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Many patients with chronic obstructive pulmonary disease (COPD) receiving supplemental oxygen state that this treatment makes them less short of breath at rest. We postulated that this phenomenon may be related to improved arterial oxygenation, reduced ventilation, or stimulation of nasal receptors caused by the flow of gas. Eight patients who reported this phenomenon were studied in a quiet room. Each patient received zero flow, 2, or 4 L/min of air or oxygen through nasal cannula for 5 min at each level in random order in a single blind manner. At the end of each period, arterial blood gas composition was measured, and breathlessness was assessed with a visual analog scale. The scale was calibrated to read from zero (not at all breathless) to 100 (extremely short of breath). The entire protocol was repeated after application of topical lidocaine to the nasal passages. Results were assessed by analysis of variance. We found no significant effect of inspired oxygen concentration, gas flow, arterial oxygen tension, or arterial carbon dioxide tension on breathlessness. There was, however, a significant increase in breathlessness after nasal anesthesia from 44 +/- 3 SEM to 52 +/- 4 SEM (p less than 0.005). We suggest that the reduction of breathlessness in these patients by nasal oxygen is a placebo effect caused by wearing the nasal cannulas and is unrelated to gas flow or the increased arterial oxygen tension.

The mortality of diabetic patients with autonomic neuropathy (DAN) is higher than that in those without autonomic neuropathy (DM). To test the hypothesis that this may be due to respiratory rather than cardiac dysfunction, we evaluated ventilatory responses to isocapnic-hypoxic and hyperoxic-hypercapnic conditions in 14 diabetic patients (8 DAN and 6 DM) and compared the results with those in 8 normal subjects. In all groups tested there was a significant linear correlation between end-tidal CO2 and minute ventilation and between end-tidal CO2 and mouth occlusion pressure (p100), as an index of the drive to breathe. There were no significant differences between the slopes and intercepts in the groups tested. A significant linear correlation was found between the O2 saturation and both minute ventilation and p100. There were no significant differences in the relationship between minute ventilation and O2 saturation, but the slopes and the intercepts of the regression lines of p100 vs. O2 saturation were significantly different in the DAN compared with those in normal subjects and DM. Additionally, five of eight patients with DAN lost their ventilatory drive and ventilatory responses to hypoxemia compared with only one of six DM. These findings suggest that a disorder in the ventilatory response to hypoxemia exists in some DAN.

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