Some Effects of Change in Position on

Pulmonary Function in Bronchial Asthma*

ALAN L. MICHELSON, M.D. and FRANCIS C. LOWELL, M.D.

Boston, Massachusetts

P ATIENTS with bronchial asthma often de- scribe an increase in severity of symptoms

after retiring at night. This symptomatic increase in asthma is variable, as is the time of onset after assuming the recumbent position. The phenomenon has been ascribed most often to changes in the volume of various lung com- partments, exposure to allergens or to relaxation in sleep and the attendant physiologic changes.

We have studied the role that a shift from the erect to the supine position may play by measur- ing changes in the compartmental volume and rate of airflow during a maximal expiratory effort in a group of asthmatic patients and in normal healthy control subjects.

METHODS

Twenty-six asthmatic subjects varying in age from eighteen to sixty-five years and thirteen normal con- trol subjects varying in age from twenty-one to fifty- five years were studied. The asthmatic subjects in- cluded nine females and seventeen males. Seventeen of the twenty-six patients had had severe asthma for five or more years. The remaining nine patients had had mild to moderate asthma of two to three years’ duration, all had highly reversible disease, and all were sensitive by skin test to one or more allergens. The normal subjects included seven females and three males, all of whom had no history or evidence of respiratory disease.

These subjects were tested at various intervals during a six-month period. The study was conducted in the following manner. Measurements were made with the subject in the erect and in the recumbent position, using a standard tilt-table. Respiration was recorded using a closed system previously described [I] and minute ventilation, vital capacity, total lung capacity, expiratory reserve volume, functional residual capacity and residual volume were obtained by the helium dilution method [2].

The measurements were first made with the subject in the erect position. The subject was then placed in the recumbent position for five to ten minutes and the

measurements were repeated. The asthmatic subjects were tested on more than one occasion and therefore at various stages of their illness.

RESULTS

The results of forty-one separate determina- tions in the twenty-six asthmatic pati,ents and of thirteen determinations in the ten &ontrol sub- jects are shown in Table I. ‘r

The changes in vital capacity in both groups are shown graphically in Figure 1. Statistic analysis showed that upon assuming the recum- bent position the decrease in vital capacity in the control group was significantly greater (p = <.035) than in the asthmatic group.

In addition, the volume expired during the first second in both the asthmatic group and in the normal control group was studied and com- pared. No significant change occurred in either group upon assuming the recumbent position.

COMMENTS

This study was largely limited to the static changes in pulmonary function which occur in changing from the erect to the supine position. It was anticipated that when this shift was made a fall in vital capacity would occur, super- imposed on an already decreased vital capacity, and that this would explain the almost universal complaint among asthmatic patients that they become worse during the sleeping hours. As seen graphically in Figure 1, not only was the decrease in vital capacity not seen as frequently as had been anticipated, but an increase oc- curred in a significant number of patients, for the most part in those who were sickest.

It has been known for over 100 years that the vital capacity decreases in the normal subject when the recumbent position is assumed [3], Hamilton and others have demonstrated that the greater portion of the decrease in vital capac-

* From the Evans Memorial, Massachusetts Memorial Hospitals, and the Department of Medicine, Boston University School of Medicine, Boston, Massachusetts.

FEBRUARY, 1958 225

226 Pulmonary Function in Bronchial Asthma--Michelson, Lowell

ity can be explained by the increased pul- monary blood volume attending the supine position [4]. This decrease in vital capacity can be modified by the application of pressure cuffs on the extremities to prevent return of venous blood to the thoracic cavity [5]. McMichael and

TABLE I CHANGES IN THE COMPARTMENTAL LUNG VOLUMES UPON

TILTING TO THE HORIZONTAL POSITION

Direction of Change *

Patients Normal Subjects

No. % No. %

Vital Cajmcity

Decrease.. 21 52 11 85 Increase. 10 24 0 0 Nochange... 10 24 2 15

- Total Lung Cafmcity

Decrease. 29 71 9 69 Increase..... 9 22 4 31 No change. 3 7 0 0

Expiratory Reserve Volume

Decrease. 27 66 13 100 Increase..... 11 27 0 0 No change.. 3 7 0 0

Functional Residual Capacity

Decrease.. 32 78 9 70 Increase..... 9 22 2 15 No change. . 0 0 2 15

_ Residual Volume

Decrease.. 23 56 8 62 Increase..... 13 32 3 23 No change. 5 12 2 15

* > 100 ml.

McGibbon, continuing the earlier studies by Hurtado and Fray [6,7], studied patients in both the erect and supine positions and found that the total lung volume, functional residual capac- ity, vital capacity and residual volume decreased during recumbency. Not only do the abdominal contents push the diaphragm cephalad, with concomitant pooling of blood in the lesser cir-

culation, but the recumbent position may place the muscles of respiration at a disadvantage. Among the factors mentioned, the cephalad shift of the diaphragm with its effects on the subdivisions of the pulmonary volume has received most attention, and the changes ob- served in this study are presumably a reflection of this shift, perhaps combined with the shift in blood into the thoracic cage.

Some studies in chronic obstructive pulmonary emphysema, a disease exhibiting many of the features of asthma, indicate that the cephalad shift of the diaphragm induced by pneumo- peritoneum is beneficial [8]. This conclusion should be tempered, however, by the statement of many patients with emphysema that ab- dominal compression aggravates symptoms. This is not surprising when it is recalled that the lowered diaphragm in emphysema is a conse- quence, not the cause, of the pulmonary lesion, characterized as it is by obstruction to air flow readily demonstrable with even the crudest measurements. In emphysema, resistance to flow in the airway increases as the lung dimin- ishes in volume and indeed this may be regarded as a gross exaggeration of similar changes which take place in the normal subject. Thus, any measure which would result in compression of the lung would be expected to aggravate the functional defect and indeed this is borne out by our own clinical experience. In adopting a position of inspiration, with its associated in- creased patency of the airway, the patient with obstructive pulmonary disease suffers less from the consequences of a narrowed airway and in this sense the inspiratory position and lowered diaphragm are an adjustment to the disease process. Eating a large meal, bending forward to tie a shoe or wearing a tight belt have been aggravating factors in our patients with any form of severe diffuse bronchial obstruction. We believe, therefore, that it is premature at this time to assume that the benefits attributed to pneumoperitoneum in emphysema are neces- sarily a result of the upward shift of the dia- phragm, a shift which presumably occurs in some degree in any person, when changed from the erect to the supine position.

Bronchial asthma exhibits the same changes as emphysema with the difference that the vital capacity tends to be decreased roughly in pro- portion to the severity of symptoms and the disease process is usually entirely or to a large degree reversible. Other factors such as a change

AMERICAN JOURNAL OF MEDICINE

Pulmonary Function in Bronchial Asthma--Michelson, Lowell

ml. + 700\

00

0

+ 600~

t

me - 400 0

.a*

l

0

l

me l eee l e

l

l

NORMAL SlmECTS

t,[ i

ASTHMATIC PATIENTS FIG. 1. Change in vital capacity upon tilting to the horizontal position.

227

in the intrapulmonary distribution of the inspired air, local changes in blood flow, or changes in compliance and mechanical resist- ance within the lung [9] may play a part when the subject’s position is shifted, changes which would not be revealed by the studies carried out here or by those which have been made in the past. In addition, it has been the common clini- cal experience that, in contradistinction to pa- tients with obstructive emphysema, those with bronchial asthma seem to have increased symp- toms upon lying down.

Certain considerations may explain the clini- cal impression that, for a given degree of respira-

FEBRUARY, 1958

tory obstruction, the patient with asthma will be far more dyspneic than the patient with emphysema, and one would therefore expect that orthopnea, a response to dyspnea, would likewise be more common in the asthmatic subject. This difference may be explained in part at least by the relatively frequent occur- rence of respiratory acidosis in emphysema on the one hand and its infrequency in asthma. Not only will a lower level of ventilation than would otherwise be necessary suffice for the excretion of CO2 in the presence of respiratory acidosis, but the consequent decrease in respiratory work upon assuming the recumbent position will lessen

228 Pulmonary Function in Bronchial Asthma-Michelson, Lowell

the amount of CO2 which must be disposed of. Furthermore, as there appears to be an asso- ciated decrease in the respiratory responsiveness to CO*, a rise in COZ accompanying aggrava- tion of obstruction would be accompanied by less dyspnea in the presence of respiratory acidosis than in its absence. The asthmatic subject with a paroxysmal illness will not allow this “adapta- tion” to occur and therefore drives his respira- tory muscles to achieve the excretion of COP. In so doing he increases the amount of CO2 to be excreted and thereby establishes a vicious circle. We are not aware that these factors have been studied in relation to postural effects. It would be premature at this time to assume that the clinically recognized differences in the two con- ditions are a consequence of a difference in the nature of the respiratory difficulty other than that pertaining to the magnitude of the respira- tory defect and its persistence.

SUMMARY

1. The compartmental lung volumes in twenty-six asthmatic patients and in ten normal subjects were studied in an effort to determine whether or not the change from the erect to the supine position could explain the increase in respiratory symptoms which so commonly occurs at night in bronchial asthma.

2. The predominant change in both groups was a fall in the vital capacity upon assuming the

horizontal position. However, the vital capacity increased in one-third of the patients with asthma whereas no such increase was observed among the normal subjects.

3. Factors other than an immediate change in the vital capacity and compartmental lung volumes must play a role in the genesis of a nocturnal increase in symptoms in asthmatic patients.

REFERENCES

1. LOWELL, F. C., SCHILLER, I. W. and LOWELL, A. The use of a closed-system in the study of asthma and emphysema. J. Allergy, 23: 335, 1952.

2. MCMICHAEL, J. A rapid method for determining lung capacity. Clin. SC., 4: 167, 1938.

3. HUTCHINSON, J. Encyclopedia of Anatomy and Physiology, 1849-1852.

4. HAMILTON, W. F. and MORGAN, A. B. Mechanisms of the postural reduction in vital capacity in rela- tion to orthopnea and storage of blood in the lungs. Am. J. Physiol., 99: 526, 1932.

5. Dow, P. The venous return as a factor affecting the vital capacity. Am. J. Physiol., 127: 793, 1939:

6. MCMICHAEL. J. and MCGIBBON. J. P. Postural changes in’the lung volume. Clin.‘Sc., 4: 175, 1939.

7. HURTADO, A. and FRAY, W. W. Studies of total pul- monary capacity and its subdivisions. m. Changes with nosture. J. Clin. Znvestieation. 12: 825. 1933.

8. CARTE.;, M. G., GAENSLER, E’. A. and KYL~ONEN, A. Pneumoperitoneum in the treatment of pulmonary emphysema. New England J. Med., 243: 549, 1950.

9. ATTINGER. E. 0.. HERSCHFUS, J. A. and SECAL, M. The mechanics’ of breathing in different body posi- tions. n. In cardiopulmonary disease. J. Clin. Investigation, 25: 912-920, 1956.

AMERICAN JOURNAL OF MEDICINE