Breath-by-breath variation of FRC: effect on VO2 and VCO2 measured at the mouth

Abstract

We examined breath-by-breath (B-B) variations of FRC (delta FRC) and their effect on measured O2 and CO2 gas exchange in 52 2- to 4-min segments of continuous air breathing obtained in 29 patients (age range 6--50 yr). Respiratory frequency ranged from 13 to 43 breaths/min, VE from 6.7 to 22.5 l/min (BTPS), and expired VT from 234 to 1,370 ml (BTPS). Computer analysis was based on the following source data measured at the mouth: inspired (VI) and expired (VE) gas flow, FN2, FO2 and FCO2. The analysis provides B-B evaluation of VI, VE, delta FRC in terms of VN2, and VO2 and VCO2 at the mouth and at the alveolar level, i.e., after correction for delta FRC. Significant B-B variations of FRC were found in all studies. delta FRC ranged from +360 to -360 ml (BTPS). For single respiratory cycles VI - VE is primarily a function of N2 exchange at the mouth (VMN2). VO2 and VCO2, uncorrected for delta FRC, are significantly more dispersed about mean values than the corrected gas uptakes (P less than 0.0005). The data support the view that the assumption of VIN2 = VEN2 is invalid for single respiratory cycles. Determination of breath-by-breath VO2 and VCO2 should therefore, not be based on steady-state gas uptake equations. It requires measurement of both inspired and expired breath volumes and evaluation of N2 gas exchange.

Gas exchange during exercise in different evolutional stages of chronic Chagas' heart disease

“…These were expressed in STPD (0°C, 760mmHg, dry) and obtained by numerical integration of the product of the gas flow and fractions, and these signals were previously synchronized. As these measurements were taken at the mouth, the estimation of alveolar gas exchanges was performed compensating the variations in the functional residual capacity through measurements of the nitrogen gas 15 . The V O2 and V CO2 were calculated through the product of the volumes at each cycle and the instant respiratory frequency, and expressed in STPD.…”

Exercise response before and after termination of atrial tachycardia after congenital heart disease surgery.

“…Minute-by-minute group means of Vo2 indicated no significant differences at rest and during the 1st 4 minutes of exercise (Figure 3). During subsequent minutes, AVo2 tended to become progressively greater (significant for the 5th, 7th, and 9th minutes of work) after conversion to sinus rhythm.…”

Variability of End-Expiratory Lung Volume in Premature Infants

“…In adults, two studies [17,18] have shown that the EELV level fluctuates around its mean value, with cycle-by-cycle differences which may reach 360 ml [17] . Low-frequency oscillations were suspected in a 4-patient study [18] .…”

“…Variability of end-expiratory lung volume (EELV) has been reported mainly in adults [17,18] . Studies in animals suggest that EELV fluctuations may partly manifest autocorrelation [19] .…”