diagrammatically in Fig. 4. This was the original
prototype of the Blease `Pulmo¯ator' which operated
on the `bag in a bottle' principle. The driving air came
from the compressor side of a rotary vacuum pump,
belt-driven by an electric motor. Blease chose to
purchase this, because it was smaller and cheaper than
a designated compressor. The remainder of the apparatus
was Blease's invention. Within the compression chamber
a blow-off valve was operated by a cam, connected by
worm-gearing to the rotary pump. Adjustable springloaded valves controlled the minimum and maximum
pressures. The frequency of cycling (respiration) was
controlled by the speed of the motor, while the
inspiratory: expiratory ratio was controlled by the
characteristics of the camÐthe disadvantage being that
these were independent of pulmonary pressures. The
cam and valve mechanism clearly came from car
technology.
Blease lodged another patent in 194815 (pressure pre-set
ventilator) whereby the prototype was improved (Fig. 5).
The cycling mechanism was changed to a spring and ratchet
device (Fig. 6) reminiscent of motorcycle technology. Only
one model of this early `Pulmo¯ator' was built. To facilitate
easy transport by motorcar it was made in two parts: the
930
The inventions of John Blease
Fig 5 Drawing of early Blease `Pulmo¯ator', 1949 (modi®ed from
British Patent 649,229). Key: 1, face-mask; 2, ¯exible tubing; 3, valved
head; 4, air chamber; 5, casing, housing the operating mechanism; 6,
carbon dioxide absorber (soda-lime); 7, pipe for introduction of
anaesthetic gas from source; 8, source; 9, pump for supplying air through
tubing 13, to another air chamber (within 5, separated by a ¯exible
diaphragm from a vacuum chamber); 10, manually controlled valve to
disconnect tubing 2 from head 3 and connect 2 to tubing 11 leading to
rubber bag 12 for manual respiration; 14, knob to control needle valve
for adjusting inspiratory time; 15, knob to control needle valve for
adjusting expiratory time; 16, control lever for compression spring
(resisting the diaphragm), which regulates in¯ation pressure; 17, control
lever for slide valve to hold lungs in¯ated; 18, lever for manual control
of respiration; 19, pressure gauge. Modus operandi The `bag in a bottle'
is rhythmically squeezed by the electric compressor through the `cycling
box', which is a spring-diaphragm-ratchet device explained in Fig. 6.
`bag in bottle' with a `Blease 1 cycling box' being the ®rst
part, and the belt driven vacuum pump the second. In 1950,
Dr H. J. V. Morton (an anaesthetist at Hillingdon Hospital,
Uxbridge) used it to perform controlled ventilation of
patients undergoing hernia repair. He recorded pneumographs and showed that the machine could produce a
respiratory pattern very close to `normal', i.e. spontaneous
respiration, under cyclopropane anaesthesia.16
The `new Blease Pulmo¯ator' (P.1) launched about
the end of 1950 was the ®rst ventilator freely available
commercially in Britain. The basic workings were as
described above, but the `bag in a bottle' was replaced
Fig 6 Drawing of New Blease `Pulmo¯ator' (P.1), 1952. Key: 1, pressure
chamber; 2, compressed air inlet; 3, concertina reservoir bag; 4, tubing to
patient; 5, ¯exible diaphragm; 6, compression spring within vacuum
chamber; 7, exhaust valve; 8, control lever for cycling pressure; 9, needle
valve controlling duration of expiratory phase; 10, needle valve
controlling rate of in¯ation; 11, slide valve to hold lungs in¯ated; 12,
control lever for 11; 13, positive pressure safety valve; 14, valve to allow
spontaneous breathing (inactivating ventilator); 15, adjustable springloaded spill valve; 16, `manual/auto' control; 17, one-way valve; 18,
breathing bag (for manual ventilation); 19, pointers; 20, calibrated scale;
21, manometer; 22, notched disc; 23, compression/expansion spring; 24,
activating rod; 25 and 26, ratchet bars; 27 and 28, striking pins; 29,
connecting rod. Modus operandi Compressed air enters the main
chamber and acts on the outside of the concertina bellows, the contents
of which therefore in¯ate the patient's lungs. During this phase the
diaphragm is displaced to the right and the notched disc rotates
clockwise. At the crucial point the ratchet mechanism ¯icks over,
opening the exhaust valve so that the pressure in the main chamber falls
to atmospheric and expiration occurs. The spring pressing on the
diaphragm causes it to move in the opposite direction until the ratchet
¯icks over again, closing the valve and restarting the inspiratory phase.
by concertina bellows in a perspex cylinder (initially not
antistatic)Ðincluded in another patent applied for by
Blease in 1951.17 Measurement of the tidal volume was
facilitated by adjustable pointers and a calibrated scale
arranged outside the perspex cylinder (Fig. 6). The
clinical use of this ventilator was described in 1952.18
By 1953, driven by the need for vacuum pumps, Blease
left Multitone Electric Co. and joined Edwards High
Vacuum (now Edwards BOC). Operating from 12 Hinde
Street, London W1, he was able to manufacture many
`Pulmo¯ators' (P.1): about three or four a month, all
made one at a time! It is estimated that, over 5 yr, a
total of 200 were produced; no serial numbers were
issued (personal communication, Tony and Doreen
Blease). In 1953, he incorporated the P.1 into a selfcontained anaesthetic machine (the `combined pulmo¯ator', P.2). This included rotameters (for oxygen,
nitrous oxide, cyclopropane and carbon dioxide), racks
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McKenzie
Fig 7 Drawing of triggering device, 1959 (modi®ed from British Patent
848,725). Key: 1 air chamber; 3 Venturi-effect device; 5 two-way
differential valve; 6 collapsible bellows; 7, 8 one-way valves; 9 pipe to
patient; 10 diaphragm; 11 low-pressure chamber; 12 rod with valves 13;
14 spring with regulator 15; 16, 17 adjustable bleed valves; 18 triggering
mechanism comprising chamber 19 with bowed diaphragm 20, springloaded by spring 21 with regulator 22; 23 rod; 24 non-return valve; 25
pipe, leading from patient connection through a one-way valve 27 to the
Venturi-effect device 3, which operates to apply a partial vacuum to the
patient's lungs; 26 pipe leading from 25 to the chamber 19 of the
triggering mechanism; 28 pressure gauge; 29 pointer, which moves over
a scale 30, to indicate the degree of de¯ation of bellows 6 (i.e. tidal
volume). Modus operandi If the patient attempts to breathe, the slight
negative pressure in the breathing system lifts the diaphragm 20, opening
the valve 24 and admitting air to the low pressure chamber 11.
Thereupon the diaphragm 10 moves quickly to the left, closing valve 13.
As a result the pressure in the air chamber 1 builds up, squeezing the
contents of the bellows into the patient's lungs.
for gas cylinders, blood pressure apparatus, suction
apparatus, bronchoscope ®ttings, instrument trays and a
metal water container.
Other devices of use in anaesthesia
John Blease applied his mind to several other aspects of
anaesthesia. In November 1948 he registered another two
inventions at the Patent Of®ce, London. These were an
improved assembly for tracheal tubes19 and interchangeable
apparatus for varying the proportion of gas ¯ow through
carbon dioxide absorbing material.20 In November and
December 1950 he registered two more inventions! The ®rst
of these was a hypodermic needle with a securing transverse
plate and an inclined external end for easy attachment of
either a diaphragm cap or a syringe;21 the second was a
double-cuffed tracheal tube.22 In 1953 he invented a device
for controlling the ¯ow of iv ¯uid through resilient tubing.23
Stimulated by the 1952 poliomyelitis epidemic in
Copenhagen he designed a manual resuscitator, incorporat-
Fig 8 Blease `Pulmo¯ator' Model P11 (courtesy of Mr MA Blease).
ing a non-return valve with no resistance to expiration. This
was reviewed in 1954.24
Improvements in pulmonary ventilation
Next John Blease looked again at respiration. In 1953 he
designed an improved control valve for use in either an
anaesthetic machine or portable resuscitation apparatus.25 In
1957, Blease moved his company to Rye®eld Crescent,
Northwood Hills, Middlesex where, in bigger premises, he
expanded the manufacture of `Pulmo¯ators'. The same year
he lodged a patent for a triggering device (Fig. 7).26 This was
utilized in model P.3 which also had an injector, providing
variable negative pressure during the expiratory phase.27
The P.3 was designed only for `open circuit' and was
intended for short or long term use in cases of respiratory
paralysis/insuf®ciency. Next, model P.4 was designed for
anaesthetic use only with a `closed or semi-closed circuit'.
The injector was modi®ed so that variable degrees of
negative or positive pressure during expiration were
possible.27 A combined ventilator/anaesthetic apparatus
(model P.5) was also produced. Model P.6 of the
`Pulmo¯ator' incorporated a gauze-covered air `intake',
i.e. ®lter, so that in addition to anaesthesia, the ventilator
could be used for emergency treatment of respiratory
insuf®ciency in a hospital ward. Designed only for `open
circuit' it was also combined with anaesthetic apparatusÐ
model P.7. In 1959 these `Pulmo¯ators' were functionally
932
The inventions of John Blease
Fig 9 Drawing of apparatus for constant volume ventilation, 1959
(modi®ed from British Patent 885,221). Key: 1, transparent chamber
which is cyclically pressurized and vented to atmosphere through
opening 2, (by pressure-operated valve mechanism); 3, collapsible
bellows; 4, inlet pipe for admission of air or gases; 5, inlet port; 6, outlet
port; 7, outlet pipe to patient; 8, scale with pointer 9 for indication of
tidal volume; 10, threaded rod with knob 11 at its upper end and a stop
12 at its lower end, arranged to co-operate with an abutment 13; 14,
depending rod; 15, lock nut. Modus operandi Adjustment of 10±15
facilitates presetting the stroke of the bellows.
analysed27Ðall were constant ¯ow generators in inspiration,
with pressure cycling of inspiration-expiration and time
cycling of expiration-inspiration. In the expiratory phase all
were pressure generators: P.1 atmospheric followed by
positive pressure, P.3 constant negative pressure, P.4 and P.6
having negative and positive pressure components.
By 1960 the Blease `Pulmo¯ator' model P.10 was
commercially available. It incorporated a large two-way
valve for selection of either `open circuit' or `closed circuit',
and had two concertina bellows units. This `all-purpose'
ventilator was also combined with anaesthetic apparatusÐ
model P.11 (Fig. 8). In `closed circuit' this machine
operated as a P.5, and in `open circuit' as a P.7. Another
patent, which Blease had lodged in 1957 for a constant
volume ventilator28 (Fig 9) was utilized by 1960 in
`Pulmo¯ator' models P.3ÐP.11. In reality this was a
bellows stroke-limiting `stop', which enabled tidal volume
to be preset. In the successive models of `Pulmo¯ator' the
basic workings were the same: each new invention was
simply added on.
Fig 10 Drawing of prototype of Manley ventilator, 1960 (modi®ed from
British Patent 900,866). Key: 1, bellows, connected to a source of gases
under pressure, and in communication with a 2nd bellows 2 through tube
3 containing a two-way tap 4; 5, valve (V1); 6, pivoted frame, biassed by
means of tension spring 7; 8, pivoted frame, adjustably biassed by a
movable jockey weight 9; 10, movable contact coupled to valve 5 (V1);
11, arcuate arm, having adjustable stop member 12; 13, contact, coupled
to valve 5 (V1); 14, wide bore tube leading from bellows 2 to inhalation
valve 15 (V2) attached to 16 spring biased diaphragm in small pressure
chamber; 17, ¯exible tubing to patient; 18, exhalation valve (V3)
attached to 19 spring biased diaphragm in small pressure chamber; 20,
expiratory valve; 21, by-pass tube from two-way tap 4 to facilitate
manual respiration; 22, breathing bag; 23, tube, pneumatically linking
valves V1, V2 and V3; 24 valve (needle and seating) which closes when
bellows 1 is empty, providing a constant back pressure on the rotameters.
Modus operandi: Inspiration; pressure generator (from weighted bellows
2). Bellows 1 ®lls during this phase. Inspiratory±expiratory cycling; time
cycled by the ®lling of bellows 1 until contact 10 trips a toggle and lever
(bistable) system and valve 5 (V1) opens. Due to the pneumatic linking
23, this causes valve 15 (V2) to close and valve 18 (V3) to open.
Expiration; passive pressure generation to atmosphere. Bellows 1 empties
and bellows 2 ®lls during this phase. Expiratory-inspiratory cycling;
volume cycled by the setting of 12, so that when bellows 2 has ®lled to
the set volume, contact 13 trips the toggle and lever (bistable) system in
the other directionÐvalve 5 (V1) closes, valve 15 (V2) opens and valve
18 (V3) closes.
The Manley ventilator
In July 1960, Blease Anaesthetic Equipment Ltd ®led a
patent application for a new mechanical ventilator designed
by Roger E. W. Manley.29 This machine incorporated two
bellows in communication with each other (Fig. 10).
Simultaneously, a second patent application was ®led for
a combination of two valves designed to improve the
performance of the new ventilator.30 At that time Roger
Manley was a Senior House Of®cer at Westminster
Hospital, who had been impressed by the need for a simple,
reliable and inexpensive ventilator. Using various parts
including the bellows from a Blease `Pulmo¯ator', he had
assembled in the garage of his home a working model of a
ventilator, powered by the fresh gases from the anaesthetic
machine. Encouraged by Dr Geoffrey S. W. Organe and
other anaesthetic staff at Westminster Hospital, Manley had
then taken his prototype to John Blease, who agreed to
develop and market it. In his paper `A new mechanical
933
McKenzie
Acknowledgements
I thank Mr Tony Blease and the late Mrs Doreen Blease for their help and
cooperation as well as two illustrations. Original drawings of John Blease's
patented inventions were obtained from the national patent collection in the
British Library, London, which is open to the public; permission to
reproduce these drawings was kindly given by Tony Blease and Blease
Medical Equipment Ltd. I thank the Thackray Medical Museum and Prof.
Leslie Rendell-Baker for each providing an illustration.
References
Fig 11 Mr and Mrs J. H. Blease, London, 1955 (ã Leslie Rendell-Baker,
1955).
ventilator' published in Anaesthesia in 1961,31 Manley
thanked John Blease `for his continued help in developing
the production model of the ventilator'. The Blease±Manley
ventilator (minute volume divider) was an immediate and
lasting success, many models being still in use around the
world.
Retirement
In his commercial endeavours John Blease was supported
by his wife, Doreen, who was Company Secretary for many
years (Fig. 11); his son Tony demonstrated and serviced
`Pulmo¯ators' all over the world. Perhaps not surprisingly,
Roger Manley also joined the ®rm. John Blease decided for
health reasons to retire in 1964. The Company was sold in
1965 and in 1966 moved to Deansway, Chesham,
Buckinghamshire (the present address of Blease Medical
Equipment Ltd). Blease remained active in retirement. In
1983, his achievements were recognised by the Liverpool
Society of Anaesthetists, which elected him an Honorary
Member. He died in 1985 at the age of 79 yrs.10 Modern
anaesthesia owes much to his legacy of inventions!
934
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2 Blease JH, Fowler G. Improvements in Anaesthetic Apparatus.
British Patent 519,203, 1940
3 Blease JH, Fowler G. Improvements in Anaesthetising Apparatus.
British Patent 535,447, 1941
4 Minnitt RJ (ed.). Handbook of Anaesthetics, 5th edn. Edinburgh: E &
S Livingstone, 1940; 133±5
5 Blease JH, Fowler G. Improvements in Anaesthetizing Apparatus.
British Patent 548,617, 1942
6 Blease JH, Alexander & Fowler Ltd. Improvements in
Anaesthetizing Apparatus. British Patent 562,887, 1944
7 Bieber EI. An all-purpose anaesthetic machine. BMJ 1944; 1:
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8 Minnitt RJ, Gillies J. Textbook of Anaesthetics, 6th edn. Edinburgh: E
& S Livingstone, 1944; 146±8
9 Times Pictorial (Dublin), 5th February 1944
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12 Mushin WW, Rendell-Baker L, Thompson PW, Mapleson WW.
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chloride). Proc R Soc Med 1946; 39: 400±10
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Respiration, Resuscitation and Anaesthesia. British Patent
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15 Blease JH. Improvements in Apparatus for the Control of
Respiration, Resuscitation and Anaesthesia. British Patent
649,229, 1951
16 Morton HJV. Respiratory patterns during surgical anaesthesia.
Anaesthesia 1950; 5: 112±28
17 Blease JH. Improvements in Apparatus for the Control of
Respiration and Anaesthesia. British Patent 695,586, 1953.
18 Musgrove AH. Controlled respiration in thoracic surgery. A new
mechanical respirator. Anaesthesia 1952; 7: 77±85
19 Blease JH. Improved endo-tracheal assembly. British Patent
649,230, 1951
20 Blease JH. Improvements in or relating to Anaesthetic
Apparatus. British Patent 653,216, 1951
21 Blease JH. Improvements in or relating to Needles for Use in
Intravenous Injection. British Patent 689,131, 1953
22 Blease JH. An improved Endotracheal Tube. British Patent
693,510, 1953
23 Blease JH. Means for controlling the Flow of Liquid through
Resilient Tubing. British Patent 731,988, 1955.
24 Kilpatrick A. Positive ventilation with the Blease manual
resuscitator. Anaesthesia 1954; 9: 303±8
25 Blease JH. Improved human respiration control valve. British
Patent 750,152, 1956.
The inventions of John Blease
26 Blease Anaesthetic Equipment Ltd. Improvements in Apparatus
for Assisting Respiration. British Patent 848,725, 1960.
27 Mushin WW, Rendell-Baker L, Thompson PW. Automatic
Ventilation of the Lungs, 1st edn. Oxford: Blackwell, 1959; 160±8
28 Blease Anaesthetic Equipment Ltd. Improvements in apparatus
for the Control of Respiration in Resuscitation and Anaesthesia.
British Patent 885,221, 1961
935
29 Blease Anaesthetic Equipment Ltd. Improvements in Respiration
Machines. British Patent 900,866, 1962
30 Blease Anaesthetic Equipment Ltd. Improvements in Valves.
British Patent 908,974, 1962
31 Manley RW. A new mechanical ventilator. Anaesthesia 1961; 16:
317±23