Diagnostic Significance of Arterial-Alveolar Nitrogen Tension Difference in Assessment of Ventilation-Perfusion Ratio Inequality

¹ Assistant Professor of Medicine, School of Medicine, Keio University, Tokyo, Japan

Arterial-alveolar N₂ tension difference (aADN₂) was studied as a measure to assess ventilation-perfusion ratio uneveness in the lungs in 186 healthy subjects, 37 patients with manifested asthma, 28 with chronic pulmonary emphysema and 36 with bronchitis. The healthy subjects exhibited a different distribution pattern in incidence of aADN₂ with regard to their age groups. The mean, standard deviation, and 95 percent upper confidence limit for young healthy adults was 3.3 mmHg, 2.4 mmHg, 8.1 mmHg, respectively. Those for healthy aged persons were 5.6 mmHg, 3.3 mmHg, 12.2 mmHg, respectively. The author proposed aADN₂ of 8.0 mmHg as the upper diagnostic limit for young adults 40 years of age or younger, 12.0 mmHg for healthy persons aged more than 40 years. If the subject's age was not considered, 10.0 mmHg was the proposed upper diagnostic limit. aADN₂ of patients with manifested asthma, chronic pulmonary emphysema, and bronchitis showed a tendency to increase more than the proposed upper diagnostic limit. aADN₂ for some bronchitic and asthmatic patients was increased, even though their FEV_1.0 percent remained within normal limits. aADN₂ Obtained in patients with manifested asthma decreased after bronchodilator aerosol inhalation. Changes in aADN₂ after administration of a bronchodilator did not reveal a statistically consistent correlation between FEV_1.0 percent and FMF. aADN₂ was increased in patients with depressed Co pulmonary diffusing capacity. aADN₂, in general, was inversely correlated with the breathholding CO pulmonary diffusing capacity.