[Show abstract][Hide abstract] ABSTRACT: The equilibrium CO2 rebreathing technique has been widely used for the noninvasive determination of cardiac output. Recently, several investigators have used this technique in conjunction with auscultatory blood pressure measurements to calculate total peripheral resistance. To examine the validity of this approach, we attempted to determine whether the CO2 rebreathing procedure has a significant effect on blood pressure. The participants in the present study were 10 male subjects, 24 +/- 1 yr of age (mean +/- SE). Each subject performed two trials-one with CO2 rebreathing and one without. Both trials consisted of three stages (rest, 25%, and 50% VO2peak), each stage lasting 15 min. During the rebreathing trial, the CO2 rebreathing technique was administered at 10 min into each stage. There were no statistically significant differences in the heart rate, systolic blood pressure, diastolic blood pressure, and mean arterial blood pressure responses between the two trials. These results indicate that the equilibrium CO2 rebreathing technique does not alter auscultatory blood pressures at rest and during exercise up to intensities of 50% VO2peak.
No preview · Article · Aug 1996 · Medicine & Science in Sports & Exercise
[Show abstract][Hide abstract] ABSTRACT: The carbon dioxide rebreathing technique is widely used for determination of cardiac output during exercise. The equilibration method of Collier et at. (J. Appl. Physiol. 9:25, 1956) is generally preferred over the exponential method of Defares (J. Appl. Physiol. 13:159, 1968). However, the equilibration method requires the volume and initial CO2 percentage in the rebreathing bag to be adjusted according to the work rate. A device for mixing two gases (100% O2 and 20% CO2/80% O2) was constructed for this purpose. Multistage regulators are attached to the gas tanks and connected to a medical gas mixer via high-pressure air hoses. A variable time-delay switch causes a solenoid valve to open for 1.0-10s to deliver a predetermined gas volume. The device was found to accurately deliver a preset volume and concentration of gas to the rebreathing bag. A gas mixing apparatus simplifies the equilibration CO2 rebreathing technique by allowing the investigator to easily select the initial volume and percentage of CO2.
No preview · Article · Jan 1996 · Medicine & Science in Sports & Exercise