Alveolar distribution of argon, previously inhaled fast, at 7 atmospheres absolute (ATA)

The model that explained the argon expirogram at 1 ATA (Respir. Physiol. 86:1–14, 1991) was improved by introducing the variable time. Thus, expirograms of Ar after 5–20s of apnea (FASEB J. 20:A1258, 2006) were also explained (figure, left side). Now, experiments conducted at 7 ATA are presented. The same subject was studied at 1 and 7 ATA (FRC=4L, RV=1.4L, TLC=7.9L). He inhaled 1.9L of 79% Ar and 21% O 2 . The mass spectrometer remained at 1 ATA. The inspiration was performed from FRC fast (2s) and the expiration lasted 3s. The results are shown in the Figure (right side), the filled symbols are experimental data at 7ATA (Cruz, Lanphier and Farhi. IUPS 1968) and the open symbols at 1 ATA (Cruz, 1991); the curves were obtained with the model (5s breath holding was omitted for clarity). The alveolar distribution of Ar is different: 238 ml of Ar reached RV at 0s, 7 ATA as compared to 70ml at 1 ATA. As a consequence, Ar rises at 7 ATA instead of falling at 1 ATA. The dead space volumes required to fit the data were 425ml, 340ml, 280ml and 158ml for 0s, 5s, 10s and 20s, respectively, for 1 ATA; and 425ml, 313ml, 187ml and 138ml for 7 ATA. In conclusion, at 7 ATA, the model showed better argon mixing; and argon expirograms seen at 5s, 10s and 20s reflected the argon movement from trachea to ERV, dropping at 20s, which is manifested by 69ml of argon moving to RV. Supported in part by Centro de Enseñanza, Investigación y Servicios (CEIS).