Relative Ventilation and Perfusion of

Left Versus Right Lung in Mitral Stenosis

ARTHUR DAWSON, MD, FACC JOSE M. ROCAMORA, MD

JACOB R. MORGAN, MD, FACC

La Jolla and San Diego California

We measured relative ventilation, perfusion and ventilation/perfusion ratio of the left versus the right lung using a radioactive xenon method in 15 seated patients with mitral stenosis. The relative ventilation/per- fusion ratio of the left lung was significantly less in these patients than in 11 normal subjects and there was a significant negative correlation between the ventifation/perfusion ratio of the left lung and pulmonary intravascular pressure. There was little difference between relative perfusion of the two lungs, and the reduced ventilation/perfusion ratio of the lefl lung seems to be mainly due to relative hypoventflat!on, per- haps the result of compression or distortion of the left main stem bron- chus. None of the patients had more than a slight reduction in the ven- tilation/perfusion ratio of the left lung, and it is not likely that between lungs differences in regional function significantly affect the efficiency of gas exchange.

We found no significant correlation between the relative ventilation/ perfusion ratio of the left lung and pulmonary intravascular pressure in 10 patients with mitral stenosis studied in the supine position.

As shown originally by Dollery and West’ and since confirmed by several investigators,2-4 in mitral stenosis there is reversal of the apex to base gradient of pulmonary blood flow normally observed in seated subjects. None of these investigators described a difference between the relative function of the right and left lungs, but Spellberg et a1.5 have recently reported that in acquired heart disease the relative ven- tilation/perfusion ratio of the left lung is abnormally reduced. Using lung scans, they studied their patients in the supine position only and recorded the percent of total counts over each lung during ventilation (inhaled 133xenon) and perfusion (intravenous ggmtechnetium- albumin).

Since they did not perform lung scans after rebreathing of ry3xenon, they could not analyze relative ventilation/volume and rela- tive perfusion/volume ratios separately. We have recently reviewed some of our own data on relative regional ventilation and perfusion in seated patients with mitral stenosis to see whether we could find evi- dence of hypoventilation of the left lung.

From the Division of CardioPulmonary Diseases, Scripps Clinic and Research Foundation, La Jolla, Calif., and the Department of Cardiology, U. S. Naval Hospital. San Diego, Calif. This study was supported in part by U. S. Public Heafth Services Grant HL 10009. Manuscript accepted January 2, 1974.

Address for reprints: Arthur Dawson, MD. Di- vision of CardioPulmonary Diseases, Scripps Clinic and Research Foundation, 476 Prospect St., La Jolla, Calif. 92037.

Method

Regional lung function was measured by a method, modified from that of Ball et a1.,6 that has been described in more detail in previous reports from this laboratory.7*8 The patient sits erect in a chair with six collimated scintil- lation detectors viewing his posterior chest. The detectors are mounted on a rack that can be moved into two positions and data are recorded from a total of 12 segments of lung, 6 equally spaced in a vertical line over each lung from about 3 to 5 cm below the apex to about 2 to 4 cm below the right diaphragm.

The regional perfusion measurements are made after about 1.0 mc of 13sxenon in saline solution is injected rapidly through a small catheter in an antecubital vein while the patient holds his breath at his resting end-expira-

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LEFT VS RIGHT LUNG IN MITRAL STENOSIS--DAWSON ET AL.

tion position. When most of the 13sxenon has reached the alveoli (as judged by a stable count rate over the chest), he inhales fully and holds his breath at his total lung capacity while the count rate is recorded in each of the two positions of the detectors.

For the ventilation measurements, the patient slowly in- hales an inspiratory capacity breath consisting of an initial 500 ml (or 25 percent of his measured inspiratory capacity, whichever is less) of 133xenon in air and the remainder of room air. Again he holds his breath at his total lung capaci- ty while the count rate is recorded for 5 to 10 seconds in the two positions of the detector rack.

Both ventilation and perfusion measurements were per- formed in duplicate and the results were averaged. At the end of the study, the count rates were recorded during breath-holding at total lung capacity after 5 minutes of re- breathing la3xenon in air from a closed circuit spirometer,

Calculations: It was assumed that after the patient had rebreathed 133xenon in air for 5 minutes the isotope con- centration was uniform throughout the lungs. Therefore, if perfusion per unit volume were uniform throughout the lungs the same fraction of the total counts should be re- corded over the left lung after the intravenous injection of 133xenon as after rebreathing. The relative perfusion of the left lung (QL) is defined as

Qt. = G~',~)/&JTR) where Lp is the sum of the count rates recorded at the 6 left lung detector positions after intravenous injection of ls3xenon, Tp is the count rates summed for all 12 detectors after the intravenous injection, Ln is the left lung total count rate after rebreathing and Tn is the count rate after rebreathing summed for all 12 detectors. Similarly,

Vi, = (L,/TvML,/T~

where Lv and Tv are, respectively, the left lung and total counts after the single breath ventilation measurement.

TABLE I

Vt,/Qi, represents the ventilation/perfusion ratio of the left lung relative to the average ventilation/perfusion ratio of both lungs (or strictly the 12 segments of both lungs “seen” by the detectors).

Patient selection: Since Spellberg et al.” reported the most severe abnormalities in mitral valve disease, we stud- ied data from 15 patients with isolated or predominant mi- tral stenosis from a larger series of patients with various types of acquired heart disease. Lung function testing (spi- rometry and determination of lung volumes, steady-state diffusing capacity and arterial blood gases) showed that none of the patients had more than mild obstructive or “re- strictive” lung disease. The data were compared with simi- lar measurements from 11 normal subjects (age range 21 to 42 years). Ten additional patients with mitral stenosis were studied in the supine position, but no comparable data were available from normal subjects in this position.

Results

Sitting Position

Normal subjects: In 11 normal subjects relative ventilation per unit volume and perfusion per unit volume were almost equal in the left and right lungs (Table I). Values for Vr, ranged from 0.91 to 1.09, for QL from 0.90 to 1.07 and for Vr,/Qr, from 0.90 to 1.12. The average normal VL/QL ratio was 1.024, similar to the value of 1.02 reported by Spellberg and asso- ciate@ in normal supine subjects studied by a slightly different method.

Mitral stenosis: In the patients with mitral steno- sis, the left lung was slightly less well ventilated per unit volume than in normal subjects, but the differ- ence was not significant at the 95 percent confidence level (P <O.l by one-tailed Wilcoxon’s rank-sum test). Ql. values differed little in normal subjects and

Relative left Lung Function in 15 Seated Patients with Mitral Stenosis

Case no.

1 2 3 4 5 6 7 8 9

10 11 12 13 14 15 Mean

f SE Mean f SE

in 11 normal subjects

Age (yr) & Sex VL QL VL/QL PAP (mm Hg) PCP (mm Hg) PaOz (mm Hg) ~~- __-

47F 1.08 1.23 0.88 43F 1.07 0.94 1.14 46F 0.96 1.03 0.93 61F 1.02 0.99 1.04 32F 0.96 0.96 1.01 36F 1.02 1.02 1.00 49F 0.97 1.02 0.95 30F 0.89 0.94 0.94 41F 1.02 1.04 0.99 62F 0.97 1.00 0.97 65M 0.89 0.86 1.03 48F 0.96 0.97 1.00 45F 0.94 0.93 1.01 42F 0.91 1.01 0.91 33M 1.01 1.01 1.00 45.1 0.978 0.997 0.987

zk2.8 f0.015 f0.021 zkO.016 29.1 1.005 0.984 1.024

z!z2.5 f0.017 ztO.016 zko.021

72127 . . .

60/25 40/20 32112 36112 3418 80/32 35/12 64126 2916 56131 34117 40119 45117 46.9/18.9

zt4.4/+2.2 . . . . . .

30 85 . . . 88 24 68 18 89 14 97 21 93 15 101 36 83 18 92 22 74 12 89 35 87 18 . . . 19 83 17 98 21.4 87.6

12.0 zt2.4 . . . . . . . . . . . .

PAP = pulmonary arterial pressure (systolic/diastolic); PaO, = arterial oxygen tension; PCP = mean pulmonary capillary wedge pres- sure; QL = relative perfusion of left lung (see text); SE = standard error; VL = relative ventilation of left lung.

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LEFT VS. RIGHT LUNG IN MITRAL STENOSIS-DAWSON ET AL.

TABLE II

Relative Left Lung Function in Supine Patients with Mitral Stenosis

Case no.

-

Age (yr) & Sex VI.

_. ._ _-.._. _ -. ._-_

QI. VIJ’QI, PAP (mm Hg) PCP (mm Hg) PaOz (mm Hg)

16 40F 0.99 0.97 1.03 35112 16 89

17 49M 0.92 0.94 0.97 36/20 26 88

18 45M 1.10 1.09 1.01 54 123 19 78

19 48M 1.03 1.06 0.98 56/30 24 65

20 60F 1.07 1.02 1.06 36/11 13 62

21 42M 0.92 0.94 0.98 34114 13 66

22 46F 1.10 1.08 1.02 32116 14 81

23 55F 0.98 1.07 0.91 75135 30 80

24 21M 0.97 1.05 0.93 36117 18 101

25 31F 1.10 1.03 1.07 53/20 28 88

Mean 43.7 1.018 1.025 0.996 44.7119.8 20.1 79.8

I& SE zk3.6 10.023 ho.018 ztO.016 zk4.5/d.4 zt2.0 Ik3.9

Abbreviations as in Table I.

patients with mitral stenosis. In patients with mitral stenosis the relative ventilation/perfusion ratio of the left lung (VL/QL) was significantly less than in nor- mal subjects (P <0.05 by one-tailed Wilcoxon’s rank- sum test). In patients with mitral stenosis Vr./Qr, showed a significant negative rank correlation (r,) with pulmonary arterial systolic pressure (rs = -0.56, P <0.05) and with pulmonary capillary wedge pres- sure (r, = -0.56, P <0.05) but no significant correla- tion with arterial oxygen tension. VL and QL showed no statistically significant correlation with pulmo- nary intravascular pressure or arterial oxygen ten- sion. Left/right ventilation, perfusion and ventila- tion/perfusion values were not significantly different in upper and lower zones. Left/right ventilation and ventilation/perfusion values analyzed separately in upper and lower zones were slightly less in patients with mitral stenosis than in normal subjects but none of the differences were statistically significant.

In agreement with Jebavy et a1.,4 we found that apex to base ventilation ratios and apex to base per- fusion ratios were greater than normal in patients with mitral stenosis and that both increased signifi- cantly with increasing pulmonary intravascular pres- sure.

Supine Position

The data from patients studied in the supine posi- tion are given in Table II. We had no comparable data from normal subjects in this position. As judged from pulmonary intravascular pressures, the severity of mitral stenosis was similar in the supine and seat- ed patients. The mean arterial oxygen tension was al- most 8 mm Hg less in the supine subjects, but the difference was not statistically significant (0.1 > P >0.05 by two-sample t test). The VL/QL ratio was al- most the same in supine and seated subjects and, al- though VL and QL values were slightly less in supine subjects, the differences were not significant. We found no significant correlation between VL, QL or VL/QL ratio and arterial oxygen tension or pulmonary intravascular pressure.

Discussion

Our results in seated patients with mitral stenosis agree with those of Spellberg et al.5 obtained in pa- tients with acquired heart disease in the supine posi- tion: That is, the relative ventilation/perfusion ratio of the left lung is abnormally reduced in the patients and there is a significant negative correlation be- tween this ratio and pulmonary intravascular pres- sure. Our method allowed us to measure relative ven- tilation/volume and perfusion/volume ratios sepa- rately and our results suggest that the reduced venti- lation/perfusion ratio of the left lung is due mainly to hypoventilation hut there may be some contribution from relative overperfusion of the left lung since QL was slightly greater in patients than in normal con- trol subjects. There was no significant difference in the ratio of left to right lung ventilation in the upper and lower zones. This finding suggests that there is underventilation of the whole left lung, perhaps as a result of compression or distortion of the left main stem bronchus. Most of our patients did not have marked cardiomegaly, and it is not likely that expan- sion of the left lung was impeded by enlargement of the heart into the left hemithorax.

The abnormality of regional function relations of the right and left lungs in mitral stenosis is very slight compared with the gross distortion of the nor- mal relative function of the apex and base, and it is not surprising that it was not commented upon in previous studies of regional lung function in mitral stenosis.‘-4 However, another explanation might be that when regional ventilation is measured with an inspiratory capacity breath entirely labeled with ra- dioactive gas, as in the studies of Dawson,2 Hughes9 and GlazierlO and their co-workers, its distribution is mainly determined by relative regional compliance. l 1 In our study and in that of Spellberg et a1.,5 lssxenon was distributed to the alveoli as a “bolus” or during normal breathing, and relative resistance would also affect its distribution. If in acquired heart disease there is partial obstruction of the left bronchus with- out a selective decrease in left lung compliance, rela-

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LEFT VS. RIGHT LUNG IN MITRAL STENOSIS-DAWSON ET AL.

tive hypoventilation of the left lung would be appar- ent only when a resistance-sensitive method was used to administer the radioactive gas.

We have no satisfactory explanation for our inabil- ity to reproduce the findings of Spellberg and asso- ciates in our patients studied in the supine position other than to speculate that there were chance differ- ences in our clinical material. Nor is it clear to us why we found no instances of marked relative hypoventi- lation of the left lung such as those reported by

1.

2.

3.

4.

5.

Bollery CT, West JB: Regional uptake of radioactive oxygen, carbon monoxide and carbon dioxide in the lungs of patients wkh mitral stenosis. Circ Res 8765-771, 1960 Dswson A, Kaneko K, McGregor M: Regional lung function in patients wlth mitral stenosis studii wkh xenon133 during air and oxygen breathing. J Clin Invest 44: 999-1008, 1965 Friedman WF, Braunwald E: Alterations in regional pulmonary blood Now in mitral valve disease studied by radioisotope scan- ning. Circubtion 34: 383-376. 1968 Jebavy P, Runczik I, Gp~eft A, et al: Regional pulmonary func- tion in patients wlth mitral stenosis in relation to haemodynamic data. Br Heart J 32: 330-336.1970 Spellberg RD, Burprenant EL, O’ReHly RJ: Hypoventilation of left lung in acquired heart disease. Am J Roentogenol 118: 785-791, 1973

6. Ball WC Jr, Stewart PE, Newsham LGS et al: Regional pulmo-

Spellberg et al. in several patients with mitral valve disease. The lowest VLIQL ratio in our group of pa- tients was 0.91, whereas several patients in their se- ries had a “left lung index” (comparable with our VJQt, ratio) of less than 0.75, and our results do not support their suggestion that left lung hypoventila- tion contributes to arterial hypoxemia in acquired heart disease.5 However, it should be pointed out that most of our patients had a normal arterial oxy- gen tension.

References

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11.

nary function studied with xenon 133. J Clin Invest 41:519-531, 1962 Dawson A: Regional pulmonary blood flow in sitting and supine man during and after acute hypoxia. J Clin Invest 48:301-310. 1969 Dawson A: Regional lung function during early acclimatization to 3,100 m altitude. J Appl Physiol33:218-223.1972 Hughes JMB, Glazier JB, Roeenzwelg DY, et al: Factors deter- mining the distribution of pulmonary blood flow in patients with raised pulmonary venous pressure. Clin Sci 37:847-858. 1969 Glazier JB, Dollery CT, Hughes JMB: Effect of acetylcholine on regional pulmonary blood flow in patients with mitral stenosis. Circulation 38:136-143, 1968 Robertson PC, Anthonieen NR. Ross D: Effect of inspiratory flow rate on regional distribution of inspired gas. J Appl Fhysiol 26~438-443, 1989

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