JOURNAL  OF  THE  SOUTH  AFRICAN  LOGOPEDIC  SOCIETY November 

New Aspects of Voice Physiology 
VOCAL FOLD VIBRATIONS WITHOUT AIR-STREAM IN A LIVING HUMAN BEING 

By G. H. BRECKWOLDT, Ph. D. 

JOHANNES MtiLLER (1801-1858) had shown 
the medical world that there were certain laws of 
voice-production which could be demonstrated in 
experiments with the larynges of  corpses. In these 
experiments he showed that (1) the pitch of  the 
tone thus artificially  produced depended on the 
tension of  the vocal folds.  In other words, if  the 
air-stream remained constant and the tension of 
the folds  of  the same larynx was increased, the 
pitch of  the tone went up. He found  that (2) with 
an increasing intensity of  the air-stream the 
volume of  the tone increased and the pitch went up. 
If,  however, (3) the pitch of  the tone was to remain 
constant but its volume to increase, the air-stream 
must be increased but the tension of  the vocal folds 
must be decreased. MtjLLER regulated the ten-
sion of  the folds  with weights. The air pressure was 
produced by means of  bellows (cf.  H. GUTZMANN, 
"Sprachheilkunde" Berlin, 1924, p.14 seq.) ' 

Scientists who held against MULLER'S 
EXPERIMENT the fact  that he had gained his 
results from  experiments with the heads of  bodies 
and not with living individuals, were directed to 
experiments demonstrating subglottal pressure "in 
vivo" i.e. in patients who, after  tracheotomy had 
to wear a cannula. These experiments were sup-
posed to show, similar to MULLER'S findings,  that 
voice pitch depends upon the interaction of  vocal 
fold  tension and air-pressure, (cf.  CAGNIARD DE 
LA TOUR 1857). The general idea was that the 
breath-stream activated, i.e. vibrated the otherwise 
passive vocal folds. 

As early as 1898 EWALD and after  him NAGEL, 
in 1906-07, criticised the theory that the vocal cords 
vibrate through the air-stream only; they thought 
that the air-stream caused the muscles within the 
folds  to vibrate on their own. (cf.  G. PANCON-
CELLI-CALZIA, "Die Stinmatnung" Leipzig, 1956 
p.64). CALZIA says that their criticism was justi-
fied,  but that their explanation was wrong. 

Before  R. HUSSON began his experiments in 
Voice Physiology there were no experiments in this 
field  of  any importance, (for  the following:  cf.  R. 
HUSSON: "Physiology of  the Vibrations of  the 
Vocal Folds," Logopaedie en Phoniatrie, Rotter-
dam, October 1956, and HUSSON'S numerous 
publications). Up to HUSSON'S researches we find 
the conventional idea that the larynx can be com-
pared with various musical instruments, such as a 
horn, a cushion-whistle or organ-pipe, etc. 

F i g . l . 
C U S H I O N - W H I S T L E by W E T H L O . 

<G. P A N C O N C E L L I - C A L Z I A : D I E E X P E B I M E N T E L L E 
P H O N E T I K , Berlin 1924, p.39). 

In order to put an end to this state of  affairs, 
since 1950 experimental investigations have been 
undertaken by the "Laboratoire de Physiologie" of 
the Sorbonne in co-operation with the directors of 
a great number of  Paris hospitals. 

THE ACTION POTENTIALS OF THE 
N. RECURRENS IN PHONATION 

The action potentials of  the N. recurrens, which 
should determine the voice production have been 
obtained by experiments "in vivo" (in cases which 
had to undergo laryngectomy) in the Hopital 
Boulincourt, Paris, by ANDRE MOULONGUET 
(1953). 

After  a year's work, in 1956, MOULONGUET 
was successful  in making photographs and 
sound recordings. These recordings show that a 
congruity exists between the rhythm of  the action 
potentials of  the N. recurrens and the rhythm of 
the contractions of  the motor units in the musculus 
vocalis. 

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JOURNAL  OF  THE  SOUTH  AFRICAN  LOGOPEDIC  SOCIETY 

ELECTROMYOGRAPHY OF THE VOCAL 
FOLDS 

Electromyography of  the vocal folds  was also 
performed  on human beings "in vivo." The sub-
jects had undergone either an extirpation of  the 
root of  the tongue or a hemilaryngectomy. The 
vocal folds  ΛνβΓβ visible and directly approachable 
at several points. 

In June and December, 1954, electromyographs 
were made without voice. Herefrom  one can 
conclude: 
1. that the vocal folds  are the seat of  a strong 

electrical activity, which is minimal during 
inspiration and maximal in expiration. 

2. that the contraction periods of  a motor unit of 
the vocal folds  are extremely short, from 
0.0008"—0.0009". This is the quickest move-
ment that has been found  up to date in the mus-
culature of  man. 

In May, 1955, an exceptionally important finding 
was made. A patient managed with only his larynx 
— there was no connection with the bucco-pharyn-
geal cavity — to produce small scales of  6-7 tones. 
One could then make a myograph during the voice 
utterance, and film  and sound-recordings were 
made. 

It appeared that . . . 
1. during the utterance the motor unit of  the vocal 

folds  synchronised itself  with the fundamental 

F i g . 2. 

Recording of  the Action Potentials of  the 
recurrent nerve in a human being and " i n 
v i v o . " Final stage in M O U L O N G U E T ' S 

experiment (Paris, 1953). 

The electrodes are placed on the recurrent 
nerve of  the locally anaesthetised patient, 
and the microphone is put in front  of  the 
patient's mouth. The surgeon closes the 
opening of  the tracheal cannula with his 
finger  and asks the patient to utter any one 
sound and hold it for  some time. 

(A. M O U L O N G U E T , P. L A G E T , R. H U S -
S O N : . "Demonstration chez l'homme, de 
l'existence . . . . " . Bulletin de l'Acad6mie 
Nationale de Medicine, p.475). 

tone, i.e. with the frequency  of  the impulses 
imparted on the folds  by the N. recurrens. 

2. every crest in the electromyograph is formed 
by the simultaneous contraction of  the group of 
motor units that are nearest to the electrode. 

Precautions were taken so that no microphonic 
distortion was possible. 

DIRECT STIMULATION OF THE 
N. RECURRENS 

Direct electrical stimulation of  the N. recurrens 
was first  performed  on a dog, in 1951-1952, under 
general anaesthetic. Experiments were carried out 
in the Physiological Laboratories of  the Sorbonne 
by PAUL LAGET. 

The stimulation took place with frequencies  vary-
ing from  100-700Hz. No air passed through the 
glottis. Observation with the stroboscope showed 
that . . . 
1. between 100-500 Hz the vocal folds  vibrated 

with slight amplitude but with the same fre-
quency as the stimulation. The vibration is 
maximal between 150 and 200 Hz: from  300 
Hz onwards it is very small, but it increases 
with the intensity of  the stimulation. 

2. about 500 Hz the vibration only appears at 
minimal stimulation. 

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2 JOURNAL  OF  THE  SOUTH  AFRICAN  LOGOPEDIC  SOCIETY November 

On another occasion the N. recurrens was stim-
ulated with frequencies  of  100-700 Hz. The elec-
trical activity of  the vocal folds  was homorhythm-
ical in every instant. 

VOCAL FOLD VIBRATIONS WITHOUT 
AIR-STREAM IN A LIVING HUMAN 

BEING 

Until February, 1956, the experiments by LAGET 
on dogs, which were described just now, were the 
only ones in which vocal fold  vibrations were ex-
perimentally created in which there was no occur-
rence of  air stream through the glottis. This effect 
was achieved by motor recurrens impulses which 
went out to the larynx muscles. 

On the 1st February, 1956, JEAN PIQUET, 
G. DELACROIX and C. LIBERSA, succeeded in 
filming  vocal cord vibrations of  a 
living human being, through whose glottis 
there passed no air-stream. The N. recurrens 
was not electrically stimulated, but it was the 
patient himself  who produced the vibrations. In 
the following  I am giving a brief  report of  this 
experiment as it is recorded in the publication of 
the Academie Des Sciences of  Paris, dated 27th 
February, 1956. 

Whenever possible, experimental control is used 
on a human being during an operation. This idea, 
which LERICHE had, we have applied in order to 
examine the role of  the subglottal pressure in the 
creating of  vocal fold  vibrations in the case of  a 
horizontal supraglottal laryngectomy. Thanks to 
this method, one gets an excellent view of  the 
glottis through the pharyngeal opening. One vocal 
fold  is completely mobile, the other is fixed  in a 
paramedian position. One lets the patient utter a 
sound (vowel [a:]) ; one studies frequency  and 
intensity, one films  the event with an ultra-rapid 
camera in colour. 

Later on one opens the trachea and introduces 
a small probe through the opening. This probe is 
fitted  with a tiny rubber balloon which prevents 
air escape and is joined to a water-manometer. One 
lets the patient produce the vowel Ia:l, while one 
measures frequency  and intensity. One records the 
pressure as given by the manometer, and the sound 
is recorded by means of  a magnetophone. This has 
been done on various occasions. The vibrations of 
the vocal folds  have been recorded on a film  with 
a rapid camera. One can then state the following 
facts: 

1. The intensity of  a sound stands in direct rela-
tionship to the subglottal pressure. 

2. The subglottal pressure for  a rather loud sound 
is comparatively small. For a sound of  70 phon 
pressure is 24 cm. water. For a sound of  77 
phon pressure is 30 cm. water. 

It does not satisfy  us any more to say that the 
vocal folds  function  like a "reed instrument." 

We can determine that during a sustained tone 
no change in subglottal pressure takes place. The 
reclosure of  the vocal folds  is a muscular effect  and 
not the result of  sub-atmospheric pressure. 

At another experiment the larynx was instru-
mentally completely closed off  from  the tracheal 
pulmonary system. The patient was also asked to 
utter [a;] and the following  was found: 

1. A normal adduction movement of  the vocal 
folds. 

2. One vibration lasted a fraction  of  a second, but 
no tone was observed except a short rattle. 

Films were made of  this as well. The vibrations 
were recorded and corresponded precisely to the 
previous recording. We can thus prove that the 
vocal folds  can vibrate without air-stream during a 
certain length of  time (our recording was limited 
to one second). 

We can also state the following: 

1. A vocal fold,  immovably fixed  in paramedian 
position, can vibrate. 

2. The vibrations of  the vocal folds  are not imme-
diately maximal but are increasing in amplitude 
(the latter phenomenon being known under the 
name of  "KAISER Effect"). 

The above experiments were conducted in order 
to show that the subglottal pressure is not neces-
sary to ensure vibration of  the vocal folds,  but that 
the subglottal pressure plays a decisive role for 
the intensity of  a sound and not at all for  the 
pitch. 

In a sequel to this article I will discuss . . . 
1. The Chronaxy Measurement of  the N. recurrens 

and its Applications. 
2. A New Method to classify  singing Voices. 
3. A Correlation between Hand Dominance and 

Disturbances in recurrent Chronaxy in cases of 
Phonasthenia. 

4. I will give a critical discussion of  the old and 
new ideas about Voice Physiology. 

5. There will be a Bibliography. 

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