Lesson 4

Exercise Minute Ventilation related to Work Rate

VE versus time and work rate. This plot normally becomes curvilinear as work rate is increased above the aerobic threshold, except VE is limited by obesity and obstructive lung disease.

Tidal Volume as a Function of Exercise Minute Ventilation
Tidal volume (Vt) versus VE. The patient’s vital capacity (VC) and inspiratory capacity (IC) are  shown on the vertical axis, and actually measured maximum voluntary ventilation (MVV) or FEV1, times 40 is shown on the horizontal axis. Ventilatory frequency can be plotted as isopleths through the origin. With airflow limitation, maximal exercise VE approximates the MVV, resulting in a low breathing reserve (MVV – VE) at maximal exercise.

End-Tidal Oxygen and Carbon Dioxide
PETO2, PETCO2 and SpO2 versus time and work rate. Low PETCO2 signals either hyperventilation or VA/Q abnormality. Arterial blood gases are plotted on this graph to detect the presence of high and low VA/Q mismatching.

panel 1 panel 7 panel 9

Question: Is exercise limited by reduced ventilatory capacity? (panel 1,7,9)

Example of possible Disorders: Lung; chest wall

Marker for Abnormality: BR (breathing reserve) – high or low
Ventilatory response – high or low




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