Oronasal distribution of respiratory airflow

Respiration Physiology (1981) 43, 69 75 © Elsevier/North-Holland Biomedical Press

O R O N A S A L DISTRIBUTION OF RESPIRATORY A I R F L O W * * *

V. N I I N I M A A j, P. COLE 2, S. MINTZ: and R.J.

SHEPHARD

~

i Department o[' Preventive Medicine and Biostatistcs, Universi O, o[" Toronto, Toronto and 2 Gage Research Institute, Toronto, Canada

Abstract. The oronasal distribution of respiratory airflow was determined during incrementally graded submaximal exercise in 30 (14 M, 16 F) healthy adult volunteers. Nasal airflow was measured by a pneurnotachograph attached to a nasal mask. Oral airflow was determined as the difference between nasal airflow and total pulmonary airflow, the latter being measured by a head-out exercise body plethysmograph. The two airflow signals were sampled every 20 msec by a microprocessor, which calculated the oral and nasal minute volumes (separating inspiration and expiration) and produced an on-line print-out of the results. Twenty subjects ('normal augmenters') switched from nasal to oronasal breathing at a 'qE of 35.3___ 10.8 1.rain - I , four subjects ('mouth breathers') habitually breathed oronasally, five subjects ('hose breathers') persistently breathed through the nose only, and one subject showed no consistent nose/mouth breathing pattern. After the switch to oronasal breathing, the nasal portion of VE decreased suddenly to 57')/0 of total ~'F. With a further increase of VE, oral minute volume increased rapidly, equalling nasal minute volume at a VE of 45 l . m i n -1, and accounting for 61 ?o of the total ventilation at high respiratory minute volumes (90 1. rain-~). During oronasal breathing, normal augmenters inspired some 2 l - m i n - J more nasally than they expired. Similarly, the nasal inspiration of m o u t h breathers exceeded expiration by 2 1 . m i n - I at rest, but the difference increased to 13.5 1. m i n - 1 at a "qE of 81.5 1 - m i n - I .

Airflow distribution Exercise Human

Nasal airflow Oral airflow Ventilation

The distribution of respiratory airflow between oral and nasal routes has had little investigation. Uddstr6mer (1940) reported that in a group of normal subjects at rest, Acc~7~ted./br publieation 10 September 1980 * This work was supported in part by a grant from physicians Services Inc. Foundation of Ontario, Canada. ** Based in part on material presented by one of us (V.N.) in fulfillment of the requirements of a Ph.D. degree within the University of Toronto. Reprint requests: Dr. Veli Niinimaa, Faculty of Physical Education, The University of Calgary, Calgary, Alberta, T2N 1N4 Canada. 69

70

v. NIIN1MAA et al.

80 to 82% of the airflow was nasal. During recovery from exercise ('¢E 22.6 1- min '), the nasal portion of respiratory airflow decreased to 60.2_+ 23.23;. However, in habitual mouth breathers, some 66% of the respiratory airflow was nasal. Camner and Bakke (1980) observed that with subjects engaged in quiet reading, over 90',% of the respired air was nasal. During casual conversation, the nasal portion decreased to 50%, but during continuous counting aloud only 20?,0 of the total expiratory airflow passed via the nasal route. Bouhuys (1977, p. 28) and Proctor (1964, p. 312) have suggested that very little air passes through the nose during mouth breathing because of the high resistance of the nose relative to that of the oral cavity. However, it may be that respirologists have obtained falsely low values for oral resistance when the mouth has been wedged open by a mouthpiece. Saketkhoo et al. (1979) noted that subjects appeared to breath mainly through the nose at rest and during light to moderate exercise, although the authors did not attempt to partition the nasal and oral airflows. Thus the pattern of oronasal airflow distribution pattern has yet to be established clearly for either resting or exercising subjects.

Methods

Volunteers (14 M, 16F), ranging in age from 15 to 35 years, were recruited through notices placed on the University of Toronto campus. Subjects were examined by an otolaryngologist in order to exclude those individuals with obstructive abnormalities of the airways. Pulmonary function (FVC, FEV~0 and Vs0) was determined, a three-stage submaximal bicycle ergometer test was used to assess their aerobic fitness (Vow(max)). Nasal airflow was measured by a face mask (U.S. Divers scuba mask) that covered the nose and the eyes. A # 2 Fleisch pneumotachograph was mounted in the window of the face mask. Oral airflow was determined as the difference between nasal airflow and total pulmonary airflow, the latter being measured by a head-out exercise body plethysmograph (Niinimaa et al., 1979). Nasal and oral airflows were determined in duplicate on separate testing days with the subject at rest and during continuous pedalling of the ergometer at power settings of 0, 10, 20 . . . . . 60',% of the subjects' predicted maximum physical working capacity, as determined during an initial submaximal bicycle ergometer test. Measurements were taken of 10 consecutive breaths during the last 30 sec of each 2-min stage. The two airflows were sampled by a microprocessor every 20 msec, integrating flow data to volumes. Results were printed online upon completion of a measurement. A more detailed description of the methodology is available elsewhere (Niinimaa et al., 1980).

71

O R O N A S A L A I R F L O W DISTRIBUTION TABLE I Physical characteristics of subjects (~ +_ SD) n

Age(years) Height (cm) Body Mass (kg) Vo2(max) (1 .rain -1 s'rPD)* (ml-kg l . m i n - I SVPD)* PWC(max) (W)*

Men

Women

14

16

21.6+_ 3.8 178.0 +- 4.4 70.5 +- 9.1 4.03+_ 1.02 57.6 +_ 14.4 289.2 +_ 70.8

22.9 165.4 59.6 2.71 45.6 185.0

+_ 5.4 +- 5.9 +- 5.3 +_ 0.51 + 7.8 +_ 34.6

* Predicted values. PWC(max) Maximum physical working capacity.

Results

Physical characteristics of the subjects (table 1) did not differ from those of the average Canadian, except for aerobic power, which was significantly higher (P < 0.001, students t-test, Bailey et al., 1974). Lung function ranged from 97.3 to 112.2~o of predicted values. At rest, 83~o (25/30) of the subjects breathed nasally only, while the mouth breathers (4/30) respired oronasally. As respiratory minute volume increased with exercise, normal augmenters (20/30) switched from nasal to oronasal breathing at 9E of 35.3+-- 10.8 1. min ~ BTPS, corresponding to a work rate of 105.0+- 30.1 W (Niinimaa et al., 1980). Nose breathers (5/30, all females) respired persistently nasally during the submaximal exercise of up to 160.0+- 23.0 W. One subject exhibited an inconsistent and unpredictable nose/mouth breathing pattern. At the switching point (average 9E 35.3 1. min-~ BTPS), the normal augmenters" nasal minute volume decreased suddenly to 19.8 1 • rain- t (fig. 1), while the remainder of their respiratory minute volume increased further, a greater portion of ventilation became oral, the nasal and oral minute volumes becoming"equal at a 9 [ of 45 1 • rain t. With still greater total respiratory minute volumes, oral minute volumes exceeded nasal minute volumes, the difference increasing to ~ome 17.5 1-min ' at a 9E of 90 1-min-~. At the switching point, nasal minute'volume accounted for 573o of the total respiratory minute volume (fig. 2). This proportion decreased to 40?% as 9E increased to 90 1. min -I. Correspondingly, the oral portion of respiratory minute volume increased from 43 to 60?4,. The oronasal distributio n pattern of mouth breathers was generally similar to that of normal augmenters. However, a significant difference was noted in that nasal minute volume was smaller at all respiratory minute volumes (P < 0.001), and the oral minute volume was correspondingly higher (fig. 1). Expressed as a percentage, the oral airflow proportion increased to approximately 70°/,; of total

72

V. NIINIMAA et al. 0ronasal dlstribution o f

respired air

60 NORMAL

~

Nasal

AUGMENTERS '*~'~ 0ral

3~" ****

50

~" ,.~,'.~" "b'~ ~ "

MOUTH -Nasal BREATHERS - - - - 0ral

0

I I0

I 20

TOTAL

I 30

m

RESPIRATORY

i° 40

, 50

MINUTE

i 60

i l0

VOLUME

-,.

i 80

i 90

( 1 . r a i n "1 B T P S )

Fig. I. Distribution of respired air between nasal and oral routes at rest and during graded exercise (linear regression fitted by the method of least squares).

respiratory minute volume at "VE of 81.5 1. min -~ in mouth breathers, compared with only 61~o in normal augmenters (fig. 2). During oronasal breathing normal augmenters inspired nasally some 2 1 • rain r BTPS more than they expired. This difference remained constant in the respiratory

Nose/mouth airflow proportions during oronasal breathing 80 -~.

>~

Normal augmenters Mouth breathers

oRAL

60

_J O ptL O

%

/

\

/

40 bJ C) fr bJ n j 20

m

0

10

2mO

3~

Switching

point

m

m

m

m

I

m

40

50

60

70

80

90

TOTAL RESPIRATORY MINUTE VOLUME (I- rain "I BTPS )

Fig. 2. Percentage of airflow passing via nasal and oral routes during oronasal breathing in "normal augmenters' and 'mouth breathers'.

73

ORONASAL AIRFLOW DISTRIBUTION Inspfratory and expiratory nasal atrflows during oronasal breathing 40

NOR#4AL

~

Inspired

BREATHERS ~

Expired

J

c E

30

~ ~T ~

.~~.~**~,,

hl

W

2O

Z

I[ ..J

< Z

Switching point

I0 '

20 '

30'

:o

50 '

60 '

;0

80'

90 "

TOTAL RESPIRATORY MINUTE VOLUME (1.rain -1 BTPS)

Fig. 3. lnspiratory and expiratory nasal airflows during oronasal breathing in "normal augmenters' and "mouth breathers' (linear regressions fitted by the method of least squares).

minute volume range of 35.3 to 90 1 - min-J (fig. 3). Also in mouth breathers nasal inspiration exceeded nasal expiration by 2 1. rain-~ at rest, however, with increasing total respiratory minute volume, inspired nasal minute volume increased significantly (P < 0,05) faster than the expired nasal minute volume, the difference increasing to 13.7 l . m i n -~ at a VE of 81.5 1.min ~.

Discussion All respired air was passed via the nose in 671~o of the subjects both at rest and during light exercise (power output < 105.0+_ 30.1 W). At the switching point from pure nasal to oronasal breathing (average VE 35.3_+ 10.8 1. min -~ BTPS), the oral minute volume increased suddenly from nil to 15.5 1 -min -~, while the nasal minute volume decreased correspondingly from 35.3 to 19.8 1 - min-~ (fig. 1). With a further increase of total respiratory minute volume to 90 1 • min ~, the nasal minute volume increased to 36.6 1. rain-'. Present results confirm the observations of Saketkhoo et al. (1979) that at rest and during light exercise, most respiratory airflow is nasal. Present results clearly negate earlier assertions that very little air passes through the nose during oronasal breathing (Bouhuys, 1977, p. 28; Proctor, 1964, p. 312). The ratio of oral and nasal minute volumes suggests that immediately after the switch to oronasal breathing, the oral airflow impedance is greater than that of the nasal passages. Oral obstruction is probably controlled by the size of opening between the lips, and by the positioning of the tongue against the palate. As

74

v. N I I N I M A A et al.

the nasal airflow increases, it becomes more turbulent, and the airflow resistance increases exponentially (power 1.7, Drettner, 1979). However, with increasing exercise, the lumen of nasal cavities increases (Dallimore and Eccles, 1977; Richerson and Seebohm, 1968) partially counteracting the otherwise inevitable dramatic increase of nasal airflow impedance. At a VE of 45 1.min ~, nasal impedance apparently matches that of the oral airway and at larger respiratory minute volumes it exceeds that of the oral airway. Nevertheless, even at a VE of 90 1 • min-~, 40~o of the respired air passes through the nose. The oronasal airflow distribution pattern in mouth breathers was similar to that of normal augmenters (during oronasal breathing) excepting for the larger oral minute volume at all respiratory minute volumes. The difference is most likely due to a greater nasal airflow impedance in the mouth breathers, as shown by their larger nasal work of breathing per unit of ventilation (Niinimaa et al., 1980). -,,o, confirms previous The proportion of mouth breathers in the present study (13""~ studies, which indicated that the percentage of mouth breathers lay between 10.5 and 15.8 (Uddstr6mer, 1940; Saibene et al., 1978). Both normal augmenters and mouth breathers inspired nasally more than they expired, the difference being a constant 2 1- min-~ in normal augmenters, but in mouth breathers increasing from 2 to 13.5 1-rain ~ with larger respiratory minute volumes. Similarly, nasal inhalation exceeds exhalation during thermal panting in dogs (Schmidt-Nielsen el al., 1970). A possible explanation for the difference between inspiratory and expiratory nasal and oral minute volumes is an alternation of oral airflow impedance over the breathing cycle, with an increase during inspiration and a decrease during expiration. The changes in oral airflow obstruction may be larger than appears from the differences in inspired and expired nasal minute volumes, since in resting subjects the nasal impedance to inspired airflow is greater than the impedance to expired airflow (Cole el al., 1979).

References Bailey, D . A . , R.J. Shephard, R.J. Mirwald and G . A . McBride (1974). A current view of Canadian cardiorespiratory fitness. Can. Med. Assoc. J. 111 : 25 30. Bouhuys, A. (1977). The Physiology of Breathing. A Textbook for Medical Students. New York, G r u n e and Stratton. Camner, P. and B. Bakke (1980). Nose or m o u t h breathing? Environ. Res. 21: 394-398. Cole, P., V. Niinimaa, S. Mintz and F. Silverman (1979). Work of nasal breathing: Measurement of each nostril independently using a split mask. Acta Otolarvngol. 88:148 154. Dallimore, N.S. and R. Eccles (1977). Changes in h u m a n nasal resistance associated with exercise, hyperventilation and rebreathing. Acta Otolaryngol. 84: 416-421. Drettner, B. (1979). The role of nose in the functional unit of the respiratory system. Rhinol. 17 : 3 11. Niinimaa, V., P. Cole, S. Mintz and R.J. Shephard (1979). A head-out exercise body plethysmograph. J. Appl. Physiol. 47: 1336-1339. Niinimaa, V., P. Cole, S. Mintz and R.J. Shephard (1980). The switching point from nasal to oronasal breathing. Respir. Physiol. 42:61 71.

ORONASAL AIRFLOW DISTRIBUTION

75

Proctor, D. F. (1964). Physiology of the upper airway. In: Handbook of Physiology. Section 3, Vol. 1, edited by W. O. Fenn and H. Rahn. Washington, D.C. American Physiological Society, pp. 309 345. Richerson, H. B. and P. M. Seebohm (1968). Nasal airway response to exercise. J. Allergy 41 : 468-475. Saibene, F., P. Mognoni, C. L. Lafortuna and W. Mostardi (1978). Oronasal breathing during exercise. pfliigers Arch. 46 : 369- 371. Saketkhoo, K., I. Kaplan and M. Sackner (1979). Effects of exercise on nasal mucous velocity and nasal airflow resistance in normal subjects. J. Appl. Physiol. 4 6 : 3 6 9 371. Schmidt-Nielsen, K., W. L. Bretz and C . W . Taylor (1970). Panting in dogs: unidirectional airflow over evaporative surfaces. Science 169:1102 1104. Uddstr/Smer, M. (1940). Nasal respiration. Acta Otolaryngol. Suppl. 4 2 : 3 146.