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The relationship between arterialized blood lactate concentration [( La-]) and O2 uptake (VO2) was examined during a total of 23 tests by eight subjects. Exercise was on a cycle ergometer with work rate incremented from loadless pedaling to exhaustion as a 50-W/min ramp function. Two different mathematical models were studied. One model employed a log-log(More)
The constancy of the time course (i.e., dynamic linearity) of the O2 uptake (VO2) response to exercise was examined by testing the law of superposition on data from impulse and step work rate forcings. Two impulses (10 s at a 235-W increase above a 25-W base line, I-235; and 5 s at a 475-W increase above a 25-W base line, I-475), four steps (ST) (25-65 W,(More)
A computerized prediction-correction scheme has been devised for the control of alveolar gases. First, a model is run off-line to predict the inspiratory gas tensions at each second that should yield the desired alveolar patterns. Second, during the experiment, there is feedback correction based on the deviation of the actual alveolar values from the(More)
A computer-controlled gas-mixing system that manipulates inspired CO2 and O2 on a breath-to-breath basis has been developed. The system uses pairs of solenoid valves, one pair for each gas. These valves can either be fully shut when a low voltage is applied, or fully open when a high voltage is applied. The valves cycle open and shut every 1/12 s. A circuit(More)
Ramp work rate tests have been used to estimate aerobic parameters in exercise stress testing. Previous studies have suggested an assumption of a linear dynamic system for O2 uptake kinetics. The implication is that model parameters estimated from ramp tests should be similar to those estimated from other dynamic tests. In nine healthy subjects, we found(More)
A recently developed nonparametric regression technique, called a polynomial smoothing spline, is presented for detecting the ventilatory threshold (VT) and respiratory compensation (RC) points from gas exchange response data taken during an incremental exercise test. This type of curve fitting has the advantage of not requiring investigators to specify, a(More)
Pseudorandom binary sequence (PRBS) exercise tests involve repeated switching between two work rates (WR) according to a computer-generated pattern. This paper presents an approach to analysis of O2 uptake (VO2) in the time domain. First, the autocorrelation function (ACF) of the input WR was recognized to be a triangular-shaped pulse that can be taken to(More)
A dynamic end-tidal forcing technique for producing step changes in end-tidal CO2 with end-tidal O2 held constant independent of the ventilation response or the mixed venous return is introduced for characterizing the human ventilation response to end-tidal CO2 step changes for both normoxic (PAO2 = 125 Torr) and hypoxic (PAO2 = 60 Torr) conditions. The(More)
A mathematical model has been developed that permitted the calculation of the flow-weighted mean tissue O2 consumption (VO2T) at the onset of a step increase in work rate. From breath-by-breath measurements of alveolar O2 consumption (VO2A) and cardiac output (Q) by impedance cardiography and assumptions about the site of depletion of O2 stores, the rate of(More)