Aortic blood flow was measured using MA2PSB flow probe (Transonic Systems Inc. Ithaca, NY) connected to the transit-time flowmeter (TS420, Transonic Systems Inc., Ithaca, NY).
Expiratory flow was measured using a pneumotachograph (1100 Series, Hans Rudolph, Inc. Shawnee, KS), as previously described.46 (link) Mixed expired O2 (FchO2), CO2 (FchO2), and H2S fractions (FchH2S) were measured continuously using O2 (Oxystar-100, CWE Inc. Ardmore, PA), CO2 (model 17630, VacuMed, Ventura, CA), and H2S (Interscan RM series; range: 0–200 ppm, Interscan Corporation, Simi Valley, CA) analyzers.
Electrocardiogram (ECG) was recorded by a bioelectric amplifier (Differential AC amplifier, Model 1700, A-M Systems, Sequim, WA).
All signals were digitized at 400 Hz using an analog-to-digital data acquisition system (Power Lab 16/35, AD Instruments, Inc. Colorado Springs, CO) and were visualized online. All data were stored for further analysis by LabChart7 (AD Instruments, Inc. Colorado Springs, CO).