Human breath isoprene and its relation to blood cholesterol levels: new measurements and modeling

Numerous publications have described measurements of breath isoprene in hum ans, and there has been a hope that breath isoprene analyses could be a non invasive diagnostic tool to assess blood cholesterol levels or cholesterol synthesis rate. However, significant analytic problems in breath isoprene a nalysis and variability in isoprene levels with age, exercise, diet, etc., have limited the usefulness of these measurements. Here, we have applied pr oton transfer reaction-mass spectrometry to this problem, allowing on-line detection of breath isoprene. We show that breath isoprene concentration in creases within a few seconds after exercise is started as a result of a rap id increase in heart rate and then reaches a lower steady state when breath rate stabilizes. Additional experiments demonstrated that increases in hea rt rate associated with standing after reclining or sleeping are associated with increased breath isoprene concentrations. An isoprene gas-exchange mo del was developed and shows excellent fit to breath isoprene levels measure d during exercise. In a preliminary experiment, we demonstrated that atorva statin therapy leads to a decrease in serum cholesterol and low-density-lip oprotein levels and a parallel decrease in breath isoprene levels. This wor k suggests that there is constant endogenous production of isoprene during the day and night and reaffirms the possibility that breath isoprene can be a noninvasive marker of cholesterologenesis if care is taken to measure br eath isoprene under standard conditions at constant heart rate.