19144

Why am I not surprised that the pH of lung moisture decreases during an asthma attack? Poor ventilation of the alveoli would retain carbon dioxide, which is carbonic acid in solution. Does the change in pH correspond to a buildup of carbonate or bicarbonate in the blood? Would it be a better measure of an asthmatic episode to measure CO₂ retention?

Bart Bresnik
Mansfield, Mass.

I wonder if the acidity of the exhaled moisture was due to acidity in the lung fluid or to refluxed fluids from the upper gastrointestinal tract. Very often, chronic cough and asthmalike symptoms are due to gastroesophageal reflux disease (GERD), and not due to asthma. This could have implications for treatment, as antacids would not be of use if the acidity were in fact due to acidic pulmonary fluid. This is obviously preliminary work, and as is usual with good science, it raises more questions as it searches for answers.

Gregory F. Nye
North Falmouth, Mass.

Researcher Benjamin Gaston of the University of Virginia Health System in Charlottesville replied to the first letter, “Carbon dioxide levels tend to be slightly low, if anything, in patients with asthma. We actually controlled very carefully for CO₂, fastidiously removing it from each sample . . . . What we saw had little or nothing to do with blood pH/CO₂.” To the second letter, Gaston answers that none of the patients had GERD symptoms and that several aspects of the study rule out GERD. “We believe that we have now defined the biochemical basis for low airway pH in these patients, and it doesn’t involve GERD or stomach acidification mechanisms,” says Gaston .–D. Christensen