Measuring Peripheral Chemoreflex Hypersensitivity in Heart Failure

Figures

• 

  Figure 1. An example of the measurement of peripheral chemoreflex sensitivity using the continuous transient hypoxic method in an isocapnic condition (A). The rise in ventilation (V̇E) is plotted against the fall in oxygen saturation to build a regression function (B). The slope of this function, or hypoxic ventilatory response (HVR), is considered a measure of peripheral chemoreflex sensitivity (liters per minute per % oxygen saturation). (C,D) show the effect of isocapnic CO2 tension (PCO2) on HVR. Note that the HVR varied with isocapnic PCO2 tension; with greater levels of isocapnia, the sensitivity of the peripheral chemoreceptors to hypoxia is increased, resulting in a greater HVR. In contrast, during the poikilocapnic test, PCO2 fell as V̇E rose, and the ventilatory response to hypoxia was nearly eliminated. See text for details.

• 

  Figure 2. A comparison of isoxic hyperoxic (PO2 = 150 mmHg) ventilatory responses to CO2 (white circles and gray lines) with isoxic hypoxic (PO2 = 50 mmHg) ventilatory responses to CO2 (black circles and black lines) between two patients with heart failure with reduced ejection fraction. Note that the gain (or sensitivity) is less in patient 1 (A) vs patient 2 (B). However, the ventilatory recruitment threshold (VRT) for the peripheral chemoreflex (PCR) occurs at a higher PCO2 in patient 2 vs. 1. The arrows provide an estimation of the HVR attributable to the PCR at isocapnic PCO2 corresponding to rest, +3 mmHg above rest, and + 3 mmHg above the VRT for patient 1 (blue arrows) and patient 2 (red arrows). After determining the ventilation at an isocapnic PCO2 in hyperoxia to measure the central chemoreflex (CCR) contribution, hypoxia is introduced, and the ventilation measured again at the isocapnic PCO2. Because patient 2 has a great VRT than patient 1, the HVR corresponding isocapnic PCO2 at rest and + 3 mmHg above rest incorrectly indicate that the PCR sensitivity of patient 1 is the same or greater than patient 2. By contrast, when hypoxia is introduced at an isocapnic PCO2 of +3 mmHg…