If variation in ventilatory drive, both endowed and acquired, determines the extent and quality of adaptation to the hypoxia of high altitude, such variation might also contribute to the variable clinical profile of patients with hypoxic disease at low altitude, such as chronic obstructive pulmonary disease. It has long been known that such patients present a varied clinical picture illustrated by patients presenting at the extreme edges of the spectrum—the pink puffer and blue bloater. More common is the broad range of PaC02 observed with a given degree of severe airway obstruction, indicating that the ventilatory adaptation to severe airway obstruction is quite variable. The presence of intense dyspnea in the eucapnic pink puffer and its absence in the hypercapnic blue bloater have suggested the terms “fighter” and “nonfighter,” reflecting possible underlying differences in ventilatory drive. Indeed, early studies indicated decreased ventilatory responsiveness to hypercapnia in patients with airway obstruction but decreased ventilatory responses to chemical stimuli in patients with major mechanical impediment to breathing may reflect either mechanical limitation or true differences in ventilatory control. In subsequent studies, the response to hypercapnia was measured as ventilatory effort assessed as inspiratory work of breathing, diaphragmatic EMG, or inspiratory occlusion pressure and found that in severe airway obstruction, hypoventilating patients, generally corresponding to the blue-bloater profile, produced a lower respiratory effort response to hypercapnia than that in patients with similar degrees of obstruction and eucapnia (Fig 5). Similar decreases in occlusion pressure responses to hypoxia have also been observed. buy levaquin online
Figure 5. Arterial carbon dioxide tension in patients with chronic obstructive pulmonary disease, plotted in relation to severity of obstruction (left) and to the strength of the hypercapnic response measured as the inspiratory occlusion pressure (right). The data show no clear relation between PaC08 and the severity of airway obstruction but indicate a clear tendency for development of hypercapnia in subjects with low hypercapnic response.
Tags: Chronic obstructive pulmonary disease, Hypercapnia, Hypoxia